Direct,rapid titration of 8-quinolinol : Application of constant-current potentiometry

The major problems in the direct bromination titration of the important analytical reagent 8-quinolinol have been slow reaction rate and difficulty of end-point detection. A reaction-rate study showed that perchloric acid as the titratiun medium gives a sufficiently high reaction rate for direct titration. End-points are simply and conveniently detected using constant-current potentiometry. Metal ions do not interfere. Excellent agreement between titration by the proposed method and the conventional indirect iodomrtric method was observed.     

Mass transfer of acetylacetone,ethylene glycol mono-n-butyl ether and ethylene glycol monophenyl ether across water-carbon tetrachloride and water-chloroform interfaces

The interfacial mass transfer kinetics of acetylacetone (acac), ethylene glycol mono-_n-butyl ether (EGBE) and ethylene glycol monophenyl ether (EGPE) across water-carbon tetrachloride (Ccl₄) and water-chloroform (CHCl₃) interfaces were studied by stirring the two phases at various speeds, maintaining a quiescent interface with a constant area. In the analysis of data, two rate-determining steps consisting of a diffusion toward the interface and a mass exchange between the interface and bulk phases are considered. It is shown that the transfer of EGBE and EGPE in both CHCl₃ and Ccl₄ systems is controlled by the diffusion step even at high stirring speeds, whereas the transfer of acac in Ccl₄ is controlled by the interfacial exchange step at high stirring speeds. An irreversible transfer has been also observed in the EGBE and EGPE systems at low stirring speeds.     

Interaction and Stability of Mixed Micelle and Monolayer of Nonionic and Cationic Surfactant Mixtures

Interaction and stability of binary mixtures of cationic surfactants hexadecyltrimethylammonium bromide (HTAB) or hexadecylpyridinium bromide (HPyBr) with nonionic surfactant decanoyl-N-methyl-glucamide (Mega-10) have been studied at different mole fraction of cationic surfactants by using interfacial tension measurements and fluorescence probe techniques. From interfacial tension measurements, the critical micellar concentration and various interfacial thermodynamic parameters have been evaluated. The experimental cmc's were analyzed with the pseudophase separation model, the regular solution theory, and the Maeda's approach. These approaches allowed us to determine the interaction parameter and composition in the mixed state. By using the static quenching method, the mean micellar aggregation numbers of pure and mixed micelles of HTAB + Mega-10 were obtained. It has been observed that the aggregation number of mixed micelles deviates negatively from the ideal behavior. The micropolarity of the micelle was monitored with pyrene fluorescence intensity ratio and found to be increase with the increase of ionic content. The polarization of fluorescence probe Rhodamine B was monitored at different mole fraction of cationic surfactants.     

Electrospray mass analysis of chemical oxidation of 1,2-diarylcyclopropanes by Cu(II) salt

Electrospray ionization mass spectrometry was used to study chemical electron-transfer reactions of 1,2-diarylcyclopropanes by Cu(II) salt in acetonitrile. The ion [M ? H]⁺ with a hydrogen atom loss and the solvent adduct ions, [M+42]⁺, etc., were detected as the initial reaction products, where [M+42]⁺ represents the ion whose mass is 42 u greater than the parent molecule M. From the study of deuterated derivatives, the hydrogen abstraction was revealed to occur at the 3 position of the cyclopropanes, and the mechanism of the hydrogen abstraction reaction and of the solvent addition were discussed.     

Discovery of a Single Monooxygenase that Catalyzes Carbamate Formation and Ring Contraction in the Biosynthesis of the Legonmycins

Pyrrolizidine alkaloids (PAs) are a group of natural products with important biological activities. The discovery and characterization of the multifunctional FAD‐dependent enzyme LgnC is now described. The enzyme is shown to convert indolizidine intermediates into pyrrolizidines through an unusual ring expansion/contraction mechanism, and catalyze the biosynthesis of new bacterial PAs, the so‐called legonmycins. By genome‐driven analysis, heterologous expression, and gene inactivation, the legonmycins were also shown to originate from non‐ribosomal peptide synthetases (NRPSs). The biosynthetic origin of bacterial PAs has thus been disclosed for the first time.     

Synthesis of biologically active (-)-dehydroiso-β-lapachone and the determination of its absolute configuration

Synthesis of dehydoriso-β-lapachone (1) in both racemic and enantioenriched forms is achieved starting from reduced naphthoquinone equivalents. As for the synthesis of enantioenriched dehydroiso-β-lapachone, introduction of the asymmetric center was carried out by catalytic asymmetric epoxidation of the unfunctionalized trisubstituted olefin using Shi epoxidation diketal catalyst. The construction of isopropenylfurano-1,2-(β)-naphthoquinone was carried out by acidic ring-opening reaction of the epoxynaphthalene and the following diammonium cerium(IV) nitrate (CAN) oxidation. The absolute configuration of naturally occurring (-)-dehydroiso-β-lapachone was finally determined as (R) by comparing the measured optical rotation value of the synthetic (R)-dehydroiso-β-lapachone.     

Alkylbenzolsulfonate zur Erzeugung niedriger Grenzfl?chenspannungen zwischen Kohlenwasserstoffen und Wasser

Ohne Zusammenfassung     

Synthesis of (±)-methylenolactocin and (±)-trans cognac lactone

The title compounds were efficeintly synthesized from 3-fuancarboxylic acid via the Birch recuction-elimination.     

Micellar behavior of short chains phospholipids binary mixture in an aqueous medium: interfacial and fluorescence study

The mixed micellar behavior of short chain zwitterionic phospholipids 1,2-dioctanoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-diheptanoyl-sn-glycero- 3-phosphocholine (DHPC) have been studied at the air-water interface and in the aqueous bulk phase via interfacial tension and pyrene fluorescence (I₁/I₃) intensity measurements, respectively. The critical micellar concentration (cmc) and the thermodynamic parameters such as the free energy of micellization have been evaluated. The interfacial study reveals that a mixed monolayer is formed at the air-water interface by the adsorption of both of the phospholipids. This has been confirmed by evaluating interfacial parameters; the maximum surface excess (_max) or the minimum area per molecule (A_min) of those monomers. Their mixing behaviors have also been expressed in terms of the regular solution interaction parameter, , in the mixed micelle. The parameters are not significantly different from each other, and very close to zero; in other words they are consistent with ideal behavior. The equilibrium distribution of components between the micelle and the aqueous bulk was evaluated by Motomura's formulation. The micellar mole fraction evaluated from regular solution theory and Motomura's formulation also lies close to that corresponding to ideal behavior.