Synthetic nanotubes of organic and inorganic tubular constructs have very high potential in the fields of chemical, biological and materials science. Organic and inorganic tubular constructs are graphite and related boron nitride and tungsten disulfide nanotubes. They are also zeolites and similar mesoporous inorganics, polymeric lipid-based tubules, tubular mesophases, carbohydrate-based nanotubes and other organic systems.

Self-assembling peptide nanotubes have proved to be useful in the design of solid-state porous materials, soluble cylindrical supramolecular structures, biologically relevant ion channels and transmembrane pore assemblies. They are also useful as solid surface-supported ion sensors and in the fabrication of inorganic nanocluster composites.

Fundamental approaches are employed in the design of open ended hollow tubular structures.

To form hollow-core bundle or barrel-shaped frameworks aggregation of rod or stave like subunits can be used. Examples for this is the membrane channel proteins such as the a-helical subunit B of cholera toxin, the potassium channel as well as the b-barrel structures of porins and a-hemolysin.

Another approach involves coiling of one or more linear molecule(s) into a helical conformation. Example for this is b-helical structures formed by the natural antibiotic gramicidin A and related synthetic peptides.

A tubular structure can also be made from a two-dimensional sheet like starting material, either by rolling or by closing its opposing edges. Such processes have been noted in the formation of carbon nanotubes from graphite.

Mineralization or polymerization templated by aggregates of organic molecules constitutes the method of choice for preparation of mesoporous silicates and related materials.

Finally, extended tubular arrays can also be prepared by stacking toroidal or disk-shaped subunits. A good example for this is the self-assembly of the tobacco mosaic virus (TMV) coat protein.

Of these various approaches, the last two have offered the most design flexibility and synthetic convergence. Certain cyclic peptides can adopt the required flat ring-shaped conformational states with self-complementary recognition surfaces that can be used to direct noncovalent stacking and self-assembly of tubular structures.

Surface properties

Self-assembling peptide nanotubes possess two inherent design advantages, viz., the outside surface properties and the tubes internal diameter can be controlled simply by the appropriate choice of the amino acid side chains and the number of the amino acids employed, respectively. In particular the ability to tailor surface characteristics of nanotubes has enabled their use where the physical properties of the media are important. One such example is the design of Tran membrane channels. Such self-assembling Tran membrane peptide nanotubes exhibits significant in vitro antibacterial activity and as such may open avenues for the discovery of antimicrobial and cytotoxic agents.