Effect of 13C-14N Dipolar Interactions on Spin-Lattice Relaxation Times and Intensities of Nonprotonated Carbon Resonances

Raymond S. Norton, Adam Allerhand

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Spin-lattice relaxation times (T1) and integrated intensities of the resonances in proton-decoupled natural-abundance 13C Fourier transform NMR spectra of adenosine 5′-monophosphate and guanosine S'-monophosphate (in H2O and D2O, at 40-44 °C, at 15.18 MHz, in 20-mm sample tubes) are compared with calculated values that take into account 13C-1H and 13C-14N dipolar relaxation. In each case, T1 values of methine carbons of the base were used to obtain a rotational correlation time, which was then used, together with interatomic distances from crystallographic data, to compute T1 values of nonprotonated carbons. Nonprotonated carbons which are directly bonded to nitrogens and which have no hydrogens two bonds removed yield theoretical T1 values strongly affected by 13C-14N dipolar interactions. For carbons in this category, calculated T1 values which include 13C-14N dipolar interactions are in much better agreement with experimental values than calculated values which consider only 13C-1H interactions. Integrated intensities were calculated by considering variations in the nuclear Overhauser enhancement that result from differences in relative contributions to 1/T1 from 13C-1H and 13C-14N dipolar relaxation. The calculated intensities are in excellent agreement with the experimental ones.

Original languageEnglish
Pages (from-to)1007-1014
Number of pages8
JournalJournal of the American Chemical Society
Issue number4
Publication statusPublished - 1 Feb 1976
Externally publishedYes

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