Cu(II) promoted oxidation of L-valine by hexacyanoferrate(III) in cationic micellar medium

The kinetics of Cu(II) accelerated L-valine (Val) oxidation by hexacyanoferrate(III) in CTAB micellar medium were investigated by measuring the decline in absorbance at 420 nm. By adjusting one variable at a time, the progression of the reaction has been inspected as a function of [OH⁻], ionic strength, [CTAB], [Cu(II)], [Val], [Fe(CN)₆³⁻], and temperature using the pseudo-first-order condition. The results show that [CTAB] is the critical parameter with a discernible influence on reaction rate. [Fe(CN)₆]^3- interacts with Val in a 2:1 ratio, and this reaction exhibits first-order dependency with regard to [Fe(CN)₆³⁻]. In the investigated concentration ranges of Cu(II), [OH⁻], and [Val], the reaction demonstrates fractional-first-order kinetics. The linear increase in reaction rate with added electrolyte is indicative of a positive salt effect. CTAB significantly catalyzes the process, and once at a maximum, the rate remains almost constant as [CTAB] increases. Reduced repulsion between surfactant molecules' positive charge heads brought on by the negatively charged [Fe(CN)₆]^3-, OH⁻, and [Cu(OH)₄]^2- molecules may be responsible for the observed drop in CMC of CTAB.     

Surfactant effect on electrochemical-induced synthesis of α-Ni(OH)2

Nickel hydroxide films were electrosynthesized in the presence of different diluted surfactant solutions by galvanostatic electroprecipitation. Lamellar α-Ni(OH)₂ films are obtained using cationic surfactant cetyltrimethylammonium bromide (CTAB), anionic surfactant sodium dodecyl sulfate (SDS), and also neutral surfactant Tween® 80. The films were structurally and morphologically characterized by X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy, and electrochemically by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The results evidenced that SDS remains intercalated between the lamellae of α-Ni(OH)₂. Albeit the presence of CTAB and Tween® 80, it was noticed in FTIR spectra that the surfactants did not intercalate. The morphology was affected by the presence of different surfactants. All studied surfactants displaced the oxidation potential (E _O) of Ni²⁺/Ni³⁺ process to less positive values. Also, the presence of surfactants improved the electrode charge efficiency and the charge response for the same number of moles of nickel ions deposited. The ratio of the charge and frequency change is 4.4 times bigger for films deposited with SDS when compared with pure α-Ni(OH)₂ films.     

Study of the reaction Fe(CN)5(4‐CNpy)3− + S2O82− in aqueous salt and micellar solutions

The reaction Fe(CN)₅(4‐CNpy)³⁻ + S₂O₈²⁻ (4‐CNpy=4‐cyanopyridine) was studied in aqueous salt solutions in the presence of several electrolytes as well as in anionic, cationic, and nonionic surfactant solutions. In aqueous salt solutions the noncoulombic interactions seem to be important in determining the positive salt effects observed. The salting effects are influencing the activity coefficients of any participant in the reaction, including those ion pairs which can be formed between the anionic reagents and the cations which come from the added salts. The changes in surfactant concentration in anionic and nonionic surfactant solutions do not affect the reaction rate, which is similar to that in pure water at the same ionic strength. In cationic micellar solutions an increase in the rate constant compared to that in pure water is found; the reaction rate decreasing when the surfactant concentration increases. The kinetic trends can be explained assuming that the reagents are totally bound to the micelles and, therefore, an increase in the surfactant concentration results in a decrease in the reagent concentrations at the micellar phase and thus in a decrease in the observed rate constant. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet: 31: 229–235, 1999     

Effects of alkyltrimethylammonium bromide surfactants on the kinetics of the oxidation of tris(1,10-phenanthroline)iron(II) by azido-pentacyanocobaltate(III) complex

