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21.
Panagiotis Misaelides David Fellhauer Xavier Gaona Marcus Altmaier Horst Geckeis 《Journal of Radioanalytical and Nuclear Chemistry》2017,311(3):1665-1671
The 232Th-uptake ([Th(IV)]° = 9.7 × 10?5 M) from carbonate solutions ([CO 3 2 ]tot = 0.25 M, 9.0 < pHc < 10.8) by raw and HDTMA-modified HEU-type zeolitic-, chabazitic- and phillipsitic-tuffs was investigated. The strong uptake by the HDTMA-tuffs at pHc≈9 was assigned to the Th(CO3) 5 6? and ThOH(CO3) 4 5? predominance. The sorption coefficients (R d) decreased with increasing pHc indicating carbonate competition. Enhanced R d values for pHc > 10.5 are likely due to ThO2(am)-precipitation. The 237Np-uptake ([Np(V)]° = 2.6 × 10?5 M) from carbonate solutions ([CO 3 2 ]tot = 0.25 and 3.0 × 10?4 M) by raw and HDTMA-modified HEU-type zeolitic tuff and pulverized pure heulandite crystals was studied under Ar-atmosphere at 6 < pHc < 11. The R d values for both elements indicated the modified tuffs potential to remove tetravalent- and pentavalent actinides from environmental matrices. 相似文献
22.
Eric S. Simon Panagiotis G. Papoulias Philip C. Andrews 《Journal of the American Society for Mass Spectrometry》2010,21(9):1624-1632
The fragmentation characteristics of peptides derivatized at the side-chain ε-amino group of lysyl residues via reductive
amination with benzaldehyde have been examined using collision-induced dissociation (CID) tandem mass spectrometry. The resulting
MS/MS spectra exhibit peaks representing product ions formed from two independent fragmentation pathways. One pathway results
in backbone fragmentation and commonly observed sequence ion peaks. The other pathway corresponds to the unsymmetrical, heterolytic
cleavage of the Cζ-Nε bond that links the benzyl derivative to the side-chain lysyl residue. This results in the elimination of the derivative
as a benzylic or tropylium carbocation and a (n − l)+-charged peptide product (where n is the precursor ion charge state). The frequency of occurrence of the elimination pathway
increases with increasing charge of the precursor ion. For the benzylmodified tryptic peptides analyzed in this study, peaks
representing products from both of these pathways are observed in the MS/MS spectra of doubly-charged precursor ions, but
the carbocation elimination pathway occurs almost exclusively for triply-charged precursor ions. The experimental evidence
presented herein, combined with molecular orbital calculations, suggests that the elimination pathway is a charge-directed
reaction contingent upon protonation of the secondary ε-amino group of the benzyl-derivatized lysyl side chain. If the secondary
ε-amine is protonated, the elimination of the carbocation is observed. If the precursor is not protonated at the secondary
ε-amine, backbone fragmentation persists. The application of appropriately substituted benzyl analogs may allow for selective
control over the relative abundance of product ions generated from the two pathways. 相似文献
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A straightforward size exclusion chromatography (SEC) method was developed and validated for the determination of total polivinylpyrrolidone (PVP) in ophthalmic solutions using the unusual combination of size exclusion chromatography (SEC), ultraviolet-visible detection and quantitation of an analyte peak that elutes in the total exclusion volume of the column. Samples of opthalmic solutions are diluted with water and injected onto a TSKgel G1000PW, 7.5 mm i.d. × 30 cm, 12 μm column at 50°C, with 80:20 0.1M sodium acetate-methanol mobile phase and UV detection at 220 nm. Validation was successful for a stability indicating pharmaceutical method, with parameters including specificity, accuracy, linearity, and precision within typical pharmaceutical acceptance criteria. A stress study with acid, base, peroxide, heat, and light indicates that there is no interference from drug, product, or excipients. 相似文献
27.
