Carbohydrate clustering in aqueous solutions and the dynamics of confined water.
We use molecular dynamics simulations to investigate structure and dynamics of fructose aqueous solutions in the 1-5 M concentration range at ambient conditions. We analyze hydration structures, H-bond statistics, and size distribution of H-bonded carbohydrate clusters as functions of concentration. We find that the local tetrahedral order of water is reasonably well-preserved and that the solute tends to appear as scattered "isolated" molecules at low concentrations and as H-bonded clusters for less diluted solutions. The sugar cluster size distribution exhibits a sharp transition to a percolated cluster between 3.5 and 3.8 M. The percolated cluster forms an intertwined network of H-bonded saccharides that imprisons water. For the dynamics, we find good agreement between simulation and available experimental results for the self-diffusion coefficients. Water librational dynamics is little affected by sugar concentration, whereas reorientational relaxation is described by a concentration-independent bulk-like component attributed to noninterfacial water molecules and a slower component (strongly concentration dependent) that arises from interfacial solvent molecules and, hence, depends on the dynamics of the cluster structure itself. Analysis of H-bonding survival probability functions indicates that the formation of carbohydrate clusters upon increasing concentration enhances the H-bond relaxation time and slows down the entire system dynamics. We find that multiexponential or stretched-exponential fits alone cannot describe the H-bond survival probabilities for the entire postlibrational time span of our data (0.1-100 ps), as opposed to a combined stretched-plus-biexponential function, which provides excellent fits. Our results suggest that water dynamics in concentrated fructose solutions resembles in many ways that of protein hydration water.
Sonoda
Milton T
MT
Institute of Chemistry, State University of Campinas-UNICAMP, Campinas, SP, Brazil.
Skaf
Munir S
MS
D002241:Carbohydrates / Q000737:chemistry*; D003198:Computer Simulation; D005609:Free Radicals / Q000737:chemistry; D006860:Hydrogen Bonding; D007201:Indicator Dilution Techniques; D008958:Models, Molecular; D015394:Molecular Structure; D011336:Probability; D012996:Solutions; D014867:Water / Q000737:chemistry*
D002241:Carbohydrates; D005609:Free Radicals; D012996:Solutions; D014867:Water