High pH effect on S-state turnover in chloroplasts studied by thermoluminescence. Short-time alkaline incubation reversibly inhibits S3-to-S4 transition

The influence of high pH on the functioning of the oxygen-evolving system was studied with isolated thylakoids by measuring flash oxygen yield in parallel with thermoluminescence B band which originates in the recombination between the positive charges on S₂ and S₃, the oxidized states of the water-oxidizing enzyme, and the negative charges on Q⁻_B, the semireduced form of the secondary quinone acceptor of Photosystem II. It was found that a mild alkaline incubation of thylakoids (3 min at pH = 8.8–9.1 in darkness) largely inhibits O₂ evolution, while much less the B-band amplitude. The flash-induced period-four oscillation of the B band was abolished at high pH, showing normal oscillatory response only after the 1st and 2nd flashes, but no more oscillation after the 3rd flash. These observations indicated an inhibition of S₃-to-S₄ transition by high pH and were correlated primarily with the liberation of the 33 kDa peripheral protein followed by release of functional Mn. The above phenomena were largely reversed when the pH was returned to neutral. A possible mechanism of high pH inhibition of oxygen-evolving system is discussed.     

Binding of the inhibitor NH3 to the oxygen-evolving apparatus of spinach chloroplasts

Experiments are described on flash-induced luminescence of isolated spinach chloroplasts after addition of NH₄Cl. The results indicate a binding of NH₃, presumably in competition with water, in the oxidation states S₂ and S₃, i.e. the states reached upon illumination of dark-adapted material with one and two flashes, respectively. In the initial state S₁, no binding of NH₃ occurs. In state S₂ the binding of ammonia is rapid (half-time about 0.5 s) and rapidly reversible; in state S₃ the binding is slower (half-time about 10 s) and slowly reversible. NH₃ bound to S₄ prevents the oxidation of water. NH₃ bound to S₂ decreases the rate of the back reaction of reduced primary acceptor (Q⁻), indicating a charge stabilization, i.e. a decrease in the redox potential of S₂ due to interaction with ammonia. In Tris-washed chloroplasts, the stability of the positive charge generated in a flash is much smaller than in normal chloroplasts and not increased by NH₃. On the basis of these observations it is postulated that, in the absence of NH₃, states S₂ and S₃ are stabilized by manganese-coordinated, bound water.     

Effect of low temperature (−30 to −60°C) on the reoxidation of the Photosystem II primary electron acceptor in the presence and absence of 3(3,4-dichlorophenyl)-1,1-dimethylurea

The fluorescence yield has been measured on spinach chloroplasts at low temperature (−30 to −60°C) for various dark times following a short saturating flash. A decrease in the fluorescence yield linked to the reoxidation of the Photosystem II electron acceptor Q is still observed at −60°C. Two reactions participate in this reoxidation: a back reaction or charge recombination and the transfer of an electron from Q⁻ to Pool A. The relative competition between these two reactions at low temperature depends upon the oxidation state of the donor side of the Photosystem II center:

1. (1) In dark-adapted chloroplasts (i.e. in States S₀+S₁ according to Kok, B., Forbush, B. and McGloin, M. (1970) Photochem. Photobiol. 11, 457–475), Q, reduced by a flash at low temperature, is reoxidized by a secondary acceptor and the positive charge is stabilized on the Photosystem II donor Z. Although this reaction is strongly temperature dependent, it still occurs very slowly at −60°C.

2. (2) When chloroplasts are placed in the S₂+S₃ states by a two-flash preillumination at room temperature, the reoxidation of Q⁻ after a flash at low temperature is mainly due to a temperature-independent back reaction which occurs with non-exponential kinetics.

3. (3) Long continuous illumination of a frozen sample at −30°C causes 6–7 reducing equivalents to be transferred to the pool. Thus, a sufficient number of oxidizing equivalents should have been generated to produce at least one O₂ molecule.

4. (4) A study of the back reaction in the presence of 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) shows the superposition of two distinct non-exponential reactions one temperature dependent, the other temperature independent.

