title: Dynamic chemical devices: generation of reversible extension/contraction molecular motion by ion-triggered single/double helix interconversion.
abstract: The polyheterocyclic strands 1-H and 2-H adopt a helical shape enforced by the pyridine-pyrimidine helicity codon. The crystal structure of 2-H shows the formation of stacks of dimers of right- and left-handed individual helices. Treatment of 1-H and 2-H with silver triflate results in the generation of double-helical entities 1-DH and 2-DH, containing two strands and two silver ions. NMR studies and determination of the crystal structure of 2-DH indicate that the duplex is stabilized by coordination of each Ag(+) ion to two terminal bipyridine units, one from each strand, and by pronounced pi-pi stacking interactions between the internal heterocycles of the strands, yielding a very robust double helical structure. Reversible interconversion of the single and double helix may be achieved by addition of a cryptand capable of sequestering Ag(+) and releasing it by protonation. Thus, successive addition of acid and base leads to reversible interconversion between the shorter ( approximately 3.6 A) single helix and the longer ( approximately 10.3 A) double helix, resulting in the generation of pronounced extension/contraction motion. The system 1,2-H/1,2-DH represents a dynamic chemical device undergoing ionic modulation of reversible molecular mechanical motion fueled by acid/base neutralization.
authors.affiliation: Laboratoire de Chimie Supramoléculaire, ISIS Université Louis Pasteur, CNRS UMR 7006 4 rue Blaise Pascal, 67000 Strasbourg, France.
authors.forename: Mihail
authors.initials: M
authors.lastname: Barboiu
authors.forename: Gavin
authors.initials: G
authors.lastname: Vaughan
authors.forename: Nathalie
authors.initials: N
authors.lastname: Kyritsakas
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Lehn
mesh_terms: D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D011725:Pyridines / Q000737:chemistry*; D011743:Pyrimidines / Q000737:chemistry*
chemical_list: D011725:Pyridines; D011743:Pyrimidines; D004247:DNA