New insights on ChlD1 function in Photosystem II from site-directed mutants of D1/T179 in Thermosynechococcus elongatus

The monomeric chlorophyll, Chl_D1, which is located between the P_D1P_D2 chlorophyll pair and the pheophytin, Pheo_D1, is the longest wavelength chlorophyll in the heart of Photosystem II and is thought to be the primary electron donor. Its central Mg²⁺ is liganded to a water molecule that is H-bonded to D1/T179. Here, two site-directed mutants, D1/T179H and D1/T179V, were made in the thermophilic cyanobacterium, Thermosynechococcus elongatus, and characterized by a range of biophysical techniques. The Mn₄CaO₅ cluster in the water-splitting site is fully active in both mutants. Changes in thermoluminescence indicate that i) radiative recombination occurs via the repopulation of *Chl_D1 itself; ii) non-radiative charge recombination reactions appeared to be faster in the T179H-PSII; and iii) the properties of P_D1P_D2 were unaffected by this mutation, and consequently iv) the immediate precursor state of the radiative excited state is the Chl_D1⁺Pheo_D1^? radical pair. Chlorophyll bleaching due to high intensity illumination correlated with the amount of ¹O₂ generated. Comparison of the bleaching spectra with the electrochromic shifts attributed to Chl_D1 upon Q_A^? formation, indicates that in the T179H-PSII and in the WT*3-PSII, the Chl_D1 itself is the chlorophyll that is first damaged by ¹O₂, whereas in the T179V-PSII a more red chlorophyll is damaged, the identity of which is discussed. Thus, Chl_D1 appears to be one of the primary damage site in recombination-mediated photoinhibition. Finally, changes in the absorption of Chl_D1 very likely contribute to the well-known electrochromic shifts observed at ~430?nm during the S-state cycle.     

Femtosecond primary charge separation in Synechocystis sp. PCC 6803 photosystem I

The ultrafast (< 100 fs) conversion of delocalized exciton into charge-separated state between the primary donor P700 (bleaching at 705 nm) and the primary acceptor A₀ (bleaching at 690 nm) in photosystem I (PS I) complexes from Synechocystis sp. PCC 6803 was observed. The data were obtained by application of pump-probe technique with 20-fs low-energy pump pulses centered at 720 nm. The earliest absorbance changes (close to zero delay) with a bleaching at 690 nm are similar to the product of the absorption spectrum of PS I complex and the laser pulse spectrum, which represents the efficiency spectrum of the light absorption by PS I upon femtosecond excitation centered at 720 nm. During the first ∼ 60 fs the energy transfer from the chlorophyll (Chl) species bleaching at 690 nm to the Chl bleaching at 705 nm occurs, resulting in almost equal bleaching of the two forms with the formation of delocalized exciton between 690-nm and 705-nm Chls. Within the next ∼ 40 fs the formation of a new broad band centered at ∼ 660 nm (attributed to the appearance of Chl anion radical) is observed. This band decays with time constant simultaneously with an electron transfer to A₁ (phylloquinone). The subtraction of kinetic difference absorption spectra of the closed (state P700⁺A₀A₁) PS I reaction center (RC) from that of the open (state P700A₀A₁) RC reveals the pure spectrum of the P700⁺A₀⁻ ion-radical pair. The experimental data were analyzed using a simple kinetic scheme: An* [(PA₀)*A₁ P⁺A₀⁻A₁] P⁺A₀A₁⁻, and a global fitting procedure based on the singular value decomposition analysis. The calculated kinetics of transitions between intermediate states and their spectra were similar to the kinetics recorded at 694 and 705 nm and the experimental spectra obtained by subtraction of the spectra of closed RCs from the spectra of open RCs. As a result, we found that the main events in RCs of PS I under our experimental conditions include very fast (< 100 fs) charge separation with the formation of the P700⁺A₀⁻A₁ state in approximately one half of the RCs, the ∼ 5-ps energy transfer from antenna Chl* to P700A₀A₁ in the remaining RCs, and ∼ 25-ps formation of the secondary radical pair P700⁺A₀A₁⁻.     

