Single-Layered Chiral Nanosheets with Dual Chiral Void Spaces for Highly Efficient Enantiomer Absorption

Although considerable effort in recent years has been devoted to the development of two-dimensional nanostructures, single-layered chiral sheet structures with a lateral assembly of discrete clusters remain elusive. Here, we report single-layered chiral 2D sheet structures with dual chiral void spaces in which discrete clusters of planar aromatic segments are arranged with in-plane AB order in aqueous methanol solution. The chirality of the sheet is induced by the slipped-cofacial stacks of rectangular plate-like aromatic segments in the discrete clusters which are arranged laterally with up and down packing, resulting in dual chiral void spaces. The chiral nanosheets function as superfast enantiomer separation nanomaterials, which rapidly absorb a single enantiomer from a racemic mixture with greater than 99 % ee.     

Single‐Layered Chiral Nanosheets with Dual Chiral Void Spaces for Highly Efficient Enantiomer Absorption

Although considerable effort in recent years has been devoted to the development of two‐dimensional nanostructures, single‐layered chiral sheet structures with a lateral assembly of discrete clusters remain elusive. Here, we report single‐layered chiral 2D sheet structures with dual chiral void spaces in which discrete clusters of planar aromatic segments are arranged with in‐plane AB order in aqueous methanol solution. The chirality of the sheet is induced by the slipped‐cofacial stacks of rectangular plate‐like aromatic segments in the discrete clusters which are arranged laterally with up and down packing, resulting in dual chiral void spaces. The chiral nanosheets function as superfast enantiomer separation nanomaterials, which rapidly absorb a single enantiomer from a racemic mixture with greater than 99 % ee.     

Synthesis and redox properties of racemic electroactive polymers containing axially chiral adamantyl segments

A method of introducing chirality directly into a polymer backbone has been developed that employs the dissymmetry of an adamantane derivative with axial chirality. This new chiral adamantane building block was readily functionalized with electroactive thiophene rings using palladium-catalyzed cross-coupling methodology. The two resulting electroactive monomers were electropolymerized to create racemic electroactive polymers containing phenyl-capped oligothiophene segments alternating with chiral adamantyl segments. Synthesis, electrochemistry, and spectroelectrochemistry studies are reported.     

Spectroscopic investigation on chirality transfer in additive-driven self-assembly of block polymers

Chiral supramolecules prepared by the additive-driven self-assembly of block copolymers provide a facile method to construct helical nanostructures. In this study, we investigated the chiral transfer from chiral tartaric acid to poly(styrene)-b-poly(ethylene oxide) using small-angle X-ray scattering, transmission electron microscopy, circular dichroism, and vibrational circular dichroism. The results showed that the chirality was transferred to both the segments of block copolymer irrespective of the interaction with the chiral additives and formation of helical phase structure. However, the chirality transfer was carried out using different methods: for poly(ethylene oxide) segments, the chirality transfer was carried out via direct hydrogen bond formation; for polystyrene segments, the chirality transfer was carried out via the cooperative motion of block copolymers during the thermal annealing.     

Chiroptical inversion induced by sandwiching units in chiral polythiourethane

Chiroptical behavior of a hydrogen-bond-regulated chiral polythiourethane segment was inversed by sandwiching sterically demanding segments in copolymers prepared by cationic ring-opening copolymerization of chiral cyclic thiourethanes derived from L-serine.     

Total synthesis of epothilone a through stereospecific epoxidation of the p-methoxybenzyl ether of epothilone C

The total synthesis of epothilone A is described by the coupling four segments 4-7 a. Three of the segments, 4, 5 and 7 a, have only one chiral center; all other chiral centers were introduced by simple asymmetric catalytic reactions. The key steps are the ring opening of epoxide 5 with acetylide 8 for the construction of the C12-C13 cis double bond and a practical hydrolytic kinetic resolution (HKR) developed by Jacobsen group for the introduction the chiral center at C3. Especially, the stereospecific epoxidation of 3-O-PMB epothilone C 3 b through long-range effect of 3-O-PMB protecting group gave high yields of the C12-C13 alpha-epoxide for the synthesis of target molecule.     

