Synthesis and DNA binding properties of a cationic 2,2':6',2"-terpyridine cobalt(II) complex containing an oligopeptide

The first example of DNA metallointercalator containing an oligopeptide moiety is presented. The ternary cobalt(II) complex [(DOTA)Co(II)(TPY)](ClO(4))(2) (DOTA=1,4,7,10-tetraaza-cyclododecane-2,9-dione, TPY=2, 2':6',2"-terpyridine) was found to be efficient in binding ct-DNA. The binding constant was determined by spectrophotometric titration. In vitro antitumor studies shows that this complex has significant antitumor activity. The single-crystal of a six coordinated oligopeptide cobalt(II) complex [Co(II)(DOTA)(2)](ClO(4))(2) is also reported. The stabilities and species distributions of Co(II)-DOTA (1:1) and DOTA-Co(II)-TPY (1:1:1) systems were investigated by potentiometry titration.     

Synthesis, structure and DNA interaction of cobalt(III) bis-complexes of 1,3-bis(2-pyridylimino)isoindoline and 1,4,7-triazacyclononane

The complex [CoL(2)](ClO(4)).MeOH (1), where HL is the tridentate 3N ligand 1,3-bis(2-pyridylimino)isoindoline, has been isolated and its X-ray crystal structure successfully determined. It possesses a distorted octahedral structure in which both the ligands are coordinated meridionally to cobalt(III) via one deprotonated isoindoline (L(-)) and two pyridine nitrogen atoms. Interestingly, the average dihedral angle between pyridine and isoindoline rings is 25.9 degrees , indicating that the ligand is twisted upon coordination to cobalt(III). The interaction of the complex with calf-thymus DNA has been studied using various spectral methods and viscosity and electrochemical measurements. For comparison, the DNA interaction of [Co(tacn)(2)]Cl(3) (2), where tacn is facially coordinating 1,4,7-triazacyclononane, has been also studied. The ligand-based electronic spectral band of 1 and the N(sigma)-->Co(III) charge transfer band of 2 exhibit moderate hypochromism with small or no blue shift on interaction with DNA. The intrinsic binding constants calculated reveal that the monopositive complex ion [CoL(2)](+) exhibits a DNA-binding affinity lower than the tripositive complex ion [Co(tacn)(2)](3+). The steric clashes with DNA exterior caused by the second L(-) ligand bound to cobalt(III), apart from the lower overall positive charge on the [CoL(2)](+) complex, dictates its DNA-binding mode to be surface binding rather than partial intercalative interaction expected of the extended aromatic chromophore of deprotonated isoindoline anion. An enhancement in relative viscosity of CT DNA on binding to 1 is consistent with its DNA surface binding. On the other hand, a slight decrease in viscosity of CT DNA was observed on binding to 2 revealing that the smaller cation leads to bending (kinking) and hence shortening of DNA chain length. The electrochemical studies indicate that the DNA-bound complexes are stabilised in the higher Co(III) rather than the lower Co(II) oxidation state, suggesting the importance of electrostatic forces of DNA interaction.     

Syntheses,characterization and DNA-binding studies of ruthenium(II) terpyridine complexes: [Ru(tpy)(PHBI)]2+ and [Ru(tpy)(PHNI)]2+

Two novel tridentate ligands, 2-(2-benzimidazole)-1,10-phenanthroline (PHBI) and 2-(2-naphthoimidazole)-1,10-phenanthroline (PHNI), and their heteroleptic complexes [Ru(tpy)(PHBI)](ClO(4))(2).2H(2)O (1) and [Ru(tpy)(PHNI)](ClO(4))(2).H(2)O (2) (tpy=2,2':6',2"-terpyridyl) have been synthesized and characterized by elemental analysis, mass spectra, 1H NMR, and electronic spectroscopy. The electrochemical behaviors of the two novel complexes were studied by cyclic voltammetry. The DNA-binding properties of the two complexes were investigated by spectroscopic methods and viscosity measurements. The results indicated that the two complexes interact with DNA in different binding modes. Complex 1 may bind to DNA via electrostatic interaction, while complex 2 binds to DNA by partial intercalation via the extended naphthyl ring into the base pairs of DNA.     

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.     

