On the possible roles of N-terminal His-rich domains of Cu,Zn SODs of some Gram-negative bacteria

The Cu,Zn superoxide dismutases (Cu,Zn SOD) isolated from some Gram-negative bacteria possess a His-rich N-terminal metal binding extension. The N-terminal domain of Haemophilus ducreyi Cu,Zn SOD has been previously proposed to play a copper(II)-, and may be a zinc(II)-chaperoning role under metal ion starvation, and to behave as a temporary (low activity) superoxide dismutating center if copper(II) is available. The N-terminal extension of Cu,Zn SOD from Actinobacillus pleuropneumoniae starts with an analogous sequence (HxDHxH), but contains considerably fewer metal binding sites. In order to study the possibility of the generalization of the above mentioned functions over all Gram-negative bacteria possessing His-rich N-terminal extension, here we report thermodynamic and solution structural analysis of the copper(II) and zinc(II) complexes of a peptide corresponding to the first eight amino acids (HADHDHKK-NH₂, L) of the enzyme isolated from A. pleuropneumoniae. In equimolar solutions of Cu(II)/Zn(II) and the peptide the MH₂L complexes are dominant in the neutral pH-range. L has extraordinary copper(II) sequestering capacity (K_D,Cu = 7.4 × 10^− 13 M at pH 7.4), which is provided only by non-amide (side chain) donors. The central ion in CuH₂L is coordinated by four nitrogens {NH₂,3N_im} in the equatorial plane. In ZnH₂L the peptide binds to zinc(II) through a {NH₂,2N_im,COO⁻} donor set, and its zinc binding affinity is relatively modest (K_D,Zn = 4.8 × 10^− 7 M at pH 7.4). Consequently, the presented data do support a general chaperoning role of the N-terminal His-rich region of Gram-negative bacteria in copper(II) uptake, but do not confirm similar function for zinc(II). Interestingly, the complex CuH₂L has very high SOD-like activity, which may further support the multifunctional role of the copper(II)-bound N-terminal His-rich domain of Cu,Zn SODs of Gram-negative bacteria. The proposed structure for the MH₂L complexes has been verified by semiempirical quantum chemical calculations (PM6), too.     

Growth, reproductive and photosynthetic responses to copper in the yellow-horned poppy, Glaucium flavum Crantz.

Glaucium flavum Crantz. is found in an anthropized coastal grassland at the joint estuary of the Tinto and Odiel rivers (SW Spain), growing under the influence of high levels of copper contamination derived from nearby petrochemical industries, with no obvious adverse affects on the performance of the plant. In addition, this species exhibits a series of ecological characteristics which may render it appropriate for use in the phytoremediation of contaminated areas. Nonetheless, the response of G. flavum to elevated copper concentrations has not been studied. A greenhouse experiment was conducted to investigate the effects of a range of Cu concentrations (0 to 47 mmol l⁻¹) on the growth, reproduction and photosynthetic performance of G. flavum, by measuring relative growth rate, fruit and seed production, chlorophyll fluorescence parameters, gas exchange and photosynthetic pigment concentrations. We also determined total copper, nitrogen, phosphorous, sulphur, calcium and magnesium concentrations. G. flavum survived with concentrations of up to 730 mg Cu kg⁻¹ DW in the leaves, when treated with 30 mmol Cu l⁻¹ (2000 mg l⁻¹). Quantum efficiency of PSII, net photosynthesis rate, as well as leaf Ca and Mg concentrations were all negatively affected by Cu concentrations greater than 9 mmol l⁻¹ in the nutrient solution. Our results indicate that the reduction in photosynthetic performance may be attributed to the adverse effect of excess Cu on the photosynthetic apparatus of the plant, both directly, via a decrease in pigment concentrations, and indirectly, via interference of Cu with Ca ions of PSII. Growth and seed production were only slightly affected by leaf tissue concentrations as high as 230 mg Cu kg⁻¹ dry mass, which suggests that this species could play an important role in phytoremediation of Cu-contaminated soils.     

