The reaction of malvin chloride (malvidin 3,5-diglucoside) with a flavonoid compound rutin (quercetin 3-rutinoside) is investigated. Reactions of these molecules are observed through UV−vis absorption spectra, to identify the factors that influence the copigmentation as well as the characteristics of the copigment formed. It is established that the copigmentation process takes place in buffer solutions at a specific pH value and that it is conditioned by the mole ratio and temperature. Copigment formation is defined by kinetic and thermodynamic parameters. Keywords: Copigmentation; anthocyans; rutin; UV−vis spectra

Using UV−vis spectrophotometry we have established that a process of copigmentation takes place between an anthocyan molecule, malvin chloride (malvidin 3,5-diglucoside), and a nonglycosidized pentahydroxyflavone, quercetin (3,5,7,3‘,4‘-pentahydroxyflavone). The kinetic and thermodynamic parameters, by which the process is characterized, were correlated to the structure, i.e., the nature and position of the substituents in the interacting molecules. Keywords: Copigmentation; quercetin; UV−vis spectra; kinetic and thermodynamic parameters

It has been generally accepted that, due to high ionization potential values, single electron transfer followed by proton transfer (SET-PT) is not a plausible mechanism of antioxidant action in flavonoids. In this paper the SET-PT mechanism of quercetin (Q) was examined by revealing possible reaction paths of the once formed quercetin radical cation (Q(+)˙) at the M0-52X/6311+G(d,p) level of theory. The deprotonation of Q(+)˙ was simulated by examining its chemical behavior in the presence of three bases: methylamine (representative of neutral bases), the MeS anion (CH3S(-)) and the hydroxide anion (representative of anionic bases). It was found that Q(+)˙ will spontaneously be transformed into Q in the presence of bases whose HOMO energies are higher than the SOMO energy of Q(+)˙ in a given medium, implying that Q cannot undergo the SET-PT mechanism in such an environment. In the reaction with the MeS anion in both gaseous and aqueous phases and the hydroxide anion in the gaseous phase Q(+)˙ accepts an electron from the base, and so-formed Q undergoes the hydrogen atom transfer mechanism. On the other hand, SET-PT is a plausible mechanism of Q in the presence of bases whose HOMO energies are lower than the SOMO energy of Q(+)˙ in a given medium. In such cases Q(+)˙ spontaneously donates a proton to the base, with energetic stabilization of the system. Our investigation showed that Q conforms to the SET-PT mechanism in the presence of methylamine, in both gaseous and aqueous phases, and in the presence of the hydroxide anion, in the aqueous solution.

The process of copigmentation between malvin chloride (malvidin 3,5-diglucoside) and morin hydrate (3,5,7,2‘4‘-pentahydroxyflavone) was studied. The UV−vis absorption spectra were used to define the optimum conditions for the formation of copigment, as well as their characteristics. It was established that the copigmentation process does not depend only on the number of hydroxy groups but also on their mutual position. The copigment formation is spectrally manifested in a bathochromic and hyperchromic shift of the longest wavelength absorption band. The copigment formed is defined by kinetic and thermodynamic parameters. Keywords: Copigmentation; morin; UV−vis spectra; kinetic and thermodynamic parameters

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