Highly phosphorylated derivatives of chitin, partially deacetylated chitin and chitosan as new functional polymers: preparation and characterization

New functional chitin derivatives, i.e. variously phosphorylated derivatives of chitin and deacetylated chitins (DA-chitins), were prepared by the reaction of chitin or DA-chitins with phosphorus pentoxide in methanesulphonic acid. Degree of substitution (DS) of the products estimated from i.r. spectra, 13C n.m.r. spectra and elemental analyses increases with increase in the amount of phosphorus pentoxide employed, and products become nearly fully substituted when 4.0 mol. equiv. of phosphorus pentoxide to the residue is employed. 13C n.m.r. study suggested that the hydroxyl groups of C-3 and C-6 positions are equally substituted with the phosphate group. Chitin phosphates (P-chitins) are easily soluble in water independent of DS. However DA-chitin phosphates (P-DA-chitins) of high DS are insoluble in water owing to the amphoteric property, while those of low DS are water soluble. The water-soluble products behave as typical polyelectrolyte viscometrically. Two pKa values of the introduced phosphate groups were estimated to be around 3.7 and 8.2–8.5 by potentiometric titration. Preliminary experiment for adsorption of Cu2+ ion onto P-chitin (DS 1.0) by gel filtration showed that one copper ion was chelated to two phosphated N-acetyl-d-glucosamine residues, suggesting its high metal-binding ability.