Paramagnetic Copper Centers Research Articles

Unraveling Multicopper [Cu3] and [Cu6] Clusters with Rare μ3-Sulfato and Linear μ2-Oxido-Bridges as Potent Antibiofilm Agents against Multidrug-Resistant Staphylococcus aureus.

In this research article, two multicopper [Cu3] and [Cu6] clusters, [Cu3(cpdp)(μ3-SO4)(Cl)(H2O)2]·3H2O (1) and [Cu6(cpdp)2(μ2-O)(Cl)2(H2O)4]·2Cl (2) (H3cpdp = N,N'-bis[2-carboxybenzomethyl]-N,N'-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol), have been explored as potent antibacterial and antibiofilm agents. Their molecular structures have been determined by a single-crystal X-ray diffraction study, and the compositions have been established by thermal and elemental analyses, including electrospray ionization mass spectrometry. Structural analysis shows that the metallic core of 1 is composed of a trinuclear [Cu3] assembly encapsulating a μ3-SO42- group, whereas the structure of 2 represents a hexanuclear [Cu6] assembly in which two trinuclear [Cu3] motifs are exclusively bridged by a linear μ2-O2- group. The most striking feature of the structure of 2 is the occurrence of an unusual linear oxido-bridge, with the Cu3-O6-Cu3' bridging angle being 180.00°. Whereas 1 can be viewed as an example of a copper(II)-based compound displaying a rare μ3:η1:η1:η1 bridging mode of the SO42- group, 2 is the first example of any copper(II)-based compound showing an unsupported linear Cu-O-Cu oxido-bridge. Employing variable-temperature SQUID magnetometry, the magnetic susceptibility data were measured and analyzed exemplarily for 1 in the temperature range of 2-300 K, revealing the occurrence of antiferromagnetic interactions among the paramagnetic copper centers. Both 1 and 2 exhibited potent antibacterial and antibiofilm activities against methicillin-resistant Staphylococcus aureus (MRSA BAA1717) and the clinically isolated culture of methicillin-resistant S. aureus (MRSA CI1). The mechanism of antibacterial and antibiofilm activities of these multicopper clusters was investigated by analyzing and determining the intracellular reactive oxygen species (ROS) generation, lipid peroxidation, microscopic observation of cell membrane disruption, membrane potential, and leakage of cellular components. Additionally, 1 and 2 showed a synergistic effect with commercially available antibiotics such as vancomycin with enhanced antibacterial activity. However, 1 possesses higher antibacterial, antibiofilm, and antivirulence actions, making it a potent therapeutic agent against both MRSA BAA1717 and MRSA CI1 strains.

Novel copper(II) coordination polymer containing the drugs nalidixic acid and 8-hydroxyquinoline: Evaluation of the structural, magnetic, electronic, and antitumor properties

Herein we describe the synthesis, structural characterization, physical/spectroscopic studies and evaluation of the antitumoral activity of a new copper(II) coordination polymer, [Cu(ndx)(8-hq)]n, where H(ndx) is nalidixic acid and H(8-hq) is 8-hydroxyquinoline. Single crystal X-ray diffraction shows a zigzag polymeric chain, where the adjacent copper atoms are connected via anti-anti μ-carboxylate bridge of ndx. This structural feature is quite different from those previously proposed for quinolone complexes. Variable-temperature magnetic susceptibility measurements showed weak antiferromagnetic interactions between the paramagnetic copper centers (−0.49 cm−1). In solution, the compound exists as neutral mononuclear species and it can inhibit the growth of a human chronic myelogenous leukemia cell line (K562) in a concentration-dependent manner with IC50 value lower than those of the corresponding free ligands. At similar doses, the compound does not alter the viability of human keratinocytes (HaCaT cell line). Spectroscopic data and viscosity measurements show that the compound binds to DNA (Kb = 2.47 × 105 M−1) interacting with it by a non-intercalative mode.

