Shigemitsu Ohsawa

Evaluation of phase transition temperature of liposomes by using the tautomerism of α-Benzoylacetoanilide

Abstract The phase transition temperatures for liposomes of dipalmitoyl- and distearoylphosphatidylcholines (abbreviated here as DPPC and DSPC) and for the other liposomes containing small amounts of soybean oil in the bilayer were determined from the changes of absorbance ratios ( R E K ) of enolic form to ketonic form in UV spectra for the tautomer of α-benzoylacetoanilide (BAA) incorporated into the liposomes. R E K values changed with increasing temperature and showed a maximum at a certain temperature. The DPPC liposome showed maximum at the temperature of 41°C corresponding to the phase transition temperature (Tc) of these lipids. The DSPC liposome showed the maximum at 54°C. The Tc values for other liposomes containing soybean oil could be determined in the same way. This method using the tautomerism of BAA was found to be very useful for the determination of the Tc.