Rubin Gulaboski | University Goce Delcev (original) (raw)

Papers by Rubin Gulaboski

Biophysical Chemistry, 2008

A new method is introduced to determine the kinetic parameters of electron transfer reactions of ... more A new method is introduced to determine the kinetic parameters of electron transfer reactions of biologically important compounds, based on the measurements of the halfpeak width (∆E p/2 ) of the square-wave voltammograms. A simple surface (diffusionless) redox reaction, and a simple electrode reaction occurring from dissolved state are considered as model systems. In the region of quasireversible electron transfer, the halfpeak widths of theoretical square-wave voltammograms are linear functions of the logarithm of the dimensionless kinetic parameter ln(K) that characterizes the rate of the electron transfer reaction. The dimensionless kinetic parameter K is defined as K = k s (fD) -0.5 for the redox reaction taking place from dissolved state, whereas for the surface redox reaction K is defined as K = k s /f (k s is the standard rate constant of electron transfer, f is the SW frequency, and D is the diffusion coefficient). A set of linear regression equations for the dependences ∆E p/2 vs. ln(K) are derived, which can be used for rapid and precise determination of the charge-transfer kinetic parameters. The estimated values for the standard rate constants of various biologically relevant redox systems using this approach are in very good agreement with the experimental values determined by other squarewave voltammetric methods. The square-wave voltammetric half-peak width method can be used as a simple and reliable alternative to other voltammetric methods developed for the kinetic characterization of electron transfer rates.

Langmuir, 2003

Polyelectrolyte/gold nanoparticle multilayers composed of poly(L-lysine) (pLys) and mercaptosucci... more Polyelectrolyte/gold nanoparticle multilayers composed of poly(L-lysine) (pLys) and mercaptosuccinic acid (MSA) stabilized gold nanoparticles (Au NPs) were built up using the electrostatic layer-by-layer self-assembly technique upon a gold electrode modified with a first layer of MSA. The assemblies were characterized using UV-vis absorption spectroscopy, cyclic and square-wave voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. Charge transport through the multilayer was studied experimentally as well as theoretically by using two different redox pairs [Fe(CN) 6 ] 3-/4and [Ru(NH 3 ) 6 ] 3+/2+ . This paper reports a large sensitivity to the charge of the outermost layer for the permeability of these assemblies to the probe ions. With the former redox pair, dramatic changes in the impedance response were obtained for thin multilayers each time a new layer was deposited. In the latter case, the multilayer behaves as a conductor exhibiting a strikingly lower impedance response, the electric current being enhanced as more layers are added for Au NP terminated multilayers. These results are interpreted quite satisfactorily by means of a capillary membrane model that encompasses the wide variety of behaviors observed. It is concluded that nonlinear slow diffusion through defects (pinholes) in the multilayer is the governing mechanism for the [Fe(CN) 6 ] 3-/4species, whereas electron transfer through the Au NPs is the dominant mechanism in the case of the [Ru(NH 3 ) 6 ] 3+/2+ pair.

An alternative approach for numerical calculation of the square-wave voltammograms using the math... more An alternative approach for numerical calculation of the square-wave voltammograms using the mathematical programming package MATHCAD is presented. A quasi-reversible redox reaction is considered and a mathematical model is developed under conditions of the square-wave voltammetry (SWV). Application of the mathematical model in MATHCAD is discussed and the file used for numerical simulation is presented. The relationships between the properties of the SW response and the parameters of both the quasireversible redox reaction and the excitation signal are discussed.

For the first time, the standard Gibbs energies of transfer of anions and cations across the nitr... more For the first time, the standard Gibbs energies of transfer of anions and cations across the nitrobenzene|heavy water interface are reported as measured by an electrochemical technique. The data have been obtained with the help of three-phase electrodes consisting of a nitrobenzene droplet that contains an electroactive compound (either decamethylferrocene to transfer anions or iron(III) tetraphenyl porphyrin chloride to transfer

Croatica Chemica Acta

An extended theoretical treatment of a two-step surface redox reaction under the conditions of sq... more An extended theoretical treatment of a two-step surface redox reaction under the conditions of square-wave voltammetry (SWV) is presented. The theoretical model is applicable to any reversibility of both redox steps of the EE reaction. The integral equations representing this theoretical model were solved numerically. The apparent reversibility of the redox steps depends on two dimensionless kinetic parameters, k 1 and k 2 , defined as k 1 = k s,1 /f and k 2 = k s,2 /f, where k s,1 and k s,2 are the standard rate constants of the first and second redox steps, respectively, and f is the excitation signal frequency. The response consists of either a single or two separate SW peaks, depending mainly on the difference between the formal potentials of the first and second redox steps as well as on the ratio of the kinetic parameters k 1 /k 2 . The effect of the electron transfer coefficients of both redox steps is also discussed. A part of the theoretical results are qualitatively illustrated by SW voltamograms of the azo-dye Sudan-III.

