Electron paramagnetic resonance saturation studies of P-700 reaction center chlorophyll in plant photosynthesis

Electron paramagnetic resonance (EPR) power saturation and saturation recovery methods have been used to determine the spin lattice, T₁, and spin-spin, T₂, relaxation times of P-700⁺ reaction-center chlorophyll in Photosystem I of plant chloroplasts for 10 K T 100 K. T₁ was 200 μs at 100 K and increased to 900 μs at 10 K. T₂ was 40 ns at 40 K and increased to 100 ns at 10 K. T₁ for 40 K T 100 K is inversely proportional to temperature, which is evidence of a direct-lattice relaxation process. At T = 20 K, T₁ deviates from the 1/T dependence, indicating a cross relaxation process with an unidentified paramagnetic species. The individual effects of ascorbate and ferricyanide on T₁ of P-700⁺ were examined: T₁ of P-700⁺ was not affected by adding 10 mM ascorbate to digitonin-treated chloroplast fragments (D144 fragments). The P-700⁺ relaxation time in broken chloroplasts treated with 10 mM ferricyanide was 4-times shorter than in the untreated control at 40 K. Ferricyanide appears to be relaxing the P-700⁺ indirectly to the lattice by a cross-relaxation process. The possibility of dipolar-spin broadening of P-700⁺ due to either the iron-sulfur center A or plastocyanin was examined by determining the spin-packet linewidth for P-700⁺ when center A and plastocyanin were in either the reduced or oxidized states. Neither reduced center A nor oxidized plastocyanin was capable of broadening the spin-packet linewidth of the P-700⁺ signal. The absence of diplolar broadening indicates that both center A and plastocyanin are located at a distance at least 3.0 nm from the P-700⁺ reaction center chlorophyll. This evidence supports previous hypotheses that the electron donor and acceptor to P-700 are situated on opposite sides of the chloroplast membrane. It is also shown that the ratio of photo-oxidized P-700 to photoreduced centers A and B at low temperature is 2 : 1 if P-700 is monitored at a nonsaturating microwave power.     

Molecular structures and some properties of tris(2-aminoethyl) amine cobalt(III) complexes with thiocarboxylato-O,S such as 3-mercaptopropionato, 2-mercaptoacetato and their derivatives

Cobalt(III) complexes with a thiolate or thioether ligand, t-[Co(mp)(tren)]⁺ (2), t-[Co(mtp)(tren)]²⁺ (1Me) and t-[Co(mta)(tren)]²⁺ (2Me), (mp = 3-mercaptopropionate, MA = 3-(methylthio)propionate and MTA = 2-(methylthio)acetate) have been prepared in aqueous solutions. The crystal structures of 1, 2, 1Me and 2Me were determined by X-ray diffraction methods. The crystal data are as follows, t-[Co(mp)(tren)]ClO₄ (1CIO₄): monoclinic, P2₁/n, A = 10.877(8), B = 11.570(4), c = 12.173(7) Å, β = 92.20(5)°, V = 1531(1) ų, Z = 4 and R = 0.060; t-[Co(ma)(tren)]Cl·3H₂O (2Cl·3H₂O): monoclinic, P2₁/n, a = 7.7688(8), B = 27.128(2), C = 7.858(1) Å, β = 100.63(1)°, V = 1627.7(3) ų, Z = 4 and R = 0.066; (+)₄₆₅^CD-t-[Co(mtp)(tren)](ClO₄)₂ ((+)₄₆₅^CD-1Me(ClO₄)₂): orthorhombic, P2₁2₁2₁, A = 10.6610(7), B = 11.746(1), C = 15.555(1) Å, V = 1947.9(3) ų, Z = 4 and R = 0.068; (+)₄₆₅^CD-t-[Co(mta)(tren)](ClO₄)₂ ((+)₄₆₅^CD-2Me(ClO₄)₂): orthorhombic, P2₁2₁2₁, a = 10.564(1), B = 11.375(1), C = 15.434(2) Å, V = 1854.7(4) ų, Z = 4 and R = 0.047. All central Co(III) atoms have approximately octahedral geometry, coordinated by four N, one O, and one S atoms. All of the complexes are only isomer, of which the sulfur atom in the didentate-O,S ligands are located at the trans position to the tertiary amine nitrogen atom of tren. 1 and 1Me contain six-membered chelate ring, and 2 and 2Me do five-membered chelate ring in the didentate ligand. The chirality of the asymmetric sulfur donor atom in (+)₄₆₅^CD-1Me is the S configuration and that in (+)₄₆₅^CD-2Me is the R one. The ¹H NMR, ¹³C NMR and electronic absorption spectral behaviors and electrochemical properties of the present complexes are discussed in relation to their stereochemistries.     

