Acceptors, primary reaction between

Induced chain reactions occur when the very slow reaction between acceptor and actor is catalyzed by the inductor. Actually it means that primary reaction between actor and inductor induces a chain reaction between actor and acceptor. That is why this group of reactions is called induced chain reactions. 

The primary reaction between good donor solvents, such as Tetralin and octahydrophenanthrene, and acceptors can give rather "ideal" products. For example, at moderate dibenzyl acceptor concentrations (10-20%) dibenzyl is converted only to toluene in these solvents. However, when poor solvents are introduced, secondary reactions become quite important and "non-ideal" products are recovered. The type of secondary... 

Thus, Ip (inductor peroxide, primary oxide) derived from I d is converted by Ac d into the end-product, I(,x, which is inactive regarding the induction, i.e. coupling cannot turn into catalysis. Moreover, since there are several consecutive steps, and since the direct reaction between actor and acceptor is very slow, it follows that the value of Fj will not be changed by altering the ratio, ([Ac]/[I])o. However, in most cases studied the function Fj = /(Ac/I)q attains a limiting value, or at least varies therefore it has to be concluded that Manchot s concept cannot be maintained in its original form. 

In fact, in the latter case, the catalyst (injected into the system with initial reagents) only speeds up interaction between the IP of the primary reaction and the acceptor. Therefore, D < v and, consequently, chemical conjugation takes place. This means that no matter how the reaction between the acceptor and the IP is intensified by the catalyst, the induction factor (the determinant) may not exceed v. When analyzing conjugated catalytic reactions, it should be taken into account that the amount of acceptor involved in the reaction may be significantly increased by application of a catalyst in both conjugated reactions. 

In the present state of our knowledge two electron acceptors are implicated between P-700 and the bound iron-sulfur centres. They are named Aq and Aj because they have not been chemically identified. The first evidence for the existence of these acceptors came from kinetic absorption studies, under conditions where Fx (or A2) was reduced or inactive [37,39]. An important development resulted from the discovery of a spin-polarized triplet state [21,22] and the hypothesis of its formation as a result of a back-reaction between P-700" and a reduced primary acceptor. The analysis of the triplet signal versus the extent of reduction of the acceptors [43,44] led to the present hypothesis of two acceptors, Aq and Aj, arranged sequentially. 

A laser flash photolytic study of the reaction between 2,2 -dipyridyl and tryptophan has been described. The primary photochemical step has been demonstrated to be pH independent and involves an electron transfer from the tryptophan to the dipyridyl triplet state. The triplet excited state of some peptide conjugates is produced on irradiation by a nanosecond laser flash. C-C Bond cleavage is the result of irradiation of the pinacols (214) in chloroform. This yields the corresponding aldehydes. The mechanism of the cleavage process has been shown to involve single electron transfer with chloroform as the electron acceptor. A study of intramolecular charge separation in aminophenyl(phenyl)acetylene and A, A-dimethylaminophenyl(phenyl)-acetylene has been reported. ... 

WW Parson (1969) The reaction between primary and secondary eiectron acceptors in bacteriai photosynthesis. Biochim Biophys Acta 189 384-396... 

Fig. 5. Schematic of the primary events of bacterial photosynthesis. An approximate redox scale is shown on the left. The numbers above the arrows are the rate constants for the electron transfer reactions between the components. P is the photoactive bacteriochlorophyll a. 1 is the intermediate acceptor believed to be bacteriopheophytin a. The Q s are ubiquinone molecules.

A particularly difficult situation arises when combining in the same reaction the use of these rather unreactive acceptors such as enones with the incorporation of ketones as Michael donors in which the formation of the intermediate enamine by condensation with the amine catalyst is much more difficult. For this reason, the organocatalytic Michael addition of ketones to enones still remains rather unexplored. An example has been outlined in Scheme 2.22, in which it has been shown that pyrrolidine-sulfonamide 3a could catalyze the Michael reaction between cyclic ketones and enones with remarkably good results, although the reaction scope was exclusively studied for the case of cyclic six-membered ring ketones as nucleophiles and 1,4-diaryl substituted enones as electrophiles. In this system the authors also pointed toward a mechanism involving exclusively enamine-type activation of the nucleophile, with no contribution of any intermediate iminium species which could eventually activate the electrophile. Surprisingly, the use of primary amines as catalysts in this transformation has not been already considered. 

Equilibrium constants between redox carriers are easily computed from their midpoint potentials, determined by conventional redox titrations. Equilibrium constants may be also determined in situ by measuring the redox state of the carriers, either in the dark or in conditions where the rate of the photosynthetic process is light-limited. Surprisingly enough, the value of the apparent equilibrium constants of electron transfer reactions between the primary PSII acceptor and the primary PSI donor measured in the absence of mediators [1,2] was found much lower than expected from the redox potential titrations. The equilibrium constants were slowly increasing during a dark adaptation of several minutes. No satisfying interpretation has been proposed for these paradoxical results. 

Fo to P have attributed the I-D transient to oxidation of the primary quinone electron acceptor by an electron acceptor/ probably located between and the plastoquinone pool (B). Fig.2A shows a decrease in the rate of rise of fluorescence from Fo to P indicating a decrease in the rate of reduction. This could be explained by a weaker association of the antenna with the PSII reaction centre. It could also be a result of migration of LHC from the appressed grana region to the non appressed stroma lamellae resulting from statel-statell transitions. 

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