Dimer-of-dimers model for the oxygen-evolving complex of photosystem II. Synthesis and properties of [MnIV4O5(terpy)4(H2O)2](ClO4)6

A dimer-of-dimers model compound for the oxygen-evolving complex of photosystem II, [[(H(2)O)(terpy)Mn(IV)(micro-O)(2)Mn(IV)(terpy)](2)(micro-O)](ClO(4))(6) (terpy = 2,2':6',2' '-terpyridine), has been prepared and characterized by X-ray crystallography and ESI-MS. Low pH was found to promote the disproportionation of [Mn(III/IV)(2)O(2)(terpy)(2)(OH(2))(2)](3+) to Mn(2+) and a Mn(IV/IV)(2)O(2)(terpy)(2) species; the latter complex slowly dimerizes to form the title complex. Protonation of a micro-oxo bridge is proposed to initiate the disproportionation, based on analogy with the [Mn(III/)(IV)(2)O(2)(bpy)(4)](3+) system.     

Phase transitions of polycrystalline [Fe(H2O)6](ClO4)3 and [Cr(H2O)6](ClO4)3 studied by DSC

The effects of heat treatment on soymilk protein denaturation were studied by differential scanning calorimetry (DSC) and electrophoresis. Transition behavior of soymilk was studied by DSC. Three endotherms were found in DSC heating curves; the transition observed at around 70°C is attributed to the denaturation of 7S (b-conglycinin) and the transition at around 90°C is to 11S (glycinin). The denaturation temperature increased with the increasing soymilk protein content. The change of electrophoretic patterns after heat treatments indicated that soy proteins were dissociated into subunits, some of which coalesced. When the heating temperature is below their denaturation temperature, the protein fractions cannot completely be denatured even after heat exposure for extended periods of time. This revised version was published online in August 2006 with corrections to the Cover Date.     

DSC study of the phase transitions in [Ni(D2O)6](ClO4)2 and [Ni(H2O)6](ClO4)2

DSC measurements were carried out for [Ni(H₂O)₆](ClO₄)₂ (sampleH) and [Ni(D₂O)₆](ClO₄)₂ (sampleD) in the temperature range 300–380 K. For both compounds two anomalies on the DSC curves were detected. The results for sampleH are compared to those previously obtained using adiabatic calorimetry method. For both compounds studied in this work the high-temperature transition appears at the same temperature while the low-temperature one is shifted towards higher temperatures in sampleD. Disorder connected with H₂O or D₂O groups is suggested in the intermediate phase between the low- and high-temperature transitions.     

Electrochemical and chemical formation of [Mn4(IV)O5(terpy)4(H2O)2]6+, in relation with the photosystem II oxygen-evolving center model [Mn2(III,IV)O2(terpy)2(H2O)2]3+

To examine the real ability of the binuclear di-mu-oxo complex [Mn2(III,IV)O2(terpy)2(H2O)2]3+ (2) to act as a catalyst for water oxidation, we have investigated in detail its redox properties and that of its mononuclear precursor complex [Mn(II)(terpy)2]2+ (1) in aqueous solution. It appears that electrochemical oxidation of 1 allows the quantitative formation of 2 and, most importantly, that electrochemical oxidation of 2 quantitatively yields the stable tetranuclear Mn(IV) complex, [Mn4(IV)O5(terpy)4(H2O)2]6+ (4), having a linear mono-mu-oxo{Mn2(mu-oxo)2}2 core. Therefore, these results show that the electrochemical oxidation of 2 in aqueous solution is only a one-electron process leading to 4 via the formation of a mono-mu-oxo bridge between two oxidized [Mn2(IV,IV)O2(terpy)2(H2O)2]4+ species. 4 is also quantitatively formed by dissolution of the binuclear complex [Mn2(IV,IV)O2(terpy)2(SO4)2] (3) in aqueous solutions. Evidence of this work is that 4 is stable in aqueous solutions, and even if it is a good synthetic analogue of the "dimers-of-dimers" model compound of the OEC in PSII, this complex is not able to oxidize water. As a consequence, since 4 results from an one-electron oxidation of 2, 2 cannot act as an efficient homogeneous electrocatalyst for water oxidation. This work demonstrates that a simple oxidation of 2 cannot produce molecular oxygen without the help of an oxygen donor.     

