p-Hydroxyphenyl-pyranoanthocyanins: An Experimental and Theoretical Investigation of Their Acid-Base Properties and Molecular Interactions.
The physicochemical properties of the wine pigments catechyl-pyranomalvidin-3-O-glucoside (PA1) and guaiacyl-pyranomalvidin-3-O-glucoside (PA2) are extensively revisited using ultraviolet (UV)-visible spectroscopy, dynamic light scattering (DLS) and quantum chemistry density functional theory (DFT) calculations. In mildly acidic aqueous solution, each cationic pigment undergoes regioselective deprotonation to form a single neutral quinonoid base and water addition appears negligible. Above pH = 4, both PA1 and PA2 become prone to aggregation, which is manifested by the slow build-up of broad absorption bands at longer wavelengths (λ ≥ 600 nm), followed in the case of PA2 by precipitation. Some phenolic copigments are able to inhibit aggregation of pyranoanthocyanins (PAs), although at large copigment/PA molar ratios. Thus, chlorogenic acid can dissociate PA1 aggregates while catechin is inactive. With PA2, both chlorogenic acid and catechin are able to prevent precipitation but not self-association. Calculations confirmed that the noncovalent dimerization of PAs is stronger with the neutral base than with the cation and also stronger than π-π stacking of PAs to chlorogenic acid (copigmentation). For each type of complex, the most stable conformation could be obtained. Finally, PA1 can also bind hard metal ions such as Al3+and Fe3+and the corresponding chelates are less prone to self-association.
Institut National de la Recherche Agronomique (INRA), UMR1083 Sciences pour l'œnologie, 2 place Pierre Viala, 34060 Montpellier CEDEX, France. avallverdu@ub.edu.|CIBER Fisiopatología de la Obesidad y la Nutrición (CIBEROBN), Instituto de Salud Carlos III, 28903 Madrid, Spain. avallverdu@ub.edu.
Anna
A
Vallverdú-Queralt
INSERM UMR 850, University of Limoges, School of Pharmacy, 2 rue du Dr. Marcland, F-87025 Limoges, France. michal.biler@seznam.cz.|Department of Biophysics, Centre of the Region Haná for Biotechnological and Agricultural Research, Palacký University, Šlechtitelů 27, 78371 Olomouc, Czech Republic. michal.biler@seznam.cz.
Michal
M
Biler
Institut National de la Recherche Agronomique (INRA), UMR1083 Sciences pour l'œnologie, 2 place Pierre Viala, 34060 Montpellier CEDEX, France. meudec@supagro.inra.fr.
Emmanuelle
E
Meudec
Institut National de la Recherche Agronomique (INRA), UMR1083 Sciences pour l'œnologie, 2 place Pierre Viala, 34060 Montpellier CEDEX, France. leguerneve@supagro.inra.fr.
Christine Le
CL
Guernevé
Institut National de la Recherche Agronomique (INRA), UMR1083 Sciences pour l'œnologie, 2 place Pierre Viala, 34060 Montpellier CEDEX, France. vernhet@supagro.inra.fr.
Aude
A
Vernhet
Institut National de la Recherche Agronomique (INRA), UMR1083 Sciences pour l'œnologie, 2 place Pierre Viala, 34060 Montpellier CEDEX, France. mazauric@supagro.inra.fr.
Jean-Paul
JP
Mazauric
Institut National de la Recherche Agronomique (INRA), UMR1083 Sciences pour l'œnologie, 2 place Pierre Viala, 34060 Montpellier CEDEX, France. jean-luc.legras@inra.fr.
Jean-Luc
JL
Legras
INRA, UMR408 SQPOV, University of Avignon, 84000 Avignon, France. michele.loonis@inra.fr.
Michèle
M
Loonis
INSERM UMR 850, University of Limoges, School of Pharmacy, 2 rue du Dr. Marcland, F-87025 Limoges, France. patrick.trouillas@unilim.fr.|Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacký University Olomouc, tř. 17. listopadu 12, 77146 Olomouc, Czech Republic. patrick.trouillas@unilim.fr.
Patrick
P
Trouillas
Institut National de la Recherche Agronomique (INRA), UMR1083 Sciences pour l'œnologie, 2 place Pierre Viala, 34060 Montpellier CEDEX, France. cheynier@supagro.inra.fr.
Véronique
V
Cheynier
INRA, UMR408 SQPOV, University of Avignon, 84000 Avignon, France. olivier.dangles@univ-avignon.fr.
Olivier
O
Dangles
D000535:Aluminum / Q000737:chemistry; D000872:Anthocyanins / Q000737:chemistry*; D002392:Catechin / Q000737:chemistry; D011232:Chemical Precipitation; D002726:Chlorogenic Acid / Q000737:chemistry; D003116:Color; D019281:Dimerization; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D007502:Iron Chelating Agents / Q000737:chemistry*; D008968:Molecular Conformation; D010860:Pigments, Biological / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory; D013237:Stereoisomerism; D013816:Thermodynamics; D014920:Wine / Q000032:analysis*
D000872:Anthocyanins; D007502:Iron Chelating Agents; D010860:Pigments, Biological; D011522:Protons; D002726:Chlorogenic Acid; D002392:Catechin; D000535:Aluminum; D007501:Iron
UV-visible absorption; acid-base; copigmentation; metal complexation; pyranoanthocyanins; self-association