Copper and zinc binding properties of the N-terminal histidine-rich sequence of Haemophilus ducreyi Cu,Zn superoxide dismutase

The Cu,Zn superoxide dismutase (Cu,ZnSOD) isolated from Haemophilus ducreyi possesses a His-rich N-terminal metal binding domain, which has been previously proposed to play a copper(II) chaperoning role. To analyze the metal binding ability and selectivity of the histidine-rich domain we have carried out thermodynamic and solution structural analysis of the copper(II) and zinc(II) complexes of a peptide corresponding to the first 11 amino acids of the enzyme (H₂N-HGDHMHNHDTK-OH, L). This peptide has highly versatile metal binding ability and provides one and three high affinity binding sites for zinc(II) and copper(II), respectively. In equimolar solutions the MHL complexes are dominant in the neutral pH-range with protonated lysine ε-amino group. As a consequence of its multidentate nature, L binds zinc and copper with extraordinary high affinity (K_D,Zn = 1.6 × 10⁻⁹ M and K_D,Cu = 5.0 × 10⁻¹² M at pH 7.4) and appears as the strongest zinc(II) and copper(II) chelator between the His-rich peptides so far investigated. These K_D values support the already proposed role of the N-terminal His-rich region of H. ducreyi Cu,ZnSOD in copper recruitment under metal starvation, and indicate a similar function in the zinc(II) uptake, too. The kinetics of copper(II) transfer from L to the active site of Cu-free N-deleted H. ducreyi Cu,ZnSOD showed significant pH and copper-to-peptide ratio dependence, indicating specific structural requirements during the metal ion transfer to the active site. Interestingly, the complex CuHL has significant superoxide dismutase like activity, which may suggest multifunctional role of the copper(II)-bound N-terminal His-rich domain of H. ducreyi Cu,ZnSOD.     

EDTA-assisted phytoextraction of heavy metals by turfgrass from municipal solid waste compost using permeable barriers and associated potential leaching risk

A column experiment with horizontal permeable barriers was conducted to investigate phytoextraction of heavy metals by Lolium perenne L. from municipal solid waste compost following EDTA application, as well as to study the effects of L. perenne and permeable barriers on preventing metal from leaching. In columns with barriers, EDTA addition yielded maximum concentrations of Cu, Zn and Pb of 155, 541 and 33.5 mg kg⁻¹ in shoot, respectively. This led to 4.2, 2.1 and 7.4 times higher concentrations of Cu, Zn and Pb compared to treatment with no chelating agent, respectively. In treatments with 10 mmol kg⁻¹ EDTA, the barriers reduced leaching of Cu, Zn and Pb by approximately three times, respectively, resulting in leaching of total initial Cu, Zn and Pb by 27.3%, 25.2% and 28.8%, respectively, after four times’ irrigation. These results indicate that L. perenne and permeable barriers are effective to reduce leaching of heavy metals and minimize the risk of contaminating groundwater in EDTA-enhanced phytoremediation. Thus these findings highlight that turfgrass and permeable barriers can effectively prevent metal leaching.     

Effects of vegetation and fertilizer on metal and Sb plant uptake in a calcareous shooting range soil

Shooting range soils frequently contain anomalous concentrations of metals (e.g. Pb, Zn, Mn) and Sb coming from bullets which may be released into the environment. In a pot experiment, we investigated metal and Sb uptake by three plant species (Plantago lanceolata, Lolium perenne and Triticum aestivum) growing on a calcareous shooting range soil (pH 7.8; 500 mg kg⁻¹ Pb, 21 mg kg⁻¹ Sb) and the uptake changes when an acidic fertilizer solution was applied to the soil. Metal and Sb solubility in the soil was determined by extraction with 0.1 M NaNO₃. In addition, we measured pH, electrical conductivity and dissolved organic carbon in drainage samples. The results showed significant increase over time of pH (from 7.8 to 8.3) and decrease of electrical conductivity and dissolved organic carbon (from 230 to ∼130 mg L⁻¹). Fertilizer application increased NaNO₃-extractable Pb and Sb and root:shoot biomass ratio but not plant metal uptake. In T. aestivum spikes accumulated more Zn, Ni and Cu than shoots and grains. Mn and Zb uptake was correlated in L. perenne shoots. P. lanceolata, a Sb-bioindicator, did not accumulate high amounts of Sb (<1 mg kg⁻¹).     

