Oxygen—evloving Activity in PhotosystemⅡ Core Complex of Photosynthetic Membrane in the Presence of Native Lipid

The techniques of oxygen electrode polarography and Fourier transform infrared (FT‐IR) spectroscopy were employed to explore the involvement of digalactosyl diacylglycerol (DGDG) in functional and structural roles in the photosystem II core complex (PSIICC). It was shown that DGDG exhibited the ability to stimulate the oxygen evolution in PSIICC, which was accompanied by the changes in the structures of PSIICC proteins. The results revealed that there existed hydrogen‐bonding interactions between DGDG molecules and PSIICC proteins. It is most likely that the sites of PSIICC interaction with DGDG are in the extrinsic protein of 33 kDa.     

Mn2Ca双金属簇合物组装去Mn光系统II水氧化复合物的研究

报道了Mn₂Ca双金属簇合物与去锰的PSII 颗粒的光组装过程, 发现Mn₂Ca化合物具有明显的恢复去锰PSII的电子传递和放氧活性的能力, 并且表现了比MnCl₂更高的光组装效率. 我们认为该化合物中Ca与Mn原子之间的羧酸酯桥的连接方式可能有利于水氧化复合物(WOC)的光组装及锰簇的稳定.     

光合放氧复合物结构及其放氧机理的研究

光合水氧化是地球上最重要的生化过程之一.光合放氧生物包括光系统Ⅰ(PSⅠ)和光系统Ⅱ(PSⅡ)两种类型反应中心,光系统Ⅱ反应中心能以水作为电子给体,利用光能氧化水产生质子和氧气.对于水如何被氧化这个难题前人已做了大量的工作,但到目前为止放氧复合物(OEC)的结构及水氧化的机理仍不清楚.本文结合当前研究结果,就光合放氧复合物的结构及光合放氧机理进行了综述,希望能有助于推进这方面的工作.     

LaCl3提高菠菜光系统Ⅱ活性的作用机制

The effect of LaCl3 on the K3Fe(CN)6 (FeCy) reduction rate and the oxygen-evolving rate of PSU particles of spinach, and the spectral characterization of the D1/D2/Cytb559 of a PSII reaction center complex consisting of three polypeptides from spinach were studied. The experimental results showed that LaCl3 could significantly accelerate the transformation from light energy to electric energy, the electron transport, water photolysis and oxygen evolution of PSII of spinach, which was related to the spectral characterization of the D1/D2/Cytb559 complex.Soret band and Q band of Chl-a of UV-vis spectrum of D1/D2/Cytb559 complex were blue shifted, and the fluorescence emission peak was blue shifted in LaCl3 treated spinach compared with that in the control. The EXAFS (extended X-ray absorption fine structure spectroscopy) revealed that La^3 was coordinated with 8 nitrogen or oxygen atoms in the first coordination shell with La-N or La-O bond length of 0.254 nm, and with 6 nitrogen or oxygen atoms in the second coordination shell with La-N or La-O bond length of 0.321 nm in the D1/D2/Cytb559 complex. The CD suggested that the secondary structure of D1/D2/Cytb559 complex have been litfie affected by the treatment of LaCl3.     

Mn2Ca双金属簇合物组装去Mn光系统II水氧化复合物的研究

报道了Mn₂Ca双金属簇合物与去锰的PSII 颗粒的光组装过程, 发现Mn₂Ca化合物具有明显的恢复去锰PSII的电子传递和放氧活性的能力, 并且表现了比MnCl₂更高的光组装效率. 我们认为该化合物中Ca与Mn原子之间的羧酸酯桥的连接方式可能有利于水氧化复合物(WOC)的光组装及锰簇的稳定.     

Rationalizing the Geometries of the Water Oxidising Complex in the Atomic Resolution,Nominal S3 State Crystal Structures of Photosystem II

