The derivation and characterization of quinine charge-transfer complexes with inorganic and organic acceptors in liquid and solid form

Quinine (QN), chloroquine (CQ), and hydroxychloroquine (HCQ) belong to the 4-aminoquinoline family. QN was used to treat the Spanish Flu, while CQ and HCQ are under consideration for the treatment of COVID-19. This work aimed to investigate the charge-transfer (CT) interaction between QN compound with five acceptor molecules: iodine crystals (A1), 7,7,8,8-tetracyanoquinodimethane (A2), 2,3-dichloro-5,6-dicyano-p-benzoquinone (A3), chloranilic acid (A4), and tetrafluoro-1,4-benzoquinone (A5). The experimental results indicated that QN formed stable and vividly colored CT complexes with these acceptors. Strong color changes occurred upon complexation in both liquid and solid forms. The analytical findings suggest that QN reacted with the A2, A3, A4 and A5 acceptors at a 1:1 M ratio and a 1:2 ratio with A1 acceptor. The charge migration occurred from QN to A1 via the formation of a triiodide complex, while the charge migration occurred from QN to A2, A3, A4, and A5 acceptors through an n -> pi* interaction. (C) 2022 Elsevier B.V. All rights reserved.