Electrochemical Study on DNA Damage Based on the Direct Oxidation of 8‐Hydroxydeoxyguanosine at an Electrochemically Modified Glassy Carbon Electrode

The study of DNA damage induced by Fenton reaction (Fe²⁺/H₂O₂) in vitro was performed based on the direct electrochemical oxidation of 8‐hydroxydeoxyguanosine (8‐OH‐dG), the biomarker of DNA oxidative damage, at an electrochemically modified glassy carbon electrode (GCE). The effects of antioxidants, such as ascorbic acid, and hydroxyl‐radical scavenger (mannitol) on the DNA damage were also investigated. 8‐OH‐dG, the oxidation product of guanine residues in DNA, has shown significantly oxidative peak on the electrochemically modified GCE. The oxidative peak current of 8‐OH‐dG was linear with the damaged DNA concentration in the range of 10–200 mg/L. The experimental results demonstrate that ascorbic acid has ambivalent effect on DNA oxidative stress. It can promote DNA oxidative damage when ascorbic acid concentration is below 1.5 mM and protect DNA from damage in the range of 1.5–2.5 mM. As a hydroxyl‐radical scavenger, mannitol inhibits significantly DNA oxidative damage. The influence of Fe²⁺, as reactant, and EDTA as iron chelator in the system were also studied. The proposed electrochemical method can be used for the estimation of DNA oxidative damage from new point of view.     

Carbon Nanotubes‐Based Amperometric Cholesterol Biosensor Fabricated Through Layer‐by‐Layer Technique

A carbon nanotubes‐based amperometric cholesterol biosensor has been fabricated through layer‐by‐layer (LBL) deposition of a cationic polyelectrolyte (PDDA, poly(diallyldimethylammonium chloride)) and cholesterol oxidase (ChOx) on multi‐walled carbon nanotubes (MWNTs)‐modified gold electrode, followed by electrochemical generation of a nonconducting poly(o‐phenylenediamine) (PPD) film as the protective coating. Electrochemical impedance measurements have shown that PDDA/ChOx multilayer film could be formed uniformly on MWNTs‐modified gold electrode. Due to the strong electrocatalytic properties of MWNTs toward H₂O₂ and the low permeability of PPD film for electroacitve species, such as ascorbic acid, uric acid and acetaminophen, the biosensor has shown high sensitivity and good anti‐interferent ability in the detection of cholesterol. The effect of the pH value of the detection solution on the response of the biosensor was also investigated. A linear range up to 6.0 mM has been observed for the biosensor with a detection limit of 0.2 mM. The apparent Michaelis‐Menten constant and the maximum response current density were calculated to be 7.17 mM and 7.32 μA cm^?2, respectively.     

Protein Protection by Antioxidants: Development of a Convenient Assay and Structure‐Activity Relationships of Natural Polyphenols

In this work, a convenient test of antioxidant activity was developed, with BChE‐contaminated HSA as the target of AAPH‐induced oxidation and its esterase activity as the marker of protein integrity or degradation. The method is relatively simple, of low cost, and convenient to use. Its application to natural polyphenols showed that quercetin ( 1 ), verbascoside ( 2 ), chlorogenic acid ( 3 ), caffeic acid ( 4 ), 1,3,6,7‐tetrahydroxyxanthone ( 5 ), and mangiferin ( 6 ), are good antioxidants (IC₅₀<9 μM ). 1,5‐Dihydroxy‐3‐methoxyxanthone ( 7 ), flemichin D ( 8 ), and cordigone ( 9 ) showed modest activities (ca. 50 μM <IC₅₀<350 μM ), whereas danthrone ( 10 ) was inactive. Complementary experiments with two of the more active antioxidants, namely quercetin ( 1 ) and chlorogenic acid ( 3 ) showed that both antioxidants were better radical scavengers than chain‐breaking antioxidants. The relative adiabatic oxidation potential (ΔH_ox), the relative H‐bond dissociation energy (ΔH_abs), and the first oxidation potential measured by cyclic voltammetry were found to be related to the radical‐scavenging activity of these antioxidants.     

