Chiral Pendant Groups Research Articles

Effect of amino acid pendant groups on the helical configuration of polyphenylacetylene

In this study, several polyphenylacetylenes (PPAs) derivatives containing amino acid pendant groups were synthesized using a rhodium system catalyst (Rh(nbd)BPh4). The synthesized derivatives of PPAs included single chiral PPA with a single chiral center in the pendant groups and double chiral PPA' with two chiral centers in the pendant groups. The PPA and PPA' showed strong circular dichroism (CD) signals in the main chain absorption region of the UV-vis spectrum, while the monomer showed no CD signals. Furthermore, the PPA and PPA' with different chiral pendant groups showed different Cotton effects in the CD spectra. The results showed that these polymers existed in helical conformation, and the chiral center of the pendant groups affected the polymerization and helical structure of PPAs.

Chiral information harvesting in helical poly(acetylene) derivatives using oligo(p-phenyleneethynylene)s as spacers.

A chiral harvesting transmission mechanism is described in poly(acetylene)s bearing oligo(p-phenyleneethynylene)s (OPEs) used as rigid achiral spacers and derivatized with chiral pendant groups. The chiral moieties induce a positive or negative tilting degree in the stacking of OPE units along the polymer structure, which is further harvested by the polyene backbone adopting either a P or M helix.

Chiral-to-Chiral Communication in Polymers: A Unique Approach To Control Both Helical Sense and Chirality at the Periphery.

A novel approach to the classical Sergeants and Soldiers effect, using chiral Sergeants and chiral Soldiers, allows control over both helical and external chirality in helical polymers. In the systems reported here, it is possible to induce the same helical sense ( M or P) from either of the two enantiomers of a chiral pendant group ["chiral Soldier", major component; i.e., ( R)- or ( S)-1] when it faces a single enantiomer of an appropriate "chiral Sergeant" [minor component; i.e., ( S)-2]. For instance, the copolymer series poly[( R)-1 r- co-( S)-2(1- r)], poly[( S)-1 r- co-( S)-2(1- r)], and poly[( rac)-1 r- co-( S)-2(1- r)] adopt the same P helix even though the major component shows the opposite absolute configuration. This chiral-to-chiral communication effect is transmitted by the stabilization of different conformations in each enantiomeric form of the Soldier. As a result, this groundbreaking approximation to the Sergeants and Soldiers effect allows the preparation of a single-handed helix-which depends only on the Sergeant's configuration-with different chiralities on the helix periphery. Thus, a P helix can be decorated with the R isomer, S isomer, or even a racemic mixture of the chiral Soldier. A change in the absolute configuration of the Sergeant affords the opposite M helix, which can also be decorated with the R isomer, S isomer, or racemic mixture of the chiral Soldier.

Highly Emissive, Optically Active Poly(diphenylacetylene) Having a Bulky Chiral Side Group.

A highly emissive, optically active poly(diphenylacetylene) derivative, NpSi*-PDPA, was synthesized by introducing a bulky chiral pendant group into the polymer chain. NpSi*-PDPA exists in a glassy state having a highly disordered and amorphous structure. Hence, the fractional free volume is quite high, i.e., 0.29. NpSi*-PDPA emits a green light in solution and a yellow light in film. This polymer is quite emissive, as the photoluminescence (PL) quantum yield is 56.1% in solution and 6.2% in film, and the PL lifetime is relatively long, 1.71 ns in solution and 1.05 ns in film. NpSi*-PDPA shows the strongest circular dichroism (CD) signal at 384 nm, with a magnitude of circular polarization (gCD) of 0.90 × 10-3 and an optical rotation of 110° (4.30 × 10-3 g mL-1, in CHCl3). The CD intensity is significantly increased by annealing at 80 °C, reaching an equilibrium at gCD of 7.10 × 10-3 after 72 h.

