Simultaneous Determination of Nickel and Cadmium by Adsorptive Stripping Voltammetry

A sensitive and fast method for the simultaneous determination of trace amounts of nickel and cadmium in real samples has been described using differential pulse adsorptive stripping voltammetry (DPASV) by adsorptive accumulation of the N,N′‐bis(salicylaldehydo)4‐carboxyphenylenediamine (BSCPDA)–complex on the hanging mercury drop electrode (HMDE). As supporting electrolyte 0.02 mol L^?1 ammonia buffers containing ligand has been used. Optimal analytical conditions were found to be: BSCPDA concentration of 42 μM, pH 9.6 and adsorption potential at ?50 mV versus Ag/AgCl. With an accumulation time of 20 s, the peaks current are proportional to the concentration of nickel and cadmium over the 1–180, and 0.5–200 ng mL^?1 with detection limits of 0.06 and 0.03 ng mL^?1 respectively. The sensitivity of method for determination of nickel and cadmium were obtained 0.54 and 0.98 nA mL ng^?1, respectively. The procedure was applied to simultaneous determination of nickel and cadmium in some real and synthetic artificial samples with satisfactory results.     

Fingerprinting DNA Oxidation Processes: IR Characterization of the 5‐Methyl‐2′‐Deoxycytidine Radical Cation

Methylated cytidine plays an important role as an epigenetic signal in gene regulation. Its oxidation products are assumed to be involved in active demethylation processes but also in damaging DNA. Here, we report the photochemical production of the 5‐methyl‐2′‐deoxycytidine radical cation via a two‐photon ionization process. The radical cation is detected by time‐resolved IR spectroscopy and identified by band assignment using density functional theory calculations. Two final oxidation products are characterized with liquid chromatography coupled to mass spectrometry.     

Ionic Liquid‐Carbon Nanotube Modified Screen‐Printed Electrodes and Their Potential for Adsorptive Stripping Voltammetry

Compared with paraffin oil, the use of ionic liquids as a binder in carbon paste type electrodes was shown to greatly enhance the accumulation of analytes, as illustrated with 17α‐ethynylestradiol as a model. The ionic “liquid” n‐octyl‐pyridinium hexafluorophosphate [C₈py][PF₆] was most efficient among several ionic liquids investigated. Such preconcentration allowed a [C₈py][PF₆]‐multiwalled carbon nanotubes (MWCNTs) (95 : 5 w/w) composite electrode to be useful for adsorptive stripping voltammetry. Screen‐printed electrodes modified with [C₈py][PF₆]‐MWCNTs were developed and were able to achieve high sensitivity during adsorptive stripping voltammetric measurements under optimised conditions.     

Unraveling the Degradation Mechanism of Purine Nucleotides Photosensitized by Pterins: The Role of Charge‐Transfer Steps

Photosensitized reactions contribute to the development of skin cancer and are used in many applications. Photosensitizers can act through different mechanisms. It is currently accepted that if the photosensitizer generates singlet molecular oxygen (¹O₂) upon irradiation, the target molecule can undergo oxidation by this reactive oxygen species and the reaction needs dissolved O₂ to proceed, therefore the reaction is classified as ¹O₂‐mediated oxidation (type II mechanism). However, this assumption is not always correct, and as an example, a study on the degradation of 2′‐deoxyguanosine 5′‐monophosphate photosensitized by pterin is presented. A general mechanism is proposed to explain how the degradation of biological targets, such as nucleotides, photosensitized by pterins, naturally occurring ¹O₂ photosensitizers, takes place through an electron‐transfer‐initiated process (type I mechanism), whereas the contribution of the ¹O₂‐mediated oxidation is almost negligible.     

The Use of a Solid Bismuth Microelectrode for Vanadium Quantification by Adsorptive Stripping Voltammetry in Environmental Water Samples

This paper presents for the first time the use of an environmentally friendly solid bismuth microelectrode for the voltammetric quantification of V(V) in natural water samples. These studies were designed to replace the film bismuth electrode that had been introduced to eliminate the conventional sensors based on highly toxic mercury. In the proposed procedure, V(V) is preconcentrated at the solid bismuth microelectrode surface via the formation of electroactive complexes with cupferron from a solution of 0.1-mol L⁻¹ acetate buffer, pH = 4.6 at a potential of −0.4 V. The linearity of the calibration graph is in the V(V) concentration range from 8 × 10⁻¹⁰ to 1 × 10⁻⁷ mol L⁻¹ with a preconcentration time of 1 min. The limit of detection (calculated as 3 σ) is 2.5 × 10⁻¹⁰ mol L⁻¹ for a preconcentration time of 1 min. It was also demonstrated that significant improvement in analytical parameters was achieved as a result of the activation of the solid electrode surface at a potential of −2.5 V for 2 s. The developed procedure is highly selective for the presence of foreign ions and organic compounds in tested samples. The accuracy of the recommended procedure was checked using SPS-WW1 waste water-certified reference materials of a complex composition, in which the concentration of V(V) determined by the proposed method was 95.1 ± 1.6 ng mL⁻¹. Moreover, in keeping with the outlined procedure, river, tap and rain water samples were analyzed without any pretreatment, and recovery values from 96% to 106% were obtained.     

