Inherently chiral electrodes: the tool for chiral voltammetry

2,2′-Bis[2-(5,2′-bithienyl)]-3,3′-bithianaphthene oligomers are a model case of electroactive films endowed with “inherent chirality”, originating from a stereogenic element coinciding with the whole electroactive backbone, thus resulting in impressive manifestations. This study highlights their applicative potentialities as low-cost and easy-to-prepare artificial enantiopure electrode surfaces, which display an unprecedented ability to pronouncedly separate voltammetry peaks of enantiomers of quite different chiral probes of applicative interest, concurrently with linear dynamic ranges for peak currents, affording enantiomer excess determination. Thus inherently chiral enantiopure electrodes can indeed be regarded as a key to chiral voltammetry.     

Stereospecific polymerization and chiral initiation,chiral crystallization and chiral nucleation

Helical macromolecules which are configurationally and conformationally specific can now be synthesized. Monomer structures must be selected that demand spacial restriction for monomer addition. High specificity of monomer addition during polymerization has parallels in crystallization of some inorganic salts from aqueous solution. Initiation of highly specific polymerizations with chiral initiators give helical polymers with substantial one-handedness. Nucleation of certain inorganic salts with chiral nucleating agents, the enantiomers of the salts produce enantiomerically pure chiral salts.     

Temperature effects on chiral microemulsion electrokinetic chromatography employing the chiral surfactant dodecoxycarbonylvaline

Dodecoxycarbonylvaline (DDCV) microemulsions (1% and 4%, w/v) were employed to evaluate the retention mechanism of a series of enantiomers over a temperature range of 15-35 degrees C. From the acquired retention data, van't Hoff plots were constructed and enthalpy and entropy of transfer were calculated from the slope and intercept, respectively. Resolution, enantioselectivity, distribution coefficients and Gibb's free energy were also calculated, as well as between enantiomer differences in enthalpy, entropy and Gibb's free energy. Finally, comparisons were made between the microemulsion thermodynamic data and a corresponding set of micellar data. While the 4% DDCV microemulsion did not provide a linear van't Hoff relationship, the 1% DDCV microemulsion was linear over a temperature range of 15-30 degrees C. For the 1% DDCV microemulsion, the enthalpic contribution to retention was consistently favorable (deltaH < 0), whereas the entropic contribution varied from compound to compound. Finally, while the achiral attraction of the analytes was greater for the micellar phase, the microemulsion seemed to provide a suitable difference in entropy (and Gibb's free energy) between enantiomers to achieve chiral discrimination.     

Insight into the chiral induction in supramolecular stacks through preferential chiral solvation

Preferred handedness in the supramolecular chirality of self-assembled achiral oligo(p-phenylenevinylene) (OPV) derivatives is induced by chiral solvents and spectroscopic probing provides insight into the mechanistic aspects of this chiral induction through chiral solvation.     

Tuning the chiral cavity of macrocyclic receptor for chiral recognition and discrimination

The size and shape of the chiral cavity of a macrocyclic receptor were tuned by the alteration of the binaphthyl moiety to improve the chiral recognition/discrimination ability. For example, host 3 with the 3,5-bis(trifluoromethyl)phenyl group at the 3,3'-positions showed improved enantioselectivity for small molecules such as 2-chloropropionic acid and methyl lactate as evaluated by the binding constants. This host 3 also had an excellent ability as an NMR chiral solvating agent.     

Assessing chiral self-recognition using chiral stationary phases

Chiral stationary phases were synthesized and their ability to separate racemic precursors from which they were derived was assessed. Taken in conjunction with homochiral recognition previously observed in the solid state, the results of this study reveal that a geometrically controlling π-π interaction has a profound influence on molecular recognition.     

Diastereoselective Ugi reaction without chiral amines: the synthesis of chiral pyrroloketopiperazines

The three-component Ugi reaction with chiral 2-(2-formyl-1H-pyrrol-1-yl)acetic acids prepared from natural l-aminoacids was investigated. The reaction opens a new route to chiral substituted pyrroloketopiperazines. One of the first examples of an asymmetric Ugi reaction without chiral amines is described. The reaction proceeds with moderate diastereoselectivity to give the target compounds in good yields. The scope and limitation of the approach are discussed.     

Highly potent chiral labeling reagents for the discrimination of chiral alcohols.

Highly sensitive chiral labeling reagents, (1R,2R)- and (1S,2S)-2-(2,3-anthracenedicarboximido)cyclohexanecarboxylic acids [(1R,2R)- and (1S,2S)-A] and (1R,2R)- and (1S,2S)-2-(2,3-naphthalenedicarboximido)cyclohexanecarboxylic acids [(1R,2R)- and (1S,2S)-A'], were prepared. Reagent A has enabled us to discriminate the enantiomers of anteiso fatty alcohols up to C9 methyl branching by 1H NMR, and both reagents A and A' have allowed up to C16 methyl branching at the 10(-15) molar level by fluorescence detected reversed-phase HPLC.     

Pathways to increase the dissymmetry in the interaction of chiral light and chiral molecules

The dissymmetric interaction between circularly polarised (CP) light and chiral molecules is central to a range of areas, from spectroscopy and imaging to next-generation photonic devices. However, the selectivity in absorption or emission of left-handed versus right-handed CP light is low for many molecular systems. In this perspective, we assess the magnitude of the measured chiroptical response for a variety of chiral systems, ranging from small molecules to large supramolecular assemblies, and highlight the challenges towards enhancing chiroptical activity. We explain the origins of low CP dissymmetry and showcase recent examples in which molecular design, and the modification of light itself, enable larger responses. Our discussion spans spatial extension of the chiral chromophore, manipulation of transition dipole moments, exploitation of forbidden transitions and creation of macroscopic chiral structures; all of which can increase the dissymmetry. Whilst the specific strategy taken to enhance the dissymmetric interaction will depend on the application of interest, these approaches offer hope for the development and advancement of all research fields that involve interactions of chiral molecules and light.