Dinuclear and tetranuclear complexes of copper coordinated by an anthracene-based new μ-bis(tridentate) ligand: Synthesis, structure, spectroscopy and magnetic properties

Copper(II) complexes of an anthracene-based new μ-bis(tridentate) ligand, N,N′-bis[anthracene-2-ylmethyl]-N,N′-bis[carboxymethyl]-1,3-diaminopropan-2-ol (H3acdp) with mixed donating groups, have been studied in solid state as well as in solution. The reaction of stoichiometric amounts of CuSO4·5H2O and the ligand H3acdp in the presence of NaOH at ambient temperature in methanol-dichloromethane, afforded a new dinuclear copper complex, [Cu2(acdp)(MeO)(MeOH)2] (1). On the other hand, the reaction of stoichiometric amounts of Cu(OAc)2·H2O and the ligand H3acdp in the presence of NaOH at ambient temperature in methanol-dichloromethane yielded, a novel tetranuclear copper complex, [Cu4(acdp)2(μ-OAc)2(MeOH)2]·2CH2Cl2·2CH3OH (2). Characterization of the complexes has been carried out by various analytical techniques including single crystal X-ray crystallography. The X-ray structure analyses show that the complex 1 consists of a distorted square planar copper center and a distorted square pyramidal copper center with Cu⋯Cu separation of 3.589(4)Å, whereas the complex 2 comprises four distorted square pyramidal copper centers with average intra-ligand Cu⋯Cu separation of 3.358(6)Å. The molecular architecture of complex 2 is built from the self-assembly of two neutral [Cu2(acdp)(μ-OAc)] units which are exclusively bridged by two carboxylate functionalities of the ligand. To be acquainted with the binding events of copper(II) ions with H3acdp and the structural features of the complexes in solution, UV–Vis and fluorescence titration experiments have been executed. The composition of the acdp3−/Cu2+ complexes in 1 and 2 has been found to be 1:2, based on the UV–Vis/fluorescence titration results and further confirmed by X-ray crystallography. Variable-temperature (2–300K) magnetic susceptibility measurements on powdered microcrystalline samples show that the paramagnetic copper centers in complex 2 are antiferromagnetically coupled to one another.

Copper ESEEM and HYSCORE through ultra-wideband chirp EPR spectroscopy.

The main limitation of pulse electron paramagnetic resonance (EPR) spectroscopy is its narrow excitation bandwidth. Ultra-wideband (UWB) excitation with frequency-swept chirp pulses over several hundreds of megahertz overcomes this drawback. This allows to excite electron spin echo envelope modulation (ESEEM) from paramagnetic copper centers in crystals, whereas up to now, only ESEEM of ligand nuclei like protons or nitrogens at lower frequencies could be detected. ESEEM spectra are recorded as two-dimensional correlation experiments, since the full digitization of the electron spin echo provides an additional Fourier transform EPR dimension. Thus, UWB hyperfine-sublevel correlation experiments generate a novel three-dimensional EPR-correlated nuclear modulation spectrum.

Water‐Soluble Heteronuclear [NaCuII6] Metallomacrocyclic Sandwich Complexes: Synthesis, Structure, Properties and In Vitro Biological Studies

AbstractThe water‐soluble heteronuclear metallomacrocyclic sandwich clusters [NaCu6(hpnbpda)3(OH)3(OH2)3](NO3)·4H2O (1), [NaCu6(hpnbpda)3(OH)3(OH2)3](ClO4) (2), and [NaCu6(hpnbpda)3(OH)3(OH2)3](PF6) (3) [H3hpnbpda = N,N′‐bis(2‐pyridylmethyl)‐2‐hydroxy‐1,3‐propanediamine‐N,N′‐diacetic acid] have been synthesized in methanol at room temperature and fully characterized using several analytical techniques including single‐crystal X‐ray diffraction. The molecular architecture of complex 1 is built from the template assembly of three dinuclear [Cu2(hpnbpda)]+ fragments through their weak oxophillic interactions with a central sodium(I) cation. A close analysis of the single‐crystal X‐ray structure reveals that the metallic core of cluster 1 consists of six highly distorted octahedral CuII ions arranged at the corners of a trigonal prism that encapsulates the sodium(I) ion. Complex 1 displays a rare μ3:η2:η1:η1 bridging mode of six carboxylate groups of three hpnbpda3– ligands with each bridging between two copper(II) atoms and the sodium(I) center. Variable‐temperature magnetic‐susceptibility measurements (2–300 K) on a powdered microcrystalline sample reveal that the paramagnetic copper centers in complex 1 are antiferromagnetically coupled to one another. Systematic biological investigation such as cytotoxicity assessment, DNA content analysis in terms of cell‐cycle distribution by means of the fluorescence‐activated cell sorting (FACS) method, DNA binding, DNA cleavage, and the underlying mechanism of possible apoptotic cell‐death events in human cervical cancer cells (HeLa) were carried out in detail using complex 1. The in vitro assays using complex 1 in HeLa cells provided new findings that indicate its possible future therapeutic application. Theoretical calculations were carried out to find the Fukui functions at the metal sites in complex 1 to predict the possible metal centers involved in the DNA binding.

