hydrogen bonding at 77 K.[1] ("Hydrogen bonds" in the top image are exaggerated by artifacts of the imaging technique.[2][3]
)
NC-AFM imaging of the molecular self-assembly process of 2-aminoterephthalic acid molecules on calcite(104).[4]
STM image of self-assembled Br4-pyrene molecules on Au(111) surface (top) and its model (bottom; pink spheres are Br atoms).[5]
In chemistry and materials science, molecular self-assembly is the process by which molecules adopt a defined arrangement without guidance or management from an outside source. There are two types of self-assembly: intermolecular and intramolecular. Commonly, the term molecular self-assembly refers to the former, while the latter is more commonly called folding.
Supramolecular systems
Molecular self-assembly is a key concept in
supramolecular assemblies demonstrate that a variety of different shapes and sizes can be obtained using molecular self-assembly.[10]
Molecular self-assembly allows the construction of challenging molecular
Borromean rings, interlocking rings wherein removal of one ring unlocks each of the other rings. DNA has been used to prepare a molecular analog of Borromean rings.[11] More recently, a similar structure has been prepared using non-biological building blocks.[12]
Biological systems
Molecular self-assembly underlies the construction of biologic
climb walls and adhere to ceilings and rock overhangs.[13][14]
Protein multimers
When multiple copies of a polypeptide encoded by a gene self-assemble to form a complex, this protein structure is referred to as a "multimer".[15] Genes that encode multimer-forming polypeptides appear to be common. When a multimer is formed from polypeptides produced by two different mutantalleles of a particular gene, the mixed multimer may exhibit greater functional activity than the unmixed multimers formed by each of the mutants alone. In such a case, the phenomenon is referred to as intragenic complementation.[16] Jehle pointed out that, when immersed in a liquid and intermingled with other molecules, charge fluctuation forces favor the association of identical molecules as nearest neighbors.[17]
Nanotechnology
Molecular self-assembly is an important aspect of
bottom-up approaches to nanotechnology. Using molecular self-assembly, the final (desired) structure is programmed in the shape and functional groups of the molecules. Self-assembly is referred to as a 'bottom-up' manufacturing technique in contrast to a 'top-down' technique such as lithography where the desired final structure is carved from a larger block of matter. In the speculative vision of molecular nanotechnology
, microchips of the future might be made by molecular self-assembly. An advantage to constructing nanostructure using molecular self-assembly for biological materials is that they will degrade back into individual molecules that can be broken down by the body.
DNA nanotechnology is an area of current research that uses the bottom-up, self-assembly approach for nanotechnological goals. DNA nanotechnology uses the unique molecular recognition properties of DNA and other nucleic acids to create self-assembling branched DNA complexes with useful properties.[18] DNA is thus used as a structural material rather than as a carrier of biological information, to make structures such as complex 2D and 3D lattices (both tile-based as well as using the "DNA origami" method) and three-dimensional structures in the shapes of polyhedra.[19] These DNA structures have also been used as templates in the assembly of other molecules such as gold nanoparticles[20] and streptavidin proteins.[21]
The spontaneous assembly of a single layer of molecules at interfaces is usually referred to as two-dimensional self-assembly. One of the common examples of such assemblies are
^Crick FH, Orgel LE. The theory of inter-allelic complementation. J Mol Biol. 1964 Jan;8:161-5. doi: 10.1016/s0022-2836(64)80156-x. PMID: 14149958
^Bernstein H, Edgar RS, Denhardt GH. Intragenic complementation among temperature sensitive mutants of bacteriophage T4D. Genetics. 1965;51(6):987-1002.
