Chiral and achiral macrocyclic copper(II) complexes: Synthesis, characterization, and comparative binding studies with calf-thymus DNA

The new chiral macrocyclic complexes [1,2-bis(1H-benzimidazol-2-yl)-1-(1,8-dihydro-1,3,5,8,10,12-hexaazacyclotetradecane)-2-hydroxyethanolate] copper(II) and -nickel(II) perchlorate, 3 and 4, respectively, were synthesized by the reaction of 1,2-bis(1H-benzimidazol-2-yl)ethane-1,2-diol (L) and (1,8-dihydro-1,3,5,8,10,12-hexaazacyclotetradecane)copper(II) and -nickel(II) diperchlorate complexes, 1 and 2, respectively. All complexes were characterized by various spectroscopic techniques. Molar-conductance measurements showed that all of the complexes are ionic in nature. In complexes 3 and 4, the metal center is encapsulated by the ligand L in a pentacoordinated environment. The optical-rotation values ([alpha](D)) of 3 and 4 at 25 degrees indicate that the complexes are chiral. Absorption- and fluorescence-spectral studies, cyclic voltammetry, and viscosity measurements have been carried out to assess the comparative binding of complexes 1 and 3 with calf thymus (CT)-DNA. Analysis of the results suggests that the new chiral complex 3 binds to CT-DNA through a partial intercalation mode that is different from the binding mode of parent achiral complex 1. The complexes 1 and 3 bind to CT-DNA with binding constants K(b) of 2.7 x 10(4) and 6.6 x 10(4) M(-1), respectively. Circular-dichroism (CD) studies have been further employed to ascertain the binding mode of complex 3, which is consistent with the other spectral studies.     

Synthesis, characterization, and DNA binding and cleavage properties of copper(II)-tryptophanphenyl-alanine-1,10-phenanthroline/2,2'-bipyridine complexes

The mononuclear dipeptide‐based Cu^II complexes [Cu^II(trp‐phe)(phen)(H₂O)] ⋅ ClO₄ ( 1 ) and [Cu^II(trp‐phe)(bpy)(H₂O)] ⋅ ClO₄ ( 2 ) (trp‐phe=tryptophanphenylalanine, phen=1,10‐phenanthroline, bpy=2,2′‐bipyridine) were isolated, and their interaction with DNA was studied. They exhibit intercalative mode of interaction with DNA. The intercalative interaction was quantified by Stern Volmer quenching constant (K_sq=0.14 for 1 and 0.08 for 2 ). The Cu^II complexes convert supercoiled plasmid DNA into its nicked circular form hydrolytically at physiological conditions at a concentration as low as 5 μM (for 1 ) and 10 μM (for 2 ). The DNA hydrolysis rates at a complex concentration of 50 μM were determined as 1.74 h⁻¹ (R=0.985) for 1 and 0.65 h⁻¹ (R=0.965) for 2 . The rate enhancement in the range of 2.40–4.10×10⁷‐fold compared to non‐catalyzed double‐stranded DNA is significant. This was attributed to the presence of a H₂O molecule in the axial position of the Cu complexes.     

Synthesis and characterization of a new macrocyclic copper(II) complex with an N-glycosidic pendant arm: in vitro cytotoxicity and binding studies with calf-thymus DNA

The new macrocyclic complex 2-amino-2-deoxy-N-[2-(1,3,5,8,11-pentaazacyclotridecan-3-yl)ethyl]-beta-D-glucopyranosylamine copper(II) dichloride (1a) was prepared and thoroughly characterized by various techniques. Molar-conductance measurements showed that 1a (and its Ni analogue 1b) are ionic in nature. On the basis of spectroscopic data, both complexes were assigned a square-planar geometry, and found to be highly stabile and hydrolytically robust in H2O over a wide range of pH, as confirmed by cyclic voltammetry (CV). The Cu(II) complex 1a was found to bind to CT-DNA, with a binding constant Kb of 2.4x10(3) M(-1), as derived by UV/VIS titration, and confirmed by CV, circular dichroism (CD), and viscosity measurements. DNA binding seems to occur mostly via H-bonding. In an in vitro antitumor MTT assay, 1a exhibited significant anticancer activity against the SY5Y and PC-12 cell lines, with an estimated IC50 value in the micromolar range for SYSY, similar to the standard drug 5-fluorouracil.     

