Physical Gelation by Low-Molecular-Weight Compounds and Development of Gelators

We discuss low-molecular-weight compounds, which undergo physical gelation, as gelators. There is a close relationship between crystallization and gelation with respect to the driving forces. Both crystallization and gelation are driven by non covalent interactions such as hydrogen bonding, van der Waals forces, electrostatic interactions, and pi-pi interactions. Typical gelators, which include amino acid derivatives, trans-1,2-diaminocyclohexane derivatives, and cyclic(dipeptide)s, are discussed. A concept of gelation-driving segment has been proposed. Hydrogelators, functional gelators, and polymer-type gelators are developed by using gelation-driving segments.