title: Salting-in and salting-out effects of ionic and neutral osmotica on limonene and linalool Henry's law constants and octanol/water partition coefficients.
abstract: Foliar emission rates of plant-generated volatile monoterpenes depend on monoterpene partitioning between air, aqueous and lipid-phases in the leaves. While Henry's law constants (H pc, equilibrium gas/water partition coefficient) and octanol/water partition coefficients (K OW) for pure water have been previously used to simulate monoterpene emissions from the leaves, aqueous phase in plants is a complex solution of electrolytes and neutral osmotica. We studied the effects of dissociated compounds KCl and glycine and sugars glucose, sorbitol and sucrose with concentrations between 0 and 1M on H pc and K OW values for limonene and linalool. Linalool with ca. 1500-fold lower H(pc) (2.62 Pa m(3)mol(-1) for pure water at 30 degrees C) and ca. 30-fold lower K OW (955 mol mol(-1) for pure water at 25 degrees C) is the more hydrophilic compound of the two monoterpenes. H pc of both monoterpenes increased with increasing concentration of both ionic compounds and sorbitol, but decreased with increasing glucose and sucrose concentrations. The salting-out coefficients for H pc (kH) were ca. an order of magnitude larger for more hydrophilic compound linalool than for more hydrophobic limonene. For linalool, co-solutes modified H pc by 30-50% at the highest concentration (1M) tested. The effect of temperature on the salting-out coefficient of KCl was minor. As with H pc, K OW increased with increasing the concentration of KCl, glycine and sorbitol, and decreased with increasing glucose and sucrose concentrations. For limonene, co-solutes modified K OW by 20-50% at the highest concentration used. For linalool, the corresponding range was 10-35%. Salting-out coefficients for H pc and K OW were correlated, but the lipid-solubility was more strongly affected than aqueous solubility in the case of limonene. Overall, these data demonstrate physiologically important effects of co-solutes on H pc and K OW for hydrophilic monoterpenes and on K OW for hydrophobic monoterpenes that should be included in current emission models.
authors.affiliation: Department of Plant Physiology, University of Tartu, Riia 23, Tartu 51011, Estonia.
authors.forename: Lucian
authors.initials: L
authors.lastname: Copolovici
authors.forename: Ulo
authors.initials: U
authors.lastname: Niinemets
mesh_terms: D020003:1-Octanol / Q000737:chemistry; D000080462:Acyclic Monoterpenes; D002241:Carbohydrates / Q000737:chemistry*; D053138:Cyclohexenes / Q000737:chemistry* / Q000378:metabolism; D005998:Glycine / Q000737:chemistry*; D000077222:Limonene; D039821:Monoterpenes / Q000737:chemistry* / Q000378:metabolism; D010944:Plants / Q000378:metabolism; D011189:Potassium Chloride / Q000737:chemistry*; D013696:Temperature; D013729:Terpenes / Q000737:chemistry* / Q000378:metabolism; D014867:Water / Q000737:chemistry
chemical_list: D000080462:Acyclic Monoterpenes; D002241:Carbohydrates; D053138:Cyclohexenes; D039821:Monoterpenes; D013729:Terpenes; D014867:Water; D011189:Potassium Chloride; D000077222:Limonene; C018584:linalool; D020003:1-Octanol; D005998:Glycine