Synthesis and Electrochemical and Spectroscopic Characterization of 4,7-diamino- 1,10-phenanthrolines and Their Precursors

New approaches to the synthesis of 4,7-dichloro-1,10-phenanthrolines and their corresponding 9H-carbazol-9-yl-, 10H-phenothiazin-10-yl- and pyrrolidin-1-yl derivatives were developed. Their properties have been characterized by a combination of several techniques: MS, HRMS, GC-MS, electronic absorption spectroscopy and multinuclear NMR in both solution and solid state including 15N CP/MAS NMR. The structures of 5-fluoro-2,9-dimethyl-4,7-di(pyrrolidin- 1-yl)-1,10-phenanthroline (5d), 4,7-di(9H-carbazol-9-yl)-9-oxo-9,10-dihydro-1,10-phenanthroline-5- carbonitrile (6a) and 4,7-di(10H-phenothiazin-10-yl)-1,10-phenanthroline-5-carbonitrile (6b) were determined by single-crystal X-ray diffraction measurements. The nucleophilic substitutions of hydrogen followed by oxidation produced compounds 6a and 6b. The electrochemical properties of selected 1,10-phenanthrolines were investigated using cyclic voltammetry and compared with commercially available reference 1,10-phenanthrolin-5-amine (5l). The spatial distribution of frontier molecular orbitals of the selected compounds has been calculated by density functional theory (DFT). It was shown that potentials of reduction and oxidation were in consistence with the level of HOMO and LUMO energies

Spectroelectrochemical properties of 1,10- phenanthroline substituted by phenothiazine and carbazole redox-active units

Complexes of 1,10-phenanthrolines with cations of transition metals have broad range of applications. This work aims at designing and investigating phenothiazine and carbazole substituted 1,10-phenanthrolines as ligands for future complexes with transient metal cations. The combined electrochemical, spectroelectrochemical and DFT studies were employed to demonstrate the effect of broken symmetry in substituted 4,7-di(phenothiazine)-1,10-phenanthrolines on their spectroelectrochemical properties. A reversible color change (new absorption band around 500 nm) due to phenothiazine radical cation was observed in the first oxidation step. Results further indicate that phenothiazine substituents behave as two equivalent but almost electronically isolated redox centres. The work additionally presents a comprehensive reaction mechanistic study of oxidation and reduction processes complemented by HPLC-MS/MS identification

On reduction of the drug diflunisal in non-acqueous media

The electrochemical reduction of diflunisal was studied in dimethyl sulfoxide on static mercury drop electrode. Diflunisal yields one irreversible wave at -1.2 V (vs. Ag | AgCl | 1 M LiCl electrode) due to the reduction of the carboxylic functional group in the molecule. The electrochemical properties of the drug were compared with the ones of the chlorinated analogue. The study is based on cyclic voltammetry, tast polarography, and constant potential electrolysis. The experimental findings are supported by molecular orbital calculations. The mechanism of reduction of the carboxylic moiety was found to involve two electrons and two protons. The reduction pathway leads to formation of an aldehyde derivative

Oxidation mechanisms of Diflunisal on Glassy Carbon Electrode

The electrochemical oxidation of diflunisal in acetonitrile was studied on a glassy carbon electrode. Diflunisal yields one irreversible oxidation wave at 1.6 V (vs. Ag/AgCl/1M LiCl electrode). The oxidation mechanism depends on the basicity of the solvent. The study is based on cyclic voltammetry, electroanalytical methods and UV-Vis spectroelectrochemistry. The degradation products were determined by separation techniques (HPLC-DAD, GC-MS)

Determination of Plant Hormone Indole-3-Acetic Acid in Aqueous Solution

An electroanalytical method was developed for the determination of the phytohormone indole-3-acetic acid in water using a glassy-carbon electrode. The differential pulse voltammetry was combined with a purification step which involved the extraction of plant tissue and the separation of plant pigments by passing through column Oasis MCX. Indole-3-acetic acid can be determined under optimum conditions with a limit of quantification (LOQ) 2.7 106 mol L1. The linearity range was from 1.8106 to 6.6104 mol L1. The electroanalytical determination of indole-3-acetic acid is selective, fast and economic. The presence of other phytohormones as abscisic acid and cytokinins as isopentenyladenine, isopentenyladenosine, trans-zeatin, zeatin riboside does not interfere the determination of indole-3-acetic acid in plant sample

