Synergistic effects in competitive adsorption of carbohydrates on an ion-exchange resin.

Adsorption of the three carbohydrates sucrose, glucose and fructose from aqueous solutions was investigated on an ion-exchange resin. The adsorption equilibrium of single components, binary and ternary mixtures was quantified by frontal analysis and the adsorption-desorption method. The experiments covered a concentration range up to 600 g/L at 60 degrees C and 80 degrees C. Within this range the adsorption isotherms of carbohydrates exhibited anti-Langmuirian behavior. Data of mixture adsorption revealed reversed competitive (synergistic or cooperative) effects, i.e., an increase of the concentration of one component of the mixture enhanced the adsorption of others. To model such an adsorption behavior the anti-Langmuir model has been used. The isotherm parameters determined for single components were used to simulate the competitive adsorption equilibria through the IAS (ideal adsorbed solution) theory. Finally, dynamic concentration profiles of multicomponent mixtures have been recorded. The shapes of adsorption and desorption curves confirmed the observed competitive effects found in the equilibrium studies. The breakthrough curves measured were simulated using the equilibrium theory as well as a numerical solution of the equilibrium dispersive model.

Comparison of possible arrangements of five identical columns in preparative chromatography.

Goal of the paper is to demonstrate how configuration of a certain number of identical HPLC columns influences on the effectiveness of the isolation of a target component. There are two extreme configurations: all the available columns are operated in parallel (provided there are enough pumps available) or all the columns are connected in series. Various combinations of columns connected parallel and in series are possible. Besides batch operation more sophisticated multicolumn arrangements allowing continuous separation are considered. In particular, in this work different configurations of five columns were examined. For illustration the separation of a binary mixture was considered. As the objective function the productivity of the less retained component has been used. A standard model capable to describe the propagation of chromatographic bands has been used to optimize the operating conditions for various possible multicolumn arrangements.

Effect of mobile phase composition on the SMB processes efficiency. Stochastic optimization of isocratic and gradient operation.

The solvent composition was adjusted in a theoretical study in order to maximize the efficiency of a simulated moving bed (SMB) process. The isocratic realization of the process as well as the solvent gradient mode were considered. The solvent composition and the flow rates were used as decision variables in a random search optimization algorithm known to be a reliable tool for nonlinear programming problems. The results of the optimization indicate that the optimal composition of the mobile phase depends strongly on the feed concentration. The asymmetry of the internal concentration profiles, which has a negative effect on the separation efficiency, can be partly damped by an increase of the solvent strength. In the cases studied the optimal solvent strength determined for concentrated feed streams is higher than that for diluted ones. Moreover, the optimum is strongly influenced by the value of the selectivity factor and its dependency on the mobile phase composition. Different results were obtained for cases, in which the separation factor increases with increasing the modifier concentration, than for cases, in which the separation factor decreases with increasing the modifier concentration. A similar analysis was performed for a solvent gradient SMB process, in which different solvents are used at the two inlet ports: a weak solvent in the feed stream and a strong solvent in the desorbent stream. Again the optimal mobile phase composition was strongly affected by the type of the isotherms and their non-linearity. The potential of a gradient SMB process in terms of increasing the productivity and reducing the eluent consumption is exemplified.

Inducible nitric oxide synthase and Salmonella infection.

Salmonella infection is associated with the increased expression of inducible nitric oxide synthase in macrophages and other cells. This review summarizes current knowledge of the molecular mechanisms involved in the induction process, and discusses the functional significance of nitric oxide production in the context of host defense against Salmonella.

Comparative modeling of breakthrough curves of bovine serum albumin in anion-exchange chromatography.

The experimental results of a previous study of the mass transfer kinetics of bovine serum albumin (BSA) in ion-exchange chromatography, under nonlinear conditions, were reevaluated using the general rate model of chromatography. Solutions of this model were obtained numerically. The influences of axial dispersion, the resistance to mass transfer from the bulk mobile phase to the surface of the packing particles, and the intraparticle mass transfer resistances on the profiles of the breakthrough curves of BSA were investigated. The results obtained are compared to those of a previous investigation of the same data, using the simple transport-dispersive model and the lumped pore diffusion model. The results obtained show that the use of an oversimplified model for the analysis of chromatographic data can lead to erroneous interpretations of the experimental data and to misunderstandings of the fundamentals of the processes involved. Finally, a theoretical comparison between the properties and the range of application of the three models is provided.

Inducible nitric oxide synthase expression before and after eradication of Helicobacter pylori in different forms of gastritis.

