Current Peak Height Research Articles

Многофакторный анализ патогенеза ранних прогрессирующих стадий ретинопатии недоношенных

The retinopathy of prematurity (ROP) is a vasoproliferative disease causing visual impairment. Perpose. To investigate the pathogenic features of ROP. Material and methods. 1254 patients (2508 eyes), operated patients 163 (326 eyes), were included in the study; blood tests were taken from 192 patients (384 eyes). Results. Patients with lower weight, advanced stage of ROP showed greater decline in hemoglobin, lactate and thrombin time in comparison to the babies at risk; T-regulators, such as CD4+CD25highFoxp3+CD127low, correlated with gestational age and the stage of ROP; their level was increased or remained within normal range in aggressive posterior disease (AP-ROP). Serum levels of VEGFA165 and VEGFA165R1 in ROP surpassed those in babieswith congenital cataracts (p < 0.01). 19 pro-angiogenic genes (VEZF1, LTF, CSF1R, EGR1, FGF1, PTN, IFITM, HSP90AB1, HSP90B1, PRDX1, JMJD, ACTA2, XBP1, CCNG1, S100A10, IRS2, UPP1, MGP, OLFML3) and 19 antiangiogenic genes (RHBDF1, CTNNA1, F11R, PSEN2, RHBDF1, PLG, COL18A1, VHL1, EIF4A1, EIFH4, ANKRD23, MIR-16, RAB6B, TSP1, RACK1, NR2E3, TKT, VLDLR, IGFBP4) were detected. Multisensor stripping voltammetry in serum of full-term and premature babieswith ROP demonstrated significant shift of current peak height after injection of Hg (p < 0,01), Cd and Pb (p < 0,05). Conclusion. Premature patients with early stages of ROP have distinctive features of their homeostasis. Keywords: оphthalmology, CD4+CD25highFoxp3+CD127low, blood, blood serum, newborn children, cataract, retinopathy of prematurity, helth children, laboratory diagnostics, expression, antiangiogene, s factors, proangiogene, s factors, gene, multisensory inversion voltammetry, planar electrodes

Properties of electrochemically copolymerized aniline and melamine on functionalized multiwalled‐carbon nanotube film electrodes

AbstractThe electrochemical properties of polymerized aniline (PANI) and polymerized melamine (PMEL) that were electrochemical copolymerized (PANIMEL) on a glassy carbon electrode (GCE) that had been coated with functionalized multiwalled carbon nanotubes (fMWCNT) to form a PANIMEL/fMWCNT/GCE film electrode were studied, with an aim toward electrochemical energy storage (EES). A number of factors, such as the choice of working electrode, electrolyte, switching potential, applied scan rate, and type of fMWCNTs, were initially investigated and evaluated during the individual electrochemical polymerization of aniline and melamine via successive potential cycling. The electrochemical copolymerisation of aniline and melamine was then studied with an ideal monomeric ratio of 1:3 that gave an optimal ratio of the voltammetric peak current heights with distinguishable redox peak potentials. Variable scan rate cyclic voltammetry (CV) of the electrosynthesized copolymer film electrode confirmed the dominance of the surface‐confined electron transfer process at the electrode. The electrochemical stability of the copolymer film electrode was also assessed and revealed a limited cyclability of the daughter polymeric melamine, which was hypothesized to be due to an excessive nitrogen content combined with a low porosity that led to a poor ion intercalation‐deintercalation mechanism. Electrochemical impedance spectroscopy (EIS) was performed to evaluate the electrochemical performance of the copolymerized film electrode with other control electrodes. The corresponding EIS results suggested that the copolymerized film electrode was electrochemically superior to the PMEL/fMWCNT/GCE film electrode but was inferior to the PANI/fMWCNT/GCE film electrode.

