C-H vs C-C bond activation of acetonitrile and benzonitrile via oxidative addition: rhodium vs nickel and Cp* vs Tp' (Tp' = hydrotris(3,5-dimethylpyrazol-1-yl)borate, Cp* = η(5)-pentamethylcyclopentadienyl)

The photochemical reaction of (C(5)Me(5))Rh(PMe(3))H(2) (1) in neat acetonitrile leads to formation of the C-H activation product, (C(5)Me(5))Rh(PMe(3))(CH(2)CN)H (2). Thermolysis of this product in acetonitrile or benzene leads to thermal rearrangement to the C-C activation product, (C(5)Me(5))Rh(PMe(3))(CH(3))(CN) (4). Similar results were observed for the reaction of 1 with benzonitrile. The photolysis of 1 in neat benzonitrile results in C-H activation at the ortho, meta, and para positions. Thermolysis of the mixture in neat benzonitrile results in clean conversion to the C-C activation product, (C(5)Me(5))Rh(PMe(3))(C(6)H(5))(CN) (5). DFT calculations on the acetonitrile system show the barrier to C-H activation to be 4.3 kcal mol(-1) lower than the barrier to C-C activation. A high-energy intermediate was also located and found to connect the transition states leading to C-H and C-C activation. This intermediate has an agostic hydrogen interaction with the rhodium center. Reactions of acetonitrile and benzonitrile with the fragment [Tp'Rh(CNneopentyl)] show only C-H and no C-C activation. These reactions with rhodium are compared and contrasted to related reactions with [Ni(dippe)H](2), which show only C-CN bond cleavage.     

Electronic structure of iron chlorins: characterization of bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(III)triflate and bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(II)

The synthesis and characterization of the two iron chlorin complexes [Fe(III)(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) and Fe(II)(TPC)[(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2))](2) (2) are reported. The crystal structure of complex 1 has been determined. The X-ray structure shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 2.034(4) A, and to the pyrrole trans to it N(2), 2.012(4) A, are longer than the distances to the two remaining nitrogens [N(1), 1.996(4) A, and N(3), 1.984(4) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole. The (1)H NMR isotropic shifts at 20 degrees C of the different pyrrole protons of 1 varied from -0.8 to -48.3 ppm according to bis-ligated complexes of low-spin ferric chlorins. The EPR spectrum of [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) in solution is rhombic and gives the principal g values g(1) = 2.70, g(2) = 2.33, and g(3) = 1.61 (Sigmag(2) = 15.3). These spectroscopic observations are indicative of a metal-based electron in the d(pi) orbital for the [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) complex with a (d(xy))(2)(d(xz)d(yz))(3) ground state at any temperature. The X-ray structure of the ferrous complex 2 also shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 1.991(5) A, and to the pyrrole trans to it N(2), 2.005(6) A, are slightly different from the distances to the two remaining nitrogens [N(1), 1.988(5) A, and N(3), 2.015(5) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole.     

Trifluorosulfane ligand as an analogue of the nitrosyl ligand: highly exothermic fluorine transfer reactions from sulfur to metal in the chemistry of SF3 metal carbonyls of the first row transition metals