Three atomic resolution crystal structures of Photosystem II, in the double flashed, nominal S₃ intermediate state of its Mn₄Ca Water Oxidising Complex (WOC), have now been presented, at 2.25, 2.35 and 2.08 Å resolution. Although very similar overall, the S₃ structures differ within the WOC catalytic site. The 2.25 Å structure contains only one oxy species (O5) in the WOC cavity, weakly associated with Mn centres, similar to that in the earlier 1.95 Å S₁ structure. The 2.35 Å structure shows two such species (O5, O6), with the Mn centres and O5 positioned as in the 2.25 Å structure and O5−O6 separation of ∼1.5 Å. In the latest S₃ variant, two oxy species are also seen (O5, Ox), with the Ox group appearing only in S₃, closely ligating one Mn, with O5−Ox separation <2.1 Å. The O5 and O6/Ox groups were proposed to be substrate water derived species. Recently, Petrie et al. (Chem. Phys. Chem., 2017 ) presented large scale Quantum Chemical modelling of the 2.25 Å structure, quantitatively explaining all significant features within the WOC region. This, as in our earlier studies, assumed a ‘low’ Mn oxidation paradigm (mean S₁ Mn oxidation level of +3.0, Petrie et al., Angew. Chem. Int. Ed., 2015 ), rather than a ‘high’ oxidation model (mean S₁ oxidation level of +3.5). In 2018 we showed (Chem. Phys. Chem., 2018 ) this oxidation state assumption predicted two energetically close S₃ structural forms, one with the metal centres and O5 (as OH⁻) positioned as in the 2.25 Å structure, and the other with the metals similarly placed, but with O5 (as H₂O) located in the O6 position of the 2.35 Å structure. The 2.35 Å two flashed structure was likely a crystal superposition of two such forms. Here we show, by similar computational analysis, that the latest 2.08 Å S₃ structure is also a likely superposition of forms, but with O5 (as OH⁻) occupying either the O5 or Ox positions in the WOC cavity. This highlights a remarkable structural ‘lability’ of the WOC centre in the S₃ state, which is likely catalytically relevant to its water splitting function.     

光合放氧复合物锰簇光组装

在光系统II水氧化过程中, 由锰簇及其附近一个具氧化还原活性的酪氨酸Y_Z组成的光合放氧复合物通过4个连续的氧化还原反应将水裂解为质子和氧气。在光系统II的功能性组装过程中,光合放氧复合物锰簇是通过一个被称作光组装的过程形成的。结合当前的研究进展,本文详尽地介绍了光合放氧复合物锰簇光组装的动力学模型、与锰簇形成相关的蛋白及锰簇的外围配体、锰与去锰光系统II的结合特性、其它辅助因子对锰簇光组装的影响及锰簇光组装的机理。此外,结合我们的研究结果,对人工合成的锰化合物与去锰光系统II放氧复合物的光组装进行了综述和讨论。本文最后介绍了目前光合放氧复合物锰簇结构及功能研究中存在的一些问题,并对光合放氧复合物锰簇结构及功能研究的应用前景进行了展望。     

A Computational Study of the S2 State in the Oxygen-Evolving Complex of Photosystem II by Electron Paramagnetic Resonance Spectroscopy

The S₂ state produces two basic electron paramagnetic resonance signal types due to the manganese cluster in oxygen-evolving complex, which are influenced by the solvents, and cryoprotectant added to the photosystem II samples. It is presumed that a single manganese center oxidation occurs on S₁ → S₂ state transition. The S₂ state has readily visible multiline and g4.1 electron paramagnetic resonance signals and hence it has been the most studied of all the Kok cycle intermediates due to the ease of experimental preparation and stability. The S₂ state was studied using electron paramagnetic resonance spectroscopy at X-band frequencies. The aim of this study was to determine the spin states of the g4.1 signal. The multiline signal was observed to arise from a ground state spin ½ centre while the g4.1 signal generated at ≈140 K NIR illumination was proposed to arise from a spin 52 center with rhombic distortion. The ‘ground’ state g4.1 signal was generated solely or by conversion from the multiline. The data analysis methods used involved numerical simulations of the experimental spectra on relevant models of the oxygen-evolving complex cluster. A strong focus in this paper was on the ‘ground’ state g4.1 signal, whether it is a rhombic 52 spin state signal or an axial 32 spin state signal. The data supported an X-band CW-EPR-generated g4.1 signal as originating from a near rhombic spin 5/2 of the S₂ state of the PSII manganese cluster.     

Investigation of Photosystem II Functional Size in Higher Plants under Physiological and Stress Conditions Using Radiation Target Analysis and Sucrose Gradient Ultracentrifugation

The photosystem II (PSII) reaction centre is the critical supramolecular pigment–protein complex in the chloroplast which catalyses the light-induced transfer of electrons from water to plastoquinone. Structural studies have demonstrated the existence of an oligomeric PSII. We carried out radiation inactivation target analysis (RTA), together with sucrose gradient ultracentrifugation (SGU) of PSII, to study the functional size of PSII in diverse plant species under physiological and stress conditions. Two PSII populations, made of dimeric and monomeric core particles, were revealed in Pisum sativum, Spinacea oleracea, Phaseulus vulgaris, Medicago sativa, Zea mais and Triticum durum. However, this core pattern was not ubiquitous in the higher plants since we found one monomeric core population in Vicia faba and a dimeric core in the Triticum durum yellow-green strain, respectively. The PSII functional sizes measured in the plant seedlings in vivo, as a decay of the maximum quantum yield of PSII for primary photochemistry, were in the range of 75–101 ± 18 kDa, 2 to 3 times lower than those determined in vitro. Two abiotic stresses, heat and drought, imposed individually on Pisum sativum, increased the content of the dimeric core in SGU and the minimum functional size determined by RTA in vivo. These data suggest that PSII can also function as a monomer in vivo, while under heat and drought stress conditions, the dimeric PSII structure is predominant.     

