Reaction of α,β-unsaturated acid chlorides with β-diketones. Synthesis of 4,6,7,8-tetrahydro-2H-1-benzopyran-2,5(3H)-diones

Reaction of an α,β-unsaturated acid chloride with the anion of 5,5-dimethyl-1,3-cyclohexane-dione ( 2 ) gives either the enol ester ( 4 ) or a cyclized product ( 5 ), depending upon the reaction conditions. When the acid chloride is in excess, the ester is obtained. When the anion is in excess and the acid chloride is acryloyl or crotonyl, the cyclized product is obtained. A similar cyclized product ( 9 ) was formed from acryloyl chloride and an excess of the anion of 4-hydroxy-6-methyl-2-pyrone ( 8 ).     

EXCITATION ENERGY TRANSFER IN THE CRYPTOPHYTES. FLUORESCENCE EXCITATION SPECTRA AND PICOSECOND TIME-RESOLVED EMISSION SPECTRA OF INTACT ALGAE AT 77 K

Excitation spectra of chlorophyll- a (Chl- a ) fluorescence in intact cells of Cryptomonas ovata, Chroomonas pauciplastida and Chroomonas salina were determined at 77 K. For all species the excitation spectra for emission from Chl- a associated with photosystem II (PSII) showed increased contributions by a carotenoid (493 nm) and phycobiliproteins, and decreased contributions by carotenoid (417 nm, 505 nm) and Chl- a (445 nm) as compared to excitation spectra for emission from Chl- a associated with photosystem I (PSI). Excitation spectra of C. salina and C. ovata showed an increased contribution by Chl- c ² to PSII Chl- a fluorescence emission. In all three species the absorbance band positions of Chl- a , as determined from the excitation spectra, were similar to those previously described in green plants. green algae and phycobilisome-containing organisms. Time-resolved 77 K fluorescence emission spectra of C. ovata and C. salina showed successive emission from both phycoerythrin and Chl- c ², PSII Chl- a , and PSI Chl- a. C. pauciplastida showed successive emission from phycocyanin, PSII Chl- a , and PSI Chl- a. Spectral red-shifts with time were observed for the phycobiliprotein peaks in all three species. The fluorescence decay of phycoerythrin in C. ovata and C. salina was faster than that of phycocyanin in C. pauciplastida. The results are discussed in relation to the organization of the antenna pigments of PSII and PSI in the cryptophyte algae.     

Water adsorption, desorption, and clustering on FeO(111)

The adsorption of water on FeO(111) is investigated using temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). Well-ordered 2 ML thick FeO(111) films are grown epitaxially on a Pt(111) substrate. Water adsorbs molecularly on FeO(111) and desorbs with a well resolved monolayer peak. IRAS measurements as a function of coverage are performed for water deposited at 30 and 135 K. For all coverages (0.2 ML and greater), the adsorbed water exhibits significant hydrogen bonding. Differences in IRAS spectra for water adsorbed at 30 and 135 K are subtle but suggest that water adsorbed at 135 K is well ordered. Monolayer nitrogen TPD spectra from water covered FeO(111) surfaces are used to investigate the clustering of the water as a function of deposition or annealing temperature. Temperature dependent water overlayer structures result from differences in water diffusion rates on bare FeO(111) and on water adsorbed on FeO(111). Features in the nitrogen TPD spectra allow the monolayer wetting and 2-dimensional (2D) ordering of water on FeO(111) to be followed. Voids in a partially disordered first water layer exist for water deposited below 120 K and ordered 2D islands are found when depositing water above 120 K.     

Light olefin production from CO/H2 over silica supported Fe/Mn/K catalysts derived from a bimetallic carbonyl anion, [Fe2Mn(CO)12]?

Fe/Mn/K catalysts derived from support of the anionic carbonyl, [Fe₂Mn(CO)₁₂]^– on silica were compared with catalysts prepared by aqueous impregnation methods, and found to be more selective for production of C₂–C₄ olefins. Addition of K had little effect, whereas variations in reaction conditions altered selectivity owing to secondary reactions of the alkene products.

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Fe/Mn/K, , [Fe₂Mn(CO)₁₂]^–, , , , C₂–C₄. , , .

     

Neolemnane and eremophilane sesquiterpenoids from the pacific soft coral lemnalia africana

Two new sesquiterpenoids of the unprecedented neoiemnane ring system, and one eremophflane-derived sesquiterpene diol have been isolated from the pacific soft-coral Lemnalia africana. The structure of the novel neolemnane compounds, 4 and 5, were confirmed by X-ray crystallography, and the diol, 6, has been described based upon spectral analysis and chemical modification.     