The variety of known very stable PF(3) metal derivatives analogous to metal carbonyls suggests the synthesis of SF(3) metal derivatives analogous to metal nitrosyls. However, the only known SF(3) metal complex is the structurally uncharacterized (Et(3)P)(2)Ir(CO)(Cl)(F)(SF(3)) synthesized by Cockman, Ebsworth, and Holloway in 1987 and suggested by electron counting to have a one-electron donor SF(3) group rather than a three-electron donor SF(3) group. In this connection, the possibility of synthesizing SF(3) metal derivatives analogous to metal nitrosyls has been investigated using density functional theory. The [M]SF(3) derivatives with [M] = V(CO)(5), Mn(CO)(4), Co(CO)(3), Ir(CO)(3), (C(5)H(5))Cr(CO)(2), (C(5)H(5))Fe(CO), and (C(5)H(5))Ni analogous to known metal nitrosyl derivatives are all predicted to be thermodynamically disfavored with respect to the corresponding [M](SF(2))(F) derivatives by energies ranging from 19.5 kcal/mol for Mn(SF(3))(CO)(4) to 5.4 kcal/mol for Co(SF(3))(CO)(3). By contrast, the isoelectronic [M]PF(3) derivatives with [M] = Cr(CO)(5), Fe(CO)(4), Ni(CO)(3), (C(5)H(5))Mn(CO)(2), (C(5)H(5))Co(CO), and (C(5)H(5))Cu are all very strongly thermodynamically favored with respect to the corresponding [M](PF(2))(F) derivatives by energies ranging from 64.3 kcal/mol for Cr(PF(3))(CO)(5) to 31.6 kcal/mol for (C(5)H(5))Co(PF(3))(CO). The known six-coordinate (Et(3)P)(2)Ir(CO)(Cl)(F)(SF(3)) is also predicted to be stable relative to the seven-coordinate (Et(3)P)(2)Ir(CO)(Cl)(F)(2)(SF(2)). Most of the metal SF(3) complexes found in this work are singlet structures containing three-electron donor SF(3) ligands with tetrahedral sulfur coordination. However, two examples of triplet spin state metal SF(3) complexes, namely, the lowest energy (C(5)H(5))Fe(SF(3))(CO) structure and a higher energy Co(SF(3))(CO)(3) structure, are found containing one-electron donor SF(3) ligands with pseudo square pyramidal sulfur coordination with a stereochemically active lone electron pair.     

Micro-Raman observation on the HPO4(2-) association structures in an individual dipotassium hydrogen phosphate (K2HPO4) droplet

A single K(2)HPO(4) droplet with size of ～50 μm on a Teflon substrate was forced to enter into the supersaturated state by decreasing the relative humidity (RH), allowing accurate control over the concentration of the solute within a droplet of a nanogram. The K(2)HPO(4) solutions from dilute (0.1-1.0 mol·L(-1) bulk) to concentrated state (a droplet from RH 98.2% to 25.1%) were studied through micro-Raman spectroscopy in the spectral region of about 200-4000 cm(-1). The area ratio between the water stretching band to the sum of the ν(1)-PO(3), ν(2)-POH, and ν(4)-PO(3) bands of the HPO(4)(2-) at various RHs was used to describe the dehydration behavior of a microsized single K(2)HPO(4) droplet in dehumidifying process. The peak position of the v(1)-PO(3) band for the 1 mol·L(-1) bulk solution appeared at 991 cm(-1) and moved to 986 cm(-1) at 98.2% RH, to 978 cm(-1) at 70.2% RH, and then to 964 cm(-1) at 30.0% RH for a droplet, accompanying an increase of the full width at half-height (fwhh) of this peak from 16.3 to 17.2, 22.2, and then to 24.2 cm(-1), indicating transition of the HPO(4)(2-) anions from monomers to dimers/trimers/oligomers and then to polyanions with chain structures in the K(2)HPO(4) solutions. After 25.1% RH, the solid was proved to be K(2)HPO(4)·3H(2)O according to the Raman spectral features. Furthermore, the O-H stretching envelope of a K(2)HPO(4) droplet showed that the intensity ratios of the strong hydrogen bonding component (3255 cm(-1)) to the weak one (3417 cm(-1)) and the cage-like water (2925 cm(-1)) to the weak one (3417 cm(-1)) were sensitive to the HPO(4)(2-) association structures, which can be used to understand the effects of dimers/trimers/oligomers and chain structures of the HPO(4)(2-) associations on the hydrogen bonding of water molecules.     

Hydroxy peroxy nitrites and nitrates from OH initiated reactions of isoprene

The reaction of hydroxy peroxy radicals (RO(2)) with NO represents one of the most crucial tropospheric processes, leading to terrestrial ozone formation or NO(x)() removal and chain termination. We investigate the formation of hydroxy peroxy nitrites (ROONO) and nitrates (RONO(2)) from the OH-isoprene reactions using DFT and ab initio theories and variational RRKM/master equation (vRRKM/ME) formalism. The binding energies of ROONO from NO addition to RO(2) are determined to be in the range of 20-22 kcal mol(-)(1), and the bond dissociation energies of ROONO to form an alkoxy radical (RO) and NO(2) range from 6 to 9 kcal mol(-)(1). Isomerization of ROONO to RONO(2) is exothermic by 22-28 kcal mol(-)(1). The entrance and exit channels of the RO(2)-NO reaction are found to be barrierless, and the rate constants to form ROONO are calculated to be 3 x 10(-)(12) to 2 x 10(-)(11) cm(3) molecule(-)(1) s(-)(1) using the canonical variational transition state theory. The vRRKM/ME analysis reveals negligible stabilization of excited ROONO and provides an assessment of ROONO isomerization to RONO(2).     

