83554-48-7Relevant academic research and scientific papers
The hemiacetal-cis-chalcone equilibrium of malvin, a natural anthocyanin
Brouillard, Raymond,Lang, Jacques
, p. 755 - 761 (2007/10/02)
In slightly acidic aqueous solutions, malvin essentially exists, in a stable form, as a fast equilibrating reaction between a ring structure, the hemiacetal B, and a chain structure, the cis-chalcone CE.The temperature-jump technique has been used for the determination of the relaxation time τ characterizing this equilibrium.At 20 deg C τ-values were found to be in the range 1 s (for the more acidic solutions) to 2 x 10-4 s (for the neutral solutions).Both buffered and unbuffered solutions were investigated.It was found that τ is largly dependent upon pH andupon the concentration of the buffer.For instance, at constant pH, a plot of the observed first-order rate constant τ-1 versus the acetic acid - sodium acetate buffer concentration shows a nonlinear variation that can only be interpreted as a change in the proton transfer rate-limiting step with the buffer concentration.At 20 deg C, the constant K = E>/ is 0.25 (+/- 0.05) and the enthalpy change ΔH associated with this equilibrium is 20.7 (+/-2) kJ mol-1.Therefore, increasing the temperature greatly enhances the stability of the open cis-chalcone isomer.Possible implications arising from the existence of a fast chemical ring-closure reaction, in the case of natural anthocyanins, for the biosynthesis of flavonoids are discussed.In particular, it is suggested that, along with the main biosynthetic pathway to flavonoids, a minor pathway involving the anthocyanin cis-chalcone CE could also occur under favorable circumstances.Physico-chemical conditions in the plant organelles containing flavonoids (vacuoles) make this alternative plausible.
