Molecular Organization in Hydrotrope Assemblies

Abstract

Hydrotropes are a class of compounds that are widely used in chemical, cosmetic, and pharmaceutical industries. Though amphiphilic in character, they have short hydrophobic regions and thus differ from classical surfactants. Yet they display substantial (and often selective) ability to solubilize lipophilic compounds in water. Beyond the minimal hydrotropic concentration, the molecules self-aggregate to produce the operating assembly. We show in this paper, based on crystal structure analysis of several hydrotropes, that these compounds form open-layer assemblies, reminiscent of lamellar liquid crystals consisting of alternating hydrophobic clustering of the nonpolar regions adjacent to ionic or polar regions that are knitted together in a two-dimensional network. Stacking of aromatic rings is not seen. Two types of assemblies are seen, one with a more open and extended hydrophobic layer than the other. We suggest that the solubilizates enter the hydrophobic layers of microunits producing a cooperative and mutual stabilizing effect. The observed open layer structure of hydrotropes might also account for the occasional ability of these compounds to solubilize even better than micelles.

Liquid Crystals in Aqueous Solutions of Sodium Naphthenates

“…The high ability of SN for toluene solubilization compared with SXS can be explained following the model suggested by Srinivas et al (22). According to this model, hydrotropes form a layered structure in solution.…”

Interação tensoativo/hidrótropo em sistemas aquosos, utilizando ressonância magnética nuclear de ¹H e 13C

“…Desta forma as interações hidrótropo-copolímero não associado devem prevalecer sobre as interações hidrótropo-micela. Por outro lado, estudos recentes de difração de raios-X realizados por Srinivas et al 21 sugerem que, além da concentração crítica de agregação, as moléculas de hidrótropos formam estruturas laminares em que subsistiriam regiões hidrófobas formadas pela associação dos grupos não polares da molécula e regiões hidrófilas provenientes da associação dos grupos polares. Os autores estimam que estas estruturas seriam determinantes do efeito hidrotrópico, e sugerem que as moléculas de compostos anfifílicos poderiam se incorporar às regiões hidrófobas, aumentando assim sua solubilidade.…”

Enhancement of Solubility and Mass Transfer Coefficient of Benzoic Acid Through Hydrotropy

“…This increase in solubility in water is probably due to the formation of organized assemblies of hydrotrope molecules at critical concentrations 2, 3 . Hydrotropes are water-soluble and surface-active compounds, which can signifi cantly enhance the solubility of organic compounds, drugs, biochemicals and petro-products…”