Десет домашни сорти ориз (кочански, број 51, осоговка, прима риска, бисер-2, број 69, монтеса, на... more Десет домашни сорти ориз (кочански, број 51, осоговка, прима риска, бисер-2, број 69, монтеса, нада-115, ранка и Б-30-303), и три перспективни линии (линија 79/22-2, линија 78/12-3-4 и линија 78/12-3-5) се евалуирани за висина на стеблото, должина и ширина на листот, должина на главната метличка, број на зрна во главната метличка и маса на зрна од главната метличка. Меѓу испитуваните генотипови е утврдена значајна фенотипска разновидност за сите испитувани својства. Коефициентот на варијација е најголем за должина на листот (9,93 %), а најмал за висина на стеблото (3,05 %). Според добиените резултати, испитуваните генотипови ориз претставуваат широк потенцијал за создавање на нови селекциски популации.

Electrochimica Acta, 2015

EC' catalytic mechanism electrode reaction kinetics standard rate constant enzymatic biosensors p... more EC' catalytic mechanism electrode reaction kinetics standard rate constant enzymatic biosensors protein-film voltammetry A B S T R A C T Several new theoretical aspects of the electrocatalytic (regenerative) EC' mechanism under conditions of square-wave (SWV) and staircase cyclic voltammetry (SCV) are presented. Elaborating the effect of the rate of the catalytic reaction in the diffusion-controlled catalytic mechanism (diffusional EC' mechanism) and surface catalytic mechanism (surface EC' mechanism), we refer to several phenomena related to the shift of the position and the half-peak width of the net peak in square-wave voltammetry (SWV). If the rate of the catalytic reaction is much higher than the kinetics of the electrode reaction, a linear dependence between the peak potential of the simulated net SWV peaks and the logarithm of the catalytic parameter can be observed. The intercept of that linear dependence is a function of the kinetics of the electrode reaction. Based on this finding, we propose a new methodology to determine the electrode kinetics rate constant. The proposed approach relies on the variation of the concentration of the regenerative reagent. To the best of our knowledge, this is one of very few voltammetric approaches for electrode kinetic measurements not based on the time or potential variation in the experimental analyzes. In addition, we present a brief analysis of the catalytic mechanism under conditions of staircase cyclic voltammetry in order to emphasize the main differences between SCV and SWV.

ABSTRACT http://www.chipsbooks.com/hbfdinst.htm

Journal of Solid State Electrochemistry, 2015

A coupled electron-ion transfer reaction at thin organic-film-modified electrodes (TFE) is studie... more A coupled electron-ion transfer reaction at thin organic-film-modified electrodes (TFE) is studied in the presence of glucose oxidase (GOx) under voltammetric conditions. TFE consists of a graphite electrode modified with a nitrobenzene solution of decamethylferrocene (DMFC) as a redox mediator and tetrabuthylammonium perchlorate as an organic-supporting electrolyte, in contact with aqueous buffer solutions containing percholarte ions and GOx. The redox turnover of DMFC coupled with perchlorate transfer across water|nitrobenzene interface composes the coupled electronion transfer reaction. Glucose oxidase strongly adsorbs at the liquid|liquid interface affecting the coupled electron-ion transfer reaction by reducing the surface area of the liquid interface, prompting coadsorption of the transferring ion and lowering down slightly the rate of the ion transfer reaction. Although the enzyme exists as a polyvalent anion over the pH interval from 5.6 to 7, it does not participate directly in the ionic current across the liquid interface and percholrate remains the main transferring ion. Raman spectroscopic data, together with the voltammetric data collected by three-phase droplet electrodes, indicate that the adsorption of the enzyme does not depend either on the redox mediator (DMFC) or the organicsupporting electrolyte, while being driven by intrinsic interactions of the enzyme with the organic solvent. The overall electrochemical mechanism is mathematically modeled by considering linear adsorption isotherm of the transferring ion, semi-infinite mass transfer regime, and phenomenological second-order kinetic model.