Misdirected π-donor ligands: (η-C5H5)2Zr(Cl) (SR) with sterically more demanding R groups have lower rotational barriers

Rotational barriers about the M-S bonds of 16-electron bent metallocene monothiolates (η⁵-C₅H₅)₂Zr(Cl) (SR) (R = −CH₃, −CH₂CH₃, −CH(CH₃)₂, −C(CH₃)₃) (1a–d) have been measured by dynamic ¹H NMR methods: 32, 33, 35 and 26 kJ mol⁻¹, respectively. The ground-state orientation about the Zr-S bonds of 1 that maximizes Spπ → Mdπ bonding (Cl-Zr-S-R ≈ 90°) also maximizes CpR steric interaction, whereas the rotational transition-state orientation (Cl-Zr-S-R ≈ 0°) is one that minimizes Spπ → Mdπ bonding and maximizes ClR steric interaction. Deviation from a ground-state orientation that is ideal for Spπ → Mdπ bonding might be expected as the size of the R group and CpR steric interaction increases. Thus, the aberrant trend for the R = −C(CH₃)₃ derivative could be attributed to a ground-state steric effect where the sterically demanding −C(CH₃)₃ group forces an unfavorable (misdirected) orientation for Mdπ-Spπ bonding, but a favorable orientation with respect to CpR and ClR steric interactions. However, the solid-state structures of (η⁵-C₅H₅)₂Zr(SR)₂ (R = −CH₃, −CH₂CH₃, −CH(CH₃)₂, −C(CH₃)₃) (2a–d) exhibit regular variation of their metric parameters as evidenced by their Zr-S-C bond angles of 108, 109, 113, and 124° and S-Zr-S′ bond angles of 97, 99, 100 and 106°, respectively. Neither the S′-Zr-S-R torsion angles nor the dihedral angles that describe the relationship between the S/Zr/S′ and Cp(centroid)/Zr/Cp′ (centroid) planes (both indicators of the relative orientation of the Zr dπ acceptor orbital and the thiolate S pπ donor orbital) reflect the steric demand of the R group. Thus, the size of the R group imposes a measured effect on the geometry of 2 and the tert-butyl group is not extraordinary. Although the enthalpic and entropic effects could not be deconvoluted for rotation about the Zr-S bond of 1 in the present study, literature precedents suggest that both enthalpic and entropic effects may play a role in determining the irregular trend that is observed.     

The coordination chemistry of cationic main group clusters: syntheses and structures of [Fe3(Se2)2(CO)10] and [Fe4(Se2)3(CO)12]

The reactions of the polysulfur and selenium cationic clusters S₈²⁺ and Se₈²⁺ with various iron carbonyls were investigated. Several new chalcogen containing iron carbonyl cluster cations were isolated, depending on the nature of the counteranion. In the presence of SbF₆⁻ as a counterion, the cluster [Fe₃(E₂)₂(CO)₁₀] [SbF₆]₂·SO₂ (E = S, Se) could be isolated from the reaction of E₈²⁺ and excess iron carbonyl. The cluster is a picnic-basket shaped molecule of two iron centers linked by two Se₂ groups, with the whole fragment capped by an Fe(CO)₄ group. Crystallographic data for C₁₀O₁₂Fe₃Se₄Sb₂F₁₂S (I): space group monoclinic P2₁/c, A = 11.810(9), b = 24.023(6), c = 10.853(7) Å, β = 107.15(5)°, V = 2942(3) ų, Z = 4, R = 0.0426, R_w = 0.0503. When Sb₂F₁₁⁻ is present as the counterion, or Se₄[Sb₂F₁₁]₂ is used as the cluster cation source, a different cluster can be isolated, which has the formula [Fe₄(Se₂)₃(CO)₁₂] [SbF₆]₂·3SO₂. The dication contains two Fe₂Se₂ fragments bridged by an Se₂ group. Crystallographic data for C₁₂O₁₈Fe₄Se₆Sb₂F₁₂S₃ (III): space group triclinic , b = 18.400(9), C = 10.253(4) Å, = 93.10(4), β = 103.74(3), γ = 93.98(3)°, V = 1995(1) ų, Z = 2, R = 0.0328, R_w = 0.0325. The CO stretches in the IR spectrum all show a large shift to higher wavenumbers, suggesting almost no τ backbonding from the metals. This also correlates with the observed bond distances. All the compounds are extremely sensitive to air and water, and readily lose SO₂ when removed from the solvent. Thus all the crystals were handled at −100°C. The clusters seem to be either insoluble or unstable in all solvents investigated.     