Copper(II) PMDTA and copper(II) TMEDA complexes: precursors for the synthesis of dinuclear dicationic copper(II) complexes

Copper(II) cations coordinated with PMDTA (pentamethyldiethylenetriamine) and TMEDA (tetramethylethylenediamine) possess a high synthetic potential. The synthesis of these cations was carried out by metathesis reactions with silver salts. The cationic copper(II) complexes, [Cu(PMDTA)(Me₂CO)Cl]⁺, [Cu(PMDTA)(H₂O)Cl]⁺, [Cu(PMDTA)(DMF)]⁺, [Cu(PMDTA)Cl]⁺, [Cu(PMDTA)OAc]⁺, [Cu(PMDTA)(MeCN)₂]²⁺, [Cu₂(TMEDA)₂Cl₃]⁺ and [Cu(TMEDA)(MeCN)₃]²⁺ were synthesised as PF₆ salts, crystallised and characterised by single-crystal X-ray diffraction.     

Dinuclear terephthalato-bridged copper(II) complexes: Syntheses, spectral and structural characterization, and magnetic properties

Herein, we report the syntheses, spectral and structural characterization, and magnetic behavior of four new dinuclear terephthalato-bridged copper(II) complexes with formulae [Cu₂(trpn)₂(μ-tp)](ClO₄)₂ · 2H₂O (1), [Cu₂(aepn)₂(μ-tp)(ClO₄)₂] (2), [Cu₂(Medpt)₂(μ-tp)(H₂O)₂](ClO₄)₂ (3) and [Cu₂(Et₂dien)₂(μ-tp)(H₂O)](ClO₄)₂ (4) where tp = terephthalate dianion, trpn = tris(3-aminopropyl)-amin, aepn = N-(2-aminoethyl)-1,3-propanediamine, Medpt = 3,3′-diamino-N-methyldipropylmine and Et₂dien = N,N-diethyldiethylenetriamine. The structures of these complexes consist of two μ-tp bridging Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry of the Cu(II) ions in these compounds may be described as close to square-based pyramid (SP) with severe significant distortion towards trigonal bipyramid (TBP) stereochemistry in 1. The visible spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Cu(II) centers. Also, the solid infrared spectral data for the stretching frequencies of the tp-carboxalato groups, the ν(COO⁻) reveals the existence of bis(monodentate) coordination mode for the bridged terephthalate ligand. The susceptibility measurements at variable temperature over the range 2-300 K are reported. Despite the same bonding mode of the tp bridging ligand, there has been observed slight antiferromagnetic coupling for the compounds 1 and 4 with J values of −0.5 and −2.9 cm³ K mol⁻¹, respectively, and very weak ferromagnetic coupling for 2 and 3 with J values of 0.8 and 10.1 cm³ K mol⁻¹, respectively. The magnetic results are discussed in relation to other related μ-terephthalato dinuclear Cu(II) published compounds.     

Dinuclear fumarato- and terephthalato-bridged copper(II) complexes: Structural characterization and magnetic properties

The dinuclear dicarboxylato-bridged copper(II) complexes [Cu₂(TPA)₂(μ-tp)](ClO₄)₂ · H₂O (1), [Cu₂(TPA)₂(μ-fum)](ClO₄)₂ · 2H₂O (2) and [Cu₂(pmedien)₂(μ-fum)(H₂O)₂](ClO₄)₂ (3) (tp = terephthalate dianion, fum = fumarate dianion, TPA = tris(2-pyridylmethyl)amine and pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine) were synthesized and structurally characterized by X-ray crystallography. The structures of the TPA complexes 1 and 2 consist of μ-tp or μ-fum bridging two Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry around the Cu(II) ions in these compounds has a distorted trigonal bipyamidal geometry, TBP with four nitrogen atoms from the TPA ligand and a coordinated oxygen atom supplied by the carboxylate group of the bridged dicarboxylato ligand. Complex 3 has a distorted square pyramidal geometry achieved by the three N-atoms of the pmedien, one fum-carboxylate-oxygen and by an oxygen atom from a coordinated water molecule. The intradimer Cu…Cu distances in these complexes are 11.078(3), 8.663(4) and 9.520(3) Å for 1, 2 and 3, respectively. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Cu(II) centers. Also, analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(mondentate) coordination mode for the bridged dicarboxylato ligands in compounds 1 and 2. The susceptibility measurements at variable temperature over the 2-300 K range are reported. For 1-3, it has been observed slight antiferromagnetic coupling with J values of −0.8, −3.0 and −2.9 cm⁻¹, respectively.     

