Molecular Recognition of Amino Acids by Copper(II) Complexes of 6^A,6^X-Diamino-6^A,6^X-dideoxy-β-cyclodextrin (X = B, C, D)

Abstract

The three regioisomers of beta-cyclodextrin 6-difunctionalized with NH(2) groups (6(A),6(X)-diamino-6(A),6(X)-dideoxy-beta-cyclodextrin, A,X-CDNH(2), X = B, C, or D) were synthesized. Their binary and ternary copper(II) complexes with amino acids were characterized by ESR and electronic spectroscopy. 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-CDNH(2))](2+) was used as eluent. The two complexes with the other two regioisomers did not show chiral recognition ability. Circular dichroism (c.d.) spectroscopy studies of the ternary complexes with D- and L-amino acids carried out in the presence and in the absence of 1-adamantanol, suggested a recognition mechanism that involves the cyclodextrin cavity, only in the case of ternary A,B-CDNH(2) complexes.

Copper(II) complexes of peptide fragments of the prion protein. Conformation changes induced by copper(II) and the binding motif in C-terminal protein region

“…Copper(II) complexes with different equatorial CuN 2 O 2 , CuN 3 O or CuN 4 chromophores, in the case of amine, imidazole or only one amide nitrogens [41][42][43][44] show g k values ranging from 2.24 and 2.26 and A k from Table 2 Spectroscopic parameters for copper(II) complexes with PrP Ac180-193NH 2 and PrP 180-193 0.0180 to 0.0190 cm À1 . When considering CuN 4 chromophores in which two or more amide nitrogen donors are present [45][46][47], values of g k ¼ 2.17-2.19 and A k ¼ 0.0190-0.0210 are easily obtained.…”

Bioconjugates of cyclodextrins of manganese salen-type ligand with superoxide dismutase activity

“…The metal complexes of diamino cyclodextrins have been previously characterized and the ability of the two nitrogen atoms on adjacent glucose rings to complex metal ions has been shown [47,48].…”

3-Amino derivative of β-cyclodextrin: thermodynamics of copper(II) complexes and exploitation of its enantioselectivity in the separation of amino acid racemates by ligand exchange capillary electrophoresis

“…In the cyclodextrin metal complexes the metal ion can cooperate with the binding properties of CD cavity, as a supplementary recognition site. Copper(II) or nickel(II) complexes of cyclodextrins monofunctionalized with diamines have been used as molecular receptors and enantioselective binding of amino acids has been verified [10][11][12][13][14][15][16][17][18][19][20][21].…”

“…If the ligand of the added complex is chiral, LEC can be used to obtain the separation of racemates, by exploiting the diastereoisomerism between the complexes of the two enantiomers. Moreover, by using different techniques, it was possible to compare spectroscopic evidence and thermodynamic results concerning the formation of the ternary complexes with chromatographic results, thus getting a better insight on the observed enantioselectivity [11,16,17].…”