The redox reaction between tris(1,10-phenanthroline)iron(II), [Fe(phen)₃]²⁺, and azido-pentacyanocobaltate(III), [Co(CN)₅N₃]^3? was investigated in three cationic surfactants: dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB) in the presence of 0.1?M NaCl at 35°C. Second-order rate constant in the absence and presence of surfactant, k_w and k_ψ, respectively, were obtained in the concentration ranges DTAB?=?0???4.667?×?10^?4?mol?dm^?3, TTAB?=?0–9.364?×?10^?5?mol?dm^?3, CTAB?=?0???6.220?×?10^?5?mol?dm^?3. Electron transfer rate was inhibited by the surfactants with premicelllar activity. Inhibition factors, k_w/k_ψ followed the trend CTAB?>?TTAB?>?DTAB with respect to the surfactant concentrations used. The magnitudes of the binding constants obtained suggest significant electrostatic and hydrophobic interactions. Activation parameters ΔH^≠, ΔS^≠, and E_a have larger positive values in the presence of surfactants than in surfactant-free medium. The electron transfer is proposed to proceed via outer-sphere mechanism in the presence of the surfactants.     

Kinetics and mechanism of the ligand substitution reaction between aquapentacyanoruthenate(II) and 4-cyanopyridine in the presence of anionic surfactant micelles

The kinetics of ligand substitution between aquapentacyanoruthenate(II) ion, [Ru(CN)₅H₂O]³⁻ and 4-cyanopyridine (4-CNpy) has been investigated spectrophotometrically in the presence of anionic surfactant micelle, namely sodium dodecylsulphate (SDS) at 400 nm (λ_max of the intense yellow product [Ru(CN)₅4-CNpy]³⁻) under pseudo-first-order conditions using at least 10% excess of 4-CNpy over [Ru(CN)₅H₂O]³⁻. The reaction was studied as a function of [Ru(CN)₅H₂O³⁻], [4-CNpy], [SDS], pH, ionic strength and temperature, by varying each of these variables one at a time. The reaction exhibited overall second-order kinetics, being first order each in [4-CNpy] and [Ru(CN)₅H₂O³⁻] over a wide concentration range. Variation of ionic strength of the medium had a significant negative effect on the rate. The SDS micelle, being negatively charged, does not reveal any regular effect except at or near its critical micelle concentration (c.m.c). The rate of reaction was measured at different temperatures, and the activation parameters were computed using Arrhenius and Eyring plots. A plausible mechanism consistent with the experimental results has been proposed.     

Interaction of Sulfonated Ruthenium(II) Polypyridine Complexes with Surfactants Probed by Luminescence Spectroscopy

Novel anionic [RuL₂L′]²⁻ complexes, where L stands for (1,10‐phenanthroline‐4,7‐diyl)bis(benzenesulfonate) (pbbs; 3a ) or (2,2′‐bipyridine)‐4,4′‐disulfonate (bpds; 3b ), and L′ is N‐(1,10‐phenanthrolin‐5‐yl)tetradecanamide (pta; 2a ) or N‐(1,10‐phenanthrolin‐5‐yl)acetamide (paa; 2b ), were synthesized, and their interaction with the prototypical surfactants sodium dodecylsulfate (SDS), cetyl trimethyl ammonium bromide (CTAB), and Triton X‐100 (TX‐100) was investigated by electronic absorption, luminescence spectroscopy, emission‐lifetime determinations, and O₂‐quenching measurements. [Ru(pbbs)₂(pta)]²⁻ ( 5a ) displayed cooperative self‐aggregation in aqueous medium at concentrations above 1.3 μM ; the observed association was enhanced in the presence of either β‐cyclodextrin or NaCl. This amphiphilic Ru^II compound showed the strongest interaction with all the detergents tested: nucleation of surfactant molecules around the luminescent probe was observed below their respective critical micellar concentrations. As much as a 12‐fold increase of the emission intensity and a 3‐fold rise in the lifetime were measured for 5a bound to TX‐100 micelles; the other complexes showed smaller variations. The O₂‐quenching rate constants decreased up to 1/8 of their original value in H₂O (e.g., for [Ru(bpds)₂(pta)]²⁻ ( 6a ) bound to CTAB micelles). Luminescence‐lifetime experiments in H₂O/D₂O allowed the determination of the metal‐complex fraction exposed to solvent after binding to surfactant micelles. For instance, such exposure was as low as 25% for pta complexes⋅CTAB aggregates. The different behaviors observed were rationalized in terms of the Ru^II complex structure, the electrostatic/hydrophobic interactions, and the probe environment.     

