DNA immobilization on a polypyrrole nanofiber modified electrode and its interaction with salicylic acid/aspirin.

A double-stranded calf thymus DNA (dsDNA) was physisorbed onto a polypyrrole (PPy) nanofiber film that had been electrochemically deposited onto a Pt electrode. The surface morphology of the polymeric film was characterized using scanning electron microscopy (SEM). The electrochemical characteristics of the PPy film and the DNA deposited onto the PPy modified electrode were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Then the interaction of DNA with salicylic acid (SA) and acetylsalicylic acid (ASA), or aspirin, was studied on the electrode surface with DPV. An increase in the DPV current was observed due to the oxidation of guanine, which decreased with the increasing concentrations of the ligands. The interactions of SA and ASA with the DNA follow the saturation isotherm behavior. The binding constants of these interactions were 1.15×10(4)M for SA and 7.46×10(5)M for ASA. The numbers of binding sites of SA and ASA on DNA were approximately 0.8 and 0.6, respectively. The linear dynamic ranges of the sensors were 0.1-2µM (r(2)=0.996) and 0.05-1mM (r(2)=0.996) with limits of detection of 8.62×10(-1) and 5.24×10(-6)µM for SA and ASA, respectively.

Electrochemically fabricated polypyrrole nanofiber-modified electrode as a new electrochemical DNA biosensor.

A new biosensor employing immobilized DNA on a nano-structured conductive polymer fixed onto a platinum electrode is presented. Upon optimization of synthesis parameters, polypyrrole nanofibers, 30-90 nm in diameter, were synthesized in an aqueous media by the electropolymerization of pyrrole using normal pulse voltammetry (NPV). The nanofiber film was investigated by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Double-stranded DNA was physisorbed onto the PPy nanofiber films. Various parameters, including the pH and DNA concentration, were optimized. The DNA immobilized on the nanofiber films was characterized using differential pulse voltammetry (DPV) and Fourier-transform infrared (FTIR) spectroscopy. Using DPV to study the interaction of spermidine with DNA, a binding constant (K) value of 4.08 x 10(5)+/-0.05 M(-1) was obtained. For the determination of spermidine, the proposed method exhibited a good dynamic range, correlation coefficient (0.05-1.0 microM and 0.9983, respectively) and a low detection limit (0.02 microM), although Ca(2+) ions were found to electrostatically bind to DNA and weaken the spermidine-DNA interaction.

Sonochemical-assisted synthesis of nano-structured lead dioxide.

PbO(2) nano-powder was synthesized by the ultrasonic irradiation of an aqueous suspension of dispersed beta-PbO, as precursor, in the presence of ammonium peroxydisulfate as an oxidant. The reaction rate increased with an increase in temperature and ammonium peroxydisulfate concentration. In the presence of ammonium peroxydisulfate, the increased concentration of hydroxyl radical facilitated the oxidation of beta-PbO to PbO(2) under ultrasonic irradiation. The PbO(2) nano-powder was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the applied ultrasonic wave determines the particle size. PbO(2) samples prepared under optimized experimental conditions have lead dioxide particles in the range of 50-100 nm, as shown by SEM. The XRD results reveal that only beta-PbO(2) is formed under optimum conditions. When the reaction mixture was stirred instead of ultrasonically irradiated, only a fraction of the lead oxide was converted to lead dioxide, and lead sulfate was the main reaction product.

Prediction of selectivity coefficients of a theophylline-selective electrode using MLR and ANN.

The selectivity coefficient of 24 interfering compounds (drugs, amino acids and organic compounds) of a theophylline-selective electrode was predicted using an artificial neural network (ANN). The multiple linear regression (MLR) technique was used to select the descriptors as inputs for the artificial neural network. The neural network employed here is a connected back-propagation model with a 2-2-1 architecture. Two topological indices for the interfering compounds, namely, Narumi harmonic topological index, HNar, and sum of topological distances between nitrogen and oxygen, T(Ncdots, three dots, centeredO), were taken as inputs for the ANN. Standard errors of training and prediction were 0.954 and 0.945, respectively, for the MLR model and 0.032 and 0.007, respectively, for the ANN model. Two topological indices for the interference of the electrode were taken as inputs for ANN.

QSAR analysis for ADA upon interaction with a series of adenine derivatives as inhibitors.

The kinetic parameters of adenosine deaminase such as Km and Ki were determined in the absence and presence of adenine derivatives (R1-R24) in sodium phosphate buffer (50 mM; pH 7.5) solution at 27 degrees C. These kinetic parameters were used for QSAR analysis. As such, we found some theoretical descriptors to which the binding affinity of adenosine deaminase (ADA) towards several adenine nucleosides as inhibitors is correlated. QSAR analysis has revealed that binding affinity of the adenine nucleosides upon interaction with ADA depends on the molecular volume, dipole moment of the molecule, electric charge around the N1 atom, and the highest of positive charge for the related molecules.

Direct determination of triamterene by potentiometry using a coated wire selective electrode.

A coated wire triamterene-selective electrode based on the incorporation of a triamterene-tetraphenylborate ion-pair in a poly(vinylchloride) coating membrane was constructed. The influence of membrane composition, temperature, pH of the test solution, and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a triamterene concentration range from 1.0 x 10(-6) to 3.5 x 10(-2) M, at 25 degrees C, and was found to be very selective, precise, and usable within the pH range 4.5-7.5. The standard electrode potentials, E degrees, were determined at 15, 20, 25, 30, 35, 40 and 45 degrees C and used to calculate the isothermal temperature coefficient (dE degrees /dt) of the electrode. Temperatures higher than 45 degrees C seriously affected the electrode performance. The electrode was successfully applied to the potentiometric determination of triamterene hydrochloride both in pure solutions and in pharmaceutical preparations.

