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.     

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.     

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.     

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.     

Redox Isomerism in the S3 State of the Oxygen-Evolving Complex Resolved by Coupled Cluster Theory

The electronic and geometric structures of the water-oxidizing complex of photosystem II in the steps of the catalytic cycle that precede dioxygen evolution remain hotly debated. Recent structural and spectroscopic investigations support contradictory redox formulations for the active-site Mn₄CaO_x cofactor in the final metastable S₃ state. These range from the widely accepted Mn^IV₄ oxo-hydroxo model, which presumes that O−O bond formation occurs in the ultimate transient intermediate (S₄) of the catalytic cycle, to a Mn^III₂Mn^IV₂ peroxo model representative of the contrasting “early-onset” O−O bond formation hypothesis. Density functional theory energetics of suggested S₃ redox isomers are inconclusive because of extreme functional dependence. Here, we use the power of the domain-based local pair natural orbital approach to coupled cluster theory, DLPNO-CCSD(T), to present the first correlated wave function theory calculations of relative stabilities for distinct redox-isomeric forms of the S₃ state. Our results enabled us to evaluate conflicting models for the S₃ state of the oxygen-evolving complex (OEC) and to quantify the accuracy of lower-level theoretical approaches. Our assessment of the relevance of distinct redox-isomeric forms for the mechanism of biological water oxidation strongly disfavors the scenario of early-onset O−O formation advanced by literal interpretations of certain crystallographic models. This work serves as a case study in the application of modern coupled cluster implementations to redox isomerism problems in oligonuclear transition metal systems.     

Oxygen-evolving Activity in Photosystem II Core Complex of Photosynthetic Membrane in the Presence of Native Lipid

ＩｎｔｒｏｄｕｃｔｉｏｎＯｘｙｇｅｎｉｃｐｈｏｔｏｓｙｎｔｈｅｓｉｓｉｓｃａｒｒｉｅｄｏｕｔｉｎｐｈｏｔｏｓｙｎ ｔｈｅｔｉｃｍｅｍｂｒａｎｅｓｉｎｗｈｉｃｈｈｉｇｈｌｙｏｒｇａｎｉｚｅｄｐｉｇｍｅｎｔ ｐｒｏ ｔｅｉｎｃｏｍｐｌｅｘｅｓａｒｅｅｍｂｅｄｄｅｄｉｎｔｈｅｌｉｐｉｄｍａｔｒｉｘ .Ｉｔｉｓｗｅｌｌｅｓｔａｂｌｉｓｈｅｄｔｈａｔｓｐｅｃｉｆｉｃｉｎｔｅｒａｃｔｉｏｎｓｍｉｇｈｔｅｘｉｓｔｂｅ ｔｗｅｅｎｐｉｇｍｅｎｔ ｐｒｏｔｅｉｎｃｏｍｐｌｅｘｅｓａｎｄｌｉｐｉｄｓ .Ｆｏｒｅｘａｍ ｐｌｅ…     

Determination of the Nanostructure of Polymer Materials by Electron Paramagnetic Resonance Spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy is one the few methods that can characterize structural features in the range between 0.5 and 5 nm in systems that lack long‐range order. Approaches based on EPR spectroscopy provide good structural contrast even in complex materials, as the sites of interest can be selectively labeled or addressed by suitably functionalized spin probes using well established techniques. This article assesses the EPR experiments available for distance measurements on nanoscales in terms of the accessible distance range, precision, and sensitivity. Recommendations are derived for the proper choice of experiment for a given problem. Both simple and sophisticated methods for data analysis are described and their limitations are evaluated. It is discussed which assumptions must be made to extract a pair correlation function from EPR data. Finally, applications to the study of polymer chain conformation and the structure of ionically functionalized diblock copolymers are highlighted.     

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.     

