Theoretical Characterization by Density Functional Theory (DFT) of Delphinidin 3-O-Sambubioside and Its Esters Obtained by Chemical Lipophilization
Anthocyanins are water-soluble phenolic pigments. However, their poor solubility in lipidic media limits their use. This hurdle can be overcome with the lipophilization of anthocyanins, which consists of adding an aliphatic chain to a hydrophilic compound, in order to increase its solubility in lipids. Still, the unspecific chemical lipophilization of anthocyanin-esters produces molecules with different properties from their precursors. In this work, experimental changes of anthocyanin-esters
... tained by chemical lipophilization are investigated in silico aiming specifically at observing their molecular behavior and comparing it with their anthocyanin precursor. Thus, the analysis of delphinidin 3-O-sambubioside and its esters employing Density Functional Theory (DFT) methods, such as the hybrid functional B3LYP in combination with the 6-31++G(d,p) Pople basis set, provides the ground state properties, the local reactivity and the molecular orbitals (MOs) of these compounds. Excited states properties were analyzed by TD-DFT with the B3LYP functional, and the M06 and M06-2X meta-GGA functionals. Local reactivity calculations showed that the electrophilic site for all the anthocyanin-esters was the same as the one for the anthocyanin precursor, however the nucleophilic site changed depending localization of the esterification. TD-DFT results indicate that the place of esterification could change the electronic transitions and the MOs spatial distribution. Molecules 2018, 23, 1587 2 of 16 reaction consists of adding an aliphatic chain to the hydrophilic anthocyanin, in order to change the polarity in the molecule and favor its solubility in non-polar matrixes. For example, a recently reported enzymatic lipophilization of malvidin 3-O-glucoside with oleic acid and Candida antarctica lipase B as catalyst generated a single anthocyanin-ester with attractive color characteristics  . In a different study  , a chemical reaction was performed with delphinidin 3-O-sambubioside (DpS) and octanoyl chloride in an acidic medium; the reaction produced mono-, di-and tri-esters which could not be purified and fully characterized by experimental methods. Figure 1. Structure of anthocyanidins: pelargonidin, cyanidin, peonidin, delphinidin, malvidin and petunidin.