Chiral Recognition and Resolution Based on Helical Polymers

Helical polymers have attracted a great deal of attention and been extensively investigated due to their various applications.One of the most importa nt applicati ons of helical polymers is chiral recog nition and resolutio n ofe nan tiomersforthe reas on that a pair of e nan tiomers is comm only with differe nt physiological and toxicological behaviors in biological systems.Helical polymers usually prese nt un expected high chiral recogniti on ability to a variety of racemic compo unds.Whatzs more,the chiral recog nition and resolution abilities of the system are depe ndent on the highly ordered helical structures of the helical polymers.This mini review mainly focuses on the recent progress in chiral recognition and resolution based on helical polymers.The synthetic methodology for helical polymers is firstly discussed briefly.Then recent advances of chiral recog nition and resoluti on systems based on helical polymers,especially polyacetylenes and polyisocya nides,are described.We hope this mini review will in spire more in terest in developing helical polymers and en courage further advances in chiral-related disciplines.

Multi‑color Tunable and White Circularly Polarized Luminescent Composite Nanofibers Electrospun from Chiral Helical Polymer

Circularly polarized luminescence(CPL)-active nanomaterials have attracted tremendous attention.However,it is still a big challenge to conveniently fabricate multi-color and white CPL-active nanomaterials on a large scale.Herein,a simple and scalable approach to achieve the above goals is presented.Multicolor CPL-active nanofibers are fabricated from chiral helical substituted polyacetylene,achiral fluorescent dyes and polyacrylonitrile via uniaxial electrospinning;the highest luminescence dissymmetry factor(glum)of the resulting nanofibers can reach 10^(−2).Furthermore,white CPL-active nanofibers are obtained by coaxial electrospinning,in which the resulting core-shell structure has excellent adjustability and can be utilized to physically isolate different fluorescent dyes to reduce energy transfer efficiency;therefore,stable white CPL emissions can be achieved with high g_(lum) values up to 10^(−3).Notably,the prepared white-emission CPL nanofibrous films show bright white circularly polarized light when coated on UV chips,demonstrating their future application in constructing low-cost and flexible light-emitting devices such as circularly polarized light-emitting diodes.

Unimolecular Transmembrane Na^(+) Channels Constructed by Pore-Forming Helical Polymers with a 2.3A Aperture

To understand the relationships between channel size and ion selectivity,we have developed a new type of artificial ion channel based on pore-forming helical polymers consisting of phenanthrolineoxadiazole units with a pore aperture 2.3A close to the diameter of the Na^(+)ion(2.04A).Successful preparation of high molecular weight helical polymers(HP1)gives rise to a 4.6 nm long artificial unimolecular transmembrane channel.The transport property of artificial channel HP1 was elaborately investigated by means of vesicle-based kinetic assay and symmetry/asymmetry bilayer membrane(BLM)experiments as well.These results unambiguously demonstrate that HP1 is a Na^(+)-selective channel with extremely high transport activity(EC_(50)=0.017 mol% relative to lipid).Moreover,the Na^(+)/K^(+)selectivity ratio of HP1 reaches 1.9,as determined by asymmetry BLM experiments.Owing to the narrowest 2.3A size constraint so far,HP1 transport naked Na^(+)ion across the membrane,which represents a different Na^(+)transport mode from that of natural Na^(+)channels,which transports partially hydrated Na^(+)ions during transmembrane conduction.This study provides crucial insights on the chemical basis of ion selectivity in the field of ion channels.

Helical Coordination Polymer with a 3-Fold Interpenetration Structure Based on 5-(Hydroxymethyl)isophthalic Acid

5-（Hydroxymethyl） isophthalic acid （H2HIA） as a novel organic ligand was prepared from 3,5-bis（methoxycarbonyl）benzoic acid by a two-step method. And then, a 3D helical coor- dination polymer with a 3-fold interpenetration structure, namely [Zn1/2（HIA）1/2（DPEE）1/2]n （1）, was hydrothermally synthesized at 160 ℃, using H2HIA ligands to assemble with DPEE ligands and Zn2＋ ions. Complex 1 crystalizes in orthorhombic system, space group Pnna, with a = 8.2118（5）, b = 17.1698（7）, c =14.9922（7） ？, V = 2113.82（18） ？3, μ = 1.194 mm-1, Z = 4 and S = 0.967. Moreover, some physical characteristics of complex 1, such as powder X-ray diffraction （PXRD）, thermogravimetry analyses （TGA） and photoluminescent properties, were also investigated.