How the molecular structure determines the flow of excitation energy in plant light-harvesting complex II

Excitation energy transfer in the light-harvesting complex II of higher plants is modeled using excitonic couplings and local transition energies determined from structure-based calculations recently (Müh et al., 2010). A theory is introduced that implicitly takes into account protein induced dynamic localization effects of the exciton wavefunction between weakly coupled optical and vibronic transitions of different pigments. Linear and non-linear optical spectra are calculated and compared with experimental data reaching qualitative agreement. High-frequency intramolecular vibrational degrees of freedom are found important for ultrafast subpicosecond excitation energy transfer between chlorophyll (Chl) b and Chla, since they allow for fast dissipation of the excess energy. The slower ps component of this transfer is due to the monomeric excited state of Chlb 605. The majority of exciton relaxation in the Chla spectral region is characterized by slow ps exciton equilibration between the Chla domains within one layer and between the lumenal and stromal layers in the 10-20 ps time range. Subpicosecond exciton relaxation in the Chla region is only found within the terminal emitter domain (Chls a 610/611/612) and within the Chla 613/614 dimer. Deviations between measured and calculated exciton state life times are obtained for the intermediate spectral region between the main absorbance bands of Chla and Chlb that indicate that besides Chlb 608 another pigment should absorb there. Possible candidates, so far not identified by structure-based calculations, but by fitting of optical spectra and mutagenesis studies, are discussed. Additional mutagenesis studies are suggested to resolve this issue.     

Cationic state distribution over the chlorophyll d-containing PD1/PD2 pair in photosystem II

Most of the chlorophyll (Chl) cofactors in photosystem II (PSII) from Acaryochloris marina are Chld, although a few Chla molecules are also present. To evaluate the possibility that Chla may participate in the P_D1/P_D2 Chl pair in PSII from A. marina, the P_D1^?+/P_D2^?+ charge ratio was investigated using the PSII crystal structure analyzed at 1.9-Å resolution, while considering all possibilities for the Chld-containing P_D1/P_D2 pair, i.e., Chld/Chld, Chla/Chld, and Chld/Chla pairs. Chld/Chld and Chla/Chld pairs resulted in a large P_D1^?+ population relative to P_D2^?+, as identified in Chla/Chla homodimer pairs in PSII from other species, e.g., Thermosynechococcus elongatus PSII. However, the Chld/Chla pair possessed a P_D1^?+/P_D2^?+ ratio of approximately 50/50, which is in contrast to previous spectroscopic studies on A. marina PSII. The present results strongly exclude the possibility that the Chld/Chla pair serves as P_D1/P_D2 in A. marina PSII. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.     

Biomimetic zinc(II) and cobalt(II) complexes with tri-tert-butoxysilanethiolate and imidazole ligands - Structural and spectroscopic studies

New, heteroleptic zinc and cobalt complexes with tri-tert-butoxysilanethiolate and imidazole co-ligands are characterized by crystal structure studies. The ligands exhibit different coordination modes to Co(II) ions: NOS₂ (with methanol as O-donor ligand) in 2′, NO₂S₂ in 2′′, N₂S₂ in 1, and to Zn(II) ions: N₂S₂ in 3 and N₃S in 4. Complex 2′ is a structural analog of cobalt-substituted active site of alcohol dehydrogenase. All four-coordinate Co(II) and Zn(II) complexes have tetrahedral geometry. Solution and solid state electronic spectra of cobalt(II) complexes are discussed and compared to literature data available for the cobalt-substituted liver alcohol dehydrogenase and sorbitol dehydrogenase. The EPR spectra of all cobalt complexes exhibit at 77 K a characteristic broad signal with g ∼3.6 and 5.6, strongly indicating a high-spin state, S = 3/2, of Co(II) complexes.     

Using site-directed mutagenesis to probe the role of the D2 carotenoid in the secondary electron-transfer pathway of photosystem II