Molecular cloning,characterization and mRNA expression of selenium-dependent glutathione peroxidase from abalone Haliotis discus hannai Ino in response to dietary selenium,zinc and iron

A novel selenium-dependent glutathione peroxidase (Se-GPX) was cloned from abalone Haliotis discus hannai Ino (HdhGPx) by homology cloning with degenerate primers and RACE techniques. The full length of HdhGPx cDNA was 963 bp with a 669 bp open reading frame (ORF) encoding 222 amino acids and a 101 bp eukaryotic selenocysteine insertion sequence (SECIS) in 3′ untranslated region (UTR). It was showed that HdhGPx has a characteristic codon at ²³⁵TGA²³⁷ that corresponds to selenocysteine (SeC) as U₇₂. Sequence characterization revealed that HdhGPx contains a characteristic GPx signature motif 2 (₉₆LGLPCNQF₁₀₃), an active site motif (₁₇₉WNFEKF₁₈₄). In addition, two potential N-glycosylation sites (₁₁₂NGTE₁₁₅ and ₁₃₂NLTQ₁₃₅) were identified in HdhGPx. 3D modeling analysis showed that the overall structure of HdhGPx monomer had more similarity to human GPx3 than human GPx1. Relatively higher-level mRNA expression was detected in hepatopancreas, mantle and gonad by real-time PCR assays. The relative expression levels of HdhGPx mRNA in hepatopancreas and haemocytes were detected by real-time PCR in abalone fed with nine different diets containing graded levels of selenium (0.15, 1.32 and 48.7 mg kg^− 1), zinc (6.69, 33.85 and 710.63 mg kg^− 1) and iron (29.17, 65.7 and 1267.2 mg kg^− 1) for 20 weeks, respectively. The results showed that the expressions of HdhGPx mRNA were statistically higher at adequate dietary selenium (1.32 mg kg^− 1), zinc (33.85 mg kg^− 1) and iron (65.7 mg kg^− 1) than those in low dietary minerals, respectively. But HdhGPx mRNA expression levels were down-regulated by high contents of dietary selenium (48.7 mg kg^− 1), zinc (710.63 mg kg^− 1) and iron (1267.2 mg kg^− 1), respectively. These results indicated that adequate dietary minerals could increase the mRNA expression of HdhGPx, and then to increase the total antioxidant capacities in abalone.     

One-dimensional copper(II) polymer with bridging μ-trans-oxamidate and thiocyanate ligands: Synthesis, crystal structure and DNA binding studies

A new one-dimensional copper(II) polymer, [Cu₄(dmapox)₂(SCN)₄(CH₃CH₂OH)₂]_n · 2nCH₃CH₂OH, where dmapox is the dianion of N,N′-bis[3-(dimethylamino)propyl]oxamide, was synthesized and characterized by elemental analysis, conductivity measurement, IR and electronic spectral studies. The crystal structure of the copper(II) complex has been determined by X-ray single-crystal diffraction. The complex crystallizes in triclinic, space group and exhibits infinite one-dimensional copper(II) polymeric chain bridged both by the bis-tridentate μ-trans-dmapox and μ-1,3-thiocyanate ligands. The environment around the copper(II) atom can be described as distorted square-pyramid. The Cu···Cu separations through μ-trans-oxamidate and thiocyanate bridges are 5.245(5) Å (Cu1-Cu1ⁱ)(i = −x+1, −y, −z+1), 5.262(4) Å (Cu2-Cu2ⁱⁱ)(ii = −x,−y, −z+1) and 6.022(3) Å (Cu1-Cu2), respectively. The interaction of the copper(II) complex with herring sperm DNA (HS-DNA) has been investigated by using absorption and emission spectral and electrochemical techniques and viscometry. The results reveal that the copper(II) complex interacts with the DNA in the mode of groove binding with the intrinsic binding constant of 2.38 × 10⁵ M⁻¹.     

