Lida Khalafi

Avila University · Department of Chemistry

Cyclic voltammetry (CV) is the most popular electrochemical technique for the study of electrode processes. One of the reasons for its popularity is its adjustable timescale which can vary several orders of magnitude simply by varying the rate at which the potential is scanned. Changing the scan rate affects CV features including the current, leadi...

A laboratory experiment is described in which students determine the concentration and speciation of iron in beer samples using cloud point extraction and absorbance spectroscopy. The basis of determination is the complexation between iron and 2-(5-bromo-2- pyridylazo)-5-diethylaminophenol (5-Br-PADAP) as a colorimetric reagent in an aqueous micell...

Electrochemical techniques are the most reliable techniques for determination of neurotransmitters and selective determination is their most challenging issue. Herein we have optimized the condition for oxidation of adrenaline and noradrenaline, as the most similar neurotransmitters, to find a simple and fast technique for their selective determina...

This chapter describes the cyclic voltammetry and its application in the field of physical organic chemistry. Cyclic voltammetry consists of the electrode potential ramp versus time that forms a triangular waveform and recording the current as function of potential that called cyclic voltammogram. Voltammetric measurements are performed by a potent...

A laboratory experiment is described in which students measure the amount of cetirizine in allergy-treatment tablets based on molecular recognition. The basis of recognition is competition of cetirizine with phenolphthalein to form an inclusion complex with β-cyclodextrin. Phenolphthalein is pinkish under basic condition, whereas it's complex form...

The reactions of electrochemically generated o-quinones from oxidation of catecholamines with aniline derivatives have been studied using cyclic voltammetry. There is a close and pH-dependent interplay between intra and intermolecular Michael addition reactions of side chain amine group of catecholamines and anilines toward the electrochemically ge...

Electrochemical oxidation of levodopa (LD) as one of the most well-known neurotransmitters has been studied in the presence of some aniline derivatives. The electron transfer of LD is followed by two competitive reactions in the presence of these amines. The reactions are the Michael additions of side chain amine group of LD and/or aromatic amines...

The oxidation reactions of catechol, dopamine and epinephrine have been studied in the absence and presence of N-methylaniline by UV-Vis. Spectrophotometry. A variety of reaction pathways (inter and intramolecular reactions) that followed by this oxidation have been observed depending on the nature of catechol derivatives. The observed homogeneous...

The reactions of electrochemically generated o-quinones from oxidation of catechol and 4-methylcatechol as Michael acceptors with N-methylaniline as nucleophile have been studied using cyclic voltammetry. Voltammetric responses show that oxidation of catechols is followed by Michael addition of N-methylaniline. The reaction products are believed to...

The reaction of electrochemically generated o-quinones from oxidation of esculetin as Michael acceptor with nitrite ion as nucleophile has been studied using cyclic voltammetry. The reaction mechanism is believed to be EC, including oxidation of catechol moiety of esculetin followed by Michael addition of nitrite ion. The observed homogeneous rate...

The reactions of electrochemically generated o-quinones, as Michael acceptors, from oxidation of catechols with trialkylphosphites as nucleophiles have been studied using cyclic voltammetry. The reaction mechanism is an EC mechanism and the products of reaction are believed to be dialkylphosphonate derivatives of catechol. The observed homogeneous...

The electrochemical oxidation of two flavonoids, quercetin and catechin, has been studied in the absence and presence of nitrite ion. A reaction mechanism has been proposed, based on cyclic voltammetry. Variation in the cathodic peak, due to the competition between the intramolecular Michael addition of hydroxy group and the intermolecular addition...

The reaction of electrochem. generated o-benzoquinones from the oxidn. of catechol derivs. as Michael acceptors with di-Me phosphite as nucleophile was studied using cyclic voltammetry. The reaction mechanism is believed to be EC comprising oxidn. of catechol moiety of these antioxidants followed by Michael addn. of di-Me phosphite. The obsd. homog...

The acid-base equilibrium of mycophenolate mofetil is studied in the absence and presence of β-cyclodextrin (β-CD). The conditional acidity constants are obtained by rank annihilation factor analysis (RAFA) as a function of β-CD concentrations. Also the stability constants for inclusion complexes of β-CD with both acidic and basic forms are calcula...

The reaction of electrochemically generated o-benzoquinones from oxidation of quercetin and catechin as Michael acceptors with cyanide ion as nucleophile has been studied using cyclic voltammetry. The reaction mechanism is believed to be EC; including oxidation of catechol moiety of these antioxidants followed by Michael addition of cyanide ion. Th...

The kinetic of the nitrous acid reactions with quercetin and catechin has been studied using spectrophotometric method in aqueous solution. The results show that these antioxidants participate in oxidation reactions with nitrous acid which is derived from protonation of nitrite ion in mild acidic conditions. Corresponding o-quinones as relatively s...

