Antioxidant Activity and Photosynthesis Efficiency in Melissa officinalis Subjected to Heavy Metals Stress.

The aim of this study was to assess influence of cadmium and zinc treatments on antioxidant activity combined with the photosynthesis efficiency in a popular herb lemon balm (Melissa officinalis L.). Plants were grown under greenhouse conditions by the pot method. The Mn, Cu, Cd, and Zn contents in soil and plants were measured by HR-CS FAAS. The activity of net photosynthesis, stomatal conductance, transpiration rate, intercellular CO2, and index of chlorophyll in leaves were determined for all investigated species. Reduction of the net photosynthesis was observed for cultivations subjected to either Zn or Cd treatments. Phenolic contents were determined by the chemical Folin-Ciocalteu method, while enhanced voltammetric analysis was applied to assess the antioxidant properties of plant extracts. Both of these approaches yielded similar results. Herbal extracts had exceptional antioxidant capacities and were good scavengers of free radicals and reactive oxygen species. Structural similarity of cadmium and zinc facilitated their mutual structural exchange and prompted substantial expansion of phenolics under the mixed Zn and Cd treatments.

Electrochemical and Catalytic Properties of Carbon Dioxide-Activated Graphite Felt.

The commercial graphite felt GFA 10 was subjected to an activation process with the use of CO2 at 900 °C for 35 and 70 min. Pristine and heat-treated materials were characterized using various methods: low-temperature N2 adsorption, SEM, and EDS. Voltammetric measurements of GFA samples (before and after activation) as the working electrode were carried out. Voltammograms were recorded in aqueous solutions of 4-chlorophenol and sodium sulfate as supporting electrolyte. The catalytic activity of GFA samples in the process of 4-chlorophenol oxidation with the use of H2O2 was also investigated. The influence of graphite felt thermal activation in the CO2 atmosphere on its electrochemical and catalytic behavior was analyzed and discussed. Results of the investigation indicate that GFA activated in CO2 can be applied as an electrode material or catalytic material in the removal of organic compounds from industrial wastewater. However, the corrosion resistance of GFA, which is decreasing during the activation, needs to be refined.

Characteristics of the Polyphenolic Profile and Antioxidant Activity of Cone Extracts from Conifers Determined Using Electrochemical and Spectrophotometric Methods.

The aim of the study was to analyze the polyphenolic profile of cone extracts of Douglas fir, Scots pine and Korean fir, and to study their antioxidant activity. The mechanism of electro-oxidation of polyphenols (such as procyanidins and catechins) from cone extracts was investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), as well as spectrophotometric methods-ABTS (2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate)), DPPH (2,2-diphenyl-1-picrylhydrazyl), FRAP (Ferric Reducing Antioxidant Power ) and CUPRAC (CUPric Reducing Antioxidant Capacity). The scientific novelty of the research is the comprehensive analysis of cone extracts in terms of antioxidant properties. Due to the high polyphenol content, the extracts showed significant ability to reduce oxidative reactions, as well as the ability to scavenge free radicals and transition metal ions. Douglas fir, Scots pine and Korean fir cone extracts can potentially be used as natural stabilizers, preservatives and antimicrobial substances in the food industry and in medications.

Characteristics of juglone (5-hydroxy-1,4,-naphthoquinone) using voltammetry and spectrophotometric methods.

The objective of this work was to analyse the antiradical capacity of juglone (5-hydroxy-1,4,-naphthoquinone). The influence of oxidation and reduction on juglone was investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), as well as spectrophotometric based methods. The role of juglone in oxidation processes, as either an antioxidant in browning reactions, was examined. These processes are characterized by a high chemical reactivity in redox. Juglone is irreversibly oxidized in at least one electrode step and reduced quasi-reversibly in at least three electrode steps. These results demonstrate that walnut genotypes have different radical scavenging powers. In addition, on the basis of thermogravimetry, it was demonstrated that 5-hydroxy-1,4-naphthalenedione has high thermal stability above 500 °C. The generation of reactive oxygen species and activity in redox processes show the properties of naphthoquinones that render these compounds interesting leads for the development of novel biomolecules for potential use in various therapeutic settings.

Influence of hydroxyl substitution on flavanone antioxidants properties.

