Chiral Monomer Research Articles

Preparation and application of chiral silica gel spheres based on L-glutamic

无机介孔硅球因其具有足够的机械强度、热稳定性,以及适应多种流动相的优点,成为高效液相色谱(HPLC)柱填料中使用最广泛和最重要的材料。但在此研究领域中,并未见球形的全无机手性硅胶用作HPLC手性固定相。该文以无机球形介孔硅胶作为研究对象,通过堆砌硅珠法,以硅溶胶为原料,L-谷氨酸(L-Glu)为手性源,在手性环境中制造出脲醛树脂与胶体二氧化硅混合的小球,在550 ℃高温下煅烧除去树脂部分,制备基于L-Glu的无机介孔硅胶球。通过元素分析、红外光谱、扫描电镜、透射电镜和氮气吸附等表征证明这是一种具有规则球形的手性硅胶球,其手性来源于硅胶球自身的骨架和孔结构。将L-Glu手性硅胶球作为固定相制备了HPLC色谱柱,以正己烷-异丙醇(9∶1, v/v)作为流动相,流速为0.1 mL/min,考察了该手性柱对一系列外消旋化合物的拆分性能。实验表明,该手性柱拆分了15种外消旋化合物,其中特罗格尔碱、吡喹酮、3-苄氧基-1,2-丙二醇、1,2-环氧己烷、3-羟基-2-丁酮、2-甲基四氢呋喃-3-酮、异丙基缩水甘油醚达到基线分离;还分离了10种苯系位置异构体,o,m,p-氨基苯酚、o,p-氯苯酚、o,m,p-碘苯胺、o,m,p-甲苯胺、o,m,p-二硝基苯、o,m,p-氯苯胺、o,m,p-硝基苯酚、o,m,p-溴苯胺达到基线分离。实验表明,L-Glu手性硅胶球在手性分离方面具有良好的可行性,与普通硅胶相比不需要进一步修饰就可以有较好的手性分离效果,是一种低成本、制备便捷的手性无机硅胶固定相。

Electrically modulated large range tuning of self-assembled photonic bandgaps in polymer-stabilised blue phases

ABSTRACT Developing 3D photonic nanostructures with stimuli-directed controllability has been a burgeoning but challenging area in the field of optical materials as there are numerous opportunities in next-generation communication systems. In this study, polymer-stabilised blue phase I material systems with self-assembled 3D tunable photonic bandgap (PBG) were prepared by using different acrylate monomers. From the comparison of the electric responsive behaviours, the electrical tunability of the material system was noteworthyly improved by using chiral acrylate monomers. And a reversible electrically modulated large range red shifting of the PBG was achieved through the fabrication of the chiral polymer network. Besides, the optical quality and response time can be improved by increasing the polymerisable chiral monomer concentration.

High‐Performance BioNylons from Itaconic and Amino Acids with Pepsin Degradability

AbstractThe use of renewable feedstock for polymers has led to poor thermomechanical properties with high production costs. Herein, the production of novel chiral dicarboxylic acids derived from renewable itaconic and amino acids (d‐ or l‐leucine) is reported. In this study, rigid chiral heterocyclic dicarboxylic acid monomers are obtained with high purity from itaconic acid‐derived dimethyl itaconate as a starting material. Chirally interactive polyamides are prepared via melt polycondensation of hexamethylenediamine with heterocyclic diacid monomers. Further studies are conducted on d‐ or l‐leucine‐derived polyamides with homochirality that are fully amorphous. In contrast, the crystallization degree of the composite of d‐leucine‐derived polymer chains with l‐leucine‐derived chains increases to 36%, presumably due to enhanced interaction between polymer chains with different chiralities. The chirally‐interacting composite shows a glass transition temperature, Tg, of approximately 117 °C and a melting temperature, Tm, of approximately 213 °C, which are higher than those of conventional polyamides such as polyamide 11 (Tg of approximately 57 °C). The composite also shows high Young's moduli, E, and mechanical strengths σ, ranging from 2.2–3.8 GPa and 86–108 MPa, respectively. In addition, the polyamides show degradability with a digestive enzyme, pepsin.

