Spectroscopic evidence for selenium(IV) dimerization in aqueous solution.

The aqueous speciation of selenium(iv) was elucidated by a combined approach applying quantum chemical calculations, infrared (IR), Raman, and (77)Se NMR spectroscopy. The dimerization of hydrogen selenite (HSeO3(-)) was confirmed at concentrations above 10 mmol L(-1) by both IR and NMR spectroscopy. Quantum chemical calculations provided the assignment of vibrational bands observed to specific molecular modes of the (HSeO3)2(2-) ion. The results presented will provide a better understanding of the chemistry of aqueous Se(iv) which is of particular interest for processes occurring at mineral/water interfaces.

Synthesis of macrocyclic receptors with intrinsic fluorescence featuring quinizarin moieties.

An unprecedented class of macrocycles with intrinsic fluorescence consisting of phenolic trimers and quinizarin is developed. Though they are lacking strong hydrogen bonds as observed in calixarenes, the two examples introduced here each adopt a vase-like conformation with all four aromatic units pointing in one direction (syn orientation). This "cone" conformation has been confirmed by NMR spectroscopy, molecular modeling, and X-ray crystallography. The laminar, electron-rich fluorophore as part of the macrocycle allows additional contacts to enclosed guest molecules.

Synthesis of novel celluloses derivatives and investigation of their mitogenic activity in the presence and absence of FGF2.

Novel cellulose sulfates (CS) with a controlled degree of sulfation (DS(S)) were synthesized through acetosulfation as well as direct sulfation. CS containing carboxyl (CO) or carboxymethyl (CM) groups were prepared by TEMPO oxidation or by carboxymethylation with chloroacetic acid. The derivatization was characterized by nuclear magnetic resonance and Raman spectroscopy. The derivatives were investigated regarding their cytotoxicity and mitogenic activity by modulation of 3T3 fibroblast proliferation with or without exogenous FGF2. All derivatives were non-toxic for 3T3 cells. CS strongly promoted FGF2-induced proliferation, which was positively related to overall DS(S). In the absence of FGF2, minute quantities of CS with intermediate degrees of sulfation exerted stronger mitogenic effects than heparin. No significant promoting effects of CO and CM on cell proliferation were found, though the structure of CO shows similarities to heparin.

Phosphorus-31 MAS NMR investigations of pyridine stabilized dithiomonometaphosphoryl halides.

Phosphorus-31 magic-angle spinning NMR spectroscopy was chosen in order to study a series of N-donor stabilized dithiomonometaphosphoryl halides (F, Cl, and Br) and to extract structural and bonding information from their spectra. Additionally, an unusual line splitting was observed in the 31P MAS NMR spectra of pyridine dithiomonometaphosphoryl chloride (Py-->PS2Cl) and the analogous bromide (Py-->PS2Br). It is shown that this effect is due to a residual dipolar coupling between phosphorus and chlorine or bromine, respectively. This work is to our knowledge the first observation of this effect between P and Br in 31P MAS NMR spectra.