scholarly journals Correction: Hydrodeoxygenation of guaiacol over bimetallic Fe-alloyed (Ni, Pt) surfaces: reaction mechanism, transition-state scaling relations and descriptor for predicting C–O bond scission reactivity

2018 ◽  
Vol 8 (19) ◽  
pp. 5116-5116
Author(s):  
Xiaoyang Liu ◽  
Wei An ◽  
Yixing Wang ◽  
C. Heath Turner ◽  
Daniel E. Resasco
Keyword(s):  
Reaction Mechanism ◽  
Transition State ◽  
Scaling Relations ◽  
Bond Scission ◽  
Mechanism Transition

Correction for ‘Hydrodeoxygenation of guaiacol over bimetallic Fe-alloyed (Ni, Pt) surfaces: reaction mechanism, transition-state scaling relations and descriptor for predicting C–O bond scission reactivity’ by Xiaoyang Liu et al., Catal. Sci. Technol., 2018, 8, 2146–2158.

Hydrodeoxygenation of guaiacol over bimetallic Fe-alloyed (Ni, Pt) surfaces: reaction mechanism, transition-state scaling relations and descriptor for predicting C–O bond scission reactivity

2018 ◽  
Vol 8 (8) ◽  
pp. 2146-2158 ◽  
Author(s):  
Xiaoyang Liu ◽  
Wei An ◽  
Yixing Wang ◽  
C. Heath Turner ◽  
Daniel E. Resasco
Keyword(s):  
Reaction Mechanism ◽  
Transition State ◽  
Bond Length ◽  
Metal Catalysts ◽  
Scaling Relations ◽  
Bond Scission ◽  
Mechanism Transition ◽  
Good Descriptor

Small means big: DFT-calculated C–O bond length of adsorbed intermediates can serve as a good descriptor for predicting the C–O bond scission reactivity of phenolics over metal catalysts.

Reactions of an Aluminium(I) Reagent with 1,2-, 1,3- and 1,5-Dienes: Dearomatisation, Reversibility, and a Pericyclic Mechanism

2019 ◽  
Author(s):  
Clare Bakewell ◽  
Martí Garçon ◽  
Richard Y Kong ◽  
Louisa O'Hare ◽  
Andrew J. P. White ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Dft Calculations ◽  
Transition State ◽  
Reaction Pathways ◽  
Aromatic Rings ◽  
Aromatic Character ◽  
Pericyclic Reaction

The reactions of an aluminium(I) reagent with a series of 1,2-, 1,3- and 1,5-dienes are reported. In the case of 1,3-dienes the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene containing products. This mechanism has been interrogated by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4+1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4+1) cycloaddition includes dienes that are either in part, or entirely, contained within aromatic rings. In these cases, reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2- or 1,5-dienes complementary reactivity is observed; the orthogonal nature of the C=C π-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavour a (4+1) cycloaddition. Rather, reaction pathways are determined by an initial (2+1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C=C π-bond leading to complex organometallic products that incorporate fused hydrocarbon rings.

scholarly journals Shifting the scaling relations of single-atom catalysts for facile methane activation by tuning the coordination number

2021 ◽  
Author(s):  
Changhyeok Choi ◽  
Sungho Yoon ◽  
Yousung Jung
Keyword(s):  
Transition State ◽  
Coordination Number ◽  
Active Sites ◽  
Methane Activation ◽  
Single Atom ◽  
Scaling Relations ◽  
Scaling Relationship ◽  
Relationship Of

The scaling relationship of methane activation via a radical-like transition state shifts toward a more reactive region with decreasing coordination number of the active sites.