Anion binding to a ferric porphyrin complexed with per-O-methylated beta-cyclodextrin in aqueous solution

5,10,15,20-Tetrakis(4-sulfonatophenyl)porphinato iron(III) (Fe(III)TPPS) forms a very stable 1:2 complex with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TMe-beta-CD), whose iron(III) center is located at a hydrophobic cleft formed by two face-to-face TMe-beta-CD molecules. Various inorganic anions (X(-)) such as F(-), Cl(-), Br(-), I(-), N(3)(-), and SCN(-) coordinate to Fe(III)TPPS(TMe-beta-CD)(2) to form five-coordinate high-spin Fe(III)TPPS(X)(TMe-beta-CD)(2), while no coordination occurs with ClO(4)(-), H(2)PO(4)(-), NO(3)(-), and HSO(4)(-). Except for F(-), none of the anions investigated coordinate to Fe(III)TPPS in the absence of TMe-beta-CD due to extensive hydration to the anions as well as to Fe(III)TPPS. The present system shows a high selectivity toward the N(3)(-) anion. The thermodynamics suggests that Lewis basicity, hydrophilicity, and shape of an X(-) anion are the main factors to determine the stability of the Fe(III)TPPS(X)(TMe-beta-CD)(2) complex.     

Electron-transfer reduction of dinuclear copper peroxo and bis-μ-oxo complexes leading to the catalytic four-electron reduction of dioxygen to water

The four-electron reduction of dioxygen by decamethylferrocene (Fc*) to water is efficiently catalyzed by a binuclear copper(II) complex (1) and a mononuclear copper(II) complex (2) in the presence of trifluoroacetic acid in acetone at 298 K. Fast electron transfer from Fc* to 1 and 2 affords the corresponding Cu(I) complexes, which react at low temperature (193 K) with dioxygen to afford the η(2):η(2)-peroxo dicopper(II) (3) and bis-μ-oxo dicopper(III) (4) intermediates, respectively. The rate constants for electron transfer from Fc* and octamethylferrocene (Me(8)Fc) to 1 as well as electron transfer from Fc* and Me(8)Fc to 3 were determined at various temperatures, leading to activation enthalpies and entropies. The activation entropies of electron transfer from Fc* and Me(8)Fc to 1 were determined to be close to zero, as expected for outer-sphere electron-transfer reactions without formation of any intermediates. For electron transfer from Fc* and Me(8)Fc to 3, the activation entropies were also found to be close to zero. Such agreement indicates that the η(2):η(2)-peroxo complex (3) is directly reduced by Fc* rather than via the conversion to the corresponding bis-μ-oxo complex, followed by the electron-transfer reduction by Fc* leading to the four-electron reduction of dioxygen to water. The bis-μ-oxo species (4) is reduced by Fc* with a much faster rate than the η(2):η(2)-peroxo complex (3), but this also leads to the four-electron reduction of dioxygen to water.     

Synthesis and reactivity of the hydrido- and alkylrhenium methylidene complexes Cp*(PMe3)2(R)Re=CH2 (R = H, CH3)

Protonolysis of the dimethylrhenium(III) compound Cp(PMe(3))(2)Re(CH(3))(2) (3) led to formation of the highly reactive hydridorhenium methylidene compound [Cp(PMe(3))(2)Re(CH(2))(H)][OTf] (4), which was characterized spectroscopically at low temperature. Although 4 decomposed above -30 degrees C, reactivity studies performed at low temperature indicated it was in equilibrium with the coordinatively unsaturated methylrhenium complex [Cp(PMe(3))(2)Re(CH(3))][OTf] (2). Methylidene complex 4 was found to react with PMe(3) to afford [Cp(PMe(3))(3)Re(CH(3))][OTf] (6) and with chloride anion to give Cp(PMe(3))(2)Re(Me)Cl (7). When BAr(f) anion was added to 4, the thermally stable methylrhenium methylidene complex [Cp(PMe(3))(2)Re(CH(2))(CH(3))][BAr(f)] (8) was isolated upon warming to room temperature. The mechanisms of formation of both 4 and 8 are discussed in detail, including DFT calculations. The novel carbonyl ligated complex Cp(CO)(2)Re(CH(3))OTf (12) was prepared, isolated, and found to not undergo migration reactions to form methylidene complexes.     

