Exploitation of reversed micelles as membrane mimetic reagents

The aqueous micelle model and its relation to the various models proposed for aggregation of surfactants in nonaqueous solvents, and the controversy surrounding the applicability of the critical micelle concentration to these aggregates, have been discussed. The effect of the addition of water to, and the nature of acid-base interactions in, surfactants solutions in apolar solvents have been included in a review of the kinetics of the reactivity of esters and other organic sustrates, inoragatic reaction mechanisms, catalysis by solubilized enzymes and electron and proton transfer reactions in these media. Where possible, analogies have been made with membrance mediated processes.     

Effect of di-2-ethylhexyl sodium sulfosuccinate reversed micelles on the iron-tetrasulfonatophthalocyanine-catalyzed fluorogenic oxidation reaction of L-tyrosine with hydrogen peroxide.

The catalytic behavior of iron tetrasulfonatophthalocyanine (FeTSPc) for the oxidation reaction of L-tyrosine with H2O2 in a di-2-ethylhexyl sodium sulfosuccinate (AOT) reversed-micellar system (AOT/cyclohexane) was studied. It was indicated that the reversed micelles could not only enhance the catalytic activity of FeTSPc, but could also increase the fluorescence intensity of the product. Factors that may influence the catalytic reaction, including the concentration of AOT, the cosolubilized water, temperature and pH, were further examined. The possibility of its analytical application was also tested. Experimental results show that the calibration graphs for the determinations of FeTSPc and H2O2 under optimum conditions are linear over the range of 1.0 x 10-8 - 1.0 x 10(-6) mol L(-1) and 0.0 - 3.0 x 10(-6) mol L(-1), respectively, with detection limits of 1.1 x 10(-9) mol L(-1) and 3.1 x 10(-9) mol L(-1) for FeTSPc and H2O2, respectively.     

血红蛋白作为过氧化物模拟酶催化测定过氧化氢

研究了牛血红蛋白 (Hemoglobin ,Hb)作为过氧化物模拟酶催化H2 O2 氧化隐性亮绿 (RecessiveBrilliantGreen ,RBG)显色反应的催化特性及反应条件。该体系在pH 5 .73的条件下形成的酶催化产物在 640nm处有最大吸收。体系测定H2 O2 时表观摩尔吸光系数为 7.1 5× 1 0 3L·mol-1·cm-1,测定H2 O2 检测限为 2 .8× 1 0 -6mol L。方法可用于天然水中H2 O2 的测定。     

Reaction between nitrous acid and hydrogen peroxide in perchloric acid medium

A kinetic investigation on the reaction has been carried out in HClO₄ medium under different conditions. A spectrophotometric method of estimation of nitrous acid at various time intervals has been employed. The results are interpreted on the basis ofthe following mechanism: The absolute rate constant value of 39.7 M^?1 plusmn; s^?1 for k₄ and the equilibrium constant K_eq = 116M^?1 for reaction (2) have been evaluated. The activation energy of the overall reaction has also been determined as E_a = 13.2 kcal/mol.     

N,N-diethylaniline as hydrogen donor for determination of hydrogen peroxide catalyzed by metalloporphyrins as enzyme mimetic of peroxidase

Various metalloporphyrins have been used as a catalyst instead of the peroxidase for the determination of hydrogen peroxide by formation of a dye from N,N-diethylaniline (DBA) and 4-aminoantipyrine. The difference of relative catalytic activity was investigated between enzyme and enzyme mimetics. FeT(4-TAP)P [5, 10, 15, 20-tetrakis (4-trimethyl-ammoniumphenyl)-21H, 23H-porphine] was shown as the best enzyme mimetic for horseradish peroxidase (HRP) among metalloporphyrins tested. 0 to 7.0 × 10^–5 mol/L hydrogen peroxide was determined with good accuracy and reproducibility, and giving recovery of 99.7–100.7%. DEA was certified as a sensitive color reagent in enzyme mimetic assay of hydrogen peroxide, with the apparent molar absorptivity for hydrogen peroxide was 1.37 × 10⁴ L/mol·cm.     

