Dissociation of cholesterol ester induced by the thermal effect of mid-infrared free electron laser

Cholesteryl ester is a compound of cholesterol and fatty acid,, and is highly accumulated in arteriosclerosis regions and gallstones. We have studied irradiation effects of mid-infrared free electron laser (MIR-FEL) on cholesterol ester. In order to search optimum laser conditions for efficient removal of cholesterol ester, we tuned the FEL wavelengths to 5.75 (ester bond) and 6.82 mum (methylene bond), and irradiated cholesteryl oleate, a kind of cholesterol esters. The average power density was varied in the range of 1-10 W/cm(2). Each irradiated sample was analyzed using a mass spectrometer to examine products after irradiation and obtain efficiencies of ester dissociation. The results indicate that (1) ester bond of cholesteryl oleate was dissociated to generate cholesterol and oleic acid, (2) irradiation products and dissociation efficiency of ester bond were similar regardless of the vibration modes which absorbs irradiated wavelength of MIR-FEL, and (3) the laser induced effects were considered to be thermal effects without accompanying thermal diffusion.