Pulsation of InGaAs Photodiodes in Liquid Helium for Driving Josephson Arrays in AC Voltage Realization

A commercially available InGaAs p-i-n photodiode chip has been custom packaged and high-speed operated in liquid helium. The photodiode was driven by light pulses using a dc-biased 1310-nm laser, a Mach-Zehnder modulator, and a return-to-zero pulse pattern generator up to 15 GHz clock frequencies, which produced pulse widths down to 77 ps and maximum peak current heights above 10 mA. With the prospect of using this photodiode assembly to operate pulse-driven Josephson junction arrays for ac voltage realization, pulsation modes with constant pulse width and varying pulse density were applied to the diode, which resulted in consistent pulse shapes for bit rates as high as 7.5 Gb/s. This could yield realizable peak voltages as high as 15.525 μV per Josephson junction. Time-lapse pulse measurements were performed over the span of 90 min, which demonstrated good waveform stability. Using the measured current waveforms, the behavior of a typical Josephson junction was simulated according to the Stewart-McCumber model, which resulted in an operational margin of 2 mA for the first Shapiro step.

Electroactive magnetic nanoparticles under magnetic attraction on a microchip electrochemical device

Abstract This work focused on the introduction of electrochemical moieties (electroactive molecules) onto the surface of magnetic nanoparticles (NPs) based on carbodiimide coupling chemistry and the influence of magnetic attraction at the working electrode surface on their electrochemical behaviour. The magnetic NPs were first functionalized with polyamidoamine (PAMAM) dendrimer generation 0 and then with ferrocenecarboxylic acid (Fc) as electroactive molecule. Colorimetric titration, zeta potential measurements and infrared spectroscopy proved the effective conjugation of PAMAM and Fc onto NPs. The conjugation of Fc onto the NPs was also evidenced by voltammetry as it resulted in a half-peak potential shift from 0.328 V for free Fc to 0.590 V after coupling. A transition from a reversible to an irreversible behaviour was also observed. Finally, an external magnetic field was applied on Fc-conjugated NPs to attract them onto the working electrode of a microchip electrochemical device, and the resulting modifications of the electrochemical behaviour were studied. Compared to Fc dispersed in solution, the current peak height of Fc-conjugated NPs was 2-fold higher under magnetic attraction. The mechanism of electrochemical reaction was investigated and was found to be irreversible. Surprisingly, the reaction was diffusion-controlled upon attraction.

CdS quantum dots as a scattering nanomaterial of carbon nanotubes in polymeric nanocomposite sensors for microelectrode array behavior

This work is focused on evaluating the direct electrochemical effect of semi-conducting nanocrystals when they are integrated in bulky nanocomposite sensors based on multiwalled carbon nanotubes (MWCNTs). For this aim, MWCNTs have successfully been functionalized with CdS quantum dots (CdS–QDs@MWCNTs) and then dispersed within an insulating polymeric matrix, as epoxy resin, for electroanalytical sensing purposes. After an accurate voltammetric and impedimetric characterization, some electrochemical parameters were surprisingly enhanced regarding the non-modified sensors, such as peak current height, electroactive area, and emphasizing the double-layer capacitance. These results can be explained since CdS–QDs confer to the nanocomposite sensor a microelectrode array behavior, dispersing the conductive microzones through the polymeric matrix, as revealed by morphological experiments. The feasibility of this approach was amperometrically evaluated for ascorbic acid and hydrogen peroxide, both used as reference analytes. Electroanalytical results demonstrated that this approach provides to the CdS–QDs-modified nanocomposite sensors the capability to determine low concentrations of analytes and improved sensitivities.

Fe3+/Fe2+ Mycobactin‐Complex Electrochemistry as an Approach to Determine Mycobactin Levels in Urine

AbstractMycobacterium acquire iron by producing siderophores called mycobactins, with an extremely high affinity complexation of Fe3+. The iron complex shows distinctive electrochemistry predicting 18 orders of magnitude greater affinity of the mycobactin for Fe3+ than Fe2+. A heterogeneous standard rate constant, ks of the order of 10−5 cm s−1 confirms quasi reversible electrochemistry and based on the equilibrium in the presence of excess solution Fe3+/Fe2+ the oxidation and reduction peaks for the siderophore complex could be calibrated for ferric mycobactin J (FeMJ). FeMJ spiked urine collected from cows showed a matrix effect on the current peak height. For example, 240±15 µM FeMJ was estimated in 600 µM spiked urine. However, in the presence of excess solution Fe(acac)3 the same sample yielded an estimated 580±25 µM FeMJ.

