Kinetics specific catalysis

Specific catalysis by sodium ions is also found in the oxidation of iodide ion by octacyanomolybdate(V) which otherwise shows simple, second-order kinet-ics with E = 5.68 2.57 kcal.mole" and A5 = —39 8.5 eu and /c2 = 3.52+0.13 l.mole sec , at 25.7 °C and fi = 0.1 M. Mo(IV), which is produced stoichiometrically exerts slight retardation upon the reaction. An outer-sphere one-electron transfer is proposed. 

The kinetics and mechanism of the ketone-bisulfite addition were studied by the use of the polarographic technique (Rao Salunke, Reaction Kinetics and Catalysis Letters 26 273, 1984).The specific rate was found to depend on pH. For an equimolar solution of bisulfite and acetone in a deaerated solution of potassium hydrogen phthalate buffer containing potassium iodide as the... 

From the thermodynamic data of Appendix C, show that the product of the reaction of ammonia gas with oxygen would be nitrogen, rather than nitric oxide, under standard conditions and in the absence of kinetic control by, for example, specific catalysis of NO formation by platinum. (Assume the other product to be water vapor.)... 

Kemp elimination was used as a probe of catalytic efficiency in antibodies, in non-specific catalysis by other proteins, and in catalysis by enzymes. Several simple reactions were found to be catalyzed by the serum albumins with Michaelis-Menten kinetics and could be shown to involve substrate binding and catalysis by local functional groups (Kirby, 2000). Known binding sites on the protein surface were found to be involved. In fact, formal general base catalysis seems to contribute only modestly to the efficiency of both the antibody and the non-specific albumin system, whereas antibody catalysis seems to be boosted by a non-specific medium effect. 

FER CATALYSIS GENERAL ACID CATALYSIS GENERAL BASE CATALYSIS HOMOGENEOUS CATALYST HETEROGENEOUS CATALYST INTRAMOLECULAR CATALYSIS MICELLAR CATALYSIS Mich ALT IS-MeNTEN KINETICS PHASE-TRANSFER CATALYSIS PSEUDOCATALYSIS RATE OF REACTION SPECIFIC CATALYSIS. 

The results of the above analysis of reactions involving two proton transfers may be compared with those for reactions in which only a single transfer is kinetically relevant (Sec. III.3.a). For a single transfer the existence of an equilibrium between catalyst and substrate always produces the appearance of specific catalysis by hydrogen or hydroxyl ions, and the detection of general acid-base catalysis therefore excludes... 

After optimizing the assay conditions, including ionic strength, pH, temperature, activator (Ca ) concentration, and polymer concentration, a calibration curve was developed, which allows the lipid substrate concentration to be determined from the fluorescence intensity. The calibration curve allows the enzyme catalysis kinetics parameters (e.g.. Km and Vmax) to be measured. This PLC turn-off assay is effectively inhibited by known inhibitors (F and EDTA), which demonstrates that the sensor relies on the specific catalysis reaction by PLC. It has been demonstrated to be a sensitive (detection limit 0.5nM enzyme concentration), fast (<5 min), and selective (good specificity over phospholipase A and D, and other nonspecific proteins) PLC assay, which can be carried out at very low initial substrate concentration (in the range of micromolar to nanomolar). 

Vedenyapin, A.A., Klabunovskii, E.L, Talanov, Yu.M., and Sokolova, N.P. (1975) Study of the catal5dic and asymmetric activities of Ru-catalysts. Comm. I. Study of the effect of nature of carrier on dispersity and specific catal5dic activity, Kinet Katal. (Kinetics and Catalysis, russ.) 16, 436-442, Chem. Abstr. 1975,83, 58047e, 1976, 84, 4423x. 