The vibrational spectrum of TpRhH2(H2): a computational and inelastic neutron scattering study

We report extensive density functional theory studies of the structures and vibrational frequencies of Tp^3,5-MeRhH₂(H₂) in its ground and various transition states as well as the first direct comparison of observed and calculated inelastic neutron scattering (INS) vibrational spectra on this type of compound. Geometry optimizations produced canted η²-dihydrogen dihydride local minima of C₁ symmetry; with HH distances for the C₁ minimum energy structure of 0.842 and 0.898 Å and barriers to rotation of 0.34 and 0.50 kcal mol⁻¹, respectively for B3LYP/BS1 and BP86/BS1 calculations of Tp^3,5-MeRhH₂(H₂). The latter results from one transition state rotated approximately 60° away (a second lower energy transition state which is a few hundreds of a kcal mol⁻¹ above the C₁ MIN is rotated approximately 30° away). With these calculated d(HH) values for the C₁ MIN the previously reported experimental data on the rotation of the dihydrogen ligand yields an experimental barrier to rotation of 1 kcal mol⁻¹ and places the torsional transition at 200 cm⁻¹ in the INS spectrum. Optimization of the Rh structure, that is analogous to the related Ir(V) C_s minimum found for TpIrH₄, generates a high-energy (>4 cal mol⁻¹) C_s transition state TpRh^IIIH₄ structure with an η³-H₃ ⁻ ligand. This transition state (C_s TSE) exchanges the hydrogen in the mirror plane between two chiral C₁ MIN structures. Comparisons between observed and computed INS spectra suggests that the experimental INS spectrum be viewed as resulting from a quantum-averaged ground state encompassing at least two of the low energy structures found in our calculations.     

Photooxidation of cytochrome b559 and the electron donors in chloroplast Photosystem II

The effect of light on the reaction center of Photosystem II was studied by differential absorption spectroscopy in spinach chloroplasts.

At − 196 °C, continuous illumination results in a parallel reduction of C-550 and oxidation of cytochrome b₅₅₉ high potential. With flash excitation, C-550 is reduced, but only a small fraction of cytochrome b₅₅₉ is oxidized. The specific effect of flash illumination is suppressed if the chloroplasts are preilluminated by one flash at 0 °C.

At − 50 °C, continuous illumination results in the reduction of C-550 but little oxidation of cytochrome b₅₅₉. However, complete oxidation is obtained if the chloroplasts have been preilluminated by one flash at 0 °C. The effect of preillumination is not observed in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea.

A model is discussed for the reaction center, with two electron donors, cytochrome b₅₅₉ and Z, acting in competition. Their respective efficiency is dependent on temperature and on their states of oxidation. The specific effect of flash excitation is attributed to a two-photon reaction, possibly based on energy-trapping properties of the oxidized trap chlorophyll.     

Limiting steps in Photosystem II and water decomposition in Chlorella and spinach chloroplasts

1. 1. By varying the redox potential of a chloroplast suspension, we obtained new evidence for an equilibrium between states S₀ and S₁ in the model of Kok, B., Forbush, B. and McGloin, N. (1970, Photochem. Photobiol. 11, 457–475). The mid-point potential of the S₀ to S₁ couple is close to that for the pool of the electron acceptor of System II, A to A⁻.

2. 2. The limiting steps between two consecutive photoreactions of System II in Chlorella and spinach chloroplasts, have been studied.

2.1. (a) The limiting step from S₁ to S₂ (noted γ₁ (Δt)) is not exponential. Its temperature coefficient becomes greater as the reaction proceeds. The shape of the kinetics is an intrinsic property of each center. Chloroplasts fixed with 2% glutaraldehyde, show simple first order kinetics.

2.2. (b) The limiting step from S₀ to S₁ (γ₀ (Δt)) exhibits the same characteristics as γ₁ (Δt)).

2.3. (c) The limiting step from S₂ to S₃ (γ₂ (Δt)) shows sigmoidal kinetics; two reactions are involved. One of the reactions exhibits the same properties as γ₀ (Δt) and γ₁ (Δt).

2.4. (d) The limiting step from S₃ to S₀ (γ₃ (Δt)) is a first order reaction, two times slower than the other transitions. This reaction is interpretated in terms of oxygen release.

3. 3. We also studied the limiting steps in the presence of low concentrations (50 μM) of hydroxylamine. The results favor the binding of two molecules of hydroxylamine to every photochemical center.

