Aminophylline: thermal characterization and its inhibitory properties for the carbon steel corrosion in acidic environment

Aminophylline (AMF) was studied as corrosion inhibitor for carbon steel in 1.0 mol L^?1 HCl solution using electrochemical measurements associated with UV–Vis spectrophotometry and optical microscopy. Simultaneous thermogravimetry/derivative thermogravimetry and differential scanning calorimetry analysis was performed in order to determine the temperature range in which AMF is an effective inhibitor, without the decomposition risk that could change the inhibition mechanism. Thermal behaviour restricts AMF application as corrosion inhibitor for carbon steel in 1.0 mol L^?1 HCl solution at temperatures ≤45 °C where there are no significant modifications of the adsorption mechanism. According to the results of electrochemical measurements, in association with UV–Vis spectrophotometry and optical microscopy techniques, AMF is a mixed-type inhibitor for carbon steel corrosion in 1.0 mol L^?1 HCl solution, simultaneously suppressing the anodic and cathodic processes and acting via spontaneous physisorption on the metal surfaces.     

Corrosion inhibition investigations of 3-acetylpyridine semicarbazone on carbon steel in hydrochloric acid medium

The corrosion inhibition efficiency of 3-acetylpyridine-semicarbazide (3APSC) on carbon steel (CS) in 1.0 M HCl solution has been investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies. The results show that inhibition efficiency on metal increases with the inhibitor concentration. 3APSC exhibited marked inhibition towards carbon steel in HCl medium even at low concentrations. The adsorption of inhibitor on the surfaces of the corroding metal obeys the Langmiur isotherm and thermodynamic parameters (K _ads, ?G _ads ⁰ ) were calculated. Activation parameters of the corrosion process (E _a, ?H* and ?S*) were also calculated from the corrosion rates. Polarization studies revealed that 3APSC act as a mixed-type inhibitor. Surface analysis of the metal specimens was performed by scanning electron microscopy.     

Commiphora pedunculata gum as a green inhibitor for the corrosion of aluminium alloy in 0.1 M HCl

The effect of Commiphora pedunculata (CP) gum on the inhibition of the corrosion of aluminum alloy AA 3001) in solutions of HCl was investigated using gravimetric and thermometric methods of monitoring corrosion. The results obtained indicated that CP gum is a good adsorption inhibitor for the corrosion of aluminum in solutions of HCl. The inhibition efficiency of CP gum was found to increase with an increase in concentration but to decrease with increasing temperature. The adsorption of CP gum on the surface of aluminum was found to be endothermic, spontaneous and to support the mechanism of physical adsorption. The Langmuir adsorption model has been used to describe the adsorption characteristics of CP gum on aluminum surface.     

Preparation and characterization of anticorrosion Ormosil sol–gel coatings for aluminum alloy

Organically modified silicate (Ormosil) coatings have been synthesized through the sol–gel method for corrosion protection of aluminum alloy. Silica-based unmodified coatings were also designed to investigate the effect of tetraethoxysilane (TEOS) content on the properties of the coatings. The surface morphology of the coatings was characterized by scanning electron microscopy. The corrosion resistance was evaluated by immersion test, electrochemical impedance spectroscopy and potentiodynamic polarization measurements. In addition, the surface potential differences of the coated samples were determined by scanning Kelvin probe. The results showed that a better corrosion resistance of unmodified coating was prepared by controlling the TEOS/EtOH/H₂O molar ratio of 0.109/1/1.52. Ormosil coatings provided excellent barrier properties and corrosion resistance in comparison with the unmodified sol–gel coatings. The Ormosil coating modified with triethoxyoctylsilane exhibited corrosion resistance properties superior to the other Ormosil coatings after exposure to 3.5 wt% NaCl solution for 10 days.     

Thermal behaviour of a modified encapsulation agent

Thermal behaviour of heptakis-6-iodo-6-deoxy-beta-cyclodextrin (HIDBCD) under inert and oxidative conditions was investigated by TG/DTG/DTA, FTIR, and using the hyphenate technique TG–FTIR. Due to the fact that thermal behaviour of HIDBCD was not studied before, we set our goal in the investigation of thermal degradation process in a dynamic air atmosphere vs. nitrogen atmosphere at a heating rate of 10 °C min^?1, up to 500 °C, respectively, 600 °C. It was found that the degradation process in air occurs in a single step, with a total mass loss of 99.9 %. The results of TG/DTG/DTA–FTIR indicated that the thermal behaviour of this cyclodextrin can be divided into three stages and more information was provided about the reaction sequences and the relevant products of reaction.     

