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H Poppe

Publications and source records attributed to H Poppe.

At least 19 recordsLinked to original sources
PubMed2002

Position and intensity of system (eigen) peaks in capillary zone electrophoresis.

The intensity of system (or eigen) peaks encountered in capillary zone electrophoresis (CZE) can be predicted by considering mass balances for each of the analyte constituents and each of the constituents in the background electrolyte (BGE). As a result of coherence, in each zone the proportions in which the constituent concentrations vary are fixed; they are determined by the composition of the BGE and the nature of the analyte constituent (if present) and described as eigenvectors of a transport matrix. Considering the effect of an injection, the mass balances for all constituents can be satisfied only via the intensity of each zone. This leads to an n-equations, n-unknowns problem, with the intensities as the unknowns and the mass balances as equations. The latter can be easily solved to obtain the intensities. of the zones, of analytes as well as of system peaks. In this work the approach has been applied to CZE systems with two co-ions in the BGE, and experimental results have been compared to the predictions obtained from the model. Agreement was seen to be reasonable, but the quantitative comparison often failed, probably due to experimental difficulties.

Electrophoresis, Capillary↗
PubMed2002

Mass transfer in rectangular chromatographic channels.

Rectangular channels are explored nowadays for use in chromatographic and electrophoretic separations, especially after the possibilities of micromachining have become available to separation scientist. Expressions for plate heights expected for such experiments with an infinite channel width has been given by Giddings, while Golay derived the effect of finite channel width for unretained components. However, it remains unclear how the classical equations for plate height for retained components should be modified when the effect of finite channel width is taken into account. Also, the application of electroosmotic propulsion of the mobile phase leads to a flow profile different from the Poiseuille-type profile assumed in the above treatments, and no equations seem to be available for this situation. In this work, these problems have been addressed by an approach involving numerical Fourier transforms. Expressions for the plate height contribution from mobile phase mass transfer as a function of characteristic length dc (the height of the channel, or the diameter for open cylindrical systems, OT), mean mobile phase velocity, um, diffusion coefficient Dm, retention factor, k', and width-to-height ratio, phi, can always be written as: H = dc2um/DmF(k', phi). For cylindrical open systems, F(k', phi) equals 1/96 (1 + 6k' + 11k'2)/(1 + k')2, the well-known Golay equation. In the present work, this is taken as a reference point; results are cast in the form F(k', n) = (A + Bk' + Ck'2)/(1 + k')2, where A, B and C replace the factors 1/96, 6/96 and 11/96 of the Golay equation. Values of A, B and C are reported for various values of phi. This is done for a selection from the large variety of conditions that can be imagined: Coating on one, two or four walls of the channel, non-uniform or uniform coating, pressure-driven (Poiseuille-type) or electro-osmotically-driven flow, surface charge on one, two of four walls, etc. It is found that the effect of finite channel width is large for unretained solutes (plate height for a wide channel is nearly eight times larger than that predicted when the finite channel width is ignored), whereas the plate height increase with retention is in many cases influenced only slightly.

Algorithms↗
PubMed2001

Determination of the molecular mass distribution of synthetic polymers by size-exclusion electrochromatography.

The performance of size-exclusion electrochromatography (SEEC) for the mass distribution analysis of synthetic polymers was studied and compared to conventional, pressure-driven size-exclusion chromatography (SEC). Electroosmotic flow control, within-day, day-to-day and column-to-column repeatability were determined for SEEC with respect to retention and separation efficiency. It was shown that by using the retention ratio instead of the migration time, the precision of the mass distribution calculations is sufficiently high, and that similar distributions were obtained for a sample analyzed by pressure-driven SEC and by SEEC. Furthermore, hexafluoroisopropanol was demonstrated to be a new and potent solvent for SEEC. It was used for the separation of narrow polymethylmethacrylate standards and several commercially important polymers such as polycarbonate, polycaprolactam and poly(ethylene terephthalate), using UV detection in the deep UV region (195-230 nm).

Chromatography, Gel↗
PubMed2001

Effects of pore flow on the separation efficiency in capillary electrochromatography with porous particles.

