Elucidation the Synthesis of an Antibiotic Medicine Chloramphenicol Palmitate with its Stepwise Mechanism

2021 ◽  
Vol 10 (12) ◽  
pp. 365-376
Author(s):  
Rahul Thakur
Keyword(s):  
Stepwise Mechanism

A stepwise mechanism for gas-phase unimolecular ion decompositions. Isotope effects in the fragmentation of tert-butoxide anion

1987 ◽  
Vol 109 (4) ◽  
pp. 961-970 ◽  
Author(s):  
William Tumas ◽  
Robert F. Foster ◽  
Mark J. Pellerite ◽  
John I. Brauman
Keyword(s):  
Gas Phase ◽  
Isotope Effects ◽  
Stepwise Mechanism

Effect of Medium on Reactivity for Alkaline Hydrolysis of p-Nitrophenyl Acetate and S-p-Nitrophenyl Thioacetate in DMSO-H2O Mixtures of Varying Compositions: Ground State and Transition State Contributions

2021 ◽  
Author(s):  
Ik-Hwan Um ◽  
Seungjae Kim
Keyword(s):  
Transition State ◽  
Alkaline Hydrolysis ◽  
Ground State ◽  
Rate Constants ◽  
Kinetic Data ◽  
Reaction Medium ◽  
Stepwise Mechanism ◽  
Rate Determining Step ◽  
Leaving Group ◽  
Hydrolysis Of

Second-order rate constants (kN) for reactions of p-nitrophenyl acetate (1) and S-p-nitrophenyl thioacetate (2) with OH‒ have been measured spectrophotometrically in DMSO-H2O mixtures of varying compositions at 25.0 ± 0.1 oC. The kN value increases from 11.6 to 32,800 M‒1s‒1 for the reactions of 1 and from 5.90 to 190,000 M‒1s‒1 for those of 2 as the reaction medium changes from H2O to 80 mol % DMSO, indicating that the effect of medium on reactivity is more remarkable for the reactions of 2 than for those of 1. Although 2 possesses a better leaving group than 1, the former is less reactive than the latter by a factor of 2 in H2O. This implies that expulsion of the leaving group is not advanced in the rate-determining transition state (TS), i.e., the reactions of 1 and 2 with OH‒ proceed through a stepwise mechanism, in which expulsion of the leaving group from the addition intermediate occurs after the rate-determining step (RDS). Addition of DMSO to H2O would destabilize OH‒ through electronic repulsion between the anion and the negative-dipole end in DMSO. However, destabilization of OH‒ in the ground state (GS) is not solely responsible for the remarkably enhanced reactivity upon addition of DMSO to the medium. The effect of medium on reactivity has been dissected into the GS and TS contributions through combination of the kinetic data with the transfer enthalpies (ΔΔHtr) from H2O to DMSO-H2O mixtures for OH‒ ion.

[3,3] Sigmatropic Rearrangement of Some Fluorinated 1,5-Hexadienes

2002 ◽  
Vol 67 (10) ◽  
pp. 1517-1532 ◽  
Author(s):  
William R. Dolbier ◽  
Keith W. Palmer ◽  
Feng Tian ◽  
Piotr Fiedorow ◽  
Andrzej Zaganiaczyk ◽  
...  
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Transition States ◽  
Activation Parameters ◽  
Sigmatropic Rearrangement ◽  
Semiempirical Methods ◽  
Cope Rearrangement ◽  
Computational Studies ◽  
Stepwise Mechanism ◽  
Radical Intermediates

Fluorine atoms incorporated into 1,5-hexadiene molecule should influence the kinetic as well as the thermodynamic parameters of [3,3] sigmatropic rearrangement (Cope rearrangement). Within few decades is has been documented that this transformation proceeds in a concerted manner, rather than stepwise with some radical intermediates involved. Few new terminally fluorinated 1,5-hexadienes (compounds 3, 5A, 7, 9 and 5B) have been synthesized. The activation parameters of rearrangement have been determined and compared with those known for hydrocarbon analogues. While systems developing chair-like transition states (compounds 3 and 5) showed close similarity with hydrocarbon analogues (compound 1), those developing boat-like transition states (compounds 7, 9 and 5B) may proceed through radical stepwise mechanism. Computational studies of the transition states were carried out, showing that only ab initio methods (MP2 and especially DFT) can give approximate correlation with experimental data, whereas in the case of hydrocarbon analogues even simple semiempirical methods (AM1) were reliable enough to reproduce experimental results.

Stepwise Mechanism of the Aminolysis of O-Ethyl S-(4-Nitrophenyl) Thiocarbonate

1994 ◽  
Vol 59 (13) ◽  
pp. 3572-3574 ◽  
Author(s):  
Enrique A. Castro ◽  
Maria Cubillos ◽  
Jose G. Santos
Keyword(s):  
Stepwise Mechanism

An Introduction to Neutro-Fine Topology with Separation Axioms and Decision Making

2020 ◽  
pp. 13-28
Author(s):  
admin admin ◽  
◽  
◽  
M. P. Sindhu
Keyword(s):  
Decision Making ◽  
Topological Space ◽  
Positive Solution ◽  
Real Life ◽  
Neutrosophic Set ◽  
Fine Topology ◽  
Stepwise Mechanism ◽  
The Real ◽  
Separation Axioms ◽  
Decision Making Problem

The set which describes the uncertainty incident with three levels of attributes is entitled as a neutrosophic set. The unique collection of open sets which contains all types of open sets is termed as fine-open sets. The current study introduces a topology on merging these two sets, called neutro-fine topological space. Additionally, the approach of separation axioms is implemented in such space. Furthermore, the real-life application is examined as a decision-making problem in this space. The problem is to make an unfavorable query into a favorable one by determining the complement and absolute complement of such issued neutro-fine open sets. This problem desires to find a positive solution. The solving stepwise mechanism reveals in the algorithm, also formulae provide to compute the outcome with explanatory examples.

scholarly journals Activation of DNA-PK by hairpinned DNA ends reveals a stepwise mechanism of kinase activation

2020 ◽  
Vol 48 (16) ◽  
pp. 9098-9108 ◽  
Author(s):  
Katheryn Meek
Keyword(s):  
Protein Kinase ◽  
End Joining ◽  
Dependent Protein Kinase ◽  
Kinase Activation ◽  
Stepwise Mechanism ◽  
Dependent Protein ◽  
Enzymatic Activation ◽  
Non Homologous End Joining ◽  
Dna Ends ◽  
Step Mechanism

Abstract As its name implies, the DNA dependent protein kinase (DNA-PK) requires DNA double-stranded ends for enzymatic activation. Here, I demonstrate that hairpinned DNA ends are ineffective for activating the kinase toward many of its well-studied substrates (p53, XRCC4, XLF, HSP90). However, hairpinned DNA ends robustly stimulate certain DNA-PK autophosphorylations. Specifically, autophosphorylation sites within the ABCDE cluster are robustly phosphorylated when DNA-PK is activated by hairpinned DNA ends. Of note, phosphorylation of the ABCDE sites is requisite for activation of the Artemis nuclease that associates with DNA-PK to mediate hairpin opening. This finding suggests a multi-step mechanism of kinase activation. Finally, I find that all non-homologous end joining (NHEJ) defective cells (whether deficient in components of the DNA-PK complex or components of the ligase complex) are similarly deficient in joining DNA double-stranded breaks (DSBs) with hairpinned termini.

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