Homochiral Enantiomers Research Articles

Organic Ferroelastic with Dual-Channel Manipulation Obtained by H/F Substitution.

Ferroelastic materials with high phase transition temperature have broad application prospects in information conversion and storage, shape memory, energy conversion, hyperelasticity, etc. However, most of the current reports focus on inorganic ferroelastic materials. Inorganic ferroelastic materials have the disadvantages of high energy consumption and harmful metals, which limit their application in practical work. In contrast, organic ferroelastic materials have the advantages of structural adjustability, environmental protection, easy processing, low cost, mechanical flexibility, and so on, which have great development potential in new ferroelastic materials. Here, we have successfully designed and synthesized a pair of homochiral enantiomers [(R/S)-4-fluorobenzoic acid-2-amino-2-phenylethanol] (R- and S-F) using the chemical design strategy of H/F substitution. Compared with the non-F substitution [(R/S)-benzoic acid-2-amino-2-phenylethanol] (R- and S-H), they undergo 2F1-type ferroelastic phase transitions at 370 K. Notably, the ferroelastic domains of R/S-F can be controlled through two physical channels that are temperature and stress, showing great potential in dual-channel switches.

Enantioselective liquid-liquid extraction of 2-cyclohexylmandelic acid enantiomers using chiral ionic liquids.

Obtaining optically pure compounds in an eco-friendly and cost-efficient manner plays an important role in human health and pharmaceutical industry. Racemic separation using multistage stereoselective liquid-liquid extraction has become one of the most practical and effective approach to access homochiral enantiomers. Currently, chiral ionic liquids (CILs) with structural designability have become a promising chiral additive and enable them as adjustable candidates for racemic separation. Herein, a high-effective stereoselective liquid-liquid extraction process composed of imidazolium cations and amino acid-derived anions as the chiral additive was established for racemic 2-cyclohexylmandelic acid (CHMA) separation. We have systematically investigated the choice of organic solvent, concentration of CIL, extraction temperature, and the pH of aqueous phase. For three-stage stereoselective extraction, the maximum enantiomeric excess (e.e.) for CHMA was reached up to 40.6%. Furthermore, the mechanism of steric effect and stereoselective capacity between the CILs and racemic CHMA was discussed and simulated. We envision that the work will facilitate the development of CILs in multistage liquid-liquid extraction and promote the large-scale production of optically pure enantiomers.

Influence of Wallach’s Rule on Chiral AIE Systems and Its Application in Cryptographic Information Storage

Influence of Wallach’s Rule on Chiral AIE Systems and Its Application in Cryptographic Information Storage

Controlling chirality in the synthesis of 4 + 4 diastereomeric amine macrocycles derived from trans-1,2-diaminocyclopentane and 2,6-diformylpyridine.

A few suitably long dialdehyde and primary diamine building blocks of a predetermined chirality have been designed and synthesized to enable controlled and efficient synthesis of all six possible diastereomers of 4 + 4 macrocyclic amine derived from trans-1,2-diaminocyclopentane (DACP) and 2,6-diformypyridine (DFP) units. Although two out of six diastereomers have been reported recently, their synthesis presented here is more direct and occurs with an improved yield. This family of 4 + 4 macrocycles contains one pair of homochiral enantiomers of identical RRRRRRRR and SSSSSSSS configurations of DACP units, two different meso forms (meso I of alternating RRSSRRSS and meso II of neighboring RRRRSSSS configuration of DACP moieties) as well as one pair of heterochiral enantiomers, where configuration of one diamine fragment is opposite to the other three diamine parts, RRRRRRSS and SSSSSSRR, respectively. The structures of each type of macrocycle in solid state have been confirmed by single crystal analyses of a macrocyclic amine in its suitable protonated form. The different symmetry of each type of macrocycle in solutions has been proved by 1H and 13C NMR spectra of their hydrochloride derivatives. The chiral nature of two different pairs of optically active enantiomers has been established by circular dichroism spectra. These chiral 4 + 4 diastereomeric macrocycles are receptors for chiral guests and recognize in solution 10-camphorsulfonic acid as well as chiral tartaric acid.

