Sugar‐Based Self‐Assembly of Hydrogel Nanotubes Manifesting ESIPT: Theoretical Insight and Application in Live Cell Imaging

Abstract

A biopolymeric hydrogel nanotubes (BTHBC) using 3-(benzo [d] thiazol-2-yl)-2-hydroxybenzaldehyde and chitosan have been synthesized which exhibits excited state intramolecular proton transfer (ESIPT) in both gel and solution phase. The optimized spatial structure of the monomer of BTHBC having lower energy (Energy: À1085688.464 kcal/mol) is found to be planar. FE-SEM analysis reveals that the spherical assemblies (20-100 nm) preceded gelation. Upon aging, gelation can be observed owing to the fusion of these spherical aggregates into nanotubes (200-500 nm). DFT study of BTHBC establishes that the migration of H atom from phenolic -OH group to the nitrogen of 2-(2' Hydroxyphenyl)benzothiazole (HBT) moiety is more feasible than the imine nitrogen of chitosan. The fluorescence lifetime of BTHBC is found to increase remarkably in gel phase compared to its aqueous solution. Both the cellular uptake and cell imaging efficiency suggest that the biocompatible nature of the hydrogel permits easy access of maximum number of molecules into the cells which causes enhancement of the fluorescence intensity of the cells.