Fluorescent chiral liquid-crystalline networks with dual-mode temperature response

ABSTRACT Due to the excellent optical properties and great application prospects in the optical field, both pyrene compounds (PCs) and chiral liquid crystal have attracted extensive attention in theoretical research and practical applications. Fluorescent chiral liquid-crystalline networks (FCLCN) with good liquid-crystalline properties and tunable fluorescence properties as a response to temperature were prepared using Poly(methylhydrogeno)siloxane (PMHS), chiral liquid-crystalline monomer (M1), chiral crosslinker (M2) and organic fluorescent pyrene compounds (M3). The as-prepared FCLCN display reversible chiral Grandjean texture during the heating and cooling process from the intrinsic chiral arrangement of FCLCN. The discrete pyrene chromogenic segments in FCLCN matrix endowed the networks with excellent fluorescence properties when irradiating with ultraviolet light and the fluorescence can be precisely adjusted by temperature, furthermore, the FCLCN presents highly sensitive fluorescence evolution with a high response sensitivity of 3.4% K−1. The FCLCN can be manufactured into temperature-driven dynamic fluorescence patterns with a fast and reversible response.

Chiroptical Cross‐Linked Polymers Grown via Radical Polymerization around Chiral Nanosilica

AbstractChiral polymers are often prepared by two ways depending upon chiral monomers, chiral catalysts, and chiral auxiliaries which always come from organics: one is the enantio‐selective polymerization of prochiral or racemic monomers or polymerization of optically active monomers; and the other one is the molecular imprinting technique, which creates chiral recognition sites inside a densely cross‐linked polymer gel. Herein, a unique method for the synthesis of chiroptical cross‐linked polymers via radical polymerization of achiral divinyl monomers in the mediation of the inorganic chiral nanosilica is reported. The monomers that are cross‐linkable such as divinylbenzene (DVB) and N,N′ ‐methylenebisacrylamide (MBA) are physically adsorbed onto chiral silica bundles and then polymerized by dispersion of those monomers/silica bundles in the presence of radical initiators. The products are characterized by SEM, FT‐IR, solid‐state 13C NMR, TGA, and CD. Very interestingly, the cross‐linked polymers themselves obtained via final removal of the chiral silica show remarkable chiroptical activity with mirror relationship and can make achiral guest of porphyrin adsorbed on the polymers become optically active.

Synthesis of Polymers Bearing a Chiral Backbone via Stereospecific Ionic Ring-Opening Polymerization of Chiral Donor-Acceptor Cyclopropanes.

The stereospecific ionic ring-opening polymerization of various donor-acceptor cyclopropanes is reported. The chiral cyclopropane monomers are readily prepared with established methodology and stereospecific polymerization is best conducted with a catalytic amount of MgBr2 serving as a Lewis acid and as an initiator. Polymers with molecular masses of up to 7800g mol-1 containing a stereocenter in every repeating unit are obtained and the substituents of the monomers can be readily varied to access a novel class of chiral polymers.

Spin-selective electron transmission through self-assembled monolayers of double-stranded peptide nucleic acid.

Monolayers of chiral molecules can preferentially transmit electrons with a specific spin orientation, introducing chiral molecules as efficient spin filters. This phenomenon is established as chirality-induced spin selectivity (CISS) and was demonstrated directly for the first time in self-assembled monolayers (SAMs) of double-stranded DNA (dsDNA)1 . Here, we discuss SAMs of double-stranded peptide nucleic acid (dsPNA) as a system which allows for systematic investigations of the influence of various molecular properties on CISS. In photoemission studies, SAMs of chiral, γ-modified PNA show significant spin filtering of up to P = (24.4 ± 4.3)% spin polarization. The polarization values found in PNA lacking chiral monomers are considerably lower at about P = 12%. The results confirm that the preferred spin orientation is directly linked to the molecular handedness and indicate that the spin filtering capacity of the dsPNA helices might be enhanced by introduction of chiral centers in the constituting peptide monomers.

Controlling polymer stereochemistry in ring-opening polymerization: a decade of advances shaping the future of biodegradable polyesters.