Electrochemical study of vinylsulphone azo dye Reactive Black 5 and its determination at a glassy carbon electrode

The electrochemical oxidation of vinylsulphone azo dye, Reactive Black 5 (RB5), at a glassy carbon electrode has been carried out in phosphate buffer solutions in the pH range 2.85–11.79 employing cyclic voltammetry (CV) and differential pulse voltammetry (DPV). RB5 showed one well-defined oxidation peak at 0.560 V vs. Ag-AgCl using DPV. The oxidation process was shown to be irreversible over the pH range 2.85–8.39 and was diffusion controlled. The linear relationship between the peak current height and RB5 concentrations allowed the differential pulse voltammetric determination of the dye over a wide concentration range, from 6.0 × 10−7 to 1.5 × 10−6 M with a detection limit of 4.0 × 10−7 M. The precision and recovery did not exceed 4.9 and 98.2%, respectively. A UV-Vis spectrophotometry method was also proposed for the determination of the RB5 in concentration range from 5.0 × 10−6 M to 1.0 × 10−5 M at λmax = 600 nm with limit of detection of 4.7 × 10−6 M and RSD of 1.8% for RB5 concentration of 1.0 × 10−5 M.

Simultaneous determination of serum lathosterol and cholesterol by semi-micro high-performance liquid chromatography with electrochemical detection

A simple method has been developed for the simultaneous determination of lathosterol and cholesterol by high-performance liquid chromatography with electrochemical detection (HPLC–ECD). Lathosterol was found to be electrochemically oxidized and its current peak height was linearly related to the amount of lathosterol injected, ranging from 0.15 μmol/L to 300 μmol/L ( r = 0.995). Similar results were obtained with cholesterol from 15 μmol/L to 600 μmol/L ( r = 0.995). The separation was carried out with an ODS column, acetonitrile containing 30 mmol/L lithium perchlorate as a mobile phase, and an applied potential at +2.8 V vs. Ag/AgCl. The detection limit ( S/ N = 3) of lathosterol as well as cholesterol was 0.03 μmol/L (0.15 pmol). Total lathosterol in control human and rat serum was determined by the present method with a recovery of more than 95.8% and an RSD ( n = 5) of less than 7.3%. The present method was applied to an experiment with rats to examine the effect of lathosterol feeding. There were no significant changes in serum lathosterol or cholesterol levels in rats fed with a high-lathosterol diet for six days. Therefore, we found this method to be both simple and useful for the simultaneous determination of lathosterol and cholesterol in serum.

English

The redox characteristics of the drug Bicalutamide at a glassy-carbon electrode (GCE) was investigated for the first time in aqueous media by differential-pulse voltammetry (DPV) and cyclic voltammetry (CV). In Britton-Robinson (BR) buffer of pH 2.0-10.0, an irreversible and diffusion-controlled reduction voltagram were developed. The dependence of the CV response of the developed cathodic peak on the sweep rate ( �) and on depolarizer concentration was typical electrode-coupled chemical reaction mechanism (EC) in which an irreversible reaction is interposed between the charges. In BR buffer of pH 6 - 7, a well defined cathodic peak was developed and the plot of peak current height of the DPV against Bicalutamide concentration at this peak potential was linear in the range 1×10 �8 - 2.6 ×10 �5 M with lower limits of detection (LOD) and quantization (LOQ) of 8 x 10 -8 M and 1 ×10 �7 M, with good selectivity and sensitivity. A relative standard deviation (RSD) for Bicalutamide at a concentration of 4.5×10 �5 M was 2.48% (n=6). The proposed method was successfully applied to Bicalutamide determination in pharmaceutical samples and results are very good correlations with previously reported methods.

Heterogeneous electron transfer kinetics and electrocatalytic behaviour of mixed self-assembled ferrocenes and SWCNT layers

