Who created the cell self-assembly algorithm. Legends of gray dust. The essence of the phenomenon of self-assembly

As educational program I quote material from N.V. Rebrov is a student of the national Donetsk Technical University, which, by the way, is currently being shot by the “national guard” of Ukraine with heavy guns on the instructions of Jewish Kyiv:

SELF ASSEMBLY IN NANOTECHNOLOGY

Among various promising approaches to the formation of nanostructures, nanotechnologies using self-organization are becoming increasingly important. It is assumed that self-organization will make it possible to create nanostructures from individual atoms as a “bottom-up” technology. Molecular self-assembly, in contrast to the “top-down” approach of nanotechnology, for example, lithography, where the desired nanostructure appears from a larger workpiece, is an important component of the “bottom-up” approach, where the desired nanostructure is the result of a unique programming of the shape and functional groups of molecules.

What nanostructures can be built using these technologies? Talking about different materials, since these technologies make it possible to create devices by forming them from atoms and molecules, using self-organization processes the way nature uses them. In nature, similar systems actually exist and similar processes occur. The most striking example is the example of the assembly of complex biological objects based on information recorded in DNA (see Fig. 1).

Figure 1 — Example of self-assembly of a biological structure

As it was before? We took, say, a piece of iron and made a hammer out of it, simply removing everything unnecessary (top-down technology). Nanotechnology in the near future will make it possible to make products from materials from scratch, and it will not always be necessary to add atom to atom “manually”; we will be able to use the phenomenon of self-organization, self-assembly of nanostructures and nanodevices. At the same time, it is quite difficult to expect that artificial manipulation of individual nanoobjects for the purpose of “manual” assembly of material is possible at the nanolevel. This is not yet practical (slow and requires a lot of work). Therefore, self-organization may be a natural way to obtain nanomaterials.

Self-assembly(eng. self-assembly) is a term to describe the processes as a result of which disorganized systems, thanks to the specific, local interaction of system components, come to an ordered state.

Self-assembly can be both static and dynamic. In the case of static self-assembly, the organizing system approaches a state of equilibrium, decreasing its free energy. In the case of dynamic self-assembly, it is more correct to use the term self-organization.

Self-organization in classical terms can be described as the spontaneous and reversible organization of molecular units into an ordered structure through non-covalent interactions. Spontaneity means that the interactions responsible for the formation of a self-assembled system occur on a local scale; in other words, the nanostructure builds itself.

Under certain conditions, micro- or nanoobjects themselves begin to line up in the form of ordered structures. There is no contradiction with the fundamental laws of nature here - the system in this case is not isolated, and nanoobjects are subject to some external influence. However, this impact is not directed at a specific particle, as occurs during top-down assembly, but at everything at once. You do not need to build the required structure manually, placing nanoobjects at the required points in space one after another - the conditions created are such that the nanoobjects do this themselves and at the same time. Processes that use the creation of such special conditions are called self-assembly processes, and they already play a vital role in many areas of science and technology.

For self-assembling components, all that is required is for a person to place enough of them in a test tube and allow them to automatically assemble into the desired configurations according to their natural properties.

To date, two-dimensional and three-dimensional organized arrays of Pt, Pd, Ag, Au, Fe, Co nanocrystals, Fe-Pt, Au-Ag alloys, CdS/CdSe, CdSe/CdTe, Pt/Fe, Pd/Ni nanostructures, etc. have been synthesized. d. In addition, for anisotropic nanoparticles, it was possible to achieve the formation of orientationally ordered arrays. Nanoparticles of uniform size can be “assembled” into spatially ordered structures, which are one-dimensional “threads”, two-dimensional densely packed layers, three-dimensional arrays or “small” clusters. The type of organization of nanoparticles and the structure of the resulting array depend on the synthesis conditions, particle diameter, and the nature of the external influence on the structure.

Today, various self-assembly methods are known that make it possible to obtain useful ordered structures from microparticles. To create special conditions under which self-assembly occurs in a particular system, gravitational, electric or magnetic fields, capillary forces, playing on the wettability-non-wettability of system components and other techniques can be used. Currently, self-assembly processes are beginning to be actively used in production.

The essence of the phenomenon of self-assembly

Modern science has a huge amount of factual material from experimental observations of the phenomenon of self-assembly. Particularly impressive are observations of the self-assembly of biological objects, in particular Klug's work on the assembly of plant viruses, which was awarded the 1982 Nobel Prize. Experimental studies of self-assembly are predominantly exploratory in nature and provide extensive knowledge of how this occurs. The question of why this happens this way and not otherwise is a challenge to modern natural science.

Let's consider the well-studied assembly scenario of the bacteriophage T4 virus, described in all textbooks and which is a classic object for studying self-assembly. A simplified version of the scenario is shown in Fig. 2. 54 types of proteins are involved in the assembly, which, strictly in a certain sequence, are aggregated into subaggregates of various levels and then the subaggregates are assembled into a completed viral particle, including more than a thousand protein molecules. It makes no sense to model this finely coordinated, branched hierarchical process using stochastic concepts of randomly colliding molecules.

Figure 2 — Scenario for assembly of bacteriophage T4

There is no doubt that the virus assembly process is deterministic and controllable, and to fully understand this process it is necessary to determine the means of determination and control mechanisms. Scientific thinking in the second half of the twentieth century was fascinated by the creation of the computer and the discovery of a system for controlling protein synthesis. Both systems are ideologically identical and embody the principle of concentrated control. The carrier of concentrated control is a sign system - a linear imperative control language. It is quite natural that the first attempts to mathematically model the processes of self-assembly and self-reproduction were made within the framework of automata theory, for example by von Neumann. However, experimental observation data do not confirm the validity of such models. Self-assembly processes do not fit into the concentrated control scheme.

Experimental data allows us to assert that in the process of self-assembly there is no control element and in no form is there a sign system that describes the order of assembly acts or the order of arrangement of elements in the structure of self-assembly products. The specificity of the self-assembly phenomenon is that the process is undoubtedly determined, but the determination mechanism does not fit into the simple and understandable method of concentrated control.

Self-assembly is an implementation of the distributed control method, in which control functions are implemented in the internal structure of the elements participating in the process, and control information that determines the process is distributed across all elements. Consequently, the carrier of determination in distributed control are specific sign systems that are radically different from the simplest imperative linear languages, like computer languages ​​or the DNA-protein system. The main task of studying self-assembly is to determine the logic of the relationships between elements and the search for sign systems, carriers of distributed control.

Let's consider a hypothetical self-assembly scenario that meets the requirements for implementing distributed control. Some steps of the scenario are depicted in Fig.3.

Figure 3 - Hypothetical scenario of interaction of elements

Let us assume that the assembly of the simplest structure, a tube, involves two types of molecules: a sphere and an amphora. We consider only the logical aspect of self-assembly and do not yet involve the physicochemical basis of the interaction in the description. The sphere and the amphora are abstractions endowed with the capacity for some postulated montage activity. The abstraction “combination lock” is introduced into the element. The installation act is only possible if the lock codes match. The amphora and the ball have different combination locks K1 and K2, so in the first assembly step two balls are interlocked. As a result, a subunit with a new combination lock K2 is formed. Next, an amphora with a combination lock K2 is docked to the sub-unit and a “tooth” sub-unit with a combination lock K3 is formed. Next, discs are built from the teeth as sectors, and the discs are assembled into a tube. In order to construct such a scenario, it is necessary to postulate a procedure for an elementary act of assembly.

Let us define the elementary act of assembly as a procedure consisting of four steps:

.activation of the combination lock;

.search and convergence of two elements with matching lock codes;

.lock activation

.extinguishing their activity, forming a new combination lock to continue the process.

Thus, at each assembly step, the assembly acts are determined by the states of the combination locks, and the execution of the assembly act ends with the generation of a new code and a new lock.

To date, there are mathematical tools that can describe the logical aspect of self-assembly processes. Streaming production systems meet the requirements for sign systems that support distributed control and can, at a logical level, act as determinants of the self-assembly process. The immediate next task is joint work with physical chemists and biologists to build flow production systems that simulate real scenarios of self-assembly of specific objects at a logical level. This will be followed by a search for elements of flow production systems in the physical and chemical structure of elements participating in self-assembly. The greatest readiness for such programs is in the field of plant virus research. .

If anyone thinks that Donetsk University student N.V. Rebrov wrote nonsense here, I quote material that I read 20 years ago and which I cited in my book "Geometry of Life" .

There is a very important observation from the Soviet Union about the “auto-assembly” of organic structures. Academician V.A. Engelhardt(1894-1984).

Here's what he writes about this phenomenon in the article “On some attributes of life: hierarchy, integration, “recognition.”(The article was published in the collection: “Philosophy, natural science, modernity”, Moscow, “Mysl”, 1981).

“The phenomena of “recognition” and at the same time integration in a particularly distinct, almost visually perceptible form (if you resort to the help of an electron microscope) are expressed in the processes of so-called self-assembly of supramolecular structures, such as viruses and phages, ribosomes or enzyme particles with a complex structure . A large number of processes of this kind have already been studied in detail. They essentially boil down to the fact that if a complex, multicomponent object is artificially decomposed into its component parts by one or another gentle technique, isolated from each other, and then mixed in the proper proportions and favorable conditions are created, then they will spontaneously reassemble into their original integrity. Its usefulness is easily and with utmost convincingness proven by the fact that not only its original morphological structure is restored, but also its specific biological properties, for example, catalytic activity in enzymes, infectious properties in viruses, etc.”

How do you all, friends, understand the course of the described processes? "recognition" And self-assembly molecular structures into something “whole” and at the same time animated, animated(!), cannot be imagined without processes information and energy interaction of the microworld with the macrocosm. How this process of information and energy interaction between the macro and micro world proceeds was quite clearly described by the Soviet scientist, Professor Alexander Leonidovich Chizhevsky (1897-1964), the creator of a new science - " Heliobiology".

“The process of development of the organic world is not an independent, autochthonous process, closed in itself, but is the result of the action of terrestrial and cosmic factors, of which the latter are the most important, since they determine the state of the terrestrial environment.At any given moment, the organic world is under the influence of the cosmic environment and most sensitively reflects in itself, in its functions, the changes or fluctuations that take place in the cosmic environment. We can easily imagine this dependence if we remember that even a small change in the temperature of our Sun should have entailed the most fabulous, incredible changes in the entire organic world. And there are a lot of such important factors as temperature: the space environment brings to us hundreds of different forces that are constantly changing and fluctuating from time to time. Electromagnetic radiation alone, coming from the Sun and stars, can be divided into a very large number of categories, differing from one another in wavelength, amount of energy, degree of permeability and many other properties..."

