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The complex cis-(Cl,Cl)-[RuCl2(terpy)(NO)]Cl (1) has been synthesized by the reaction of [RuCl3(H2O)2(NO)] with terpyridine (terpy) and characterized by various spectroscopic, analytical techniques and using electronic structure calculation (DFT) methods. The cytotoxic activity and the DNA-binding properties of have also been studied using biochemical techniques. The results establish unequivocally that corresponds to a so-called [RuNO]6 species, which readily releases the nitrosyl ligand upon irradiation with a mercury lamp in acetonitrile solution. DFT calculations provided a satisfactory description of structural, bonding, electronic and related properties of the new compound and throw light on the mechanism of the photo-induced NO release. Screening on A2780 (human ovarian carcinoma) cell lines showed significant cytotoxicity with an IC50 value of 0.49 microM. 31P and 23Na NMR spectroscopy along with electrophoretic mobility studies illustrated that complex primarily binds by coordination to DNA without any pi-interaction between the planar terpy ligand and the DNA bases, while weak electrostatic interactions could not be excluded. Studies on the inhibition of the restriction enzymes DraI and SmaI revealed that prefers the guanine and cytosine bases of DNA.

A general method for the synthesis of chloro(polypyridyl)ruthenium conjugated peptide complexes via a solid-phase strategy is described. The method is applied to synthesize two positional isomers of the complex [Ru(terpy)(4-CO2H-4'-Mebpy-Gly-L-His-L-LysCONH2)Cl](PF6). Even though the separation of the isomers was only partially achieved chromatographically, the isomers were unambiguously assigned by NMR spectroscopy. The interactions of the complex [Ru(terpy)(4-CO2H-4'-Mebpy-Gly-L-His-L-LysCONH2)Cl](PF6) with CT-DNA and plasmid DNA, have been studied with various spectroscopic techniques, showing that (i) the complexes coordinatively bind to DNA preferring the bases guanine and cytosine over the bases thymine and adenine after hydrolysis of the coordinated chloride, (ii) electrostatic interactions between the complex cation and the polyanionic DNA chain assist this binding (iii) only in the case of one isomer the peptide does interact further with DNA as evidenced from 31P NMR spectroscopy, (iv) DNA unwinding occurs in all cases with high binding ratio (Ru/base) values (r > 0.3).

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The complexes of general formulas [Ru II (terpy)(4-CO 2 H-4′-Mebpy)(X)] n+ (X ) NO (n ) 3) and NO 2 (n ) 1); 1, 2) and [Ru II (terpy)(4-COGHK-4′-Mebpy)(X)] (X ) NO (n ) 3) and NO 2 (n ) 1); 3, 4) were synthesized and characterized. The complex [Ru II (terpy)(4-CO 2 -4′-Mebpy)(NO 2 )]_7.5H 2 O has also been characterized by X-ray crystallographic studies. It crystallizes in the triclinic system: a ) 9.4982(1) Å, b ) 13.1330(1) Å, c ) 14.2498(2) Å; R ) 110.5870(6)×bc, ) 98.4048(5)×bc, γ ) 106.4353(5), P1 h, ) 2. The crystal structure reveals an extended hydrogen-bonding network. Two water molecules form strong hydrogen bonds with the nitro and the carboxylic oxygen atoms of two separate units of the complex, resulting in a dimeric unit. The dimers are bridged by a (H 2 O) 15 cluster, consisting of two cyclo-(H 2 O) 6 species, while an exo-H 2 O(8) connects them. Two more exo-H 2 O molecules are joined together and connect the cyclo-(H 2 O) 6 units with the H 2 O(1) of the dimeric unit. It was found that complexes 1 and 3 can be transformed into their nitro derivatives in aqueous media at neutral pH. Photorelease of NO in dry MeCN solutions was observed for complexes 1 and 3. Also, complex 2 partially releases (NO 2 ) -in MeCN upon visible light irradiation. Complex 2 interacts with short fragments (70−300 bp) of calf thymus DNA shortening slightly the apparent polynucleotide length, while the conjugation of the peptide GHK to it (2) affects its DNA-binding mode. The peptide moiety of complex 4 was found to interact with the DNA helix in a synergistic way with the whole complex. Preliminary results of photocleavage of DNA by complex 2 are also reported.

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