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901.
Vera M. Divac Marina D. Rvović Zorica M. Bugarčić 《Monatshefte für Chemie / Chemical Monthly》2008,139(11):1373-1376
A fast and efficient method for intramolecular heterocyclization of (Z)- and (E)-hex-4-en-1-ols was developed. The method does not cause side reactions of the substrates and provides the cyclic phenylselenoethers
in high yields after only few minutes. A catalytic amount of SnCl2 increased the yield, but in the presence of an equimolar amount of SnCl2, formation of corresponding cyclic ethers were almost quantitative and reaction occurred instantaneously under extremely
mild experimental conditions.
Correspondence: Zorica M. Bugarčić, Department of Chemistry, Faculty of Science, University of Kragujevac, Radoja Domanovića
12, P.O.Box 60, YU-34000 Kragujevac, Serbia. 相似文献
902.
Kavalactone derivatives were synthesized using a Heck reaction of the 4-methoxy-6-vinyl-5,6-dihydropyran-2-one with aryl iodides. The Suzuki-Miyaura reaction of an aryl boronic acid and (Z)-4-methoxy-6-(2-iodovinyl)-5,6-dihydropyran-2-one has also been successfully used to produce both Z and E isomers of lactones. 相似文献
903.
Dr. Benedict J. Elvers Sebastian Pätsch Dr. Siva S. M. Bandaru Prof. Dr. Vera Krewald Prof. Dr. Carola Schulzke Dr. Christian Fischer 《Angewandte Chemie (International ed. in English)》2023,62(25):e202303151
Heteroleptic molybdenum complexes bearing 1,5-diaza-3,7-diphosphacyclooctane (P2N2) and non-innocent dithiolene ligands were synthesized and electrochemically characterized. The reduction potentials of the complexes were found to be fine-tuned by a synergistic effect identified by DFT calculations as ligand-ligand cooperativity via non-covalent interactions. This finding is supported by electrochemical studies combined with UV/Vis spectroscopy and temperature-dependent NMR spectroscopy. The observed behavior is reminiscent of enzymatic redox modulation using second ligand sphere effects. 相似文献
904.
Dr. Silvia Vera Dr. Ane García-Urricelqui Prof. Dr. Antonia Mielgo Prof. Dr. Mikel Oiarbide 《European journal of organic chemistry》2023,26(7):e202201254
Thiourea- and squaramide-based bifunctional base catalysts represent nowadays a powerful tool in the field of asymmetric catalysis and have demonstrated very efficient for promoting a wide variety of transformations enantioselectively. New versions that incorporate one or various additional H-bond donor site(s) in the catalyst structure have been developed recently which led to more active (reduced catalyst loadings) and selective catalysts. This review highlights the pioneering ideas and the most recent contributions to the area with the material organized according to the nature of the additional H-bond donor functionality. The advantages, current limitations and perspectives of these new multifunctional catalysts are discussed. 相似文献
905.
John H. Lee C. Can Aydıner Jonathan Almer Joel Bernier Karena W. Chapman Peter J. Chupas Dean Haeffner Ken Kump Peter L. Lee Ulrich Lienert Antonino Miceli German Vera 《Journal of synchrotron radiation》2008,15(5):477-488
A GE Revolution 41RT flat‐panel detector (GE 41RT) from GE Healthcare (GE) has been in operation at the Advanced Photon Source for over two years. The detector has an active area of 41 cm × 41 cm with 200 µm × 200 µm pixel size. The nominal working photon energy is around 80 keV. The physical set‐up and utility software of the detector system are discussed in this article. The linearity of the detector response was measured at 80.7 keV. The memory effect of the detector element, called lag, was also measured at different exposure times and gain settings. The modulation transfer function was measured in terms of the line‐spread function using a 25 µm × 1 cm tungsten slit. The background (dark) signal, the signal that the detector will carry without exposure to X‐rays, was measured at three different gain settings and with exposure times of 1 ms to 15 s. The radial geometric flatness of the sensor panel was measured using the diffraction pattern from a CeO2 powder standard. The large active area and fast data‐capturing rate, i.e. 8 frames s?1 in radiography mode, 30 frames s?1 in fluoroscopy mode, make the GE 41RT one of a kind and very versatile in synchrotron diffraction. The loading behavior of a Cu/Nb multilayer material is used to demonstrate the use of the detector in a strain–stress experiment. Data from the measurement of various samples, amorphous SiO2 in particular, are presented to show the detector effectiveness in pair distribution function measurements. 相似文献
906.
The effect of iron and manganese co-doping on the light-induced, dark- and photoconductivity and holographic properties of Bi4Ge3O12 crystals in comparison with Fe- and Mn-single doping is studied. Fe+Mn co-doped crystals exhibited strong photochromic effect at room temperature, the photochromic effect being fully reversible by thermal annealing. The observed light-induced absorption changes and non-linear dependence of photoconductivity on light intensities indicate deep and shallow photoactive levels contribution to the charge transport mechanism of Fe+Mn co-doped BGO. Holographic gratings are successfully recorded at different wavelengths and a possibility to extend the photorefractive sensitivity into the red spectral range is demonstrated. It is found furthermore that Fe+Mn-doping combination leads to faster response time during holographic recording, especially after a preliminary exposure with ultraviolet light, in comparison with Fe- and Mn-single doping. 相似文献
907.
