Marc H. Prosenc

Interference of magnesium corrosion with tetrazolium-based cytotoxicity assays

Magnesium (Mg) alloys are promising materials for the development of biodegradable implants. However, the current in vitro test procedures for cytotoxicity, cell viability and proliferation are not always suitable for this class of materials. In this paper we show that tetrazolium-salt-based assays, which are widely used in practice, are influenced by the corrosion products of Mg-based alloys. Corroded Mg converts tetrazolium salts to formazan, leading to a higher background and falsifying the results of cell viability. Tetrazolium-based assays are therefore not a useful tool for testing the cytotoxicity of Mg in static in vitro assays.

A new 4c–2e bond in B6H7−

For N(C(4)H(9))(4)B(6)H(7) a proton is shown to be localised above one of the faces of the distorted octahedron, and rhomboid rings are formed as shown by topological analysis of charge densities.

Donor−Acceptor Interaction in Cationic Archetype Mono- and Dinuclear Sesquifulvalene Complexes [(η5-C5H5)Fe{µ-(η5-C5H4)(η7-C7H6)}M′L′]n+ (n = 1, 2)

In order to gain a deeper insight into structure-property relationships of the donor (D)−acceptor (A) interactions in cationic sesquifulvalene complexes the mono- and dicationic complexes [(η5-C5H5)Fe{µ-(η5-C5H4)(η7-C7H6)}M′L′]+ were synthesized as BF4 and PF6 salts: M′L′ = Cr(CO)3 (3PF6); M′L′ = none (4BF4); M′L′ = Ru(η5-C5H5)+ [5(PF6)2]; M′L′ = Ru(η5-C5Me5)+ [6(PF6)2]. The ferrocenyl substituent works as the electron donor and the tropylium moiety as the electron acceptor. For the electronic ground state the NMR spectroscopic results demonstrate an increasing charge delocalization in the order M′L′ = Cr(CO)3 < Ru(η5-C5Me5)+ < Ru(η5-C5H5) < none. The same order of the acceptor moieties is observed for the difference between the oxidation and reduction potentials, which are related to an electrochemically reversible and a complete irreversible one-electron transfer, respectively. A comparison of the structural data of 3−6 reveals a small but distinct contribution of the cross-conjugated mesomeric form to the bis(aromatic) mesomeric form in the ground state of the sesquifulvalene complexes, which increases, when the electron-withdrawing ability of the acceptor becomes stronger. The UV/Vis spectra are dominated by two intense absorption bands in the visible and near-UV region, which are assigned to a low-energy donor(metal)−acceptor charge-transfer (D−A CT) transition and to a high-energy donor(ligand)−acceptor charge-transfer (L−A CT) transition. For these archetype sesquifulvalene complexes the first hyperpolarizability β was determined by means of hyper-Rayleigh scattering (HRS). Whereas for 3 no second harmonic signal could be detected and 4 shows fluorescence due to two-photon absorptions, 5 and 6 possess appreciable β values.

Electronic Coupling through Intramolecular π–π Interactions in Biscobaltocenes: A Structural, Spectroscopic, and Magnetic Study

The paramagnetic dinuclear complexes 1,8-bis(cobaltocenyl)naphthalene (2) and 1,8-bis[(pentamethyl-η(5)-cyclopentadienyl)(η(5)-cyclopentadiendiyl)cobalt(II)]naphthalene (4) were synthesized. The molecular structures were characterized by X-ray structure analysis and consisted of two cobaltocenes linked through a distorted naphthalene clamp. Electronic interactions between the two cobalt atoms were observed by cyclic voltammetric studies. Superconducting quantum interference device (SQUID) measurements of the pure compounds and diluted in their diamagnetic iron derivatives, as well as variable-temperature NMR spectroscopy experiments in solution are presented. Magnetic measurements revealed an antiferromagnetic coupling of the electrons in complexes 2 and 4. From NMR spectroscopy experiments, Curie behavior in the temperature range from -60 to +60 °C can be deduced. The electronic structure and magnetic behavior is supported by results of broken-symmetry DFT and multireference calculations along with UV/Vis spectroscopic data, which revealed an intramolecular through space π-π interaction between the cobaltocene units.

Temperature- and moisture-dependency of CsLiB6O10. A new phase, β-CsLiB6O10

Abstract The structural behavior of the non-linear optical, nanoporous compound CsLiB6O10 was studied in a wide temperature range. Both the highly anisotropic thermal expansion of the borate with temperature variation and the deterioration of its crystals were investigated. The electron density distribution was analyzed in detail. A reversible, partial transition to a new modification, β-CsLiB6O10, was observed during cooling crystalline and moist samples of CsLiB6O10 to –25 °C. The crystal structure of the new phase is described.

Structure-property relationship in organometallic compounds regarding SHG

Structure-property relationships based on experimental as well as theoretical results will be elucidated. For this purpose different dipolar organometallic compounds were synthesized and characterized. The alteration of the donor and acceptor termini in mono- and dinuclear sesquifulvalene complexes results in spectroscopic and even structural modifications. The structural and 1H NMR spectroscopic changes correlate with the experimentally obtained first hyperpolarizability. The potent electron-donating (D) group [(CpFeCO)2(μ-CO)(μ-C=CH-)] is combined with different electron-accepting units (A), yielding the push-pull complexes [(CpFeCO)2(μCO)(μ-C=CH-CH=A)]. The extent of electron delocalization within the π-bridge connecting the donor D and the acceptor A can be monitored by means of 1H NMR spectroscopy. A correlation between the 3J(Hβ-Hγ) coupling constants and the first hyperpolarizability is found, which very much resembles the dependence of the first hyperpolarizability on the bond length alternation. In order to elucidate the dependence of the NLO response on the conformation of triply branched NLOphores, a new series of dendritic D-μ-A structures has been synthesized. A combined approach of experiments and computational predictions was applied both on the dendrimers and on the corresponding single-strand chromophores. These results demonstrate that theoretical calculations are able to reproduce experimental results and show the tendency of the effects due to structural changes