The electron transfer dynamics and electrocatalytic behaviour of ferrocene-terminated self-assembled monolayers (SAMs), co-adsorbed with single-walled carbon nanotubes (SWCNTs) on a gold electrode, have been interrogated for the first time. Ferrocene monocarboxylic acid (FMCA) or ferrocene dicarboxylic acid (FDCA) was covalently attached to the cysteamine (Cys) monolayer to form Au-Cys-FMCA and Au-Cys-FDCA, respectively. The same covalent attachment strategy was used to form the mixed SWCNTs and ferrocene-terminated layers (i.e. Au-Cys-SWCNT/FMCA and Au-Cys-SWCNT/FDCA). Using cyclic voltammetry and electrochemical impedance spectroscopy, the impact of neighbouring SWCNTs on the electron transfer dynamics of the ferrocene molecular assemblies in an acidic medium (0.5 M H(2)SO(4)) and in a solution of an outer-sphere redox probe ([Fe(CN)(6)](4-)/[Fe(CN)(6)](3-)) was explored. The electron transfer rate constants in both media essentially decreased as Au-Cys-FMCA > Au-Cys-SWCNT/FDCA > Au-Cys-FDCA > Au-Cys-SWCNT/FMCA. This trend has been interpreted in terms of several factors such as the locations of the ferrocene species in a range of environments with a range of potentials, the proximity/interactions of the ferrocenes with one another, and electrostatic interaction or repulsion existing between the negatively-charged redox probe and the modified electrodes. The thiocyanate ion (SCN(-)) was used as a model analyte to examine the influence of the neighbouring SWCNTs on the electrocatalytic ability of the ferrocene assemblies. The Au-Cys-SWCNT/FDCA showed the best catalytic activity (in terms of onset potential and catalytic peak current height) for the oxidation of SCN(-), possibly due to the repulsive interactions between the negatively charged SCN(-) and high number of surface -COOH species at the SWCNT/FDCA. This study has provided some useful insights as to how CNTs co-assembled with ferrocene-terminated thiols could impact on the electron transfer kinetics as well as the electrocatalytic detection of the self-assembled ferrocene layers.

Determination of serum cholestanol by semi‐micro high‐performance liquid chromatography with electrochemical detection

A simple and sensitive method that dose not require derivatization for determining cholestanol has been developed using HPLC with electrochemical detection (HPLC-ECD). The current peak height was linearly related to the amount of cholestanol injected, ranging from 1 to 200 muM (r = 0.999). The detection limit (S/N = 3) of cholestanol was 0.23 muM (1.2 pmol). Total cholestanol in control human and mouse serum was determined by the present method with a recovery rate of more than 90% and an RSD (n = 5) of less than 7.3%. Further, this method was successfully applied to monitor experimental hypercholestanolemia in mice fed a high-cholestanol diet, an animal model of cerebrotendinous xanthomatosis (CTX). In conclusion, we found this method to be both simple and useful for the determination of cholestanol in serum, helping in the diagnosis of CTX.

Determination of oxysterols in oxidatively modified low-density lipoprotein by semi-micro high-performance liquid chromatography with electrochemical detection

A simple method for the determination of oxysterols was developed by semi-micro high-performance liquid chromatography with electrochemical detection (semi-micro HPLC–ECD). Semi-micro HPLC–ECD was established using a C30 microbore column, acetonitrile containing 50 mmol/L LiClO 4 as a mobile phase, and an applied potential at +2.8 V versus Ag/AgCl. The current peak height was linearly related to the amount of sterol injected from 12.5 to 250 pmol ( r > 0.999) with a relative standard deviation (RSD) of less than 2.9% ( n = 6). This method was applied to the determination of seven oxysterols in oxidatively modified low-density lipoprotein (Ox–LDL). Oxysterols were determined with a recovery of more than 78.0% and an RSD of less than 2.9% ( n = 6) except for 7-ketocholesterol. 7-Ketocholesterol was determined as a sum of intact 7-ketocholesterol and its degradation product on saponification, cholesta-3,5-dien-7-one, with a recovery of 98.0% and an RSD of 2.5% ( n = 6). From these results, the current method enabled the simultaneous determination of seven oxysterols without any derivatization, providing a useful tool for the assessment of oxysterol contents in Ox–LDL.

Correlation of film structure and molecular oxygen reduction at nitrogen doped amorphous carbon thin film electrochemical electrodes

Nitrogen doped amorphous carbon (a-C:N) thin film electrodes with a range of film structures have been deposited using a filtered cathodic vacuum arc system. The correlation between film structure and electro-reduction of molecular oxygen in aqueous media at the electrodes has been explored. In aqueous 0.1 M NaOH, dioxygen reduction is inhibited at all the a-C:N electrodes compared with that at glassy carbon electrodes. The potential of the dioxygen reduction current peak shifts negatively at a-C:N electrodes as the sp 3 C fraction in the a-C:N materials increases, while the current peak height decreases simultaneously. The a-C:N electrodes possess high sensitivity for investigating the mechanism of dioxygen reduction. It was found that the catalytic H 2O 2 reduction to H 2O on carbon materials is attributed to oxygen species at sp 2 C sites.

