Sulfite induced autoxidation of NiII and CoII tetraglycine complexes. Spectrophotometric and rotating ring-disc voltammetric studies

The oxidation of Ni(II) and Co(II) tetraglycine complexes in borate buffer aqueous solution, by dissolved oxygen, is strongly accelerated by sulfite. The formation of Ni(III) and Co(III) complexes with maximum absorbances at 327 and 265 nm, respectively, was followed by spectrophotometric measurements. Ni(III) formation was also characterized by voltammetry at low temperatures, whose anodic and cathodic components were observed in the recorded voltammograms. Spectra and rotating ring-disc voltammograms, recorded at various rotation speed values, showed that the Ni(III) species decomposes. The electrochemical process related to the couple Co(II)/Co(III), in a medium containing tetraglycine, was not reversible. In both Ni(II) and Co(II) complexes the metal ion oxidation in the presence of oxygen and sulfite involves the reduction of some initial Ni(III) or Co(III) by sulfite to produce the SO(3).- radical, which rapidly reacts with dissolved oxygen to produce SO(5).-, which then oxidizes Ni(II) or Co(II).     

DNA damage by sulfite autoxidation catalyzed by cobalt complexes

DNA damage was investigated in the presence of sulfite, dissolved oxygen and cobalt(II) complexes with glycylglycylhistidine, glycylhistidyllysine, glycylglycyltyrosylarginine and tetraglycine. These studies indicated that only Co(II) complexed with glycylglycylhistidine (GGH) induced DNA strand breaks at low sulfite concentrations (1-80 microM) via strong oxidants formed in the reaction. In the presence of the other complexes, some damage occurred only in the presence of high sulfite concentrations (0.1-2.0 mM) after incubation for 4 h. In the presence of GGH, Co(II) and dissolved O2, DNA damage must involve a reactive high-valent cobalt complex. The damaging effect was increased by adding S(IV), due to the oxysulfur radicals formed as intermediates in S(IV) autoxidation catalyzed by the complex. SO3 -, HO and H radicals were detected by EPR-spin trapping experiments with DMPO (5,5-dimethyl-1-pyrroline N-oxide). The results indicate that Co(II) binds O2 in the presence of GGH, and leads to the formation of a DMPO-HO adduct without first forming free superoxide or hydroxyl radical, supporting the participation of a reactive high-valent cobalt complex.     

S(IV) induced autoxidation of Cu(II)/tetraglycine complexes in the presence of aldehydes: mechanistic considerations and analytical applications

An indirect amperometric method for the determination of sulfite in a flow injection configuration is described. The procedure is based on the amperometric measurement (E=0.1 V) of Cu(III) chemically generated by the S(IV) induced oxidation of Cu(II)/tetraglycine by dissolved oxygen. The dynamic analytical range was 5-100 muM with a detection limit of 1 muM. The repeatability for the determination (10 muM) was evaluated to be 1.4% (n=20). The method was employed for the determination of S(IV) in wine after its extraction from acidified samples by bubbling argon and the results were in agreement with those obtained by the iodometric procedure. The influence of formaldehyde and acetaldehyde on the Cu(III) formation is also discussed on the basis of the mechanism of the induced reaction.     

Synergistic effect of Ni(II) and Co(II) ions on the sulfite induced autoxidation of Cu(II)/tetraglycine complex

The synergistic effect of Ni(II) and Co(II) on the sulfite induced autoxidation of Cu(II)/tetraglycine was investigated spectrophotometrically at 25.0 degrees C, pH = 9.0, 1 x 10(-5) mol dm(-3) < or = [S(IV)] < or = 8 x 10(-5) mol dm(-3), [Cu(II)]= 1 x 10(-3) mol dm(-3), 1 x 10(-6) mol dm(-3) < or = [Ni(II)] or [Co(II)] < or = 1 x 10(-4) mol dm(-3), [O2] approximately 2.5 x 10(-4) mol dm(-3), and 0.1 mol dm(-3) ionic strength. In the absence of added nickel(II) or cobalt(II), the kinetic traces of Cu(III)G4 formation show a large induction period (about 3 h). The addition of trace amounts of Ni(II) or Co(II) increases the reaction rate significantly and the induction period drastically decreases (less than 0.5 s). The effectiveness of Cu(III)G4 formation becomes much higher. The metal ion in the trivalent oxidation state rapidly oxidizes SO3(2-) to SO3*-, which reacts with oxygen to produce SO5*-. The strongly generated oxidants oxidize Cu(II)G4 to Cu(III).     

