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I Fábián

Publications and source records attributed to I Fábián.

11 recordsLinked to original sources
PubMed2001

Kinetics and mechanism of catalytic decomposition and oxidation of chlorine dioxide by the hypochlorite ion.

The oxidation of ClO(2) by OCl(-)is first order with respect to both reactants in the neutral to alkaline pH range: -d[ClO(2)]/dt = 2k(OCl)[ClO(2)][OCl(-)]. The rate constant (T = 298 K, mu = 1.0 M NaClO(4)) and activation parameters are k(OCl) = 0.91 +/- 0.02 M(-1) s(-1), DeltaH = 66.5 +/- 0.9 kJ/mol, and DeltaS(++) = -22.3 +/- 2.9 J/(mol K). In alkaline solution, pH > 9, the primary products of the reaction are the chlorite and chlorate ions and consumption of the hypochlorite ion is not observed. The hypochlorite ion is consumed in increasing amounts, and the production of the chlorite ion ceases when the pH is decreased. The stoichiometry is kinetically controlled, and the reactants/products ratios are determined by the relative rates of the production and consumption of the chlorite ion in the ClO(2)/OCl(-) and HOCl/ClO(2)(-) reactions, respectively.

Journal Article↗
PubMed2000

Kinetics and mechanism of complex formation reactions in the Iron(III)-phosphate ion system at large iron(III) excess. Formation of a tetranuclear complex.

The kinetics and mechanism of the iron(III)-phosphate ion reaction were studied at large iron(III) excess using the stopped-flow method at 10.0 degrees C in 1.0 M NaClO4. In the first few hundred milliseconds of the reaction, the formation of a novel tetranuclear complex was confirmed. The following composition is proposed for the new species: Fe4(PO4)(OH)2(H2O)16(7+). According to detailed kinetic studies, the formation of this species is first order with respect to Fe2(OH)2(H2O)8(4+) and H2PO4- and presumably proceeds via a dinuclear intermediate species. At longer reaction times slow dissociation of the tetranuclear complex controls the formation of the thermodynamically favored Fe(PO4)(H2O)5 complex. The overall reaction was interpreted in terms of the following reactions: Fe2(OH)2(H2O)8(4+) [symbol: see text] 2Fe3+ mn; Fe2(OH)2(H2O)8(4+) + P(V) [symbol: see text] Fe2PV; Fe2PV + Fe2(OH)2(H2O)8(4+) [symbol: see text] Fe4PV; Fe3+ mn + P(V) [symbol: see text] Fe(PO4)(H2O)5. (Fe3+ mn = Fe(H2O)6(3+) + Fe(OH)(H2O)5(2+); P(V) = H3PO4 + H2PO4-; Fe2PV = Fe2(HPO4)(OH)(H2O)8(3+); Fe4PV = Fe4(PO4)(OH)2(H2O)16(7+).) The pH dependence and relevant rate and equilibrium constants are reported for the individual reaction steps.

Journal Article↗
PubMed2000

Thermodynamic, kinetic and structural studies on the ternary palladium(II) complexes of thioether ligands.

Potentiometric, calorimetric, NMR and stopped-flow kinetic studies were performed on the palladium(II) complexes of thioether and/or nitrogen donor ligands. The ternary systems always contained a tridentate ligand (dien, terpy and dianions of dipeptides, GlyGly, GlyAla and GlyMet) and a monodentate thioether (AcMet). The stability constants of thioether complexes were obtained by indirect potentiometric measurements using uridine as a competitive ligand. The thermodynamic parameters revealed that selectivity of palladium(II) for thioether binding can be significantly influenced by the other donor atoms around the metal ion. [Pd(terpy)]2+ and [Pd(GlyMet)] had the lowest affinity for thioether binding and it was explained by steric and electronic effects. Ternary complexes of nitrogen donors have higher thermodynamic stability constants than the thioether complexes, but rate constants of the substitution reactions revealed that formation of thioether complexes is the faster reaction. As a consequence, the thermodynamic equilibrium state of a multicomponent system is characterized by the coordination of N-donors, which are formed via the existence of thioether-bonded intermediates.