Building unit and topological evolution in the hydrothermal DABCO-U-F system

Compounds NDUF-1 ([C(6)H(14)N(2)](UO(2))(2)F(6); P2(1)/c, a = 6.9797(15) A, b = 8.3767(15) A, c = 23.760(5) A, beta = 91.068(4) degrees, V = 1388.9(5) A(3), Z = 4), NDUF-2 ([C(6)H(14)N(2)](2)(UO(2))(2)F(5)UF(7).H(2)O), NDUF-3 ((NH(4))(7)U(6)F(31); R3, a = 15.4106(8) A, c = 10.8142(8) A, V = 2224.1(2) A(3), Z = 3), and NDUF-4 ([NH(4)]U(3)F(13)) have been synthesized hydrothermally from fixed composition reactant mixtures over variable time periods [DABCO (C(6)H(12)N(2)), UO(2)(NO(3))(2).6H(2)O, HF, and H(2)O; 2-14 days]. Observed is a systematic evolution of the structural building units within these materials from the UO(2)F(5) pentagonal bipyramid in NDUF-1 and -2 to the UF(8) trigonal prism in NDUF-2 and finally to the UF(9) polyhedron in NDUF-3 and -4 as a function of reaction time. Coupled to this coordination change is a reduction of U(VI) to U(IV) as well as a breakdown of the organic structure-directing agent from DABCO to NH(4)(+). These processes contribute to a structural transition from layered topologies (NDUF-1) to chain (NDUF-2), back to layered (NDUF-3), and ultimately to framework (NDUF-4) connectivities. The synthesis conditions, crystal structures, and possible transformation mechanisms within this system are presented.     

Mechanistic studies of O2 reduction effected by group 9 bimetallic hydride complexes

Synthetic and kinetic studies are used to uncover mechanistic details of the reduction of O(2) to water mediated by dirhodium complexes. The mixed-valence Rh(2)(0,II)(tfepma)(2)(CN(t)Bu)(2)Cl(2) (1, tfepma = MeN[P(OCH(2)CF(3))(2)](2), CN(t)Bu = tert-butyl isocyanide) complex is protonated by HCl to produce Rh(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(3)H (2), which promotes the reduction of O(2) to water with concomitant formation of Rh(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(4) (3). Reactions of the analogous diiridium complexes permit the identification of plausible reaction intermediates. Ir(2)(0,II)(tfepma)(2)(CN(t)Bu)(2)Cl(2) (4) can be protonated to form the isolable complex Ir(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(3)H (5), which reacts with O(2) to form Ir(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(3)(OOH) (6). In addition, 4 reacts with O(2) to form Ir(2)(II,II)(tfepma)(2)(CN(t)Bu)(2)Cl(2)(η(2)-O(2)) (7), which can be protonated by HCl to furnish 6. Complexes 6 and 7 were both isolated in pure form and structurally and spectroscopically characterized. Kinetics examination of hydride complex 5 with O(2) and HCl furnishes a rate law that is consistent with an HCl-elimination mechanism, where O(2) binds an Ir(0) center to furnish an intermediate η(2)-peroxide intermediate. Dirhodium congener 2 obeys a rate law that not only is also consistent with an analogous HCl-elimination mechanism but also includes terms indicative of direct O(2) insertion and a unimolecular isomerization prior to oxygenation. The combined synthetic and mechanistic studies bespeak to the importance of peroxide and hydroperoxide intermediates in the reduction of O(2) to water by dirhodium hydride complexes.     

