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101.
Susana Dias Lucas Amélia Pilar Rauter Josef Schneider Hans Peter Wessel 《Journal of carbohydrate chemistry》2013,32(7-8):431-446
Starting from d-xylose, 2,4-anhydro-5-N-(tert-butoxycarbonyl)amino-5-deoxy-3-fluoro-d-arabinonic acid 11 was synthesized over 10 steps including ring contraction, fluorination, and ester hydrolysis. Bromine oxidation of d-xylose followed by benzylidenation in a one-pot procedure led to a ca. 1:1 mixture of lactone 3 and 2,4;3,5-dibenzylidene xylonic acid (4) as by-product. For the synthesis of the d-xylo derivative 24, the chosen starting material was 1,2-O-isopropylidene-α-d-xylofuranose. A total of 14 steps including epimerization, ring contraction, fluorination, and saponification led to the desired fluoro-oxetane δ-amino acid 24. Hydrolysis of the 3-fluoro-oxetane δ-amino esters 10 and 23 by means of LiOH was successful in agreement with the results previously reported for similar 3-methoxy oxetanes, whereas chemical hydrolysis was not possible for 3-hydroxy derivatives. 相似文献
102.
The action modes of Lippia sidoides (Cham) essential oil as penetration enhancers on snake skin 总被引:1,自引:0,他引:1
M. B. Brito Gabriela B. Barin A. A. S. Araújo D. P. de Sousa S. C. H. Cavalcanti Ana Amélia M. Lira Rogéria S. Nunes 《Journal of Thermal Analysis and Calorimetry》2009,97(1):323-327
The aim of this work was to study the effect of Lippia sidoides essential oil (LSEO) on stratum corneum lipids and the permeation of salicylic acid. DSC and FTIR spectroscopy were applied.
LSEO 1% (v/v) significantly enhanced salicylic acid flux through snake skin. According to the DSC curves changes in the transition
temperature of the lipids were observed indicating that LSEO can interact with stratum corneum. The IR spectrum of skin treated
with LSEO showed a decrease in the peak intensity for CH2 stretchings (2920–2850 cm–1) however the peak positions did not alter suggesting the extraction of the lipids. 相似文献
103.
Amílcar Pacheco 《代数通讯》2013,41(11):3689-3703
104.
Fabien Pointurier Anne-Claire Pottin Philippe Hémet Amélie Hubert 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(3-4):261-267
Formation of a polyatomic species made of an atom of a heavy element like lead, mercury or iridium, and atoms abundant in plasma (argon, nitrogen, oxygen, and hydrogen) when using an inductively coupled plasma-sector-field mass spectrometer (ICP-SFMS) may lead to false detection of femtograms (fg) of plutonium or bias in the measured concentrations. Mathematical corrections, based on the measurement of heavy element concentrations in the sample solutions and determination of the extents of formation of the polyatomic interferences, are efficient but time-consuming and degrade detection limits. We describe and discuss a new method based on the combination of, on the one hand, medium mass resolution (MR) of the ICP-SFMS to separate plutonium isotopes physically from interfering polyatomic species, and, on the other, use of a desolvation introduction system (DIS) to enhance sensitivity, thus partly compensating for the loss of transmission due to use of a higher resolution. Plutonium peaks are perfectly separated from the major interfering species (PbO2, HgAr, and IrO3) with a mass resolution of ~ 4000. The resulting nine-fold transmission loss is partly compensated by a five-fold increase in sensitivity obtained with the DIS and a lower background. The instrumental detection limits for plutonium isotopes, calculated for measurements of pure synthetic solutions, of the new method (known as MR-DIS method) and of the one currently used in the laboratory (LR method), based on a low mass resolution equal to 360, a microconcentric nebulizer and two in-line cooled spray chambers, are roughly equivalent, at around 0.2 fg ml? 1. Regarding the measurement of real-life samples, the results obtained with both methods agree and the corresponding analytical detection limits for plutonium isotopes 239Pu, 240Pu and 241Pu are of a few fg·ml? 1 of sample solution, slightly lower with the MR-DIS method than with the current LR method. Although less sensitive than other plutonium ICP-MS measurement methods described in the literature, the main advantage of the MR-DIS method is that it is robust against the risk of false plutonium detection, even in the case of relatively high concentrations of heavy elements like lead, mercury or iridium. 相似文献
105.
