Combinatorial Chemistry & High Throughput Screening - Volume 16, Issue 2, 2013

An electrochemical microsensor has been developed for the simultaneous assay of ascorbate (AA) and urate (UA) antioxidants in human blood serum. The electrode surface was modified by means of electropolymerized conductive poly(3,4-ethylenedioxythiophene) PEDOT organic films. Highly selective responses (detection potential difference more than 250 mV) were obtained for both biomarkers by optimizing the PEDOT thickness. Contrary to most previous studies the analytical performances were recorded by testing the microsensor directly in blood serum without any pretreatment of the samples. Using differential pulse voltammetry (DPV) the sensitivity and detection limit were 0.481 μA μM-1 cm-2 and 4.2 μmol L-1 for AA and 1.815 μA μM-1 cm-2 and 2.0 μmol L-1 for UA. The calibration curves were linear in the concentration range 5-200 μmol L-1 for AA and 3-700 μmol L-1 for UA. The accuracy of the sensor was satisfactorily compared with the reference analytical methods provided that the synergic effect between both antioxidants was considered. The sensor response was unmodified in the presence of the major biochemical interfering species.

The electrochemical oxidation mechanisms of rosmarinic acid (RA) and verbascoside (VB), both caffeic acid esters with two catechol moieties, were investigated. The redox mechanism is associated with the oxidation of the catechol groups, and was studied over a wide pH range by cyclic, differential pulse and square wave voltammetry, using a glassy carbon electrode. The voltammetric study revealed that both molecules, RA and VB, are reversibly oxidized in two successive pH-dependent steps each with the transfer of two electrons and two protons. Moreover, it was found that the first oxidation step is associated with the caffeic acid moiety, whereas the second oxidation step corresponds to the oxidation in VB of the hydroxytyrosol group and in RA of the 3,4-dihydroxyphenyl lactic acid residue.

Vegetal extracts are among the most important source of polyphenols in the diet, highlighting the importance of their characterization and determination. For this reason, analytical methods have gained increasing interest, with many publications devoted to this subject. Among the wide possibilities of analytical methods, electroanalytical techniques can provide valuable information, since the antioxidant activity of polyphenols is related to their electrochemical properties. This review analyzes and highlights the role of electroanalytical approaches for sensing the antioxidant capacity exhibited by vegetal extracts, as well as focuses on their importance for human health. The analytical capacity of the electrochemistry is comprehensively stated with the selected results found in the literature, mainly from 2000 up to the present date.

The prevention of oxidative reactions in a biological medium as well as the role of reactive oxygen species (ROS) in chronic degenerative diseases are questions that continue to be investigated. Electrochemical biosensors have shown attractive features to evaluate the oxidative stress condition at a level comparable to chromatographic and spectroscopic techniques. The biosensors developed so far are based on direct analysis of specific indicators such as biomarkers of oxidative stress on the monitoring of reactive oxygen species the free radicals in cells or tissues, aiming to obtain a correlation between the index obtained from these indicators with the oxidative stress levels in cells. In this review we will provide an overview of the development of electrochemical biosensors to evaluate the content of antioxidants and reactive oxygen species in physiological systems. Some discussion regarding the analysis of antioxidant capacity at the single cell level is also presented.

The present study aims to determine the antioxidant capacity of the ethanolic extracts of husk fiber of four coconut (Cocos nucifera L.) varieties (yellow dwarf, green dwarf, giant and hybrid) and to evaluate the electrochemical behavior of these extracts on a glassy carbon electrode and on a modified glassy carbon electrode. The highest values of total phenolic content were obtained for the hybrid (531 ± 24 mg GAE g-1 dry extract) and yellow dwarf (501 ± 29 mg GAE g-1 dry extract) varieties and the lowest was for the green dwarf variety with 58 ± 9 mg GAE g-1 dry extract. The ability of the extracts to scavenge DPPH˙ radicals was in the order of giant > yellow dwarf > hybrid > green dwarf and the IC50 values varied from 8.6 to 55.9 μg mL-1. All varieties showed reducing potential by the use of FRAP and CUPRAC methods, with the lowest performance obtained for the green dwarf variety. Additionally, through the use of mimetic biomembranes, ethanolic extracts of coconut husk were shown to protect lipids against oxidative damage independent of the variety. The main antioxidants identified in the extract of yellow dwarf variety by UPLC-MS were quercetin and catechin. Cyclic voltammetric studies of the ethanolic extracts on glassy carbon electrode confirmed the presence of easily oxidized compounds, and the high antioxidant capacity of the varieties. This capacity was expressed as mg quercetin equivalents g-1 dry extract and ranged from 25.9 up to 53.5 mg QE g-1. A poly-xanthurenic acid (poly-Xa)/ multi-walled carbon nanotube (MWCNT) / glassy carbon modified electrode (poly-Xa/MWCNT/GCE) was used for this purpose. Our findings suggest that these extracts are potentially important antioxidant supplements for the everyday human diet, pharmaceutical and cosmetic industries, thereby aggregating value to the enormous amount of waste from the coconut industry, mostly used for burning purposes.

