An Investigation of Weak CH...O Hydrogen Bonds in Maltose Anomers by a Combination of Calculation and Experimental Solid-State NMR Spectroscopy

摘要

Two-dimensional ~1H-~13C MAS-J-HMQC solid-state NMR spectra of the two anomeric forms of maltose at natural abundance are presented.The experimental ~1H chemical shifts of the CH and CH_2 protons are assigned using first-principles chemical shift calculations that employ a plane-wave pseudo-potential approach.Further calculations show that the calculated change in the ~1H chemical shift when comparing the full crystal and an isolated molecule is a quantitative measure of intermolecular C-H-O weak hydrogen bonding.Notably,a clear correlation between a large chemical shift change (up to 2 ppm) and both a short H...O distance (<2.7 A) and a CHO bond angle greater than 130° is observed,thus showing that directionality is important in C-H-O hydrogen bonding.