Picosecond Kerr-gated time-resolved resonance Raman spectroscopy of the [Ru(phen)(2)dppz](2+) interaction with DNA

To investigate the basis of the 'light-switch' effect, the solvent dependence of the Kerr-gated picosecond-time resolved resonance Raman (TR(3)) spectra of [Ru(bpy)(2)dppz](2+), [Ru(phen)(2)dppz](2+), and the modified complex [Ru(phen)(2)cpdppzOMe](2+) and a dimer [mu-C4(cpdppz)(2)-(phen)(4)Ru(2)](4+) were studied. The investigation focussed on comparing the behaviour of [Ru(phen)(2)dppz](2+) in acetonitrile, ethanol, H(2)O, D(2)O, and DNA. The data are consistent with a model wherein excitation induces metal-to-ligand charge transfer (MLCT) to any of the ligands (termed the 'precursor' state) which, by interligand electron transfer (ILET), produces an excited state localised on the dppz ligand, MLCT(1). In water this state relaxes with a characteristic time of approximately 6 ps to a non-emissive state (MLCT(2)). The TR(3) spectra in water, acetonitrile and DNA are all distinctly different. However, the early (4 ps) water spectrum resembles the spectrum in DNA. This interesting observation suggests that the DNA-bound excited state of the complex can be thought of as a model for the initial, poorly solvated state in water.     

Synthesis, characterization, DNA-binding and photocleavage studies of [Ru(bpy)2(PPIP)]2+ and [Ru(phen)2(PPIP)]2+

A novel ligand 2-(4'-phenoxy-phenyl)imidazo[4,5-f][1,10]phenanthroline (PPIP) and its complexes [Ru(bpy)(2)(PPIP)](2+) (1) (bpy = 2,2'-bipyridine) and [Ru(phen)(2)(PPIP)](2+) (2) (phen = 1,10-phenanthroline) have been synthesized and characterized by mass spectroscopy, (1)H NMR and cyclic voltammetry. The interaction of two complexes with calf thymus DNA (CT-DNA) was investigated by spectroscopic and viscosity measurements. The results suggest that both complexes bind to DNA via an intercalative mode. Both complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA under irradiated.     

Probing site specificity of DNA binding metallointercalators by NMR spectroscopy and molecular modeling

The molecular recognition of oligonucleotides by chiral ruthenium complexes has been probed by NMR spectroscopy using the template Delta-cis-alpha- and Delta-cis-beta-[Ru(RR-picchxnMe(2)) (bidentate)](2+), where the bidentate ligand is one of phen (1,10-phenanthroline), dpq (dipyrido[3,2-f:2',3'-h]quinoxaline), or phi (9,10-phenanthrenequinone diimine) and picchxnMe(2)() is N,N'-dimethyl-N,N'-di(2-picolyl)-1,2-diaminocyclohexane. By varying only the bidentate ligand in a series of complexes, it was shown that the bidentate alone can alter binding modes. DNA binding studies of the Delta-cis-alpha-[Ru(RR-picchxnMe(2))(phen)](2+) complex indicate fast exchange kinetics on the chemical shift time scale and a "partial intercalation" mode of binding. This complex binds to [d(CGCGATCGCG)](2) and [d(ATATCGATAT)](2) at AT, TA, and GA sites from the minor groove, as well as to the ends of the oligonucleotide at low temperature. Studies of the Delta-cis-beta-[Ru(RR-picchxnMe(2))(phen)](2+) complex with [d(CGCGATCGCG)](2) showed that the complex binds only weakly to the ends of the oligonucleotide. The interaction of Delta-cis-alpha-[Ru(RR-picchxnMe(2))(dpq)](2+) with [d(CGCGATCGCG)](2) showed intermediate exchange kinetics and evidence of minor groove intercalation at the GA base step. In contrast to the phen and dpq complexes, Delta-cis-alpha- and Delta-cis-beta-[Ru(RR-picchxnMe(2))(phi)](2+) showed evidence of major groove binding independent of the metal ion configuration. DNA stabilization induced by complex binding to [d(CGCGATCGCG)](2) (measured as DeltaT(m)) increases in the order phen < dpq and DNA affinity in the order phen < dpq < phi. The groove binding preferences exhibited by the different bidentate ligands is explained with the aid of molecular modeling experiments.     