Synthesis, structure and biomimetic properties of Cu(II)-Cu(II) and Cu(II)-Zn(II) binuclear complexes: possible models for the chemistry of Cu-Zn superoxide dismutase

Four imidazolate-bridged binuclear copper(II)-copper(II) and copper(II)-zinc(II) complexes viz., [(Bipy)(2)Cu-Im-Cu(Bipy)(2)](ClO(4))(3).CH(3)OH, [(Phen)(2)Cu-Im-Cu(Phen)(2)](BF(4))(3).2CH(3)OH, [(Bipy)(2)Cu-Im-Zn(Bipy)(2)](BF(4))(3), and [(Phen)(2)Cu-Im-Zn(Phen)(2)](BF(4))(3), (Bipy=2,2'-Bipyridyl, Phen=1-10-Phenanthroline and Im=imidazolate ion) were synthesized as a possible models for superoxide dismutase (SOD). Complex [(Bipy)(2)Cu-Im-Cu(Bipy)(2)](ClO(4))(3).CH(3)OH has been structurally characterized. This complex crystallizes in the triclinic space group P1, with the unit parameters a=8.88(5) A, b=13.79(17) A, c=20.18(18) A, alpha=76.424(8)(o), beta=85.888(6)(o), gamma=82.213(7). The metal-nitrogen bond length from 1.972-2.273 A and the distance Cu-Cu is 5.92 A. The five-coordinate geometry about the copper(II) ion is square pyramidal. Magnetic moment and electron paramagnetic resonance (e.p.r.) spectral measurements of the homobinuclear complexes have shown an antiferromagnetic exchange interaction. From the e.p.r. and UV-Vis spectral measurement studies, these complexes have been found to be stable (pH 8.5-10.5 for 1, 10.5 for 2,3 and 8.5 for 4). These complexes catalyse the dismutation of superoxide radical (O(2)(-)) at biological pH. All the observations indicate that these complexes act as good possible models for superoxide dismutase.     

Different modes of DNA cleavage activity of dihydroxo-bridged dicopper(II) complexes having phenanthroline bases

Dihydroxo-bridged dicopper(II) complexes [(Cu(phen))(2)(mu-OH)(2)](ClO(4))(2) (1), [(Cu(dpq))(2)(mu-OH)(2)](ClO(4))(2) (2) and [(Cu(dppz)(DMF))(2)(mu-OH)(2)](PF(6))(2) (3), where phen, dpq and dppz are 1,10-phenanthroline, dipyridoquinoxaline and dipyridophenazine, respectively, are prepared and their DNA binding and cleavage properties studied. Complex 3 has been structurally characterized by X-ray crystallography. The complexes have a (Cu(2)(mu-OH)(2))(2+) core with an essentially planar arrangement of two CuN(2)O(2) basal planes. The complexes are avid binder to calf thymus DNA (K(app) value of 4.8 x 10(6) and 5.9 x 10(6) M(-1) for 2 and 3, respectively, from ethidium displacement assay) and exhibits significant cleavage of supercoiled (SC) pUC19 DNA in dark in presence of mercaptopropionic acid. Besides, the dpq and dppz complexes display photo-induced DNA cleavage on UV (312 nm) and red light (632.8 nm) irradiations in absence of any additives. Mechanistic investigations reveal minor groove binding for the phen and dpq complexes, and major groove preference for the dppz species. The oxidative DNA cleavage reactions in presence of mercaptopropionic acid as a reducing agent involve hydroxyl radicals. The photo-cleavage reactions at UV light involve singlet oxygen as the reactive species, while similar reactions on red light irradiation (632.8 nm) proceed through the formation of hydroxyl radical. The complexes show significant DNA hydrolase activity in absence of any additives under dark reaction conditions.     

DNA interactions of new mixed-ligand complexes of cobalt(III) and nickel(II) that incorporate modified phenanthroline ligands

Four new mixed-ligand complexes, namely [Co(phen)(2)(qdppz)](3+), [Ni(phen)(2)(qdppz)](2+), [Co(phen)(2)(dicnq)](3+) and [Ni(phen)(2)(dicnq)](2+) (phen=1,10-phenanthroline, qdppz=naptho[2,3-a]dipyrido[3,2-H:2',3'-f]phenazine-5,18-dione and dicnq=dicyanodipyrido quinoxaline), were synthesized and characterized by FAB-MS, UV/Vis, IR, 1H NMR, cyclic voltammetry and magnetic susceptibility methods. Absorption and viscometric titration as well as thermal denaturation studies revealed that each of these octahedral complexes is an avid binder of calf-thymus DNA. The apparent binding constants for the dicnq- and qdppz-bearing complexes are in the order of 10(4) and >10(6) M(-1), respectively. Based on the data obtained, an intercalative mode of DNA binding is suggested for these complexes. While both the investigated cobalt(III) complexes and also [Ni(phen)(2)(qdppz)](2+) affected the photocleavage of DNA (supercoiled pBR 322) upon irradiation by 360 nm light, the corresponding dicnq complex of nickel(II) was found to be ineffective under a similar set of experimental conditions. The physico-chemical properties as well as salient features involved in the DNA interactions of the cobalt(III) and nickel(II) complexes investigated here were compared with each other and also with the corresponding properties of the previously reported ruthenium(II) analogues.     

