Isomerization reaction, cooperative

First Order Chemical Phase Transition in a Cooperative Isomerization Reaction. S convenient model of a first order transition is provided by a reversible isomerization reaction in a macroscopically homogeneous system... 

If the cooperativity is introduced into the rate constant for the reverse reaction via a "mean-field" dependence on Ng, then the equilibrium constant for the isomerization reaction takes the form... 

A Discrete Model of Cooperative Isomerization. The algorithm which implements the method of reactive molecular dynamics (RMD) is understood best in the context of a specific application. Therefore let us specialize now to the simple isomerization reaction (Eq. 2) to address the questions of "chemical nucleation" raised in that context. Only the main ideas are stressed here. 

Fig. 7.11 Reaction profiles for L-catalyzed isomerization of cis-to-trans ML2X2. In (A) an ionic intermediate is favored by a polar solvent. In (B) ion-pair formation arises with a less polar solvent. In (C) a non-polar solvent promotes a 5-coordinated intermediate. In (C), pseudo-rotation occurs. Based on D. G. Cooper and J. Powell, J. Amer. Chem. Soc. 95, 1102 (1973) see also Ref. 90. Reproduced with permission from D. G. Cooper and J. Powell, J. Amer. Chem. Soc. 95, 1102 (1973). (1973) American Chemical Society.

Slow transitions produced by enzyme isomerizations. This behavior can lead to a type of cooperativity that is generally associated with ligand-induced conformational changes . A number of enzymes are also known to undergo slow oligomerization reactions, and these enzymes may display unusual kinetic properties. If this is observed, it is advisable to determine the time course of enzyme activation or inactivation following enzyme dilution. See Cooperativity Bifurcation Theory Lag Time... 

Catalysts such as these are referred to as dual functionar because the platinum and the acid sites are discrete components. They cooperate in promoting the desired over-all reactions, but each appears to be responsible for certain steps. Details of the reaction mechanisms will be discussed later, but the concept of dual functionality can be illustrated by the simple reaction shown in Figure 3. Cyclohexane is dehydrogenated to benzene via cyclohexene. While the second dehydrogenation step is quite rapid, some of the cyclohexene is also trapped on acid sites and isomerized, appearing in the product largely as methyl-cyclopentane. The dual functional nature of the catalyst can be demon-... 

These spaced bimetallic precursors, 6 and 7, are also extremely poor hydroformylation catalysts (1/2-6 tumovers/h, 3 1 linear to branched aldehyde regioselectivity, 50-70% alkene isomerization and hydrogenation side reactions). Complex 7, however, is about three times faster than the monometallic analogs, consistent with Sanger s proposal (vide supra) of some bimetallic cooperativity... 

With methyl oleate, 53% yield of the terminal alcohol was observed. With unmodified internal olefins (2-decene, 2-tridecene, 4-octene), even higher regioselectivities in favor of the terminal alcohol could be achieved l/b up to 12 1). Proof was given that both rhodium and ruthenium complexes catalyze the isomerization-hydroformylation-hydrogenation reaction in a cooperative manner. 

The scope of nitriles for the carbocyanation reaction of alkynes can be expanded by cooperative nickel/Lewis acid catalysis. Alkenyl [80, 81] and alkynyl cyanides [83, 84] also participate in the addition reaction to give highly conjugated nitrile products by nickel/BPh3 catalysis (Scheme 27). The use of aluminum-based Lewis acids causes isomerization of the double bond of alkenylcyanation products, whereas alkynylcyanation is sluggish with the aluminum reagents. 

Some time ago we developed conditions to investigate this system. Conditions were defined for the successful solubilization of integral membrane enzymes, using CHAPS, a zwitterionic detergent, and for reconstituting these enzymes into proteoliposomes (Beyer et al. 1985, Beyer 1985). As it is possible to separate proteins in micellar solution under certain circumstances, it should also be possible to characterize individual enzymes of the sequence by use of the reconstituted system. Problems, however, arise in such a system when a reaction is mediated by more than one enzyme and it will be shown that indeed carotene desaturation proceeds by cooperation of the membrane-integral desaturases with peripheral protein factors. In addition to these problems there are two other crucial points as to the nature of the terminal electron acceptor and - as has also been found -the state of geometrical isomerism of the carotene intermediates. 

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