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

8-8-Diferulic acid (non-cyclic form) (4,4'-dihydroxy-3,3'-dimethoxy-beta,be ta'-bicinnamic acid) was chemically synthesised and the antioxidant propert ies were assessed using (a) inhibition of ascorbate/iron-induced peroxidati on of phosphatidylcholine liposomes, and (b) scavenging of the radical cati on of ABTS (2,2'-azinobis (3-ethyl-benzothiazoline-6-sulphonate)) relative to the water-soluble vitamin E analogue, Trolox C. The structure of the che mically synthesised 8-8 dimer was confirmed by H-1-NMR and mass spectrometr y. Its absorption properties in ethanol were: lambda(max1): 320nm; lambda(m ax2): 287nm; lambda(min): 256nm; epsilon(lambda max1) (M(-1)cm(-1)): 14200/-1700 and epsilon(lambda max2) (M(-1)cm(-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 dime rs, 8-8-diferulic acid is a better inhibitor of lipid peroxidation than fer ulic acid on a molar basis. Some of the factors possibly involved in the an tioxidant effect of these compounds are: number of free hydroxyl groups in the molecule, stability of transient radical and partition coefficient. (C) 1999 Society of Chemical Industry.