(5R,6S,5′R,6′S)-5,6,5′,6′-Diepoxy-β,β-cartin: Sythese,Spectroskopische, chiroptische und chromatographische Eigenschaften

(5R,6S,5′R,6′S)-5,6,5′,6′-Diepoxy-β,β-Carotene: Synthesis, Spectroscopical and Chiroptical Properties, and HPLC-Behaviour Using the scheme C₁₃ + C₂→C₁₅ + C₁₀→C₄₀, whereby C₁₃ = (5R,6S)-5,6-epoxy-β-ionone [8], the title compound 11a , (R = H), has been prepared and characterized. It exhibits nearly identical CD spectra as violaxanthin ( 11b , R = OH).     

Phase behavior of CO2-expanded fluorinated microemulsions

The formation of CO2-expanded, fluorinated reverse microemulsions is demonstrated for the system of perfluoropolyether (PFPE) surfactant (ClPFPE-NH4, MW = 632) and PFPE oil (PFPE, MW = 580). The phase behavior of this system is examined as a function of temperature (25-45 degrees C), pressure, CO2 concentration, and water to surfactant molar ratios (W0 = 10 and 20). Visual observations of one-phase behavior consistent with reverse microemulsion formation are further supported by spectroscopic measurements that establish the existence of a bulk water environment within the aqueous core. Microemulsion formation is not observed in the absence of CO2 for this PFPE surfactant/PFPE oil system, and a CO2 content greater than 70 mol % is required to induce microemulsion formation. Over the range of water loadings and temperatures investigated, the lowest cloud point pressure is observed at 46 bar (5 wt % ClPFPE-NH4 in PFPE oil, W0 = 20, xCO2 = 0.7, T = 25 degrees C). In the regions where one-phase behavior is observed, the cloud point pressures increase with temperature, water loadings, and CO2 content. The driving forces of microemulsion formation in the CO2-expanded fluorinated solvent are discussed relative to traditional reverse microemulsions and CO2-continuous microemulsions.     

Carotinoide aus marinen Schwämmen (Porifera): Isolierung und Struktur von sieben Hauptcarotinoiden aus Agelas schmidtii

Carotenoids from Marine Sponges (Porifera): Isolation and Structure of the Seven Main Carotenoids from Agelas schmidtii The following carotenoids were identified in the marine sponge Agelas schmidtii: α-carotene ((6′R)-β, ε-carotene ( 1 )), isorenieratene (φ,φ-carotene ( 2 )), trikentriorhodin (3,8-dihydroxy-κ,χ-caroten-6-one ( 3 )) and zeaxanthin ((3R, 3′R)-β, β-carotene-3, 3′-diol ( 4 )). In addition, three previously unknown carotenoids called agelaxanthin A, B and C were isolated. Spectroscopical and chemical structure elucidation showed agelaxanthin A to be (3 R)-β, φ-caroten-3-ol ( 6 ) and agelaxanthin C to be a methoxy-19,3′,8′-trihydroxy-7,8-didehydro-β, κ-caroten-6′-one ( 7 ) with the methoxy group at C (2), C (3) or C (4). The limited data on age-laxanthin B were compatible with the structure of a 19-O-methyl derivative of agelaxanthin C.     

Determination of boron and nitrogen in boron nitride

Improved techniques are described for the determination of boron and nitrogen in pure boron nitride. Controlled fusion of boron nitride with sodium carbonate in a muffle furnace is followed by a potentiometric titration of the boric acid. A special quartz vessel is described for the determination of nitrogen. The boron nitride is fused with sodium hydroxide and the resulting ammonia is swept into a receiver and titrated with standard hydrochloric acid. Boron and nitrogen values with their standard deviation are given for a typical pure boron nitride.     

