SEPARATION OF ENANTIOMERS AND RACEMATE FORMATION IN 2-DIMENSIONAL CRYSTALS AT THE WATER-SURFACE FROM RACEMIC ALPHA-AMINO-ACID AMPHIPHILES -DESIGN AND STRUCTURE

Studies are presented on the two-dimensional (2-D) crystalline packing arrangements of enantiomerically pure and racemic ol-amino acid RHC(N H3+)CO2- monolayers on water and on glycine aqueous solutions, as dete rmined by synchrotron grazing incidence X-ray diffraction. The amphiph iles have been designed such that their racemic mixtures form 2-D crys tals which are either heterochiral (for R = CnH2n+1-, n = 10, 12, 16) due to the tendency for herringbone chain arrangements via glide symme try or homochiral (for R = CnH2n+1CONH(CH2)(4)-, n = 11, 17, 21) by vi rtue of hydrogen bonding by translation of the amide group in the chai ns leading to a spontaneous separation into islands of opposite chiral ity. The two different crystalline motifs led to a correlation between their packing arrangements and induced oriented nucleation of 3-D cry stals of alpha-glycine by these monolayers. The relevance of the prese nt results to the possibility of ordering and spontaneous segregation of racemates of the natural hydrophobic alpha-amino acids at the air-s olution interface is discussed.