In vitro and in vivo studies of the dermally absorbed Cu(II) complexes of N5O2 donor ligands - Potential anti-inflammatory drugs

Copper complexes of N,N′-di(aminoethylene)-2,6-pyridinedicarbonylamine and bis-(N,N-dimethylethyl)-2,6-pyridinedicarboxamide have been studied by glass electrode potentiometry, NMR, UV and IR spectroscopy as potential anti-inflammatory agents for the alleviation of inflammation associated with rheumatoid arthritis. The protonation and formation constants with Cu(II), Zn(II) and Ca(II), determined at 25 °C and an ionic strength of 0.15 mol dm⁻³ were used to calculate the copper plasma mobilizing index of the ligands. Spectroscopic studies suggested that metal ion complexation promotes deprotonation and coordination of the amide nitrogens resulting in overall tetragonal distorted copper complexes. Bio-distribution and dermal absorption studies showed the complexes to have relatively long biological half-lives with 50% of the injected dose remaining in the body 24 h after administration.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.     

Magnetic, spectroscopic and X-ray crystallographic structural studies on copper(II) complexes of tridentate NNS Schiff base ligands formed from 2-acetylpyrazine and S-methyl- and S-benzyldithiocarbazates

New copper(II) complexes of general empirical formula, [Cu(NNS)X] (NNS = anionic forms of the 2-acetylpyrazine Schiff bases of S-methyl- and S-benzyldithiocarbazate, Hapsme and Hapsbz) and X = Cl⁻, Br⁻, NCS⁻ and NO₃⁻ have been synthesized and characterized. X-ray crystal structures of the free ligand, Hapsbz and the complexes, [Cu(apsbz)(NO₃)]_∞, [Cu(apsme)(NCS)]₂ and [Cu(apsme)Cl]₂ have been determined. In the solid state, the Schiff base, Hapsbz remains in its thione tautomeric form with the thione sulfur atom trans to the azomethine nitrogen atom. X-ray diffraction shows that the [Cu(apsbz)(NO₃)]_∞ complex is a novel coordination polymer in which one of the nitrogen atoms of the pyrazine ring bridges two adjacent copper(II) ions. The Schiff base is coordinated to the copper(II) ion in its iminothiolate form via the thiolate sulfur atom, the azomethine nitrogen atom and one of the pyrazine nitrogen atoms, the overall geometry of each copper atom in the polymer being close to a square-pyramid. The complexes, [Cu(apsme)X]₂ (X = NCS⁻, Cl⁻) are dimers in which each copper atom adopts a five-coordinate near square-pyramidal geometry with an N₃S₂ coordination environment. The Schiff base coordinates as a uninegatively charged tridentate ligand chelating via the pyridine and azomethine nitrogen atoms and the thiolate sulfur atoms. A nitrogen atom of a unidentate thiocayanate or chloride ligand and a bridging sulfur atom from a second ligand completes the coordination sphere. Room temperature μ_eff values for the complexes in the solid state are in the range 1.70-2.0 μ_B typical of uncoupled or weakly coupled Cu(II) centres. Variable temperature susceptibility studies show that the chain complex displays weak ferromagnetic coupling across the pyrazine bridges, while the S-bridged dinuclear compounds display either weak ferromagnetic or weak antiferromagnetic coupling that relates to subtle bridging geometry differences. EPR studies of frozen DMF solutions give rather similar g and A_Cu values for all compounds indicative of Cu(d_x²-y²) ground state orbitals on the Cu centers.     

Zinc incorporation in the otoliths of juvenile pink snapper (Pagrus auratus Forster): The influence of dietary versus waterborne sources

Separate laboratory experiments were conducted to examine if incorporation of Zn into the otoliths of juvenile pink snapper (Pagrus auratus Forster) was related to levels in the food and/or water. In the first experiment, fish were fed a regular diet (600 mg Zn kg^− 1 dw, control group) or a Zn-enriched diet (6000 mg Zn kg^− 1 dw or 9000 mg Zn kg^− 1 dw) for 35 days. In the second experiment, fish were exposed to waterborne Zn concentrations of < 0.005 µg L^− 1 (control), 50 µg L^− 1, 100 µg L^− 1 and 200 µg L^− 1 for 35 days. The sagittal otoliths were analysed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Juvenile fish exposed to higher concentrations of waterborne Zn did not display increased Zn levels in their otoliths. However, Zn levels in the otoliths of fish consuming the Zn-enriched diet were significantly higher relative to control fish. This study clearly demonstrated that dietary Zn was the major source of Zn incorporated into the otoliths by this marine fish.     

