FLUORESCENCE MICROSCOPY STUDY OF LANGMUIR MONOLAYERS OF RACEMIC AND ENANTIOMERIC N-STEAROYLTYROSINE

Monolayers of N-stearoyltyrosine have been investigated by fluorescenc e microscopy and surface pressure measurements. The racemic films are more condensed than the enantiomeric films, indicating heterochiral di scrimination. The surface pressure at the transition to the condensed phase on compression decreases monotonically between X(D)= 0 and X(D) = 0.5 at 33 degrees C. The condensed-phase domains of the monolayer of the pure L enantiomer appear as anisotropic shapes under a fluorescen ce microscope. The condensed-phase domains of the racemic monolayer ap pear more compact at lower temperatures, but their morphology becomes progressively more anisotropic as the temperature increases. The diffe rence between the surface pressure isotherm of the enantiomeric L and the racemic film are smaller and homochiral for the N-stearoyltyrosine methyl ester on a pH 7 buffered subphase than for the N-stearoyltyros ine on a pH 2 HCl acidified subphase at 22 degrees C, indicating the i mportance of hydrogen bonding in accounting for the origin of the chir al discrimination.