Synthesis and Preservation of Organic Molecules with Homochiral Excess by Adsorption on Carbon in Carbonaceous Chondrites

The nature of carbon, initial components, molecules of homochiral abiogenic synthesis and their preservation from decay and racemization for more than 4.5 billion years in carbonaceous chondrites has not been established. In the oxygen-free atmospheres of the nebula and early Earth, hydrogen and hydrogen-containing gases were oxidized with carbon monoxide and carbon dioxide to form carbon and water, as well as the intermediates of these reactions, formaldehyde and methane acid. Together with ammonia, they were the initial components of organic synthesis. According to the Rebinder rule, carbon adsorbs hydrogen well, including in organic molecules. In this connection, experiments with the assumed conditions of the early Earth were carried out by adsorption on carbon to obtain R-(rectus, Latin) ribose from formaldehyde, and S-(sinister) serine from formaldehyde, methane acid and ammonia. For other S-amino acids, a stereo chemical justification of their formation based on S-serine is given. For carbonaceous chondrites, the results of the above experiments were confirmed by the correlation of an increase in homochiral excess with an increase in the amount of hydrogen in aldonic acids and lactic acid with a coefficient of 0.94 and 0.85 in amino acids. The justification of the homochiral process will reduce the costs of searching for life on planets, for scientific research, for the production of medicines, perfumes, food, and so on. Doubts about the extraterrestrial origin of homochiral enantiomers in carbonaceous chondrites arise most often due to a lack of understanding of the reasons for their appearance. This work will significantly reduce such skepticism.

Assembly of Chiral Cluster-Based Metal-Organic Frameworks and the Chirality Memory Effect during their Disassembly.

Many metal clusters are intrinsically chiral but are often synthesized as a racemic mixture. By taking chiral Ag14(SPh(CF3)2)12(PPh3)4(DMF)4 (Ag14) clusters with bulky thiolate ligands as an example, we demonstrate herein an interesting assembly disassembly (ASDS) strategy to obtain the corresponding, optically pure crystals of both homochiral enantiomers, R-Ag14m and S-Ag14m. The ASDS strategy makes use of two bidentate linkers with different chiral configurations, namely, (1R,2R,N1E,N2E)-N1,N2-bis(pyridin-3-ylmethylene)cyclohexane-1,2-diamine (LR) and the corresponding chiral analogue LS. For comparison, we also use the racemic mixture of equimolar of LR and LS (LRS). Three three-dimensional (3D) Ag14-based metal-organic frameworks (MOFs) were characterized by X-ray crystallography to be [Ag14(SPh(CF3)2)12(PPh3)4(LR)2]n (Ag14-LR), [Ag14(SPh(CF3)2)12(PPh3)4(LS)2]n (Ag14-LS), and [Ag14(SPh(CF3)2)12(PPh3)4(LRS)2]n (Ag14-LRS), respectively. As expected, the building blocks in Ag14-LR or Ag14-LS are homochiral R-Ag14 or S-Ag14, respectively. In contrast, Ag14-LRS is achiral and crystallizes with a diamond-like structure containing alternate R-Ag14 and S-Ag14 clusters. During the assembly process, the racemic Ag14 clusters were converted to homochiral building blocks, namely, R-Ag14 for Ag14-LR and S-Ag14 for Ag14-LS. Subsequently, the chiral linkers were removed from the crystals of Ag14-LR and Ag14-LS via hydrolysis with water, and from the disassembled solid material Ag14-DR and Ag14-DS, optically pure enantiomers R-Ag14m and S-Ag14m were obtained. It is hoped that this simple assembly strategy can be used to construct cluster-based chiral assemblage materials and that the subsequent disassembly protocol can be used to obtain optically pure chiral cluster molecules from as-prepared racemic mixtures.

A Self-Assembled Homochiral Radical Cage with Paramagnetic Behaviors.

Condensation of an inherently C3 -symmetric polychlorotriphenylmethyl (PTM) radical trisaldehyde with tris(2-aminoethyl)amine (TREN) yields a [4+4] tetrahedral radical cage as a racemic pair of homochiral enantiomers in 75 % isolated yield. The structure was characterized by X-ray crystallography, confirming the homochirality of each cage framework. The homochirality results from intramolecular [CH⋅⋅⋅π] and hydrogen-bonding interactions within the cage framework. The four PTM radicals in a cage undergo weak through-space coupling. Magnetic measurements demonstrated that each cage bears 3.58 spins.

A Self‐Assembled Homochiral Radical Cage with Paramagnetic Behaviors

AbstractCondensation of an inherently C3‐symmetric polychlorotriphenylmethyl (PTM) radical trisaldehyde with tris(2‐aminoethyl)amine (TREN) yields a [4+4] tetrahedral radical cage as a racemic pair of homochiral enantiomers in 75 % isolated yield. The structure was characterized by X‐ray crystallography, confirming the homochirality of each cage framework. The homochirality results from intramolecular [CH⋅⋅⋅π] and hydrogen‐bonding interactions within the cage framework. The four PTM radicals in a cage undergo weak through‐space coupling. Magnetic measurements demonstrated that each cage bears 3.58 spins.