Calorimetry↗
PubMed1998

The determination of benzalkonium chloride in eye-drops by difference spectrophotometry.

A direct, extraction-free spectrophotometric method was developed for the determination of benzalkonium chloride (BAC) in various eye-drops. The procedure is based on ion-pair formation between BAC and 2',4',5',7'-tetrabromofluorescein (eosin-Y) which decreases the absorbance and induces a bathochromic shift of the maximum in the eosin-Y spectrum. The effects of pH, excess of reagent and ionic strength on the ion-pair formation have been studied in detail. At pH 4.40 and 9.62, the working curve is linear in the 1.98 x 10(-6) to 2.40 x 10(-5) M (0.7-8.5 microg cm[-3]) concentration range; however, the sensitivity drops to about one third in the basic solution. At pH 4.40, the analytical signal is stable for more than 60 min, while at pH 9.62 the signal changes in time and reaches the maximum value 3 min after mixing the reagent and the sample. When the active substance is beta-5-isopropyl-2'deoxyuridine and the sample contains typical additives, the reproducibility of the analytical signal at pH 4.40 is R.S.D. = 2.36% (n = 81). In the case of such samples, the linearity of the method is somewhat dependent on the composition, but generally acceptable at the 50-150% concentration levels. Eye-drops containing tobramycin, an aminoglycoside-type antibiotic, as the active substance were analyzed at pH 9.62. This was necessary to avoid strong interference from the analyte in acidic solution. In this case the linearity of the method is limited to a narrower concentration range; however, the recovery is still acceptable at the 100% level.

Benzalkonium Compounds↗
PubMed1996

Determination of vitamin C in effervescent tablets containing other vitamins together with trace elements.

A simple, rapid method is reported for the determination of vitamin C in effervescent tablets containing other vitamins and several trace elements such as Mg(II), Zn(II), Fe(II), Mn(II), Cu(II) and Mo(VI). The procedure was developed on the basis of the bromate ion-iodide ion-ascorbic acid clock reaction (Landolt reaction). Interference effects of air oxygen and metal ions and the role of pH are discussed in detail.

Ascorbic Acid↗
PubMedDate not supplied

Esophageal dysfunction in diabetes mellitus.

Detailed roengenological examinations of the esophagus were carried out in 110 diabetics and 130 controls. In 50 (45%) diabetic patients functional abnormalities were detected. Wavy esophageal contours, irregular spontaneous contractions and functional diverticula were observable. In diabetes, these changes occurred at an earlier age and more frequently than in controls. Esophageal transit time was markedly prolonged. The clinical symptoms of dysphagia were usually mild or absent. Diabetic dysphagia is one of the manifestations of diabetic visceral neuropathy. It is attributed mainly to the diabetic damage of the vagus nerve.

Adult↗
PubMedDate not supplied

[Model studies on the transport processes of anticancer platinum complexes].

Potentiometric, calorimetric, NMR and stopped-flow kinetic studies were performed on the palladium(II) complexes of thioether and/or nitrogen donor ligands. The ternary systems always contained a tridentate ligand (dien, dipic, terpy and dianions of dipeptides, GlyGly, GlyAla and GlyMet) and a monodentate thioether (AcMet). The stability constants of thioether complexes were obtained by indirect potentiometric measurements using uridine as a competitive ligand. The thermodynamic parameters revealed that selectivity of palladium(II) for thioether binding can be significantly influenced by the other donor atoms around the metal ion. [Pd(terpy)]2+, [Pd(dipic)]2+ and [Pd(GlyMet)] had the lowest affinity for thioether binding and it was explained by steric and electronic effects. Ternary complexes of nitrogen donors have higher thermodynamic stability constants than that of the thioether complexes, but rate constants of the substitution reactions revealed that the formation of thioether complexes is the faster reaction. As a consequence, the thermodynamic equilibrium state of a multicomponent system is characterized by the coordination of N-donors, which are formed via the existence of thioether bonded intermediates.

Antineoplastic Agents↗