Diperiodatoargentate(III) Oxidation of D-Galactose in Absence and Presence of Anionic and Cationic Surfactants

Diperiodatoargentate(III) (DPA) was used as an oxidizing titrant in the spectrophotometric degradation of D-galactose for the first time. The kinetics is based on the reduction of silver(III) to silver(I) by D-galactose at specified experimental conditions. Effects of added [H⁺] and [periodate] have also been investigated. The premicellar environment of cetyltrimethylammonium bromide (CTAB) and sodiumdodecyl sulphate (SDS) strongly inhibits the reaction rate. The observed rate constant is strongly affected by [CTAB] and [SDS] changes for [surfactant] <cmc. Surfactant concentration range above the cmc does not influence the reaction rate. The monoperiodatoargentate(III) ions act as an active oxidant in comparison to that of DPA. A suitable mechanism involving a two-electron transfer from D-galactose to the silver(III) species has been proposed and hence a corresponding rate equation has been derived.     

Effect of cationic and anionic surfactants on the addition–elimination-type interaction between o-toluidine and d-glucose

The kinetics of the o-toluidine–d-glucose reaction has been studied as a function of [o-toluidine], [d-glucose], [acetic acid], and temperature by UV–visible spectrophotometry at 630 nm in the absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). The reaction follows second-order kinetics, being unity in each of the reactants in both media. The effect of added surfactants has also been investigated. The model of micellar catalysis, such as the Menger–Portony model modified by Bunton, is applied to explain the catalytic role of CTAB and SDS micelles. The association/incorporation constants (K _s and K _n), the rate constant in micellar media (k _m), and the activation parameters of this system have been calculated and discussed. The value of the rate constant is found to be higher in SDS than in CTAB. Hydrophobic and electrostatic interactions are responsible for higher reaction rates in SDS. From all observed facts, a reaction mechanism involving a nucleophilic addition–elimination path has been suggested.     

Kinetics of the oxidative degradation of d-xylose in the presence and absence of cationic and anionic surfactants

The oxidative degradation of d-xylose by cerium(IV) has been found to be slow in acidic aqueous solution with the evidence of autocatalysis. The reaction is accelerated in the cetyltrimethylammonium bromide (CTAB) micellar medium but sodium dodecyl sulfate (an anionic surfactant) has no effect. The pseudo first-order rate constants have been determined at different [reductant], [oxidant], [H₂SO₄], temperature, and [CTAB]. The reaction rate increased with increasing [d-xylose] and decreased with increase in [H₂SO₄]. The CTAB-micelle-catalyzed kinetic results can be interpreted by the pseudophase model. The kinetic parameters such as association constant (K _s), micellar medium rate constant (k _m), and activation parameters (E _a, ΔH ^# and ΔS ^#) are evaluated and the reaction mechanism is proposed. The reaction rate is inhibited by electrolytes and the results provide an evidence for the exclusion of the reactive species from the reaction site.     

Effect of anionic and cationic micelles on the oxidation of <Emphasis Type="SmallCaps">D</Emphasis>-glucose by cerium(IV) in presence of H<Subscript>2</Subscript>SO<Subscript>4</Subscript>

The influence of surfactants (anionic and cationic) on the reactivity of the redox couple cerium(IV) and D-glucose was examined spectrophotometerically. Various kinetic parameters have been determined in the absence and presence of surfactants. The kinetics were followed by monitoring the disappearance of the absorbance of cerium(IV) at 385 nm. The reaction obeyed first-order kinetics with respect to [D-glucose] in both media. No effect of anionic micelles of sodium dodecyl sulfate (SDS) was observed due to electrostatic repulsion between the negative head group of SDS and reactive species of cerium(IV) (Ce(SO₄) ₃ ²⁻ ). A twofold increase in the oxidation rate was observed in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB). The observed catalytic role has been analyzed in terms of the Menger–Portnoy model. The effects of various inorganic salts (Na₂SO₄, NaNO₃ and NaCl) were also studied in micellar media.     