Secondary electron transfer in photosystem II (PSII), which occurs when water oxidation is inhibited, involves redox-active carotenoids (Car), as well as chlorophylls (Chl), and cytochrome b ₅₅₉ (Cyt b ₅₅₉), and is believed to play a role in photoprotection. Car_D2 may be the initial point of secondary electron transfer because it is the closest cofactor to both P₆₈₀, the initial oxidant, and to Cyt b ₅₅₉, the terminal secondary electron donor within PSII. In order to characterize the role of Car_D2 and to determine the effects of perturbing Car_D2 on both the electron-transfer events and on the identity of the redox-active cofactors, it is necessary to vary the properties of Car_D2 selectively without affecting the ten other Car per PSII. To this end, site-directed mutations around the binding pocket of Car_D2 (D2-G47W, D2-G47F, and D2-T50F) have been generated in Synechocystis sp. PCC 6803. Characterization by near-IR and EPR spectroscopy provides the first experimental evidence that Car_D2 is one of the redox-active carotenoids in PSII. There is a specific perturbation of the Car^?+ near-IR spectrum in all three mutated PSII samples, allowing the assignment of the spectral signature of Car _D2 ^?+ ; Car _D2 ^?+ exhibits a near-IR peak at 980 nm and is the predominant secondary donor oxidized in a charge separation at low temperature in ferricyanide-treated wild-type PSII. The yield of secondary donor radicals is substantially decreased in PSII complexes isolated from each mutant. In addition, the kinetics of radical formation are altered in the mutated PSII samples. These results are consistent with oxidation of Car_D2 being the initial step in secondary electron transfer. Furthermore, normal light levels during mutant cell growth perturb the shape of the Chl^?+ near-IR absorption peak and generate a dark-stable radical observable in the EPR spectra, indicating a higher susceptibility to photodamage further linking the secondary electron-transfer pathway to photoprotection.     

Study on synthesis, structure, and DNA-binding of Ni, Zn complexes with 2-phenylquinoline-4-carboylhydrazide

2-Phenylquinoline-4-carboylhydrazide (HL), and its novel nickel(II), zinc(II) complexes [M(HL)₂(L)]·2H₂O·NO₃ (M = Ni (1), M = Zn (2)), have been synthesized and characterized by elemental analysis, molar conductivity, and IR spectra. The crystal structure of [Ni(HL)₂(L)]·2H₂O·NO₃ obtained from ethanol solution was determined by X-ray diffraction analysis, crystallized in the rhombohedral system, space group , Z = 18, a = 31.913(3) Å, b = 31.913(3) Å, c = 27.709(2) Å, α = 90°, β = 90°, γ = 120°, R₁ = 0.0647. The interactions of the complexes and the ligand with calf thymus DNA had been investigated using UV-Vis spectra, fluorescent spectra, CD (circular dichroism) spectra, CV (cyclic voltammetry) and viscosity measurements. These compounds were tested against MFC (mouse forestomach carcinoma) cell lines. The complex 1 showed significant cytotoxic activity against MFC cell lines. The cleavage reaction on plasmid DNA has been monitored by agarose gel electrophoresis. Results suggest that the two complexes bound to DNA via a groove binding mode and the complexes can cleave pBR322 DNA.     

In situ hydrothermal syntheses, crystal structures and luminescent properties of two novel zinc(II) coordination polymers based on tetrapyridyl ligand

Two novel Zn(II) coordination polymers, [Zn(2-pytpy)(fum)]_n·nH₂O (1) and [Zn₆(4-pytpy)₃(mal)₄]_n·5n(H₂O) (2), (2-pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine, 4-pytpy = 4′-(4-pyridyl)-4,2′:6′,4″-terpyridine, H₂fum = fumaric acid and H₂mal = malic acid) have been hydrothermally synthesized and structurally characterized. Notably, in situ ligand reactions occur in the formation of complexes 1 and 2, in which maleic acid is converted into fumaric acid and malic acid, respectively. Complex 1 is a 1D infinite chain structure, which is extended into a supramolecular layer by intermolecular π…π stacking interactions. Complex 2 is a 3D network structure, in which the bidentate-bridging 4-pytpy ligands link the layers based on the tetranuclear Zn(II) subunits to form the (4,10)-connected network. The luminescent properties of 1 and 2 have been investigated with emission spectra and UV-Vis diffuse reflectance spectra in the solid state. Additionally, these two complexes possess great thermal stabilities.     

