The very different effect of water on nucleation, crystallization, and hydrate stability of zingerone and vanillate esters

Abstract

Vanillin and vanillate esters are widely used as flavorings in the food industry, and the vanillin derivative zingerone is one of the compounds found in the spice ginger. Neither the growth of single crystals of zingerone or methyl or ethyl vanillate nor their crystal structures or the crystal structures of their hydrates have been reported. In this paper a detailed study of the crystallization of methyl vanillate, ethyl vanillate, and zingerone is described and the relationship among crystal growth, habit, and intermolecular interactions in the crystal lattice is discussed. Adventitious or deliberately added water suppressed the crystal nucleation and growth of zingerone from cyclohexane solution. Good-quality single crystals of zingerone can be grown from a cyclohexane solution in closed vials if water is excluded. It was not possible to isolate a hydrate of zingerone. In contrast, the crystallization of methyl and ethyl vanillates from cyclohexane is not affected by adventitious water from the air and monohydrates are easily isolated. The crystal structures of zingerone, methyl and ethyl vanillates, and the monohydrates of the vanillates have been determined and analyzed using the PIXEL program. Observed crystal morphologies have been rationalized using intermolecular interaction energies and slice attachment energy calculations.