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Two alkoxo/hydroxide-bridged dinuclear copper(II) complexes (CuL1 and CuL2) were prepared for evaluating their activity towards the hydrolysis of p-nitrophenyl picolinate (PNPP). Importantly, this work investigated the effects of varied micelles of four surfactants, e.g., cationic gemini 16-2-16 and 16-6-16, single-chain CTAB (hexadecyltrimethylammonium bromide), and LSS ( n-lauroylsarcosine sodium), on the PNPP hydrolysis by the as-prepared copper(II) complexes. The experimental results indicate that at neutral pH both of complexes exhibited much better activity by excess four-order of magnitude rate enhancement. For instant, rate constants of PNPP hydrolysis by CuL1 and bromo-containing CuL2 are approximate 49,569.6- and 31,123.5-fold than that of PNPP spontaneous hydrolysis. In addition, the hydrolytic reactivity of the bromo-containing CuL2 is subordinate to that one without bromine, CuL1. Moreover, it is found that the micellar solution of gemini 16-6-16 is proved to be the best medium, and whereas LSS micellar solution is the worst one. Particularly, the p K values of the Cu(II)-bound HO are determined by a new methodology which is correlative to second derivatives. [ABSTRACT FROM AUTHOR]

One new hydroxyl-functionalized imidazole derivative (L) was synthesized and characterized. Further, the related mononuclear zinc(II) and cobalt(II) complexes were prepared and used as mimic hydrolases to catalyze the hydrolytic cleavage of p-nitrophenyl picolinate (PNPP) in buffered aqueous solution and a micellar solution of cetyltrimethylammonium bromide (CTAB). Observations show that for all of catalytic systems, the hydrolysis of PNPP was pH-dependent in the pH range of 7.00-8.20. Besides, hydrolysis rates of PNPP displayed a constant increase with the increasing concentration of substrate. In the case of CoL-containing system, moreover, much greater acceleration for PNPP hydrolysis was observed in comparison with the ZnL-containing system. However, micellar effect of CTAB micelle aggregates on the PNPP hydrolysis was not obvious only showing 1.0 ∼ 1.3 folds rate difference in contrast to buffered aqueous solution. [ABSTRACT FROM AUTHOR]

In this article, the effects of different micelles and Schiff base ligands on the hydrolytic kinetics of p-nitrophenyl picolinate (PNPP) were evaluated. The results reveal that the biggest rate enhancement for PNPP hydrolysis was given in Gemini 16-6-16 micellar solution relative to other four reaction media, that is, cetyltrimethylammonium bromide (CTAB), n-lauroylsarcosine sodium (LSS), polyoxyethylene (23) lauryl ether (Brij35) and pure buffer. Moreover, the hydrolytic rates of PNPP in other four media decreased in the order LSS > CTAB > Buffer > Brij35. The structural effects of Mn(III) catalysts clearly testify that a relatively open active site facilitates the formation of reactive substrate-catalyst complex. [ABSTRACT FROM AUTHOR]

Hydrolytic cleavage of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) catalyzed by Zn(II)-biap (biap: N, N- bis (2-ethyl-5-methyl-imidazole-4-ylmethyl) aminopropane) complex was investigated spectrophotometrically in a cationic Gemini surfactant 16-6-16 [Bis(hexadecyldimethylammonium)hexane bromide] micellar solution. Effects of various factors (pH, [complex], temperature [K], amine additives, etc.) on the catalytic cleavage of HPNP were evaluated systematically. Experimental observations showed that higher rate acceleration of HPNP cleavage promoted by Zn(II)-biap complex was obtained in the 16-6-16 micellar solution in comparison with the background value (ko) of HPNP cleavage. Compared with the ZnL + G(16-6-16) system, the results reveal that a 1.2 ∼ 2.9 folds rate enhancement was given in the catalytic systems containing diethylenetriamine (DETA). Additionally, the addition of diethylenetriamine (DETA) resulted in a 1.2 ∼ 2.7 folds higher rate enhancement in contrast with 1,2-Ethylenediamine (EDA). [ABSTRACT FROM AUTHOR]

Hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by three Schiff base Mn(III) complexes (MnL2Cl) were investigated in Gemini 16-6-16 micelle media. [image omitted], [image omitted] and [image omitted] systems give 835-, 969-, and 1931-fold rate enhancements in the hydrolysis of PNPP under the comparable conditions, respectively. Moreover, Effects of varied micelles on the reactivity of PNPP hydrolysis were especially studied. The results obtained indicate that rates of hydrolysis of PNPP are approximately 1.5- and 4-fold larger in Gemini 16-6-16 micelles than in CTAB micelles and Brij35 micelles, respectively. Effects of ligand structure on the activities of these three complexes are discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract: Two crowned Schiff base manganese(III) complexes (MnL2Cl, L=L1, L2) were used to catalyze the hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) in Gemini surfactants [bis(hexadecyldimethylammonium)hexane bromide (abbreviation 16-6-16, 2Br−)] solution. In comparison with the rate of BNPP spontaneous hydrolysis, a six orders of magnitude in rate enhancement was observed in /16-6-16 and /16-6-16 systems. Owing to the different structure, shows better activity than . Especially, the effects of three different micelles, i.e., 16-6-16 micelles, CTAB (hexadecyltrimethylammonium bromide) micelles, LSS (n-lauroooylsarcosine sodium) micelles, on the hydrolysis of BNPP catalyzed by were evaluated at pH7.50. Experimental observations clearly demonstrate that Gemini 16-6-16 micelle is the best one for BNPP hydrolysis among three kinds of micellar media. [Copyright &y& Elsevier]

