Antioxidant properties of 4,4'-dihydroxy-3,3'-dimethoxy-β,β'-bicinnamic acid (8-8-diferulic acid, non-cyclic form)

8-8-Diferulic acid (non-cyclic form) (4,4'-dihydroxy-3,3'-dimethoxy-β,β'-bicinnamic acid) was chemically synthesised and the antioxidant properties were assessed using (a) inhibition of ascorbate/iron-induced peroxidation of phosphatidylcholine liposomes, and (b) scavenging of the radical cation of ABTS (2,2'-azinobis (3-ethyl-benzothiazoline-6-sulphonate)) relative to the water-soluble vitamin E analogue, Trolox C. The structure of the chemically synthesised 8-8 dimer was confirmed by ¹H-NMR and mass spectrometry. Its absorption properties in ethanol were: λ(max1): 320nm; λ(max2): 287nm; λ(min): 256nm; ε(λmax1) (M^-1cm^-1): 14200±1700 and ε(λmax2) (M^-1cm^-1): 14300 ± 1300. The 8-8 dimer showed the best antioxidant properties in the aqueous phase assay among the esterified dimers present in plant cell walls. Like the other ferulic dimers, 8-8-diferulic acid is a better inhibitor of lipid peroxidation than ferulic acid on a molar basis. Some of the factors possibly involved in the antioxidant effect of these compounds are: number of free hydroxyl groups in the molecule, stability of transient radical and partition coefficient.