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

Sulfated polysaccharides that encapsulate the cells of red microalgae are h igh-molecular weight polymers (about 7 X 10(6) Da) with complex chemical st ructures. To broaden their potential industrial applications, a study was i nitiated to tailor additional characteristics by means of chemical modifica tions. 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 ch loride under basic conditions. A higher degree of substitution was obtained in lower volumes of water in which the polysaccharide solution had a gel-l ike form. The product was analyzed by infrared and vacptppm-C-13 spectrosco py. Good correlation was found between the nitrogen content of the quaterni zed polysaccharide and the IR peak ratio of the relevant C-N stretching vib rations. The solid-like (elastic) response (G') to imposed small deformatio n of the quaternized polysaccharide was higher than that of the unmodified biopolymer. (C) 2000 Elsevier Science Ltd. All rights reserved.