Mixed-ligand complexes of ruthenium(II) containing new photoactive or electroactive ligands: synthesis, spectral characterization and DNA interactions

Mixed-ligand ruthenium(II) complexes of three photoactive ligands, viz., (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-naphthyl)-1-ethene (mppne), (E)-1-(9-anthryl)-2-[2-(4-methyl-2-pyridyl)-4-pyridyl]-1-ethene (mppae) and (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-pyrenyl)-1-ethene (mpppe), in which a 2,2′-bipyridyl unit is linked via an ethylinic linkage to either a naphthalene, an anthracene or a pyrene chromophore and three electroactive ligands, viz., 4-(4-pyridyl)-1,2-benzenediol (catpy), 5,6-dihydroxy-1,10-phenanthroline (catphen) and 1,2-benzenediol (cat), were synthesized in good to moderate yields. Complexes [Ru(bpy)₂(mppne)]²⁺ (bpy is 2, 2′–bipyridyl), [Ru(bpy)₂(mppae)]²⁺, [Ru(bpy)₂(mpppe)]²⁺, [Ru(bpy)₂(sq-py)]⁺, [Ru(bpy)₂(sq-phen)]⁺ and [Ru(phen)₂(bsq)]⁺ (phen is 1,10-phenanthroline) were fully characterized by elemental analysis, IR, ¹H NMR, fast-atom bombardment or electron-impact mass, UV–vis and cyclic voltammetric methods. In the latter three complexes, the ligands catpy, catphen and cat are actually bound to the metal center as the corresponding semiquinone species, viz., 4-(4-pyridyl)-1,2-benzenedioleto(+I) (sq-py), 1,10-phenanthroline-5,6-dioleto(+I) (sq-phen) and 1,2-benzenedioleto(+I) (bsq), thus making the overall charge of the complexes formally equal to + 1 in each case. These three complexes are electron paramagnetic resonance active and exhibit an intense absorption band between 941 and 958 nm owing to metal-to-ligand charge transfer (MLCT, d _Ru→π*_sq) transitions. The other three ruthenium(II) complexes containing three photoactive ligands, mppne, mppae and mpppe, exhibit MLCT (d _Ru→π*_bpy ) bands in the 454–461-nm region and are diamagnetic. These can be characterized by the ¹H NMR method. [Ru(bpy)₂(mppne)]²⁺, [Ru(bpy)₂(mppae)]²⁺ and [Ru(bpy)₂(mpppe)]²⁺ exhibit redox waves corresponding to the Ru^III/Ru^II couple along with the expected ligand (bpy and substituted bpy) based ones in their cyclic and differential pulse voltammograms (CH₃CN, 0.1 M tetrabutylammonium hexafluorophosphate)—corresponding voltammograms of [Ru(bpy)₂(sq-py)]⁺, [Ru(bpy)₂(sq-phen)]⁺ and [Ru(phen)₂(bsq)]⁺ are mainly characterized by waves corresponding to the quinone/semiquinone (q/sq) and semiquinone/1,2-diol (sq/cat) redox processes. The results of absorption and fluorescence titration as well as thermal denaturation studies reveal that [Ru(bpy)₂(mppne)]²⁺ and [Ru(bpy)₂(mppae)]²⁺ are moderate-to-strong binders of calf thymus DNA with binding constants ranging from 10⁵ to 10⁶ M⁻¹. Under the identical conditions of drug and light dose, the DNA (supercoiled pBR 322) photocleavage activities of these two complexes follow the order:[Ru(bpy)₂(mppne)]²⁺>[Ru(bpy)₂(mppae)]²⁺, although the emission quantum yields follow the reverse order. The other ruthenium(II) complexes containing the semiquinone-based ligands are found to be nonluminescent and inefficient photocleavage agents of DNA. However, experiments shows that [Ru(bpy)₂(sq)]⁺-based complexes oxidize the sugar unit and could be used as mild oxidants for the sugar moiety of DNA. Possible explanations for these observations are presented.Electronic Supplementary Material Supplementary material is available for this article at .     