The main goal in this chapter is to obtain suitable expressions to represent the kinetics of catalytic processes. Many details of the chemical phenomena are still obscure, and so, just as in Chapter 1, we will only briefly discuss the mechanistic aspects of catalysis. Further details are presented in several books in this area— an entree to this area is provided in books on chemical kinetics and catalysis some texts specifically intended for chemical engineers are by Thomas and Thomas [1], Boudart [2], and a useful brief introduction by Thomson and Webb [3] and a discussion of several important industrial catalytic processes is given in Gates, Katzer and Schuit [62]. For further comprehensive surveys, see Emmett [4] and, for current progress, the series Advances in Catalysis [5],... 

The specific acid is defined as the protonated form of the solvent in which the reaction is being performed. For example, in water the specific acid is hydronium. In acetonitrile, the specific acid is CHaCNHh and in DMSO the specific acid is CHaSOlH )CH3. The specific base is defined as the conjugate base of the solvent. As examples, in water, acetonitrile, and DMSO, the specific bases would be hydroxide, CH2CN, and CH3SOCH2, respectively. These definitions lead to strict definitions for specific catalysis. Specific-acid catalysis refers to a process in which the reaction rate depends upon the sjrecific acid, not upon other acids in the solution. Specific-base catalysis refers to a process in which the reaction rate depends upon the specific base, not upon other bases in the solution. To understand the kinds of reaction mechanisms that would depend only upon the specific add or base, we need to examine some possible mechanisms and the associated kinetic analyses. 

One of the important mechanistic considerations involved in addition and addition-elimination reactions of carbonyl compounds is the precise sequence of events. In particular, a major focus is on whether specific or general catalysis is involved in these reactions. In Chapter 10 we will consistently state whether the reactions are subject to general or specific catalysis. Let s examine the factors under which these various mechanisms operate. Figure 9.13 A shows a two-step process involving nucleophilic addition followed by protonation. The first step is rate-determining. The acid is not part of the kinetic equation, and therefore there is no acid catalysis of any kind, specific or general. This mechanism occurs for strong nucleophiles. As we will see in Chapter 10, the addition of cyanide to an aldehyde is one example. 

The acid-protease from Rhizopus chinensis was first isolated by Fukumoto, Tsuru, and Yamamoto (1). Its optimum pH for catalytic activity was shown to be between 2.9 and 3.3 (1). Although its complete sequence has not yet been determined, some limited sequence data are available - particularly that of the 39 amino-terminal residues (2,3) and of the residues in the immediate vicinity of the catalytically active aspartic acid residues (4,5). These data show that this enzyme has substantial sequence homology with porcine pepsin. Investigations of the kinetics of catalysis (6,7) have led to proposals of an extended subsite specificity. 

Let us now consider deactivation for the reaction mechanism that obeys Michaehs-Menten kinetics, specific for enzymatic catalysis. 

The role that acid and base catalysts play can be quantitatively studied by kinetic techniques. It is possible to recognize several distinct types of catalysis by acids and bases. The term specie acid catalysis is used when the reaction rate is dependent on the equilibrium for protonation of the reactant. This type of catalysis is independent of the concentration and specific structure of the various proton donors present in solution. Specific acid catalysis is governed by the hydrogen-ion concentration (pH) of the solution. For example, for a series of reactions in an aqueous buffer system, flie rate of flie reaction would be a fimetion of the pH, but not of the concentration or identity of the acidic and basic components of the buffer. The kinetic expression for any such reaction will include a term for hydrogen-ion concentration, [H+]. The term general acid catalysis is used when the nature and concentration of proton donors present in solution affect the reaction rate. The kinetic expression for such a reaction will include a term for each of the potential proton donors that acts as a catalyst. The terms specific base catalysis and general base catalysis apply in the same way to base-catalyzed reactions. 

Specific acid catalysis is observed when a reaction proceeds through a protonated intermediate that is in equilibrium with its conjugate base. Because the position of this equilibrium is a function of the concentration of solvated protons, only a single acid-dependent term appears in the kinetic expression. For example, in a two-step reaction involving rate-determining reaction of one reagent with the conjugate acid of a second, the kinetic expression will be as follows ... 

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