István Nagypál - Academia.edu (original) (raw)
Papers by István Nagypál
The equilibrium constant for the hydrolytic disproportionation of I 2
The Journal of Physical Chemistry A, 2008
The Dushman reaction taking place after the abrupt change of the absorbance in the Landolt reacti... more The Dushman reaction taking place after the abrupt change of the absorbance in the Landolt reaction was followed by monitoring the concentration of triiodide spectrophotometrically in buffered solutions. The joint evaluation of the experimental data on the kinetic system (Landolt) and subsystem (Dushman) has revealed that the inverse of the Landolt induction time (t i ) is proportional to the combination of the concentration and the square of the concentration of both the iodide and hydrogen ions, while the inverse of t i is linearly proportional to the iodate concentration. The hydrogen sulfite dependence, however, is found to be more complex; the Landolt induction time goes through a minimum as a function of hydrogen sulfite concentration; the phenomenon that has not been reported yet. A kinetic model is suggested in which the rate law of both the Landolt and Dushman reactions is supplemented to take all the characteristics of the measured curves into account. It is demonstrated that the supercatalytic term of the Landolt reaction with respect to hydrogen ion discovered recently and the rate term of the Dushman reaction being first order with respect to iodide ion play an important role in explaining the dependencies of the Landolt induction period.
The Journal of Physical Chemistry A, 2003
The kinetics of decomposition of aqueous chlorous acid has been reinvestigated at pH 0.7-1.9, ion... more The kinetics of decomposition of aqueous chlorous acid has been reinvestigated at pH 0.7-1.9, ionic strength 1.0 M (HSO 4 -/SO 4 2-), and temperature 25.0 ( 0.1°C. Optical absorbances were collected in the 240-450 nm wavelength range for up to ∼90% decomposition for time series lasting as long as 2 days. The number of absorbing species was investigated by matrix rank analysis; no absorbing intermediate was formed in significant concentration during the decomposition. Of the many mechanistic models tested, the one that fit best included the following reactive intermediates: HOCl, Cl 2 O 2 , Cl 2 O 3 , • ClO, • OH. The stoichiometric ratio of ClO 2 produced to Cl(III) consumed varies with pH and [Cl -]. Reaction of Cl 2 O 3 with Cl(III) yields chlorate exclusively. Reaction of Cl 2 O 3 with Clfavors ClO 2 over chlorate, but does not entirely exclude chlorate, because it is produced by hydrolysis of Cl 2 O 2 . Invoking Cl 2 O 3 explains the variation in stoichiometric ratio as well as the maximum observed in the initial rate of ClO 2 formation as a function of pH. The kinetics of chlorous acid decomposition cannot be quantitatively fit through the last stages of the reaction without postulating a first-order decomposition. Scission of chlorous acid to give short-lived hydroxyl and chlorine-(II) monoxide is a plausible route for this process. A set of best-fit and literature-derived parameters is presented for the complete mechanism.
The Journal of Physical Chemistry A, 2010
The thiosulfate-iodate reaction has been studied spectrophotometrically in slightly acidic medium... more The thiosulfate-iodate reaction has been studied spectrophotometrically in slightly acidic medium at 25.0 ( 0.1°C in acetate/acetic acid buffer by monitoring the absorbance at 468 nm at the isosbestic point of iodine-triiodide ion system. The formation of iodine after the Landolt time follows a rather complex kinetic behavior depending on the pH and on the concentration of the reactants as well. It is shown that the key intermediate of the reaction is I 2 O 2 , its equilibrium formation from the well-known Dushman reaction along with their further reactions followed by subsequent reactions of HOI, HIO 2 , S 2 O 3 OH -, and S 2 O 3 Iadequately accounts for all the experimentally measured characteristics of the kinetic curves. A 19-step kinetic model is proposed and discussed with 13 fitted and 7 fixed parameters in detail.