Copper(II) complexes of salicylaldehyde hydrazones: synthesis, structure, and DNA interaction

Three hydrazone ligands, H2L1-H2L3, made from salicylaldehyde and ibuprofen- or naproxen-derived hydrazides, were prepared and transformed into the corresponding copper(II) complexes [Cu(II)L1] x H2O, [Cu(II)L2], and [(Cu(II))2(L3)2] x H2O x DMF (Scheme). The X-ray crystal structure of the last-mentioned complex was solved (Fig. 1), showing a square-planar complexation geometry, and the single units were found to form a one-dimensional chain structure (Fig. 2). The interactions of these complexes with CT-DNA were studied by different techniques, indicating that they all bind to DNA by classical and/or non-classical intercalation modes.     

Squarato-metal(II) complexes. 1: Structural and magnetic characterization of squarato-bridged dinuclear nickel(II) and copper(II) complexes

A new series of dinuclear squarato-bridged nickel(II) and copper(II) complexes [Ni₂(2,3,2-tet)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (1), [Ni₂(aepn)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (2), [Cu₂(pmedien)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂.4H₂O (3) and [Cu₂(DPA)₂(μ_1,2-C₄O₄)(H₂O)₂](ClO₄)₂ (4) where is the dianion of 3,4-dihydroxycyclobut-3-en-1,2-dione (squaric acid), 2,3,2-tet = 1,4,8,11-tetraazaundecane, aepn = N-(2-aminoethyl)-1,3-propanediamine, pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine and DPA = di(2-pyridylmethyl)amine were synthesized and structurally characterized by X-ray crystallography. The spectral and structural characterization as well as the magnetic behaviour of these complexes is reported. In this series, structures consist of the groups as counter ions and the bridging the two M(II) centers in a μ-1,3- (1-3) and in a μ-1,2-bis(monodentate) (4) bonding fashions. The coordination geometry around the Ni(II) ions in 1 and 2 is six-coordinate with distorted octahedral environment achieved by N atoms of the amines and by one or two oxygen atoms from coordinated water molecules, respectively. In the Cu(II) complexes 3 and 4, a distorted square pyramidal geometry is achieved by the three N-atoms of the aepn or DPA and by an oxygen atom from a coordinated water molecule. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the M(II) centers. The complexes show weak antiferromagnetic coupling with ∣J∣ = 1.8-4.2 cm⁻¹ in the μ-1,3- bridged squarato compounds 1-3, and J = −16.1 cm⁻¹ in the corresponding μ-1,2- bridged squarato complex 4. The magnetic properties are discussed in relation to the structural data.     

DNA binding and nuclease activity of copper(II) complexes of tridentate ligands

Two copper(II) complexes, 1 and 2 with L₁ and L₂ [L₁ = 2-hydroxybenzyl(2-(pyridin-2-yl)ethylamine); L₂ = 2-hydroxybenzyl(2-(pyridin-2-yl)methylamine)] ligands, respectively, have been synthesized and characterized. The interaction of both the complexes with DNA has been studied to explore their potential biological activity. The DNA binding properties of the complexes with calf thymus (CT) DNA were studied by spectroscopic titration. The complexes show binding affinity to CT DNA with binding constant (K_b) values in the order of 10⁵ M⁻¹. Thermal denaturation and circular dichroism studies suggest groove binding of the complexes to CT DNA. Complexes also exhibit strong DNA cleavage activity in presence of reducing agents like 3-mercaptopropionic acid and β-mercaptoethanol. Mechanistic studies reveal the involvement of reactive hydroxyl radicals for their DNA cleavage activity.     

