MOLECULAR-MOTION IN SUCROSE WATER MIXTURES IN THE LIQUID AND GLASSY STATE AS STUDIED BY SPIN PROBE ESR

Conventional and saturation transfer ESR spectroscopies are used to study the rotational behavior of two different nitroxide spin probes-4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (Tempol) and 3-maleimido-2,2,5,5-tetramethyl-1-pyrrolodinyloxy - in sucrose-water and glycerol-water mixtures as a function of temperature. The results are discussed in terms of slip and stickiness of the spin probes, which depend on the strength of the hydrogen bonds between the probe and the solvent. Except for the maleimido spin probe in anhydrous glycerol, which can form an extended solvation shell, the slip increases as the water content of the mixture decreases. This is explained by a decrease of hydrogen bonds between the probe and the solvent. In sucrose-water mixtures above 70 wt % sucrose and in sucrose-water mixtures in the glassy state the spin probes are presumably present in cavities. At the temperature at which the transition from glassy state to solution takes place, as measured with differential scanning calorimetry. an extreme increase in rotational mobility of the probes can be observed. © 1990 American Chemical Society.