Isolation and spectral characterization of thermally generated multi-<i>Z</i>-isomers of lycopene and the theoretically preferred pathway to di-<i>Z</i>-isomers

<p>Lycopene has a large number of geometric isomers caused by <i>E</i>/<i>Z</i> isomerization at arbitrary sites within the 11 conjugated double bonds, offering varying characteristics related to features such as antioxidant capacity and bioavailability. However, the geometric structures of only a few lycopene <i>Z</i>-isomers have been thoroughly identified from natural sources. In this study, seven multi-<i>Z</i>-isomers of lycopene, (9<i>Z</i>,13′<i>Z</i>)-, (5<i>Z</i>,13<i>Z</i>,9′<i>Z</i>)-, (9<i>Z</i>,9′<i>Z</i>)-, (5<i>Z</i>,13′<i>Z</i>)-, (5<i>Z</i>,9′<i>Z</i>)-, (5<i>Z</i>,9<i>Z</i>,5′<i>Z</i>)-, and (5<i>Z</i>,9<i>Z</i>)-lycopene, were obtained from tomato samples by thermal isomerization, and then isolated by elaborate chromatography, and fully assigned using proton nuclear magnetic resonance. Moreover, the theoretically preferred pathway from (all-<i>E</i>)-lycopene to di-<i>Z</i>-isomers was examined with a computational approach using a Gaussian program. Fine-tuning of the HPLC separation conditions led to the discovery of novel multi-<i>Z</i>-isomers, and whose formation was supported by advanced theoretical calculations.</p> <p>Isolation and characterization of novel (multi-<i>Z</i>)-lycopene, and a possible potential energy diagram for the formation to the isomer.</p