Ternary nickel(II) complexes as hydrolytic DNA-cleavage agents

A series of small model complexes made from Ni(II) and the ligands ethylenediamine (en), histamine (hist), and histidylleucine (HisLeu) were prepared and studied as potential hydrolytic DNA-cleavage agents. The stability constants and species-distribution curves for these complexes were determined as a function of pH. The 1 : 1 : 1 ternary complexes [Ni(II)(en)(HisLeu)] (1) and [Ni(II)(hist)(HisLeu)] (2) were the only major species present at the physiologically relevant pH of 6-7, as further corroborated by ESI-MS analysis. The complex geometries of 1 and 2 were analyzed by UV/VIS experiments and molecular dynamics (MD) simulations. Both ternary complexes were found to intercalate with DNA, as shown by UV/VIS, thermal-denaturation, and fluorescence-titration studies with ethidium bromide (EB). The intrinsic binding constants (K(b)) for the bound complexes 1DNA and 2DNA were determined as 150 and 290, resp. Gel-electrophoresis experiments revealed that 1 and 2 cleave supercoiled (type-I) to nicked-circular (type-II) DNA at physiological pH, with rate constants of 0.64 and 0.75 h(-1), resp. A tentative mechanism for this hydrolytic cleavage is proposed.     

Synthesis and DNA-cleavage properties of metal complexes of 1,4,7,10-tetraazacyclododecane (cyclen) functionalized with a pendant benzocrown ether

The synthesis and DNA-cleavage properties of a series of novel mononuclear Zn(II), Cu(II), and Co(II) complexes 2 of a crown-ether-functionalized cyclen ligand is described. The Cu complex 2b displayed the highest catalytic activity towards pUC 19 DNA. The effects of reaction time, complex concentration, and pH were investigated, showing that 2b readily and efficiently converts supercoiled (type I ) plasmid DNA to nicked (type II) DNA under physiological conditions (37 degrees, pH 7.4).     

Copper(II) complexes as superoxide dismutase mimics: Synthesis, characterization, crystal structure and bioactivity of copper(II) complexes

Two new copper(II) complexes of the type [Cu(L)X₂), where L = (E)-N-phenyl-2-[phenyl (pyridine-2-yl)methylene]hydrazinecarboxamide X = Cl/Br have been synthesized and characterized by elemental analyses, FAB (fast atomic bombardment) magnetic measurements, electronic absorption, conductivity measurements cyclic voltammetry (CV) and Electron paramagnetic resonance (epr) spectroscopy. The structures of these complexes determined by single crystal X-ray crystallography show a distorted square based pyramidal (DSBP) geometry around copper(II) metal center. The distorted CuN₂OX (X = Cl/Br) basal plane in them is comprised of two nitrogen and one oxygen atoms of the meridionally coordinated ligand and a chloride or bromide ion and axial position is occupied by other halide ion. The epr spectra of these complexes in frozen solutions of DMSO showed a signal at g ca. 2. The trend in g-value (g_|| > g_⊥ > 2.00) suggest that the unpaired electron on copper(II) has d_x²-y² character. Biological activities in terms of superoxide dismutase (SOD) and antimicrobial properties of copper(II) complexes have also been measured. The superoxide dismutase activity reveals that these two complexes catalyze the fast disproportionation of superoxide in DMSO solution.     

Synthesis and characterisation of copper(II), zinc(II) and cobalt(II) complexes of salicylglycine, a metabolite of aspirin

Copper(II), nickel(II) and cobalt(II) complexes of the aspirin metabolite salicylglycine (H₂L), of stoichiometry M(HL)₂·solvate, have been prepared and characterised. In these complexes salicylglycinate is coordinated to the metal via its carboxylato group and possibly also its amide oxygen in the copper(II) complex. Under basic conditions copper(II) forms the complex Cu(LH₋₁)·2H₂O·MeOH, in which the ligand is coordinated to the metal via its carboxylate and phenolate oxygen atoms and the deprotonated peptide nitrogen atom.     