This review highlights recent developments in the field of biodegradable polymeric materials intended to replace non-degradable conventional plastics, focusing on studies from the last ten years involving the stereoselective ring-opening polymerization of cyclic esters. This encompasses exciting advances in both catalyst design and monomer scope. Notably, the last decade has seen the emergence of metal-free stereocontrolled ROP for instance, as well as the synthesis and stereocontrolled polymerization of new types of chiral monomers. This study will emphasize recent stereoselective polymerization catalysts and chiral monomers and will focus on stereocontrol quantification, the mechanisms of stereocontrol and their differentiation if reported and studied for a specific catalyst system.

Competition between chiral solvents and chiral monomers in the helical bias of supramolecular polymers.

Solute-solvent interactions are key for the assembly and proper functioning of biomacromolecules and play important roles in many fields of organic and polymer chemistry. Despite numerous reports describing the effects of (chiral) solvents on helical conformations of (supramolecular) polymers, the combination of chiral solvents and chiral monomers is unexplored. Here we report diastereomeric differences in the supramolecular polymerization of enantiomers of chiral triphenylene-2,6,10-tricarboxamides in chiral chlorinated solvents. Competition between the preferences induced by the stereocentres of the assembled monomers and those present in the solvent molecules results in unforeseen temperature-dependent solvation effects. By combining experiments and mathematical modelling, we show that the observed differences between enantiomers originate from the combined additive entropic effects of stereocentres present in the monomer and in the solvent. Remarkably, copolymerizations show that the chiral solvent can bias the copolymer helicity and thereby overrule the helical preference of the monomers. Our results highlight the importance of cumulative solvation effects in supramolecular polymerizations.

Effect of chiral monomer containing D(+)-camphoric acid on the optical properties and phase behaviours of side-chain cholesteric liquid crystal polymers

ABSTRACT Cholesteric liquid crystals with selective reflection have important applications in the field of light control and optical thin films. In this study, a series of side-chain cholesteric liquid-crystal polymers (named as PPL series) was synthesised by a one-step hydrosilylation reaction among monomer LA containing cholesterol group, monomer LB containing D(+)-camphoric acid group and monomer LG containing cyano group. The chemical structures and the mesogenic properties of the monomers and polymers were determined by usual test methods. Testing results showed that PPL series polymers had excellent thermal stability and wide range of mesophases. As the content of monomer LB increased, PPL1-PPL6 could be observed colourful Grandjean textures and good selective reflection. The optical rotation experiment indicated that the rotation direction of the PPL series was consistent with that of the monomer LB, and the specific rotation was linearly related to the content of the monomer LB.

Biasing the Screw-Sense of Supramolecular Coassemblies Featuring Multiple Helical States.

By enchaining a small fraction of chiral monomer units, the helical sense of a dynamic polymer constructed from achiral monomer units can be disproportionately biased. This phenomenon, known as the sergeants-and-soldiers (S&S) effect, has been found to be widely applicable to dynamic covalent and supramolecular polymers. However, it has not been exemplified with a supramolecular polymer that features multiple helical states. Herein, we demonstrate the S&S effect in the context of the temperature-controlled supramolecular copolymerization of chiral and achiral biphenyl tetracarboxamides in alkanes. The one-dimensional helical structures presented in this study are unique because they exhibit three distinct helical states, two of which are triggered by coassembling with monomeric water that is codissolved in the solvent. The self-assembly pathways are rationalized using a combination of mathematical fitting and simulations with a thermodynamic mass-balance model. We observe an unprecedented case of an “abnormal” S&S effect by changing the side chains of the achiral soldier. Although the molecular structure of these aggregates remains elusive, the coassembly of water is found to have a profound impact on the helical excess.

New indole alkaloids from the seeds of Datura metel L.

Four new indole alkaloids, daturametelindoles A-D (1–4) were isolated from the EtOAc soluble partition of the ethanol extract of the Datura metel seeds. The structures of the new compounds were determined based on spectroscopic evidence, including their 1D- and 2D-NMR spectra and mass spectrometry. In particular, compounds 1–4 were all racemes, confirmed by the optical rotations and CD spectra. Unfortunately, the chiral monomers were not obtained due to the amount, but the developments of their chiral separation and chiral resolution were completed. All isolated compounds were evaluated for cytotoxic effects against human gastric adenocarcinoma cells (SGC-7901), human hepatoma (Hepg2), and human breast cancer (MCF-7).