Influence of surfactants on the adsorption and elektrokinetic properties of the system: guar gum/manganese dioxide

The adsorption of non-ionic polysaccharide—guar gum (GG) in the presence or absence of the surfactants: anionic SDS, cationic CTAB, nonionic TX-100 and their equimolar mixtures SDS/TX-100, CTAB/TX-100 from the electrolyte solutions (NaCl, CaCl₂) on the manganese dioxide surface (MnO₂) was studied. The increase of GG adsorption amount in the presence of surfactants was observed in every measured system. This increase results from formation of complexes between the GG and the surfactant molecules. This observation was confirmed by the determination of the influence of GG on surfactants adsorption on the MnO₂ surface. The increase of GG adsorption on MnO₂ was the largest in the presence of the surfactant mixtures (CTAB/TX-100; SDS/TX-100) which is the evidence of the synergetic effect. The smallest amounts of adsorption were obtained in the presence of TX-100, which results from non-ionic character of this surface active agent. In the case of single surfactant solution CTAB has the best efficiency in increasing the amount of GG adsorption on MnO₂ which results from strong interactions with GG and also with the negatively charged surface of the adsorbent. In order to determine the electrokinetic properties of the system, the surface charge density of MnO₂ and the zeta potential measurements were performed in the presence of the GG macromolecules and the above mentioned surfactants and their mixtures. The obtained data showed that the adsorption of GG or GG/surfactants complexes on the manganese dioxide surface strongly influences the diffused part of the electrical double layer (EDL)—MnO₂/electrolyte solution, but has no influence on the compact part of the electric double layer. This is the evidence that the polymers chains are directly bonded with the surface of the solid and the surfactants molecules are present in the upper part of the EDL.     

Kinetics and mechanism of the redox reaction between malachite green and iron(III) in aqueous and micellar media

The kinetics of the oxidation of malachite green (MG⁺) by Fe(III) were investigated spectrophotometrically by monitoring the absorbance change at 618 nm in aqueous and micellar media at a temperature range 20–40 °C; I = 0.10 mol dm^?3 for [H⁺] range (2.50–15.00) × 10^?4 mol dm^?3. The rate of reaction increases with increasing [H⁺]. The reaction was carried out under pseudo-first-order conditions by taking the [Fe(III)] (>10-fold) the [MG⁺]. A mechanism of the reaction between malachite green and Fe(III) is proposed, and the rate equation derived from the mechanism was consistent with the experimental rate law as follows: Rate = (k ₄ + K ₁ k ₅[H⁺]) [MG⁺][Fe(III)]. The effect of surfactants, such as cetyltrimethylammonium bromide (CTAB, a cationic surfactant) and sodium dodecylsulfate (SDS, an anionic surfactant), on the reaction rate has been studied. CTAB has no effect on the rate of reaction while SDS inhibits it. Also, the effect of ligands on the reaction rate has been investigated. It is proposed that electron transfer proceeds through an outer-sphere mechanism. The enthalpy and the entropy of the activation were calculated using the transition state theory equation.     

The α‐effect in micelles: Nucleophilic substitution reaction of p‐nitrophenyl acetate with N‐phenylbenzohydroxamate ion

Pseudo‐first‐order rate constants have been determined for the nucleophilic substitution reactions of p‐nitrophenyl acetate with p‐chlorophenoxide (4‐ClC₆H₄O^?) and N‐phenylbenzohydroxamate (C₆H₅CON(C₆H₅)O^?) ions in phosphate buffer (pH 7.7) at 27°C. The effect of cationic, (CTAB, TTAB, DTAB), anionic (SDS), and nonionic (Brij‐35) surfactants has been studied. The k_obs value increases upon addition of CTAB and TTAB. The effect of DTAB and other surfactants on the reaction is not very significant. The micellar catalysis and α‐effect shown by hydroxamate ion have been explained. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 26–31, 2006     