两个手性胶囊分子的氢键介质的动态共价键合成

从手性环己-1,2-二胺衍生的手性双头基前体出发合成了两个手性的双层结构的胶囊化合物。设计前体带有氨基和醛基,它们被连接到两个分子内氢键诱导的折叠体片段上。分子内氢键通过促进三个亚胺键的形成促进两个大环板块的选择性形成。     

Selective Synthesis of Conjugated Chiral Macrocycles: Sidewall Segments of (−)/(+)-(12,4) Carbon Nanotubes with Strong Circularly Polarized Luminescence

Carbon nanotubes (CNTs) have unusual physical properties that are valuable for nanotechnology and electronics, but the chemical synthesis of chirality- and diameter-specific CNTs and π-conjugated CNT segments is still a great challenge. Reported here are the selective syntheses, isolations, characterizations, and photophysical properties of two novel chiral conjugated macrocycles ([4]cyclo-2,6-anthracene; [4]CAn_2,6 ), as (−)/(+)-(12,4) carbon nanotube segments. These conjugated macrocyclic molecules were obtained using a bottom-up assembly approach and subsequent reductive elimination reaction. The hoop-shaped molecules can be directly viewed by a STM technique. In addition, chiral enantiomers with (−)/(+) helicity of the [4]CAn_2,6 were successfully isolated by HPLC. The new tubular CNT segments exhibit large absorption and photoluminescence redshifts compared to the monomer unit. The carbon enantiomers are also observed to show strong circularly polarized luminescence (g_lum≈0.1). The results reported here expand the scope of materials design for bottom-up synthesis of chiral macrocycles and enrich existing knowledge of their optoelectronic properties.     

Selective Synthesis of Conjugated Chiral Macrocycles: Sidewall Segments of (−)/(+)‐(12,4) Carbon Nanotubes with Strong Circularly Polarized Luminescence

Carbon nanotubes (CNTs) have unusual physical properties that are valuable for nanotechnology and electronics, but the chemical synthesis of chirality‐ and diameter‐specific CNTs and π‐conjugated CNT segments is still a great challenge. Reported here are the selective syntheses, isolations, characterizations, and photophysical properties of two novel chiral conjugated macrocycles ([4]cyclo‐2,6‐anthracene; [4]CAn_2,6 ), as (?)/(+)‐(12,4) carbon nanotube segments. These conjugated macrocyclic molecules were obtained using a bottom‐up assembly approach and subsequent reductive elimination reaction. The hoop‐shaped molecules can be directly viewed by a STM technique. In addition, chiral enantiomers with (?)/(+) helicity of the [4]CAn_2,6 were successfully isolated by HPLC. The new tubular CNT segments exhibit large absorption and photoluminescence redshifts compared to the monomer unit. The carbon enantiomers are also observed to show strong circularly polarized luminescence (g_lum≈0.1). The results reported here expand the scope of materials design for bottom‐up synthesis of chiral macrocycles and enrich existing knowledge of their optoelectronic properties.     

Chiral force constants: Recommendations for the presentation of internal coordinate force constants

Some force constants associated with the internal coordinates that sense handedness or chirality can have opposite signs in the enantiomers of chiral molecules. Examples of such force constants include interaction force constants between a torsional and stretching or bending internal coordinates. The sign reversal for these force constants in the enantiomers of chiral molecules or in opposite-handed molecular segments is best recognized by labeling them as chiral force constants. Recognition of chiral force constants suggests that certain guidelines are to be followed in the presentation of internal coordinate force constants. © 1993 by John Wiley & Sons, Inc. © John Wiley & Sons, Inc.     

Synthesis and racemization process of chiral carbon nanorings: a step toward the chemical synthesis of chiral carbon nanotubes

A simple and realistic model for the shortest sidewall segments of chiral single-walled carbon nanotubes (SWNTs) has been designed, and one of the chiral carbon nanorings, cyclo[13]paraphenylene-2,6-naphthylene ([13]CPPN, 1) has been successfully synthesized. DFT calculations reveal that the racemization energy of 1 is 8.4 kcal·mol(-1). In addition, some important energetic values, such as racemization barriers and strain energies, of other chiral carbon nanorings have been systematically estimated for future molecular design.     