Efficient plasmid DNA cleavage by a mononuclear copper(II) complex

The Cu(II) complex of the ligand all-cis-2,4,6-triamino-1,3,5-trihydroxycyclohexane (TACI) is a very efficient catalyst of the cleavage of plasmid DNA in the absence of any added cofactor. The maximum rate of degradation of the supercoiled plasmid DNA form, obtained at pH 8.1 and 37 degrees C, in the presence of 48 microM TACI.Cu(II), is 2.3 x 10(-3) s(-1), corresponding to a half-life time of only 5 min for the cleavage of form I (supercoiled) to form II (relaxed circular). The dependence of the rate of plasmid DNA cleavage from the TACI.Cu(II) complex concentration follows an unusual and very narrow bell-like profile, which suggests an high DNA affinity of the complexes but also a great tendency to form unreactive dimers. The reactivity of the TACI.Cu(II) complexes is not affected by the presence of several scavengers for reactive oxygen species or when measured under anaerobic conditions. Moreover, no degradation of the radical reporter Rhodamine B is observed in the presence of such complexes. These results are consistent with the operation of a prevailing hydrolytic pathway under the normal conditions used, although the failure to obtain enzymatic religation of the linearized DNA does not allow one to rule out the occurrence of a nonhydrolytic oxygen-independent cleavage. A concurrent oxidative mechanism becomes competitive upon addition of reductants or in the presence of high levels of molecular oxygen: under such conditions, in fact, a remarkable increase in the rate of DNA cleavage is observed.     

Light induced photoreactions with plasmid DNA by Cu/Ru and Cu/Ru/Pt multi-metallic porphyrins

Coordination of two [Ru(bipy)(2)Cl](+) moieties (where bipy = 2,2'-bipyridine) to the pyridyl nitrogens in the 5,10-positions of meso-5,10,15-(4-Pyridyl)-20-(pentafluorophenyl)porphyrin gives the diruthenium porphyrin complex II. Insertion of copper(II) into the porphyrin center allows for the third pyridyl nitrogen to coordinate to Pt(dmso)Cl(2). Electronic transitions associated with the ruthenium porphyrin include an intense Soret band and four less intense Q-bands in the visible region of the spectrum. An intense π-π* transition in the UV region associated with the bipyridyl groups and a metal to ligand charge transfer (MLCT) band appearing as a shoulder to the Soret band are also observed. A slight blue shift of the Soret band and collapse of the Q-bands into one band is observed upon insertion of Cu(II) into the porphyrin center. No change in the electronic spectrum is observed upon coordination of the Pt(dmso)Cl(2) moiety. Electrochemical properties associated with the complexes include a redox couple in the cathodic region attributed to the porphyrin and a redox couple in the anodic region due to the Ru(III/II) couple. DNA titrations of the Cu/Ru and Cu/Ru/Pt porphyrins indicate that both complexes interact strongly with DNA potentially through a partial intercalation mechanism. Gel electrophoresis studies indicate that the Cu/Ru/Pt porphyrin has a greater effect on DNA migration through the gel than the well known DNA binding agent cis-platin. Irradiation of aqueous solutions of the Cu/Ru porphyrin and supercoiled DNA at a 5:1 base pair to complex ratio (in the absence of oxygen) with visible light above 400 nm shows a nicking of the DNA. Repeat experiments in the presence of oxygen show that the Cu/Ru porphyrin photocleaves the DNA, giving the linear form, as evidenced by gel electrophoresis.     