Dinuclear copper(II) complexes with valsartan. Synthesis, characterization and cytotoxicity

Two novel dinuclear complexes involving the antihypertensive drug valsartan and copper(II) ion have been prepared in water and DMSO. The complex compositions were determined as: [Cu(vals)(H₂O)₃]₂.6H₂O and [Cu(vals)(H₂O)₂DMSO]₂.2H₂O. They were thoroughly characterized by elemental and thermal analysis, spectrophotometric titrations and UV-visible, diffuse reflectance, FTIR, Raman and EPR spectroscopies. No effect of the ligand on two tested osteoblastic cell lines in culture (one normal MC3T3E1 and one tumoral UMR106) was observed in concentrations up to 100 μM. Higher concentrations of Valsartan are required to induce cytotoxicity in both cell lines. The antiproliferative effect of the tested complex ([Cu(vals)(H₂O)₃]₂.6H₂O) in a dose-response manner, was higher in the UMR106 osteoblastic cell line than that of the MC3T3E1 normal line at concentrations ≥ 100 μM. Morphological alterations are in accordance with proliferative observations.     

Cyanato bridged binuclear nickel(II) and copper(II) complexes with pyridylpyrazole ligand: Synthesis, structure and magnetic properties

Binuclear cyanate bridged nickel(II) complex [Ni(L)(NCO)]₂(PF₆)₂ (1) and copper(II) complex [Cu(L)(NCO)]₂(PF₆)₂ (2), where L is N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine, a tetradentate N₄-coordinated ligand have been synthesized and characterized by physicochemical method. The structures of complexes 1 and 2 have been studied by single crystal X-ray diffraction analysis. The structure analysis reveals that both nickel(II) and copper(II) center are coordinated in distorted octahedral fashion and coordination mode of cyanate ligand is end-to-end (μ-1,3) for complex 1 but it is double end-on (μ-1,1) mode for complex 2. The variable temperature magnetic susceptibility data, measured from 2 to 300 K, show weak antiferromagnetic interaction with J value −6.2(1) cm⁻¹ for complex 1, whereas complex 2 has very weak ferromagnetic interaction with J value +0.5(1) cm⁻¹.     

Homoleptic copper(II) and copper(I) complexes of 5,6-dihydro-5,6-epoxy-1,10-phenanthroline. Six-coordinate copper(I) in solution

Reaction of 5,6-dihydro-5,6-epoxy-1,10-phenanthroline (L) with Cu(ClO₄)₂·6H₂O in methanol in 3:1 M ratio at room temperature yields light green [CuL₃](ClO₄)₂·H₂O (1). The X-ray crystal structure of the hemi acetonitrile solvate [CuL₃](ClO₄)₂·0.5CH₃CN has been determined which shows Jahn-Teller distortion in the CuN₆ core present in the cation [CuL₃]²⁺. Complex 1 gives an axial EPR spectrum in acetonitrile-toluene glass with g_|| = 2.262 (A_|| = 169 × 10⁻⁴ cm⁻¹) and g_⊥ = 2.069. The Cu(II/I) potential in 1 in CH₂Cl₂ at a glassy carbon electrode is 0.32 V versus NHE. This potential does not change with the addition of extra L in the medium implicating generation of a six-coordinate copper(I) species [CuL₃]⁺ in solution. B3LYP/LanL2DZ calculations show that the six Cu-N bond distances in [CuL₃]⁺ are 2.33, 2.25, 2.32, 2.25, 2.28 and 2.25 Å while the ideal Cu(I)-N bond length in a symmetric Cu(I)N₆ moiety is estimated as 2.25 Å. Reaction of L with Cu(CH₃CN)₄ClO₄ in dehydrated methanol at room temperature even in 4:1 M proportion yields [CuL₂]ClO₄ (2). Its ¹H NMR spectrum indicates that the metal in [CuL₂]⁺ is tetrahedral. The Cu(II/I) potential in 2 is found to be 0.68 V versus NHE in CH₂Cl₂ at a glassy carbon electrode. In presence of excess L, 2 yields the cyclic voltammogram of 1. From ¹H NMR titration, the free energy of binding of L to [CuL₂]⁺ to produce [CuL₃]⁺ in CD₂Cl₂ at 298 K is estimated as −11.7 (±0.2) kJ mol⁻¹.     