Two Schiff base cobalt(II) complexes containing crowned substituents have been synthesized and employed to promote the hydrolysis of p-nitrophenyl picolinate (PNPP) in a buffered micellar solution formed by a cationic Gemini surfactant, bis(hexadecyldimethylammonium)hexane bromide (G(hex)C16, 2Br-) over a pH range of 6.50–8.50. In comparison, the reactivity of PNPP hydrolysis catalyzed by the same catalysts in the other micellar system, formed by a conventional single-chain analogue, that is, hexadecyltrimethylammonium bromide (CTAB), has also been evaluated under a selected condition. The results clearly reveal that the two metallomicelles made of the aforementioned Co(II) complexes and the G(hex)C16 are both efficient for catalyzing PNPP hydrolysis with about 3 orders of magnitude in rate acceleration compared with the background rate of PNPP spontaneous hydrolysis. Moreover, the rates of PNPP hydrolysis catalyzed by the two cobalt(II) complexes in G(hex)C16 micelles are about 2 times higher than in CTAB micelles, correspondingly. In addition, observations show that steric hindrance of substituents of the two complexes is also one of the major influencing factors in the PNPP hydrolytic reaction. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 672–680, 2007 [ABSTRACT FROM AUTHOR]

Three new bi- or tetranuclear copper (II) complexes (complexes 1, 2 and 3) with reduced N-salicylate threonine were synthesized and characterized by single crystal X-ray diffraction, X-ray powder diffraction, UV–vis, and thermogravimetric analysis. Single-crystal diffraction analysis reveals that these complexes have similar coordination modes and conformations which were linked into multidimensional networks through some weak interactions. These three complexes were employed to promote the hydrolytic cleavage of p-nitrophenyl picolinate (PNPP) and p-nitrophenyl acetate (PNPA). Catalytic reactivities of the as-prepared complexes show that in the hydrolysis of p-nitrophenyl acetate (PNPA) these three complexes provide 51, 45, 39-fold rate acceleration as compared to spontaneous hydrolysis of PNPA at pH 7.0, respectively. Under selected conditions, excess three orders of magnitude rate enhancement were observed for the catalytic hydrolysis of another carboxylic ester, p-nitrophenyl picolinate (PNPP). Furthermore, these complexes efficiently promote the PNPA hydrolysis in micellar solution of cetyltrimethylammonium bromide (CTAB) or bis(hexadecylhexmethyl ammonium)ethane bromide (16−6−16) giving rise to excess two orders of magnitude rate enhancement which is approximate 2.0 − 4.0 times higher than that in the buffer. However, the introduction of micelles of n-lauroylsarcosine sodium (LSS) or double-chained C 22/8 surfactant did not increase the rate or even inhibited the hydrolysis reaction in contrast with buffered aqueous medium. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The preparation of a new surface-active sulfonated phosphine and its catalytic performance in aqueous biphasic hydroformylation of long chain olefins were reported. The amphiphilic phosphine: sodium salt of sulfonated n-C12H25O C6H4P(C6H4-p-CH3O)2 (DMOPPS) was prepared by sulfonation of the hydrophobic phosphine DMOPP in concentrated H2SO4 under N2 atmosphere at 30°C for about 5h. The rhodium complex, RhCl(CO)(TPPTS)2 [TPPTS=P(C6H4-m-SO3Na)3], was used as the catalyst precursor. The catalytic active species with the DMOPPS as ligand was in situ formed by adding DMOPPS to the RhCl(CO)(TPPTS)2 catalyst precursor. The surface-activity and micelle-forming property of this new amphiphilic phosphine were confirmed by using cryogenic transmission electron microscope (Cryo-TEM). Under the same conditions, the biphasic hydroformylation of 1-decene using DMOPPS as ligand was compared with that using traditional TPPTS as ligand. The catalysis system using DMOPPS was also compared with the previous Rh-TPPTS-surfactant [C12H25N(CH3)3I (DTAI)] system. Some reaction parameters such as stirring rates, alkyl chain length of olefins, the molar ratio of phosphine/rhodium, and the catalyst recycle were also studied in detail. The results showed that the ligand DMOPPS exhibited a micelle-forming property that could significantly enhance the hydroformylation reaction rate of long chain olefin. Moreover, the surface-active phosphine may also stabilize the aqueous/oil phase boundary, which could enhance the biphasic catalytic reaction rates. [Copyright &y& Elsevier]