Interfacial catalysis

In this treatment of interfacial catalysis we adopt the following model  

In this model it is assumed that the rate-limiting (slow) step in the reaction is still the breakdown of substrate to product. We also treat enzyme interfacial binding as an equilibrium process that can be described by an equilibrium dissociation constant ( J). We also assume that once the 

As discussed previously, the rate equation for the formation of product, the dissociation constants for enzyme-interface and enzyme-substrate complexes, and the enzyme mass balance are, respectively. 

Normalization of the rate equation by total enzyme concentration v/ Et ) and rearrangement results in the following expression for the velocity of a reaction catalyzed by an interfacial enzyme  

a velocity versus substrate concentration (a) plot is still a rectangular hyperbola (Fig. 10.3). It is informative to explore the effects of the 

The observed extraction rate constants linearly depended on both the metal ion concentration [M +] and the hydrogen ion concentration in the aqueous phase. However, the observed extraction rate constant (k ) did not decrease with an increase in the distribution constant ( Tq) of the ligand as was expected from the mechanism in the aqueous phase. Furthermore, the HSS method revealed that the dissociated form of the n-alkyl-dithizone was adsorbed at the interface generated by vigorous stirring [5]. The following scheme was proposed based on the experimental results, considering both the aqueous 

A criterion of the interfacial reaction in the chelate extraction was that the interfacial ligand concentration had to follow an adsorption isotherm. This was proved in the extraction systems of Ni(II) with 2-hydroxy oxime such as 5-nonylsalicylaldehyde oxime (P50) [31], 2-hydroxy-5-nonylacetophenone oxime (SME529) [32] and 2 -hydroxy-5 -nonylbenzophenone oxime (LIX65N) [33]. These extractants were adsorbed at the interface in their neutral forms, obeying the Langmuir isotherm  

The adsorption constants (K ) of the neutral forms were all of the order of 10 cm and the complexation rate constants of the dissociated form with the Ni(II) ion at the interface were of the order of 10 M s for the three extractants, whereas the 

TABLE 10.2. Kinetic parameters obtained in the adsorption and extraction of Ni(II) and Cu(II) with 2-hydroxy oxime in heptane/0.1 M(H,Na)C104 solution at 25°C. 

The dynamic behaviour of the 2-hydroxy oxime and its adsorptivity at the interface were well depicted by the molecular dynamics (MD) simulations [34]. It was revealed that the polar groups of —OH and =N—OH of the adsorbed 2-hydroxy oxime molecule were accommodated in the aqueous phase side so as to react with the Ni(II) ion in the aqueous phase [35]. This was thought to explain that the magnitude of the reaction rate constants of Ni(II) at the heptane/water interface and that in the aqueous phase were similar to each other. The diffusive and adsorptive behaviour of LIX65N around the interface was also simulated for 1 ns. The molecule was active around the interfacial region, moving 

formation rate constant in bulk aqueous phase + Lj ML+ k, interfacial formation rate constant. 

It has been found [117] that polyethylene glycol (PEG) produces a strong catalytic effect during the reaction of butyl bromide with KI. The yield of the butyl iodide product increases linearly with an increase in the length of the PEG chains. A similar acceleration of the reaction between solid potassium phenolate and 1-bromobutane is observed in toluene in the presence of oligoethylene glycols [178]. The synthesis of 8 esters based on alcohols and phenols in two-phase system liquid-liquid catalyzed by PEG is discussed [178a]. 

Fluorescence was to study the reaction of 5-dimethyl-amino-l-naphthalenesulfonyl chloride (dansyl chloride) with butylamine in ethyl acetate and chloroform at 60° and 40 °C, respectively. This study was conducted in the presence of polystyrene and polyoxyethylene (POE) as cosolvents as well as their respective low-molecular weight analogues, namely toluene and diethyloxyethane, respectively [180]. 

The interaction of mono- and dihalo benzenes with alkoxy ions is accelerated by the presence of polyethylene glycols which act as interfacial catalysts [182]. The percentage of conversion ( ) of CI2C6H4 in the absence of catalysts but in the presence of PEG with the weight-average molecular weight (A/w) of 150,1000,6000, 8000 and 2-10 and at 140-150°C and 6h reaction time, is 7.1, 8.2, 20.1, 33.0 and 28.1%, respectively. Bromobenzenes are more reactive than dichlorobenzenes. In the presence of PEG with Mif/ = 6000, the conversion values are 71.5 and 33.0%, respectively. The effectiveness of alkoxylation depends on the alcohol type and decreases in the sequence primary secondary tertiary. The values for 0-CI2C5H4 esteriflcation of methyl, isopropyl and rert-butyl alcohols, in the presence of a catalyst with Mvv = 8000 at 150°C and 6h reaction time are 66.0, 13.5, and 5.1%, respectively. 

Furthermore, the hydrolysis of butyl acetate and methyl pivalate in benzene in the presence of KOH at 25 °C as well as the reaction of potassium phenolate with benzyl chloride in boiling acetonitrile are accelerated by addition of polyoxyethylene [183]. The catalytic effect of POE is augmented by an increase in the number of oxyethylene units, i.e. 1 6 12. PEO is also an interfacial catalyst of the reaction of phenol and 2,4,6-trimethylphenol with methyl iodide in water-chloroform and dichloromethane. The kinetic study of the reaction between benzyl chloride and potassium acetate in the presence of PEO of variable molecular weight in toluene and butanol has been performed with IR spectroscopy [184]. The dissolution of a reagent of poor solubility is apparently a rate-limiting step of the reaction in a solution of low polarity (toluene). The presence of PEO impurities in toluene has been detected. Moreover, effect of PEO and crown ethers as phase transfer catalysts has been compared. In a low-polarity solvent, oligoethylene oxides are more effective catalysts, while in a polar solvent (butanol) the effectiveness of PEO and crown ethers as phase transfer catalysts is similar. 

