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Improved Narrowband Dipolar Recoupling for Homonuclear Distance Measurements in Rotating Solids

โœ Scribed by G. Goobes; S. Vega


Publisher
Elsevier Science
Year
2002
Tongue
English
Weight
254 KB
Volume
154
Category
Article
ISSN
1090-7807

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โœฆ Synopsis


Recovery of the magnetic dipolar interaction between nuclei bearing the same gyromagnetic ratio in rotating solids can be promoted by synchronous rf irradiation. Determination of the dipolar interaction strength can serve as a tool for structural elucidation in polycrystalline powders. Spinning frequency dependent narrowband (nb) RFDR and SEDRA experiments are utilized as simple techniques for the determination of dipolar interactions between the nuclei in coupled homonuclear spin pairs. The magnetization exchange and coherence dephasing due to a fixed number of rotorsynchronously applied ฯ€-pulses is monitored at spinning frequencies in the vicinity of the rotational resonance (R 2 ) conditions. The powder nbRFDR and nbSEDRA decay curves of spin magnetizations and coherences, respectively, as a function of the spinning frequency can be measured and analyzed using simple rate equations providing a quantitative measure of the dipolar coupling. The effects of the phenomenological relaxation parameters in these rate equations are discussed and an improved methodology is suggested for analyzing nbRFDR data for small dipolar couplings. The distance between the labeled nuclei in the 1,3-13 C 2 -hydroxybutyric acid molecule is rederived using existing nbRFDR results and the new simulation procedure. A nbSEDRA experiment has been performed successfully on a powder sample of singly labeled 1-13 C-L-leucine measuring the dipolar interaction between the labeled carboxyl carbon and the natural abundant ฮฒ-carbon. Both narrowband techniques are employed for the determination of the nuclear distances between the side-chain carbons of leucine and its carbonyl carbon in a tripeptide Leu-Gly-Phe that is singly 13 C-labeled at the leucine carbonyl carbon position.


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