Zuheir A. Issa

Effect of alkyl chain length, head group and nature of the surfactant on the hydrolysis of 1,3-benzoxazine-2,4-dione and its derivatives.

The alkaline hydrolysis of carsalam (2H-1,3-benzoxazine-2,4(3H)-dione), denoted as I, and its N-substituted derivatives i.e., N-methyl-1,3-benzoxazine-2,4-dione (II) and N-benzoyl-1,3-benzoxazine-2,4-dione (III) was studied spectrophotometrically at physiological temperature. The rate of hydrolysis was found to be independent on the substrate concentration. In case of I, the reaction was fractional order with respect to [OH(-)] while for II and III, reaction obeyed the first order kinetics. Effect of cationic surfactants with varying hydrophobic chains (cetyltrimethylammonium bromide, CTAB, tetradecyltrimethylammonium bromide, TTAB and dodecyltrimethylammonium bromide, DTAB) and with different head-group (cetyl pyridinium chloride, CPC) and anionic surfactant (sodium dodecyl sulfate, SDS) was also seen on the rate of alkaline hydrolysis of the carsalam and its derivatives. Cationic surfactants first catalyzed the rate of hydrolysis at lower concentrations followed by the inhibition at higher concentrations. The length of the alkyl chain had remarkable effect on the catalytic efficiency of the surfactants. Similarly N-substitution on substrate also increased the catalysis by micelles. The anionic surfactant SDS inhibited the rate of hydrolysis at all of the concentrations studied. The catalysis by cationic micelles followed by inhibition was treated in terms of the pseudophase ion-exchange model, while for the inhibition by SDS micelles the Menger-Portnoy model was used to fit the data. The effect of salts (NaCl, NaBr and (CH(3))(4)NBr) was also seen on the hydrolysis of II and it was found that all salts inhibited the rate of reaction. The inhibition follows the trend NaCl

Micellar effects on the alkaline hydrolysis of isatin and its derivatives.

Herein we have investigated the hydrolysis of 1H-indol-2,3-dione (isatin, I) and its derivatives of different hydrophobicities, viz. N-dimethylaminomethyl indol-2,3-dione (II), N-morpholinomethyl indol-2,3-dione (III), N-pipridinomethyl indol-2,3-dione (IV), N-heptylaminomethyl indol-2,3-dione (V), N-dodecylaminomethyl indol-2,3-dione (VI), N-hexylanilinomethyl indol-2,3-dione (VII), N-decylanilinomethyl indol-2,3-dione (VIII), and N-hexadecylanilinomethyl indol-2,3-dione (IX), in the presence of an excess amount of sodium hydroxide. All the isatin derivatives were synthesized in the laboratory. The progress of the reactions was studied by exploiting UV-visible spectrophotometry. The observed rate constant, k(w), increases linearly on increasing the hydroxide ion concentration, indicating first-order dependence on [OH(-)]. The effects of surfactants, cationic (cetyltrimethylammonium chloride, CTACl), and anionic (sodium dodecyl sulfate, SDS) were also investigated. The rate of reaction increased on increasing the concentration of CTACl and, after reaching a maximum, it started decreasing. Conversely, anionic micelles of SDS inhibited the rate of hydrolysis of isatin and its derivatives. The results of the effect of CTACl were analyzed using a pseudophase ion-exchange model while the inhibition by SDS was analyzed using a simple Menger-Portnoy model. The effects of added salts, such as NaBr, NaCl, and (CH(3))(4)NBr, were also seen on the isatin hydrolysis. It was found that the addition of salts decreased the rate enhancement efficiency of the CTACl.

Micellar effect upon the lucigenin chemiluminescent reaction system with isoprenaline

The effect of aqueous solutions of cationic surfactants such as hexadecyltrimethyl ammonium hydroxide (CTAOH), hexadecyltrimethyl ammonium bromide (CTABr), anionic micelles of sodium lauryl sulphate (SLS), and nonionic micelles of polyoxyethylene(23) dodecanol (Brij-35), upon the lucigenin chemiluminescent reaction system with isoprenaline was evaluated. A lowering of the chemiluminescence (CL) emitted from the chemiluminescence reaction of lucigenin with isoprenaline was observed in cationic and anionic micellar assemblies. In contrast, an enhancement of the CL emission was observed in the presence of nonionic micelles of Brij-35. An account is given of the practical application of the surfactant effect.

Synthesis and application of magnetite polyacrylamide amino-amidoxime nano-composites as adsorbents for water pollutants

In this work, we aimed to develop a feasible method for in situ preparation of a magnetite ionic polymer nanocomposite at room temperature. For this purpose, acrylonitrile (AN) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) monomers were copolymerized and crosslinked using different monomer mol ratios in the presence of N,N-methylenebisacrylamide (MBA) as crosslinker to produce ionic crosslinked polymers P(AN-co-AMPS. The nitrile groups were converted to amine amidoxime by reacting with hydroxylamine to increase the adsorption characteristics of the ionic polymers. The produced polymers were swelled in iron cations produced from the reaction of ferric chloride and potassium iodide, followed by reaction with an ammonium hydroxide solution to produce magnetite nano-polymer composites. We performed FT-IR and XRD analysis to determine the chemical and crystalline structures, and assessed the morphologies and magnetite content using SEM, TEM and TGA analyses. We investigated the adsorption capacity and mechanism of the prepared magnetite nano-composites as adsorbents for methylene blue, Co2+ and Ni2+ cations from water.

