Structural Features of Copigmentation of Oenin with Different Polyphenol Copigments

Abstract

The copigmentation binding constants (K) for the interaction of different copigments with oenin (major red wine anthocyanin) were determined. All tests were performed in a 12% ethanol citrate buffer solution (0.2 M) at pH 3.5, with an ionic strength adjusted to 0.5 M by the addition of sodium chloride. Over the past years, several copigmentation studies were made and many copigments were tested, but none of them included prodelphinidin B3 or a dimeric-type adduct like oenin-(O)-catechin, probably due to the difficulty in obtaining them. The data yielded from this study allowed concluding that (a) the presence of a pyrogallol group in the B ring of the flavan-3-ol structure slightly increases the copimentation potential and (b) within all copigments tested oenin-(O)-catechin was revealed to be the best. According to computational studies performed on epicatechin/oenin, epigallocatechin/oenin, procyanidin B3/oenin, and oenin-(O)-catechin/oenin complexes, the ΔGbinding energy of the oenin-(O)-catechin/oenin complex is the most negative compared to the other copigmentation complexes, hence being more stable and thermodynamically favored. All structural data show that oenin-(O)-catechin and epigallocatechin are closer to the pigment molecule, which is in accordance with these two copigments having the highest experimental copigmentation binding constants for oenin.

Copigmentation of malvidin-3-O-glucoside with five hydroxybenzoic acids in red wine model solutions: Experimental and theoretical investigations

“…As seen from Table 1, the DG°and DH°values were negative for all of these complexes, indicating that theses copigmentations were spontaneous and thermodynamically favored. This finding was consistent with some previous reports (Baranac, Petranovic, & DimitricMarkovic, 1996;Brouillard et al, 1989;Lambert et al, 2011;Malaj et al, 2013;Markovic et al, 2000;Sun et al, 2010;Teixeira et al, 2013). It was known that the enthalpy change was a measure of the energy barrier that must be overcome by the reacting molecules and related to the strength of the binding (Mercali, Jaeschke, Tessaro, & Marczak, 2013).…”

“…It could be expected that the binding strengths for the copigmentation reactions were the same as the order of K values. Of course, these results should be related to the structural features because the cofactors with more hydroxyl or methoxyl groups might form more hydrogen bonds with M3OG to showing stronger interactions, which was agreed with some previous findings (Teixeira et al, 2013). The stoichiometric constant (n) determined by the plots of ln [(A À A 0 )/A 0 ] vs ln [CP] 0 , describing the association between the cofactors and the researched anthocyanins.…”

“…The copigmentation results in an increase of absorbance in the visible range (hyperchromic shift) and a positive shift of the wavelength of the maximum absorbance (bathochromic shift), making the changes of colour tendency and intensity detectable (Malaj, De Simone, Quartarolo, & Russo, 2013;Teixeira et al, 2013). Besides, such as the ionic strength, pH, solvent, temperature, the presence of metal salts (Asen, Stewart, & Norris, 1972;Raymond Brouillard & Dangles, 1994;Mistry, Cai, Lilley, & Haslam, 1991), the molecular structures of anthocyanins and cofactors are also important for the copigmentation (Sousa et al, 2014).…”

Copigmentation between malvidin-3- O -glucoside and hydroxycinnamic acids in red wine model solutions: Investigations with experimental and theoretical methods

“…And at further higher pH value, the deprotonation reaction leads to the purple neutral quinonoid base forms (A) (Dueñas, Salas, Cheynier, Dangles, & Fulcrand, 2006). As the average pK h (2.0-3.0) values of anthocyanins are lower than the normal pH values of red wines (~3.6), the equilibrium of anthocyanins will be largely displaced toward the colorless hydrated hemiketal forms (N70%) (Teixeira et al, 2013). While nucleophilic attack of SO 2 at C 4 position of the flavylium cations may also cause discoloration of red wines.…”

“…Previous researches also reported that the infrared (IR) vibrational spectra were used to reveal the existence of hydrogen bonds in the copigmentation complex (Dimitric Markovic, Baranac, & Brdaric, 2005). Additionally, the quantum mechanics calculation was employed to study the copigmentation (Di Meo, Sancho Garcia, Dangles, & Trouillas, 2012;Nave et al, 2012), which disclosed the copigmentation mechanism from the micro perspective, including the intermolecular bonding type (Zhang et al, 2015), electron and charge transfer (Ferreira da Silva et al, 2005), copigmentation complex conformation (Sousa et al, 2014), thermodynamic parameters (Teixeira et al, 2013), and others (Kalisz, Oszmiański, Hładyszowski, & Mitek, 2013).…”