Synergism, kinetic

Studies on enzyme kinetics, substrate specificity and synergism... 

Sojo MM, Nunez-Delicado E, Sanchez-Ferrer A and Garcia-Carmona F. 2000. Oxidation of salsolinol by banana pulp polyphenol oxidase and its kinetic synergism with dopamine. J Agric Food Chem 48(11) 5543-5547. 

Synergism increases when oxidation occurs in air at p02 20 kPa. The kinetic scheme of... 

The first term represents the classic unicyclic rhodium catalysis, while the second indicates a hydride attack on an acyl species. These spectroscopic and kinetic results strongly suggested the presence of bimetallic catalytic binuclear elimination as the origin of synergism of both metals rather than cluster catalysis. This detailed evidence for such a catalytic mechanism, and its implications for selectivity and nonlinear catalytic activity illustrate the important mechanistic knowledge that can be revealed by this powerful in situ spectroscopic technique. 

The intrinsic properties of the lanthanide elements guarantee promising applications in the fields of catalysis and material science. How to cope with these features on a molecular level and under anaerobic conditions is discussed, including thermodynamic and kinetic considerations. Due to the importance of a prolific metal/ligand synergism, current developments in ligand design are emphasized. 

Because of their importance in pesticide manufacturing, chlorophe-nols are one of the most studied types of phenols. Thus, Esplugas et al. [142] studied the direct photolysis of p-chlorophenol with a 250-W, medium-pressure vapor arc lamp with and without ozone. They followed the process of mineralization from total organic carbon (TOC) data. They observed that UV photolysis hardly affected the process (5% mineralization after 30 min). When ozone was fed in at a mass flow of 23 mg/min under similar conditions, they observed almost complete mineralization. The synergism between ozone and UV light was also much more effective than ozonation alone, which, under the same operating conditions, resulted in roughly 45% mineralization. For kinetic purposes, they assumed a first-order reaction for both ozonation and UV photolysis of TOC. For the latter, they used the linear spherical model to define the radiation field inside the photoreactor. 

A typical kinetic synergism has been observed for the catalytic effect of iV,iV-dimethyl-4-(2-pyridylazo)aniline (PADA) on the extraction of Ni(pan)2 [72], The extraction rate of Ni(pan)2 into toluene is very slow even under an HSS condition. Whereas, the addition of PADA at the diluted concentration as 10-5M can accelerate the extraction rate about 10 times. The observed extracted species was only Ni(pan)2 and no net consumption of PADA was observed after the extraction, while a significant interfacial adsorption of PADA was observed during the extraction under the HSS condition as shown in Fig. 19. These results were analyzed by the mechanism of the interfacial ligand-substitution reaction ... 

Kinetic evidence for synergic adsorption of carbon monoxide and water on the low-temperature shift catalyst Cu/ZnO/Fe203 was obtained by van Herwijnen and deJong (113), and IR spectra of surface formate were detected on several oxide catalysts, including CuO/MgO, at temperatures as low as 20 JC and pressures of 20 Torr, as reported by Davydov et al. (104). Decomposition of the surface formate to C02 and H2 occurred at 100-150°C over the Cu/MgO catalyst and at 250 300°C over the MgO catalyst, and the promotion effect of copper was attributed to the formation and decomposition of a labile surface formate (HCOO)2Cu. Ueno et al. (117) have shown earlier that surface formates are formed on zinc oxide, from CO and H20 as well as from C02 and H2, and hence an associative mechanism of the shift and reverse-shift reaction, involving formate intermediate, is believed to operate on many oxide catalysts. 

Kinetic synergism of calcium and zinc with phytate causes a complexatlon less soluble than either separately. Saliva and pancreatic fluid secrete large quantities of zinc equivalent to as much as three times the dietary intake which is also vulnerable to phytate complexatlon. The mechanism of phytate action in the gastrointestinal tract is related to complexatlon and subsequent prevention of absorption and reabsorption of zinc. The complexatlon can be equated to a phytate zlnc molar ratio and the relative hazard may be subsequently estimated from such data. 

In in vivo experiments, the correlation between the radioprotecting activity and antiradical properties of synthetic antioxidants was determined [14, 15]. Kinetic studies on natural antioxidants - vitamins were carried out their constants as inhibitors of radical processes were determined [16, 17]. In the works by Khrapova et al., the chemiluminescence method adapted to studies on bioantioxidants in lipids was used with this method, the problems of synergism and anthagonism of synthetic and natural antioxidants were studied and the antioxidant system in membrane lipids was characterized as a whole [18]. 

A typical kinetic synergism in the extraction of metal ions was reported for the Ni(II)-dithizone(Hdz)-phen chloroform system [47]. The extraction equilibrium constant (log Xex) was enhanced from —0.7 to 5.3 upon the addition of phen ... 

The catalytic role of die interface was recognized in various liquid/liquid extraction systems. Interfacial adsorption of reactants was the key step in the interfacial catalysis in the extraction of metal ions. The interfacial ligand-substitution mechanism has great importance in the kinetic synergism. Some essential guidelines proposed here are highly useM, not only in solvent extraction but also in interfacial synthesis. 

Finally, the weight of evidence from kinetic studies appears to support the point of view that the addition of Mn(II), glucose, and a-lactalbumin to galactosyltransferase, prior to the expression of enzymatic activity, is governed by random synerg istic binding with galactosyltransferase. 

Ion-molecule reactions and reactions of neutral species in the gas phase have much in common. Nevertheless, because different communities were concerned, theories of the kinetics of these processes have often been developed separately, missing the chances for synergism and tor more rapid progress. Fortunately, this unsatislactoiy situation is changing and the common aspects, but also the characteristic differences are becoming identified more clearly. 

In view of this need, we discuss here a variety of electrocatalytic topics, ranging from basic and microscopic concepts to phenomenological principles. Thus, the origin of electrodic reactions, electrosorption, and electrode kinetics are introduced briefly for the benefit of the nonelectrochemist. Since electrocatalytic reactions take place at the electrode surface, attention is given to recent efforts to link catalyst activity with microscopic surface properties. These include surface crystallographic orientation, crystallite size and distribution, adsorbate-adsorbent-support synergism, multiple adsorption states, identification of surface intermediates, and electrocatalytic surface reaction mechanisms. 

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