Editorial

http://www.sciencedirect.com/science/article/B6TG0-4JW7X04-9/1/e839ed9a3d5631f25adada92860abac

Electrochemical evaluation of glutathione S-transferase kinetic parameters

Glutathione S-transferases (GSTs), are a family of enzymes belonging to the phase II metabolism that catalyse the formation of thioether conjugates between the endogenous tripeptide glutathione and xenobiotic compounds. The voltammetric behaviour of glutathione (GSH), 1-chloro-2,4-dinitrobenzene (CDNB) and glutathione S-transferase (GST), as well as the catalytic conjugation reaction of GSH to CDNB by GST was investigated at room temperature, T = 298.15 K (25 °C), at pH 6.5, for low concentration of substrates and enzyme, using differential pulse (DP) voltammetry at a glassy carbon electrode. Only GSH can be oxidized; a sensitivity of 0.14 nA/μM and a LOD of 6.4 μM were obtained. The GST kinetic parameter electrochemical evaluation, in relation to its substrates, GSH and CDNB, using reciprocal Michaelis–Menten and Lineweaver–Burk double reciprocal plots, was determined. A value of KM ~ 100 μM was obtained for either GSH or CDNB, and Vmax varied between 40 and 60 μmol/min per mg of GST

DNA imaged on a HOPG electrode surface by AFM with controlled potential

Single-molecule AFM imaging of single-stranded and double-stranded DNA molecules self-assembled from solution onto a HOPG electrode surface is reported. The interaction of DNA with the hydrophobic surface induced DNA aggregation, overlapping, intra- and intermolecular interactions. Controlling the electrode potential and using the phase images as a control method, to confirm the correct topographical characterization, offers the possibility to enlarge the capability of AFM imaging of DNA immobilized onto conducting substrates, such as HOPG. The application of a potential of +300 mV (versus AgQRE) to the HOPG enhanced the robustness and stability of the adsorbed DNA molecules, increasing the electrostatic interaction between the positively charged electrode surface and the negatively charged DNA sugar-phosphate backbone.http://www.sciencedirect.com/science/article/B6W72-4D5X9NS-1/1/d1528546598a5fb98abb8331a760556

Reversed-Phase High-Performance Liquid Chromatography with Electrochemical Detection of Anthocyanins

Abstract: Anthocyanins, flavonoid compounds present in grapes and wines, were determined by reverse-phase high-performance liquid chromatography (RP-HPLC) with electrochemical detection (RP-HPLC-ED). The method developed consists of RP-HPLC gradient elution with voltammetric detection using a glassy carbon electrode after separation in an Inertsil ODS-3V analytical column. Good peak resolution was obtained following direct injection of a 50 mL sample of anthocyanins in a mobile phase of pH 2.20. The results show that six different anthocyanins: cyanidin-3-O-glucoside chloride (kuromanin chloride), cyanidin-3,5-di-O-glucoside chloride (cyanin chloride), malvidin-3-O-glucoside chloride (oenin chloride), malvidin-3,5-di-O-glucoside chloride (malvin chloride), delphinidin-3-O-glucoside chloride (myrtillin chloride), and peonidine-3-O-glucoside chloride, all with antioxidant properties, can be separated in a single run by direct injection of solution. The limit of detection (LOD) for these compounds was lower than 0.3 mM. The method can also be applied to the analysis of these compounds in red wines and in skins and pulp extracts of red grapes, since all these antioxidants are electroactive

Development of an HPLC method with electrochemical detection of femtomoles of 8-oxo-7,8-dihydroguanine and 8-oxo-7,8-dihydro-2'-deoxyguanosine in the presence of uric acid

A selective method based on high performance liquid chromatography with electrochemical detection (HPLC-ECD) was developed to enable simultaneous detection of 8-oxo-7,8-dihydroguanine (8-oxoGua) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), products of DNA oxidative damage, in the presence of uric acid (UA), a strong interferent in their electrochemical detection. The method developed consists of HPLC isocratic elution with amperometric detection on a glassy carbon electrode, enabling a detection limit for 8-oxoGua and 8-oxodGuo lower than 1 nM in standard mixtures. Detection of low concentrations up to 25 nM of 8-oxoGua and 8-oxodGuo in the presence of UA in a 104-fold higher concentration was achieved after one-step solid phase extraction (SPE). The method was tested with urine samples and it was possible to detect and quantify the presence of 8-oxoGua, and to confirm that UA was eliminated after uricase degradation and SPE. The LOD found in urine samples was about 80 nM, a value higher than in standard mixtures, due to the increase of background current in the urine matrix. The results presented here contribute to the development of a methodological approach to simultaneous determination of 8-oxoGua and 8-oxodGuo in urine samples.http://www.sciencedirect.com/science/article/B6THP-4BG45K9-1/1/203c0cf340998db82825488fecf36e4

Synthesis and electrochemical study of new 3-(hydroxyphenyl)benzo[f]coumarins

New hydroxyl substituted 3-arylbenzo[f]coumarins (compounds 6–10) have been designed and synthesized. Their electrochemical redox mechanisms, and the influence of one or two hydroxyl groups, in different positions on the coumarin scaffold, was investigated by cyclic, differential pulse and square wave voltammetry, at a glassy carbon electrode, at different pHs, and a comparative study was performed. The structural information obtained enabled a better understanding of the structure/electrochemical relationship of hydroxyl substituted 3-arylbenzo[f]coumarins, compounds with important antioxidant properties

