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51.
Topology influences the size of macromolecules, but polymers are usually distributed with respect to molar mass, which also results in the size distribution within a polymeric sample. Due to this fact size-exclusion chromatography (SEC) is not able to separate even moderately polydisperse polymers by topology; the same is also true for the adsorption chromatography (AC). The full separation by molar mass and topology is not possible by any single mode of chromatography. These problems can be solved by means of two-dimensional chromatography which combines SEC and AC mechanisms. A theory of interactive chromatography of linear and star-shaped ideal-chain polymers is used to analyze two-dimensional chromatographic separation of polydisperse linear and star polymers. Basing on this theory, we simulate 2D-chromatograms for model mixtures of polydisperse linear and star-shaped polymers of equal average molar mass, and demonstrate that 2D-separation of such polymers by topology is possible. A possibility to separate symmetric and very asymmetric stars by 2D-chromatography is predicted. The influence of the molar-mass heterogeneity, pore size and adsorption interaction parameter on the 2D chromatographic pattern is analysed, and the conditions for a good separation of linear and star polymers are formulated. The theoretical results are in a qualitative agreement with the experimental data, which have been reported previously by Gerber and Radke. 相似文献
52.
Alexei Merzlikine Charles Rotter Brian Rago Julie Poe Curt Christoffersen V. Hayden Thomas 《Drug development and industrial pharmacy》2013,39(9):1082-1091
Background: Chitosan glutamate and polyacrylic acid (e.g., carbomer 974P) are known to modulate the tight junctions in the intestinal wall and increase permeability and blood exposure of drugs absorbed orally by the paracellular route. Aim: To assess the impact of chitosan glutamate and carbomer 974P on the absorption of paracellularly absorbed model drug, acyclovir, in vitro and in rat in vivo. Methods: The influence of chitosan glutamate and carbomer 974P (alone and in combination with EDTA–Na2) on the in vitro Caco-2 permeability and oral pharmacokinetic profile in the rat of acyclovir was investigated. Results: In the presence of chitosan glutamate, the apparent permeability of acyclovir across Caco2 monolayer increased 4.1 times relative to control. This increase was accompanied by a significant (~60%) decrease in transepithelial electrical resistance values indicating opening of the tight junctions in the cell monolayer. In rat, chitosan glutamate doubled oral bioavailability of acyclovir and tripled the amount of acyclovir excreted unchanged into urine. In contrast, the effect of carbomer 974P was not statistically significant at 5% level. Conclusions: In conclusion, chitosan glutamate (1–3%) and chitosan glutamate (1%)/EDTA–Na2 (0.01%) are effective excipients to increase permeability of acyclovir across Caco-2 cell monolayers and the oral absorption in the rat in vivo. 相似文献
53.
Joakim Pagels Alexei F. Khalizov Peter H. McMurry Renyi Y. Zhang 《Aerosol science and technology》2013,47(7):629-640
The effects of atmospheric processing on soot particle morphology were studied in the laboratory using the Differential Mobility Analyzer-Aerosol Particle Mass Analyzer (DMA-APM) and the DMA-DMA (Tandem DMA) techniques. To simulate atmospheric processing, combustion soot agglomerates were altered by sulphuric acid vapor condensation, relative humidity (RH) cycling, and evaporation of the sulphuric acid and water by heating. Primary investigated properties were particle mobility size and mass. Secondary properties, derived from these, include effective density, fractal dimension, dynamic shape factor, and the mass fraction of condensed material. A transformation of the soot particles to more compact forms occurs as sulphuric acid and water condense onto fresh soot. The particle mass increases and initially the mobility diameter decreases, indicating restructuring of the soot core, likely due to surface tension forces. For a given soot source and condensing liquid, the degree of compaction depends strongly on the mass (or volume) fraction of condensed material. For water and sulphuric acid condensing on combustion soot, a mass increase of 2–3 times is needed for a transformation to spherical particles. In the limit of spherical particles without voids, the effective density then approaches the inherent material density, the fractal dimension approaches 3 and the dynamic shape factor approaches 1. Our results indicate that under typical atmospheric conditions, soot particles will be fully transformed to spherical droplets on a time scale of several hours. It is expected that the morphology changes and addition of soluble material to soot strongly affect the optical and hygroscopic properties of soot. 相似文献
54.