Oxidative strand scission of nucleic acids by a multinuclear copper(II) complex

The compound [Cu(2)(II)(D(1))(H(2)O)(2)](ClO(4))(4).2H(2)O [D(1)=binucleating ligand with tris(2-pyridylmethyl)amine (TMPA) moieties linked in the 5-pyridyl position by a -CH(2)CH(2)- bridge] mediated efficient oxidative cleavage of pBR322 plasmid DNA under reducing conditions. A mononuclear analogue, [Cu(TMPA)(H(2)O)](ClO(4))(2), was less effective at linearizing supercoiled (Form I) plasmid DNA as compared to the binuclear complex. A new method for quenching the copper-dependent reactions has been developed to avoid plasmid scission by the binuclear complex and the standard gel loading buffer. EDTA was not sufficient for retarding copper reaction, but diethyldithiocarbamic acid was capable of inhibiting all reactivity. Investigation of oxidative cleavage of double-helical oligonucleotides by [Cu(2)(II)(D(1))(H(2)O)(2)](ClO(4))(4) confirmed the enhanced reactivity of the binuclear over the mononuclear complex and provided mechanistic insights into the nature of the reaction. Cleavage of DNA required both the binuclear complex and a reductant and likely proceeded through an O(2)-derived intermediate that does not include a diffusible hydroxyl radical. The greater efficiency of the binuclear complex relative to the mononuclear analogue is consistent with their relative abilities to activate dioxygen.     

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.     

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+).     

DNA binding and cleavage properties of certain tetrammine ruthenium(II) complexes of modified 1,10-phenanthrolines--effect of hydrogen-bonding on DNA-binding affinity

A series of ruthenium(II) mixed ligand complexes of the type [Ru(NH(3))(4)(L)](2+), where L=imidazo[4,5-f][1,10]phenanthroline (ip), 2-phenylimidazo[4,5-f][1,10]phenanthroline (pip), 2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline (hpip), 4,7-diphenyl-1,10-phenanthroline (dip), naphtha[2,3-a]dipyrido[3,2-h:2',3'-f]phenazine-5,18-dione (qdppz), 5,18-dihydroxynaphtho[2,3-a]dipyrido[3,2-H:2',3'-f]phenazine (hqdppz), have been isolated and characterized. The interaction of these complexes with calf thymus DNA (CT DNA) has been explored by using absorption, emission, and circular dichroic spectral methods, thermal denaturation studies and viscometry. All these studies suggest the involvement of the modified phenanthroline 'face' rather than the ammonia 'face' of the complexes in DNA binding. An intercalative mode of DNA binding, which involves the insertion of the modified phenanthroline ligands in between the base pairs, is suggested. The results from absorption spectral titration and circular dichroism (CD), thermal denaturation and viscosity experiments indicate that the qdppz and hqdppz complexes (K(b) approximately 10(6) and Delta T(m)=11-13 degrees C) bind more avidly than the ip, pip and hpip complexes (K(b) approximately 10(5), Delta T(m)=6-8 degrees C). Intramolecular hydrogen bonding in the hpip and hqdppz complexes increases the surface area of the intercalating diimines and enhances the DNA binding affinity substantially. The ammonia co-ligands of the complexes are possibly involved in hydrogen bonding with the intrastrand nucleobases to favour intercalation of the extended aromatic ligands. Circular dichroism spectral studies reveal that all the complexes effect certain structural changes on DNA duplex; [Ru(NH(3))(4)(ip)](2+) induces a B to A transition while [Ru(NH(3))(4)(qdppz)](2+) a B to Psi conformational change on CT DNA. Cleavage efficiency of the complexes were determined using pBR322 supercoiled plasmid DNA. All the complexes, except hqdppz complex, promote the cleavage of supercoiled plasmid (form I) to relaxed circular form (form II).     