The Journal of Physical Chemistry A, 2008
Based on the modified kinetic model of the Landolt and the Dushman reactions published recently, ... more Based on the modified kinetic model of the Landolt and the Dushman reactions published recently, an exact expression has been derived for the concentration dependence of the Landolt time. It is also shown that all the apparently contradictory formulas, regarding the concentration dependence of the Landolt time, reported previously at quite different experimental circumstances can easily be reconciled from the simplification of the newly proposed equation. It also means that the formula derived may satisfactorily be applied to calculate the Landolt time basically with no restrictions for the concentration of the reactants.
The Journal of Physical Chemistry A, 2008
The copper(II)-3-pyridylmethanol (L) system was investigated in aqueous solution by two-dimension... more The copper(II)-3-pyridylmethanol (L) system was investigated in aqueous solution by two-dimensional ESR evaluation at 298 K, and computer simulation of the individual anisotropic spectra at 77 K. The data revealed that the paramagnetic copper(II) complexes [CuL] 2+ , [CuL 2 ] 2+ , [CuL 3 ] 2+ , and [CuL 4 ] 2+ are formed up to pH ≈ 7 at a moderate or high excess of ligand. As compared with chelating ligands, two differences were observed for the complexation of 3-pyridylmethanol with copper(II): (1) In contrast with the well-resolved spectra in frozen solution, considerable line-broadening and distortion of the spectral shapes were seen at 298 K, which was interpreted in terms of isomeric equilibria and the medium-rate interconversion of various complexes on the ESR time-scale. (2) At low temperature, there were dramatic changes in the concentration distribution, the minor complexes with higher numbers of coordinating ligands ([CuL 3 ] 2+ and in particular [CuL 4 ] 2+ ) becoming strongly favored. This phenomenon is explained by the significant differences in the formation enthalpy values of various species, shifting the equilibria according to the van't Hoff equation, and a significant undercooling in the course of fast freezing of the solution, which enhances the changes of the concentration distribution.
Reaction Kinetics and Catalysis Letters, 1990
Most liquid phase autoxidation processes are autocatalytic and characterized by radical chain mec... more Most liquid phase autoxidation processes are autocatalytic and characterized by radical chain mechanisms. These features may result in exotic kinetic behavior, such as bistability, oscillation and propagating reaction fronts. Oscillations has
Improved calibration and use of stopped-flow instruments
Physical Chemistry Chemical Physics, 2000
The calibration procedure of stopped-flow instruments based on the dead-time concept has been imp... more The calibration procedure of stopped-flow instruments based on the dead-time concept has been improved. It is proved theoretically and shown experimentally that the dead-time is not a simple instrumental parameter; it depends on the rate of the reaction. Two new parameters are ...
Great Structural Variety of Complexes in Copper(II)−Oligoglycine Systems: Microspeciation and Coordination Modes as Studied by the Two-Dimensional Simulation of Electron Paramagnetic Resonance Spectra
Journal of the American Chemical Society, 2003
A series of isotropic EPR spectra recorded at various concentrations and pH (in the range 2-12) o... more A series of isotropic EPR spectra recorded at various concentrations and pH (in the range 2-12) on equilibrium systems containing copper(II) and diglycine, triglycine, or tetraglycine were analyzed. A purely mathematical method, matrix rank analysis gave the number of independent EPR-active species. Two-dimensional evaluation then resulted in the formation constants and magnetic parameters of 14 metal complexes (including microspecies) in each system. The independent paramagnetic species formed with each ligand are as follows: Cu(2+) (aqua complex), [CuLH](2+), [CuL](+), [CuLH(-1)], [CuLH(-2)](-), [CuL(2)H(2)](2+), [CuL(2)H](+), [CuL(2)], [CuL(2)H(-1)](-), and [CuL(2)H(-2)](2-). Moreover, for diglycine, the diamagnetic complex [Cu(2)L(2)H(-3)](-), and for triglycine and tetraglycine, the EPR-active species [CuLH(-3)](2-) were identified. Further, equilibria of two microspecies were demonstrated for [CuL(2)], [CuL(2)H(-1)](-), and [CuL(2)H(-2)](2-). The magnetic parameters allowed a detailed description of the coordination modes. The most important findings: (1) For the mono complexes, the in-plane sigma-bonds between copper(II) and the equatorial N donors are particularly strong when the same ligand forms several adjacent chelate rings with the participation of amino N, deprotonated peptide N(s), and the carboxylate group. (2) Structures with coupled chelate rings are likewise favored in the bis complexes. Different protonation states of the two ligands are observed in the major isomer of [CuL(2)] ((LH(-1) + LH) coordination), and in the isomers of [CuL(2)H(-2)](2-) ((LH(-2) + L) coordination) for triglycine and tetraglycine.