The autoprotonation in reduction mechanism of pesticide ioxynil

The reduction mechanism of ioxynil (3,5-diiodo-4-hydroxy-benzonitrile) was studied in dimethylsulfoxide using the electrochemical methods (tast polarography, cyclic voltammetry and controlled potential electrolysis) combined with GC/MS identification of products. The reduction is accompanied by the cleavage of iodide yielding 3-iodo-4-hydroxybenzonitrile. Surprisingly, this process requires only one electron for the exhaustive electrolysis of the starting compound. We showed that the apparent one electron reduction observed in the aprotic solvent is due to the autoprotonation by another molecule of ioxynil. The overall one electron reduction (uptake of two electrons per two molecules of ioxynil) is changed in the presence of a strong proton donor to a two electron process per one molecule

Host–Guest interaction of pesticide bifenox with cyclodextrin molecules. An electrochemical study.

The reduction of nitroaromatic compound bifenox (methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate) was studied in aprotic solvents in the absence or presence of cyclodextrin (CD) molecules of different cavity sizes. bCD and gCD form complexes with bifenox in DMSO with the complex formation constants (5+-2) x 102 M-1 [bCD-bifenox] and (3+-1) x 102 M-1[gCD-bifenox], respectively. Bifenox yields a relatively stable anion radical in dimethyl sulfoxide, which is further reduced at more negative potentials by an overall addition of three electrons and four protons to the corresponding phenylhydroxylamine. In the presence of bCD the first reduction wave of bifenox becomes irreversible, it is shifted towards more positive potentials and the uptake of more than one electron is observed (up to four electrons during the exhaustive electrolysis). The first reduction wave of bifenox is not affected by the addition of glucose confirming that a simple availability of protons from the OH groups is not the main factor in further transformation of anion radical in the presence of bCD. The complex formation with bCD facilitates the protonation and additionally protects the molecule from disintegration into 2,4-dichlorophenol. A yield of 2,4-dichlorophenol decreases in the order bCD, gCD and aCD, respectively

Katalytické vlastnosti různě imobilizované houbové tyrosinázy: Kinetická studie pro budoucí vývoj biomimetických amperometrických biosenzorů