Thermoluminescence as a probe of photosystem II. The redox and protonation states of the secondary acceptor quinone and the O2-evolving enzyme

The thermoluminescence band observed in chloroplasts after flash excitation at ambient temperatures has recently been identified as being due to recombination of the electron on the semiquinone form of the secondary plastoquinone acceptor, Q_B, with positive charges on the oxygen-evolving enzyme, S₂ and S₃ (Rutherford, A.W., Crofts, A.R. and Inoue, Y. (1982) Biochim. Biophys. Acta 682, 457–465). Further investigation of this thermoluminescence confirms this assignment and provides information on the function of PS II. The following data are reported: (1) Washing of chloroplasts with ferricyanide lowers the concentration of Q_B⁻ in the dark and predictable changes in the extent of the thermoluminescence band are observed. (2) The thermoluminescence intensity arising from S₂Q_B⁻ is approximately one half of that arising from S₃Q_B⁻. (3) Preflash treatment followed by dark adaptation results in changes in the intensity of the thermoluminescence band recorded after a series of flashes. These changes can be explained according to the above assignments for the origin of the thermoluminescence and if Q_B⁻ provides an important source of deactivating electrons for the S states. Computer simulations of the preflash data are reported using the above assumptions. Previously unexplained data already in the literature (Läufer, A. and Inoue, Y. (1980) Photobiochem. Photobiophys. 1, 339–346) can be satisfactorily explained and are simulated using the above assumptions. (4) Lowering the pH to pH 5.5 results in a shift of the S₂Q_B⁻ thermoluminescence band to higher temperatures while that arising from S₃Q_B⁻ does not shift. This effect is interpreted as indicating that Q_B⁻ is protonated and the S₂ to S₃ reaction involves deprotonation while the S₁ to S₂ reaction does not.     

Synthesis and structures of the cuboidal iron-sulfur-nitrosyl-phosphine clusters [Fe4S3(NO)4(PR3)3] (R = Et, Pr, C6H11)

A series of cuboidal iron-sulfur clusters [Fe₄S₃(NO)₄(PR₃)₃]^0,1+ (R = Et, Prⁱ, Cy) were synthesized by two routes: reductive desulfurization of [Fe₄S₄(NO)₄] by tertiary phosphines, and substitution of triphenylphosphine in [Fe₄4S₃(NO)₄(PPh₃)₃] by a more basic phosphine. The structures of 3[Fe₄S₃(NO)₄(PEt₃)₃] · 0.5Et₂O, [Fe₄S₃(NO)₄(PEt₃)₃] [Fe₄S₃(NO)₇] and partially substituted [Fe₄S₃(NO)₄(PPh₃)_2⁻ (PPrⁱ₃)] have been determined by X-ray diffraction in order to define the cuboidal Fe₄S₃ core, previously known only in Roussin's black anion and its reduced form, [Fe₄S₃(NO)₇7]^1−,2−, and as a part of the iron-molybdenum cofactor of nitrogenase.     

Alkene rotation in [Ru(η-C5H5) (L2) (η-alkene][CF3SO3] with L2 = iPr- or pTol-diazabutadiene. X-ray crystal structure of [Ru(η-C5H5(pTol-DAB) (η-ethene][CF3SO3]