Syntheses, spectra and crystal structures of ruthenium(II) complexes with polypyridyl: [Ru(bipy)2(phen)](ClO4)2 · H2O and [Ru(bipy)2(Me-phen)](ClO4)2

Two ruthenium(II) complexes with polypyridyl, Ru(bipy)₂(phen)](ClO₄)₂·H₂O (1) and [Ru(bipy)₂(Me-phen)](ClO₄)₂ (2), (phen = 1,10-phenanthroline, bipy = 2,2′-bipyridine, Me-phen = 5-methyl-1,10-phenanthroline), were synthesized and characterized by IR, MS and NMR spectra. Their structures were determined by single crystal X-ray diffraction techniques. The strong steric interaction between the polypyridyl ligands was relieved neither by the elongation of the Ru---N bonds nor increase of the N---Ru---N bite angles. The coordination sphere was distorted to relieve the ligand interaction by forming specific angles (δ) between the polypyridyl ligand planes and coordination planes (N---Ru---N), and forming larger twisted angles between the two pyridine rings for each bipy. The bond distances of Ru---N(bipy) and Ru---N(phen) were virtually identical with experimental error, as expected of π back-bonding interactions which statistically involve each of the ligands present in the coordination sphere.     

Synthesis, characterization, DNA-binding and cleavage studies of [Ru(bpy)2(actatp)]2+ and [Ru(phen)2(actatp)]2+ (actatp=acenaphthereno[1,2-b]-1,4,8,9-tetraazariphenylence)

New ligand acenaphthereno[1,2-b]-1,4,8,9-tetraazariphenylence (actatp) and its complexes [Ru(bpy)(2)(actatp)](ClO(4))(2).2H(2)O (1) (bpy=2,2'-bipyridine) and [Ru(phen)(2)(actatp)](ClO(4))(2).2H(2)O (2) (phen=1,10-phenanthroline) have been synthesized and characterized by UV-vis, 1H NMR, and mass spectra. The electrochemical behavior of the two complexes was studied by cyclic voltammetry. The interaction of the two complexes with calf thymus DNA has been investigated by spectrophotometric methods and viscosity measurements. The experimental results suggest that both complexes bind to DNA through an intercalative mode. The circular dichroism signals of the dialysates of the racemic complexes against calf thymus DNA are discussed. When irradiated at 302 nm, both complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA.     

A study of the interactions of some polypyridylruthenium (II) complexes with DNA using fluorescence spectroscopy, topoisomerisation and thermal denaturation.

The nature of binding of Ru(phen) 2+ (I), Ru(bipy) 2+ (II), Ru(terpy) 2+ (III) (phen = 1,10-phenanthroline, bipy 3 = 2,2'-bipyridyl, 3 terpy = 2,2'2," - 2 terpyridyl) to DNA, poly[d(G-C)] and poly[d(A-T)] has been compared by absorption, fluorescence, DNA melting and DNA unwinding techniques. I binds intercalatively to DNA in low ionic strength solutions. Topoisomerisation shows that it unwinds DNA by 22 degrees +/- 1 per residue and that it thermally stabilizes poly[d(A-T)] in a manner closely resembling ethidium. Poly[d(A-T)] induces greater spectral changes on I than poly[d(G-C)] and a preference for A-T rich regions is indicated. I binding is very sensitive to Mg2+ concentration. In contrast to I the binding of II and III appears to be mainly electrostatic in nature, and causes no unwinding. There is no evidence for the binding of the neutral Ru(phen)2 (CN)2 or Ru(bipy)2 (CN)2 complexes. DNA is cleaved, upon visible irradiation of aerated solutions, in the presence of either I or II.     

