Semiempirical law for the dipole moments of low-molecular-weight gelators

Some small chiral organic molecules are capable of forming gel in low-concentration solutions. This phenomenon is of great theoretical interest, but its molecular details are still unclear. High chemical diversity of such gelators impedes the investigation of their common structural properties important for gel formation. Here, we calculated the total dipole moment for a set of gelators with sufficiently different chemical structures by means of molecular dynamics simulations. It was found that all considered molecules have a dipole moment of ～3 D or more. This means that the energy of the dipole-dipole interaction between two point dipoles at a distance of 6–8 Å is ～kT. This distance roughly corresponds to molecules in close contact. This makes it possible to conclude that the dipole moment can orient gelator molecules before aggregation, thereby playing a key role in the process of gelation. This orientation effect determines the anisotropy of aggregates and the gelation of the solution.