Synthesis and properties of novel chiral side-chain liquid crystalline polysiloxanes containing different chiral pendant groups

Two novel chiral liquid crystalline monomers, and a series of their corresponding chiral side-chain polymers (P1–P7) based on poly(methylhydrogeno)siloxane have been prepared. The chemical structures and liquid crystalline properties of the synthesized monomers and polymers have been investigated using various experimental techniques. Thermal analysis shows that all polymers have wide mesophase temperature ranges with a high thermal stability. With the increase of M2 molar ratio in the polymer systems, the isotropic phase transition and glass transition temperatures of all polymers increase, and the temperature ranges of N* phase and mesophase become broad. The effect of cholesteryl mesogens on mesophase behaviors, optical properties, and molecular arrangement of LC polysiloxanes and their advanced applications have also been discussed. For homopolymer P1, it shows a single SA phase. With increasing the content of M2 in the polymer systems, P2 and P3 reveal a SA–N* phase transition when they are heated, and P4–P7 reveal a N* phase. For N* phase polymers P4–P7, the reflection wavelengths exhibit blue shift, suggesting that the pitch decreases with a decrease in the amount of the smectic domains induced by the M1. The reflection wavelengths of P4–P7 are almost across the entire visible region when they are heated, which offer stremendous potential for various optical applications. For P2 and P3, the reflection wavelengths show a very steep change around the temperature of the SA–N* phase transition, which can be used as thermally sensitive liquid crystal devices requiring fast response, such as sensors, and thermally induced tuning.

Synthesis and Chiral Recognition of Nickel(II) Macrocyclic Complex with (R)‐Naphthylethyleneamine Pendant Groups and its Self‐Assembled Framework

A novel nickel(II) hexaaza macrocyclic complex, [Ni(L(R,R))](ClO(4))(2) (1), containing chiral pendant groups was synthesized by an efficient one-pot template condensation and characterized (L(R,R) ═1,8-di((R)-α-methylnaphthyl)-1,3,6,8,10,13-hexaazacyclotetradecane). The crystal structure of compound 1 was determined by single-crystal X-ray analysis. The complex was found to have a square-planar coordination environment for the nickel(II) ion. Open framework [Ni(L(R,R))](3) [C(6)H(3)(COO)(3)](2) (2) was constructed from the self-assembly of compound 1 with deprotonated 1,3,5-benzenetricarboxylic acid, BTC(3-). Chiral discrimination of rac-1,1'-bi-2-naphthol and rac-2,2,2-trifluoro-1-(9-anthryl)ethanol was performed to determine the chiral recognition ability of the chiral complex (1) and its self-assembled framework (2). Binaphthol showed a good chiral discrimination on the framework (2). The optimum experimental conditions for the chiral discrimination were examined by changing the weight ratio between the macrocyclic complex 1 or self-assembled framework 2 and racemates. The detailed synthetic procedures, spectroscopic data including single-crystal X-ray analysis, and the results of the chiral recognition for the compounds are described.

Synthesis of stable and soluble one-handed helical poly(substituted acetylene)s without chiral pendant groups via polymer reaction in membrane state

A soluble and stable one-handed helical conjugated polymer without the coexistence of any other chiral moieties was successfully synthesized by asymmetric-induced polymerization of a chiral monomer having two hydroxyl groups followed by desubstitution of the chiral groups in a solid membrane state. The reason for the success was the polymer reaction was carried out in the membrane state. This is an alternative method to obtain such a unique chiral polymer which was obtained only by the helix-sense-selective polymerization (HSSP) we reported before. In addition the efficiency of the chiral induction was higher than that of the HSSP. It is interesting that the “Membrane state” acted like as if a protecting group.

Chiral conducting surfaces based on the electropolymerization of 3,4-ethylenedioxythiophene

The synthesis and electrochemical characterization of d- and l-proline functionalized monothiophenes are reported. Both monomers 2L and 2D showed anodic peak potentials of 1.86 V vs. Fc +/Fc and their electropolymerization affords polymers that exhibit poor stability on platinum electrodes. However, the electrochemical copolymerization using cyclic voltammetry of 2L or 2D in the presence of EDOT gives polymeric films at the surface of the electrode with specific chirality. The E 1/2 of the copolymers was found to be 0.38 V vs. Fc +/Fc. The copolymers display excellent electrochemical stability and adhesion properties on the surface of platinum and ITO electrodes. Moreover, the films also undergo a reversible color change between their doped (blue-green) and undoped (blue-brown) states. Incorporation of the chiral pendant group was confirmed through the appearance of characteristic C O stretching absorptions in the IR spectra of the copolymers.