Paramagnetic copper centers in ferroelectric lead germanate with halogens

The electron paramagnetic resonance spectrum of triclinic bivalent copper centers in copper-doped Pb5Ge3O11 single crystals has been investigated. The spectrum intensity increases after thermal treatment in a chlorine- or fluorine-containing atmosphere. The parameters of the electron Zeeman, hyperfine, and nuclear quadrupole interactions have been determined. The model of the observed centers has been proposed.

Formation of out of plane oxime metallacycles in [Cu 2] and [Cu 4] complexes

The reaction of Cu(ClO 4) 2·6H 2O with dimethylglyoxime (H 2dmg) in a 1:1 mole ratio in aqueous methanol at room temperature affords the dinuclear complex [Cu 2( μ-Hdmg) 4] ( 1). Reaction of 1 with [Cu(bpy)(H 2O) 2](ClO 4) 2 (bpy = 2,2′-bipyridine) in a 1:1 mole ratio in aqueous methanol at room temperature yields the tetranuclear complex [Cu 4( μ-Hdmg) 2( μ-dmg) 2(bpy) 2(H 2O) 2](ClO 4) 2 ( 2). The direct reaction of Cu(ClO 4) 2·6H 2O with H 2dmg and bpy in a 2:2:1 mole ratio in aqueous methanol at room temperature also yields 2 quantitatively. The complexes 1 and 2 were structurally characterized by X-ray crystallography. Unlike the binding in Ni/Co-dmg, two different types of N−O bridging modes during the oxime based metallacycle formation and stacking of square planar units have been identified in these complexes. The neutral dinuclear complex 1 has CuN 4O coordination spheres and complex 2 consists of a dicationic [Cu 4( μ-Hdmg) 2( μ-dmg) 2(bpy) 2(H 2O) 2] 2+ unit and two uncoordinated ClO 4 − anions having CuN 4O and CuN 2O 3 coordination spheres. The two copper(II) ions are at a distance of 3.846(8) Å in 1 for the trans out of plane link and at 3.419(10) and 3.684(10) Å in 2 for the trans out of plane and cis in plane arrangements, respectively. The average Cu–N oxime distances are 1.953 and 1.935 Å, respectively. The average basal and apical Cu−O oxime distances are 1.945, 2.295 and 2.429 Å. The UV–Vis spectra of 2 is similar to the spectrum of the reaction mixture of 1 and [Cu(bpy)(H 2O) 2] 2+. Variable temperature magnetic properties measurement shows that the interaction between the paramagnetic copper centers in complex 1 is antiferromagnetic in nature. The EPR spectra of frozen solution of the complexes at 77 K consist of axially symmetric fine-structure transitions (Δ M S = 1) and half-field signals (Δ M S = 2) at ca. 1600 G, suggesting the presence of appreciable Cu–Cu interactions.

Copper in α-C:H films: Low temperatures

Microwave power absorption in copper-modified α-C:H films (maximum copper content, 8%) was studied in the 3.8–20 K temperature range. The EPR spectrum is interpreted as being due to a strongly anisotropic absorption of isolated paramagnetic copper centers. A model for the formation of paramagnetic copper centers involving oxygen atoms is proposed. At temperatures above 18 K, the system exhibits a nonresonance absorption of the microwave power. The temperature dependence of this absorption signal is described by an exponential law with the parameter ΔE=250±30 K. This temperature dependence is explained assuming the existence of copper nanoclusters. The ΔE value can be considered as the depth of an energy well corresponding to the nanocluster formation.

The electron paramagnetic resonance in copper-modified amorphous carbon

Room-temperature EPR spectra of copper-modified α-C:H films exhibit signals due to the isolated paramagnetic copper centers and dangling carbon bonds. An analysis of variation of the EPR signal intensity depending of the annealing temperature (Ta≤300°C) and relaxation of the EPR and IR absorption signals upon annealing indicates that the annealing-induced modification of the α-C:H films involves hydrogen and oxygen impurities in the amorphous carbon matrix.

Paramagnetic copper centers in ZnS

The results of studies by electron paramagnetic resonance of Cu-doped ZnS crystals are presented and discussed along with similar results of other impurities having the d 9 electron configuration in additional crystals. There are ten copper centers in ZnS, and altogether properties of twenty-three related centers are tabulated. The observations are grouped into five classes, each having rather similar characteristics. Plausible models for a few centers are discussed.