Estimation of conjugated C = C bonds effective number and conjugation energy of carotenoids

• Published in: Journal of molecular modeling 2021-10, Vol.27 (10), p.281-281, Article 281
• Main Authors: Finkelshtein, Eugene I., Shamsiev, Ravshan S.
• Format: Article
• Language: English
• Subjects: Carotene; Carotenoids; Chains; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Computer Appl. in Life Sciences; Computer Applications in Chemistry; Conjugation; Electron transitions; Electronic spectra; Homology; Mathematical analysis; Molecular Medicine; Original Paper; Rings (mathematics); Theoretical and Computational Chemistry
• ISSN: 1610-2940; 0948-5023
• DOI: 10.1007/s00894-021-04896-w

Effective numbers of conjugated double C = C bonds, N eff , were estimated for the first time for three groups of carotenoids containing β-rings—β-apo-hydrocarbons, β-apo-carotenols, and β-carotene homologues. The estimations were performed by comparing the 0–0 energies of the S 0  →  S 2 transitions in the electronic spectra of the selected molecules with the energies of the respective electronic transitions of the corresponding linear carotenoids with the same number of conjugated C = C double bonds, N . To verify these results, the conjugation energies of the carotenoids were calculated for the first time and it was shown that the conjugation energy relations of the containing β-rings and linear compounds are in good agreement with the N eff / N ratios. It is also shown that the conjugation energy of the β-ring double bond with the linear conjugated chain practically does not depend on N , only slightly increasing with its length (less than 5%). According to the DFT calculations, the contribution of the β-ring C = C bond to the conjugation energy of β-apo-carotenoids and β-carotene homologues is on average about 0.3 of the contribution of the linear chain C = C bond. Thus, for β-apo-carotenoids (one β-ring), the dependence of N eff on N may be expressed by the equation N eff  = ( N  − 0.7) and for β-carotene homologues (2 β-rings) by the equation N eff  = ( N  − 1.4).