Quadrupole-enhanced proton spin relaxation for a slow reorienting spin pair: (I)-(S). A stochastic Liouville approach
2009 (English)In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 107, no 20, 2141-8 p.Article in journal (Refereed) Published
The field dependence of the proton (I) spin-lattice relaxation rate is calculated for a dipole-dipole coupled spin pair, (I = 1/2) - (S = 1), where the quadrupole nucleus (S) is 2H or 14N with asymmetry parameter η = 0. The observed relaxation profile shows a marked enhancement for equal proton Larmor and quadrupole spin frequencies (i.e. ωI = ωQ). This phenomenon is referred to as the quadrupole dip, and has been observed, for instance, in 14N-1H amide groups of immobilized proteins. In this work, an analysis of the observed relaxation enhancement is presented when the dipole-dipole coupling and the quadrupole interaction are modulated by the overall re-orientational motion. A characteristic low field dispersion is observed when (3/2) τRωI ≥ 1, where τR is the rotational correlation time and ωI is the proton Larmor frequency. At higher fields, the relaxation peak exhibits a Lorentzian-like line shape, , which is centred at the quadrupole frequency. The quadrupole spin system shows a spin-lattice T1Q and a spin-spin relaxation time T2Q that become equal in the zero field limit. In the slow tumbling limit, the quadrupole spin relaxation times, T1Q, T2Q, are equal to (3/2)τR.
Place, publisher, year, edition, pages
Taylor & Francis , 2009. Vol. 107, no 20, 2141-8 p.
quadrupole enhanced proton spin relaxation, quadrupole dip, stochastic Liouville equation
IdentifiersURN: urn:nbn:se:umu:diva-26478DOI: 10.1080/00268970903185909OAI: oai:DiVA.org:umu-26478DiVA: diva2:271396