Recent Advances in Polyphenol Research. Группа авторов

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0.33 — — Schematic illustration of (left) the polyacylated anthocyanins depiction of the relative energy levels at equilibrium using the hydration and acidity constants reported by the authors.

      Source: Dangles et al. 1993.

Schematic illustration of the energy level diagram of the compound HBA1 extended to the mono-anionic species.

      Source: Mendoza et al. 2018.

      1.4.2 2‐Hydroxyflavylium Derivatives and Flavanones

      Figure 1.6 shows the spectral variations after a direct pH jump to pH=8.1 (Slavcheva, et al. 2018). A few seconds after the pH jump the anionic hemiketal and cis‐chalcone are formed (Figure 1.6a). The system evolves and gives the anionic trans‐chalcone after c. 40 minutes. However, equilibrium is reached four hours later, only after formation of the flavanone (FLV; Figure 1.6b), indicating that the flavanone is formed from the anionic trans‐chalcone. Acidification of the flavanone does not give any spectral variation, but basification to pH=12.0 very quickly gives Ct2‐ (kobs = 3.3 s‐1). When the titration of Ct2‐ by reverse pH jump is carried out, the absorption spectra of Ct and Ct are observed according to the final pH. The spectrum of Ct is stable and the one of Ct gives the flavanone as in Figure 1.6b.

Molecular structures of 2’-hydroxy-5’-methylflavylium and its derived flavanone form. Graphs depict (a) spectral variations after a direct pH jump from pH equals 1 to pH equals 8.1 of the compound 2’-hydroxy-5-methylflavylium up to 40 minutes; (b) the same after 40 minutes up to 4 hours; (c) reverse pH jump from pH equals 12 to pH equals 8.4.

      Source: Slavcheva, et al. 2018. © 2018 Elsevier.

Schematic illustration of the concept of a timer with reset capacity through a metamorphosis cycle.

      Source: Slavcheva, et al. 2018. © 2018 Elsevier.

      1.4.3 6,8 Rearrangements