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991.
Ingrid C.R. Costa Rodrigo Octavio M.A. de Souza Uwe T. Bornscheuer 《Tetrahedron: Asymmetry》2017,28(9):1183-1187
The asymmetric synthesis of serinol-derivatives was investigated employing different amine transaminases as biocatalysts. Under the optimized conditions conversions up to 92% and excellent enantiomeric excesses up to 99% ee were obtained providing access to both, the (R)- and (S)-configurations of the serinol-monoester (2-amino-3-hydroxypropyl hexanoate). 相似文献
992.
Michelle Matos de Souza Janaina Heberle Bortoluzzi Eduardo Carasek 《Mikrochimica acta》2006,155(3-4):465-469
The efficiency of a glass-ceramic rod as a base for the preparation of SPME fibers using thermal immobilization was investigated.
Glass-ceramic and fused silica rods were thermally immobilized with poly(butylacrylate) and their absorption capacity was
compared. The absorption capacity between the fiber obtained for thermal immobilization of poly(butylacrylate) on glass-ceramic
surface and commercially PA fiber was also compared. In this study the target analytes were phthalate esters and phenols.
The results obtained for extraction of phenols from aqueous solutions using the headspace mode demonstrated the superiority
of glass-ceramic in relation the silica gel rod as a base for SPME fiber. The direct SPME extraction of phthalate esters from
aqueous solutions using commercial PA fiber and that obtained for thermal immobilization of poly(butylacrylate) on glass-ceramic
rod presented similar results. The repeatability and the reproducibility among extractions using fibers developed in our laboratory
were achieved. 相似文献
993.
994.
I.G. Souza H. Bergamin Fo F.J. Krug J.A. Nóbrega P.V. Oliveira B.F. Reis M.F. Giné 《Analytica chimica acta》1991
The simultaneous determination of chromium, nickel, manganese, silicon and iron in stainless steels was achieved by inductively coupled plasma atomic emission spectrometry (ICP-AES) after on-line electrodissolution using an improved flow-through electrolytic cell. The solution containing the electrodissolved ions was impelled by an air carrier stream in a flow-injection manifold towards a mixing-dilution chamber. From this chamber, the diluted and homogenized solution was aspirated and nebulized into the ICP torch. A quantification procedure is proposed for direct solid analysis without the use of certified reference materials. Under the proposed electrolysis conditions, up to 60 solid samples can be analysed per hour. Results obtained for alloying elements in austenitic and ferritic stainless steels were in good agreement with the certified values. 相似文献
995.
Lima Thays Souza A. La-Scalea Mauro Raminelli Cristiano Simões Fábio R. Franco Edison da Silva Gabriela Dias Salvador Michele Aparecida Homem-de-Mello Paula de Oliveira Hueder P. M. Codognoto Lúcia 《Journal of Solid State Electrochemistry》2019,23(2):553-563
Journal of Solid State Electrochemistry - A simple, fast, and direct electroanalytical method has been developed for the pesticide chlorothalonil determination using a boron-doped diamond electrode... 相似文献
996.
Luiza Goulart Liana da S. Fernandes Cláudia Lange dos Santos Jussane Rossato 《Physics letters. A》2019,383(32):125945
The electronic and structural properties of substitutional and doped phosphorene with B, N and Si were studied using first principles calculations based on density functional theory. Moreover, electronic and structural properties of functionalized phosphorene slowly increasing the concentration of doping was investigated. Phosphorene strongly binds with doped functionalization; B doped phosphorene is the most stable configuration studied. Si doped phosphorene maintains the semiconductor characteristic. B and N doped phosphorene present n-type and p-type semiconductors, respectively. Doped phosphorene with odd number of Si is a semiconductor material, doped phosphorene with an odd number of B has n-type semiconductor characteristic, and doped phosphorene with odd number of N atoms has a p-type semiconductor behaviour. Doped phosphorene with even number of Si has a metallic characteristic, while B and N doped phosphorene with even number present a semiconductor behaviour. This work reveals that phosphorene electronic properties could be changed by introducing the dopants on the system, and the properties are affected by the increasing number of dopants on phosphorene sheet. 相似文献
997.
