THE DETERMINATION OF THE MOLECULAR ORDER OF CHIRAL MONOLAYERS AT THE AIR-WATER-INTERFACE BY INFRARED REFLECTION-ABSORPTION SPECTROSCOPY - ABRIDGE BETWEEN PHYSICOCHEMISTRY AND BIOCHEMISTRY

The importance of inter- and intramolecular hydrogen-bond formation as well as of the complex formation with bivalent counterions in the aqu eous subphase (Pb2+, Zn2+) for chiral discrimination in monolayers was studied in the presence of N-acylamino acid derivatives and 2-hydroxy hexadecanoic acid (HHDA) using Langmuir-trough measurements (''macrosc opic information'') and infrared reflection-absorption spectroscopy (I RRAS) (''molecular order of the film molecules''). For L-and DL-N-octa decanoyltyrosine and its methyl ester, respectively, both methods sugg est preferential heterochiral interactions at areas >0.35 nm(2) molecu le(-1) while upon compression of the monolayer, homochiral interaction s are prevailing. However, in the case of HHDA monolayers, the macrosc opic information inferred from Pi-A isotherms and the IRRAS results ar e in contradiction. Although both in the presence of Pb2+ and Zn2+ cat ions the Pi-A isotherms of the L-enantiomer exhibit the more condensed characteristics, the IRRAS measurements revealed that Pb2+ cations in duce heterochiral interactions in compressed HHDA films, while the pre sence of Zn2+ leads to homochiral interactions.