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1.
A series of new photo‐responsive amino acid‐derived azobenzenedicarboxylic acid derivatives (S)‐ 1 a – e were synthesized. Compound (S)‐ 1 a in the trans form exhibited no circular dichroism (CD) signal in DMF under ambient conditions, whereas intense Cotton effects were observed upon UV irradiation, indicating the formation of a chiral supramolecular structure in the cis form. The CD signals disappeared when trifluoroacetic acid (TFA) was added to the solution. The ester counterpart [(S)‐ 1 a′ ] showed no CD signal. Hydrogen bonding between the carboxy groups seemed necessary for constructing the supramolecular structure. The kinetic studies of cis to trans isomerization of (S)‐ 1 a demonstrated that the formation of a chiral supramolecule enhances the stability of the cis‐azobenzene structure. The ESI mass spectrum of stilbenedicarboxylic acid (S)‐ 4 , an analogue of (S)‐ 1 b , confirmed the formation of a dimer. A theoretical CD study revealed that (S)‐ 1 a in the cis form should be present as a cyclic chiral dimer.  相似文献   

2.
Reported here is the first example of a 1,2‐dithienyldicyanoethene‐based visible‐light‐driven chiral fluorescent molecular switch that exhibits reversible trans to cis photoisomerization. The trans form in solution almost completely transforms into the cis form, accompanied by a 10‐fold decrease in its fluorescence intensity within 60 seconds when exposed to green light (520 nm). The reverse isomerization proceeds upon irradiation with blue light (405 nm). When doped into commercially available achiral liquid crystal hosts, this molecular switch efficiently induces luminescent helical superstructures, that is, a cholesteric phase. The intensity of the circularly polarized fluorescence as well as the selective reflection wavelength of the induced cholesteric phases can be reversibly tuned using visible light of two different wavelengths. Optically rewritable photonic devices using cholesteric films containing this molecular switch are described.  相似文献   

3.
Reported here is the first example of a 1,2‐dithienyldicyanoethene‐based visible‐light‐driven chiral fluorescent molecular switch that exhibits reversible trans to cis photoisomerization. The trans form in solution almost completely transforms into the cis form, accompanied by a 10‐fold decrease in its fluorescence intensity within 60 seconds when exposed to green light (520 nm). The reverse isomerization proceeds upon irradiation with blue light (405 nm). When doped into commercially available achiral liquid crystal hosts, this molecular switch efficiently induces luminescent helical superstructures, that is, a cholesteric phase. The intensity of the circularly polarized fluorescence as well as the selective reflection wavelength of the induced cholesteric phases can be reversibly tuned using visible light of two different wavelengths. Optically rewritable photonic devices using cholesteric films containing this molecular switch are described.  相似文献   

4.
A series of optically active P‐chiral oligophosphines (S,R,R,S)‐ 2 , (S,R,S,S,R,S)‐ 3 , (S,R,S,R,R,S,R,S)‐ 4 , and (S,R,S,R,S,R,R,S,R,S,R,S)‐ 5 with four, six, eight, and 12 chiral phosphorus atoms, respectively, were successfully synthesized by a step‐by‐step oxidative‐coupling reaction from (S,S)‐ 1 . The corresponding optically inactive oligophosphines 1′ – 5′ were also prepared. Their properties were characterized by DSC, XRD, and optical‐rotation analyses. While optically active bisphosphine (S,S)‐ 1 and tetraphosphine (S,R,R,S)‐ 2 behaved as small molecules, octaphosphine (S,R,S,R,R,S,R,S)‐ 4 and dodecaphosphine (S,R,S,R,S,R,R,S,R,S,R,S)‐ 5 exhibited the features of a polymer. Furthermore, DSC and XRD analyses showed that hexaphosphine (S,R,S,S,R,S)‐ 3 is an intermediate between a small molecule and a polymer. Comparison of optically active oligophosphines 1 – 5 with the corresponding optically inactive oligophosphines 1′ – 5′ revealed that the optically active phosphines have higher crystallinity than the optically inactive counterparts. It is considered that the properties of oligophosphines depend on the enantiomeric purity as well as the oligomer chain length.  相似文献   

