Trans-hydrogen bond coupling

Here, we present the example of the trans hydrogen bond coupling between the C of the acceptor and the N of the donor h/(N, C ) that is measured by excitation of double-quantum and zero-quantum coherence between the HN and the C nuclei [12] in a protein. Thus, the double-quantum coherence is split by h /(N, C )+ /(N, H) while the zero-quantum coher-... 

Tab. 9.1 Observed trans hydrogen bond couplings in nucleic acids...

Fig. 6.6 Schematics of hydrogen bonds between purine and pyrimidine bases with indicated trans-hydrogen bond scalar interactions and related coupling constants, which can be measured using NMR. In addition to correlations between exchangeable protons and nitrogens, also a relayed transfer to nonexchangeable aromatic protons, shown by a dashed arrow, can be employed. The...

Dependence of the DFT calculated trans hydrogen bond Vcn and other scalar couplings upon basis sets has been studied by Salvador and Dannenb-erg. Amide dimers have been used as peptide models in this study. 

Recently, electron-mediated, scalar couplings which are active between magnetic nuclei on both sides of the hydrogen bridge have been discovered in nucleic acids [28-41], proteins [42-54] and their complexes (Tabs. 9.1-9.3) [54—56]. These couplings are closely related to similar inter- and intramolecular couplings across H-bonds in smaller chemical compounds [57-60]. It is well established [31, 58, 61-74] that such trans H-bond scalar couplings follow the same electron-mediated polarization mechanism as any covalent... 

Further support for the non-centred enol hydrogen bond has come from 13C and 2H spin-lattice relaxation times of AA and 2H2AA from which deuterium quadrupole coupling constants are derived. These are explained in terms of a double minimum potential well67. These same workers also discuss the broadness of the <5(OHO) signal and conclude that it is due to bond lengthening rather than contributions from trans enol forms. The minimum line width for AA achieved by exhaustive drying was 0.5 Hz. 

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