Temperature-Dependent Formation of Redox Sites in Molybdenum Trioxide Studied by Electron Paramagnetic Resonance Spectroscopy

The formation and qualification of redox sites in transition metal oxides are always the active fields related to electronics, catalysis, sensors, and energy-storage units. In the present study, the temperature dependence of thermal reduction of MoO₃ was surveyed at the range of 350 ℃ to 750 ℃. Upon reduction, the formed redox species characterized by EPR spectroscopy are the Mo^V ion and superoxide anion radical (O₂^-) when the reduction was induced at the optimal temperature of 300-350 ℃. When heating-up from 350 ℃, the EPR signals started to decline in amplitude. The signals in the range of 400-450 ℃ decreased to half of that at 350 ℃, and then to zero at ~600 ℃. Further treatment at even higher temperature or prolonged heating time at 500 ℃ caused more reduction and more free electrons were released to the MoO₃ bulk, which results in a delocalized means similar to the anti-ferromagnetic coupling. These data herein are helpful to prepare and study the metal-oxide catalysts.     

群青颜料呈色机理的电子顺磁共振研究

研究了阿富汗青金石矿石、敦煌石窟青金石颜料、合成群青的呈色机理。实验表明三者均有ｇ＝２．０２９峰，前两者多一个ｇ＝２．０４７峰，４００℃时，ｇ＝２．０４７峰变平，６００℃时消失。ｇ＝２．０２９峰随温度升高而增强，８００℃时增强放慢，颜色也随温度变深。在Ｍ０Ｏ３／ＳｉＯ２和Ｍ０Ｏ３／Ａｌ２Ｏ３表面上，Ｓ２＾－的ＥＰＲ有ｇ１＝２．０４７，ｇ２＝２．２０８，ｇ３＝１．９９８三个分量。因此，群青、青金石和     

EPR法研究自由基在移植免疫中的作用

用电子顺磁共振（ＥＰＲ）法，化学发光法及荧光光谱法研究了１００例正常人、４２例角膜移值患者泪液中的自由基、超氧化物岐化酶（ＳＯＤ）和水溶性脂质过氧化物（ＷＳＬＰ）等指标．结果表明正常人泪液中自由基的自旋浓度是（３．６±０．５８）×１０１２ｓｐｉｎｓ／ｍＬ，ＳＯＤ浓度为（３．８４±１．４５）μｇ／Ｌ、水溶性脂质过氧化物相对荧光强度为９．５９８～１６．２２５Ｕ／ｍＬ．角膜移植后三项指标变化出现两个规律的峰，这种规律性变化在三项指标间存在显著的相关性．其中５例患者的特殊变化证明移植排斥反应与术后这些变化的进一步持续发展有关     

Ce1－xNdxO2－δ固溶体的电子顺磁共振谱和阻抗谱的研究

利用溶胶-凝胶方法在800 ℃焙烧10 h后, 合成了固溶体Ce_1－xNd_xO_2－δ (x＝0.05～0.55), X射线衍射(XRD)测试表明固溶体已经形成立方萤石结构; 电子顺磁共振谱(EPR)研究表明在固溶体Ce_1－xNd_xO_2－δ中随着掺杂量x的增大, Ce^3＋离子含量减少, 说明掺杂Nd^3＋离子可以抑制Ce^4＋的还原; 交流阻抗谱的测量表明固溶体Ce_0.9Nd_0.1O_2－d 具有离子导电特性, 600和700 ℃时的电导率分别为4.25×10^－3和1.12×10^－2 S•cm^－1, 活化能为0.68 eV.     

Thermal Behaviour of Tin(II) Complex With 8-hydroxyquinolinate in the Solid State

Tin(II) complexes with 8-hydroxyquinolinate in solid state have been obtained by adding aqueous ammonium to a solution containing stannous chloride and 8-hydroxiquinoline in medium of HCl and acetone up to pH 5 and 9, respectively. The products obtained show the same composition, Sn(C₉H₆ON)₂; however there are some differences regarding both the thermal behaviour in an oxidant atmosphere and morphology. These products were characterised by elemental and complexometric analysis, TG and DTA curves, infrared and X-ray diffractometry. TG curves show, above 448 K, the partial oxidation on air atmosphere of Sn(II) complexes to Sn(IV) complexes, SnO(C₉H₆ON)₂. This behaviour does not depend only on pH in which the compounds were obtained but also on the heating rate in TG curves. Sn(II) complexes volatilise almost completely on nitrogen atmosphere and partially on air atmosphere depending on the oxidation degree of the compound. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthetic, X-ray Structure, Electron Paramagnetic Resonance, and Magnetic Studies of the Manganese(II) Complex of 1-Thia-4,7-diazacyclononane ([9]aneN(2)S)

