Chemical modifications of biopolymers: quaternization of the extracellular polysaccharide of the red microalga Porphyridium sp.

Sulfated polysaccharides that encapsulate the cells of red microalgae are high-molecular weight polymers (about 7×106 Da) with complex chemical structures. To broaden their potential industrial applications, a study was initiated to tailor additional characteristics by means of chemical modifications. Here, the quaternization of the extracellular polysaccharide derived from the red microalga Porphyridium sp. was performed. The quaternization reaction was carried out with 3-chloro-2-hydroxypropyltrimethyl ammonium chloride under basic conditions. A higher degree of substitution was obtained in lower volumes of water in which the polysaccharide solution had a gel-like form. The product was analyzed by infrared and vacptppm-13C spectroscopy. Good correlation was found between the nitrogen content of the quaternized polysaccharide and the IR peak ratio of the relevant C¯N stretching vibrations. The solid-like (elastic) response (Gʹ) to imposed small deformation of the quaternized polysaccharide was higher than that of the unmodified biopolymer.