Amperometric selective biosensing of dimethyl- and diethyldithiocarbamates based on inhibition processes in a medium of reversed micelles

An amperometric tyrosinase electrode has been used for biosensing of dimethyl- and diethyldithiocarbamates based on the inhibition effects of these substances on the catalytic activity of the enzyme. A working medium consisting of reversed micelles, and phenol as the substrate has been used. The tyrosinase electrode was constructed by direct adsorption of the enzyme on the surface of a graphite-disk electrode. Reversible inhibition processes are shown to be involved for ziram, diram and zinc diethyldithiocarbamate. Following a simple regeneration of the enzyme electrode, an acceptable reproducibility for the measurements of the inhibition response was obtained. Experimental variables, such as temperature, phenol concentration and the presence of chloroform, affecting the inhibition processes, were optimized. The type of enzyme inactivation for each inhibitor tested was studied, and the inhibition constants were calculated. Detection limits of 0.074, 1.3 and 1.7 μmol l⁻¹ were achieved for ziram, diram and zinc diethyldithiocarbamate, respectively. Other carbamates belonging to families different from dimethyl- and diethyldithiocarbamates showed no amperometric response at the tyrosinase electrode, except for pyrimidine-derivative carbamates. The developed analytical methodology was applied to determine ziram in spiked apple samples.     

Photochemistry of a cyanine dye in reversed micelles

The effect of microenvironment on the existing state and spectral properties of a cyanine dye in different systems were investigated. Due to the space limitation and the polarity evolution of the water cell of reversed micelles, the optical behavior of the dye in reversed micelles was very different from in water and alcohol. The effect of surfactants with different charge on the interaction of a cyanine dye with AgCl nanoparticles in reversed micelles were also researched. The adsorption state of the dye on AgCl nanoparticles in reversed micelles was discussed.     

Oxygen reduction reaction on polycrystalline gold. Pathways of hydrogen peroxide transformation in the acidic medium

The mechanism of oxygen electroreduction on polycrystalline gold is studied in the acidic medium. Hydrogen peroxide is the main reaction product. However, two potential regions can be singled out in which the oxygen electroreduction reaction proceeds by different pathways. The first region is the potential interval close to the steady-state potential. Here, the oxygen electroreduction virtually completely produces peroxide. The second interval is the potential range of considerable cathodic polarization values. In this case, peroxide can be reduced to water. The low energy of hydrogen peroxide adsorption on gold determines the considerable overpotential of peroxide reduction. It is shown that on the gold electrode surface, the catalytic decomposition of peroxide occurs. The use of the method of electrochemical impedance spectroscopy allows the peculiarities of the oxygen reaction associated with hydrogen peroxide transformations to be revealed. In the acidic medium, the reactions of consecutive reduction of oxygen through the intermediate formation of hydrogen peroxide and the catalytic decomposition of the intermediate product are shown to proceed simultaneously. The ratio of rate constants of electrochemical stages depends on the potential. The chemical decomposition is observed both near the steady-state potential and in the cathodic region where considerable electrochemical reduction of peroxide occurs.     

The reaction between diacetyl and hydrogen peroxide: its mechanism and kinetic constants

The reaction between diacetyl and hydrogen peroxide in aqueous solution was investigated using an adiabatic reaction calorimeter. The kinetic constants are calculated using procedures based on the temperature-time behaviour of the reaction system.The mechanism of the reaction proposed fits very well with the reaction-rate equations used and the observed temperature-time data.     

Determination of hydrogen peroxide in a flow system with microperoxidase as catalyst for the luminol chemiluminescence reaction

Hydrogen peroxide is determined by a chemiluminescence method with a reagent containing 100 μM luminol and 3 μM microperoxidase at pH 10 (carbonate buffer). Microperoxidase is superior to hematin as a catalyst. The method uses an automated flow injection system with a throughput of 2 samples per minute. The log—log calibration plot is linear (slope 1.3) from the detection limit, 3 × 10^-9 M up to 10^-5 M H₂O₂. The background emission is low. Impurities in the carrier stream and from some plastics may cause elevated background unless precautions are taken.     

