L-Valinol

In this study, three functionalized chiral ionic liquids (CILs) derived from l-valinol, l-prolinol and l-phenylalaninol, namely N,N,N-trimethyl-l-valinol-bis(trifluoromethanesulfon)imide ([TMLV]+[Tf2N]-, CIL1), N,N-dimethyl-l-prolinol-bis(trifluoromethanesulfon)imide ([DMLP]+[Tf2N]-, CIL2) and N,N,N-trimethyl-l-phenylalaninol-bis(trifluoromethanesulfon)imide ([TMLP]+[Tf2N]-, CIL3), were synthesized and subsequently utilized for enantiomeric separation in capillary electrophoresis (CE) with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) as chiral selector for the first time. Compared with traditional single HP-β-CD separation system, the synergistic system exhibited substantially improved separations of six tested drugs. Using the CIL1/HP-β-CD as a model system, the influence of crucial parameters including the type and proportion of organic modifier, CILs concentration, HP-β-CD concentration and buffer pH was investigated in detail. Additionally, molecular modeling with AutoDock was applied to elucidate the enhanced enantioselectivity in the presence of CILs, which has certain guiding value in predicting the migration order of the enantiomers and studying the interactions important for the chiral recognition.

Chiral assembly and asymmetric synthesis are critically important for the generation of chiral metal clusters with chiroptical activities. Here, a racemic mixture of [K(CH3 OH)2 (18-crown-6)]+ [Cu5 (St Bu)6 ]- (1⋅CH3 OH) in the chiral space group was prepared, in which the chiral red-emissive anionic [Cu5 (St Bu)6 ]- cluster was arranged along a twofold screw axis. Interestingly, the release of the coordinated CH3 OH of the cationic units turned the chiral 1⋅CH3 OH crystal into a mesomeric crystal [K(18-crown-6)]+ [Cu5 (St Bu)6 ]- (1), which has a centrosymmetric space group, by adding symmetry elements of glide and mirror planes through both disordered [Cu5 (St Bu)6 ]- units. The switchable chiral/achiral rearrangement of [Cu5 (St Bu)6 ]- clusters along with the capture/release of CH3 OH were concomitant with an intense increase/decrease in luminescence. We also used cationic chiral amino alcohols to induce the chiral assembly of a pair of enantiomers, [d/l-valinol(18-crown-6)]+ [Cu5 (St Bu)6 ]- (d/l-Cu5V ), which display impressive circularly polarized luminescence (CPL) in contrast to the CPL-silent racemic mixture of 1⋅CH3 OH and mesomeric 1.

The amino alcohols in l-valinol were effectively separated and quantified using hydrophilic interaction chromatography with fluorescence detection. The influence of the mobile phase (salt type, buffer concentration, and pH) on retention was studied. A column TSKgel amide and mobile phase consisting of 10 mM acetate buffer pH 4.0 and acetonitrile (20:80, v/v) provided well-separated symmetric peaks of analytes. Fluorescence detection was performed using postcolumn derivatization with o-phtaldialdehyde/2-mercaptoethanol at an excitation and emission wavelength of 345 and 450 nm, respectively. Simple sample pretreatment and very high sensitivity represent the main advantages of the developed method. After validation, the method was successfully applied to the analysis of commercial samples of l-valinol.