Chiral recognition of protected amino acids by means of fluorescent binary complex pyrene/heptakis-(6-amino)-(6-deoxy)-β-cyclodextrin (original) (raw)
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Tetrahedron Asymmetry, 2002
The binary pyrene/heptakis-(6-amino-6-deoxy)-b-cyclodextrin complex: a suitable chiral discriminator. Spectrofluorimetric study of the effect of some a-amino acids and esters on the stability of the binary complex Abstract-The effect of some a-amino acids and their esters on the stability of the binary pyrene/heptakis-(6-amino-6-deoxy)-bcyclodextrin (py/am-b-CD) complex has been studied by means of fluorescence spectroscopy at two pH values (8.0 and 9.0). The binary complex was generally stabilized by adding the ternary agent at pH 8.0. A more varied substrate effect is observed at pH 9.0 where am-b-CD is present in the uncharged form. The conditional constant (i 2 ) values determined by L/D a-amino acids show that the binary complex is a suitable receptor for chiral recognition. The enantiomer selectivity values obtained, ranging from 1.2 up to 7.4, are generally higher than those reported for a-amino acids and their derivatives by modified cyclodextrins.
A spectrofluorimetric study of binary fluorophore–cyclodextrin complexes used as chiral selectors
Tetrahedron, 2005
Six binary complexes between three fluorophores (pyrene, xanthone and anthraquinone) and b-cyclodextrin (b-CD) or heptakis-(6-amino)-(6-deoxy)-b-cyclodextrin (am-b-CD) were tested at two pH values (8.0 and 9.0) as chiral selectors for three a-amino acids chosen as model. The conditional constant (b 2T) values for ternary complexes (fluorophore-CD-amino acid), determined by means of fluorescence spectroscopy, showed that the binary complexes are suitable receptors for chiral recognition. The effect of a-amino acids on stability and stoichiometric ratio of the binary complexes has also been studied. The binary complexes were in most cases stabilized by adding the ternary agent. The trend of stoichiometric ratios found is supported by variations in fluorescence spectra. Those relative to pyrene (Py) show little changes going from binary to ternary complexes, while those recorded in the presence of xanthone (Xan) give the most significant variations underlining a deep reorganization of guest. Anthraquinone (Aq) shows an intermediate behavior.
Chirality, 2003
Fluorescent monofunctionalized -cyclodextrins bearing a copper(II) binding side arm and a dansyl group (CD-NH-AA-CH 2 CH 2 NH-DNS) were designed as enantioselective sensors for unmodified ␣-amino acids. The side arm was derived from amino acid synthons (AA = L-and D-phenylalanine (1 and 2), L-and D-phenylglycine (3 and 4), L-proline (5), and L-cyclohexylglycine (6)) and was chosen in order to contain an amide, an amine, and a sulphonamide group. Enantioselectivity was evaluated by addition of copper(II) complexes of D-or L-valine and D-or L-proline. Chiral discrimination in the fluorescence response was observed in all cases, due to a ligand exchange process. The best conditions for these experiments were found to be the use of an excess (10:1) of the copper complex. The cyclodextrin 4 containing a D-phenylglycine unit was found to be poorly enantioselective, as found for 2, suggesting that the best design can be obtained by using L-amino acids. All L-amino acid containing cyclodextrins showed good enantioselectivities, some of which were higher than those already reported for 1. Other analytes related to amino acids were studied using cyclodextrins 1 and 3. Enantiomers of ␣,␣-disubstituted amino acids, N-methylamino acids, and amino acid amides were found to be discriminated, while -phenylalanine and other molecules bearing a poor anchoring group at the ␣-carbon gave poor enantioselectivity. On the basis of the present data a model for the recognition process, based on the formation of ternary diastereomeric complexes, is proposed. Chirality 15: S30-S39, 2003.
Journal of The Brazilian Chemical Society, 2007
Ligand exchange HPLC technique was applied to resolve chiral separation of aliphatic side chain aminoacid racemates. Chiral selector was copper L-phenylalaninate (II) and the results showed the elution of D enantiomer followed by L form. Considering the 3-point interaction concept, a mechanism of chiral recognition was proposed, in which no change of configuration would follow the formation of pseudo-homochiral and heterochiral complexes. To prove the reliability of this mechanism, the trans configuration of homochiral complex had to be more stable than the cis form, which was confirmed by DFT-B3LYP calculation in gas phase. The infrared frequencies were also calculated and the comparison with the subtracted and deconvoluted spectrum of the in-solution complex also pointed to the presence of the trans diasteroisomer.