Nitrogen atom transfer and redox chemistry of terpyridyl phosphoraniminato complexes of osmium (IV)

Rapid reactions occur between [Os^VI(tpy)(Cl)₂(N)]X (X = PF₆⁻, Cl⁻, tpy = 2,2′:6′,2″-terpyridine) and aryl or alkyl phosphi nes (PPh₃, PPh₂Me, PPhMe₂, PMe₃ and PEt₃) in CH₂Cl₂ or CH₃CN to give [Os^IV(tpy)(Cl)₂(NPPh₃)]⁺ and its analogs. The reaction between trans-[Os^VI(tpy)(Cl)₂(N)]⁺ and PPh₃ in CH₃CN occurs with a 1:1 stoichiometry and a rate law first order in both PPh₃ and Os^VI with k(CH₃CN, 25°C) = 1.36 ± 0.08 × 10⁴ M⁻ s⁻¹. The products are best formulated as paramagnetic d⁴ phosphoraniminato complexes of Os^IV based on a room temperature magnetic moment of 1.8 μ_B for trans-[Os^IV(tpy)(Cl)₂(NPPh₃)](PF₆), contact shifted ¹H NMR spectra and UV-Vis and near-IR spectra. In the crystal structures of trans-[Os^IV(tpy)(Cl)₂( NPPh₃)](PF₆)·CH₃CN (monoclinic, P2₁/n with a = 13.384(5) Å, b = 15.222(7) Å, c = 17.717(6) Å, β = 103.10(3)°, V = 3516(2) ų, Z = 4, R_w = 3.40, R_w = 3.50) and cis-[Os^IV(tpy)(Cl)₂(NPPh₂Me)]-(PF₆)·CH₃CN (monoclinic, P2₁/c, with a = 10.6348(2) Å, b = 15.146(9) ÅA, c = 20.876(6) Å, β = 97.47(1)°, V = 3334(2) ų, Z = 4, R = 4.00, R_w = 4.90), the long Os-N(P) bond lengths (2.093(5) and 2.061(6) Å), acute Os-N-P angles (132.4(3) and 132.2(4)°), and absence of a significant structural trans effect rule out significant Os-N multiple bonding. From cyclic voltammetric measurements, chemically reversible Os^V/IV and Os^IV/III couples occur for trans-[Os^IV(tpy)(Cl)₂(NPPh₃)](PF₆) in CH₃CN at +0.92 V (Os^V/IV) and −0.27 V (Os^IV/III) versus SSCE. Chemical or electrochemical reduction of trans-[Os^IV(tpy)(Cl)₂(NPPh₃)](PF₆) gives isolable trans-Os^III(tpy)(Cl)₂(NPPh₃). One-electron oxidation to Os^V followed by intermolecular disproportionation and PPh₃ group transfer gives [Os^VI(tpy)Cl₂(N)]⁺, [OS^III(tpy)(Cl)₂(CH₃CN)]⁺ and [Ph₃=N=PPh₃]⁺ (PPN⁺). trans-[Os^IV(tpy)(Cl)₂(NPPh₃)](PF₆) undergoes reaction with a second phosphine under reflux to give PPN⁺ derivatives and Os^II(tpy)(Cl)₂(CH₃CN) in CH₃CN or Os^II(tpy)(Cl)₂(PR₃) in CH₂Cl₂. This demonstrates that the Os^VI nitrido complex can undergo a net four-electron change by a combination of atom and group transfers.     

