Absolute rates of reaction of amino acids and model compounds with ozone have been measured in aqueous buffer solutions. For the less reactive amino acids and for amines, the rates of reaction are proportional to the amount of free (Le., unprotonated) amine present and therefore are relatively slow below p H 7. The rates of reaction of the corresponding amides are also slow. Rates of reaction of the more reactive amino acids at pH 7.0 are in the order of cysteine > tryptophan > methionine > tyrosine > histidine. 3-Hexenoic acid, a model of a polyunsaturated fatty acid (PUFA), is similar in reactivity to methionine or tyrosine. These data imply that the more reactive amino acids, whether free or in polypeptides, must be considered as possible targets for the reaction of ozone in vivo, along with the more usually considered PUFA. Which of these types of target molecules might receive the most damage in vivo probably depends on accessibility and cellular architecture, and these factors, plus the possibility of co-oxidation and other complexities, require further study.

No abstract

No abstract

No abstract

of charge delocalization over charge separation in the annulenones. ConclusionsThe published experimental value for AHfo(g) of diphenylcyclopropenone is too high by as much as 50 kcal/mol corresponding to a 2.5% error in the heat of combustion, possibly due to the presence of a small amount of impurity in the compound tested in the earlier work. More refined calorimetric measure-(28) Greenberg, A.; Liebman, J. F. J . Org. Chem. 1982Chem. ,47, 2084Chem. -2088 ments are in progress. The resonance stabilization in cyclopropenone appears to be in the range of 20 f 5 kcal/mol. The value is about 6 kcal/mol greater than in methylenecyclopropene and lends support to the view that cyclopropenone has some ground-state aromatic stabilization.Acknowledgment. The authors thank Professors Harry P. Hopkins, Jr., and Ronald Breslow for helpful discussions. A. Greenberg and R. P. T. Tomkins thank the NJIT Research Office for an SBR Grant in support of this research and Mr. Nicholas Abstract: Absolute rates of reaction of ozone with a series of alkenes bearing electron-withdrawing groups have been determined at several temperatures in CCll by a stopped-flow technique. From these data, activation parameters have been calculated and range from those of tetrachloroethylene (E, = 11 kcal/mol; log A(s-') = 6.0) to those of styrene (E, = 3.1 kcal/mol; log A(s-') = 7.5) and 1-hexene (E, = 2.4 kcal/mol; log A@-') = 6.8). These results show that the ozonation of alkenes is quite sensitive to electronic effects, with electron-deficient alkenes reacting orders of magnitude slower than electron-rich alkenes. The rate of reaction of trans-1,2-dichloroethylene is about 25 times that of the cis or the 1,l isomer, which is consistent with a 1,3-dipolar cycloaddition mechanism. Calculated entropies of activation also are consistent with this, but a general trend toward less negative entropies of activation with lower E, suggests the possibility of a change in mechanism for more electron-rich alkenes.