We have found that the discotic nematic liquid crystal, hexakis(4-nonylphenylethynyl)benzene (HNEB), doped with the racemic chromium complex Cr(Ocacac)3, shows a novel straight-needle texture with hexagonal columnar alignments, changing to a curved-needle texture under irradiation of circularly polarized light (CPL). This novel phenomenon is specific to the mixture of HNEB and Cr(Ocacac)3. The formation of curved needles means that chiroselective photoinversion of racemic Cr(Ocacac)3 by CPL irradiation induces a needle direction change in a discotic liquid crystal. The change in chirality of Cr(Ocacac)3 in HNEB induced by CPL irradiation, and the resulting nano-segregation of its enantiomers during cooling from the isotropic to mesophase of HNEB, are considered to influence changes in the alignment of columns and/or small domains of column aggregates in the discotic liquid crystal. 相似文献
4-Ferrocenylazophenol (FAP) and 8-(4-ferrocenylazophenoxy)octanyl-1-bromide (FAOB) have been synthesized and their protonation and photochemical behavior have been investigated. FAP showed reversible protonation and deprotonation behavior in the presence of trifluoroacetic acid and potassium tert-butylate, respectively. FAP and FAOB exhibit high photoreactivity, which was induced through excitation of not only the pi-pi* band by UV light but also the d-pi* band by green light. The photoreaction of FAP and FAOB in ethanol or acetonitrile with a trace amount of water afforded phenylhydrazonocyclopentadiene (PHP) derivatives, indicating that hydrolysis of the photoexcited species occurs. 相似文献
A flow-injection analysis (FIA) for the determination of dopamine has been developed. The method is based on the inhibition effect of dopamine on the iron(II)-induced chemiluminescence (CL) of 10,10'-dimethyl-9,9'-biacridinium dinitrate (lucigenin). The presence of a non-ionic surfactant, polyoxyethylene (23) lauryl ether (Brij 35), caused an increase in the inhibition effect. The present method allows the determination of dopamine over the range 1x10(-8)-2x10(-7) mol dm(-3). The relative standard deviation was 0.7% for eight determinations of 6x10(-8) mol dm(-3) dopamine. The detection limit (S/N=3) was 2x10(-9) mol dm(-3) with the sampling rate of 40 samples h(-1). The effect of other catecholamines and compounds of similar structure on the lucigenin CL reaction was studied: quinone, hydroquinone, norepinephrine, pyrocatechol and l-dopa suppressed the CL intensity. 相似文献
A short-step synthesis of , the right-hand half of antibiotic saframycin (), is described. The key steps of this synthesis are the acid catalyzed intramolecular double cyclization of and the oxidative demethylation of to the quinone (). 相似文献
A photochemically tunable photonic crystal was prepared by infiltration of the polymer liquid crystal (LC) having azo-chromophores in a SiO2 inverse opal structure. The SiO2 inverse opal film infiltrated with the polymer LC reflected a light corresponding to the periodicity as well as the refractive indices of the inverse opal structure. Linearly polarized light irradiation caused the shift of the reflection band to longer wavelength more than 15 nm. This is caused by the formation of uniaxially anisotropic molecular orientation of the polymer LC. The switched state was stable under interior light, and reversible switching of the reflection band can be achieved by the linearly and circularly polarized light irradiation. This photoswitching property will be suitable not only for various optical materials, but also for introduction of defects in the photonic crystals. 相似文献
Some classes of organometallic catalysts what induce stereospecific polymerization of methacrylonitrile have been found. They include organolithium aluminum compounds of the type LiAlR4, Li[R3AlOAlR2], and Li[R3AlN(R)AlR2], organosodium aluminum compounds of the type NaAlR4, organolithium zinc compounds of the type LiZnR3 and Li2ZnR4, organomagnesium aluminum compounds of the type RMg[AlR4] and Mg[AlR4]2, and organomagnesium compounds containing an Mg? N bond, such as and their related compounds. One of the features of the polymerization with these catalysts was that the crystalline polymers were formed at moderately high temperatures. Total conversion, solubility index, and molecular weight of the polymer increased with increasing polymerization temperature, as observed in the case of polymerization with diethylmagnesium catalyst. Catalysts with an Mg? N bond were found to be highly effective for the stereospecific polymerization. The acetone-insoluble fractions of the polymers gave x-ray diagrams identical to the crystalline polymer produced with diethylmagnesium. This indicates that the acetone-insoluble crystalline polymers produced with these catalysts have an isotactic structure. The viscosity–molecular weight relationship for crystalline polymer was conveniently determined in Cl2CHCOOH at 30°C.; [η] = 2.27 × 10?4M0.754. 相似文献