CU(II) SENSITIZES pBR322 PLASMID DNA TO INACTIVATION BY UV-B(280–315 nm)

Abstract— Copper(II), in the presence of UV-B radiation(280–315 nm), can generate single-strand breaks in the sugar-phosphate backbone of pBR322 plasmid DNA. A low level of single-strand backbone breaks occurs in the presence of Cu(II) alone, but UV-B irradiation increases the rate by the more than 100-fold. Concomitant with the damage to the DNA backbone is a loss of transforming activity. Oxygen is required for generation of the single-strand breaks but not for the loss of transforming activity. A DNA glycosylase (Fpg), which participates in the repair of certain DNA nitrogenous base damage, does not repair plasmid DNA damaged by Cu(II). The hydroxyl radical scavenging compound DMSO is only somewhat effective at protecting the physical and biological properties of the DNA. These results with Cu(II) are compared to those obtained previously with pBR322 plasmid DNA in the presence of Fe(III) and UV-A.     

Binding of metal ions to melanin and their effects on the aerobic reactivity

The binding of Mg(II), Ca(II), Zn(II), Cu(II) and Fe(III) to ETDA-washed Sepia melanin is quantified by inductively coupled plasma mass spectrometry. By monitoring the solution pH change associated with metal uptake, it is concluded that Mg(II), Ca(II) and Zn(II) bind to carboxylic acid groups in melanin, Cu(II) binds to hydroxyl (OH) groups and Fe(III) binds to OH or amine groups. The aerobic reactivity of melanins with different metal contents is analyzed by examining their ability to cause strand breaks in supercoiled pUC18 DNA. Cu(II)- and Fe(III)-enriched melanins induce the most damage. Hydroxyl radical, *OH, is proposed to be one of the reactive oxygen species responsible.     

Synthesis and characterization of 3-methyl-5-oxo-N,1-diphenyl-4,5-dihydro-1-H-pyrazole-4-carbothioamide and its metal complexes

The molecular parameters have been calculated to confirm the geometry of 3-methyl-5-oxo-N,1-diphenyl-4,5-dihydro-1-H-pyrazole-4-carbothioamide, HL. The compound is introduced as a new chelating agent for complexation with Cr(III), Fe(III), Co(II), Ni(II) and Cu(II) ions. The isolated chelates were characterized by partial elemental analyses, magnetic moments, spectra (IR, UV–vis, ESR; ¹H NMR) and thermal studies. The protonation constant of HL (5.04) and the stepwise stability constants of its Co(II), Cu(II), Cr(III) and Fe(III) complexes were calculated. The ligand coordinates as a monobasic bidentate through hydroxo and thiol groups in all complexes except Cr(III) which acts as a monobasic monodentate through the enolized carbonyl oxygen. Cr(III) and Fe(III) complexes measured normal magnetic moments; Cu(II) and Co(II) measured subnormal while Ni(II) complex is diamagnetic. The data confirm a high spin and low spin octahedral structures for the Fe(III) and Co(II) complexes. The ESR spectrum of the Cu(II) complex support the binuclear structure. The molecular parameters have also been calculated for the Cu(II) and Fe(III) complexes. The thermal decomposition stages of the complexes confirm the MS to be the residual part. Also, the thermodynamic and kinetic parameters were calculated for some decomposition steps.     

Fluorogenic Detection of Sulfite in Water by Using Copper(II) Azacyclam Complexes

Copper(II) azacyclam complexes (azacyclam = 1,3,5,8,12-pentaazacyclotetradecane) containing naphthyl or dansyl subunits can be prepared by template synthesis involving proper sulfonamide derivatives as locking fragments. The macrocyclic complexes are very poorly emissive due to the fluorescence-quenching behavior displayed by Cu²⁺ ions. However, the fluorescence can be recovered as a result of the decomposition of the complexes, which induces the release of free light-emitting subunits to the solution. This reaction takes place very slowly in neutral water but its rate is increased by the presence of sulfite. Therefore, [Cu(azacyclam)]²⁺ derivatives have been investigated as simple chemical probes for the fluorogenic detection of sulfite both on laboratory and real samples. Preliminary tests performed on samples of white wine provided sulfite concentration values that are in agreement with those obtained by a standard analytical method.     

