Thermodynamics of borate ester formation by three readily grafted carbohydrates

Abstract

Borate ester association constants for d- glycero- d- gulo-heptonamide ( 1), N-methyl- d-glucamine ( 2), and disorbitylamine ( 3) were derived from 11B NMR observations. Significant electrostatic effects were observed in the formation of borate esters with the ammonium derivative ( 2). 11B NMR studies of 3 were consistent with the simultaneous formation of intramolecular tetradentate borate diesters and oligomeric chains of 3 connected by intermolecular borate diesters. The process enthalpies for formation of borate monoesters and diesters with 1 are Δ H 1°=−37.2±4.9 kJ/mol and Δ H 2°=−19.6±2.5 kJ/mol, respectively. The corresponding process entropies are Δ S 1°=−51±17 J/mol/K and Δ S 2°=−28±8 J/mol/K.