Separation Of Racemic Amino Acids Research Articles

Enantioselective Separation of Racemic Tryptophan with Sonochemically Prepared Egg Albumin Microspheres

AbstractNew approaches for chiral resolution are gaining importance and are of economic interest for the development of pharmaceuticals, agrochemicals, chiral sensors and food additives. Herein we disclose the first examples in which sonochemically prepared egg albumin microspheres (EAMs) were used for chiral resolution of an amino acid. When EAMs were in contact with an aqueous solution of racemic tryptophan (Trp) they selectively interacted with L‐Trp leading to 94% enantiomeric excess (ee) of D‐Trp. In a control experiment in which the egg protein, without applying ultrasonic waves to form microspheres, was dissolved and exposed to racemic Trp, no chiral resolution was observed. The effects of temperature and concentration were studied in detail. These preliminary results show that EAMs produced by sonication may provide a simple, cost‐effective an unconventional way to chiral separation of racemic amino acids.

On the Centenary of Emanuel Gil‐Av, Former Professor of the Weizmann Institute of Science and Pioneer of Enantioselective Chromatography

AbstractEmanuel Gil‐Av (Zimkin) was born in 1916 and passed away in 1996. The introduction of chemical selectivity into the chromatographic separation process constitutes his main scientific contribution. This approach culminated in the first enantiomeric separation of racemic amino acids by gas chromatography on an optically active chiral stationary phase in 1966, together with Binyamin Feibush and Rosita Charles‐Sigler. Thus the year 2016 marks an important date to remember and to appreciate the invaluable achievements of Gil‐Av in the realm of chirality carried out at the Weizmann Institute of Science, Israel.

Immobilized chiral tropine ionic liquid on silica gel as adsorbent for separation of metal ions and racemic amino acids

Tropine-type chiral ionic liquid with proline anion was immobilized on silica gel by chemical modification method for the first time, which was proved by elemental, infrared spectrum and thermogravimetric analysis. Secondly, the performance of this kind of ionic liquid-modified silica gel was investigated in the adsorption of some metal ions, which included Cu2+, Fe3+, Mn2+ and Ni2+. Then the effects of time, initial concentration and temperature on adsorption for Cu2+ ions were studied in detail, which was followed by the further research of adsorption kinetics and thermodynamics. The adsorption could be better described by pseudo-second-order kinetics model and that the process was spontaneous, exothermic and entropy decreasing. In the mode of ‘reuse after adsorption’, the ionic liquid-modified silica gel with saturated adsorption of Cu2+ was finally used in resolution of racemic amino acids for the first time. The static experiment showed that adsorption rate of two enantiomers was obviously different. Inspired by this, the complex was packed in chromatographic column for the separation of racemic amino acids and d-enantiomers were firstly eluted by water or ethanol. Steric hindrance was found as one of key influencing factors for its effect on the stability of the complex.

Specific cooperative effect for the enantiomeric separation of amino acids using aqueous two-phase systems with task-specific ionic liquids

Aqueous two-phase systems (ATPS) based on hydrophilic ionic liquid (IL) and inorganic salt solution were designed and prepared for the enantiomeric separation of racemic amino acids. Two different kinds of hydrophilic ionic liquids (IL-1 and IL-2) containing functional groups were synthesized to separate racemic amino acids. Preliminary experiments showed that d-enantiomer of amino acids cooperatively interacted with ILs, which pushed d-enantiomer to remain in the bottom IL-rich phase. By contrast, l-enantiomer was transferred into the top Na2SO4-rich phase. The enantioselectivity of IL-1 was better than that of IL-2 because of their different intermolecular interactions. Various factors influencing separation efficiency were also systematically investigated including extraction time, IL volume and temperature. Furthermore, the mechanism was studied by 1H NMR and DFT calculations, which showed that the hydrogen bond between the carboxylate and amide groups and the resonance-assisted hydrogen bond between amino and hydroxyl groups conditioned the movement between the residues and ILs. Finally, IL-1 was validated with other general amino acids by the same procedures based on ATPS.

Chiral separation of racemic amino acids with novel polyamides having N-α-acetyl-l-glutamyl residue as a diacid component

Novel polyamides with asymmetric carbons in their main chains were obtained from aromatic diamines, 4,4′-diaminodiphenylmethane (DADPM) or 1,3-phenylenediamine (1,3-PDA), and N-α-protected l-glutamic acid, N-α-acetyl-l-glutamic acid (Ac-l-Glu-OH). Newly prepared polyamides showed optical rotation, implying that optically active polyamides were successfully obtained in the present study. These two types of chiral polyamides showed chiral recognition ability, which was studied by surface plasmon resonance (SPR) spectroscopy; they recognized d-glutamic acid in preference to the corresponding l-isomer. The adsorption selectivity was determined to be 1.66 for 1,3-PDA-Ac-l-Glu and 1.49 for DADPM–Ac-l-Glu. Enantioselective electrodialysis was studied adopting racemic N-α-acetyl-tryptophan (Ac-Trp) mixtures as model pairs of enantiomers. The membranes selectively transported Ac-d-Trp. Permselectivity toward the d-isomer reached 2.03.

