ABSTRACT
Catechol, also known as pyrocatechol or 1,2-dihydroxybenzene, is an organic compound with the molecular formula C6H4(OH)2 (Figure 8.1). In humans, catechols can occur as metabolites in the degradation of benzene or estrogens (Bolton et al., 1998; Porteous et al., 1949) or as endogenous compounds, such as neurotransmitter and their precursors (adrenaline, noradrenaline, dopamine, and l-3,4dihydroxyphenylalaline [l-DOPA]) (Schweigert et al., 2001). Additionally, catechols can be taken up in the form of tobacco smoke (as catechol, catechol semiquinones, and polymerized catechols) (Pryor et al., 1998; Stone et al., 1995). The toxicity of catechols for microorganisms has been demonstrated in the past years (Boyd et al., 1997; Capasso et al., 1995; Fritz et al., 1991; Hellmér et al., 1992) and has been suggested to be the reason for the difculties in cultivating microorganisms on benzene, toluene, or chlorobenzene (Fritz et al., 1991). Several studies additionally indicated the toxicity of catechols for water ea, zebra sh, trout, rabbit, cat, rat, mouse, and human cell lines (Garton and Williams, 1948; Hattula et al., 1981; Pellack-Walker et al., 1985; Rahouti et al., 1999; Schweigert et al., 2001; Van Den Heuvel et al., 1999). Indeed, in the environment toxic concentrations of catechols have been found (Capasso et al., 1995). Despite the facts that catechols are ubiquitous and their toxicity has been observed in a variety of organisms, the modes of action causing the toxicity are hardly understood. Catechols can form stable complexes with various di-and trivalent metal ions, the complexes with trivalent ions being the most stable. Catechols can also undergo redox reactions, cycling between catechols, semiquinone radicals, and orthobenzoquinone (Schweigert et al., 2001).