106.
Prof. Dr. Sílvia Chaves Dr. Sérgio M. Marques Dipl.‐Chem. André M. F. Matos Dipl.‐Chem. Andreia Nunes Dr. Lurdes Gano Dr. Tiziano Tuccinardi Prof. Dr. Adriano Martinelli Prof. Dr. M. Amélia Santos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(34):10535-10545
Two new tripodal tris(3‐hydroxy‐4‐pyridinone) hexadentate chelators—NTA(BuHP)3 and NTP(PrHP)3 (NTA=nitrilotriacetic acid, NTP=nitrilotripropionic acid, HP=hydroxypyridone)—have been developed and studied in solution for their iron and aluminium binding affinity, and also assayed in vivo for their capacity to remove metal from an animal model that is overloaded. These chelators are positional isomers, possessing identical general structures based on aminotricarboxylic acid skeletons attached to three bidentate 3‐hydroxy‐4‐pyridinones (3,4‐HPs), but differing in the position of the amide linkage along the chelating “arm”. In spite of expected differences in the tripodal ligands, such as acidity and hydrogen‐bonding networks, they share important properties, namely, a mild hydrophilic character (log P ca. ?1.2 to ?1.4) and a strong chelating affinity for Fe and Al (pFe=27.9 and pAl=22.0 for NTA(BuHP)3; pFe=29.4 and pAl=22.4 for NTP(PrHP)3). They also evidenced identical effects on the biodistribution and on the excretion of a radiotracer (67Ga) previously administered to mice, as models of iron overload animals. Comparison of the new compounds with reported analogues shows good improvement in terms of solution and in vivo sequestering properties, thus giving support to expectations about their potential clinical application as metal removal agents. 相似文献
107.
Guillaume Frutsaert Louis Delon Ghislain David Bruno Améduri Deborah J. Jones Xavier Glipa Jacques Rozière 《Journal of polymer science. Part A, Polymer chemistry》2010,48(1):223-231
New alternating copolymers comprising a chlorotrifluorinated backbone and imidazole‐terminated pendant ethylene oxide groups have been prepared with a view to their use as a component of proton‐conducting membranes in polymer electrolyte fuel cells. A vinyl ether containing an imidazole (Imi) function protected by a benzyl group (BVI) was first synthesized in a three‐step reaction. It was then copolymerized in solution with chlorotrifluoroethylene (CTFE) by conventional radical copolymerization leading to alternating poly(BVI‐alt‐CTFE) copolymers in good yields. Deprotection of the benzyl group under hydrogen produced a chlorotrifluorinated poly(Imi‐alt‐CTFE) copolymer. The polymer was subsequently used to form blend membranes with sulfonated poly(ether ether ketone) (sPEEK). The conductivity of blend membranes of poly (Imi‐alt‐CTFE) with sPEEK lies in the range of 4–10 mS cm?1 at 40–70 °C and, for blend membranes rich in poly(Imi‐alt‐CTFE), is little dependent on relative humidity between 30 and 100%. It is surmised that the polymer and membrane composition favor microstructural phase separation into chlorotrifluorinated polymer backbone domains and regions in which imidazole groups are clustered. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 223–231, 2010 相似文献
108.