Ruthenium(II)-phenanthroline-biotin complexes: synthesis and luminescence enhancement upon binding to avidin

We report the synthesis, characterization, and avidin-binding properties of two novel ruthenium complexes, [Ru(bpy)(2)(phen-biotin)][PF(6)](2) 1 and [Ru(phen)(2)(phen-biotin)][PF(6)](2) 2 (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline, phen-biotin = 5-(10-amidobiotinyl)-1,10-phenanthroline)). We demonstrate that both biotinylated compounds bind to avidin through their biotin moieties with high affinity and in a 4:1 ratio. The binding of compounds 1 and 2 to avidin results in an enhancement in luminescence intensity ( approximately 1.4x, approximately 1.6x, respectively), relative to the unbound biotinylated ruthenium complexes. This behavior is markedly different from biotinylated organic dyes, whose fluorescence is quenched upon binding to avidin. Thus, ruthenium-biotin complexes 1 and 2 can form the basis of new, simplified biotin-avidin assays, which involve luminescence detection of the relevant biotinylated molecule through cross-linking with avidin.     

Synthesis, DNA-binding and photocleavage studies of cobalt(III) mixed-polypyridyl complexes: [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+)

Two novel cobalt(III) mixed-polypyridyl complexes [Co(phen)(2)(dpta)](3+) and [Co(phen)(2)(amtp)](3+) (phen=1,10-phenanthroline, dpta=dipyrido-[3,2-a;2',3'-c]- thien-[3,4-c]azine, amtp=3-amino-1,2,4-triazino[5,6-f]1,10-phenanthroline) have been synthesized and characterized. The interaction of these complexes with calf thymus DNA was investigated by spectroscopic, cyclic voltammetry, and viscosity measurements. Results suggest that the two complexes bind to DNA via an intercalative mode. Moreover, these Co(III) complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365nm. The mechanism studies reveal that hydroxyl radical (OH()) is likely to be the reactive species responsible for the cleavage of plasmid DNA by [Co(phen)(2)(dpta)](3+) and superoxide anion radical (O(2)(-)) acts as the key role in the cleavage reaction of plasmid DNA by [Co(phen)(2)(amtp)](3+).     

Magnetic, spectroscopic, structural and biological properties of mixed-ligand complexes of copper(II) with N,N,N,N″,N″-pentamethyldiethylenetriamine and polypyridine ligands

Two new mixed ligand complexes of copper(II) with N,N,N^′,N″,N″-pentamethyldiethylenetriamine and polypyridine ligands have been prepared and characterized by means of spectroscopic, magnetic and single-crystal X-ray diffraction methods. These two complexes are isomorph and isostructure in which the coordination polyhedron about the copper(II) ion is distorted square pyramidal. [Cu(PMDT)(bipy)]²⁺ and [Cu(PMDT)(phen)]²⁺ show an absorption wavelength maximum at 625 and 678 nm, respectively, assigned to the d-d transition. Antibacterial, antifungal and superoxide dismutase activities of these complexes have also been measured. It was observed that [Cu(PMDT)(bipy)](ClO₄)₂ was more effective against P. Pyocyanea and Klebsiella sp. than S. aureus. Similarly, Fusarium sp. was highly susceptible against [Cu(PMDT)(bipy)](ClO₄)₂ but less susceptible against [Cu(PMDT)(phen)](ClO₄)₂.     

Redox and ligand exchange reactions of potential gold(I) and gold(III)-cyanide metabolites under biomimetic conditions

Biomimetic pathways for the oxidation of [Au(CN)(2)](-), a gold metabolite, and further cyanation of the gold(III) products to form Au(CN)(4)(-) were investigated using 13C NMR and UV-Visible spectroscopic methods. Hypochlorite ion, an oxidant released during the oxidative burst of immune cells, was employed. The reaction generates mixed dicyanoaurate(III) complexes, trans-[Au(CN)(2)X(2)](-), where X(-) represents equilibrating hydroxide and chloride ligands, and establishes the chemical feasibility of dicyanoaurate oxidation by OCl(-) to gold(III) species. This oxidation reaction suggests a new procedure for synthesis of H[Au(CN)(2)Cl(2)]. Reaction of trans-[Au(CN)(2)X(2)](-) (X(-)=Cl(-) and Br(-)) or [AuCl(4)](-) with HCN in aqueous solution at pH 7.4 leads directly to [Au(CN)(4)](-) without detection of the anticipated [Au(CN)(x)X(4-x)](-)intermediates, which is attributed to the cis- and trans-accelerating effects of the cyanides. The reduction of [Au(CN)(4)](-) by glutathione and other thiols is a complex, pH-dependent process that proceeds through two intermediates and ultimately generates [Au(CN)(2)](-). These studies provide further insight into the possible mechanisms of an immunogenically generated gold(I)/gold(III) redox cycle in vivo.     