I can only add: similar to how people are born in Nature according to the principle "self-assembly" various viruses and phages, also according to the principle of “self-assembly” in the ocean world broadcast, which the ancient sages rightly considered cradle of life and the medium of distribution of heat and light, all life in general was born. When making sense of this information, I would recommend taking into account the fact that spontaneous generation complex life forms on earth occur occasionally and these evolutionary processes, apparently, are associated with cataclysms on a global scale, for example, such as the change of the Earth's poles or the fall of giant asteroids to the Earth. In nature, nothing happens by chance, everything is natural, therefore, any global process necessarily connected with something else global process. And when something is dying on a planetary or even a cosmic scale, something else is born at the same time.

Deputy Director of the Foresight Center of the Institute for Statistical Research and Economics of Knowledge at the National Research University Higher School of Economics Alexander Chulok read at the Central Park of Culture and Leisure named after. Gorky lecture on scientific and technological progress and its impact on humanity. In addition to the topic of technology development, Stocking spoke about the emergence of new markets and the death of old ones, as well as the problems associated with these processes.

In response to the question “how to guess the future now?” I have to disappoint you: this is almost impossible. However, the future can be shaped the way we want it to be. An economy of expectations has arrived, which is largely due to fundamentally new needs and new approaches to working with information. Now I will briefly talk about what key changes await us in the next 20 years in the main sectors of the economy.

Medicine and healthcare

Health is the first thing that worries a person. In Russia, there is an increasingly noticeable trend towards taking care of one’s physical condition: everyone wants to be fit, beautiful, athletic and, of course, healthy. There is a clear trend towards personalization in healthcare.

I'll show you with this example. Medical developments will make it possible to adapt a treatment regimen to a specific person based on deciphering his genome (already a “basic” set costs 100 euros, but what will happen when the cost drops tenfold?), analysis of his environment, how he lives, what breathes. In the future, instead of standard medications, individual treatment regimens will be sold, according to which, say, you need to get up at 6 am, sleep until 9, be sure to eat strawberries and under no circumstances be in the sun before 10 pm in Turkey, but if it is the sun Egypt - then there are no questions.

Alexander Chulok
Photo: hse.ru

A separate question is whether patients will adhere to the required treatment regimen? Most people take the pills, say, not for five days, as they should, but for three and quit - it helped, why continue to take it? In the case of chronic diseases, almost every second person ignores doctors' orders. Implantable microchips will allow you to forget about the schedule for taking medications and optimize their dosage.

I hope we will see the end of traditional medical examination: there will be no need to go to the clinic to get tested, a special wrist bracelet will monitor the state of the body. There are already mobile devices that record dozens of different biometric indicators.

Are big pharmaceutical companies ready for such changes? Obviously they will have to adapt. As well as pharmacies, which in their current form will also no longer be needed, because a person will be able to print any drug on a home 3D printer.

The development of 3D printing is associated with the next trend - organ replacement. Last year, an old woman in Belgium had her jaw replaced by having it printed on a 3D printer. The news then quickly spread throughout the world, but in total the operation cost about a million euros. In 20 years, many people will have some kind of printed organ in their bodies. Now they are already printing a lung, a kidney, an eye.

Attempts to “fix” what is already “broken” will become a thing of the past; doctors will not say, if you get sick, then come. The medicine that is now developing in the USA, Germany, and Israel is preventative medicine. Its basic task is to prevent the disease, and not to treat its consequences.

Improving human properties is another rapidly developing trend in medicine. Now there is a merging of nano-, bio-, info- and cognitive technologies that make it possible to radically strengthen a person, optimize his intellectual and physical characteristics literally beyond the intuition of the most brilliant designer. A few years ago, a congress of futurologists took place in the Swiss city of Lucerne, who said that by 2045 a person would gain immortality, and thoughts would be transmitted from person to person, which could lead to the formation of new communities.

Now imagine this picture: a 120-year-old man who passes the GTO better than a thirty-year-old, runs cross-country and whose brain works five times better and has ten times more experience. The employer will hire him, and not the young man, who still needs to learn a lot. What should 30-year-old loafers do? And this is a global challenge. Many countries have already seriously thought about this.

Now there is a lot of analytics based on the analysis of social network data, some talk about their control. But how will you control your thoughts? For example, if earlier in a number of European countries, when you were caught on a recording made by a city camera, you could demand that you be cut out of it, now what will you cut out? Satellite? Interface? Facebook or Mindbook?

It is obvious that technology will increasingly influence the geopolitical situation: if a country does not “fit in” with the new technological wave and does not provide its citizens with a high quality of life, it risks losing the most active creative layer, pulsating with ideas.

Information and telecommunication systems

We are witnessing the rapid and total penetration of information and telecommunication technologies (ICT). Who would have imagined 70 years ago that we would talk using small boxes? Now almost everyone goes with mobile phones, some - with smartphones in the form of a bracelet. The distance between the device and the human body is 2-3 centimeters. And it is shrinking; in the future, devices will simply go under the skin. A little more and we will have brain-computer interfaces.

Photo: Jordi Boixareu / Zumapress / Global Look

Now it’s difficult to imagine how virtual reality and augmented reality will change our thinking. Our society will disintegrate - we will listen to a lecture, sitting in virtual reality glasses in the country, while being in a virtual room or school. Nowadays, thanks to services such as Coursera, you can watch excellent courses in almost all areas of knowledge. And for now you are just listening to webinars, but in the future technologies will appear that will allow you to be inside this virtual room.

For example, the market for augmented reality technologies in surgery is about $5 billion, and this is just one application. There are already prototypes of helmets that allow you to obtain up-to-date and complete information about the object under construction: who created it, how much it costs and what problems it may have. This is a completely different level of analysis, management and control.

The time is coming for fully digital factories. For example, Amazon.com does not have a single person in its warehouses; robots are responsible for almost all processes. We have only a few rare examples of attempts to create such productions. It is obvious that the effect of their spread will be equivalent to telegraph technology for the world of pigeon mail. The world is moving to platform solutions, this is a completely different production paradigm, and we, for example, are all trying to establish a consolidated discussion in the country on 3D printers, while abroad they have long been sold in specialized stores, or discussing solar panels, and developments have already appeared transparent solar battery. The next step is to replace the windows with them and move towards a completely energy-independent home. And if it is also connected to a smart grid - a smart distributed energy system, then it will also begin to release energy into the network, thereby achieving a positive balance. How much do you pay for electricity? Now imagine that this money will be paid to you.

Energy

Most likely, the energy sector of the future will be autonomous, smart, environmentally friendly and adaptive to human needs. Many people have external batteries that charge mobile devices, but a film has now been developed that allows you to charge your phone in a few minutes. In the future, its battery will last not 3-4 days, but a month or two, years.

The next trend in energy is everything independent. In America, the technology of an autonomous soldier has been developing for several decades, charging equipment simply by walking. Now imagine that you are in a kind of “energy cocoon”; you are connected through a special suit or device to the general power distribution network. It will be possible to exchange energy directly. Tesla's recently introduced home storage device is just the first move. It is very expensive and not yet particularly effective, but colossal breakthroughs in the energy sector are expected.

In classical foresights, it is customary to study not only those trends that are most likely to occur, but also those events whose probability of occurrence is minimal, but if they happen, then such a “wild card” will not be of any use to anyone. One of these, alas, unpleasant “wildcards” was the accident at Fukushima; few people expected it, but the effect was colossal. Now many are analyzing the effects of the development of accessible technologies for extracting methane from gas hydrates, shale, and oil production from unconventional fields. But these are all events in the zone of our managerial foresight, but what if we create efficient, cheap, “green”, and at the same time miniature energy sources, for example nuclear mini-reactors? Their impact on existing value chains will be enormous.

Transport

Transport technologies will provide the effect of space compression. Unfortunately, Russian infrastructure still acts as a strong barrier to the development of this trend in our country. But I would really like to spend a weekend in Kamchatka or Baikal. As we ponder road construction plans, China's high-speed trains are seriously aiming to break the 1,000-kilometer-per-hour barrier using magnetic levitation technology.

Modern vehicles will, of course, operate not only on the ground, but also in the air, and some may go beyond the atmosphere. Many countries are already developing a “space elevator”. The development of tether systems, including the development of a “space elevator,” will make it possible to change orbits spacecraft, move cargo between orbital stations, launch small spacecraft and deliver payloads into orbit. The key barrier here is the cable itself, which must not even withstand the elevator, but its own weight. Fiber as thick as a hair must withstand a ton (currently 500-600 kilograms). To make such a cable, nanotechnology is needed. They will create a real revolution in many industries.

Manufacturing, science and education

Now we are trying to introduce additive technologies - 3D printing, and they will be replaced by molecular self-assembly - this is an even more advanced technology. At the molecular level, it will be possible to collect anything. Using nanofactories, it will be possible to create things, products; in the future, a cow will not be needed to produce milk. These technologies are the killers of 3D printers.

3D printed jaw implant
Photo: uhasselt.be

The key problem in everything smart (smart networks, cities, homes, businesses, etc.) is modeling. And here our mathematicians come to the rescue. Here our country definitely has a chance to achieve a leading position in the market. However, we observe an interesting pattern: as soon as a researcher increases the level of citations, his affiliation and affiliation with one or another university often changes: if in his early works it is indicated that the person is from Russia, then in later works - bang! - already some American university.

China followed this path. The Chinese bought professors based on their citation index, along with their families, and gave them salaries the same as in America. They told them: “work, but the rights to the created intellectual property will belong to the PRC.” Now there are Chinese cars, Chinese planes - everything is made in China.

We spend about $15 billion a year on science, while the United States spends $450 billion. If you look at the distribution in world science, there are very few of us there. And such a moment. There is a method called “analysis of research fronts”. If other scientists suddenly begin to actively cite researchers who work in certain areas, it means that it is in these areas of science that a breakthrough is possible. But if publications abroad, say, on medicine, are directly related to biochemistry, chemistry, physics, engineering, then in the publications of Russian scientists there are almost no such connections. Our main field of science is astronomy.

Original article: Molecular Mimetic Self-Assembly of Colloidal Particles. Zhengwei Mao, Haolan Xu, Dayang Wang *//Advanced Functional Materials, Volume 20 Issue 7, Pages 1053 - 1074.

Moscow State University named after M.V. Lomonosov,Faculty of Materials Science , Rabstract of a 3rd year graduate studentVolykhov Andrey Alexandrovich

1. Introduction

For decades, colloidal particles have been important objects of research. Many objects of different chemical nature, such as clay, ink, fog, micelles, paints, proteins, bacteria, red blood cells, can be considered as colloidal particles. They can be used and studied in the light of physics with minimal attention to their chemical properties at the molecular level. The ubiquitous existence of colloidal particles and the enormous diversity of their chemical nature highlight their importance for our lives, which cannot be neglected, but which has not been sufficiently studied.

