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排序方式: 共有173条查询结果,搜索用时 15 毫秒
61.
Nathália Kelly de Araújo Cristiane Fernandes de Assis Everaldo Silvino dos Santos Gorete Ribeiro de Macedo Louise Fonseca de Farias Humberto Arimatéia Jr. Matheus de Freitas Fernandes Pedrosa Maria Giovana Binder Pagnoncelli 《Applied biochemistry and biotechnology》2013,170(2):292-300
Obtaining oligosaccharides from chitosan has been the focus of several studies in the pharmaceutical, chemical, food, and medical areas, due to their functional properties. Here, we evaluated the production potential of biologically functional chitooligosaccharides using enzymes extracts produced by Paenibacillus chitinolyticus and Paenibacillus ehimensis. After 48 h of fermentation, these microorganisms were able to produce chitosanases, which generated oligomers with a degree of polymerization between dimers and hexamers. The maximum conversion of chitosan to oligomers was 99.2 %, achieved after 12 h incubation of chitosan with enzymes produced by P. ehimensis. The chitooligosaccharides generated were capable of scavenging the 2,2-diphenyl-1-picrylhydrazyl radical, reaching a maximum scavenging rate of 61 and 39 % when produced with P. ehimensis and P. chitinolyticus enzymes, respectively. The use of these enzymes in the crude form could facilitate their use in industrial applications. 相似文献
62.
Marcos Costa de Souza William Pires de Macedo Thiago Silva Torres Leandro Ferreira Pedrosa Helmut G. Alt 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1885-1893
This article describes an improved method to synthesize phosphoramidic acid aminoalkyl esters from diamines by the adaptation of industrial patents. Four mono-phosphorylated products having amino sites were obtained in good a yield. Such compounds have potential coordination properties with transition metals and also potential biological activity. 相似文献
63.
Lucas C. Recco Dr. Ihor Tokarev Prof. Dr. Sergiy Minko Prof. Dr. Valber A. Pedrosa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(5):1226-1230
Herein we demonstrate a plasmonic nanobiosensor that explores chain reaction amplification mechanisms to transduce chemical signals released in biocatalytic reactions, turning optical signals into a visual spectral range. The sensor has a very simple design: gold nanoparticles resting in the surface of a grafted P2VP film. Changes in the gold nanoparticles’ position causes changes in the plasmon coupling mode. This is detected by means of a maximum absorbance shift. 相似文献
64.
Angel Alberola Celia Andrs Alfonso Gonzlez Ortega Rafael Pedrosa Martina Vicente 《Journal of heterocyclic chemistry》1986,23(6):1781-1783
The trimethylsilyl derivative of formonometine reacts sequentially with two different organometallic derivatives to afford regiospecifically and with good yield 2,4-dialkylisoflavenes unsymmetrically substituted. 相似文献
65.
M. A. Pedrosa C. Hidalgo E. Calderon A. Alonso R. O. Orozco J. L. De Pablos TJ-II team P. Balan 《Czechoslovak Journal of Physics》2005,55(12):1579-1587
The influence of plasma density and edge gradients in the development of perpendicular sheared flow has been investigated
in the plasma edge region of the TJ-II stellarator. It has been experimentally observed that the generation of spontaneous
perpendicular sheared flow (i.e. the naturally occurring shear layer) requires a minimum plasma density or gradient. It has
been found that there is a coupling between the onset of sheared flow development and an increase in the level of plasma edge
turbulence; once sheared flow is fully developed the level of fluctuations and turbulent transport slightly decreases whereas
edge gradients and plasma density increase. The resulting shearing rate is close to the one required to trigger a transition
to improved confinement regimes with reduction of edge turbulence, showing that spontaneous sheared flows and fluctuations
keep themselves near marginal stability.
Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005. 相似文献
66.
67.
