Cis−Trans Isomerizations of β-Carotene and Lycopene: A Theoretical Study

Abstract

The all-trans to mono-cis isomerizations of polyenes and two C40H56 carotenes, beta-carotene and lycopene, at the ground singlet (S0) and triplet (T1) states are studied by means of quantum chemistry computations. At the S0 state of polyenes containing n acetylene units (Pn), we find that the energy barrier of the central C=C rotation decreases with n. In contrast, however, at the T 1 state, the rotational barrier increases with n. For the C40H56 carotenes, the rotational barriers of lycopene are lower than those of their beta-carotene counterparts. This difference renders the rotational rates of lycopene to be 1-2 orders of magnitude higher than those of beta-carotene at room temperature. For both these carotenes, the barrier is lowest for the rotation toward the 13-cis isomer. The relative abundances are in the following order: all-trans > 9-cis > 13-cis > 15-cis. Although the 5-cis isomer of lycopene has the lowest energy among the cis isomers, its formation from the all-trans form is restricted, owing to a very large rotational barrier. The possible physiological implications of this study are discussed.

Plant Carotene Cis-Trans Isomerase CRTISO

“…S8). It is also noted that the abundance of the various lycopene species at equilibrium corresponds roughly to their relative theoretical energy levels calculated by Guo et al (31).…”

“…Quantum chemistry calculations indicate that the 5-cis isomer of lycopene (f) has the lowest energy among the lycopene cis isomers considered in this investigation (31). However, its formation from all-trans-lycopene (step g Ͼ f, k 18 in Fig.…”

“…However, its formation from all-trans-lycopene (step g Ͼ f, k 18 in Fig. 8) is assumed to occur at a very low rate due to the predicted presence of a large rotational energy barrier (31). In the presence of CRTISO, this isomer (f) was found to be formed from poly-cis configured precursors but not from all-trans-lycopene (supplemental Fig.…”

In vitro antioxidant capacity of tomato products: Relationships with their lycopene, phytoene, phytofluene and alpha-tocopherol contents, evaluation of interactions and correlation with reflectance measurements

“…The major (Z)-isomer in both types of samples was (5Z)-LYC. The differentiation between different LYC isomers is important as they are thought to have different properties, bioavailabilities and metabolic fates (Guo, Tu, & Hu, 2008;Honest, Zhang, & Zhang, 2011). In fact, it is well known that human plasma and tissues contain high levels of (Z)-isomers of LYC, despite the fact most of the dietary LYC is (all-E)-LYC (Fr€ ohlich, Kaufmann, Bitsch, & B€ ohm, 2006;Stahl & Sies, 1992).…”

Isolation and characterization of (15 Z )-lycopene thermally generated from a natural source

“…The other theoretically-possible mono-Zisomer by heating, (15Z)-lycopene ( Fig. 1), was rationally synthesized via a Wittig reaction [14,15], but still remains to be assumed because it could not be prepared nor identified during the heat or photoirradiation process, possibly because of thermodynamic instability, the presence of a small amount of the lycopene isomer generated by isomerization [16], and hence difficulty in separation by ordinary chromatographic means. On the other hand, the structure [17,18], thermal isomerization [19], and bioavailability and function [20] of a similar symmetrical carotenoid of (15Z)-bcarotene have been extensively examined.…”