This perspective explores the dissymmetric interaction between circularly polarised (CP) light and chiral molecules. Such interactions are central to many applications from next generation displays to asymmetric photochemical synthesis.     

Addition of lactate-derived chiral allyltrichlorostannanes to chiral aldehydes

Chiral lactate-derived allyltrichlorostannanes reacted with chiral α-methyl β-alkoxy and syn and anti α-methyl-β-alkoxy aldehydes to give the corresponding homoallylic alcohols with moderate to high 1,4-syn-diastereoselectivities.     

Study of the behaviour of chiral alcohols by gas chromatography on chiral phases

Summary In order to study the resolution of chiral alcohols by gas chromatography twelve chiral phases derived from (+) tartaric acid were synthetized. The different factors whichcould modify the resolution were studied: importance of trapped fractions of the peak, structures of the chiral phases and racemic compounds.     

Diastereomeric recognition of chiral foldamer receptors for chiral glucoses

[reaction: see text] Three chiral aromatic hydrazide foldamers have been designed and synthesized, in which two R- or S-proline units were incorporated at the terminals of their backbones. The 1H NMR, circular dichroism (CD), and fluorescent experiments and molecular dynamics simulations revealed that the foldamers adopted a chiral helical conformation and complexed alkylated glucoses in chloroform with a good diastereomeric selectivity.     

含磷手性化合物在多聚糖类手性固定相上的手性分离

在纤维素 三(3,5 二甲基苯基氨基甲酸酯)(ChiralcelOD)和直链淀粉 三(3,5 二甲基苯基氨基甲酸酯)(ChiralpakAD H)手性固定相上,采用高效液相色谱正相条件,分离了系列含磷手性化合物。考察了流动相中有机改性剂的种类及浓度对手性分离的影响;研究了化合物的结构与保留及对映体选择性的关系;并探讨了手性识别机理。     

Determination of the enantiomeric composition of chiral carboxylic acids using chiral derivatization and HPLC

Summary The enantiomers of chiral carboxylic acids were separated as their diastereomeric amides with (1R,2R)-(−)-1-(4-nitrophenyl)-2-amino-1,3-propanediol (“levobase”) and with “dextrobase” (the enantiomer of levobase) by high-performance liquid chromatography using a conventional C-18 column and various solvent systems containing acetonitrile, methanol, water, and phosphoric acid.     

New chiral benzothiazine ligand and its use in the synthesis of a chiral receptor

The development of chiral ligands to direct the course and stereoselectivity of many catalytic asymmetric reactions is an important area of interest for many research groups. As part of a program examining the chemistry of 2,1-benzothiazines, we have prepared a new chiral benzothiazine ligand. This ligand can be made in as few as three steps from commercially available starting materials. Presented herein is the synthesis of the ligand along with the synthesis of a chiral molecular receptor that potentially presages a new class of chiral molecular tweezers.     

On the abundance of chiral crystals

A common perception of many chemists is that non-biological chiral crystals comprise a small fraction of all crystals, as is the case of chiral non-biological molecules (~10%). We show that the proportion of non-biological chiral crystals is as high as 23%; and only ~6% of these are labelled as chiral.     

Advanced dress-up chiral columns: New removable chiral stationary phases for enantioseparation of chiral carboxylic acids

This paper describes the preparation of new dress-up columns featuring reproducibly removable and replaceable chiral stationary phases. After synthesizing perfluroalkylated quinine and quinidine derivatives as chiral stationary phase compounds (F-CSPs), we adsorbed them reversibly onto a fluorous LC column through pumping of their solutions. Using this dress-up chiral column and fluorophobic elution of aqueous ammonium formate/MeOH mixtures, we could enantioseparate four racemic N-acetyl amino acids, dichlorprop, and sixteen fluorescent 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC)-derivatized amino acids. Dressing and undressing of the coated F-CSPs could be controlled by varying the fluorophilicity and fluorophobicity of the eluent. The relative standard deviations of the retention times, the retention factors, the number of theoretical plates, the enantioseparation factors, and the resolutions of each of four preparations of such dress-up columns were all less than or equal to 5.26% (from 20 repeated analyses); the reproducibilities from four different preparations were all less than or equal to 10.6%. These columns also facilitated highly sensitive and selective analyses of AQC-amino acids when detected using LC–MS/MS.     

双手性选择单元手性固定相的研究进展

手性固定相（chiral stationary phase,CSP）作为手性色谱分离的核心技术,在手性化合物的识别和分离中得到广泛应用。以双手性选择单元结合作为CSP是近些年的研究热点,研究表明,两种手性选择单元相结合的CSP可增加手性识别位点,显著提高分离效果。本文介绍了近几年双手性选择单元手性固定相在手性分离中的研究进展,并对其发展前景进行了展望。     

Optimization of the chiral resolution of baclofen by capillary electrophoresis using beta-cyclodextrin as the chiral selector

The chiral resolution of baclofen was achieved by capillary electrophoresis using a fused-silica capillary (60 cm x 75 microm ID). The background electrolyte (BGE) was phosphate buffer (pH 7.0, 50 mM)-acetonitrile (95:5 v/v) containing 10 mM beta-cyclodextrin. The applied voltage was 15 kV. The values of alpha and R(s) were 1.06 and 1.00, respectively. The electrophoretic conditions were optimized varying the pH and the ionic strength of the BGE, concentrations of beta-cyclodextrin and acetonitrile and the applied voltage.