Improvement of molecular gel formation efficiency by adjusting preorganization of amino acid-derived flexible molecules. A NMR and thermodynamic study

Abstract

The efficiency of the formation of molecular gels of simple de-rivatives of l-valineand l-isoleucine is greatl yimproved in dif-ferent organic solvents when ahexyl fragment is replaced byabulkier cyclohexyl one. Astudy using NMR and IR spectrosco-py provides information on the preferred conformation softhemolecules, indicat ing that the cyclohexyl moiety preclud es in-tramolecular Hbondingand preorganises the system for inter-molecular interactions, which are responsible for fiber forma-tion. NMR data of the gels provides thermod ynamic data on fi-brillization, revealing that the origin of this effect is mainly en-tropic. Electron microscopy (SEM and TEM) images show fibril-lar and tape-like objects, which are observed commonly inmolecular gels. Rheological measurements revealsignificantdifferences between cyclohexyl and hexyl appendedgelators.These findings could contribute to the rational design of small,flexible, buildingblocks forself-assembly