Reaction mechanism studies. 5. The mechanism of the diaxial → diequatorial rearrangement of β-chlorothioethers

1968 ◽  
Vol 46 (1) ◽  
pp. 9-13 ◽  
Author(s):  
J. F. King ◽  
K. Abikar
Keyword(s):  
Reaction Mechanism ◽  
Transition State ◽  
Nitro Group ◽  
Ion Pair ◽  
Concerted Mechanism

p-Methoxy- and p-nitro substituted analogues (1b and 1c) of the diaxial β-chlorothioether 2β-chloro-3α-(phenylthio)-5α-cholestane (1a), have been prepared and found to undergo the diaxial → diequatorial rearrangement. The rates of rearrangement of these compounds show the sequence p-methoxy > H > p-nitro. It is concluded that the transition state for the rearrangement is polarized in the sense of a sulfonium chloride (3). The rearrangement of 1a is 1600 times faster in butanol than in decalin (at 110°). There is thus no inherent insensitivity to solvent change in a rearrangement in which there may be a "four-atom arrangement" in the transition state, a conclusion relevant to previous work on the diaxial → diequatorial rearrangement of 1,2-dibromides (1). It was further found that the nitro group slowed the rearrangement (at 110°) more in butanol than in decalin, an observation regarded as consistent with, but not requiring, the incursion of a merged ion-pair, cyclic concerted mechanism.

Substituent effects on rates of formation of methoxy-substituted carbonyl ylides from 2-aryl-2-methoxy- and 5-aryl-2-methoxy-Δ3-1,3,4-oxadiazolines

1984 ◽  
Vol 62 (8) ◽  
pp. 1646-1652 ◽  
Author(s):  
Michel Békhazi ◽  
Peter J. Smith ◽  
John Warkentin
Keyword(s):  
Transition State ◽  
Electron Density ◽  
Rate Constants ◽  
Substituent Effects ◽  
Partial Identification ◽  
Trans Isomers ◽  
First Order Kinetics ◽  
Bond Scission ◽  
Carbonyl Ylide ◽  
Substituent Constants

2-Aryl-2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazolines (4) and 5-aryl-2-methoxy-2,5-dimethyl-Δ3-1,3,4-oxadiazolines (5) were synthesized. Compounds 4 decompose in solution with first order kinetics. Rate constants are correlated with Hammett substituent constants (σ−) with ρ(49.2 °C) = 0.74 and 0.89 for CCl4, and CD3OD, respectively. The final products from 4 indicate that thermolysis involves the cleavage of both C—N bonds, to form N2 and, initially, a carbonyl ylide. Compounds 5, which were obtained as mixtures of cis/trans isomers containing several impurities, and which therefore gave poorer kinetic data, decomposed in CDCl3 solution with [Formula: see text] Carbonyl ylide intermediates, similar to those from the closelyrelated compounds 4, were assumed on the basis of analogy and on the basis of partial identification of products. The effects of para substituents in the aryl groups of 4 and 5 show that the transition states have greater electron density at C-2 of 4 and at C-5 of 5 than do the starting materials. In spite of the increase in electron density at C-2 of 4, the transition state must be less polar, overall, than the ground state because rate constants for thermolysis of 4 in methanol are smaller than those for CCl4, solvent. A plausible explanation for the substituent effects and the solvent effects is that the loss of N2 is concerted, with a transition state resembling more closely a spin paired 1,3-diradical than a 1,3-dipole. Alternative stepwise mechanisms, in which C2—N3 bond scission of 4 and C5—N4 bond scission of 5 are the rate-determining steps, leading to 1,5-diradical intermediates, can not be excluded on the basis of the evidence.

Determination and use of a transition state for the enzyme estrone sulfatase (ES) from a proposed reaction mechanism

2001 ◽  
Vol 11 (23) ◽  
pp. 3001-3005 ◽  
Author(s):  
Sabbir Ahmed ◽  
Karen James ◽  
Caroline P Owen ◽  
Chirag K Patel ◽  
Mijal B Patel
Keyword(s):  
Reaction Mechanism ◽  
Transition State ◽  
Estrone Sulfatase

scholarly journals Theoretical study on pegylation reaction mechanisms of IFN-α-2a, IFN-α-2b and IFN-β-1a

2017 ◽  
Vol 82 (7-8) ◽  
pp. 841-850
Author(s):  
Mohammad Taqavian ◽  
Daryoush Abedi ◽  
Fatemeh Zigheimat ◽  
Leila Zeidabadinejad
Keyword(s):  
Polyethylene Glycol ◽  
Reaction Mechanism ◽  
Dft Calculations ◽  
Transition State ◽  
Reaction Mechanisms ◽  
Theoretical Study ◽  
Computational Study ◽  
Single Transition ◽  
Experimental Works ◽  
Ab Initio And Dft