Stochastic behavior and stirring rate effects in the chlorite–iodide reaction
The Journal of Chemical Physics, 1988
The autocatalytic reaction between chlorite and iodide ions in a closed system is a clock reactio... more The autocatalytic reaction between chlorite and iodide ions in a closed system is a clock reaction, showing a sudden appearance of brown I followed by a rapid disappearance of the color. Under certain conditions, the reaction time displays a striking irreproducibility. This ...
Sensitivity analysis of multiple chemical equilibria: Sensitivity coefficients and response equilibria
The Journal of Chemical Physics, 1995
ABSTRACT
Peculiar kinetics of the complex formation in the iron(III)-sulfate system
International Journal of Chemical Kinetics, 2008
The formation of iron(III)sulfate complexes has been studied by several researchers. Whiteker an... more The formation of iron(III)sulfate complexes has been studied by several researchers. Whiteker and Davidson 1 found spectrophotometrically that both FeSO and Fe(SO 4 ) species are formed at pH 0. Lister and Rivington 2 stated that FeHSO and Fe(SO 4 )(HSO 4 ) species also ...
Inorganic Chemistry, 2008
The effect of chloride ion on the chlorine dioxide formation in the ClO 2 --HOCl reaction was stu... more The effect of chloride ion on the chlorine dioxide formation in the ClO 2 --HOCl reaction was studied by following · ClO 2 concentration spectrophotometrically at pH 5-6 in 0.5 M sodium acetate. On the basis of the earlier experimental data collected without initially added chloride and on new experiments, the earlier kinetic model was modified and extended to interpret the two series of experiments together. It was found that the chloride ion significantly increases the initial rate of · ClO 2 formation. At the same time, the · ClO 2 yield is increased in HOCl but decreased in ClO 2 excess by the increase of the chloride ion concentration. The two-step hydrolysis of dissolved chlorine through Cl 2 + H 2 O H Cl 2 OH -+ H + and Cl 2 OH -H HOCl + Cland the increased reactivity of Cl 2 OHcompared to HOCl are proposed to explain these phenomena. It is reinforced that the hydrolysis of the transient Cl 2 O 2 takes place through a HOCl-catalyzed step instead of the spontaneous hydrolysis. A seven-step kinetic model with six rate parameters (constants and/or ratio of constants) is proposed on the basis of the rigorous least-squares fitting of the parameters simultaneously to 129 absorbance versus time curves measured up to ∼90% conversion. The advantage of this method of evaluation is briefly outlined.
Biochemistry, 1994
NF-M13 [H-(Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly)-OH], NF-M 17 [H-(Glu-Glu-Lys-Gly-... more NF-M13 [H-(Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly)-OH], NF-M 17 [H-(Glu-Glu-Lys-Gly-Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly)-OH] , and their phosphorylated derivatives, representing the C-terminal phosphorylation domain of the neurofilament protein midsize subunit, have four possible binding sites for metal ions: the COO-group of glutamate, the OH group of the serine
The Journal of Physical Chemistry A, 1997
We present a new method for the decomposition of an experimental absorbance matrix into concentra... more We present a new method for the decomposition of an experimental absorbance matrix into concentration and molar absorption coefficient matrices. The decomposition in general is not unambiguous; therefore, the method may yield only ranges for these matrices. The experimental matrix is not changed, so deviations from the original data can be monitored element by element. Consequently, all chemical constraints (such as stoichiometry) can be taken into account. The method, which does not require an explicit chemical model, is used to analyze the reaction between a Co(II)-EDTA complex and H 2 O 2 .
