Gated reactions

We recently examined a two-state case that represents the simplest model for any gated reaction [10a, b]. Consider a donor-acceptor pair, [d, a], as part of a system that exhibits two conformations, B(boat) and C(chair). For concreteness, we may imagine d and a as attached at the 1,4 positions on a cyclohexane ring the same formal situation will be realized in far more interesting ways with protein complexes. In this case, each of the three system states shown in Scheme... 

Guzman, J. and B. C. Gates, Reactions of Au(CH3)2(acac) on Y-AI2O3 Characterization of the Surface Organic, Organometallic, Metal Oxide and Metallic Species , Langmuir (2003), 19, 3897-03. 

A wide range of reactions of polar compounds was claimed to be catalysed by zeolites of high Si02/Al203 ratio, such as de-aluminated mordenite and HZSM-5. The liquid-phase dehydration of t-butanol catalysed by H-mordenite was studied by Ignace and Gates.Reaction took place within the pore structure and was hindered by the difficulty of transport of reactant, product, and diluent molecules. Barrer and Oei found that ethylvinyl, n-butylvinyl, and isobutylvinyl ethers all react readily over H-mordenite near room temperature... 

Northrop, S. H. McCammon, J. A. (1984). Gated reactions. Journal of the American Chemical Society, 106,930-4. 

In certain enzyme-substrate encounters the reactivity of the enzyme may vary with time. This may be due to a necessary conformational change or the movement of flexible loops acting as trapdoors at the entrance of the active site. Simulation of these gated reactions can be studied implicitly and explicitly using Brownian dynamics methods. Implicitly, the dynamics of the gate can be described by the rate constants... 

Wlren the door is open, the optimal net flux into the store isgiven by equation (C2.14.7). It may be that the stochastically gated diffusion treated by Szabo et aJ [47], see also [48] is a good representation of typical biological storage reactions (C2.14.8). 

Szabo A, Shoup D, Northrup S H and McCammon J A 1982 Stochastically gated diffusion-influenced reactions J. Chem. Phys. 77 4484-93... 

Our discussion of chemical reactions of alkadienes will be limited to those of conju gated dienes The reactions of isolated dienes are essentially the same as those of individual alkenes The reactions of cumulated dienes are—like their preparation— so specialized that their treatment is better suited to an advanced course m organic chemistry... 

A steroid very closely related structurally to cholesterol is its 7 dehydro derivative 7 Dehydrocholesterol is formed by enzymatic oxidation of cholesterol and has a conju gated diene unit m its B ring 7 Dehydrocholesterol is present m the tissues of the skin where it is transformed to vitamin D3 by a sunlight induced photochemical reaction... 

The PSII complex contains two distinct plastoquiaones that act ia series. The first is the mentioned above the second, Qg, is reversibly associated with a 30—34 kDa polypeptide ia the PSII cote. This secondary quiaone acceptor polypeptide is the most rapidly tumed-over proteia ia thylakoid membranes (41,46). It serves as a two-electron gate and connects the single-electron transfer events of the reaction center with the pool of free... 

Current research aims at high efficiency PHB materials with both the high speed recording and high recording density that are required for future memory appHcations. To achieve this aim, donor—acceptor electron transfer (DA-ET) as the hole formation reaction is adopted (177). Novel PHB materials have been developed in which spectral holes can be burnt on sub- or nanosecond time scales in some D-A combinations (178). The type of hole formation can be controlled and changed between the one-photon type and the photon-gated two-photon type (179). 

In the post-World War II years, synthesis attained a different level of sophistication partly as a result of the confluence of five stimuli (1) the formulation of detailed electronic mechanisms for the fundamental organic reactions, (2) the introduction of conformational analysis of organic structures and transition states based on stereochemical principles, (3) the development of spectroscopic and other physical methods for structural analysis, (4) the use of chromatographic methods of analysis and separation, and (5) the discovery and application of new selective chemical reagents. As a result, the period 1945 to 1960 encompassed the synthesis of such complex molecules as vitamin A (O. Isler, 1949), cortisone (R. Woodward, R. Robinson, 1951), strychnine (R. Woodward, 1954), cedrol (G. Stork, 1955), morphine (M. Gates, 1956), reserpine (R. Woodward, 1956), penicillin V (J. Sheehan, 1957), colchicine (A. Eschenmoser, 1959), and chlorophyll (R. Woodward, 1960) (page 5). ... 

In 1960, Dann, Chiesa and Gates of the Kodak Research Laboratories found that the disulfur analog of then unknown 18-crown-6 resulted from the reaction shown in Eq. (6.3). Since the complexation properties of such substances were not yet recognized, especially as they might apply to transition metals, this early and pioneering work has not had the recognition it probably deserved. 

The chiral BOX-metal(II) complexes can also catalyze cycloaddition reactions of other ketonic substrates [45]. The reaction of ethyl ketomalonate 37 with 1,3-conju-gated dienes, e.g. 1,3-cyclohexadiene 5c can occur with chiral BOX-copper(II) and zinc(II) complexes, Ph-BOX-Cu(OTf)2 (l )-21a, and Ph-BOX-Zn(OTf)2 (l )-39, as the catalysts (Scheme 4.29). The reaction proceeds with good yield and ee using the latter complex as the catalyst. Compared to the copper(II)-derived catalyst, which affects a much faster reaction, the use of the zinc(II)-derived catalyst is more convenient because the reaction gives 94% yield and 94% ee of the cycloaddition product 38. The cycloaddition product 38 can be transformed into the optically active CO2-... 

It was mentioned above that in order for the AND gate shown in figure 3.82-b to operate properly, the gliders in input A must be delayed by a time equal to the distance between the two annihilation reactions. The same is true of the operation of the OR gate, shown in figure 3.82-c. 

Gates, B. J., and DeLuca, M. (1975). The production of oxyluciferin during the firefly luciferase light reaction. Arch. Biochem. Biophys. 169 616-621. 

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