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- Hydrogen bonds (3) (entfernen)
Organometallic oligoamides built from three to four ferrocene amino acid units (H-Fca-OH,1-amino-1'-ferrocene carboxylic acid) fold into hydrogen bonded secondary structures featuring eight-membered rings by cooperative hydrogen bonds. NMR studies and DFT calculations (CAM-B3LYP, LANL2DZ, IEFPCM (THF) reveal that the organometallic zigzag foldamer structures are highly resistant toward denaturation by hydrogen bond acceptors such as dimethyl sulfoxide and 2,4-lutidine. Replacing one ferrocene amino acid unit by the organic alpha-amino acid glycine at the C-terminal end (Fca goes to Gly) significantly destabilizes the secondary zigzag structure facilitating denaturation by DMSO. Highly stabilized ordered poly(Fca) architectures are very attractive for future applications of switchable hydrogen-bonded redox-active materials.
Crystal structures of four different di-aryl-1,3,4-oxadiazole compounds (aryl = 2-pyridyl-, 3-pyridyl-, 2-aminophenyl-, 3-aminophenyl-) are determined. Crystallization of di(2-pyridyl)-1,3,4-oxadiazole yielded monoclinic and triclinic polymorphs. The structures are characterized by the occurrence of ππ interactions. Additionally, in case of the aminophenyl compounds intra- as well as intermolecular hydrogen bonds are found that influence the packing motif as well. Since these molecules are often used as ligands in metalorganic complexes similarities and differences of the molecular conformation between the molecules in the pure crystals and that of the ligands in the complexes are discussed.
The measurement of biologically relevant anions, such as fluoride, is an important task in analytical chemistry, in particular, for dental health and osteoporosis. Although a large number of fluoride probes are known, the applicability under relevant conditions is limited to a few examples. To improve this situation, BODIPY-amidothiourea dyes with varying hydrogen-bond donating strengths were developed, the most H-acidic of which (1 c) could detect F- from an inorganic source (NaF) in 50?% aqueous solution (DMSO/water 1:1, v/v) with 0.01 ppm sensitivity through selective fluorescence quenching by a photoinduced electron-transfer (PET) process. Use of the probe and a reference dye with a test-strip assay and a portable and rapidly recording lateral-flow fluorescence reader made determination of F- in neat aqueous solutions, such as spiked water samples and toothpaste extracts, possible in a self-referenced manner, achieving a detection limit of 0.2 ppm.