The equilibrium constant for the hydrolytic disproportionation of I 2
The Journal of Physical Chemistry A, 2008
The Dushman reaction taking place after the abrupt change of the absorbance in the Landolt reacti... more The Dushman reaction taking place after the abrupt change of the absorbance in the Landolt reaction was followed by monitoring the concentration of triiodide spectrophotometrically in buffered solutions. The joint evaluation of the experimental data on the kinetic system (Landolt) and subsystem (Dushman) has revealed that the inverse of the Landolt induction time (t i ) is proportional to the combination of the concentration and the square of the concentration of both the iodide and hydrogen ions, while the inverse of t i is linearly proportional to the iodate concentration. The hydrogen sulfite dependence, however, is found to be more complex; the Landolt induction time goes through a minimum as a function of hydrogen sulfite concentration; the phenomenon that has not been reported yet. A kinetic model is suggested in which the rate law of both the Landolt and Dushman reactions is supplemented to take all the characteristics of the measured curves into account. It is demonstrated that the supercatalytic term of the Landolt reaction with respect to hydrogen ion discovered recently and the rate term of the Dushman reaction being first order with respect to iodide ion play an important role in explaining the dependencies of the Landolt induction period.
The Journal of Physical Chemistry A, 2003
The kinetics of decomposition of aqueous chlorous acid has been reinvestigated at pH 0.7-1.9, ion... more The kinetics of decomposition of aqueous chlorous acid has been reinvestigated at pH 0.7-1.9, ionic strength 1.0 M (HSO 4 -/SO 4 2-), and temperature 25.0 ( 0.1°C. Optical absorbances were collected in the 240-450 nm wavelength range for up to ∼90% decomposition for time series lasting as long as 2 days. The number of absorbing species was investigated by matrix rank analysis; no absorbing intermediate was formed in significant concentration during the decomposition. Of the many mechanistic models tested, the one that fit best included the following reactive intermediates: HOCl, Cl 2 O 2 , Cl 2 O 3 , • ClO, • OH. The stoichiometric ratio of ClO 2 produced to Cl(III) consumed varies with pH and [Cl -]. Reaction of Cl 2 O 3 with Cl(III) yields chlorate exclusively. Reaction of Cl 2 O 3 with Clfavors ClO 2 over chlorate, but does not entirely exclude chlorate, because it is produced by hydrolysis of Cl 2 O 2 . Invoking Cl 2 O 3 explains the variation in stoichiometric ratio as well as the maximum observed in the initial rate of ClO 2 formation as a function of pH. The kinetics of chlorous acid decomposition cannot be quantitatively fit through the last stages of the reaction without postulating a first-order decomposition. Scission of chlorous acid to give short-lived hydroxyl and chlorine-(II) monoxide is a plausible route for this process. A set of best-fit and literature-derived parameters is presented for the complete mechanism.
The Journal of Physical Chemistry A, 2010
The thiosulfate-iodate reaction has been studied spectrophotometrically in slightly acidic medium... more The thiosulfate-iodate reaction has been studied spectrophotometrically in slightly acidic medium at 25.0 ( 0.1°C in acetate/acetic acid buffer by monitoring the absorbance at 468 nm at the isosbestic point of iodine-triiodide ion system. The formation of iodine after the Landolt time follows a rather complex kinetic behavior depending on the pH and on the concentration of the reactants as well. It is shown that the key intermediate of the reaction is I 2 O 2 , its equilibrium formation from the well-known Dushman reaction along with their further reactions followed by subsequent reactions of HOI, HIO 2 , S 2 O 3 OH -, and S 2 O 3 Iadequately accounts for all the experimentally measured characteristics of the kinetic curves. A 19-step kinetic model is proposed and discussed with 13 fitted and 7 fixed parameters in detail.
The Journal of Physical Chemistry A, 2008
Based on the modified kinetic model of the Landolt and the Dushman reactions published recently, ... more Based on the modified kinetic model of the Landolt and the Dushman reactions published recently, an exact expression has been derived for the concentration dependence of the Landolt time. It is also shown that all the apparently contradictory formulas, regarding the concentration dependence of the Landolt time, reported previously at quite different experimental circumstances can easily be reconciled from the simplification of the newly proposed equation. It also means that the formula derived may satisfactorily be applied to calculate the Landolt time basically with no restrictions for the concentration of the reactants.
