Xiancheng Zeng

Micellar Catalysis of Composite Reactions—The Effect of SDS Micelles and Premicelles on the Alkaline Fading of Crystal Violet and Malachite Green

ABSTRACT The effect of SDS micelles and premicelles on the reversible alkaline fading reactions of crystal violet and malachite green were studied. Micellar and premicellar catalysis models for 1-1 type reversible reactions were proposed. The rate constants of forward and backward reactions and equilibrium constants of these reversible alkaline fading reactions in SDS micellar solutions were obtained from a micellar catalytic model. Under the premicellar condition the average number of SDS molecules per substrate molecule with n surfactant molecules was obtained from a premicellar catalytic model. The results indicated that both SDS micelles and premicelles exhibited an inhibiting effect on the forward reaction, while they exhibited an accelerating effect on the backward reaction. These results can reasonably be accounted for in terms of electrostatic interactions.

Studies on BNPP Cleavage by Schiff Base Complexes Containing Benzoaza‐15‐Crown‐5 in DHAB Micellar Solution

Two novel benzoaza‐crown Schiff base cobalt (II) and manganese (III) complexes were synthesized and characterized. The hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP) catalyzed by the two complexes was studied in buffer solution containing dihexadecyldimethylammonium bromide (DHAB) at 25°±0.1°C and different pH values. The kinetic mathematical model of BNPP hydrolysis was proposed, and the effects of different reaction conditions on BNPP hydrolysis were discussed. The results indicate that the two complexes (MnLCl and CoL) can efficiently accelerate the catalytic cleavage of BNPP in DHAB micellar solution. The pseudo‐first‐order rate constants (k obsd) of BNPP hydrolysis catalyzed by the metallomicelles of MnLCl/DHAB and CoL/DHAB are 2.32×107 times and 1.45×107 times higher than that of the BNPP spontaneous hydrolysis, respectively. Possible reasons for the huge rate accelerations include the lower critical micelle concentration (cmc) of DHAB and formation of metallomicelles made of complexes and DHAB. Furthermore, the BNPP cleavage catalyzed only by the two complexes was investigated in buffer solution. It was found that the hydrolytic rates of BNPP catalyzed only by the two complexes were about 1% of those catalyzed by MnLCl/DHAB and CoL/DHAB systems at 25°C, pH=7.00, and [BNPP]=2.0×10−4 mol · dm−3.

Effects of Amine Additives on Critical Micelle Concentration of Ionic Surfactants

Abstract This paper describes the effect of four types of amine (ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine) as polar additives on the critical Micellar concentrations (CMCs) of ionic surfactants, [cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS)] in buffered solutions (I = 0.1 M KNO3, 0.01 M Tris–TrisH+) at pH 7.00 ± 0.01 by electrical conductivity. It was found that the CMCs of these surfactants all decreased with increasing amine concentrations and the extent of effect followed the sequence: tetraethylenepentamine > triethylenetetramine > diethylenetriamine > ethylenediamine. Based on these results, several empirical linear models were obtained. From the experimental data, it is apparent that the extent of decreasing CMCs of CTAB and SDS by the same amine is roughly similar, and this may be ascribed to the polarity of additives and hydrogen bond interactions.

Comparative kinetics of carboxylic esters hydrolysis catalyzed by the zinc(II) complex of a macrocyclic Schiff base ligand

The comparative kinetic investigation of the hydrolysis of p-nitrophenyl picolinate (PNPP) and p-nitrophenyl acetate (PNPA) catalyzed by the tetracoordinate macrocyclic Schiff base complex of zinc(II) (1) at 30 °C is reported. The results indicate that the (1) catalyzed hydrolyses of PNPP and PNPA are acid-base catalytic processes and that the active species is the metal bound hydroxide ion, namely, ZnL—OH−. (1) promoted hydrolysis of PNPP proceeds much faster than that of PNPA. At pH 7.51, the apparent second-order rate constants kc for hydrolysis of PNPP and PNPA are 0.254 and 7.28 × 10−3 mol−1 dm3 s−1, respectively. The difference in hydrolytic rates may be attributed to the difference of hydrolytic mechanisms by which the PNPP and PNPA operate. The reasons are discussed in detail.

Studies on the reaction kinetics and the mechanism of hydrolysis of bis(4-nitrophenyl) phosphate (BNPP) catalyzed by oxamido-bridged dinuclear copper(II) complexes in micellar solution

Oxamido-bridged dinuclear copper(II) complexes, used as symmetric two-center catalysts for the cleavage of BNPP, were synthesized and characterized. The reaction kinetics and the mechanism of hydrolysis of BNPP catalyzed by metallomicelles, made from complex (A) or (B) and a surfactant (LSS or CTAB), were investigated. A kinetic mathematical model for BNPP cleavage was also proposed. The results showed that the reaction rate for the catalytic hydrolysis of BNPP, compared with spontaneous hydrolysis of BNPP, increased by a factor of ca. 1 × 106 due to the synergistic effect of two copper ions in the complex and the local concentration effect of the micelle. The study indicates that the metallomicelle-containing oxamido-bridged dinuclear copper(II) complex may be a potential catalyst for the hydrolysis of BNPP.