Low-temperature electron transfer suggests two types of QA in intact photosystem II

The correlation between the reduction of Q_A and the oxidation of Tyr_Z or Car/Chl_Z/Cyt_b559 in spinach PSII enriched membranes induced by visible light at 10 K is studied by using electron paramagnetic resonance spectroscopy. Similar g = 1.95-1.86 Q_A^-•EPR signals are observed in both Mn-depleted and intact samples, and both signals are long lived at low temperatures. The presence of PPBQ significantly diminished the light induced EPR signals from Q_A^-•, Car^+•/Chl^+• and oxidized Cyt_b559, while enhancing the amplitude of the S₁Tyr_Z• EPR signal in the intact PSII sample. The quantification and stability of the g = 1.95-1.86 EPR signal and signals arising from the oxidized Tyr_Z and the side-path electron donors, respectively, indicate that the EPR-detectable g = 1.95-1.86 Q_A^-• signal is only correlated to reaction centers undergoing oxidation of the side-path electron donors (Car/Chl_Z/Cyt_b559), but not of Tyr_Z. These results imply that two types of Q_A^-• probably exist in the intact PSII sample. The structural difference and possible function of the two types of Q_A are discussed.     

Syntheses, structures and photophysical properties of a series of Zn-Ln coordination polymers (Ln = Nd, Pr, Sm, Eu, Tb, Dy)

Six novel heterometallic Zn-Ln coordination polymers {[ZnLnCl(pydc)₂(H₂O)₆]·3H₂O}_n (Ln = Nd 1, Pr 2, Sm 3, Eu 4, Tb 5, Dy 6; pydc = pyridine-2,5-dicarboxylate) were synthesized by the hydrothermal method, and their structures were measured by the single-crystal X-ray diffraction. The IR and UV-Vis-NIR absorption spectra, and the luminescence spectra in the visible and near-infrared (NIR) regions of the six complexes were determined at room temperature. They possess the same crystal structure, and the Zn(II) and Ln(III) ions in each complex are bridged into 1D infinite chain by pyridine-2,5-dicarboxylates. Meanwhile, there are numerous hydrogen bonds which result in the 3D hydrogen bonding network in the crystal. In the visible and NIR regions, the emission spectra of the complexes show the characteristic bands of the corresponding Ln(III) ions, which are mainly attributed to the sensitization from the d-L-moiety to f-L-moiety after forming the Zn-Ln complexes. In this paper, we first report the Zn-Sm complex which can exhibit the emission bands of Sm(III) in the NIR region, and discuss the sensitization from the d-L-moiety to f-L-moiety on the basis of the different characteristics of levels for different Ln(III) ions.     

Synthesis, crystalline structure and photoluminescence investigations of the new trivalent rare earth complexes (Sm, Eu and Tb) containing 2-thiophenecarboxylate as sensitizer

New complexes with the general formula [RE(TPC)₃ · (H₂O)₂], where RE=Eu³⁺, Sm³⁺, Gd³⁺, Tb³⁺ and TPC=2-thiophenecarboxylate, have been prepared and investigated by photoluminescence spectroscopy. These compounds were characterized by complexometric titration, elemental analyses and infrared spectroscopy. The X-ray crystal structure has been determined for the [Eu(TPC)₃ · (H₂O)₂] compound, indicating that this complex is in dimeric form bridged by two carboxylate ions with monoclinic crystal system and space group P2₁/n. The coordination polyhedron can be described as a distorted square antiprism, where six oxygen atoms belong to the TPC ligand and two oxygen atoms belong to the water molecules, with site symmetry close to C_2v. The theoretical value of the intensity parameter , which is in agreement with the experimental one, indicates that the Eu³⁺ ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the ligand triplet state (T) of TPC to the excited levels of the Eu³⁺ ion is discussed. The emission quantum efficiency of the ⁵D₀ emitting level of the Eu³⁺ ion was also determined. In the case of the Tb³⁺ ion, the photoluminescence data show the high emission intensity of the characteristic transitions ⁵D₄ → ⁷F_J (J=0-6), indicating that the TPC ligand is a good sensitizer. It is also noticed that the complexes with the Eu³⁺ and Tb³⁺ ions are more luminescent than the complex with the Sm³⁺ ion.     