Thermal properties of polycrystalline [Mn(NH3)6](ClO4)2

A flavor precursor α-ionyl-β-d-glucoside (IG) was synthesized by Koenigs–Knorr method, and its structure was characterized by proton nuclear magnetic resonance spectroscopy, Fourier transform-infrared spectroscopy, and electro spray ionization mass spectroscopy (MS). Thermal degradation behaviors of the intermediate α-ionyl-tetra-O-acetyl-β-d-glucoside (IAG) and IG were analyzed by thermogravimetry and online pyrolysis (Py)-gas chromatography–MS. Flavor release property of IG was investigated with cigarettes as the carrier. The results indicated that fracture temperature of glycosidic bond was about 200 °C for IAG, and was about 190 °C for IG. Py of IAG and IG could generate several aroma compounds such as megastigmatriene, α-ionol, α-ionone, and 3-oxo-α-ionol. IG added in cigarettes could be pyrolyzed to release α-ionol, α-ionone, and 3-oxo-α-ionone, and increase the release amount of megastigmatrienone in mainstream smoke during smoking. The release amount of characteristic flavor components in mainstream smoke remain stable after the cigarette sample with IG placed in standard condition for 30 days, and there was no significant difference in the single puff release amounts, which confirmed the flavor release stability and uniformity of IG under heating treatment.     

The mixed-valent manganese [3 x 3] grid [Mn(III)4Mn(II)5(2poap-2H)6](ClO4)10.10 H2O, a mesoscopic spin-1/2 cluster

The magnetic susceptibility and low-temperature magnetization curve of the [3 x 3] grid [Mn(III)4Mn(II)5(2poap-2H)6](ClO4)10.10 H2O (1) are analyzed within a spin Hamiltonian approach. The Hilbert space is huge (4,860,000 states), but the consequent use of all symmetries and a two-step fitting procedure nevertheless allows the best-fit determination of the magnetic exchange parameters in this system from complete quantum mechanical calculations. The cluster exhibits a total spin S = 1/2 ground state; the implications are discussed.     

A tetranuclear manganese carboxylate cluster with bis(2-pyridyl)amine ligation: [Mn4O2(O2CEt)7(bpya)2](ClO4)

The title complex has been prepared and characterized by X-ray crystallography, magnetochemistry, cyclic voltammetry and ¹H NMR spectroscopy. The complex contains a [Mn₄(μ₃-O)₂]⁸⁺ core with bridging EtCO₂ ⁻ and chelating bpya groups. The magnetochemical studies indicate an S=0 ground state as a result of antiferromagnetic exchange interactions between the Mn^III ions. The ¹H NMR spectra support retention of the solid-state structure on dissolution in MeCN.     

Characterization of the O(2)-evolving reaction catalyzed by [(terpy)(H2O)Mn(III)(O)2Mn(IV)(OH2)(terpy)](NO3)3 (terpy = 2,2':6,2"-terpyridine).

The complex [(terpy)(H(2)O)Mn(III)(O)(2)Mn(IV)(OH(2))(terpy)](NO(3))(3) (terpy = 2,2':6,2' '-terpyridine) (1)catalyzes O(2) evolution from either KHSO(5) (potassium oxone) or NaOCl. The reactions follow Michaelis-Menten kinetics where V(max) = 2420 +/- 490 mol O(2) (mol 1)(-1) hr(-1) and K(M) = 53 +/- 5 mM for oxone ([1] = 7.5 microM), and V(max) = 6.5 +/- 0.3 mol O(2) (mol 1)(-1) hr(-1) and K(M) = 39 +/- 4 mM for hypochlorite ([1] = 70 microM), with first-order kinetics observed in 1 for both oxidants. A mechanism is proposed having a preequilibrium between 1 and HSO(5-) or OCl(-), supported by the isolation and structural characterization of [(terpy)(SO(4))Mn(IV)(O)(2)Mn(IV)(O(4)S)(terpy)] (2). Isotope-labeling studies using H(2)(18)O and KHS(16)O(5) show that O(2) evolution proceeds via an intermediate that can exchange with water, where Raman spectroscopy has been used to confirm that the active oxygen of HSO(5-) is nonexchanging (t(1/2) > 1 h). The amount of label incorporated into O(2) is dependent on the relative concentrations of oxone and 1. (32)O(2):(34)O(2):(36)O(2) is 91.9 +/- 0.3:7.6 +/- 0.3:0.51 +/- 0.48, when [HSO(5-)] = 50 mM (0.5 mM 1), and 49 +/- 21:39 +/- 15:12 +/- 6 when [HSO(5-)] = 15 mM (0.75 mM 1). The rate-limiting step of O(2) evolution is proposed to be formation of a formally Mn(V)=O moiety which could then competitively react with either oxone or water/hydroxide to produce O(2). These results show that 1 serves as a functional model for photosynthetic water oxidation.     