Electrochemical characterization of cationic surfactants’ adsorption on a disturbed n-alkanethiolate self-assembled monolayer-modified polycrystalline gold electrode

The adsorption of cetyltrimethylammonium bromide (CTAB) on disturbed n-alkanethiolate self-assembled monolayers (SAMs) was investigated by electrochemical methods with potassium ferricyanide [K₃Fe(CN)₆] as a probe. Compared with the completely restrained signal at ordinary compact n-alkanethiolate SAMs, the electrochemical response of K₃Fe(CN)₆ at the disturbed n-alkanethiolate SAMs was partly restored and became progressively reversible in the presence of increasing concentrations of CTAB, which was employed to characterize the adsorption of cationic surfactants on hydrophobic SAMs. The effect of CTAB concentration on electrochemical impedance spectroscopy (EIS) plots indicated that CTAB experienced two different types of adsorptive behavior at the disturbed n-alkanethiolate SAMs: monomer adsorption at low concentrations below 1×10^–6 M and monolayer adsorption at CTAB concentrations above 1×10^–5 M. The adsorption of a series of cationic surfactants with similar structures to CTAB on disturbed n-alkanethiolate SAMs was also explored. These surfactants had similar adsorptive behavior and showed nearly linear adsorption characteristics with the length of their hydrophobic tails.     

Study of Ligand Substitution Reactions at Pentacyanoferrates(II) in Aqueous Salt and Micellar Solutions

The ligand substitution reactions Fe(CN)(5)(4-(t)bupy)(3-) + 4-CNpy and Fe(CN)(5)(4-(t)bupy)(3-) + pzCO(2)(-) (4-(t)Bupy = 4-tert-butylpyridine; 4-CNpy = 4-cyanopyridine; pzCO(2)(-) = pyrazinecarboxylate) were studied in several aqueous salt and micellar solutions. Kinetic data in aqueous solutions showed that the two processes follow a dissociative mechanism, D, and the dependence of the first-order rate constants on [salt] on electrolyte aqueous solutions allow the estimation of the activation volumes corresponding to both reactions. Under true first-order conditions no kinetic micellar effects were found in anionic (SDS) and nonionic (Triton X-100) aqueous micellar solutions. In cationic micellar solutions (CTAB, CTAC, and TTAB) small kinetic micellar effects were found. These were related to the different ionic concentrations and the different polarity and structure of the Stern layer surrounding the cationic micellar aggregates, where the reactions take place, with respect to pure water. Copyright 2000 Academic Press.     

Spectroscopic analysis of naphtholazobenzimidazole in organised solution

Micelle–water partition coefficient (K_x ) of naphtholazobenzimidazole dye (NAB) in aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) has been determined spectrophotometerically. Changes in absorption patterns of dye caused by surfactants and solvents were quantified in terms of dye–surfactant ratio (n _D/n _S) and solvent water partition coefficients (P), respectively. Multiple residence sites have been suggested for dye molecules within micelles, based on shifts in azo-hydrazone tautomeric equilibrium. Micelle–water partition coefficients were used to evaluate the influence of dye on critical micelle concentration of CTAB and SDS. At same micelle concentration, M, the relative solubility of NAB was greater in cationic surfactant CTAB than in anionic surfactant SDS.     

Solvent and salt effects on the kinetics of the reaction between [Ru(NH3)5pz]2+ and [Fe(CN)5H2O]3–

The kinetics of replacement of H₂O by [Ru(NH₃)pz]²⁺ (pz = pyrazine) in [Fe(CN)₅H₂O]^3? have been studied in various concentrated electrolyte solutions and in various water–cosolvent mixtures, at 298 K. Salt and cosolvent effects can be rationalized taking into account specific medium effects on both the encounter complex formation process and the ligand‐substitution process, once the encounter complex is formed. These effects in water–cosolvent mixtures depend on the solvation of the reactants by the components of the mixture, as well as on the solvent–solvent interactions in these mixtures. Salt effects seem to be related to a primary salt effect as well as to the effect of the cations on the electronic density on the iron complex. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 367–373, 2003     

The Viscous Properties of Anionic/Cationic and Cationic/Nonionic Mixed Surfactant Systems