New supramolecular complexes generated from Mn, Fe, Co, Zn, Fe with a bent dipyridyl ligand: Metal- and anion-directed assembly

Assemblies of an angular dipyridyl ligand 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (4-bpo) with a series of metal perchlorate afford five new supramolecular complexes with the general formula of [M(4-bpo)₂(H₂O)₄] · (4-bpo)₂ · (anion) · (solvent), in which M = Mn^II for 1, Fe^II for 2, Co^II for 3, Zn^II for 4, and Fe^III for 5. Although similar molecular structures and compositions are found for these mononuclear complexes, they display two types of supramolecular lattices. Complexes 1, 4 and 5 similarly crystallize in space group P2/n or P2/c. The complex cations, free 4-bpo and lattice water are linked to generate 2D layered frameworks with the aid of hydrogen bonding, and the counter anions are located within and between (also methanol in 5) these 2D arrays. However, complexes 2 and 3 are isostructural in space group . Two types of alternate 2D layers consisting of complex cations and free 4-bpo components, respectively, are observed with the anions and lattice water locating between them. These motifs are interlinked by complicated hydrogen-bonding to form a 3D intercalated network. Moreover, when Co(NO₃)₂ is used instead of Co(ClO₄)₂ in the assembly of 3, a 1D polymeric chain complex {[Co(4-bpo)(H₂O)₂(NO₃)₂](H₂O)₃}_n (6) is generated. These results indicate that the choice of metal ion and anion exerts a significant influence on governing the target complexes. A comparison of the structural features for all metal perchlorate complexes with 4-bpo is also briefly discussed.     

Synthesis, structures and luminescent properties of new heterobimetallic Zn-4f Schiff base complexes

A series of new 3d-4f heterobimetallic Schiff base complexes of the general formula [Zn(μ-L²)Ln(NO₃)₃(H₂O)_n] (Ln = La 1, Nd 2, Gd 3, Er 4 and Yb 5; n = 1 or 2; H₂L² = N,N′-bis(3-methoxy-5-p-tolylsalicylidene)ethylene-1,2-diamine) are synthesized and characterized. Complexes 1, 2, 4 and 5 are structurally characterized by X-ray crystallography. The photophysical properties of these complexes are also investigated. At room temperature, complexes 1-5 exhibit similar solution absorption and emission spectra in the UV-Vis region. Furthermore, compounds 2, 4 and 5 exhibit solution emission corresponding to the lanthanide(III) ion in the near-infrared region at room temperature. The triplet state emission of the 3d-4f bimetallic complexes without energy transfer is also determined through the photophysical study of complex 3.     

The C-N coupling reaction of pendant naphthyl group of palladium(II) complexes of 1-alkyl-2-(naphthyl-β-azo)imidazoles. Structural characterization, spectral and redox properties, and correlation with DFT computed data

The reaction of Pd(β-NaiR)Cl₂ (2) [β-NaiR (1) = 1-alkyl-2-(naphthyl-β-azo)imidazoles] with ArNH₂ in MeCN has yielded a C-N coupled product chloro[1-alkyl-2-{(7-imidoaryl)naphthyl-β-azo}imidazole-N,N′,N′′]palladium(II), Pd(β-NaiR-N-Ar)Cl (3-5) and coupling takes place at ortho-C-H position of pendant naphthyl group. The structural confirmation has been achieved by single crystal X-ray structure determination of the representative complexes, Pd(β-NaiEt)Cl₂ (2b) and Pd(β-NaiEt-N-C₆H₄-Cl-p)Cl (5b). The electronic spectra of the products, 3-5, exhibit characteristic transition within 600-900 nm those are absent in Pd(β-NaiR)Cl₂ (2). Cyclic voltammogram shows one oxidative response and two ligand reductions. The products are emissive. The excited state decays via radiative and non-radiative biexponential routes. The electronic structure, spectra and redox properties are explained by DFT computation.     

Synthetic, spectroscopic and X-ray crystallographic structural studies on copper(II) complexes of the aminoguanizone of pyruvic acid

Copper(II) complexes of general empirical formula, CuX(Hagpa) · nH₂O and Cu(agpa) · 2H₂O (H₂agpa = aminoguanizone of pyruvic acid, X = Cl⁻, Br⁻, , CH₃COO⁻, , n = 0, 1, 1.5, 2), have been synthesized and characterized by IR, EPR spectroscopy and X-ray crystallography. The IR spectra of the complexes showed the ONN coordination of the ligand to copper(II) ion. The crystal structures of H₂agpa · H₂O and complexes [Cu(Hagpa)Br] and [Cu₂(Hagpa)₂(H₂O)₂(SO₄)] · DMSO showed an invariable conformation and coordination mode for the uninegatively charged tridentate ligand and revealed the formation of linear polymers in which bromide or sulfate anions bridge the copper(II) ions. The EPR spectra for complexes CuX(Hagpa) · nH₂O are described by spin Hamiltonian for S = 1/2, without hyperfine structure. The g-tensor is symmetrical for Cu(agpa) · 2H₂O, has tri-axial anisotropy for sulfate complexes, and exhibits axial symmetry for the other compounds investigated.     

