Micelles oxidation catalyst

The enzyme cholesterol oxidase is an effective oxidation catalyst when used in a micellular system involving scCC>2 and water [25], The use of a perfluoropoly-ether-based surfactant causes the formation of reverse-micelles in which the... 

Yuasa M, Masaki T, Kida T, Shimanoe K, Yamazoe N (2009) Nano-sized PdO loaded SnO nanoparticles by reverse micelle method for highly sensitive CO gas sensor. Sens Actuators B 136 99-104 Zhang J, Colbow K (1997) Surface silver clusters as oxidation catalysts on semiconductor gas sensors. Sens Actuators B 40 47-52... 

We have been developing methods to prepare and characterize supported attune catalysts nsing readily available commercial snpports. One potential means of depositing amines on oxide surfaces is shown in Scheme 38.1, in which the micelle s role is to space the amines on the snrface. Cnrrent work is directed towards characterizing these samples, particularly applying flnorescence resonance energy transfer (FRET) techniques. 

Figure 11.8 Formation of ordered nanoparticles of metal from diblock copolymer micelles, (a) Diblock copolymer (b) metal salt partition to centres of the polymer micelles (c) deposition of micelles at a surface (d) micelle removal and reduction of oxide to metal, (e) AFM image of carbon nanotubes and cobalt catalyst nanoparticles after growth (height scale, 5 nm scan size, lxl pm). [Part (e) reproduced from Ref. 47].

HTAB has been used, on the one hand, to increase the CL intensity of the reaction of 2,6,7-trihydroxy-9-(4 chlorophenyl)-3-fluorene with hydrogen peroxide in alkaline solution, in the presence of traces of Co(II) as a catalyst [43]. As a consequence, a CL method has been established for determination of ultratraces of Co(II). On the other hand, HTAB micelles sensitize the CL oxidation of pyro-gallol with A-bromosuccimide in an alkaline medium [44], while anionic and nonionic surfactants inhibit the CL intensity of this reaction (Table 3). This sensitized process allows the determination of pyrogallol by flow injection in an interval of 5 X 10 7-3 X 10 5 M. 

The CL system luminol-hydrogen peroxide was characterized by Hoshino and Hinze in HTAC reversed micelles, formed in a 6 5 (v/v) chloroform-cyclohexane mixture [63], The results indicate that such a CL system can be used from an analytical point of view in a pH interval of 7.8-9.0 without the need to add a catalyst or a co-oxidant. In these conditions an analytical method was established for determination of hydrogen peroxide that, apart from supplying much milder conditions compared to the usual situation in an aqueous medium, is also acceptably precise and reproducible. 

The metal-catalysed autoxidation of alkenes to produce ketones (Wacker reaction) is promoted by the presence of quaternary ammonium salts [14]. For example, using copper(II) chloride and palladium(II) chloride in benzene in the presence of cetyltrimethylammonium bromide, 1-decene is converted into 2-decanone (73%), 1,7-octadiene into 2,7-octadione (77%) and vinylcyclohexane into cyclo-hexylethanone (22%). Benzyltriethylammonium chloride and tetra-n-butylammo-nium hydrogen sulphate are ineffective catalysts. It has been suggested that the process is not micellar, although the catalysts have the characteristics of those which produce micelles. The Wacker reaction is also catalysed by rhodium and ruthenium salts in the presence of a quaternary ammonium salt. Generally, however, the yields are lower than those obtained using the palladium catalyst and, frequently, several oxidation products are obtained from each reaction [15]. 

Thus, C14MV2- quenches the excited state of [Ru(bipy)3]2+ with a rate constant fcq = 8 x 10s mol-1 dm3 s-1 and this is unaffected by cetyltrimethylammonium chloride (CTAC), up to concentrations of 5 x 10-2 mol dm-3, indicating that mixed CTAC/C14MV2- micelles are not formed.139 In the absence of CTAC, kb in this system is 4x 109 mol-1 dm3 s-1, but flash photolysis showed that this drops to kb s2x 107 mol-1 dm3 s-1 in micellar solution. Thus, the more hydro-phobic radical cation, C14MV+, is solubilized by CTAC micelles, which, having a positive surface, do not allow approach of the oxidized [Ru(bipy)3]3C This then gives an efficiency of 30% for the redox reaction. This study was extended by the removal of the CTAC from solution and the introduction of a Pt catalyst protected by a positively charged polysoap.138 This work is described in Section 61.5.4.7.2. 

An important group of surface-active nonionic synthetic polymers (nonionic emulsifiers) are ethylene oxide (block) (co)polymers. They have been widely researched and some interesting results on their behavior in water have been obtained [33]. Amphiphilic PEO copolymers are currently of interest in such applications as polymer emulsifiers, rheology modifiers, drug carriers, polymer blend compatibilizers, and phase transfer catalysts. Examples are block copolymers of EO and styrene, graft or block copolymers with PEO branches anchored to a hydrophilic backbone, and star-shaped macromolecules with PEO arms attached to a hydrophobic core. One of the most interesting findings is that some block micelle systems in fact exists in two populations, i.e., a bimodal size distribution. 

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