Chiral Recognition And Separation Of Amino Acid Based On Supramolecular Gels

The research of chiral recognition and enantiomeric separation has important theoretical significance and practical value in the field of biology, medicine and materials. Supramolecular gel can induce the supramolecular-chirality and the chirality could be amplified. Based on this characteristic, the gel can be used for chiral recognition and separation, which provides a new potential method. In this paper, it was found that the chiral gelator DBC(N, N'-dibenzoyl-L-cysteine) can induce a great supramolecular chirality when the supramolecular hydrogel formed. Through the different fluorescence spectra of the fluorescent probes in the gel by adding the amino acid enantiomers, the chiral recognition of glutamine acid(Glu) enantiomers can be effectively achieved; the supramolecular metal composite gels can be formed by metal coordination between the DBC and metal ions, which can enhance the sensitivity of chiral recognition effectively; in addition, we prepared the chiral silver nanoclusters(Ag NCs) by reducing the Ag-GSH gel under the Ultraviolet(UV) irradiation, and used the fluorescent signals of the Ag NCs for the study of chiral recognition of phenylalanine(Phe); moreover, we loaded the Ag NCs into an agarose hydrogel, by which we realized effectively the good separation of Phe enantiomers. The results are as follows:1. The chiral recognition of Glu can be effectively achieved with the DBC supramolecular hydrogel, which based on the different effects on the kinetics of gel formation and fluorescence intensity by adding the Glu enantiomers. In comparison to D-Glu, the add of L-Glu resulted in a slower gel-formation speed; meanwhile, L-Glu would lead to a significantly greater quenching degree than D-Glu of the fluorescence, and the Relative Difference(RD) of it could up to 40%. The study showed that the optimum concentration range of the recognizable Glu is 3.0×10-4mol/L~ 5.0×10-3mol/L by the DBC supramolecular hydrogel of 0.25wt%. We also found that the supramolecular chirality of DBC gel turned reversed to the sol; and only the DBC aggregation is available for the chiral recognition.2. A complex metal hydrogel system can be formed by Al3+ and DBC. Compared to the DBC supramolecular gels, DBC-Al gel system has a more pronounced sensitizing effect on the chiral recognition sensitivity of Glu,of which the RD increased twofold. This is due to the complexation of the metal and the gel lead to a denser structure and a stronger supramolecular chirality.3. The fluorescence optical-active AgNCs can be formed by a UV-irradiation reduction of the Ag-GSH hydrogel, which are available for chiral recognition of the Phe. Compared to L-Phe, D-Phe can cause a greater enhancement on the fluorescence of the system, and the RD of it could up to 30%. The study of TEM showed that the add of D-Phe could cause a partial reunion of the Ag NCs, which is the reason of the chiral recognition.4. We prepared Agarose/ AgNCs composite hydrogel by load the AgNCs to the gel. The Ag NCs was stereo selective and the gel can be used for adsorption, hence we use the composite hydrogel for the Phe enantiomeric separation. The results shown that the system preferentially adsorbed D-Phe of which diffused to the gel. Under the optimal conditions, the maximum adsorption of D-Phe was about 50%, but for L-Phe it was only about 7%. This method showed significant advantages in a large adsorption capacity, fast adsorption speed and high separation efficiency.