In
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...
and
materials science, molecular self-assembly is the process by which
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and b ...
s adopt a defined arrangement without guidance or management from an outside source. There are two types of
self-assembly: intramolecular and intermolecular. 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 chemistry. This is because assembly of molecules in such systems is directed through
non-covalent interaction
In chemistry, a non-covalent interaction differs from a covalent bond in that it does not involve the sharing of electrons, but rather involves more dispersed variations of electromagnetic interactions between molecules or within a molecule. The c ...
s (e.g.,
hydrogen bond
In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...
ing, metal coordination,
hydrophobic forces,
van der Waals force
In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and ...
s,
pi-stacking interactions, and/or electrostatic) as well as electromagnetic interactions. Common examples include the formation of
colloids,
biomolecular condensates,
micelle
A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated coll ...
s,
vesicles
Vesicle may refer to:
; In cellular biology or chemistry
* Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane
* Synaptic vesicle
; In human embryology
* Vesicle (embryology), bulge-like features o ...
,
liquid crystal phases, and
Langmuir monolayers by
surfactant
Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsion#Emulsifiers , ...
molecules. Further examples of
supramolecular assemblies
In chemistry, a supramolecular assembly is a complex of molecules held together by noncovalent bonds. While a supramolecular assembly can be simply composed of two molecules (e.g., a DNA double helix or an inclusion compound), or a defined nu ...
demonstrate that a variety of different shapes and sizes can be obtained using molecular self-assembly.
Molecular self-assembly allows the construction of challenging molecular
topologies. One example is
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.
More recently, a similar structure has been prepared using non-biological building blocks.
Biological systems
Molecular self-assembly underlies the construction of biologic
macromolecular assemblies and
biomolecular condensates in living organisms, and so is crucial to the function of
cells
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
. It is exhibited in the self-assembly of
lipid
Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids in ...
s to form the
membrane, the formation of double helical DNA through hydrogen bonding of the individual strands, and the assembly of proteins to form
quaternary structures. Molecular self-assembly of incorrectly folded proteins into insoluble
amyloid fibers is responsible for infectious
prion
Prions are misfolded proteins that have the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseases in humans and many other animals. It i ...
-related neurodegenerative diseases. Molecular self-assembly of nanoscale structures plays a role in the
growth
Growth may refer to:
Biology
* Auxology, the study of all aspects of human physical growth
* Bacterial growth
* Cell growth
* Growth hormone, a peptide hormone that stimulates growth
* Human development (biology)
* Plant growth
* Secondary grow ...
of the remarkable
β-keratin lamellae/
setae
In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms.
Animal setae
Protostomes
Annelid setae are stiff bristles present on the body. ...
/
spatulae structures used to give
geckos the ability to
climb walls and adhere to ceilings and rock overhangs.
Protein multimers
When multiple copies of a polypeptide encoded by a
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
self-assemble to form a complex, this protein structure is referred to as a multimer. Genes that encode multimer-forming polypeptides appear to be common. When a multimer is formed from polypeptides produced by two different
mutant
In biology, and especially in genetics, a mutant is an organism or a new genetic character arising or resulting from an instance of mutation, which is generally an alteration of the DNA sequence of the genome or chromosome of an organism. It ...
allele
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution.
::"The chrom ...
s 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
Epistasis is a phenomenon in genetics in which the effect of a gene mutation is dependent on the presence or absence of mutations in one or more other genes, respectively termed modifier genes. In other words, the effect of the mutation is dep ...
. Jehle
[Jehle H. Intermolecular forces and biological specificity. Proc Natl Acad Sci U S A. 1963;50(3):516-524. doi:10.1073/pnas.50.3.516] 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.
Nanotechnology
Molecular self-assembly is an important aspect of
bottom-up approaches to
nanotechnology
Nanotechnology, also shortened to nanotech, is the use of matter on an atomic, molecular, and supramolecular scale for industrial purposes. The earliest, widespread description of nanotechnology referred to the particular technological goal ...
. 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
Lithography () is a planographic method of printing originally based on the immiscibility of oil and water. The printing is from a stone (lithographic limestone) or a metal plate with a smooth surface. It was invented in 1796 by the German a ...
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
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.
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
DNA origami is the nanoscale folding of DNA to create arbitrary two- and three-dimensional shapes at the nanoscale. The specificity of the interactions between complementary base pairs make DNA a useful construction material, through design of ...
" method) and three-dimensional structures in the shapes of
polyhedra.
These DNA structures have also been used as templates in the assembly of other molecules such as
gold nanoparticles and
streptavidin
Streptavidin is a 66.0 (tetramer) kDa protein purified from the bacterium '' Streptomyces avidinii''. Streptavidin homo-tetramers have an extraordinarily high affinity for biotin (also known as vitamin B7 or vitamin H). With a dissociation ...
proteins.
Two-dimensional monolayers
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
Langmuir-Blodgett monolayers and multilayers of surfactants. Non-surface active molecules can assemble into ordered structures as well. Early direct proofs showing that non-surface active molecules can assemble into higher-order architectures at solid interfaces came with the development of
scanning tunneling microscopy and shortly thereafter.
Eventually two strategies became popular for the self-assembly of 2D architectures, namely self-assembly following ultra-high-vacuum deposition and annealing and self-assembly at the solid-liquid interface.
The design of molecules and conditions leading to the formation of highly-crystalline architectures is considered today a form of 2D
crystal engineering at the
nanoscopic scale
The nanoscopic scale (or nanoscale) usually refers to structures with a length scale applicable to nanotechnology, usually cited as 1–100 nanometers (nm). A nanometer is a billionth of a meter. The nanoscopic scale is (roughly speaking) a l ...
.
See also
*
Assembly theory
Assembly theory is a theory that characterizes object complexity. When applied to molecule complexity, its authors claim it to be the first technique that is experimentally verifiable, unlike other molecular complexity algorithms that lack expe ...
*
Foldamer
In chemistry, a foldamer is a discrete chain molecule ( oligomer) that folds into a conformationally ordered state in solution. They are artificial molecules that mimic the ability of proteins, nucleic acids, and polysaccharides to fold i ...
*
Ice-nine
*
Macromolecular assembly
*
Self-assembly of nanoparticles
*
Supramolecular assembly
References
{{Nanotech2
Supramolecular chemistry
Self-organization
ar:تجميع ذاتي جزيئي