TENSOR DETERMINATION OF N1 SITE IN DEOXYGUANOSINE

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Solid-state NMR spectra contain a wealth of information regarding orientation of specific nuclei. The chemical shift anisotropy (CSA) can be represented as a second rank tensor with orientation dependence in its frequency distribution. The interpretation of the CSA frequency requires that the orientation of the elements of the tensor be mapped into the molecular frame of reference. The deoxyguanosine base was synthetically labeled with 15N in position N1. The tensor analysis was made by measuring the two-dimensional solid-state NMR PISEMA spectrum of the powder material. The one-dimensional 15N spectrum yields the principal elements of the CSA tensor and the two-dimensional spectrum can be simulated to determine the orientation of the 15N-1H dipolar coupling tensor relative to the CSA tensor. The orientation of the dipolar tensor is along the vector connecting the two nuclei, hence an anchor to the molecular frame of reference. The principal values of the 15N CSA tensor for the guanosine base are ?11= 54 ppm; ?22=108 ppm; and ?33=201 ppm relative to external ammonium sulfate. The simulated two-dimensional spectrum indicates that the ?33 element is colinear with the N-H bond. The principle elements ?11 and ?22 lie in the plane of the purine ring. This relation can now be used to elicit structural information from 15N chemical shift frequencies of oriented DNA.