An increased expression of inducible nitric oxide synthase (iNOS) has been observed in the inflamed human gastric mucosa as well as in some tumors. This observation suggests a pathobiological role of elevated NO production. The purpose of this study was to compare the immunohistochemical iNOS expression in the different kinds of gastritis before and after the eradication of Helicobacter pylori. We performed iNOS and H. pylori immunohistochemical staining and counted iNOS positive cells. We detected elevated expression of iNOS around sites infected with H. pylori. iNOS expression in chemical gastritis was strongly elevated in mucosal glands. After treatment, we found a significant difference in iNOS expression in patients with classical H. pylori-induced antrum predominant gastritis and in patients with active autoimmune gastritis. In the special case of progressed gastritis with intestinal metaplasia we found persistence of intestinal metaplasia, and we could not find a significant difference in the number of positive iNOS cells before and after treatment. The persistence of IM as a possibly precancerous lesion is probably at least in the antrum a source of continuous iNOS induction even after H. pylori eradication.

Helicobacter pylori and gastric cancer:current status of the Austrain Czech German gastric cancer prevention trial (PRISMA Study).

AIM: To test the hypothesis that Helicobacter pylori eradication alone can reduce the incidence of gastric cancer in a subgroup of individuals with an increased risk for this fatal disease. METHODS: It is a prospective, randomized, double blind, placebo controlled multinational multicenter trial. Men between 55 and 65 years of age with a gastric cancer phenotype of Helicobacter pylori gastritis are randomized to receive a 7 day course of omeprazole 2 X 20mg, clarithromycin 2 X 500mg, and amoxicillin 2 X 1g for 7 days, or omeprazole 2 X 20mg plus placebo. Follow-up endoscopy is scheduled 3 months after therapy, and thereafter in one-year intervals. Predefined study endpoints are gastric cancer, precancerous lesions (dysplasia, adenoma), other cancers, and death. RESULTS: Since March 1998, 1524 target patients have been screened, 279 patients (18.3%) had a corpus dominant type of H. pylori gastritis, and 167 of those were randomized (58.8%). In the active treatment group (r = 86), H. pylori infection infection was cured in 88.9% of patients. Currently, the cumulative follow-up time is 3046 months (253.38 patient years, median follow up 16 months). So far, none of the patients developed gastric cancer or any precancerous lesion. Three (1.8%) patients reached study endpoints other than gastric cancer. CONCLUSION: Among men between 55 and 65 years of age, the gastric cancer phenotype of H. pylori gastritis appears to be more common than expected. Further follow up and continuing recruitment are necessary to fulfil the main aim of the study.

Ablation of Barrett's epithelium by endoscopic argon plasma coagulation in combination with high-dose omeprazole.

BACKGROUND: Barrett's esophagus is a premalignant condition induced by gastroesophageal reflux. The aim of this prospective study was to assess the efficacy of argon plasma coagulation in combination with high-dose omeprazole therapy to ablate nondysplastic Barrett's epithelium. METHODS: In 73 patients with histologically confirmed Barrett's epithelium, argon plasma coagulation was used in combination with maximal acid suppression (omeprazole 40 mg three times a day). Histologic and endoscopic changes were evaluated at 6- and 12-month intervals. RESULTS: In 69 of 70 patients (98.6%) complete squamous regeneration was achieved after a median of 2 argon plasma coagulation sessions (range 1 to 5). During a median follow-up of 12 months (range 2 to 51 months) there has been no relapse or evidence of the development of dysplasia under continuous acid suppression. Three patients (4.3%) developed a mild stricture of the distal esophagus that resolved after a single session of bougie dilation. CONCLUSIONS: In our experience, argon plasma coagulation in combination with high-dose omeprazole treatment is an effective and safe technique for complete ablation of nondysplastic Barrett's epithelium. Restoration of squamous mucosa after argon plasma coagulation appears to be long-lasting.

Determination of mobile phase effect on single-component adsorption isotherm by use of numerical estimation.

Numerical estimation was used to determine adsorption isotherm parameters of a single-component in a normal-phase system. The distribution isotherm of methyl deoxycholate was described between the mobile phase containing hexane, ethyl acetate, methanol with varied concentration and a silica gel adsorbent. The effect of the mobile phase composition on the isotherm parameters and the band profiles was investigated. The results obtained were used to simulate the overload gradient elution. The validity of the method proposed was verified by comparison of the computer simulations with the experimental band profiles.

Calculation of chromatographic band profiles with an implicit isotherm.

The numerical method for solving the mathematical model of chromatography process coupled with implicit isotherm has been proposed. The exemplary predictions of elution band profiles were performed for competitive adsorption data of 2-phenylethanol and 3-phenylpropanol on ODS-silica with methanol-water as the mobile phase. The simulations of chromatography process with various isotherm models taking into account lateral interactions in adsorbed phase and surface heterogeneity were discussed.