Supramolecular chemistry is a field of science that goes beyond the scope of particles and focuses on scientific systems consisting of a discrete number of assembled subunits or components. The forces responsible for the spatial organization can vary from weak (electrostatic or hydrogen bonds) to strong (covalent bonds), provided that the degree of electronic relations between molecular components remains small in relation to the corresponding energy parameters of the substance.
Important concepts
While traditional chemistry focuses on covalent bonds, the supramolecular one explores the weaker and reversible non-covalent interactions between molecules. These forces include hydrogen bonding, metal coordination, hydrophobic van der Waals arrays, and electrostatic effects.
Important concepts that have been demonstrated with this discipline include partial self-assembly, folding, recognition, a guest host, mechanically coupled architecture, and dynamic covalent science. The study of non-covalent types of interactions in supramolecular chemistry is crucial for understanding many biological processes from cell structure to vision, which rely on these forces. Biological systems are often a source of inspiration for research. Supermolecules belong to molecules and intermolecular bonds, like particles to atoms, and covalent bonds.
History
The existence of intermolecular forces was first postulated by Johannes Diderich van der Waals in 1873. However, Nobel laureate Herman Emil Fischer developed the philosophical roots of supramolecular chemistry. In 1894, Fisher suggested that the enzyme-substrate interaction takes the form of a “lock and key,” the fundamental principles of molecular recognition and the chemistry of a guest host. At the beginning of the 20th century, non-covalent bonds were studied in more detail, and the hydrogen bond was described by Latimer and Rodebusch in 1920.
Using these principles has led to a deeper understanding of protein structure and other biological processes. For example, an important breakthrough that enabled the elucidation of the double helical structure from DNA occurred when it became clear that there were two separate nucleotide strands connected through hydrogen bonds. The use of non-covalent relationships is important for replication because they allow you to separate the strands and use them as a matrix for new double-stranded DNA. At the same time, chemists began to recognize and study synthetic structures based on non-covalent interactions, such as micelles and microemulsions.
In the end, chemists were able to take these concepts and apply them to synthetic systems. A breakthrough occurred in the 1960s - the synthesis of crowns (ethers by Charles Pedersen). After this work, other researchers, such as Donald J. Crum, Jean-Marie Len and Fritz Vogtl, became active in the synthesis of form-ion selective receptors, and during the 80s, research in this area gained momentum. Scientists have worked with concepts such as mechanical blocking molecular architecture.
In the 90s, supramolecular chemistry became even more problematic. Researchers such as James Fraser Stoddart developed molecular mechanisms and very complex self-organizing structures, and Itamar Wilner studied and created sensors and methods of electronic and biological interaction. During this period, photochemical motifs were integrated into supramolecular systems to increase functionality, studies of synthetic self-replicating bonds began, and work continued on devices for processing molecular information. The evolving science of nanotechnology has also had a strong influence on this topic by creating building blocks such as fullerenes (supramolecular chemistry), nanoparticles, and dendrimers. They are involved in synthetic systems.
The control
Supramolecular chemistry deals with subtle interactions, and therefore, control over the processes involved may require great accuracy. In particular, non-covalent bonds have low energies, and often it is not enough for activation, for education. As the Arrhenius equation shows, this means that, unlike chemistry forming a covalent bond, the creation rate does not increase at higher temperatures. In fact, the equations of chemical equilibrium show that low energy leads to a shift towards destruction of supramolecular complexes at higher temperatures.
However, low degrees can also create problems for such processes. Supramolecular chemistry (UDC 541–544) may require that the molecules distort in thermodynamic unfavorable conformations (for example, during the “synthesis” of rotaxanes with sliding). And it may include some covalent science, which is consistent with the above. In addition, the dynamic nature of supramolecular chemistry is used in many mechanics. And only cooling will slow down these processes.
Thus, thermodynamics is an important tool for the design, control and study of supramolecular chemistry in living systems. Perhaps the most striking example is warm-blooded biological organisms that completely stop working outside of a very narrow temperature range.
Surrounding sphere
The molecular environment around the supramolecular system is also of paramount importance for its functioning and stability. Many solvents have strong hydrogen bonds, electrostatic properties and charge transfer ability, and therefore they can enter into complex equilibria with the system, even completely destroying the complexes. For this reason, the choice of solvent may be critical.
Molecular self-assembly
This is the construction of systems without guidance or control from an external source (except to provide a suitable environment). Molecules are directed to collection through non-covalent interactions. Self-assembly can be subdivided into intermolecular and intramolecular. A similar action also allows you to build larger structures, such as micelles, membranes, vesicles, liquid crystals. This is important for crystal engineering.
MR and complexation
Molecular recognition is the specific binding of a guest particle to a complementary host. Often the definition of which species is it and which “guest” appears arbitrary. Molecules can identify each other using non-covalent interactions. Key applications in this area are sensor design and catalysis.
Pattern Directional Synthesis
Molecular recognition and self-assembly can be used with reactive substances in order to preliminarily organize a chemical reaction system (for the formation of one or more covalent bonds). This can be considered a special case of supramolecular catalysis.
Non-covalent bonds between the reactants and the “matrix” hold the reaction centers close to each other, contributing to the desired chemistry. This method is especially useful in situations where the desired conformation of the reaction is thermodynamically or kinetically unlikely, for example, when producing large macrocycles. This preliminary self-organization in supramolecular chemistry also serves such purposes as minimizing adverse reactions, reducing activation energy, and obtaining the desired stereochemistry.
