DETERMINATION OF LOCAL-STRUCTURE IN SOLID NUCLEIC-ACIDS USING DOUBLE-QUANTUM NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

A theoretical analysis of dipolar recoupling with a windowless multipu lse irradiation (DRAWS) is presented. Analytical expressions that desc ribe the degree to which the DRAWS pulse sequence recouples the dipola r interaction as a function of offset and spinning rate sire derived u sing Floquet theory. Numerical methods are used to assess the performa nce of DRAWS in the preparation and detection of multiple quantum cohe rence. Simulations indicate that the mutual orientation of two or more CSA tensors can be obtained with high accuracy from double quantum sp ectra prepared and detected by DRAWS irradiation (DQDRAWS). These expe ctations are born out by experiment and in particular, the mutual orie ntation of three C-13 CSA tensors in selectively labeled 2'-deoxythymi dine are determined from DQDRAWS data. The results of the DQDRAWS anal ysis of CSA tensor orientation in 2'-deoxythymidine are shown to be in excellent agreement with results obtained by conventional methods. Us ing these CSA tensor orientations and an independent measurement of in ternuclear distance, a practical strategy is proposed and executed for deriving the mutual orientation of purine and pyrimidine bases in a D NA 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. (C) 1997 American Institute of P hysics.