New insights into cardiotoxicity induced by chiral fluoxetine at environmental-level: Enantioselective arrhythmia in developmental zebrafish (Danio rerio).

Fluoxetine is frequently detected in aquatic environment, and chronic FLX exposure exhibits adverse effects on aquatic communities. Its chirality makes the adverse effects more complicated. This study aimed at the enantioselective cardiotoxicity in developmental zebrafish induced by racemic (rac-)/S-/R-fluoxetine. The accumulation profiles demonstrated that biotransformation of fluoxetine to norfluoxetine occurred during rac-fluoxetine exposure, with a higher enrichment of S-norfluoxetine than R-norfluoxetine. Heart malformations including pericardial edema, circulation abnormalities, and thrombosis were observed, and enantioselective changes also occurred. According to H&E staining and Masson's trichrome staining, the loose severity of cardiac structure and cardiac fibrosis in rac-norfluoxetine treated group was worse than that in fluoxetine treated groups. Results of toxicity-associated parameters in our homochiral enantiomers' exposure also indicated that the toxicity induced by S-fluoxetine was more severe than R-fluoxetine. Enantioselective arrhythmia in developmental zebrafish after chiral fluoxetine exposure could be caused by myocardial fibrosis, abnormal developmental processes, and the biotransformation of fluoxetine to norfluoxetine could make that worse. Our findings can be used to assess the environmental risk of the two enantiomers of fluoxetine that induce cardiotoxicity in aquatic organisms.

Chiral Self-Sorting in Truxene-Based Metallacages

Two chiral face-rotating metalla-assembled polyhedra were constructed upon self-assembling achiral components, i.e., a tritopic ligand based on a truxene core (10,15-dihydro-5H-diindeno[1,2-a;1′,2′-c]fluorene) and two different hydroxyquinonato–bridged diruthenium complexes. Both polyhedra were characterized in solution as well as in the solid state by X-ray crystallography. In both cases, the self-sorting process leading to only two homo-chiral enantiomers was governed by non-covalent interactions between both truxene units that faced each other.

Phosphorescent Decanuclear Bimetallic Pt6M4 (M = Zn, Fe) Tetrahedral Cages.

Coordination-driven self-assembly delivers discrete, nanoscopic architectures that may preserve or enhance the physicochemical properties of their parent building blocks. Herein, we report the syntheses, characterization, and photophysical properties of two tetrahedral cages, [ZnII4L6](PF6)8 (C1) and [FeII4L6](OTf)8 (C2), where L = PtII(PEt3)2(C≡C-bpy)2 (PEt3 = triethylphosphine; C≡C-bpy = 5-ethynyl-2,2'-bipyridine) and OTf = trifluoromethanesulfonate. C1 and C2 were assembled in isolated yields of 72% and 81% by treating 2 equiv of Zn(NO3)2·6H2O or Fe(OTf)2 with 3 equiv of L, respectively. Both cages were fully characterized by NMR, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction (SCXRD). The local D3 symmetry at each polypyridyl metal node raises the possibility of a number of isomeric cages; however, only the homochiral enantiomers (ΔΔΔΔ and ΛΛΛΛ) are formed based on 1H NMR and SCXRD. C1 exhibits phosphorescence centered at 545 nm with a quantum yield of 10% in N2-degassed acetonitrile at 25 °C. The quantum yield of C2 is significantly lower due to a nonradiative relaxation from 5MC (MC = metal-centered) states introduced by the FeII nodes.

Temperature-Induced Syntheses, Iodine Elimination, Enantiomers Resolution, and Single-Crystal-to-Single-Crystal Transformation of Imidazole-Co(II) Coordination Polymers with Amino-isophthalic Acid as Co-Ligand

On the basis of a temperature-induced effect, the solvothermal reaction of Co(Ac)2·4H2O, 5-amino-2,4,6-triiodoisophthalic acid (H2atibdc), and 1,4-bis(2-methyl-imidazol-1-yl)butane (bib) at 80 °C gave a new coordination polymer [Co(bib)(atibdc)] (1), which shows a two-dimensional (2D) network with left- and right-handed helical chains. By raising the reaction temperature to 130 °C, a pair of homochiral enantiomers [Co(bib)(atibdc)]·2H2O (2, 2M, and 2P) were successfully obtained, displaying a three-dimensional (3D) framework with three kinds of unique helical chains. Keeping the temperature of the reaction system to 150 °C, excited, an in situ iodine elimination reaction occurred, and a new linker 5-aminoisophthalic acid (H2aipa) was generated, which then cooperated with the bib ligand to construct a coordination polymer [Co(bib)(aipa)] (3), showing a 3D 3-fold interpenetrating architecture. The comparison of final solid structures exhibits an exclusive temperature-induced effect on the construction of th...