DNA binding of iron(II) complexes with 1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline: salt effect,ligand substituent effect,base pair specificity and binding strength

The DNA binding of iron(II) mixed-ligand complexes containing 1,10-phenanthroline(phen) and 4,7-diphenyl-1,10-phenanthroline(dip), [Fe(phen)(3)](2+), [Fe(phen)(2)(dip)](2+) and [Fe(phen)(dip)(2)](2+) has been characterized by spectrophotometric titration and melting temperature measurements. The salt concentration dependence of the binding constant has allowed us to dissect the DNA-binding constant and free energy change of each iron(II) complex into the nonelectrostatic and polyelectrolyte contributions. A comparison of the nonelectrostatic components in the binding free energy changes among iron(II) complexes has made it possible to rigorously evaluate the contribution of the ligand substituents to the DNA-binding event. The peripheral substitution of phen by two phenyl groups increases the nonelectrostatic binding constant of the iron(II) complex more than 20 times, which is equivalent to approximately 7.5 kJ mol(-1) of more favorable contribution to the DNA binding. In general, the iron(II) complexes studied have higher affinity towards the more facile A-T sequence than the G-C sequence. This preferential binding may be attributed to the steric effect induced by the ancillary part of the ligands in the course of DNA binding. The binding of disubstituted iron(II) complex to DNA is quite strong as reflected in the modest increase in the denaturation temperature (T(m)) of double helical DNA upon the interaction with the iron(II) complex.     

Synthesis, X-ray crystal structures and biomimetic and anticancer activities of novel copper(II)benzoate complexes incorporating 2-(4'-thiazolyl)benzimidazole (thiabendazole), 2-(2-pyridyl)benzimidazole and 1,10-phenanthroline as chelating nitrogen donor ligands

Cu(BZA)(2)(EtOH)(0.5) (1) was generated by the reaction of copper(II) hydroxide with benzoic acid (BZAH). [Cu(TBZH)(2)(BZA)](BZA).0.5TBZH.H(2)O (2) and [Cu(2-PyBZIMH)(2-PyBZIM)(BZA)].1.66EtOH (3) were obtained when 1 reacted with Thiabendazole (TBZH) and 2-(2-pyridyl)benzimidazole (2-PyBZIMH), respectively. [Cu(BZA)(2)(phen)(H(2)O)] (4) was isolated from the reaction of benzoic acid and 1,10-phenanthroline (phen) with copper(II)acetate dihydrate. Molecular structures of 2, 3 and 4 were determined crystallographically. 2 and 3 are hydrogen bonded dimers and trimers, respectively. The copper centres in complexes 2 and 3 are bis-chelate derivatives that have N(4)O ligation and their geometry is very similar being approximately square-pyramidal. However whereas in complex 2 both TBZH ligands are neutral in 3 one of the 2-PyBZIMH chelators is deprotonated on each copper. The structural results for 4 represent a re-examination of this crystallographically known compound for which no hydrogen atom coordinates have been previously reported. It crystallises as a hydrogen bonded dimmer and is a mono-chelate of phen with each copper centre possessing N(2)O(3) ligation and square pyramidal geometry. The catalase and superoxide dismutase (SOD) activities of the four complexes along with those of the known phenanthroline complexes [Cu(mal)(phen)(2)] and [Cu(phendione)(3)](ClO(4))(2) (malH(2)=malonic acid and phendione=1,10-phenanthroline-5,6-dione) were investigated. Complexes 1-4, the metal free ligands and a simple copper(II) salt were assessed for their cancer chemotherapeutic potential against the hepatocellular carcinoma (Hep-G(2)) and kidney adenocarcinoma (A-498) cell lines. TBZH, 2-PyBZIMH and benzoic acid when uncoordinated to a metal centre offer poor chemotherapeutic potential. copper(II) benzoate is significantly more active than the free acid. The bis-chelate derivatives [Cu(TBZH)(2)(BZA)](BZA).0.5TBZH.H(2)O (2) and [Cu(2-PyBZIMH)(2-PyBZIM)(BZA)].1.66EtOH (3) elicit a significant cytotoxic response to the cancer cell lines tested. Replacing TBZH and 2-PyBZIMH with phen to give [Cu(BZA)(2)(phen)(H(2)O)] (4) does not significantly increase the anti-cancer activity.     