Chiral eighteen-component three-dimensional supramolecular entities stabilized by the hydrogen bonding and coordination interactions

A new class of chiral eighteen-component three-dimensional supramolecular entities has been assembled in toluene and chloroform from twelve zinc porphyrin-appended 2-(ethylamino)- pyrimido[4,5-b][1,8]naphthyridin-4(3H)-one monomers and six chiral bipyridyl compounds. The heterocyclic segments form two C₆-symmetric cyclic hexamers, which are stabilized by a well-established DDA-AAD hydrogen bonding motif, while the six chiral bispyridine ligands are coordinated to the corresponding zinc porphyrin units to give the two-layered architectures. The structures have been characterized by the ¹H NMR, UV-vis and circular dichroism experiments, which also reveals that, when the concentration of the monomers is high enough, the chiral supramolecular entity can be formed exclusively.     

Phospholipid tubelets

A novel electron microscopy specimen protocol shows that the presumed phospholipid bilayer membrane ribbons that wind helically to form the cylinders known as "tubules" are actually flattened tubes. These flattened tubes are alternatively found with a helical twist about the tube's long axis or occasionally flat with no winding or twist. Flat, cylindrically wound and axially twisted segments are routinely found along a single tube's length, and at the helically wound and axially twisted segment junctions, the chiral sense of the structure often, but not always, changes chiral sense.     

Amplification of Chirality in Helical Supramolecular Columns

Strong amplification of chirality occurs in dynamic, but highly ordered, helical columns in n-butanol, for which one chiral seed molecule suffices to render a column of 400 molecules to become homochiral. The chiral columns are formed in a thermally dependent stepwise process. The transition from achiral stacks to helical columns is highly cooperative owing to well-defined intermolecular interactions. `Sergeant and Soldiers' measurements allow for the calculation of the association constant and cooperativity length of the homochiral segments. The `Sergeant and Soldiers' data on the number of molecules within a column show a strikingly good match with data obtained from a theoretical model describing the self-assembly of the discotic molecules as a function of temperature and concentration.     

Orientational ordering of a ferroelectric liquid crystal with high spontaneous polarization

The orientational ordering of the liquid crystal, 3M2CPHOB ((2S, 3S)-3-methyl-2-chloropentanoic acid-4′,4″-hexyloxybiphenyl ester) in its smectic A and chiral smectic C phases has been studied by carbon-13 2D N.M.R. The technique used is separated local-field spectroscopy, which produces a first-order splitting for each carbon signal, from which carbon-proton dipolar constants can be determined. The order parameters for different molecular segments of the liquid crystal can then be calculated. The C-H bond order parameter at the chiral centre with a chlorine atom is unusually large, which is a strong indication of hindered rotation of the molecular segment at the chiral centre. The carbon-13 chemical shifts of 3M2CPHOB were also measured as a function of temperature, and the relation between the chemical shifts and the order parameters is discussed.     

Orientational ordering of a ferroelectric liquid crystal with high spontaneous polarization

The orientational ordering of the liquid crystal, 3M2CPHOB ((2S, 3S)-3-methyl-2-chloropentanoic acid-4',4'-hexyloxybiphenyl ester) in its smectic A and chiral smectic C phases has been studied by carbon-13 2D N.M.R. The technique used is separated local-field spectroscopy, which produces a first-order splitting for each carbon signal, from which carbon-proton dipolar constants can be determined. The order parameters for different molecular segments of the liquid crystal can then be calculated. The C-H bond order parameter at the chiral centre with a chlorine atom is unusually large, which is a strong indication of hindered rotation of the molecular segment at the chiral centre. The carbon-13 chemical shifts of 3M2CPHOB were also measured as a function of temperature, and the relation between the chemical shifts and the order parameters is discussed.     

