Determination of local structure in solid nucleic acids using double quantum nuclear magnetic resonance spectroscopy

Abstract

A theoretical analysis of dipolar recoupling with a windowless multipulse irradiation (DRAWS) is presented. Analytical expressions that describe the degree to which the DRAWS pulse sequence recouples the dipolar interaction as a function of offset and spinning rate are derived using Floquet theory. Numerical methods are used to assess the performance of DRAWS in the preparation and detection of multiple quantum coherence. Simulations indicate that the mutual orientation of two or more CSA tensors can be obtained with high accuracy from double quantum spectra prepared and detected by DRAWS irradiation (DQDRAWS). These expectations are born out by experiment and in particular, the mutual orientation of three 13C CSA tensors in selectively labeled 2-deoxythymidine are determined from DQDRAWS data. The results of the DQDRAWS analysis of CSA tensor orientation in 2-deoxythymidine are shown to be in excellent agreement with results obtained by conventional methods. Using these CSA tensor orientations and an independent measurement of internuclear distance, a practical strategy is proposed and executed for deriving the mutual orientation of purine and pyrimidine bases in a DNA dodecamer from DQDRAWS data. The DQDRAWS method for determining the mutual orientation of rigid bodies in macromolecules is compared and contrasted to distance-based methods.