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41.
The investigation is based on the nano-or ultrafiltration of inorganic salts in the presence of a polyelectrolyte in the feed
solution. Cellulose acetate membranes are selected with a pore size of 10–20 nm. The membranes are imaged using atomic force
microscope. The membrane is completely impermeable to the polyelectrolyte. Polyelectrolyte concentrations are taken in the
range of 0.5–1 g/l to avoid a gel layer formation over the membrane. It is discovered that, at such low polyelectrolyte concentration,
inorganic salt concentration in the permeate is higher than in the feed solution. This process therefore deviates from conventional
membrane separation processes, where the permeate salt concentration is lower or equal to the salt concentration in the feed
solution. It is shown that during the nano-or ultrafiltration of inorganic salts in the presence of polyelectrolyte, the ratio
of salt concentration in the permeate to feed increases when the initial salt concentration in the feed solution is low. Concentration
polarization has a negative impact on this concentrating effect. In the case of this investigation, KCl, KNO3, K2SO4 are taken as inorganic salts, N,N-dimethyl-N-2-propenyl-2-propen-1-aminium chloride homopolymer is selected as a polyelectrolyte.
The text was submitted by the authors in English. 相似文献
42.
Bitan G Tarus B Vollers SS Lashuel HA Condron MM Straub JE Teplow DB 《Journal of the American Chemical Society》2003,125(50):15359-15365
Aberrant protein oligomerization is an important pathogenetic process in vivo. In Alzheimer's disease (AD), the amyloid beta-protein (Abeta) forms neurotoxic oligomers. The predominant in vivo Abeta alloforms, Abeta40 and Abeta42, have distinct oligomerization pathways. Abeta42 monomers oligomerize into pentamer/hexamer units (paranuclei) which self-associate to form larger oligomers. Abeta40 does not form these paranuclei, a fact which may explain the particularly strong linkage of Abeta42 with AD. Here, we sought to determine the structural elements controlling paranucleus formation as a first step toward the development of strategies for treating AD. Because oxidation of Met(35) is associated with altered Abeta assembly, we examined the role of Met(35) in controlling Abeta oligomerization. Oxidation of Met(35) in Abeta42 blocked paranucleus formation and produced oligomers indistinguishable in size and morphology from those produced by Abeta40. Systematic structural alterations of the C(gamma)(35)-substituent group revealed that its electronic nature, rather than its size (van der Waals volume), was the factor controlling oligomerization pathway choice. Preventing assembly of toxic Abeta42 paranuclei through selective oxidation of Met(35) thus represents a potential therapeutic approach for AD. 相似文献
43.
Superheated water extraction, steam distillation and Soxhlet extraction of essential oils of Origanum onites 总被引:2,自引:0,他引:2
Superheated water extraction (SWE) at various temperatures (100, 125, 150 and 175°C), steam distillation, and Soxhlet extraction were compared in the extraction of essential oils from two samples of the plant Origanum onites, one cultivated, the other wild. C18 solid-phase extraction was used to elute the essential oils from the SWE aqueous extract. The compositions of the extracted essential oils obtained from all three methods were then characterized by comprehensive GC×GC/time-of-flight mass spectrometry (TOF/MS). The highest essential oil yields were obtained by using SWE at 150°C with a flow rate of 2 mL min–1 and a pressure of 60 bar for 30 min: these were 3.76 and 4.11% for wild and cultivated O. onites samples, respectively, expressed as a percentage of 100 g of dry (leaf) matter. The yields obtained using SWE at 150°C were slightly higher than those from conventional methods. Steam distillation was performed for 3 h, and Soxhlet extraction was completed in 12 h. The major compounds found were borneol, terpinen-4-ol and carvacrol. 相似文献
44.
Al-Subu Mohammad M. Jondi Waheed J. Dado Saida A. Hilal Hikmat S. 《Transition Metal Chemistry》2002,27(2):223-227
The kinetics of oxidation of 1-octene and heptanal by 18-crown-6-ether-solubilized KMnO4 in benzene and CH2Cl2 have been investigated. In benzene, the oxidation of 1-octene is first order with respect to the oxidant and zero order with respect to the substrate, whereas in CH2Cl2 the reaction is first order with respect to both substrate and oxidant. The reaction of heptanal followed different kinetics being first order with respect to both substrate and oxidant, regardless of whether benzene or CH2Cl2 was employed as the solvent. The values of activation energy E
a, standard enthalpy H
*, standard entropy change S
*, and standard free energy G
*, for the reaction, are reported. Mechanistic pathways for the studied reactions are also proposed. 相似文献
45.