One‐Pot Solvent Free Synthesis and DNA Binding Studies of Thieno[2,3‐b]‐1,8‐Naphthyridines

With the aim of evaluating interaction between double‐stranded calf thymus (ds)DNA and sulphur containing fused planar rings, the derivatives of 1,8‐naphthyridine containing thiono groups were synthesized by the condensation of 2‐mercapto‐3‐formyl[1,8]naphthyridines using 1‐chloroacetone, 2‐chloroacetamide, chloroaceticacid, and 2‐chloro‐1‐phenylethanone in the presence of anhydrous potassium carbonate as s catalyst under solvent free microwave irradiation. The structures of the compounds were elucidated on the basis of elemental analysis, IR, 1H NMR, and mass spectra. The interaction of thieno[2,3‐b]‐1,8‐naphthyridine‐2‐carboxylic acid (TNC) (3a) with ct‐DNA was studied by UV‐Vis spectrophotometry, viscosity, thermal denaturation, as well as cyclic voltammetry experiments. On binding to DNA, the absorption spectrum underwent bathochromic and hypochromic shifts. Binding parameters, determined from spectrophotometric measurements indicated a binding constant of K b =2.1×106 M−1. The thieno[2,3‐b]‐1,8‐naphthyridine‐2‐carboxylic acid (3a) increases the viscosity of sonicated rod‐like DNA fragments. The binding of TNC to DNA increased the melting temperature by about 4°C. The decrease in peak current heights and shifts of peak potential values are observed by the addition of calf thymus DNA in cyclic voltammetry studies.

Determination of total cholesterol in serum by high-performance liquid chromatography with electrochemical detection

A simple and sensitive HPLC method that does not require derivatization for determining cholesterol has been developed. Investigation of voltammetric behavior of cholesterol showed that cholesterol could be oxidized on a glassy carbon electrode in non-aqueous solvents. This was applied to the development of a method by HPLC with electrochemical detection (HPLC-ED). The HPLC-ED was optimized using the separation of cholesterol and oxysterols including 26-hydroxycholesterol and 24S-hydroxycholesterol. The separation was carried out with a Develosil C30-UG-3 column; acetonitrile-2-propanol (9:1, v/v) containing 50mM LiClO4 as a mobile phase; and an applied potential at 1.9V versus Ag/AgCl. The current peak height was linearly related to the amount of cholesterol injected from 0.5–100μM (r>0.999). The detection limit (S/N=3) of cholesterol was 0.36μM (1.8pmol). Cholesterol at 100μM was directly detected with a relative standard deviation (RSD) of less than 1.0% (n=8). Total cholesterol and free cholesterol in control human serum were determined by the present method with the recovery of more than 90% and the RSD (n=6) of less than 3.0%.

Note on the theory of three-dimensional growth of the porous passivating layers on metals

An analytical relationship “the current peak height—the potential sweep rate” is derived for the three-dimensional film formation under ohmic resistance control. The model takes into account both the changing of the coverage degree and the thickening of the surface film. It is shown that a criterion for definition of the growth type (2D or 3D) of the surface film can be offered. An offered model is tested for anodic oxidation of silver in sulfuric acid solution.

A numerical model for current transients during micro-indentation of passive iron surface

During in situ micro-indentation of passive iron in pH 8.4 borate solution, a couple of anodic current peaks emerged; the first peak during loading and the second peak during unloading. The current transients, associated with rupture and repair of the passive film, were influenced by the indentation conditions. For instance, the current peak height, the current peak area and the time required for complete repassivation are strongly dependent on indentation rate. A numerical model was proposed to correlate the current transient during loading with mechanical deformation of the passive surface. The comparison between the current transient measured experimentally and that estimated from the load transient suggested that the ruptured area of passive film was about 10% of the surface area deformed by the contact with the indenter.

