Deshmukh Milind M, Bartolotti Libero J, Gadre Shridhar R
Department of Chemistry, University of Pune, Pune 411 007, India.
J Phys Chem A. 2008 Jan 17;112(2):312-21. doi: 10.1021/jp076316b. Epub 2007 Dec 18.
In spite of many theoretical and experimental attempts for understanding intramolecular hydrogen bonding (H-bonding) in carbohydrates, a direct quantification of individual intramolecular H-bond energies and the cooperativity among the H-bonded networks has not been reported in the literature. The present work attempts, for the first time, a direct estimation of individual intramolecular O-H...O interaction energies in sugar molecules using the recently developed molecular tailoring approach (MTA). The estimated H-bond energies are in the range of 1.2-4.1 kcal mol(-1). It is seen that the OH...O equatorial-equatorial interaction energies lie between 1.8 and 2.5 kcal mol(-1), with axial-equatorial ones being stronger (2.0-3.5 kcal mol(-1)). The strongest bonds are nonvicinal axial-axial H-bonds (3.0-4.1 kcal mol(-1)). This trend in H-bond energies is in agreement with the earlier reports based on the water-water H-bond angle, solvent-accessible surface area (SASA), and (1)H NMR analysis. The contribution to the H-bond energy from the cooperativity is also estimated using MTA. This contribution is seen to be typically between 0.1 and 0.6 kcal mol(-1) when H-bonds are a part of a relatively weak equatorial-equatorial H-bond network and is much higher (0.5-1.1 kcal mol(-1)) when H-bonds participate in an axial-axial H-bond network.
尽管人们为理解碳水化合物中的分子内氢键（H键）进行了许多理论和实验尝试，但文献中尚未报道对单个分子内H键能量以及H键网络间协同性的直接量化。本研究首次尝试使用最近开发的分子剪裁方法（MTA）直接估算糖分子中单个分子内O-H...O相互作用能。估算得到的H键能量在1.2 - 4.1 kcal mol⁻¹范围内。可以看出，OH...O赤道-赤道相互作用能在1.8至2.5 kcal mol⁻¹之间，轴向-赤道相互作用更强（2.0 - 3.5 kcal mol⁻¹）。最强的键是非邻位轴向-轴向H键（3.0 - 4.1 kcal mol⁻¹）。H键能量的这种趋势与早期基于水-水H键角、溶剂可及表面积（SASA）和¹H NMR分析的报道一致。还使用MTA估算了协同性对H键能量的贡献。当H键是相对较弱的赤道-赤道H键网络的一部分时，这种贡献通常在0.1至0.6 kcal mol⁻¹之间，而当H键参与轴向-轴向H键网络时则高得多（0.5 - 1.1 kcal mol⁻¹）。