Frontiers in Bioengineering and Biotechnology
The interaction between homochiral substituted perylene bisimide (PBI) molecule and the D enantiomer of phenylalanine amino acid was monitored. Spectroscopic transitions of PBI derivative in aqueous solution in the visible range were used to evaluate the presence of D-phenylalanine. UV-visible, fluorescence, FT-IR, and AFM characterizations showed that D-phenylalanine induces significant variations in the chiral perylene derivative aggregation state and the mechanism is enantioselective as a consequence of the 3D analyte structure. The interaction mechanism was further investigated in presence of interfering amino acid (D-serine and D-histidine) confirming that both chemical structure and its 3D structure play a crucial role for the amino acid discrimination. A D-phenylalanine fluorescence sensor based on perylene was proposed. A limit of detection (LOD) of 64.2 ± 0.38 nM was calculated in the range 10 −7 -10 −5 M and of 1.53 ± 0.89 µM was obtained in the range 10 −5 and 10 −3 M.
Proceedings of the National Academy of Sciences, 2002
In a systematic study of molecular recognition of amino acid derivatives in solid-state -cyclodextrin (-CD) complexes, we have determined crystal structures for complexes of -cyclodextrin͞Nacetyl-L-phenylalanine at 298 and 20 K and for N-acetyl-D-phenylalanine at 298 K. The crystal structures for the N-acetyl-L-phenylalanine complex present disordered inclusion complexes for which the distribution of guest molecules at room temperature is not resolvable; however, they can be located with considerable confidence at low temperature. In contrast, the complex with N-acetyl-D-phenylalanine is well ordered at room temperature. The latter complex presents an example of a complex in this series in which a water molecule is included deeply in the hydrophobic torus of the extended dimer host. In an effort to understand the mechanisms of molecular recognition giving rise to the dramatic differences in crystallographic order in these crystal structures, we have examined the intermolecular interactions in detail and have examined insertion of the enantiomer of the D-complex into the chiral -CD complex crystal lattice.
Proceedings of the …, 2002
In a systematic study of molecular recognition of amino acid derivatives in solid-state -cyclodextrin (-CD) complexes, we have determined crystal structures for complexes of -cyclodextrin͞Nacetyl-L-phenylalanine at 298 and 20 K and for N-acetyl-D-phenylalanine at 298 K. The crystal structures for the N-acetyl-L-phenylalanine complex present disordered inclusion complexes for which the distribution of guest molecules at room temperature is not resolvable; however, they can be located with considerable confidence at low temperature. In contrast, the complex with N-acetyl-D-phenylalanine is well ordered at room temperature. The latter complex presents an example of a complex in this series in which a water molecule is included deeply in the hydrophobic torus of the extended dimer host. In an effort to understand the mechanisms of molecular recognition giving rise to the dramatic differences in crystallographic order in these crystal structures, we have examined the intermolecular interactions in detail and have examined insertion of the enantiomer of the D-complex into the chiral -CD complex crystal lattice.
Journal of Separation Science, 2002
The gas chromatographic separation of enantiomers of seven N-TFA-O-alkyl amino acid derivatives was studied on four different permethyl-and 2,6-di-O-methyl-3-Opentyl-b-and -c-CD stationary phases.It was shown that the separation of enantiomers N-TFA-O-alkyl amino acid derivatives depends both on the length of the linear alkyl chain attached to the stereogenic carbon (R 1 ) and to the ester part of the amino acid derivative (R 2 ). The cyclodextrin cavity size also affected selectivity. The separation of the amino acid derivatives decreases with increasing length of both the R 1 and R 2 alkyl chains on b-CD stationary phases, but improves on c-CD stationary phases. The separation of enantiomers of all N-TFA-O-methyl amino acid esters, is better on the larger c-cyclodextrin CSPs except for enantiomers of N-TFA-O-alkyl esters of alanine which are better separated on b-CD stationary phases.