The conversion of some catecholamines, such as l-dopa, dopamine and methyldopa, to their corresponding nitro-derivatives, or their oxidative degradation, in the presence of nitrous acid/nitrite ion equilibria has been studied using voltammetric techniques in aqueous solution. The results indicate that nitrous acid, as an oxidant, converts the catec...

Conversion of catechols to corresponding nitro derivatives in the presence of nitrous acid dissociation is studied using voltammetry and UV-vis spectrophotometry. The results indicate that the quinones derived from oxidation of catechols by nitrous acid participate in Michael addition reaction with nitrite ion in very mild acidic solutions. Rank an...

Rank annihilation factor analysis (RAFA) was used to investigate the effects of inclusion of eriochrome black T (EBT) on its complexation reaction with Ca2+ and Mg2+ at different pH values. Addition of β-cyclodextrin (β-CD) to Ca-EBT or Mg-EBT caused decomposition of the 1:1 metal complex and increase in EBT concentration in solution due to the for...

The acid dissociation constants of methyl red, 4-nitrophenol, 4-nitrocatechol, and neutral red were studied in water and ethanol−water cosolvents and in the presence of β-cyclodextrin (β-CD). Apparent acidity constants of these acid−base indicators were derived using rank annihilation factor analysis on spectrophotometric data. Formation constants...

In this paper application of some functionalized cyclodextrins with ability of molecular recognition are described. Combination of size selectivity in cyclodextrins with some selective analytical response produces a molecular sensor for selective chemical, pharmaceutical and environmental analysis.

Rapid, simple, and accurate spectrophotometric method is presented for the determination of ibuprofen by batch and flow injection analysis methods. The method is based on ibuprofen competitive complexation reaction with phenolphthalein‐β‐cyclodextrin (PHP‐β‐CD) inclusion complex. The increase in the absorbance of the solution at 554 nm by the addit...

The catalytic effect of beta-cyclodextrin (beta-CD) on the intramolecular cyclization reaction of catecholamines dopamine, methyldopa and levodopa after their oxidation with periodate was investigated spectrophotometrically using rank annihilation factor analysis (RAFA). The method was based on the effect of beta-CD concentration on the intramolecu...

A simple procedure for the kinetic spectrophotometric determination of the formation constant of 1:1 (XL) complexes (or adducts) using rank annihilation factor analysis (RAFA) is proposed. The method was based on the effect of the concentration of L (or X) on the reaction of X (or Q with a reagent (Z). The rate constants for the reactions of X (or...

The effects of �-cyclodextrin (�-CD) inclusion on the kinetics of the oxidation of several cathechol derivatives, including 4-tert-butylcatechol, 3-methylcatechol and 3-methoxycatechol, with iodate was studied spectrophotometrically. The rate of the oxidation reactions decreased by increasing �-CD concentration as a result of inclusion. The stabili...

The effects of addition of �-cyclodextrin (�-CD) to the neutral red-cetyltrimethylammonium bromide (CTAB) associates in pH 7 phosphate buffer solutions were investigated. Addition of �-CD to neutral red-CTAB association causes decomposition of the associate by displacement of neutral red with �-CD. The inclusion complex of CTAB with �-CD is more st...

A rapid, simple, and accurate spectrophotometric method is presented for the determination of fluoxetine by batch and flow injection analysis methods. The method is based on fluoxetine competitive complexation reaction with phenolphthalein-beta-cyclodextrin (PHP-beta-CD) inclusion complex. The increase in the absorbance of the solution at 554 nm by...

A sensitive and simple spectrophotometric method for the determination of dopamine, methyldopa, levodopa and catechole in either pure form, pharmaceutical formulations and in water is described. The method is based on their oxidation reaction with periodate followed by oxidative coupling with 4-aminobenzoic acid at pH 4 leading to the formation of...

Rank annihilation factor analysis (RAFA) was used to the spectrophotometric studies of acid–base equilibria in the presence of �-cyclodextrin (�-CD). When the conditional acidity constants (�-CD concentration dependent acidity constant) acts as an optimizing object, and simply combined with the pure spectrum of acidic and basic forms, the rank of o...

Electrochemical oxidation of some catecholamines such as dopamine (1), l-dopa (2) and methyldopa (3) has been studied in the presence of 4-aminobenzoic acid (4). Some electrochemical techniques such as cyclic voltammetry using diagnostic criteria derived by Nicholson and Shain for various electrode mechanisms and controlled-potential coulometry wer...

A method for the determination of sulfide based on its interference with the determination of Hg by cold vapor atomic absorption spectrometry is described. The decrease in mercury absorbance at 253.7nm is proportional to the concentration of sulfide over the range of 10–320ngmL–1. The limit of detection was found to be 7ngmL–1 and the relative stan...

Electrochemical oxidation of some catecholamines such as dopamine (1), L-dopa (2), and methyldopa (3) has been studied in various pH values, using cyclic voltammetry. The results indicate participation of catecholamines (1–3) in intramolecular cyclization reaction to form the corresponding o-quinone derivatives (1d–3d). In various pHs, based on ECE...