The effect of pore flow on the separation efficiency of capillary electrochromatography (CEC) has been studied using columns packed with particles with different pore sizes. A previously developed model was used to predict the (relative) pore flow velocity in these columns under various experimental conditions. Equations are derived describing the effect of pore flow on peak broadening in CEC. The theory has been compared with practice in the reversed-phase CEC separation of various polyaromatic hydrocarbons. It is shown, by theory and experimentally, that the mass-transfer resistance contribution to peak dispersion can be effectively eliminated when using porous particles with a high (> or =50 nm) average pore diameter. Moreover, at high pore-to-interstitial flow ratios the flow inhomogeneity contribution (the A term in the plate height equation) is also shown to decrease. Under optimal conditions, a reduced plate height of 0.3 for the nonretained compound could be obtained. It is argued that fully perfusive porous particles can be a more efficient separation medium in CEC than nonporous particles.

Journal Article↗
PubMed2001

Size-exclusion electrochromatography with controlled pore flow.

In size-exclusion electrochromatography (SEEC) there exists an optimum in pore-to-interstitial flow ratio with respect to the resolution. Two methods for finding and controlling the optimal pore-to-interstitial flow ratio in SEEC have been studied: (i) varying the ionic strength of the mobile phase and (ii) the application of a hydrodynamic flow in addition to the electrco-driven flow. Both methodologies have been evaluated in terms of efficiency and applicability with columns packed with silica particles containing pores of either 10 or 50 nm in diameter, and with different ionic strength mobile phases. Using the first method with the 10-nm pore particles, the flow ratio could be adjusted within an appropriate range. However, with the wide-pore (50 nm) particles it appeared that the pore-to-interstitial flow ratio was too high at all conditions tested to obtain proper selectivity. In the second approach, the desired pore flow was generated by the electric field and the pore-to-interstitial flow ratio could then be adjusted by an applied pressure over the column. This method was applicable with both particle types studied. The application of a (low) voltage gradient in addition to a pressure-driven flow resulted in a sharply improved separation efficiency as a result of a strongly improved mass transfer due to intra-particle electroosmotic flow. When optimized, pressurized SEEC generates identical separation efficiencies for polystyrene standards as are obtained with pure SEEC, while the reduction in selectivity, in comparison to pressure-driven SEC, is kept minimal.

Chromatography, Gel↗
PubMed2000

Modelling of the pore flow in capillary electrochromatography.

Pore flow in capillary electrochromatography (CEC) on porous silica particles has been investigated. To that end the migration behaviour of narrow polystyrene (PS) standards dissolved in di-methylformamide (DMF) with lithium chloride in 1 and 10 mmol/l concentration has been measured. These data have been compared to theoretical predictions. The latter were based on a model comprising cylindrical pores of varying diameter as measured experimentally by porosimetry, while the flow in each set of pores was calculated with the expression given by Rice and Whitehead. A reasonable to good agreement between experimental and predicted data was observed, provided it was assumed that pores of differing diameter occur in series. It was found that the flow in pores with a nominal size of 100 A can be considerable compared to the interstitial flow, especially at 10 mmol/l ionic strength. It is concluded that pore flow within porous particles in CEC, of great importance for improved efficiency in both interactive and exclusion type CEC, can be predicted fairly reliably by means of the Rice and Whitehead expression.

Dimethylformamide↗
PubMed2000

Loteprednol etabonate: a soft steroid for the treatment of allergic diseases of the airways.

