Synthesis, structure, and nuclease properties of several binary and ternary complexes of copper(II) with norfloxacin and 1,10 phenantroline.

Three new binary Cu(II) complexes of norfloxacin have been synthesized and characterized. We also report the synthesis, characterization and X-ray crystallographic structures of a new binary compound, [Cu(HNor)(2)]Cl(2).2H(2)O (2) and two new ternary complexes norfloxacin-copper(II)-phen, [Cu(Nor)(phen)(H(2)O)](NO(3)).3H(2)O (4), and [Cu(HNor)(phen)(NO(3))](NO(3)).3H(2)O (5). The structure of 2 consists of two crystallographically independent cationic monomeric units of [Cu(HNor)(2)](2+), chloride anions, and uncoordinated water molecules. The Cu(II) ion is placed at a center of symmetry and is coordinated to two norfloxacin ligands which are related through the inversion center. The structures of 4 and 5 consist of cationic units ([Cu(Nor)(phen)(H(2)O)](+) for 4 and [Cu(HNor)(phen)(NO(3))](+) for 5), nitrate counteranions, and lattice water molecules that provide crystalline stability through a network of hydrogen-bond interactions. The complexes exhibit a five coordinated motif in a square pyramidal environment around the metal center. The ability of compounds 4 and 5 to cleave DNA has also been studied. Mechanistic studies with different inhibiting reagents reveal that hydroxyl radicals, singlet oxygen, and superoxide radicals are all involved in the DNA scission process mediated by these compounds.

DNA interaction of new copper(II) complexes with sulfonamides as ligands.

New copper(II) complexes with sulfonamide ligands have been prepared and characterized. Sulfonamide ligands were prepared through a reaction between 8-aminoquinoline and either 2-mesitylene (Hqmesa), 4-tert-butylbenzene (Hqtbsa), or alpha-toluene (Halphaqtsa) sulfonyl chlorides. The structural analysis carried out for complex [Cu(alphaqtsa)(2)] indicated that the local environment of the Cu(II) cation is between a square planar and a tetrahedral geometry, with stacking of the benzene rings of the sulfonyl ligands between neighbor molecules. Powder EPR spectra at room temperature gave rhombic spectra for the [Cu(alphaqtsa)(2)] and [Cu(qmesa)(2)] complexes and an axial spectrum for the [Cu(qtbsa)(2)] complex, probably due to the steric hindrance of the methyl groups. Complexes [Cu(alphaqtsa)(2)] and [Cu(qmesa)(2)] are artificial chemical nucleases that degrade DNA in the presence of sodium ascorbate. A study of the radical scavengers revealed that the ROS (reactive oxygen species) involved in the DNA damage were hydroxyl, singlet oxygen-like species, and superoxide anion.

DNA cleavage reaction induced by dimeric copper(II) complexes of N-substituted thiazole sulfonamides.

A new dinuclear copper(II) complex has been synthesised and structurally characterised: [Cu2(tz-ben)4] (Htz-ben = N-thiazol-2-yl-benzenesulfonamide). Its crystal structure, magnetic properties and electronic paramagnetic resonance (EPR) spectra were studied in detail. In the compound the metal centres are bridged by four non-linear triatomic NCN groups. The coordination geometry of the copper ions in the dinuclear entity is distorted square pyramidal (4+1). Two thiazole N and two sulfonamido N atoms occupy the equatorial positions and one sulfonamido O atom is in the axial position. Magnetic susceptibility data show a strong antiferromagnetic coupling, -2J = 114.1 cm(-1). The EPR spectra of a polycrystalline sample of compound has been obtained at the X- and Q-band frequencies at different temperatures. Above 20K the spectra are characteristic of S = 1 species with a zero field splitting parameter D = 0.4 cm(-1). The EPR parameters are discussed in terms of the known binuclear structures. The chemical nuclease ability of the title complex and that of the related [Cu2(tz-tol)4] compound (Htz-tol = N-thiazol-2-yl-toluenesulfonamide) is reported. The participation of hydroxyl radicals and a singlet oxygen-like entity in the DNA cleavage reaction has been deduced from the assays with radical oxygen scavengers.