5.
Compounds with stereogenic phosphorus atoms are frequently used as ligands for transition‐metal as well as organocatalysts. A direct catalytic enantioselective method for the synthesis of P ‐chiral compounds from easily accessible diaryl phosphinamides is presented. The use of rhodium(III) complexes equipped with a suitable atropochiral cyclopentadienyl ligand is shown to enable an enantiodetermining C−H activation step. Upon trapping with alkynes, a broad variety of cyclic phosphinamides with a stereogenic phosphorus(V) atom are formed in high yields and enantioselectivities. Moreover, these can be reduced enantiospecifically to P ‐chiral phosphorus(III) compounds.  相似文献   

6.
A new (S)‐binaphthalene‐based polymer ( P ‐ 1 ) was synthesized by the polymerization of 5,5′‐((2,5‐dibutoxy‐1,4‐phenylene)bis(ethyne‐2,1‐diyl))bis(2‐hydroxy‐3‐(piperidin‐1‐ylmethyl) benzaldehyde ( M ‐ 1 ) with (S)‐2,2′‐dimethoxy‐(1,1′‐binaphthalene)‐3,3′‐diamine ( M ‐ 2 ) through the formation of a Schiff base; the corresponding chiral polymer ( P ‐ 2 ) could be obtained by the reduction of polymer P ‐ 1 with NaBH4. Chiral polymer P ‐ 1 exhibited a remarkable “turn‐on” fluorescence‐enhancement response towards (D )‐phenylalaninol and excellent enantioselective recognition behavior with enantiomeric fluorescence difference ratios (ef) as high as 8.99. More importantly, chiral polymer P ‐ 1 displays a bright blue fluorescence color change upon the addition of (D )‐phenylalaninol under a commercially available UV lamp, which can be clearly observed by the naked eye. On the contrary, chiral polymer P ‐ 2 showed weaker enantioselective fluorescence ability towards the enantiomers of phenylalaninol.  相似文献   

7.
Chiral, pH‐responsive hydrogels are constructed by poly(ethylene glycol) diacrylate/α‐cyclodextrin (PEGDA/α‐CD) inclusion complex and L‐N‐acryloyl‐alanine or D‐N‐acryloyl‐alanine (L‐NAA or D‐NAA) by an effective free radical polymerization approach. PEGDA containing two C=C end groups was used simultaneously to introduce α‐CD units in the resulting hydrogels and to serve as a cross‐linking agent, by which forming the designed hydrogels in quantitative yield. Hydrophilic α‐CD moieties acted as pore‐forming agent, while the L(D)‐NAA‐based polymer chains bearing –COOH groups enabled the hydrogels to display remarkable swelling–deswelling behavior in response to pH variation. The chiral NAA monomer‐derived polymer chains rendered the hydrogels with intriguing optical activity, according to circular dichroism spectra. Scanning electron microscopy revealed the uniformly porous microstructures of hydrogels. More remarkably, the L‐NAA‐based hydrogels preferentially adsorbed trans‐4‐hydroxy‐d ‐proline and preferentially released trans‐4‐hydroxy‐l ‐proline, while D‐NAA‐based hydrogels provided opposite results. The hydrogels also demonstrated remarkable enantioselective release ability towards chiral drug ibuprofen. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

8.
The construction of stimuli‐responsive materials by using naturally occurring molecules as building blocks has received increasing attention owing to their bioavailability, biocompatibility, and biodegradability. Herein, a symmetrical azobenzene‐functionalized natural glycyrrhizic acid (trans‐ GAG ) was synthesized and could form stable supramolecular gels in DMSO/H2O and MeOH/H2O. Owing to transcis isomerization, this gel exhibited typical light‐responsive behavior that led to a reversible gel–sol transition accompanied by a variation in morphology and rheology. Additionally, this trans‐ GAG gel displayed a distinct injectable self‐healing property and outstanding biocompatibility. This work provides a simple yet rational strategy to fabricate stimuli‐responsive materials from naturally occurring, eco‐friendly molecules.  相似文献   

