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161.
162.
K. Tõnsuaadu M. Borissova V. Bender J. Pelt 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2395-2407
The thermal reactions in the mixtures of hydroxylapatite or fluorapatite and (NH4)2SO4up to 500°C were studied with the purpose of elaborating the conditions of obtaining calcium–ammonium cyclophosphate that could be used as fertilizer. Thermal analysis with a simultaneous FTIR analysis of the evolved gases as well as the analyses of chemical and phase composition of solid products were performed. The thermal changes in the mixtures could be divided into three steps: (1) decomposition of (NH4)2SO4and reactions of apatite with these products at 250–420°C, (2) calcium ammonium polyphosphate formation at 290–450°C, and (3) reaction of CaSO4with CaNH4P3O9at 320–500°C. Higher concentrations of NH3in the gas phase promote the formation of CaNH4P3O9and increase its stability. Calcination at temperatures above 350°C causes decomposition of CaNH4P3O9with a decrease in the content of water-soluble phosphorus and evolvement of SO2. 相似文献
163.
Dmitri Panov Anu Ploom Ants Tuulmets 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2807-2816
Rate constants for the reactions of methylvinyldichlorosilane and tetraethoxysilane with alkylmagnesium chlorides RMgCl (R = Et, n-Bu, i-Bu, i-Pr, s-Bu, t-Bu) in diethyl ether were determined. Excellent correlations of rate data with steric constants ES(Si) by Cartledge and v′ by Charton were found for the reaction of methylvinyldichlorosilane. Linear correlations with break points were obtained for the tetraethoxysilane reaction. It was assumed that this could be referred to a change in the reaction mechanism. 相似文献
164.
Maciel E da Silva RN Simões C Domingues P Domingues MR 《Journal of the American Society for Mass Spectrometry》2011,22(10):1804-1814
Non-oxidized phosphatidylserine (PS) is known to play a key role in apoptosis but there is considerable research evidence
suggesting that oxidized PS also plays a role in this event, leading to the increasing interest in studying PS oxidative modifications.
In this work, different PS (1-palmitoyl-2-linoleoyl-sn-glycero-3-phospho-L-serine (PLPS), 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine
(POPS), and 1,2-dipalmitoyl-sn-glycero-3-phospho-L-serine (DPPS) were oxidized in vitro by hydroxyl radical, generated under
Fenton reaction conditions, and the reactions were monitored by ESI-MS in negative mode. Oxidation products were then fractionated
by thin layer chromatography (TLC) and characterized by tandem mass spectrometry (MS/MS). This approach allowed the identification
of hydroxyl, peroxy, and keto derivatives due to oxidation of unsaturated fatty acyl chains. Oxidation products due to oxidation
of serine polar head were also identified. These products, with lower molecular weight than the non-modified PS, were identified
as [M – 29 – H]– (terminal acetic acid), [M – 30 – H]– (terminal acetamide), [M – 13 – H]– (terminal hydroperoxyacetaldehyde), and [M – 13 – H]– (terminal hydroxyacetaldehyde plus hydroxy fatty acyl chain). Phosphatidic acid was also formed in these conditions. These
findings confirm the oxidation of the serine polar head induced by the hydroxyl radical. The identification of these modifications
may be a valuable tool to evaluate phosphatidylserine alteration under physiopathologic conditions and also to help understand
the biological role of phosphatidylserine oxidation in the apoptotic process and other biological functions. 相似文献
165.
Octahedral silver nano-plates were synthesized from aqueous solution of silver nitrate and polyvinyl alcohol. The colloid formed is dried on glass plates by simple dip-coating method to inhibit the growth of the particles, and to analyze the samples. Samples were characterized by X-ray diffractometer, transmission electron microscope (TEM), thermo-gravimetric analysis (TGA), and differential scanning calorimetry (DSC) techniques. The UV–Vis absorption spectra of these silver nano-plates revealed a high intense plasmon absorption peak near 425 nm. In addition three emission peaks were observed when the excitation was fixed at 222 nm. 相似文献
166.
Comparing the quality and predictiveness between 3D QSAR models obtained from manual and automated alignment 总被引:2,自引:0,他引:2
Tervo AJ Nyrönen TH Rönkkö T Poso A 《Journal of chemical information and computer sciences》2004,44(3):807-816
A set of 113 flexible cyclic urea inhibitors of human immunodeficiency virus protease (HIV-1 PR) was used to compare the quality and predictive power of CoMFA and CoMSIA models for manually or automatically aligned inhibitor set. Inhibitors that were aligned automatically with molecular docking were in agreement with information obtained from existing X-ray structures. Both alignment methods produced statistically significant CoMFA and CoMSIA models, with the best q(2) value being 0.649 and the best predictive r(2) being 0.754. The manual alignment gave statistically higher values, whereas the automated alignment gave more robust models for predicting the activities of an external inhibitor set. Both models utilized similar amino acids in the HIV-1 PR active site, supporting the idea that hydrogen bonds form between an inhibitor and the backbone carbonyl oxygens of Gly48 and Gly48' and also the backbone NH group of Asp30, Gly48, Asp29', and Gly48' of the enzyme. These results suggest that an automated inhibitor alignment can yield predictive 3D QSAR models that are well comparable to manual methods. Thus, an automated alignment method in creating 3D QSAR models is encouragable when a well-characterized structure of the target protein is available. 相似文献
167.
