Abstract: Chemical enhancers are widely employed to overcome the skin barrier in transdermal drug delivery systems. The penetration mechanism of chemical enhancers is the key point to develop a new transdermal drug delivery system. Azone is a common chemical enhancer and could make the stratum corneum(SC) lipid fluidization. However the protein also contributes to the skin barrier. Transport of large molecules was blocked by the keratin matrix even with an aqueous lipid pathway under a high-voltage pulsing. In this paper the effects of azone on the keratin in the mouse SC were investigated by determination of the molecular mobility and secondary structure of keratin. ¹³C NMR spectroscopy recorded a decreased spin-lattice relaxation time of keratin(t₁) for the carbon in the main and graft chain when treated with azone. ATR-FTIR spectra showed that amide Ⅱ absorption peak of keratin shifted from 1 544.7 to 1 541.4 cm^-1 after the treatment with azone. It was concluded that azone could change the keratin conformation structure partially from α-helix to β-sheet or random coil, leading to a loose keratin structure, therefore reduced the drug transdermal delivery barrier.

Key words: Azone, Keratin, ¹³C NMR, Spin-lattice relaxation time t₁