9.
Differentiation of β ‐amino acid enantiomers with two chiral centres was investigated by kinetic method with trimeric metal‐bound complexes. Four enantiomeric pairs of β ‐amino acids were studied: cis‐(1R,2S)‐, cis‐(1S,2R)‐, trans‐(1R,2R)‐ and trans‐(1S,2S)‐2‐aminocyclopentanecarboxylic acids (cyclopentane β ‐amino acids), and cis‐(1R,2S)‐, cis‐(1S,2R)‐, trans‐(1R,2R)‐, and trans‐(1S,2S)‐2‐aminocyclohexanecarboxylic acids (cyclohexane β ‐amino acids). The results showed that the choice of metal ion (Cu2+, Ni2+) and chiral reference compound (α‐ and β ‐amino acids) had an effect on the enantioselectivity. Especially, aromaticity of the reference compound was noted to enhance the enantioselectivity. The fixed‐ligand kinetic method, a modification of the kinetic method, was then applied to the same β ‐amino acids, with dipeptides used as fixed ligands. With this method, dipeptide containing an aromatic side chain enhanced the enantioselectivity. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

10.
An aldehyde that is not fluorescent responsive toward a chiral diamine has been converted to a sensitive fluorescence enhancement sensor through incorporation of an additional hydrogen bonding unit to increase the structural rigidity of the reaction product of the aldehyde with the diamine. This new chiral aldehyde is synthesized in one step from the reaction of (S)‐3‐formylBINOL with salicyl chloride. When treated with trans‐1,2‐cyclohexanediamine in ethanol, it shows greatly enhanced fluorescence at λ=410 nm with good enantioselectivity. NMR and mass spectroscopic methods are used to investigate the reaction of the chiral aldehyde with the diamine. This study has revealed a two‐stage reaction mechanism including a fast imine formation and a slow ester cleavage.  相似文献   

11.
Summary: Optically active poly[(R)‐ or (S)‐1,4‐bis(2‐(3′,4′‐ethylenedioxy)thienyl)‐2‐benzoic acid 1‐methylheptyl ester] was prepared by an electrochemical technique and characterized by circular dichroism measurements. It was found that the optical activity and optical rotation of the film could be controlled by adjusting the electronic state of the electrochemical process. Polymer films prepared in the oxidized state exhibit a weak Cotton effect, while the reduced polymer film exhibits the expected mirror‐image bisignate Cotton effect in the region of the ππ* transition of the polymer main chain. These results indicate that the main chain itself is chiral in the film state. This procedure has great potential for the preparation of functional electrochromic devices and the improved preparation of durable electrochromic devices based on the good film‐forming properties of the chiral polymer.

Cyclic voltammogram and CD spectra of the chiral polymer thin film produced here.  相似文献   


12.
Four aggregation‐induced emission (AIE)‐active chiral binaphthyl‐based molecules, (R/S)‐ 1 and (R/S)‐ 2 , were designed and synthesized. Interestingly, all of them can exhibit reversal circularly polarized luminescence (CPL) signals from solution to aggregation, which could be attributed to the different dihedral angle of binaphthyl units from cis‐conformation in pure THF solution to trans‐conformation in THF/water mixtures.  相似文献   

13.
In the title coordination polymer, [Pb(NCS)2(C12H12N2)], the coordination geometry about the PbII atom is a distorted octahedron, composed of two N atoms from bpe ligands [bpe is 1,2‐bis(4‐pyridyl)ethane], two other N atoms from NCS? groups and two neighbouring S atoms through short contacts. The trans‐bpe ligands act as bridges between two PbII centres resulting in the formation of a linear chain. The terminal S atoms of the NCS? ligands make short contacts with the PbII atom of neighbouring chains to form an infinite two‐dimensional polymeric structure.  相似文献   