There are several approaches for developing new antiallergic/antiasthmatic agents. One of them is the improvement of an existing class of effective drug classes. Due to some undesired effects of intranasal or inhaled corticosteroids, there is a need for better tolerated corticosteroids. Loteprednol etabonate belongs to the so-called class of soft steroids because it is metabolized by a one-step reaction (hydrolysis) without using the cytochrome P450 monooxygenase system. In in vitro investigations using human cells, loteprednol inhibited the release of proinflammatory cytokines (e.g., TNF-alpha, GM-CSF, IL-4, IL-5) according to its relative binding potency to the glucocorticoid receptor. In in vivo animal studies, loteprednol effectively inhibited allergically induced vascular leakage in the nasal cavity of actively sensitized Brown Norway rats and rhinorrhea in actively sensitized domestic pigs following nasal challenge. In several models of allergic asthma, it was clearly demonstrated that loteprednol was able to suppress the allergically induced late phase eosinophilia in mice, rats and guinea pigs. After intrapulmonary administration of loteprednol, only a slight, statistically nonsignificant reduction in thymus weight was observed in a dose range far less than the therapeutically relevant doses. Its therapeutic ratio is clearly superior to those of beclomethasone and budesonide. Loteprednol is a safe steroid with an extremely wide range between therapeutic and side effect inducing doses. Its elimination profile, its pronounced binding to plasma protein and erythrocytes and the low oral bioavailability makes this drug highly suitable for nasal or pulmonary use.

Journal Article↗
PubMed1999

Capillary electrochromatography with macroporous particles.

The performance of macro-porous particles in capillary electrochromatography is studied. Three reversed-phase stationary phases with pore diameters between 500 A and 4000 A have been tested for separation efficiency and mobile phase velocity. With these stationary phases, a large portion of the total flow appears to be through the pores of particles, thereby increasing the separation efficiency through a further decrease of the flow inhomogeneity and through enhancement of the mass transfer kinetics. The effects of pore size and mobile phase composition on the plate height and mobile phase velocity have been studied. With increasing buffer concentrations and larger pore diameters, higher mobile phase velocities and higher separation efficiencies have been obtained. Columns packed with 7 microns particles containing pores with a diameter of 4000 A generated up to 430,000 theoretical plates/m for retained compounds. Reduced plate heights as low as 0.34 have been observed, clearly demonstrating that a significant portion of the flow is through the pores. For the particles containing 4000 A pores no minimum was observed in the H-u plot up to linear velocities of 3.3 mm/s, suggesting that the separation efficiency is dominated by axial diffusion. On relatively long (72 cm) columns, efficiencies of up to 230,000 theoretical plates/column have been obtained under non-optimal running conditions. On short (8.3 cm) columns fast separations could be performed with approximately 15,000 theoretical plates generated in less than 30 s.

Chromatography↗
PubMed1999

New aminocarboxamides with class III anti-arrhythmic activity.

In the search for new anti-arrhythmic substances we discovered the class III activity of aminocarboxamides. These compounds show a prolongation of the effective refractory period. With some of them the prolongation is more pronounced after faster than after slower stimulation of the guinea pig papillary muscle. They should therefore be of interest in the treatment of cardiac arrhythmias after myocardial infarction and atrial fibrillation. The chemical synthesis, the structure-activity relationships of the new derivatives, their efficacy on the action potential duration (APD) and the effective refractory period (ERP) in vitro of isolated guinea pig papillary muscles are described and discussed in this paper. Since AWD 160-275 (13) and AWD 23-111 (14) exerted a pronounced APD90 and ERP prolongation at faster stimulation, they were selected for further electrophysiological characterization in vitro and in vivo. Anti-arrhythmic and pro-arrhythmic effects were determined in several animal models in comparison with dofetilide, sematilide, and sotalol. 13 was found to be effective in preventing programmed electrical stimulation-induced arrhythmias in anaesthetized dogs and may therefore contribute to the therapy of dysrhythmias after myocardial infarction. The pro-arrhythmic effect of 14, investigated in a model of triggered activity in chloralose-anaesthetized rabbits under methoxamine infusion, is low in comparison with other class III anti-arrhythmics.

Action Potentials↗
PubMed1998

1,5-Disubstituted indazol-3-ols with anti-inflammatory activity.

