Thermodynamics of borate ester formation by three readily grafted carbohydrates

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 ΔH1°=−37.2±4.9 kJ/mol and ΔH2°=−19.6±2.5 kJ/mol, respectively. The corresponding process entropies are ΔS1°=−51±17 J/mol/K and ΔS2°=−28±8 J/mol/K.