The simplest definition of colloidal particles is that they are microscopic objects found in an extended medium in the form of particles whose dimensions in at least one direction range from a few nanometers to micrometers. Compared to bulk materials, they are small enough to disperse homogeneously in the medium. This was the reason for the development of colloidal chemistry and technology, since it is necessary to convert solid substances of organic or inorganic nature into small soluble particles for a variety of practical applications - the production of pigments, clothing, food and pharmaceutical industries.

Compared to molecules, colloidal particles are large enough to scatter light (the so-called Tyndall effect). One of the classes of colloidal particles is drops and bubbles in a liquid or solid medium, having a spherical shape due to minimization of surface energy. Another class of colloidal particles are macromolecules such as polymers, particularly proteins, and molecular aggregates such as surfactant micelles. In a liquid environment, they form not truly molecular, but packed structures due to weak intermolecular interactions. The third class of colloidal particles are solid objects of various shapes, for example, spheres, cubes, rods, disks, etc.

The diversity of colloidal particles allows one to study many fundamental problems in thermodynamics. In accordance with the terms of molecules, supramolecular formations and bulk crystals, the terms “colloidal molecules”, “supraparticles”, “supracrystals” are used for colloidal particles.

Modern colloidal chemistry allows the preparation of colloidal particles from a wide range of organic and inorganic materials, monodisperse in size, shape and surface properties, which are required to study the effect of particle size on their properties, necessary for potential practical applications. Depending on the material and synthesis method, aggregates of colloidal particles can be “amorphous,” “polycrystalline,” or “monocrystalline.” In the case where attractive forces, for example, van der Waals forces, prevail between particles, the particles agglomerate and, as a result, fall out of solution, forming a glassy precipitate in which the particles are disordered. When repulsive forces, such as electrostatic or steric, are strong enough to overcome particle aggregation, particles can self-organize into periodic arrays to increase entropy if the particle volume fraction exceeds a critical value, for example, for hard spheres - 0.50. This applies to particles that are monodisperse in shape and size.

Long-term sedimentation under the influence of gravity or controlled removal of solvent leads to the formation of periodic structures of close-packed particles - colloidal crystals. The entropy-driven self-assembly of monodisperse particles depends little on their size. Long-range order in periodic ordering has been discovered for colloidal crystals of nanoparticles smaller than 10 nm produced by controlled solvent evaporation.

Self-organization is common in biological systems when biological molecules are ordered at different levels of hierarchy with the necessary spatial and temporal characteristics. The dynamic nature of self-assembly plays a key role in life processes. However, hexagonal or square packing in colloidal crystals is too simple compared to the variety of structures in biological molecules and supramolecules. For colloidal clusters, it is in principle possible, although difficult, to precisely control the spatial arrangement of particles in clusters by specifying the shape, size of the clusters and, in particular, the number and location of functional groups on the surface. Thus, colloidal clusters can be created using well-known molecular synthesis and self-assembly methods. For millimeter-sized blocks with a specifically modified surface that imitates the functional groups of molecules, self-assembly into complex structures resembling molecular and supramolecular ones has already been achieved. However, at the mesoscopic level, such a task turns out to be much more difficult. In the phase diagram corresponding to the ordering of particles, the fields of the crystalline and liquid phases coexist; therefore, the equilibrium between the phases is dynamic. The process of self-assembly of colloidal particles resembles crystallization, but only roughly, since it does not reveal such details as the preferential growth of certain crystallographic faces. IN Lately Great progress has been made in creating specific particles with anisotropic surfaces with different areas for which attractive or repulsive forces act. The groups of van Blaaderen and Murray used two different types of colloidal particles with oppositely charged surfaces, the nature of which resembles "ionic" crystallization.

This review offers an examination of current advances in molecular-like self-assembly of colloidal particles and the associated fundamental and technical challenges. The presented works fall into three categories: 1) studies of the behavior of particles at interfaces similar to surfactant molecules; 2) synthesis of anisotropic colloidal particles, especially those containing spatially separated areas on the surface with specific properties that imitate the valences of atoms; 3) anisotropic self-assembly and crystallization of colloidal particles.

2. Particles as surfactants

In a two-phase system consisting of two immiscible liquids, such as water/air or water/oil, it is well known but not well explained that colloidal particles can behave like surfactant molecules, namely, it is energetically advantageous for them to aggregate at the interface, thereby stabilizing the foam or emulsion. The attachment of solid particles to boundaries was discovered by Ramsden back in 1903. In 1907, Pickering conducted a detailed study of how inorganic particles stabilize emulsions. Since then, emulsions stabilized by colloidal particles are called Pickering emulsions. The surface activity of the particles can be explained as a result of partial wetting of the particle surface with both water and oil. The energy required to remove a particle of radius r from the water/oil interface with tension γ is expressed as follows:

-ΔE = πr 2 γ (1 ± cos θ) 2 , (1)

where θ is the contact angle created by the particle on the water/oil surface. It defines the distribution of particles at the water/oil interface (Fig. 1A). For hydrophilic particles θ< 90º, то есть большее количество частиц находится в водной фазе, что заставляет изгибаться монослой частиц и приводит к образованию эмульсии масла в воде. Для гидрофобных частиц θ >90º, and the formation of an emulsion of water in oil is observed, having spoiled it. In this respect, the action of particles is similar to the action of surfactants. However, the adsorption of particles at interfaces is irreversible, unlike surfactants.

For particles less than 20 nm, the linear voltage τ begins to play a noticeable role, so expression (1) is written as:

-ΔE = πr 2 γ (2 cos θ e (1 - cos θ) - sin 2 θ) + 2πrτ sin θ, (2)

where θ e is the equilibrium contact angle in the absence of linear voltage. When it is not 90º, the positive line voltage prevents particles from attaching to the interface. Only at θ close to 90º can relatively stable adsorption of small particles at the interface occur. The difference in the behavior of surfactants and colloidal particles is explained by the fact that surfactant molecules have hydrophilic and hydrophobic parts separated in space, while the surface of colloidal particles is isotropic. Therefore, colloidal particles cannot be packed into structures similar to liquid crystalline ones, for example, micelles. In most cases, colloidal particles are surface active but not amphiphilic.

2.1 Microparticles at interfaces

Microparticles are widely used in industry as emulsion stabilizers. Such emulsions, from the point of view of the influence of stabilizer and electrolyte concentrations, behave in the same way as stabilized surfactants. The associated monolayers of colloidal particles provide mechanical and steric barriers to the emulsion droplets that prevent coalescence (Figure 1B). “Bound” here means that the particles tightly cover the surface and there are attractive forces between the particles. However, Pickering emulsions do not require a dense layer - stable emulsions are formed even with 5% surface coverage of particles. Khorozov and Binks experimentally showed that well-ordered and densely packed monolayers of particles stabilize the thin oil films separating water droplets and prevent coalescence of water droplets even in emulsions with very low oil content (Figure 1B). In the case of surfactants, such efficiency as in the case of Pickering emulsions cannot be achieved.

In surfactant-water-oil systems, the type of emulsion can be changed - from an oil-in-water emulsion to a water-in-oil emulsion - by changing the ratio of water to oil. Such a phase transition is practically not observed in the case of particles. The reason for this is that the surface wettability of colloidal particles is fixed. To change the wettability of colloidal particles, Binks et al grafted carboxyl groups onto the surface of polystyrene microspheres. When the carboxyl groups were completely ionized (pH > 10), the spheres became highly hydrophilic due to their negative charge and stabilized oil droplets in water. By lowering the pH of the medium or increasing its ionic strength to reduce the removal of protons from the surface of the particles, the authors made the particles hydrophobic, thereby obtaining a water-in-oil emulsion (Fig. 1C). Experiments were carried out for particles ranging in size from 200 nm to 3.2 µm. The same authors coated 150 nm polystyrene spheres with a block copolymer of 2-(dimethylamino)ethyl methacrylate (DMA) and methyl methacrylate. Hydrophobic blocks of methyl methacrylate were adsorbed on the surface, leaving a crown of poly-DMA blocks sensitive to external influences on the outside. At pH 8.1, deprotonation of poly-DMA occurred, and with increasing temperature, a transition from hydrophilicity to hydrophobicity occurred. Due to this temperature sensitivity, below 55ºC there was an emulsion of oil in water, above 65ºC - water in oil, and at intermediate temperatures - both types.

The similarity between colloidal particles and surfactants lies not only in the stabilization of emulsions, but also in the organization of particles at interfaces. Pieranski first observed the formation of a two-dimensional colloidal crystal at the water/air interface and proposed that the asymmetric charge distribution on the colloidal particles leads to dipole repulsion of the particles, which stimulates their smosassembly. Once colloidal monolayer crystals are formed, they can be transferred to another substrate using the Langmuir–Blodgett method. Moreover, it is possible to create free and unbroken films of colloidal crystals up to several square millimeters in size. Water/oil interfaces are less commonly used to create colloidal crystals than water/air interfaces. However, since the charges at particle/oil boundaries are higher than at particle/air boundaries, the particle ordering appears to be more stable. Binks and colleagues showed that ordering is controlled by the Coulomb interaction between particles, which depends on the magnitude of the angle θ, and the order-disorder transition occurs at angles θ from 115º to 129º.

Emulsion droplets were also used to order the particles. Nagayama and co-workers first proposed a method for self-assembling particles into micrometer-sized hollow clusters, where the particles were held together in clusters by small molecules such as lysine and casein. They first proposed the term "superparticles" for the hollow clusters obtained in this way. Dinsmore's group showed that by sintering colloidal particles at temperatures higher than the glass transition temperature of the particle material, it was possible to bind the particles together to form micrometer-sized hollow clusters (Figure 1D). They proposed calling such clusters “colloidosomes” by analogy with liposomes—capsules made of lipid bilayers. They also proved that the permeability of the resulting hollow clusters depends on the size of the constituent particles and sintering time. Paunov's group prepared colloidosomes from water-in-oil emulsions stabilized by polymer microrods.

2.2 Nanoparticles at interfaces

For colloidal nanoparticles smaller than 20 nm, positive linear tension and significant thermal energy fluctuations promote particle detachment from interfaces. Stable attachment is only possible with a contact angle close to 90º, however, this means partial wetting of the surface of the particles with both water and oil, which entails their low colloidal stability. Therefore, a hydrophobic coating is necessary for the particles. Compared to microparticles, the behavior of nanoparticles at interfaces is less well understood. The earliest research using interfaces to self-order nanoparticles concerned the two-dimensional crystallization of proteins at air/water interfaces, in some cases involving a lipid monolayer. Fujioshi's group has developed a way to use water/oil interfaces to create two-dimensional crystals of proteins and other macromolecules.