Oxalate, squarate and croconate complexes with bis(2-pyrimidylcarbonyl)amidatecopper(II): synthesis, crystal structures and magnetic properties

The preparation and magnetic properties of three copper(II) compounds of formulae [Cu₂(bpcam)₂(H₂O)₂(C₂O₄)] (1), [Cu₂(bpcam)₂(H₂O)₄(C₄O₄)] · 10 H₂O (2) and Cu₂(bpcam)₂(C₅O₅)(H₂O)₃ (3) [bpcam = bis(2-pyrimidyl)amidate, and are reported. The structures of two of them (1 and 2) have been solved by single crystal X-ray diffraction and consists of centrosymmetric discrete copper(II) dinuclear units bridged by bis-bidentate oxalate (1) and bis-monodentate squarate (2), with the bpcam group acting as a terminal tridentate ligand. Each copper atom in 1 exhibits a distorted elongated octahedral coordination geometry. Three bpcam nitrogen atoms and one oxalate oxygen define the basal plane while the other oxalate oxygen and a water molecule take up the axial positions. Each copper atom in 2 is in an elongated octahedral surrounding with three bpcam nitrogen atoms and one squarate oxygen in the equatorial plane and two water molecules in the axial positions. The intramolecular copper-copper separations are 5.677(1) (1) and 7.819(53) Å (2). Magnetic susceptibility measurements for 1-3 in the temperature range 1.9-290 K show the occurrence of weak ferromagnetic interactions through oxalato (J = +0.75 cm⁻¹) and squarato (J = +1.26 cm⁻¹), the Hamiltonian being defined by . These values are analyzed and discussed in the light of the available magneto-structural data for analogous systems. The quasi-Curie law observed in 3 (θ = −1.15 K) contrasts with the significant antiferromagnetic interaction through bis-chelating croconate in other structurally characterized croconate-bridged copper(II) complexes and rules out the presence of bridging croconate in this compound.     

Mononuclear copper(II) complexes with quinolones and nitrogen-donor heterocyclic ligands: Synthesis, characterization, biological activity and interaction with DNA

The neutral mononuclear copper(II) complexes with the quinolone antibacterial drugs, pipemidic acid and N-propyl-norfloxacin, in the presence or absence of nitrogen-donor heterocyclic ligands, 2,2′-bipyridine, 1,10-phenanthroline or 2,2′-dipyridylamine, have been prepared and characterized spectroscopically. The interaction of copper(II) with the deprotonated quinolone ligand leads to the formation of the neutral mononuclear complexes of the type [Cu(quinolone)₂(H₂O)] (1)–(2) while the presence of the N-donor ligand leads to the formation of the neutral mononuclear complexes of the type [Cu(quinolone)(N-donor)Cl] (3)–(8). In all the complexes, copper(II) is pentacoordinate having a distorted square pyramidal geometry. The electron paramagnetic resonance spectra of 1 and 2 are typical of mononuclear Cu(II) complexes, while for the mixed-ligands complexes 3–8 a mixture of dimeric and monomeric species is indicated. The interaction of the complexes with calf-thymus DNA has been investigated with diverse spectroscopic techniques and has shown that the complexes can be bound to calf-thymus DNA by the intercalative mode. The antimicrobial activity of the complexes has been tested on three different microorganisms. All the complexes show an increased biological activity in comparison to the corresponding free quinolone ligand.     

Synthesis and DNA binding/cleavage of mononuclear copper(II) phenanthroline/bipyridine proline complexes

The complexes [Cu(II)(phen)(L-Pro)(H2O)]+ ClO4(-) (1; phen = 1,10-phenanthroline) and [Cu(II)(bipy)(L-Pro)(H2O)]+ ClO4(-) (2; bipy = 2,2'-bipyridine) were synthesized and characterized by IR, magnetic susceptibility, UV/VIS, EPR, ESI-MS, elemental analysis, and theoretical calculations. The metal center was found in a square-pyramidal geometry. UV/VIS, thermal-denaturation, and fluorescence-spectroscopic studies were conducted to assess the interaction of the complexes with CT-DNA. An intercalative mode of binding was found, with intrinsic binding constants (Kb) of 3.86x10(3) and 4.6x10(3) M(-1) and Stern-Volmer quenching constants (K) of 0.15 and 0.11 for 1 and 2, respectively. Interestingly, none of the Cu(II) complexes was able to cleave pUC-19 DNA, which is attributed to the absence of a Pro amide H-atom and inhibition of the formation of an OH radical from the axially coordinated H2O molecule.