Surface-enhanced Raman spectra study of metal complexes of N-D-glucosamine beta-naphthaldehyde and glycine and their interaction with DNA

Copper(II), zinc(II), cobalt(II) and cobalt(III) complexes of N-D-glucosamine beta-naphthaldehyde (C17H19O6N, NG) and glycine were synthesized. The four novel metal complexes, Cu(II)C19H28O11N2(CuGNG), Zn(II)C19H24O9N2 (ZnGNG), Co(II)C19H28O11N2(Co(II)GNG) and Co(III)C21H29O12N2(Co(III)GNG) were characterized by means of infrared (IR), electronic absorption spectroscopy and NMR etc. The surface-enhanced Raman spectra of the four complexes and their interaction with DNA were studied. By comparison of the surface-enhanced Raman spectra (SERS), the information of the four complexes' SER active sites and adsorption orientation were obtained. Combined with fluorescence spectra of Ethidium bromide (EthBr) DNA system, we concluded that none of the four complexes intercalate into DNA and that the presence of the glycine ligand lowered the anticancer activity of NG series complexes.     

Solution chemistry of copper(II)-gentamicin complexes: relevance to metal-related aminoglycoside toxicity

The adverse effect to the inner ear of aminoglycosides, drugs widely administered for the treatment of serious infections, appears to result from the interaction of these drugs with Cu(II) or Fe(II)/Fe(III) ions. To understand more completely the metal-induced side effects of one such antibiotic, gentamicin, we studied copper(II) coordination to gentamicin C1a by potentiometry, UV-vis, CD, and EPR spectroscopies, and ESI mass spectrometry. Only monomeric complexes of the CuH(n)L stoichiometry, with n ranging from 3 to -2, were detected over the pH range of 4-12. CuH(3)L and CuH(2)L complexes exhibit the same coordination mode, binding copper(II) through the amino nitrogen atom and a deprotonated alcoholic oxygen atom of the garosamine ring. In the CuHL and CuL complexes a second amino nitrogen atom of the purpurosamine ring participates in central ion coordination. Finally, the additional axial binding of the deprotonated oxygen of the hydroxyl group of the 2-deoxystreptamine moiety occurs in the CuH(-)(1)L and CuH(-)(2)L complexes. Interactions of the Cu(II)-gentamicin-H(2)O(2) system at pH 7.4 with N,N-dimethyl-p-nitrosoaniline, arachidonic acid, and plasmid DNA confirmed that gentamicin complexes facilitate oxidative reactions leading to peroxidation of arachidonic acid and scission of double-stranded DNA mediated by copper-bound reactive oxygen species. However, the stability constants of Cu(II)-gentamicin complexes are inferior to the binding constants of copper(II) complexes with other components of human serum or cells. Computer simulations of copper(II) distribution in the human blood plasma showed that the concentration of gentamicin would have to be at impossible levels (100 M) before a significant fraction of Cu(II) ions would be bound to gentamicin. Further, once introduced into aqueous solution, histidine replaces gentamicin in Cu(II)-gentamicin complexes. Therefore, Cu(II)-gentamicin complexes might not exist under physiological conditions.     

Heterotrimetallic 4f-3d coordination polymers: synthesis, crystal structure, and magnetic properties

A series of cyano-bridged heterotrimetallic complexes [CuL](2)Ln(H(2)O)(2)M(CN)(6).7H(2)O have been synthesized by the reactions of CuL (L(2)(-) = dianion of 1,4,8,11-tetraazacyclotradecane-2,3-dione), Ln(3+) (Ln = Gd or La), and [M(CN)(6)](3)(-) (M = Co, Fe, or Cr). X-ray diffraction analysis reveals that these complexes are isostructural and have a novel chain structure. The Ln(3+) ion is eight-coordinated by six oxygen atoms of two CuL and two water molecules and two nitrogen atoms of the bridging cyano ligands of two [M(CN)(6)](3)(-), while the [M(CN)(6)](3)(-) anion connects two Ln(3+) using two trans-CN(-) ligands giving rise to a chainlike structure. In the chain, every CuL group tilts toward the CN(-) ligand of adjacent [M(CN)(6)](3)(-) with the Cu-N(cyano) contacts ranging from 2.864(6) to 2.930(6) A. Magnetic studies on the CuGdCo complex (1) indicate the presence of ferromagnetic coupling between Cu(II) and Gd(III). The CuLaCr (5) and CuLaFe (2) complexes exhibit ferromagnetic interaction between paramagnetic Cu(II) and Cr(III)/Fe(III) ions through the weak cyano bridges (Cu-N(cyano) = 2.930(6) A for 2). A global ferromagnetic interaction is operative in the CuGdFe complex (3) with the concurrence of dominant ferromagnetic Cu(II)-Gd(III) and minor antiferromagnetic Gd(III)-Fe(III) as well as the ferromagnetic Cu(II)-Fe(III) interaction. For the CuGdCr complex (4), an overall antiferromagnetic behavior was observed, which is attributed to the presence of dominant antiferromagnetic Cr(III)-Gd(III) coupling and the minor ferromagnetic Cu(II)-Gd(III) and Cu(II)-Cr(III) interaction. Moreover, a spin frustration phenomenon was found in complex 4, which results from the ferro-ferro-antiferromagnetic exchanges in the trigonal Cu-Gd-Cr units. The magnetic susceptibilities of these complexes were simulated using suitable models. The magneto-structural correlation was investigated. These complexes did not show a magnetic phase transition down to 1.8 K.     