Reaction of manganese(II) perchlorate hexahydrate with a methanol solution of 1-thia-4,7-diazacyclononane ([9]aneN(2)S) resulted in the isolation of the manganese(II) complex [Mn([9]aneN(2)S)(2)](ClO(4))(2). The X-ray structure of this complex is reported: crystal system orthorhombic, space group Pbam, No. 55, a = 7.937(2) ?,b = 8.811(2) ?, c = 15.531(3) ?, Z = 2, R = 0.0579. The complex is high spin (S = (5)/(2)) with an effective magnetic moment (&mgr;(eff)) 5.82 &mgr;(B) at 298 K and 5.65 &mgr;(B) at 4.2 K. Computer simulation of the Q-band EPR spectrum of [Mn([9]aneN(2)S)(2)](ClO(4))(2) yields g = 1.99 +/- 0.01, |D| = 0.19 +/- 0.005 cm(-)(1), and E/D = 0.04 +/- 0.02. For the analogous hexaamine complex [Mn([9]aneN(3))(2)](ClO(4))(2) ([9]aneN(3) = 1,4,7-triazacyclononane) analysis of the EPR spectra produced the following values: g = 1.98 +/- 0.01, |D| = 0.09 +/- 0.003 cm(-)(1), and E/D = 0.1 +/- 0.01. The spin Hamiltonian parameters for [Mn([9]aneN(2)S)(2)](ClO(4))(2) derived from the EPR spectra produced a good fit to the magnetic susceptibility data.     

Methane Oxidation over Cu2+/[CuOH]+ Pairs and Site-Specific Kinetics in Copper Mordenite Revealed by Operando Electron Paramagnetic Resonance and UV/Visible Spectroscopy

Cu-exchanged mordenite (MOR) is a promising material for partial CH₄ oxidation. The structural diversity of Cu species within MOR makes it difficult to identify the active Cu sites and to determine their redox and kinetic properties. In this study, the Cu speciation in Cu-MOR materials with different Cu loadings has been determined using operando electron paramagnetic resonance (EPR) and operando ultraviolet-visible (UV/Vis) spectroscopy as well as in situ photoluminescence (PL) and Fourier-transform infrared (FTIR) spectroscopy. A novel pathway for CH₄ oxidation involving paired [CuOH]⁺ and bare Cu²⁺ species has been identified. The reduction of bare Cu²⁺ ions facilitated by adjacent [CuOH]⁺ demonstrates that the frequently reported assumption of redox-inert Cu²⁺ centers does not generally apply. The measured site-specific reaction kinetics show that dimeric Cu species exhibit a faster reaction rate and a higher apparent activation energy than monomeric Cu²⁺ active sites highlighting their difference in the CH₄ oxidation potential.     

时间域方法分析镍卟啉的共振拉曼强度与S2激发态结构

研究了入射光波长与S0→S2跃迁共振的情形下,卟啉镍配合物（NiP）的振动拉曼光谱。用时间域方法计算了NiP的共振拉曼强度和吸收光谱。结果表明,相对于基态,S2态NiP的分子构型沿着ν8和ν2简正坐标有较大的位移。这些简正坐标主要涉及卟啉环的CαCm键和CβCβ键伸缩运动,以及CαCmCα变角运动。与基态相比, S2态的CβCβ、 CαCm和CαN键分别增大0.27、 0.14、 0.07 pm,而CαCβ键则减小0.20 pm,与前人的赝势分子轨道计算（SPMO）结果相近。还从RR强度角度讨论了S2态的Jahn-Teller畸变。