E.s.r., visible and SOD studies of imidazolate bridged Cu(2)(II,II), Cu(II)Zn(II) and Cu(II)Ni(II) complexes with pentamethyldiethylenetriamine as capping ligand: a plausible model for superoxide dismutase

X-band e.s.r. and electronic spectra of imidazolate bridged homobinuclear Cu-Cu complex, [(PMDT)Cu-Im-Cu(PMDT)](ClO(4))(3) and heterobinuclear Cu-Zn and Cu-Ni complexes, viz. [(PMDT)Cu-Im-Zn(PMDT)](ClO(4))(3), [(PMDT)Cu-Im-Ni(PMDT)] (ClO(4))(3), where PMDT=pentamethyldiethylenetriamine, Im=Imidazolate ion and related mononuclear complexes, [(PMDT)Cu(OH(2))](2+) and [(PMDT)Cu(ImH)](2+) have been described. Superoxide dismutase activities of these complexes have also been measured.     

DNA-binding and cleavage studies of novel binuclear copper(II) complex with 1,1'-dimethyl-2,2'-biimidazole ligand

DNA-binding properties of novel binulear copper(II) complex [Cu(2)(Dmbiim)(4)(H(2)O)(2)](ClO(4))(4).6H(2)O, where Dmbiim = 1,1'-Dimethyl-2,2'-biimidazole are investigated using electronic absorption spectroscopy, fluorescence spectroscopy, viscosity measurement and voltammetry. The results show that the copper(II) complex interacts with DNA through minor groove binding. The interaction between the complex and DNA has also been investigated by gel electrophoresis, interestingly, we found that the copper(II) complex can cleave circular plasmid pBR322 DNA efficiently in the presence of AH(2) (ascorbic acid) at pH 8.0 and 37 degrees C.     

Three new Cu(II) and Cd(II) complexes with 3-(2-pyridyl)pyrazole-based ligand: syntheses, crystal structures, and evaluations for bioactivities

Three new complexes [Cu(L)(2)(NO(3))](NO(3))(H(2)O)(1/2)(CH(3)OH)(1/2) (1), [Cd(L)(2)(NO(3))(2)](H(2)O)(3) (2) and [Cd(L)(2)(ClO(4))(CH(3)OH)](ClO(4))(H(2)O)(1/4)(CH(3)OH) (3) (L=1-[3-(2-pyridyl)pyrazol-1-ylmethyl]naphthalene) were synthesized and characterized by elemental analyses, IR and X-ray diffraction analysis. Among them, the Cu(II) and Cd(II) ions were both coordinated by four N donors from two distinct L ligands via N,N-bidentate chelating coordination mode. Additional weak interactions, such as the face-to-face pi-pi stacking and C-Hcdots, three dots, centeredO H-bonding interactions, linked the mononuclear unit into 1D chain and further into 2D network. Complexes 1-3 were subjected to biological assays in vitro against six different cancer cell lines. All of them exhibited cytotoxic specificity and notable cancer cell inhibitory rate. The interactions of 1-3 with calf thymus DNA were investigated by thermal denaturation, viscosity measurements, spectrophotometric and electrophoresis methods. The results indicate that these complexes bound to DNA by intercalation mode via the ligand L and had different nuclease activities, which were in good agreement with their DNA-binding strength. Moreover, the central metal ions of 1-3 played a vital role in DNA-binding behaviors, DNA-cleavage activities and cytotoxicities, whereas the contribution of the different counter anions to their bioactivities also should not be ignored.     

Oxidative DNA cleavage mediated by a new copper (II) terpyridine complex: crystal structure and DNA binding studies

The copper (II) complex [Cu(Itpy)(2)](ClO(4))(2) (1), (Itpy=imidazole terpyridine) has been synthesized and structurally characterized. Crystal structure of the complex shows the complex to be a monomeric copper (II) species with two Itpy ligands coordinated to the metal ion to give a six coordinate complex. The complex has a distorted octahedral geometry with axial elongation. Variable temperature crystal structure data shows dynamic nature of the Jahn-Teller distortion. The complex is an avid DNA binder with a binding constant of 4.26+/-0.20x10(3)M(-1). Observed changes in the viscosity and circular dichroic spectrum of calf thymus DNA solution in the presence of complex 1 suggests intercalative binding of complex 1 to DNA. The complex cleaves supercoiled pBR322 DNA oxidatively in the presence of hydrogen peroxide.     

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.     