Thermal decomposition study of HAuCl4·3H2O and AgNO3 as precursors for plasmonic metal nanoparticles
K. Otto I. Oja Acik M. Krunks K. Tõnsuaadu A. Mere 《Journal of Thermal Analysis and Calorimetry》2014,118(2):1065-1072
Thermal decomposition of HAuCl4·3H2O and AgNO3, as precursors for Au and Ag nanoparticles, respectively, was monitored by coupled TG–DTA with TG/EGA–FTIR and EGA–MS techniques in a flowing 80 %Ar + 20 %O2 and Ar atmospheres in the temperature range of 30–600 °C. The intermediate and final products of thermal decomposition were analysed by ex situ XRD and FTIR techniques. The thermal degradation of HAuCl4·3H2O starts immediately after melting at 75 °C and takes place in three steps in the temperature range of 75–320 °C with total mass loss of 49.4 and 49.7 % in artificial air and Ar atmospheres, respectively. EGA by MS and FTIR revealed a simultaneous release of H2O and HCl in the temperature range of 75–235 °C. EGA by MS revealed a release of Cl2 at around 225 °C and in the interval of 250–320 °C. According to the XRD analysis, the main solid product in the end of the first decomposition step at 190 °C is AuCl3; in the end of the second decomposition step at 240 °C is AuCl and the final product at 320 °C is Au. The thermal decomposition of AgNO3 takes place in a single step in the temperature range of 360–515 °C with a total mass loss of 39.0 and 37.8 % in flowing artificial air and Ar atmospheres, respectively. According to EGA–MS and EGA–FTIR the main evolved gases are NO2, NO and O2. The final product of the thermal decomposition at 600 °C is Ag irrespective of the atmosphere. 相似文献
168.
Juan José Villaverde Sónia A. O. Santos Elisabete Maciel Mário M. Q. Simões Carlos Pascoal Neto M. Rosário M. Domingues Armando J. D. Silvestre 《Journal of mass spectrometry : JMS》2012,47(2):163-172
This study reports the identification of oligomeric alkenylperoxides by electrospray ionization mass spectrometry (ESI‐MS) and tandem mass spectrometry (ESI‐MS2), during the oxidation of oleic, linoleic and linolenic acids with Fenton's (Fe2+/H2O2) and Fe2+/O2 systems. The reactions were followed by ferrous oxidation‐xylenol orange method together with GC‐MS and GC‐FID, allowing to observe that both oxidation systems are different in terms of hydroperoxide evolution, probably due to the presence of different intermediate reactive species: perferryl ion and OH· radical responsible for the decomposition of lipid hydroperoxides and formation of new compounds. The analysis of ESI‐MS in the negative mode, obtained after oxidation of each fatty acid, confirmed the presence of the monomeric oxidation products together with other compounds at high mass region above m/z 550. These new ions were attributed to oligomeric structures, identified by the fragmentation pathways observed in the tandem mass spectra. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
169.
Variability of calcium binding to EF-hand motifs probed by electrospray ionization mass spectrometry
Anu K. Moorthy S. K. Singh B. Gopal A. Surolia M. R. N. Murthy 《Journal of the American Society for Mass Spectrometry》2001,12(12):1159-1301
The modulation of calcium binding by the EF-hand motifs present in a calmodulin (CAM) homologue, a calcium binding protein (CaBP) from Entamoeba histolytica by three external parameters-pH, ligand coordinator EGTA, and fragmentor voltage was investigated by mass spectrometry. Calcium binding follows expected patterns at highly acidic and alkaline pH with the preponderance of the apo and the completely saturated forms, respectively. Surprisingly, additional nonspecific binding is observed near neutral pH. Studies on EGTA chelation and effects of fragmentor voltage showed cooperativity in calcium removal in at least one of the domains. Similar studies on a smaller construct containing the two high affinity carboxy terminal sites revealed interesting differences and provided an estimate of the specificity and tolerance of the EF-hand motifs to calcium binding and removal. 相似文献
170.
R. J. N. Bettencourt da Silva M. Filomena G. F. C. Camões João Seabra e Barros 《Accreditation and quality assurance》1998,3(4):155-160
Every analytical result should be expressed with some indication of its quality. The uncertainty as defined by Eurachem ("parameter
associated with the result of a measurement that characterises the dispersion of the values that could reasonably be attributed
to the, . . ., quantity subjected to measurement") is a good tool to accomplish this goal in quantitative analysis. Eurachem
has produced a guide to the estimation of the uncertainty attached to an analytical result. Indeed, the estimation of the
total uncertainty by using uncertainty propagation laws is components-dependent. The estimation of some of those components
is based on subjective criteria. The identification of the uncertainty sources and of their importance, for the same method,
can vary from analyst to analyst. It is important to develop tools which will support each choice and approximation. In this
work, the comparison of an estimated uncertainty with an experimentally assessed one, through a variance test, is performed.
This approach is applied to the determination by atomic absorption of manganese in digested samples of lettuce leaves. The
total uncertainty estimation is calculated assuming 100% digestion efficiency with negligible uncertainty. This assumption
was tested.
Received: 3 November 1997 · Accepted: 2 January 1998 相似文献