Brownian dynamics computer simulations of aggregation in 2D colloidal suspensions are discussed. The simulations are based
on the Langevin equations, pairwise interaction between colloidal particles and take into account Brownian, hydrodynamic and
colloidal forces. The chosen mathematical model enables to predict the correct values of diffusion coefficient of freely moving
particle, the mean value of kinetic energy for each particle in ensemble of interacting colloidal particles and residence
times of colloidal particles inside the potential wells of different depths. The simulations allow monitoring formation and
breakage of clusters in a suspension as well as time dependence of the mean cluster size.
The article is published in the original. 相似文献
46.
47.
Victor Kochkodan Nidal Hilal Olga Kochkodan 《Advances in colloid and interface science》2010,159(2):180-188
In this work, thin-layer composite membranes imprinted with desmetryn or ibuprofen were prepared and studied for selective recognition of the template compounds in aqueous solutions. The imprinted membranes were developed using photoinitiated copolymerization of 2-acrylamido-2-methyl-1-propane sulphonic acid and N,N'-methylene-bis-acrylamide, in the presence of desmetryn or via copolymerization of dimethylaminoethyl methacrylate, and trimethylopropane trimethacrylate, in the presence of ibuprofen, followed by deposition of the imprinted layers on the surface of porous microfiltration supports of various chemical nature. Atomic force microscopy was used to study the surface morphological characteristics of the developed membranes. Molecularly recognition properties of imprinted membranes were evaluated by measuring their capability to bind the template molecules from polycomponent aqueous solutions. It was shown that obtained membranes may be used as selective recognising elements of portative differential capacitor sensor device for express monitoring of the target molecules in water. The sensor performance is based on registration of the alteration of dielectric permeability of composite imprinted membrane at selective binding of template molecules, when the analyzed feed solution is filtered through the membrane sample. 相似文献
48.
Tetrakis(selenodiazole)porphyrazine and its vanadyl (VO2+) complex have been prepared and characterized by FT-IR, UV–vis, and MALDI-MS. The magnetic properties of the complex have
been investigated by EPR spectroscopy. 相似文献
49.
50.
Discovery of inhibitors that elucidate the role of UCH-L1 activity in the H1299 lung cancer cell line 总被引:17,自引:0,他引:17
Liu Y Lashuel HA Choi S Xing X Case A Ni J Yeh LA Cuny GD Stein RL Lansbury PT 《Chemistry & biology》2003,10(9):837-846
Neuronal ubiquitin C-terminal hydrolase (UCH-L1) has been linked to Parkinson's disease (PD), the progression of certain nonneuronal tumors, and neuropathic pain. Certain lung tumor-derived cell lines express UCH-L1 but it is not expressed in normal lung tissue, suggesting that this enzyme plays a role in tumor progression, either as a trigger or as a response. Small-molecule inhibitors of UCH-L1 would be helpful in distinguishing between these scenarios. By utilizing high-throughput screening (HTS) to find inhibitors and traditional medicinal chemistry to optimize their affinity and specificity, we have identified a class of isatin O-acyl oximes that selectively inhibit UCH-L1 as compared to its systemic isoform, UCH-L3. Three representatives of this class (30, 50, 51) have IC(50) values of 0.80-0.94 micro M for UCH-L1 and 17-25 micro M for UCH-L3. The K(i) of 30 toward UCH-L1 is 0.40 micro M and inhibition is reversible, competitive, and active site directed. Two isatin oxime inhibitors increased proliferation of the H1299 lung tumor cell line but had no effect on a lung tumor line that does not express UCH-L1. Inhibition of UCH-L1 expression in the H1299 cell line using RNAi had a similar proproliferative effect, suggesting that the UCH-L1 enzymatic activity is antiproliferative and that UCH-L1 expression may be a response to tumor growth. The molecular mechanism of this response remains to be determined. 相似文献