Kinetics and mechanism of oxidation of some reducing sugars by diperiodatoargentate(III) in alkaline medium

Summary The kinetics of oxidation of d-glucose, d-galactose, d-fructose, d-ribose, d-arabinose, d-xylose and 2-deoxyd-glucose by diperiodatoargentate(III) (DPA) have been investigated in alkaline medium. The order of the reaction with respect to [DPA] is unity while the order with respect to [sugar] is < 1 over the concentration range studied. The rate increases with an increase in [OH ^–] and there is a marginal decrease in the rate with an increase in [IO _inf4 ^sup– ]. No significant dependence on ionic strength was found, but the rate increases with a decreasing dielectric constant. Formic acid and the corresponding aldonic acids were detected as the products of oxidation. The participation of the open chain form of the sugar and a mechanism involving the initial formation of a complex between the enediol of the sugar and Ag^III are proposed.     

Investigation of the mechanism of oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-cystine by diperiodatoargentate(III) in aqueous alkaline medium by stopped flow technique

The kinetics of oxidation of l-cystine by diperiodatoargentate(III) (DPA) in alkaline medium at a constant ionic strength of 0.10 mol dm⁻³ was studied spectrophotometrically. The reaction exhibits a 1:2 stoichiometry (l-cys:DPA) and is first order in [DPA]. The order in both [l-cystine] and [alkali] changes from first to zero order as their concentrations increase. Added periodate retards the rate of reaction. The effects of added products have been investigated. The active species of silver(III) is identified as monoperiodatoargentate(III) (MPA). The oxidation is thought to proceed via an MPA–l-cystine complex, which decomposes in a rate-determining step to give a free radical followed by a fast step to give the products. The products were identified by spot test, IR and GC–MS. The reaction constants involved in different steps of the mechanism were evaluated. The activation parameters with respect to the slow step of the mechanism were computed and discussed.     

Micelle-assisted cerium(IV) oxidation of <Emphasis Type="SmallCaps">L</Emphasis>-sorbose in aqueous sulfuric acid

Spectrophotometric kinetic technique has been used to investigate the effect of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) surfactants on the redox reaction of cerium(IV)+l-sorbose in aqueous sulfuric acid media. The anionic SDS has no effect, whereas the reaction rate increases in the presence of cationic CTAB, which is due to favorable conditions provide by the cationic micelles. The reaction rate decreases with [H₂SO₄], and no acid-dependent path has been observed. At constant [H₂SO₄], the rate of the reaction is dependent on the first powers of the l-sorbose and cerium(IV) concentrations. The CTAB-assisted reaction is retarded by addition of electrolytes (Na₂SO₄, NaNO₃, and NaCl), which is attributed to the competition between electrolyte anions and cerium(IV)-sulfato species. Bromide ion (of CTAB or externally added in the form of NaBr) is not oxidized by the cerium(IV) (as a main or side reaction).     

Kinetic study of ruthenium(III)-catalyzed oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-alanine by diperiodatoargentate(III) in aqueous alkaline medium

The kinetics of Ru(III)-catalyzed oxidation of l-alanine (Ala) by diperiodatoargentate(III) (DPA) in alkaline medium at 25 °C and a constant ionic strength of 0.90 mol dm⁻³ was studied spectrophotometrically. The products are acetaldehyde, Ag(I), ammonia and bicarbonate. The [Ala] to [DPA] stoichiometry is 1:1. The reaction is first order in both [Ru(III)] and [DPA] and has less than unit order in both [Ala] and [alkali]. Addition of periodate has a retarding effect on the reaction. The effects of added products, ionic strength and dielectric constant of the reaction medium have been investigated. The reaction proceeds via a Ru(III)–Ala complex, which further reacts with one molecule of monoperiodatoargentate(III) in the rate-determining step. The reaction constants were calculated at different temperatures and the activation parameters have been evaluated.     

Rearrangement of a trishomocubane derivative to a tetracyclo[6.3.0.02,6.03,10]undec-4-ene

Reaction of 8,8,11,11-tetrafluoropentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecane with idio trimethylsilane leads to the expectedd ₃-trishomocubane derivative, but reaction with the more electrophilic boron tribromide yields a tetracyclo[6.3.0.0^2,6.0^3,10]undec-4-ene derivative which was characterized by X-ray diffraction. The most easily visualized pathway for this transformation would be an initial rearrangement of the starting material to ad ₃-trishomocubane followed by additional bond breaking to form the undec-4-ene compound. Molecular mechanics calculations indicate the brominatedd ₃-trishomocubane is about 4 kcal/mol more stable than the brominated undec-4-ene molecule and the associated carbonium ions show the same ordering. These data would indicate an alternate reaction pathway must be operative; however, semiempirical calculations predict the reverse ordering of the above energies.     

