title: Deterministic and Stochastic Chiral Symmetry Breaking Exhibited by Racemic Aminomethylenehelicene Oligomers.
abstract: Racemic mixtures of aminomethylenehelicene (P)- and (M)-pentamers exhibited deterministic and stochastic chiral symmetry breaking during hetero-double-helix formation and self-assembly in solution. Heating a 50:50 mixture of (P)- and (M)-pentamers at 90 °C, and then cooling the mixture to 70 °C resulted in hetero-double-helix formation; a Cotton effect with negative Δε at λ=315 nm appeared. Chiral self-assembly occurred when the mixture was cooled to 25 °C. A strong tendency of deterministic chiral symmetry breaking appeared at the molecular and self-assembled levels, which was indicated by the negative Δε at λ=315 nm that appeared in most cases in repeated experiments. Mixtures containing 60:40 and 40:60 (P)-/(M)-pentamers also self-assembled with the same chirality. When a homo-double-helix (P)-/(M)-pentamer and a random coil (M)-/(P)-pentamer were mixed, the chiral self-assembly formed stochastically, and heating and cooling resulted in deterministic chiral symmetry breaking.
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: Masanori
authors.initials: M
authors.lastname: Shigeno
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: Masahiko
authors.initials: M
authors.lastname: Yamaguchi
keywords: chiral symmetry breaking; circular dichroism; double helix; helicenes; self-assembly