Nucleophilicity and pH of water inside lipidic nano-channels of lyotropic liquid crystalline phases

Abstract

Weak nucleophilicity at physiological condition (pH 7.0) limits the utilization of bulk water as a good nucleophile. In this study, we have shown that, unique topological features of lipidic hexagonal (HII) and cubic Ia3d and Pn3m phases are highly suitable to modulate nucleophilicity of encapsulated water inside the nano-channels. Apart from this unique observation, we have also extended our study to measure the pH of water inside the nanochannels of LLC phases, which will be beneficial for the application of these materials to pH sensitive drug loading. To achieve our targets, sanguinarine (SANG), an isoquinolinone alkaloid, has been chosen to probe the water inside the nanochannels of LLC phases. Based on the distinct/relative optical switching ability of SANG, the pH of water inside the nanochannels of LLC phases is found to be basic (pH ~8) in nature. As a result, encapsulated water inside the lipidic LLC phases becomes effective nucleophile compared to water present in neutral bulk water. We believe that our study will enable to establish water nanochannels of lipidic liquid crystalline (LLC) phases as effective nucleophilic reaction nano-chambers to perform nucleophilic reactions, which otherwise impossible in neutral bulk water.