Smart Molecular Helical Springs as Tunable Receptors

Abstract

The rational construction and operation of an ideal helical spring has been investigated. The infinite helices, [Ag(Py 2 O)]X (Py 2 O ) 3,3′-oxybispyridine; X -) NO 3 -, BF 4 -, ClO 4 -, and PF 6 -), have been constructed in high yield via cooperative effects of the skewed conformer of Py 2 O and the potential linear geometry of the N-Ag(I)-N bond. Crystallographic characterization reveals that the polymer framework is an ideal cationic cylindrical helix and that its counteranions are pinched in two columns inside the helix. The four anions have been exchanged for each other in an aqueous solution without destruction of the helical skeleton. In particular, [Ag(Py 2 O)]NO 3 prepared by the counteranion exchange can be isolated as crystals suitable for X-ray crystallography in water. The helical pitch is reversibly stretched via the counteranion exchange from 7.430(2) to 9.621(2) Å, and is exactly proportional to the volume of the anion guests. This pitch-tuning is attributed to subtle change in the nonrigid dihedral angles between two pyridyl groups around O and Ag atoms that act as hinges within the helical subunit. Thermal analyses indicate that the helical compounds are stable up to 231-332 °C in the solid state.

Self-assembly of physically crosslinked micelles of poly(2-acrylamido-2-methyl-1-propane sulphonic acid-co-isodecyl methacrylate)-copper(II) complexes

“…The basis of molecular assembly is the meaningful and organized connections between molecular structures by means of covalent bonds, hydrogen bonds, p-p interaction and their combination [4]. The nature of assembly of metal-polymers is highly influenced by a number of factors, such as the coordination ability of metal ions, the structural characterization of organic ligands, solvent system, temperature, pH of the solution, ratio of metal to ligand and counter ions [5,6]. An alteration in any of these factors often results in new complexes with different structural topologies and functions.…”

Dynamic chemical devices: Modulation of contraction/extension molecular motion by coupled-ion binding/pH change-induced structural switching

“…For instance, chemists have designed entities such as synthetic chains of amino acids (19) or aromatic helical backbones (20), responsive polymers (21,22), or other species (for a selection, see refs. [23][24][25][26][27], which undergo important shape changes, e.g., folding͞unfolding, rotation or linear motions in response to external stimuli (light, temperature, pressure, or medium effects).…”

Crystal structure of trans-tetraaquabis(4-(pyridin-4-ylsulfonyl)pyridine-κN)cobalt(II) diperchlorate dihydrate, C20H28Cl2CoN4O18S2

“…Transition metal complexes of di-4-pyridylsul de and its positional isomers have been already studied [2][3][4]. Only several metal complexes with 4-(pyridin-4-ylsul nyl)pyridine, and one derivate of di-4-pyridylsul de, were reported recentely [5].…”