Synthesis and Characterization of a Novel Waugh-Type Polyoxometalate K1.5(NH4)4.5[MnMo9O32]·4.2H2O

A new molybdomanganate based on the Waugh-type polyoxoanion K1,5(NH4)4,5[MnMo9O32]·4.2H2O (1) has been synthesized in aqueous solution and characterized by single crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis and cyclic voltammetry measurements. The title compound was crystallized in the trigonal system, space group R3 with a = 15.950 (3) A, b = 15.950 (3) A, c = 12.447 (2) A, γ = 120°, V = 2742.3 (9) A3, Z = 3, R1 = 0.031 and wR2 = 0.088. Left-handed and right-handed [MnMo9O32]6− polyanions enantiomers can be observed in compound (1). The homochiral enantiomers are consolidated by many hydrogen bonds involving ammonium cations and water molecules which are stacked into a 3D framework.

Spontaneous chiral resolution of a rare 3D self-penetration coordination polymer for sensitive aqueous-phase detection of picric acid.

Two unprecedented homochiral enantiomers based on two different kinds of rigid ligands, namely [Cd(NDC)L]2·H2O (1R and 1L), have been synthesized under hydrothermal conditions through spontaneous resolution. Their structures were determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, IR, and thermogravimetric (TG) analysis. The resulting framework 1, constructed by four kinds of homo-handed helical chains represents the first 3D self-penetrating framework formed by decoration of single (10,3)-a net with helical chains. The single (10,3)-a net in 1 formed by three kinds of different homo-handed helical chains is different from the standard one, which should be ascribed to the usage of V-shaped ligand L. A unique self-penetration motif can be discovered in 1 where one helical chain alternately passes through 10-membered shortest circuits linked to each other and in contrary, the corresponding circuits are bound to the helical chain. Interestingly, 1 exhibits fluorescent emission in both the solid and solution phase. The uncoordinated nitrogen atom and amino group from the triazole core on the crystal surface make it suitable to detect picric acid in water. The luminescence intensity of 1 in water can be efficiently quenched by the addition of picric acid (PA). The sensitive detection of PA can be continuously performed for at least five cycles without diminishing the fluorescence intensity and destroying the framework structure of 1. The possible quenching mechanisms for PA are also investigated.

Spontaneous Resolution in the Ionothermal Synthesis of Homochiral Zn(II) Metal–Organic Frameworks with (10,3)-a Topology Constructed from Achiral 5-Sulfoisophthalate

Two homochiral enantiomers {(EMIM)[Zn(SIP)(IM)]}n (1a and 1b, EMIM = 1-ethyl-3-methylimidazolium) possessing chiral (10,3)-a topology constructed from an achiral rigid 5-sulfoisophthalate (SIP) ligand and imidazole (IM) have been obtained by spontaneous resolution under ionothermal conditions. The homochiral enantiomers show second-order nonlinear optical effects and photoluminescence.

Ionic Ferroelectrics Based on Nickel Schiff Base Complexes

Two novel homochiral enantiomers, trinuclear ionic clusters [(NiL(1))(2)Na](+)NCS(-).MeOH.Et(2)O (1) and [(NiL(2))(2)Na](+)NCS(-).MeOH.Et(2)O (2) [H(2)L(1) = N,N'-bis(3-methoxysalicylidene)-(1R,2R)-1,2-diphenylenediamine; H(2)L(2) = N,N'-bis(3-methoxysalicylidene)-(1S,2S)-1,2-diphenylenediamine], have been synthesized and structurally characterized. Both complexes have C(2) symmetry and crystallize in space group P2(1). Ferroelectric measurements reveal that complexes 1 and 2 represent a new type of ionic ferroelectric based on metal-organic coordination with a polarization value higher than that of KH(2)PO(4).