Reaction of RuCl(η⁵-C₅H₅(pTol-DAB) with AgOTf (OTf = CF₃SO₃) in CH₂Cl₂ or THF and subsequent addition of L′ (L′ = ethene (a), dimethyl fumarate (b), fumaronitrile (c) or CO (d) led to the ionic complexes [Ru(η⁵-C₅H₅)(pTol-DAB)(L′)][OTf] 2a, 2b and 2d and [Ru(η⁵-C₅H₅)(pTol-DAB)(fumarontrile-N)][OTf] 5c. With the use of resonance Raman spectroscopy, the intense absorption bands of the complexes have been assigned to MLCT transitions to the iPr-DAB ligand. The X-ray structure determination of [Ru(η⁵-C₅H₅)(pTol-DAB)(η²-ethene)][CF₃SO₃] (2a) has been carried out. Crystal data for 2a: monoclinic, space group P2₁/n with A = 10.840(1), b = 16.639(1), C = 14.463(2) Å, β = 109.6(1)°, V = 2465.6(5) ų, Z = 4. Complex 2a has a piano stool structure, with the Cp ring η⁵-bonded, the pTol-DAB ligand σN, σN′ bonded (Ru-N distances 2.052(4) and 2.055(4) Å), and the ethene η²-bonded to the ruthenium center (Ru-C distances 2.217(9) and 2.206(8) Å). The C = C bond of the ethene is almost coplanar with the plane of the Cp ring, and the angle between the plane of the Cp ring and the double of the ethene is 1.8(0.2)°. The reaction of [RuCl(η⁵-C₅H₅)(PPh)₃ with AgOTf and ligands L′ = a and d led to [Ru(η⁵-C₅H₅)(PPh₃)₂(L′)]OTf] (3a) and (3d), respectively. By variable temperature NMR spectroscopy the rottional barrier of ethene (a), dimethyl fumarate (b and fumaronitrile (c) in complexes [Ru(η⁵-C₅H₅)(L₂)(η²-alkene][OTf] with L₂ = iPr-DAB (a, 1b, 1c), pTol-DAB (2a, 2b) and L = PPh₃ (3a) was determined. For 1a, 1b and 2b the barrier is 41.5±0.5, 62±1 and 59±1 kJ mol⁻¹, respectively. The intermediate exchange could not be reached for 1c, and the ΔG^# was estimated to be at least 61 kJ mol⁻. For 2a and 3a the slow exchange could not be reached. The rotational barrier for 2a was estimated to be 40 kJ mol⁻. The rotational barier for methyl propiolate (HC≡CC(O)OCH₃) (k) in complex [Ru(η⁵-C₅H₅)(iPr-DAB) η²-HC≡CC(O)OCH₃)][OTf] (1k) is 45.3±0.2 kJ mol⁻¹. The collected data show that the barrier of rotational of the alkene in complexes 1a, 2a, 1b, 2b and 1c does not correlate with the strength of the metal-alkene interaction in the ground state.     

The deactivation of Photosystem II in Chlorella as a second-order process

The kinetics of deactivation of the S₃ state in Chlorella have been observed under a variety of conditions. The S₃ state appears to decline in a dark period coming after a sequence of 30 saturating flashes in a second-order reaction, the rate constant of which is 0.132/[S*₃] s⁻¹ and which involves an electron donor, D₁, of concentration 1.25[S*₃] where [S*₃] is the concentration of the S₃ state when the oxygen yield of the light flashes is constant. If a 1 min period of 650 nm illumination is employed after the sequence of flashes, the subsequent S₃ state deactivation kinetics are more complex. There is an initial phase of S₃ state deactivation, accounting for about 35% of the original S₃ state, which is complete in less than 100 ms. The remaining 65% of the S₃ state appears to deactivate in a second-order reaction, the rate constant of which is 1.36/[S*₃] s⁻¹ and which involves an electron donor of initial concentration 0.58[S*₃]. If a 1 min period of 710 nm illumination comes after the 30 flashes, at least 98% of the S₃ state deactivates according to first-order kinetics. It is shown that this can be explained using a second-order model if there is an electron donor present of which the concentration is large compared with [S*₃]. However, S₃ state deactivation observed after 5 min of dark and two saturating flashes can be described neither by a first-order model nor a second-order model. Deactivation of the S₂ state after a 5 min dark period and one saturating flash follows second-order kinetics with a rate constant of 0.2/[S*₃] s⁻¹ and appears to involve an electron donor of initial concentration 1.3[S*₃]. Arguments are presented which tend to rule out the primary electron acceptor to Photosystem II as being any of the electron donors but it appears quite possible that the large plastoquinone pool is involved.     

The response of sweet corn to HF and SO2 under field conditions

“Marcorss” sweet corn plants grown in field plots were exposed continuously in open-top chambers for 32 days to ambient air, charcoal-filtered air or charcoal-filtered air containing HF (ca. 0.5 μgF m⁻³), SO₂ (ca. 235 μg m⁻³), or the two pollutants combined. Elliptical chlorotic leasions appeared after 23 days on leaves of plants exposed to SO₂/HF, and shortly thereafter on plants exposed to all other treatments. At harvest, the number of plants with lesions was significantly greater in chambers supplied with SO₂/HF than in chambers with SO₂, HF, or filtered air.

The different treatments had no effect on fresh or dry weights of leaves, husks, or tassels, height of plants, or number of kernels per ear. Exposure to SO₂/HF reduced the fresh and dry weights of stalks. There were fewer mature ears in the SO₂/HF and unfiltered air treatments than in the others. The reduction in yield from SO₂/HF was about the same as that ascribed to ambient photochemical oxidants in the unfiltered air treatment.