Ultrasensitive Simultaneous Quantification of Nanomolar Level of Cd and Zn by Cathodic Adsorptive Stripping Voltammetry in Some Real Samples

A novel, simple and sensitive adsorptive stripping voltammetry method was developed for simultaneous determination of Cd and Zn using N‐Nitrozo‐N‐phenylhydroxylamine (Cupferron) as a selective complexing agent. Cadmium and zinc metals gave peaks that were distinctly separated by 450–1200 mV, allowing their determination over a wide range of concentrations. The influence of pH and the nature of supporting electrolytes, concentration of ligand, preconcentration time and applied potential were investigated. The detection limits were 0.058 ng/mL for Zn and 0.092 ng/mL for Cd, and the RSD at a concentration level of 50 ppb, were 1.8–2.1 % for both zinc and cadmium, respectively. The method was applied to the determination of cadmium and zinc in blood, drug, food and water samples with the satisfactory results.     

An Extremely Narrow‐Band‐Gap Conjugated Polymer with Heterocyclic Backbone and its Use in Optoelectronic Devices

Summary: A novel narrow‐band‐gap conjugated polymer with heterocyclic backbone, poly[4,7‐bis(4‐decanyl‐2‐thienyl)‐2′,1′,3^′‐benzothiadiazole‐thiophene‐2,5‐] (PDDBT, E_g = 1.38 eV) was synthesized by a Stille coupling reaction. Prototype bulk heterojunction photovoltaic cells from PDDBT and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) with a ITO/PEDOT:PSS/PDDBT:PCBM(1:3)/Ba/Al device architecture showed power conversion efficiencies up to 0.13% under AM1.5 solar simulator (100 mW · cm⁻²) with an open‐circuit voltage V_oc of 0.65 V, a short‐circuit current density J_sc of 0.6 mA · cm⁻², and a photocurrent response up to 880 nm. The electroluminescent device from PDDBT showed a near‐infrared light emission peak at around 830 nm with maximal external quantum efficiency of 0.08% and a turn‐on voltage at 3.5 V.

Normalized PL and EL spectra of PDDBT and photosensitivity of PVCs based on PDDBT/PCBM (1:3) blend. The scheme shows the chemical structure of PDDBT.     

Electrochemical Study and Direct Determination of Adenosine‐5′‐Monophosphate Coupled to 6‐Thioguanosine and a Glassy Carbon Modified Electrode with Gold Nanoparticles

The direct accumulation of 6‐thioguanosine (6‐TG) and its electrochemistry has been studied by cyclic voltammetry in different conditions physical and chemical. In a first moment the surface of electrode was modified with gold nanoparticles. This modification was realized by electrodeposition on the active surface of a glassy carbon electrode with a HAuCl₄ solution. The nucleotide 6‐thioguanosine was deposited in this gold nanoparticles monolayer. The study of accumulation of other nucleotide, adenosine 5′‐monophosphate (AMP), was realized by the direct reaction with 6‐TG deposited. The conditions of the reaction and its electrochemical response were tested to fix the ideal conditions of its determination. The ideal conditions of formation of the monolayer and its electrochemical response were studied; the possibility of preconcentration of 6‐TG nucleotide in gold nanoparticles, the possibility of catalysis and limits of identification and quantification were also determined. The method proposed can be applied in direct determination of oligonucleotides. In this respect we applied it in the determination of AMP in a commercial product of infantile nutrition.     

ABTS‐Multiwalled Carbon Nanotubes Nanocomposite/Bi Film Electrode for Sensitive Determination of Cd and Pb by Differential Pulse Stripping Voltammetry

A 2,2′‐azinobis (3‐ethylbenzothiazoline‐6‐sulfonate) diammonium salt (ABTS)‐multiwalled carbon nanotubes (MWCNTs) nanocomposite/Bi film modified glassy carbon (GC) electrode was constructed for the differential pulse stripping voltammetric determination of trace Pb²⁺ and Cd²⁺. This electrode was more sensitive than ABTS‐free Bi/GC and Bi/MWCNTs/GC electrodes. Linear responses were obtained in the range from 0.5 to 35 μg L^?1 for Cd²⁺ and 0.2 to 50 μg L^?1 Pb(II), with detection limits of 0.2 μg L^?1 for Cd²⁺ and 0.1 μg L^?1 for Pb²⁺, respectively. This sensor was applied to the simultaneous detection of Cd²⁺ and Pb²⁺ in water samples with satisfactory recovery.     

