Electrochemical study of the interaction between dsDNA and copper(II) using carbon paste and hanging mercury drop electrodes

Microchimica Acta - The interaction of copper(II) with double-stranded (ds) calf thymus DNA was studied in solution as well as at the electrode surface by means of differential pulse stripping...     

Interaction of the mutagen ethidium bromide with DNA, using a carbon paste electrode and a hanging mercury drop electrode

The interaction of ethidium bromide (2,7-diamino-10-ethyl-9-phenylphenanthridinium bromide; EB) with double stranded (ds) calf thymus DNA and thermally denatured single stranded (ss) DNA was studied in solution and at the electrode surface by means of transfer voltammetry using a carbon paste electrode (CPE) as working electrode in 0.2 M acetate buffer, pH 5.0. As a result of intercalation of this dye between the base pairs of dsDNA, the characteristic peak of dsDNA, due to the oxidation of guanine residues, decreased and after a particular concentration of EB a new peak at +0.81 V appeared, probably due to the formation of a complex between dsDNA and EB. The non-intercalated EB gives another peak, but at an increased concentration of the dye. A similar behaviour was observed during the interaction of the dye with ssDNA.Furthermore, the interaction of EB with ds, ss and supercoiled (sc) DNA was studied at the hanging mercury drop electrode (HMDE) surface by means of alternating current voltammetry in 0.3 M NaCl and 50 mM sodium phosphate buffer (pH 8.5) as supporting electrolyte. dsDNA yields a smaller peak at −1.42 V (peak III) compared to the one yielded by ssDNA, since the latter is a relaxed and more accessible form. By addition of EB into the buffer solution an increase of peak III was observed in the dsDNA form as well as in ssDNA resulting from their interaction with EB. Furthermore, the appearance of peak III in covalently closed circular scDNA after exposure to increasing concentrations of EB is a result of the introduction of ‘free ends’ in DNA affecting its structural integrity.     

Electrochemical behaviour of tilmicosin at the hanging mercury drop electrode

The electrochemical behaviour of tilmicosin (TIM) was investigated using cyclic voltammetry and square-wave voltammetry in Britton-Robinson buffers (pH 2–12). The voltammograms of TIM showed one-irreversible peak which attributed to reduction of the >C=C< group in the entire pH values. However, an additional peak was shown over the pH range 2.00 to 4.00. Its peak potential is more positive potential from that of >C=C< group, and its potential was not practically dependent on the pH. On the other hand, the peak potential of >C=C< group was shifted to the more negative values with increasing pH. According to the obtained voltammetric data, the probable reaction mechanism for the reduction of TIM was proposed. Moreover, the adsorption of TIM on the mercury electrode surface by means of square-wave adsorptive stripping voltammetry measurements is studied at different pH values. The peak current variations with the deposition time and TIM concentration were observed.     

槲皮素在悬汞电极上的伏安行为研究

应用循环扫描伏安法考察槲皮素在悬汞电极上的电化学行为,并用线性扫描伏安法测定其含量。在0.1mol/LNa2CO3-NaHCO3(pH9.51)缓冲溶液中,槲皮素在-1.33V(vs.Ag/AgCl)处出现灵敏的还原峰,峰电流与其浓度在2.0×10-6～2.0×10-5mol/L(r=0.9989)范围内呈良好的线性关系。该方法可直接用于罗布麻叶中槲皮素的含量测定。     

甘草苷在悬汞电极上的电化学行为及方法研究

运用循环伏安法(CV)考察了甘草苷在悬汞电极(HMDE)上的电化学还原行为,在-0.7~-1.7 V(vs.SCE)电位窗口及0.10 mol/L(NH4)2SO4溶液中甘草苷在HMDE上的循环伏安行为是一在低扫描速度(<100 mV/s)下受吸附控制,在高扫描速度下受扩散控制的不可逆还原过程,还原峰电位(Epc)为-1.491 V。运用计时库仑法(CC)、计时电流法(CA)测定并计算了甘草苷的电荷传递系数α、扩散系数D以及表观速率常数Kf等电极过程动力学参数。初步探讨了甘草苷在HMDE上的反应机理,同时运用方波伏安法(SWV)研究了甘草苷在HMDE上的方波伏安行为,还原峰电流与其浓度在1.2×10-6~1.2×10-5mol/L及1.2×10-5~1.2×10-3mol/L范围内呈良好的线性关系,相关系数R=0.9936及0.9966,检出限8.0×10-7mol/L,据此可建立直接电化学测定甘草苷含量的方法。     

Sensitive detection of cyclophosphamide using DNA-modified carbon paste, pencil graphite and hanging mercury drop electrodes

