MICROSCOPIC FT-IR DSC SYSTEM USED TO SIMULTANEOUSLY INVESTIGATE THE CONVERSION PROCESS OF PROTEIN-STRUCTURE IN PORCINE STRATUM-CORNEUM AFTER PRETREATMENT WITH SKIN PENETRATION ENHANCERS/

A newly developed microscopic Fourier transform infrared (FT-IR) spect rometry combined with differential scanning calorimetry (DSC) was used to investigate the thermal response and IR spectral changes of protei n structure in porcine stratum corneum (SC) after pretreatment with th e skin penetration enhancers propylene glycol (PG), azone/PG, oleic ac id (OA)/PG, vitamin C, and vitamin C + OA/PG. The amide I and II bands of protein were used as probe to determine the structural transformat ion of protein with temperature. A reheating process was also performe d. Dual effects of enhancer and temperature on the protein conformatio nal changes of porcine SC were studied. The results indicate that the new FT-IR/DSC system can continuously determine the thermoresponsive c onversion process from alpha-helix to beta-sheet in keratin structure of procine SC pretreated with different enhancers. The thermally induc ed keratin conversion in protein structure of porcine SC, independent of pretreatment with skin penetration enhancers, was irreversible. The process of conformational transition in protein was found to be parti ally from alpha-helix to random coil structure or partially from alpha -helix to beta-sheet structure during heating. The kinetics of this co nversion between first-heating and second-heating processes were signi ficantly different; the process of conversion for all first-heated por cine SC samples during second-heating process were slower than that of procine SC samples during first-heating process. Moreover, it was als o found that the skin penetration enhancers, when present during the h eating process, were able to synergistically and promotively alter the keratin conversion in protein structure of porcine SC, with the PG, O A/PG and azone/PG enhancers being the most effective.