Design of a dinuclear nickel(II) bioinspired hydrolase to bind covalently to silica surfaces: synthesis, magnetism, and reactivity studies

Presented herein is the design of a dinuclear Ni(II) synthetic hydrolase [Ni(2)(HBPPAMFF)(μ-OAc)(2)(H(2)O)]BPh(4) (1) (H(2)BPPAMFF = 2-[(N-benzyl-N-2-pyridylmethylamine)]-4-methyl-6-[N-(2-pyridylmethyl)aminomethyl)])-4-methyl-6-formylphenol) to be covalently attached to silica surfaces, while maintaining its catalytic activity. An aldehyde-containing ligand (H(2)BPPAMFF) provides a reactive functional group that can serve as a cross-linking group to bind the complex to an organoalkoxysilane and later to the silica surfaces or directly to amino-modified surfaces. The dinuclear Ni(II) complex covalently attached to the silica surfaces was fully characterized by different techniques. The catalytic turnover number (k(cat)) of the immobilized Ni(II)Ni(II) catalyst in the hydrolysis of 2,4-bis(dinitrophenyl)phosphate is comparable to the homogeneous reaction; however, the catalyst interaction with the support enhanced the substrate to complex association constant, and consequently, the catalytic efficiency (E = k(cat)/K(M)) and the supported catalyst can be reused for subsequent diester hydrolysis reactions.     

Studies with Polyfunctionally Substituted Heteroaromatics: The Reaction of Heterocyclic Enaminonitriles with α‐β‐Unsaturated Nitriles

5‐Amino‐4‐cyano‐3‐phenylpyrazole ( 1 ) reacts with cinnamonitriles ( 2 ) to yield the pyrazolo[1,5‐a]pyrimidines ( 3 ). Also, 5‐amino‐4‐cyano‐1‐phenylpyrazole ( 4 ) reacts with cinnamonitriles ( 2 ) to yield the pyrazolo[3,4‐b]pyridine derivatives ( 5 ). In contrast to this reaction, enaminothiophene ( 6 ) reacts with cinnamonitriles ( 2 ) to yield compound ( 7 ) not ( 8 ). The enaminopyrane ( 9 ) reacts with cinnamonitriles ( 2 ) to yield ( 10 ). Finally we have attempted to add cinnamonitriles ( 2 ) to thiopyrane ( 13 ); only rearrangement and aromatization product ( 14 ) was isolated.     

Influence of thiolate ligands on reductive N-O bond activation. Probing the O2(-) binding site of a biomimetic superoxide reductase analogue and examining the proton-dependent reduction of nitrite

Nitric oxide (NO) is frequently used to probe the substrate-binding site of "spectroscopically silent" non-heme Fe(2+) sites of metalloenzymes, such as superoxide reductase (SOR). Herein we use NO to probe the superoxide binding site of our thiolate-ligated biomimetic SOR model [Fe(II)(S(Me(2))N(4)(tren))](+) (1). Like NO-bound trans-cysteinate-ligated SOR (SOR-NO), the rhombic S = 3/2 EPR signal of NO-bound cis-thiolate-ligated [Fe(S(Me(2))N(4)(tren)(NO)](+) (2; g = 4.44, 3.54, 1.97), the isotopically sensitive ν(NO)(ν((15)NO)) stretching frequency (1685(1640) cm(-1)), and the 0.05 ? decrease in Fe-S bond length are shown to be consistent with the oxidative addition of NO to Fe(II) to afford an Fe(III)-NO(-) {FeNO}(7) species containing high-spin (S = 5/2) Fe(III) antiferromagnetically coupled to NO(-) (S = 1). The cis versus trans positioning of the thiolate does not appear to influence these properties. Although it has yet to be crystallographically characterized, SOR-NO is presumed to possess a bent Fe-NO similar to that of 2 (Fe-N-O = 151.7(4)°). The N-O bond is shown to be more activated in 2 relative to N- and O-ligated {FeNO}(7) complexes, and this is attributed to the electron-donating properties of the thiolate ligand. Hydrogen-bonding to the cysteinate sulfur attenuates N-O bond activation in SOR, as shown by its higher ν(NO) frequency (1721 cm(-1)). In contrast, the ν(O-O) frequency of the SOR peroxo intermediate and its analogues is not affected by H-bonds to the cysteinate sulfur or other factors influencing the Fe-SR bond strength; these only influence the ν(Fe-O) frequency. Reactions between 1 and NO(2)(-) are shown to result in the proton-dependent heterolytic cleavage of an N-O bond. The mechanism of this reaction is proposed to involve both Fe(II)-NO(2)(-) and {FeNO}(6) intermediates similar to those implicated in the mechanism of NiR-promoted NO(2)(-) reduction.     