Ab initio and DFT calculations have been carried out to study the reaction mechanism between interferons (IFNs) ?-2a, ?-2b and ?-1a and polyethylene glycol (PEG) group. The calculations show that the mechanisms are concerted, in agreement with the results of experimental works. However, although it appears that there is one single transition state, the characteristics of its structure reveal a very synchronous reaction mechanism. The reactions are clearly exothermic and as well have feasible activation energies. Our computational study shows that the lowest transition state energies are related to Lys 134, His 34 and Met 1 of IFN-?-2a, IFN-?-2b and IFN-?-1a, respectively.

Reactions of an Aluminium(I) Reagent with 1,2-, 1,3- and 1,5-Dienes: Dearomatisation, Reversibility, and a Pericyclic Mechanism

2019 ◽  
Author(s):  
Clare Bakewell ◽  
Martí Garçon ◽  
Richard Y Kong ◽  
Louisa O'Hare ◽  
Andrew J. P. White ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Dft Calculations ◽  
Transition State ◽  
Reaction Pathways ◽  
Aromatic Rings ◽  
Aromatic Character ◽  
Pericyclic Reaction

The reactions of an aluminium(I) reagent with a series of 1,2-, 1,3- and 1,5-dienes are reported. In the case of 1,3-dienes the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene containing products. This mechanism has been interrogated by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4+1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4+1) cycloaddition includes dienes that are either in part, or entirely, contained within aromatic rings. In these cases, reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2- or 1,5-dienes complementary reactivity is observed; the orthogonal nature of the C=C π-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavour a (4+1) cycloaddition. Rather, reaction pathways are determined by an initial (2+1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C=C π-bond leading to complex organometallic products that incorporate fused hydrocarbon rings.

His-391 of β-galactosidase (Escherichia coli) promotes catalyes by strong interactions with the transition state

2001 ◽  
Vol 79 (2) ◽  
pp. 183-193 ◽  
Author(s):  
Reuben E Huber ◽  
Isabel Y Hlede ◽  
Nathan J Roth ◽  
Kyle C McKenzie ◽  
Kiran K Ghumman
Keyword(s):  
Escherichia Coli ◽  
Transition State ◽  
Strong Interactions ◽  
Wild Type ◽  
Substrate Analogs ◽  
Transition State Analogs ◽  
Transition State Stabilization ◽  
Large Numbers ◽  
Important Residue ◽  
Mechanism Transition

His-391 of β-galactosidase (Escherichia coli) was substituted by Phe, Glu, and Lys. Homogeneous preparations of the substituted enzymes were essentially inactive unless very rapid purifications were performed, and the assays were done immediately. The inactive enzymes were tetrameric, just like wild-type β-galactosidase and their fluorescence spectra were identical to the fluorescence spectrum of wild-type enzyme. Analyses of two of the substituted enzymes that were very rapidly purified to homogeneity and rapidly assayed while they were still active (at only a few substrate concentrations so that the data could be rapidly obtained), showed that the kinetic values were very similar to the values obtained with the same enzymes that were only partially purified. This showed that the kinetics were not affected by the degree of purity and allowed kinetic analyses with partially purified enzymes so that large numbers of points could be used for accuracy. The data showed that His-391 is a very important residue. It interacts strongly with the transition state and promotes catalysis by stabilizing the transition state. Activation energy differences (ΔΔGs‡), as determined by differences in the kcat/Km values, indicated that substitutions for His-391 caused very large destabilizations (22.8-35.9 kJ/mol) of the transition state. The importance of His-391 for transition state stabilization was confirmed by studies that showed that transition state analogs are very poor inhibitors of the substituted enzymes, while inhibition by substrate analogs was only affected in a small way by substituting for His-391. The poor stabilities of the transition states caused significant decreases of the rates of the glycolytic cleavage steps (galactosylation, k2). Degalactosylation (k3) was not decreased to the same extent.Key words: β-galactosidase, mechanism, transition state, binding, histidine, catalysis.

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