NITROGEN FIXATION,HYDROGEN CYCLING,AND ELECTRON TRANSPORT KINETICS IN TRICHODESMIUM ERYTHRAEUM (CYANOBACTERIA) STRAIN IMS1011

This study describes the relationships between dinitrogen (N₂) fixation, dihydrogen (H₂) production, and electron transport associated with photosynthesis and respiration in the marine cyanobacterium Trichodesmium erythraeum Ehrenb. strain IMS101. The ratio of H₂ produced:N₂ fixed (H₂:N₂) was controlled by the light intensity and by the light spectral composition and was affected by the growth irradiance level. For Trichodesmium cells grown at 50 μmol photons · m^?2 · s^?1, the rate of N₂ fixation, as measured by acetylene reduction, saturated at light intensities of 200 μmol photons · m^?2 · s^?1. In contrast, net H₂ production continued to increase with light levels up to 1,000 μmol photons · m^?2 · s^?1. The H₂:N₂ ratios increased monotonically with irradiance, and the variable fluorescence measured using a fast repetition rate fluorometer (FRRF) revealed that this increase was accompanied by a progressive reduction of the plastoquinone (PQ) pool. Additions of 2,5‐dibromo‐3‐methyl‐6‐isopropyl‐p‐benzoquinone (DBMIB), an inhibitor of electron transport from PQ pool to PSI, diminished both N₂ fixation and net H₂ production, while the H₂:N₂ ratio increased with increasing level of PQ pool reduction. In the presence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), nitrogenase activity declined but could be prolonged by increasing the light intensity and by removing the oxygen supply. These results on the coupling of N₂ fixation and H₂ cycling in Trichodesmium indicate how light intensity and light spectral quality of the open ocean can influence the H₂:N₂ ratio and modulate net H₂ production.     

Electron-spin resonance studies of the bound iron-sulfur centers in Photosystem I II. Correlation of P-700 triplet production with urea/ferricyanide inactivation of the iron-sulfur clusters

Photosystem I charge separation in a subchloroplast particle isolated from spinach was investigated by electron spin resonance (ESR) spectroscopy following graduated inactivation of the bound iron-sulfur centers by urea-ferricyanide treatment. Previous work demonstrated a differential decrease in iron-sulfur centers A, B and X which indicated that center X serves as a branch point for parallel electron flow through centers A and B (Golbeck, J.H. and Warden, J.T. (1982) Biochim. Biophys. Acta 681, 77–84). We now show that during inactivation the disappearance of iron-sulfur centers A, B, and X correlates with the appearance of a spin-polarized triplet ESR signal with |D| = 279·10⁻⁴ cm⁻¹ and |E| = 39·10⁻⁴ cm⁻¹. The triplet resonances titrate with a midpoint potential of +380 ± 10 mV. Illumination of the inactivated particles results in the generation of an asymmetric ESR signal with g = 2.0031 and ΔH_pp = 1.0 mT. Deconvolution of the P-700⁺ contribution to this composite resonance reveals the spectrum of the putative primary acceptor species, A₀, which is characterized by g = 2.0033 ± 0.0004 and ΔH_pp = 1.0 ± 0.2 mT. The data presented in this report do not substantiate the participation of the electron acceptor A₁ in PS I electron transport, following destruction of the iron-sulfur cluster corresponding to center X. We suggest that A₁ is closely associated with center X and that this component is decoupled from the electron-transport path upon destruction of center X. The inability to photoreduce A₁ in reaction centers lacking a functional center X may result from alteration of the reaction center tertiary structure by the urea-ferricyanide treatment or from displacement of A₁ from its binding site.     