DPPH (= 2,2‐Diphenyl‐1‐picrylhydrazyl = 2,2‐Diphenyl‐1‐(2,4,6‐trinitrophenyl)hydrazyl) Radical‐Scavenging Reaction of Protocatechuic Acid Esters (= 3,4‐Dihydroxybenzoates) in Alcohols: Formation of Bis‐alcohol Adduct

Protocatechuic acid esters (= 3,4‐dihydroxybenzoates) scavenge ca. 5 equiv. of radical in alcoholic solvents, whereas they consume only 2 equiv. of radical in nonalcoholic solvents. While the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents as compared to that in nonalcoholic solvents is due to a nucleophilic addition of an alcohol molecule at C(2) of an intermediate o‐quinone structure, thus regenerating a catechol (= benzene‐1,2‐diol) structure, it is still unclear why protocatechuic acid esters scavenge more than 4 equiv. of radical (C(2) refers to the protocatechuic acid numbering). Therefore, to elucidate the oxidation mechanism beyond the formation of the C(2) alcohol adduct, 3,4‐dihydroxy‐2‐methoxybenzoic acid methyl ester ( 4 ), the C(2) MeOH adduct, which is an oxidation product of methyl protocatechuate ( 1 ) in MeOH, was oxidized by the DPPH radical (= 2,2‐diphenyl‐1‐picrylhydrazyl) or o‐chloranil (= 3,4,5,6‐tetrachlorocyclohexa‐3,5‐diene‐1,2‐dione) in CD₃OD/(D₆)acetone 3 : 1). The oxidation mixtures were directly analyzed by NMR. Oxidation with both the DPPH radical and o‐chloranil produced a C(2),C(6) bis‐methanol adduct ( 7 ), which could scavenge additional 2 equiv. of radical. Calculations of LUMO electron densities of o‐quinones corroborated the regioselective nucleophilic addition of alcohol molecules with o‐quinones. Our results strongly suggest that the regeneration of a catechol structure via a nucleophilic addition of an alcohol molecule with a o‐quinone is a key reaction for the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents.     

Iron(III)‐mediated AGET ATRP of styrene using tris(3,6‐dioxaheptyl)amine as a ligand

A commercially available tris(3,6‐dioxaheptyl)amine (TDA‐1) was used as a novel ligand for activator generated by electron transfer atom transfer radical polymerization (AGET ATRP) of styrene in bulk or solution mediated by iron(III) catalyst in the presence of a limited amount of air. FeCl₃ · 6H₂O and (1‐bromoethyl)benzene (PEBr) were used as the catalyst and initiator, respectively; and environmentally benign ascorbic acid (VC) was used as the reducing agent. The polymerizations show the features of “living”/controlled free‐radical polymerizations and well‐defined polystyrenes with molecular weight M_n = 2400–36,500 g/mol and narrow polydispersity (M_w/M_n = 1.11–1.29) were obtained. The “living” feature of the obtained polymer was further confirmed by a chain‐extension experiment. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2002–2008, 2009     

Simultaneous Detection of Homocysteine and Cysteine in the Presence of Ascorbic Acid and Glutathione Using a Nanocarbon Modified Electrode

The simultaneous electrochemical detection of homocysteine and cysteine using an absorbed ortho‐quinone species, catechol, at the nanocarbon modified glassy carbon electrode was achieved via 1,4‐Michael addition reaction. The detection was done in the presence and the absence of each other as well as with both glutathione and ascorbic acid present in order to investigate the selectivity of homocysteine and cysteine. A determination of homocysteine sensitivity is (0.882±0.296) nA nM^?1 with a LOD of ca. 11 nM and cysteine sensitivity is (7.501±0.202) mA µM^?1 with a LOD of ca. 5.0 µM within a range of 0–0.1 mM.     

