Locating hydrogen atoms in single crystal and uniaxially aligned amino acids by solid-state NMR

We demonstrate a novel method to locate hydrogen atoms in amino acids, which involves measuring the CαHα bond vector geometry through orientationally dependent dipolar coupling frequencies measured by Lee-Goldburg cross polarization (LGCP). A 2D LGCP experiment is used to measure the polar angle of the CαHα bond vector in a single crystal of the model compound l-alanine. It is also demonstrated that by coupling the 13Cα1Hα LGCP experiment to a 13Cα15N REDOR experiment, one can determine the complete three-dimensional geometry of the CαHα and CαN vectors in a single crystal. These measurements allow for location of hydrogen atoms in crystalline biological macromolecules.