Linus Chiang Amélie Kochem Olivier Jarjayes Tim J. Dunn Dr. Hervé Vezin Miyuki Sakaguchi Prof. Takashi Ogura Dr. Maylis Orio Prof. Yuichi Shimazaki Prof. Fabrice Thomas Prof. Tim Storr 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(44):14117-14127
Square‐planar nickel(II) complexes of salen ligands, N,N′‐bis(3‐tert‐butyl‐(5R)‐salicylidene)‐1,2‐cyclohexanediamine), in which R=tert‐butyl ( 1 ), OMe ( 2 ), and NMe2 ( 3 ), were prepared and the electronic structure of the one‐electron‐oxidized species [ 1 – 3 ]+. was investigated in solution. Cyclic voltammograms of [ 1 – 3 ] showed two quasi‐reversible redox waves that were assigned to the oxidation of the phenolate moieties to phenoxyl radicals. From the difference between the first and second redox potentials, the trend of electronic delocalization 1 +.> 2 +.> 3 +. was obtained. The cations [ 1 – 3 ]+. exhibited isotropic g tensors of 2.045, 2.023, and 2.005, respectively, reflecting a lower metal character of the singly occupied molecular orbital (SOMO) for systems that involve strongly electron‐donating substituents. Pulsed‐EPR spectroscopy showed a single population of equivalent imino nitrogen atoms for 1 +., whereas two distinct populations were observed for 2 +.. The resonance Raman spectra of 2 +. and 3 +. displayed the ν8a band of the phenoxyl radicals at 1612 cm?1, as well as the ν8a bands of the phenolates. In contrast, the Raman spectrum of 1 +. exhibited the ν8a band at 1602 cm?1, without any evidence of the phenolate peak. Previous work showed an intense near‐infrared (NIR) electronic transition for 1 +. (Δν1/2=660 cm?1, ε=21 700 M ?1 cm?1), indicating that the electron hole is fully delocalized over the ligand. The broader and moderately intense NIR transition of 2 +. (Δν1/2=1250 cm?1, ε=12 800 M ?1 cm?1) suggests a certain degree of ligand‐radical localization, whereas the very broad NIR transition of 3 +. (Δν1/2=8630 cm?1, ε=2550 M ?1 cm?1) indicates significant localization of the ligand radical on a single ring. Therefore, 1 +. is a Class III mixed‐valence complex, 2 +. is Class II/III borderline complex, and 3 +. is a Class II complex according to the Robin–Day classification method. By employing the Coulomb‐attenuated method (CAM‐B3LYP) we were able to predict the electron‐hole localization and NIR transitions in the series, and show that the energy match between the redox‐active ligand and the metal d orbitals is crucial for delocalization of the radical SOMO. 相似文献
109.
JP Coelho AF Cristino PG Matos AP Rauter BP Nobre RL Mendes JG Barroso A Mainar JS Urieta JM Fareleira H Sovová AF Palavra 《Molecules (Basel, Switzerland)》2012,17(9):10550-10573
An overview of the studies carried out in our laboratories on supercritical fluid extraction (SFE) of volatile oils from seven aromatic plants: pennyroyal (Mentha pulegium L.), fennel seeds (Foeniculum vulgare Mill.), coriander (Coriandrum sativum L.), savory (Satureja fruticosa Béguinot), winter savory (Satureja montana L.), cotton lavender (Santolina chamaecyparisus) and thyme (Thymus vulgaris), is presented. A flow apparatus with a 1 L extractor and two 0.27 L separators was built to perform studies at temperatures ranging from 298 to 353 K and pressures up to 30.0 MPa. The best compromise between yield and composition compared with hydrodistillation (HD) was achieved selecting the optimum experimental conditions of extraction and fractionation. The major differences between HD and SFE oils is the presence of a small percentage of cuticular waxes and the relative amount of thymoquinone, an oxygenated monoterpene with important biological properties, which is present in the oils from thyme and winter savory. On the other hand, the modeling of our data on supercritical extraction of volatile oil from pennyroyal is discussed using Sovová's models. These models have been applied successfully to the other volatile oil extractions. Furthermore, other experimental studies involving supercritical CO2 carried out in our laboratories are also mentioned. 相似文献