A colorimetric assay for d-Penicillamine in urine and plasma samples based on the aggregation of gold nanoparticles

We report herein the development of a highly sensitive colorimetric method for detection of d-Penicillamine using citrate-capped gold nanoparticles (AuNPs). This assay relies upon the distance-dependent of gold nanoparticles surface plasmon resonance band of gold nanoparticles. By replacing the thiol-containing chelator drug, d-Penicillamine, with citrate on the gold nanoparticles surface, a new peak appearing at a longer wavelength intensifies and shifts further to the red from the original peak position due to aggregation of gold nanoparticles which depends on ionic strength, gold nanoparticles and d-Penicillamine concentration. During this process, the plasmon band at 521 nm decreases gradually along with the formation of a new red-shifted band at 630 nm. The calibration curve which is derived from the ratio intensities of absorbance at longer wavelength (630 nm) to original wavelength (521 nm) displays a linear relation in the range of 5.0 × 10^?6–3.0 × 10^?4 M d-Penicillamine. Lower limit of detection for d-Penicillamine, at the signal-to-noise ratio of 3 (3σ), was 3.8 × 10^?6 M. The developed methodology was successfully applied for the determination of d-Penicillamine in human urine and plasma.     

Interaction of radium with freshwater sediments and their mineral components

Radiotracer method has been used for investigation of the adsorption and desorption of traces of radium on muscovite and feldspar (albite) under conditions similar to those prevailing in waste and surface waters. The effects of pH, liquid to solid ratio, time, ionic strength (Na⁺) and presence of Ca²⁺ or SO ₄ ^2? ions have been studied. It has been concluded that both minerals can significantly affect the fate and migration of radium in surface waters if present as major components of bottom sediments or as suspended solids in concentrations of several milligrams per liter or higher. Muscovite can absorb radium even from moderately acidic waters. Radium adsorbed on muscovite and albite cannot be easily released upon an increase of the salinity of ambient water. However, almost complete desorption can be achieved with 1M HCl. Mechanisms of radium adsorption on both minerals and character of the adsorption sites are discussed.     

Novel worm-like amphiphilic micelles of folate-targeted cyclodextrin/retinoic acid for delivery of doxorubicin in KG-1 cells

Folate-targeted cyclodextrin/retinoic acid (CD/RA) conjugate was synthesized using carbonyldiimidazole (CDI) and dimethylaminopyridine (DMAP). The structure of the produced macromolecule was studied by FTIR and ¹HNMR. The developed macromolecule could self-aggregate to form micelles. Critical micelle concentration (CMC) of the macromolecule was determined by pyrene as a fluorescent probe. Doxorubicin (DOX)-loaded micelles were prepared by direct dissolution method. To optimize the effect of cyclodextrin type (α or β), the molar ratio of RA to CD and the drug content, a full factorial design was used and their effects on particle size, polydispersity index, zeta potential, loading efficiency (LE%), and release efficiency (RE₂₄%) in 24 h were studied. Orientation of folate ligand on the surface of the micelles was studied by X-ray photoelectron spectroscopy (XPS) technique. The cytotoxicity of DOX-loaded micelles was studied on KG-1 cells which overexpressed folate receptor (FR) and FR-negative HepG2 cells using MTT assay. FTIR and ¹HNMR spectra confirmed successful production of the micelles and XPS spectra showed surface orientation of folate. The best results obtained from β-cyclodextrin with molar ratio of 4 to RA and 15 % drug content. The optimized micelles showed the particle size of 103?±?4 nm, zeta potential of ?36 mV, polydispersity index of 0.28?±?0.05, LE% of 100 %, and RE₂₄% of 69.88?±?1.6 %. The IC₅₀ of targeted micelles was half of non-targeted micelles and free DOX.     

