Biomedical subjects
Publications and source records attributed to M Zajac.
The stability of the lyophilized substance of cefodizime disodium was investigated. The test for the stability in solid state with and without presence of humidity was arried out by the HPLC method. Kinetic and thermodynamic parameters of the decomposition reaction were calculated.
The overall apparent first-order rate constants for the reaction of autoxidation of Narcotine (NC) - k1 and Cotarnine (CT) - k2 and the rate constants for autoxidation of the protonated (ks) and undissociated (kb) forms have been determined. The kinetic equation for the reaction of autoxidation at constant concentration of NC, CT and the atmospheric oxygen depending on the pH of the reaction medium has been established as: k1 = ks([H+]/([H+]+K'a))+kb(K'a/([H+]+K'a), k2=(ks[H+]+K'a))+kb (K'a/([H+]+K'a) (1+1+1/kt+1K)). The following thermodynamic parameters for the rate constants ks and kb have been calculated: deltaH not equal to, log A and deltaS not equal to.
General first-order rate constants for autoxidation of sulfadiazine, sulfamerazine, sulfadimidine, sulfaperine and sulfamethoxydiazine in the air oxygen atmosphere, in solutions of pH 4-7, at 403, 411 and 418 K were determined from the absorbance measurements in 0-1 mole/dm3 HCl at 243 or 333 nm, using the so-called "subtraction technique". The thermodynamic parameters of this reaction were determined (deltaHa, deltaH not equal to, deltaS not equal to, deltaG not equal to and logA). The effect of the substituents in positions 4, 5 and 6 of the pyrimidine ring on the rate of autoxidation was interpreted in terms of the Hammett equation.
The following products of acid hydrolysis of sulfadimidine (SDMP) were isolated and identified: sulfanilic acid (Sac), sulfanilamide (SA), 2-amino-4, 6-dimethylprimidine (ADMP) and 2-hydroxy-4, 6-dimethylpyrimidine (HDMP). The apparent first-order rate constants (k1, k2 and k3) were determined for the reaction: (formula: see text). The catalytic rate constants kH+ = ki/[H+] and the thermodynamic parameters delta Ha, delta H not equal to, deltaS not equal to, deltaG not equal to and log A were also determined for that reaction.
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In the experiments carried out on 94 rats the role of the function of gastric mechanoreceptors in the regulation of food and water intake was studied. We tried to assess whether this mechanoreception could serve as reinforcement in the induction of an instrumental feeding reflex. Distension of the stomach with a balloon inhibited significantly food intake in free consumption as well as in the instrumental reflex. On the other hand, no such effect was observed on water intake. The trial of development of an instrumental food reflex reinforced with stomach distension gave a negative result. The obtained results are explained as due to an ontogenetically fixed specific mode of food and water intake, and a modified concept of reduction-drive of reinforcement as proposed by Konorski is tentatively suggested for this explanation.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
The products of spontaneous hydrolysis of sulfadimidine are: sulfanilamide, aniline, 2-hydroxy- 4,6-dimethylpyrimid and ammonium carbonate. The mechanism of spontaneous hydrolysis of sulfadimidine is proposed.
General, k, and specific, k1 and k2, first-order rate constants for the parallel reaction of hydrolysis catalized by H+ ions were estimated for sulfadiazine (I), sulfamerazine (II), sulfadimidine (III), sulfaperine (IV) and sulfamethoxydiazine (V), hydrolyzed in 1 mole/dm3 HCl at 333, 343, 355 and 363 K. General first-order rate constants for the spontaneous hydrolysis of I--V in borate buffer pH 9.20 at 403, 411 and 418 K were also determined. Thermodynamic parameters of the reaction (delta Ha, deltaH not equal to, deltaS not equal to, deltaG not equal to and log A) were calculated. The effect of substituents in positions 4, 5 and 6 of the pyrimidine ring on the rate of hydrolysis was interpreted in terms of Hammett equation.
In 79 rats with chronically implanted gastric tubes or thermodes the participation of pharyngo-oesophageal thermoreception was investigated in the process of development of a water-reinforced conditioned instrumental reflex. It was found that only cooling of the pharynx and oesophagus was an effective stimulus reinforcing instrumental conditioning. The conditioned reflex could not be developed when the reinforcing stimulus was the sensation of warmth in the throat and oesophagus, and gastrointestinal interoception. It is suggested in the discussion that cold thermoreception in the area of the throat and oesophagus has acquired its reinforcing character through conditioning.
The rates of hydrolysis of beta-lactam ring of dicloxacillin (DC) in the pH range 1.10-9.65 at 293, 303 and 313 K were determined. Specific rate constants were calculated for: H degree ions, undissociated phosphoric acid and H2PO4- ions catalysis of hydrolysis of undissociated DC molecule; for H+, OH-, HPO4(-2) and CH3COO- ions and undissociated phosphoric and acetic acids catalysis of hydrolysis of dissociated DC species and spontaneous hydrolysis of dissociated DC species. For each process the thermodynamic parameters were determined.
Ampicillin sodium salt degradation in solid state relies on a sequential reaction consisting of three pseudo first-order processes. The above salt is much more susceptible to degradation than acidic forms of ampicillin. The anhydrous acidic form of ampicillin is very stable in solid phase. Therefore, it can be recomended to be formulated in peroral ampicillin pharmaceutical preparations. Ampicillin trihydrate, now used in pharmaceutical formulations, is less stable than the last mentioned compound. It degrades according to Prout-Tompkins' model.
The kinetics of hydrolysis of ceftazidime in aqueous solutions at 323 K, 333 K, 343 K and 353 K over the pH-range (0.43-9.76) and at 295 K, 303 K and 308 K over the pH-range (9.17-13.16) has been investigated. The decomposition was followed by HPLC and UV spectral methods. The pH-rate profile was accounted for by the specific acid catalyzed reactions and also by assuming spontaneous water-catalyzed decomposition of molecule ceftazidime in various grade of dissociation. Various buffer substances were found to exhibit general acid and base catalysis of the degradation. Thermodynamic parameters of the reaction: energy, entropy and enthalpy of activation and the frequency factor for the specific rate constants were determined.
The kinetics of degradation of ceftazidime in aqueous solutions containing various carbohydrates (glucose and fructose) or polyhydric alcohols (sorbitol and mannitol) was investigated over the pH range 9.92-10.93 at 35 degrees C. A relationship between the degradation rate and the hydroxy compound concentration was observed at each pH studied, and the rate-accelerating effect of the compounds was directly proportional to the hydroxide ion activity.
Degradation of ceftazidime in aqueous solutions was studied at 298 K in acidic, basic and neutral conditions. The subsequent stage of hydrolysis involved the hydrolysis of the group at C-3, opening of the beta-lactam ring, and epimerization at C-6 or C-7. The decomposition of ceftazidime and the formation and identification of product C (pyridine) was followed by HPLC.