Spontaneous resolution of two homochiral ferroelectric cadmium(ii) frameworks and an achiral framework from a one-pot reaction involving achiral rigid ligands

Unprecedented two homochiral Cd(II) enantiomers and one achiral Cd(II) complex obtained from one pot reaction with achiral mixed rigid ligands 1,3,5-tris(1-imidazolyl)benzene (tib) and 1,4-benzenedicarboxylate (BDC2−) feature interesting entangled structures in which the ligands display huge distortion, and the homochiral enantiomers show ferroelectric property.

Homochiral zinc phosphonates with layered and open framework structures using polycarboxylate as second linkers

Reactions of zinc sulfate and (R)- or (S)-(1-phenylethylamino)methylphosphonic acid (pempH(2)) in the presence of 1,4-benzenedicarboxylic acid (H(2)bdc) result in homochiral enantiomers (R)- and (S)-[Zn(4)(pempH)(4)(bdc)(2)].2H(2)O (). When H(2)bdc is replaced by 1,2,4,5-benzenetetracarboxylic acid (H(4)btec), enantiomers (R)- and (S)-[Zn(3)(pempH)(2)(btec)(H(2)O)(2)].H(2)O () are obtained. Compounds have a layer structure in which the chiral inorganic double chains, made up of corner-sharing {ZnO(4)} and {PO(3)C} tetrahedra, are connected by bdc(2-). While in compounds , chiral chains of zinc phosphonate are each connected to their four equivalent neighbors through btec(4-) linkages, resulting in an open framework structure. All these compounds are optically active, exhibiting second harmonic generation (SHG) responses 0.2 or 0.8 times that of urea.

Non-Linear Effects in Asymmetric Reactions: Negative and Positive Stereoselectivity in the Formation of Homoleptic 1:2 Metal to Ligand Complexes of Chiral 1,9-Disubstituted Semicorrin Ligands

The stereoselectivity of the formation of bis-chelates with the 1,9-disubstituted chiral semicorrin ligands (1S,9S)-dimethyl 5-cyanosemicorrin-1,9-dicarboxylate (1) for Co2+, Ni2+, Cu2+, and Pd2+ and with its (1S,9S)-diethyl analogue 2 for Co2+ and Cu2+ have been measured by the method of continuous variation of enantiomers, and with 1 for Zn2+ by NMR. Positive selectivities were found for Co2+, Ni2+, and Zn2+ complexes, whereas very high negative selectivities prevail in the complexes of Cu2+ and Pd2+. These results are rationalised by X-ray structural determinations of some of the corresponding complexes. The optically active Cu2+ and Pd2+ complexes show distorted square planar structures with chirality predetermined by the chirality of the ligand. Ni2+ complexes are five or hexacoordinated and exhibit a distorted tetrahedral arrangement of the four coordinated nitrogen atoms. In the optically active compound the ester moiety is coordinated by the oxygen atom of the alkoxy group and the arrangement of the two N-N chelate rings shows ?-(S,S) chirality. Interestingly, with the racemic ligand, it is not the more stable heterochiral, but the racemic complex containing the two homochiral enantiomers which is obtained. The coordination of the ester groups occurs by the carbonyl oxygen and the chirality is opposite to the optically active compound, e.g ?(S,S)/?-(R,R). The structure of the optically active zinc compound shows very weak interaction with the alkoxy group of one ester moiety of each ligand molecule and the chirality of the N-N-chelate rings is ?-(S,S). Again, the compound obtained with the racemic ligand contains the enantiomers of the homochiral complex, the chirality of which is ?-(R,R)/?-(S,S). The results are discussed with respect to the possibility to perform asymmetric amplifications of the 1:1 complexes of semicorrin ligands as enantioselective catalysts.

Syntheses and resolutions of new chiral biphenyl backbones: 2-amino-2′-hydroxy-6,6′-dimethyl-1,1′-biphenyl and 2-amino-2′-hydroxy-4,4′,6,6′-tetramethyl-1,1′-biphenyl

The new chiral backbones ( R)-(+)- and S-(−)-2-amino-2′-hydroxy-6,6′-dimethyl-1,1′-biphenyl and ( R)-(+)- and ( S)-(−)-2-amino-2′-hydroxy-4,4′,6,6′- tetramethyl-1,1′-biphenyl were synthesized from o-methylaniline and 2,4-dimethyl-aniline respectively in seven steps. A new resolution method was developed to provide homochiral enantiomers (from diastereomeric salts) in reasonably high yields. The absolute configuration of the new biphenyls was confirmed by X-ray structural analysis.