ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Acidity constants of hydroxyl groups placed in nine selected flavanones from citrus fruits

Lucia Bartella, Luana Malacaria, Rosangela Elliani, Mario Prejanò, Ilaria Santoro, Leonardo Di Donna, Tiziana Marino, and Emilia Furia

Department of Chemistry and Chemical Technologies, University of Calabria, Arcavacata di Rende, Italy

E-mail: emilia.furia@unical.it

Received: 26 March 2025  Accepted: 16 June 2025

Abstract:

The knowledge of acid–base dissociation constants, that are characteristic of specific groups or of a combination of groups, is important to fully understand the properties of a molecule in a biological system. In this work, acidity constants of nine flavanones were determined by performing potentiometric titrations in both pH ways, from acid to base and vice versa. The evaluation was carried out in aqueous media (i.e. 0.16 M NaCl) at 37 °C in a wide pH range (from 2 to 9). Results obtained allow the experimental pK_a assignation to hydroxyl groups belonging to selected flavanones, namely naringenin, hesperetin and eriodictyol, as well as their corresponding glycosides and 3-hydroxy-3-methyl glutaryl (HMG) derivatives: naringin, neohesperidin and neoeriocitrin, and melitidin, brutieridin and peripolin, respectively. To confirm the experimental results, quantum chemical calculations were additionally performed on aglycones and on HMG-containing compounds. The well-known instability of these analytes in basic solution produces some differences between the pK_a values obtained in this work and those obtained under different experimental approaches previously reported.

Keywords: Flavanones; Citrus fruits; Acidity constants; Potentiometric measurements; Aqueous solution; DFT

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-025-04191-5

Chemical Papers 79 (9) 6295–6302 (2025)