Mushroom tyrosinase was immobilized by direct embedding into electrode material (modified carbon paste electrode), incorporation of cross-linked enzyme aggregates into a polymer membrane (glassy carbon electrode covered by thin layer of Nafion (R)), and covalent attachment using self-assembled monolayers (gold electrode with the chemically bound enzyme). Both, standard UV-Vis spectrophotometry and amperometry in a batch configuration are presented as complementary methods to study the tyrosinase enzyme kinetics, whose catecholase activity results in electroactive products (ortho-quinones). Due to higher sensitivity of amperometric detection, evident advantage in the enzyme consumption was obtained. Prepared amperometric tyrosinase biosensors were characterized using cyclic voltammetry and atomic force microscopy. The Michaelis constant values of immobilized and unbound tyrosinase (free enzyme solution) towards dopamine and catechol were compared. The apparent Michaelis constant values for immobilized tyrosinase are significantly lower than the declared value of 0.840 mmol L-1 dopamine for the unbound enzyme. The enzymetyrosinase arranged in self-assembledmonolayer serves as an efficient sensor due to lowapparent Michaelis constant of 0.061 mmol L-1 dopamine and high maximum reaction velocity of 0.458 mu A s(-1). This fact reflects the ideal arrangement of enzymemolecules causing high availability of the binding site. Tris-glycine sodiumdodecyl sulphate polyacrylamide gel electrophoresis and atomic force microscopy clarified that the protein of molecular weight 25 kDa is bound preferably on chemically modified gold electrode. A sensor prepared by the immobilization of tyrosinase on gold electrode results in higher catecholase activity towards dopamine than in case of CPE and GC electrodes, where enzyme is immobilized physically.Houbová tyrosináza byla imobilizována přímým zapuštěním do elektrodového materiálu (modifikovaná uhlíková pastová elektroda), zabudováním zesítěných enzymových agregátů do polymerní membrány (skelná uhlíková elektroda pokrytá tenkou vrstvou Nafionu (R) a kovalentní vazbou pomocí samovolně sestavené monovrstvy (zlatá elektroda s chemicky vázaným enzymem). Standardní UV-Vis spektrofotometrie a amperometrie v dávkové konfiguraci jsou prezentovány jako doplňkové metody ke studiu kinetiky enzymu tyrosinázy, jehož katecholázová aktivita vede k elektroaktivním produktům (ortho-chinony). Díky vyšší citlivosti amperometrické detekce byla získána evidentní výhoda ve spotřebě enzymu. Připravené amperometrické tyrozinázové biosenzory byly charakterizovány pomocí cyklické voltametrie a mikroskopie atomových sil. Byly porovnány hodnoty Michaelisovy konstant imobilizované a nenavázané tyrosinázy (roztok volného enzymu) vůči dopaminu a katecholu. Zdánlivé Michaelisovy hodnoty konstant pro imobilizovanou tyrosinázu jsou významně nižší než deklarovaná hodnota 0,840 mmol L-1 dopaminu pro nenavázaný enzym. Enzym tyrosináza uspořádaná v samostatně sestavené monovrstvě slouží jako účinný senzor díky nízké zjevné Michaelisově konstantě 0,061 mmol L-1 dopaminu a vysoké maximální reakční rychlosti 0,458 uAs (-1). Tato skutečnost odráží ideální uspořádání molekul enzymu způsobujících vysokou dostupnost vazebného místa. Gelová elektroforéza a mikroskopie atomových sil tris-glycin natriumdodecylsulfát polyakrylamid objasnily, že protein o molekulové hmotnosti 25 kDa je výhodně navázán na chemicky modifikovanou zlatou elektrodu. Senzor připravený imobilizací tyrosinázy na zlaté elektrodě má za následek vyšší aktivitu katecholázy vůči dopaminu než v případě elektrod CPE a GC, kde je enzym fyzicky imobilizován

On the difference in decomposition of taxifolin and luteolin vs. fisetin and quercetin in aqueous media

The decomposition of flavonols quercetin and fisetin, flavone luteolin and flavanone taxifolin was studied in slightly alkaline solution under ambient conditions. The study was based on spectrophotometry and high-pressure liquid chromatography. Products formed by atmospheric oxygen oxidation and hydrolysis were identified by HPLC–DAD and HPLC–ESI-MS/MS. Only small differences in the chemical structure of flavonoids resulted in extremely variable oxidation pathways and products. Oxidation of flavonols led to the formation of both a benzofuranone derivative and several open structures. On the contrary, the benzofuranone derivative was not found as a product of taxifolin and luteolin oxidative decomposition. These compounds were oxidized to their hydroxylated derivatives and typical open structures. Quercetin was not identified as a possible oxidation product of taxifolin

New Spectroelectrochemical Insights into Manganese and Rhenium Bipyridine Complexes as Catalysts for the Electrochemical Reduction of Carbon Dioxide

This study aimed to demonstrate the behavior of different complexes using IR spectroelectrochemistry (SEC), a technique that combines IR spectroscopy with electrochemistry. Four different Mn and Re catalysts for electrochemical CO2 reduction were studied in dry acetonitrile. In the case of Mn(apbpy)(CO)3Br (apbpy = 4(4-aminophenyl)-2,2′-bipyridine), SEC suggested that a very slow catalytic reduction of CO2 also occurs in acetonitrile in the absence of proton donors, but at rather negative potentials. In contrast, the corresponding Re(apbpy)(CO)3Br clearly demonstrated slow catalytic conversion at the first reduction potential. Switching to saturated CO2 solutions in a mixture of acetonitrile and 5% water as a proton donor, the SEC of Mn(apbpy)(CO)3Br displayed a faster catalytic behavior