Spectroscopic and structural studies of the complex of [Cu6(bpy)10(mu-CO3)2(mu-OH)2](ClO4)6 . 4H2O

The electronic absorption spectrum (diffuse reflection spectrum) of the crystal of [Cu6(bpy)10([mu-CO3)2(mu-OH)2](ClO4)6 . 4H2O has been measured. The experimental results are discussed quantitatively with ligand field theory and the radial wave function of non-free copper(II), and calculation values agree well with the experimental results. The d-d absorption spectrum of a novel hexanuclear copper(II) complex was explained satisfactorily. Especially, complexity of multinuclear crystal structures determined that of spectral behaviors. It provides significant to grope spectral nature from coordination structures.     

稀土钬及铒钇丙氨酸配合物的量热与热分析研究

合成了两种固态稀土丙氨酸配合物[Ho2(Ala)4(H2O)8]Cl6和[ErY(Ala)4(H2O)8](ClO4)6 (Ala为丙氨酸),用量热和热分析方法研究了这两种配合物的热力学性质.用全自动高精密绝热量热计测定了在78～377 K温区内的低温热容.对于[Ho2(Ala)4(H2O)8]Cl6,在214～255 K温区内发现一固-固相变,其相变温度为235.09 K.对于[ErY(Ala)4(H2O)8](ClO4)6,在99～121 K温区内也发现一固-固相变,其相变温度为115.78 K. [Ho2(Ala)4(H2O)8]Cl6固-固相变焓为3.02 kJ• mol－1,相变熵为12.83 J•K－1•mol－1； [ErY(Ala)4(H2O)8](ClO4)6 固-固相变焓为1.96 kJ•mol－1,相变熵为16.90 J•K－1•mol－1.同时,用TG技术在40～800 ℃温区研究了两配合物的热稳定性.由TG/DTG曲线分析可知, [Ho2(Ala)4(H2O)8]Cl6从80 ℃到479 ℃热分解分两步完成, [ErY(Ala)4(H2O)8](ClO4)6从120 ℃到430 ℃热分解分三步完成.     

Synthesis and Structure of [Er4（μ3—OH）4（Hpro）4（Pro）2（H2O）7]（ClO4）6.7H2O

1 INTRODUCTION The design and synthesis of polynuclear com- plexes have attracted chemists?attention in the contemporary chemistry, since their clusters maybe lead to novel materials with magnetic, optical, electronic and catalytic properties of the constituent metals[1～3]. It is also prevalently interesting to synthesize high-nuclearity metal complexes for their nanoscopic dimensions[3, 4]. Spectroscopic properties of the lanthanides are widely used in the study of biological systems. …     

Substitution reactions of [Pt(terpy)X]2+ with some biologically relevant ligands. Synthesis and crystal structure of [Pt(terpy)(cyst-S)](ClO4)2.0.5H2O and [Pt(terpy)(guo-N7)](ClO4)2.0.5guo.1.5H2O

