Search results for "THERMODYNAMICS"

Fractal Dimension of Transdermal-Delivery Drug Models: 4-Alkylanilines

2008

Abstract The pathways that exist in porous membranes used to deliver drugs form fractal percolating paths. For a homologous series of 4-alkylanilines, the fractal dimension D is calculated as a model for transdermal-delivery drugs. Program TOPO is used for the calculation of the solvent-accessible surface AS, which is denoted by the centre of a probe, which is allowed to roll on the outside while maintaining contact with the bare molecular surface S. AS depends on the probe radius R. For 4-alkylanilines, the quadrupole moment Θ is doubled. The hydrophobic contribution to AS is doubled while its hydrophilic part remains constant. D increases 11%. Geometric descriptor and topological index re…

Isolation and concentration of organophosphorus pesticides from water using a c18 reversed phase

1989

Abstract A simple, rapid and effective method for the extraction and enrichment of organophosphorus pesticides based on the use of Sep-Pak C 18 cartridges was studied as alternative method to those based on extraction with organic solvents. The influence of the elution solvent, pH, salinity and volume of water filtered was studied for ten organophosphorus pesticides. The pesticides were determined by gas chromatography with a BP-1 capillary column and a thermionic detector. Recoveries at the 100 and 200 ng/1 spiking levels were greater than 85%, except for disulfoton.

Universal model for the calculation of all organic solvent–water partition coefficients

1998

Abstract We present the basis for building a universal organic solvation model to calculate solubility in any organic solvent and in water, as well as the organic solvent–water partition coefficient ( P ). Log P values are of the same order of magnitude as reference calculations but for a few cases which are discussed. Normalized log P contributions are sensitive to the rest of the atoms. When comparing porphin with phthalocyanine, the latter results in an amphipathic molecule. For C 70 , the contribution of a–e carbons to log P correlates with the distances from the nearest pentagon. The method has been also applied to benzobisthiazole oligomers and phenyl alcohols.

Liquid/Gas and Liquid/Liquid Phase Behavior of n-Butane/1,4-Polybutadiene versus n-Butane/1,2-Polybutadiene

2005

Solutions of 1,4-polybutadiene (1,4-PB, 98% cis) and of 1,2-polybutadiene (1,2-PB) in n-butane (n-C 4 ) were studied with respect to their vapor pressure and to their demixing into two liquid phases under isochoric conditions within the temperature range from 25 to 75 °C. 1,2-PB mixes homogeneously with n-C 4 at any ratio, in contrast to 1,4-PB, which exhibits a miscibility gap extending from practically pure solvent to approximately 40 wt % polymer. Corresponding to these solubility differences, the vapor pressures for the system n-C 4 /1,4-PB are considerably higher than for n-C 4 /1,2-PB at the same concentration and temperature. The experimental results are modeled accurately and consis…

Determination of rate constants of ion transfer kinetics across immiscible electrolyte solutions

1998

Abstract The rotating diffusion cell was used to study ion transfer across the interface between two immiscible electrolyte solutions. Tetrabutylammonium was chosen as the transferring cation and lithium chloride as the supporting electrolyte in aqueous phase. Tetrabutylammonium tetrakis-(4-fluorophenyl)-borate in 2-nitrophenyl-octylether was used as the organic electrolyte solution supported in the porous membrane. The quasi-steady state current–voltage curves were measured both by applying potential steps and by imposing a slow potential sweep. The analysis of experimental results was based on the comparison with the theoretical current–voltage curves and on the Koutecky–Levich plots. The…

Study on the efficiency of assembled packed microbore columns in HPLC

1984

Stainless steel columns (internally mirror-finished, 125 or 250nm in length, of bore 1.0 or 1.6mm) were slurry-packed with 5µm and 4µm reversed phase silicas (Hypersil ODS, LiChrosorb RP-8 and RP-18 and Superspher RP-8. The HPLC equipment consisted of a pump LC5A (Shimadzu) or a pump 2150 (LKB Instruments), a rheodyne valve 7413 with loops of 0.5, 1.0 and 5.0mm3 and a Jasco-Uvidec 100-II UV detector, variously with one of three specially constructed cells of 0.2, 0.4 and 1.3mm3 volume. Columns were assembled using two types of coupling device employing a stainless steel capillary of 0.12mm bore. The effect of sample volume, design of coupling device in assembled column, detector cell volume…

Ein automatisches viskosimeter zur flüssigkeitschromatographie

1968

Eine Viskosimeterapparatur wird beschrieben, die ein automatisches sukzessives Einfullen und Meessen von Flussigkeiten erlaubt. Bei chromatographischen Prozessen ermoglicht es das Gerat, auser der bisher ublichen Verfolgung der Konzentration auch das Molekulargewicht des gelosten Stoffes im Eluat zu bestimmen. Fur eine Elutionsgeschwindigkeit von 1 ml/min ist es moglich, das mittlere viskosimetrische Molekulargewicht in Intervallen von jeweils 2 ml oder auch 1 ml fur den gesamten Elutionsvorgang anzugeben. A viscometer system is described, which allows automatic successive loading and measuring of liquids. For chromatographic columns the apparatus can registrate not only the concentration b…

Liquid chromatography detectors second, completely revised edition by R. P. W. Scott Perkin-Elmer Corporation, Instrument Group, Main Avenue, Norwalk…

1986

Gelchromatographische refraktionierung, 1. Ein verfahren zur korrektur von gelchromatogrammen

1979

A mathematical method is proposed for calculating the gel chromatogram w(v0) after correction with the instrument spreading function D(v, v0) and for calculating D(v,v0) using experimental data on the basis, that a gel chromatographic polymer fraction of the chromatogram e(v) is collected and injected again. The chromatogram of this fraction c(v) can be described by the integral equation: where v0 is the elution volume and v1 is the volume at which the fraction is collected. The solution of this equation simultaneously with Tung's equation by way of minimizing is suggested.

How copper ions and membrane environment influence the structure of the human and chicken tandem repeats domain?

2019

Abstract Prion proteins (PrPs) from different species have the enormous ability to anchor copper ions. The N-terminal domain of human prion protein (hPrP) contains four tandem repeats of the –PHGGGWGQ– octapeptide sequence. This octarepeat domain can bind up to four Cu2+ ions. Similarly to hPrP, chicken prion protein (chPrP) is able to interact with Cu2+ through the tandem hexapeptide -HNPGYP- region (residues 53–94). In this work, we focused on the human octapeptide repeat (human Octa4, hPrP60–91) (Ac-PHGGGWGQPHGGGWGQPHGGGWGQPHGGGWGQ-NH2) and chicken hexapeptide repeat (chicken Hexa4, chPrP54–77) (Ac-HNPGYPHNPGYPHNPGYPHNPGYP-NH2) prion protein fragments. Due to the fact that PrP is a membr…