NMR 1H-Shielding Constants of Hydrogen-Bond Donor Reflect Manifestation of the Pauli Principle.

NMR spectroscopy is one of the most useful methods for detection and characterization of hydrogen bond (H-bond) interactions in biological systems. For H bonds X-H···Y, where X and Y are O or N, it is generally believed that a decrease in 1H-shielding constants relates to a shortening of H-bond donor-acceptor distance. Here we investigated computationally the trend of 1H-shielding constants for hydrogen-bonded protons in a series of guanine C8-substituted GC pair model compounds as a function of the molecular structure. Furthermore, the electron density distribution around the hydrogen atom was analyzed with the Voronoi deformation density (VDD) method. Our findings demonstrate that 1H-shielding values of the hydrogen bond are determined by the depletion of charge around the hydrogen atom, which stems from the fact that electrons obey the Pauli exclusion principle.