VIBRATIONAL SPECTROSCOPIC STUDIES OF AQUEOUS DEXTRAN SULFATE

The interaction between water and polyelectrolytes was investigated us ing aqueous dextran sulphate systems. The results indicated that the h ydrogen-bonding network of water in the system is affected by the pres ence of a highly charged polyanion with both surface hydrophobic and h ydrophilic sites. This is reflected in the spectral profile of the 0-H stretching mode of water in the region 3000-4000 cm-1. Comparison wit h aqueous sodium methyl sulphate and sodium sulphate systems suggests that two regions of water are present in the dextran sulphate system. Water in the region associated with the hydrophobic carbohydrate skele ton appears to be more strongly hydrogen bonded than bulk water wherea s that in the vicinity of the hydrophilic -SO3- groups is more weakly hydrogen bonded. Variations in the vibrational spectra were dependent on the extent of the different populations of water present and can be explained by invoking the concepts of long-range intermolecular coupl ing. Analysis of the dextran skeletal bands in the region 750-1850 cm- 1 confirmed that the -SO3- sites play an important role in the hydrati on of dextran sulphate. The presence of two symmetric -SO3- stretching modes in the Raman spectra of these systems, both of which are sensit ive to the hydration state of the molecule, has been explained in term s of a model based on non-equivalent -SO3- sites.