Molecular Organization of Gel Fibrils as Revealed by VCD

This chapter is concerned with VCD application to gels. When a chiral low molecular weight gelator (LMWG) forms a gel from an organic solvent, it often leads to the appearance of helically wound fibrils. S- or R-12-hydroxystearic acid (denoted as S- or R-12-HOA), for example, forms a transparent gel from benzene. Helical fibrils (e.g., 100–200 nm in pitch length) are observed by electron microscopy. When VCD spectra are measured on the gels, enormously large VCD signals are observed. The enhancement is rationalized in terms of the mechanism that gelator molecules are linked stereoregularly under the uniform conformation. The conformation of a gelator molecule is deduced by analyzing VCD spectra with the help of theoretical simulation. It presents an example of VCD application to supramolecular chirality. VCD studies are further extended to gels formed by LMWGs with perfluoroalkyl chains. Attention is focused on how the helicity of a fibril is related to the molecular chirality of a perfluoroalkyl chain.