ABSTRACT
Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for determining the molecular structure of sterols. NMR is a non-destructive method that requires only a modest quantity of sample. X-ray crystallography gives a precisely defined conformation, but the crystal structure may deviate subtly from the sterol conformation in the fluid environment of a biological system. Unlike X-ray crystallographic results, which can be unambiguously condensed to a set of atomic coordinates, NMR analysis of a sterol typically employs a variety of spectral techniques, the results of which are combined to establish the chemical structure. Assigning the NMR signals to individual carbons and hydrogens of a sterol molecule provides an exacting test of the correctness of a proposed sterol structure as well as insight into the conformation. Strategies for assigning signals depend on many factors, including the density of functional groups in the sterol molecule, spectral techniques available, and the accessibility of substituent increments and models for chemical shift comparison.
