title: Spatially Heterogeneous Nature of Self-Catalytic Reaction in Hetero-Double Helix Formation of Helicene Oligomers.
abstract: A 1:1 mixture of pseudoenantiomeric aminomethylenehelicene oligomers, (P)-tetramer and (M)-pentamer, in fluorobenzene show a self-catalytic phenomenon in the formation of hetero-double helices from random coils. This study visualizes the spatially heterogeneous nature of the self-catalytic reaction in dilute solution. UV/Vis imaging analysis of the mixture at 70 °C, containing random coils, exhibits a homogeneous bright area. When the solution is cooled from 70 to 30 °C and held at that temperature, dark domains of approximately 1 mm in size appear, which move approximately at a rate of 1 mm min-1. The dark domains indicate that weaker UV/Vis absorption results from the formation of hetero-double helices, which is supported by circular dichroism (CD) imaging experiments. Then a homogeneous mixture is regenerated upon heating to 55 °C, as shown by CD imaging. Under self-catalytic conditions, a homogeneous solution spontaneously changed to a heterogeneous solution in the process of hetero-double-helix formation.
authors.affiliation: Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Sendai, 980-8578, Japan.
authors.forename: Yo
authors.initials: Y
authors.lastname: Kushida
authors.affiliation: Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Sendai, 980-8578, Japan.
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Sawato
authors.affiliation: Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Sendai, 980-8578, Japan.
authors.forename: Nozomi
authors.initials: N
authors.lastname: Saito
authors.affiliation: Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Sendai, 980-8578, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Shigeno
authors.affiliation: Central Research Laboratory, Hamamatsu Photonics K. K. Hamakita, Hamamatsu, Shizuoka, 434-8601, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Satozono
authors.affiliation: Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Sendai, 980-8578, Japan. yama@m.tohoku.ac.jp.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Yamaguchi
keywords: UV/Vis spectroscopy; circular dichroism; heterogeneous solutions; imaging; self-catalysis