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Bernold Hasenknopf

Publications and source records attributed to Bernold Hasenknopf.

9 recordsLinked to original sources
PubMed2006

A strategy for the analysis of chiral polyoxotungstates by multinuclear (31P, 183W) NMR spectroscopy applied to the assignment of the 183W NMR spectra of alpha1-[P2W17O61]10- and alpha1-[YbP2W17O61]7-.

This paper describes the complete assignment of the 183W NMR spectra of the chiral polyoxometalates alpha1-[P2W17O61]10- and alpha1-[YbP2W17O61]7- in aqueous solution. These spectra display each 17 lines of equal intensity with a relatively narrow chemical shift distribution. The identification of signals is based on selective 31P-183W decoupling and recognition of particular sets of coupling constants for tungsten atoms around the lacunary site. Further assignment is obtained by 183W 2D-COSY NMR experiments. We demonstrate herewith a new way for the unambiguous assignment of 183W NMR spectra of polyoxotungstates without any symmetry elements or tungsten atoms in special positions. This way relies on the correlation of the magnitude of 2J(W-W) coupling constants with the geometry of oxo-bridges in polyoxotungstates. These results open the way to monitor interaction sites of chiral polyoxotungstates with organic ligands.

Journal Article↗
PubMed2006

Production and reactions of organic-soluble lanthanide complexes of the monolacunary Dawson [alpha1-P2W17O61]10- polyoxotungstate.

The incorporation of lanthanides into polyoxometalates provides entry to new classes of potentially useful materials that combine the intrinsic properties of both constituents. To utilize the [alpha1-Ln(H2O)4P2W17O61]7- species in applications of catalysis and development of luminescent materials, the chemistry of this family of lanthanide polyoxometalates in organic solvents has been developed. Organic-soluble polyoxometalate-lanthanide complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] (Ln = La(III), Sm(III), Eu(III), Yb(III)) were prepared and characterized by elemental analysis, acid-base titration, IR, 31P NMR, and mass spectrometry. The synthetic procedure involves a cation metathesis reaction in aqueous solution under strict pH control. A solid-liquid-phase transfer protocol yielded a unique species (TBA)8K3[Yb(alpha1-YbP2W17O61)2] with three ytterbium ions and two [alpha1-P2W17O61]10- polyoxotungstates. A centrosymmetric dimeric complex [{alpha1-La(H2O)4P2W17O61}2]14- was crystallized from aqueous solution and characterized by X-ray diffraction. ESI mass spectral analysis of the complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] shows that similar dimers exist in organic solution, in particular for the early lanthanides. Fragmentation in the mass spectrometer of the complexes from dry acetonitrile solution involves double protonation of an oxo ligand and loss of one water molecule. Low mass tungstate fragments combine into [(WO3)n]2- (n = 1-5) ions and their condensation products with phosphate. Reaction of TBA5H2[alpha1-Eu(H2O)4P2W17O61] with 1,10-phenanthroline or 2,2'-bipyridine showed an increase of the europium luminescence. This result is explained by the formation of a ternary complex of [alpha1-Eu(H2O)4P2W17O61]7- and two sensitizing ligands.

Cations↗
PubMed2005

Efficient preparation of functionalized hybrid organic/inorganic Wells-Dawson-type polyoxotungstates.

Hybrid organic/inorganic Wells-Dawson polyoxotungstates have been prepared through addition of functionalized tricholorostannanes to lacunary alpha(2)- and alpha(1)-[P(2)W(17)O(61)](10-). Coupling of amines and alcohols to polyoxotungstate platforms led to new structures in good yields. Coupling of chiral amines to the previously unknown organotin-substituted alpha(1) derivatives allowed the isolation of diastereomers, which feature in some cases split (1)H, (13)C, and (31)P NMR spectra. This is the first example of NMR observation of a single pair of diastereomers in the alpha(1)-Wells-Dawson series. It opens the way to potential resolution of those chiral polyoxotungstates.

Journal Article↗
PubMed2005

Polyoxometalates: introduction to a class of inorganic compounds and their biomedical applications.

An increasing number of potential applications for polyoxometalates in human medicine have been reported in the literature. These inorganic complexes are composed of early transition metals (mainly molybdenum, tungsten and vanadium) and oxygen. The present review gives an introduction into the chemistry of these compounds, and an overview of the principal studies of their biological and biochemical effects and their therapeutic potential. The reported antitumoral and antibiotic properties of molybdates and tungstates in vitro and in vivo are compiled and discussed, as are their influences on the blood glucose level in diabetic animals. Aspects of antiviral activities and cell penetration are treated.

Animals↗
PubMed2003

Supramolecular control of [2 + 2] photodimerization via hydrogen bonding.

The use of supramolecular catalysis to control the photoinduced dimerization of styrene, cinnamate, and stilbene chromophores is reported. The strategy employs the formation of a 2:1 supramolecular assembly in the presence of 5,5-dihexylbarbituric acid (DHB). A 3- to 10-fold increase in dimerization efficiency is observed in its presence, concomitant with accrued selectivity for the syn photodimers. The origin of the regioselectivity in the presence of DHB is discussed in terms of topochemical control within the supramolecular architecture.

Journal Article↗