The enthalpimetric determination of inhibition constants for the inhibition of urease by acetohydroxamic acid.

The effect of concentration of acetohydroxamic acid (AHA) on inhibition of jack bean urease in phosphate buffer, pH 7.0, at 25 degrees C, was studied. The measurements were performed at urease concentration of 2.5 mg/100 cm3 for concentrations of urea and AHA ranging in the range of 2-50 mmol dm-3 and 0.25-10 mmol dm-3, respectively. The reactions were monitored by two techniques: analytical and enthalpimetric. For the analytical technique the growth of ammonia concentration in the course of the reaction was determined. From the recorded progress curves the following parameters were calculated for each inhibitor concentration: the initial reaction rate, the steady-state rate and the inversion constant. From these parameters the inhibition constants of the initial and steady-state stages of the reaction, Ki and Ki, were calculated. The former constant did not change whereas the latter one proved to decrease quickly with an increase in inhibitor concentration. This behaviour resulted from the fact that the inactive complex EI was not a product of internal inversion but was formed in the reaction: 2/3I + EI-->(EI.2/3I). The dissociation constant of this complex is equal to about 0.3 x 10(-3) (mol dm-3)2/3.

Development of urease-chitosan membrane.

Urease was covalently immobilized on glutaraldehyde-pretreated chitosan membrane. The optimum immobilization conditions were determined with respect to glutaraldehyde pretreatment of membranes (concentration and pH of glutaraldehyde solution, time of membrane-glutaral-dehyde reaction) and to reaction of glutaraldehyde-pretreated membranes with urease (concentration and pH of urease solution). The obtained membrane has high enzymatic activity, and can be applied for enzymatic removal of urea e.g. in the treatment of chronic or acute uraemia.

Urease immobilized on chitosan membrane: preparation and properties.

Urease was covalently immobilized on glutaraldehyde-pretreated chitosan membranes. The optimum immobilization conditions were determined with respect to glutaraldehyde pretreatment of membranes and to reaction of glutaraldehyde-pretreated membranes with urease. The immobilized enzyme retained 94% of its original activity. The properties of free and immobilized urease were compared. The Michaelis constant was about five times higher for immobilized urease than for the free enzyme, while the maximum reaction rate was lower for the immobilized enzyme. The stability of urease at low pH values was improved by immobilization; temperature stability was also improved. The optimum temperature was determined to be 65 degrees C for the free urease and 75 degrees C for the immobilized form. The immobilized enzyme had good storage and operational stability and good reusability, properties that offer potential for practical application.

Extraction of Cu(II) from hydrochloric acid media by Amberlite LA-1 hydrochloride dissolved in 1,2-dichloroethane.

The extraction of hydrogen chloride by a secondary amine (B), Amberlite LA-1, dissolved in 1,2-dichloroethane was studied by two-phase potentiometric titration. The results, treated by a general minimizing program, indicate dimerization: 2BHClright harpoon over left harpoonright harpoon over left harpoon(BCHl)(2). The equilibrium constant of this reaction was calculated. The extraction of cu(II) from 6M hydrochloric acid by Amberlite LA-1 hydrochloride (BCHl) dissolved in 1,2-dichloroethane, was also studied. The extraction of cu(II) can be explained as due to formation of two species, (BCHl)(2) CuCl(2) and (BCHl)(3) CuCl(2), in the organic phase. The formation constants of these species were calculated.

The extraction of Zn(II), Cd(II) and Pb(II) from hydrochloric acid media by amberlite LA-2 hydrochloride dissolved in 1,2-dichloroethane.

The extraction of HC1 by the secondary amine (B), known as Amberlite LA-2, dissolved in 1,2-dichloroethane and the aggregation of BHC1 have been studied by using a two-phase potentiometric titration technique. The experimental data, treated by a general minimizing program, indicate dimerization: 2 BHClright harpoon over left harpoon(BHCl)(2). The equilibrium constant of this reaction was calculated. The extraction of ZnCl(2), CdCl(2) and PbCl(2) from 0.2,0.5, 1.0 and 2.0M HCl, and 1MNaCl by Amberlite LA-2 hydrochloride (BHCl), dissolved in 1,2-dichloroethane, has been studied. The complexes (BHCl)(2)ZnCl(2), (BHCl)(2)CdCl(2) and (BHCl)(2)PbCl(2) were found to exist, irrespective of the composition of the aqueous phase. The formation constant of the first was calculated.

[Porous tarflen as a possible membrane material for membrane blood oxygenators. III. O2 and CO2 transport in the system modeling an artificial lung]. / Porowaty tarflen jako ewentualny material membranowy w oksygenatorach membranowych krwi. Czesc III. Transport O2 i CO2 w ukladzie modelujacym sztuczne pluco.

Diffusional examinations of tarflen porous barriers of home make and porous teflon membranes of American make as well as selected nonporous membranes were performed in a system: O2--barrier--water + CO2, in order to evaluate the influence of aqueous phase on O2 and CO2 transport rate through barriers listed above. It was found that the effectiveness of O2 and CO2 exchange through the porous barriers in the examined system is controlled by O2 transport through the boundary water layer in contradistinction to the nonporous membranes. The effect of reduction of O2 and CO2 transport through the porous barriers, caused by the aqueous phase was noted. The higher the water pressure on a barrier the larger the effect is. Considerable water permeability of porous barriers as compared to that of nonporous membranes was stated. The results of the performed examinations indicate the usefulness of porous tarflen materials as a membrane material in membrane oxygenators of blood.

[Porous tarflen as a possible membrane material in membrane blood oxygenators. I. Structural properties]. / Porowaty tarflen jako ewentualny material membranowy w oksygenatorach membranowych krwi. Czesc. I. Wlasciwosci strukturalne.

Hydrophobic porous teflon membranes are one of the most promising types applied in membrane oxygenators. The usefulness of porous tarflen materials (tarflen--Polish name of teflon produced by Zaklady Azotowe in Tarnów, Poland) for this application was evaluated by comparing their properties with those of American porous teflon membranes used in membrane oxygenators. Structural properties of tarflen materials were examined. The character of the surface of the examined materials is shown in the scanning electron micrographs. Tests of wettability of the materials by water, plasma and blood were also performed. It was found all the studied tarflen samples are macroporous. Their structure, as compared to the other materials, is simple. Values of water entry pressure show that the best tarflen samples for application in membrane oxygenators are those which are made of the smallest fraction of granulated tarflen product. It was found that plasma proteins do not adsorb on the tarflen surface.

[Membrane oxygenators of the blood]. / Oksygenatory membranowe krwi.

The development, application and construction of membrane oxygenators are reviewed. Although far from the perfection of the natural lung whose "poor" copy they are, these oxygenators represent an important stage of development of extracorporeal oxygenation of blood. From among the designs proposed so far these oxygenators are the least traumatic to blood, particularly as compared with the direct contacting oxygenators (bubbles and films oxygenators) and are the only ones suitable for long term clinical application in pulmonary and cardiac insufficiency treatment. Silicones are the most frequently used membrane material. The search for new membrane materials of high respiratory gases permeability as well as good blood compatibility is, apart from the studies on new designs, the main area of investigation on membrane oxygenators. Porous teflon membranes seem to be the most promising material.