Density Functional Calculations of 55Mn, 14N and 13C Electron Paramagnetic Resonance Parameters Support an Energetically Feasible Model System for the S2 State of the Oxygen‐Evolving Complex of Photosystem II

Metal and ligand hyperfine couplings of a previously suggested, energetically feasible Mn₄Ca model cluster ( SG2009^?1 ) for the S₂ state of the oxygen‐evolving complex (OEC) of photosystem II (PSII) have been studied by broken‐symmetry density functional methods and compared with other suggested structural and spectroscopic models. This was carried out explicitly for different spin‐coupling patterns of the S=1/2 ground state of the Mn^III(Mn^IV)₃ cluster. By applying spin‐projection techniques and a scaling of the manganese hyperfine couplings, computation of the hyperfine and nuclear quadrupole coupling parameters allows a direct evaluation of the proposed models in comparison with data obtained from the simulation of EPR, ENDOR, and ESEEM spectra. The computation of ⁵⁵Mn hyperfine couplings (HFCs) for SG2009^?1 gives excellent agreement with experiment. However, at the current level of spin projection, the ⁵⁵Mn HFCs do not appear sufficiently accurate to distinguish between different structural models. Yet, of all the models studied, SG2009^?1 is the only one with the Mn^III site at the Mn_C center, which is coordinated by histidine (D1‐His332). The computed histidine ¹⁴N HFC anisotropy for SG2009^?1 gives much better agreement with ESEEM data than the other models, in which Mn_C is an Mn^IV site, thus supporting the validity of the model. The ¹³C HFCs of various carboxylates have been compared with ¹³C ENDOR data for PSII preparations with ¹³C‐labelled alanine.     

Synthesis and Crystal Structure of a Copper(II) Complex with Benzilic Acid and 1,10-Phenanthroline

A new complex [Cu(phen)3][(C6H5)2C(OH)COO]2·6H2O was prepared by self-assembly of benzilic acid, 1,10-phenanthroline (phen), and copper perchlorate. It crystallizes in triclinic, space group P1, with a = 1.14661(17), b = 1.6455(2), c = 1.6457(2) nm, α = 74.779(2), β = 74.904(3), γ = 84.424(3)o, V = 2.8914(7) nm3, Dc = 1.340 g/cm3, Z = 2, F(000) = 1218, GOOF = 1.018, the final R = 0.0643 and wR = 0.1633. The crystal structure shows that the copper ion is coordinated with six nitrogen atoms from six 1,10-phenanthroline molecules, forming a distorted octahedral coordination geometry.     

一维链状镉配合物的合成及结构表征

在甲醇体系中合成了镉配合物[Cd(L)₂(H₂O)₂](ClO₄)₂·MeOH (1)[L=1,3,5-三(3-吡啶基甲氧基)苯]。通过元素分析及X-射线单晶衍射对其进行了表征。结构分析结果表明该化合物属于三斜晶系,P1空间群,晶胞参数为a=1.057 1(5) nm,b=1.059 0(5) nm,c=1.270 8(7) nm,α=87.460(16)°,β=81.895(17)°,γ=62.326(14)°,晶胞体积V=1.247 0(11) nm³,Z=1,D_calc=1.569 g·cm^-3,F(000)=604,μ=6.26 cm^-1,R=0.035 2,wR=0.066 4。在化合物1中,每个Cd(II)的配位环境为变形八面体,而每个配体L通过其两个吡啶基团连接2个Cd(II)形成一维链状结构,并进一步通过O-H…N,O-H…O和C-H…O氢键作用形成了一个具有三维结构的超分子化合物。     

双核铜(Ⅱ)配合物在H2O2存在下对DNA的氧化切割活性

A novel dinuclear copper(Ⅱ) complex, [Cu₂(phen)(dipic)₂(H₂O)₂]·2H₂O (phen=1,10-phenanthroline, dipicH₂=2,6-pyridinedicarboxylic acid), has been prepared and structurally characterized. The complex crystallizes in the triclinic system, space group P1 with cell parameters a=0.846 0(17) nm, b=1.289 5(3) nm, c=1.452 7(3) nm, α=77.42(3)°, β=79.11(3)°, γ=87.08(3)°, and V=1.518 8(6) nm³. The dinuclear complex shows potential DNA cleavage activity at micromolar concentration in the presence of H₂O₂ and exhibits higher nuclease efficiency than mononuclear complex [Cu(dipic)(H₂dipic)]·H₂O. Without external reductants, the added H₂O₂ may contribute to the generation of hydroxyl radicals that result in DNA strand scission.CCDC:291786.     

