Structure of genipin in solution: a combined experimental and theoretical study

Abstract

A combined experimental and theoretical study is here presented on the structure of genipin, a widely used molecule, whose applications range from natural cross-linker for proteins to regulating agent for drug delivery to precursor of natural dye. In particular the tridimensional structure of the genipin in solution has been studied by NMR spectroscopy and the experimental outcomes have been then supported by Density Functional Theory (DFT) calculations on the electronic structure and spectroscopic parameters. The equilibrium between open and closed-ring tautomers of genipin in solution has been also theoretically investigated. The mechanism of ring opening has been elucidated and the catalytic role of water has been clearly shown. Beyond the excellent agreement between experiments and theoretical calculations (in particular concerning ¹H-NMR data), our results unravel the nature of the most stable isomer of genipin and related reactive species in solution.