title: Estimation of the solubility parameters of model plant surfaces and agrochemicals: a valuable tool for understanding plant surface interactions.
abstract: BACKGROUND
  Most aerial plant parts are covered with a hydrophobic lipid-rich cuticle, which is the interface between the plant organs and the surrounding environment. Plant surfaces may have a high degree of hydrophobicity because of the combined effects of surface chemistry and roughness. The physical and chemical complexity of the plant cuticle limits the development of models that explain its internal structure and interactions with surface-applied agrochemicals. In this article we introduce a thermodynamic method for estimating the solubilities of model plant surface constituents and relating them to the effects of agrochemicals.
  
  
  RESULTS
  Following the van Krevelen and Hoftyzer method, we calculated the solubility parameters of three model plant species and eight compounds that differ in hydrophobicity and polarity. In addition, intact tissues were examined by scanning electron microscopy and the surface free energy, polarity, solubility parameter and work of adhesion of each were calculated from contact angle measurements of three liquids with different polarities. By comparing the affinities between plant surface constituents and agrochemicals derived from (a) theoretical calculations and (b) contact angle measurements we were able to distinguish the physical effect of surface roughness from the effect of the chemical nature of the epicuticular waxes. A solubility parameter model for plant surfaces is proposed on the basis of an increasing gradient from the cuticular surface towards the underlying cell wall.
  
  
  CONCLUSIONS
  The procedure enabled us to predict the interactions among agrochemicals, plant surfaces, and cuticular and cell wall components, and promises to be a useful tool for improving our understanding of biological surface interactions.
authors.affiliation: Genetics and Eco-physiology Research Group, School of Forest Engineering, Technical University of Madrid, Ciudad Universitaria s/n, 28040, Madrid, Spain.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Khayet
authors.forename: Victoria
authors.initials: V
authors.lastname: Fernández
mesh_terms: D000268:Adhesiveness / Q000187:drug effects; D016573:Agrochemicals / Q000737:chemistry* / Q000494:pharmacology*; D002212:Capsicum / Q000187:drug effects; D002473:Cell Wall / Q000187:drug effects; D005052:Eucalyptus / Q000187:drug effects; D057927:Hydrophobic and Hydrophilic Interactions / Q000187:drug effects; D019441:Plant Epidermis / Q000187:drug effects* / Q000502:physiology* / Q000648:ultrastructure; D010944:Plants / Q000187:drug effects* / Q000378:metabolism*; D027861:Prunus / Q000187:drug effects; D012995:Solubility; D013499:Surface Properties / Q000187:drug effects; D013816:Thermodynamics; D014885:Waxes / Q000737:chemistry / Q000378:metabolism
chemical_list: D016573:Agrochemicals; D014885:Waxes