SAXS and ATR-FTIR studies on EBT-TSX mixtures in their sol-gel phases

Our previous study demonstrated that mixtures of tamarind seed xyloglucan (TSX) with appropriate concentrations of eriochrome black T (EBT) produced a gel that could be of benefit for medical use. Here, the sol-gel systems of various fresh and aged mixtures were further investigated using rheological measurements. The nanostructural changes of EBT-TSX sol-gel phases were analyzed using SAXS. The interactions between EBT and TSX in the sol and gel states were examined using ATR-FTIR. SAXS data analysis demonstrated that the mixture containing lower concentration of EBT formed rod-like structures and that with higher concentrations of EBT produced flat particles. The sizes of the TSX structures from the aged mixtures in the gel stage were larger than those from the same mixtures in the sol state. ATR-FTIR spectral changes revealed that the azo and sulfonic acid groups of EBT interacted with the TSX, and the characteristic spectrum of the sulfonic acid group of EBT could discriminate between the sol and gel state of the EBT-TSX systems. The interactions between EBT and TSX may cause conformational changes to TSX and facilitate the sol-gel transition or formation of a gel.