Russell and co-workers showed that CdSe quantum dots with a diameter of less than 5 nm were adsorbed at the toluene/water interface and thereby stabilized water droplets in toluene. The attachment of particles to the interface depended on the particle size according to equation (2): smaller quantum dots, adsorbed at the interface first, were replaced by larger ones. Wang et al. showed that nanoparticles can adsorb at water/oil interfaces only if the particles have a hydrophobic coating. Both hydrophilic gold and silver particles and hydrophobic maghemite particles were able to attach to interfaces after coating with ligands (Fig. 2A). Wang and co-workers measured the contact angle for films of nanoparticles transferred from the interface and obtained values ​​close to the theoretical 90º. On the contrary, the θ values ​​for the initial films turned out to be greater or less than 90º, depending on the initial coating of the particles. In Vanmekelberg's work, hydrophilic gold nanoparticles became surface active after the addition of ethanol, which lowered the surface charge density on the particles. Freezing the self-assembly of nanoparticles by gelling makes it possible to obtain thin films with controlled permeability. Water/oil interfaces have also been used to self-assemble viral particles, the cross-linking of which results in semipermeable membranes (Figure 2B). Wang's group used gold and CdTe nanoparticles coated with mercaptopropionic or mercatobenzoic acid to theoretically and experimentally investigate the effect of particle surface charge on their attachment to interfaces (Figure 2C). Binding was observed at low pH due to protonation of carboxyl groups, which reduced the surface charge and therefore increased hydrophobicity. Deprotonation at high pH led to the redispersion of particles in the bulk of the aqueous phase. It is assumed that increasing the surface charge not only reduces the surface activity of the particles, but also increases the electrostatic repulsion. These experiments indicate that the binding of nanoparticles to interfaces is reversible.

Based on the results of early studies of the transfer of colloidal nanoparticles from the aqueous to the oil phase using surfactants, the reversibility of particle adsorption at interfaces was already assumed. However, translation could not be achieved. The transfer of particles to another phase using a surfactant is limited in particle size: particles larger than 10 nm are difficult to transfer. Wang and co-workers successfully used pH to direct particles from water to the oil phase and vice versa across interfaces by growing pH-sensitive poly(2-dimethylaminoethyl methacrylate) “brushes” on the particles via surface-initiated atom transfer radical polymerization. However, the transfer efficiency was quite low. To improve it, Wang's group coated the nanoparticles with temperature-sensitive copolymer "brushes." The resulting nanoparticles transitioned from the aqueous to the oil phase as the solution ionic strength or temperature increased (Figure 2D). ... The same group achieved success in transporting particles across water/organogel and hydrogel/water interfaces by degrading their hydrophobic polymer shell, showing that strong hydrogen bonding at the surface is required for particle transport into the aqueous phase.

3. Anisotropic particles

As noted above, colloidal particles are mostly surface-active, but not amphiphilic, since their surfaces are isotropically hydrophilic or hydrophobic, unlike surfactants, whose molecules combine a hydrophilic and a hydrophobic fragment. For colloidal particles to mimic the behavior of surfactant molecules, they must also contain spatially separated hydrophilic and hydrophobic parts. Such particles are named after the two-faced Roman god Janus, Janus particles. Recently, the technique of creating anisotropic particles has advanced from the creation of Janus particles with two zones of different wettability to the production of particles with multiple zones of different chemical natures on the surface, which better model association processes occurring at the atomic and molecular levels. Such particles are called “patchy”. They were first obtained by Glotser's group in 2004. Janus particles can be considered a special case of spotted particles with two spots at opposite poles. Nelson theoretically predicted that functional spots on the surface of particles could manifest themselves as valencies at the nanoscale, determining the bonding directions of neighboring particles. This section is devoted to methods for the synthesis of Janus particles and “spotted” particles. These methods can be divided into surface modification methods and direct synthesis methods, and each of these groups can be further subdivided into template-free and template-free synthesis methods.

3.1 Spatially selective surface modification using a template

Since colloidal particles consist of either one component or several components, but homogeneously mixed within the particle, it is very difficult to modify certain areas of the particle surface. Space-selective modification usually requires the use of templates or masks. The main disadvantage of this method is the extremely low yield of the product. Advantages include gentle control of the size and geometry of the modified regions of colloidal particles and the ability to vary both particles and coating materials. This is a complex process involving, at a minimum, template assembly, surface modification, and template removal. In this case, the limiting factor for the success of the method is the process of obtaining the template. Due to the high curvature of the surface of colloidal particles, conventional lithographic methods are not applicable to them. The developed methods are divided into three categories: 1) selective surface modification at interfaces, 2) colloidal lithography, 3) soft lithography. These categories are described below.

3.1.1 Interfaces for creating Janus particles

In 1989, Veissier et al reported the first success in selectively hydrophobizing one half of glass droplets with a diameter of 50-90 μm using octadecyltrichlorosilane, while the other half remained hydrophilic by introducing cellulose masking. They proposed the term "Janus drops" for the resulting particles. This success prompted further research to modify half of the particles using various methods using solid/air interfaces as templates. Among them, the most commonly used is physical deposition of metals from vapor, in particular thermal or using an electron beam. When colloidal particles are contained in a polymer matrix, it is possible to achieve precise control of the decorated areas on the surface of the particles by plasma burning the matrix. To date, it has not been possible to obtain Janus particles smaller than 50 nm due to the impossibility of ensuring the self-assembly of such particles into a monolayer on the surface of the substrate.

Liquid/solid interfaces are used to create asymmetric colloidal particles through chemical modification. Fujimoto and co-workers demonstrated two approaches to modifying particles at such boundaries. In one approach, particles were adsorbed onto a solid substrate previously coated with functional molecules, and then, through a chemical reaction, the molecules in direct contact with the particle were covalently bound to it. The second involved depositing a colloidal solution of small particles on a monolayer of larger particles, oppositely charged. In this case, electrostatic interaction led to surface decoration on only one side. Velegol's group has recently achieved success in the selective self-assembly of polyanions onto positively charged species, allowing precise control of the surface area for modification (Figure 3a). Li and co-workers used the first approach to tether thiol-terminated polyethylene glycol to 12 nm gold particles on the solid substrate side (Figure 3b).

Boundaries such as oil/water or air/water were used as “templates”. Raven et al. used the Langmuir method to bind SiO 2 particles to the water/air interface and modified the particles on the water side with negatively charged gold nanoparticles. Chen's group was able to create Janus particles by replacing the original hydrophobic ligands of gold nanoparticles tethered to the air/water interface with hydrophilic ones. The oil/water interface appears to be preferable to the air/water interface since it does not rely on the Langmuir method and allows for mass production of Janus particles, given the extremely large interface areas for Pickering emulsions. However, phase selectivity is difficult to guarantee for oil-in-water emulsions due to the possibility of particle rotation. Currently, it is possible to selectively modify only submicrometer-sized particles. Paunov and Keir developed a two-step gelation process—first the aqueous phase with gellan, then the decane phase with polydimethylsiloxane (PDMS)—to transfer particles from the decane/water interface to the air/PDMS interface (Figure 3c). Granik et al. used molten wax/water interfaces to adsorb silica particles and performed selective modification on the free side of the particles. For small particles, phase-selective surface modification results in monolayer or multilayer films composed of hydrophobic or hydrophilic particles rather than Janus nanoparticles. The first report of a successful synthesis comes from Xu's group, which used a water-in-oil emulsion to selectively grow gold nanoparticles on iron oxide, FePt, and gold nanoparticles (Figure 3d). The reason for the success is the rapid growth of hydrophilic silver particles on hydrophobic nanoparticles with good matching of unit cell parameters, which gives high stability of dimer particles and freezes their rotation.

3.1.2 Colloidal lithography

In a colloidal crystal, the particles in the lower layers are arranged in an orderly manner under the voids in the upper layers. Thus, an ordered array of colloidal particles provides an effective template for modifying the particles of the lower layer. Using this idea, Wang's group produced micrometer- and submicrometer-sized colloidal particles with a variety of surface modification motifs by thermal metal deposition. They were also able to provide stereo decoration with a certain number of gold dots, using intermediate arrays of the two outer layers as masks for gold deposition (Fig. 4a). Pawar and Kretzschmar recently proposed a simple colloidal lithography technique using adjacent particles of the same layer as masks.

Moskowitz et al. and Shin et al. showed that contact regions with neighboring particles are inaccessible to the external reaction medium, thus the contact regions produce reverse reproduction on the particle surface after modification (Fig. 4b). Shin proposed the name "contact area lithography" for this technique. Zhao et al. used the method for weakly agglomerated colloidal crystals. Compared to Wang and Kretzschmar's colloidal lithography results, contact region lithography produces features on smaller particles, down to 100 nm. However, all types of the method have limitations associated, firstly, with the polycrystallinity of colloidal crystals and, as a consequence, poor reproducibility; secondly, with the difficulty of dispersing particle arrays back into solution, which leads to low yield; thirdly, with restrictions on particle size, since it is not possible to obtain colloidal crystals of sufficient size from particles less than 10 nm. However, colloidal lithography remains the only method that provides surface decoration according to a three-dimensional pattern.

3.1.3 Contact printing

Placing elastomeric marks on the surface of particles leads to the simplest method - contact printing. In this case, only the side of the particle facing the elastomeric mark is modified. Paunov and his co-authors obtained particles with opposite charges on different sides both by grafting cationic hydrophobic surfactants onto large negatively charged particles and by grafting small negatively charged particles onto large positively charged ones. Rubner and co-workers used contact printing of a polyelectrolyte layer onto microparticles coated with layers of cross-linked polymer (Figure 4c). Xia's group has achieved modification of certain faces of a silver nanocrystal with hydrophobic ligands. Although the method is quite simple, it cannot be applied to particles smaller than 100 nm.

3.1.4 Traditional lithography

For targeted synthesis of templates, traditional photolithography techniques were modified. This approach is applicable for particles larger than 1 µm. Here are 2 examples. Delville's group used photochemical deposition of chromium salts to pattern the surface of 10-micrometer silica particles. Groves et al used UV-ozone photolithography of 7-micrometer quartz particles, patterned using a micromask (Figure 4d).

3.2 Spatially selective surface modification without using a template

The use of template modification methods is limited by the complexity of obtaining the template. Of course, Janus particles already obtained using a template can be subject to further modification without a template, but further we will consider direct modification of the surface without any templates. The most direct way of such modification is to use a hard needle or a narrow beam. Yamazaki and Namatsu created ordered arrays of 100 nm diameter rods on 25 micrometer polymethyl methacrylate particles using electron beam lithography. However, this method is not applicable to smaller particles.

Chemical methods for template-free modification are currently mainly based on the different reactivity of the faces of inorganic nanoparticles. The feasibility of this approach depends very much on the material. Murphy et al showed that cetyltrimethylammonium bromide preferentially binds to the (100) faces of silver nanorods rather than the (111) faces (Figure 5a).