Cu(II) complexes with a sulfonamide derived from benzoguanamine. Oxidative cleavage of DNA in the presence of H2O2 and ascorbate.

Reaction between benzoguanamine (2,4-diamino-6-phenyl-1,3,5-triazine) and 2-mesitylenesulfonyl chloride leads to formation of a sulfonamide able to form two mononuclear Cu(II) complexes with a CuL(2) stoichiometry. The local environment of the metal cation is a distorted octahedron, with two ligands and two solvent molecules; both complexes crystallize in the monoclinic structure, space group P2(1), with Z=2. In the presence of ascorbate/H(2)O(2,) the two complexes significantly cleavage double-strand pUC18 DNA plasmid. Both complexes exhibit more nuclease efficiency that the copper phenantroline complex. From scavenging reactive oxygen studies we conclude that the hydroxyl radical and a singlet oxygen-like entity, such a peroxide copper complex, are the radical species involved in the DNA damage.

Antibacterial studies, DNA oxidative cleavage, and crystal structures of Cu(II) and Co(II) complexes with two quinolone family members, ciprofloxacin and enoxacin.

Nine coordination compounds of Cu(II) and Co(II) with Ciprofloxacin (HCp) and Enoxacin (HEx) as ligands have been prepared and characterized. Single crystal structural determinations of [Cu(HCp)2(ClO4)2].6H2O (1) and [Co(HEx)2(Ex)]Cl.2CH(3)OH.12H2O (4) are reported. The crystal of 1 is composed of [Cu(HCp)2(ClO4)2] units with the two perchlorate anions semicoordinated, and uncoordinated water molecules. The copper ion, at a crystallographic inversion centre, is in a tetragonally distorted octahedral environment. The structure of 4 consists of cationic monomeric [Co(HEx)2(Ex)]+ units, chloride anions, and uncoordinated methanol and water molecules. The complex is six-coordinate, with a slightly distorted octahedral environment around the metal centre. Some complexes of ciprofloxacin and enoxacin were screened for their activity against several bacteria, showing activity similar to that of the corresponding free ligands. All compounds tested were more active against Gram-negative bacteria than against Gram-positive bacteria. Ciprofloxacin hydrochloride and its complexes were more active than enoxacin and its complexes. In addition, the bactericidal studies against Staphylococcus aureus ATCC 25923 reveal that one complex exhibits the "paradoxical effect" (diminution in the number of bacteria killed at high drug concentration), which has been described and related to the mechanism of action of quinolones, but three other complexes do not, suggesting different mechanisms of bactericidal action. The ability of Cu(HCp)2(NO3)2.6H2O to cleave DNA has been determined. The results show that the complex behaves as an efficient chemical nuclease with ascorbate/hydrogen peroxide activation. Mechanistic studies using different inhibiting reagents reveal that hydroxyl radicals are involved in the DNA scission process mediated by this compound.

Functional superoxide dismutase mimics. Structural characterization and magnetic exchange interactions of copper(II)-N-substituted sulfonamide dimer complexes.

Dinuclear copper(II) complexes with N-substituted sulfonamide ligands as superoxide dismutase (SOD) mimics have been investigated. The new N-(thiazol-2-yl)toluenesulfonamide (Htz-tol) and N-(thiazol-2-yl)naphthalenesulfonamide (Htz-naf) ligands have been prepared and structurally characterized. The complexes derived from these ligands, [Cu(2)(tz-tol)(4)] (1) and [Cu(2)(tz-naf)(4)] (2), have been synthesized, and their crystal structure, magnetic properties, and EPR spectra were studied in detail. In both compounds the metal centers are bridged by four nonlinear triatomic NCN groups. The coordination geometry of the coppers in the dinuclear entity of 1 and 2 is distorted square planar with two N-thiazole and two N-sulfonamido atoms. Magnetic susceptibility data show a strong antiferromagnetic coupling, with -2J = 121.3 cm(-1) for compound 1 and -2J = 104.3 cm(-1) for compound 2. The EPR spectra of the polycrystalline samples of compounds 1 and 2 have been measured at the X- and Q-band frequencies at different temperatures. Above 20 K the spectra are characteristic of S = 1 species with zero-field splitting parameter D = 0.230 cm(-1) for compound 1 and 0.229 cm(-1) for compound 2. The EPR parameters are discussed in terms of the known binuclear structures. The complexes exhibit high SOD activity, as shown by the low IC(50) values obtained with the xanthine/xanthine oxidase/NBT assay: 0.13 microM for compound 1; 0.17 microM for compound 2.

