Spectral and Theoretical Investigation of Inclusion Complex between Cinnamic Acid and Hydroxycinnamic Acids with Native Cyclodextrins

Abstract

Cyclodextrins (α-CD and β-CD) effects on three hydroxycinnamic acids (2-hydroxy, 3-hydroxy and 4-hydroxy) were examined and compared with cinnamic acid (CA) by UV–visible, emission and PM3 studies. Two emission peaks were observed for CA molecules in water and in CDs solution. The shorter wavelength (SW) emission peak was appeared around 300 nm from the locally excited state and the longer wavelength (LW) emission peak in the range of 400–500 nm for intramolecular charge transfer (ICT) state. The LW emission intensity dramatically increased with the β-CD concentrations while in α-CD solution, the SW emission intensity was increased. The formation of solid inclusion complexes were investigated using FT-IR, 1H NMR and SEM techniques. Considering size and shape of the guests and CD molecules and results of all experimental part, CA/HCA molecules were partially encapsulated within the CD cavity. PM3 calculation was also carried out to assign the encapsulation of the CA/HCA molecules.