Determination of 13C CSA Tensors: Extension of the Model-independent Approach to an RNA Kissing Complex Undergoing Anisotropic Rotational Diffusion in Solution
Authors: Ravindranathan, Sapna; Kim, Chul-Hyun; Bodenhausen, Geoffrey
Source: Journal of Biomolecular NMR, Volume 33, Number 3, November 2005 , pp. 163-174(12)
Abstract:Chemical shift anisotropy (CSA) tensor parameters have been determined for the protonated carbons of the purine bases in an RNA kissing complex in solution by extending the model-independent approach [Fushman, D., Cowburn, D. (1998) J. Am. Chem. Soc. 120, 7109–7110]. A strategy for determining CSA tensor parameters of heteronuclei in isolated X–H two-spin systems (X = 13C or 15N) in molecules undergoing anisotropic rotational diffusion is presented. The original method relies on the fact that the ratio 2=R2auto/R2cross of the transverse auto- and cross-correlated relaxation rates involving the X CSA and the X–H dipolar interaction is independent of parameters related to molecular motion, provided rotational diffusion is isotropic. However, if the overall motion is anisotropic 2 depends on the anisotropy D||/D⊥ of rotational diffusion. In this paper, the field dependence of both 2 and its longitudinal counterpart 1=R1auto/R1cross are determined. For anisotropic rotational diffusion, our calculations show that the average av = 1/2 (1+2), of the ratios is largely independent of the anisotropy parameter D||/D⊥. The field dependence of the average ratio av may thus be utilized to determine CSA tensor parameters by a generalized model-independent approach in the case of molecules with an overall motion described by an axially symmetric rotational diffusion tensor.
Document Type: Research Article
Affiliations: Email: s.ravindranathan@.ncl.res.in
Publication date: 2005-11-01