Tartaric Acid Derivatives Column Brace Hydrotalcite Chiral Adsorption Separation Of Tryptophan

The structures of layered double hydroxides(LDHs) were summarized as well as the preparation methods, properties and applications of LDHs in this chapter. The chiral adsorption properties of LDHs intercalated by chiral selectors (di-p-toluoyl-tartaric acid(DTTA) or dibenzoyl-tartaric acid(DBTA)) were studied in detail, in order to discuss the applications of these kinds of intercalated LDHs on selectively separating racemic mixtures.The LDHs with different chiral space (D-DTTA-LDHs, L-DTTA-LDHs, L-DBTA-LDHs and D-DBTA-LDHs) were prepared by introducing four kinds of tartrate acid derivatives, D-DTTA, L-DTTA, D-DBTA and L-DBTA respectively using anion exchange methods, and MgAl-LDHs synthesized by coprecipitation was taken as precursors. The enantioselective adsorption of dl-Tryptophan (dl-Trp) on these kinds of LDHs was investigated in detail. The results show that L-DTTA-LDHs or L-DBTA-LDHs could selectively absorb d-Trp, while D-DTTA-LDHs or D-DBTA-LDHs could preferentially absorb l-Trp. The selective adsorption primarily relied on the supramolecular weak interactions such as hydrogen bond, Van der Waals force, electrostatic force as well as stereo hindrance effect between Trp and LDHs intercalated by chiral moleculars.The mechanisms of the enantioselective adsorption were discussed according to a series of models, such as dynamics models (Pseudo-first-order model and Pseudo-second-order model), intrapaticle diffusion model, isotherms (Langmuir and Fruendlich model) and thermodynamics, because of the adsorption in solid-aqueous system. The adsorption conduct can be better described by pseudo-first-order model and Fruendlich model than pseudo-second-order and Langmuir models. The reaction speed was controlled by the intraparticle diffusion rate in the initial stage of chiral adsorption according to the fitting results of intraparticle diffusion model. The key thermodynamics parameters ΔG°and ΔH°re negative or positive respectively, thus it can be seen that the selective adsorption of dl-Trp on tartaric acid derivatives intercalated LDHs was spontaneous endothermic process on heterogeneous surface.