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

Abstract

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.

Relationships between NMR shifts and interaction energies in biphenyls, alkanes, aza‐alkanes, and oxa‐alkanes with X─H…H─Y and X─H…Z (X, Y = C or N; Z = N or O) hydrogen bonding

“…For a wide variety of organic and inorganic compounds with O─H … O hydrogen bonding, the bond‐polarisation energy approach gives an interpretation of a shift correlation with the inverse of the H … O distance . Voronoi deformation density calculations on a deoxyribonucleic acid base pair show that the shielding of the hydrogen‐bonded hydrogen is determined by the depletion of charge; no relationship between depletion of charge and bond strength or any other parameter was established. What we need is a relationship between depletion of charge at the hydrogen‐bonded hydrogens and the accumulation of charge or electron density between these atoms to form a bond.…”

“…Energies for intramolecular C─H … N interactions range from 1 to 2 kcal mol −1 up to 6 kcal mol −1 and have been extensively investigated for nucleobase pairs . Intermolecular N─H … N and N─H … O bonding is commonplace, notably in deoxyribonucleic acid and nucleobase pairs, and has been considered in mainly theoretical studies of other structures …”

The Nature of Hydrogen Bonds: A Delineation of the Role of Different Energy Components on Hydrogen Bond Strengths and Lengths

“…Obeying the Pauli principler esults in ad epletion of electron density aroundt he hydrogen atom, which explainsthe downfield 1 Hchemical shift upon HB formation. [71] Furthermore, Pauli repulsion has been shown to be crucial for ac orrect description of the HB strengthsa nd lengths.…”

“…The Pauli repulsion is defined as the repulsive interactions between the monomer's filled orbitals (Figure e), and originates from the fact that electrons with the same spin cannot be at the same position in space. Obeying the Pauli principle results in a depletion of electron density around the hydrogen atom, which explains the downfield 1 H chemical shift upon HB formation . Furthermore, Pauli repulsion has been shown to be crucial for a correct description of the HB strengths and lengths.…”

Epoxy-based composites reinforced with imidazolium ionic liquid-treated aramid pulp

“…Thus, the signals of the peaks related to the imidazolium ring hydrogens (C 2 -H, C 4 -H, C 5 -H) shifted to higher frequencies. This larger proton de-shielding may be associated with a hydrogen bond strengthening [28,29]…”