The Journal of Physical Chemistry A, 2008
The copper(II)-3-pyridylmethanol (L) system was investigated in aqueous solution by two-dimension... more The copper(II)-3-pyridylmethanol (L) system was investigated in aqueous solution by two-dimensional ESR evaluation at 298 K, and computer simulation of the individual anisotropic spectra at 77 K. The data revealed that the paramagnetic copper(II) complexes [CuL] 2+ , [CuL 2 ] 2+ , [CuL 3 ] 2+ , and [CuL 4 ] 2+ are formed up to pH ≈ 7 at a moderate or high excess of ligand. As compared with chelating ligands, two differences were observed for the complexation of 3-pyridylmethanol with copper(II): (1) In contrast with the well-resolved spectra in frozen solution, considerable line-broadening and distortion of the spectral shapes were seen at 298 K, which was interpreted in terms of isomeric equilibria and the medium-rate interconversion of various complexes on the ESR time-scale. (2) At low temperature, there were dramatic changes in the concentration distribution, the minor complexes with higher numbers of coordinating ligands ([CuL 3 ] 2+ and in particular [CuL 4 ] 2+ ) becoming strongly favored. This phenomenon is explained by the significant differences in the formation enthalpy values of various species, shifting the equilibria according to the van't Hoff equation, and a significant undercooling in the course of fast freezing of the solution, which enhances the changes of the concentration distribution.
Reaction Kinetics and Catalysis Letters, 1990
Most liquid phase autoxidation processes are autocatalytic and characterized by radical chain mec... more Most liquid phase autoxidation processes are autocatalytic and characterized by radical chain mechanisms. These features may result in exotic kinetic behavior, such as bistability, oscillation and propagating reaction fronts. Oscillations has
Improved calibration and use of stopped-flow instruments
Physical Chemistry Chemical Physics, 2000
The calibration procedure of stopped-flow instruments based on the dead-time concept has been imp... more The calibration procedure of stopped-flow instruments based on the dead-time concept has been improved. It is proved theoretically and shown experimentally that the dead-time is not a simple instrumental parameter; it depends on the rate of the reaction. Two new parameters are ...
Great Structural Variety of Complexes in Copper(II)−Oligoglycine Systems: Microspeciation and Coordination Modes as Studied by the Two-Dimensional Simulation of Electron Paramagnetic Resonance Spectra
Journal of the American Chemical Society, 2003
A series of isotropic EPR spectra recorded at various concentrations and pH (in the range 2-12) o... more A series of isotropic EPR spectra recorded at various concentrations and pH (in the range 2-12) on equilibrium systems containing copper(II) and diglycine, triglycine, or tetraglycine were analyzed. A purely mathematical method, matrix rank analysis gave the number of independent EPR-active species. Two-dimensional evaluation then resulted in the formation constants and magnetic parameters of 14 metal complexes (including microspecies) in each system. The independent paramagnetic species formed with each ligand are as follows: Cu(2+) (aqua complex), [CuLH](2+), [CuL](+), [CuLH(-1)], [CuLH(-2)](-), [CuL(2)H(2)](2+), [CuL(2)H](+), [CuL(2)], [CuL(2)H(-1)](-), and [CuL(2)H(-2)](2-). Moreover, for diglycine, the diamagnetic complex [Cu(2)L(2)H(-3)](-), and for triglycine and tetraglycine, the EPR-active species [CuLH(-3)](2-) were identified. Further, equilibria of two microspecies were demonstrated for [CuL(2)], [CuL(2)H(-1)](-), and [CuL(2)H(-2)](2-). The magnetic parameters allowed a detailed description of the coordination modes. The most important findings: (1) For the mono complexes, the in-plane sigma-bonds between copper(II) and the equatorial N donors are particularly strong when the same ligand forms several adjacent chelate rings with the participation of amino N, deprotonated peptide N(s), and the carboxylate group. (2) Structures with coupled chelate rings are likewise favored in the bis complexes. Different protonation states of the two ligands are observed in the major isomer of [CuL(2)] ((LH(-1) + LH) coordination), and in the isomers of [CuL(2)H(-2)](2-) ((LH(-2) + L) coordination) for triglycine and tetraglycine.