A series of new indazol-3-ol derivatives was synthesized. Some of these compounds exhibit interesting anti-inflammatory activities in various models of inflammation. 5-Methoxy-1-[quinoline-2-yl-methoxy)-benzyl]-1H-indazol-3-ol (27) strongly inhibits the oxidation of arachidonic acid to 5-hydroperoxyeicosatetraenoic acid catalyzed by 5-lipoxygenase (IC50 = 44 nM). 27 also inhibits the contraction of sensitized guinea pig tracheal segments (IC50 = 2.9 microM). In guinea pigs treated with 27 (1 mg/kg i.p.) 2 h before antigen provocation, there was a marked inhibition (47%) of the antigen-induced airway eosinophilia. After topical application of 1 microgram/ear 27 inhibits the arachidonic acid induced mouse ear edema (41%).

Animals↗
PubMed1998

Effects of a selective PDE4 inhibitor, D-22888, on human airways and eosinophils in vitro and late phase allergic pulmonary eosinophilia in guinea pigs.

The actions of a novel selective inhibitor of type 4 cyclic nucleotide phosphodiesterase (PDE4), D-22888, on human airway smooth muscle tone and human eosinophil respiratory burst in vitro and bronchoalveolar eosinophilia in allergen-challenged sensitized guinea pigs in vivo were assessed. D-22888 was a selective inhibitor of PDE4, exhibiting an IC50 against human neutrophil PDE4 of 0.15 microM, compared to IC 50 values of 4.4 microM and 1.1 microM for human platelet PDE3 and PDE5, respectively. D-22888 relaxed inherent tone in human bronchial rings in a concentration-dependent manner with an IC50 of 5.0 microM (geometric mean, 95% ci 3.0-8.4 microM) and also caused a concentration-dependent inhibition of opsonized zymosan-induced superoxide anion generation by human eosinophils with an IC50 of 3.1 microM (1.0-9.2 microM). Treatment of actively sensitized guinea pigs with single oral doses of D-22888 2 h before or 4 h after challenge reduced bronchoalveolar lavage (BAL) eosinophil numbers, 24 h after aerosol allergen challenge, by 48% and 73% at 10 mg/kg and 30 mg/kg, respectively, 2 h pre-challenge and 68% at 30 mg/kg 4 h post-challenge. Chronic twice-daily oral dosing with D-22888 for three days caused inhibition of 24 h post-challenge BAL eosinophilia, amounting to 88% at 30 mg/kg. These in vivo actions were comparable with those achieved with other selective PDE4 inhibitors and with the corticosteroid, dexamethasone. We conclude that D-22888 exerts actions on airway smooth muscle and eosinophil recruitment and activation that suggest that D-22888 may be a promising new drug for use in the treatment of allergic obstructive airways>> diseases such as bronchial asthma.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1998

[A new class-III antiarrhythmic preparation among the dicyclohexylamides of aminocarboxylic acids].

The Institute of Pharmacology, Academy of Medical Sciences, jointly with AWD (Germany) has synthesized and tested a novel class III antiarrhythmic coded AWD-160-275, a derivative of dicyclohexylamides of aminocarboxylic acids. The compound was shown to prolong cardiac repolarization, to increase atrial and ventricular refractory periods, to decrease sinus nodal automatism, and to unchange intraventricular conduction. The compound proved to be superior to the reference drugs in the rate and duration of antiarrhythmic and antifibrillatory action. In therapeutical doses it has no antiarrhythmic effect. The specific feature of the agent is that there is no relation of longer effective refractory periods to the frequency of stimulation. This property may be useful in treating tachyarrhythmias.

Action Potentials↗
PubMed1997

Comparison of five methods for the study of drug-protein binding in affinity capillary electrophoresis.

The qualitative and quantitative aspects of capillary electrophoretic methods used to study drug-protein interactions, viz. the affinity capillary electrophoresis (ACE). Hummel-Dreyer (HD), frontal analysis (FA), vacancy peak (VP) and vacancy affinity capillary electrophoresis (VACE) methods have been investigated. In the ACE and the VACE methods the binding parameters can be calculated from the change in the electrophoretic mobility of the drug on complexation with a protein. In the frontal analysis and the vacancy peak method the free drug concentration is measured with UV detection. In the Hummel-Dreyer method the amount of drug bound is measured with UV detection. For the comparison of these five methods the warfarin-bovine serum albumin (BSA) system was used. Several factors that might influence the determination of association parameters were examined. With the FA, VP, HD and VACE methods the absolute numbers of the different binding sites involved in the complex formation can be determined, a major advantage in drug-binding studies.

