Quantitative measurement of transverse and longitudinal cross-correlation between C-13-H-1 dipolar interaction and C-13 chemical shift anisotropy: Application to a C-13-labeled DNA duplex

Measurement of both longitudinal and transverse relaxation interference (cr oss-correlation) between C-13 chemical shift anisotropy and C-13-H-1 dipola r interactions is described. The ratio of the transverse to longitudinal cr oss-correlation rates readily yields the ratio of spectral densities J(0)/J (omega(C)), independent of any structural attributes such as internuclear d istance or chemical shift tensor. The spectral density at zero frequency J( 0) is also independent of chemical exchange effects. With limited internal motions, the ratio also enables an accurate evaluation of the correlation t ime for overall molecular tumbling. Applicability of this approach to inves tigating dynamics has been demonstrated by measurements made at three tempe ratures using a DNA decamer duplex with purines randomly enriched to 15% in C-13. (C) 1999 Academic Press.