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| Identifier |
uch.med.phd//2001alegakis |
| Title |
Συμπολυμερή της βινυλοπυρρολιδόνης ως αντίδοτα εξωγενών ουσιών: παρασκευή και φυσικοχημικές μελέτες |
| Alternative Title |
Copolymers of vinylpyrrolidone as antidotes of exogenous subastances. Preparation and phycicochemical properties |
| Creator |
Alegakis, Athanasios
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| Abstract |
The main purpose of the presented study concerns the preparation of new polymeric material for the inactivation of mycotoxins. The binding of mycotoxins is achieved through adsorption phenomena. It was also studied the adsorption of the widely used antibiotics in veterinary, oxytetracycline and chlortetracycine on activated charcoal. The dissertation is divided into four sections. In the first section the adsorption of oxytetracycline and chlortetracycline on activated charcoal is studied. Tetracyclines are antibiotics with a wide antimicrobial spectrum which make them useful in veterinary. Their use is not only concerns diseases but they are used and as chemoprophylactic agents. They are also used as a growth factor and in some cases as an antifungal factor. Activated charcoal has been experimentally studied as an antifungal agents against mycotoxicoses. It is a material used -not very extensively- alone or in combination with vitamins, antibiotics in case of mycotoxicoses. The simultaneous use of these agents -tetracycline and activated charcoal can be justified as inappropriate according to the results of the in vitro experiments presented. The kinetics and the isothermal adsorption were studied. The adsorption was studied in vitro in conditions where the stomach pH (2.35) is simulated and experimental temperature was at room temperature. The kinetics showed that adsorption equilibrium was reached in one (1) hour. The use of a second order equation and its extremely good fitting shows that the rate of adsorption is high. In the same conclusions we reach using exponential equations with two terms.The quantity of the adsorbed antibiotics to the initial quantity of antibiotics is very high at the start of the adsorption (~60% is adsorbed in less that a minute) in comparison the rest time (35% in 50 minutes approximately). Experiments of isothermal adsorption showed that great quantities of the antibiotics adsorbed per gram of activated charcoal, (oxytetracycline and chlortetracycline 402 mg/g and 397 mg/g respectively. For the calculation of the absorption capacities Freundlich and Langmuir isotherms were used, while the second showed a better fiting. The resulted chemical constants showed a strong binding (Koxytetracycline = 150.5 Kg/L, Kchlortetracylcine= 125.3 Kg/L). Same results were resulted when Freundlich isotherm is used. The similar values that calculated for parameters qads/m and K were expected due to similarities in terms of chemical structrure and molecular geometry. The procedure of the polymeric deactivators' synthesis is presented in the second section. The synthesized copolymers belong to the cross linked cryogels of PVP with methylene-bisacrylamide as a crosslinker. They were synthesized at temperatures ranging from -12οC to -20 oC, using varous catalysts (TEMED, K2S2O8 and (NH4)2S2O8). The cryogels differed at the %content of methylene-bisacrylamide molecules, the quanity of the used catalysts and the polymerization time interval. The produced structures exhibit great hydration capacities. The hydration capacity of the produced polymers was studied and it gave high values (400%-1400% at time interval of 2 h). No relation between the synthesis parameters and the hydration or asdorption capacities of the polymers was obtained. That suggested that the adsorption capacities should be studied in relation to the structure of the produced cryogels. (active surface area, number and distribution of the pores etc). The porous structure of the cryogels may be attributed to the water crystals formed at these extremely low temperatures. The effect of the produced cryogels on the mycotoxins ochratoxin-A, zearalenone and T-2 toxin is studied in the third section. The conditions of the in vitro experiments resembled these of the intestinal environment (pH=7.3 and temperature T = 37οC). The experiments of this section aimed to access the adsorption capacity of polymers and compare this to the adsorption capacity of other adsorptive polymers, such as crosslinked PVP (Polyplasdone), bentonite and activated charcoal. The study was conducted using a set quantity of each toxin and of each adsorptive material. The stability of the mycotoxins in solution and at various temperatures was also studied. Zearalenone and ochratoxin A where stable under the used experimental conditions while T-2 toxin was not. Activated charcoal exhibited the greatest adsorption capacity. It reduced the quantity of the mycotoxins to below levels of detection of the liquid chromatography method used. Polyplasdone gave adsorption values around 483 μg/g for zearalenone and 200 μg/g for ochratoxin. The polymeric cryogels gave adroption values ranging from 345-490 μg/g for zearalenone and from 170 to 316 μg/g for ochratoxin Α. One cryogel gave adroption values of 1266 μg/g for zearalenone and 1184 μg/g for ochratoxin Α. Zearalenone was adsrbed to a greater extend than ochratoxin Α by most cryogels and this was indicated by the statistically significant differences observed. The estimation of the kinetics and the isothermal adsorption on selected forms of cryogels was conducted in the fourth section. Kinetics of adsorption was studied for the CPVP11 cryogels on various mycotoxins, using exponential growth equations and a second order equation, while the last showed the better results. Independently to the kinetic model it is resulted that the adsorption process has high rates. It is claimed that the best fitting of the second order model shows that adsorption process has two stages. It was supposed that the first stage -which was the quicker- the substances are adsorbed on the cryogels' surface, in the second stage substanes were diffused through the inner surface. Isothermal studies caried using various quantities of adsorptive materials, as well as various concentrations of mycotoxins. The equations Langmuir and Freundlich were utilised for the fitting of the results. The second one gave better results in the cases of ochratoxin adsorption while the first gave the best results in the systems of zearalenone-cryogels systems. The better fitting of the Freundlich equation indicates that the surface area of the polymers is heterogenious with more than one-attachment groups. The Langmuir isotherm gave better results at higher concentrations of polymers, maybe due to the incomplete coverage of the attachment groups. Cryogel CPVP11 exhibited better adsorption capacity for ochratoxin A k= 5038 μg/g and n= 0.877. The calculated constants k in the cryogel-ochratoxin A systems ranged from 98-141 μg/g. The Langmuir isotherm calculated the adsorption capacities of cryogels CPVP1 and CPVP2 as 1212 and 1089 μg/g respectively. The values given by the Freundlich isotherm for the same systems were 579 and 743 μg/g respectively. Chemical kinetic studies conducted for mycotoxin solutions with polymer CPVP11, using 1st order kinetic with one and two terms. In both cases we satisfactory fittings were obtained. (R2 > 0.990). Irrespective of the model used, we can say that adsorption takes place at a very fast pace. As indicated by the better fitting of the model with two parameters, the adsorption processes happen at two steps. We may assume that in the first step, which is the fastest one the substance gets attached to the surface of the cryogel, while in the second step the molecules of the substance diffuse in the porous material of the polymer. To summarise the results of the in vitro experiments indicate that the synthesised cryogels may be used satisfactorily in order to combat the problem of mycotoxins.
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| Issue date |
2001-05-01 |
| Date available |
2001-08-02 |
| Collection
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School/Department--School of Medicine--Department of Medicine--Doctoral theses
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Type of Work--Doctoral theses
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| Permanent Link |
https://elocus.lib.uoc.gr//dlib/c/6/c/metadata-dlib-2001alegakis.tkl
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| Views |
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