HF combined with SO₂ had no effect on accumulation of S as compared with SO₂ alone, but there was a striking reduction in accumulation of foliar F in plants exposed to SO₂/HF as compared with HF alone.     

The new enneanuclear nickel carbonyl anion [Ni9(CO)16] and its relationships with the [Ni12(CO)21] and [Ni6Rh3(CO)17] clusters

The reaction of [N(PPh₃)₂]₂[Ni₆(CO)₁₂] with Cu(PPh₃)_xCl (x=1, 2), as well as the degradation of [N(PPh₃)₂]₂[H₂Ni₁₂(CO)₂₁] with PPh₃, affords the new and unstable dark orange–brown [N(PPh₃)₂]₂[Ni₉(CO)₁₆].THF salt in low yields. This salt has been characterized by a CCD X-ray diffraction determination, along with IR spectroscopy and elemental analysis. The close-packed two-layer metal core geometry of the [Ni₉(CO)₁₆]²⁻ dianion is directly related to that of the bimetallic [Ni₆Rh₃(CO)₁₇]³⁻ trianion and may be envisioned to be formally derived from the hcp three-layer geometry of [Ni₁₂(CO)₂₁]⁴⁻ by the substitution of one of the two outer [Ni₃(CO)₃(μ−CO)₃]²⁻ layers with a face-bridging carbonyl group.     

A novel series of complexones with bis- or biazole structure as mixed ligands of paramagnetic contrast agents for MRI

We describe the syntheses, physicochemical properties and biological evaluation of a novel series of complexones containing bis- or biazoles moieties and two iminodiacetic acid units as novel ligands for paramagnetic lanthanides. The complexones were prepared by reaction of the corresponding 1,1′-bishaloethylbi- or bispyrazoles with methyl iminodiacetate and subsequent NaOH hydrolysis. 1,1′-Bisbromoethyl precursors were obtained by direct alkylation with an excess of 1,2-dibromoethane, or by heating the corresponding alcohol in HCl. Sigmoidal binding isotherms and MO calculations supported as most stable structures in solution, those containing two Gd(III) atoms bound per molecule of complexone with half saturation values S_0.5 (M⁻¹, 22 °C, pH 7.2) in the range 6.5 10⁻⁶0.5<36.1 10⁻⁶. Relaxivity properties [r₁, r₂, s⁻¹ mM⁻¹ Gd(III)] determined at 1.5 Tesla gave values (12.0<r₁<17.7, 12.2<r₂<20), improving significantly the relaxivities of reference compounds such as Gd(III)EDTA (5.2, 5.6) or Gd(III)DTPA (4.30, 4.30). These improvements involve mainly increased hydration and slower rotational motions. In vitro toxicity experiments are reported.     

大气CO2浓度和气温升高对麦田节肢动物群落的影响

为了预测气候变化对麦田节肢动物群落多样性的影响, 本研究在麦田开放环境中设置4种处理, 分别是高温(高于当时气温2℃和当前CO₂浓度)、高CO₂浓度(500 μL/L和当时气温)、高温+高CO₂浓度和对照(当前CO₂浓度和气温)等, 采用定期随机抽样方法调查节肢动物群落的多样性, 用经典的多样性指数对整体节肢动物群落以及不同食性节肢动物群落多样性进行分析。共采到节肢动物3纲10目42科52种。仅“高温”和“高温+高CO₂”处理显著增大节肢动物群落的均匀度, 其余处理均无显著影响。“高温+高CO₂”处理的影响随小麦生长发育期不同而略有差异, 在苗期可增大Shannon-Wiener多样性指数, 而在后期使该指数减小; “高温+高CO₂”与“高温”处理的群落多样性较为相似。对不同食性节肢动物群落的分析表明, 与对照相比, 植食性昆虫群落在“高CO₂”下丰富度显著增大; 寄生性昆虫群落的多度在“高温”下显著增大; 腐食性等节肢动物群落的多度在“高CO₂+高温”和“高温”处理下有所增大、均匀度在“高温”下略降低, 但均未达统计上的显著水平; 捕食性节肢动物群落不受影响。本研究说明, CO₂浓度和气温升高不同程度地影响麦田节肢动物群落的物种多样性, 两类因素同时升高与各自单独升高的影响不完全一致。     

Effect of chloride ions on the S-state distribution and deactivation kinetics in preparations of the cyanobacterium Anacystis nidulans

