Chemical shift anisotropies decay rates

Spin-spin relaxation, also called transverse relaxation, is a process in which the magnetization in the x-y plane, perpendicular to the static laboratory field, decays. In section III.C.l., we will write down expressions for 1/ as they relate to the corresponding T s for dipolar and chemical shift anisotropy relaxations. It will be pointed out that, in the presence of extreme narrowing due to rapid molecular motion, T -Tg, with the consequence that these two relaxation rates do not contain different information in this limit, which almost always occurs in liquids. 

The difference in the relaxation rates of ZQ and DQ coherences is the result of three principal mechanisms. These include the cross-correlation between the chemical shift anisotropies of the two participating nuclei, dipolar interactions with remote protons as well as interference effects due to the time-modulation of their isotropic chemical shifts as a consequence of slow mus-ms dynamics. The last effect when present, dominates the others resulting in large differences between the relaxation rates of ZQ and DQ coherences. Majumdar and Ghose have presented four TROSY-based experiments that measure this effect for several pairs of backbone nuclei. These experiments allow the detection of slow dynamic processes in the protein backbone including correlated motion over two and three bonds ". A suite of TROSY-based NMR relaxation dispersion experiments that measure the decay of DG and ZQ coherences as a... 

Slow conformational fluctuation was characterized by the difference decay rates (Rcc) ofDQC and ZQC selected by CPMG experiments [98,99]. The relaxation rates, DQC = (>2)(N H + N H ) and ZQC =(>2) (N H + N H ), depend on the pulse repetition rate if there are local motions on slow timescale (ps—ms). This dispersion effect occurs when the two nuclei experience slow correlated modulations of the isotropic chemical shifts. The difference of the decay rates, Rcc, is the sum of chemical shift anisotropy cross-correlation (CSA/CSA) and isotropic chemical shift modulation (CSM/CSM) as well as additional dipole/dipole crosscorrelation (DD/DD) contributions due to coupftngs to neighbouring nuclei ... 

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