The behavior of mixed cationic/anionic and cationic/nonionic surfactants solutions have been studied by viscosimetry. The systems studied were sodium dodecyl sulfate (SDS)/cetyltrimethylammonium bromide (CTAB) and CTAB/Brij (polyoxyethylene lauryl ether, n = 10 and 23) in aqueous and sodium chloride solutions. The relative viscosity of single nonionic surfactant solutions is larger than that of SDS or CTAB solutions. It increases with the number of ethylene oxide groups. In the mixed systems, viscosity deviates from ideal behavior. The deviation results from electrostatic interactions. The surfactant mixture composition affects the self-assembled microstructure and rheology. A new mixed system that forms clear micellar solution above CMC was detected. In CTAB/Brij systems, the experimental data also deviate from ideal behavior due to mixed micelle formation and electroviscous effect. This effect is less pronounced than that of SDS/CTAB system and could be suppressed by adding an electrolyte (NaCl).     

Properties and Extraction for [Ni(NH3)6]2+ of ATPS-a Formed by Aqueous Cationic–Anionic Surfactant Mixtures

The properties and extraction for [Ni(NH₃)₆]²⁺ of anionic aqueous two-phase systems (ATPS-a) that formed in mixtures of cetyltrimethylammonium bromide (CTAB) and excess sodium dodecyl sulfate (SDS) aqueous solutions were investigated. The results showed that the properties and extraction effects were strongly affected by the surfactant concentration, the temperature of system, and the mole fraction of surfactants. The increase of temperature induces narrower phase region and larger phase volume ratio. In addition, [Ni(NH₃)₆]²⁺ was extracted into the surfactant-rich phase with higher distribution coefficient when the liquid crystal had the birefringent properties. Moreover, the distribution coefficient can be improved through reducing the concentration of surfactant from 0.15 to 0.05 mol · L^?1 or increasing mole fraction of CTAB from 21.9% to 23.1%. The results showed that ATPS of cationic–anionic surfactants was efficient for [Ni(NH₃)₆]²⁺ extraction with distribution coefficients of 13.5 when the total surfactant concentration was 0.05 mol · L^?1, mole fraction of CTAB was 21%, and temperature was 34°C.     

Salt effects upon reactions of different charge type reactants: Peroxodisulphate Oxidations of Fe(CN)4(bpy)2−, cis-Fe(CN)2(bpy)2 and Fe(bpy)32+ and Iron(II) Oxidation by Co(NH3)5Cl2+

Salt effects on the oxidation of the iron(II) complexes Fe(CN)₄(bpy)^2?, cis-(CN)₂(bpy)₂ and Fe(bpy)₃²⁺ by S₂O₈^2? as well as on the reaction Fe²⁺ + Co(NH₃)₅Cl²⁺ have been studied in concentrated electrolyte solutions at 298.2 K. We have gone from anion–anion to cation–cation reaction with the intermediate cases of anion–neutral and cation–anion reactions. Results show that the main cause of the kinetic salt effects observed is the interaction between supporting electrolytes and the solvent. © 1994 John Wiley & Sons, Inc.     

Interaction of ions with phosphatidylcholine and phosphatidylethanolamine at the n-heptane/water interface: I. Inorganic ions

Electrocapillary phenomena at the n-heptane/water interface in the presence of phosphatidylcholine or phosphatidylethanolamine in alkane were studied by the drop-volume technique. The regulating role of the electric field was established in phospholipid interaction with inorganic ions: changes in interfacial pressure at the n-heptane/water interface with addition of electrolytes were observed only when an electric field was applied to the system of two immiscible liquids. It is suggested that ions can penetrate and bond by phospholipid functional groups at the phase boundary only after reorientation of the latter in the electric field. As in the case of ionic surfactants, change in interfacial pressure was directly proportional to the cube root of the concentration of electrolyte. It is assumed that as a result of preferential binding by phospholipid functional groups of ions of one sign, lipid molecules are charged and at the phase boundary behave themselves like ionic surfactants. Experiments with salts of multicharged ions, La³⁺, [Fe(CN)₆]³⁻, and [Fe(CN)₆]⁴⁻, have shown that mainly phospholipid functional groups bind cations.     