Swelling Behavior of Chemically Ion-Doped Hydrogels

Summary: Poly(acrylamide-co-N,N′-methylenebisacrylamide) gels were synthesized in the presence of pyranine fluoroprobe (trisodium 8-hydroxypyrene-1,3,6-trisulfonate). Pyranine binds to polymer chains through its OH group via radical addition. Thus, the final gels were doped with the pyranines having SO ions as side groups and Na⁺ as counter-ions. The swelling behavior of gels prepared with varying amounts of pyranine and monomer concentrations were studied. The swelling ratio of the synthesized gels did not exceed 35 except the 2 M gel containing 10⁻² M pyranine which are the concentrations for the abnormal swelling behavior. At this particular concentration of monomer (acrylamide) and pyranine, the mass ratio m/m₀, the mass of the swollen gel to the mass of the dried gel, reaches about 1300; a stepwise behavior was observed in the swelling kinetics. The swelling kinetics of polyacrylamide gels containing unbound (free) pyranine were compared with the swelling behavior of the gels containing chemically bound pyranine.     

Computational and experimental validation of free radical scavenging properties of high‐performance thin‐layer chromatography quantified phenyl myristate in Homalium nepalense

Phenyl myristate was isolated from Homalium nepalense, which is known for its therapeutic virtues in traditional medicine. However, the study of radical scavenging‐capacity of phenyl myristate is limited by its relatively low abundance in medicinal plants. We have studied the isolation, structure‐elucidation, and bioactivities of high‐performance thin‐layer chromatography validated phenyl myristate from hydroalcohol‐extract of bark of H. nepalense. The chemical structure of phenyl myristate was elucidated by spectroscopic methods. The chromatography was performed on high‐performance thin‐layer chromatography aluminum plates coated with silica‐gel 60 F₂₅₄. Determination and quantitation of phenyl myristate were performed by densitometric‐scanning at 254 nm (chloroform‐methanol, 9:1, v/v; R_f 0.49). The method was validated according to International Council for Harmonisation guidelines in terms of linearity, specificity, sensitivity, accuracy, precision, robustness, and stability. Linearity‐range of phenyl myristate was 100–500 ng/5 µL with correlation‐coefficient r² = 0.9997. Limits of detection and quantitation were 3.35 and 10.17 ng, respectively. Phenyl myristate showed significant free‐radical‐scavenging activities in 2,2?diphenyl?1?picrylhydrazyl, oxygen‐radical‐absorbance‐capacity, and ex vivo cell‐based‐antioxidant‐protection‐in‐erythrocytes assays. Molecular‐docking approach of phenyl myristate showed effective binding at active sites of human serum albumin (HSA) with the lowest binding energy (?8.4 kcal/mol) that was comparable with ascorbic acid (?5.0 kcal/mol). These studies provide mechanistic insight into the potential free radical scavenging activities of phenyl myristate.     

Synthesis of H‐shaped A3BA3 copolymer by methyl‐2‐nitrosopropane induced single electron transfer nitroxide radical coupling

Amphiphilic H‐shaped [poly(ethylene oxide)]₃‐polystyrene‐[poly(ethylene oxide)]₃(PEO₃‐PS‐PEO₃) copolymer was synthesized by 2‐methyl‐2‐nitrosopropane (MNP) induced single electron transfer nitroxide radical coupling (SETNRC) using PEO₃‐(PS‐Br) as a single precursor. First, the A₃B star‐shaped precursor PEO₃‐(PS‐Br) was synthesized by atom transfer radical polymerization (ATRP) using three‐arm star‐shaped PEO₃‐Br as macro‐initiator. Then, in the presence of Cu(I)Br/Me₆TREN, the bromide group at PS end was sequentially transferred into carbon‐centered radical by single electron transfer and then nitroxide radical by reacting with MNP in mixed solvents of dimethyl sulfoxide (DMSO)/tetrahydrofuran (THF), and in situ generated nitroxide radical could again capture another carbon‐centered radical by fast SETNRC to form target PEO₃‐PS‐PEO₃ copolymer. The MNP induced SETNRC could reach to a high efficiency of 90% within 60 min. After the product PEO₃‐PS‐PEO₃ was cleaved by ascorbic acid, the SEC results showed that there was about 30% fraction of product formed by single electron transfer radical coupling (SETRC) between carbon‐centered radicals. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Kinetic Study of Peroxidase‐Catalyzed Coupling of Benzene‐1,4‐diamine and N‐(2‐Aminoethyl)naphthalen‐1‐amine: Development of Micromolar Hydrogen Peroxide Reaction System

