Three-Dimensional Structures of 3/4/5-O-feruloylquinic Acids by NMR Spectroscopy and Quantum Chemistry Calculation

3/4/5-O-feruloylquinic acids (3/4/5-O-FQA) have antioxidant activity, which is beneficial to disease prevention and human health maintenance, however, their exact 3D structures are still unknown. In the present work, the structures of 3/4/5-O-FQA in gas phase, D2O solution and DMSO-d6 solution are investigated respectively using 1H nuclear magnetic resonance (NMR) spectroscopy combined with quantum chemistry calculation. We observed a difference of 4.147° in dihedral angle τ (H3C3O1C9) on the esterification site H-3 for 3-O-FQA in D2O and DMSO-d6 solutions, which can explain the difference on 1H NMR spectra for H-3 atom of 3-O-FQA in the two solutions. This work presents the 3D structures of 3/4/5-O-FQA, offering valuable insights for further studies on their properties and potential applications.