Alkyl Chain Length Dependent Hydrogelation of <scp>l</scp>-Tryptophan-Based Amphiphile

Abstract

The search for low molecular weight hydrogelators (LMWHs) with varying structural motif is getting intense because of its potential application in biomedicines as well as the diversified area of nanobiotechnology. Hydrophobic interaction is one of the most crucial parameters in the design and development of such LMWHs. To this notion, a methodical investigation was carried out to find the influence of varying alkyl chain length of amphiphile on water gelation efficacy, which has been only marginally addressed in the literature to date. We have synthesized a series of low molecular weight L-tryptophan-based gelators, some of which are excellent gelator for plain water, an essential criterion for biological use. The alkyl chain induced hydrophobicity at the molecular level has remarkable influence in modulating water immobilization. Water gelation efficiency was improved more than 100 times on moving from 10 to 18 carbon atoms. The self-aggregation behavior of these thermoreversible hydrogelators investigated through different spectroscopic and microscopic techniques showed that an optimum balance between hydrophilicity and hydrophobicity is indeed essential, which can be largely regulated by varying the alkyl chain length. Thus, the study offers better understanding toward tailoring the properties of gel in plain water and thereby paving the way for potential applications.