Syntheses,Structures,and Photoluminescent Properties of Two Zn(Ⅱ)Coordination Polymers with Helical Chains Structures

Two novel coordination polymers with helical chains, {[Zn（L）（H2O）]·H2O}n（1） and {[Zn（L）（p-bix）]·3.5H2O}n（2）, where H2 L = 5-（4-hydroxypyridinium-1-ylmethyl） isophthalic acid and p-bix = 1,4-bis（imidazol-1-ylmethyl）benzene, have been hydrothermally synthesized, and charac-terized by elemental analysis, powder X-ray diffraction（PXRD）, IR, thermal gravimetric analyses（TGA） and also by single-crystal X-ray diffraction. Both complexes 1 and 2 crystallize inmonoclinic, space group P21/c. Compound 1 displays a two-dimensional（2D） structure with two distinct types of helical chains; 2 shows a layered coordination polymer with two types of helical chains and features an interesting 2D→3D interdigitated architecture. Meanwhile, the luminescent properties of 1 and 2 have also been investigated in detail.

Synthesis,Crystal Structure and Fluorescence Property of the Ag(Ⅰ) Coordination Polymer Constructed by 2D[Ag(1,3-BIP)(PMA)_(0.5)]_n^(n-)Layers and 1D[Ag(1,3-BIP)(H_2O)]_n^(n+) Chains

A new AgO） coordination polymer, {[Ag（1,3-BIP）（H20）][Ag（1,3- BIP）（PMA）0.5.- 4H20}n （PMA = 1,2,4,5-benzenetricarboxylic acid, 1,3-BIP = 1,3-bis（imidazole）propane）, have been synthesized and characterized by single-crystal X-ray diffraction, powder XRD, FTIR, TGA and elemental analysis techniques. The single-crystal X-ray diffraction reveals that the title complex is formed by 1D polymeric cationic chains of [Ag（1,3-BIP）（H2O）]n^n＋ and 2D polymetric anionic layer of [Ag（1,3-BIP）（PMA）0.5]n^n-, which are further linked by intermolecular H-bonding to form a 3D supramolecular framework. In addition, the photoluminescence property of the title complex in the solid state at room temperature was also investigated.

Structure and Photochemical Properties of a Chiral Cd Coordination Polymer Based on 4,4'-(Hexafluoroisopropylidene)Bis(benzoic acid)and 1,3-Di(pyridineyl)benzene

One new chiral metal-organic coordination polymer,[Cd2（dpb）（H2hfipbb）2]n,was obtained under hydrothermal conditions of 1,3-di（pyridineyl）benzene（dpb） and 4,4＇-（hexafluoroisopropylidene）bis（benzoic acid）（H2hfipbb）. The title compound reveals a three-dimensional（3D） framework with two types of helical chains [Cd（COO）]n,which are linked each other to further form a double helical chain [Cd2（COO）2]n by sharing the same Cd（Ⅱ） ions. The dpb connects the double helical chains to generate a 3D framework. These unique structures were studied by single-crystal X-ray and other spectroscopy techniques. In addition,the luminescent,fluorescence lifetime and second harmonic generation efficiency properties in the solid state have been studied.

Synthesis of Helical Poly(phenylacetylene)s Carrying Dendritic Pendants with Varied Branching Densities Through Polymerization in Different Solvents

Helical poly(phenylacetylene)s(PPAs)have received extensive attention because of their features in dynamic chirality and promising applications.Therefore,understanding relationship among the polymer molecular structures,polymerization conditions and tunability of their chirality is of key scientific value.Recently,we developed a novel class of dendronized PPAs carrying 3-fold dendritic oligo(ethylene glycols)(OEGs)via alanine linkage,and found that these bulky polymers exhibited tunable helical conformations through thermally-mediated dehydration and aggregation.Herein,we report on synthesis of a homologous series of dendronized PPAs that carry 2-fold,3-fold or 6-fold dendritic OEG pendants,and focus on effects of molecular topological structures,peripheral units and polymerization solvents on the thermoresponsiveness and their conformation switching behaviors.Effects of branching density and peripheral units(ethoxyl or methoxyl)of the dendritic OEG pendants were examined,and found to play a decisive role on the helical conformation and thermoresponsiveness of these dendronized PPAs due to their different bulkiness and overall hydrophilicity.In addition,different polymerization solvents were checked for their possible influence on the polymerization,thermoresponsive behavior and the chirality of the resulting polymers.For polymerization in selective solvents like water or methanol,the obtained dendronized PPAs exhibited weak thermal transitions,while polymerization in non-selective solvent like THF furnished PPAs with characteristic thermoresponsive behavior,indicating that solvents were involved in the process of polymerization of the dendronized macromonomers.More interestingly,different chiralities of the PPAs through polymerization in various solvents were retained,irrelevant to the purification process and solvents treatments.This work suggests that the topological structures together with polymerization solvents can modulate the thermoresponsive behavior and helical conformation of the dendronized PPAs.