14.
Chiral cyclic α,α‐disubstituted amino acids, (3S,4S)‐ and (3R,4R)‐1‐amino‐3,4‐(dialkoxy)cyclopentanecarboxylic acids ((S,S)‐ and (R,R)‐Ac5cdOR; R: methyl, methoxymethyl), were synthesized from dimethyl L ‐(+)‐ or D ‐(?)‐tartrate, and their homochiral homoligomers were prepared by solution‐phase methods. The preferred secondary structure of the (S,S)‐Ac5cdOMe hexapeptide was a left‐handed (M) 310 helix, whereas those of the (S,S)‐Ac5cdOMe octa‐ and decapeptides were left‐handed (M) α helices, both in solution and in the crystal state. The octa‐ and decapeptides can be well dissolved in pure water and are more α helical in water than in 2,2,2‐trifluoroethanol solution. The left‐handed (M) helices of the (S,S)‐Ac5cdOMe homochiral homopeptides were exclusively controlled by the side‐chain chiral centers, because the cyclic amino acid (S,S)‐Ac5cdOMe does not have an α‐carbon chiral center but has side‐chain γ‐carbon chiral centers.  相似文献   

15.
The treatment of the recently reported potassium salt (S)‐N,N′‐bis‐(1‐phenylethyl)benzamidinate ((S)‐KPEBA) and its racemic isomer (rac‐KPEBA) with anhydrous lanthanide trichlorides (Ln=Sm, Er, Yb, Lu) afforded mostly chiral complexes. The tris(amidinate) complex [{(S)‐PEBA}3Sm], bis(amidinate) complexes [{Ln(PEBA)2(μ‐Cl)}2] (Ln=Sm, Er, Yb, Lu), and mono(amidinate) compounds [Ln(PEBA)(Cl)2(thf)n] (Ln=Sm, Yb, Lu) were isolated and structurally characterized. As a result of steric effects, the homoleptic 3:1 complexes of the smaller lanthanide atoms Yb and Lu were not accessible. Furthermore, chiral bis(amidinate)–amido complexes [{(S)‐PEBA}2Ln{N(SiMe3)2}] (Ln=Y, Lu) were synthesized by an amine‐elimination reaction and salt metathesis. All of these chiral bis‐ and tris(amidinate) complexes had additional axial chirality and they all crystallized as diastereomerically pure compounds. By using rac‐PEBA as a ligand, an achiral meso arrangement of the ligands was observed. The catalytic activities and enantioselectivities of [{(S)‐PEBA}2Ln{N(SiMe3)2}] (Ln=Y, Lu) were investigated in hydroamination/cyclization reactions. A clear dependence of the rate of reaction and enantioselectivity on the ionic radius was observed, which showed higher reaction rates but poorer enantioselectivities for the yttrium compound.  相似文献   

16.
The catalytic asymmetric aziridination of imines and diazo compounds (AZ reaction) mediated by boroxinate catalysts derived from the VANOL and VAPOL ligands was investigated with chiral imines derived from five different chiral, disubstituted, methyl amines. The strongest matched and mismatched reactions with the two enantiomers of the catalyst were noted with disubstituted methyl amines that had one aromatic and one aliphatic substituent. The synthetic scope for the AZ reaction was examined in detail for α‐methylbenzyl amine for cis‐aziridines from α‐diazo esters and for trans‐aziridines from α‐diazo acetamides. Optically pure aziridines could be routinely obtained in good yields and with high diastereoselectivity and the minor diastereomer (if any) could be easily separated. The matched case for cis‐aziridines involved the (R)‐amine with the (S)‐ligand, but curiously, for trans‐aziridines the matched case involved the (R)‐amine with the (R)‐ligand for imines derived from benzaldehyde and n‐butanal, and the (R)‐amine with the (S)‐ligand for imines derived from the bulkier aliphatic aldehydes pivaldehyde and cyclohexane carboxaldehyde.  相似文献   