Rate of electron transfer between plastocyanin, cytochrome ƒ, related proteins and artificial redox reagents in solution

The rate of electron transfer between reduced cytochrome ƒ and plastocyanin (both purified from parsley) has been measured as k = 3.6 · 10⁷ M⁻¹ · s⁻¹, at 298 °K and pH 7.0, with activation parameters ΔH^‡ = 44 kJ · mole⁻¹ and ΔS^‡ = +46 J · mole⁻¹ · °K⁻¹. Replacement of cytochrome ƒ with red algal cytochrome c-553, Pseudomonas cytochrome c-551 and mammalian cytochrome c gave rates at least 30 times slower: k = 5 · 10⁵, 7.5 · 10⁵ and 1.0 · 10⁶ M⁻¹ · s⁻¹, respectively.

Similar measurements made with azurin instead of plastocyanin gave k = 6 · 10⁶ and approx. 2 · 10⁷ M⁻¹ · s⁻¹ for reaction of reduced azurin with cytochrome ƒ and algal cytochrome respectively.

Rate constants of 115 and 80 M⁻¹ · s⁻¹ were found for reduction of plastocyanin by ascorbate and hydroquinone at 298 °K and pH 7.0. The rate constants for the oxidation of plastocyanin, cytochrome ƒ, Pseudomonas cytochrome c-551 and red algal cytochrome c-553 by ferricyanide were found to be between 3 · 10⁴ and 8 · 10⁴ M⁻¹ · s⁻¹.

The results are discussed in relation to photosynthetic electron transport.     

Flash-induced absorption changes in Photosystem I,Radical pair or triplet state formation?

Absorption changes induced in chlorophyll protein (CP 1) particles by short laser flashes have been analyzed in order to decide whether a state lasting for a few microseconds at 21°C or 800 μs at 10 K corresponds to the biradical P-700⁺ ... A⁻₁ (A₁ being a chlorophyll a) or to a triplet state produced in a submicrosecond recombination of the preceding state. At 21°C the spectrum of the flash-induced ΔA (720–870 nm) presents a flat-topped band from 740 to 820 nm, clearly different from that of P-700⁺. A saturation curve (ΔA vs. laser energy), obtained with a 2 or 10 ns laser pulse, indicates that ΔA saturates at a value 2- or 3-times smaller than that expected on the basis of the chemical oxidation of P-700. At 21°C the size of flash-induced ΔA is slightly decreased (5–15%) when the sample is subjected to a 400 G magnetic field. The kinetics of decay are not affected; they are not affected either by the oxygen concentration. At 10 K the spectrum of the flash-induced ΔA has been measured between 650 and 1700 nm. Between 650 and 720 nm, the spectrum presents only one major negative peak at 702 nm; it is quite different from that due to the chemical oxidation of P-700 (which has additional peaks at 688 and 677 nm). Between 720 and 870 nm, the spectrum is identical to that obtained at 21°C. Above 870 nm, the spectrum includes a broad band around 1250 nm, which is absent in P-700⁺. A saturation curve leads to a maximum ΔA greater than that at 21°C and which is also greater with a 1 μs dye laser flash than with a 10 ns ruby laser flash. An analysis of the spectral data indicates that these do not fit correctly with the hypothesis of a contribution of P-700⁺ and of a chlorophyll a anion radical. They fit more closely with the hypothesis of a triplet state of P-700, a hypothesis which is discussed in relation to other experimental data.     

Quantum yield and rate of formation of the carotenoid triplet state in photosynthetic structures

The formation of the triplet state of carotenoids (detected by an absorption peak at 515 nm) and the photo-oxidation of the primary donor of Photosystem II, P-680 (detected by an absorption increase at 820 nm) have been measured by flash absorption spectroscopy in chloroplasts in which the oxygen evolution was inhibited by treatment with Tris. The amount of each transient form has been followed versus excitation flash intensity (at 590 or 694 nm). At low excitation energy the quantum yield of triplet formation (with the Photosystem II reaction center in the state Q⁻) is about 30% that of P-680 photo-oxidation. The yield of carotenoid triplet formation is higher in the state Q⁻ than in the state Q, in nearly the same proportion as chlorophyll a fluorescence. It is concluded that, for excited chlorophyll a, the relative rates of intersystem crossing to the triplet state and of fluorescence emission are the same in vivo as in organic solvent. At high flash intensity the signal of P-680⁺ completely saturates, whereas that of carotenoid triplet continues to increase.