Adsorption of copper and zinc by biochars produced from pyrolysis of hardwood and corn straw in aqueous solution

Biochars produced by pyrolysis of hardwood at 450 °C (HW450) and corn straw at 600 °C (CS600) were characterized and investigated as adsorbents for the removal of Cu(II) and Zn(II) from aqueous solution. The adsorption data were well described by a Langmuir isotherm, with maximum Cu(II) and Zn(II) adsorption capacities of 12.52 and 11.0 mg/g for CS600, 6.79 and 4.54 mg/g for HW450, respectively. Thermodynamic analysis suggested that the adsorption was an endothermic process and did not occur spontaneously. Although Cu(II) adsorption was only marginally affected by Zn(II), Cu(II) competed with Zn(II) for binding sites at Cu(II) and Zn(II) concentrations ?1.0 mM. Results from this study indicated that plant-residue or agricultural waste derived biochar can act as effective surface sorbent, but their ability to treat mixed waste streams needs to be carefully evaluated on an individual basis.     

Square-planar copper(II) complexes with tetradentate amido-carboxylate ligands. Crystal structure of Na2[Cu(obap)]2 · 2H2O. Strain analysis and spectral assignments of complexes

Novel N-N-N-O-type of tetradentate ligands H₃obap (H₃obap = oxamido-N-aminopropyl-N′-benzoic acid) and H₃maeb (H₃maeb = malamido-N-aminoethyl-N′-benzoic acid) and the corresponding square-planar copper(II) complexes have been prepared and characterized. The obap³⁻ and maeb³⁻ ligands coordinate to the copper(II) ion via four ligating atoms (three deprotonated atoms: one carboxylate oxygen and two deprotonated amide nitrogens; one amine nitrogen) with in-plane square chelation. A four coordinate, square-planar geometry has been established crystallographically for the binuclear Na₂[Cu(obap)]₂ · 2H₂O complex. Structural data correlating the square-planar geometry of the [Cu(obap)]⁻ unit and an extensive strain analysis are discussed in relation to the information obtained for similar complexes. The infrared and electronic absorption spectra of the complexes are discussed in comparison to the related complexes of known geometries. Antibacterial activity of ligands and copper(II) complexes towards common Gram-negative and Gram-positive bacteria are reported as well.     

[Cu4(H2O)4(dmapox)2(btc)]n · 10nH2O: The first two-dimensional polymeric copper(II) complex with bridging μ-trans-oxamidate and μ4-1,2,4,5-benzentetracarboxylato ligands: Synthesis, crystal structure and DNA binding studies

