On the reaction of ozone with beta-carotene, a naturally occurring polyene

The reaction of beta-carotene with ozone was studied in detail by UV-Vis-NIR spectroscopy. The radical cation of beta-carotene was observed during the ozonization of this molecule. Ozonization causes trans-cis isomerization of beta-carotene at its 15-15' site and then a scission to retinal which in its turn is then degraded by further ozonization to unsaturated and conjugated aldehydes and dialdehydes. The antiozonant properties of beta-carotene were tested by measuring the viscosity change undergone by an ozonized standard solution of cis-1,4-polybutadiene in the presence of beta-carotene and without any protection. Surprisingly it was found that the dienic rubber scavenges the oxygen and protects beta-carotene from ozone attack. In these conditions the behaviour of linear and conjugated polyene beta-carotene was found fully comparable to the behaviour of the tridimensional weakly cross-conjugated polyene C-60 fullerene. Cis-1,4-polybutadiene ozonized in the presence and without beta-carotene was studied by FT-IR spectroscopy. (C) 1996 Elsevier Science Limited