A kinetic and mechanistic study of oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-lysine by the analytical reagent diperiodatoargentate(III) in aqueous alkaline medium

The kinetics of oxidation of l-lysine by diperiodatoargentate(III) (DPA) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm⁻³ was studied spectrophotometrically. The oxidation products are aldehyde, 5-aminopentanal and Ag(I). The main products were identified by spot test, IR and GC-MS. The stoichiometry is [l-lysine]:[DPA] = 1:1. The reaction is first order with respect to diperiodatoargentate(III) concentrations, whereas the order with respect to l-lysine and alkali concentrations changes from first order to zero order as the l-lysine and alkali concentrations are increased. The effects of added products, periodate, ionic strength, and dielectric constant of the reaction medium were investigated. Based on the experimental results, a mechanism involving complex formation between DPA species and l-lysine is proposed. The reaction constants involved in the mechanism were evaluated. The activation parameters with respect to the slow step of the mechanism were determined and discussed.     

Nucleation and growth kinetics of silver nanoparticles prepared by glutamic acid in micellar media

The title reaction in the presence of cetyltrimethylammonium bromide (CTAB) has been followed spectrophotometrically at 325 nm. In the process of reduction, characteristic surface resonance plasmon absorption peaks appear for the silver nanoparticles (NP) and the intensities increase with reaction time. UV–visible spectra suggest that [CTAB] and glutamic acid influence the morphology of the silver NP and act as shape‐directing agents, whereas [Ag⁺] has no effect. The effects of the total [glutamic acid], [CTAB], and [Ag⁺] on the apparent rate constants of silver NP formation are determined. The sigmoidal curve of absorbance versus reaction time indicates an autocatalytic path involved in the growth process. The α‐amino and ? COOH groups undergo chemical transformation (oxidative deamination and decarboxylation). The particles are spherical in shape with average diameters ranging between 12 and 25 nm, and their size distribution is wide. A plausible mechanism has been proposed with the following rate law: (d[silver sol])/dt = k[Ag⁺][Glutamic acid]_T. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 680–691, 2012     

Mechanism of the oxidation of d-glucose onto colloidal MnO2 surface in the absence and presence of TX-100 micelles

Aqueous colloidal manganese dioxide (MnO₂) was prepared via titration by using potassium permanganate and sodium thiosulphate in aqueous neutral medium. The kinetics of oxidation of d-glucose onto the surface of colloidal MnO₂ have been studied spectrophotometrically. The results show that the rate of initial stage (nonautocatalytic path) increases with increasing the [d-glucose], [H⁺], and temperature and also upon addition of nonionic surfactant Triton X-100 (TX-100), which indicates that the surfactant enhances the concentration of d-glucose at the surface of the colloidal MnO₂. Hydrogen bonding interaction seemingly arises between –OH groups of d-glucose and oxygen of the ether linkages of polyoxyethylene chain of TX-100. A possible mechanism of the oxidative degradation of d-glucose is discussed in terms of d-glucose/TX-100 and colloidal MnO₂ interaction.     

Fluorescent sensing layer for the determination of<Emphasis Type="SmallCaps"> L</Emphasis>-malic acid in wine

An enzymatic method for determining L-malic acid in wine based on an L-malate sensing layer with nicotinamide adenine dinucleotide (NAD⁺), L-malate dehydrogenase (L-MDH) and diaphorase (DI), immobilized by sol-gel technology, was constructed and evaluated. The sol-gel glass was prepared with tetramethoxysilane (TMOS), water and HCl. L-MDH catalyzes the reaction between L-malate and NAD⁺, producing NADH, whose fluorescence (λ _exc = 340 nm, λ _em = 430 nm) could be directly related to the amount of L-malate. NADH is converted to NAD⁺ by applying hexacyanoferrate(III) as oxidant in the presence of DI. Some parameters affecting sol-gel encapsulation and the pH of the enzymatic reaction were studied. The sensing layer has a dynamic range of 0.1–1.0 g/L of L-malate and a long-term storage stability of 25 days. It exhibits acceptable reproducibility [s _r(%)≈10] and allows six regenerations. The content of L-malic acid was determined for different types of wine, and polyvinylpolypyrrolidone (PVPP) was used as a bleaching agent with red wine. The results obtained for the wine samples using the sensing layer are comparable to those obtained from a reference method based on UV-vis molecular absorption spectrometry, if the matrix effect is corrected for.     

