Proton transfer contact information

The contact hyperfine shift contains information on conformational arrangements because it is somehow related to chemical bonds. The information, however, is generally hidden, with the exception of few cases. For example, if we have a CH moiety of an sp3 carbon bound to an sp2 carbon which bears spin density in the pz orbital, we have already seen that a spin density of the same sign is transferred to the methyl protons (Section 2.3.2). A mechanism to originate spin density at the methyl proton is the direct overlap between the sp2 carbon pz and the Is hydrogen orbital [51-54] (Fig. 2.14). Such overlap depends on the dihedral angle between the pz(axis)-C-C plane and the C-C-H plane (Fig. 2.14). The relationship is described by the general Karplus equation [55]... 

More information on the chemical structure of bone apatite can be obtained from H—> P CP. First, consider the dependence of peak intensity J(f) on contact time t (also denoted CT) in the conventional variable-contact time experiment (Fig. 11). Such an experiment monitors the CP kinetics, which is very specific for a particular material [12]. There are two models of the CP kinetics, I-T-S and I-S [12]. In this notation, the spin polarization is transferred from spins I to spins S, in our case from protons to P, respectively. 

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