Host-guest interactions of 5-fluorouracil in supramolecular organogels

Supramolecular organogels were formed by the self-assembly of gelator 1,3:2,4-di-O-benzylidene-d-sorbitol (DBS) in 1,2-propylene glycol. 5-Fluorouracil (5-Fu) was entrapped in the organogels as guest molecules. Field-emission scanning electron microscopic measurements of the organogels indicate that the diameters of the fibrillar aggregates formed by DBS self-assembly were in the range of 20-70 nm. The host-guest interactions between 5-Fu and supramolecular gel matrix were investigated by using temperature-dependent differential UV spectroscopy and differential scanning calorimetry. The red shifts of the absorption band of 5-Fu in the organogels are indicative of the interaction between 5-Fu and DBS. The red shifts were enhanced upon decreasing the temperature. Calculation of optimized geometries revealed the formation of hydrogen bonds between 5-Fu and DBS aggregates. The analysis of differential scanning calorimetric data for the organogels with and without 5-Fu further showed that the self-assembly of DBS was interfered by the 5-Fu in the organogels, resulting in a decrease in the dissociating temperature of DBS aggregates.