Kinetics of Hydrolysis of Diperiodatoargentate(III) Ion and its Reduction by Paracetamol

The kinetics of hydrolysis and reduction of the diperiodatoargentate(III) ion (DPA) has been studied in aqueous acidic medium spectrophotometrically. Upon dilution the silver (III) complex was found to be unstable in the presence of H₂O. Addition of [H⁺], largely increased the hydrolysis rate, whereas [OH⁻] does not have any effect. Under pseudo-first-order conditions ([paracetamol] > [DPA]), the reduction rate was very fast. Second-order conditions were used to determine the reaction rate. The reaction was acid-catalyzed and the rate decreased by the addition of periodate. The Arrhenius equation was valid for the reaction. The changes observed in the direction of the rate constant-[H⁺] profile correspond to aquation of the diperiodatoargentatate(III) complex. The proposed mechanism and the derived rate law are consistent with the observed kinetics.     

Presence and origin of large amounts of d-proline in the urine of mutant mice lacking d-amino acid oxidase activity

Using a column-switching HPLC system combining a micro-ODS column and a chiral column, the amounts of d-proline (d-Pro) have been determined in 18 tissues, plasma and urine of mice. To avoid the enzymatic degradation of d-amino acids in vivo, a mutant mouse strain lacking d-amino acid oxidase activity (ddY/DAO⁻ mouse) was used. In the brain, relatively large amounts of d-Pro were observed in the anterior pituitary, posterior pituitary and pineal glands. In the peripheral tissues, the amounts of d-Pro were high in the pancreas and kidney. Above all, it is surprising that the ddY/DAO⁻ mice excreted large amounts of d-Pro in their urine (433 nmol/mL, 20 times that of l-Pro). The origin of d-Pro has also been investigated. By comparing germ-free mice and gnotobiotic mice, intestinal bacteria were shown to have no effect on the urinary d-Pro amount. Concerning the dietary origin, a notable amount of d-Pro was still excreted in the urine after starvation for 4 days, suggesting that some of the d-Pro is produced in the mice. Age-dependent changes in the urinary d-Pro amount have also been investigated from the postnatal 1st month up to 12 months, and ddY/DAO⁻ mice were found to excrete large amounts of d-Pro in the urine constantly throughout their lives. Kenji Hamase is Associate Professor in the Department of Bioanalytical Chemistry, Graduate School of Pharmaceutical Sciences at Kyushu University. His current research interests focus on the development of analytical methods for d-amino acids and the study of their physiological functions and diagnostic values. He received the Japanese Society for Analytical Chemistry Award for Young Scientists in 2003, and the PSJ Award for Young Scientists in 2006.     

Oxidation of d-Glucose by Silver(III) Periodate Complex in the Presence of Ru(III)/Os(VIII) as a Homogeneous Catalyst: A Comparative Mechanistic Study (Stopped Flow Technique)

The kinetics of the oxidation of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalyzed oxidation of d-glucose (d-Glu) by silver(III) periodate complex (DPA) in aqueous alkaline medium at 298 K and constant ionic strength 0.003 mol·dm^?3 was studied spectrophotometrically. The reaction between d-Glu and DPA in alkaline medium exhibits 1:2 stoichiometry in both catalyzed reactions (d-Glu:DPA). The main products were identified as D-arabinonic acid and formic acid by spot tests, GC–MS spectra and chromatographic techniques. The reaction orders with respect to various species concentrations were determined. Also, the active species of catalyst and oxidant have been identified. Probable mechanisms were proposed. The activation parameters with respect to the slow step of the mechanism were computed and discussed and thermodynamic quantities were also calculated. It has been observed that the catalytic efficiency for the present reaction is in the order Os(VIII) > Ru(III).     

