5862-47-5Relevant academic research and scientific papers
Effects of Volume and Surface Property in Hydrolysis by Acetylcholinesterase. The Trimethyl Site
Cohen, Saul G.,Elkind, Jerome L.,Chishti, S. Bano,Giner, Jose-L. P.,Reese, Heide,Cohen, Jonathan B.
, p. 1643 - 1647 (2007/10/02)
β-Substituted ethyl acetates, XCH2CH2OCOCH3, have been prepared, and their hydrolysis by acetylcholinesterase has been studied.Log of enzymic reactivity, normalized for intrinsic reactivity in hydrolysis by hydroxide, log(kcat/Km)n, rises linearly with increasing refraction volume, MR (or RD25), for substrates with β-X = H, Cl, Br, CH3CH2, (CH3)2CH, (CH3)2S+, (CH3)3N+, and (CH3)3C.Larger substituents may by accommodated, (CH3)3Si and (CH3CH2)3N+, with no further increase in rate.Substrates with β-substituents CH3S, CH3S(O), (CH3)3N+(OH), and CH3S(O2) are less reactive than consistent with the relation with MR by factors of 5-40, indicating that hydrophobic surface and desolvation of the substrate-enzyme interface may be necessary for maximum reactivity correlated with MR.Values of log (kcat/Km)n for substrates with β-substituents X = CH3S, Cl, Br, CH3CH2, (CH3)2CH, (CH3)3C, and (CH3)3Si rise linearly with increasing hydrophobicity, ?, but reactivity of substrates with X = (CH3)3N+ and (CH3)2S+ are more reactive than consistent with a relation to ? by factors of 300 and 40 and with X = CH3S(O2), CH3S(O), and (CH3)2N+(OH), by factors of 7-100.Reactivity appears related to (i) volume of the β-substituent and its fit in its subsite, which is trimethyl rather than anionic, and (ii) the hydrophobicity of its surface.
Effects of Polar β Substituents in the Gas-Phase Pyrolysis of Ethyl Acetate Esters
Chuchani, Gabriel,Martin, Ignacio,Hernandez, Jose A. A.,Rotinov, Alexandra,Fraile, German,Bigley, David B.
, p. 944 - 948 (2007/10/02)
The rates of the gas phase pyrolysis of six β-substituted ethyl acetates were studied in a static system over the temperature range 319-450 deg C and the pressure range 63-207 mmHg.In seasoned vessels the reactions are homogenous, follow a first-order rate law, and are unimolecular.The temperature dependence of the rate constants is given by the following Arrhenius equations for the compounds indicated: 2-(dimethylamino)ethyl acetate, log k(s-1) = (13.90 +/- 0.30) - (220.4 +/- 3.8) kJ*mol-1 (2.303RT)-1; 2-methoxyethyl acetate, log k(s-1) = (12.04 +/- 0.24) -(203.7 +/- 2.9) kJ*mol1- (2.303RT)-1; 2-(methylthio)ethyl acetae, log k(s-1 = (11.27 +/- 0.39) - (179.0 +/- 4.6) kJ*mol-1 (2.303RT)-1; 2-chloroethyl acetate, log k(s-1) = (12.14 +/- 0.66) - (202.0 +/- 8.4)kJ*mol-1 (2.303RT)-1; 2-fluoroethyl acetate, log k(s-1) = (12.68 +/- 0.60) - (211.2 +/- 7.1) kJ*mol-1 (2.303RT)-1; 2-cyanoethylacetate, Log k(s-1) = (11.51 +/- 0.13) - (171.9 +/- 1.7) kJ*mol-1 (2.303RT)-1.The effect of substituents in the gas-phase elimination of β-substituted ethyl acetates may be grouped in three types.The linear correlation of several -I electron-withdrawing groups along strong ? bonds is presented and discussed.A small amount of anchimeric assistance is proposed in the pyrolysis of the 2-(methyltio)ethyl acetate.The experimental data are consistent with the transition state where the Cα-O bond polarization is the rate-determining process.
