Effective mercury(II) bioremoval from aqueous solution, and its electrochemical determination.

This work proposed mercury elimination using agricultural waste (Allium Cepa L.). The biomass removed 99.

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.

Deprotonation mechanism and acidity constants in aqueous solution of flavonols: a combined experimental and theoretical study.

Four flavonols, namely quercetin, morin, kaempferol, and myricetin, were studied using spectrophotometry (UV-vis) in aqueous solution. The study was performed varying the pH to analyze the stability of these compounds, and to estimate their acidity constants. In addition, the deprotonation mechanisms were studied using computational chemistry within the density functional theory framework.

Searching for Computational Strategies to Accurately Predict pKas of Large Phenolic Derivatives.

Twenty-two reaction schemes have been tested, within the cluster-continuum model including up to seven explicit water molecules. They have been used in conjunction with nine different methods, within the density functional theory and with second-order Møller-Plesset. The quality of the pKa predictions was found to be strongly dependent on the chosen scheme, while only moderately influenced by the method of calculation.

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.

Amperometric biosensor based on a high resolution photopolymer deposited onto a screen-printed electrode for phenolic compounds monitoring in tea infusions.

An amperometric biosensor based on laccase, from Trametes versicolor (LTV), was developed and optimized for monitoring the phenolic compounds content in tea infusions. The fungal enzyme was immobilized by entrapment within polyvinyl alcohol photopolymer PVA-AWP (azide-unit pendant water-soluble photopolymer) onto disposable graphite screen-printed electrodes (SPE). Sensitivity optimization in terms of pH, temperature and applied potential was carried out.

Determination of pKa values of tenoxicam from 1H NMR chemical shifts and of oxicams from electrophoretic mobilities (CZE) with the aid of programs SQUAD and HYPNMR.

In this work it is explained, by the first time, the application of programs SQUAD and HYPNMR to refine equilibrium constant values through the fit of electrophoretic mobilities determined by capillary zone electrophoresis experiments, due to the mathematical isomorphism of UV-vis absorptivity coefficients, NMR chemical shifts and electrophoretic mobilities as a function of pH. Then, the pK(a) values of tenoxicam in H(2)O/DMSO 1:4 (v/v) have been obtained from (1)H NMR chemical shifts, as well as of oxicams in aqueous solution from electrophoretic mobilities determined by CZE, at 25 degrees C. These values are in very good agreement with those reported by spectrophotometric and potentiometric measurements.

Deprotonation mechanism of new antihypertensive piperidinylmethylphenols: a combined experimental and theoretical study.

Four new antihypertensive piperidinylmethylphenol compounds were synthesized for their potential antihypertensive and antiarhythmic properties. The pKa values were determined experimentally, with the aid of the program SQUAD, by capillary zone electrophoresis (CZE) at T=298.15 K and 0.

Acetylcholinesterase-based biosensors for quantification of carbofuran, carbaryl, methylparaoxon, and dichlorvos in 5% acetonitrile.

Amperometric acetylcholinesterase biosensors have been developed for quantification of the pesticides carbofuran, carbaryl, methylparaoxon, and dichlorvos in phosphate buffer containing 5% acetonitrile. Three different biosensors were built using three different acetylcholinesterase (AChE) enzymes-AChE from electric eel, and genetically engineered (B394) and wild-type (B1) AChE from Drosophila melanogaster. Enzymes were immobilized on cobalt(II) phthalocyanine-modified electrodes by entrapment in a photocrosslinkable polymer (PVA-AWP).

Sensitive amperometric biosensor for dichlorovos quantification: Application to detection of residues on apple skin.

This paper presents the construction of an amperometric biosensor for the highly sensitive detection of the organophosphorus insecticide dichlorvos, based on the inhibition of acetylcholinesterase (AChE). The sensitivity of three AChEs from different sources were tested and compared: AChEs from Electric eel (Ee) and genetically engineered (B394) and wild type (B1) from Drosophila melanogaster (Dm). The enzymes were immobilized by entrapment in a photocrosslinkable PVA-SbQ polymer on a screen printed graphite electrode.

Development of a capillary electrophoresis method for the characterization of "palo azul" (Eysenhardtia polystachya).

The tree Eysenhardtia polystachya (Ortega) Sarg. has quite a wide popular use within the traditional Mexican medicine as herbal remedy. Popular practices constitute a relevant enough basis to design optimum analytical methods in order to determine basic principles of diverse medicinal plants.

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.

UV-visible spectroscopic and electrochemical study of the complex formation between Fe(II) and 5-amino-1,10-phenantroline (5-Aphen) in aqueous solution.

The system Fe(II)-5-Aphen-H(2)O was studied. The spectroscopic and electrochemical results show that only one stable complex between Fe(II) and 5-Aphen forms, having a 1:3 stoichiometric ratio. The spectrophotometry study allowed determination of the formation constant of the complex (logbeta(3)=23.

Spectrophotometric determination of acidity constants of salicylaldoxime in aqueous solution at 25 degrees C and ionic strength of 0.5 M controlled with NaCl.

The equilibrium constants of salicylaldoxime in water at 25 degrees C, 0.5 M of ionic strength with NaCl and concentration of 1x10(-4) M were determined spectrophotometrically. The spectral data were processed using SQUAD program.

UV/vis, 1H, and 13C NMR spectroscopic studies to determine mangiferin pKa values.

The acid constants of mangiferin (a natural xanthonoid) in aqueous solution were determined through an UV/vis spectroscopic study employing the SQUAD program as a computational tool. A NMR study complements the pK(a) values assignment and evidences a H-bridge presence on 1-C. The chemical model used was consistent with the experimental data obtained.

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.

Spectrophotometric and electrochemical determination of the formation constants of the complexes Curcumin-Fe(III)-water and Curcumin-Fe(II)-water.

The formation of complexes among the Curcumin, Fe(III) and Fe(II) was studied in aqueous media within the 5-11 pH range by means of UV-Vis spectrophotometry and cyclic voltammetry. When the reaction between the Curcumin and the ions present in basic media took place, the resulting spectra of the systems Curcumin-Fe(III) and Curcumin-Fe(II) presented a similar behaviour. The cyclic voltammograms in basic media indicated that a chemical reaction has taken place between the Curcumin and Fe(III) before that of the formation of complexes.

Determination of acidity constants of curcumin in aqueous solution and apparent rate constant of its decomposition.

The stability of curcumin (H3Cur) in aqueous media is improved when the systems in which it is present are at high pH values (higher than 11.7), fitting a model describable by a pseudo-zero order with a rate constant k' for the disappearance of the Cur3- species of 1.39 (10(-9)) Mmin(-1).

Speciation of the new ligand di-isopropyliminodiacetoamide with Cu(II) using computational processing and graphical methods.

The importance assigned to chelating agents in diverse areas has impelled studies concerning their development as related to metal ions representing a biological concern. The synthesis of di-isopropyliminodiacetoamide (D) is presented in this work. The acidity constant obtained for D was pKa = 5.