3D Structure Elucidation Using NMR Chemical Shifts

Abstract

Abstract The NMR chemical shift is virtually always available from conventional NMR experiments. In contrast to X-ray diffraction it is caused by the density distribution of the valence electrons, hence it contains genuine information about the valence structure of the molecular system. This paper reviews the available theoretical, empirical and semi-empirical methods to obtain 3D structure information from chemical shifts. Besides direct empirical correlations of chemical shifts an overview of computational quantum chemical methods is presented. A critical survey is given how these methods can be used in structure refinement procedures. Special attention is paid to methods for protein and peptide structure analysis using chemical shifts. Computed and empirical chemical shift maps are discussed and compared to direct refinement methods. Chemical shift tensors or their principal components can provide additional data to characterise structural motifs in proteins. Furthermore, methods are discussed to extract orientational constraints from chemical shift tensors in macroscopically aligned samples. Applications are presented for structure elucidation in solution and in the solid state, including the first applications of chemical shifts to crystal structure refinements.