Oxidative cleavage of DNA by a new ferromagnetic linear trinuclear copper(II) complex in the presence of H2O2/sodium ascorbate.

A new trinuclear copper(II) complex has been synthesized and structurally characterized: [Cu(3)(L)(2)(HCOO)(2)(OH)(2)](infinity) (HL = (N-pyrid-2-ylmethyl)benzenesulfonylamide). In the complex, the central copper ion is six-coordinated. The coordination spheres of the terminal copper atoms are square pyramidal, the apical positions being occupied by a sulfonamido oxygen of the contiguous trimer. As a consequence, the complex can be considered a chain of trinuclear species. The three copper atoms are in a strict linear arrangement, and adjacent coppers are connected by a hydroxo bridge and a bidentate syn-syn carboxylato group. The mixed bridging by a hydroxide oxygen atom and a bidentate formato group leads to a noncoplanarity of the adjacent basal coordination planes with a dihedral angle of 61.4(2) degrees. Susceptibility measurements (2-300 K) reveal a strong ferromagnetic coupling, J = 79 cm(-1), leading to a quartet ground state that is confirmed by the EPR spectrum. The ferromagnetic coupling arises from the countercomplementarity of the hydroxo and formato bridges. The trinuclear complex cleaves DNA efficiently, in the presence of hydrogen peroxide/sodium ascorbate. tert-Butyl alcohol and sodium azide inhibit the oxidative cleavage, suggesting that the hydroxyl radical and singlet oxygen are involved in the DNA degradation.

Nuclease activity of [Cu(sulfathiazolato)(2)(benzimidazole)(2)]2MeOH. Synthesis, properties and crystal structure.

The [Cu(sulfathiazolato)(2)(benzimidazole)(2)]2MeOH complex has been synthesised and characterised. It crystallises in the monoclinic system, space group C1c1, with unit cell dimensions a=18.829(7) A, b=12.206(3) A, c=17.233(5) A, alpha=90.06(2) degrees, beta=97.28(3) degrees, gamma=90.21(3) degrees and Z=4. The geometry around the copper(II) ion is intermediate between tetrahedral and square planar. The complex produces cleavage of plasmid pUC18 in presence of reducing agents. The efficiency of cleavage reaction of the title compound with pUC18 and with different reducing agents follows the order ascorbate-H(2)O(2)>ascorbate>MPA>dithiothreitol>H(2)O(2).

Copper(II) complexes with 4-amino-N-[4,6-dimethyl-2-pyrimidinyl]benzenesulfonamide. Synthesis, crystal structure, magnetic properties, EPR, and theoretical studies of a novel mixed mu-carboxylato, NCN-bridged dinuclear copper compound.

New Cu(II) complexes of sulfamethazine (4-amino-N-[4,6-dimethyl-2-pyrimidinyl]benzenesulfonamide, HL) [Cu(2)(CH(3)COO)(2)(L)(2)].2dmf (1) and ([Cu(L)(2)].2H(2)O)(infinity) (2) were prepared and structurally characterized. Compound 1 crystallizes in the monoclinic system, space group P2(1)/n, with a = 8.9486(9) A, b = 15.0956(12) A, c = 16.542(3) A, beta = 105.584(15) degrees, and Z = 2. Compound 2 crystallizes in the monoclinic system, space group P2(1)/c, with a = 13.8097(8) A, b = 14.5765(4) A, c = 13.7853(15) A, beta = 96.033(9) degrees, and Z = 1. In compound 1 two copper ions are linked by two syn-syn acetates and two nonlinear NCN bridging groups pertaining to the deprotonated sulfamethazine ligands. Each copper center presents a nearly square planar geometry. Magnetic susceptibility data for 1 show a strong antiferromagnetic coupling with 2J = -216.7 cm(-)(1). The EPR spectra at the X- and Q-band frequencies present the signals corresponding to the dinuclear entity, being the zero-field splitting parameter, D = 0.265 cm(-)(1). The antiferromagnetic exchange coupling is discussed using DFT calculations on some model compounds with NCN bridging ligands and also on model structures with mixed mu-acetato and NCN bridges. The copper in the polymeric compound 2 is five coordinate. The CuN(5) chromophore has a highly distorted square pyramidal geometry with small axial N-Cu-N angles of 65.53(14) and 59.90(13) degrees. In the structure a sulfamethazinate anion binds to one copper through the sulfonamido and pyrimidine N atoms and to an adjacent copper via the amino N atom.

