title: Theoretical and experimental investigation of the oxidized and oxygenated forms of pyrocatechuic acid (2,3-dihydroxybenzoic acid).
abstract: The catecholic derivative 2,3-dihydroxybenzoic acid (2,3-DHBA or pyrocatechuic acid) represents a diversity of actions in enzymatic processes. In the present study DFT calculations (at the B3LYP/TZVP level of theory) have been performed for neutral 2,3DHBA and its dimer (models 1-1a), several semiquinone forms of 2,3-DHBA, namely the neutral (models 2-4), the monoionized (models 5-7), the di-ionized (models 8) and the dimer 7a. The more stable species in each case are those with the carboxyl group protonated. Oxygenated adducts were also constructed (models 10-15) in which the dioxygen is either H-bonded to the catecholic or carboxylic hydrogen or it is concerned to act on the intradiol or extradiol carbon atoms. The side-on placement of O(2) on C(2) facilitates the intradiol C-C cleavage. Protonation of the oxygenated on C(1) adduct leads to decarboxylation of 2,3-DHBA. Isolation in the solid state and characterization by ESMS, IR, NMR, electronic spectra of the blue-green oxidized product of 2,3-DHBA (solid 1) supports the possibility of the existence of the semiquinone form or the hydroperoxide-adduct. Experimental spectroscopic data are correlated to the calculated spectroscopic parameters. In the ESMS the decarboxylation and degradation products as well a peroxo-adduct have been detected. Oxygenated species may also account for the plethora of redox signals in the cyclic voltammograms of solid 1 (in DMSO solutions).
authors.affiliation: Department of Chemistry, Section III, University of Athens, Panepistimiopolis, 15771 Athens, Greece.
authors.forename: Panayiotis
authors.initials: P
authors.lastname: Petropouleas
authors.forename: George
authors.initials: G
authors.lastname: Koufopoulos
authors.forename: Despina
authors.initials: D
authors.lastname: Hatzipanayioti
mesh_terms: D004121:Dimethyl Sulfoxide / Q000737:chemistry; D055664:Electrochemical Techniques; D062385:Hydroxybenzoates / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics
chemical_list: D062385:Hydroxybenzoates; C009135:2,3-dihydroxybenzoic acid; D010100:Oxygen; D004121:Dimethyl Sulfoxide