A charge‐transfer salt composed of methyl viologen and hexacyanidoferrate(II)

The methyl viologen dication, used under the name Paraquat as an agricultural reagent, is a well‐known electron‐acceptor species that can participate in charge‐transfer (CT) interactions. The determination of the crystal structure of this species is important for accessing the CT interaction and CT‐based properties. The title hydrated salt, bis(1,1′‐dimethyl‐4,4′‐bipyridine‐1,1′‐diium) hexacyanidoferrate(II) octahydrate, (C₁₂H₁₄N₂)₂[Fe(CN)₆]·8H₂O or (MV)₂[Fe(CN)₆]·8H₂O [MV²⁺ is the 1,1′‐dimethyl‐4,4′‐bipyridine‐1,1′‐diium (methyl viologen) dication], crystallizes in the space group P 2₁/c with one MV²⁺ cation, half of an [Fe(CN)₆]⁴⁻ anion and four water molecules in the asymmetric unit. The Fe^II atom of the [Fe(CN)₆]⁴⁻ anion lies on an inversion centre and has an octahedral coordination sphere defined by six cyanide ligands. The MV²⁺ cation is located on a general position and adopts a noncoplanar structure, with a dihedral angle of 40.32 (7)° between the planes of the pyridine rings. In the crystal, layers of electron‐donor [Fe(CN)₆]⁴⁻ anions and layers of electron‐acceptor MV²⁺ cations are formed and are stacked in an alternating manner parallel to the direction of the −2a + c axis, resulting in an alternate layered structure.     

表面活性剂辅助合成LiNi0.8Co0.1Mn0.1O2正极材料

通过添加烷基季铵盐类表面活性剂来调控材料形貌和粒径的改性方法,在LiNi_0.8Co_0.1Mn_0.1O₂前驱体合成过程中添加表面活性剂十二烷基三甲基溴化铵(DTAB)和十六烷基三甲基溴化铵(CTAB),利用尿素作为配合剂和沉淀剂,采用溶剂热法合成LiNi_0.8Co_0.1Mn_0.1O₂前驱体。最后,高温混锂煅烧合成椭球形的空心多孔材料。相比于不添加表面活性剂的样本,改性的材料有着更小的粒径和更加规整的形貌。电化学测试表明,添加DTAB和CTAB之后,首次充电容量分别达到223与251 mAh·g^-1(0.1C)。其中,添加CTAB的样品首次放电容量达到216 mAh·g^-1(0.1C),100次循环后容量保持率为85.1%,高于LiNi_0.8Co_0.1Mn_0.1O₂的81.7%(0.1C)。表面活性剂的改性显著提高了材料的电化学性能,为高镍三元正极材料的改性提供了一种新的思路。     

Spectrophotometric study of interaction and solubilization of procaine hydrochloride in micellar systems

The interaction of Procaine hydrochloride (PC) with cationic, anionic and non-ionic surfactants; cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and triton X-100, were investigated. The effect of ionic and non-ionic micelles on solubilization of Procaine in aqueous micellar solution of SDS, CTAB and triton X-100 were studied at pH 6.8 and 29°C using absorption spectrophotometry. By using pseudo-phase model, the partition coefficient between the bulk water and micelles, K_x, was calculated. The results showed that the micelles of CTAB enhanced the solubility of Procaine higher than SDS micelles (K_x = 96 and 166 for SDS and CTAB micelles, respectively) but triton X-100 did not enhanced the solubility of drug because of weak interaction with Procaine. From the resulting binding constant for Procaine-ionic surfactants interactions (K_b = 175 and 128 for SDS and CTAB surfactants, respectively), it was concluded that both electrostatic and hydrophobic interactions affect the interaction of surfactants with cationic procaine. Electrostatic interactions have a great role in the binding and consequently distribution of Procaine in micelle/water phases. These interactions for anionic surfactant (SDS) are higher than for cationic surfactant (CTAB). Gibbs free energy of binding and distribution of procaine between the bulk water and studied surfactant micelles were calculated.