title: Spontaneous helical folding of bis(Ni-salphen) complexes in solution and in the solid state: spectroscopic tracking of the unfolding process induced by Na(+) ions.
abstract: Four kinds of bis(Ni-salphen) complexes containing a 2-methylenepropane-1,3-diyl linker were synthesised and characterised. Crystal structural analysis revealed that one of the complexes folded into a helical structure, in which two Ni atoms were at a distance of 3.2 Å from each other. NMR measurements suggested that a similar folded state was maintained in solution, and the energy barrier for refolding through an unfolded state was 47 kJ mol(-1). The folded complex also exhibited a significant bathochromic shift in its UV-Vis absorption structure. Addition of sodium ions caused unfolding of the complexes, and the corresponding spectra were attributed to a virtually isolated state. DFT calculations reproduced well the energy barrier and folding-induced bathochromic shift.
authors.affiliation: Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan. houjou@iis.u-tokyo.ac.jp.
authors.forename: Hiroto
authors.initials: H
authors.lastname: Achira
authors.forename: Muneyuki
authors.initials: M
authors.lastname: Ito
authors.forename: Toshiki
authors.initials: T
authors.lastname: Mutai
authors.forename: Isao
authors.initials: I
authors.lastname: Yoshikawa
authors.forename: Koji
authors.initials: K
authors.lastname: Araki
authors.forename: Hirohiko
authors.initials: H
authors.lastname: Houjou