High-capacity loading of 5-fluorouracil on the methoxy-modified kaolinite

Kaolinite and methoxy-modified kaolinite were used as carriers for the loading of 5-fluorouracil (5FU) for the first time. The kaolinite products were characterized using X-ray diffraction, transmission electron microscopy, elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The loading mechanism of 5FU on kaolinite was as follows: the 5FU molecules were initially anchored to the external surface of kaolinite through hydrogen bonding, and the added 5FU then formed hydrogen-bonded aggregates with the anchored 5FU on the external surface of kaolinite. The surface-loaded 5FU was crystallite. The 5FU-loading content in the methoxy-modified kaolinite was 55.4 mass%, which was 147.3% greater than that in unmodified kaolinite. The high-capacity loading of 5FU on methoxy-modified kaolinite resulted from two factors: (i) the interlayer space of the methoxy-modified kaolinite acted as an additional loading site that was available for the intercalation of 5FU; (ii) the loading of 5FU on the external surface of the methoxy-modified kaolinite was high because of the high affinity between 5FU and the methoxy-modified kaolinite. The 5FU-loading content of the interlayer-loaded 5FU and the surface-loaded 5FU in the methoxy-modified kaolinite was 14.6 mass% and 40.8 mass%, respectively. The interlayer-loaded 5FU was in an amorphous state, and of higher thermal stability than the surface-loaded 5FU. Methoxy-modified kaolinite is a promising drug carrier in pharmaceutical industry.