Effect of conformation and water interactions of sucrose, maltitol, mannitol and xylitol on their metastable zone width and ease of nucleation

Metastable zone widths (MSZW) in supersaturated solutions of sucrose, maltitol, mannitol and xylitol were found to be noticeably different. To explain these differences, it is necessary to determine the parameters affecting molecular interactions in water-sugar systems, especially the water-sugar and sugar-sugar association prior to nucleation. Apart from specific hydration, each solute adopts a characteristic conformation as concentration is increased in the aqueous medium leading to the preponderance of sugar-sugar or sugar-water interactions. Moreover, the association of solute molecules is at the origin of solution properties like viscosity, diffusivity and surface tension, which play an important part in nucleation and crystal growth. This work reports results on MSZW of sucrose, maltitol, mannitol and xylitol as well as viscosity at saturation concentration and surface tension. Conformation of the studied saccharides in solution and in the crystalline state is compared to literature values and comments on the stability of the hydrogen bonding in the different aqueous solution are given. Conclusions are drawn to explain the ease of nucleation for each of the sugars. (C) 2009 Elsevier Ltd. All rights reserved.