14N Nuclear quadrupole interaction in Cu(II) doped l-alanine

The ¹⁴N nuclear quadrupole interaction tensor P_N measured by ENDOR in Cu(II) doped l-alanine is analyzed in terms of the Townes and Dailey theory assuming a tetrahedrally bonded N atom. The results of this analysis are compared with those for the ¹⁴N in pure l-alanine and it is found that the principal directions of the P_N tensor are drastically changed upon metal complexation as a consequence of the higher electron affinity of Cu(II) with respect to C and H. Comparison of the corresponding bond populations in pure and Cu(II) doped l-alanine indicates that the Cu draws 0.11 more electron from the N than the substituted H atom.