A novel chromogenic method to measure the peroxidase activity using para‐phenylenediamine dihydrochloride (=benzene‐1,4‐diamine hydrochloride; PPDD) and N‐(1‐naphthyl)ethylenediamine dihydrochloride (=N‐(2‐aminoethyl)naphthalen‐1‐amine; NEDA) is presented. The PPDD entraps the free radical and gets oxidized to electrophilic diimine, which couples with NEDA to give an intense red‐colored chromogenic species with maximum absorbance at 490 nm. This assay was adopted for the quantification of H₂O₂ between 20 and 160 μM . Catalytic efficiency and catalytic power of the commercial peroxidase were found to be 4.47×10⁴ M ^?1 min^?1 and 3.38×10^?4 min^?1, respectively. The catalytic constant (k_cat) and specificity constant (k_cat/K_m) at saturated concentration of the co‐substrates were 0.0245×10³ min^?1 and 0.0445 μM ^?1 min^?1, respectively. The chromogenic coupling reaction has a minimum interference from the reducing substances such as ascorbic acid, L ‐cystein, citric acid, and oxalic acid. The method being simple, rapid, precise, and sensitive, its applicability has been tested in the crude vegetable extracts that showed peroxidase activity.     

New Methylene Blue (NMB) Encapsulated in Mesoporous AlMCM‐41 Material and Its Application for Amperometric Determination of Ascorbic Acid in Real Samples

New methylene blue (NMB) dye incorporated into AlMCM‐41 surfactant‐free and hybrid surfactant‐AlMCM‐41 mesophase. UV‐vis evidence shows that new methylene blue dye protonated in both cases of zeolites. New methylene blue is electroactive in zeolites and their electrochemical activity has been studied by cyclic voltammetry and compared to that of NMB in aqueous solutions. New methylene blue molecules are not released to the solution during CV measurements and are accessible to H₃O⁺ ions. The presence of surfactant affects the kinetics of the redox process through proton ions diffusion. The midpoint potentials (E_m) values show that new methylene blue dye incorporated into AlMCM‐41 can be reduced easily with respect to solution new methylene blue. New methylene blue interacting with surfactant polar heads and residual Br^? ions as a results, it shows a couple of peaks in high potential with respect to new methylene blue solution. The electrode made with methylene blue‐AlMCM‐41 without surfactant was used for the mediated oxidation of ascorbic acid. The anodic peak current observed in cyclic voltammetry was linearly dependent on the ascorbic acid concentration. The calibration plot was linear over the ascorbic acid concentration range 1.0×10^?5 to 5.0×10^?4 M. The detection limit of the method is 1.0×10^?5 M, low enough for trace ascorbic acid determination in various real samples.     

Practical Metal‐Free C(sp3)?H Functionalization: Construction of Structurally Diverse α‐Substituted N‐Benzyl and N‐Allyl Carbamates

Described is a practical and universal C H functionalization of readily removable N‐benzyl and N‐allyl carbamates, with a wide range of nucleophiles at ambient temperature promoted by Ph₃CClO₄. The metal‐free reaction has an excellent functional‐group tolerance, and displays a broad scope with respect to both N‐carbamates and nucleophile partners (a variety of organoboranes and C H compounds). The synthetic utility in target‐ as well as diversity‐oriented syntheses is demonstrated.     

Amperometric Biosensor for Choline Based on Gold Screen‐Printed Electrode Modified with Electrochemically‐Deposited Silica Biocomposite

A mediator‐free choline biosensor was developed using the electrochemically assisted sol‐gel deposition on gold screen‐printed electrodes. The addition of 12 mM of cationic surfactant CTAB in silica sol allowed enhancing the stability of the sensor. The modified electrode demonstrated catalytic activity and stable amperometric response to choline for over 3 weeks of exploitation with the sensitivity of 6 µA mM^?1 and LOD of 6 µM. The interference of ascorbic acid was reduced by pretreating the analyzed solution with MnO₂ powder. The application of the sensor with the purpose of identifying choline in the baby milk demonstrated satisfactory metrological characteristics.     