Carbon composite-based DNA sensor for detection of bacterial meningitis caused by Neisseria meningitidis

Carbon/1-octadecanethiol-carboxylated multiwalled carbon nanotubes (cMWCNT) composite was used to construct a DNA sensor for detection of human bacterial meningitis caused by Neisseria meningitidis. The carbon composite electrode was used to covalently immobilize 5′-amine-labeled 19-mer single-stranded DNA (ssDNA) probe, which was hybridized with 1.35?×?10²–3.44?×?10⁴ pM (0.5–128 ng/5 μl) of single-stranded genomic DNA (ssG-DNA) of N. meningitidis for 10 min at room temperature (RT). The surface topography of the DNA sensor was characterized by using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) while electrochemically characterized by electrochemical impedance. The immobilization of ssDNA probe and hybridization with ssG-DNA were detected electrochemically by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at RT in 30 min with a response time of 1 min. The DNA sensor showed high pathogenic specificity and can distinguish among complement, noncomplement, one base mismatch, and triple base mismatch oligomer targets. The limit of detection (LOD) and sensitivity of the sensor were approximately 68 pM and 38.095 (μA/cm²)/nM of ssG-DNA, respectively, using DPV. The improved sensitivity and LOD of the sensor can be attributed to the higher efficiency of probe immobilization due to high surface area-to-volume ratio and good electrical activity of cMWCNT. Figure

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Adsorption and inhibition effect of curcumin on mild steel corrosion in hydrochloric acid

The inhibition effect of curcumin on the corrosion of mild steel in 1.0 M HCl solution was studied by weight loss, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) methods. The experimental results suggest that this compound is an efficient corrosion inhibitor and the inhibition efficiency increases with the increase in inhibitor concentration. Adsorption of this compound on mild steel surface obeys Langmuir isotherm. Also the objective of this work is to attempt to find relationships between electronic structure and inhibition efficiency. The structural parameters, such as the frontier molecular orbital energies (E _HOMO and E _LUMO), gap of energy ΔE, from the molecule to iron as well as electronic parameters such as Mulliken atomic populations were calculated and discussed using the Density Functional Theory method (DFT).     

Indicator-free impedimetric detection of BCR/ABL fusion gene based on ordered FePt nanoparticle-decorated electrochemically reduced graphene oxide

A novel indicator-free DNA hybridization biosensor with a graphene-based nanocomposite as the enhanced sensing platform was developed for the detection of the BCR/ABL fusion gene in chronic myelogenous leukemia. The platform was constructed by homogenously distributing ordered FePt nanoparticles (NPs) onto the electrochemically reduced graphene oxide (ERGNO). The surface structure and electrochemical performance of the FePt/ERGNO nanocomposite were systematically investigated. Owing to the synergistic effects of FePt NPs and ERGNO with a large surface area and excellent electron transfer ability, the obtained nanocomposite greatly facilitated the sensing behavior for DNA detection, resulting in excellent sensitivity and selectivity. A remarkable change has been observed in the impedance spectra before and after hybridization of the probe single-stranded DNA (ssDNA) with the target DNA. Under the optimized conditions, the complementary target genes could be quantified in a wide range of 1.0?×?10^?14 to 1.0?×?10^?9 mol/L with a detection limit of 2.6?×?10^?15 mol/L. The approach does not need an oligonucleotide probe or target to be labeled previously, which makes it advantageous in terms of simplicity and noninvasiveness.     

Polarography of hexavalent molybdenum in hypophosphorous acid solutions

The polarographic behaviour and determination of Mo(VI) in hypophosphorous acid solutions of concentrations varying from 0.1 to 5.0 mol l^?1 andT=25±0.1 °C have been investigated. It was shown that reduction of MoO ₄ ^2? takes place along a single or two waves depending upon the acid concentration. Microcoulometric experiments have been performed at the limiting region of the different waves obtained at different acid concentrations. A scheme for the mechanism of reduction occuring at theDME has been deduced. A method for analytical determination of Mo(VI) on both the micro- and macro-scales in hypophosphorous acid solutions has been reported. Analysis of a binary mixture Mo(VI)/Cd(II) and a tertiary mixture Mo(VI)/Cd(II)/Zn(II) in mol l^?1 hypophosphorous acid has been investigated.     

Preparation,thermal property,and thermal stability of microencapsulated n-octadecane with poly(stearyl methacrylate) as shell

This study focused on preparation and thermal properties of poly(stearyl methacrylate) shell (PSMA) microcapsules containing n-octadecane as a phase change material (PCM). Pentaerythritol triacrylate (PETA) and divinylbenzene (DVB) were employed as crosslinking agents. The surface morphologies, particle sizes, and distributions of the microencapsulated phase change material (microPCM) were studied by scanning electron microscopy. The thermal properties, thermal reliabilities, and thermal stabilities of the microPCMs were investigated by differential scanning calorimetry and thermal gravimetric analysis. The microPCM with DVB exhibits higher phase change enthalpies of melting (87.9 J g^?1) and crystallization (94.8 J g^?1) and a greater thermal stability in comparison with the microPCM with PETA. The phase change temperatures and enthalpies of the microPCMs varied little after thermal cycles. Thermal images showed that the gypsum board with PSMA/n-octadecane microPCM possessed temperature-regulated property. Therefore, microencapsulated n-octadecane with PSMA as shell has good thermal energy storage and thermal regulation potential.     

