title: Mechanism of helix induction in poly(4-carboxyphenyl isocyanide) with chiral amines and memory of the macromolecular helicity and its helical structures.
abstract: An optically inactive poly(4-carboxyphenyl isocyanide) (poly-1-H) changed its structure into the prevailing, one-handed helical structure upon complexation with optically active amines in dimethylsulfoxide (DMSO) and water, and the complexes show a characteristic induced circular dichroism in the polymer backbone region. Moreover, the macromolecular helicity induced in water and aqueous organic solutions containing more than 50 vol % water could be "memorized" even after complete removal of the chiral amines (h-poly-1b-H), while that induced in DMSO and DMSO-water mixtures containing less than 30 vol % water could not maintain the optical activity after removal of the chiral amines (poly-1a-H). We now report fully detailed studies of the helix induction mechanism with chiral amines and the memory of the macromolecular helicity in water and a DMSO-water mixture by various spectroscopic measurements, theoretical calculations, and persistence length measurements together with X-ray diffraction (XRD) measurements. From the spectroscopic results, such as circular dichroism (CD), absorption, IR, vibrational CD, and NMR of poly-1a-H, h-poly-1b-H, and original poly-1-H, we concluded that the specific configurational isomerization around the C horizontal lineN double bonds occurs during the helicity induction process in each solvent. In order to obtain the structural information, XRD measurements were done on the uniaxially oriented films of the corresponding methyl esters (poly-1-Me, poly-1a-Me, and h-poly-1b-Me) prepared from their liquid crystalline polymer solutions. On the basis of the XRD analyses, the most plausible helical structure of poly-1a-Me was proposed to be a 9-unit/5-turn helix with two monomer units as a repeating unit, and that of h-poly-1b-Me was proposed to be a 10-unit/3-turn helix consisting of one repeating monomer unit. The density functional theory calculations of poly(phenyl isocyanide), a model polymer of h-poly-1b-Me, afforded a 7-unit/2-turn helix as the most possible helical structure, which is in good agreement with the XRD results. Furthermore, the persistence length measurements revealed that these structural changes accompany a significant change in the main-chain stiffness. The mechanism of helix induction in poly-1-H and the memory of the macromolecular helicity are discussed on the basis of these results.
authors: Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan.
authors: Yoko
authors: Y
authors: Hase
authors: Kanji
authors: K
authors: Nagai
authors: Hiroki
authors: H
authors: Iida
authors: Katsuhiro
authors: K
authors: Maeda
authors: Noriaki
authors: N
authors: Ochi
authors: Kyoichi
authors: K
authors: Sawabe
authors: Koichi
authors: K
authors: Sakajiri
authors: Kento
authors: K
authors: Okoshi
authors: Eiji
authors: E
authors: Yashima
mesh_terms: D000042:Absorption; D000588:Amines / Q000737:chemistry*; D004952:Esters / Q000737:chemistry; D007553:Isotope Labeling; D050866:Liquid Crystals / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry*; D012545:Schiff Bases / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013057:Spectrum Analysis; D013237:Stereoisomerism; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D000588:Amines; D004952:Esters; D011108:Polymers; D012545:Schiff Bases; D012997:Solvents; C545306:poly(4-carboxyphenyl isocyanide); D014867:Water