Effects of ethanol and other alkanols on the kinetics and the activation parameters of thermal death inSaccharomyces cerevisiae

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Abstract
Ethanol, isopropanol, propanol, and butanol enhanced thermal death in Saccharomyces cerevisiae by increasing ΔS‡, the entropy of activation of thermal death while ΔH‡, the enthalpy of activation, was not significantly affected. The relation between ΔS‡ and alkanol concentration was linear with a different slope for each alkanol: ΔS‡X = ΔS‡0 + CAEX, where X is the alkanol concentration and CAE the entropy coefficient for the aqueous phase defined as increase in entropy of activation per unit concentrations of the alkanol. CAE was correlated with the lipid‐buffer partition coefficients of the alkanols while CME, the entropy coefficient for the lipid phase, was nearly identical for the four alkanol and averaged 37.6 entropy units per mole of alkanol per kilogram of membrane. As predicted by these results, the specific death rates (Kd) at constant temperature were an exponential function of the alkanol concentration and behaved in agreement with the following equation: In KXd = In K0d + (CAE/R)X, where R is the gas constant. It was concluded that the alkanols enhanced thermal death through nonspecific action on membrane structure.