Coordination networks from Cu cations and tetrakis(methylthio)benzenedicarboxylic acid: tunable bonding patterns and selective sensing for NH(3) gas

This paper aims to illustrate the rich potential of the thioether-carboxyl combination in generating coordination networks with tunable and interesting structural features. By simply varying the ratio between Cu(NO(3))(2) and the bifunctional ligand tetrakis(methylthio)benzenedicarboxylic acid (TMBD) as the reactants, three coordination networks can be hydrothermally synthesized in substantial yields, which present a distinct evolution with regard to metal-ligand interactions. Specifically, Cu(TMBD)(0.5)(H(2)TMBD)(0.5)·H(2)TMBD (1) was obtained with a relatively small (1:1) Cu(NO(3))(2)/TMBD ratio, and crystallizes as an one-dimensional (1D) coordination assembly based on Cu(I)-thioether interactions, which is integrated by hydrogen-bonding to additional H(2)TMBD molecules to form a three-dimensional (3D) composite network with all the carboxylic acid and carboxylate groups remaining uncoordinated to the metal ions. A medium (1.25:1) Cu(NO(3))(2)/TMBD ratio leads to compound Cu(2)TMBD, in which Cu(I) ions simultaneously bond to the carboxylate and thioether groups, while an even higher (2.4:1) Cu(NO(3))(2)/TMBD ratio produced a mixed-cation compound Cu(II)(2)OHCu(I)(TMBD)(2)·2H(2)O (2), in which the carboxylic groups are bonded to (cupric) Cu(II) ions, and the thioether groups to Cu(I). Despite the lack of open channels in 2, crystallites of this compound exhibit a distinct and selective absorption of NH(3), with a concomitant color change from green to blue, indicating substantial network flexibility and dynamics with regards to gas transport.     

Mn(II) and Zn(II) interactions with peptide fragments from Parkinson's disease genes

Two peptide sequences from PARK9 Parkinson's disease gene, ProAspGluLysHisGluLeu, (P(1)D(2)E(3)K(4)H(5)E(6)L(7)) (1) and PheCysGlyAspGlyAlaAsnAspCysGly (F(1)C(2)G(3)D(4)G(5)A(6)N(7)D(8)C(9)G(10)) (2) were tested for Mn(II), Zn(II) and Ca(II) binding. The fragments are located from residues 1165 to 1171 and 1184 to 1193 in the PARK9 encoded protein. This protein can protect cells from poisoning of manganese, which is an environmental risk factor for a Parkinson's disease-like syndrome. Mono- and bi-dimensional NMR spectroscopy has been used to understand the details of metal binding sites at different pH values and at different ligand to metal molar ratios. Mn(II) and Zn(II) coordination with peptide (1) involves imidazole N(ε) or N(δ) of His(5) and carboxyl γ-O of Asp(2), Glu(3) and Glu(6) residues. Six donor atoms participate in Mn(II) binding resulting in a distorted octahedral geometry, possibly involving bidentate interaction of carboxyl groups; four donor atoms participate in Zn(II) binding resulting in a tetracoordinate geometry. Mn(II) and Zn(II) coordination involves the two cysteine residues with peptide (2); Mn(II) accepts additional ligand bonds from the carboxyl γ-O of Asp(4) and Asp(8) to complete the coordination sphere; the unoccupied sites may contain solvent molecules. The failure of Ca(II) ions to bind to either peptide (1) or (2) appears to result, under our conditions, from the absence of chelating properties in the chosen fragments.     

Higher triplet excited states of benzophenones and bimolecular triplet energy transfer measured by using nanosecond-picosecond two-color/two-laser flash photolysis

The lifetimes of benzophenone in the higher triplet excited state (BP(T(n))) and several BP derivatives in the T(n) states were measured directly to be tau(T(n))=37+/-7 ps and 20-33 ps, respectively, by using the nanosecond-picosecond (ns-ps) two-color/two-laser flash photolysis method. Based on the direct measurements of tau(T(n)) of BP(T(n)), the triplet energy transfer (TET) from BP(T(n)) to quenchers (Q), such as carbon tetrachloride (CCl4), benzene (Bz), and p-dichlorbenzene (DCB), was investigated. The fast TET from BP(T(n)) to Q can be attributed to the lifetime-dependent quenching process, according to the Ware theoretical model of the bimolecular energy transfer reaction. The contribution of the lifetime-dependent term on k(TET) was 27, 60, and 86% for CCl4, Bz, and DCB as the Q of BP(T(n)), respectively, indicating that the TET from BP(T(n)) to Q is influenced not only by tau(T(n)), but also by the size of Q.     

