title: High acidity tolerance in lichens with fumarprotocetraric, perlatolic or thamnolic acids is correlated with low pKa1 values of these lichen substances.
abstract: The depsidone fumarprotocetraric acid as well as the depsides perlatolic and thamnolic acids are lichen secondary metabolites. Their first dissociation constants (pK(a1)) in methanol were determined to be 2.7 for perlatolic acid and 2.8 for fumarprotocetraric and thamnolic acids by UV spectroscopy. Lower pK(a1) values are, so far, not known from lichen substances. Several lichens producing at least one of these compounds are known for their outstanding tolerance to acidic air pollution. This is demonstrated by evaluating published pH preferences for central European lichens. The low pK(a1) values suggest that strong dissociation of the studied lichen substances is a prerequisite for the occurrence of lichens with these compounds on very acidic substrata, as protonated lichen substances of different chemical groups, but not their conjugated bases, are known to shuttle protons into the cytoplasm and thereby apparently damage lichens.
authors.affiliation: Albrecht von Haller Institute of Plant Sciences, Dept. Plant Ecology, University of Göttingen, Untere Karspüle 2, D-37073 Göttingen, Germany. mhauck@gwdg.de
authors.forename: Markus
authors.initials: M
authors.lastname: Hauck
authors.forename: Sascha-René
authors.initials: SR
authors.lastname: Jürgens
authors.forename: Siegfried
authors.initials: S
authors.lastname: Huneck
authors.forename: Christoph
authors.initials: C
authors.lastname: Leuschner
mesh_terms: D001565:Benzoates / Q000737:chemistry / Q000378:metabolism*; D005650:Fumarates / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008011:Lichens / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001565:Benzoates; D005650:Fumarates; C522034:perlatolic acid; C026307:fumarprotocetraric acid