2.7. Phase-Solubility Studies

Solubilizing properties of unmodified α-CD and per-6-thiolated α-CD for the model BCS Class IV drug FUR in aqueous solution were studied at room temperature according to an already established method.¹⁹ In detail, FUR was added (CD and FUR in molar ratio of 1:2) to an aqueous solution containing increasing amounts of α-CD and per-6-thiolated α-CD ranging from 0.5 to 5 mM. The suspension was homogenized at room temperature using a thermomixer (Thermomixer C, Eppendorf, Austria) at 750 rpm until equilibrium in solubility was reached (3–4 days). After filtration (polyvinylidene fluoride filter with pore size: 0.45 μm), the obtained clear solutions were diluted 10 times, and FUR was quantified photometrically at 276 nm. The apparent stability constant (K_C) was determined from the slope of the straight line using eq 2

where S₀ represents the solubility of FUR in water.