Food Analytical Methods, 2015

An analytical method for determination of multielement composition of Vranec wines using microwav... more An analytical method for determination of multielement composition of Vranec wines using microwave digestion for sample preparation and inductively coupled plasma mass spectrometry (ICP-MS) was optimized and validated. Best recoveries, ranging from 87 to 114 %, were obtained for all analyzed elements, using a volume of 5 mL wine and 5 mL HNO 3 for sample microwave digestion. In total, 38 elements (Ag, Te, Ti, Tl, V, Zn) were determined in wines. The calibration curves of all elements were linear with correlation coefficients (R 2 ) ranging from 0.9920 for 11 B to 1.0000 for 53 Cr and 88 Sr. The accuracy of the method was checked with a standard addition method showing good repeatability and reproducibility (relative standard deviation, RSD <10 %). Vranec wines were fermented with Saccharomyces cerevisiae yeast strains commercial Clos, RC212, D254, and BDX, and six autochthonous Vinalco yeasts. The content of total elements in all Vranec wines ranged between 348 to 678 mg/L, observing lower amounts in wines fermented with the autochthonous Vinalco yeast. The content of harmful elements, such as Pb and Cu, was below the maximal allowed concentration in all wines.

A novel methodological approach for processing electrochemical data measured under conditions of ... more A novel methodological approach for processing electrochemical data measured under conditions of square-wave voltammetry (SWV) is proposed. The methodology takes advantage of the chronoamperometric characteristics of the electrochemical system observed in the course of the voltammetric experiment, which are commonly not considered in conventional SWV. The method requires processing of a single voltammogram only, measured under given set of the potential modulation parameters (i.e. SW frequency and height of the potential pulses). The core idea is to analyze the variation of the current with time, considering the last quarter time period of each potential pulse of the potential modulation, instead of measuring the single current value from the very end of the pulses. Hence, a single point current measurement is replaced with a multisampling current procedure, leading to a series of new SW voltammograms measured at different time increments of each potential pulse. The novel method is illustrated by the theoretical analysis of a quasireversible electrode reaction of a dissolved and surface confined redox couple, as well as a reversible electrode reaction preceded by a chemical equilibrium reaction (C r E r mechanism).

Biophysical Chemistry, 2008

A new method is introduced to determine the kinetic parameters of electron transfer reactions of ... more A new method is introduced to determine the kinetic parameters of electron transfer reactions of biologically important compounds, based on the measurements of the halfpeak width (∆E p/2 ) of the square-wave voltammograms. A simple surface (diffusionless) redox reaction, and a simple electrode reaction occurring from dissolved state are considered as model systems. In the region of quasireversible electron transfer, the halfpeak widths of theoretical square-wave voltammograms are linear functions of the logarithm of the dimensionless kinetic parameter ln(K) that characterizes the rate of the electron transfer reaction. The dimensionless kinetic parameter K is defined as K = k s (fD) -0.5 for the redox reaction taking place from dissolved state, whereas for the surface redox reaction K is defined as K = k s /f (k s is the standard rate constant of electron transfer, f is the SW frequency, and D is the diffusion coefficient). A set of linear regression equations for the dependences ∆E p/2 vs. ln(K) are derived, which can be used for rapid and precise determination of the charge-transfer kinetic parameters. The estimated values for the standard rate constants of various biologically relevant redox systems using this approach are in very good agreement with the experimental values determined by other squarewave voltammetric methods. The square-wave voltammetric half-peak width method can be used as a simple and reliable alternative to other voltammetric methods developed for the kinetic characterization of electron transfer rates.

Langmuir, 2003

Polyelectrolyte/gold nanoparticle multilayers composed of poly(L-lysine) (pLys) and mercaptosucci... more Polyelectrolyte/gold nanoparticle multilayers composed of poly(L-lysine) (pLys) and mercaptosuccinic acid (MSA) stabilized gold nanoparticles (Au NPs) were built up using the electrostatic layer-by-layer self-assembly technique upon a gold electrode modified with a first layer of MSA. The assemblies were characterized using UV-vis absorption spectroscopy, cyclic and square-wave voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. Charge transport through the multilayer was studied experimentally as well as theoretically by using two different redox pairs [Fe(CN) 6 ] 3-/4and [Ru(NH 3 ) 6 ] 3+/2+ . This paper reports a large sensitivity to the charge of the outermost layer for the permeability of these assemblies to the probe ions. With the former redox pair, dramatic changes in the impedance response were obtained for thin multilayers each time a new layer was deposited. In the latter case, the multilayer behaves as a conductor exhibiting a strikingly lower impedance response, the electric current being enhanced as more layers are added for Au NP terminated multilayers. These results are interpreted quite satisfactorily by means of a capillary membrane model that encompasses the wide variety of behaviors observed. It is concluded that nonlinear slow diffusion through defects (pinholes) in the multilayer is the governing mechanism for the [Fe(CN) 6 ] 3-/4species, whereas electron transfer through the Au NPs is the dominant mechanism in the case of the [Ru(NH 3 ) 6 ] 3+/2+ pair.

