Mechanically interlocked molecular architectures are connections of molecules not through traditional bonds, but instead as a consequence of their topology

Topology (chemistry)

In chemistry, topology provides a convenient way of describing and predicting the molecular structure within the constraints of three-dimensional space. Given the determinants of chemical bonding and the chemical properties of the atoms, topology provides a model for explaining how the atoms...

. This connection of molecules is analogous to keys on a key chain loop. The keys are not directly connected to the key chain loop but they cannot be separated without breaking the loop. On the molecular level the interlocked molecules cannot be separated without significant distortion of the covalent bond

Covalent bond

A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....

s that make up the conjoined molecules. Examples of mechanically interlocked molecular architectures include catenane

Catenane

A catenane is a mechanically-interlocked molecular architecture consisting of two or more interlocked macrocycles. The interlocked rings cannot be separated without breaking the covalent bonds of the macrocycles. Catenane is derived from the Latin catena meaning "chain"...

s, rotaxane

Rotaxane

A rotaxane is a mechanically-interlocked molecular architecture consisting of a "dumbbell shaped molecule" which is threaded through a "macrocycle" . The name is derived from the Latin for wheel and axle...

s, molecular knot

Molecular knot

In chemistry, a molecular knot, or knotane, is a mechanically-interlocked molecular architecture that is analogous to a macroscopic knot. A molecular knot in a trefoil knot configuration is chiral, having at least two enantiomers. Examples of naturally formed knotanes are DNA and certain proteins....

s, and molecular Borromean rings

Molecular Borromean rings

Molecular Borromean rings are an example of a mechanically-interlocked molecular architecture in which three macrocycles are interlocked in such a way that breaking any macrocycle allows the others to disassociate. They are the smallest examples of Borromean rings. The synthesis of molecular...

.

The synthesis of such entangled architectures has been made efficient through the combination of supramolecular chemistry

Supramolecular chemistry

Supramolecular chemistry refers to the area of chemistry beyond the molecules and focuses on the chemical systems made up of a discrete number of assembled molecular subunits or components...

 with traditional covalent synthesis, however mechanically interlocked molecular architectures have properties that differ from both “supramolecular assemblies” and “covalently bonded molecules”. Recently the terminology "mechanical bond

Mechanical bond

The mechanical bond is a type of chemical bond found in mechanically-interlocked molecular architectures such as catenanes and rotaxanes. Unlike classical molecular structures, interlocked molecules consist of two or more separate components which are not connected by chemical bonds...

" has been coined to describe the connection between the components of mechanically interlocked molecular architectures. Although research into mechanically interlocked molecular architectures is primarily focused on artificial compounds, many examples have been found in biological systems including: cystine knot

Cytokine

Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...

s, cyclotides or lasso-peptides such as microcin J25 which are protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

, and a variety of peptide

Peptide

Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...

s. There is a great deal of interest in mechanically interlocked molecular architectures to develop molecular machine

Molecular machine

A molecular machine, or nanomachine, is any discrete number of molecular components that produce quasi-mechanical movements in response to specific stimuli . The expression is often more generally applied to molecules that simply mimic functions that occur at the macroscopic level...

s by manipulating the relative position of the components.