Abstract
The longitudinal relaxation of the two carbon-13 nuclei of doubly enriched glycine ( 13C and 2H) has been investigated by the conventional nonselective [180°-τ-90°] pulse sequence. Some approximations are proposed which lead to a straightforward interpretation of the experimental results, a refined analysis being carried out by means of a general computer program previously described. These results together with those of other isotopomers (normal glycine NH 2CH 2000H and NH 2 12CH 2 13COOD) allow the determination of random field rates at the two carbons and of the spectral densities relative to the carbon-carbon and methylene carbon-proton dipolar interactions. These spectral densities yield the following correlation times: τ CC = 17 ± 4 psec and τ CH = 5.5 ± 0.3 psec. In addition, the effect of a dipolar chemical shift anisotropy interference term has been observed by applying the sequence [180°-τ-30°]. Its sign is in agreement with a positive carbon-carbon indirect coupling and a positive carbonyl chemical shift anisotropy.
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