Enzyme kinetics

A study of the kinetic behavior of the oxygen atom transfer reaction of Mo2o3 (Et2dtc)2 (THF) 2I2, (I), with a variety of derivatives of pyridine N-oxides has been performed. The reaction behaves in pseudo-first-order fashion under conditions of excess N-oxide. Plots of kobs vs. [N-oxide] do not give straight lines, while plots of 1/kobs vs. 1/[N-oxide] are linear. The rate constant k is taken as the inverse of the slope of this latter plot. There is a marked dependence of the rate on the functional group in the 4-position of the pyridine ring with the relative rates -CH3 > -H > -Cl > -CN. The above observations can be used to support a mechanism in which a rapid pre-equilibrium, with a large equilibrium constant, is followed by a rate-determining breaking of the Mo-O-Mo bridge.

The conversion of alkynyl carbonyls to allenyl carbonyls via manganese mediated coordination followed by a base-catalyzed isomerization was carried out using a range of chiral and achiral amine bases. Chiral amidine and chiral DBU derivatives were synthesized to carry out the isomerization enantioselectively. We employed HPLC equipped with a chiral column to determine the enantiomeric excess. We also proved that the mechanism of that the manganese-coordinated alkyne/allene rearrangement reaction involved an intermediate cumenolate. It was also confirmed that amine base with pKa lower than that of DBU (pKa = 13.6) would not carry out the isomerization. Alkoxy base were also used in isomerization and the mechanism was also investigated.