Syntheses and DNA-binding studies of two ruthenium(II) complexes containing one ancillary ligand of bpy or phen: [Ru(bpy)(pp[2,3]p)2](ClO4)2 and [Ru(phen)(pp[2,3]p)2](ClO4)2

Two new ruthenium(II) complexes of [Ru(bpy)(pp[2,3]p)2](ClO4)2 and [Ru(phen)(pp[2,3]p)2](ClO4)(2) (bpy=2,2'-bipyridine, phen=1,10-phenanthroline, pp[2,3]p=pyrido[2',3':5,6]pyrazino[2,3-f][1,10]phenanthroline) have been synthesized and characterized by elemental analysis and 1H NMR spectra. The calf thymus DNA-binding properties of the two complexes were investigated by UV-visible and emission spectroscopy, competitive binding experiments with ethidium bromide and viscosity measurements. The results indicate that the two complexes intercalate between the base pairs of the DNA tightly with intrinsic DNA-binding constants of 3.08 x 10(6) and 6.53 x 10(6) M(-1) in buffered 50 mM NaCl, respectively, which are much larger than 6.9 x 10(5) M(-1) for [Ru(bpy)2(pp[2,3]p)](ClO4)2 containing two ancillary ligands of bpy.     

DNA binding by Ru(II)–bis(bipyridine)–pteridinyl complexes

The interactions of five bis(bipyridyl) Ru(II) complexes of pteridinyl-phenanthroline ligands with calf thymus DNA have been studied. The pteridinyl extensions were selected to provide hydrogen-bonding patterns complementary to the purine and pyrimidine bases of DNA and RNA. The study includes three new complexes [Ru(bpy)(2)(L-pterin)](2+), [Ru(bpy)(2)(L-amino)](2+), and [Ru(bpy)(2)(L-diamino)](2+) (bpy is 2,2'-bipyridine and L-pterin, L-amino, and L-diamino are phenanthroline fused to pterin, 4-aminopteridine, and 2,4-diaminopteridine), two previously reported complexes [Ru(bpy)(2)(L-allox)](2+) and [Ru(bpy)(2)(L-Me(2)allox)](2+) (L-allox and L-Me(2)allox are phenanthroline fused to alloxazine and 1,3-dimethyalloxazine), the well-known DNA intercalator [Ru(bpy)(2)(dppz)](2+) (dppz is dipyridophenazine), and the negative control [Ru(bpy)(3)](2+). Reported are the syntheses of the three new Ru-pteridinyl complexes and the results of calf thymus DNA binding experiments as probed by absorption and fluorescence spectroscopy, viscometry, and thermal denaturation titrations. All Ru-pteridine complexes bind to DNA via an intercalative mode of comparable strength. Two of these four complexes-[Ru(bpy)(2)(L-pterin)](2+) and [Ru(bpy)(2)(L-allox)](2+)-exhibit biphasic DNA melting curves interpreted as reflecting exceptionally stable surface binding. Three new complexes-[Ru(bpy)(2)(L-diamino)](2+), [Ru(bpy)(2)(L-amino)](2) and [Ru(bpy)(2)(L-pterin)](2+)-behave as DNA molecular "light switches."     