Total Synthesis of Siomycin A: Construction of Synthetic Segments

The five practical segments for the total synthesis of siomycin A, that is, the dehydropiperidine segment A ( 5 ), the pentapeptide segment B ( 3 ), the dihydroquinoline segment C ( 6 ), and the β‐phenylselenoalanine dipeptide segments D ( 7 ) and E ( 4 ), were synthesized. Segment A ( 5 ) was constructed by the coupling of the azomethine ylide and the chiral sulfinimine, followed by the stereoselective reduction of the six‐membered imine function. Segment B ( 3 ) was synthesized by the phenylselenylation of the β‐lactone, stereoselective vinylzinc addition to the chiral sulfinimine, and oxazoline–thioamide conversion. Segment C ( 6 ) was prepared by the one‐pot olefination of the tetrahydroquinoline N‐oxide using triflic anhydride and triethylamine, stereoselective reduction of the methyl ketone function, and regioselective Yb(OTf)₃‐catalyzed epoxide opening by the amino group. Segments D ( 7 ) and E ( 4 ) were synthesized by coupling of the properly protected β‐phenylselenoalanines.     

Cholesterol-based dimesogenic bidentate ligands and their Cu(II) and Pd(II) metallomesogens

The synthesis and evaluation of the liquid crystalline properties of non-conventional liquid crystals, consisting of two non-identical mesogenic segments interconnected via a paraffinic chain spacer, are of considerable current interest. In particular, chiral dimesogens possessing a cholesteryl ester unit as the chiral entity joined to other aromatic mesogens through a polymethylene spacer have shown unique and interesting thermal behaviour. In continuation of our investigations on this topic, here we present the synthesis and characterization of the first examples of cholesterol-based unsymmetrical dimesogenic bidentate ligands and their Cu(II) and Pd(II) metal-organic systems (metallomesogens). Our studies reveal that the dimesogenic bidentate ligands exhibit multiple mesophases, whereas their metal complexes stabilize only the mesophase.     

Synthesis and characterization of non‐symmetric chiral dimers

A new class of cholesterol‐based non‐symmetric dimers have been synthesized and characterized. They comprise O‐alkylated cinnamic acid and pro‐mesogenic cholesterol segments interlinked covalently through a methylene spacer varying in its length and parity. All the dimers and some of the key precursors have been studied for their phase behaviour. All the intermediates show mesomorphism. Importantly, the thermal properties of dimers are found to be critically dependent on the parity of the flexible spacer. The dimers with odd‐parity spacer display chiral nematic and/or twist grain boundary phases. In contrast, the dimers with even‐parity spacer are either crystalline or exhibit metastable chiral nematic and/or twist grain boundary phases with the exception of one compound for which two unknown mesophases have been observed. The odd–even effect was found to be indistinct for selective reflection wavelengths of the chiral nematic phase. For some dimers, a variation in the pitch of the chiral nematic phase as a function of temperature was observed. Cyclic voltammetry experiments revealed the electrochemical properties of a representative liquid crystal dimer.     

Chiral amphiphilic self-assembled alpha,alpha'-linked quinque-, sexi-, and septithiophenes: synthesis, stability and odd-even effects

The synthesis, characterization, and self-assembly in butanol of a series of well-defined alpha,alpha'-linked quinqui-, sexi-, and septithiophenes substituted, via ester links at their termini, by chiral oligo(ethylene oxide) chains carrying an alpha, beta, delta, and epsilon methyl, respectively, are reported. Studies of the self-assembly of these molecules using UV/visible absorption, luminescence, and circular dichroism spectroscopies reveal, for the sexithiophene case, that the magnitude of the observed Cotton effect in the aggregates diminishes progressively as the chiral substituent is moved away from the thiophene segment. The stability of the assemblies increases with the length of the oligothiophene and as the substituent chiral unit is moved away from the aromatic core, being greatest for the unsubstituted case. The sign of the Cotton effect alternates in an "odd/even" manner as the position of the chiral substituent is moved along the oligo(ethylene oxide) chain and on going from the quinquethiophene to the septithiophene having the same side chain. Atomic force microscopy on materials deposited from solution on an aluminum or glass surface and optical measurements show that capsules are formed from the oligothiophenes with H-type packing of the aromatic segments.