Development and ossification of the feeding apparatus in the larvae of two co‐occurring species of kob (Sciaenidae), Argyrosomus japonicus and Argyrosomus inodorus,in South Africa

The teeth of the oral jaws of two sympatric species of Argyrosomus, Argyrosomus japonicus and Argyrosomus inodorus, found along the South African coast developed first on the premaxilla and then on the dentary of the lower jaw. Teeth were observed on the premaxilla of A. inodorus [head length (L_H) = 1·0 mm; notochord length (L_N) = 2·7 mm] at a smaller size than in A. japonicus (L_H = 1·2 mm; L_N = 4·7 mm). The ventral elements of the gill arches (hypo‐ and basibranchials) were not ossified by the end of preflexion. The fifth ceratobranchial began ossifying and possessed pharyngeal teeth by 1·2 mm L_H (L_N = 4·7 mm) in A. japonicus and 1·1 mm L_H (L_N = 3·2 mm) in A. inodorus. To complement the osteological data, stomach contents were also analysed as a proxy for feeding apparatus functionality. Prey were first present in the stomach of A. japonicus at 1·2 mm L_H (L_N = 4·7 mm) and only 22% of the stomachs contained no prey suggesting that A. japonicus is already actively foraging by preflexion. In comparison, 83% of the stomachs of A. inodorus contained no prey and a single prey item was present in the largest examined specimen (L_H = 1·6 mm; L_N = 5·4 mm). Elements of the feeding apparatus begin to ossify early during ontogeny. While the overall pattern of ossification is similar between the two species, A. japonicus may be able to begin feeding at smaller head lengths relative to A. inodorus in their nursery habitats.     

Reactions of VCl3, VCl4 and TiX4 (XCl,Br) with benzofuroxan and its 5-methyl-, 5-chloro- and 5-methoxi-derivatives. I.

By means of the reaction between VCl₃ and benzofuroxan the compound VCl₃·2C₆H₄N₂O₂ was obtained, while in reaction with TiX₄ (XCl, Br) the compounds with stoichiometry TiX₄·C₆H₄N₂O₂ (X Cl, Br) were obtained.Furthermore, with some benzofuroxan derivatives (5-methyl, 5-chloro and 5-methoxi) the complexes MCl₄·2YC₆H₃N₂O₂ (MTi, V; YCH₃O, Cl, CH₃), TiCl₄·YC₆H₃N₂O₂ (YCH₃O, CH₃) and TiBr₄·YC₆H₃N₂O₂ (YCH₃O, Cl, CH₃) have been isolated.The compounds were characterized by elementary analysis, cryoscopic molecular weight determination in nitrobenzene, magnetic measurements and IR, Vis and EPR spectroscopy.     

Multispectroscopic insight,morphological analysis and molecular docking studies of CuII-based chemotherapeutic drug entity with human serum albumin (HSA) and bovine serum albumin (BSA)

The interaction studies of Cu^II nalidixic acid–DACH chemotherapeutic drug entity, [C₃₆H₅₀N₈O₆Cu] with serum albumin proteins, viz., human serum albumin (HSA) and bovine serum albumin (BSA) employing UV–vis, fluorescence, CD, FTIR and molecular docking techniques have been carried out. Complex [C₃₆H₅₀N₈O₆Cu] demonstrated strong binding affinity towards serum albumin proteins via hydrophobic contacts with binding constants, K?=?3.18?×?10⁵ and 7.44?×?10⁴ M^–1 for HSA and BSA, respectively implicating a higher binding affinity for HSA. The thermodynamic parameters ΔG, ΔH and ΔS at different temperatures were also calculated and the interaction of complex [C₃₆H₅₀N₈O₆Cu] with HSA and BSA was found to be enthalpy and entropy favoured, nevertheless, complex [C₃₆H₅₀N₈O₆Cu] demonstrated higher binding affinity towards HSA than BSA evidenced from its higher binding constant values. Time resolved fluorescence spectroscopy (TRFS) was carried out to validate the static quenching mechanism of HSA/BSA fluorescence. The collaborative results of spectroscopic studies indicated that the microenvironment and the conformation of HSA and BSA (α–helix) were significantly perturbed upon interaction with complex [C₃₆H₅₀N₈O₆Cu]. Hirshfeld surfaces analysis and fingerprint plots revealed various intermolecular interactions viz., N–H····O, O–H····O and C–H····O linkages in a 2–dimensional framework that provide crucial information about the supramolecular architectures in the complex. Molecular docking studies were carried out to ascertain the preferential binding mode and affinity of complex [C₃₆H₅₀N₈O₆Cu] at the target site of HSA and BSA. Furthermore, only for Transmission electroscopy microscopy micrographs of HSA and BSA in presence of complex [C₃₆H₅₀N₈O₆Cu] revealed major protein morphological transitions and aggregation which validates efficient delivery of complex by serum proteins to the target site.