“SERGEANTS AND SOLDIERS RULE” IN HELICAL SUBSTITUTED- ACETYLENE COPOLYMER EMULSIONS

The ＂sergeants and soldiers rule＂ occurring in helical copolymer emulsions derived from an achiral monomer （M1） and a chiral monomer （M2） was observed. TEM, GPC, and 1H-NMR techniques in combination demonstrate the formation of nanoparticles constituted by the copolymers. CD and UV-Vis spectra show the （co）polymer chains in the nanoparticles adopt helical structures of a predominant helicity, and the copolymers follow the ＂sergeants and soldiers rule＂ in forming helical structure.

Helical Poly(α,β-unsaturated ketone)with Bulky Pendant of Binaphthyl from Anionic Polymerization of(−)-Menthyl(S)-6'-Acrylyl-2'-methyloxy-1,1'-binaphthalene-2-carboxylate

(−)-Menthyl(S)-6'-acrylyl-2'-methyloxy-1,1'-binaphthalene-2-carboxylate(3)was synthesized and anionically polymerized using n-BuLi as an initiator in toluene.The monomer 3 was levorotatory and had an[α]_(D)^(25)value of−72.4,but its corresponding polymer poly-3 was dextrorotatory and showed an[α]_(D)^(25)value of+162.0.Poly-3 was confirmed to exist in the form of one-handed helical structure in solution by means of comparing the specific optical rotation and the CD spectra with that of 3 and the model compounds such as(−)-menthyl(S)-6'-propionyl-2'-methyloxy-1,1'-binaphthalene-2-carboxylate 2b and(−)-menthyl(S)-6'-heptanoyl-2'-methyloxy-1,1'-binaphthalene-2-carboxylate 2c.This conclusion was also confirmed by the fact that the g-value of poly-3 is about 11 times of that of monomer 3.

Chiral electron deficient ruthenium helical coordination polymer as a catalyst for the epoxidation of substituted styrenes

An air and moisture stable ruthenium（Ⅲ） formate complex[Ru（HCO2）Cl2]n has been synthesized and examined in the epoxidation of substituted styrenes.X-ray crystallographic data of this complex were determined and showed that the formate ligand coordinates to the ruthenium centers in a μ~2-η~2 fashion（syn,syn）.Its asymmetric unit contains one Ru（Ⅲ） ion together with the half of a formate ligand and one chloride anion,which are bridged between the metal centers,forming a 1-D chain coordination polymer.This electron deficient helical coordination polymer was employed in the epoxidation of parafluorostyrene,affording the epoxide product in 92%yield.Natural chirality of this coordination polymer is applicable in asymmetric epoxidation reactions.

Helical Covalent Polymers with Unidirectional Ion Channels as Single Lithium-Ion Conducting Electrolytes

Single-ion conducting polymer electrolytes have attracted great attention as safe alternatives to liquid electrolytes in high energy density lithium-ion batteries.Herein,we report the first example of a crystalline anionic helical polymer as a single lithium-ion conducting solid polymer electrolyte(SPE).Single-crystal X-ray analysis shows that the polymer folds into densely packed double helices,with bundles of unidirectional negatively charged channels formed that can facilitate lithium-ion transportation.

Synthesis and structure of the first propeller-shaped helical coordination polymer { [ Ag( S , S) -bis( oxazoline) ] (OTf)}_∞

A mixture of (S, S)-bis(oxazoline) ligand (1) with silver trifluoromethane sulfonate afforded a helical coordination polymer (2). Its structure was determined by X-ray angle-crystal diffraction.