Communication of metal ions in the dinuclear ruthenium complexes containing 4,4′-bipyridine, 1,4-diisocyanobenzene, and pyrazine bridging ligands: Synthesis, characterization and structure determination

Reaction of [Ru(2,2′-bipyridine)(2,2′:6′,2″-terpyridine)Cl]PF₆ (abbreviated to [Ru(bipy)(terpy)Cl]PF₆) with 0.5 equiv of the bidentate ligand L produces the dinuclear complexes [{Ru(bipy)(terpy)}₂(μ-L)](PF₆)₄ (L = 4,4′-bipyridine 1, 1,4-diisocyanobenzene 2 and pyrazine 3) in moderate yields. Treating [Ru(bipy)(terpy)Cl]PF₆ with equal molar of 1,4-diisocyanobenzene affords [Ru(bipy)(terpy)(CNC₆H₄NC)](PF₆)₂ (2a). These new complexes have been characterized by mass, NMR, and UV-Vis spectroscopy, and the structures of 1-3 determined by an X-ray diffraction study. Cyclic voltammetric studies suggest that metal communication between the two ruthenium ions increases from 1 to 2 to 3.     

Synthesis,crystal structure,and nuclease activity of planar mono-heterocyclic base copper(II) complexes

A series of mononuclear copper(II) complexes having a 1:1 molar ratio of copper and the planar heterocyclic base like 1,10-phenanthroline (phen), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) are prepared from a reaction of copper(II) nitrate.trihydrate and the base (L) in ethanol or aqueous ethanol at different temperatures. The complexes [Cu(dpq)(NO(3))(2)] (2), [Cu(dpq)(NO(3))(H(2)O)(2)](NO(3)) (3), [Cu(dpq)(NO(3))(2)(H(2)O)(2)].2H(2)O (4.2H(2)O) and [Cu(dppz)(NO(3))(2)(H(2)O)].H(2)O (5.H(2)O) have been characterized by X-ray crystallography. The crystal structures show the presence of the heterocyclic base in the basal plane. The coordination geometries of the copper(II) centers are axially elongated square-pyramidal (4+1) in 2, 3 and 5, and octahedral (4+2) in 4. The nitrate anion in the coordination sphere displays unidentate and bidentate chelating bonding modes. The axial ligand is either H(2)O or NO(3) in these structures giving a Cu-L(ax) distance of approximately 2.4 A. The one-electron paramagnetic complexes (mu approximately 1.8 mu(B)) exhibit axial EPR spectra in DMF glass at 77 K giving g(parallel)>g( perpendicular ) with an A(parallel) value of approximately 170G indicating a [d(x)2(-y)2](1) ground state. The complexes are redox active and display a quasireversible cyclic voltammetric response for the Cu(II)/Cu(I) couple near 0.0 V vs. SCE giving an order of the E(1/2) values as 5(dppz)>2-4 (dpq)>[Cu(phen)(2)(H(2)O)](2+)>1 (phen). The complexes bind to calf thymus DNA giving an order 5 (dppz)>2 (dpq)>[Cu(phen)(2)(H(2)O)](2+)>1 (phen). An effect of the extended planar ring in dpq and dppz is observed in the DNA binding. The complexes show nuclease activity with pUC19 supercoiled DNA in DMF/Tris-HCl buffer containing NaCl in presence of mercaptopropanoic acid as a reducing agent. The extent of cleavage follows the order: [Cu(phen)(2)(H(2)O)](ClO(4))(2)>5>2 approximately 3 approximately 4>1. The bis-phen complex is a better cleaver of SC DNA than 1-5 having mono-heterocyclic base. Mechanistic investigations using distamycin reveal minor groove biding for the phen, dpq complexes, and a major groove binding for the dppz complex 5. The cleavage reactions are found to be inhibited in the presence of hydroxyl radical scavenger DMSO and the reactions are proposed to proceed via sugar hydrogen abstraction pathway. The ancillary ligand is found to have less effect in DNA binding but are of importance in DNA cleavage reactions.     