Synthesis and Characterisation of Photolabile SPhNPPOC-Protected (R)-MiniPEG Containing Chiral γ-Peptide Nucleic Acid Monomers

Peptide nucleic acid (PNA) microarrays are expected to be developed as a new generation of gene detection tools. However, poor water solubility and the limitation of the sequence design of achiral PNA probes mainly hinder their application. Accordingly, (R)-diethylene glycol containing a chiral PNA (miniPEG-γPNA) has been developed to solve these problems. Light-directed synthesis is an effective method to fabricate high-density microarrays. Thiophenyl-2-(2-nitrophenyl)propoxycarbonyl (SPhNPPOC) is a newly synthesised photolabile protective group with high photolytic efficiency. Protecting the PNA monomers with SPhNPPOC may improve the preparation process of PNA microarrays by light-directed synthesis in terms of shortening the deprotection time and restraining side reactions. In this article, SPhNPPOC/carbobenzoxy (Cbz)-protected chiral miniPEG-γPNA monomers are synthesised, and the photo-deprotection rate is approximately twice that of a 2-(2-nitrophenyl)propyloxycarbonyl (NPPOC)-protected monomer. The monomers are expected to be used for the efficient and rapid fabrication of chiral miniPEG-γPNA microarrays through a photolithographic strategy.

The Thermal Properties and Degradability of Chiral Polyester-Imides Based on Several l/d-Amino Acids.

Eight kinds of chiral diacid monomers were prepared with amino acids with different side groups or configurations. Polyester-imides (PEIs) were synthesized from these diacid monomers and diphenol monomers through polycondensation reaction, and the performances and properties were compared with the chiral polyamide-imides (PAIs) previously synthesized by our work group. Their thermal properties were analyzed by thermo gravimetric analysis (TGA) and dynamic thermomechanical analysis (DMA), and it was found that the glass transition temperature (Tg) of PEI was mainly affected by the volume of side groups. Their degradability was studied through buffer degradation experiments, and the changes in their water contact angle, molecular weight, structure and appearance during the degradation process were characterized by contact angle tester, gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). With degradation, the hydrophilicity of PEI was improved, and when amino acids with larger side groups or D configuration were introduced into the backbone of PEI, the degradability decreased.

A straightforward access to functionalizable polymers through ring-opening metathesis polymerization of levoglucosenone-derived monomers

Levoglucosenone (LGO) is a cellulose-derived and commercially available platform molecule that is produced at an industrial scale. LGO contains a highly reactive double bond that was used to produce two isomers of norbornene-containing LGO monomers, endo-N-LGO (1) and exo-N-LGO (2). Furthermore, Baeyer-Villiger oxidation of 1 was performed to yield a highly-valuable chiral monomer, endo-N-HBO (3). The norbornene moiety of the prepared monomers was readily polymerized by ring-opening metathesis polymerization (ROMP) in the presence of GI catalyst to access highly thermostable polymers with Td5% up to 360 °C in the case of N-LGO-based polymers and Td5% in the range of 374–380 °C when 3 was polymerized, such range of Td5% being the highest reported up-to-date for the LGO-derived polymers. The effect of monomer concentration over the polymerization process was studied and showed that 4 M solutions lead to a better monomer conversion while preserving the control over the polymer structure and reducing the environmental factor (E factor). GI was found active in the ROMP of 3 without the need of protecting the hydroxy group and thus leading to pendent hydroxy functional polymers. Furthermore, for the first time, copolymers containing both LGO and HBO reactive moieties were prepared by random copolymerization of 1 and 3.

