Thermodynamics of borate ester formation by three readily grafted carbohydrates
摘要:
Borate ester association constants for D-glycero-D-gulo-heptonamide (1), N-methyl-D-glucamine (2), and disorbitylamine (3) were derived from B-11 NMR observations. Significant electrostatic effects were observed in the formation of borate esters with the ammonium derivative (2). B-11 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 Delta H(1)degrees = -37.2 +/- 4.9 kJ/mol and Delta H(2)degrees = -19.6 +/- 2.5 kJ/mol, respectively. The corresponding process entropies are Delta S(1)degrees = -51 +/- 17 J/mol/K and Delta S(2)degrees = -28 +/- 8 J/mol/K. (C) 1998 Elsevier Science Ltd. All rights reserved.