Circular dichroism of tocopherols versus tocotrienols

Abstract

Vitamin E is an essential nutrient of still increasing economic importance. Vitamin E derivatives include many nonracemic chiral compounds whose chirooptical characterization is scarcely described in the literature. We report the CD spectra of delta-tocopherol and its unsaturated analog delta-tocotrienol. TDDFT calculations demonstrate that the weak CD of delta-tocopherol is determined by the helicity of dihydropyrane ring. In addition, the moderate CD of delta-tocotrienol is due to the exciton interaction between the aromatic ring and the closest alkene group. Direct exciton-coupled CD calculations on structures generated by two different conformational sampling approaches reveal that, although such exciton coupling is expected to be weak, it is sufficient to explain the spectral differences between tocopherol and tocotrienol.

Vitamin E Circular Dichroism Studies: Insights into Conformational Changes Induced by the Solvent’s Polarity

“…The data highlights the correspondence between the absorbance band and the measured molar ellipticity. Mazzini et al reported the CD spectra of δ -tocopherol and tocotrienol homologues, as well as garcinoic acid ( δ -tocotrienolic acid) in methanol in the near and medium UV range [17], and our spectra from dToc in methanol are in good qualitative agreement (discussed further below).…”

“…Calculations by Mazzini suggest this to be the ${}^1$L${}_{\mathrm{normala}}$ chromane band; however, they claim it is below the larger ${}^1$B${}_{\mathrm{normalb}}$ band. Although it does seem to be present in their dToc/methanol data, it does not play a significant role in the much larger tocotrienol signal, and therefore Mazzini et al do not focus on it [17]. …”

“…Mazzini et al attribute the negative, high energy band seen in aToc and dToc to a valence to Rydberg electron transition, where it becomes positive with a switch from P-helicity (positive dihedral angle C-8a, O, C-2, C-3) to M-helicity of the chromane [17]. This raises the question of why the other bands do not change sign.…”

“…A few CD spectra of tocotrienols, tocopherols, and tocopherol esters have been published over the years; however, to the best of our knowledge, there are no published electronic CD spectra of α -tocopherol, the most biologically active member of the vitamin E family [5,17]. In addition, there has been only one study in the mid-UV region (190–220 nm), where features of the CD signal increase significantly.…”

New Anthracene Derivatives – Structure Elucidation and Antimicrobial Activity

“…The discrepancy observed for the first CD band at 350-450 nm is not uncommon for aromatic π-π* 1 L b -type transitions. [14][15][16] Thus, the absolute configuration of 1 is (1ЈS,2ЈR,3ЈS,4ЈR)-1. As the CD spectrum of 5 is nearly identical to that of 1 ( Figure S2), the absolute configuration of 5 [17,18] is also assigned as (1ЈS,2ЈR,3ЈS,4ЈR)-5.…”