Properties and reactivity of myoglobin reconstituted with chemically modified protohemin complexes.

The synthetic complexes protohemin-6(7)-L-arginyl-L-alanine (HM-RA) and protohemin-6(7)-L-histidine methyl ester (HM-H) were prepared by condensation of suitably protected Arg-Ala or His residues with protohemin IX. HM-RA and HM-H were used for reconstitution of apomyoglobin from horse heart, yielding the Mb-RA and Mb-H derivatives, respectively, of the protein. The spectral, binding and catalytic properties of Mb-RA and Mb-H are significantly different from those of Mb. As shown by MM and MD calculations, these differences are determined by some local structural changes around the heme which are generated by increased mobility of a key peptide segment (Phe43-Lys47), containing the residue (Lys45) that in native Mb interacts with one of the porphyrin carboxylate groups. In the reconstituted Mbs this carboxylate group is bound to the Arg-Ala or His residue and is no longer available for electrostatic interaction with Lys45. The mobility of the peptide segment near the active site allows the distal histidine to come to a closer contact with the heme, and in fact Mb-RA and Mb-H exist as an equilibrium between a high-spin form and a major low-spin, six-coordinated form containing a bis-imidazole ligated heme. The two forms are clearly distinguishable in the NMR spectra, that also show that each of them consists of a mixture of the two most stable isomers resulting from cofactor reconstitution, as also anticipated by MM and MD calculations. Exogenous ligands such as cyanide, azide, or hydrogen peroxide can displace the bound distal histidine, but their affinity is reduced. On the other hand, mobilization of the peptide chain around the heme in the reconstituted Mbs increases the accessibility of large donor molecules at the heme periphery, with respect to native Mb, where a rigid backbone limits access to the distal pocket. The increased active site accessibility of Mb-RA and Mb-H facilitates the binding and electron transfer of phenolic substrates in peroxidase-type oxidations catalyzed by the reconstituted proteins in the presence of hydrogen peroxide.

Countercomplementarity and strong ferromagnetic coupling in a linear mixed mu-acetato, mu-hydroxo trinuclear copper(II) complex. Synthesis, structure, magnetic properties, EPR, and theoretical studies.

The structural and magnetic data of the trinuclear compound [Cu3(L)2(CH3COO)2(OH)2(dmf)2] (HL = N-(2-methylpyridyl)toluensulfonylamide) are reported. The compound crystallizes in the monoclinic system, space group P2(1)/n (no. 14), with a = 11.6482(6) A, b = 13.5772(6) A, c = 13.5306(7) A, alpha = 90 degrees, beta = 92.859(5) degrees, gamma = 90 degrees, and Z = 2. The three copper atoms form an exact linear arrangement. Neighboring coppers are connected by a hydroxo bridge and a bidentate syn-syn carboxylato group. The coordination spheres of the terminal copper atoms are square pyramidal with a dmf molecule as the apical ligand. The central copper has a regular square planar geometry. The mixed bridging by a hydroxide oxygen atom and a bidentate carboxylato group leads to a noncoplanarity of the adjacent basal coordination planes with a dihedral angle of 51.96(9) degrees. Susceptibility measurements (2-300 K) reveal a strong ferromagnetic coupling, J = 93(6) cm-1, in the mixed-bridged moiety leading to a quartet ground state that is confirmed by the EPR spectra. The ferromagnetic exchange coupling is discussed using DFT calculations on model compounds that have shown a countercomplementary effect of the hydroxo and acetate bridges.

