Spin lattice relaxation in an AM[X/sub n/] system: application to $sup 13$C relaxation in enriched molecules
In $sup 13$C-enriched molecules, $sup 13$C--$sup 13$C dipolar interactions can contribute significantly to the relaxation of $sup 13$C nuclei which are not directly bonded to protons. Comparison of the relaxation behavior of the $sup 13$C--$sup 13$C multiplet lines with that of the singlet for which there are no $sup 13$C--$sup 13$C dipolar interactions allows a quantitative analysis of this interaction. However, since $sup 13$C--$sup 13$C dipolar interactions are necessarily weak, substantial contributions to the relaxation of nonprotonated carbon atoms are made by protons attached to adjacent atoms. The general features of the spin lattice relaxation behavior of an AM]X] system in which ]X] represents the decoupled protons, A, the nonprotonated carbon, and M, the adjacent protonated carbon, have been derived. In general, the A relaxation will be nonexponential and dependent on the initial state of the M/sub z/ magnetization. The measurements on $sup 13$C-enriched were found to be sensitivE to internal and/or anisotropic motions. Such rotations affect the $sup 13$C-- $sup 13$C and $sup 13$C-$sup 1$H dipolar interactions differently, depending on the particular geometry involved and the axis of rotation. These techniques have been applied to the observed relaxation behavior of 6-phosphogluconate enriched to the 79% level. In this case the contributions to the intramolecular dipolar relaxation ofthe carboxyl carbon consist primarily of the $sup 13$C--$sup 13$C interaction with its adjacent carbon, the $sup 13$C-$sup 1$H interaction with the proton on the adjacent carbon, and a significant contribution from the proton attached to the third carbon in the chain. It is found that the carboxyl relaxation will be exponential and independent of the initial value of M/sub z/. (AIP)
- Research Organization:
- University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico 87544
- NSA Number:
- NSA-33-008883
- OSTI ID:
- 4142986
- Journal Information:
- J. Chem. Phys., v. 63, no. 10, pp. 4442-4449, Journal Name: J. Chem. Phys., v. 63, no. 10, pp. 4442-4449; ISSN JCPSA
- Country of Publication:
- United States
- Language:
- English
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