Enantioselective complexation of amino acids by 6(A)-deoxy-6(A)-hydroxyethylamino-beta-cyclodextrin and its metallo-derivatives in aqueous solution

Enantioselectivity towards several amino acids by metallo-6(A)-deoxy-6(A)-h ydroxyethyl-amino-beta-cyclodextrins (metallo-beta CDea's) was investigated by potentiometric titration of the various amino acid/metallo-beta CDea sy stems with NaOH solution. It was shown that the cyclodextrin derivative is capable of distinguishing between enantiomers of amino acid species in the presence of certain metal ions (Co2+, Ni-2+, Cu2+ and Zn2+). Ni2+-beta CDea complexes show the most enantioselectivity, whereas for Cu2+- and Co2+-bet a CDea complexes less selectivity is observed. As expected, Zn2+-beta CDea complexes exhibit no enantioselectivity. Stability and selectivity, however , do not go hand in hand, since the most stable complexes are formed with C u2+. Several factors play a role in determining stability and selectivity i n binary and ternary complexes and further study is required to gain a more comprehensive understanding of these.