Relationship between molecular structure and moisture-retention ability of carboxymethyl chitin and chitosan

Carboxymethyl chitins and chitosans (CM-chitins, CM-chitosans) of different substitution sites were prepared under different reaction conditions, and partially depolymerized. carboxymethyl chitins of various molecular weights from 24.8 x 10(4) to 0.26 x 10(4) were obtained by degrading with chemical reagents. Degree of substitution (DS) was estimated by potentiometric titration. Substitution site was confirmed by infrared and C-13-NMR spectra. Molecular weights were determined with gel permeation chromatography and gel permeation chromatography combined with laser light scattering (GPC-LLS). Moisture-absorption and retention abilities of these compounds were tested in comparison with those of hyaluronic acid (HA). The results reveal that 6-carboxymethyl group in the molecular structure of chitin and chitosan is a main active site responsible for moisture retention. Although carboxymethylation at OH-3 and N position is not essential, they contribute to the ability. Moisture-retention ability is also related to molecular weight; that is, higher molecular weight helps to improve moisture-retention ability. 6-O-CM-chitin (chitosan) with a DS above 0.8 and molecular weight higher than 24.8 x 10(4) has the potential to substitute for HA for use in cosmetics and clinical medicine. (C) 2002 John Wiley & Sons, Inc. J Appl Polym Sci 83: 1233-1241,2002.