Synthesis and characterization of novel liquid crystalline polymers containing cholesteryl pendant groups

In order to investigate the chiral effect of cholesteryl pendant groups on the induction of the cholesteric phase, a new cholesteryl-containing liquid crystalline monomer was synthesized and copolymerized with an achiral comonomer in various molar ratios. The layer-like arrangement of the smectic mesophase with different monomeric compositions of copolymers was investigated using an X-ray diffraction analysis. The cholesteric liquid phase was induced by the chiral segments; the dependence of the reciprocal central reflection wavelength on the mole fraction of the chiral monomer for copolymers was investigated. This paper demonstrates the effect of chiral pendant groups on the induction of the cholesteric phase and layered molecular arrangement of side-chain liquid crystalline polymers.

Synthesis and characterization of macrocyclic nickel(II) complexes with α-methylbenzyl groups as chiral pendants

Novel nickel(II) hexaaza macrocyclic complexes, [Ni(LR,R)](ClO4)2 (1) and [Ni(LS,S)](ClO4)2 (2), containing chiral pendant groups have been synthesized by an efficient one-pot template condensation and characterized (LR,R/S,S=1,8-di((R/S)-α-methylbenzyl)-1,3,6,8,10,13-hexaazacyclotetradecane). The crystal structures of 1 and 2 were determined by single-crystal X-ray analysis. Each complex has a square-planar coordination environment for the nickel(II) ion, and is either an R or an S enantiomorph depending on the pendant groups. The circular dichroism spectrum of 1 showed a negative, positive and negative peak at 345, 440, and 492nm, respectively, and that of 2 exhibited an enantiomeric pattern.

Synthesis, Helicity, and Chromism of Optically Active Poly(phenylacetylene)s Carrying Different Amino Acid Moieties and Pendant Terminal Groups

Functional phenylacetylene derivatives containing l-alanine and l-leucine moieties with chiral menthyl and achiral n-octyl terminal groups {HC[triple bond]C-C6H4-p-CONHCH(R)CO2R': R = CH3, R'= (-)-(1R,2S,5R)-menthyl [1(-)]; R = CH2CH(CH2)3, R' = (-)-(1R,2S,5R)-menthyl [2(-)]; R'= CH2CH(CH2)3, R' = (+)-(1S,2R,5S)-menthyl [2(+)]; R'= CH2CH(CH2)3, R' = (CH2)7CH3 (2o)} are synthesized. Polymerizations of the acetylene monomers are effected by organorhodium catalysts, giving corresponding polymers P1(-), P2(-), P2(+), and P2o of high molecular weights (Mw up to 1.2 x 10(6)) in high yields (up to 89%). The polymers are thermally stable (Td >or= 300 degrees C) and soluble in common organic solvents. The polymer structures are characterized by IR, NMR, UV, and CD spectroscopies. Intense CD signals are observed in the visible spectral region, indicating that the polymer chains are taking a helical conformation with an excess of preferred handedness. The backbone conjugation and chain helicity of the polymers can be tuned by changing their molecular structures [(a)chiral pendant groups] and by applying external stimuli (solvent and pH). Addition of trifluoroacetic acid to the polymer solutions decreases their molar ellipticities and enhances their backbone conjugations, inducing a halochromism with a continuous and reversible color change (yellow <==> red).

Synthesis of calix[4]arene derivatives bearing chiral pendant groups as ligands for enantioselective catalysis

New chiral calix[4]arene derivatives have been synthesized by appending at the lower rim amino acid ( l-tyrosine, l-aspartic acid, l-valine, and l-tryptophan) or pinene-like (myrtenyl and homomyrtenyl) units or by distal intrabridging with a binaphthyl amine scaffold. The application of these derivatives in enantioselective catalysis was studied by testing the catalytic activities of the corresponding Ti(IV)/calixarene complexes, prepared in situ, in the asymmetric aldol reaction of Chan’s silyloxydiene with p-nitrobenzaldehyde.

Poly(phenyleneethynylene) polymers bearing glucose substituents as promising active layers in enantioselective chemiresistors

Poly(phenyleneethynylene) (PPE) conjugated polymers bearing glucose units are used as enantioselective active layers in vapor-sensing devices. As a novel approach, a conjugated polymer bearing chiral pendant groups is used to detect different enantiomers, natural and synthetic menthol molecules in the present case. The surface analytical characterization of the organic layer reveals a compact and smooth morphology. By means of a quartz crystal microbalance revealing system, the polymer bearing glucose chiral sites is demonstrated to interact more favorably with the natural menthol. Promising perspectives are seen for the use of such polymers in chiral, chemically sensitive resistors or even transistors.

