Study on the hydration structure of L-xylo and D-arabo ascorbic acid solutions by time domain reflectometry

The hydration structure of L-xylo and D-arabo ascorbic acids in aqueous solutions were investigated by a dielectric relaxation measurement over a wide frequency range from 10 MHz to 10 GHz from a standpoint on the difference of biological activity at 25 °C. In order to clarify the hydration structure the concentration dependence of dielectric relaxation was investigated not only in aqueous solution but in water–ethanol mixtures. Two kinds of dielectric relaxation processes were observed in each isomerism solution. The low frequency process is assigned to cooperative motions of ascorbic acid molecules and hydrated water. The high frequency process is assigned to reorientational motions of bulk water. From the results of the dehydration process out of the ascorbic acid surface by ethanol it is concluded that the amount of hydrated water of the L-xylo ascorbic acid is more than that of the D-arabo ascorbic acid.