ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
We report the determination of two- and three-bond 1H-15N spin-spin couplings in the nmr spectra of a polypeptide. The 1H- and 15N-nmr spectra of 99.2% 15N-enriched alumichrome have been studied at 360 MHz and 10.1 MHz, repectively. While some 2J1H15N and 3J1H15N coupling are of the order of 5 Hz, most splitting resulting from the heteronuclear interaction are ≲2 Hz, which introduces strigent requirements of spectral resolution. In the 1H spectra these requirements were met by digital deconvolution with a sine bell routine combined with positive exponential filtering. Although the 15N spectra clearly exhibit features of fine structure, mainly because of the intrinsic higher nmir sensitivity of protons, observation of 1H-15N spin-spin couplings was found to be more practical in the 1H than in the 15N spectra. We find that the alumichrome data do not satisfy a simple cyclic relationship linking the heteronuclear couplings to the crystallographic ψ dihedral angles. It is suggested that a formal treatment of the ψ-related interresidue 1H-15N coupling might have to take into account a more complex dependence of the intervening 3J on the overall local electronic structure, which is dependent on φ,ψ, and ω simultaneoulsy. In contrast, our analysis indicates that χ1 can be readily determined from the measurement of the corresponding heteronuclear 3J coupling in the 1Hβ or in the amide 15N resonances. Karplus relationships are proposed that relate this heteronuclear 3J to the corresponding dihedral angle θ and which, on average, yield \documentclass{article}\pagestyle{empty}\begin{document}$$ {}^3 J\left( \theta \right)= - 4.4\,{\rm cos}^2 \theta + 1.2 {\rm cos}\theta + 0.1_5$$\end{document}
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.1978.360171118
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