Electro-optic studies on novel chiral liquid crystalline polysiloxanes with the N * phase

The electro-optical response of two novel side chain liquid crystalline polysiloxane copolymers containing chiral pendant groups was investigated. It was found that both copolymers possessed N* phase with a long pitch and therefore the origin of the electro-optical response detected in this phase was considered to be the electroclinic effect.

Cooperative chiral order in copolymers of chiral and achiral units

Polyisocyanates can be synthesized with chiral and achiral pendant groups distributed randomly along the chains. The overall chiral order, measured by optical activity, is strongly cooperative and depends sensitively on the concentration of chiral pendant groups. To explain this cooperative chiral order theoretically, we map the random copolymer onto the one-dimensional random-field Ising model. We show that the optical activity as a function of composition is well-described by the predictions of this theory.

The selective extraction and transport of amino acids by calix[4]arene-derived esters

New calix[4]arene analogs having chiral pendant groups efficiently extracted Phe, Phg, and Trp esters as well as their Z-carboxylates. These receptors also recognized the chirality of the L-amino acids in transport experiments.

Main-chain cholesteric liquid crystalline polyesters with chiral pendant groups. 1. Model compounds and polyesters containing a chiral substituted hydroquinone

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMain-chain cholesteric liquid crystalline polyesters with chiral pendant groups. 1. Model compounds and polyesters containing a chiral substituted hydroquinoneKoichi Fujishiro and Robert W. LenzCite this: Macromolecules 1992, 25, 1, 81–87Publication Date (Print):January 1, 1992Publication History Published online1 May 2002Published inissue 1 January 1992https://doi.org/10.1021/ma00027a014RIGHTS & PERMISSIONSArticle Views83Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-Alerts Get e-Alerts

Main-chain cholesteric liquid crystalline polyesters with chiral pendant groups. 2. Cholesteric copolyesters containing chiral and achiral substituted hydroquinones

Copolyesters based on 2-[(S)-(+)-methyl-1-butoxy]hydroquinone as the chiral monomer with several nonchiral hydroquinones were prepared. Copolymerization was effective in forming an identifiable cholesteric phase with a wide mesophase temperature range which was influenced to some extent by the spacer length. The results suggest that formation of the cholesteric phase in these polymers was influenced by a balance between the helical twisting power of the chiral substituent and the mobility of the main chain.

New thermotropic chiral nematic copolymers using (1S,2S,3S,5R)-(+)- and (1R,2R,3R,5S)-(-)-isopinocampheol as building blocks

Thermotropic chiral nematic side-chain copolymers were synthesized and characterized by using (1S,2S,3S,5R)-(+)- and (1R,2R,3R,5S)-([minus])-isopinocampheol as the chiral building blocks. The helical twisting power was found to correlate with the volume swept out by the chiral pendant group via rotation for a given nematogenic monomer. However, the enhanced mesomorphic order introduced in both the nematogenic and chiral monomers as a result of an increased extent of conjugation or a shortened spacer length was found to reduce the helical twisting power of the resultant copolymer. Hence, both factors have to be taken into account as the helical twisting power of a copolymer system is to be optimized for a specific application. The present work also generalized the previous observation that the inversion of chirality of the pendant group results in helical sense reversal, although the role of the absolute configuration of the chiral moiety is not yet clearly understood.

Developments in polysiloxane stationary phases in gas chromatography

Summary Although the requirements of stationary phases have continued to become more stringent with the development of instrumental techniques the polysiloxanes have remained as the major group of stationary phases. While the early industrial polysiloxane products have long been replaced by refined specially products, development has continued with the preparation of polysiloxanes specifically for gas chromatography and particularly capillary gas chromatography. The efficiency of polar capillary columns has been low but recent advances with immobilized phases have been most promising. The acknowledged thermal stability of the polysiloxane backbone has been employed in several ways. Such as with chiral pendant groups to facilitate the separation of optically active materials and with mesogenic groups to provide phases with superior properties to the low-molecular-weight liquid-crystal materials. Further modification of the polysiloxanes has been achieved by the inclusion of other metallic atoms. The most important development in recent years is the introduction of bonded or immobilized phases. Extensive studies have allowed the production of efficient polar capillary columns which are now commercially available.