PubMed · 5639027
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J Ross, S Kochwa, L R Wasserman. 1968-01-22. Iron-transferrin complex formation.. https://doi.org/10.1016/0005-2795(68)90259-6
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Resistive or hybrid magnets can achieve substantially higher fields than those available in superconducting magnets, but their spatial homogeneity and temporal stability are unacceptable for high-resolution NMR. We show that modern stabilization and shimming technology, combined with detection of intermolecular zero-quantum coherences (iZQCs), can remove almost all of the effects of inhomogeneity and drifts, while retaining chemical shift differences and J couplings. In a 25-T electromagnet (1 kHz/s drift, 3 kHz linewidth over 1 cm(3)), iZQC detection removes >99% of the remaining inhomogeneity, to generate the first high-resolution liquid-state NMR spectra acquired at >1 GHz.
The packing geometry of amino acids in folded proteins is analyzed via a modified Voronoï tessellation method which distinguishes bulk and surface. From a statistical analysis of the Voronoï cells over 40 representative proteins, it appears that the packings are in average similar to random packings of hard spheres encountered in condensed matter physics, with a quite strong fivefold local symmetry. Moreover, the statistics permits one to establish a classification of amino acids in terms of increasing propensity to be buried in agreement with what is known from chemical considerations.
Marcus theory has explained how thermal nuclear motions modulate the energy gap between donor and acceptor sites in protein electron transfer reactions. Thermal motions, however, may also modulate electron tunneling between these reactions. Here we identify a new mechanism of nuclear dynamics amplification that plays a central role when interference among the dominant tunneling pathway tubes is destructive. In these cases, tunneling takes place in protein conformations far from equilibrium that minimize destructive interference. As an example, we demonstrate how this dynamical amplification mechanism affects certain reaction rates in the photosynthetic reaction center and therefore may be critical for biological function.