Communicated by Ramaswamy H. Sarma     

Chalcogen- and halogen-bonds involving SX<Subscript>2</Subscript> (X = F,Cl, and Br) with formaldehyde

The capacity of SX₂ (X = F, Cl, and Br) to engage in different kinds of noncovalent bonds was investigated by ab initio calculations. SCl₂ (SBr₂) has two σ-holes upon extension of Cl (Br)?S bonds, and two σ-holes upon extension of S?Cl (Br) bonds. SF₂ contains only two σ-holes upon extension of the F?S bond. Consequently, SCl₂ and SBr₂ form chalcogen and halogen bonds with the electron donor H₂CO while SF₂ forms only a chalcogen bond, i.e., no F···O halogen bond was found in the SF₂:H₂CO complex. The S···O chalcogen bond between SF₂ and H₂CO is the strongest, while the strongest halogen bond is Br···O between SBr₂ and H₂CO. The nature of these two types of noncovalent interaction was probed by a variety of methods, including molecular electrostatic potentials, QTAIM, energy decomposition, and electron density shift maps. Termolecular complexes X₂S···H₂CO···SX′₂ (X = F, Cl, Br, and X′ = Cl, Br) were constructed to study the interplay between chalcogen bonds and halogen bonds. All these complexes contained S···O and Cl (Br)···O bonds, with longer intermolecular distances, smaller values of electron density, and more positive three-body interaction energies, indicating negative cooperativity between the chalcogen bond and the halogen bond. In addition, for all complexes studied, interactions involving chalcogen bonds were more favorable than those involving halogen bonds.

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Graphical Abstract Molecular electrostatic potential and contour map of the Laplacian of the electron density in Cl₂S···H₂CO···SCl₂ complex

     

Synthesis,inhibitory activity and molecular docking studies of two Cu(II) complexes against Helicobacter pylori urease

Two mononuclear copper(II) complexes, [Cu(C₁₅H₁₆NO₂)₂] (1) and [Cu(C₆H₉N₂O₄)₂·3H₂O] (2·3H₂O), were synthesised and structurally characterised by single-crystal X-ray analysis. The copper(II) atom adopts a square-planar environment in complex 1, while the geometry in 2·3H₂O could be described as the distorted square pyramidal. Complexes 1 and 2·3H₂O were evaluated for their inhibitory activities against Helicobacter pylori (H. pylori) urease in vitro. They both were found to have strong inhibitory activities against H. pylori urease comparable to that of acetohydroxamic acid (AHA). A docking simulation was performed to position 2 into the H. pylori urease active site to determine the probable binding conformation.     

PHOTOAUTOTROPHIC GROWTH OF A RECENTLY ISOLATED N2-FIXING MARINE NON-HETEROCYSTOUS FILAMENTOUS CYANOBACTERIUM, SYMPLOCA SP. (CYANOBACTERIA)

