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201.
Xiaoyi Gong Margaret Figus Jolanta Plewa Dorothy A. Levorse Lili Zhou Christopher J. Welch 《Chromatographia》2008,68(3-4):219-225
The acid dissociation constant (pK a) is a key physicochemical parameter for characterizing active pharmaceutical ingredients (APIs). Early determination of pK a values is highly desirable in drug discovery, pharmaceutical process research and formulation design. To overcome the challenges of limited sample availability and potential low purity of API samples at early stages of drug development, as well as to increase sample analysis throughput, a multiplexed 96-channel capillary electrophoresis with UV detection was evaluated as a practical approach for high throughput pK a estimation of proprietary APIs in support of pharmaceutical research. Proprietary APIs with diverse structures were examined using the approach. The pK a values were successfully determined with good accuracy and precision. System robustness was demonstrated and analysis of at least eight samples can be completed within 1 h. A rapid pK a estimation procedure for marginally soluble APIs was proposed by performing single-point multiplexed CE–UV measurement without extrapolation using 10 or 20% methanol as co-solvent. Direct pK a estimation of APIs using DMSO solution samples and crude reaction samples containing a large amount of solvents and reagents and high level of impurities was also demonstrated using the multiplexed CE–UV approach. 相似文献
202.
Kong Y Grembecka J Edler MC Hamel E Mooberry SL Sabat M Rieger J Brown ML 《Chemistry & biology》2005,12(9):1007-1014
Targeting the microtubule system represents an attractive strategy for the development of anticancer agents. In this study, we report a class of combretastatin A-4 (CA-4) analogs derivatized with a boronic acid moiety replacing the hydroxyl group on the C-ring of CA-4. Docking studies of the X-ray structures of our aryl-boronic analogs onto an X-ray structure of the alpha,beta-tubulin heterodimer suggested that cis-6 was a potent inhibitor of the colchicine binding. The model indicated that there would be strong hydrogen bonding between the boronic acid moiety and Thr-179 and Val-181 of alpha-tubulin. We demonstrate that the cis-6 boronic acid bioisostere of CA-4: (1) inhibits tubulin assembly, (2) competitively displaces colchicine, and (3) is a low-nanomolar inhibitor of human cancer cell lines. We present this isostere as a class of potent analogs of CA-4. 相似文献
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206.
Arvydas Survila Jolanta Pileckien? Stas? Kanapeckait? Putinas Kalinauskas Giedrius Stalnionis 《Journal of Solid State Electrochemistry》2012,16(2):521-527
In accordance with thermodynamic analysis, cuprous oxide layers are formed spontaneously in the Cu|Cu(II), gluconic acid system
at pH > 3.7 under open-circuit conditions. A current peak of Cu2O reduction is observed on cathodic voltammograms at ca −0.7 V, its height being dependent on the exposure time. The analysis
of the charge transferred in this region yields the rate of Cu2O formation equal to 1.25 × 10−10 mol cm−2 s−1. The light perturbation of Cu electrode under open-circuit conditions results in the generation of a negative photopotential,
which is indicative of n-type conductivity. The threshold wavelength is equal to ∼590 nm and is consistent with a band gap of ∼2.1 eV. Anodic photocurrents,
which are observed near the open-circuit potential, decrease with cathodic polarization and change their sign at ∼0.05 V.
Analysis of impedance data was performed, invoking the equivalent circuit that accounts for the two-step charge transfer.
In the presence of Cu2O, some retardation of Cu(II) reduction was found to occur with a slight increase in the admittance of the double layer. The
suggestion has been made that oxide layers formed in Cu(II) gluconate solutions cannot be compact and uniformly distributed
over the entire electrode surface. Relevant investigations of surface morphology support this conclusion. 相似文献
207.
Jolanta Kowalonek 《European Polymer Journal》2010,46(2):345-1945
The new biodegradable blends composed of natural pectin and synthetic polymer: polyvinylpyrrolidone were obtained by casting from aqueous solutions. The molecular interactions between components have been studied by FTIR. The blends were exposed to UV-irradiation and the changes in chemical structure were investigated using absorption spectroscopy (FTIR and UV-Vis). The morphology of sample surfaces before and after exposure to UV was observed by atomic force microscopy. Insoluble gel, formed as a result of photocrosslinking, was appointed gravimetrically. The relation between the blend composition and the efficiency of observed photoreactions has been considered. 相似文献
208.
Jolanta Nieszporek 《Electroanalysis》2012,24(7):1584-1590
The results of kinetic measurements of Zn2+ electroreduction on mercury electrode in the presence of tetramethylthiourea showed the two‐step character of the electrode process. The acquisition of nonlinear wide potential range Tafel plots was found to offer a good opportunity to examine the Zn2+ electroreduction mechanism. Three mechanisms including the ion transfer step followed by the electron exchange step (IE mechanism), the adsorption step (IA mechanism) and the chemical step followed by electron transfer (CE) were applied. The accelerating influence of tetramethylthiourea on Zn2+ electroreduction was found to result from possible complexes formation in the diffuse layer. The ion transport step is probably combined with the loss or exchange of a ligand. The second step probably consists in the electron transfer or adsorption process connected with partial charge transfer. 相似文献
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Liliana Mazur Anna E. Koziol Bo?ena Modzelewska-Banachiewicz Marzena Ucherek Micha? Zimecki Jolanta Artym 《Journal of chemical crystallography》2011,41(6):880-885