The interaction of cyclophosphamide (CP) with calf thymus double-stranded DNA (dsDNA) and thermally denatured single-stranded DNA (ssDNA) immobilized at the carbon paste (CPE) and pencil graphite electrodes (PGE), was studied electrochemically based on oxidation signals of guanine and adenine using differential pulse voltammetry (DPV).As a result of the interaction of CP with DNA, the voltammetric signals of guanine and adenine increased in the case of dsDNA while a slight increase was observed in ssDNA. The effect of experimental parameters such as the interaction time between CP and DNA forms and the concentration of CP, were studied using DPV with CPE and PGE. Additionally, reproducibility and detection limits were determined using both electrodes. A comparison of the analytical performance between CPE and PGE was done. Our results showed that these two different DNA biosensors could be used for the sensitive, rapid and cost effective detection of CP itself as well as of CP-DNA interaction.Furthermore, the interaction of CP with dsDNA and ssDNA was studied in solution and at the electrode surface by means of alternating current voltammetry (ACV) in 0.3 M NaCl and 50 mM sodium phosphate buffer (pH 8.5) supporting electrolyte, using a hanging mercury drop electrode (HMDE) as working electrode.The conclusions of this study were mainly based on tensammetric peaks I (at −1.183 V) and II (−1.419 V) of DNA. This study involved the interaction of CP with surface-confined and solution phase DNA where experimental parameters, such as the concentration of CP and the interaction time, were studied. By increasing the concentration of CP, an increase of peak II was observed in both ds and ssDNA, while an increase of peak I was observed only in the case of dsDNA. An overall conclusion of the study using HMDE was that the interaction of CP with surface-confined DNA significantly differed from that with solution phase DNA. The increase of peaks I and II was lower in the case of interaction of CP with surface-confined DNA, probably due to steric positioning of DNA at the electrode surface.     

Flow-through voltammetry (FTV) with the hanging mercury drop electrode (HMDE)

A flow-through cell with integrated hanging mercury drop electrode for voltammetric, inverse voltammetric, adsorptive voltammetric, and chronoamperometric methods is described. HMDE droplets are automatically formed and renewed. By optimizing the flow-channel the sensitivity could be increased approximately five times in comparison with batch methods using the same deposition conditions.Dedicated to Professor Dr. Rolf Neeb on the occasion of his 65th birthday     

Stripping polarography and the reduction of copper(II) in sea water at the hanging mercury drop electrode

An approximate but general theoretical treatment for reversible and irreversible stripping polarographic systems is presented. The treatment is based on the development of an average current (i), which at plating times exceeding 15 s. is analogous to the instantaneous current in d.c. polarography. Plots of i vs. (E – E°) are generated for reversible and irreversible waves and are discussed for the reduction of copper(II) in sea water as an example. From stripping polarography and anodic stripping voltammetry, this work indicates that the overall reduction of copper(II) at the natural pH is kinetically hindered and thus is “irreversible”. The reversibility and the determination of copper in sea water by a.s.v. can be improved by acidification and/or by the addition of ethylenediamine.     

Voltammetric determination of mesotrione at hanging mercury drop electrode

A study of the electrochemical reduction of the mesotrione pesticide on a hanging mercury drop electrode (HMDE) was performed as a basis for the development of a sensitive analytical method for natural samples. The electrochemical characteristics of herbicide mesotrione dissolved in a phosphate buffer (pH 7.0) have been determined by means of electrochemical techniques such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) over a wide range of pH from 2.0 to 10.0. The experimental parameters, such as electrolyte type and its pH, pulse amplitude, and scan rate were optimized. The method was applied to the determination of the pesticide in a spiked soil samples. Using this method, a linear calibration curve for mesotrione was obtained up to the 0.1 μM range in pH 7 phosphate buffer solution with a detection limit (S/N = 3) of 50 nM. The method can be applied successfully to the determination of mesotrione in soils. The text was submitted by the authors in English.     