Photoautotrophic growth of a marine non-heterocystous filamentous cyanobacterium, Symploca sp. strain S84, was examined under nitrate-assimilating and N₂-fixing conditions. Under continuous light, photon flux density of 55 μmol photons·m⁻² ·s⁻¹ was at a saturating level for growth, and light did not inhibit the growth rate under N₂-fixing conditions even when the photon flux density was doubled (110 μmol photons·m⁻² ·s⁻¹). Doubling times of the N₂-fixing cultures under 55 and 110 μmol photons·m⁻² ·s⁻¹ were about 30 and 31 h, respectively. Under 110 μmol photons·m⁻² ·s⁻¹ during the light phase of an alternating 12:12-h light:dark (L:D) cycle, the doubling time of the N₂-fixing culture was also about 30 h. When grown diazotrophically under a 12:12-h L:D regime, C₂H₂ reduction activity was observed mainly during darkness. In continuous light, relatively large cyclic fluctuations in C₂H₂ reduction were observed during growth. The short-term (<4 h) effect of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU; 5 μM) indicated that C₂H₂ reduction activity was not influenced by photosynthetic O₂ evolution. Long-term (24 h) effects of DCMU indicated that photosynthesis and C₂H₂ reduction activity occur simultaneously. These results indicate that strain S84 grows well under diazotrophic conditions when saturating light is supplied either continuously or under a 12:12-h L:D diel light regime.     

Hydrogen bonding interactions in PN···HX complexes: DFT and ab initio studies of structure, properties and topology

Spin-restricted DFT (X3LYP and B3LYP) and ab initio (MP2(fc) and CCSD(fc)) calculations in conjunction with the Aug-CC-pVDZ and Aug-CC-pVTZ basis sets were performed on a series of hydrogen bonded complexes PN···HX (X = F, Cl, Br) to examine the variations of their equilibrium gas phase structures, energetic stabilities, electronic properties, and vibrational characteristics in their electronic ground states. In all cases the complexes were predicted to be stable with respect to the constituent monomers. The interaction energy (ΔE) calculated using a super-molecular model is found to be in this order: PN···HF > PN···HCl > PN···HBr in the series examined. Analysis of various physically meaningful contributions arising from the Kitaura-Morokuma (KM) and reduced variational space self-consistent-field (RVS-SCF) energy decomposition procedures shows that the electrostatic energy has significant contribution to the over-all interaction energy. Dipole moment enhancement (Δμ) was observed in these complexes expected of predominant dipole-dipole electrostatic interaction and was found to follow the trend PN···HF > PN···HCl > PN···HBr at the CCSD level. However, the DFT (X3LYP and B3LYP) and MP2 levels less accurately determined these values (in this order HF < HCl < HBr). Examination of the harmonic vibrational modes reveals that the PN and HX bands exhibit characteristic blue- and red shifts with concomitant bond contraction and elongation, respectively, on hydrogen bond formation. The topological or critical point (CP) analysis using the static quantum theory of atoms in molecules (QTAIM) of Bader was considered to classify and to gain further insight into the nature of interaction existing in the monomers PN and HX, and between them on H-bond formation. It is found from the analysis of the electron density ρ _c , the Laplacian of electron charge density ∇²ρ_c, and the total energy density (H _c ) at the critical points between the interatomic regions that the interaction N···H is indeed electrostatic in origin (ρ_c > 0, ∇²ρ_c > 0 and H_c > 0 at the BCP) whilst the bonds in PN (ρ_c > 0, ∇²ρ_c > 0 and H_c < 0) and HX ((ρ_c > 0, ∇²ρ_c < 0 and H_c < 0)) are predominantly covalent. A natural bond orbital (NBO) analysis of the second order perturbation energy lowering, E⁽²⁾, caused by charge transfer mechanism shows that the interaction N···H is n(N) → BD*(HX) delocalization.     

Synthesis,Structure, and Biological Activities of a New μ‐Oxamido‐Bridged Dicopper(II) Complex: The Influence of Hydrophobicity of Bridging Ligand on DNA Binding and Cytotoxic Activities