The rate of triplet-triplet energy transfer from chlorophyll a to carotenoids has been derived from the rise time of the absorption change at 515 nm, in chloroplasts and in several light-harvesting pigment-protein complexes. In all cases the rate is very high, around 8 · 10⁷ s⁻¹ at 294 K. It is about 2–3 times slower at 5 K. The transitory formation of chlorophyll triplet has been verified in two pigment-protein complexes, at 5 K.     

Isolation of a photosystem 2 preparation from higher plants with highly enriched oxygen evolution activity

Detergent-treatment of higher plant thylakoids with Triton X-100 at pH 6.3 has been used to purify a PS2 fraction with very high rates of oxygen evolution (1000 μmol.mg chl⁻¹.h⁻¹). A photosynthetic unit size of about 300 chlorophyll (chl) molecules has been determined by optical methods, suggesting an average turnover time for PS2 of about 2 ms. The donor system for P680⁺ is particularly well preserved in the preparation, as judged by P680⁺ reduction kinetics, the detection by EPR of Signal II_LT and the presence of the high potential form of cytochrome b-559 (at a ratio of 1:1 with the reaction centre).     

不同波长光源对新蚜虫疠霉产孢能力的影响及霉菌蓝光受体基因的克隆和表达分析

光在调控真菌的多种生理过程中发挥着重要作用。为探究光照对新蚜虫疠霉Pandora neoaphidis产孢的影响,本文研究了不同波长光源(蓝光、绿光、白光、红光、黄光)和无光黑暗条件对新蚜虫疠霉分生孢子弹射能力的影响,通过cDNA末端的快速扩增(RACE)对新蚜虫疠霉的蓝光受体蛋白基因pnwc-1进行克隆并对其进行生物信息学分析,利用qRT-PCR对蓝光光源不同照射时长下pnwc-1的表达量进行了定量分析。结果表明,蓝色光源(波长460–465nm)照射后的新蚜虫疠霉菌丝产生的分生孢子数量显著高于其他波长光源,排序为:蓝光>绿光>白光>红光>黄光>无光。另外,分析克隆获得的全长为2 423bp的pnwc-1基因发现,其编码的蛋白具有蓝光受体蛋白典型的保守结构域,同源比对结果显示新蚜虫疠霉与接合菌门真菌归为一类但相对独立。qRT-PCR的定量分析结果表明随着照射时长增加,蓝光处理能显著提高pnwc-1的表达量,而且pnwc-1的相对表达量与累积产孢量存在正相关(R2=0.9798)。本研究为后续蓝光及其受体基因功能的深入研究提供了实验基础,并促进以新蚜虫疠霉为代表的虫霉目真菌在害虫生物防治中的应用。     

The rhodium(III) trisacetonitrile complexes: a re-investigation of the synthesis of fac- and mer- [RhCl3(CH3CN)3], their characterization by 2D NMR spectroscopy and the X-ray crystal structure of mer-[RhCl3(CH3CN)3] · CH3CN

It is shown that the reaction of RhCl₃·3H₂O with acetonitrile normally produces mixtures of mer- and fac-[RhCl₃(CH₃CN)₃] (1a and 1b, respectively). The IR and ¹H NMR spectra of these isomers were re-investigated. Their two-dimensional (¹⁰³Rh,¹H) NMR spectra were also recorded. Equilibrium and exchange studies of 1a and 1b in CD₃C were performed. It was found that in 1a the exchange rate of the nitrile molecule trans to Cl is much faster than those of mutually trans nitriles. Also the nitrile molecules in 1b underwent fast exchange in CD₃CN; however, their rate was slightly faster than that of the more labile CH₃CN in 1a. The X-ray crystal structure of mer-[RhCl₃(CH₃CN)₃]·CH₃CN (1c) was determined. Crystal data: triclinic space group

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A convenient electrochemical preparation of reduced methyl viologen and a kinetic study of the reaction with oxygen using an anaerobic stopped-flow apparatus

1. Single reduced methyl viologen (MV^.+) acts as an electron donor in a number of enzyme systems. The large changes in extinction coefficient upon oxidation (λ_max 600 nm; MV^.+, = 1.3 · 10⁴ M⁻¹ · cm⁻¹; oxidised form of methyl viologen (MV²⁺), = 0.0) make it ideally suited to kinetic studies of electron transfer reactions using stopped-flow and standard spectrophotometric techniques.