Kinetics and mechanism of the formation of silver nanoparticles by reduction of silver (I) with maltose in the presence of some active surfactants in aqueous medium

The kinetics and mechanism of the formation of silver nanoparticles by reduction of Ag⁺ with maltose were studied spectrophotometrically by monitoring the absorbance change at 412 nm in aqueous and micellar media at a temperature range 45–60 °C. The reaction was carried out under pseudo-first-order conditions by taking the [maltose] (>tenfold) the [Ag⁺]. A mechanism of the reaction between silver ion and maltose is proposed, and the rate equation derived from the mechanism was consistent with the experimental rate law. The effect of surfactants, namely cetyltrimethylammonium bromide (CTAB, a cationic surfactant) and sodium dodecyl sulfate (SDS, an anionic surfactant), on the reaction rate has been studied. The enthalpy and the entropy of the activation were calculated using the transition state theory equation. The particle size of silver sols was characterized by transmission electron microscopy and some physiochemical and spectroscopic tools.     

Oxidation of L-phenylalanine by diperiodatoargentate(III) in aqueous alkaline medium. A Mechanistic approach

The kinetics of oxidation of L-phenylalanine (L-Phe) by diperiodatoargentate(III) (DPA) in alkaline medium at a constant ionic strength of 0.25 mol/dm⁻³ has been studied spectrophotometrically. The reaction between DPA and L-phenylalanine in alkaline medium exhibits 1: 1 stoichiometry (L-phenylalanine: DPA). The reaction shows first order in [DPA] and has less than unit order dependence each in both [L-Phe] and [Alkali] and retarding effect of [IO₄⁻] under the reaction conditions. The active species of DPA is understood to be as monoperiodatoargentate(III) (MPA). The reaction is shown to proceed via a MPA-L-Phe complex, which decomposes in a rate-determining step to give intermediates followed by a fast step to give the products. The products were identified by spot and spectroscopic studies. The reaction constants involved in the different steps of the mechanisms were calculated. The activation parameters with respect to slow step of the mechanism were computed and discussed. The thermodynamic quantities were also determined for the reaction.     

Quantitative determination of protein of bacterial origin on the basis ofd-aspartic acid andd-glutamic acid content

Summary In recent decades several methods have been developed for determination of the proportion of nitrogen-containing substances passed from the rumen into the abomasum, or small intestine, which are of microbial origin. Recently, when examining thed-amino acid content of foodstuffs, particularly milk and milk products, it was observed that, in addition tod-alanine (d-Ala,d-glutamic acid (d-Glu) andd-aspartic acid (d-Asp) can also be detected in similar quantities, primarily in products which have links with bacterial activity. This gave rise to the idea of examining the diaminopimelic acid (DAPA),d-Glu, andd-Asp content of bacteria extracted from the rumen of cattle, and that of chyme from the same cattle, to establish whetherd-Asp andd-Glu can be used to estimate protein of bacterial origin. The investigations performed have provided evidence that bothd-Asp andd-Glu might be appropriate for determination of protein of bacterial origin. The results obtained using these two bacterial markers (d-Asp andd-Glu) proved to the approximately 10% lower than those obtained using DAPA; this was not because of to error attributable to the new markers but rather to the unreliability of determination using DAPA Analyses performed on samples of known bacterial protein content indicate thatd-Asp andd-Glu gave almost identical results for bacterial protein content which were very close to the theoretical (calculated) values. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001.     

Effect of Cationic Micelles on the Kinetics of Interaction of [Cr(III)-Gly-Gly] with Ninhydrin

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of chromium dipeptide complex ([Cr(III)-Gly-Gly]²⁺) with ninhydrin under varying conditions has been investigated. The rates of the reaction were determined in both water and surfactant micelles in the absence and presence of various organic and inorganic salts at 70 °C and pH 5.0. The reaction followed first- and fractional-order kinetics with respect to [Cr(III)-Gly-Gly²⁺] and [ninhydrin]. Increase in the total concentration of CTAB from 0 to 40×10⁻³ mol·dm⁻³ resulted in an increase in the pseudo-first-order rate constant (kψ) by a factor of ca 3. Quantitative kinetic analysis of kψ−[CTAB] data was performed on the basis of the pseudo-phase model of the micelles. As added salts induce structural changes in micellar systems that may modify the substrate-surfactant interactions, the effect of some inorganic (NaBr, NaCl, Na₂ SO₄) and organic (NaBenz, NaSal, NaTos) salts on the rate was also explored. It was found that the tightly bound counterions (derived from organic salts) were the most effective.