Application of Adsorptive Stripping Voltammetry for Determination of Uranium in the Presence of 3-Hydroxy-2-Naphthoic Hydrazide

Abstract

A new method is presented for determination of uranium based on a cathodic adsorptive stripping of the complex of uranium with a 3-hydroxy-2-naphthoic hydrazide at a hanging mercury drop electrode (HMDE). The most suitable operating conditions and parameters, such as pH, deposition potential, deposition time, ligand concentration, and others, were selected and the determination of uranium from aqueous solutions using the standard addition method was possible. Under optimum conditions, the measured peak current is proportional to the concentration of uranium over the range of 1–500 nA with a detection limit of 0.75 nM.     

DNA Determination in the Presence of Copper in Diluted Alkaline Electrolyte by Adsorptive Stripping Voltammetry at the Mercury Film Electrode

A stripping method for the determination of single‐stranded DNA in presence of copper at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation of adenine (from acid‐treated DNA) at thin‐film mercury electrode followed by linear scan voltammetry measurement of the surface species. Optimum experimental conditions were found to be the use of a 5.0×10^?3 M NaOH solution, an accumulation potential of ?0.40 V and a scan rate of 200 mV s^?1. The response of adenine–copper is linear over the concentration range 50–250 ppb. For an accumulation time of 15 minutes, the detection limit was found to be 4 ppb. The more convenient relation to measuring the ssDNA in presence of metals and nitrogenated bases were also investigated. The utility of the method is demonstrated by the presence of adenosine‐triphosphate (ATP) and amino acids.     

Synthesis and Crystal Structures of O‐2′,3′‐Cyclic Cyclopentanone and Cyclohexanone Ketals of the Cytostatic 5‐Fluorouridine

The synthesis of two O‐2′,3′‐cyclic ketals, i.e., 5 and 6 , of the cytostatic 5‐fluorouridine ( 2 ), carrying a cyclopentane and/or a cyclohexane ring, respectively, is described. The novel compounds were characterized by ¹H‐, ¹⁹F‐, and ¹³C‐NMR, and UV spectroscopy, as well as by elemental analyses. Their crystal structures were determined by X‐ray analysis. Both compounds 5 and 6 show an anti‐conformation at the N‐glycosidic bond which is biased from +ac to +ap compared to the parent nucleoside 2 . The sugar puckering is changed from ^2′E to _3′E going along with a reduction of the puckering amplitude τ_m by ca. 10–13° due to the ketalization. The conformation about the sugar exocyclic bond C(4′)? C(5′) of 5 and 6 remains unchanged, i.e., g⁺, compared with compound 2 .     

Validation of Some Procedures for Quantifying Platinum at sub‐μg/L Level in Some Real Matrices by Catalytic Adsorptive Stripping Voltammetry

The potential toxicological properties of platinum group elements, usually present in real matrices at sub‐ng/g level, explain the increasing interest in developing specific and sensitive analytical methods. In this work, a validation study was performed in order to ensure the fitness‐for‐purposes of procedures developed for quantifying platinum in tap water, beer and lettuce using an extremely sensitive method based on catalytic adsorptive stripping voltammetry. The work involved the estimation of selectivity, detection and quantitation limits, range, accuracy (trueness plus precision), uncertainty of measurement (UOM), robustness and recovery. The results are discussed in the light of the most recent literature findings.     

Semi‐synthesis and NMR spectral assignments of flavonoid and chalcone derivatives

Previous investigations of the aerial parts of the Australian plant Eremophila microtheca and Syzygium tierneyanum resulted in the isolation of the antimicrobial flavonoid jaceosidin ( 4 ) and 2′,6′‐dihydroxy‐4′‐methoxy‐3′,5′‐dimethyl chalcone ( 7 ), respectively. In this current study, compounds 4 and 7 were derivatized by acetylation, pivaloylation, and methylation reactions. The final products, 5,7,4′‐triacetoxy jaceosidin ( 10 ), 5,7,4′‐tripivaloyloxy jaceosidin ( 11 ), 5,7,4′‐trimethoxy jaceosidin ( 12 ), 2′,6′‐diacetoxy‐4′‐methoxy‐3′,5′‐dimethyl chalcone ( 13 ), 2′‐hydroxy‐4′‐methoxy‐6′‐pivaloyloxy‐3′,5′‐dimethyl chalcone ( 14 ), and 2′‐hydroxy‐4′,6′‐dimethoxy‐3′,5′‐dimethyl chalcone ( 15 ) were all fully characterized by NMR and MS. Derivatives 10 and 13 have been previously reported but were only partially characterized. This is the first reported synthesis of 11 and 14 . The natural products and their derivatives were evaluated for their antibacterial and antifungal properties, and the natural product, jaceosidin ( 4 ) and the acetylated derivative, 5,7,4′‐triacetoxy jaceosidin ( 10 ), showed modest antibacterial activity (32–128 µg/ml) against Staphylococcus aureus strains. Copyright © 2016 John Wiley & Sons, Ltd.     