Nelson theoretically predicted that when anisotropic objects are deposited onto spherical particles, they crystallize with tetrahedral symmetry. However, experimental use of this fact is difficult. Stellacchi's group showed the presence of phase separation of different thiol ligands near the surface of gold and silver nanoparticles due to high surface curvature (Figure 5b). They also managed to achieve selective replacement of thiol ligands located in polar positions with ligands of the third type.

3.3 Template synthesis

Along with the intensive development of spatially selective surface modification, many methods have been proposed for the synthesis of anisotropic colloidal particles consisting of two or more spatially separated parts with different chemical compositions and/or different ligands. The attachment of smaller particles to larger particles is described in Section 3.1, but this is more likely to be a modification of the surface since the adsorption of small particles on large particles is not well controlled.

Koo and co-workers succeeded in joining 50nm and 100nm latex particles together using electrostatic interaction. Using the macroporous structures of the top layer of a colloidal crystal as a mask, Yang and co-workers achieved plasma etching of the spheres of the bottom layer. The best template for the synthesis of anisotropic particles turned out to be membranes with cylindrical pores. Fitzmaurice and co-workers used such membranes to attach gold particles one at a time to quartz particles, thereby creating chains of unit-thick gold nanoparticles with a controlled number of particles on the quartz particles (Fig. 6a). Nathan's group created submicrometer-sized "barcodes" from electrochemically deposited gold and silver using a porous aluminum oxide membrane (Fig. 6b). Mirkin's group developed this strategy by creating sub-micrometer rods composed of gold and polypyrrole blocks that vary in hydrophobicity and charge.

A promising option for template synthesis of anisotropic particles is the use of templates to create clusters of colloidal particles. Xia's group used spatial constraints and capillary forces to draw particles into cavities to create clusters (Fig. 6c). Pine et al. used emulsion droplets as templates for clustering colloidal particles (Fig. 6d), and Young et al. were able to create mixed clusters of the two using this method. various types particles The method has the same disadvantages as template surface modification, but it allows one to obtain more complex structures by creating colloidal analogues of molecules.

3.4 Template-free synthesis

In contrast to the limited progress in template synthesis, template-free synthesis has developed greatly in the last 5 years.

3.4.1 Face-selective crystal growth

The method uses the difference in surface energies between different crystal faces. It allows you to obtain Janus particles in the shape of a dumbbell, “snowman” or “acorn”. The first, simplest option is to use nanoastics as seeds for the growth of crystals of other materials. Banin and co-workers selectively grew gold dots on the tops of nanometric cadmium selenide rods and tetrapods (Figure 7A). Gao's group created dumbbell-shaped Ag-Se nanoparticles by sequentially reducing silver nitrate and sodium selenite with an ascorbic acid solution. Xu and co-workers grew a shell of cadmium sulfide on specified faces of FePt particles using lattice parameter matching. Raven's group synthesized flower-shaped colloidal particles with a silica core and a shell of a specified number of polystyrene globules (Figure 7B). Kuhn and co-workers electrochemically grew gold nanoparticles at the ends of carbon nanotubes. Xia's group used gold nanoparticles as a site for the polymerization of styrene to produce anisotropic gold-polystyrene particles (Figure 7C).

The second way is to simultaneously crystallize two different precursors into one particle. Thus, Teranisi and co-workers obtained acorn-like particles of PdS x -Co 9 S 8 by reduction of cobalt and palladium acetylacetonates in dioctyl ether in the presence of octadecanethiol. Sunn et al synthesized dumbbell-shaped gold-iron oxide nanoparticles by decomposition of iron carbonyl and tetrachloroauric acid (Figure 7D). Hieon and co-workers synthesized a wide class of anisotropic metal/metal oxide particles by simple thermal decomposition of oleate (for the oxide part) and oleamine (for the metal part) complexes.

The third way is stepwise epitaxy based on vapor-liquid-crystal growth catalyzed by gold nanoparticles. For example, Yang and co-workers synthesized nanowires with Si/SiGe superlattices through a combination of laser ablation and chemical vapor deposition, and Samuelson synthesized InAs/InP using chemical epitaxy. It should be noted that although the resulting colloidal particles consist of two parts of different chemical natures, their surface has common chemical properties due to a uniform coating of stabilizing ligands. To introduce differences requires spatially selective modification, which, however, occurs easily in this case.

3.4.2 Microphase separation

Yabu and co-workers reported an elegant new method—self-assisted precipitation—to produce polystyrene-polyisoprene diblock copolymer microparticles (Figure 8A). It turned out that the resulting structures exhibited the ability to microphase separate nanostructures both on the surface and inside the nuclei. The type of resulting structures was determined by the ratio of components in the copolymer. Stewart and co-workers created Janus micelles from two block polymers, consisting of a mixed coacervate core and two shell hemispheres: one of polyacrylamide, the other of polyethylene oxide. To date, controlled microphase separation is the only, albeit complex, method that makes it possible to obtain specified mesostructures on the surface of particles, varying over a wide range.

In general, this method is a variation of a broader approach - the use of partial non-wetting between two immiscible phases. Partial nonwetting has long been used to create anisotropic polystyrene particles by using styrene to grow and polymerize on the surface of the particle. Due to excessive growth of styrene on the surface and limited wetting, it beads up, which leads to the formation of anisotropic particles (Fig. 8B). Weitz and colleagues optimized this method to create anisotropic particles of different shapes by controlling the direction of phase separation (Figure 8C). Wang's group obtained anisotropic polystyrene particles by joint effect from protrusion of the substance due to electrical effects in the polyelectrolyte and partial non-wetting of polystyrene by the polyelectrolyte coating (Fig. 8D). Using a similar approach, AgI-silica and Ag-silica Janus particles were synthesized by Melveni's group. Chen and co-workers produced asymmetrically coated gold particles using material protrusion caused by ligand exchange.

3.4.3 Microfluidic synthesis

Recently, many microfluidic methods have been developed to produce anisotropic particles with low size dispersion and well-controlled structure. However, the disadvantages of such a synthesis are the complexity of manufacturing devices and the limitation on particle size of 1 μm.

Kumacheva and co-workers produced a continuous microfluidic synthesis of double and triple droplets, which were then converted into anisotropic particles due to photopolymerization (Fig. 9A). Doyle and colleagues combined microfluidics with photolithography to produce elongated Janus particles decorated with a pattern on one side (Figure 9B). Nishidako and co-workers used a microfluidic technique to embed functional materials, particularly magnetic nanoparticles and liquid crystals, into a single hemisphere of Janus particles. Weitz's group synthesized Janus particles with one hemisphere of hydrogel and the second of aggregates of colloidal particles. Lahanna's group has developed a new microfluidic synthesis, electrohydrodynamic injection, to produce Janus particles up to 170 nm in size, consisting of a polyethylene oxide hemisphere and an aminodextran hemisphere (Figure 9C).

4. Molecular-like self-assembly of colloidal nanoparticles

From what was described earlier it is clear that there is no single method for obtaining anisotropic particles; each method has its own disadvantages. However, they make it possible to obtain a sufficient number of particles with a given size, composition and surface chemical properties. The next question is whether anisotropic colloidal particles can mimic the behavior of molecules.

Binks and Fletcher showed theoretically that when a particle transitions from a chemically isotropic surface to a Janus-like surface, the particles acquire high surface activity over the entire range of polar angles. From the point of view of surface activity, Janus particles are amphiphilic surfactants. Nelson pioneered the theoretical concept of valences of colloidal particles, thus likening their self-assembly to molecular chemistry. Glotzer's group modeled particle behavior using empirical pairwise interaction potentials that model weak attraction over large distances and repulsion under direct contact (Figure 10A). Such modeling showed that highly anisotropic particles can form stable structures, such as chains, planes, icosahedrons, square pyramids, tetrahedral, as well as twisted and ladder structures. The same group simulated particle self-assembly using Monte Carlo methods and found similarities in the ordering of conical-shaped particles to the folding of protein chains in viruses. Sciortino's group systematically modeled the thermodynamics and kinetics of the particles, showing that the "spotty" particles behave like an associated fluid such as water. The presence of spots is equivalent to the presence of directional valences in particles. Thus, on the phase diagram of self-assembly of particles, due to a decrease in the region of coexistence of gas and liquid, which no longer intersects the glass transition line, a new field is formed where the particles form a stable spatially connected network (Fig. 10B). This field is not observed in the case of homogeneous particles. Doye and his co-authors solved the inverse problem - they successfully used anisotropic colloidal particles to simulate the thermodynamics and kinetics of self-assembly of protein complexes. Kretzschmar and his colleagues simulated the self-assembly of particles with one, two, and three spots on the surface by varying the temperature, the nature of the interactions, and the concentration of the particles. This work examines possible experimental methods for direct self-ordering when connecting “spots” on particles with bifunctional ligands, especially minimizing the formation of unwanted structures (Fig. 10C).

The molecular-like properties of anisotropic colloidal particles are confirmed by studies of the physical properties of their agglomerates. The spatial arrangement of particles affects the mechanical, magnetic, optical and electrical properties of conglomerates. This has stimulated much research into the use of colloidal “speckled” particles to mimic the self-assembly of molecules. Thus, Banin and co-workers used dithiol ligands to bind gold-decorated CdSe nanorods into dumbbell-shaped structures. Murphy's group produced chains of gold nanorods linked with streptavidin. Stellacchi and colleagues produced chains of gold nanoparticles by linking ligands selectively modified at polar positions (Figure 11A). However, the formation of additional structures due to non-covalent interactions, such as van der Waals forces and capillary effects, makes this approach not so easy to apply and interpret the results.

Janus particles with hemispheres that differ in surface charge or wettability can assemble into dimers, trimers, etc. Kumacheva and colleagues developed a method for controlling the surface hydrophobicity of "spotted" particles. They produced chains, rings, and rods from gold particles by modifying them with thiol-modified polyethylene by varying the solvent composition (Figure 11B). Mirkin's group produced both flat and curved sheets of gold nanorods connected by polypyrrole blocks (Figure 11C). This behavior mimics self-assembly during the formation of block copolymers. This work shows the role of the geometric parameters of “spotted” particles in the formation of a particular structure. Velev and his co-authors initiated the self-organization of Janus particles coated on one side with metals by applying an electric or magnetic field. Hatton obtained magnetite Janus particles 5 nm in size, which self-organized into clusters when the pH was lowered or the temperature increased above 31ºC.

Granik and co-workers studied the self-assembly of Janus particles with oppositely charged hemispheres by epifluorescence microscopy and Monte Carlo simulations (Figure 12A). The particle size (1 μm) was much larger than the electrostatic shielding radius (10 nm), so the interaction was not determined by electrostatic forces. Granik's group, using a similar combination of methods, studied the self-assembly of Janus particles with hydrophilic and hydrophobic hemispheres. The formation of worm-like structures was observed due to the shielding of electrostatic interaction between neighboring particles, but this occurred not due to the sequential addition of other particles, but due to the adhesion of the clusters themselves to each other. This also highlights the similarities with intermolecular interactions.