Stochastic behavior and stirring rate effects in the chlorite–iodide reaction
The Journal of Chemical Physics, 1988
The autocatalytic reaction between chlorite and iodide ions in a closed system is a clock reactio... more The autocatalytic reaction between chlorite and iodide ions in a closed system is a clock reaction, showing a sudden appearance of brown I followed by a rapid disappearance of the color. Under certain conditions, the reaction time displays a striking irreproducibility. This ...
Sensitivity analysis of multiple chemical equilibria: Sensitivity coefficients and response equilibria
The Journal of Chemical Physics, 1995
ABSTRACT
Peculiar kinetics of the complex formation in the iron(III)-sulfate system
International Journal of Chemical Kinetics, 2008
The formation of iron(III)sulfate complexes has been studied by several researchers. Whiteker an... more The formation of iron(III)sulfate complexes has been studied by several researchers. Whiteker and Davidson 1 found spectrophotometrically that both FeSO and Fe(SO 4 ) species are formed at pH 0. Lister and Rivington 2 stated that FeHSO and Fe(SO 4 )(HSO 4 ) species also ...
Inorganic Chemistry, 2008
The effect of chloride ion on the chlorine dioxide formation in the ClO 2 --HOCl reaction was stu... more The effect of chloride ion on the chlorine dioxide formation in the ClO 2 --HOCl reaction was studied by following · ClO 2 concentration spectrophotometrically at pH 5-6 in 0.5 M sodium acetate. On the basis of the earlier experimental data collected without initially added chloride and on new experiments, the earlier kinetic model was modified and extended to interpret the two series of experiments together. It was found that the chloride ion significantly increases the initial rate of · ClO 2 formation. At the same time, the · ClO 2 yield is increased in HOCl but decreased in ClO 2 excess by the increase of the chloride ion concentration. The two-step hydrolysis of dissolved chlorine through Cl 2 + H 2 O H Cl 2 OH -+ H + and Cl 2 OH -H HOCl + Cland the increased reactivity of Cl 2 OHcompared to HOCl are proposed to explain these phenomena. It is reinforced that the hydrolysis of the transient Cl 2 O 2 takes place through a HOCl-catalyzed step instead of the spontaneous hydrolysis. A seven-step kinetic model with six rate parameters (constants and/or ratio of constants) is proposed on the basis of the rigorous least-squares fitting of the parameters simultaneously to 129 absorbance versus time curves measured up to ∼90% conversion. The advantage of this method of evaluation is briefly outlined.
Biochemistry, 1994
NF-M13 [H-(Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly)-OH], NF-M 17 [H-(Glu-Glu-Lys-Gly-... more NF-M13 [H-(Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly)-OH], NF-M 17 [H-(Glu-Glu-Lys-Gly-Lys-Ser-Pro-Val-Pro-Lys-Ser-Pro-Val-Glu-Glu-Lys-Gly)-OH] , and their phosphorylated derivatives, representing the C-terminal phosphorylation domain of the neurofilament protein midsize subunit, have four possible binding sites for metal ions: the COO-group of glutamate, the OH group of the serine
The Journal of Physical Chemistry A, 1997
We present a new method for the decomposition of an experimental absorbance matrix into concentra... more We present a new method for the decomposition of an experimental absorbance matrix into concentration and molar absorption coefficient matrices. The decomposition in general is not unambiguous; therefore, the method may yield only ranges for these matrices. The experimental matrix is not changed, so deviations from the original data can be monitored element by element. Consequently, all chemical constraints (such as stoichiometry) can be taken into account. The method, which does not require an explicit chemical model, is used to analyze the reaction between a Co(II)-EDTA complex and H 2 O 2 .