Equilibrium and dynamics of the binding of calcium ion to sorbitol (D-glucitol)

Abstract

Carbon-13 n.m.r, spectra have been used to estimate the equilibrium constant and ultrasonic relaxation methods used to observe the rate of calcium binding to sorbitol (D-glucitol). The interaction is weak, with equilibrium constants in D₂O of approximately 0.61. mol^-1 at 36ºC and 1.21. mol^-1 at 4ºC. The concentration dependence of the relaxation time is consequently small and the formation rate constant only approximately determined at 40ºC as (1-2) × 10⁸ 1, mol^-1 s^-1. The magnitude of the ¹³C chemical shifts on binding calcium ion suggests that coordination may not occur at the hydroxy groups of carbons C2,C3 and C4 as previously observed with lanthanide ions. The site of lanthanide binding was confirmed in this work by gadolinium ion broadening of the ¹³C n.m.r. resonances.