It is clear that dipole interactions lead to chain structures, and, more importantly, can manifest themselves in the indirect creation of anisotropic structures. Phillips and co-authors showed that dipole-dipole interactions ensure the self-assembly of magnetite particles even in zero magnetic field. Wang and co-workers showed that the chain length formed by dipole interactions between gold particles increases as the electrostatic repulsion between particles decreases due to an increase in ionic strength or a decrease in solvent polarity (Figure 12B). The role of electrostatic interaction is twofold: on the one hand, it is isotropic and therefore enhances the anisotropic self-assembly of charged particles; on the other hand, it determines the size of particle aggregates. Förster and co-workers achieved control over the structure of assemblies (chains, branched networks, hollow spheres - colloidosomes) of CdSe/CdS core-shell particles simply by changing the density of polymer chains grafted onto the particle (Figure 12C). Kotov and his colleagues arranged hydrated CdTe nanoparticles into nanopillars and nanosheets. Solomon's group developed a microfluidic method for controlled assembly of particles into two- and three-block chains (Figure 12D). All these results show that the self-assembly of particles is controlled not only by “spots” on the surface, but also by other reasons, in particular, dipole interactions.

5. Conclusions

The behavior of colloidal particles modified in a certain way at interfaces in two-phase systems consisting of two immiscible phases can be used to model the behavior of surfactants. This encourages the use of a variety of interface structures in two-phase systems to self-assemble colloidal particles into hierarchical structures. Many approaches have been proposed to the synthesis of anisotropic particles - “Janus” and “spotty”, with different sizes and properties. However, there remain many opportunities to improve the quality of “spots”, yield percentage, expand the range of materials, particle size, etc. In addition, the challenge is to accurately characterize the morphology and chemical properties of surfaces, especially for nanometric particles.

To date, no known anisotropic colloidal particles can fully simulate the behavior of molecules in practice, despite enormous progress in theoretical calculations. There are a number of reasons limiting the implementation of this idea. First, most studies rely on visualization of particle arrays in the dried state, whereas direct or indirect data on the arrangement of particles in solution are required. Secondly, the colloidal particles currently being studied are rigid building blocks; they do not have the flexibility and ability to adapt to the spatial configuration inherent in amphiphilic molecules. Third, experimental manipulation of the various forces acting on particles has so far been difficult. Fourth, even if covalent bonding is assumed between adjacent particles, other factors such as polar interactions and capillary forces come into play. Therefore, one should be critical of the results of particle self-assembly. On the other hand, the mechanism governing the self-organization of particles has not been fully disclosed. For example, the mechanism for the formation of specific crystal faces for selective anisotropic growth does not correspond to accepted growth mechanisms, neither classical concentration fluctuations, nor the La Mer model, nor agglomeration.

The analogy between colloidal particles and atoms and molecules has now been recognized in many aspects, such as thermodynamics, interactions, especially electronic, photonic and mechanical properties. Therefore, now many chemists, physicists, materials scientists, and engineers are striving to obtain colloidal particles that imitate the properties of molecules. This is the basis of materials science - understanding the design principles of natural materials and creating new materials that use or imitate the same principles. Ultimately, creating particles with the properties of molecules will allow colloidal chemistry to truly become nanochemistry, in which colloidal particles play as important a role at the mesoscopic level as atoms and molecules play at the microscopic level. Through collaboration on targeted synthesis of particles with specialized properties, rigorous experimental studies of particles and their self-assembled assemblies, and advanced theoretical modeling techniques, the prospects for molecular-like self-assembled colloidal particles look very promising.

Bibliography

D. F. Evans, H. Wennerstrom, The Colloidal Domain, Wiley, New York. 1994.

D. W. Oxtoby, Nature, 1990, 347, 725.

H. Weller, Angew. Chem. Int. Ed. 1993, 32, 41.

A. P. Alivisatos, Science 1996, 271, 933.

C. Collier, T. Vossmeyer, J. Heath, Annu. Rev. Phys. Chem. 1998, 49, 371.

A. W. Castleman, Jr., S. N. Khanna, J. Phys. Chem. C 2009, 113, 2664.

C. Lopez, Adv. Mater. 2003, 5, 1679.

M. V. Artemyev, U. Woggon, R. Wannemacher, Appl. Phys. Lett. 2001, 78, 1032.

M. V. Artemyev, U. Woggon, R. Wannemacher, H. Jaschinski, W. Langbein, Nano Lett. 2001, 1, 309.

A. van Blaaderen, Science 2003, 310, 470.

E. W. Edwards, D. Wang, H. Mohwald, Macromol. Chem. Phys. 2007, 208, 439.

R. Klajn, K. J. M. Bishop, M. Fialkowski, M. Paszewski, C. J. Campbell, T. P. Gray, B. A. Grzybowski, Science 2007, 316, 261.

M. P. Pileni, Acc. Chem. Res. 2008, 41, 1799.

E. Matijivic, Langmuir, 1994, 10, 8.

D. Horn, J. Rieger, Angew. Chem. Int. Ed. 2001, 40, 4330.

P. N. Pusey, W. van Megen, Nature, 1986, 320, 340.

C. Murray, C. Kagan, M. Bawendi, Annu. Rev. Mater. Sci. 2000, 30, 545.

J. S. Lindsey, New J. Chem. 1991, 15, 153.

J.-M. Lehn, Angew. Chem. Int. Ed. 1990, 29, 1304.

G. Schmid, U. Simon, Chem. Commun. 2005, 697.

N. B. Bowden, M. Weck, I. S. Choi, G. M. Whitesides, Acc. Chem. Res. 2001, 34, 231.

D. Wang, H. Mo¨hwald, J. Mater. Chem. 2004, 14, 459.

M. E. Leunissen, C. G. Christova, A.-P. Hynninen, C. Patrick Royall, A. I. Campbell, A. Imhof, M. Dijkstra, R. van Roij, A. van Blaaderen, Nature, 2005, 437, 235.

E. V. Shevchenko, D. V. Talapin, N. A. Kotov, S. O’Brien, C. B. Murray, Nature, 2006, 439, 55.

W. Ramsden, Proc. R. Soc. London 1903, 72, 156.

S. U. Pickering, J. Chem. Soc. 1907, 91, 2001.

B. P. Binks, Curr. Opin. Colloid Inter. Sci. 2002, 7, 21.

R. Aveyard, B. P. Binks, J. H. Clint, Adv. Colloid Interface Sci. 2003, 100-102, 503.

R. Aveyard, J. H. Clint, J. Chem. Soc., Faraday Trans. 1996, 92, 85.

E. Vignati, R. Piazza, T. P. Lockhart, Langmuir. 2003, 19, 6650.

T. S. Horozov, B. P. Binks, Angew. Chem. Int. Ed. 2006, 45, 773.

A. Kabalnov, H. Wennerstro¨m, Langmuir 1996, 12, 276.

B. P. Binks, S. O. Lumsdon, Langmuir 2000, 16, 2539.

B. P. Binks, J. A. Rodrigues, Angew. Chem. Int. Ed. 2005, 44, 441.

B. P. Binks, R. Murakami, S. P. Armes, S. Fujii, Angew. Chem. Int. Ed. 2005, 44, 4795.

J. I. Amalvy, G. F. Unali, Y. T. Li, S. Granger-Bevan, S. P. Armes, B. P. Binks, J. A. Rodrigues, C. P. Whitby, Langmuir 2004, 20, 4345.

P. Pieranski, Phys. Rev. Lett. 1980, 45, 569.

S. Reculusa, S. Ravaine, Chem. Mater. 2003, 15, 598.

Z.-Z. Gu, D. Wang, H. Mohwald, Soft Matter. 2007, 3, 68.

T. Horozov, R. Aveyard, J. H. Clint, B. P. Binks, Langmuir 2003, 19, 2822.

T. S. Horozov, R. Aveyard, B. P. Binks, J. H. Clint, Langmuir 2005, 21, 7405.

O. D. Velev, K. Furusawa, K. Nagayama, Langmuir 1996, 12, 2374.

O. D. Velev, K. Furusawa, K. Nagayama, Langmuir 1996, 12, 2385.

O. D. Velev, K. Nagayama, Langmuir 1997, 13, 1856.

A. D. Dinsmore, M. F. Hsu, M. G. Nikolaides, M. Marquez, A. R. Bausch, D. A. Weitz, Science 2002, 298, 1006.

M. F. Hsu, M. G. Nikolaides, A. D. Dinsmore, A. R. Bausch, V. D. Gordon, X. Chen, J. W. Hutchinson, D. A. Weitz, Langmuir 2005, 21, 2963.

F. Nobel, O. J. Cayre, R. G. Alargova, O. D. Velev, V. N. Paunov, J. Am. Chem. Soc. 2004, 126, 8092.

P. Fromherz, Nature 1971, 231, 267.

E. F. Uzgiris, R. D. Kornberg, Nature 1983, 301, 125.

K. Aoyama, K. Ogawa, Y. Kimura, Y. Fujiyoshi, Ultramicroscopy 1995, 57, 345.

Y. Lin, H. Skaff, T. Ermick, A. D. Dinsmore, T. P. Russell, Science 2003, 299, 226.

Y. Lin, A. Boker, H. Skaff, D. Cookson, A. D. Dinsmore, T. Emrick, T. P. Russell, Langmuir 2005, 21, 191.

H. Duan, D. Wang, D. Kurth, H. Mohwald, Angew. Chem. Int. Ed. 2004, 43, 5639.

F. Reincke, S. G. Hickey, W. K. Kegel, D. Vanmaekelbergh, Angew Chem. Int. Ed. 2004, 43, 458.

Y. Lin, H. Skaff, A. Boker, A. D. Dinsmore, T. Emrick, T. P. Russell, J. Am. Chem. Soc. 2003, 125, 12690.

H. Skaff, Y. Lin, R. Tangirala, K. Breitenkamp, ​​A. Boker, T. P. Russell, T. Emrick, Adv. Mater. 2005, 17, 2082.

H. Duan, D. Wang, N. Sobal, M. Giersig, D. Kurth, H. Mohwald, Nano. Lett. 2005, 5, 949.

J. R. Russell, Y. Lin, A. Boker, L. Su, P. Carl, H. Zettl, J. He, K. Sill, R. Tangirala, T. Emrick, K. Littrell, P. Thiyagarajan, D. Cookson , A. Fery, Q. Wang, T. P. Russell, Angew Chem. Int. Ed. 2005, 44, 2420.

F. Reincke, W. K. Kegel, H. Zhang, M. Nolte, D. Wang, D. Vanmaekelbergh, H. Mo¨hwald, Phys. Chem. Chem. Phys. 2006, 8, 3828.

