Protein-film voltammetry is recognized as a very efficient tool in mechanistic enzymology, but it is also seen as a relevant approach to gain thermodynamic and kinetic information related to the redox chemistry of many enzymes. This technique requires a small amount of redox enzyme, whose molecules form monomolecular film on the working electrode surface. In this paper we present a simple and timeindependent cyclo-voltammetric method for the determination of kinetics of the chemical step of an electrochemical-catalytic (EC') mechanism in protein-film scenario. Theoretical results of a surface EC' mechanism show that the limiting cyclo-voltammetric catalytic current, measured at large overpotentials, depends solely on the rate of the chemical regenerative reaction. At large overpotentials, the limiting current of the steady-state cyclic voltammograms is independent on all kinetics and thermodynamic parameters related to the electrode reaction of adsorbed enzyme. The approach proposed relies on the dependence of the magnitude of limiting current of the experimental cyclic steady-state voltammograms as a function of the substrate concentration.

Intra-hospital

In this work, we present theoretical results in cyclic staircase voltammetry of a surface catalytic mechanism that features reversible chemical step, the so-called "surface catalytic EC rev ' mechanism". We consider specific surface regenerative mechanism, in which both of the electro-inactive substrates are present in large excess in electrochemical cell from the beginning of the experiment. The chemical reversibility brings at this mechanism more complexity in respect to the features of wellelaborated surface catalytic EC' mechanism coupled with chemically irreversible regenerative reaction. As we present plenty of simulated cyclic voltammograms, we also propose methods to get insight to kinetics and thermodynamics parameters relevant to chemical regenerative step. The elaboreted results can be important in analysing the kinetics and thermodynamics of many drugdrug and drug-DNA interactions, for example. In addition, with the results elaborated in this work we can access relevant information about the chemistry of important lipophilic enzymes studied in protein-film voltammetry set up.

Abstract:The present study investigates the total arsenic (As) content in the samples of drinking water in the Republic of Macedonia, which is obtained from different water sources, such as: springs, surface accumulations, underground accumulations and drilled wells. From January 2013 to December 2013, a total of 780 samples obtained from the public water supply systems at 35 measurement points distributed throughout the whole territory of the Republic of Macedonia were analyzed on the total As content. A flow injection atomic absorption spectrometry (FIAS) was employed for the determination of the total As content after wet digestion of the samples with nitric acid (67%, W/V) and hydrogen peroxide (30%, V/V). The results of the study revealed that in 96.7% of the tested samples, As content was below established maximum allowable concentration (MAC) of 10 µg/L. As concentrations up to 26.4 µg/L were found in the samples of drinking water that comes from the water sources located in the vicinity of Kozhuf Mountain, which is due to the mineral composition of the mountain body rich with As containing minerals: lorandite, orpiment, realgar, arsenopyrite etc. Higher As concentrations (5.47 µg/L -26.6 µg/L) were also found in the samples of drinking water obtained from the water supply system of the towns from the Dojran Municipality which are located in the vicinity of thermal-mineral area of Mala Boshka -Toplec. It can be concluded that the presence of total As in the potable water in the Republic of Macedonia comes only from natural sources.

We consider theoretically a specific electrochemical-catalytic mechanism associated with reversible regenerative chemical reaction, under conditions of cyclic staircase voltammetry (CSV). We suppose scenario in which two electrochemically inactive substrates “S” and “Y”, together with initial electrochemically active reactant Ox are present in voltammetric cell from the beginning of the experiment. Substrate “S” selectively reacts with initial electroactive reactant Ox and creates electroactive “product” Red (+ Y) in a reversible chemical fashion. The initial chemical equilibrium determines the amounts of Ox and Red available for electrode transformation at the beginning of the electrochemical experiment. Under conditions of applied potential, the electrode reaction Ox(aq) + ne– ⇋ Red(aq) occurs, producing flow of electric current. Under such circumstances, the chemical reaction coupled to the electrochemical step causes a regeneration of initial electroactive species during the time-frame of current-measuring segment in CSV. The features of cyclic voltammograms get significantly affected by the kinetics and thermodynamics of reversible regenerative reaction. We elaborate several aspects of this specific electrode mechanism, and we focus on the role of parameters related to chemical step to the features of calculated voltammograms. While we provide a specific set of results of this particular mechanism, we propose methods to get access to relevant kinetic and thermodynamic parameters relevant to regenerative chemical reaction. The results elaborated in this work can be valuable in evaluating kinetics of many drug-drug interactions, but they can be relevant to study interactions of many enzyme-substrate systems, as well.