To investigate the chemical conformations and functions of the -Phe-Phe-Val- or -Phe-Phe- sequences contained in the Alzheimer's disease related beta-amyloid peptide, a series of mini parallel double-stranded peptides conjugated with two peptide residues to one spacer were designed and prepared. The structure of the compounds was elucidated by circular dichroism (CD) spectrum and NMR two dimensional (2D) nuclear Overhauser enhancement and exchange spectroscopy (NOESY) measurments. The structure of 1,2-ethano-bis(L-Phe-L-Phe-L-Leu), 1,12-dodecano-bis(L-Phe-L-Phe-L-Leu), 1,12-dodecano-bis(L-Phe-L-Phe-L-Val), and 1,12-dodecano (D-Phe-D-Phe-D-Leu) conjugated with L-Leu and L-Val residues show a beta-turn-like nucleation. The dihedral angles (theta = +75 degrees, omega = +180 degrees, phi = +90 degrees, phi = -87 degrees, psi = +180 degrees) obtained from experimental coupling constant (J) data, etc. support that 1,12-dodecano-bis(L-Phe-L-Phe) adopts beta-turn mimic nucleation. The 1,12-dodecano- bis(L-Leu-L-Leu-L-Phe), 1,12-dodecano-bis(L-lle-L-Phe-L-Leu), and 1,12-dodecano-bis(L-Phe-L-Val-L-Leu), etc. adopt most probably a random structure by CD studies. It was found by titration spectrum that an inclusion complex of 1:1 ratio (association constant; azobenzene (guest, Ka=1.0 x 10(4)M-1) is formed between 1,12-dodecano-bis(L.-Phe-L-Phe-L-Leu) and [L0]=1.758 x 10(-5)M-1). Moreover, the stability of the complexes was increased in order of 1,12-dodecano-bis(L-Phe-L-Phe-L-Leu) x azobenzene> 1,12-dodecano-bis(L-Phe-L-Phe-L-Val) x azobenzene> 1,12-dodecano-bis(L-Phe-L-Val-L-Leu) azobenzene. The data show that X-Phe-L-Phe-L-spacer(S)-L-Phe-L-Phe-X (X=amino acids; S = 1,2-ethano- and 1,12-dodecano-) plays an important role as a binding site of the artificial receptor. The hydrophobic interaction of the four Phes in the two strands is a very interesting issue in the physiological action of proteins as well as the conformation of the backbone of X-L-Phe-L-Phe-spacer(S)-iL-Phe-l.-Phe-X. 相似文献
The reactions of 3-acetyl-4-ethoxycarbonyl- or 3,4-diethoxycarbonylpyrrolo[1,2-a]pyrimidine derivatives 7a,b , which were prepared by condensation of the 2-aminopyrrole ( 4 ) with ethyl 3-ethoxymethylene-2,4-dioxovalerate ( 5a ) or ethyl ethoxymethyleneoxaloacetate ( 5b ), with diazomethane are described. Thus, reaction of 7a , with diazomethane gave ethyl 2a-acetyl-7-cyano-2a,3a-dihydro-5,6-dimethyl-3H -cyclopropa[e]pyrrolo[1,2-a]pyrimidine-3a-carboxylate ( 11 ) in 74% yield, which was readily transformed into the 1-pyrrol-2-yl-pyrrole ( 18 ) by treatment with potassium hydroxide. On the other hand, reaction of 7b with diazomethane afforded three products whose structures were assigned as diethyl 7-cyano-2a,3a-dihydro-5,6-dimethyl-3H-cyclopropa[e]pyrrolo[1,2-a]pyrimidine-2a,3a-carboxylate ( 20 ), 6-cyano-7,8-dimethyl-3a,3b,5,9a-tetrahydro-4H -aziridino[c]-1H or 3H-pyrazolo[3,4-e]pyrrolo[1,2-a]pyrimidine-3a,9a-dicarboxylates ( 21,22 ). Ring Transformation of 20 to 25 was not observed. 相似文献
New high temperature aromatic polybenzoxazinones of high molecular weight have been prepared by the cyclopolycondensation of 4,4′-diaminobiphenyl-3,3′-dicarboxylic acid (I) with aromatic dicarboxylic acid halides (II). The low temperature solution polymerization techniques afforded poly(amic acid) (III) of high molecular weight in the first step. An open-chain precursor subsequently underwent thermal cyclodehydration along the polymer chain at 200–350°C. in the second step, to give in quantitative yield a fully aromatic polybenzoxazinone (IV) of outstanding heat stability both in nitrogen and in air. The poly(amic acid) is soluble in N-methyl-2-pyrrolidone, and tough, transparent films can be cast from solution. Insoluble aromatic polybenzoxazinone films which possess excellent oxidative and thermal stability were obtained by the heat treatment of the polyamic acid. A detailed account of polymerization conditions in the low temperature solution polymerization of polybenzoxazinones is given, and the reaction mechanisms of cyclopolycondensation of poly(amic acids) and the formation of polybenzoxazinones are discussed. 相似文献
Three new unstable metabolites, (6E,10Z)-2′-O-methylmyxalamide D (1), 2′-O-methylmyxalamide D (2) and (6E)-2′-O-methylmyxalamide D (3) were isolated from the myxobacterium Cystobacter fuscus. The planar structures were elucidated by spectroscopic analyses to be geometrical isomers of a polyene amide related to a myxobacterial metabolite, myxalamide D (4). Their absolute stereochemistry was determined by synthesis of degradation products. Antifungal activities of 1-3 as well as their acetates were evaluated against the phythopathogenic fungus Phythopthora capsici. 相似文献