American Chemical Society
ja051019a_si_002.txt (4.14 kB)

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

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posted on 2005-07-27, 00:00 authored by Jonathan R. Yates, Tran N. Pham, Chris J. Pickard, Francesco Mauri, Ana M. Amado, Ana M. Gil, Steven P. Brown
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 CH2 protons are assigned using first-principles chemical shift calculations that employ a plane-wave pseudopotential 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 Å) and a CHO bond angle greater than 130° is observed, thus showing that directionality is important in C−H···O hydrogen bonding.