A two-dimensional copper(II) polymer with formula of [Cu₄(H₂O)₄(dmapox)₂(btc)]_n · 10nH₂O, where dmapox is the dianion of N,N′-bis[3-(dimethylamino)propyl]oxamide and btc is the tetra-anion of 1,2,4,5-benzenetetracarboxylic acid, was synthesized and characterized by elemental analysis, conductivity measurement, IR and electronic spectral studies. The crystal structure of the complex has been determined by X-ray single-crystal diffraction. The structure consists of crystallized water molecules and neutral two-dimensional copper(II) coordination polymeric networks constructed both by the bis-tridentate μ-trans-dmapox and tetra-monodentate μ₄-btc bridging ligands. Each btc ligand links four trans-dmapox-bridged binuclear copper(II) building blocks [Cu₂(H₂O)₂(trans-dmapox)]²⁺ and each binuclear copper(II) building block attaches to two btc ligands forming an infinite 2D layer which consists of 4+4 grids with dimensions of 13.563(5) × 15.616(5) Å. The environment around the copper(II) atom can be described as a distorted square-pyramid and the Cu?Cu separations through μ-trans-dmapox and μ₄-btc bridging ligands are 5.225 Å (Cu1-Cu1ⁱ), 5.270 Å (Cu2-Cu2ⁱⁱ), 6.115 Å (Cu1-Cu2), 9.047 Å (Cu1-Cu2ⁱⁱⁱ) and 10.968 Å (Cu1-Cu1ⁱⁱⁱ), respectively. Abundant hydrogen bonds among the crystallized, the coordinated water molecules, and the uncoordinated carboxyl oxygen atoms cross-link the two-dimensional layers into an overall three-dimensional channel-like framework. The interaction of the copper(II) polymer with calf thymus DNA (CT-DNA) has been investigated by using absorption, emission spectral and electrochemical techniques. The results indicate that the copper(II) polymer interacts with DNA strongly (K_b = 4.8 × 10⁵ M⁻¹ and K_sv = 1.1 × 10⁴) and the interaction mode between the copper(II) polymer and DNA may be the groove binding. To the best of our knowledge, this is the first report about the crystal structure and DNA-binding studies of a two-dimensional copper(II) polymer bridged both by the trans-oxamidate and btc ligands.     

Nonlinear modelisation of heavy metal removal from aqueous solution using Ulva lactuca algae

After extensive analysis, Ulva lactuca dried algae, collected from the Monastir coastal zone, was proven to be successful as an adsorbent for the removal of certain inorganic pollutants. The main objective of this study was the nonlinear modeling of heavy metal removal from an aqueous solution, using a freely available and well analyzed biomaterial, as well as the evaluation of its efficacy on various metal ion sorptions. Although relatively low specific surface area, compared to more conventional adsorbents, the selected biomaterial displays very interesting retention capacities when used with aqueous inorganic pollutants. The pseudo, first and second-order kinetic models were used to investigate the kinetic retention mechanism. Assuming the nonlinear form, the results indicate that the retention mechanism is diffusion controlled. Concerning the heavy metal uptake capacity, it was found that the selected biomaterial has a retention capacity of 67 mg g⁻¹ of Ni(II), 112 mg g⁻¹ of Cu(II), 127 mg g⁻¹of Cd(II) and 230 mg g⁻¹ of Pb(II).     

Structure and magnetic properties of a tetranuclear Cu(II) complex containing the 2-(pyridine-2-yliminomethyl)-phenol ligand

A tetranuclear Cu(II) complex [Cu₄L₄(H₂O)₄](ClO₄)₄ has been synthesized using the terdentate Schiff base 2-(pyridine-2-yliminomethyl)-phenol (HL) (the condensation product of salicylaldehyde and 2-aminopyridine) and copper perchlorate. Chemical characterizations such as IR and UV/Vis of the complex have been carried out. A single-crystal diffraction study shows that the complex contains a nearly planar tetranuclear core containing four copper atoms, which occupy four equivalent five-coordinate sites with a square pyramidal environment. Magnetic measurements have been carried out over the temperature range 2-300 K and with 100 Oe field strengths. Analysis of magnetic susceptibility data indicates a strong antiferromagnetic (J₁ = −638 cm⁻¹) exchange interaction between diphenoxo-bridged Cu(II) centers and a moderate antiferromagnetic (J₂ = −34 cm⁻¹) interaction between N-C-N bridged Cu(II) centers. Magnetic exchange interactions (J’s) are also discussed on the basis of a computational study using DFT methodology. The spin density distribution (singlet ground state) is calculated to visualize the effect of delocalization of spin density through bridging groups.     

Synthesis, structure and magnetic studies of two-dimensional network of Cu(II) polymer using malonate and 4,4′-azobispyridine ligands

The malonato-bridged copper(II) complex [Cu(mal)(H₂O)(azpy)_1/2] · H₂O (1) (mal = malonate, azpy = 4,4′-azobispyridine) has been synthesized and characterized by X-ray diffraction. The structure of 1 consists of malonato-bridged uniform copper(II) chains which are covalent connected through azpy to form two-dimensional wavelike network. The magnetic pathway of complex 1 is through a single syn-anti carboxylate bridge connecting equatorial and equatorial positions of adjacent copper(II) atoms, and have the value of the intrachain ferromagnetic coupling (J = 8.73(3) cm⁻¹) and interchain antiferromagnetic coupling (zJ′ = − 1.31(1) cm⁻¹) through a numerical expression for a ferromagnetic uniform chain.     

