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Chiral Conformation (chiral + conformation)
Selected AbstractsMethacrylic Polymers Containing Optically Active Side-Chain Carbazole: Synthesis, Characterization and Photoconductive PropertiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2008Luigi Angiolini Abstract Two novel optically active polymethacrylates bearing in the side chain a cyclic chiral group of one prevailing absolute configuration linked to the carbazole chromophore, deriving from the related monomers (S)-(,)-3-methacryloyloxy- N -[3-(9-ethylcarbazolyl)]pyrrolidine [(S)-(,)-MECP] and (S)-(+)-2-methacryloyloxy- N -[3-(9-ethylcarbazolyl)]succinimide [(S)-(+)-MECSI], have been prepared and characterized with the aim to obtain materials suitable to photoconductive applications. Poly[(S)-(,)-MECP] and poly[(S)-(+)-MECSI] exhibit remarkable thermal stability, with glass transition temperature around 200,°C and decomposition temperatures in the range 330,350,°C. Spectroscopic, thermal and chiroptical characterizations indicate the occurrence of dipolar interactions among the side chain moieties and the presence of chiral conformation at least for chain segments of the macromolecules. The photoconductive properties are discussed in terms of extent of conjugation in the side chain based on the electron-acceptor or electron-donator properties of the optically active ring linked to the carbazole group. [source] Circular Dichroism of the Photoreceptor Pigment OxyblepharisminPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2005Osvaldo Pieroni ABSTRACT Circular dichroism (CD) was used to study the structure of oxyblepharismin (OxyBP), the photoreceptor chromophore for the photophobic response of the blue form of Blepharisma japonicum. Both the chromophore associated to its native protein and the free chromophore in ethanol solution were investigated. CD spectra in the far-UV range indicate that OxyBP induces a slight increase in the ,-helix content of the protein matrix. CD spectra in the near-UV and visible region of the spectrum show that OxyBP adopts a chiral conformation with a preferential geometry not only when associated to its protein matrix, but also when isolated and dissolved in ethanol. This experimental result is related to the existence of a high-energy interconversion barrier between two enantiomeric structures of the molecule and discussed on the basis of an asymmetric biosynthesis of its precursor, blepharismin. [source] 4-Oxocyclohexanecarboxylic acid: hydrogen bonding in the monohydrate of a ,-keto acidACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2004Alan Barcon The title monohydrate, C7H10O3·H2O, aggregates as a complex hydrogen-bonding network, in which the water molecule accepts a hydrogen bond from the carboxyl group of one molecule and donates hydrogen bonds to ketone and carboxyl Czdbnd;O functions in two additional molecules, yielding a sheet-like structure of parallel ribbons. The keto acid adopts a chiral conformation through rotation of the carboxyl group by 62.50,(15)° relative to the plane defined by its point of attachment and the ketone C and O atoms. Two C,H,O close contacts exist in the structure. [source] Carbohydrate-derived alkylcobalt carbonyl: {[(1,2:5,6-Di-O,O-isopropylidene-,-D-glucofuranos-3-yl)oxycarbonyl]methyl}cobalt tricarbonyl triphenylphosphineCHIRALITY, Issue 8 2001Claudia Zucchi Abstract A carbohydrate-derivative alkylcobalt carbonyl, {[(1,2:5,6-di-O,O-isopropylidene-,-D-glucofuranos-3-yl)oxycarbonyl]methyl}cobalt tricarbonyl triphenylphosphine (3) was prepared and characterized by IR, NMR, and CD spectra, as well as by X-ray diffraction. The supramolecular chemistry in the crystalline P212121 (chiral) phase and in solution was analyzed and compared. The bulky carbohydrate-based ligand stabilized one chiral conformation, which, however, is less ordered than for analogous compounds with more flexible and less bulky chiral groups. Intermolecular, H-bond interactions are more important in the P212121 phase of complex 3 than at other analogous compounds. Chirality 13:458,464, 2001. © 2001 Wiley-Liss, Inc. [source] Photochromic and Photoresponsive Properties of Methacrylic Polymers Bearing Optically Active Hydroxysuccinimide in the Side ChainMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 21 2007Luigi Angiolini Abstract The photochromic and photoresponsive properties of a series of optically active azoaromatic polymers, containing in the side chain the rigid (S)- and/or (R)-hydroxysuccinimide residue, have been investigated in solution and in the solid state as thin films by observing the trans - cis photoisomerisation of the azobenzene chromophore, and the results are compared to the corresponding monomeric (S) and (R) model compounds. The presence of exciton splitting due to dipole-dipole interactions between the trans -azoaromatic rings in the CD spectra confirms the intrinsic chirality of the macromolecules. Thin films of the polymers display the same chiroptical properties as the solution, thus suggesting that the macromolecules maintain chiral conformations also in the solid amorphous state. [source] Optically Active Methacrylic Copolymers Bearing Side-Chain Bisazoaromatic and Bulky Achiral MoietiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2007Luigi Angiolini Abstract The synthesis of two novel series of optically active methacrylic copolymers that contain a side-chain chiral moiety linked to a photochromic bisazoaromatic chromophore has been carried out by radical copolymerization of the monomer (S)-3-methacryloyloxy-1-[4,-phenylazo-(4-azobenzene)]pyrrolidine with highly sterically hindered monomers such as tert- butyl methacrylate or triphenylmethyl methacrylate with the aim to investigate the effect on the optical activity of the resulting derivatives. The copolymeric products have been fully characterized and their spectroscopic and thermal properties compared to those of the related optically active homopolymer and the copolymers with methyl methacrylate, previously reported. The optical activity displayed by the polymers is discussed in terms of extent of chiral conformations assumed by the macromolecules as a consequence of the insertion of co-monomers capable of affecting the dipole-dipole interactions that occur in these derivatives between the side-chain bisazoaromatic chromophores disposed according to a mutual chiral arrangement. [source] | ||||||||||