Lucas C. Moore Anna Lo Jason S. Fell Matthew R. Duong Jose A. Moreno Barry E. Rich Martin Bravo Dr. James C. Fettinger Lucas W. Souza Prof. Marilyn M. Olmstead Prof. Kendall N. Houk Prof. Jared T. Shaw 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(52):12214-12220
Diastereoselective Lewis acid-mediated additions of nucleophilic alkenes to N-sulfonyl imines are reported. The canonical polar Felkin–Anh model describing additions to carbonyls does not adequately describe analogous additions to N-sulfonyl imines. Herein, we describe the development of conditions to produce both syn and anti products with high diastereoselectivity and good yields. A stereoelectronic model consistent with experimental outcomes is also proposed. 相似文献
998.
Felipe L. Oliveira Dr. Stefania P. de Souza Dr. Jonathan Bassut Prof. Heiddy M. Álvarez Prof. Yunier Garcia-Basabe Prof. Rodrigo O. M. Alves de Souza Prof. Pierre M. Esteves Prof. Raoni S. B. Gonçalves 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(69):15863-15870
Sustainability in chemistry heavily relies on heterogeneous catalysis. Enzymes, the main catalyst for biochemical reactions in nature, are an elegant choice to catalyze reactions due to their high activity and selectivity, although they usually suffer from lack of robustness. To overcome this drawback, enzyme-decorated nanoporous heterogeneous catalysts were developed. Three different approaches for Candida antarctica lipase B (CAL-B) immobilization on a covalent organic framework (PPF-2) were employed: physical adsorption on the surface, covalent attachment of the enzyme in functional groups on the surface and covalent attachment into a linker added post-synthesis. The influence of the immobilization strategy on the enzyme uptake, specific activity, thermal stability, and the possibility of its use through multiple cycles was explored. High specific activities were observed for PPF-2-supported CAL-B in the esterification of oleic acid with ethanol, ranging from 58 to 283 U mg−1, which was 2.6 to 12.7 times greater than the observed for the commercial Novozyme 435. 相似文献
999.
André V.-H. Soares Sumeet S. Kale Udo Armbruster Fabio B. Passos Shubhangi B. Umbarkar Mohan K. Dongare Andreas Martin 《国际化学动力学杂志》2019,51(8):634-640
Glycerol acetylation is a very interesting reaction for studies of consecutive kinetics. In this short communication, we present a pseudo-homogeneous model for the synthesis of triacetyl glycerol from the reaction of glycerol and acetic acid over strongly acidic Amberlyst-15 and Amberlyst-70 catalysts, considering a dimerization of diacetyl glycerol (DAG) into diglycerol tetraacetate as a parallel reaction and compare the results with a model without side reactions. The best fits were obtained for apparent zeroth-order dimerization and first-order consecutive reactions in the presence of acetic acid in excess and with removal of water. An adaptation was made for DAG. The proposed model shows that the formation of DAG is faster than the consumption of glycerol, which could be an explanation for the occurrence of DAG dimerization instead of other parallel reactions in acetylation. 相似文献
1000.
Eduardo Q. Luz Diego Seckler Janylson Souza Araújo Leonardo Angst David B. Lima Elise Ane Maluf Rios Ronny R. Ribeiro Daniel S. Rampon 《Tetrahedron》2019,75(9):1258-1266
A mild and efficient iron (III)-catalyzed C3 chalcogenylation of indoles has been developed and the role of the iodide ions in this transformation was investigated. EPR experiments revealed the reduction of Fe(III) to Fe(II) under the reaction conditions, supporting the formation of molecular iodine in the system, which in effect catalyze the reaction. The scope of the chalcogenylation was broad and the synthesis of more functionalized 3-selenylindoles was explored. 相似文献