A new μ‐oxamido‐bridged dicopper(II) complex, [Cu₂(papo)(H₂O)‐ (phen)]Cl·CH₃OH·H₂O, where H₃papo and phen represent N‐(2‐hydroxyphenyl)‐N'‐(3‐aminopropyl)oxamide and 1,10‐phenanthroline, respectively, has been synthesized and characterized by elemental analysis, molar conductivity measurement, infrared and electronic spectra studies, and single‐crystal X‐ray diffraction. The complex crystallizes in the triclinic space group P‐1. Each copper(II) ion is located in a slightly distorted square‐pyramidal environment. The Cu···Cu distance through the oxamide bridge is 5.1848(7) Å. The three‐dimensional supramolecular structure is built‐up by hydrogen bonds and π–π stacking interactions. The dicopper(II) complex exhibits cytotoxic activity against the SMMC‐7721 and A549 cell lines. The reactivity toward herring sperm DNA and protein bovine serum albumin (BSA) reveals that the dicopper(II) complex can interact with the DNA by the intercalation mode, and effectively quench the intrinsic fluorescence of BSA via a static mechanism. The influence of hydrophobicity of the bridging ligand on DNA‐binding properties and in vitro cytotoxic activities of this kind of dicopper(II) complexes was investigated.     

Comparison of the effects of one-side- and two-side Mg2+ on the reconstitution of mitochondrial H+-ATPase

Three types of proteoliposome containing mitochondrial H⁺-ATPase have been prepared: Mg²⁺-‘free’, one-side and two-side Mg²⁺-containing proteoliposomes. The ATPase activity as well as its sensitivity to oligomycin or N,N'-dicyclohexylcarbodiimide of the three proteoliposome preparations has been compared. They decreased in the order : L ·(H⁺-ATPase)_+Mg²⁺ > L · (H⁺-ATPase)_+Mg²⁺ > L · (H⁺-ATPase)_−Mg²⁺. The fluidity of the proteoliposomes has also been compared by fluorescence polarization probes diphenylhexatriene (DPH) or 7-(9-anthroyloxy)stearic acid (7-AS). The degree of polarization for DPH in these proteoliposomes decreased in the order: L · (H⁺-ATPase)_+Mg²⁺ > L · (H⁺-ATPase)_+Mg²⁺ > L · (H⁺-ATPase)_−Mg²⁺, while that for 7-AS: L · (H⁺-ATPase)_+Mg²⁺ ≈ L · (H⁺-ATPase)_+Mg²⁺ > L · (H⁺-ATPase)_−Mg²⁺.Lipid fluidityMitochondrial H⁺-ATPaseOne-side Mg²⁺ effectTwo-side Mg²⁺ effectLipid-protein interaction     

Studies on the metal-amide bond. XX. A structural comparison of an unusual dimeric cobalt(III) complex,fac-[Co2(bpen)3]·12H2O,with the free ligand N,N′-Bis(2′-pyridinecarboxamide)-1,2-ethane,bpenH2

The crystal and molecular structures of the ligand bpenH₂ (N,N′-bis(2′-pyridinecarboxamide)-1,2-ethane) and its deprotonated dimeric cobalt(III) complex fac-[Co₂(bpen)₃]·12H₂O have been determined by single-crystal X-ray diffraction methods. Crystal data: (a) bpenH₂, C₁₄H₁₄N₄O₂, orthorhombic, space group Pccn, a=9.638(1), b= 15.288(1), c = 8.684(1) Å, Z=4; (b) Co₂(bpen)₃· 12H₂O, C₄₂H₆₀N₁₂O₁₈Co₂, triclinic, space group P$\text{1}$, a = 11.128(3), b = 14.316(5), c = 16.466(4) Å, α= 92.02(2)°, β = 95.21(2)°, γ = 99.30(2)°, Z = 2.The structures were refined to R 0.034 and 0.053 for 1064 and 7748 independent reflexions, respectively. The bpenH₂ molecule has a space group imposed centre of symmetry, with the amide group adopting a trans configuration in the closely planar picolinamide moiety. The cobalt complex is dimeric in which three bpen ligands, acting each as a bis(N₂-bidentate), bridge the two metal atoms. Each cobalt atom is octahedral with CoN_py 1.944(3) and Co N_am 1.933(3) Å. The Co··Co separation is 5.493(1) Å. The symmetry of the dimeric molecule is D₃ which is consistent with that indicated from solution NMR studies.     

