Mo(II) complexes: a new family of cytotoxic agents?

Several molybdenum complexes, [Mo(η(3)-C(3)H(5))X(CO)(2)(N-N)] (N-N = 1,10-phenanthroline, phen: X = CF(3)SO(3)T1, X = Br B1, X = Cl C1; N-N = 2,2'-bipyridyl, X = CF(3)SO(3)T2, X = Br B2) and [W(η(3)-C(3)H(5))Br(CO)(2)(phen)] (W1) have been synthesized and characterized. Their antitumor properties have been tested in vitro against human cancer cell lines cervical carcinoma (HeLa) and breast carcinoma (MCF-7) using a metabolic activity test (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, MTT), leading to IC(50) values ranging from 3 to 45 μM, approximately. Most complexes exhibited significant antitumoral activity. Complexes B1 and T2 were chosen for subsequent studies aiming to understand their mechanism of action. Cellular uptake of molybdenum and octanol/water partition assays revealed that both B1 and T2 exhibit a selective uptake by cells and intermediate partition coefficients. The binding constants of B1 and T2 with ct DNA, as determined by absorption titration, are 2.08 (± 0.98) × 10(5) and 3.68 (± 2.01)x 10(5)M(-1), respectively. These results suggest that they interact with DNA changing its conformation and possibly inducing cell death, and may therefore provide a valuable tool in cancer chemotherapy.

Synthesis, structure, and photophysical characterization of blue-green luminescent zinc complexes containing 2-iminophenanthropyrrolyl ligands

New 2-iminophenanthro[9,10-c]pyrrole ligand precursors containing phenyl or 2,6-diisopropylphenyl groups at the imine nitrogen substituent, 2-arylformiminophenanthro[9,10-c]pyrroles (aryl = phenyl IIa, 2,6-diisopropylphenyl IIb) were synthesized and deprotonated in situ with NaH, originating solutions of the corresponding sodium salts (IVa, IVb). The reaction of these salts with zinc chloride gave the homoleptic bis-ligand Zn(II) complexes [Zn(kappa(2)N,N'-2-arylformiminophenanthro[9,10-c]pyrrolyl)(2)] (aryl = phenyl 2a, 2,6-diisopropylphenyl 2b). The new ligand precursors and complexes were characterized by NMR, elemental analysis, UV/vis spectroscopy, and X-ray crystallography, when possible. The photophysical characterization was carried out using steady-state and picosecond time-resolved luminescence techniques in solution. The influence of the pi-extended conjugation of the condensed phenanthro group on the deprotonated iminopyrrolyl ligands coordinated to Zn(2+) greatly enhances fluorescence quantum yields of the complexes (2a, 2b) in relation to those of their ligand precursors (IIa, IIb). Complex 2a shows emission in the green spectral region (lambda(max) = 494 nm), presenting the highest fluorescence quantum yield (phi(f) = 8.8%). In the case of the complex 2b (phi(f) = 3.9%), the bulkiness of the 2,6-diisopropyl substituents of the arylimino group highly restricts the aryl ring rotation toward coplanarity with the ligand framework, inducing a shift in the emission to the blue region (lambda(max) = 459 nm). The values of the radiative (k(f)) and radiationless rate constants (k(nr)) show that the fluorescence quantum yield enhancement in the complexes results from a 50-fold increase in k(f) values, indicating much more allowed pi-pi* transitions in complexes 2a and 2b than those occurring in the ligand precursors IIa and IIb, with an essentially n-pi* character. These assignments were confirmed by density-functional theory (DFT) and time-dependent DFT (TD-DFT) molecular orbital calculations. Simple 2-aryliminopyrrole ligand precursors (Ia, Ib) and their Zn(II) complexes (1a, 1b) were also prepared to compare their photophysical properties with those of the corresponding 2-aryliminophenanthro[9,10-c]pyrrolyl compounds.

Soluble redox-active polymetallic chains [{Ru0(CO)(L)(bpy)}m](n) (bpy = 2,2'-bipyridine, L = PrCN, Cl-; m = 0, -1): electrosynthesis and characterization

Electrochemical and spectroelectrochemical techniques were employed to study in detail the formation and so far unreported spectroscopic properties of soluble electroactive molecular chains with nonbridged metal-metal backbones, namely, [{Ru(0)(CO)(PrCN)(bpy)}(m)](n) (m = 0, -1) and [{Ru(0)(CO)(bpy)Cl}(m)](n) (m = -1, -2; bpy = 2,2'-bipyridine). The precursors cis-(Cl)-[Ru(II)(CO)(MeCN)(bpy)Cl(2)] (in PrCN) and mer-[Ru(II)(CO)(bpy)Cl(3)](-) (in tetrahydrofuran (THF) and PrCN) undergo one-electron reductions to reactive radicals [Ru(II)(CO)(MeCN)(bpy(*-))Cl(2)](-) and [Ru(II)(CO)(bpy(*-))Cl(3)](2-), respectively. Both [bpy(*-)]-containing species readily electropolymerize on concomitant dissociation of two chloride ligands and consumption of a second electron. Along this path, mer-to-fac isomerization of the bpy-reduced trichlorido complex (supported by density functional theory calculations) and a concentration-dependent oligomerization process contribute to the complex reactivity pattern. In situ spectroelectrochemistry (IR, UV/vis) has revealed that the charged polymer [{Ru(0)(CO)(bpy)Cl}(-)](n) is stable in THF, but in PrCN it converts readily to [Ru(0)(CO)(PrCN)(bpy)](n). An excess of chloride ions retards this substitution at low temperatures. Both polymetallic chains are completely soluble in the electrolyte solution and can be reduced reversibly to the corresponding [bpy(*-)]-containing species.