Rearrangement of the tris(2-pyridylthio)methanido ligand in an iron(II) complex containing an Fe-C bond

Iron(II) tris(2-pyridylthio)methanido (1) containing an Fe-C bond, obtained from the reaction of tris(2-pyridylthio)methane (HL(1)) and iron(II) triflate, reacts with protic acid to generate iron(II) bis(2-pyridylthio)carbene (1a). The carbene complex is converted to an iron(II) complex (2) of the 1-[bis(2-pyridylthio)methyl]pyridine-2-thione ligand (L(3)) upon treatment with a base. Complex 2 reversibly transforms to 1a in the presence of an acid. During the transformation of 1 to 2, a novel rearrangement of L(1) to L(3) takes place. The iron(II) complexes are reactive toward dioxygen to form the corresponding iron(III) complexes.     

A mass spectrometric study of metal binding to osteocalcin

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry was used to investigate Ca(2+), Mg(2+), and La(3+) binding to bovine bone osteocalcin (OCN). OCN was shown to bind 3 mol Ca(2+) per mol protein. There was also evidence for the presence of four additional metal binding sites. Ca(2+) increased the formation of the OCN dimer. Mg(2+) bound to OCN to the same extent as Ca(2+) but did not induce the dimerization of OCN. La(3+) bound to a lesser extent than either Ca(2+) or Mg(2+) to OCN and, like Mg(2+), did not influence dimerization. Each Gla residue of OCN participates in Ca(2+) binding, whereas Mg(2+) binding may occur preferentially at sites other than Gla residues. This implies that the different natures of Ca(2+)- and Mg(2+)-containing OCN complexes influence the tendency of OCN to form a dimer.     

吡啶高三蝶烯的合成

2-溴-4-甲基吡啶（1）经氯代和碘代反应合成了2-溴-4-碘甲基吡啶（3）,3和蒽酮（4）反应生成10,10-二（2-溴-4-吡啶甲基）-9（10H）蒽酮（5）,5在3 MPa下与NaOCH3反应得到10,10-二（2-甲氧基-4-吡啶甲基）-9（10H）蒽酮（6）,6经硼氢化钠还原得到蒽醇（7）,7在对甲苯磺酸催化...     

Direct evidence of redox interaction between metal ion and support oxide in Ce(0.98)Pd(0.02)O(2-δ) by a combined electrochemical and XPS study

A combined electrochemical method and X-ray photo electron spectroscopy (XPS) has been utilized to understand the Pd(2+)/CeO(2) interaction in Ce(1-x)Pd(x)O(2-δ) (x = 0.02). A constant positive potential (chronoamperometry) is applied to Ce(0.98)Pd(0.02)O(2-δ) working electrode which causes Ce(4+) to reduce to Ce(3+) to the extent of ~35%, while Pd remains in the +2 oxidation state. Electrochemically cycling this electrode between 0.0-1.2 V reverts back to the original state of the catalyst. This reversibility is attributed to the reversible reduction of Ce(4+) to Ce(3+) state. CeO(2) electrode with no metal component reduces to CeO(2-y) (y~0.4) after applying 1.2 V which is not reversible and the original composition of CeO(2) cannot be brought back in any electrochemical condition. During the electro-catalytic oxygen evolution reaction at a constant 1.2 V for 1000 s, Ce(0.98)Pd(0.02)O(2-δ) reaches a steady state composition with Pd in the +2 states and Ce(4+): Ce(3+) in the ratio of 0.65:0.35. This composition can be denoted as Ce(4+)(0.63)Ce(3+)(0.35)Pd(0.02)O(2-δ-y) (y~0.17). When pure CeO(2) is put under similar electrochemical condition, it never reaches the steady state composition and reduces almost to 85%. Thus, Ce(0.98)Pd(0.02)O(2-δ) forms a stable electrode for the electro-oxidation of H(2)O to O(2) unlike CeO(2) due to the metal support interaction.