Effect of included guest molecules on the normal state conductivity and superconductivity of beta''-(ET)(4)[(H(3)O)Ga(C(2)O(4))(3)].G (G = pyridine,nitrobenzene)

Normal state conductivity and superconductivity together with bulk magnetic susceptibility and magnetization measurements have been measured for two molecular charge-transfer salts: beta' '-(ET)4[(H3O)Ga(C2O4)3]G (ET = bis(ethylenedithio)tetrathiafulvalene, G = pyridine for compound I and nitrobenzene for compound II). With the exception of the included guest molecules (G) the crystal structures are almost identical. Both show minima in their electrical transport at 130 K for I and at 160 K for II, but at lower temperatures their behaviors differ markedly. The resistance of I reaches a maximum at 50 K with a further small peak at 2 K and possible superconductivity only below 2 K, whereas that of II increases continuously down to 7.5 K, where an abrupt transition to a superconducting state occurs.     

Enantioselective Preparation of 2‐Aminomethyl Carboxylic Acid Derivatives: Solving the β2‐Amino Acid Problem with the Chiral Auxiliary 4‐Isopropyl‐5,5‐diphenyloxazolidin‐2‐one (DIOZ). Preliminary Communication

Multigram amounts of suitably protected β²‐amino acids with 17 of the 20 proteinogenic side chains are prepared by diastereoselective reactions of Li, B, or Ti enolates of the corresponding 3‐acyl‐4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐ones (acyl‐DIOZ; 1 ) with appropriate electrophiles (amidomethylation, hydroxyalkylation, (benzyloxycarbonyl)methylation) in yields of 55–90% and with diastereoselectivities of 80 to >97% (Scheme). The primary products 2 – 8 thus obtained are converted to protected β²‐amino acids by standard procedures (Table 1). Many of the DIOZ derivatives are highly crystalline compounds (31 X‐ray crystal structures in Table 2). The chiral auxiliary DIOZ, readily prepared in either enantiomeric form, is recovered with high yield.     

Photoinduced morphism of gemini surfactant aggregates

The photochemical behaviour of an azobenzene chromophore inserted in a gemini surfactant imparts photocontrol to the resulting amphiphile assemblies, including the collapse, upon irradiation, of the multi lamellar vesicles formed in aqueous solution.     

Very general formation of tetrahydropterin cation radicals during reaction of iron porphyrins with tetrahydropterins: model for the corresponding NO-synthase reaction

Electron transfer from tetrahydropterins to iron porphyrins, with formation of intermediate tetrahydropterin cation radicals, is a very general reaction that was shown to occur not only with tetrahydrobiopterin, as originally found in NO-synthases, but also with another important biological cofactor, tetrahydrofolate, and various iron porphyrins, either in their ferric state, or in the Fe(II)O(2) state, as in the first model of the corresponding NO-synthase reaction described in this paper.     

Chemical modification of acetylcholinesterase with methoxypolyethylene glycol

Acetylcholinesterase (AChE) (EC 3.1.1.7) was modified with activated monomethoxypolyethylene glycol (mPEG). A decrease of 50% in the catalytic activity was measured during the coupling reaction and the change in the surface properties of AChE was used to separate by hydrophobic interaction chromatography the native and the modified enzyme. The native and the modified enzymes were found to have the same optimalcatalytic conditions. Moreover, the Michaelis constant of both enzymes were similar, whereas theV _m and the bimolecular-velocity constant calculated for organophosphorus inhibitors were slightly higher for the modified AChE. Finally, the modification with mPEG did not improve the thermal stability, whereas the stability in a few organic solvents increased.     

Fluorescence spectroscopy for monitoring deterioration of extra virgin olive oil during heating

The potential of fluorescence spectroscopy for characterizing the deterioration of extra virgin olive oil (EVOO) during heating was investigated. Two commercial EVOO were analysed by HPLC to determine changes in EVOO vitamin E and polyphenols as a result of heating at 170°C for 3 h. This thermal oxidation of EVOO caused an exponential decrease in hydroxytyrosol and vitamin E (R²=0.90 and 0.93, respectively) whereas the tyrosol content was relatively stable. At the same time, amounts of preformed hydroperoxides (ROOH), analysed by an indirect colorimetric method, decreased exponentially during the heating process (R²=0.94), as a result of their degradation into secondary peroxidation products. Fluorescence excitation spectra with emission at 330 and 450 nm were recorded to monitor polyphenols and vitamin E evolution and ROOH degradation, respectively. Partial least-squares calibration models were built to predict these indicators of EVOO quality from oil fluorescence spectra. A global approach was then proposed to monitor the heat charge from the overall fluorescence fingerprint. Different data pretreatment methods were tested. This study indicates that fluorescence spectroscopy is a promising, rapid, and cost-effective approach for evaluating the quality of heat-treated EVOO, and is an alternative to time-consuming conventional analyses. In future work, calibration models will be developed using a wide range of EVOO samples.     

Collective behavior of Franck-Condon excited states and energy transfer in DNA double helices

Absorption of UV radiation by DNA bases is known to induce carcinogenic mutations. The lesion distribution depends on the sequence around the hotspots, suggesting cooperativity between bases. Here we show that such cooperativity may intervene at the very first step of a cascade of events by formation of Franck-Condon states delocalized over several bases and subsequent energy transfer faster than 100 fs. Our study focuses on the double helix poly(dA).poly(dT), whose fluorescence, induced by femtosecond pulses at 267 nm, is probed by the upconversion technique and time-correlated single photon counting, over a large time domain (100 fs to 100 ns). The time-resolved fluorescence decays and fluorescence anisotropy decays are discussed in relation with the steady-state absorption and fluorescence spectra in the frame of exciton theory.     

Characterization of surfactant complex mixtures using Raman spectroscopy and signal extraction methods: Application to laundry detergent deformulation

This paper presents the analysis of surfactants in complex mixtures using Raman spectroscopy combined with signal extraction (SE) methods. Surfactants are the most important component in laundry detergents. Both their identification and quantification are required for quality control and regulation purposes. Several synthetic mixtures of four surfactants contained in an Ecolabel laundry detergent were prepared and analyzed by Raman spectroscopy. SE methods, Independent Component Analysis and Multivariate Curve Resolution, were then applied to spectral data for surfactant identification and quantification. The influence of several pre-processing treatments (normalization, baseline correction, scatter correction and smoothing) on SE performances were evaluated by experimental design. By using optimal pre-processing strategy, SE methods allowed satisfactorily both identifying and quantifying the four surfactants. When applied to the pre-processed Raman spectrum of the Ecolabel laundry detergent sample, SE models remained robust enough to predict the surfactant concentrations with sufficient precision for deformulation purpose. Comparatively, a supervised modeling technique (PLS regression) was very efficient to quantify the four surfactants in synthetic mixtures but appeared less effective than SE methods when applied to the Raman spectrum of the detergent sample. PLS seemed too sensitive to the other components contained in the laundry detergent while SE methods were more robust. The results obtained demonstrated the interest of SE methods in the context of deformulation.