The effect of the concentration of interfacial transfer catalysts in aprotic solvents in contact with solid salts (sodium 2,4-dinitrophenolate) has been investigated with regard to their effectiveness for reaching the solid-liquid equilibrium in benzene, chlorobenzene, dichloromethane and acetonitrile at 25 °C [185], Polyethylene glycols with 300, 600 and 2000 mol. wt., trianthrylmethylammonium chloride, dodecyldi-methylammonium chloride, tetrabutylammonium chloride and a crown ether, have 

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From the fundamental knowledge concerning the interfacial complexation mechanism obtained from the kinetic studies on chelate extraction, ion-association extraction, and synergistic extraction, one can design the interfacial catalysis. The main strategy is to raise the concentration of the reactant or intermediate at the interface. 

In the mechanism of an interfacial catalysis, the structure and reactivity of the interfacial complex is very important, as well as those of the ligand itself. Recently, a powerful technique to measure the dynamic property of the interfacial complex was developed time resolved total reflection fluorometry. This technique was applied for the detection of the interfacial complex of Eu(lII), which was formed at the evanescent region of the interface when bathophenanthroline sulfate (bps) was added to the Eu(lII) with 2-thenoyl-trifuluoroacetone (Htta) extraction system [11]. The experimental observation of the double component luminescence decay profile showed the presence of dinuclear complex at the interface as illustrated in Scheme 5. The lifetime (31 /as) of the dinuclear complex was much shorter than the lifetime (98 /as) for an aqua-Eu(III) ion which has nine co-ordinating water molecules, because of a charge transfer deactivation. 

Pacific Northwest National Laboratory, Institute for Interfacial Catalysis,... 

Alexander, G. Volkov. Interfacial Catalysis, Marcel Dekker (2003). 

Okada S, Jelinek R, Charych D (1999) Induced color change of conjugated polymeric vesicles by interfacial catalysis of phospholipase A(2). Angew Chem Int Ed 38 655-659... 

Selected entries from Methods in Enzymology [vol, page(s)] Add-base catalysis [with site-directed mutants, 249, 110-118 altered pH dependencies, 249, 110] commitment to [in determination of intrinsic isotope effects, 249, 343, 347-349 in interfacial catalysis, 249, 598-599 equilibrium isotope exchange in, 249, 443-479 hydrogen tunneling in, 249, 373-397] interfacial [competitive inhibitors, kinetic characterization, 249, 604-605 equilibrium parameters, 249, 587-594 forward commitment to, 249, 598-599 interpretation, 249, 578-586 (constraining variables for high processivity, 249, 582-586 kinetic variables at interface,... 

MICELLAR SUBSTRATES. Phospholipids in micelles are frequently found to be more active substrates in lipolysis than those phospholipids residing in a lipid bilayer". Dennis first described the use of Triton X-100 to manipulate the amount of phospholipid per unit surface area of a micelle in a systematic analysis of the interfacial interactions of lipases with lipid micelles. Verger and Jain et al have presented cogent accounts of the kinetics of interfacial catalysis by phospholipases. The complexity of the problem is illustrated in the diagram shown in Fig. 2 showing how the enzyme in the aqueous phase can bind to the interface (designated by the asterisk) and then become activated. Once this is achieved, E catalyzes conversion of S to release P. ... 

This broad class of hydrolases constitutes a special category of enzymes which bind to and conduct their catalytic functions at the interface between the aqueous solution and the surface of membranes, vesicles, or emulsions. In order to explain the kinetics of lipolysis, one must determine the rates and affinities that govern enzyme adsorption to the interface of insoluble lipid structures -. One must also account for the special properties of the lipid surface as well as for the ability of enzymes to scooC along the lipid surface. See specific enzyme Micelle Interfacial Catalysis... 

O Connor CJ. Interfacial catalysis by microphases in apolar media. Surfactant Sci Ser 1987 21 187-255. 

Jelinek R, Okada S, Norvez S, Charych D. Interfacial catalysis by phosphohpases at conjugated lipid vesicles colorimetric detection and NMR spectroscopy. Chem Biol 1998 5 619-629. 

Chaudhari, R.V., Bhanage, B.M., Deshpande, R.M. and Delmas, H. (1995) Enhancement of interfacial catalysis in a biphasic system using catalyst-binding ligands. Nature, 373, 501. 

Refs. [i] Volkov AG (1989) Bioelectrochem Bioenerg21 3 [ii] Volkov AG (2002) Biocatalysis Electrochemical mechanisms of respiration and photosynthesis. In Volkov AG (ed) Interfacial catalysis. MarcelDekker, New York... 

Interfacial catalysis of formation and dissociation of lanthanide complexes [83].539... 

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. 

In addition to the analysis of dynamic disorder, single-molecule approaches have the unique potential to reveal a number of processes that cannot be observed at the ensemble level. In the following, we wish to provide examples of how experiments with single enzymes can be extended beyond studies of dynamic disorder. We will show that single-molecule studies can identify rare events of enzyme inactivation, investigate cascade reactions, and determine the mechanism of interfacial catalysis at a phospholipid membrane. 

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