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121.
Bismuth as BiCl4− and BH4− ware successively retained in a column (150 mm × 4 mm, length × i.d.) packed with Amberlite IRA-410 (strong anion-exchange resin). This was followed by passage of an injected slug of hydrochloric acid resulting in bismuthine generation (BiH3). BiH3 was stripped from the eluent solution by the addition of a nitrogen flow and the bulk phases were separated in a gas–liquid separator. Finally, bismutine was atomized in a quartz tube for the subsequent detection of bismuth by atomic absorption spectrometry. Different halide complexes of bismuth (namely, BiBr4−, BiI4− and BiCl4−) were tested for its pre-concentration, being the chloride complexes which produced the best results. Therefore, a concentration of 0.3 mol l−1 of HCl was added to the samples and calibration solutions. A linear response was obtained between the detection limit (3σ) of 0.225 and 80 μg l−1. The R.S.D.% (n = 10) for a solution containing 50 μg l−1 of Bi was 0.85%. The tolerance of the system to interferences was evaluated by investigating the effect of the following ions: Cu2+, Co2+, Ni2+, Fe3+, Cd2+, Pb2+, Hg2+, Zn2+, and Mg2+. The most severe depression was caused by Hg2+, which at 60 mg l−1 caused a 5% depression on the signal. For the other cations, concentrations between 1000 and 10,000 mg l−1 could be tolerated. The system was applied to the determination of Bi in urine of patients under therapy with bismuth subcitrate. The recovery of spikes of 5 and 50 μg l−1 of Bi added to the samples prior to digestion with HNO3 and H2O2 was in satisfactory ranges from 95.0 to 101.0%. The concentrations of bismuth found in six selected samples using this procedure were in good agreement with those obtained by an alternative technique (ETAAS). Finally, the concentration of Bi determined in urine before and after 3 days of treatment were 1.94 ± 1.26 and 9.02 ± 5.82 μg l−1, respectively. 相似文献
122.
JL García Ruano E Torrente A Parra J Alemán AM Martín-Castro 《The Journal of organic chemistry》2012,77(15):6583-6599
In this work, we report the use of the asymmetric intramolecular Pauson-Khand reactions of 4-aryl-4-cyano-1,6-enynes for obtaining enantiomerically enriched bicyclo[3.3.0]octenones, and the influence of both the quaternary stereocenter and the sulfur functions located at ortho-position of the aryl group, on their stereoselectivity and reactivity. The sulfenyl derivatives bearing substituted or unsubstituted triple bonds and mono- and disubstituted alkene moieties afford bicyclo[3.3.0]octenones in high yields with complete diastereocontrol. These results are explained by assuming the association of the lone electron pair at sulfur to the Co-alkyne complexes. 相似文献
123.
Brgles M Bertoša B Winkler W Kurtović T Allmaier G Marchetti-Deschmann M Halassy B 《Analytical and bioanalytical chemistry》2012,402(9):2737-2748
The ammodytoxins (Atxs) are neurotoxic phospholipases which occur in Vipera ammodytes ammodytes (Vaa) snake venom. There are three Atx isoforms, A, B, and C, which differ in only five amino acid positions at the C-terminus
but differ substantially in their toxicity. The objective of this study was to establish an analytical method for unambiguous
identification of all three isoforms and to use the method to assess a procedure for purification of the most toxic phospholipase,
AtxA, from the venom. Isolation procedure for AtxA consisted of isolation of Atx-cross-reactive material (proteins recognized
by anti-Atx antibodies), by use of an affinity column, then cation exchange on CIM (Convective Interaction Media) disks. The
purification procedure was monitored by means of reversed-phase chromatography (RPC) and mass spectrometry (MS). Although
previous cation exchange of the pure isoforms enabled separate elution of AtxA from B and C, separation of AtxA from Atxs
mixture was not accomplished. RPC was not able to separate the Atx isoforms, whereas an MS based approach proved to be more
powerful. Peptides resulting from tryptic digestion of Atxs which enable differentiation between the three isoforms were successfully
detected and their sequences were confirmed by post-source decay (PSD) fragmentation. Separation of Atx isoforms by ion-exchange
chromatography is most presumably prevented by Atxs heterodimer formation. The tendency of Atxs to form homodimers and heterodimers
of similar stability was confirmed by molecular modeling. 相似文献
124.
Reboredo S Reyes E Vicario JL Badía D Carrillo L de Cózar A Cossío FP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(23):7179-7188
The catalytic enantioselective [3+2] cycloaddition between azomethine ylides and α,β-unsaturated aldehydes catalyzed by α,α-diphenylprolinol has been studied in detail. In particular, the reaction has been extended to the use of 2-alkenylidene aminomalonates generated in situ as azomethine ylide precursors. These reactions lead to the formation of pyrrolidines containing a 5-alkenyl side chain with potential for chemical manipulation. Moreover, a detailed and concise computational study has been carried out to understand the exact nature of the mechanism of this reaction and especially the consequences derived from the incorporation of the chiral secondary amine catalyst on the reaction pathway. 相似文献
125.