Synthesis and DNA binding of mu-[2,9-bis(2-imidazo[4,5-f][1,10]phenanthroline)-1,10-phenanthroline]bis[1,10-phenanthrolinecopper(II)

A binuclear complex [(phen)Cu(mu-bipp)Cu(phen)](ClO(4))(4), where phen=1,10-phenanthroline and bipp=2,9-bis(2-imidazo[4,5-f][1,10]phenanthroline)-1,10-phenanthroline, has been synthesized and its interaction with calf-thymus DNA in the buffer containing 5mM Tris and 50mM NaCl has been studied by means of electronic absorption titration, luminescence titration and viscometric measurements. The absorbance of the complex in the range of 320-400 nm, which is mainly based on bipp showed no obvious change upon addition of DNA, while the peak at 270 nm, which is determined by both phen and bipp decreased by up to 18%. The emission band of the complex around 360 nm decreased remarkably in presence of DNA. The emission quenching of this complex by [Fe(CN)(6)](4-) was depressed greatly when bound to DNA. The relative viscosity of DNA was increased by this complex more significantly than a bipp directed intercalating reagent. These results suggest that this complex binds to calf thymus DNA by intercalation of the two phenanthrolinecopper terminals. The apparent intrinsic binding constant of the complexes with DNA was 1.6 x 10(4)M(-1) as determined by UV-visible titration.     

Reaction of a model siderophore with Ni(II), Co(II) and Zn(II) in aqueous solution: kinetics and spectroscopy

A spectroscopic study was performed showing that the [Fe(III)(L(2-))(2)](1-) (L(2-)=dopacatecholate) complex reacts with Ni(II), Co(II) and Zn(II) in an aqueous solution containing S(2)O(3)(2-) resulting in the soluble [M(L(1-))(3)](1-) (L(1-)=dopasemiquinone; M=Ni(II), Co(II) or Zn(II) complex species. The Raman and IR spectra of the [CTA][M(L(1-))(3)] complexes, CTA=hexadecyltrimethylammonium cation, in the solid state were obtained. The kinetic constants for the metal substitution reactions were determined at four different temperatures, providing values for DeltaH(not equal), DeltaS(not equal) and DeltaG(not equal). The reactions were slow (k=10(-11) Ms(-1)) and endothermic. The system investigated can be considered as a simplified model to explain some aspects of siderophore chemistry.     

Binding and oxidative cleavage studies of DNA by mixed ligand Co(III) and Ni(II) complexes of quinolo [3,2-b]benzodiazapine and 1,10-phenanthroline

Two mixed ligand complexes of the type [M(phen)(2)(qbdp)](PF(6))n.xH(2)O where M = Co(III) and Ni(II), qbdp = quinolo[3,2-b] benzodiazepine and phen = 1,10-phenanthroline, n = 3 or 2, x = 2 or 3 have been synthesized and characterized by employing analytical and spectral methods. The DNA binding property of the complexes with calf thymus-DNA has been investigated by using absorption spectra, viscosity measurements as well as thermal denaturation studies. The absorption spectral results indicate that the Co(III) and Ni(II) complexes intercalate between the base pairs of the DNA tightly with intrinsic DNA binding constant of 6.4 x 10(4) and 4.8 x 10(4) M(-1) in Tris HCl buffer containing 50 mM NaCl, respectively. The large enhancement in the relative viscosity of DNA on binding to the quinolo [3,2-b] benzodiazepine supports the proposed DNA binding modes. The complexes on reaction with super coiled (SC) DNA shows nuclease activity.     

Ruthenium(II) polypyridyl complexes: synthesis and studies of DNA binding, photocleavage, cytotoxicity, apoptosis, cellular uptake, and antioxidant activity

Two ruthenium (II) complexes [Ru(dmb)2(APIP)](ClO4)2 (APIP=2-(2-aminophenyl)imidazo[4,5-f?][1,10]phenanthroline, dmb=4,4'-dimethyl-2,2'-bipyridine; 1) and [Ru(dmb)2(HAPIP)](ClO4)2 (HAPIP=2-(2-hydroxyl-4-aminophenyl)imidazo[4,5-f?][1,10]phenanthroline; 2) were synthesized and characterized. DNA binding was investigated by electronic absorption titration, luminescence spectra, thermal denaturation, viscosity measurements, and photocleavage. The DNA binding constants for complexes 1 and 2 were 4.20 (±0.14)×10(4) and 5.45 (±0.15)×10(4) M(-1). The results suggest that these complexes partially intercalate between the base pairs. The cytotoxicity of complexes 1 and 2 was evaluated by MTT assay. Cellular uptake was observed under fluorescence microscopy; complexes 1 and 2 can enter into the cytoplasm and accumulate in the nuclei. Apoptosis and the antioxidant activity against hydroxyl radicals (?OH) were also explored.