Molecular simulation of sucrose solutions near the glass transition temperature

The physical properties of aqueous sucrose near the glass transition temper ature have been studied using Monte Carlo and molecular dynamics simulation s. The sucrose solutions ranged in concentration from 6 to 100 wt% and in t emperature from 300 to 600 K. For concentrated solutions (greater than or e qual to 80 wt%), a parallel tempering Monte Carlo algorithm was implemented to circumvent the slow system dynamics and improve sampling of configurati on space. Parallel-tempered density calculations agree more closely with ex perimental data than conventional NPT results. Our simulations indicate tha t aqueous sucrose retains two intramolecular hydrogen bonds even in dilute solutions. The two hydrogen bonds detected in crystalline sucrose were also observed in the sucrose solutions of 50 wt% sucrose and greater. The hydra tion number was calculated for sucrose and compared with that for trehalose . Sucrose is less hydrated than trehalose for all concentrations studied. U sing parallel-tempered NPT density results, molecular dynamics simulations were utilized to estimate the diffusion of water near the glass transition for concentrated sugar solutions. Diffusion coefficients in aqueous sucrose appear to be a factor of 2 greater than those in trehalose solutions.