Preparative isolation and purification of 12 main antioxidants from the roots of Polygonum multiflorum Thunb. using high‐speed countercurrent chromatography and preparative HPLC guided by 1,1′‐diphenyl‐2‐picrylhydrazyl‐HPLC

A hyphenated strategy by off‐line coupling of 1,1′‐diphenyl‐2‐picrylhydrazyl‐high‐performance liquid chromatography, high‐speed countercurrent chromatography, and preparative high‐performance liquid chromatography was established to screen and separate antioxidants from ethyl acetate fraction of the roots of Polygonum multiflorum. Under the targeted guidance of 1,1′‐diphenyl‐2‐picrylhydrazyl‐high‐performance liquid chromatography experiment, 12 compounds were identified as potential antioxidants and readily isolated by high‐speed counter‐current chromatography and preparative high‐performance liquid chromatography. Ultraviolet spectroscopy, mass spectrometry, and ¹H NMR spectroscopy were employed to identify their structures, which were assigned as gallic acid ( 1 , 6.2 mg, 98.28%), catechin ( 2 , 8.8 mg, 90.69%), epicatechin ( 3 , 4.1 mg, 96.71%), polydatin ( 4 , 5.3 mg, 94.91%), 2,3,5,4′‐tetrahydroxy stilbene‐2‐Ο‐β‐D‐glucoside ( 5 , 20.2 mg, 95.23%), piceatannol ( 6 , 5.3 mg, 96.85%), rutin ( 7 , 5.4 mg, 97.92%), resveratrol ( 8 , 5.2 mg, 96.94%), isorhapontigenin ( 9 , 11.4 mg, 94.81%), hyperoside ( 10 , 9.7 mg, 98.52%), rhein ( 11 , 4.9 mg, 97.46%), and emodin ( 12 , 8.2 mg, 95.74%). Notably, compounds 6 and 9 were isolated from Polygonum multiflorum for the first time. In addition, antioxidant activity of compounds 1–12 were evaluated, and compounds 1–8 and 10 exhibited stronger antioxidant activity than ascorbic acid (positive control). These results indicated that the proposed method is a highly efficient strategy to screen and isolate antioxidants from complex natural products.     

An Electrochemical Method for Sensitive Determination of Antioxidant Capacity

A simple and sensitive electrochemical method for the determination of antioxidant capacity has been studied. 4‐hydroxybenzoic acid (4‐HBA) was used as a trapping agent for photogenerated ^.OH radicals, leading to 3,4‐dihydroxybenzoic acid (3,4‐DHBA). Square‐wave voltammetry was used to quantify the amount of 3,4‐DHBA formed from the reaction between 4‐HBA and ^.OH. Addition of antioxidants induced the competition between 4‐HBA and antioxidants toward ^.OH elimination, resulting in a decrease of the measured current. The IC₅₀ for different standard antioxidants was calculated and expressed in Trolox equivalent antioxidant capacity (TEAC). The proposed method was successfully compared to a fluorimetric one.     

Rapid Synthesis of Novel and Known Coumarin‐3‐carboxylic Acids Using Stannous Chloride Dihydrate under Solvent‐Free Conditions

Various coumarin‐3‐carboxylic acid (=2‐oxo‐2H‐1‐benzopyran‐3‐carboxylic acid; CcaH) derivatives have been synthesized in good yields using catalytic amounts of SnCl₂?2 H₂O under solvent‐free conditions. This inexpensive, nontoxic, and readily available catalytic system (10 mol‐%) efficiently catalyzes the Knoevenagel condensation and intramolecular cyclization of various 2‐hydroxybenzaldehydes or acetophenones with Meldrum's acid. High product yields, use of inexpensive and safe catalyst, and solvent‐free conditions display both economic and environmental advantages.     