The roles of Ca²⁺ and Cl⁻ on the photosynthetic O₂ yield under flash illumination have been examined in EDTA-washed preparations of the cyanobacterium Anacystis nidulans. Especially the effect of Cl⁻ deficiency on the O₂ yield and on the S-state distribution was analyzed. As the results show, omission of both Ca²⁺ and Cl⁻ (Mn²⁺ present) almost totally inhibited O₂ evolution. When Ca²⁺ was replaced by Na⁺, a substantial reduction of the O₂ yield was observed, but only a minor change in the S-state distribution occurred. However, when Cl⁻ was displaced by NO⁻₃, which is equivalent to Cl⁻ deficiency of the water-splitting complex, a substantial reduction of the O₂ yield and in addition a significant change in the S-state distribution was observed. The comparison of deactivation kinetics in NO⁻₃ containing samples with those in control samples indicated that Cl⁻ deficiency allowed accumulation of oxidizing equivalents up to the S₃ state but modified the final step of O₂ evolution. Moreover, those centers which advanced to the S₃ state in the absence of Cl⁻ deactivated in a special way which involved a faster deactivation of S₂ and an increased formation of S₋₁.     

Optical outer-sphere charge transfer in aqueous ion pairs with sulfidic anions as donors

Various sulfidic anions and the oxidizing cations [Ru(NH₃)₆]³⁺ and N,N′-dimethyl-4,4′-bipyridinium²⁺ (paraquat²⁺) form ion pairs in aqueous solutions which display outer-sphere charge-transfer (CT) absorptions. The CT energies are used to establish a series of sulfidic anions with increasing CT donor strength: SCN⁻2O₃ ²⁻4 ³⁻3S³⁻2 ⁻2S₂ ⁻4 ²⁻.     

The synthesis and properties of binuclear pentacyanoiron(III)-μ-cyano- amminetetracyanoiron(III) [(C6H5)4P]4[(NC)5Fe---NC---Fe(CN)4NH3]·6H2O

The binuclear cyanoferrate, tetraphenylphosphonium pentacyanoiron(III)-μ-cyano-amminetetracyanoiron(III), [(C₆H₅)₄P]₄[Fe₂(CN)₁₀NH₃]⁴⁻, was synthesized by air oxidation of aqueous solutions of Na₃[Fe(CN)₅NH₃] · 3H₂O. Single crystal X-ray diffraction studies show the compound to contain the binuclear, cyano-bridged anion, [(NC)₅Fe---NC---Fe(CN)₄NH₃]⁴⁻. This compound is structurally identical to the one prepared by A. Ludi et al., [Inorg. Chim. Acta, 34, 113 (1979)], with the exception that [Fe(CN)₆]³⁻ is not required for the synthesis of this compound. The Fe(III) atoms are antiferromagnetically coupled through the CN⁻ bridge, as shown by a maximum in the magnetic susceptibility at 50 K. The electronic and IR spectra of the complex in the solid state and in solution are discussed.     

Hetero-polynuclear complexes containing bridging diphenylphosphino-alkenes and -alkynes. The crystal structure of an Rh2{μ−ν:ν−P(Ph2) (CH2)3C≡CR}Co2 complex

The phosphinoalkenes Ph₂P(CH₂)_nCH=CH₂ (n= 1, 2, 3) and phosphinoalkynes Ph₂P(CH₂)_n C≡CR (R = H, N = 2, 3; R = CH₃, N = 1) have been prepared and reacted with the dirhodium complex (η−C₅H₅)₂Rh₂(μ−CO) (μ−η²−CF₃C₂CF₃). Six new complexes of the type (ν−C₅H₅)₂(Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH₃C₅H₄)Mn(CO)₂thf resulted in coordination of the manganese to the alkene function. The Rh₂---Mn complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂P(CH₂)₃CH=CH₂} (η−CH₃C₅H₄)Mn(CO)₂] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co₂(CO)₈ resulted in the coordination of Co₂(CO)₆ to the alkyne function. The Rh₂---Co₂ complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂PCH₂C≡CCH₃}Co₂(CO)₂], C₃₇H₂₅Co₂F₆O₇PRh₂, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group (C_i¹, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on |F| was 0.052 fo observed (I > 3σ(I)) reflections. The Rh₂ and Co₂ parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh₂ and perpendicular for Co₂. Attempts to induce Rh₂Co₂ cluster formation were unsuccessful.