2, School of Materials and Chemical Technology, Tokyo Institute of Technology, Yokohama, , Japan
The principle of self-assembly is fundamental in the formation of higher order structures from small molecules. Many kinds of such structures have been formed from small amino acids and short peptides as useful materials for bio-medical purposes . They also have a fundamental importance as the starting ingredients for the creation of life on the Earth. From this point of view, we first studied the adsorption mechanism of amino acids and peptides to solid surfaces  and proceeded to investigate the formation of self-assembled structures in solution and on solid surfaces. In this study, we present the formation of new types of self-assembled structures of poly-glycine, short peptides and alpha-hydroxyacids and show their interesting structural properties obtained with the atomic force microscope (AFM).
Poly-glycine is water insoluble but soluble in tetrafluoroacetic acid (TFA). Dilution of its TFA solution with deionized water led to the formation of small self-assembled structures. AFM observation revealed the formation of thin and flat films (1 – 2 nm thick and 200 – 500 nm wide) and isolated fibers (10 – 50 nm wide). Because poly-Gly does not have charges except for at its N- and C-termini, some types of rather strong non-ionic attractive force, most likely involving van der Waals force, must be working at the basic level. The thickness of the film implies an alignment of a few poly-Glycine helices in the vertical direction and many of them into an ordered side-side arrangement. Such a uniformly flat structure suggests its possible role as a reliable and well defined platform for further assemblage with other molecules as a composite film.
We also found that some short peptides and alpha-hydroxy acids self-assembled into long strings as well as a hydrogel structure under an aqueous condition at specific pHs. The hydrogel has a nano-mesh like structure that can be reconstructed on mineral surfaces and visualized with AFM. We are particularly interested in possible roles of these structures as potential functional biomaterial in the origin of life on the Earth.