Insights into Electronucleation and Electrodeposition of Nickel from a Non-aqueous Solvent Based on NiCl·6HO Dissolved in Ethylene Glycol.

This work deals with nickel electronucleation and growth processes onto a glassy carbon electrode from NiCl·6HO dissolved in ethylene glycol (EG) solutions with and without 250 mM NaCl as a supporting electrolyte. The physicochemical properties of EG solutions, namely, viscosity and conductivity, were determined for different Ni(II) concentrations. From cyclic voltammetry, it was found that in the absence of the supporting electrolyte, the cathodic efficiency of Ni electrodeposition is about 88%; however, in the presence of the supporting electrolyte, the cathodic efficiency was reduced to 26% due to water (added along the supporting electrolyte) reduction on the growing surfaces of Ni nuclei.

Adsorption and corrosion inhibition behaviour of new theophylline-triazole-based derivatives for steel in acidic medium.

The design and synthesis of a series of theophylline derivatives containing 1,2,3-triazole moieties are presented. The corrosion inhibition activities of these new triazole-theophylline compounds were evaluated by studying the corrosion of API 5 L X52 steel in 1 M HCl medium. The results showed that an increase in the concentration of the theophylline-triazole derivatives also increases the charge transference resistance ( ) value, enhancing inhibition efficiency and decreasing the corrosion process.

Electrochemical quantification of the antioxidant capacity of medicinal plants using biosensors.

The working area of a screen-printed electrode, SPE, was modified with the enzyme tyrosinase (Tyr) using different immobilization methods, namely entrapment with water-soluble polyvinyl alcohol (PVA), cross-linking using glutaraldehyde (GA), and cross-linking using GA and human serum albumin (HSA); the resulting electrodes were termed SPE/Tyr/PVA, SPE/Tyr/GA and SPE/Tyr/HSA/GA, respectively. These biosensors were characterized by means of amperometry and EIS techniques. From amperometric evaluations, the apparent Michaelis-Menten constant, Km', of each biosensor was evaluated while the respective charge transfer resistance, Rct, was assessed from impedance measurements.

Guest-host complex formed between ascorbic acid and β-cyclodextrin immobilized on the surface of an electrode.

This work deals with the formation of supramolecular complexes between ascorbic acid (AA), the guest, and β-cyclodextrin (β-CD), the host, that was first potentiodynamically immobilized on the surface of a carbon paste electrode (CPE) throughout the formation of a β-CD-based conducting polymer (poly-β-CD). With the bare CPE and the β-CD-modified CPE, an electrochemical study was performed to understand the effect of such surface modification on the electrochemical response of the AA. From this study it was shown that on the modified-CPE, the AA was surface-immobilized through formation of an inclusion complex with β-CD, which provoked the adsorption of AA in such a way that this stage became the limiting step for the electrochemical oxidation of AA.

Multicomponent click synthesis of new 1,2,3-triazole derivatives of pyrimidine nucleobases: promising acidic corrosion inhibitors for steel.

A series of new mono-1,2,3-triazole derivatives of pyrimidine nucleobases were synthesized by one-pot copper(I)-catalyzed 1,3-dipolar cycloaddition reactions between N-1-propargyluracil and thymine, sodium azide and several benzyl halides. The desired heterocyclic compounds were obtained in good yields and characterized by NMR, IR, and high resolution mass spectrometry. These compounds were investigated as corrosion inhibitors for steel in 1 M HCl solution, using electrochemical impedance spectroscopy (EIS) technique.

Synthesis of new 1,2,3-triazole derivatives of uracil and thymine with potential inhibitory activity against acidic corrosion of steels.

Ten 1,4-disubstituted 1,2,3-triazoles were synthesized from one of 1-(azido-methyl)benzene, 1-(azidomethyl)-4-fluorobenzene, 1-(azidomethyl)-4-chlorobenzene, 1-(azidomethyl)-4-bromobenzene or 1-(azidomethyl)-4-iodobenzene, generated in situ from sodium azide and the corresponding benzyl halide, and dipropargyl uracil or dipropargyl thymine. Optimal experimental conditions were established for the conventional click chemistry. The corrosion inhibiting properties of some of these compounds, which were determined by means of an electrochemical technique, are also presented.