2. A convenient electrochemical preparation of large amounts of MV^.+ has been developed.

3. A commercial stopped-flow apparatus was modified in order to obtain a high degree of anaerobicity.

4. The reaction of MV^.+ with O₂ produced H₂O₂ (k > 5 · 10⁶ M⁻¹ · s⁻¹, pH 7.5, 25 °C). H₂O₂ subsequently reacted with excess MV^.+ (k = 2.3 · 10³ M⁻¹ · s⁻¹, pH 7.5, 25 °C) to produce water. The kinetics of this reaction were complex and have only been interpreted over a limited range of concentrations.

5. The results support the theory that the herbicidal action of methyl viologen (Paraquat, Gramoxone) is due to H₂O₂ (or radicals derived from H₂O₂) induced damage of plant cell membrane.     

Molecular orbital studies of oxygen activation and mechanisms of cytochromes P-450-mediated oxidative metabolism of xenobiotics

Molecular dimensions and molecular orbital calculations of the electronic structures of 56 substrates, inhibitors and inducers of the cytochromes P-448 and other families of the cytochromes P-450 are reported. Substrates of the cytochromes P-448 are shown to be planar molecules with relatively large values of area/depth², and to have electronic structures with relatively low values for ΔE, the difference in energy between the frontier orbitals (E(LEMO) − E(HOMO)). Substrates of other families of the cytochromes P-450 are globular molecules, with relatively low values of area/depth² and relatively high values of ΔE. Molecular orbital calculations of the active oxygen species, singlet oxygen and superoxy anion, have also been made. Singlet oxygen is a poor electron donor (low values of E(HOMO)) but a good electron acceptor (low values of E(LEMO)), whereas superoxy anion is a good electron donor and a poor electron acceptor. Cytochrome P-448 substrates, which are good electron donors, would preferentially accept singlet oxygen, a good electron acceptor; substrates of the other families of cytochrome P-450, which are less effective electron donors, would preferentially accept superoxy anion, a good electron donor, although substrates of both cytochromes P-448 and other P-450s may accept both species of active oxygen. Together with recent published evidence, these data provide a greater understanding of the mode of activation of oxygen by the various families of the cytochromes P-450, and to the insertion of active oxygen into the substrates. Mechanisms are proposed for the oxygenation of substrates, namely, epoxidation involving singlet oxygen and hydroxylation by superoxy anion. Finally, a detailed explanation of the cytochrome P-450 cycle is discussed, and mechanisms of the different types of oxidative metabolism are presented.     

Synthesis, radiolabeling and receptor binding of [3H][(1S,2R)ACPC2]endomorphin-2

Previously, we have shown that substitution of Pro² for cis-2-aminocyclopentanecarboxylic acid, ACPC in endomorphin-2 results in an analogue with greatly augmented proteolytic stability, high μ-opioid receptor affinity and selectivity. We now report the synthesis and biochemical characterization of [³H][(1S,2R)ACPC²]endomorphin-2 with a specific activity of 1.41 TBq/mmol (38.17 Ci/mmol). Specific binding of [³H][(1S,2R)ACPC²]endomorphin-2 was saturable and of high affinity with an equilibrium dissociation constant, K_d = 1.80 ± 0.21 nM and receptor density, B_max = 345 ± 27 fmol × mg protein⁻¹ at 25 °C in rat brain membranes. Similar affinity values were obtained in kinetic and displacement assays. Both Na⁺ and Gpp(NH)p decreased the affinity proving the agonist character of the radioligand. [³H][(1S,2R)ACPC²]endomorphin-2 retained the μ-specificity of the parent peptide. The new radioligand will be a useful tool to map the topographical requirements of μ-opioid peptide binding due to its high affinity, selectivity and enzymatic stability.     