The enzymatic properties of Octopus vulgaris hemocyanin: o-diphenol oxidase activity.

Hemocyanin and tyrosinase are dinuclear copper proteins capable of reversibly binding dioxygen. Despite the great similarity of structure and properties of their active site, the two proteins perform different biological functions (oxygen transport/storage versus monooxygenase and oxidase activity). In this paper, we show that Octopus vulgaris hemocyanin exhibits a tyrosinase-like activity; namely, it is capable of utilizing dioxygen for the oxidation of o-diphenol to quinone. The reaction is specific for this isomer of diphenol, the meta and para isomers being unreactive, and is strongly controlled by steric factors. Dioxygen represents a cosubstrate of the reaction, and it is involved in the catalytic turnover by binding to the dinuclear copper site of the protein to form, under steady-state conditions, oxy-Hc, which is the active species. The generation of semiquinone radicals, detected by EPR and by their reaction with N,N,N',N'-tetramethyl-1,4-phenylenediamine, strongly supports a reaction mechanism in which such radicals represent the reaction products of one-electron oxidation of the substrate, quinone being generated by dismutation of semiquinones. Met-Hc is regenerated by the substrate to the deoxy form. To close the catalytic cycle, the proposed reaction mechanism also involves the participation of two transient protein forms with the total oxidation state of the active site (V and IV) intermediate between that of oxy-Hcy, [CuIIO22-CuII]VI, and deoxy-Hc, [CuICuI]II. A mathematical model has been elaborated to describe the reaction kinetics. The differences in reaction mechanisms between hemocyanin and tyrosinase are discussed in terms of accessibility to exogenous molecules of their active sites.

The binding of azide to copper-containing and cobalt-containing forms of hemocyanin from the mediterranean crab Carcinus aestuarii.

To establish the competence of the active site of hemocyanin to acquire diverse coordination geometries, the binding of azide to three forms of a crab hemocyanin, the dinuclear cupric or met-hemocyanin, the mononuclear cupric or met-apo-hemocyanin, and the mononuclear Co(II)-substituted derivative has been studied by near-ultraviolet circular dichroism and EPR spectroscopies. The near-ultraviolet circular dichroism spectra of the various derivatives present qualitatively similar features, namely a negative peak around 335 nm in the case of the two copper-containing derivatives and a three-component pattern with the Co(II) derivative. Upon decreasing the pH from 7.0 to 5.5 a decrease of optical activity is observed with all protein samples. The characteristic CD features, attributable to N(imidazole)-to-metal and to OH -to-metal charge-transfer transitions, are strongly affected by azide binding. In particular, the intensity of the negative band exhibited by the two copper-containing protein forms decreases with the onset of a new negative feature with maximum around 400 nm diagnostic for azide-to-Cu(II) charge-transfer transitions. The visible region is affected as well, indicating that changes in the coordination sphere of copper take place. The affinity for azide of the different protein forms is higher at low pH. EPR measurements on the paramagnetic met-apo-hemocyanin derivative as a function of pH demonstrate heterogeneity in the coordination environment at low pH. In the presence of azide an increase of rhombic distortion of the EPR spectra is observed and on the basis of the identified sets of copper hyperfine features in the course of azide titration experiments two different azide bound forms of met-apo-hemocyanin can be detected. The CD and EPR data at the different pH values are consistent with a reaction scheme in which azide replaces a fourth ligand in the metal-coordination sphere, identified as a water or hydroxide molecule.

Synthesis and characterization of metal(II)-8-quinolinsulfonamidato (sa-) complexes (M = Co, Ni, Cu, and Zn). Crystal structure of [Zn(sa)2(NH3)]NH3 complex. Carbonic anhydrase inhibitory properties.

