Selective fluorescence sensing of copper(II) and water via competing imine hydrolysis and alcohol oxidation pathways sensitive to water content in aqueous acetonitrile mixtures.

Addition of hydrazines to a 1,8-disubstituted anthraquinone macrocycle containing a polyether ring produces site-selective imination, where hydrazone formation produces the more sterically hindered adduct. Reduction of the remaining carbonyl group to a secondary alcohol followed by addition of copper(II) ion causes intense yellow fluorescence to occur, which is selective for this metal cation and allows this system to be used as a fluorescence sensor. In the presence of water, a green-fluorescent intermediate appears, which slowly decomposes to produce the original starting anthraquinone. The addition of a large amount of water radically changes the reaction pathway. In this case, oxidation of the secondary alcohol is kinetically faster than hydrolysis of the hydrazone, although the same anthraquinone product is ultimately produced. Stern-Volmer data suggest that dioxygen quenches the green emission through both dynamic and static mechanisms; the static ground-state effect is most likely due to association of oxygen with the copper-bound fluorescent intermediate.

Large amplitude, proton- and cation-activated latch-type mechanical switches: O-protonated amides stabilized by intramolecular, low-barrier hydrogen bonds within macrocycles.

Large amplitude molecular switches have been developed using oxonium ions as the novel switching mechanism. Macrocycles that contain a polyether ring that are preorganized and of optimum geometry such that strong, linear Low-Barrier Hydrogen Bonds (LBHB, 2.4 to 2.6 A in length) are formed between a protonated amide oxygen and a cyclic ether, that lend significant iminol character to the amide. Deprotonation yields a large conformational change between closed and open forms, mindful of a new hinged, latch-type mechanical proton switch. Numerous open and closed forms have been characterized by X-ray crystallography, and the intramolecular hydrogen bond that forms between the protonated amide oxygen and the cyclic polyether oxygen accounts for the stability of these new acids. The open form of the deprotonated adducts persist in solution as indicated by the magnitude of coupling constants and other Nuclear Overhauser Effect experiments. Different saturated and unsaturated solid acids have been characterized including products derived from acetonitrile, propionitrile, caprylonitrile, acrylonitrile and adiponitrile, and also by reaction with primary amides in the case of phenyl and norbornene derivatives. We have also demonstrated that metal cations can replace the proton in the switching mechanism, characteristic of nascent synthetic pores.

Substitution of thiophene oligomers with macrocyclic end caps and the colorimetric detection of Hg(II).

Alkyl substitution at the α position(s) of mono-, bi-, and terthiophenes via electrophilic addition of macrocyclic end caps combines linear, π-conjugated aromatic compounds and annular macrocycles. Addition of the Hg(II) ion to terthiophene adducts produces intense color changes, allowing for the selective, colorimetric detection of mercury(II). Chemical oxidation of the asymmetric terthiophene adduct produces the sexithiophene oligomer.