Kinetics of Ca~2+ complexation with some carbohydrates in aqueous solutions

摘要

For solutions of four saccharides in water with alkaline-earth chlorides added ultrasonic attenuation spectra between 100 kHz and 2 GHz are reported and compared to those for carbohydrate solutions without salt.Calcium chloride does not alter the relaxation times in the spectra of D-glucose and D(+ )-maltose solutions,reflecting the exocyclic hydroxymethyl group rotation,a saccharide-saccharide association,and,with the disaccharide,also motions of both rings of a molecule relative to one another.The spectra of D-xylose and D-fructose solutions are substantially changed by the salts.With both saccharides an additional term with relaxation time around some nanoseconds exists which is assigned to a rearrangement of a carbohydrate-cation complex.Other relaxation terms of these saccharide solutions are also subject to noticeable changes by the salt,indicating specific carbohydrate-cation interactions.The ultrasonic spectra show that such interactions may exist also with carbohydrates which do not display the particular hydroxyl group sequences that are considered to promote complexation with cations.