Linked Life Data

12787905

Source:http://linkedlifedata.com/resource/pubmed/id/12787905

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
4
pubmed:dateCreated
2003-6-5
pubmed:abstractText
We studied the spin-lattice relaxation of the 13C magnetisation, M(C), in 13C-enriched single crystal of aspirin (only methyl carbons enriched to 99%) at the carbon resonance frequency of 54.5 MHz. After the carbon saturation the recovery appears exponential except below 30K, where it is biexponential due to the presence of the level crossing omega(t)=omega(C)+omega(H) (the symbols refer, respectively, to the tunnel frequency and the carbon and proton resonance frequencies in angular units). After the saturation of the proton magnetisation, M(H), the description of the M(C) recovery needs three exponentials. The evaluation of the time constants is easiest from the data in this case, since M(C) varies with time in an initial growth-subsequent decrease (or an initial decrease-subsequent growth depending on temperature) manner, instead of the monotonous growth after the carbon saturation. Experimental data agree semiquantitatively with the predictions of our recent model. According to the model the relaxation of M(C) is coupled to M(H) and the tunnel energy TE at temperatures below the minimum of the 13C relaxation time. Sufficiently above this minimum M(C) is coupled to M(H) and the rotational polarization (but not to TE) in agreement with experiment. Also the effect of torsional oscillations of a methyl group on the magnitude of various 13C-related transition rates was considered in detail. In aspirin the rates are reduced roughly by 10% and the reduction should become larger in samples with a larger tunnel splitting. The reduction also changes somewhat the angular dependence of these rates.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jun
pubmed:issn
0926-2040
pubmed:author
pubmed:issnType
Print
pubmed:volume
23
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
224-42
pubmed:meshHeading
pubmed:year
2003
pubmed:articleTitle
Spin-lattice relaxation of 13CH3 groups in 13C-enriched aspirin after proton saturation.
pubmed:affiliation
Wihuri Physical Laboratory, Department of Physics, Turku University, Turku Yliopisto, FIN-20014, Finland. mikko.kankaanpaa@utu.fi
pubmed:publicationType
Journal Article, Evaluation Studies, Validation Studies