Reductive Amination of Aldehydes and Ketones with Sodium Triacetoxyborohydride. Studies on Direct and Indirect Reductive Amination Procedures(1)

Sodium triacetoxyborohydride is presented as a general reducing agent for the reductive amination of aldehydes and ketones. Procedures for using this mild and selective reagent have been developed for a wide variety of substrates. The scope of the reaction includes aliphatic acyclic and cyclic ketones, aliphatic and aromatic aldehydes, and primary and secondary amines including a variety of weakly basic and nonbasic amines. Limitations include reactions with aromatic and unsaturated ketones and some sterically hindered ketones and amines. 1,2-Dichloroethane (DCE) is the preferred reaction solvent, but reactions can also be carried out in tetrahydrofuran (THF) and occasionally in acetonitrile. Acetic acid may be used as catalyst with ketone reactions, but it is generally not needed with aldehydes. The procedure is carried out effectively in the presence of acid sensitive functional groups such as acetals and ketals; it can also be carried out in the presence of reducible functional groups such as C-C multiple bonds and cyano and nitro groups. Reactions are generally faster in DCE than in THF, and in both solvents, reactions are faster in the presence of AcOH. In comparison with other reductive amination procedures such as NaBH(3)CN/MeOH, borane-pyridine, and catalytic hydrogenation, NaBH(OAc)(3) gave consistently higher yields and fewer side products. In the reductive amination of some aldehydes with primary amines where dialkylation is a problem we adopted a stepwise procedure involving imine formation in MeOH followed by reduction with NaBH(4).     

The solid solutions Na3(1−x)Alx2xPO4: room temperature powder neutron diffraction studies of the two compositions x=0.025 and x=0.2

The crystal structures of the high-temperature modifications of sodium and silver orthophosphates have been determined using powder neutron diffraction (PND) data. II-Na₃PO₄ adopts the space group Fm3m with at 400°C. The PO³⁻₄ group is centered around the origin, but it shows high orientational disorder. The sodium ions occupy the and sites. II-Ag₃PO₄, at 650°C, is similar with . The structure of I-Ag₃PO₄ at room temperature

Full-size image (<1K)

has been re-examined by single-crystal X-ray diffraction. The derived model, with R=0.019 for 116 independent reflections, is in agreement with the latest work reported in the literature. The structure of I-Ag₃PO₄ at 375°C, as determined by PND, has , and displays no gross modifications from that observed at 25°C, although the anisotropic nature of the silver sites is markedly more pronounced at this higher temperature. The cation mobility is discussed in relation to the high-temperatures structures.     

OXYGEN QUENCHING OF CHLOROPHYLL FLUORESCENCE IN CHLOROPLASTS

Abstract— Three phases of chlorophyll a fluorescence quenching by O₂ are observed in green plants. The effects of various inhibitors on photosynthetic partial processes in chloroplasts were investigated in attempts to (1) localize the O₂-quenching sites and (2) assess possible physiological significance of O₂-quenching. Our results localize the most sensitive (and presumably functionally important) phase to a site between plastoquinone and the photosystem I acceptor, chlorophyll (P₇₀₀), possibly plastocyanin. It is suggested that PC may transfer electrons to oxygen in addition to P₇₀₀.     

High accuracy analysis by isotope dilution mass spectrometry using an iterative exact matching technique

The selection of an appropriate isotope dilution mass spectrometry technique for the practical application of this potentially primary method of analysis is highly important. The NARL approach for the application of the exact matching double isotope dilution mass spectrometry technique developed by Henrion is presented. NARL's approach utilises exact matching to minimise the effect of measurement biases within the method but also includes the thorough examination of all other biasing factors. The approach has been successfully tested in international CCQM intercomparisons with other national metrology institutes.     

Cluster chemistry: XVI. Synthesis and crystal structure of AuFe3(μ3-HCNBut)(CO)9(PPh3), an AuFe3 butterfly cluster

The reaction between AuCl(PPh₃ and [Fe(μ₃-HCNBu^t)(CO)₉]^? gives AuFe₃(μ₃-HCNBu^t)(CO)₉(PPh₃), crystals of which are triclinic, space group P$\text{1}$, with a 12.815(3), b 16.265(4), c 19.106(3) Å, α 67.15(3), β 73.46(2), γ 73.12(2)° and Z = 4. The comlex contains an AuFe₃ “butterfly” cluster, the Fe₃ face of which is bridged by the HCNBu^t ligand bonded in the (2σ + π) mode on the side opposite to the Au(PPh₃) moiety, which, contrary to expectation based on the analogy with H, bridges the two Fe atoms σ-bonded to N, and π-bonded to the CN group. The AuFe₂/Fe₃ dihedral angles in the two independent molecules differ significantly, with values of 110.9 and 132.1°.