M. Sastry, Curr. Sci. 2003, 85, 1735.

H. Duan, M. Kuang, D. Wang, D. Kurth, H. Mo¨hwald, Angew. Chem. Int. Ed. 2005, 44, 1717.

E. W. Edwards, M. Chanana, D. Wang, H. Mo¨hwald, Angew. Chem. Int. Ed. 2008, 47, 320.

E. W. Edwards, M. Chanana, D. Wang, H. Mo¨hwald, J. Phys. Chem. C 2008, 112, 15207.

Z. Mao, J. Guo, S. Bai, T.-L. Nguyen, H. Xia, Y. Xia, P. Mulvaney, D. Wang, Angew. Chem. Int. Ed. 2009, 48, 4953.

Z. L. Zhang, S. C. Glotzer, Nano Lett. 2004, 4, 1407.

Z. L. Zhang, A. S. Keys, T. Chen, S. C. Glotzer, Langmuir 2005, 21, 11547.

D. R. Nelson, Nano Lett. 2002, 2, 1125.

C. Casagrande, P. Fabre, E. Raphae¨l, M. Veyssie´, Europhs. Lett. 1989, 9, 251.

H. Takei, N. Shimizu, Langmuir 1997, 13, 1865.

J. C. Love, B. D. Gates, D. B. Wolfe, K. E. Paul, G. M. Whitesides, Nano Lett. 2002, 2, 891.

Y. Lu, H. Xiong, X. Jiang, Y. Xia, J. Am. Chem. Soc. 2003, 125, 12724.

Z. Bao, L. Chen, M. Weldon,

E. Chandross, O. Cherniavskaya, Y. Dai, J. B. H. Tok, Chem. Mater. 2002, 14, 24.

K. Fujimoto, K. Nakahama, M. Shidara, H. Kawaguchi, Langmuir 1999, 15, 4630.

K. Nakahama, H. Kawaguchi, K. Fujimoto, Langmuir 2000, 16, 7882.

C. E. Snyder, A. M. Yake, J. D. Feick, D. Velegol, Langmuir 2005, 21, 4813.

B. Wang, B. Li, B. Zhao, C. Y. Li, J. Am. Chem. Soc. 2008, 130, 11594.

L. Petit, E. Sellier, E. Duguet, S. Ravaine, C. Mingotaud, J. Mater. Chem. 2000, 10, 253.

S. Pradhan, L. Xu, S. Chen, Adv. Funct. Mater. 2007, 17, 2385.

V. N. Paunov, O. J. Cayre, Adv. Mater. 2004, 16, 788.

S. Jiang, S. Granick, Langmuir 2008, 24, 2438.

J. Wang, D. Wang, N. S. Sobal, M. Giersig, M. Jiang, H. Mo¨hwald, Angew. Chem. Int. Ed. 2006, 45, 7963.

B. Wang, M. Wang, H. Zhang, N. S. Sobal, W. Tong, C. Gao, Y. Wang, M. Giersig, D. Wang, H. Mo¨hwald, Phys. Chem. Chem. Phys. 2007, 9, 6313.

H. Gu, Z. Yang, J. Gao, C. K. Chang, B. Xu, J. Am. Chem. Soc. 2005, 127, 34.

G. Zhang, D. Wang, H. Mo¨wald, Nano Lett. 2005, 5, 143.

G. Zhang, D. Wang, H. Mo¨wald, Angew. Chem. Int. Ed. 2005, 44, 7767.

G. Zhang, D. Wang, H. Mo¨wald, Chem. Mater. 2006, 18, 3985.

A. B. Pawar, I. Kretzschmar, Langmuir 2008, 24, 355.

A. B. Pawar, I. Kretzschmar, Langmuir 2009, 25, 9057.

G. Braun, L. Pavel, A. R. Morrill, D. S. Seferos, G. C. Bazan, N. O. Reich, M. Moskovits, J. Am. Chem. Soc. 2007, 129, 7760.

C. Bae, J. Moon, H. Shin, J. Kim, M. M. Sung, J. Am. Chem. Soc. 2007, 129, 14232.

L. Wang, L. Xia, G. Li, S. Ravaine, X. S. Zhao, Angew. Chem. Int. Ed. 2008, 47, 4725.

O. Cayre, V. N. Paunov, O. D. Velev, Chem. Commun. 2003, 2296.

O. Cayre, V. N. Paunov, O. D. Velev, J. Mater. Chem. 2003, 13, 2445.

Z. F. Li, D. Lee, M. F. Rubner, R. E. Cohen, Macromolecules 2005, 38, 7876.

M. Rycenga, J. M. Mclellan, Y. Xia, Adv. Mater. 2008, 20, 2416.

E. Hugonnot, A. Carles, M.-H. Delville, P. Panizza, J. P. Delville, Langmuir 2003, 19, 226.

C. Yu, A. N. Parikh, J. T. Groves, Adv. Mater. 2005, 17, 1477.

M. A. Correa-Duarte, V. Salgueirino-Maceira, B. Rodr´ıguez-Gonzalez, L. Liz-Marzan, A. Kosiorek, W. Kandulski, M. Giersig, Adv. Mater. 2005, 17, 2014.

K. Yamazaki, H. Namatsu, Microelectron. Eng. 2004, 73-74, 85.

K. K. Caswell, J. N. Wilson, U. H. F. Bunz, C. J. J. Murphy, J. Am. Chem. Soc. 2003, 125, 13914.

A. Jackson, J. W. Myerson, F. Stellacci, Nat. Mater. 2004, 3, 330.

G. A. DeVries, M. Brunnbauer, Y. Hu, A. M. Jackson, B. Long, B. T. Neltner, O. Uzun, B. H. Wunsch, F. Stellacci, Science 2007, 315, 358.

H. Y. Koo, D. K. Yi, S. J. Yoo, D. Y. Kim, Adv. Mater. 2004, 16, 274.

D.-G. Choi, S. G. Jang, S. Kim, E. Lee, C.-S. Han, S. M. Yang, Adv. Funct. Mater. 2006, 16, 33.

L. Nagle, D. Fitzmaurice, Adv. Mater. 2003, 15, 933.

S. R. Nicewarner-Pen˜a, R. Griffith Freeman, B. D. Reiss, L. He, D. J. Pena, I. D. Walton, R. Cromer, C. D. Keating, M. J. Nathan, Science 2001, 294, 137.

S. Park, J.-H. Lim, S.-W. Chung, C. A. Mirkin, Science 2004, 303, 348.

Y. Yin, Y. Lu, B. Gates, Y. Xia, J. Am. Chem. Soc. 2001, 123, 8718.

Y. Yin, Y. Lu, Y. Xia, J. Am. Chem. Soc. 2001, 123, 771.

V. N. Manoharan, M. T. Elsesser, D. J. Pine, Science 2003, 301, 483.

Y.-S. Cho, G.-R. Yi, J.-M. Lim, S.-H. Kim, V. N. Manoharan, D. J. Pine, S.-M. Yang, J. Am. Chem. Soc. 2005, 127, 15969.

T. Mokari, E. Rothenberg, I. Popov, R. Costi, U. Banin, Science 2004, 304, 1787.

X. Gao, L. Yu, R. I. MacCuspie, H. Matsui, Adv. Mater. 2005, 17, 426.

H. Gu, R. Zheng, X. Zhang, B. Xu, J. Am. Chem. Soc. 2004, 126, 5664.

A. Perro, E. Duguet, O. Lambert, J.-C. Taveau, E. Bourgeat-Lami, S. Ravaine, Angew. Chem. Int. Ed. 2009, 48, 361.

C. Warakulwit, T. Nguyen, J. Majimel, M. Delville, V. Lapeyre, P. Garrigue, V. Ravaine, J. Limtrakul, A. Kuhn, Nano Lett. 2008, 8, 500.

A. Ohnuma, E. C. Cho, P. H. C. Camargo, L. Au, B. Ohtani, Y. Xia, J. Am. Chem. Soc. 2009, 131, 1352.

T. Teranishi, Y. Inoue, M. Nakaya, Y. Oumi, T. Sano, J. Am. Chem. Soc. 2004, 126, 9914.

H. Yu, M. Chen, P. M. Rice, S. X. Wang, R. L. White, S. Sun, Nano. Lett. 2005, 5, 379.

S. Choi, H. B. Na, Y. I. Park, K. An, S. G. Kwon, Y. Jang, M. Park, J. Moon, J. S. Son, I. C. Song, W. K. Moon, T. Hyeon, J. Am. Chem. Soc. 2008, 130, 15573.

Y. Wu, R. Fan, P. Yang, Nano Lett. 2002, 2, 83.

M. T. Bjo¨rk, B. J. Ohlsson, T. Sass, A. I. Persson, C. Thelander, M. H. Magnusson, K. Deppert, L. R. Wallenberg, L. Samuelson, Nano Lett. 2002, 2, 87.

T. Higuchi, A. Tajima, K. Motoyoshi, H. Yabu, M. Shimomura, Angew. Chem. Int. Ed. 2009, 48, 5125.

H. Yabu, T. Higuchi, M. Shimomura, Adv. Mater. 2005, 17, 2062. I. K. Voets, A. de Keizer, P. de Waard, P. M. Frederik, P. H. Bomans, H. Scmaltz, A. Walther, S. M. King, F. A. M. Leemakers, M. A. Cohen Stuart, Angew. Chem. Int. Ed. 2006, 45, 6673.

H. R. Sheu, M. S. El-Aasser, J. W. Vanderhoff, J. Polym. Sci. Part A: Polym. Chem. 1990, 18, 629.

M. Okubo, T. Fujibayashi, M. Yamada, H. Minami, Colloid Polym. Sci. 2005, 283, 1041.

E. B. Mock, H. De Bruyn, B. S. Hawkett, R. G. Gilbert, C. F. Zukoski, Langmuir 2006, 22, 4037.

W. K. Kegel, D. Breed, M. Elsesser, D. J. Pine, Langmuir 2006, 22, 7135.

J.-W. Kim, R. J. Larsen, D. A. Weitz, Adv. Mater. 2007, 19, 2005.

