Physical and Theoretical Chemistry

Biography

Biography: Dafna Knani

Abstract

The organic gelator 1,3(R):2,4(S)-dibenzylidene-D-sorbitol (DBS) self-organizes to form a 3-D network at relatively low concentrations in a variety of nonpolar organic solvents and polymer melt. DBS could be transformed into a hydrogelator by introduction of hydrophilic groups, which facilitate its self-assembly in aqueous medium. In this work, we have investigated the hydrogelators DBS-COOH and DBS-CONHNH₂ and the organogelator DBS by molecular modeling. We have used quantum mechanics (QM) to elucidate the preferred geometry of one molecule and a dimer of each of the gelators, and molecular dynamics (MD) to simulate the pure gelators and their mixtures with water.

The results of the simulation indicate that the interaction between DBS-COOH molecules is the strongest of the three and its water compatibility is the highest. Therefore, DBS-COOH seems to be a better hydrogelator than DBS-CONHNH₂ and DBS.  Intermolecular H-bonding interactions are formed between DBS, DBS-COOH and DBS-CONHNH₂ molecules as pure substances, and they dramatically decrease in the presence of water. In contrast, the intramolecular interactions increase in water. This result indicate that in aqueous environment the molecular structure tend to be more rigid and fixed in the preferred conformation. The most significant intramolecular interaction is formed between O3 Acetal and H-O6 groups. Due to the H-bonds, DBS, DBS-COOH and DBS-CONHNH₂ molecules form a rigid structure similar to liquid crystal forming molecules, which might explain their tendency to create nanofibrils. It was found that the aromatic rings do not contribute significantly to the inter-and intra-molecular interactions. Their main role is probably to stiffen the molecular structure.

Figure 1: DBS, DBS-COOH and DBS-CONHNH₂ molecular structure.