Synthesis,characterization, antifungal,antibacterial and DNA cleavage studies of some heterocyclic Schiff base metal complexes

Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from indole-3-carboxaldehyde and m-aminobenzoic acid were synthesized and characterized by elemental analysis, molar conductance, IR, UV–Vis, magnetic moment, powder XRD and SEM. The IR results demonstrate the bidentate binding mode of the ligand involving azomethine nitrogen and carboxylato oxygen atoms. The electronic spectral and magnetic moment results indicate that Co(II) and Ni(II) complexes have tetrahedral geometry, while Cu(II) complex is square planar. Powder XRD and SEM indicate the crystalline state and surface morphology studies of the complexes. The antimicrobial activity of the synthesized ligand and its complexes were screened by disc diffusion method. The results show that the metal complexes were found to be more active than the ligand. The nuclease activity of the ligand and its complexes were assayed on CT DNA using gel electrophoresis in the presence of H₂O₂. The Cu(II) complex showed increased nuclease activity in the presence of an oxidant when compared to the ligand and other complexes.     

Dinaphthotetraaza[14]annulene copper(II) complexes in the electrocatalytic reduction of carbon dioxide and bisulfite anion

A modified synthetic route for the complexes [Cu(II)5,7,12,14-tetramethyldinaphtho [b,i][1,4,8,11]tetraaza[14]annulene], [Cu(II)tmdnTAA], and [Cu(II) 5,7,12,14-tetramethyl-6,13-dichloro-dinaphtho[b,i][1,4,8,11]tetraaza[14]annulene], [Cu(II)dCltmdnTAA], is presented in this work. The electrochemical characterization of both complexes and their precursors, [bis(2,4-pentanedionato)copper(II)], [Cu(II)(acac)₂] and [bis(3-chloro-2,4-pentanedionato)copper(II)], [Cu(II)(3-Cl-acac)₂], respectively, under nitrogen and carbon dioxide is also presented. The voltammetric response of [Cu(II)(acac)₂] and [Cu(II)(3-Cl-acac)₂] are different compared to [Cu(II)tmdnTAA] and [Cu(II)dCltmdnTAA] under nitrogen. Precursors show the reduction of Cu(I) to Cu(0) and the tetraazadinaphtho[14]annulene complexes do not. The chlorine substituted complex has a lower reduction potential than the unsubstituted homologue under nitrogen atmosphere. However, the contrary response is obtained in the presence of carbon dioxide: the unsubstituted complex is more catalytic in terms of potential because the current discharge appears 270?mV shifted to the anodic region. These facts can be explained in terms of electronic and steric effects. The modified electrode obtained by oxidative electropolymerization of [Cu(II)tmdnTAA] over glassy carbon electrode presented a suitable amperometric response for the sulfite reduction in acidic medium (pH?=?2.7). A linear correlation was observed for the catalytic current and sulfite concentration between 0.6–6.0?mM range.     