Synthesis and characterization of a molecularly imprinted polymer and its application as SPE enrichment sorbent for determination of trace methimazole in pig samples using HPLC-UV

A novel molecularly imprinted polymer that could be applied as enrichment sorbent was prepared using methimazole (MMZ) as the template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross-linker. Though evaluated by static, kinetic and competitive adsorption tests, the polymer exhibited high adsorption capacity, fast kinetics and good selective ability. A method for determination of trace MMZ was developed using this polymer as enrichment sorbent coupled with high performance liquid chromatography focusing on complex biological matrices. Under the optimum experimental conditions, the MMZ standard is linear within the concentration range studied, that is, from 0.5 μg L⁻¹ to 150 μg L⁻¹ (r² = 0.9941). Lower limits of detection (LOD, at S/N = 3) and quantification (LOQ, at S/N = 10) in pig samples were 0.63 μg kg⁻¹ and 2.10 μg kg⁻¹ for kidney, 0.51 μg kg⁻¹ and 1.70 μg kg⁻¹ for liver, 0.56 μg kg⁻¹ and 1.86 μg kg⁻¹ for muscle, respectively. Recoveries and relative standard deviation (RSD, n = 9) values for precision in the developed method were from 71.14% to 88.41% and from 2.53% to 6.18%.     

Spectroscopic and magnetic properties of diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand with perchlorate transition metal salts. Crystal structure of [Cu(4-pmOpe)2(ClO4)2]

The perchlorate M(II) (M = Cu, Ni, Co) complexes with the diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand of the composition [M(4-pmOpe)₂ (H₂O)₂](ClO₄)₂ (M = Ni, Co) and [Cu(4-pmOpe)₂(ClO₄)₂] were prepared and studied. The ligand contains two donor atoms, i.e. pyridine nitrogen and phosphoryl oxygen atoms. In particular, the crystal structure of [Cu(4-pmOpe)₂(ClO₄)₂] was determined by the X-ray method. Its structure consists of a one-dimensional polymeric chain in which copper(II) ions are N,O-bridged by two 4-pmOpe organic ligands in a trans arrangement. Two perchlorate ions occupy the fifth and the sixth coordination sites. The Cu?Cu distance is 9.180 Å. The crystal packing is determined by the weak intermolecular C-H?O hydrogen contacts. The coordination compounds were identified and characterized by elemental analysis, spectroscopic and magnetic studies. Spectroscopic and magnetic results of the copper(II) compound are presented in the light of the crystal structure. The magnetic data indicate very weak intra- and interchain magnetic exchange interactions (J^’ = −0.43 and zJ^’ = 0.29 cm⁻¹, respectively). The spectroscopic and magnetic properties of the Co(II) and Ni(II) complexes indicate octahedral and polymeric structure of both compounds in which 4-pmOpe ligand also acts as N,O-bridge between metal ions.     

One trinuclear copper(II) complex derived from a new Schiff base ligand based on the dianion of 4-chloro-6-(hydroxymethyl)-2-((3-aminopropylimino)methyl)-phenol: Synthesis, structure, spectroscopic and magnetic properties

A linear trinuclear copper(II) complex (1), prepared from a new Schiff base ligand, namely the dianion of 4-chloro-6-(hydroxymethyl)-2-((3-aminopropylimino)methyl)-phenol, was synthesized and characterized in this paper. The X-ray structural study reveals that the geometry of the central Cu2 ion is elongated octahedral and that of the two side Cu(II) ions is distorted square pyramidal. The magnetic susceptibility measurements from 2 to 300 K reveal medium antiferromagnetic interactions between the Cu(II) ions with a J value of −64.6(1) cm⁻¹.