Study of the chelating capacity of nucleobase analogs with biological interest: Ab initio molecular orbital calculations and single-crystal X-ray structural study of 6-amino-5-formyl-1,3-dimethyluracil-benzoylhydrazone

Ab initio molecular orbital calculations at the RHF/6-31G* level using the GAUSSIAN94 program package have allowed us to simulate the molecular struct ures for different conformations of 6-amino-5-formyl-1,3-dimethyluracil-ben zoylhydrazone. The contribution of the atomic orbitals of the potential don or atoms to the higher occupied molecular orbitals allows us to propose the oretical arguments to justify the different chelating behavior found for th is compound in several metal complexes. Further, the molecular structure of 6-amino-5-formyl-1,3-dimethyluracil-benzoylhydrazone has been determined b y single-crystal X-ray diffraction methods. The compound crystallizes in th e monoclinic system (space group P2(1)/n) with cell dimensions: a = 12.111( 5), b = 5.743(5), c = 22.636(5) Angstrom, beta = 98.60(5)degrees. The struc ture was solved from 1719 reflections with I>2 sigma (I). The final R [I>2 sigma (I)] was 0.0506 for 217 parameters. The azomethine double bond substi tuents are in the E conformation and the N51 atom is in the cis position wi th respect to the N6 atom, due to the formation of an intramolecular hydrog en bond N6-H . . . N51. The geometrical data are in good agreement with tho se calculated by means of ab initio methods.