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Chemical Modifier (chemical + modifier)
Selected AbstractsInvestigation of nail permeation enhancement by chemical modification using water as a probeJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2002Gouri G. Malhotra Abstract Our objective was to screen molecules that could interact with keratin in the human nail and thereby improve the topical penetration of actives into and through the nail plate. We used specialized Franz-type diffusion cells for our permeation experiments and water as a marker molecule. Aqueous/hydroalcoholic gels containing the enhancers were spiked with tritiated water and compared with a control (without enhancer). We computed the normalized water flux (defined as a product of flux and nail thickness) for each gel. We defined an enhancement factor for water as the ratio of the normalized water flux from a gel containing enhancer to that of the control. Our results indicate that the chemical structure of the modifier is most important in determining its ability to enhance penetration. The best enhancement effect was obtained using N-(2-mercaptopropionyl) glycine, a mercaptan derivative of an amino acid, in combination with urea. The concentration of each chemical modifier was linearly related to normalized water flux and mercaptan levels were more important that urea levels in penetration enhancement. Barrier integrity of nails was compromised after treatment with effective chemical modifiers. Thus, we have developed a suitable technique to screen nail penetration enhancers using water as a probe. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:312,323, 2002 [source] Sensitive determination of bromine and iodine in aqueous and biological samples by electrothermal vaporization inductively coupled plasma mass spectrometry using tetramethylammonium hydroxide as a chemical modifierRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2008Hiroko Kataoka A procedure for the simultaneous determination of bromine and iodine by inductively coupled plasma (ICP) mass spectrometry was investigated. In order to prevent the decrease in the ionization efficiencies of bromine and iodine atoms caused by the introduction of water mist, electrothermal vaporization was used for sample introduction into the ICP mass spectrometer. To prevent loss of analytes during the drying process, a small amount of tetramethylammonium hydroxide solution was placed as a chemical modifier into the tungsten boat furnace. After evaporation of the solvent, the analytes instantly vaporized and were then introduced into the ICP ion source to detect the 79Br+, 81Br+, and 127I+ ions. By using this system, detection limits of 0.77,pg and 0.086,pg were achieved for bromine and iodine, respectively. These values correspond to 8.1,pg,mL,1 and 0.91,pg,mL,1 of the aqueous bromide and iodide ion concentrations, respectively, for a sampling volume of 95,µL. The relative standard deviations for eight replicate measurements were 2.2% and 2.8% for 20,pg of bromine and 2,pg of iodine, respectively. Approximately 25 batches were vaporizable per hour. The method was successfully applied to the analysis of various certified reference materials and practical situations as biological and aqueous samples. There is further potential for the simultaneous determination of fluorine and chlorine. Copyright © 2008 John Wiley & Sons, Ltd. [source] Determination of refractory elements in atmospheric particulates using slurry sampling electrothermal vaporization inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry with polyvinylidene fluoride as chemical modifierRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2006Yuefei Zhang Electrothermal vaporization (ETV) inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) with polyvinylidene fluoride (PVDF) as chemical modifier are critically compared for the determination of refractory elements in coal fly ash and airborne particulates. The atmospheric particulates that collected on a PVDF filter were introduced into the graphite furnace in the form of a slurry by dissolving the filter in dimethylformamide, and the dissolved filter PVDF, along with additional added PVDF powder, was used as a chemical modifier for subsequent ETV-ICP-OES and ETV-ICP-MS determination. The vaporization behaviors of analytes (Ti, Zr, V, Mo, Cr, La) in ETV-ICP-OES/MS were studied in detail, and the optimal ETV operating parameters were obtained. Under the optimized operating conditions, the detection limits of target elements were 0.08,2.7,ng,m,3 for ETV-ICP-OES and 0.5,50,pg,m,3 for ETV-ICP-MS, respectively, with analytical precisions of 3.5,7.3% for ETV-ICP-OES and 3.9,9.6% for ETV-ICP-MS, respectively. The tolerable amounts of matrix elements for ETV-ICP-OES are higher than for ETV-ICP-MS. Both ETV-ICP-OES and ETV-ICP-MS were used to directly determine the trace refractory elements in coal fly ash and airborne particulates and the analytical results are comparable. Copyright © 2006 John Wiley & Sons, Ltd. [source] Extracellular glucose concentration alters functional activity of the intestinal oligopeptide transporter (PepT-1) in Caco-2 cellsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2003Vanessa M. D'Souza Abstract The objective of this study was to determine the effect of different cell culture media glucose concentrations on the functional activity of PepT-1 in Caco-2 cells. Uptake kinetics of Gly-Sar into Caco-2 cells that were maintained in iso-osmotic media containing 25 or 5.5 mM glucose were determined in the presence and absence of amino acid-selective chemical modifiers and dithiothreitol. Inhibition of Gly-Sar uptake into Caco-2 cells was measured in the presence of dipeptides and xenobiotics exhibiting various binding affinities for the PepT-1. The effect of extracellular glucose on PepT-1 gene expression was assessed using comparative RT-PCR. Long-term exposure of Caco-2 cells to 25 mM glucose reduced maximum transport capacity for Gly-Sar uptake without altering PepT-1 gene expression. In contrast, binding affinity of Gly-Sar and other dipeptides or xenobiotics was not significantly changed. Chemical modification of Lys and Tyr residues decreased Vmax, while Cys modification increased the maximum transport capacity of the carrier. Preincubation of Caco-2 cells with dithiothreitol restored PepT-1 activity in cells maintained at 25 mM glucose. In conclusion, cell culture media containing 25 mM glucose decreases maximum transport capacity of PepT-1 in Caco-2 cells without affecting substrate recognition, at least in part, mediated via an oxidative pathway. © 2003 Wiley-Liss Inc. and the American Pharmaeceutical Association J Pharm Sci 92:594,603, 2003 [source] Investigation of nail permeation enhancement by chemical modification using water as a probeJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2002Gouri G. Malhotra Abstract Our objective was to screen molecules that could interact with keratin in the human nail and thereby improve the topical penetration of actives into and through the nail plate. We used specialized Franz-type diffusion cells for our permeation experiments and water as a marker molecule. Aqueous/hydroalcoholic gels containing the enhancers were spiked with tritiated water and compared with a control (without enhancer). We computed the normalized water flux (defined as a product of flux and nail thickness) for each gel. We defined an enhancement factor for water as the ratio of the normalized water flux from a gel containing enhancer to that of the control. Our results indicate that the chemical structure of the modifier is most important in determining its ability to enhance penetration. The best enhancement effect was obtained using N-(2-mercaptopropionyl) glycine, a mercaptan derivative of an amino acid, in combination with urea. The concentration of each chemical modifier was linearly related to normalized water flux and mercaptan levels were more important that urea levels in penetration enhancement. Barrier integrity of nails was compromised after treatment with effective chemical modifiers. Thus, we have developed a suitable technique to screen nail penetration enhancers using water as a probe. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:312,323, 2002 [source] | ||||||||||