Low-spin, mononuclear, Fe(III) complexes with P,N donor hemilabile ligands: A combined experimental and theoretical study

Two new mononuclear Fe(III) complexes, [FeCl₃{PPh₂(p-C₆H₄NMe₂)-P}₃](1) (PPh₂(p-C₆H₄NMe₂): 4-(dimethylamino)phenyldiphenylphosphine) and [FeCl₃(PPh₂py-P)(PPh₂py-P,N)] (2) (PPh₂py: diphenyl(2-pyridyl)phosphine) were synthesized by reacting anhydrous FeCl₃ with respective ligand in acetonitrile solution under refluxing condition. Both the complexes were characterized by elemental analysis, FAB-Mass, FTIR, UV-Vis, ESR, Cyclic Voltammetry and magnetic measurement. The FAB mass spectra of complexes 1 and 2 show molecular ion peak at m/z 1078 [M]⁺ and m/z 687 [M−1]⁺, respectively, indicating mononuclear nature of the complexes. UV-Vis spectra of the complexes were consistent with low-spin, octahedral geometry. The variable temperature magnetic susceptibility measurement (73-323 K) of these complexes is also consistent with the paramagnetic nature of the complexes with a ground state spin S = ½. The Fe(III) centers of these two complexes remain low-spin, both at room temperature and liquid nitrogen temperature, was also indicated by the ESR analysis. Cyclic Voltammetry of both the complexes show an irreversible oxidation wave attributed to Fe³⁺ → Fe⁴⁺ + e⁻ along with the peak for ligand oxidation. Theoretical calculations (B3LYP) of the complexes show that for complex 1, a trans geometry of the two phosphorous atoms and for complex 2, a mer,cis structures are the most favored geometrical isomer. TDDFT calculations were performed to interpret the observed bands in the UV-Visible spectra.     

Physiological alterations due to field salinity stress in melon (<Emphasis Type="Italic">Cucumis melo</Emphasis> L.)

This study was aimed to assess physiological responses of melon (Cucumis melo L.) cultivars to salinity stress under field conditions. Seventeen melon cultivars including 16 widely distributed native and one exotic (‘Galia’) were subjected to 2-year (2014–2015) field salinity stress. Leaf relative water content (RWC), membrane stability index (MSI), pigments [chlorophyll a, b, total chlorophyll (TChl), carotenoid (Car) and their ratios], malondialdehyde (MDA), H₂O₂ content, proline content (Pro), total soluble sugar content (TSC), salinity tolerance and susceptibility indices as well as yield were evaluated. The results of combined analysis of variance showed significant genotypic variation for all the traits and significant effect of salinity stress on all the traits with the exception of Chla/Chlb and TChl/Car ratios. Overall, field salinity stress caused an increase in leaf MDA, H₂O₂, Chla, Chlb, TChl, Car, Pro and TSC and caused a reduction in leaf MSI and RWC as well as yield. The results of correlation coefficients showed that accumulation of osmolytes (proline and TSC) led to an increase in RWC and a decrease in MDA contents. In addition, the results of multiple regression analysis showed that leaf MDA, TSC, MSI and Chla contents were the most important predictors of yield justifying 72% total variation of yield under saline conditions. These results may highlight a dynamic interplay among biomarkers for lipid peroxidation (MDA), sugar osmolytes (TSC) and photosynthetic pigment (Chla) to maintain cell viability and cell wall integrity under salinity stress conditions in melon.     

Syntheses, crystal structures and thermal behaviors of three complexes with 4-acyl pyrazolone derivatives

Three new complexes, [Zn(PPePeP-PNH)(CH₃OH)]₂(CH₃OH) [PPePeP-PHN = N-(1-phenyl-3-phenylethyl-4-phenylethylene-5-pyrazolone) p-nitrobenzoylhydrazide] (1), [Mn(PPePeP-PNH)(CH₃OH)₂]₂(CH₃OH) (2), [Mn(PM4MbP-PNH)(C₂H₅OH)₃] [PM4MbP-PHN = N-(1-phenyl-3-methyl-4-(p-methylbenzoylene)-5-pyrazolone) p-nitrobenzoylhydrazide] (3), have been prepared and characterized by elemental analyses, IR spectra, UV-Vis absorption spectra, thermal-analyses and X-ray diffraction studies. The structural analyses show that the N(2) atoms of the pyrazolyl heterocycles play an important role in building the N-H?O hydrogen bonds of 1, 2, 3 and 1, 2 formed 2D networks and 3 formed 1D chain linked by hydrogen bonds, respectively.     

