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Helical Sense (helical + sense)
Selected AbstractsCounterintuitive influence of microscopic chirality on helical order in polymersJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2004Kap Soo Cheon Abstract Studies of copolymers of chiral and achiral units forming a helical array correlate to statistical physical predictions of the influence of the chiral units on the helical sense taken by the array. In the absence of conflict among the chiral units for helical sense control, the sergeants and soldiers experiment, a larger chiral bias leads to increased control. However, when conflict exists among the chiral units for helical sense control, the majority rule experiment, a larger chiral bias leads to decreased control of the helical sense and therefore a smaller optical activity. Changing the achiral units in the majority rule experiment can change the nature of the statistical physics between statistical and thermal randomness. In general, the experiments quantitatively demonstrate that the effect of chirality is not an intrinsic property of the chiral moiety but rather depends on the molecular environment. Copyright © 2004 John Wiley & Sons, Ltd. [source] Long-range effects of chirality in aromatic poly(isocyanide)sJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2006David B. Amabilino Abstract The preparation of optically active atropoisomeric polymers which present chiral backbones, thanks to induction during their synthesis from stereogenic centers, located far away from the skeleton is possible, thanks principally to semirigid conformations of the promesogenic spacers between them. The result is that chiral "information" can be passed as far as 21 Å from the asymmetric center to the carbon atom that forms the polymeric chain in poly(isocyanide)s. The sense of chiral induction in these conformationally rigid polymers parallels the helical sense of the cholesteric phases, as well as to the helical senses of chiral smectic C phases, induced by the monomers in nematic and smectic C phases, respectively. All these phenomena obey the odd,even rules proposed for chiral sense changes in these liquid crystalline phases. Noncovalent interactions play an important part in the induction process, in which steric arguments can be used to justify the inductions observed. The methodology can be used to prepare macromolecules, which display switching behavior upon thermal or electrochemical stimulus. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3161,3174, 2006 [source] Helix Formation in Synthetic Polymers by Hydrogen Bonding with Native Saccharides in Protic MediaCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2006Minoru Waki Abstract Water-soluble poly(m -ethynylpyridine)s were designed to realize saccharide recognition in protic media. UV/Vis, 1H NMR, and fluorescence measurements revealed that the polymer forms a helical higher order structure by solvophobic interactions between the ethynylpyridine units in the protic medium. The resulting pore in the helix behaves like a binding pocket in proteins, by taking advantage of inwardly directed hydrogen-bonding functional groups of the polymers. Molecular recognition of native saccharides by the polymers was investigated by circular dichroism (CD). The chirality of the saccharide was transferred to the helical sense of the polymers, accompanied by the appearance of induced CDs (ICDs) in the absorptive region of the polymers. In MeOH/water (10/1), mannose and allose showed intense ICDs, and the apparent association constant between the polymer and D -mannose was 14,M,1. [source] Long-range effects of chirality in aromatic poly(isocyanide)sJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2006David B. Amabilino Abstract The preparation of optically active atropoisomeric polymers which present chiral backbones, thanks to induction during their synthesis from stereogenic centers, located far away from the skeleton is possible, thanks principally to semirigid conformations of the promesogenic spacers between them. The result is that chiral "information" can be passed as far as 21 Å from the asymmetric center to the carbon atom that forms the polymeric chain in poly(isocyanide)s. The sense of chiral induction in these conformationally rigid polymers parallels the helical sense of the cholesteric phases, as well as to the helical senses of chiral smectic C phases, induced by the monomers in nematic and smectic C phases, respectively. All these phenomena obey the odd,even rules proposed for chiral sense changes in these liquid crystalline phases. Noncovalent interactions play an important part in the induction process, in which steric arguments can be used to justify the inductions observed. The methodology can be used to prepare macromolecules, which display switching behavior upon thermal or electrochemical stimulus. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3161,3174, 2006 [source] Synthesis and Polymerization of Optically Active N -Propargylphosphonamidates: A Novel Helical Polymer Carrying a P-Chiral CenterMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2006Dongmei Yue Abstract Summary: A diastereomeric pair of novel N -propargylphosphonamidates, HCCCH2NHP(O)(CH3)O- L -menthyl was synthesized by the successive condensations of methylphosphonic dichloride with L -menthol and propargylamine. The (R)-P-isomer (1a) was isolated, and the absolute configuration was determined by XRD. Polymerization of 1a, and a mixture of 1a and (S)-P-isomer (1b) was carried out with a zwitterionic Rh complex as a catalyst. cis -Stereoregular polymers with number-average molecular weights of 5,600,9,800 were obtained in good yields. Poly(1a) and poly(1a29 - co - 1b71) exhibited large specific rotations (+408 and ,146°), and intense Cotton effects ([,],=,+2.25 and ,0.9,×,104 deg,·,cm2,·,dmol,1) based on the conjugated polyacetylene backbone around 325 nm in CHCl3, indicating that these polymers have helical structures, whose predominant helical senses are opposite. Polymerization of N -propargylphosphonamidate. [source] | |||||||||||||