The reaction of methyl p-nitrophenyl sulfate with hydrogen peroxide anion determination of pKa of hydrogen peroxide in methanol by a kinetic spectrophotometric procedure

A kinetic spectrophotometric investigation of the reaction of the hydrogen peroxide anion with methyl p-nitrophenyl sulfate in methanol solvent resulted in the evaluation of the pK_a of HOOH in methanol at 25°C as 15.8 ± 0.2. Since normal kinetic procedures for the determination of the equilibrium constant K for the process CH₃O^? + H₂O₂ ? CH₃OH + HO were found to be associated with high uncertainty, another procedure was devised to establish the magnitude of K. This method is based on an analysis of the changing slopes of plots of pseudo-first-order rate constants against the total base concentration as the stoichiometric amount of hydrogen peroxide is varied. The method is applicable to any system in which anionic nucleophiles generated in situ compete with solvent anions. Such a corroboration of kinetically determined equilibrium constants is believed essential. The kinetic data allow the specific rate constant k_HOO-for the reaction of methyl p-nitrophenyl sulfate with hydrogen peroxide anions to be evaluated and yield the rate constant ratio k/k = 8.8 ± 2.2. This confirms the existence of an α effect at saturated carbon in this system.     

Determination of proteins at nanogram levels by their quenching effect on the chemiluminscence reaction between luminol and hydrogen peroxide with manganese-tetrasulfonatophthalocyanine as a new catalyst

The manganese-tetrasulfonatophthalocyanine (MnTSPc) catalyzed luminol-hydrogen peroxide chemiluminescence (CL) systems can be quenched in the presence of proteins. A highly sensitive CL quenching method has been developed for the determination of proteins. Under optimum conditions, the linear ranges of the calibration curves were 0.1-20 microg/mL for human serum albumin (HSA), 0.2-20 microg/mL for human gamma-IgG, and 0.5-50 microg/mL for the bovine serum albumin (BSA) with the corresponding detection limits were 1.9 ng/mL, 2.7 ng/mL, and 3.4 ng/mL. The method has been applied to the analysis of total proteins in human serum samples and the results were in good agreement with clinical data provided.     

Pentacoordinate phosphoranes with reversed apicophilicity as stable intermediates in a mitsunobu-type reaction

Diisopropyl azodicarboxylate (DIAD) undergoes a cycloaddition reaction with the cyclic phosphites CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)PX (1) [X = NCS (a), N(3) (b), Cl (c), NHMe (d) and Ph (e)] to afford the novel pentacoordinate phosphoranes 2a-e as crystalline solids. This result is different from the reaction of PPh(3) with DIAD used in the well-known Mitsunobu reaction. X-ray crystallography of 2a, 2b, and 2d reveals that the nitrogen, rather than the oxygen, occupies an apical position of the trigonal bipyramidal phosphorus. This is in violation of the commonly accepted preferences for substituents in trigonal bipyramidal phosphorus. In 2e, although the oxygen of the five-membered ring occupies the expected apical position, the phenyl group also occupies (the other) apical position, forcing the more electronegative oxygen atoms of the eight-membered ring to span equatorial-equatorial positions. In contrast to the above, the isocyanato compound CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)PNCO (1f), upon treatment with DIAD, affords compound 3 to which a tetracoordinate structure is assigned.     

Fluorescence investigation of affinity interaction between bovine serum albumin and triazine dye in reversed micelles

The effect of Cibacron Blue 3GA (CB) on the fluorescence emission spectra of bovine serum albumin (BSA) was investigated in cationic reversed micelles formed with cetyltrimethylammonium bromide (CTAB) compared with that in aqueous phase. The anionic CB had electrostatic interactions with cationic CTAB and affinity interactions with BSA in the reversed micelles. The addition of CB in the reversed micellar phase led to a great decrease in the fluorescence intensity of BSA and a remarkable red shift of the wavelength of emission maximum (λ_max). The fluorescence intensity of BSA decreased and the λ_max decreased 5 nm (blue shift) without the addition of CB in the reversed micellar phase. The fluorescence intensity of BSA with the addition of CB had the strongest value in the aqueous phase with the presence of CTAB, a less strong value in the reversed micellar phase, and a weak value in the aqueous phase without the presence of CTAB. The increase in λ_max of BSA with the addition of CB in the reversed micellar phase might indicate the decrease in the hydrophobic microenvironment of the Trp residue of BSA, contrary to those microenvironments in the absence of CB.