Photochemistry of some alkoxycarbonylplatinum(II) complexes

Alkoxycarbonylplatinum(II) complexes trans-Pt(CO₂CH₂R)Cl(PPh₃)₂, where R = H, Me and Ph, were synthesized in two steps and were characterized by infrared and ultraviolet absorption, proton and phosphorus-31 nuclear magnetic resonance, and mass spectral techniques, and by elemental analysis. Irradiation of the complexes in the solid state or in fluid solution with 254 nm light causes a steady decrease in the intensities of the infrared absorptions in the 1650 and 1070 cm^?1 regions, which is interpreted as signifying labilization of the alkoxycarbonyl ligand. In dichloromethane solution, irradiation causes dissociation of the alkoxycarbonyl ligand, which then decomposes into carbon monoxide and an alkoxide ion. The carbon monoxide is thought to re-coordinate to afford the stable product trans-PtCl(CO)(PPh₃)₂⁺. In the presence of oxygen, triphenylphosphine which dissociates from the metal, is photooxidized to form triphenylphosphine oxide in a parallel photoreaction. Disappearance quantum yields for the alkoxycarbonyl complexes are quite small, Φ ～ 10^?4?10^?3 mol/einstein, and follow the trend H > Me > Ph.     

Optisch aktive Lycopin-epoxide und Lycopin-glycole: Synthesen und chiroptische Eigenschaften

Optically Active Lycopene Epoxides and Lycopene Glycols: Synthesis and Chiroptical Properties We present extensive spectral and chiroptical data on the pure and crystalline lycopene diepoxides 1–3 and glycols 4–9 . A first synthetic approach to 1–9 with (+)-malic acid as starting material afforded 30 as a complex mixture of isomers (Scheme 1). Pure stereoisomers 1–9 were obtained using the enantiomerically pure epoxygeraniol 31 as starting material (Scheme 2). Differentiation of the (5Z)-from the (all-E)-isomers by ¹H-NMR and UV/VIS alone is very difficult.     

Absolute Konfiguration der Equisetumalkaloide (+)-Palustrin,Palustridin ((+)-Monohydrochlorid) sowie der (−)-Dihydropalustraminsäure und weiterer Derivate. 16. Mitteilung über Schachtelhalmalkaloide

Determination of the absolute configuration of alkaloids from Equisetum sp.,e.g. (+)-palustrin, palustridin ((+)-hydrochloride), and (?)-dihydropalustramic acid and derivatives The absolute configuration of the title alkaloids has been determined using chiroptical methods (ORD., superposition of CD. values of appropriate models and a modified Horeau method). (+)-Palustrin is (13R, 17 S, 1′S)-17-(1-hydroxypropyl)-1,5,10-triazabicyclo [11.4.0]heptadec-15-en-11-on.     

New phototriggers: extending the p-hydroxyphenacyl pi-pi absorption range

[equation--see text] Introducing 3-methoxy or 3,5-dimethoxy substituents on the 4-hydroxyphenacyl (pHP) photoremovable protecting group has been explored with two excitatory gamma-amino acids, L-glutamic acid and gamma-amino butyric acid (GABA). These substituents significantly extend the absorption range of the pHP chromophore, e.g., the tail of absorption bands of 2a,b extend above 400 nm, well beyond the absorptions of aromatic amino acids and nucleotides. Irradiation releases the amino acids with rate constants of approximately 10(7) s(-)(1) and appearance efficiencies (Phi(app)) of 0.03-0.04. The photoproducts are formed through the pHP excited triplet and are primarily products of photoreduction and photohydrolysis. 1a,b also rearranged to the phenylacetic acid 3.     

Simultaneous quantification of analytes in quaternary mixtures using dual pulse staircase voltammetry and genetically optimised neural networks

This paper describes the simultaneous quantification of four aliphatic compounds (ethanol, methanol, fructose and glucose) mixed in varying concentrations. The method used employs dual pulse staircase voltammetry (DPSV) to acquire an electrochemical voltammogram from the mixture. An artificial neural network, optimised using an elitist genetic algorithm, is then used to determine the concentration of each individual analyte from the voltammogram. The best average RMS errors achieved when testing with unseen data were 5.03%, 7.72%, 3.29% and 4.00% for maximum analyte concentrations of ethanol, methanol, fructose and glucose respectively. This work represents an important step forward because DPSV data is notoriously difficult to calibrate due to complex electrode-analyte interactions, and had not previous been shown to be amenable to quaternary mixtures.