Polythiophene-block-poly(phenyl isocyanide) Copolymers: One-pot Synthesis, Properties and Applications

Conjugated block copolymers have gained increasing interests in recent years. Development of a novel method for facile synthesis of conjugated block copolymers with desired structures and functions is greatly desired. In this mini review, we summarized the recent advances in one-pot synthesis of conjugated block copolymers containing π-conjugated polythiophene and helical polyisocyanide segments by using a nickel（Ⅱ） complex as single catalyst. The sequential living polymerization of the two monomers proceeded in a controlled manner, affording expected block copolymers in high yields with controlled molecular weights（Mns） and narrow molecular weight distributions（Mw/Mns）. By using this method, a family of block copolymers with expected structure and tunable compositions can be facilely prepared. Introducing functional groups onto the pendant, these block copolymers can exhibit interesting self-assembly property, tunable light emission and multi-responsiveness.

Optically Active Helical Polyisocyanides Bearing Chiral Phosphine Pendants: Facile Synthesis and Application in Enantioselective Rauhut-Currier Reaction

Three novel enantiopure phenyl isocyanide monomers with BH3-protected phosphine functional group were designed and synthesized. Polymerization of these monomers using a alkyne-Pd（II） complex as a catalyst led to the formation of respective helical polyisocyanides in high yields with controlled molecular weights（Mns） and narrow molecular weight distributions（Mw/Mns）. Removing the protecting BH3 groups afforded helical poly（phenyl isocyanide）s bearing phosphine pendants. Thanks to the chiral induction of monomer, the isolated helical polyisocyanides showed high optical activity, as revealed by circular dichroism（CD） and absorption spectroscopies and polarimetry. The helical structures of these polymers were quite stable in various organic solvents with different polarities and in a wide temperature range. Moreover, these helical polymers could be used as organocatalysts and showed good performance in enantioselective cross Rauhut-Currier reaction. The enantiomeric excess（ee） values of the isolated products of cross Rauhut-Currier reaction could be up to 90%. The polymer organocatalysts could be easily recovered from the reaction mixtures and reused at least five times in the reaction without significant loss of their enantioselectivities and catalytic activities.

Asymmetric Polymerization of N-Vinylcarbazole with Optically Active Anionic Initiators

The anionic polymerization of N-vinylcarbazole（NVC） by using optically active anionic initiators such as the lithium salts of（S）-1-（9H-fluoren-2-yl）-4-isopropyl-4,5-dihydrooxazole（（S）-1-FIDH） and（S）-2-（9H-fluoren-2-yl）-4-isopropyl-4,5-dihydrooxazole（（S）-2-FIDH） and complexes of（-）-Sparteine with n-butylithium（n-Bu Li-（-）-Sp） or fluorenyl lithium（FILi-（-）-Sp） was achieved. The yield and specific rotation of poly（N-vinylcarbazole）s（poly（NVC）s） were considerably affected by the molar ratio of（S）-FIDH to NVC. The highest yield and specific rotation were obtained with Li-（S）-1-FIDH as an initiator, with a molar ratio of monomer and initiator [M]/[I] = 10/1. The effects of the chiral initiators, type of solvent and the polymerization temperature were investigated. The obtained optical activity of polymers was attributed to asymmetric induction of the chiral initiators.

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.

Circularly polarized luminescence of coordination aggregates

The development and applications of materials with efficient circularly polarized luminescence(CPL)have become an interdisciplinary frontier research topic.We summarize herein the recent advance in the development and applications of CPLactive aggregates based on metal-ligand coordination materials(termed as“coordination aggregates”).The materials surveyed are classified as aggregates of smallmolecular metal complexes,which include monocomponent assemblies of Pt(II)complexes and other complexes and binary aggregates of metal complexes,and CPL-active metal-ligand coordination helicates,polymers,and frameworks.The efforts in improving the dissymmetry luminescence factors and quantum yields of these materials and the use of the aggregation strategy in enhancing the performance of isolated molecules are discussed.The recent applications of chiral metal complexes in circularly polarized organic light-emitting diodes(OLEDs)based on solution-or evaporation-processed procedures are surveyed.In addition,the uses of lanthanide complexes in CPL-contrast imaging and as CPL probes are highlighted.The common discussion on the mechanism of aggregation-enhanced CPLs and a perspective on future works of CPL-active coordination aggregates are finally given.