Effects of divalent cations on the ultrasonic absorption coefficient of negatively charged liposomes (LUV) near their phase transition temperature

摘要: Abstract The ultrasonic absorption coefficient per wavelength (αλ), as a function of temperature and frequency, was determined for large unilamellar vesicles (LUV) in the vicinity their phospholipid phase transition temperature, using double crystal acoustic interferometer. (The were composed 4:1 (w/w) mixture dipalmitoylphosphatidylcholine (DPPC) dipalmitoylphosphatidylglycerol (DPPG)). It has been found that αλ reaches maximum ( ) max at t m phospholipids bilayer, an relaxation frequency 2.1 MHz. Divalent cations (Ca 2+ Mg ), added to LUV suspensions, shifted higher temperatures, dependent upon concentration divalent cation. also shape versus curve significantly changed, representing changes Van't Hoff enthalpy transition, therefore, cooperative unit transition. This suggests interact individually with negatively charged headgroups DPPG DPPC headgroups, thus decreasing observed upward shift interaction increases activation energy and, However, did not change addition thus, time event responsible ultrasound is changed by cations.