Stereochemical dynamics of crown ethers: Ring inversion in isomeric dicyclohexano-18-crown-6 systems as studied by 13C magnetic resonance at low temperature

Molecular signal transduction by conformational transmission: use of tetrasubstituted perhydroanthracenes as transducers

2,3,6,7-Tetrasubstituted cis-anti-cis perhydroanthracenes have been studied as conformational transducers for molecular signal transduction. 2,2'-Bipyridine groups attached to the perhydroanthracene through ether linkages were chosen as receptor substituents, while pyrene groups were selected as effectors. A chelation-induced triple ring flip of the perhydroanthracene could be achieved by the complexation of zinc(II) ions at the bipyridine sites of ligands 13 and 15. It was found that two pyrene substituents attached to the perhydroanthracene via a linker with an E double bond and an ester group could be used to monitor the triple ring flip. In the equatorial positions, the pyrenes are sufficiently close to form an excimer in the excited state, giving a fluorescence signal at 480 nm. In the axial positions, they are far away from each other and give mainly a monomer fluorescence signal at 380 nm. Both the bipyridine receptor and the pyrene effector are present in compound 33. The conformational switching 34-->35 (the two conformers of 33) has successfully been used for a signal transduction over a signal distance of 2 nm.

Synthesis, Reactivity, and Structure of [H(13)O(6)][PtCl(5)(H(4)O(2))].2(18-cr-6): A Crown Ether Complex of a Pentachloroaquaplatinic Acid with an [H(13)O(6)](+) Cation in a Cage of Three Crown Ether Molecules

An aqueous solution of H(2)[PtCl(6)].6 H(2)O reacts with crown ether 18-crown-6 to give [H(13)O(6)][PtCl(5)(H(4)O(2))]. 2(18-cr-6)(1) (1) and (H(3)O)(2)[PtCl(6)].2(18-cr-6) (2a). In the presence of HCl, only 2a is formed; in an analogous manner, (H(3)O)(2)[PtCl(6)].2(15-cr-5).2 H(2)O (2b) and (H(3)O)(2)[PtCl(6)].2(DCH-18-cr-6)(1) (2c) were obtained. 1 is gradually decomposed in water to give [PtCl(4)(H(2)O)(2)].(18-cr-6).2H(2)O (3). 1-3 were characterized by microanalysis and IR and NMR spectroscopy ((1)H, (13)C, (195)Pt). The X-ray structure analysis of 1 (orange needles; space group P2(1)2(1)2(1), a = 7.938(1) Å, b = 15.691(2) Å, c = 34.861(4) Å; Z = 4) shows an anionic entity [PtCl(5)(H(4)O(2))](-) and a cationic entity [H(13)O(6)](+) which are separated by a crown ether molecule 18-cr-6. The [H(13)O(6)](+) cations exhibit the structure [H(3)O(H(4)O(2))(2)(H(2)O)](+) and are also separated by crown ether molecules in such a way that the crystal is threaded by chains built up of 18-cr-6/[H(13)O(6)](+) units at which the 18-cr-6/[PtCl(5)(H(4)O(2))](-) moieties are fixed as lateral branches. Thus, the cations [H(13)O(6)](+) are embedded in three crown ether molecules. All terminal hydrogens are involved in hydrogen bridges to oxygen atoms of the crown ether molecules. The O(w).O(cr) distances are distinctly longer in the mean than the O(w).O(w) distances within the [H(13)O(6)](+) moiety.

Dicyclohexylethyleneglycol, -diethyleneglycol, -triethyleneglycol, and related monosubstituted cyclohexanes. Conformational analysis using low-temperature 13C and 1H NMR spectroscopy

Two conformations of each of the title molecules have been detected by 100 MHz 13C NMR at 210 K. For the dicyclohexyl systems, the conformations are related via a single ring inversion. In each case the equatorial–axial conformer is 4.7 ± 0.4 kJ/mol less stable than the diequatorially substituted form in CD2Cl2 solution. For monosubstituted models, the conformational free energy (−ΔG0) values of the -O-CH2-CH2-OCH3, -OCH2-CH2-O-CH2-CH3, and -O-CH2-CH2-O-CH-(CH3)2 groups have been determined to be 5.4,6.1, and 6.1 ± 0.2 kJ/mol, respectively. In methanol, the latter equilibria are slightly more biased towards the axially substituted conformers. Keywords: substituted ethylene glycols, conformational equilibria.