After the process has passed, the template may remain in place, be forcibly deleted or “automatically” decomplexed due to various product recognition properties. The pattern can be as simple as a single metal ion, or extremely complex.
Mechanically interconnected molecular architectures
They consist of particles that are connected only as a consequence of their topology. Some non-covalent interactions may exist between different components (often those used to build the system), but covalent bonds do not exist. Science - supramolecular chemistry, in particular matrix-directed synthesis, is the key to effective bonding. Examples of mechanically interconnected molecular architectures include catenans, rotaxanes, nodes, Borromean rings, and ravels.
Dynamic covalent chemistry
In it, bonds are destroyed and formed in a reversible reaction under thermodynamic control. While covalent bonds are the key to the process, the system is guided by non-covalent forces to form structures with the lowest energy.
Biomimetics
Many synthetic supramolecular systems are designed to copy the functions of biological spheres. These biomimetic architectures can be used to study both the model and the synthetic implementation. Examples include photoelectrochemical, catalytic systems, protein engineering, and self-replication.
Molecular technology
These are partial assemblies that can perform functions such as linear or rotational motion, shifting, and gripping. These devices exist on the border between supramolecular chemistry and nanotechnology, and prototypes have been demonstrated using similar concepts. Jean-Pierre Sauvage, Sir J. Fraser Stoddart and Bernard L. Fering shared the 2016 Nobel Prize in Chemistry for the design and synthesis of molecular machines.
Macrocycles
Macrocycles are very useful in supramolecular chemistry, as they provide entire cavities that can completely surround guest molecules and be chemically modified to fine-tune their properties.
Cyclodextrins, calixarenes, cucurbituryls and crown ethers are easily synthesized in large quantities and are therefore convenient for use in supramolecular systems. More complex cyclophanes and cryptands can be synthesized to provide individual recognition properties.
Supramolecular metallocycles are macrocyclic aggregates with metal ions in the ring, often formed from angular and linear modules. Conventional metal cycle shapes in these types of applications include triangles, squares, and pentagons, each of which has functional groups that connect the parts through self-assembly.
Metallacrowns are metallomacrocycles generated by a similar approach with condensed chelate rings.
Supramolecular chemistry: objects
Many such systems require that their components have a suitable distance and conformations relative to each other, and therefore easily used structural units are required.
Typically, spacers and connecting groups include polyester, biphenyls and triphenyls and simple alkyl chains. The chemistry for creating and combining these devices is very well understood.
Surfaces can be used as scaffolding for the order of complex systems, as well as for pairing electrochemical with electrodes. Regular surfaces can be used to create monolayers and multilayer self-assembling.
The understanding of intermolecular interactions in solids has undergone a significant revival due to the contribution of various experimental and computational methods in the last decade. This includes studies of high pressure in solids and crystallization of in situ compounds that are liquids at room temperature, along with the use of electron density analysis, crystal structure prediction and solid state DFT calculations to enable a quantitative understanding of nature, energy and topology.
Photo-electrochemically active units
Porphyrins and phthalocyanines have highly regulated photochemical energy, as well as the potential for complex formation.
Photochromic and photoisomerizable groups have the ability to change their shapes and properties when exposed to light.
TTF and quinones have more than one stable oxidation state and therefore can be switched using reductive chemistry or electronic science. Other units, such as benzidine derivatives, viologen groups and fullerenes, have also been used in supramolecular devices.
Biologically obtained units
The extremely strong complexation between avidin and biotin promotes blood coagulation and is used as a recognition motif for creating synthetic systems.
The binding of enzymes to their cofactors was used as a way to obtain modified, electrically contacting, and even photo-switchable particles. DNA is used as a structural and functional unit in synthetic supramolecular systems.
Material technology
Supramolecular chemistry has found many applications, in particular, molecular self-assembly processes were created to develop new materials. Large structures can be easily accessed using an upstream process, as they are composed of small molecules that require fewer steps to synthesize. Thus, most approaches to nanotechnology are based on supramolecular chemistry.
Catalysis
Their development and understanding is the main application of supramolecular chemistry. Non-covalent interactions are extremely important in catalysis, binding the reagents in the conformation, suitable for the reaction, and lowering the energy in the transition state. Template-directed synthesis is a special case of a supramolecular process. Encapsulation systems, such as micelles, dendrimers and cavitands, are also used in catalysis to create a microenvironment suitable for reactions and which cannot be used on a macroscopic scale.
The medicine
A method based on supramolecular chemistry has led to numerous applications in the creation of functional biomaterials and therapeutic agents. They provide a range of modular and generic platforms with customizable mechanical, chemical and biological properties. These include systems based on peptide assembly, host macrocycles, high-affinity hydrogen bonds, and metal-ligand interactions.
The supramolecular approach has been widely used to create artificial ion channels for the transport of sodium and potassium into and out of cells.
Such chemistry is also important for the development of new pharmaceutical treatments by understanding the interaction at the binding site of the drug. The drug delivery area has also achieved critical success as a result of supramolecular chemistry. It provides encapsulation and targeted release mechanisms. In addition, such systems have been designed to break down protein-protein interactions that are important for cellular function.
Template effect and supramolecular chemistry
In science, a template reaction is any of a class of ligands based actions. They occur between two or more adjacent coordination sites on the metal center. The terms "template effect" and "self-assembly" in supramolecular chemistry are mainly used in coordination science. But in the absence of an ion, the same organic reagents produce different products. This is the template effect in supramolecular chemistry.