η and η olefin complexation by S, S-[Ru(Me2edda)]: a structural change to accommodate bidentate dienes

[Ru^II(Me₂edda)(H₂O)₂] (1), Me₂edda²⁻ = N,N′-dimethylethylenediaminediacetate, exhibits a sterically-controlled molecular recognition in forming η² and η⁴ olefin complexes. 1 exists with an N₂O₂ in-plane set of chelate donors and axial H₂O ligands. The two CH₃ functionalities of Me₂edda²⁻ are poised above and below the N₂O₂ plane of the glycinato rings. Studies herein of the 2,2′-bipyridine complex, [Ru^II(Me₂edda)(bpy)], with bidentate bpy chelation as established via ¹H NMR and electrochemical methods show 1 to be ligated in the S,S configuration with the glycinato rings in-plane as a cis-O form. 1 is sterically discriminating in forming η² complexes with smaller olefins (ethylene, 2-propene, cis-2-butene, methyl vinyl ketone and 3-cyclohexene-1-methanol), but rejects larger decorated ring structures and branched olefins (1,2-dimethyluracil, cyclohexene-1-one 2-methyl-2-propene). η² complexes of 1 have characteristic Ru^II/III DPP waves near 0.55 V which vary slightly with olefin structure. Potentially bidendate dienes (1,3-butadiene, 1,3-cyclohexadiene and 2,5-norbornadiene (nbd) form η⁴ complexes as shown by Ru^II/III waves between 0.94 and 1.30 V, indicate of a highly stabilized Ru^II center by π-backboning. An η²η⁴ ‘equilibrium’ with apparent K = 22 at 25 °C is observed for nbd coordinated to 1. (The η² and η⁴ distribution may be a kinetic one and not a thermodynamic one). To allow formation of the cis η⁴ complexes, 1 must undergo a shift of one or both glycinato donors from the N₂O₂ plane into the axial site away from the dimethyl functionalities. η⁴ chelation by 1,3-butadiene has been confirmed by ¹H NMR spectral assignments of two [Ru^II(Me₂edda)] isomers, one in the axial rans-O glycinato configuration, e.g. 1,3-butadiene is bidentate in the original N₂O₂ plane and a second unsymmetrical glycinato arrangement with in-plane and axial glycinato as well as in-plane and axial η⁴-1,3-butadiene coordination. [Ru^II(hedta)(H₂O)]⁻ (2), hedta³⁻ = N-hydrpxyethylenediaminetriacetate, is less discriminating for olefin structures, forming η² complexes with all eleven olefins and dienes mentioned for studies with 1. However, 2 does not undergo displacement of a carboxylate donor by the second olefin unit of a diene [Ru^II(hedta)(diene)]⁻ complexes possess a pendant non-coordinated olefin and on η²-bound olefin in the complex, indicated by a normal Ru^II(pac)(olefin)Ru^II/III wave near 0.55 V.     

Augmentation of Soil with Sporangia of Actinoplanes spp. for Biological Control of Pythium Damping-off

A method was developed for applying strains of Actinoplanes spp. that are hyper-parasites of oospores of Pythium ultimum to soil for reducing Pythium damping-off of plants. The method is based on the augmentation of soil with sporangia of a strain of Actinoplanes spp. borne on clay granules. In vitro sporulation of strains K30, W57, W257 and 25844 was: (1) greater for most strains on dilute Czapek-Dox agar than on four other agar media; (2) inhibited by continuous exposure to fluorescent light of intensity 4-150 μEm^-2s^-1, but not by exposure to 1 μEm^-2s^-1 or darkness; (3) greater at 20-307deg;C than at 10°C;and (4) greater at pH 6-7 than at pH 5 or 8. On solid carriers treated with dilute Czapek-Dox broth (pH 7) and incubated in the dark at 30°C for 3 weeks, strains sporulated poorly or not at all on vermiculite, perlite and rice hulls, but sporulated abundantly (10⁷-10⁹ colony-forming units (CFU) g^-1 of granules) on montmorillonite clay granules. When strains 25844, W57 and W257 were applied as granules (4 10⁷ - 4 × 10⁸ CFU g^-1) at 5% (w/w) to field plots infested with 750-1000 oospores of P. ultimum g^-1 of soil, only strain 25844 consistently increased emergence and reduced root rot of table beets 8- 1 at 24-28 days after planting compared with controls. Strain 25844 (10⁸ CFU g^-1 of granules) at 1% (w/w) also increased the emergence of bush beans at 28 days after planting in P. ultimum-infested plots, but lower rates were ineffective. The inoculum viability of strain 25844 on clay granules declined 100-fold during 2 months of storage at 5-35°C, but thereafter remained stable for another 4 months. Strain 25844 on 6-month-old granules retained a high degree of hyper-parasitic activity toward oospores of P. ultimum. Augmentation of field soil with sporangia of Actinoplanes spp. is a valid approach to the biological control of pythium damping-off.     