Metallomicellar catalysis: Hydrolysis of phosphodiester with Cu(II) and Zn(II) complexes in micellar solution

Abstract The effects of two metal complexes of 2,2′‐dipyridylamine (bpya) ligand, [(bpya)Cu]Cl2 and [(bpya)Zn]Cl2, in promoting the hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP) have been kinetically investigated in Brij35 micellar solution and at 298 K, pH ranging from 6.41 to 8.6. In neutral micellar solution at 298 K, pH 7.02, the rate constants for the catalytic hydrolysis of BNPP by [(bpya)Cu]Cl2 and [(bpya)Zn]Cl2 are 1.2 × 106 times and 1.5 × 105 times higher than those for the spontaneous hydrolysis, respectively. Kinetic studies show that the active species in the catalytic hydrolysis of BNPP is the aquo‐hydroxy form, and the relative kinetic and thermodynamic parameters indicate that the mechanism of the reaction involves intramolecular nucleophilic attack on the metal center‐bound diester.

Heterobinuclear copper(II)–lanthanoid(III) complexes bridged by N,N′-oxamidobis(benzoato)cuprate(II)

Eight new μ-oxamido-bridged copper(II)–lanthanoid(III) heterobinuclear complexes described by the overall formula Cu(obbz)Ln(Me-phen)2NO3 (Ln = Y, La, Nd, Eu, Gd, Tb, Ho, Er), where obbz denotes the oxamidobis(benzoato) and Me-phen represents 5-methyl-1,10-phenanthroline (Me-phen), have been synthesized and characterized by the elemental analyses, spectroscopic (i.r., u.v., e.s.r.) studies, magnetic moments (at room temperature) and by molar conductivity measurements. The temperature dependence of the magnetic susceptibility of Cu(obbz)Gd(Me-phen)2NO3 has also been measured over the 4.2 ∼ 300 K range. The least-squares fit of the experimental susceptibilities based on the spin Hamiltonian operator, Ĥ = −2 JŜ1 · Ŝ2, yielded J = + 2.18 cm−1. The observed GdIII–CuII coupling is ferromagnetic. A plausible mechanism for a ferromagnetic coupling between GdIII–CuII is discussed in terms of spin-polarization.

Effects of Metal Ions on the Micellization of Ionic Surfactants

The effect of metal ions (Cu(II), Zn(II), Co(II), Ni(II), La(III), Fe(III)) on the critical micelle concentration (CMC) of ionic surfactants (sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (CTAB)) were investigated at 25±0.1°C, μ = 0.1 M (KNO3), using conductivity method in this paper. A series of general empirical expressions about the relationship between the CMC values for SDS and CTAB and the concentrations of metal ions have been derived. The results showed that the CMC values for both SDS and CTAB decreased with increasing the concentrations of metal ions. This can be interpreted by the counterion effect and the entropy driving effect.

Thermo-kinetic research method for simple-order reactions: Time-parameter method

On the basis of thermo-kinetic theories, a novel thermo-kinetic research method, the time-parameter method for simple-order reactions, has been proposed in this paper. In order to test the validity of this method, the saponification of ethyl buryate and ethyl benzoate in aqueous ethanol solvent and the formation of hexamethylenetetramine in aqueous solution have been studied. The rate constants calculated with this method are in agreement with those in the literature. Therefore, the time-parameter method is believed to be correct.

PNPP Cleavage Catalyzed by Schiff Base Mn(III) Complexes Containing Polyether Side Chains in CTAB Micellar Solutions

Two Schiff base Mn(III) complexes containing polyether side chain were synthesized and characterized. The catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) by the two complexes in the buffered CTAB micellar solution in the pH range of 6.60–8.20 was investigated kinetically in this study. The influences of acidity, temperature, and structure of complex on the catalytic cleavage of PNPP were also studied. The mechanism of PNPP hydrolysis catalyzed by Schiff base manganese(III) complexes in CTAB micellar solution was proposed. The relative kinetic and thermodynamic parameters were determined. Comparied with the pseudo‐first‐order rate constant (k 0) of PNPP spontaneous hydrolysis in water, the pseudo‐first‐order rate constants (k obsd) of PNPP catalytic hydrolysis are 1.93×103 fold for MnL1 2Cl and 1.06×103 fold for MnL2 2Cl in CTAB micellar solution at pH=7.00, T=25°C, and [S]=2.0×10−4mol · dm−3, respectively. Furthermore, comparing the k obsd of PNPP catalytic hydrolysis by metallomicelles with that of PNPP hydrolysis catalyzed only by metal complexes or CTAB micelle at the above‐mentioned condition, metallomicelles of MnL2(L=L1, L2) Cl/CTAB exhibit notable catalytic activities for promoting PNPP hydrolysis, and MnL1 2Cl/CTAB system is superior in promoting cleavage of PNPP relative to MnL2 2Cl/CTAB system under the same experimental conditions. The results indicate that the rate of PNPP catalytic cleavage is influenced by the structures of the two complexes, the acidity of reaction systems, and the solubilization of PNPP in CTAB micelles.