MOLECULAR RECOGNITION OF AMINO-ACIDS BY COPPER(II) COMPLEXES OF ),6(X)-DIAMINO-6(A),6(X)-DIDEOXY-BETA-CYCLODEXTRIN (X=B,C,D)

The three regioisomers of beta-cyclodextrin 6-difunctionalized with NH 2 groups ,6(X)-diamino-6(A),6(X)-dideoxy-beta-cyclodextrin, A,X-CDNH2, X = B, C, or D) were synthesized. Their binary and ternary copper(II) complexes with amino acids were characterized by ESR and electronic s pectroscopy. Furthermore, the binary copper(II) complexes were used as eluent in ligand exchange chromatography (LEC), to resolve racemates of unmodified amino acids. HPLC separation of enantiomers of aromatic amino acids was obtained only when the complex [Cu(A,B-CDNH2)](2+) was used as eluent. The two complexes with the other two regioisomers did not show chiral recognition ability. Circular dichroism (c.d.) spectr oscopy studies of the ternary complexes with D- and L-amino acids carr ied out in the presence and in the absence of 1-adamantanol, suggested a recognition mechanism that involves the cyclodextrin cavity, only i n the case of ternary A,B-CDNH2 complexes.