Animals↗
PubMed1997

Behavior of peptides in capillary electrophoresis: effect of peptide charge, mass and structure.

In the last decade the large potential of capillary electrophoresis as a technique for separation and characterization of peptides has been demonstrated extensively. In this field, a large number of chemical structures has to be taken into consideration, for which very often no data or even standards are available. As a result, there has been a strong desire to relate electrophoretic behavior to molecular properties and structure of the compounds. The activities in that direction, in the area of capillary zone electrophoresis, are critically reviewed. Special attention is paid to peptide charge, mass, hydrophobicity and structure, and their influence on the selectivity of the separation. Also, some complexation phenomena are discussed.

Computer Simulation↗
PubMed1997

New 5-aminoacyl-5,10-dihydro-11H-dibenzo[b,e][1,4]diazepin-11-ones with antiarrhythmic activity.

A series of new 5-substituted tricyclic 5,10-dihydro-11H-dibenzo[b,e][1,4]-diazepin-11-ones was identified as potential antiarrhythmic agents against bradyarrhythmias [1, 2]. The in vitro and in vivo interactions of the compounds with muscarinic receptors and the antiarrhythmic activity were examined. In receptor binding studies some derivatives showed a high affinity to the cardiac M2 receptor (Ki 10 nmol/l), an equal or smaller affinity to cortical M1 receptor and a lower affinity to the glandular M3 binding site. Functional experiments showed the derivatives as competitive antagonists with high affinity to the cardiac and smaller affinity to the intestinal muscarinic receptor. In vivo experiments correspond with the M2 selectivity. First the vagal or agonist-induced bradycardia was inhibited in rats and guinea pigs while the McNA-343 induced increase of blood pressure, methacholine-induced bronchi and bladder constriction as well as the salivation were inhibited only at higher doses. In conscious cats the tachycardia was examined in comparison with pupillomotoricity. The effect duration and the therapeutical range were determined in comparison to the M2 selective blocking agent AF-DX116. The antiarrhythmic activity was examined compared to quinidine sulfate in CaCl2-arrhythmia of rats, in atrial fibrillation and atrial flutter in dogs according to Scherf [2] and in electric induced atrial fibrillation under vagal stimulation in cats. In the atrial arrhythmias the derivatives are clearly longer effective than quinidine sulfate. The antiischemic activity was examined in the two-stages coronary ligature in dogs according to Harris. The long-running regularization of ectopies (about 2 h after i.v. injection) occurred without decrease of the heart rate, an effect particularly convenient to therapy of bradycardic dysrhythmias.

Animals↗
PubMed1996

Critical evaluation of the applicability of capillary zone electrophoresis for the study of hapten-antibody complex formation.

The applicability of capillary zone electrophoresis (CZE) for the determination of association constants of an hapten-antibody complex with values as high as 10(7) (mol/I)-1 was investigated (dissociation constant in the nmol range). As a reference method the well known, enzyme-linked immunosorbent assay (ELISA) was selected. The study describes the optimisation of the experimental conditions of the CZE technique. The CZE measurements were optimised according to an experimental design. The results of the CZE and ELISA methods are compared giving consideration to the reproducibility (repeatability) of the two methods.

Antibodies, Monoclonal↗
PubMed1996

Selectivity change in the separation of proteins and peptides by capillary electrophoresis using high-molecular-mass polyethyleneimine.

A study of the capillary electrophoretic separations of proteins and peptides using high-molecular-mass polyethyleneimine (PEI) is presented. Experiments were performed in the PEI-coated capillaries together with the use of this polymer as a buffer additive under different separation conditions. The effects of pH and the concentration of PEI in the buffer on the electroosmotic flow and the migration orders of biopolymers were investigated. The use of the cationic polymer offers an alternative for the modification of the separation selectivity and resolution of biopolymers.

Amino Acid Sequence↗