81408-98-2Relevant academic research and scientific papers
Parallel Behavior in Kinetic and NMR Effects: Secondary Deuterium Isotope Effects on the Alkaline Hydrolysis of Esters
Matta, Michael S.,Broadway, Dale E.,Stroot, Michele K.
, p. 4916 - 4918 (2007/10/02)
β-Deuterium secondary kinetic isotope effects (β-D KIEs) on the alkaline hydrolysis of the p-nitrophenyl esters of acetic, propanoic, butanoic, and pentanoic acids in pH 10.70, 0.20 M carbonate buffer at 25 deg C tend to increase with increasing chain length of the esters up to the pentanoate.The β-D KIEs are respectively 0.975 +/- 0.004, 0.960 +/- 0.002, 0.940 +/- 0.001, and 0.948 +/- 0.004.The activation energies of the esterolyses of the isotopically light esters follow a similar pattern, as do the 13C NMR nuclear shieldings in CDCl3 of the isotopically light parent carboxylic acids (20.9, 27.4, 35.9, and 33.8 (ppm)) and 13C NMR one-bond isotope shifts produced by disubstitution of deuterium for hydrogen at the α-carbons of the acids (0.45, 0.55, 0.60, and 0.59 (ppm)).Correlation of nuclear shieldings and isotope shifts is known from previous work.The possibility is considered that all of the kinetics-based and NMR relationships are linked through the operation of a common ground-state feature of the ester and acid alkyl chains.
Correlative Variations in Enzyme-Derived and Substrate-Derived Structures of Catalytic Transition States. Implications for the Catalytic Strategy of Acyl-Transfer Enzymes
Stein, Ross L.,Elrod, James P.,Schowen, Richard L.
, p. 2446 - 2452 (2007/10/02)
Acetylchymotrypsin, acetyl elastase and (carbobenzyloxy)glycyl elastase all undergo hydrolysis with the same overall solvent isotope effect, which arises from a single protonic site n/k1 = 2.45(1-n + n/2.45)>. chymotrypsin, however, shows a larger effect arising from at least two sites n/k1 = 3.34(1-n + n/1.85)2>.Formylchymotrypsin and acetylchymotrypsin undergo deacylation with α-deuterium and β-deuteium secondary isotope effects, respectively, that suggest fractional tetrahedral character at the transition state of about 0.44 (vs. 0.58 - 0.66 for similar nonenzymic reactions) when compared to equilibrium isotope effects for complete addition.The effect for acetyl elastase suggests much less tetrahedral character (0.27).Addition of an N-acyl function leads to a more inverse isotope effect, per deuterium, and thus to an apparent increase in tetrahedral character: to 0.84 for chymotrypsin; to 0.43 for (carbobenzyloxy)glycyl elastase.It is concluded that enzyme-substrate interactions at the transition state can alter both enzyme structure, as shown by the solvent isotope effects, and substrate structure as shown by the substrate isotope effects.Such alterations, in the combination of enzyme with natural substrate, probably adjust both structures for optimal catalytic interaction.
