Biomedical subjects

Emil Roduner

Publications and source records attributed to Emil Roduner.

6 recordsLinked to original sources

PubMed2007

Local ordering in liquids: solvent effects on the hyperfine couplings of the cyclohexadienyl radical.

Ordering of solvent molecules in the vicinity of a dipolar free radical affects its hyperfine coupling constants (hfcs). Specifically, it is demonstrated how the variation of the experimental methylene proton and muon hfcs of the muoniated cyclohexadienyl radical in several solvents and solvent mixtures of varying polarity can be accounted for by a dipole-dipole reaction field model that is based on the model of Reddoch and Konishi (J. Chem. Phys. 1979, 70, 2121) which was developed to explain the solvent dependence of the 14N hfc in the di-tert-butyl-nitroxide radical. Ab initio calculations were carried out with the cyclohexadienyl radical in an electric field to model the electric field arising from the electric dipole moments of the surrounding solvent molecules. An extension of the model that includes the dipole-quadrupole interaction can account for the larger hfc in benzene compared with that in octadecane, and it is predicted that the hfc will be proportional to the concentration of quadrupole moments to the 4/3 power. The influence of hydrogen bonding between the radicals' pi electrons and the OH groups of the solvent on the hfcs is also discussed. Comparison with gas-phase data permits a separation of vibrational effects and reveals that approximately 28% of the temperature dependence in water is due to increasing solvent disorder.

Journal Article↗

PubMed2006

ESR observation of the formation of an Au(II) complex in zeolite Y.

Herein we communicate the first time observation of an Au(II) complex stabilized in a zeolite Y supercage, as evidenced by electron spin resonance (ESR); confinement in the zeolite pores obviously stabilizes this unusual oxidation state and prevents it from undergoing disproportionation.

Electron Spin Resonance Spectroscopy↗

PubMed2006

Ferroelectricity of pyridinium perchlorate, a molecular level point of view.

The behavior of ferroelectric and thermodynamic parameters of pyridinium perchlorate (PyClO(4)) was simulated based on experimental NMR data and properties of the individual constituting ions. Dynamic (2)H NMR spectroscopy was used to investigate the order-disorder character of ferroelectricity in PyClO(4). Quadrupole echo and inversion recovery experiments were performed in the range from 140 to 300 K. The spectra can be simulated by a rotational jump motion of the pyridinium cations about their pseudo-C(6) axis. This confirms that the ferroelectricity of this compound below a first-order phase transition at 248 K is primarily due to the ordering of cations along a ferroelectric axis. In an intermediate phase between 248 and 233 K, the cation-anion sublattice displacement mechanism also gives a small positive contribution to ferroelectricity. In the family of the ferroelectric pyridinium salts, the paraelectric-ferroelectric phase transition temperature increases with the size and polarizability of the constituting anions, suggesting that the main interaction for ferroelectric ordering occurs via an indirect superexchange mechanism, whereas in compounds with small anions of low polarizability the direct dipole-dipole interaction dominates and leads to antiferroelectric order.

Journal Article↗

PubMed2006

Size matters: why nanomaterials are different.

Gold is known as a shiny, yellow noble metal that does not tarnish, has a face centred cubic structure, is non-magnetic and melts at 1336 K. However, a small sample of the same gold is quite different, providing it is tiny enough: 10 nm particles absorb green light and thus appear red. The melting temperature decreases dramatically as the size goes down. Moreover, gold ceases to be noble, and 2-3 nm nanoparticles are excellent catalysts which also exhibit considerable magnetism. At this size they are still metallic, but smaller ones turn into insulators. Their equilibrium structure changes to icosahedral symmetry, or they are even hollow or planar, depending on size. The present tutorial review intends to explain the origin of this special behaviour of nanomaterials.

Journal Article↗

PubMed2005

FTIR spectroscopic study of titanium-containing mesoporous silicate materials.

The surface acidity of different mesoporous titanium-silicates, such as well-organized hexagonally packed Ti-MMM, Ti-MMM-2, Ti-SBA-15, and amorphous TiO(2)-SiO(2) mixed oxides (aerogels and xerogels), was studied by means of FTIR spectroscopy of CO adsorbed at 80 K and CD(3)CN adsorbed at 293 K. The surface hydroxyl groups of mesoporous titanium-silicates with 2-7 wt % Ti revealed a Brönsted acidity slightly higher to that of pure silicate. TiO(2)-SiO(2) xerogels revealed the highest Brönsted acidity among the titanium-silicates studied. CO adsorption revealed two additional sites on the surface in comparison to pure silicate, characterized by nu(CO) from 2185 (high pressure) to 2178 (low pressure) cm(-1) and from 2174 (high pressure) to 2170 (low pressure) cm(-1). These bands are due to CO adsorbed on isolated titanium cations in the silica surrounding or having one Ti(4+) cation in their second coordination sphere and due to CO interactions with Ti-OH groups, respectively. CD(3)CN adsorption similarly revealed the existence of two additional sites, which were not detected for pure silicate: at 2289 cm(-1) due to CD(3)CN interaction with titanol groups and from 2306 (low pressure) to 2300 (high pressure) cm(-1) due to acetonitrile interaction with isolated framework titanium cations with probably one Ti(4+) cation in their second coordination shell. The spectroscopic results are compared with computational data obtained on cluster models of titanium-silicate with different titanium content. According to the IR data, the Ti accessibility on the surfaces for mesoporous titanium-silicates with similar Ti loading (2 wt %) was found to fall in the order TiO(2)-SiO(2) aerogel approximately TiO(2)-SiO(2) xerogel > Ti-MMM approximately Ti-MMM-2 > Ti-SBA-15. This order (except TiO(2)-SiO(2) xerogel) correlates with the catalytic activity found previously for titanium-silicates in 2,3,6-trimethylphenol oxidation with H(2)O(2).

Journal Article↗

PubMed2004

Partitioning of small amphiphiles at surfactant bilayer/water interfaces: an avoided level crossing muon spin resonance study.

The temperature-dependent variation of local environment and reorientation dynamics of the small amphiphile 2-phenylethanol in lamellar phase dispersions of the dichain cationic surfactants, 2,3-diheptadecyl ester ethoxypropyl-1,1,1-trimethylammonium chloride (DHTAC) and dioctadecyldimethylammonium chloride (DODMAC), and the nonionic surfactant, tetra(ethylene glycol) n-dodecyl ether (C12E4), have been determined using avoided level crossing muon spin resonance spectroscopy (ALC-muSR). For cosurfactant radicals the hydrophobic or hydrophilic character of the surrounding media can be determined from their magnetic resonance signatures. Comparison of the three different bilayer-forming surfactant systems shows that the ALC-muSR technique is able to distinguish both major and subtle differences in the partitioning of the cosurfactant radicals between the different systems.

Electron Spin Resonance Spectroscopy↗