Substitution reactions of the complexes [Pt(terpy)(H(2)O)](2+), [Pt(terpy)(cyst-S)](2+) and [Pt(terpy)(guo-N(7))](2+), where terpy = 2,2':6',2"-terpyridine, cyst = L-cysteine and guo = guanosine, with some biologically relevant ligands such as inosine (INO), inosine-5'-monophosphate (5'-IMP), guanosine-5'-monophosphate (5'-GMP), l-cysteine, glutathione, thiourea, thiosulfate and diethyldithiocarbamate (DEDTC), were studied in aqueous 0.10 M NaClO(4) at pH 2.5 and 6.0 using variable-temperature and -pressure stopped-flow spectrophotometry. The reactions of [Pt(terpy)(H(2)O)](2+) with INO, 5'-IMP and 5'-GMP showed that these ligands are very good nucleophiles. The second order rate constants varied between 4 x 10(2) and 6 x 10(2) M(-1) s(-1) at 25 degree C. The [Pt(terpy)(cyst-S)](2+) complex is unreactive towards nitrogen donor nucleophiles, and cysteine cannot be replaced by N(7) from INO, 5'-IMP and 5'-GMP. However, sulfur donor nucleophiles such as thiourea, thiosulfate and diethyldithiocarbamate could displace the Pt-cysteine bond. Diethyldithiocarbamate is the best nucleophile and the order of reactivity is: thiourea < thiosulfate < DEDTC with rate constants of 0.936 +/- 0.002, 5.99 +/- 0.02 and 8.88 +/- 0.07 M(-1) s(-1) at 25 degree C, respectively. The reactions of [Pt(terpy)(guo-N(7))](2+) with sulfur donor ligands showed that these nucleophiles could substitute guanosine from the Pt(ii) complex, of which diethyldithiocarbamate and thiosulfate are the strongest nucleophiles. The tripeptide glutathione is also a very efficient nucleophile. Activation parameters (Delta H(++), Delta S(++) and Delta V(++)) were determined for all reactions. The crystal structures of [Pt(terpy)(cyst-S)](ClO(4))(2).0.5H(2)O and [Pt(terpy)(guo-N(7))](ClO(4))(2).0.5guo.1.5H(2)O were determined by X-ray diffraction. Crystals of [Pt(terpy)(cyst-S)](ClO(4))(2).0.5H(2)O are orthorhombic with the space group P2(1)2(1)2(1), whereas [Pt(terpy)(guo-N(7))](ClO(4))(2).0.5guo.1.5H(2)O crystallizes in the orthorhombic space group P2(1)2(1)2. A typical feature of terpyridine complexes can be found in both molecular structures: the Pt-N (central) bond distance, 1.982(7) and 1.92(2) A, respectively, is shorter than the other two Pt-N distances, being 2.043(7) and 2.034(7) A in [Pt(terpy)(cyst-S)](ClO(4))(2).0.5H(2)O and 2.03(2) and 2.04(2) A in [Pt(terpy)(guo-N(7))](ClO(4))(2).0.5guo.1.5H(2)O, respectively. In both crystal structures two symmetrically independent cations representing different conformers are present in the asymmetric unit. The results are analysed in reference to the antitumour activity of Pt(II) complexes, and the importance of the rescue agents are discussed.     

Synthesis and Structural Characterization of [Mn（phen）2（H2O）2]（OAc）2.6H2O

1 INTRODUCTION Water oxidation to oxygen gas by photo- synthetic apparatus of green plants and cyano- bacteria is the origin of this gas in the atmosphere. The water oxidation center is a tetranuclear, oxide- bridged manganese cluster with O,N-based peri- pheral ligation by amino acid side-chain group[1, 2]. The binding of aqua to the Mn site may be impor- tant to the oxidation of aqua for producing dioxygen. 1,10-Phenanthroline has been adopted to simulate coordination sphere of manga…     

Crystal structure of diaquabis(nitroamino-guanidine)nickel(II)perchlorate [Ni(CH5N5O2)2-(H2O)2](ClO4)2

Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 3, pp. 141–145, May–June, 1992.     

Calorimetric study and thermal analysis of [ErY(Ala)4(H2O)8](ClO4)6 (Ala=ALANINE)

A solid complex of rare-earth compounds with alanine, [ErY(Ala)₄(H₂O)₈](ClO₄)₆ (Ala=alanine), was synthesized, and a calorimetric study and thermal analysis for it was performed through adiabatic calorimetry and thermogravimetry. The low-temperature heat capacity of [ErY(Ala)₄(H₂O)₈](ClO₄)₆ was measured with an automated adiabatic precision calorimeter over the temperature range from 78 to 377 K. A solid-solid phase transition was found between 99 and 121 K with a peak temperature at 115.78 k. The enthalpy and entropy of the phase transition was determined to be 1.957 Kj mol^-1, 16.90 j mol^-1 k^-1, respectively. Thermal decomposition of the complex was investigated in the temperature range of 40~550°C by use of the thermogravimetric and differential thermogravimetric (TG/DTG) analysis techniques. The TG/DTG curves showed that the decomposition started from 120 and ended at 430°C, completed in three steps. A possible mechanism of the thermal decomposition was elucidated. This revised version was published online in July 2006 with corrections to the Cover Date.