Exploring conformational energy landscape of glassy disaccharldes by cross polarization magic angle spinning ~(13)C NMR and numerical simulations.I.Methodological aspects

摘要

This article demonstrates the ability of chemical shift surfaces to provide information on distributions of various conformations of disaccharides in the glassy,solid state.The validity of the general method leading to a simulation of inhomogeneous ~(13)C chemical shift distributions is discussed in detail.In particular,a proper consideration of extrema and saddle points of the chemical shift map correctly accounts for the observed discontinuities in the experimental cross polarization magic angle spinning spectra.Provided that these basic requirements are met,density functional theory/gauge-independent atomic orbital chemical shift maps calculated on relaxed conformations lead to a very satisfactory description of the experimental line shapes.Using amorphous trehalose as a model disaccharide,the simulation unambiguously defines the range of most populated conformations in the glass.