The influence of cationic and anionic surfactants and short‐chain alcohols in the mobile phase on the retention of five antioxidants has been studied. The solutes chosen were butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and propyl, octyl, and dodecyl gallates (PG, OG, DG).The surfactants were hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), and n‐propanol (PrOH) was the selected alcohol. A simple isocratic reversed‐phase method for the antioxidant determination is proposed. Separation of five primary antioxidants takes 18 min with the mobile phase SDS 0.10 M/H3PO4 0.01 M/PrOH 30%. Variation of the percentage of alcohol in the mobile phase permits optimization of the retention times of the antioxidants. Detection limits in the pg range were obtained for the all solutes. The method was used to determine the antioxidants in olive oil at three different levels, giving mean recoveries close to 100% for all the solutes (BHA 102%, PG 99%, OG 99%, DG 99%) except BHT (84%). 相似文献
908.
Nunzio Cardullo Vera Muccilli Vita Di Stefano Sonia Bonacci Lucia Sollima Maria Grazia Melilli 《Molecules (Basel, Switzerland)》2022,27(8)
Inulin is considered a dietary fiber and represents a noteworthy ingredient for food biofortification due to its health effects and its neutral taste. The aim of the work was the evaluation of the quality of pasta produced using whole-meal flours of two ancient Sicilian landraces (Senatore Cappelli-CAP and Timilia—TIM) fortified with two types of inulin (long-chain topinambur inulin IT and low-chain chicory inulin IC), at two different levels of substitution (2 and 4%) to evaluate its possible effect on α-amylase inhibition. The color indices L* and a* were mainly influenced by cultivars, while IT improved the sensory attributes, mainly the elasticity sensation, and influenced less the other sensory attributes: adhesiveness, color, odor, taste, and Over Quality Score for both landraces. The cooking quality was linked mainly to the landrace used, due to the very different gluten matrix of CAP and TIM. IC and IT showed promising α-Amy inhibitory activity with comparable IC50 values of 0.45 ± 0.04 and 0.50 ± 0.06 mg/mL. The enrichment of spaghetti with inulin with an inhibitory effect on α-amylase determined the hypoglycemic properties of pasta, thus lowering the corresponding IC50 value. 相似文献
909.
Hashimoto JC Paschoal JA Queiroz SC Ferracini VL Assalin MR Reyes FG 《Journal of AOAC International》2012,95(3):913-922
A simple method using LC/MS/MS was developed and validated to determine residues of malachite green (MG) and leucomalachite green (LMG) in fish fillet. A modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) technique was used to perform the sample preparation. The optimal extraction and cleanup conditions were established using an experimental design. The validation parameters obtained to determine both MG and LMG complied with the requirements established by regulatory agencies for the presence of such substances in fish, which establish that the method must attain, at least, a minimum required performance limit of 2 ng/g. The accuracy values ranged between 95 and 107%, and the precision values were lower than 11.2%. The method was used in the analysis of tilapia samples (n = 20) commercialized in Campinas, SP, Brazil. None of the samples presented detectable levels of MG or LMG residues. 相似文献
910.
Lewis acidic properties of transition aluminas whose surfaces have been doped with alkaline-earth metal cations (Ca2+ and Ba2+) were studied by means of the room temperature adsorption of carbon monoxide. The vibrational features of CO adsorbed at
the surface of doped aluminas were investigated by IR spectroscopy in comparison with pure parent aluminas, while the quantitative
and energetic features were studied by adsorption microcalorimetry. Various CO adspecies were found to form at the surface
of both pure and doped-alumina, owing to the structural heterogeneity of the Al2O3 surface and to the presence of alkaline-earth metal cations. The surface heterogeneity was revealed by different vco stretching frequencies, namely vco≈2230, 2218 and 2205 cm−1 for coordinatively unsaturated tetrahedral Al3+ cations in different crystallographic configurations, and vco≈2186 and 2172 cm−1 for coordinatively unsaturated Ca2+ and Ba2+ cations, respectively. Heats of adsorption of ≈80, 70 and 55 kJ/mol were assigned to the formation of Al3+/CO complexes, ≈45 kJ/mol for Ca2+/CO and ≈30 kJ/mol for Ba2+/CO complexes. The latter value was estimated through a correlation curve existing between vco stretching frequencies and adsorption enthalpies. This correlation, already proposed in the past for CO adsorbed on non-d/d0/d10 metal cations, has been revisited and confirmed here, by including Al2O3 data for which an apparent lack of correlation between the two parameters was first observed. With respect to pure alumina,
the population of Lewis acidic sites was found to be significantly depressed by the presence of alkaline-earth cus metal cations.
These acidic sites are intrinsically weaker than tetrahedral cus Al3+ cations, as witnessed by smaller upward shifts of the vco stretching frequencies with respect to CO gas and lower heats of adsorption, in accordance with expectations from the charge/ionic
radius ratios. Ca2+ cations were found to compete in adsorbing CO with Al3+ cations more efficiently than the larger Ba2+ cations. In the case of CaO/Al2O3 systems outgassed at 1023 K, a thin surface layer of calcium aluminate, not detected by XRD or HRTEM, was suggested to form. 相似文献