Hervé David

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

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.

From iridoids to dyes: a theoretical study on genipin reactivity

A mechanistic theoretical study of the reaction between methylamine and genipin, an iridoid obtained from some natural sources, is here presented. Starting from the opening of the genipin six-membered ring experimentally hypothesized and proved in our previous theoretical work, methylamine reaction with the three different forms of genipin in equilibrium has been studied in terms of activation enthalpies and product stabilization. The kinetically favored reaction pathways, initiated by the attack of the amine on the carbonyl groups of the dialdehydic open-ring form of genipin, have been then studied until the formation of the first orange/red product. The catalytic role of a few water molecules has been clearly shown for many reactions in the process and a fundamental redox autocatalytic cycle has been proposed for the formation of the orange/red product. This mechanism explains well the experimental evidence previously reported in literature. 1H-NMR and UV-visible spectra have been reproduced for each stable intermediate of the process.

Theoretical approaches for predicting the color of rigid dyes in solution

Aiming at developing an affordable and easily implementable computational protocol for routine prediction of spectral properties of rigid molecular dyes, density functional theory, and time‐dependent density functional theory were used in conjunction with a vibronic coupling scheme for band shape estimate. To predict the perceived color of molecules in solution, a model has been setup linking the UV‐vis spectra predicted at ab initio level to the L*a*b* colorimetric parameters. The results show that a mixed protocol, implying the use of a global hybrid functional for the prediction of adiabatic energy differences and a range separated hybrid for the prediction of potential energy curvature, allows perceived colors to be quantitatively predicted, as demonstrated by the comparison of L*a*b* colorimetric parameters obtained from computed and experimental spectra.