H. K. Yu, Z. Mao, D. Wang, J. Am. Chem. Soc. 2009, 131, 6366.

M. Giersig, T. Ung, L. M. Liz-Marzan, P. Mulvaney, Adv. Mater. 1997, 9, 570.

T. Chen, M. Yang, X. Wang, L. H. Tan, H. Chen, J. Am. Chem. Soc. 2008, 130, 11858.

Z. Nie, W. Li, M. Seo, S. Xu, E. Kumacheva, J. Am. Chem. Soc. 2006, 128, 9408.

D. C. Pregibon, M. Toner, P. S. Doyle, Science 2007, 315, 1393.

T. Nisisako, T. Torii, T. Takahashi, Y. Takizama, Adv. Mater. 2006, 18, 1152.

R. K. Shah, J.-W. Kim, D. A. Weitz, Adv. Mater. 2009, 21, 1949.

K. Roh, D. C. Martin, J. Lahann, Nat. Mater. 2005, 4, 759.

B. P. Binks, P. D. I. Fletcher, Langmuir 2001, 17, 4708.

T. Chen, Z. Zhang, S. c, Glotzer, Proc. Natl. Acad. Sci. USA 2007, 104, 717.

F. Sciortino, Eur. Phys. J.B 2008, 64, 505.

A. W. Wilber, J. P. K. Doye, A. A. Louis, E. G. Noya, M. A. Miller, P. Wong, J. Chem. Phys. 2007, 127, 085106.

G. Villar, A. W. Wilber, A. J. Williamson, P. Thiara, J. P. K. Doye, A. A. Luis, M. N. Jochum, S. C. F. Lweis, E. D. Levy, Phys. Rev. Lett. 2009, 102, 118106.

A. B. Pawar, I. Kretzschmar, G. Aranovich, M. D. Donohue, J. Phys. Chem. B 2007, 111, 2081.

S. K. Friedlander, J. Nanoparticle Res. 1999, 1, 9.

Z. Nie, D. Fava, E. Kumacheva, S. Zou, G. C. Walker, M. Rubinstein, Nat. Mater. 2007, 6, 609.

N. Zhao, K. Liu, J. Greener, Z. Nie, E. Kumacheva, Nano Lett. 2009, 9, 3077.

S. Gangwal, O. J. Cayre, O. D. Velev, Langmuir 2008, 24, 13312.

K. S. Smoukov, S. Gangwal, M. Marquez, O. D. Velev, Soft Matter 2009, 5, 1285.

T. Isojima, M. Lattuada, J. B. Vander Sande, T. A. Hatton, ACS Nano 2008, 2, 1799.

L. hong, A. Cacciuto, E. Luijten, S. Granick, Nano Lett. 2006, 6, 2510.

L. Hong, A. Cacciuto, E. Luijten, S. Granick, Langmuir 2008, 24, 621.

P. I. C. Teixeira, J. M. Tavares, M. M. Telo da Gama, J. Phys.: Condens. Matter 2000, 12, R411.

T. Tlusty, S. A. Safran, Science 2000, 290, 1328.

K. Butter, P. H. H. Bomans, P. M. Frederik, G. J. Vroege, A. P. Philipse, Nat. Mat. 2003, 2, 88.

H. Zhang, D. Wang, Angew. Chem. Int. Ed. 2008, 47, 3984.

H. Zhang, K. Fung, J. Hartmann, C. T. Chan, D. Wang, J. Phys. Chem. C 2008, 112, 16830.

M. S. Nikolic, C. Olsson, A. Salcher, A. Kornowski, A. Rank, R. Schubert, A. Fromsdorf, H. Weller, S. Forster, Angew. Chem. Int. Ed. 2009, 48, 2752.

Z. Tang, N. A. Kotov, M. Giersig, Science 2002, 297, 237.

Z. Tang, Z. Zhang, Y. Wang, S. C. Glotzer, N. A. Kotov, Science 2006, 314, 274.

K. E. Sung, S. A. Vanapalli, D. Mukhija, H. A. McKay, J. Mirecki Millunchick, M. A. Burns, M. J. Solomon, J. Am. Chem. Soc. 2008, 130, 1335.

Y. Lin, A. Boker, J. He, K. Sill, H. Xiang, C. Abetz, X. Li, J. Wang, T. Emrick, S. Long, Q. Wang, A. Balazs, T. P. Russell , Nature 2005, 434, 55.

V. K. LaMer, R. H. Dinegar, J. Am. Chem. Soc. 1950, 72, 4847.

V. Privman, D. V. Goia, J. Park, E. Matijevic, J. Colloid Interface Sci. 1990, 213, 36.

H. Colfen, S. Mann, Angew. Chem. Int. Ed. 2003, 42, 2350.

Fig. 1. The molecular structure of a polyhedron obtained by self-assembly of 144 molecules, deciphered by X-ray crystallography" border="0">

A group of chemists from Japan managed to break the record they set for the self-assembly of molecular geometric shapes. Scientists were able to select the conditions and components so that the self-assembly reaction of a molecular polyhedron, similar to viral capsids (protein shells), took place in the solution. The new record holder consisted of 144 molecules. This discovery has enormous application potential, as smaller structures have long been used for catalysis, hypersensitive sensors, energy storage, explosives stabilization, and more.

If you look at experimental chemistry philosophically, all of it is essentially self-assembly. The chemist only adds some reagents to others, but they interact in solution on their own: as a rule, nothing except diffusion and electrostatics pushes them towards each other. Crystals grow in the same way: one molecule “sticks” to another, “selecting” the most energetically favorable conformation.

In principle, this happens in a living cell. Molecules, floating in the cytoplasm, themselves assemble into structures, then these structures catalyze the self-assembly of other structures, up to a multicellular organism. All this looks like a huge working factory without a single worker, shop manager, director or cleaner. Everything works according to (bio)chemical laws without anyone's conscious supervision or control - this is the result of evolution, gradual complication, the survival of working systems and the death of non-working ones.

Research into the laws of self-assembly of molecules began with attempts to copy natural processes. However, biological objects are such that it is sometimes difficult for the human brain to even imagine their shape. This poses a serious problem for biochemical research. So gradually, in the early 90s, an idea arose: why, in fact, is it necessary to study only natural self-assembly? Is it possible to approach from the other side? Choose models that are easier to research and try to understand nature based on them. That is, first collect the knowledge scattered under the burning lantern, and only then go to the extinguished lanterns. Well, what could be simpler than geometric shapes? This idea, as often happens, arose independently in different scientific teams - the group of Peter J. Stang from the USA and the group of Makoto Fujita from Japan.

Almost immediately it became clear that we could not stop at two-dimensional structures and try to assemble three-dimensional structures in a similar way - molecular “cages”; rice. 3. To obtain three-dimensional figures, donors and/or acceptors with three or more active ends are needed.

The reactions turned out to have a somewhat unexpected, and even counterintuitive, property: if you mix several different “blue” molecules with “red” ones, they still “select” from the solution those that give the most ordered structures, without mixing with each other. Thus, not only self-assembly, but also self-sorting is actually carried out (Fig. 4). This is explained by the fact that the most ordered structures also turned out to be the most energetically favorable.

At first glance, the field of research into the self-assembly of molecular geometric shapes may seem very narrow, representing little more than academic interest. There are indeed plenty of such areas that someday will be useful (or not useful) for something, but in the case under discussion this is not the case at all. Both the structures and the methods for obtaining them (as well as the discovered patterns) very quickly found a huge number of immediate and long-term applications. As expected, these studies have led to greater understanding of how self-assembly of biological structures (such as viral capsids) works.

Self-assembly methods have formed the basis of a huge field of research on metal-organic coordination polymers (MOFs). Structures obtained by such methods are used as hypersensitive sensors, since when interacting with certain substances they change their physical properties. Molecular “cages” speed up organic reactions by using internal cavities to bring reactants closer to each other (as enzymes do in nature). They are also used to stabilize explosive or self-igniting substances, such as white phosphorus. Drugs are inserted into certain types of molecular “cells” and delivered to target organs, bypassing healthy ones. And this is not a complete list.

Of course, academic research in such a useful area has not stopped. In particular, one of the interesting questions that self-assembly researchers are asking is what is the largest number of molecules that can “self-assemble” into an ordered structure without any outside help? In nature, hundreds of components can perform such a trick (for example, the same viral capsids). Will chemists be able to compete with nature?

The penultimate record was set in Fujita's group. In early 2016, by carefully calculating the topology of the desired structure and planning the geometry of the molecular “constructor parts”, they managed to (self)assemble a structure belonging to the class of Archimedean solids, from 90 particles: 30 tetravalent palladium acceptors and 60 bipyridine donors (second from the right in Fig. 5).

The barrier of one hundred components had not yet been overcome at that time, and some believed that it was insurmountable. Ignoring the predictions of skeptics, in a new study, scientists aimed at the next Archimedean polyhedron, of 180 particles: 60 palladium acceptors and 120 pyridine donors (the structure on the far right in Fig. 5).

Having made the appropriate calculations, chemists synthesized the molecular building blocks for it, made a solution of the ingredients in the ratio of one acceptor to two donors, and monitored the reaction using NMR spectroscopy. When all the starting reagents had reacted, crystals were isolated from the solution and their molecular structure was characterized by X-ray diffraction. To the surprise of the experimenters, they saw a polyhedron with a structure far from expected (Fig. 6, left).

Just like the previous record holder, it consisted of 30 acceptors and 60 donors (“aha!” exclaimed the skeptics), only it did not belong to Archimedean polyhedra, but was close to another class of figures - Goldberg polyhedrons (see Goldberg polyhedron).

Goldberg polyhedra are geometric figures discovered by mathematician Michael Goldberg in 1937. Classic Goldberg polyhedra consist of pentagons and hexagons connected to each other according to certain rules (by the way, the truncated icosahedron, familiar to many from the shape of a soccer ball, is an example of a Goldberg polyhedron). Even though the polyhedra in the work discussed are composed of triangles and squares, they are related to Goldberg polyhedra, as proven using graph theory.

The scientists made additional calculations, from which it followed that this structure is metastable and that there is a more energetically stable polyhedron of 48 acceptors and 96 donors, which can be obtained from the same initial molecules. All that remained was to find suitable conditions for its production, isolation and characterization. After numerous attempts, at different temperatures and using different solvents, crystals were obtained that, under a microscope, were visually different from the previous ones. Using tweezers, they were selected from previously characterized ones, and X-ray diffraction analysis confirmed: a new record holder, consisting of 144 molecules, was obtained by self-assembly (Fig. 6, right).

Given the history of successful searches for applications for smaller analogues, the authors hope that the newly discovered molecules, as well as the methods that have been developed for them, will find interesting applications. They are not going to stop there and intend to obtain even larger structures from a larger number of components.

Sources:
1) Rajesh Chakrabarty, Partha S. Mukherjee, Peter J. Stang. Supramolecular Coordination: Self-Assembly of Finite Two- and Three-Dimensional Ensembles // Chemical Reviews. 2011. V. 111, pp. 6810–6918. DOI: 10.1021/cr200077m.
2) Daishi Fujita, Yoshihiro Ueda, Sota Sato, Nobuhiro Mizuno, Takashi Kumasaka, Makoto Fujita. Self-assembly of tetravalent Goldberg polyhedral from 144 small components // Nature. 2016. V. 510, pp. 563–567. DOI: 10.1038/nature20771.

Grigory Molev