A series of binucleating tetrakis(methylimidazole) ligands of the gene
ral type (MeIm)(2)C(OH)-spacer-C(OH)(MeIm)(2) were prepared, where MeI
m = 1-methylimidazol-2-yl and the spacer was one of several different
rigid (5 = 1,4-C6H4, 6 = trans-C2H2, 14 = (2 alpha,3a beta,5 alpha,6a
beta)-octahydro-3a,6a-dimethylpentalene 15 = (2 alpha,3a alpha,5 alpha
,6a alpha)-octahydro-3a,6a-dimethylpentalene, 16 = 2 alpha,3a alpha,5
beta,6a alpha)-octahydro-3a,6a-dimethylpentalene) or flexible ((CH2)(n
) 7, n = 0; 8, n = 1; 9, n = 2; 10, n = 3; 11, n = 8) spacers. A highl
y rigid binucleating ligand, (3a alpha,6a ylimidazol-2-yl)methylene)-3
a,6a-dimethylpentalene (17), was also prepared and characterized. The
effectiveness of the rigid binuclear complexes of Cu(II), Ni(II), and
Zn(II) as catalysts for the hydrolysis of the phosphate diester sodium
bis(4-nitrophenyl) phosphate was similar to corresponding mononuclear
complexes with ligand 4 = (MeIm)(2)C(OH)CH3 or bipyridine. A signific
ant DNA binding ability was observed for the binuclear complexes, whic
h was not evident with the mononuclear compounds. In gel electrophores
is mobility studies, the cationic dimetal complexes with the tetrakis(
methylimidazole) ligands significantly retarded the migration of super
coiled plasmid DNA. The binucleating ligands with flexible organic spa
cer groups and the mononuclear metal complexes did not show this effec
t. In ultrafiltration experiments with tritium labeled ligands, all th
e cationic dimetal complexes showed evidence for DNA binding, whereas
the mononuclear complexes of 4 did not. Similar results were obtained
for DNA precipitation studies. Without added metal ions, none of the l
igands evidenced a significant DNA binding ability. Simple amine polyc
ations and mononuclear cations, such as Mg(II), were not able to disru
pt the binding of the binuclear complexes to DNA, unless added in a la
rge excess. Nickel(II) complexes that contained ligands 7, 9, and 15 w
ere crystallized and characterized by X-ray crystallography. In additi
on, the Zn(II) complexes present in solution with ligands 4, 14, and 1
5 were studied by H-1 NMR spectroscopy. Reasons for the enhanced bindi
ng ability of dimetal complexes to DNA and the role of a flexible or r
igid spacer group are discussed.