A new sulfonamide, 8-quinolinsulfonamide(Hsa), has been prepared and examined as a chelating agent towards metal(II) ions. The spectroscopic properties of the M(II) sulfonamidato complexes has been studied. The inhibitory properties of the ligand and the synthesised complexes were tested. The crystal structure of the [Zn(sa)2(NH3)].NH3 complex was determined by single-crystal X-ray diffraction. Crystal data of the zinc(II) complex: a = 16.217(4)A, b = 8.041(1)A, c = 15.606(4)A, beta = 95.75(1) degrees, Z = 4, and V = 2024.6(7)A3. The refinement of the structure based on 6047 reflections attained to R = 0.049 and Rw = 0.052. The zinc(II) ion is surrounded by four N atoms of two sulfonamidato ligands and one N atom of an ammonia molecule in an trigonal bipyramid arrangement.

The oxidation of hemocyanin. Kinetics, reaction mechanism and characterization of met-hemocyanin product.

The reaction that gives met-hemocyanin from Octopus vulgaris oxy-hemocyanin has been reinvestigated under several experimental conditions. Various anions including azide, fluoride and acetate have been found to promote this reaction. Kinetic data indicate that the reaction mechanism is different from that currently accepted involving a peroxide displacement of bound dioxygen through an associative chemistry on an open axial position of the copper ions [Hepp, A. F., Himmelwright, R. S., Eickman, N. C. & Solomon, E. I. (1979) Biochem. Biophys. Res. Commun. 89, 1050-1057; Solomon, E. I. in Copper proteins (Spiro, T. G., ed.) pp. 43-108, J. Wiley, New York]. Our study suggests that the protonated form of the anion is likely to be the species reacting with the oxygenated form of the protein. Furthermore, it is also proposed that protonation of bound dioxygen generates an intermediate hydroperoxo-dicopper(II) complex to which the exogenous anion is also bound. This intermediate in not accumulated and preceds the release of hydrogen peroxide by reaction with water. Upon dialysis it leads to the met-hemocyanin form. The structure of this dinuclear copper(II) derivative contains a di-mu-hydroxo bridge but there is evidence from optical and circular dichroism spectra for partial protonation of these bridges at low pH. As a consequence, while one azide molecule binds in the bridging mode to met-hemocyanin with low affinity (K = 30 M-1) at pH 7.0, it binds with much higher affinity at pH 5.5 (K = 1500 M-1), where a second azide ligand also binds in the terminal mode (K = 20 M-1). The coordination mode of the azide ligands is deduced from the optical and circular dichroism spectra of the protein complexes.

Metal complexes of the carbonic anhydrase inhibitor methazolamide (Hmacm). Crystal structure of the Zn(macm)2(NH3)2. Anticonvulsant properties of the Cu(macm)2(NH3)3(H2O).

Complexes of Co(II), Cu(II), and Zn(II) with deprotonated methazolamide and ammonia are synthesized and characterized. The complex Zn(macm)2(NH3)2 crystallizes in the monoclinic C2/c space group with a = 13.468(1), b = 6.759(1), c = 23.014(2) A, beta = 90.27(1), and Z = 4. The structure was refined to R = 0.049 (Rw = 0.053). The Zn(II) ion is coordinated to two deprotonated sulfonamido nitrogen atoms of the macm- ligand and two nitrogen atoms of the ammonia ligands in a distorted tetrahedron. The Zn(macm)2(NH3)2 complex is shown to be a simple model for the methazolamide inhibition of CA. EHMO calculations applied to fractional coordinates of the Zn(macm)2(NH3)2 complex indicate that the atomic orbitals of the Zn do not contribute to HOMO and LUMO of the complex. The characteristics of the Cu(macm)2(NH3)3(H2O) as an anticonvulsant agent are tested.

Anticonvulsant properties of copper acetazolamide complexes.

Two copper acetazolamide complexes were synthesized for evaluation as anticonvulsant agents. These complexes were found to be more effective as anticonvulsants than the acetazolamide.

Acetazolamide-M(II) [M(II) = Co(II),Ni(II),Cu(II)] complexes with ethylamine, diethylamine, triethylamine, and potassium hidroxide.

Complexes of Co(II), Ni(II), and Cu(II) with dideprotonated Acm are synthesized and characterized. Acm acts as bidentate ligand through the N-sulfonamido atom and the N-thiadiazole atom except for K6CoAcm4.6H2O in which Acm behaves as monodentate through the N-sulfonamido atom.