Solvolysis of charged active esters of carboxylic acids with cyclo (l- or d-Glu-l-His)

Cyclic dipeptide cyclo(l- or d-Glu-l-His) carrying an anionic site and a nucleophilic site has been synthesized and used as a catalyst for the solvolysis of cationic esters in aqueous alcohols. In the solvolysis of 3-acyloxy-N-trimethylanilinium iodide (S⁺_n, n = 2 and 10) and Cl^?H₃N⁺(CH₂)₁₁COOPh(NO₂), no efficient nucleophilic catalysis was observed. On the other hand, in the solvolysis of Gly-OPh(NO₂)·HCl, Val-OPh(NO₂)·HCl and Leu-OPh(NO₂)·HCl a very efficient general base-type catalysis by cyclo(l-Glu-l-His) was observed. In particular, with the latter two substrates the catalysis by cyclo(l-Glul-His) was more efficient than that by imidazole, although the catalysis was not enantiomer-selective. The diastereomeric cyclic dipeptide cyclo(d-Glu-l-His) was almost inactive under the same conditions. Confomation of cyclo(l- or d-Glu-l-His) in aqueous solution was investigated and the structure/catalysis relationship is discussed.     

XRD and DFT-modelized structures of a pteridine-2,4(1H,3H)-dithione/N,N′-dimethylformamide H-bonded cluster (2:2). MO study of the coordination ability

The title compound, C₆H₄N₄S₂·C₃H₇NO, crystallizes in the monoclinic space group C 2/c with a = 26.673(5), b = 5.397(1), c = 16.522(3) Å, β = 95.49(3)°, Z = 8, R = 0.0461 for 1891 reflections with I > 2σ(I) and 174 parameters (4 restraints). Single pteridine-2,4(1 H,3 H)-dithione and dimethylformamide molecules are packed via N-H···O and N-H···N hydrogen bonds into centrosymmetric clusters containing two molecules of each class; these are roughly planar and placed into two different sets of planes -both containing the [−1,0,2] direction- mutually angled by 77.8°. Despite the distance between two neighbor planes in each set is ca. 3.4 Å, the analysis of π,π-stacking interactions shows too large slippage distance between aromatic rings from contiguous planes. Additional σ-π interactions between S2, S4 and O1S atoms and pyrazine or pyrimidine rings from adjacent molecules are present. The structure for the cluster [DTLM-DMF]₂ has been simulated by using the density functionals B1B95 (6-31 G(d) and 6-31+G(d) basis sets) and M06-2X (6-31 G(d) basis set). As a result, the M06-2X/6-31 G(d) approach provides the best agreement with the experimental XRD data. For a better evaluation of the intermolecular interactions, the superposition of two dimeric adducts [DTLM-DMF]₂ has been modelized. The binding capability of DTLM ligand was simulated on systems containing two metal-binding modes to palladium (N5-S4 and N1-S2) with different chelate size. The analysis of the frontier orbitals points out that the link with the metallic centers will take place through the sulfur atoms.

     

Time-dependent density functional theory study on the electronic excited-state hydrogen bonding of the chromophore coumarin 153 in a room-temperature ionic liquid

In the present work, in order to investigate the electronic excited-state intermolecular hydrogen bonding between the chromophore coumarin 153 (C153) and the room-temperature ionic liquid N,N-dimethylethanolammonium formate (DAF), both the geometric structures and the infrared spectra of the hydrogen-bonded complex C153–DAF⁺ in the excited state were studied by a time-dependent density functional theory (TDDFT) method. We theoretically demonstrated that the intermolecular hydrogen bond C₁?=?O₁···H₁–O₃ in the hydrogen-bonded C153–DAF⁺ complex is significantly strengthened in the S₁ state by monitoring the spectral shifts of the C=O group and O–H group involved in the hydrogen bond C₁?=?O₁···H₁–O₃. Moreover, the length of the hydrogen bond C₁?=?O₁···H₁–O₃ between the oxygen atom and hydrogen atom decreased from 1.693 Å to 1.633 Å upon photoexcitation. This was also confirmed by the increase in the hydrogen-bond binding energy from 69.92 kJ mol^?1 in the ground state to 90.17 kJ mol^?1 in the excited state. Thus, the excited-state hydrogen-bond strengthening of the coumarin chromophore in an ionic liquid has been demonstrated theoretically for the first time.     