An alternative approach for numerical calculation of the square-wave voltammograms using the math... more An alternative approach for numerical calculation of the square-wave voltammograms using the mathematical programming package MATHCAD is presented. A quasi-reversible redox reaction is considered and a mathematical model is developed under conditions of the square-wave voltammetry (SWV). Application of the mathematical model in MATHCAD is discussed and the file used for numerical simulation is presented. The relationships between the properties of the SW response and the parameters of both the quasireversible redox reaction and the excitation signal are discussed.

For the first time, the standard Gibbs energies of transfer of anions and cations across the nitr... more For the first time, the standard Gibbs energies of transfer of anions and cations across the nitrobenzene|heavy water interface are reported as measured by an electrochemical technique. The data have been obtained with the help of three-phase electrodes consisting of a nitrobenzene droplet that contains an electroactive compound (either decamethylferrocene to transfer anions or iron(III) tetraphenyl porphyrin chloride to transfer

Croatica Chemica Acta

An extended theoretical treatment of a two-step surface redox reaction under the conditions of sq... more An extended theoretical treatment of a two-step surface redox reaction under the conditions of square-wave voltammetry (SWV) is presented. The theoretical model is applicable to any reversibility of both redox steps of the EE reaction. The integral equations representing this theoretical model were solved numerically. The apparent reversibility of the redox steps depends on two dimensionless kinetic parameters, k 1 and k 2 , defined as k 1 = k s,1 /f and k 2 = k s,2 /f, where k s,1 and k s,2 are the standard rate constants of the first and second redox steps, respectively, and f is the excitation signal frequency. The response consists of either a single or two separate SW peaks, depending mainly on the difference between the formal potentials of the first and second redox steps as well as on the ratio of the kinetic parameters k 1 /k 2 . The effect of the electron transfer coefficients of both redox steps is also discussed. A part of the theoretical results are qualitatively illustrated by SW voltamograms of the azo-dye Sudan-III.

Десет домашни сорти ориз (кочански, број 51, осоговка, прима риска, бисер-2, број 69, монтеса, на... more Десет домашни сорти ориз (кочански, број 51, осоговка, прима риска, бисер-2, број 69, монтеса, нада-115, ранка и Б-30-303), и три перспективни линии (линија 79/22-2, линија 78/12-3-4 и линија 78/12-3-5) се евалуирани за висина на стеблото, должина и ширина на листот, должина на главната метличка, број на зрна во главната метличка и маса на зрна од главната метличка. Меѓу испитуваните генотипови е утврдена значајна фенотипска разновидност за сите испитувани својства. Коефициентот на варијација е најголем за должина на листот (9,93 %), а најмал за висина на стеблото (3,05 %). Според добиените резултати, испитуваните генотипови ориз претставуваат широк потенцијал за создавање на нови селекциски популации.

Electrochimica Acta, 2015

EC' catalytic mechanism electrode reaction kinetics standard rate constant enzymatic biosensors p... more EC' catalytic mechanism electrode reaction kinetics standard rate constant enzymatic biosensors protein-film voltammetry A B S T R A C T Several new theoretical aspects of the electrocatalytic (regenerative) EC' mechanism under conditions of square-wave (SWV) and staircase cyclic voltammetry (SCV) are presented. Elaborating the effect of the rate of the catalytic reaction in the diffusion-controlled catalytic mechanism (diffusional EC' mechanism) and surface catalytic mechanism (surface EC' mechanism), we refer to several phenomena related to the shift of the position and the half-peak width of the net peak in square-wave voltammetry (SWV). If the rate of the catalytic reaction is much higher than the kinetics of the electrode reaction, a linear dependence between the peak potential of the simulated net SWV peaks and the logarithm of the catalytic parameter can be observed. The intercept of that linear dependence is a function of the kinetics of the electrode reaction. Based on this finding, we propose a new methodology to determine the electrode kinetics rate constant. The proposed approach relies on the variation of the concentration of the regenerative reagent. To the best of our knowledge, this is one of very few voltammetric approaches for electrode kinetic measurements not based on the time or potential variation in the experimental analyzes. In addition, we present a brief analysis of the catalytic mechanism under conditions of staircase cyclic voltammetry in order to emphasize the main differences between SCV and SWV.