Martínez-Haya B Hortal AR Hurtado P Lobato MD Pedrosa JM 《Journal of mass spectrometry : JMS》2007,42(6):701-713
Molecular weight distributions (MWDs) of model polyaromatic hydrocarbons (PAHs) and complex asphaltene samples have been investigated in laser desorption/ionization mass spectrometry (LDI-MS) experiments. Special efforts are devoted to the characterization of aggregation effects during the desorption process. It is found that non-covalent clusters of the PAHs and asphaltenes form readily in the desorbing plume. Aggregation is favoured in the experiments performed on dense samples at high laser energy and under continuous ion extraction conditions. In the absence of polar groups in the analyte molecules, the aggregation propensity correlates well with the size of the polycondensed system and with its degree of pericondensation, in qualitative agreement with previous theoretical predictions. For the polydispersed asphaltenes from two different crude oils, MWDs peaking at masses smaller than 500 amu with a high-mass tail extending up to about 3000 amu have been observed, yielding average weights around 900 amu. Such MWDs are in good agreement with previous mass spectrometric measurement, as well as with diffusion studies in solution. In addition, stable asphaltene aggregates have been detected giving rise to two broad bands in the mass spectrum corresponding to average molecular weights of 2200-3100 amu and 15,000-19,000 amu, respectively. It is concluded that the strong aggregation propensity of asphaltenes is likely to be responsible for the apparent inconsistency between the MWD for these compounds determined by different groups in independent LDI-MS experiments. The reliability of different sample preparation procedures, including solvent-free methods, is discussed, and strategies are outlined that serve to apply the potentiality of LDI mass spectrometry to the characterization of covalent and non-covalent compounds in complex carbonaceous systems. 相似文献
68.
Giovana A. Bataglion Gustavo Henrique Martins Ferreira Souza Gabriel Heerdt Nelson H. Morgon José Diogo Lisboa Dutra Ricardo Oliveira Freire Marcos N. Eberlin Alessandra Tata 《Journal of mass spectrometry : JMS》2015,50(2):336-343
Traveling wave ion mobility mass spectrometry (TWIM‐MS) is shown to be able to separate and characterize several isomeric forms of diterpene glycosides stevioside (Stv) and rebaudioside A (RebA) that are cationized by Na+ and K+ at different sites. Determination and characterization of these coexisting isomeric species, herein termed catiomers, arising from cationization at different and highly competitive coordinating sites, is particularly challenging for glycosides. To achieve this goal, the advantage of using CO2 as a more massive and polarizable drift gas, over N2, was demonstrated. Post‐TWIM‐MS/MS experiments were used to confirm the separation. Optimization of the possible geometries and cross‐sectional calculations for mobility peak assignments were also performed. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
69.
Alagia M Candori P Falcinelli S Pirani F Mundim MS Richter R Rosi M Stranges S Vecchiocattivi F 《Physical chemistry chemical physics : PCCP》2011,13(18):8245-8250
A time-of-flight mass spectrometer with a position sensitive ion detector was used to study the dissociative double ionization of benzene by UV synchrotron radiation. The threshold energy for the main dissociative processes, leading to CH(3)(+) + C(5)H(3)(+), C(2)H(3)(+) + C(4)H(3)(+) and C(2)H(2)(+) + C(4)H(4)(+) ion pairs were characterized by exploiting a photoelectron-photoion-photoion-coincidence technique, giving 27.8 ± 0.1, 29.5 ± 0.1, and 30.2 ± 0.1 eV, respectively. The first reaction also proceeds via the formation of a metastable C(6)H(6)(2+) dication. The translational kinetic energy of the ionic products was evaluated by measuring the position of ions arriving to the detector. Theoretical calculations of the energy and structure of dissociation product ions were performed to provide further information on the dynamics of the charge separation reactions following the photoionization event. 相似文献
70.
Davide Bacciu Terence A. Etchells Paulo J. G. Lisboa Joe Whittaker 《Computational Statistics》2013,28(2):621-646
Conditional independence graphs are now widely applied in science and industry to display interactions between large numbers of variables. However, the computational load of structure identification grows with the number of nodes in the network and the sample size. A tailored version of the PC algorithm is proposed which is based on mutual information tests with a specified testing order, combined with false negative reduction and false positive control. It is found to be competitive with current structure identification methodologies for both estimation accuracy and computational speed and outperforms these in large scale scenarios. The methodology is also shown to approximate dense networks. The comparisons are made on standard benchmarking data sets and an anonymized large scale real life example. 相似文献