Abiotic Inactivation of Extracellular Biochemicals in Soil.

Organisms release a wide range of biologically-active biochemicals into soil interstitial waters that may undergo chemical degradation during transit to the organisms.  Our objective is to build the basis for predicting pathways and rates for chemical degradation.  We need to explore how the identity and number of functional groups and overall biochemical structure affect speciation, i.e. protonation level, metal coordination, and adsorption.  We need to explore how structure and speciation tie in with inherent reactivity.  We also need to explore how ambient geochemical conditions affect reactivity, i.e. pH, major ion composition, presence of dissolved and particulate-bound natural organic matter, and identity/surface area loading of mineral surfaces.  Ferulic acid, caffeic acid, and gentisic acid serve as illustration.  Ferulic acid possesses a phenolic group and a methoxy group ortho- to one another on an aromatic ring, and is hence susceptible towards oxidation by manganese(III) and iron(III,IV) (hydr)oxides.  It also contains an alkene group that can engage in resonance interactions with the aromatic ring.  To what extent does this alkene group contribute to reactivity?  Caffeic acid poses similar issues, but this time with a better-understood catecholate functional group.  Gentisic acid lacks the alkene group, but instead has a carboxylate group that can engage in resonance interactions with the aromatic ring.  It is known that the carboxylate group raises the reduction potential of gentisic acid relative to other hydroxyaromatics, but how does it affect its reactivity?  As far as oxidant surfaces are concerned, birnessite is a cation-exchange material but pyrolusite is not.  Birnessite possesses a lower pH of zero proton condition than pyrolusite.  How do such surface properties influence rates of ferulic acid, caffeic acid, and gentisic acid oxidation?  Can insights gained from investigations of manganese-containing oxidant surfaces be applied to iron-containing oxidant surfaces?