Stopped-flow mechanistic study of bromide substitution by an organonitrile at an iron(II) phosphinic centre; a π-electron driven process

The kinetics of the displacement reactions of the bromide ligands of trans-[FeBr₂(depe)₂] (depe = Et₂PCH₂CH₂PEt₂) by the organonitrile NCCH₂C₆H₄OMe-4, in tetrahydrofuran (either in the absence or in the presence of added Br⁻), to give the corresponding mono- and dinitrile complexes trans-[FeBr(NCCH₂C₆H₄OMe-4)(depe)₂]⁺ and trans-[Fe(NCCH₂C₆H₄OMe-4)₂(depe)₂]²⁺, have been investigated by stopped-flow spectrophotometry. The substitution reaction occurs by a mechanism involving rate-limiting dissociation of bromo ligands to form the unsaturated intermediates [FeBr(depe)₂]⁺ (k₁ = 1.52 ± 0.02 s⁻¹) and [Fe(NCR)(depe)₂]²⁺ (k₃ = 0.063 ± 0.008 s⁻¹) which add the nitrile ligand to form those nitrile complexes. The competition between the nitrile and Br⁻ for such metal centres has also been investigated and a stronger inhibiting effect of added Br⁻ is observed for the substitution of the second bromo ligand relative to the first one. The kinetic data are rationalized in terms of π-electronic effects of these unsaturated metal centres and of the bromide and nitrile ligands.     

Simultaneous production of two different gel-forming exopolysaccharides by an Alteromonas strain originating from deep sea hydrothermal vents

Exopolysaccharide production by the marine bacterium Alteromonas sp. strain 1644 was shown to be stimulated by restricted growth conditions and was optimized in nitrogen limited fed-batch cultures. Exopolysaccharides were either partly secreted in the medium or stayed firmly cell-associated. The cell-polysaccharide associations could be destroyed by dialysis against distilled water, allowing polysaccharide purification. The chemical and rheological characterization of this last polysaccharide showed that it was different from the secreted polysaccharide that has been previously described (polysaccharide 1644). At low ionic concentration (below 0.03 M whatever the nature of the ions), solutions of this new polysaccharide had very low viscosities. However, at higher ionic concentration, it formed a gel or exhibited in solution at low polymer concentration an unusually high temperature dependent viscosity. This behaviour was also dependent on the nature of the ions and the following sequences for cations and anions were NH4 ⁺ > Mg²⁺ > Na ⁺ > Li⁺ > K⁺ > TMA⁺ and Br⁻ > NO₃⁻ > SO₄²⁻ > Cl⁻ > I⁻ respectively.     

An in vitro Cr release assay for Ascaris suum infective larvae

This report describes the use of ⁵¹Cr release as a measure of the viability of Ascaris suum inefective larvae after treatment with sodium hypochlorite or kalafungin. Inefective larvae of A. suum were treated with varying dilutions of these compounds and percent ⁵¹Cr release and percent visual larval damage were recorded. An 8% solution of sodium hypochlorite released >90% of the ⁵¹Cr and produced >90% visual larval damage. Kalafungin released >32% ⁵¹Cr and produced >60% visual larval damage at a concentration of 1 μg·ml⁻¹. The results demonstrate that both assays are equal indicators of the viability of A. suum infective larvae when the cytotoxic agent is sodium hypochlorite. Kalafungin, an inhibitor of mitochondrial function, is detected more efficiently using percent visual larval damage when compared to ⁵¹Cr release.     