Matsoukas MT Zoumpoulakis P Tselios T 《Journal of chemical information and modeling》2011,51(9):2386-2397
Aliskiren is a nonpeptide antihypertensive drug that potently inhibits the human enzyme renin in vitro and in vivo. Many clinical trials have shown the efficacy of aliskiren to lower blood pressure in correlation with other antihypertensive agents. In this report, the conformational behavior of aliskiren is studied in water, trifluoroethanol, and dimethylformamide solutions by means of 2D-NMR spectroscopy and molecular dynamics simulations. The stereochemical characteristics of aliskiren in different solutions, in combination with the previously published crystal structure of the renin-aliskiren complex have been investigated. The aim of this study was to explore the conformational behavior of this first successful renin inhibitor in relation to its environment. In aqueous solution, aliskiren adapts a U-shape conformation, whereas in DMF, the molecule is basically endowed with an "extended" conformation, which has more similarities to the one bound to the receptor. 相似文献
28.
Which, if any, hydrates will crystallise? Predicting hydrate formation of two dihydroxybenzoic acids
Braun DE Karamertzanis PG Price SL 《Chemical communications (Cambridge, England)》2011,47(19):5443-5445
A study of two dihydroxybenzoic acid isomers shows that computational methods can be used to predict hydrate formation, the compound:water ratio and hydrate crystal structures. The calculations also help identify a novel hydrate found in the solid form screening that validates this study. 相似文献
29.
We fabricated a TiO(2)-ZrO(2) affinity chromatography micro-column on 2 mm PMMA plates, and demonstrated the enrichment and separation of (a) a standard mono- and tetra-phosphopeptide, and (b) phosphopeptides contained in a tryptic digest of β-Casein. The chromatography column consisted of 32 parallel microchannels with common input and output ports and was fabricated by lithography directly on the polymeric substrate followed by plasma etching (i.e. standard MEMS processing) and sealed with lamination. The liquid deposited TiO(2)-ZrO(2) stationary phase was characterized by X-ray diffraction and was found to be mostly TiO(2) and ZrO(2) in crystalline phases. Off-chip UV detection and MALDI MS identification of the separated effluents were used. The chip had a capacity of >1.4 μg (0.7 nmol) of a prototype mono-phosphopeptide and a recovery of 94 ± 3%, and can be used with small samples (less than 0.1 μL depending on the syringe pump used). The chip design allows an expansion of its capacity by means of increasing the number of parallel microchannels at a constant sample volume. Our approach provided an alternative to off-line extraction tips (with typical capacities of 1-2 μg and sample volumes of 1-10 μL), and to on-chip efforts based on packed bed and frit formats. 相似文献
30.
The stability of equilibrium and the possibility of generation of business cycles in a discrete interregional Kaldorian macrodynamic model with fixed exchange rates are explored using numerical methods. One of the aims is to illustrate the feasibility and effectiveness of the numerical approach for dynamical systems of moderately high dimensionality and several parameters. The model considered is five-dimensional with four parameters, the speeds of adjustment of the goods markets and the degrees of economic interactions between the regions through trade and capital movement. Using a grid search method for the determination of the region of stability of equilibrium in two-dimensional parameter subspaces, and coefficient criteria for the flip bifurcation - and Hopf bifurcation - curve, we determine the stability region in several parameter ranges and identify Hopf bifurcation curves when they exist. It is found that interregional cycles emerge only for sufficient interregional trade. The relevant threshold is predicted by the model at 14 - 16 % of trade transactions. By contrast, no minimum level of capital mobility exists in a global sense as a requirement for the emergence of interregional cycles; the main conclusion being, therefore, that cycles may occur for very low levels of capital mobility if trade is sufficient. Examples of bifurcation and Lyapunov exponent diagrams illustrating the occurrence of cycles or period doubling, and examples of the development of the occurring cycles, are given. Both supercritical and subcritical bifurcations are found to occur, the latter type indicating coexistence of a point and a cyclical attractor. 相似文献