Abstract
On the basis of the dispersion-corrected density functional theory, a computational model is proposed to describe the oenin/syringic acid copigmentation and to explore the non-covalent interaction between the anthocyanin and the copigment in the framework of implicit solvent approach. The predicted binding free energy and visible spectrum shift of this copigmentation complex are in accordance with the experimental observations. The used model provides a good structural description of oenin/syringic acid complex and suggests that the intermolecular hydrogen bonding, in which the hydroxyl-rich sugar moiety in oenin plays a key role, may be the determinant for the formation and nature of the copigmentation complex.
Highlights
Since a normal pH of red wines is around 3.5, syringic acid shall mainly exhibit in the protonated state under such a condition, which is just what we studied and discussed above
- Eleven preferable conformers for the copigmentation complex oenin/syringic acid were selected after an accurate sampling of the conformational space
The stabilization of the lowest lying energy conformer was proved to be due in large part to the intermolecular hydrogen bonds (HBs) interactions
Summary
Red wine color depends mainly on composition of anthocyanins (Han et al, 2015, 2019) whose flavylium cation skeleton, prone to hydration or proton transfer reactions, leads to the decline of chromatic quality of red wines (Fulcrand et al, 2006; Escribano-Bailon and Santos-Buelga, 2012; Trouillas et al, 2016). Anthocyanins present an inherent nature of associating with copigments (Escribano-Bailon and Santos-Buelga, 2012; Trouillas et al, 2016; Cortez et al, 2017; Qian et al, 2017; Gras et al, 2018), e.g., colorless polyphenols, which allows to maintain the flavylium cation state and to stabilize the color (Boulton, 2001; Gómez-Míguez et al, 2006; Malaj et al, 2013; Trouillas et al, 2016; Qian et al, 2017; Ertan et al, 2018; Gras et al, 2018; He et al, 2018; Tan et al, 2018; You et al, 2018; Fan et al, 2019; Klisurova et al, 2019; Sun et al, 2019; Xue et al, 2019; Xu et al, 2019) This phenomenon is known as copigmentation effect. That may be the reason why often in the experiments a small number of copigments is taken into account (Boulton, 2001; Gómez-Míguez et al, 2006; Kunsági-Máté et al, 2006; Lambert et al, 2011; Kalisz et al, 2013; Malaj et al, 2013; Teixeira et al, 2013; Xu et al, 2015, 2019; Zhang et al, 2015; Ertan et al, 2018; He et al, 2018; Tan et al, 2018; You et al, 2018; Fan et al, 2019; Klisurova et al, 2019; Sun et al, 2019; Xue et al, 2019)
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