title: Heating/cooling stimulus induces three-state molecular switching of pseudoenantiomeric aminomethylenehelicene oligomers: reversible nonequilibrium thermodynamic processes.
abstract: A 1:1 mixture of pseudoenantiomeric aminomethylenehelicene (P)-tetramer and (M)-pentamer formed three states, namely, the heterodouble helices B and C and the random coil A. At high temperatures, A is the most stable. At low temperatures, C is the most stable, and the structural changes from A to the metastable state B to the product C occur, where B and C have pseudoenantiomeric helical structures. Heating then converts C to A. Essentially, all the molecules change their structure from A to B to C to A. Various nonequilibrium reversible thermodynamic responses appeared depending on thermal conditions: The metastable states A and B can be interconverted with thermal hysteresis without forming C in a far-from-equilibrium manner; three-state hysteresis occurs; states A and B can be frozen at low temperatures and defrosted by warming. An energy and population model for the three-state switching is given, involving inversion of thermodynamic stability and thermal hysteresis.
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.forename: Yo
authors.initials: Y
authors.lastname: Kushida
authors.forename: Masahiko
authors.initials: M
authors.lastname: Yamaguchi
mesh_terms: D003080:Cold Temperature; D006358:Hot Temperature; D008744:Methylamines / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011083:Polycyclic Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D008744:Methylamines; D011083:Polycyclic Compounds; C031660:helicenes