Proton-linked bi- and tri-metallic gold cyanide complexes observed by ESI-MS spectrometry

Electrospray ionization spectra of potential cyanide-containing gold-drug metabolites revealed additional, weak, unanticipated peaks at approximately twice the mass of the gold(I) and gold(III) cyanide complexes. The exact masses correspond to proton-linked bimetallic complexes, [H[Au(CN)(m)](2)](-), (m=2,4). Further investigation revealed a total of 12 examples, including trimetallic complexes, [H(2)[Au(CN)(m)](3)](-); mixed species with two complexes, [H[Au(CN)(2)][Au(CN)(4)]](-); and thiolato species, [H[(RS)Au(CN)(3)](2)](-). trans-[AuX(2)(CN)(2)Cl(2)](-) and trans-[AuX(2)(CN)(2)Br(2)](-) generated (35)Cl/(37)Cl and (79)Br/(81)Br isotopic patterns for the protonated bi- and tri-metallic analogues which were in good agreement with the presence of four or six halide ligands, respectively. Concentration-dependent studies demonstrated that the signals are independent of the solution concentrations of mono-metallic precursors, suggesting formation in the gas phase during or following droplet desolvation.     

Developing red-emissive ruthenium(II) complex-based luminescent probes for cellular imaging

Ruthenium(II) complexes have rich photophysical attributes, which enable novel design of responsive luminescence probes to selectively quantify biochemical analytes. In this work, we developed a systematic series of Ru(II)-bipyrindine complex derivatives, [Ru(bpy)(3-n)(DNP-bpy)(n)](PF(6))(2) (n = 1, 2, 3; bpy, 2,2'-bipyridine; DNP-bpy, 4-(4-(2,4-dinitrophenoxy)phenyl)-2,2'-bipyridine), as luminescent probes for highly selective and sensitive detection of thiophenol in aqueous solutions. The specific reaction between the probes and thiophenol triggers the cleavage of the electron acceptor group, 2,4-dinitrophenyl, eliminating the photoinduced electron transfer (PET) process, so that the luminescence of on-state complexes, [Ru(bpy)(3-n)(HP-bpy)(n)](2+) (n = 1, 2, 3; HP-bpy, 4-(4-hydroxyphenyl)-2,2'-bipyridine), is turned on. We found that the complex [Ru(bpy)(DNP-bpy)(2)](2+) remarkably enhanced the on-to-off contrast ratio compared to the other two (37.8 compared to 21 and 18.7). This reveals a new strategy to obtain the best Ru(II) complex luminescence probe via the most asymmetric structure. Moreover, we demonstrated the practical utility of the complex as a cell-membrane permeable probe for quantitative luminescence imaging of the dynamic intracellular process of thiophenol in living cells. The results suggest that the new probe could be a very useful tool for luminescence imaging analysis of the toxic thiophenol in intact cells.     

Synthesis, characterization, DNA-binding and photocleavage of complexes [Ru(phen)2(6-OH-dppz)]2+ and [Ru(phen)2(6-NO2-dppz)]2+

Two new complexes, ([Ru(phen)(2)(6-OH-dppz)](2+)) (1) and ([Ru(phen)(2)(6-NO(2)-dppz)](2+)) (2) (phen=1,10-phenanthroline; 6-OH-dppz=6-hydroxyl-dipyrido[3,2-a:2',3'-c]phenazine; 6-NO(2)-dppz=6-nitro-dipyrido[3,2-a:2',3'-c]phenazine), have been synthesized and characterized by elemental analysis, ES-MS (electrospray mass spectra), (1)H NMR, UV-Vis (UV-visible) and CV (cyclic voltammetry). The DNA-binding behaviors of both complexes have been studied by spectroscopic methods and viscosity measurements. The results indicate that the two complexes all bind to calf thymus DNA (CT-DNA) in an intercalative mode, and the DNA-binding affinity of complex 2 is greater than that of complex 1. In addition, complex 1 can promote photocleavage of pBR322 DNA upon irradiation, whereas complex 2 can promote cleavage of pBR322 DNA both upon irradiation and in the dark, with more efficient cleavage occurring upon irradiation. Theoretical studies for these complexes have been also carried out with the density functional theory (DFT) method. The difference in the DNA-binding behaviors of the two complexes can be reasonably explained by the DFT calculations.