Jolanta Skalska Piotr Bednarczyk Marta Piwońska Bogusz Kulawiak Grzegorz Wilczynski Krzysztof Do?owy Alexei P. Kudin Wolfram S. Kunz Adam Szewczyk 《International journal of molecular sciences》2009,10(3):1104-1120
The mitochondrial response to changes of cytosolic calcium concentration has a strong impact on neuronal cell metabolism and viability. We observed that Ca2+ additions to isolated rat brain mitochondria induced in potassium ion containing media a mitochondrial membrane potential depolarization and an accompanying increase of mitochondrial respiration. These Ca2+ effects can be blocked by iberiotoxin and charybdotoxin, well known inhibitors of large conductance potassium channel (BKCa channel). Furthermore, NS1619 – a BKCa channel opener – induced potassium ion–specific effects on brain mitochondria similar to those induced by Ca2+. These findings suggest the presence of a calcium-activated, large conductance potassium channel (sensitive to charybdotoxin and NS1619), which was confirmed by reconstitution of the mitochondrial inner membrane into planar lipid bilayers. The conductance of the reconstituted channel was 265 pS under gradient (50/450 mM KCl) conditions. Its reversal potential was equal to 50 mV, which proved that the examined channel was cation-selective. We also observed immunoreactivity of anti-β4 subunit (of the BKCa channel) antibodies with ~26 kDa proteins of rat brain mitochondria. Immunohistochemical analysis confirmed the predominant occurrence of β4 subunit in neuronal mitochondria. We hypothesize that the mitochondrial BKCa channel represents a calcium sensor, which can contribute to neuronal signal transduction and survival. 相似文献
55.
Elena R. Ranyuk Alexei D. Averin Irina P. Beletskaya 《Advanced Synthesis \u0026amp; Catalysis》2010,352(13):2299-2305
Asymmetric amination of 1,5‐dichloroanthraquinone and 1,5‐dichloroanthracene with di‐ and trioxadiamines catalyzed by palladium complexes with various chiral phosphine ligands gave chiral macrocycles with ee values of up to 60%. The dependence of the chemical yields and enantiomeric excess on the nature of the starting compounds and the phosphine ligands employed was demonstrated. An unexpected spontaneous resolution upon crystallization of the macrocycle comprising anthraquinone and dioxadiamine moieties was observed while in the case of the macrocycle with a trioxadiamine linker racemic monocrystals were obtained. Crystallization of the enantiomerically enriched mixtures afforded chiral macrocycles with 88–99% ee. 相似文献
56.
Alexei V. Shevchenko Elena V. Dudnik Alexei K. Ruban Vladimir M. Vereshchaka Viktor P. Red’ko Lidiya M. Lopato 《Powder Metallurgy and Metal Ceramics》2005,44(3-4):105-111
The properties of ZrO2 - 3 mole% Y2O3 nanocrystalline powder prepared by diffusion impregnation are studied. The original nanocrystalline powder of M-ZrO2 is prepared with hydrothermal treatment of aqueous zirconium hydroxychloride solution by different regimes. It is found that after diffusion impregnation for all of the powders with yttrium oxide two solid solutions are formed (F-ZrO2 and M-ZrO2) in mixture. It is established that the morphological features typical for the original powders are retained. The efficiency of diffusion impregnation is determined by the slightly-agglomerated powder with a high degree of crystallinity.__________Translated from Poroshkovaya Metallurgiya, Nos. 3–4(442), pp. 3–11, March–April, 2005. 相似文献
57.
58.
Comparative Cytotoxicity of Artemisinin and Cisplatin and Their Interactions with Chlorogenic Acids in MCF7 Breast Cancer Cells 下载免费PDF全文
Dr. John O. Suberu Dr. Isolda Romero‐Canelón Dr. Neil Sullivan Prof. Alexei A. Lapkin Dr. Guy C. Barker 《ChemMedChem》2014,9(12):2791-2797
In parts of Africa and Asia, self‐medication with a hot water infusion of Artemisia annua (Artemisia tea) is a common practice for a number of ailments including malaria and cancer. In our earlier work, such an extract showed better potency than artemisinin alone against both chloroquine‐sensitive and ‐resistant parasites. In this study, in vitro tests of the infusion in MCF7 cells showed high IC50 values (>200 μM ). The combination of artemisinin and 3‐caffeoylquinic acid (3CA), two major components in the extract, was strongly antagonistic and gave a near total loss of cytotoxicity for artemisinin. We observed that the interaction of 3CAs with another cytotoxic compound, cisplatin, showed potentiation of activity by 2.5‐fold. The chelation of cellular iron by 3CA is hypothesized as a possible explanation for the loss of artemisinin activity. 相似文献
59.
60.
Urmila Shirwadkar Jarek GlodoEdgar V. van Loef Rastgo HawramiSharmishtha Mukhopadhyay Alexei ChurilovWilliam M. Higgins Kanai S. Shah 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2011,652(1):268-270
Investigations of Ce3+-doped Cs2LiLaBr6 (CLLB) crystals show a systematic trend in their scintillation properties with varying Ce concentrations. The concentration studies provide input in the optimization of growth of the CLLB crystals. Scintillation properties viz. radioluminescence, energy resolution, light yield, decay times, and non-proportionality are discussed for samples from 0% to 20% Ce concentration. 相似文献