Self-assembly of chitosan oligosaccharide lactate and its interaction with curcumin : extension to an enzyme-free cholesterol sensor using nano-hybrid structure -

Abstract

Chitosan, is water lowly soluble polysaccharide. It has a high amine function density along its chain. This characteristic makes it soluble in acidic media. In addition to other properties it is biodegradable and biocompatible that broadens its biological application. On the other hand, extensive research is currently being held on curcumin due to its therapeutic benefits, which remains limited due to its low bioavailability and poor stability. Therefore, several methods were developed for curcumin encapsulation and incorporation in different systems in order to improve its delivery. At the same time recently use of curcumin as a fluorescent probe is being realized as its fluorescence spectral properties are sensitive to environmental changes. In this work, Chitosan Oligosaccharide Lactate (COL), which is a modified form of chitosan to improve water solubility of chitosan, especially for the uses in drug delivery and biomedical applications, is studied in solution. The self-assembly of COL in aqueous environment has been investigated. Fluorescence of curcumin has been followed to determine the concentration at which chitosan aggregates, known as critical aggregation concentration (cac) and compared with other conventionally adopted methods such as electrical conductivity and fluorescence of pyrene. The size has been estimated using Scanning Electron Microscopy (SEM). It is found that self-assembly of COL in solution forms nano-aggregates of size 10-30 nm with a (cac) of ~5 M. Fluorescence quenching of pyrene establishes that one COL chain may form around 5 independent hydrophobic microdomains during self-assembly in solution that are crucial to drug-polymer contact. Binding constant of curcumin and its partition coefficient with COL have been determined in double distilled water and at different ionic strength. Interaction of COL curcumin implies two different kinds of binding mechanisms of curcumin with the pre- and nano-aggregated forms of COL; respectively. A strong ground state interaction between c