Kinetics and mechanism of the electrochemical formation of iron oxidation products on steel immersed in sour acid media.

From electrochemical techniques (cyclic voltammetry, potential steps, and EIS), XRD, and SEM-EDX, the kinetics and mechanism of anodic film formation applying anodic potential steps on steel immersed in sour acid media was determined. It was found, from a thermodynamic analysis, based on equilibrium phase diagrams of the system considered in this work, that iron oxidation may produce different new solid phases, depending on the applied potential, the first being the iron oxidation associated with formation of FeS((c)) species, which in turn can be reoxidized to FeS(2(c)) or even to Fe(2)O(3(c)) at higher potential values. From analysis of the corresponding experimental potentiostatic current density transients, it was concluded that the electrochemical anodic film formation involves an E(1)CE(2) mechanism, whereby the first of the two simultaneous processes were the Fe electrochemical oxidation (E(1)) followed by FeS precipitation (C) that occurs by 3D nucleation and growth limited by mass transfer reaction and FeS oxidation (E(2)) forming a mix of different stoichiometry iron sulphides and oxides.

Quantum chemical calculations on the interaction between flavonol and functional monomers (methacrylic acid and 4-vinylpyridine) in molecularly imprinted polymers.

Quantum chemical calculations were performed to characterize the interaction of the flavonol molecule (FL) with methacrylic acid (MAA) and 4-vinylpyridine (4VPy) in the formation of imprinted polymers. The polarizable continuum model (PCM) was used to gain insight on the type of interaction between the reactant molecules under vacuum conditions and in the presence of different solvents. The effect of solvent on the pre-polymerization complex formation was evaluated through the stability energy, in which chloroform behaves as the best solvent for the synthesis of the imprinted polymers since it facilitates the reaction by lowering its degree of stabilization.

Experimental correlation between the pKa value of sulfonphthaleins with the nature of the substituents groups.

This work presents the results obtained from a spectrophotometry study performed on some indicators of the sulfonphtaleins like phenol red (PR), thymol blue (TB), bromothymol blue (BTB), xylenol orange (XO) and methylthymol blue (MTB). During the first stage the acidity constants of some of the indicators were determined using the data from spectrophotometry, potentiometry and with the use of the software SQUAD. These were as follows: for the equilibrium 2H+BTB<-->H(2)BTB, log beta(2)=15.

New insights on the nature of the chemical species involved during the process of dopamine deprotonation in aqueous solution: theoretical and experimental study.

Due to dopamine's chemical structure and the fact that it has three pKa values, its deprotonation process, in aqueous solution, may involve different chemical species. For instance, the first deprotonation step, from the fully protonated dopamine molecule (H3DA+) to the neutral one (H2DA), will result in zwitterionic species if a proton from one of the OH groups in the catechol ring is lost or into a neutral species if the proton is lost from the amino group. Given that the interaction of such a product with its environment will be quite different depending on its nature, it is very important, therefore, to have an accurate knowledge of which is the dopamine chemical species that results after each deprotonation step.

Development of a novel nitrate-selective composite sensor based on doped polypyrrole.

The manufacture and evaluation of a novel sensor built with a composite material, highly selective to nitrate ions using doped polypyrrole as a recognition agent, are presented. When the ratio of recognition agent to graphite was optimized at 1:1, and the sensitivities found closely approached nernstian behavior. The stability times attained were less than 14 min with response times also below 20 s.

Mercury ions removal from aqueous solution using an activated composite membrane.

This work presents the results concerning the first use of activated composite membranes (ACMs) for the removal of Hg(II) ions from aqueous solution, using as the ligand di-(2-ethylhexyl)dithiophosphoric acid (DTPA). The effects on the removal percentage of Hg(ll) of variables such as pH, the nature of the acid, the concentration of mercury (in the feed solutions), and the ligand content (in the membrane) as well as the total surface membrane area exposed to the Hg(II) aqueous solution were studied. During the course of the removal experiments, the membrane was immersed in the Hg(II) aqueous solution in acid media and samples of the solution were taken at different times to enable monitoring of the mercury concentration changes.