Many compounds can interact with DNA leading to changes of DNA structure as point mutation and bases excision, which could trigger some metabolic failures, which leads to the changes in DNA structure resulting in cancer. Oxidation of nucleic acid bases belongs to the one of the mostly occurred type of DNA damaging leading to the above mentioned phenomena. The investigation of processes of DNA oxidation damage is topical and electrochemical methods include a versatile and sensitive tool for these purposes. 8-hydroxydeoxyguanosine (8-OHdG) is the most widely accepted marker of DNA damage. Oxidative damage to DNA by free radicals and exposure to ionizing radiation generate several other products within the double helix besides mentioned oxidation products of nucleic acid bases. The basic electrochemical behaviour of nucleic acids bases on various types of carbon electrodes is reviewed. Further, we address our attention on description of oxidation mechanisms and on detection of the most important products of nucleic bases oxidation. The miniaturization of detector coupled with some microfluidic devices is suggested and discussed. The main aim of this review is to report the advantages and features of the electrochemical detection of guanine oxidation product as 8-OHdG and other similarly produced molecules as markers for DNA damage.

A new and simple high-performance liquid chromatography method was developed and validated for the simultaneous determination of retinol, retinyl palmitate, β-carotene, α-tocopherol and vitamin C in rat serum treated with Plantago Major L. and 7,12 dimethylbenz[a]anthracene. High-performance liquid chromatography analysis was performed utilizing an Inertsil ODS3 reversed phase column with methanol-tetrahydrofuran-water as mobile phase under gradient conditions, at 1.5 mL min-1 flow rate and 25 °C. Diode-array detection was at 325, 450, 290 and 270 nm (retinol and retinyl palmitate), β-carotene, α-tocopherol and vitamin C, respectively and runnig time 18 min. The high-performance liquid chromatography assay and extraction procedure proposed are simple, rapid, sensitive and accurate. The method was then applied for the determination of retinol, retinyl palmitate, β-carotene, α-tocopherol and vitamin C in rat serum. Results of this study demonstrated that; at 60th day DMBA-treated group, there was a significant decrease in vitamin levels compared to the levels of control group. A significant increase was observed in vitamin levels of 7,12 dimethylbenz[a]anthracene+Plantago Major L.-treated group compared to the DMBA-treated group. Additionally, the results obtained in the study are found to be in agreement with data reported in the literature.

A convenient one-pot, three-component reaction of aromatic aldehydes, 6-amino-1,3-dimethyluracil and active methylene compounds in the presence of Zr(HSO4)4 as a heterogeneous catalyst, under solvent-free conditions brings a very simple and highly efficient method for the preparation of pyrimido[4,5-b]quinolines, pyrimido[5',4':5,6]pyrido[2,3- d]pyrimidines, indeno[2',1':5,6]pyrido[2,3-d]pyrimidines and a new class of pyrimidinedione derivatives in excellent yields. This approach is general and provides several advantages such as simple reaction set-up, very mild reaction conditions, high yields, recyclability of the catalyst and environmentally friendly benign.

A new linderone A, namely 2-cinnamoyl-3-hydroxy-4, 5-dimethoxycyclopenta-2, 4-dienone (5), together with three known flavonoids (1-3) and one linderone (4), were isolated from the bark of Lindera oxyphylla. Extensive spectroscopic analysis including 1D and 2D-NMR spectra determined their sturctures. In addition, the antioxidant activity of all the compounds has been determined using 2, 2-diphenyl-1-picrylhydrazyl radical scavenging (DPPH), ferric reducing antioxidant power (FRAP) and ferrous ion chelating (FIC) methods. Compound 3 showed excellent DPPH scavenging activity with IC50% value of 8.5 ± 0.004% (μg/mL) which is comparable with vitamin C. This compound, also showed an absorbance value of 1.00 ± 0.06% through FRAP test when compared with Butyl Hydroxy Aniline (BHA). However, FIC showed low activity for all the isolated compounds (chelating activity less than 50%) in comparison with ethylene diamine tetra acetic acid (EDTA). Anticancer activity for all compounds has also been measured on A375 human melanoma, HT-29 colon adenocarcinoma, MCF-7 human breast adenocarcinoma cells, WRL-68 normal hepatic cells, A549 non-small cell lung cancer cells and PC-3 prostate adenocarcinoma cell line. Compound 1 showed A549=65.03%, PC-3=30.12%, MCF-7=47.67, compound 2 showed PC-3=90.13%, compound 3 showed MCF-7=79.57 and for compound 5 MCF-7 is 96.33.