In-situ Measurement of UO2 2+ Concentration in Molten NaCl-2CsCl by Differential Pulse Voltammetry

In order to assess the applicability of the Differential Pulse Voltammetry technique to the in-situ measurement of UO2 2+ concentration in the oxide electro-winning process, DPV measurements for UO2Cl2 in molten NaCl-2CsCl were studied. DPV measurement of UO2 2+ in NaCl-2CsCl at 923 K, with a set of optimized parameters (potential sweep rate −0.1 V/s, pulse cycle 0.1 s, pulse width 10 ms and pulse potential height 50 mV), showed a clear current peak at −0.9 V vs. Cl2/Cl−. This was attributed to the reduction of UO2 2+ to UO2 +. The relation between the current peak height and the analytical concentration of the UO2 2+ showed good proportionality in the concentration region up to 0.06 mol.l −1, and the applicability of UO2 2+ concentration measurement by DPV was confirmed up to 0.4 mol.l −1. In order to assess the interference by the coexisting fission product elements to the measurement of UO2 2+ concentration, DPV measurements of UO2 2+ concentration in molten NaCl-2CsCl containing PdCl2, NdCl3, SmCl3 and CeCl3 were also performed. Even before removing Pd, the current peak at −0.9 V vs. Cl2/Cl− by the reduction of UO2 2+ to UO2 + was found to be distinguishable from the reduction currents of Pd2+ to Pd at −0.7 V vs. Cl2/Cl−. As a result, the application of DPV measurement technique to the in-situ monitoring of UO2 2+ concentration in the oxide electro-winning method requires the improvement of the DPV measuring condition or the electrode structure on higher UO2 2+ concentration condition.

Analysis of domperidone in pharmaceutical formulations and wastewater by differential pulse voltammetry at a glassy-carbon electrode

The redox characteristics of the drug domperidone at a glassy-carbon electrode (GCE) in aqueous media were critically investigated by differential-pulse voltammetry (DPV) and cyclic voltammetry (CV). In Britton-Robinson (BR) buffer of pH 2.6-10.3, an irreversible and diffusion-controlled oxidation wave was developed. The dependence of the CV response of the developed anodic peak on the sweep rate (nu) and on depolizer concentration was typical of an electrode-coupled chemical reaction mechanism (EC) in which an irreversible first-order reaction is interposed between the charges. The values of the electron-transfer coefficient (alpha) involved in the rate-determining step calculated from the linear plots of E (p,a) against ln (nu) in the pH range investigated were in the range 0.64 +/- 0.05 confirming the irreversible nature of the oxidation peak. In BR buffer of pH 7.6-8.4, a well defined oxidation wave was developed and the plot of peak current height of the DPV against domperidone concentration at this peak potential was linear in the range 5.20 x 10(-6) to 2.40 x 10(-5) mol L(-1) with lower limits of detection (LOD) and quantitation (LOQ) of 6.1 x 10(-7) and 9.1 x 10(-7) mol L(-1), respectively. A relative standard deviation of 2.39% (n = 5) was obtained for 8.5 x 10(-6) mol L(-1) of the drug. These DPV procedures were successfully used for analysis of domperidone in the pure form (98.2 +/- 3.1%), dosage form (98.35 +/- 2.9%), and in tap (97.0 +/- 3.6%) and wastewater (95.0 +/- 2.9%) samples. The method was validated by comparison with standard titrimetric and HPLC methods. Acceptable error of less than 3.3% was also achieved.

Flow-injection pulse amperometric detection based on ion transfer across a water-plasticized polymeric membrane interface for the determination of imipramine

A flow-injection pulse amperometric method for determining imipramine, based on ion transfer across a plasticized poly(vinyl chloride) (PVC) membrane, was developed. A four-electrode potentiostat with ohmic drop compensation was used, while a flow-through cell incorporated the four electrodes and the membrane, which contained tetrabutylammonium tetraphenylborate. The influence of the applied potential, the flow-injection variables and of the pH on the determination of imipramine was studied. In the selected conditions, a linear relationship between current peak height and imipramine concentration over a range of 1 × 10 −6 to 8 × 10 −5 M imipramine was found. Good repeatability and between-day reproducibility were obtained. No interference was observed on the part of some common ions and pharmaceutical excipients. The method proposed was applied satisfactorily to the determination of imipramine in pharmaceuticals and human serum.