Catalytic currents of albumin at the hanging mercury drop electrode

Bovine serum albumin (BSA), as well as completely reduced BSA denoted by P (SH)₃₅, are adsorbed on the hanging mercury drop electrode (HMDE) from alkaline buffer solutions. When time is allowed, a monolayer is adsorbed from very dilute (10^?9M) BSA solutions in ammoniacal and borate buffers. With a monolayer of adsorbed protein the voltammograms at the HMDE are then identical in a given ammoniacal or borax buffer containing cobalt(III) or (II) and different BSA concentrations. Voltammograms of P (SH)₃₅ are virtually identical with those of native BSA. At the HMDE the second Brdi?ka current is proportional to concentration of cobalt(III) or (II) and the first current nearly so. Incompletely or completely adsorbed BSA or P (SH)₃₅ is not desorbed on keeping the HMDE for one hour in ammonia buffers. An incomplete layer of adsorbed BSA or P (SH)₃₅ is relatively rapidly desorbed at ?1.6 V (vs. SCE) and a complete film at ?1.65 V, some desorption occurring at ?1.6 V. Upon desorption, the second Brdi?ka current decreases faster than the first one; this is particularly striking in 1 M ammonia buffer. The rate of desorption is increased by calcium chloride, but the rate of adsorption is not, or only slightly, increased in the presence of calcium. Incomplete adsorption occurs at ?1.60 V (vs. SCE) and no adsorption at ?1.65 V. Indications are obtained that “presodium currents” yield a slight plateau at ?1.67 to ?1.70 V, the plateau currents being attributed to adsorbed BSA, while unadsorbed BSA yields catalytic currents without a plateau, the currents merging with the residual one of the buffer. Calcium chloride greatly increases the presodium currents. From many kinetic data obtained at the dropping mercury electrode (DME) and from results at the HMDE it is concluded that, depending on the BSA concentration, Brdi?ka currents at the DME are partly of a kinetic and partly of a surface adsorption nature and partly diffusion-controlled. Adsorption equilibrium is not attained at the DME at 25° at concentrations of BSA smaller than 10^?6M.     

Electrochemical behavior of phytochelatins and related peptides at the hanging mercury drop electrode in the presence of cobalt(II) ions

Direct current voltammetry and differential pulse voltammetry have been used to investigate the electrochemical behaviour of two phytochelatins: heptapeptide (gamma-Glu-Cys)3-Gly and pentapeptide (gamma-Glu-Cys)2-Gly, tripeptide glutathione gamma-Glu-Cys-Gly and its fragments: dipeptides Cys-Gly and gamma-Glu-Cys at the hanging mercury drop electrode in the presence of cobalt(II) ions. Most interesting results were obtained with direct current voltammetry in the potential region of -0.80 V up to -1.80 V. Differential pulse voltammetry of the same solutions of Co(II) with peptides gives more complicated voltammograms with overlapping peaks, probably in connection with the influence of adsorption at slow scan rates necessarily used in this method. However, in using Brdicka catalytic currents for analytical purposes, differential pulse voltammograms seem to be more helpful. Presented investigations have shown that particularly the prewave of cobalt(II) allows distinguishing among phytochelatins, glutathione, and its fragments.     

Electrochemical behaviour of sertraline at a hanging mercury drop electrode and its determination in pharmaceutical products

The electrochemical behaviour of sertraline at a hanging mercury drop electrode (HMDE) was described. Different voltammetric techniques, such as cyclic, linear sweep, differential pulse and square wave voltammetry, were used. Voltammograms were obtained at different pH values with a Britton-Robinson buffer solution used as supporting electrolyte. The best results were found by square wave voltammetry with electrodeposition at alkaline pH using a borate buffer with a pH = 8.2 for the samples, containing 12% (v/v) methanol. Under optimised conditions, a linear relationship between 2.33 × 10^–7 and 3.15 × 10^–6 M of sertraline with a limit of detection of 1.98 × 10^–7 M was obtained. The electrochemical method developed was applied to the determination of sertraline in pharmaceutical formulations. Recoveries were close to 100%, thus proving efficacy of the proposed method for the quantification of sertraline in commercial samples. Received: 26 September 2000 / Revised: 1 December 2000 / Accepted: 5 December 2000     

Electrochemical behaviour of sertraline at a hanging mercury drop electrode and its determination in pharmaceutical products

The electrochemical behaviour of sertraline at a hanging mercury drop electrode (HMDE) was described. Different voltammetric techniques, such as cyclic, linear sweep, differential pulse and square wave voltammetry, were used. Voltammograms were obtained at different pH values with a Britton-Robinson buffer solution used as supporting electrolyte. The best results were found by square wave voltammetry with electrodeposition at alkaline pH using a borate buffer with a pH = 8.2 for the samples, containing 12% (v/v) methanol. Under optimised conditions, a linear relationship between 2.33 x 10(-7) and 3.15 x 10(-6) M of sertraline with a limit of detection of 1.98 x 10(-7) M was obtained. The electrochemical method developed was applied to the determination of sertraline in pharmaceutical formulations. Recoveries were close to 100%, thus proving efficacy of the proposed method for the quantification of sertraline in commercial samples.     

