Induced catalysis

According to the authors mentioned above, induced chain reactions (Livingston ) or induced catalysis (Bray and Ramsey ) take place when the very slow reaction between the acceptor and actor is catalyzed by the inductor. However, since the chemical characters of the acceptor and the inductor are the same, the actor reacts with the inductor, too, thus a part of it will be excluded from the catalysis. The principal characteristics of reactions of this type according to Luther and Schilow are that the value of Fj largely exceeds 2 and that the plot of Fj rm 5([Ac]/[I])o rises exponentially. 

From the above it is obvious that merely the magnitude of the numerical value of Fj and the shape of the plot of Fj versus ([Ac]/[I])o do not make it possible to classify induced reactions correctly. It is necessary to learn more about the mechanism of induced reactions. The schemes presented show clearly that a genuine coupled reaction can be regarded as an open-chain, and an induced catalysis as a closed-chain reaction. However, these limiting types of reactions occur only rarely. 

An additional example of cycloamylose-induced catalysis which can probably be attributed to a microsolvent effect is the oxidation of a-hy-droxyketones to a-diketones (Scheme VIII). The rate of this oxidation is accelerated by factors ranging from 2.1 to 8.3 as the structure of the substrate is varied. As noted by Cramer (1953), these accelerations may be attributed to a cycloamylose-induced shift of the keto-enol equilibrium to the more reactive enol form. 

Recently, an example of cycloamylose-induced catalysis has been presented which may be attributed, in part, to a favorable conformational effect. The rates of decarboxylation of several unionized /3-keto acids are accelerated approximately six-fold by cycloheptaamylose (Table XV) (Straub and Bender, 1972). Unlike anionic decarboxylations, the rates of acidic decarboxylations are not highly solvent dependent. Relative to water, for example, the rate of decarboxylation of benzoylacetic acid is accelerated by a maximum of 2.5-fold in mixed 2-propanol-water solutions.6 Thus, if it is assumed that 2-propanol-water solutions accurately simulate the properties of the cycloamylose cavity, the observed rate accelerations cannot be attributed solely to a microsolvent effect. Since decarboxylations of unionized /3-keto acids proceed through a cyclic transition state (Scheme X), Straub and Bender suggested that an additional rate acceleration may be derived from preferential inclusion of the cyclic ground state conformer. This process effectively freezes the substrate in a reactive conformation and, in this case, complements the microsolvent effect. 

When a reaction influences the rate of some other reaction which does not occur under ordinary conditions, the phenomenon is called induced catalysis. For example... 

Tas, A., Plasma Induced Catalysis, Ph.D. dissertation, Technische Universiteit Eindhoven, The Netherlands (1995). 

ZACHEIS, G. A., GRAY, K. A., KAMAT, P. V., Radiation-Induced Catalysis on Oxide Surfaces Degradation of Hexachlorobenzene on y-Irradiated Alumina Nanoparticles , J. Phys. Chem. B 1999,103, 2142-2150. 

Tas. M. A. Plasma-induced catalysis A feasibility study and fundamentals Eindhoven University of Technology 1995 Ph.D. Dissertation... 

The attachment of a pyridinium cation as an electron acceptor unit between the photosensitizer and catalyst units (31) did not induce catalysis (TNco < 1)> and the TN remained lower than that of the mixed system of the corresponding model complexes, 16 and 24 (TNco = 2) [41]. 

The induced catalysis by NPs is showing special interest in the DNA biosensing technology. The application of NPs as catalysts in DNA detection systems is related to the decrease of overpotentials of the involved redox species including also the catalyzed reduction of other metallic ions used in labeling-based h34)ridization sensing. Although the most exploited materials in catalysis are the metals... 

The topics discussed in the book include electrochemical detection of DNA hybridization based on latex/gold nanoparticles and nanotubes nanomaterial-based electrochemical DNA detection electrochemical detection of microorganism-based DNA biosensor gold nanoparticle-based electrochemical DNA biosensors electrochemical detection of the aptamer-target interaction nanoparticle-induced catalysis for DNA biosensing basic terms regarding electrochemical DNA (nucleic acids) biosensors screen-printed electrodes for electrochemical DNA detection application of field-effect transistors to label-free electrical DNA biosensor arrays and electrochemical detection of nucleic acids using branched DNA amplifiers. 

Compared with chiral nonracemic a-amino carbonyl compounds - which are not suitable substrates for MBH reaction, mainly due to their racemization under normal conditions after prolonged exposure times to catalyst or due to poor diastereoselectivity " a-keto lactams, enantiopure 3-oxo-azetidin-2-ones 168, readily react with various activated vinyl systems promoted by DABCO to afford the corresponding optically pure MBH adducts 169 without detectable epimerization (Scheme 1.69). " However, the Lewis acid-mediated reaction of electron-deficient alkynes with azetidine-2,3-diones 168 as an entry to p-halo MBH adduets was not very sueeessful the coupling product 170 was achieved with concomitant acetonide cleavage as a single ( )-isomer in low yield, in the presence of trimethylsilyl iodide under BF3 OEt2-induced catalysis (Scheme 1.69). 

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