COPPER QUENCHING OF THE VARIABLE FLUORESCENCE IN Dunaliella tertiolecta. NEW EVIDENCE FOR A COPPER INHIBITION EFFECT ON PSII PHOTOCHEMISTRY

Abstract— The copper quenching effect on fluorescence in Dunaliella tertiolecta was studied. 30% of variable fluorescence was quenched in the presence of 70 μ,M CuS0₄. We confirmed that the copper inhibitory effect on photosystem II (PSII) activity is located on its oxidizing side. Further, we indicate that the complementary area is decreased by copper. Since the quantum yield of PSII photochemistry was lowered and the rate of PSII primary electron acceptor Q_A remained unaffected, we can conclude that some PSII reaction centers were inactivated by copper.     

Angular distribution of intensity of rayleigh scattering from comblike branched molecules

The angular distribution function P(θ) for intensity of light scattered by a dilute solution of comblike branched molecules has been determined for three situations of some interest for evaluation of experimental data: (1) the molecules are identical with branches of equal length attached equidistantly along linear backbone chains; (2) the molecules are homogeneous in mass, with the same number of branches on each molecule, but the branches are distributed at random along the chain; (3) branches and main chains are still uniform, but the molecules are heterogeneous in mass with the number of branches per molecule distributed according to the binomial distribution and the branches in any molecule spaced randomly along the backbone. Examination of numerical results shows that the scattering functions for models (1) and (2) are not very different. The function for case (3) is somewhat different from the others when the mean number of branches per molecule is small but they contain a large fraction of the mass of the molecule. Over a limited range of the pertinent variables (corresponding roughly to observations on typical vinyl polymers of molecular weights up to 10⁶) all three functions agree quite well with P(θ) for homogeneous linear chains with the same mean-square radius of gyration.     

Novel illustrations of the specific reactivity of 1,1-diamino-2,2-dinitroethene (DADNE) leading to new unexpected compounds

1,1-Diamino-2,2-dinitroethene (DADNE) was further investigated and evaluated in oxidation and azidation reactions. DADNE gave new unexpected products as a result of its specific reactivity as previously observed. The X-ray structure determination was the key of success in this work enabling us to perfectly characterise the new products and argue about the reaction mechanisms as well. Once again, the nucleophilic gem-dinitrocarbon of DADNE seemed to be directly involved in these transformations. Attempts to change the regioselectivity were performed by modifying the experimental conditions.     

Mass spectrometric study of SF6-N2 plasma during etching of silicon and tungsten

The reaction products in the SF₆-N₂ mixture rf plasma during reactive ion etching of Si and W have been measured by a mass spectrometric method. Two kinds of cathode materials were used in this work; they were stainless steel for the Si etching, and SiO₂ for the W etching. The main products detected in the etching experiments of Si and W included SF₄, SF₂, SO₂, SOF₂, SOF₄, SO₂F₂, NSF, NF₃, N₂F₄, N_xS_y, NO₂, and SiF₄. In the W etching with the SiO₂ cathode, additional S₂F₂, N₂O, and WF₆ molecules were also obtained. The formation reactions about the novel NSF compound and the sulfur oxyfuorides were discussed.     

Influence of operating conditions on the retention of phosphate in water by nanofiltration

The objective of this study was to investigate the retention of phosphate anions, H₂PO₄⁻ and HPO₄²⁻, by nanofiltration. The first part of this study deals with the characterisation of the NF200 membrane used in permeation experiments with aqueous solutions of neutral organic and charged inorganic solutes. In the second part the effects of feed pressure, ionic strength, concentration and pH on the retention of phosphate anions were investigated. Results show that the membrane is negatively charged, its pore radius is around 0.5 nm and the retention order for the salts tested was R(Na₂SO₄) > R(NaCl) > R(CaCl₂). The retentions of phosphate anions are in the order of 85% for H₂PO₄⁻ and 96% for HPO₄²⁻. They are relatively high when compared to retentions of other anions with the same charge. The retentions of phosphate anions, particularly the monovalent species, depend on the chemical parameters (feed concentration, ionic strength, and pH) and applied pressure. The experimental data were analysed using the Speigler–Kedem model and the transport parameters, i.e., the reflection coefficient (σ) and solute permeability (P_s) have been determined.     

Dibromo[5,10,15,20‐tetrakis(4‐methoxyphenyl)porphyrinato‐κ4N]platinum(IV) chloroform acetonitrile solvate

In the title compound, [PtBr₂(C₄₈H₃₆N₄O₄)]·0.896CHCl₃·0.569CH₃CN, the centrosymmetric metal complex is octahedral, with the porphyrin ring essentially planar and the Br atoms occupying axial positions. The two independent methoxy­phenyl substituents are tilted at angles of 89.0 and 67.0° with respect to the porphyrin plane. The Pt—N distances are 2.035 (4) and 2.036 (4) Å and the Pt—Br distance is 2.4666 (6) Å. Chloro­form and aceto­nitrile solvent mol­ecules, exhibiting substantial disorder, occupy positions between the porphyrin mol­ecules. This is the first crystal and molecular structure of a Pt^IV–porphyrin complex to be reported.     

Structural Effects on the Intrinsic Basicities of alpha,beta-Unsaturated Lactones and Ketones

The proton affinities of 2(5H)-furanone, 1 (836 kJ/mol), 5,6-dihydro-2H-pyran-2-one, 2 (862 kJ/mol), cyclopentenone, 3 (857 kJ/mol), and cyclohexenone, 4 (863 kJ/mol), have been measured by Fourier transform ion cyclotron resonance techniques. A comparison is made with (reexamined) data concerning saturated cyclic and unsaturated aliphatic analogs. Three general observations are made. First, the basicity is found to increase with the size of the ring. Second, unsaturated lactones are more basic than their corresponding aliphatic unsaturated esters. Third, unsaturated and saturated lactones have almost identical gas-phase basicities, while unsaturated and saturated lactones have almost identical gas-phase basicities, while unsaturated cyclic ketones are more basic than their saturated analogs. All these experimental findings have been rationalized by means of ab initio calculations up to the G2(MP2,SVP) level. The basicity trends along the series are the result of two main factors: the different hybridization pattern of the carbonyl carbon as the size of the ring changes and, in the case of lactones, the nonbonding interaction between the proton attached to the carbonyl group and the ether-like oxygen which contributes to the enhanced stability of the protonated form. For unsaturated ketones the C=C double bond participates fully in the change in charge distribution induced by the protonation, while for unsaturated lactones the existence of an oxygen atom within the ring impedes this shift of the electron density.     

Cytosporacin,a highly unsaturated polyketide: application of the ACCORD-ADEQUATE experiment to the structural determination of natural products

Cytosporacin (1), a novel antibacterial polyketide containing naphthopyranone and isochromandione moieties, was isolated from the fermentation broth of the fungus Cytospora rhizophorae. A (1)H-detected ACCORD-ADEQUATE pulse sequence that distinguished (2)J(CH) from (3)J(CH) correlations provided critical information for structural determination. NOE studies established the relative configuration and revealed the presence of two rotamers. A biosynthetic (13)C-labeling experiment indicated that cytosporacin was derived from acetate origin.