A series of d transition metal coordination complexes: Structures and comparative study of surface electron behaviors (n = 9, 8, 7, 6, 5)

Ten transition metal coordination complexes [Cu₂(phen)(p-tpha)(μ-O)]_n1, [Cu(m-tpha)(imH)₂]_n2, [Ni(5-Haipa)₂(H₂O)₂]_n3, [Ni(phen)₂(H₂O)₂]·btc·[Ni(H₂O)₆]_0.5·9H₂O 4, [Co(2,5-pdc)(H₂O)₂]_n·nH₂O 5, [Co₂(2,5-pdc)₂(H₂O)₆]_n·2nH₂O 6, [Fe(2,5-Hpdc)₂(H₂O)₂]·H₂O 7, [Co(C₆H₄NO₂)₃]·H₂O 8, [Fe₂(μ₂-btec)(μ₂-H₂btec)(bipy)₂(H₂O)₂]_n9, [Mn(phen)(2,5-pdc)(H₂O)₂]·H₂O 10 (H₄btec = 1,2,4,5-benzenetetracarboxylic acid, phen = 1,10-phenanthroline, 2,5-H₂pdc = 2,5-pyridine-dicarboxylic acid, p-tpha = p-phthalic acid, m-tpha = m-phthalic acid, bipy = 2,2′-bipyridine, 5-H₂aipa = 5-aminoisophthalic acid, imH = imidazole, H₃btc = 1,3,5-benzenetricarboxylic acid) were synthesized through hydrothermal method. They were characterized by UV-Vis absorption spectra, single-crystal X-ray diffraction and surface photovoltage spectra (SPS). Structural analysis indicated that the complexes 1, 2, 3, 5, 6 and 9 were linked into infinite structures bridged by organic acid ligands. The other four complexes were molecular complexes and further connected to 2D or 3D structures by the hydrogen bonds. The SPS of complexes 1-10 indicate that there are positive response bands in the range of 300-800 nm showing different levels of photo-electric conversion properties. The intensity, position, shape and the number of the response bands in SPS are obviously different since the structure, species, valence, dⁿ electrons configuration and coordinated environment of the center metals are different. There are good relationships between SPS and UV-Vis spectra.     

Dicopper(II) complexes showing DNA hydrolase activity and monomeric adduct formation with bis(4-nitrophenyl)phosphate

Ferromagnetic dicopper(II) complexes [Cu₂(μ-O₂CCH₃)(μ-OH)(L)₂(μ-L¹)](PF₆)₂, where L = 1,10-phenanthroline (phen), L¹ = H₂O in 1 and L = dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq), L¹ = CH₃CN in 2, are prepared and structurally characterized. Crystals of 1 and 2 belong to the monoclinic space group of P2₁/n and P2₁/m, respectively. The copper(II) centers display distorted square-pyramidal geometry having a phenanthroline base and two oxygen atoms of the bridging hydroxo and acetate group in the basal plane. The fifth coordination site has weak axially bound bridging solvent molecule H₂O in 1 and CH₃CN in 2. The Cu···Cu distances are 3.034 and 3.046 Å in 1 and 2, respectively. The complexes show efficient hydrolytic cleavage of supercoiled pUC19 DNA as evidenced from the mechanistic studies that include T4 DNA ligase experiments. The binuclear complexes form monomeric copper(II) adducts [Cu(L)₂(BNPP)](PF₆) (L = phen, 3; dpq, 4) with bis(4-nitrophenyl)phosphate (BNPP) as a model phosphodiester. The crystal structures of 3 and 4 reveal distorted trigonal bipyramidal geometry in which BNPP binds through the oxygen atom of the phosphate. The kinetic data of the DNA cleavage reactions of the binuclear complexes under pseudo- and true-Michaelis-Menten conditions indicate remarkable enhancement in the DNA hydrolysis rate in comparison to the control data.