Transition state enthalpies of transfer in aqueous dimethyl sulphoxide solutions. The hydroxide-catalysed racemisation ofD-α-methyl-α-phenylacetophenone

1976 ◽  
pp. 102-104 ◽  
Author(s):  
Devendra K. Jaiswal ◽  
John R. Jones ◽  
Richard Fuchs
Keyword(s):  
Transition State ◽  
Dimethyl Sulphoxide ◽  
Enthalpies Of Transfer

scholarly journals Benzyloxycarbonylprolylprolinal, a transition-state analogue for prolyl oligopeptidase, forms a tetrahedral adduct with catalytic serine, not a reactive cysteine

1997 ◽  
Vol 322 (3) ◽  
pp. 839-843 ◽  
Author(s):  
Ara KAHYAOGLU ◽  
Khadijeh HAGHJOO ◽  
Ferenc KRAICSOVITS ◽  
Frank JORDAN ◽  
Laszlo POLGAR
Keyword(s):  
Chemical Shift ◽  
Chemical Modification ◽  
Transition State ◽  
Molecular Mass ◽  
Serine Protease ◽  
13C Nmr ◽  
Dimethyl Sulphoxide ◽  
Tetrahedral Complex ◽  
Prolyl Oligopeptidase ◽  
Transition State Analogue

N-Benzyloxycarbonyl-l-prolyl-l-[1-13C]prolinal was synthesized starting with reduction of l-[1-13C]Pro to l-[1-13C]prolinol, followed by coupling with N-benzyloxycarbonyl-l-Pro to N-benzyloxycarbonyl-l-Pro-l-[1-13C]prolinol (Z-Pro-[1-13C]prolinol), and finally oxidation of the alcohol to the aldehyde with dimethyl sulphoxide. While the 13C NMR chemical shift of the aldehyde carbon is 202 p.p.m., that of the aldehyde hydrate is between 91.6 and 91.8 p.p.m., that of the dithiothreitol adduct is between 74.8 and 75.0 p.p.m., and that in the presence of the serine protease prolyl oligopeptidase is at 92.3 p.p.m.. The linewidth of the latter is 114 Hz, roughly consistent with the molecular mass of 80 kDa reported for the enzyme. Inverse detection experiments gave a 1H resonance at 5.29 p.p.m. with a linewidth of 80 Hz, also consistent with the expected chemical shift and linewidth for a hemiacetal bound to such a large enzyme, while the free hydrate gave resonances at 5.18 and 5.25 p.p.m., with very much narrower linewidths. It is concluded that Z-Pro-prolinal, a putative transition-state analogue for prolyl oligopeptidase, forms a tetrahedral complex with the enzyme at its catalytic serine, rather than at a neighbouring cysteine that was found to be highly reactive according to chemical modification studies.

Kinetics of the hydrolysis of acetic anhydride and the reaction of 4-nitrophenyl acetate with imidazole in aqueous-organic mixed solvents

1974 ◽  
Vol 27 (7) ◽  
pp. 1423 ◽  
Author(s):  
DG Oakenfull
Keyword(s):  
Acetic Anhydride ◽  
Organic Solvent ◽  
Transition State ◽  
Activity Coefficients ◽  
Butyl Alcohol ◽  
Dimethyl Sulphoxide ◽  
Kinetics Of Hydrolysis ◽  
State Activity ◽  
Kinetics Of ◽  
Hydrolysis Of

With the general aim of elucidating the role of water structure in the kinetics of hydrolysis, a comparative study has been made of the kinetics of the hydrolysis of acetic anhydride and the reaction of 4-nitrophenyl acetate with imidazole in mixtures of water with ethanol, t-butyl alcohol, dimethyl sulphoxide and dioxan. Both rate constants were always reduced by the addition of organic solvent. Transition state activity coefficients were measured for both reactions in dimethyl sulphoxide-water mixtures and compared with the activity coefficient of phenylalanine (a model zwitterionic transition state). Activation parameters were measured for the hydrolysis of aceticanhydride in t-butyl alcohol-water and dimethyl sulphoxide-water mixtures. Semilogarithmic plots of rate constant against Winstein's Y-value were non-linear for some of the solvents and this fact, coupled with the effect of dimethyl sulphoxide on the transition state activity coefficients, leads to the conclusion that specific interactions of the solvent with the reactants and with the transition state could be of major importance in controlling the reaction rate.There was no obvious relationship between the effect of an organic solvent on the kinetics of hydrolysis of acetic anhydride and its effect on the structure of water.

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