TEMPERATURE-DEPENDENCE OF CHIRAL DISCRIMINATION IN LANGMUIR MONOLAYERS OF N-ACYL AMINO-ACIDS AS INFERRED FROM II A MEASUREMENTS AND INFRARED REFLECTION-ABSORPTION SPECTROSCOPY/

N-Hexadecanoylalanine monolayers were investigated on pure aqueous sub phases and in the presence of 1 mM solutions of CaCl2 and ZnCl2, respe ctively, in the temperature range between 293 and 308 K using Langmuir trough measurements and IR reflection-absorption spectroscopy (IRRAS) . The overwhelming importance of the temperature for chiral recognitio n processes was particularly clearly shown in the presence of Zn2+ in the subphase where a change from homo- to heterochiral preference was observed by IRRAS measurements within a temperature range of 5 deg onl y. This change was not reflected by corresponding changes in Langmuir curves. This result implies that chiral interactions on a molecular sc ale inferred from IRRAS and on a macroscopic scale (Langmuir curves) m ay be at variance because of a different importance of hydrogen bond a nd complex formation at these scales. Calcium ions exert strong expand ing effects, thus weakening the homochiral effect on the macroscopic l evel and even inducing a heterochiral effect on the molecular level at 293 K. A comparison between the results obtained in the presence of N -hexadecanoylalanine and its methyl ester, respectively, supports the hypothesis that hydrogen bond formation via the carboxyl group also pl ays an important role for chiral recognition.