Anthocyanins/Anthocyanidins are pigments produced by plants that are found in wine and other familiar food sources, which display dramatic absorption of light with wavelengths in the visible region of the electromagnetic spectrum. These anthocyanin/anthocyanidins pigments appear yellow, red, blue, or purple, depending on their pH conditions and differing R groups. These pigments contribute to overall wine quality, since they determine the color of the wine as well as contribute to acid-base and oxidation chemistry. The anthocyanin solutions in this study were newer (2013 Barbera D’Asti) and aged wine (2004 Barbaresco Riserva) samples diluted with various solutions that contained combinations of water, tartaric acid, ethanol, and sodium hydroxide. UV-vis spectrophotometry was used to quantify the anthocyanins in monomer form and as they polymerize over time. The absorption values at 420 and 520 nm were used to calculate the Intensity and Hue of the color. To better understand the detailed absorption spectrum of specific anthocyanins, we employed time dependent density functional theory to predict the computational difference of UV-vis absorption spectra of various anthocyanidins with distinct side groups, under different pH conditions. For instance, exchanging one hydroxide (OH) group for a methyl (CH<sub>3</sub>) group results in a shift of 5 nm in the maximum absorbance wavelength, while exchanging one OH group for a methoxy (OCH<sub>3</sub>) group results in a much more dramatic shift. Creating a predictive understanding of each molecule with modified R groups from natural plant pigment absorption spectra may be useful in designing molecular structures with optimal spectra for light harvesting applications.

Experimental and first principles prediction of UV-vis spectra of natural dye molecules as a function of solvent and pH

251st National Meeting (2016)

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