Do We See the True Color of Anthocyanidins?

Area of Science:

• Plant biochemistry
• Computational chemistry
• Color science

Background:

• Anthocyanins are natural pigments in plants, responsible for vibrant colors in petals, leaves, and fruits.
• They are potential candidates for natural dyes due to their color-changing properties with pH.
• The structural transformations of anthocyanidins, such as flavylium cation, quinoidal base, and quinoidal base anion, are associated with red, purple, and blue colors, respectively.

Purpose of the Study:

• To computationally evaluate the color of quinoidal base monomers of anthocyanins.
• To predict color changes upon dimerization or complex formation of anthocyanin molecular species.
• To clarify the actual contributors to the observed colors in anthocyanin solutions.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Time-Dependent DFT (TD-DFT) calculations for color prediction.
• Modeling of dimerization and complex formation of anthocyanin species.

Main Results:

• The study computationally determined the colors associated with specific anthocyanin structures.
• Predicted color shifts were observed for dimerized and complexed anthocyanin species.
• Calculations indicated that observed solution colors result from a mixture of multiple coexisting molecular species.

Conclusions:

• The perceived colors of anthocyanin solutions are not solely due to individual molecular species like quinoidal bases.
• A combination of various coexisting molecular forms, influenced by chemical equilibrium, dictates the observed colors.
• Computational modeling provides a method to understand the complex color phenomena in anthocyanin systems.