Magnetically Separable Chiral Periodic Mesoporous Organosilica Nanoparticles

We describe, for the first time, a successful strategy for synthesizing chiral periodic mesoporous organosilica nanoparticles (PMO NPs). The chiral PMO nanoparticles were synthesized in a sol–gel process under mild conditions; their preparation was mediated by hydrolysis and condensation of chiral-bridged organo-alkoxysilane precursor compounds, (OR‘)3Si-R-Si(OR‘)3, in the presence of cetyltrimethylammonium bromide (CTAB) surfactant. The resulting nanoparticles were composed merely from a chiral- bridged organo-alkoxysilane monomer. These systems were prepared by applying different surfactants and ligands that finally afforded monodispersed chiral PMO NPs consisting of 100% bridged-organosilane precursor. In addition, the major advancement that was achieved here was, for the first time, success in preparing magnetic chiral PMO NPs. These nanoparticles were synthesized by the co-polymerization of 1,1′-((1R,2R)-1,2-diphenylethane-1,2-diyl)bis(3-(3-(triethoxysilyl) propyl) urea) chiral monomer by an oil in water (o/w) emulsion process, to afford magnetic chiral PMO NPs with magnetite NPs in their cores. The obtained materials were characterized with high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) spectroscopy, powder X-ray diffraction (XRD), solid-state NMR analysis, circular dichroism (CD) analysis, and nitrogen sorption analysis (N2-BET).

Biobased Cycloolefin Polymers: Carvone-Derived Cyclic Conjugated Diene with Reactive exo-Methylene Group for Regioselective and Stereospecific Living Cationic Polymerization.

Carvone, a naturally abundant chiral cyclic α,β-unsaturated carbonyl compound, was chemically transformed into cyclic exo-methylene conjugated dienes. The exo-methylene group had high reactivity in cationic polymerization and was efficiently polymerized in a controlled manner via regioselective 1,4-conjugated additions using initiating systems effective for living cationic polymerization of vinyl ethers. The obtained polymers with 1,3-cyclohexenyl units and tetra-substituted olefins in the main chain showed high glass transition temperatures over 110 °C. The chiral monomer underwent stereospecific polymerization to result in polymers with low solubility and weak packing of the rigid main chain in the lamellar layers. The racemic mixture resulted in soluble amorphous polymers, which were subsequently hydrogenated into cycloolefin polymers with enhanced thermal properties.

Chiral polymer network stabilised blue phase liquid crystals

ABSTRACT The effect of chiral polymer network in polymer-stabilised blue phase liquid crystals (PS-BPLCs) is investigated. Compared with the conventional polymer network, the chiral polymer network can induce and stabilise the blue phase with less proportion of chiral dopant and monomer. Benefiting from twisting power and good compatibility of the chiral monomer, the driving capability of chiral PS-BPLC can be much improved by 65% compared with that of conventional PS-BPLCs. The hysteresis and residual birefringence issues also can be improved by introducing a chiral monomer with high stiffness and small molecule weight.

Electrically tunable photonic band gap structure in monodomain blue-phase liquid crystals

Photonic band gap materials have the ability to modulate light. When they can be dynamically controlled beyond static modulation, their versatility improves and they become very useful in scientific and industrial applications. The quality of photonic band gap materials depends on the tunable wavelength range, dynamic controllability, and wavelength selectivity in response to external cues. In this paper, we demonstrate an electrically tunable photonic band gap material that covers a wide range (241 nm) in the visible spectrum and is based on a monodomain blue-phase liquid crystal stabilized by nonmesogenic and chiral mesogenic monomers. With this approach, we can accurately tune a reflection wavelength that possesses a narrow bandwidth (27 nm) even under a high electric field. The switching is fully reversible owing to a relatively small hysteresis with a fast response time, and it also shows a wider viewing angle than that of cholesteric liquid crystals. We believe that the proposed material has the potential to tune color filters and bandpass filters.

Preparation and optical properties of linear polysiloxane-based glassy cholesteric liquid crystals with green reflected colour

ABSTRACT A new series of glassy chiral-nematic liquid crystals P-ChxNy , were synthesised by hydrosilylation reaction of chiral mesogenic monomer Ch and nematic monomer N grafted onto polymethylhydrosiloxane. The mesomorphic properties, phase behaviour and selective reflection were studied by differential scanning calorimetry (DSC), polarising optical microscopy (POM), and UV-VIS spectrum. Both the Tg and Tc gradually increased as the amount of unit Ch in the copolymer increased. A series of morphologically stable, glassy chiral-nematic liquid crystals were obtained. Among these copolymers, the well-oriented glassy film of the polymer P-Ch4N3 exhibited a selective reflection band centred at approximately 532 nm with green reflected colour below Tg .