Electrochemical detection of in situ adriamycin oxidative damage to DNA

Adriamycin intercalation and in situ interaction with double helix DNA was investigated using a voltammetric DNA-biosensor. Oxidation and reduction of adriamycin molecules intercalated in double helix DNA were investigated in order to understand the in vivo mechanism of action with this anti-neoplasic drug. The results showed that the interaction of adriamycin with DNA is potential-dependent causing contact between DNA guanine and adenine bases and the electrode surface such that their oxidation is easily detected. A mechanism for adriamycin reduction and oxidation in situ when intercalated in double helix DNA immobilised onto the glassy carbon electrode surface is presented and the formation of the mutagenic 8-oxoguanine explained.http://www.sciencedirect.com/science/article/B6THP-44PVS7R-M/1/1474d369a4b1d556b84d548d2df2543

Synthetic oligonucleotides: AFM characterisation and electroanalytical studies

One of the most important steps in designing more sensitive and stable DNA based biosensors is the immobilisation procedure of the nucleic acid probes on the transducer surface, while maintaining their conformational flexibility. MAC Mode AFM images in air demonstrated that the oligonucleotide sequences adsorb spontaneously on the electrode surface, showing the existence of pores in the adsorbed layer that reveal big parts of the electrode surface, which enables non-specific adsorption of other molecules on the uncovered areas. The electrostatic immobilisation onto a glassy carbon electrode followed by hybridisation with a complementary sequence and control with a non-complementary sequence was studied using differential pulse voltammetry and electrochemical impedance spectroscopy. Changes in the oxidation currents of guanosine and adenosine were observed after hybridisation events as well as after control experiments. Modification of the double layer capacitance that took place after hybridisation or control experiments showed that non-specific adsorption of complementary or non-complementary sequences occur allowing the formation of a mixed multilayer.http://www.sciencedirect.com/science/article/B6W72-4GP1VK1-1/1/c44e3d2a4c722d5cec59a4d09d0a744

Horizontal Vortex Tubes near a Simulated Tornado: Three-Dimensional Structure and Kinematics

Supercell thunderstorms can produce a wide spectrum of vortical structures, ranging from midlevel mesocyclones to small-scale suction vortices within tornadoes. A less documented class of vortices are horizontally-oriented vortex tubes near and/or wrapping about tornadoes, that are observed either visually or in high-resolution Doppler radar data. In this study, an idealized numerical simulation of a tornadic supercell at 100 m grid spacing is used to analyze the three-dimensional (3D) structure and kinematics of horizontal vortices (HVs) that interact with a simulated tornado. Visualizations based on direct volume rendering aided by visual observations of HVs in a real tornado reveal the existence of a complex distribution of 3D vortex tubes surrounding the tornadic flow throughout the simulation. A distinct class of HVs originates in two key regions at the surface: around the base of the tornado and in the rear-flank downdraft (RFD) outflow and are believed to have been generated via surface friction in regions of strong horizontal near-surface wind. HVs around the tornado are produced in the tornado outer circulation and rise abruptly in its periphery, assuming a variety of complex shapes, while HVs to the south-southeast of the tornado, within the RFD outflow, ascend gradually in the updraft.The first author is supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Grant number 88881.129505/2016-01 of the “Programa de Doutorado Pleno no Exterior” (DPE – 3830) under the Brazilian Ministry of Education. The second author is supported NSF Grant AGS-1261776 and NOAA VORTEX-SE Grant NA17OAR4590188. Open Access fees paid for in whole or in part by the University of Oklahoma Libraries.Ye

AFM and electroanalytical studies of synthetic oligonucleotide hybridization

The first and most important step in the development and manufacture of a sensitive DNA-biosensor for hybridization detection is the immobilization procedure of the nucleic acid probe on the transducer surface, maintaining its mobility and conformational flexibility. MAC Mode AFM images were used to demonstrate that oligonucleotide (ODN) molecules adsorb spontaneously at the electrode surface. After adsorption, the ODN layers were formed by molecules with restricted mobility, as well as by superposed molecules, which can lead to reduced hybridization efficiency. The images also showed the existence of pores in the adsorbed ODN film that revealed large parts of the electrode surface, and enabled non-specific adsorption of other ODNs on the uncovered areas. Electrostatic immobilization onto a clean glassy carbon electrode surface was followed by hybridization with complementary sequences and by control experiments with non-complementary sequences, studied using differential pulse voltammetry. The data obtained showed that non-specific adsorption strongly influenced the results, which depended on the sequence of the ODNs. In order to reduce the contribution of non-specific adsorbed ODNs during hybridization experiments, the carbon electrode surface was modified. After modification, the AFM images showed an electrode completely covered by the ODN probe film, which prevented the undesirable binding of target ODN molecules to the electrode surface. The changes of interfacial capacitance that took place after hybridization or control experiments showed the formation of a mixed multilayer that strongly depended on the local environment of the immobilized ODN.http://www.sciencedirect.com/science/article/B6TFC-4CYNVTG-7/1/9dd6257bfec8e07f1a15905be07dbd1