A computational approach to the photochemical properties of 3-hydroxycinnamic acids

TOBIAS SCHMIDT DE LEÓN; PAU ARROYO MAÑEZ; MARIA LAURA SALUM; GABRIEL DE PIANO; F. JAVIER LUQUE; ROSA ERRA-BALSELLS

Castellón de la Plana

Congreso; 10th Congress on Electronic Structure: Principles and Applications; 2016

Cinnamic acid derivatives in both E and Z isomers are present in all kinds of plants, and hence in herbs and derived medicines, cosmetics and foods. In nature, these compounds act as antioxidant and growth regulators in plants, fungi, bacteria and viruses, and their therapeutic and technological applications have increased exponentially. For example, two members of the family, 3,5-dimetoxy-4-hydroxy-cinnamic and α-cyano-4-hydroxy-cinnamic acids, are used as MALDI-MS photosensitizers for proteomic analysis. For this reason, deeper understanding of the physicochemical properties is necessary. Because of their molecular structure cinnamic acids can exist in E- and Z-forms, but only the E-isomers are commercially available. So, very few studies over Z-cinnamic acids have been reported. A novel and successful method of synthesis of Z-cinnamic acids by photoisomerization using commercial E-cinnamic acids has been developed by Salum et al1. During the studies of photoisomerization of E-cinnamic acids in acetonitrile a peculiar distinctive trend was observed: while E-3-hydroxycinnamic acid in the photostationary point presents an E/Z ratio of 32:68, in presence of base (amine), forming an ionic liquid (IL), this ratio falls to 18/82. This behaviour was only observed in presence of hydroxyl group, but not with other substituents like methoxy. Furthermore, the meta position seems to be necessary. A previous combined spectroscopic and computational study by our group about cinnamic acids in solution was highly useful to understand the structure of Z-isomers in polar solvents2. The results showed up the importance of the loss of planarity in the carboxylic sidechain. In the case of 3-hydroxycinnamic acids, the structure favours the interaction between the amine and both polar groups of the acid, inducing an extra stabilization that prevents isomerization like in other cinnamic acids. In this work, we present a thorough computational analysis that allows us to explain the experimental results. References1.M. L. Salum, C. J. Robles, R. Erra-Balsells. Org. Lett. 2010, 12, 4808-4811.2.M. L. Salum, P. Arroyo Mañez, F. J. Luque, R. Erra-Balsells. J. Photochem. Photobiol. B: Biol. 2015, 148, 128-135.