Kinetic-spectrophotometric determination of propylthiouracil based on its inhibitory effect on the reduction of neutral red by hypophosphite.

A new kinetic-spectrophotometric method for determination of propylthiouracil (PTU) is described. The proposed method is simple, rapid, inexpensive and sensitive for the determination of PTU in pure and tablet forms. This method is based on the inhibitory effect of propylthiouracil on the palladium(II)-catalyzed reaction between neutral red and hypophosphite ions. The effect of various parameters such as: dye, hypophosphite, and Pd(II) concentrations, pH, ionic strength, and temperature were optimized. Two distinct linear calibration graphs were observed in the ranges 0.006-0.033 (n = 6, r = 0.9991) and 0.033-0.300 ppm (n = 10, r = 0.9980). The variable time method was used. The limit of detection was 0.004 ppm. The proposed method was applied for the determination of propylthiouracil in pure and tablet forms.

A PVC-based 1,8-diaminonaphthalen electrode for selective determination of vanadyl ion.

A PVC membrane vanadyl (VO(2+)) ion-selective electrode was constructed using 1,8-diaminonaphthalen (DAN) as a neutral carrier. The electrode shows good Nernstian response for VO(2+) ions over a wide concentration range (1.0x10(-1)-1.0x10(-5) M). The optimum composition of the membrane was 55 wt.% poly(vinylchloride), 35 wt.% 2-nitrophenyl octyl ether (NPOE), 5 wt.% ionophore, and 5 wt.% potassium tetrakis(p-chlorophenyl)borate (KTpClPB). It has relatively fast response time and can be used at least for 5 weeks without any considerable divergence in potentials. The proposed electrode revealed relatively good selectivity for VO(2+) over wide variety of other metal ions. The electrode was used for the potentiometric titration of VO(2+) ions with EDTA.

Differential pulse anodic stripping voltammetric determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone modified carbon paste electrode.

A sensitive and selective method for the determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone (AQ) modified carbon paste electrode has been developed. The method is based on non-electrolytic preconcentration via complex formation with modifier, followed by an accumulation period with a negative potential (-1.5 V), and then by a proper anodic stripping. The analytical performance was evaluated with respect to the quantity of modifier in the paste, concentration of electrolyte solution, preconcentration time, lead(II) concentration, and other variables. A linear calibration graph was obtained in the concentration range 2.00x10(-9)-1.06x10(-5) M Pb(II) (n=21, r=0.9999) with 30 s preconcentration time. The detection limit was found to be 1x10(-9) M. For eight preconcentration/determination cycles, the differential pulse voltammetric response was reproduced with 5.0 and 3.7% relative standard deviations at 2.00x10(-8) and 2.00x10(-6) M Pb(II), respectively. Rapid and convenient renewal of electrode surface allows the use of a single modified electrode surface in multiple analytical determinations over several weeks. Many coexisting metal ions had little or no effect on the determination of lead(II). The developed method was applied to lead determination in waste waters.

Copper(II)-selective membrane electrodes based on some recently synthesized mixed aza-thioether crowns containing a 1,10-phenanthroline sub-unit.

Three different mixed aza-thioether crowns containing a 1,10-phenanthroline sub-unit were investigated to characterize their abilities as copper(II) ion carriers in PVC-membrane electrodes. The electrode based on L1 exhibited a Nernstian response for Cu(2+) ions over a wide concentration range (2x10(-1) to 1x10(-5) M) with a limit of detection of 8.0x10(-6) M (0.5 p.p.m.). The response time of sensor is 15 s, and the membrane can be used for more than 3 months without observing any deviation. The electrode revealed comparatively good selectivities with respect to many alkali, alkaline earth, transition and heavy metal ions, and could be used in a pH range of 2.5-5.5. It was applied to the direct determination and potentiometric titration of the copper(II) ion.

A sensitive flow-injection method for determination of trace amounts of nitrite.

A new sensitive colour reaction for nitrite determination is presented. In acidic medium, nitrite was reacted with safranine to form a diazonium salt which caused the reddish-orange dye colour of the solution to change to blue. The carrier stream, into which the sample solution was injected, was doubly distilled water. The reagent solution stream, which contained safranine dye, hydrochloric acid and potassium chloride, was mixed with the carrier in a 3-m length of silicon tubing (bore 0.5 mm) maintained at 30 degrees C in a thermostatic bath. The absorbance intensity was measured at 520 nm. The detection limit was 20 ng ml(-1) and the RSD% of 20 injections of 1 mug ml(-1) of nitrite was 0.65%. Analysis can be done at a rate of up to 30 h(-1). Under the optimum conditions in the concentration range of 30-4000 ng ml(-1) of nitrite ion, a linear calibration graph was obtained (r=0.9999). The method was applied successfully to the determination of nitrite in sausages.

Flow injection spectrophotometric determination of trace amounts of selenium.

A simple, rapid and sensitive flow injection spectrophotometric method for determination of selenium (0.005-1.5 mug ml(-1)) is described. The method is based on the catalytic effect of Se(IV) on the reduction reaction of thionine (TN) with sulphide ion, monitored spectrophotometrically at 598 nm. The detection limit is 5 ng ml(-1) the relative standard deviation for eight replicate measurements is 1.1% for 1 mug ml(-1) of selenium. The sampling rate is 25-30 samples h(-1). The procedure was applied successfully to the determination of selenium in real samples.