Simultaneous Determination of 4‐Chlorophenol and Oxalic Acid Using an Expanded Graphite‐Epoxy Composite Electrode

An expanded graphite‐epoxy composite electrode (EG‐Epoxy) was employed for the simultaneous determination of 4‐chlorophenol (4‐CP) and oxalic acid (OA) by using cyclic voltammetry (CV), chronoamperometry (CA), and differential pulse voltammetry (DPV). The results indicated that OA could be determined in the presence of the same concentrations of 4‐CP within the concentration range of 0.1 mM to 0.5 mM with a relative standard deviation (RSD) smaller than 5%. Electrode fouling occurred during CA for 4‐CP concentrations larger than 0.5 mM. The DPV method was used for the simultaneous determination of 4‐CP and OA before and after electrochemical oxidation by chronopotentiometry under galvanostatic conditions (j=0.04 mA cm^?2, t=2 h) of a tap water sample spiked with 0.19 mM 4‐CP and 0.1 M Na₂SO₄.     

Antioxidant activity and kinetics studies of eugenol and 6-bromoeugenol

In this work, we report the antioxidant and free radical scavenging activity of 6-bromoeugenol and eugenol. EC₅₀, the concentration providing 50% inhibition, is calculated and the antioxidant activity index (AAI) is evaluated. The antioxidant activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging method. EC₅₀ values of 6-bromoeugenol, ascorbic acid and eugenol were 34.270 μg/mL, 54.888 μg/mL and 130.485 μg/mL, respectively. 6-Bromoeugenol showed higher AAI value (1.122) followed by ascorbic acid (0.700), then by eugenol (0.295). We also investigate the kinetics of DPPH radical scavenging activity of our products to determine the useful parameter TEC₅₀ to evaluate their antiradical efficiency (ARE). Our results have shown high ARE. This study has provided the following ARE ( × 10^? 3) order for the tested antioxidants: ascorbic acid (70.119)>6-bromoeugenol (34.842) > eugenol (21.313). Finally, we classify ascorbic acid and eugenol as fast kinetics reaction (TEC₅₀ 8.82 and 11.38 min, respectively) and 6-bromoeugenol as medium kinetics reaction (TEC₅₀ 39.24 min).     

Bioassay‐guided Isolation and Antioxidant Activity of Sulfur‐containing Compounds from Clinacanthus nutans

Clinacanthus nutans has been used in traditional herbal medicine for cancer prevention, but the specific bioactive compounds responsible for the observed activities have not been explored. Different polar solvents such as methanol, chloroform, ethyl acetate, and hexane were used for the extraction. The extracts, fractions, and isolated compounds were subjected to DPPH and ferric reducing antioxidant potential (FRAP) assays. Methanol extracts show significant free‐radical scavenging activity of 69.09% in DPPH and 56.49% FRAP. Purification of MeOH extracts afforded the fraction FB28 and two new sulfur‐containing compounds, named clinamide D and E ( 1 , 2 ). Compound ( 1 ) proved to be more active with an IC₅₀ value for DPPH radical scavenging of 118.27 ± 0.01 µg/mL and reduction of Fe³⁺–TPTZ complex of 386.24 ± 0.02, higher than that of the standard ascorbic acid. Sulfur‐containing compounds isolated from C. nutans is a potential natural antioxidant.     

Rapid Synthesis of Thiophene‐Based,Organic Dyes for Dye‐Sensitized Solar Cells (DSSCs) by a One‐Pot,Four‐Component Coupling Approach

This one‐pot, four‐component coupling approach (Suzuki–Miyaura coupling/C?H direct arylation/Knoevenagel condensation) was developed for the rapid synthesis of thiophene‐based organic dyes for dye‐sensitized solar cells (DSSCs). Seven thiophene‐based, organic dyes of various donor structures with/without the use of a 3,4‐ethylenedioxythiophene (EDOT) moiety were successfully synthesized in good yields based on a readily available thiophene boronic acid pinacol ester scaffold (one‐pot, 3‐step, 35–61 %). Evaluation of the photovoltaic properties of the solar cells that were prepared using the synthesized dyes revealed that the introduction of an EDOT structure beside a cyanoacrylic acid moiety improved the short‐circuit current (J_sc) while decreasing the fill factor (FF). The donor structure significantly influenced the open‐circuit voltage (V_oc), the FF, and the power conversion efficiency (PCE). The use of a n‐hexyloxyphenyl amine donor, and our originally developed, rigid, and nonplanar donor, both promoted good cell performance (η=5.2–5.6 %).