Slippage of η-allenyl/propargyl to an η structure and tautomerization of η-propargyl to η-allenyl in ligand addition and substitution reactions of platinum(II) complexes

Reactions of [(PPh₃)₂Pt(η³-CH₂CCPh)]OTf with each of PMe₃, CO and Br⁻ result in the addition of these species to the metal and a change in hapticity of the η³-CH₂CCPh to η¹-CH₂CCPh or η¹-C(Ph)=C=CH₂. Thus, PMe₃ affords [(PMe₃)₃Pt(η¹-C(Ph)=C=CH₂)]⁺, CO gives both [trans-(PPh₃)₂Pt(CO)(η¹-CH₂CCPh)]⁺ and [trans-(PPh₃)₂Pt(CO)(η¹-C(Ph)=C=CH₂)]⁺, and LiBr yields cis-(PPh₃)₂PtBr(η¹-CH₂CCPh), which undergoes isomerization to trans-(PPh₃)₂PtBr(η¹-CH₂CCPh). Substitution reactions of cis- and trans-(PPh₃)₂PtBr(η¹-CH₂CCPh) each lead to tautomerization of η¹-CH₂CCPh to η¹-C(Ph)=C=CH₂, with trans-(PPh₃)₂PtBr(η¹-CH₂CCPh) affording [(PMe₃)₃Pt(η¹-C(Ph)=C=CH₂)]⁺ at ambient temperature and the slower reacting cis isomer giving [trans-(PPh₃)(PMe₃)₂Pt(η¹-C(Ph)=C=CH₂)]⁺ at 54 °C . All new complexes were characterized by a combination of elemental analysis, FAB mas spectrometry and IR and NMR (¹H, ¹³C{¹H} and ³¹P{¹H}) spectroscopy. The structure of [(PMe₃)₃Pt(η¹-C(Ph)=C=CH₂)]BPh₄·0.5MeOH was determined by single-crystal X-ray diffraction analysis.     

全细胞多重PCR检测蓝藻、微囊藻及产毒微囊藻方法初探

选取三对分别针对微囊藻、蓝藻16S rDNA及微囊藻毒素合成酶基因mcyB的保守序列的特异性引物209F/409R、27F1/409R、MTR/MTF,其中409R为一条共用引物。设计并优化了一种可以同时检测蓝藻和微囊藻的两重全细胞PCR方法和一种可以同时检测蓝藻、微囊藻和可产毒微囊藻的三重全细胞PCR方法,并且测试了这两种PCR反应的灵敏度区间,分别为10⁵～10³cell·mL^-1、10⁵～10²cell·mL^-1。对采集水库水样检测结果表明双重全细胞PCR方法可以直接应用于对天然水样的检测,三重全细胞PCR方法可用于实验室培养藻细胞的筛查。全细胞多重PCR方法具有快速、简便、准确等特点,在水体微囊藻毒素检测预警方面具有应用价值。     

Energy transfer within the isolated light-harvesting B800–850 pigment-protein complex of Rhodobacter sphaeroides

We have used picosecond absorption spectroscopy with low intensity (5 · 10¹¹–5 · 10¹² photons · pulse⁻¹ · cm⁻²) continuously tunable infrared (800–900 nm) pulses to study the energy transfer dynamics in the isolated B800–850 pigment-protein complex of Rhodobacter sphaeroides. Our results suggest the following picture of the energy transfer dynamics: (i) a fast transfer, within approx. 1 ps, from BChl 800 to BChl 850; (ii) transfer among different BChl 800's with a rate which is at the most of the same order of magnitude as that of BChl 800 → BChl 850 transfer; (iii) very fast transfer (k > 1 · 10¹² s⁻¹) between BChl 850 molecules. Assuming Förster type of energy transfer maximum distances of about 22 and 15 Å are obtained for the BChl 800–BChl 850 and BChl 850–BChl 850 separations, respectively.