The coordination chemistry of N-(2-pyridyl)pyridine-2′-carboxamide; A potentially tridentate ligand containing one secondary amide and two 2-pyridyl donor groups

New complexes of the general compositions M(LH)X₂ (M = Co, Zn; X = Cl, Br, I), Zn(LH)(NCS)₂, Zn(LH)(NO₃)₂ ·H₂O, Cu(LH)X₂ (X = Cl, Br, ONO₂), Ni(LH)Cl₂·H₂O, Co(LH)₂X₂ (X = NCS, ONO ₂), Ni(LH)₂X₂ (X = Cl, Br, NCS, ONO₂), Pt(LH)₂Cl₂ and MLCl·nH₂O (M = Ni, Cu, Pd; n = 2, 3), where LH = N-(2-pyridyl)pyridine-2′-carboxamide, have been isolated. The complexes were characterized by elemental analyses, conductivity measurements, X-ray powder patterns, thermal methods, magnetic susceptibilities and spectroscopic (IR, ligand field, ¹H NMR) studies. Pseudotetrahedral, square planar, square pyramidal and distorted octahedral stereochemistries are tentatively assigned in the solid state. Most complexes appear to be monomeric, while polymeric structural types are attributed for Ni(LH)Cl₂·H₂O and CuLCl·2H₂O. The neutral amide group of LH is coordinated to Co(II), Ni(II), Cu(II) and Zn(II) through oxygen, while N-coordination is observed for PdLCl·2H₂O. The amide group of L⁻ is bound to different Cu(II) atoms in CuLCl·2H₂O through both its nitrogen and oxygen. The rare O-coordination of the deprotonated amide bound is proposed for NiLCl· 3H₂O. The N(1) atom is not involved in coordination except in the complexes Ni(LH)Cl₂·H₂O, NiLCl· 3H₂O and CuLCl·2H₂O, where both pyridine residues are coordinated. The variation in structural types observed is believed to be a consequence of the stereochemical adaptability of the ligand to the electronic demands of the metal ions.     

Antibacterial,antifungal and in vitro antileukaemia activity of metal complexes with thiosemicarbazones

1‐phenyl‐3‐methyl‐4‐benzoyl‐5‐pyrazolone 4‐ethyl‐thiosemicarbazone (HL) and its copper(II), vanadium(V) and nickel(II) complexes: [Cu(L)(Cl)]·C₂H₅OH·( 1 ), [Cu(L)₂]·H₂O ( 2 ), [Cu(L)(Br)]·H₂O·CH₃OH ( 3 ), [Cu(L)(NO₃)]·2C₂H₅OH ( 4 ), [VO₂(L)]·2H₂O ( 5 ), [Ni(L)₂]·H₂O ( 6 ), were synthesized and characterized. The ligand has been characterized by elemental analyses, IR, ¹H NMR and ¹³C NMR spectroscopy. The tridentate nature of the ligand is evident from the IR spectra. The copper(II), vanadium(V) and nickel(II) complexes have been characterized by different physico‐chemical techniques such as molar conductivity, magnetic susceptibility measurements and electronic, infrared and electron paramagnetic resonance spectral studies. The structures of the ligand and its copper(II) ( 2 , 4 ), and vanadium(V) ( 5 ) complexes have been determined by single‐crystal X‐ray diffraction. The composition of the coordination polyhedron of the central atom in 2 , 4 and 5 is different. The tetrahedral coordination geometry of Cu was found in complex 2 while in complex 4 , it is square planar, in complex 5 the coordination polyhedron of the central ion is distorted square pyramid. The in vitro antibacterial activity of the complexes against Escherichia coli, Salmonella abony, Staphylococcus aureus, Bacillus cereus and the antifungal activity against Candida albicans strains was higher for the metal complexes than for free ligand. The effect of the free ligand and its metal complexes on the proliferation of HL‐60 cells was tested.     