Hydrogen peroxide formation upon oxidation of oxalic acid in presence and absence of oxygen and of manganese(II)--III. Iron(III) and copper(II) as retarders

The formation of considerable amounts of hydrogen peroxide upon the slow addition of various oxidizing agents to oxalic acid in dilute sulphuric acid in the presence of oxygen and Mn(II) is greatly retarded in the presence of Fe(III) or Cu(II). With hydrogen peroxide as oxidizing agent and a trace of Fe(II) there is considerable decomposition of peroxide, under a nitrogen atmosphere, after a few hours at 25 degrees in light (from a tungsten lamp), and less decomposition in the dark. This decomposition is decreased by Mn(II) and also when the original mixture contains Fe(III). With oxygen as the oxidizing agent Fe(II) is about 100 times as effective an inhibitor of peroxide formation as Fe(III). With all oxidizing agents used, Cu(II) is some 6-10 times more effective as a retarder than Fe(III). The inhibition is accounted for by the reaction Fe(III) [or Cu(II)] + CO(-)(2) --> Fe(II) [or Cu(I)] + CO(2).     

A series of trinuclear Cu(II)Ln(III)Cu(II) complexes derived from 2,6-Di(acetoacetyl)pyridine: synthesis, structure, and magnetism

A series of trinuclear Cu(II)Ln(III)Cu(II) complexes with the bridging ligand 2,6-di(acetoacetyl)pyridine have been prepared by one-pot reaction with Cu(NO(3))(2).3H(2)O and Ln(NO(3))(3).nH(2)O in methanol. X-ray crystallographic studies for all the complexes indicate that two L(2)(-) ligands selectively sandwich two Cu(II) ions with the 1,3-diketonate entities and one Ln(III) ion with the 2,6-acetylpyridine entity to form a trinuclear CuLnCu core bridged by the enolate oxygen atoms. Cryomagnetic properties of the complexes are studied with respect to the electronic structure of the Ln ion.     

Electrochemical and electrocatalytic properties of meso-triphenylcorrole and its complexes with Mn(III), Co(III), Cu(III), and Zn(II)

The method of cyclic voltammetry (CV) was used to compare electrochemical and electrocatalytic properties of meso-triphenylcorrole [H₃(ms-Ph)₃Cor] and also its complexes with Mn(III), Co(III), Cu(III), and Zn(II) in 0.1M KOH. Metal-localized redox transitions are detected in the complexes of Mn (III ?? IV) and (III ?? II), Co (III ?? II), Cu (III ?? II). It is shown that the manganese complex features most effective catalytic properties in the reaction of molecular oxygen electroreduction.     

Spectral, thermal, kinetic, molecular modeling and eukaryotic DNA degradation studies for a new series of albendazole (HABZ) complexes

This work represents the elaborated investigation for the ligational behavior of the albendazole ligand through its coordination with, Cu(II), Mn(II), Ni(II), Co(II) and Cr(III) ions. Elemental analysis, molar conductance, magnetic moment, spectral studies (IR, UV-Vis and ESR) and thermogravimetric analysis (TG and DTG) have been used to characterize the isolated complexes. A deliberate comparison for the IR spectra reveals that the ligand coordinated with all mentioned metal ions by the same manner as a neutral bidentate through carbonyl of ester moiety and NH groups. The proposed chelation form for such complexes is expected through out the preparation conditions in a relatively acidic medium. The powder XRD study reflects the amorphous nature for the investigated complexes except Mn(II). The conductivity measurements reflect the non-electrolytic feature for all complexes. In comparing with the constants for the magnetic measurements as well as the electronic spectral data, the octahedral structure was proposed strongly for Cr(III) and Ni(II), the tetrahedral for Co(II) and Mn(II) complexes but the square-pyramidal for the Cu(II) one. The thermogravimetric analysis confirms the presence or absence of water molecules by any type of attachments. Also, the kinetic parameters are estimated from DTG and TG curves. ESR spectrum data for Cu(II) solid complex confirms the square-pyramidal state is the most fitted one for the coordinated structure. The albendazole ligand and its complexes are biologically investigated against two bacteria as well as their effective effect on degradation of calf thymus DNA.     

Cu(II), Eu(III)单核、双核隔室配合物的XPS研究

用X射线光电子能谱(XPS)研究了Cu(II),Eu(III)和配体6,11-二甲基-7,10-二氮杂十六-5,11-二烯-2,4,13,15-四酮(H~4daaen)形成的单核、双核隔室配合物的电子结构和成键特性;观察到配体分子中有明显的电荷转移现象;并对Cu2p~3~/~2伴峰现象进行了分析。