Guest‐dependent conformation of 18‐crown‐6 tetracarboxylic acid: Relation to chiral separation of racemic amino acids

(+)-18-crown-6 tetracarboxylic acid (18C6H(4)) has been used as a chiral selector for various amines and amino acids. To further clarify the structural scaffold of 18C6H(4) for chiral separation, single crystal X-ray analysis of its glycine(+) (1), H3O+ (2), H5O2+ (3), NH4+ (4), and 2CH3NH3+ (5) complexes was performed and the guest-dependent conformation of 18C6H(4) was investigated. The crown ether ring of 18C6H4 in 3, 4, and 5 took a symmetrical C2 or C2-like conformation, whereas that in 1 and 2 took an asymmetric C1 conformation, which is commonly observed in complexes with various optically active amino acids. The overall survey of the present and related complexes suggests that the molecular conformation of 18C6H4 is freely changeable within an allowable range, depending on the molecular shape and interaction mode with the cationic guest. On the basis of the present results, we propose the allowable conformational variation of 18C6H4 and a possible transition pathway from its primary conformation to the conformation suitable for chiral separation of racemic amines and amino acids.

Chiral Separation of Racemic Amino Acids through DNA‐Polydiallyldimethylammonium Polyion Complex Membranes

AbstractNovel polyion complex membrane was prepared from DNA‐Na and polydiallyldimethylammonium chloride (PDADMAC). The newly prepared DNA‐PDADMA polyion complex membrane showed a chiral separation ability, which was measured by using various racemic amino acids as model racemic mixtures. The membrane transported the L‐isomer of Trp or Phe in preference to the corresponding D‐isomer and permselectivities toward the L‐isomer were determined to be 1.26 for L‐Trp and 1.25 for L‐Phe, respectively. From adsorption experiments, it was revealed that the permselectivity was mainly governed by adsorption selectivity.

Chiral Separation of Racemic Amino Acids through Membranes derived from Modified Polysulfone Having Perillaldehyde Moiety as a Side Group

Chiral Separation of Racemic Amino Acids through Membranes derived from Modified Polysulfone Having Perillaldehyde Moiety as a Side Group

Simultaneous analysis of enantiomeric composition of amino acids and N-acetyl-amino acids by enantioselective chromatography.

Among the three chiral columns, CHIROBIOTIC T, CHIRLPAK WH, and CHIRALCEL OD-R, tested for the separation of racemic amino acids and N-acetyl-amino acids, only CHIROBIOTIC T chiral column which is based on covalently bonded amphoteric glycopeptide, teicoplanin, as the stationary phase ligand could be successfully developed to enantiomerically separate racemic amino acids and N-acetyl amino acids simultaneously. This method can be used to determine the enantiomeric composition of amino acids and N-acetyl-amino acids in the catalysis of D-aminoacylase or L-aminoacylase and the conversion rate of N-acylamino acid racemases.

Enantiomer separation by high-performance liquid chromatography with ( R, R)-tartaric acid mono-amide derivatives as bifunctional chiral selectors

Three mono-amide derivatives of ( R, R)-tartaric acid derived from ( R)-1 -(α-naphthyl)ethylamine (I), ( S)-valine-( S)-1-(α-naphthyl)ethylamide (II) and ( R)-valine--( R)-1-(α-naphthyl)ethylamide (III) were prepared and their chromatographic properties as chiral selectors were examined by HPLC. The enantiomeric separation of derivatives of racemic amino acids, amines, carboxylic acids and alcohols was achieved with these chiral selectors ionically bonded to 3-aminopropyl silica gel using organic mobile phases. In this separation the chiral amine or amino acid amide moiety may play an important role in chiral recognition. On the other hand, the direct separation of racemic amino acids and hydroxy acids was accomplished with these chiral selectors in the form of copper(II) complexes coated on the reversed-phase materials using aqueous mobile phases containing copper(II) ions. In this separation the ( R, R)-tartaric acid moiety may contribute to the chiral recognition. These results clearly show that these ( R, R)-tartaric acid mono-amide derivatives can act as bifunctional chiral selectors, and they are promising for the enantiomeric separation of a wide range of racemic compounds by HPLC.

Chromatographic separation of racemic amino acids by use of chiral crown ether-coated reversed-phase packings

Chromatographic packings for optical resolution of underivatized racemic amino acids were prepared by dynamic coating of a chiral crown ether on reversed-phase packings, and their characteristics were examined. Almost all the amino acids commonly found in proteins were finely separated into their enantiomers when a dilute aqueous solution of perchloric acid was used as the eluent. The enantiomers forming more stable complexes with the chiral crown ether were eluted after those forming less stable complexes. The retention and resolution of racemic amino acids depended on the eluent, the column temperature and the amount of crown ether coated. The separation coefficients, α, increased with decreasing column temperature and/or with increasing amount of crown ether coated.

Ligand chromatography of racemates with L-aspartic and L-glutamic acids on asymmetrical sorbents

Asymmetrical sorbents forming complexes with L-aspartic and L-pyroglutamic acids were synthesized by aminating a chloromethylated and corsslinked polystyrene with the dimethyl esters of L-aspartic and L-glutamic acids. The first sorbent was found to be suitable for the separation of racemic amino acids by ligand exchange chromatography.

Resolution and Separation of Racemic Amino Acids by Gas Chromatography and the Application to Protein Analysis

Resolution and Separation of Racemic Amino Acids by Gas Chromatography and the Application to Protein Analysis