The aim of our study was to determine the effect of the position of the hydroxyl group on the antioxidant properties of flavonoid derivatives. For this purpose, we performed electrochemical analysis and quantum-mechanical calculations to describe the mechanisms of electrochemical oxidation, and we selected the two methods of ABTS (2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) and DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate), which allowed us to determine the ability to scavenge free radicals. On the basis of the research, we found that the derivatives of flavonoids, which have a hydroxyl group substituted at the R-3 position on the C ring, have outstanding antioxidant activity. Flavone, which had an OH group substituted at the R-6 and R-7 position on the ring A, showed similar antioxidant activity to flavone without -OH groups in the structure and slightly higher activity than the di-substituted flavone on the ring A.

Atmospheric corrosion of metals in industrial city environment.

Atmospheric corrosion is a significant problem given destruction of various materials, especially metals. The corrosion investigation in the industrial city environment was carried out during one year exposure. Corrosion potential was determined using the potentiometric method. The highest effect of corrosion processes was observed during the winter season due to increased air pollution. Corrosion of samples pre-treated in tannic acid before the exposure was more difficult compared with the samples without pretreatment. The corrosion products determined with the SEM/EDS method prove that the most corrosive pollutants present in the industrial city air are SO2, CO2, chlorides and dust.

Characteristics of compounds in hops using cyclic voltammetry, UV-VIS, FTIR and GC-MS analysis.

The article presents the antioxidant properties of the extracts of hop EI and EII, by the electrochemical methods on a platinum electrode and comparative analysis of the composition of the extracts of hops using UV-VIS, FTIR and GC-MS methods. The hops extract EI, was obtained from the waste of the hops cone. The hops extract EII, was obtained from the hops cone itself. Hops contain a wide range of polyphenolic compounds with antioxidant properties divided in various chemical classes. Flavonoids and other polyphenolic compounds contained in hops show antioxidant capacity because of the presence of hydroxyl groups in various configurations and numbers within their molecules. The electrochemical properties and antioxidant capacity of hop samples were determined to select the most effective antioxidant. Based on the cyclic and pulse voltammograms, it was observed that hop extract EI contains polyphenols that are oxidised at a less positive potential than extract EII, i.e., it shows better antioxidant capacity. From the analysis of the UV-VIS and FTIR spectra and the GC-MS analysis, it was observed that extract EI contains less phenyl compounds than EII. In addition to flavonoids, EII contains hop acids and chlorophyll. The solutions of hop extracts show very good antioxidant capacities; therefore, they can effectively inhibit or slow negative oxidation reactions and scavenge free radicals and reactive oxygen species (ROS).

Electrooxidation of morin hydrate at a Pt electrode studied by cyclic voltammetry.

The process and the kinetics of the electrochemical oxidation of morin in an anhydrous electrolyte have been investigated using cyclic and differential pulse voltammetry. The oxidation mechanism proceeds in sequential steps related to the hydroxyl groups in the three aromatic rings. The oxidation of the 2',4'dihydroxy moiety at the B ring of morin occurs first, at very low positive potentials, and is a one-electron, one-proton irreversible reaction. The rate constant, electron transfer coefficient and diffusion coefficients involved in the electrochemical oxidation of morin were determined. The influence of the deprotonation of the ring B hydroxyl moiety is related to the electron/proton donating capacity of morin and to its radical scavenging antioxidant activity.

Electrooxidation of flavonoids at platinum electrode studied by cyclic voltammetry.

Flavonoids are natural vegetable dyes synthesized from phenylalanine. They are responsible for colour of blooming plant portions. Moreover, they are very important for human health due to their activity as free radical acceptors. Cyclic and differential pulse voltammetry was used in the determination of kinetic parameters of flavonoids electrooxidation. Electrochemical measurements of the oxidation of organic compounds can be helpful in understanding how these compounds are metabolised by living organisms. Flavonoids electrochemical oxidation is an irreversible reaction at a platinum electrode. In the case of morin hydrate, rutin, dihydroxyflavone, trihydroxyflavone, hesperidin, quercetin, the first step of the electrooxidation includes an exchange of two electrons during the oxidation of hydroxyl groups in the ring B. Hydroxyl groups in the rings A and C are probably oxidised in subsequent steps. The heterogeneous rate constants (k(bh)) determined for the flavonoids electrooxidation are as follows: morin - 3.59×10(-4), rutin - 4.42×10(-4), dihydroxyflavone - 4.54×10(-4), trihydroxyflavone - 4.19×10(-4), hesperidin - 4.50×10(-4) and quercetin - 4.63×10(-4)cms(-1). Their anodic transition coefficient ranged from 0.63 to 0.48 (n=2). Xanthone and flavone were oxidised easiest and quickest among other substrates at the platinum electrode with the heterogeneous rate constants (k(bh)) of 7.08×10(-4) and 6.46×10(-4)cms(-1), respectively.