Simultaneous Determination of Adenosine and Adenosine‐5′‐triphosphate at Nanogold Modified Indium Tin Oxide Electrode by Osteryoung Square‐Wave Voltammetry

Simultaneous determination of adenosine and adenosine‐5′‐triphosphate has been described using nanogold modified indium tin oxide electrode. Gold nanoparticles catalyze adenosine oxidation which results in increasing separation of oxidation peaks of adenosine and ATP, making it possible to determine adenosine and adenosine‐5′‐triphosphate simultaneously. The detection limits for adenosine and ATP were found as 0.07 μM and 0.10 μM respectively with sensitivity 22.9 nA μM^?1 and 20.9 nA μM^?1. The proposed method was also used for sensing the compounds in biological samples. Influence of various square‐wave parameters and different pH conditions on peak current has also been reported.     

Iodine‐Catalyzed Synthesis of Spiro[1,3,4‐benzotriazepine‐2,3′‐indole]‐2′,5(1H,1′H)‐diones under Mild Conditions

The I₂‐catalyzed preparation of spiro[1,3,4‐benzotriazepine‐2,3′‐indole]‐2′,5(1H,1′H)‐diones from 2‐aminobenzohydrazide and isatins in MeCN at room temperature in good‐to‐excellent yields is described. The structure of 3 was corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS data). A plausible mechanism for this type of reaction is proposed (Scheme 2).     

Synthesis,structure, and activity of (PhCH2NH2)2CuCl2 for oxidative coupling of 2‐naphthylamine

(PhCH₂NH₂)₂CuCl₂ ( 2 ), an effective oxidation reagent for oxidative coupling of 2‐naphthylamine ( 1 ) to form 2,2′‐diamino‐1,1′‐binaphthyl ( 4 ), is studied. Oxidative coupling of 2‐naphthylamine ( 1 ) is carried out at room temperature in methanol by (PhCH₂NH₂)₂CuCl₂ ( 2 ), which is prepared from CuCl₂·2H₂O and benzylamine in methanol, to give a novel copper complex, [{1,1′‐(C₁₀H₆)₂‐2,2′‐(NH₂)₂}₂CuCl]Cl·CH₃OH·3H₂O ( 3 ), in good yield. Treatment of 3 with aqueous HCl (37%), followed by addition of NH₃·H₂O (25%), gives 2,2′‐diamino‐1,1′‐binaphthyl ( 4 ) in a moderate yield (total yield from 1 : > 70%). Both 2 and 3 have been characterized by various techniques, such as infrared spectroscopy, elemental analyses and X‐ray diffraction. Copyright © 2007 John Wiley & Sons, Ltd.     

Tissue distribution and metabolism of the putative cancer chemopreventive agent 3′,4′,5′‐trimethoxyflavonol (TMFol) in mice

3′,4′,5′‐Trimethoxyflavonol (TMFol) is a synthetic flavonol with preclinical cancer chemopreventive properties. The hypothesis was tested that, in mice, p.o. administration of TMFol results in measureable levels of the parent in target tissues. A single oral dose (240 mg/kg) was administered to mice (n = 4 per time point) with time points ranging from 5 to 1440 min. TMFol and its metabolites were identified and quantitated in all tissues by high‐performance liquid chromatography (HPLC). Plasma levels of TMFol were at the limit of quantification or below, although metabolites were identified. Peak levels of TMFol in the gastrointestinal tract and the prostate averaged 1671 ± 265 µg/g (5.3 µmol/g) and 6.0 ± 1.6 µg/g (18.4 nmol/g), and occurred 20 and 360 min post‐dose, respectively. The area under the tissue concentration–time curve (AUC) for TMFol was greater than those of the metabolites, indicating that TMFol is relatively metabolically stable. Micromolar TMFol levels are easily achieved in the prostate and gastrointestinal tract, suggesting that TMFol might exert chemopreventive efficacy at these tissue sites. Further investigations are warranted to elucidate the potential chemopreventive potency of TMFol. Copyright © 2012 John Wiley & Sons, Ltd.