Effect of nitrate and thiosulfate concentration on the denitrification activity of bacterial isolates

The denitrification activity of five bacterial isolates was studied in samples of soil and freshwater sediments and from a wastewater treatment plant. The bacteria were exposed in a mineral medium supplied with Na₂S₂O₃·5H₂O (electron donor) and KNO₃ (electron acceptor). The effect of different concentrations of donor and/or acceptor of electrons was evaluated by the method of acetylene inhibition of N₂O-reductase. No positive influence on denitrification activity was observed with increased levels of individually added substrates. Three bacterial isolates exhibited a significant increase of denitrification activity when measured in the presence of both tested substances.     

Synthesis,characterization, DNA interaction,and cytotoxicity of novel Pd(II) and Pt(II) complexes

Four complexes [Pd(L)(bipy)Cl]·4H₂O (1), [Pd(L)(phen)Cl]·4H₂O (2), [Pt(L)(bipy)Cl]·4H₂O (3), and [Pt(L)(phen)Cl]·4H₂O (4), where L = quinolinic acid, bipy = 2,2’-bipyridyl, and phen = 1,10-phenanthroline, have been synthesized and characterized using IR, ¹H NMR, elemental analysis, and single-crystal X-ray diffractometry. The binding of the complexes to FS-DNA was investigated by electronic absorption titration and fluorescence spectroscopy. The results indicate that the complexes bind to FS-DNA in an intercalative mode and the intrinsic binding constants K of the title complexes with FS-DNA are about 3.5?×?10⁴ M^?1, 3.9?×?10⁴ M^?1, 6.1?×?10⁴ M^?1, and 1.4?×?10⁵ M^?1, respectively. Also, the four complexes bind to DNA with different binding affinities, in descending order: complex 4, complex 3, complex 2, complex 1. Gel electrophoresis assay demonstrated the ability of the Pt(II) complexes to cleave pBR322 plasmid DNA.     

Copper(II) and zinc(II) complexes with Schiff-base ligands derived from salicylaldehyde and 3-methoxysalicylaldehyde: Synthesis,crystal structures,magnetic and luminescence properties

The following Schiff bases were employed as ligands in synthesizing copper(II) and zinc(II) complexes: N-[(2-pyridyl)-methyl]-salicylimine (Hsalampy), N-[2-(N,N-dimethyl-amino)-ethyl]-salicylimine (Hsaldmen), and N-[(2-pyridyl)-methyl]-3-methoxy-salicylimine (Hvalampy). The first two ligands were obtained by reacting salicylaldehyde with 2-aminomethyl-pyridyne and N,N-dimethylethylene diamine, respectively, while the third one results from the condensation of 3-methoxysalicylaldehyde with 2-aminomethyl-pyridine. Four new coordination compounds were synthesized and structurally characterized: [Cu(salampy)(H₂O)(ClO₄)] 1, [Cu₂(salampy)₂(H₂trim)₂] 2 (H₂trim^? = the monoanion of the trimescic acid), [Cu₄(valampy)₄](ClO₄)₄ · 2CH₃CN 3, and [Zn₃(saldmen)₃(OH)](ClO₄)₂ · 0.25H₂O 4. The crystal structure of 1 consists of supramolecular dimers resulted from hydrogen bond interactions established between mononuclear [Cu(salampy)(H₂O)(ClO₄)] complexes. Compound 2 is a binuclear complex with the copper ions connected by two monoatomic carboxylato bridges arising from two molecules of monodeprotonated trimesic acid. The crystal structure of 3 consists of tetranuclear cations with a heterocubane {Cu₄O₄} core, and perchlorate ions. Compound 4 is a trinuclear complex with a defective heterocubane structure. The magnetic properties of complexes 1–3 have been investigated. Compound 4 exhibits solid-state photoluminescence at room temperature.