Temperature dependencies of Henry’s law constants and octanol/water partition coefficients for key plant volatile monoterpenoids

Abstract: To model the emission dynamics and changes in fractional composition of monoterpenoids from plant leaves, temperature dependencies of equilibrium coefficients must be known. Henry’s law constants (H pc, Pam3 mol−1 and octanol/water partition coefficients (K OW, molmol−1) were determined for 10 important plant monoterpenes at physiological temperature ranges (25–50°C for H pc and 20–50°C for K OW). A standard EPICS procedure was established to determine H pc and a shake flask method was used for the measurements of K OW. The enthalpy of volatilization (ΔH vol) varied from 18.0 to 44.3kJmol−1 among the monoterpenes, corresponding to a range of temperature-dependent increase in H pc between 1.3- and 1.8-fold per 10°C rise in temperature. The enthalpy of water–octanol phase change varied from −11.0 to −23.8kJmol−1, corresponding to a decrease of K OW between 1.15- and 1.32-fold per 10°C increase in temperature. Correlations among physico-chemical characteristics of a wide range of monoterpenes were analyzed to seek the ways of derivation of H pc and K OW values from other monoterpene physico-chemical characteristics. H pc was strongly correlated with monoterpene saturated vapor pressure (P v), and for lipophilic monoterpenes, ΔH vol scaled positively with the enthalpy of vaporization that characterizes the temperature dependence of P v Thus, P v versus temperature relations may be employed to derive the temperature relations of H pc for these monoterpenes. These data collectively indicate that monoterpene differences in H pc and K OW temperature relations can importantly modify monoterpene emissions from and deposition on plant leaves. [Copyright &y& Elsevier]