Synthesis, spectroscopy and electrochemical behaviors of nickel(II) complexes with tetradentate shiff bases derived from 3,5-Bu(2)(t)-salicylaldehyde

Nickel(II) complexes of a series of N,N'-polymethylenebis(3,5-Bu(2)(t)-salicylaldimine) ligands containing 2,4-di-Bu(2)(t)-phenol arms, NiL(x), were synthesized and their spectroscopic and redox properties were examined. The UV-vis, (1)H NMR spectroscopic and magnetic results indicate that complexes NiL(1)-NiL(4) unlike NiL(5) and NiL(6) have a square-planar structure in the solid state and in solution. Cyclic voltammograms of NiL(x) (x=1-4) complexes displayed two-step oxidation processes. The first oxidation peak potentials of all Ni(II) complexes corresponds to the reversible one-electron oxidation process of the metal center, yielding Ni(III) species. The second oxidation peak of the complexes was assigned as the ligand based oxidation generating a coordinated phenoxyl radical species.     

Platinated copper(3-clip-phen) complexes as effective DNA-cleaving and cytotoxic agents

The synthesis and biological activity of three heteronuclear platinum-copper complexes based on 3-Clip-Phen are reported. These rigid complexes have been designed to alter the intrinsic mechanism of action of both the platinum moiety and the Cu(3-Clip-Phen) unit. The platinum centers of two of these complexes are coordinated to a 3-Clip-Phen moiety, an ammine ligand and two chlorides, which are either cis or trans to each other. The third complex comprises two 3-Clip-Phen units and two chloride ligands bound in a trans fashion to the platinum ion. DNA-cleavage experiments show that the complexes are highly efficient nuclease agents. In addition, a markedly difference in their aptitude to perform direct double-strand cleavage is observed, which appears to be strongly related to the ability of the platinum unit to coordinate to DNA. Indeed, complex 6 is unable to coordinate to DNA, which is reflected by its incapability to carry out double-strand breaks. Nonetheless, this complex exhibits efficient DNA-cleavage activity, and its cytotoxicity is high for several cell lines. Complex 6 shows better antiproliferate activity than both cisplatin and Cu(3-Clip-Phen) toward most cancer cell lines. Furthermore, the cytotoxicity observed for 1 is for most cell lines close to that of cisplatin, or even better. Cu(3-Clip-Phen) induces very low cytotoxic effects, but a marked migratory activity. Complex 6 presents DNA-cleavage properties comparable to the one of Cu(3-Clip-Phen), but it does not show any migratory activity. Interestingly, both Cu(3-Clip-Phen) and 6 induces vacuolisation processes in the cell in contrast to complex 1 and cisplatin. Thus, the four complexes cisplatin tested, Cu(3-Clip-Phen), 1 and 6 stimulate different cellular responses.     

Synthesis of hetaryl‐substituted benzoxazoles via oxidative cyclization of phenolic schiff's bases

2‐(1H‐Pyrrol‐2‐yl)benzo[d]oxazoles, 4‐(benzo[d]oxazol‐2‐yl)quinoline and 2‐(benzo[d]oxazol‐2‐yl)‐4,6‐dimethylquinolines were obtained in good yield by the oxidative intramolecular ring closing reactions of phenolic Schiff's bases with the effect of manganese triacetate.     

Selective copper(II)-mediated oxidative coupling of a nucleophilic reagent to the para-methyl group of 2,4,6-trimethylphenol

A copper(II) neocuproine system has been developed for the efficient and very selective 1,6-addition of a nucleophile to the para-methyl group of 2,4,6-trimethylphenol. Crystallographic and spectroscopic data point towards the involvement of a micro-methoxo-micro-phenoxo-bridged copper species which appears to generate a highly reactive quinone methide intermediate that can be attacked by a nucleophilic reagent.     

Preparation of 1,2- and 1,4-dihydro derivatives of 6,7-dimethyl-2,3-diphenylquinoxaline via its dianion formed by reductive metallation

Treatment of 6,7-dimethyl-2,3-diphenylquinoxaline with sodium in tetrahydrofuran formed a monomeric dianion. The chemical behavior of this dianion was investigated by a variety of reagents. As the result, alkylation reactions gave 1,2-dihydro derivatives, while acylation reactions occured at 1,4-positions. Annulation of the pyrazine ring system was accomplished by treating the dianion with oligomethylene dichlorides, Cl(CH₂) _n Cl, n = 2–4.     

Unique ligand-based oxidative DNA cleavage by zinc(II) complexes of hpyramol and hpyrimol

The zinc(II) complexes reported here have been synthesised from the ligand 4-methyl-2-N-(2-pyridylmethyl)aminophenol (Hpyramol) with chloride or acetate counterions. All the five complexes have been structurally characterised, and the crystal structures reveal that the ligand Hpyramol gradually undergoes an oxidative dehydrogenation to form the ligand 4-methyl-2-N-(2-pyridylmethylene)aminophenol (Hpyrimol), upon coordination to Zn(II). All the five complexes cleave the phiX174 phage DNA oxidatively and the complexes with fully dehydrogenated pyrimol ligands were found to be more efficient than the complexes with non-dehydrogenated Hpyramol ligands. The DNA cleavage is suggested to be ligand-based, whereas the pure ligands alone do not cleave DNA. The DNA cleavage is strongly suggested to be oxidative, possibly due to the involvement of a non-diffusible phenoxyl radical mechanism. The enzymatic religation experiments and DNA cleavage in the presence of different radical scavengers further support the oxidative DNA cleavage by the zinc(II) complexes.     

In situ recording of particle network formation in liquids by ion conductivity measurements

The formation of fractal silica networks from a colloidal initial state was followed in situ by ion conductivity measurements. The underlying effect is a high interfacial lithium ion conductivity arising when silica particles are brought into contact with Li salt-containing liquid electrolytes. The experimental results were modeled using Monte Carlo simulations and tested using confocal fluorescence laser microscopy and ζ-potential measurements.     

Interaction of alkali metals with unsaturated heterocyclic compounds. The reductive metalation of 1,4-diphenylphthalazine

1,4-Diphenylphthalazine ( 1 ) was reduced in tetrahydrofuran by sodium metal to a monomeric dianion 2 . Chemical reactions of this new dianion were examined with various reagents. Generally, the protonation, acylation and alkylation products were 1,2-dihydrophthalazine derivatives. An annulation of the phthalazine ring system was accomplished by treating the dianion with 1,3-dichloropropane or 1,4-dichlorobutane. With 1,2-dichloroethane however, only 1,4-diphenylnaphthalene was detected.