17.
Four chiral polymers P-1, P-2, P-3 and P-4 were synthesized by the polymerization of (S)-2,2'-dioctoxy-1,1'- binaphthyl-6,6'-boronic acid (S-M-3) with (S)-6,6'-dibromo-1,1'-binaphthol (S-M-1), (R)-6,6'-dibromo-1,1'- binaphthol (R-M-1), (S)-3,3'-diiodo-1,1'-binaphthol (S-M-2) and (R)-3,3'-diiodo-1,1'-binaphthol (R-M-2) under Pd-catalyzed Suzuki reaction, respectively. All four polymers can show good solubility in some common solvents due to the nonplanarity of the polymers in the main chain backbone and flexible alkyl groups in the side chain. The analysis results indicate that specific rotation and circular dichroism (CD) spectral signals of the alternative S-S chiral polymers P-1 and P-3 are larger than those of S-R chiral polymers P-2 and P-4, but their UV-Vis and fluorescence spectra are almost similar. The results of asymmetric enantioselectivity of four polymers for diethylzinc addition to benzaldehyde indicate that catalytically active center is (R) or (S)-1, 1'-binaphthol moieties.  相似文献   

18.
Reaction of biotin {C10H16N2O3S, HL; systematic name: 5‐[(3aS,4S,6aR)‐2‐oxohexahydro‐1H‐thieno[3,4‐d]imidazol‐4‐yl]pentanoic acid} with silver acetate and a few drops of aqueous ammonia leads to the deprotonation of the carboxylic acid group and the formation of a neutral chiral two‐dimensional polymer network, poly[[{μ3‐5‐[(3aS,4S,6aR)‐2‐oxohexahydro‐1H‐thieno[3,4‐d]imidazol‐4‐yl]pentanoato}silver(I)] trihydrate], {[Ag(C10H15N2O3S)]·3H2O}n or {[Ag(L)]·3H2O}n, (I). Here, the AgI cations are pentacoordinate, coordinated by four biotin anions via two S atoms and a ureido O atom, and by two carboxylate O atoms of the same molecule. The reaction of biotin with silver salts of potentially coordinating anions, viz. nitrate and perchlorate, leads to the formation of the chiral one‐dimensional coordination polymers catena‐poly[[bis[nitratosilver(I)]‐bis{μ3‐5‐[(3aS,4S,6aR)‐2‐oxohexahydro‐1H‐thieno[3,4‐d]imidazol‐4‐yl]pentanoato}] monohydrate], {[Ag2(NO3)2(C10H16N2O3S)2]·H2O}n or {[Ag2(NO3)2(HL)2]·H2O}n, (II), and catena‐poly[bis[perchloratosilver(I)]‐bis{μ3‐5‐[(3aS,4S,6aR)‐2‐oxohexahydro‐1H‐thieno[3,4‐d]imidazol‐4‐yl]pentanoato}], [Ag2(ClO4)2(C10H16N2O3S)2]n or [Ag2(ClO4)2(HL)2]n, (III), respectively. In (II), the AgI cations are again pentacoordinated by three biotin molecules via two S atoms and a ureido O atom, and by two O atoms of a nitrate anion. In (I), (II) and (III), the AgI cations are bridged by an S atom and are coordinated by the ureido O atom and the O atoms of the anions. The reaction of biotin with silver salts of noncoordinating anions, viz. hexafluoridophosphate (PF6) and hexafluoridoantimonate (SbF6), gave the chiral double‐stranded helical structures catena‐poly[[silver(I)‐bis{μ2‐5‐[(3aS,4S,6aR)‐2‐oxohexahydro‐1H‐thieno[3,4‐d]imidazol‐4‐yl]pentanoato}] hexafluoridophosphate], {[Ag(C10H16N2O3S)2](PF6)}n or {[Ag(HL)2](PF6)}n, (IV), and catena‐poly[[[{5‐[(3aS,4S,6aR)‐2‐oxohexahydro‐1H‐thieno[3,4‐d]imidazol‐4‐yl]pentanoato}silver(I)]‐μ2‐{5‐[(3aS,4S,6aR)‐2‐oxohexahydro‐1H‐thieno[3,4‐d]imidazol‐4‐yl]pentanoato}] hexafluoridoantimonate], {[Ag(C10H16N2O3S)2](SbF6)}n or {[Ag(HL)2](SbF6)}n, (V), respectively. In (IV), the AgI cations have a tetrahedral coordination environment, coordinated by four biotin molecules via two S atoms, and by two carboxy O atoms of two different molecules. In (V), however, the AgI cations have a trigonal coordination environment, coordinated by three biotin molecules via two S atoms and one carboxy O atom. In (IV) and (V), neither the ureido O atom nor the F atoms of the anion are involved in coordination. Hence, the coordination environment of the AgI cations varies from AgS2O trigonal to AgS2O2 tetrahedral to AgS2O3 square‐pyramidal. The conformation of the valeric acid side chain varies from extended to twisted and this, together with the various anions present, has an influence on the solid‐state structures of the resulting compounds. The various O—H...O and N—H...O hydrogen bonds present result in the formation of chiral two‐ and three‐dimensional networks, which are further stabilized by C—H...X (X = O, F, S) interactions, and by N—H...F interactions for (IV) and (V). Biotin itself has a twisted valeric acid side chain which is involved in an intramolecular C—H...S hydrogen bond. The tetrahydrothiophene ring has an envelope conformation with the S atom as the flap. It is displaced from the mean plane of the four C atoms (plane B) by 0.8789 (6) Å, towards the ureido ring (plane A). Planes A and B are inclined to one another by 58.89 (14)°. In the crystal, molecules are linked via O—H...O and N—H...O hydrogen bonds, enclosing R22(8) loops, forming zigzag chains propagating along [001]. These chains are linked via N—H...O hydrogen bonds, and C—H...S and C—H...O interactions forming a three‐dimensional network. The absolute configurations of biotin and complexes (I), (II), (IV) and (V) were confirmed crystallographically by resonant scattering.  相似文献   