The Effect of O6+ and Si7+ ion beam irradiations on poly(lactide-co-glycolide) (50: 50) copolymer

Sterilization by ion beam radiations unfortunately also has a significant effect on the degradation of many polymers. The aim of present study is to examine the effect of heavy ion beam irradiation on poly(lactide-co-glycolide) (PLGA) (50: 50). The radiation effect is manifested through its degradation behavior and changes in the morphological, optical and structural properties. PLGA films are prepared by solvent casting method and subsequently irradiated with swift heavy ions O⁶⁺ and Si⁷⁺ ion with fluence in the range of 5 × 10¹⁰?1 × 10¹² ions/cm². The dominant effect on PLGA films is chain scission as evidenced by change in surface modification. Changes in optical and structural properties were analyzed by UV-Vis, XRD and FTIR spectrometric techniques. XRD technique is not responsive to degradation occurring in samples. Surface modifications caused by ion irradiations have been observed with SEM.     

Simultaneous sensing of L-tyrosine and epinephrine using a glassy carbon electrode modified with nafion and CeO2 nanoparticles

An electrochemical sensor was developed and tested for detection of L-tyrosine in the presence of epinephrine by surface modification of a glassy carbon electrode (GCE) with Nafion and cerium dioxide nanoparticles. Fabrication parameters of a surfactant-assisted precipitation method were optimized to produce 2–3 nm CeO₂ nanoparticles with very high surface-to-volume ratio. The resulting nanocrystals were characterized structurally and morphologically by X-ray diffractometery (XRD), scanning and high resolution transmission electron microscopy (SEM and HR-TEM). The nanopowder is sonochemically dispersed in a Nafion solution which is then used to modify the surface of a GCE electrode. The electrochemical activity of L-tyrosine and epinephrine was investigated using both a Nafion-CeO₂ coated and a bare GCE. The modified electrode exhibits a significant electrochemical oxidation effect of L-tyrosine in a 0.2 M Britton-Robinson (B-R) buffer solution of pH 2. The electro-oxidation peak current increases linearly with the L-tyrosine concentration in the molar concentration range of 2 to 160 μM. By employing differential pulse voltammetry (DPV) for simultaneous measurements, we detected two reproducible peaks for L-tyrosine and epinephrine in the same solution with a peak separation of about 443 mV. The detection limit of the sensor (signal to noise ratio of 3) for L-tyrosine is ~90 nM and the sensitivity is 0.20 μA μM^?1, while for epinephrine these values are ~60 nM and 0.19 μA μM^?1. The sensor exhibited excellent selectivity, sensitivity, reproducibility and stability as well as a very good recovery time in real human blood serum samples.

Simultaneous electrochemical determination of L-tyrosine and epinephrine in blood plasma with Nafion-CeO₂/GCE modified electrode showing a 443 mV peak-to-peak potential difference between species oxidation peak currents.     

Titanium dioxide nanoparticle based solid phase extraction of trace Alizarin Violet,followed by its specrophotometric determination

Nanometer-sized titanium dioxide (nano-TiO₂) is shown to be a viable material for the preconcentration of Alizarin Violet (AV, a common dye and biological stain). In the preconcentration step, a 5-ring cyclic ester is formed between the ortho-dihydroxy groups of AV and two hydroxy groups of the titanic acid on the surface of the nano-TiO₂. Under optimized conditions, the adsorption capacity of nano-TiO₂ is?~?20 μg?·?mg^?1, the adsorption efficiency is 98 %. The adsorbed AV can be eluted with 5 mL of 5 mol?·?L^?1 5-sulfosalicylic acid with an elution efficiency of more than 91.8 %. The preconcentration factor is 50 in case of 250 mL samples. Spectrophotometric determination of AV in the eluate gives a linear calibration plot in the range between 18.8 μg?·?L^?1 and 10 mg?·?L^?1 and a detection limit (3 s; for n?=?11) of 18.8 μg?·?L^?1. The method is simple and fast. It was successfully applied to the analysis of AV in spiked natural waters, and recoveries were found to range between 94.2 and 97.3 %.