Synthesis of dispersed and stabilized silver nanoparticles in acidic media

The present work aims to prepare citrate-reduced silver particles (AgNPs) coated with poly(vinyl pyrrolidone) (PVP) and modified polyethylene thiol monomethylether. Modified AgNPs derivatives were exposed to synthetic human stomach fluid (SSF) (pH 1.5) and changes in size, shape, hydrodynamic diameter and chemical composition were determined during a 1 hour exposure period using UV-Vis, high resolution transmission electron microscopy/energy dispersive X-ray spectroscopy (TEM/EDS), dynamic light scattering (DLS) and X-ray powder diffraction (XRD) combined with Rietveld analysis. Exposure of AgNPs to SSF produced stabilized SPR peak at 414 nm which changed according to the exposure time and the conditions of preparation of AgNPs. Changes in aggregation and morphology of the particles were also observed as well as production of silver chloride which appeared physically associated with particle aggregates. The XRD data indicated that the there is no any silver oxide (Ag2O) particles formed or aggregated with silver nanoparticles.

Kinetics of the autoxidation of adrenaline and [copper(II)(adrenaline)] 2+ in alkaline aqueous and micellar media

The kinetics of autoxidation of adrenaline and [Cu(adrenaline)]2+ complex by dissolved oxygen in alkaline aqueous and micellar media has been studied. The reaction is initiated by the removal of amino-H+ protons of adrenaline by hydroxide ion, followed by cyclization. The values of (1/kobs) for the autoxidation of both species were found to be linearly dependent upon 1/[OH−]. The reaction follows a consecutive pathway in which the intermediate adrenochrome remains stable for few minutes, and then undergoes further reactions to yield adrenolutin and other products. The [Cu(adrenochrome)]+ complex is stable for a few hours. Studies on the effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) on the reactivity of both species revealed different behaviors. The micelles of CTAB catalyzed the rates of autoxidation for both species, whereas SDS micelles inhibited the autoxidation of adrenaline but catalyzed the rate of autoxidation of [Cu(adrenaline)]2+. Addition of the reactive counterion surfactant, cetyltrimethylammonium hydroxide (CTAOH) initially increased the rate constant with the increasing [CTAOH], until it reached a plateau for kψ−[CTAOH]. Salts such as NaCl, NaBr, tetramethyl ammonium bromide, and tetraethyl ammonium bromide increased the rate when added at lower concentrations, but had negligible effect at higher concentrations. The results obtained in micellar media were treated according to Berezin’s Pseudophase Model. The various kinetic parameters for the reactions occurring in aqueous and in micellar media are reported.

Micellar Effects upon the Alkaline Hydrolysis of Acetaminophen Prodrugs: Carboxylic and Carbonic Acid Esters

The rates of alkaline hydrolysis for four carboxylate esters (4-acetaminophenyl acetate, 4-acetaminophenyl butyrate, 4-acetaminophenyl heptanoate and 4-acetaminophenyl benzoate) and three carbonate ester (4-acetaminophenyl methylcarbonate, 4-acetaminophenyl ethylcarbonates and 4-acetaminophenyl propylcarbonates) prodrugs of acetaminophen derivatives were determined in aqueous and micellar media. The cationic micelles of cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium sulfate [(CTA)2SO4] catalyzed the rate of the reaction. The anionic sodium dodecyl sulphate (SDS) and non-ionic Brij-35 surfactants inhibited the rate of the reaction. Added salt did not influence the rate of the reaction in the aqueous medium but decreased the values of observed rate constant in the micellar media. The rate enhancement in cationic micelles was treated by applying the pseudophase ion exchange model while the inhibition effect on the rate of hydrolysis was described using the Poisson–Boltzman pseudophase model. The binding constant (Ks) for the acetaminophen derivatives increased with increasing hydrocarbon chain length while the values of micellar rate constant (km) decreased with the increase in chain length. The increase in values of Ks and decrease in km are ascribed to the hydrophobic interaction between the acetaminophen derivative and surfactant molecule and molecular orientation of the substrate in the micelles.

Uncatalyzed cis to trans isomerization of cis-[PtCl2(PBu3)(PhCN)] complex in different solvents. Evidence for an initial dimer formation

Abstract The rates of spontaneous cis-trans isomerization of the complex cis-[PtCl2(PBu3)(PhCN)] have been measured in different solvents. Values of kobs decrease with the polarity of the solvent (benzene ∼ toluene

Kinetics of hydrolysis of procaine in aqueous and micellar media

CHCl3 ∼ DMF). 31P and 195Pt NMR spectroscopy provide (for the first time) strong evidence for dimer formation (sym. trans-[Pt2(μ- Cl)2(Cl)2(PBu3)2]) which are intermediates in spontaneous cis/trans isomerization.