19.
Starting with achiral phosphines and (1S,2S)‐2‐(methylamino)‐1‐phenylpropan‐1‐ol ((+)‐pseudoephedrine) or (1R,2S)‐2‐(methylamino)‐1‐phenylpropan‐1‐ol ((−)‐ephedrine), as chiral auxiliaries, diastereoisomerically pure oxazaphospholes were prepared (Scheme 1). The configuration at the P‐atom is controlled by the configuration at the Ph‐substituted C(1) of (+)‐pseudoephedrine or (−)‐ephedrine, respectively. This was confirmed by X‐ray crystal‐structure analyses of two intermediate compounds in the synthesis route to the chiral triarylborane‐phosphane adducts.  相似文献   

20.
A six‐membered ring lactam derivative was introduced in a parallel manner into uranyl–salophens with R/S configuration (R‐/S‐AUSRLs), which were used as receptors to coordinate with guests of cis?/trans‐methylcyclohexylamines (cis?/trans‐MCHAs). Using density functional theory calculations at the B3LYP/6‐311G** level and RECP, an insight into the coordination complexes of the R‐/S‐AUSRLs with cis?/trans‐MCHAs was obtained. The results showed that the U atoms of receptors could coordinate with the N atoms of four kinds of cis?/trans‐1,2 or ? 1,4 guests, but the two kinds of cis?/trans‐1,3 guests could not be converged by the same method in the process of structural optimization due to steric hindrance, and thus the cis?/trans‐1,3 guests could not be coordinated with the R‐/S‐AUSRLs. The mode of coordination of the R‐/S‐AUSRLs with the guests displayed a significant difference. And the change of R‐AUSRL coordination ability to the cis?/trans‐MCHAs was very large, but that of S‐AUSRL was small. Overall, the stability of the R‐series coordination complexes was higher than that of the corresponding S‐series coordination complexes, and the R‐AUSRL receptor had better coordination selectivity and higher molecular recognition to the cis?/trans‐MCHA guests than the S‐AUSRL receptor. However, the coordination ability of S‐AUSRL with the cis?/trans‐MCHAs was stronger than that of R‐AUSRL. It was expected that these results could provide insightful information and theoretical guidance for understanding the molecular recognition of R‐/S‐AUSRLs for cis?/trans‐type cyclohexylamine derivatives.  相似文献   

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