Nanometer-sized titanium dioxide is a viable material for the preconcentration of Alizarin Violet (AV), before its spectrophotometrical determination. The method is simple and fast. It was successfully applied to the analysis of AV in spiked natural waters, and recoveries were found to range between 94.2 and 97.3 %.     

A polyaniline-magnetite nanocomposite as an anion exchange sorbent for solid-phase extraction of chromium(VI) ions

This work describes a novel polyaniline-magnetite nanocomposite and its application to the preconcentration of Cr(VI) anions. The material was obtained by oxidative polymerization of aniline in the presence of magnetite nanoparticles. The parameters affecting preconcentration were optimized by a Box-Behnken design through response surface methodology. Extraction time, amount of magnetic sorbent and pH value were selected as the main factors affecting sorption. The sorption capacity of the sorbent for Cr(VI) is 54 mg g^?1. The type, volume and concentration of the eluents, and the elution time were selected as main factors in the optimization study of the elution step. Following sorption and elution, the Cr(VI) ions were reacted with diphenylcarbazide, and the resulting dye was quantified by HPLC with optical detection at 546 nm. The limit of detection is 0.1 μg L^?1, and all the relative standard deviations are <6.3 %. The nanocomposite was successfully applied to the rapid extraction and determination of trace quantities of Cr(VI) ions in spiked water samples. Figure

A schematic procedure of magnetic solid phase extraction     

Rapid diagnostics of characteristics and stability of fuel cells with proton-conducting electrolyte

Processes underlying the degrading of membrane-electrode assemblies of hydrogen-air fuel cells with Nafion 212 and MF-4SK membranes under the conditions of their accelerated stress testing and long-term life tests are analyzed. The cathode platinum catalyst corrosion was shown to be the main cause of the degrading of the fuel cell’s kinetically controlled current-voltage characteristics; the corrosion is accompanied by the platinum nanoparticles’ growth and the platinum ion partial transfer into the membrane. The overvoltage components of the membrane-electrode assembly and their changing during accelerated stress testing are determined. The voltage decrease at currents >0.5 A/cm² is shown to be mainly caused by the transport and ohmic resistance growth. The transport resistance components are calculated; the dependence of the cathode active layer resistance on the platinum catalyst surface area is revealed.     

Analysis of drug interactions with very low density lipoprotein by high-performance affinity chromatography

High-performance affinity chromatography (HPAC) was utilized to examine the binding of very low density lipoprotein (VLDL) with drugs, using R/S-propranolol as a model. These studies indicated that two mechanisms existed for the binding of R- and S-propranolol with VLDL. The first mechanism involved non-saturable partitioning of these drugs with VLDL, which probably occurred with the lipoprotein’s non-polar core. This partitioning was described by overall affinity constants of 1.2 (±0.3)?×?10⁶ M^?1 for R-propranolol and 2.4 (±0.6)?×?10⁶ M^?1 for S-propranolol at pH 7.4 and 37 °C. The second mechanism occurred through saturable binding by these drugs at fixed sites on VLDL, such as represented by apolipoproteins on the surface of the lipoprotein. The association equilibrium constants for this saturable binding at 37 °C were 7.0 (±2.3)?×?10⁴ M^?1 for R-propranolol and 9.6 (±2.2)?×?10⁴ M^?1 for S-propranolol. Comparable results were obtained at 20 and 27 °C for the propranolol enantiomers. This work provided fundamental information on the processes involved in the binding of R- and S-propranolol to VLDL, while also illustrating how HPAC can be used to evaluate relatively complex interactions between agents such as VLDL and drugs or other solutes.     

Separation of tin from some metals by extraction chromatography

Much attention has been devoted to Sn (IV) strongly retained on the TBP-Daiflon column from 2M HCl in extraction chromatography. The separations of Sn?Cu, Zn, As, Cd, Sb, Pb,¹¹³Sn-¹²⁵Sb,¹¹³Sn-^113mIn (^113mIn milking) and Sn?Hg?Fe were successfully achieved without any contamination. In the separations, except for the last, only tin was retained separately on the column upon passing the mixed solution. The daughter indium was eluted with 0.5M HCl. In the last separation, iron was eluted with 0.5 M HCl, tin with 0.1M HCl and mercury with 2M HNO₃, for these metals retained on the column. Radioactive tracers for tin, iron, mercury and antimony were used.