Synthesis and Crystal Structure of a Novel Polymeric Thiocyanato-Bridged Heteronuclear Complex of Copper(II) and Cadmium(II)

The title polymeric complex of Cu(II) and Cd(II) bridged by thiocyanate, Cu(en)₂[Cd(SCN)₃]₂, has been prepared and its structure determined by X-ray diffraction (XRD) methods. The crystal structure reveals that the Cu(II) atom is in an elongated octahedral coordination formed by two SCN^– anions and two en molecules. The Cd(II) atom is in a distorted octahedral coordination formed by six bridging SCN^– anions. Two different bridging thiocyanate anions exist in the complex. Both 1,1--SCN^– and 1,3--SCN^– anion act a role of bridge ligand and link Cu(II), Cd(II) atoms, and adjacent Cd(II). Cd(II) atoms form the three-dimensional (3-D) network polymeric structure. The IR and UV-Vis spectra have also been investigated.     

Effect of Surfactant Microenvironment on SOD-like Activity of Cu(II)-Salicylate Complex

Cu(II)-salicylate was synthesized and characterized by X-ray diffraction. The reaction mechanism of the Cu(II) complex with superoxide anion was studied by ESR spectroscopy, and its (superoxide dismutase) SOD-like activity was determined by a modified illumination method in phosphate buffer (pH = 7.8), micelle solutions and lamellar liquid crystals formed from surfactants CTAB and TX-100. X-ray diffraction indicated that the Cu(II) complex had a formula Cu₂(Hsal)₄EtOHH₂O and a similar structure to the SOD active site. EPR spectra proved that the reaction mechanism of the Cu(II) complex catalyzing O ₂ ^.- dismutation was the same as that of the proposed dismutation reaction catalyzed by SOD. Results obtained by the NBT method indicated that the Cu(II)-complex showed SOD-like activity, and the effect of microenvironment created by surfactants on its activity was same as on SOD activity. The order of the inhibition of NBT reduction by the Cu(II)-complex in different microenvironments was: in phosphate buffer (pH = 7.8) > in TX-100 micelle > in TX-100 liquid crystal, and in nonionic TX-100 organized assemblies > in cationic CTAB organized assemblies. These results were explained by the catalytic effect of micelles, and by the space restriction and high viscosity of organized assemblies of surfactants.     

金属铜配合物的合成、晶体结构、抗癌活性及与牛血清白蛋白的相互作用

合成了一个含有席夫碱配体的四配位的铜配合物,通过元素分析、红外光谱对其进行表征并通过X射线单晶衍射仪测试它的结构,属于单斜晶系。此外,通过MTT法(MTT为3-(4,5-二甲基噻唑-2)-2,5-二苯基四氮唑溴盐)测试了配合物对宫颈癌细胞、胃癌细胞、肝癌细胞和乳腺癌细胞的细胞毒性。结果表明铜配合物对4种肿瘤细胞的活性比顺铂高。通过荧光光谱法研究了配合物与牛血清白蛋白的相互作用,荧光光谱表明配合物与血清结合过程中发生了静态猝灭,并且计算了结合常数、结合位点数、结合距离和热力学常数ΔH,ΔS和ΔG。     

Synthesis and Structure of L-Aspartato-nickel(II) Complex with Benzimidazole

1INTRODUCTIONThereisgreatinterestinthecoordinationabili-tyofaminoacidtometalionsandhydrogenbondinginvolvedintheaminoacid[1].Asabinaryaminoacid,theasparticacidisespeciallyimportantfromeitherbiologicalorsimplecoordinativepointofview.Somereportsshowedthechan…     

A Fluorescent Cobalt（II） Complex for the Recognition of Cations and Small Molecules： Synthesis, Structure and Characterization

A fluorescent cobalt(Ⅱ) complex, 1 [Co(H2bibim)2(5-nipa)], for the recognition of cations and small molecules constructed with 5-nitroisophthalic acid (5-H2nipa) and 2,2-biben-zimidazole(H2bibim) has been synthesized by hydrothermal methods and structurally characterized by elemental analysis, IR spectroscopy, PL and single-crystal X-ray diffraction. The cobalt units are six-coordinated by two H2bibim ligands and one 5-nitroisophthalic acid group, which are further connected into a three-dimensional (3D) network by intermolecular hydrogen bonds. Complex 1 exhibits fluorescence and thus has detection capabilities for different cations and small solvent molecules in the solution state at room temperature.