Electrochemical determination of lead(II) using a montmorillonite calcium-modified carbon paste electrode

Utilizing the fascinating properties of montmorillonite calcium (MMT-Ca), such as huge cationic exchange capacity, strong adsorptive ability, high chemical and mechanical stability, an MMT-Ca modified carbon paste electrode (CPE) was constructed for the sensitive determination of Pb²⁺. In 0.01 mol·L⁻¹ HCl, Pb²⁺ was firstly exchanged and accumulated on an MMT-Ca modified CPE surface and secondly reduced to Pb at −0.90 V. In the following potential sweep from −0.90 to −0.50 V, reduced Pb was oxidized, resulting in an obvious stripping peak at −0.58 V. After optimizing the parameters, such as determining medium, content of MMT-Ca, accumulation potential and time, an electrochemical method was developed for the analysis of Pb²⁺. Compared with bare CPE, the MMT-Ca modified CPE significantly enhances the sensitivity of Pb²⁺ analysis. The limit of detection is evaluated to be 6.0 × 10⁻⁹ mol L⁻¹ Pb²⁺. Finally, this method was successfully employed to determine trace levels of Pb²⁺ in water samples. The first two authors contribute equally do this work     

Adsorptive stripping voltammetry of chlordiazepoxide at the hanging mercury drop electrode

Controlled adsorptive accumulation at the hanging mercury drop electrode enables 0.8–11 × 10^?5 M chlordiazepoxide to be quantified by differential-pulse stripping voltammetry with accumulation times of 1–3 min. With 3-min accumulation, the peak current is enhanced 12-fold for 1.0 × 10^?7 M chlordiazepoxide compared to the current from differential pulse polarography. The detection limit is 0.9 × 10^?9 M for 4-min accumulation. The procedure is applied to spiked human serum after preseparation of the drug on a Sep-Pak C₁₈ cartridge.     

Anodic stripping voltammetry of germanium at the hanging mercury drop electrode

The Ge(IV)—Ge(0) system was investigated by cyclic and stripping voltammetry at HMDE in acidic pyrogallol medium and in phosphate, borate and carbonate buffers. It was found that germanium electrodeposited from dilute Ge(IV) solutions dissolved anodically forming two peaks corresponding to the oxidation of the unstable homogeneous and stable heterogeneous amalgams. Both peaks can be exploited analytically for the determination of traces of germanium but due to the complex nature of the germanium amalgam the sensitivity and reproducibility of the determinations are lower compared to the results obtained for metals well-soluble in mercury.     

Study of interactions between DNA-ethidium bromide (EB) and DNA-acridine orange (AO), in solution, using hanging mercury drop electrode (HMDE)

The interaction of ethidium bromide (EB) and acridine orange (AO) with double stranded (ds), thermally denatured (ss) and supercoiled (sc) DNA, in solution, was studied by alternating current voltammetry (AC voltammetry) at the hanging mercury drop electrode (HMDE) in 0.3 M NaCl+50 mM sodium phosphate buffer (pH 8.5). Their interaction with DNA is shown to be time dependent and completely different. The changes at peak 2 (peak at −1.20 V) of dsDNA form and the appearance of peak 3 (peak at −1.42 V) in scDNA form are presented as criteria declaring the different mechanism of interaction of EB and AO with DNA. Additionally, the appearance of a new peak at around −0.44 V as a result of DNA and AO interaction, differentiates the studied behaviors. The comparison of the electrochemical behaviors of these compounds highlights the differences in the mechanism of interaction.     

Differential pulse cathodic stripping voltammetry of the copper complexes of glycyl-L-histidyl-glycine at a hanging mercury drop electrode

The behaviour of the copper complexes of glycyl-L-histidyl-glycine (GHG) was investigated using cyclic voltammetry and differential pulse voltammetry after their adsorptive accumulation on the surface of a hanging mercury drop electrode (HMDE). The nature of the observed cathodic and anodic peaks was established and optimum conditions were found for the differential pulse cathodic stripping voltammetric detemination of GHG at the 1 x 10(-8)M concentration level using adsorptive accumulation at -0.20 V vs. Ag/AgCl reference electrode and the cathodic stripping peak around -0.4 V (pH 8.3). This peak corresponds to the reduction of the Cu(I)-GHG complex formed at the HMDE surface as an intermediate in the reduction of Cu(II)-GHG to Cu(O)amalgam.     

Response surface methodology for optimisation of 4,6-Dinitro-o-cresol quantification using hanging mercury drop electrode

A method for the pesticide DNOC (4,6-Dinitro-o-cresol) quantification using hanging mercury drop electrode (HMDE) and stripping square wave voltammetry (SSWV) optimisation is proposed. As a continuous cathodic current decrease was observed during the experiments, a waiting time, together with solution pH and SWV instrumental variables were optimised by factorial designs. From the two reduction current peaks values, only one was considered as dependent variable in the optimisation process. While the cathodic current peak and standard deviation were used in the waiting time and solution pH optimisation process, the instrumental parameters for SWV were optimised by using only current peak values. With the optimal parameters, a calibration curve from (0.01–0.55) × 10^?6 mol L^?1 with LOD of 2 × 10^?8 mol L^?1 was obtained. The proposed method was checked for DNOC quantification in different water samples obtained from Cordoba area and very good results, with recovery values around 102% were observed.