ABSTRACT http://www.chipsbooks.com/hbfdinst.htm

Journal of Solid State Electrochemistry, 2015

A coupled electron-ion transfer reaction at thin organic-film-modified electrodes (TFE) is studie... more A coupled electron-ion transfer reaction at thin organic-film-modified electrodes (TFE) is studied in the presence of glucose oxidase (GOx) under voltammetric conditions. TFE consists of a graphite electrode modified with a nitrobenzene solution of decamethylferrocene (DMFC) as a redox mediator and tetrabuthylammonium perchlorate as an organic-supporting electrolyte, in contact with aqueous buffer solutions containing percholarte ions and GOx. The redox turnover of DMFC coupled with perchlorate transfer across water|nitrobenzene interface composes the coupled electronion transfer reaction. Glucose oxidase strongly adsorbs at the liquid|liquid interface affecting the coupled electron-ion transfer reaction by reducing the surface area of the liquid interface, prompting coadsorption of the transferring ion and lowering down slightly the rate of the ion transfer reaction. Although the enzyme exists as a polyvalent anion over the pH interval from 5.6 to 7, it does not participate directly in the ionic current across the liquid interface and percholrate remains the main transferring ion. Raman spectroscopic data, together with the voltammetric data collected by three-phase droplet electrodes, indicate that the adsorption of the enzyme does not depend either on the redox mediator (DMFC) or the organicsupporting electrolyte, while being driven by intrinsic interactions of the enzyme with the organic solvent. The overall electrochemical mechanism is mathematically modeled by considering linear adsorption isotherm of the transferring ion, semi-infinite mass transfer regime, and phenomenological second-order kinetic model.

Food Analytical Methods, 2015

An analytical method for determination of multielement composition of Vranec wines using microwav... more An analytical method for determination of multielement composition of Vranec wines using microwave digestion for sample preparation and inductively coupled plasma mass spectrometry (ICP-MS) was optimized and validated. Best recoveries, ranging from 87 to 114 %, were obtained for all analyzed elements, using a volume of 5 mL wine and 5 mL HNO 3 for sample microwave digestion. In total, 38 elements (Ag, Te, Ti, Tl, V, Zn) were determined in wines. The calibration curves of all elements were linear with correlation coefficients (R 2 ) ranging from 0.9920 for 11 B to 1.0000 for 53 Cr and 88 Sr. The accuracy of the method was checked with a standard addition method showing good repeatability and reproducibility (relative standard deviation, RSD <10 %). Vranec wines were fermented with Saccharomyces cerevisiae yeast strains commercial Clos, RC212, D254, and BDX, and six autochthonous Vinalco yeasts. The content of total elements in all Vranec wines ranged between 348 to 678 mg/L, observing lower amounts in wines fermented with the autochthonous Vinalco yeast. The content of harmful elements, such as Pb and Cu, was below the maximal allowed concentration in all wines.

A novel methodological approach for processing electrochemical data measured under conditions of ... more A novel methodological approach for processing electrochemical data measured under conditions of square-wave voltammetry (SWV) is proposed. The methodology takes advantage of the chronoamperometric characteristics of the electrochemical system observed in the course of the voltammetric experiment, which are commonly not considered in conventional SWV. The method requires processing of a single voltammogram only, measured under given set of the potential modulation parameters (i.e. SW frequency and height of the potential pulses). The core idea is to analyze the variation of the current with time, considering the last quarter time period of each potential pulse of the potential modulation, instead of measuring the single current value from the very end of the pulses. Hence, a single point current measurement is replaced with a multisampling current procedure, leading to a series of new SW voltammograms measured at different time increments of each potential pulse. The novel method is illustrated by the theoretical analysis of a quasireversible electrode reaction of a dissolved and surface confined redox couple, as well as a reversible electrode reaction preceded by a chemical equilibrium reaction (C r E r mechanism).