Gao J Lowe MA Conte S Burkhardt SE Abruña HD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(27):8521-8526
Organosulfur compounds with multiple thiol groups are promising for high gravimetric energy density electrochemical energy storage. We have synthesized a poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT)/poly(3,4-ethylenedioxythiophene) (PEDOT) composite cathode for lithium-ion batteries with a new method and investigated its electrochemical behavior by charge/discharge cycles and cyclic voltammetry (CV) in an ether-based electrolyte. Based on a comparison of the electrochemical performance with a carbonate-based electrolyte, we found a much higher discharge capacity, but also a very attractive cycling performance of PDMcT by using a tetra(ethylene glycol) dimethyl ether (TEGDME)-based electrolyte. The first discharge capacity of the as-synthesized PDMcT/PEDOT composite approached 210 mAh g(-1) in the TEGDME-based electrolyte. CV results clearly show that the redox reactions of PDMcT are highly reversible in this TEGDME-based electrolyte. The reversible capacity remained around 120 mAh g(-1) after 20 charge/discharge cycles. With improved cycling performance and very low cost, PDMcT could become a very promising cathode material when combined with a TEGDME-based electrolyte. The poor capacity in the carbonate-based electrolyte is a consequence of the irreversible reaction of the DMcT monomer and dimer with the solvent, emphasizing the importance of electrolyte chemistry when studying molecular-based battery materials. 相似文献
126.
Pereira JF Gudiña EJ Dória ML Domingues MR Rodrigues LR Teoxeira JA Coutinho JA 《European journal of mass spectrometry (Chichester, England)》2012,18(4):399-406
In this work, biosurfactants produced by two Pseudomonas aeruginosa strains isolated from Brazilian crude oils were identified by proton nuclear magnetic resonance ((1)H NMR) and further characterized by mass spectrometry (MS) coupled with electrospray ionization (ESI) and tandem mass spectrometry (MS/MS) analysis in positive mode and their surface activities evaluated. Mono-rhamnolipids and di-rhamnolipids were identified for both isolates, but the most abundant were found to be mono-rhamnolipids. The similarity of rhamnolipids produced by the two strains was in good agreement with their surface activities. Both biosurfactants exhibited similar aqueous solution surface tensions, high emulsification indexes and critical micelle concentration values. The results obtained show that ESI-MS and MS/MS analysis alone provide a fast and highly specific characterization of biosurfactants produced by microbial strains. 相似文献
127.
The molecular shape of proteinogenic glutamic acid has been determined for the first time. Vaporization of the solid amino acid by laser ablation in combination with Fourier transform microwave spectroscopy made possible the detection of five different structures in a supersonic jet. These structures have been identified through their rotational and (14)N quadrupole coupling constants. All conformers show hydrogen bonds linking the amino and alpha carboxylic group through N-H···O═C (type I) or N···H-O (type II) interactions. In three of them there are additional hydrogen bonds established between the amino group and the carboxylic group in the gamma position. Entropic effects related to the side chain have been found to be significant in determining the most populated conformations. 相似文献
128.
Hidalgo A Jiménez LP Ramos LA Mroginski MA Jios JL Ulic SE Echeverría GA Piro OE Castellano E 《The journal of physical chemistry. A》2012,116(3):1110-1118
The (Z)-4,4,4-trifluoro-3-(2-hydroxyethylamino)-1-(2-hydroxyphenyl)-2-buten-1-one (C(12)H(12)F(3)NO(3)) compound was thoroughly studied by IR, Raman, UV-visible, and (13)C and (19)F NMR spectroscopies. The solid-state molecular structure was determined by X-ray diffraction methods. It crystallizes in the P2(1)/c space group with a = 12.1420(4) ?, b = 7.8210(3) ?, c = 13.8970(5) ?, β = 116.162(2)°, and Z = 4 molecules per unit cell. The molecule shows a nearly planar molecular skeleton, favored by intramolecular OH···O and NH···O bonds, which are arranged in the lattice as an OH···O bonded polymer coiled around crystallographic 2-fold screw-axes. The three postulated tautomers were evaluated using quantum chemical calculations. The lowest energy tautomer (I) calculated with density functional theory methods agrees with the observed crystal structure. The structural and conformational properties are discussed considering the effect of the intra- and intermolecular hydrogen bond interactions. 相似文献
129.
Fernández M Vicario JL Reyes E Carrillo L Badía D 《Chemical communications (Cambridge, England)》2012,48(15):2092-2094
We have developed an efficient procedure for the easy and straightforward preparation of functionalized dihydropyridazines as highly enantiopure materials by reaction of pyruvaldehyde 2-tosyl hydrazone with a variety of α,β-unsaturated aldehydes using a chiral secondary amine as catalyst. The overall process consists of a cascade reaction involving an initial aza-Michael reaction, in which the stereocentre is installed, followed by an intramolecular aldol reaction/dehydration step. 相似文献
130.
JL García Ruano L Marzo V Marcos C Alvarado J Alemán 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(32):9775-9779
Center of attention: A new approach for the synthesis of enantiomerically enriched allenes by isomerization of 2-p-tolylsulfinylphenyl propargylic derivatives is presented, which in turn are prepared by reaction of sulfinylated lithium benzylcarbanions with arylsulfonylacetylenes. The high control of stereoselectivity in both steps is exerted by the sulfinyl group. 相似文献