Institute for Radiochemistry

Garching bei Munchen, Germany

Institute for Radiochemistry

Garching bei Munchen, Germany
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The analysis of structures in crystal chemistry is mainly based on geometric parameters such as distances, coordination numbers and connectivity of polyhedral constituents. We thereby venture to define sizes and even charges of ions based on a large data set of distances, and we compile them in tables of radii. In turn we allocate charges by comparison of such “sizes”. Quantum chemical approaches offer a direct path to such an analysis by presenting electron densities, force constants, energies etc. In this paper we present the results of DFT calculations combined with a Bader analysis of the electron densities, and we compare the results of charge allocation by both approaches in the series of Ti-O compounds where already the geometric description seems to drum home the information. We point out that a comparison of distances alone can be misleading in the attempt to localize different charges of ions. The pattern of distances and seeming sizes is severely influenced by the topology of catenation of coordination polyhedra. © 2017 Elsevier Masson SAS

Vukics V.,University of Innsbruck | Guttman A.,University of Innsbruck | Guttman A.,Institute for Radiochemistry
Mass Spectrometry Reviews | Year: 2010

Flavonoids are secondary plant metabolites of great structural variety and high medicinal significance. The search for new chemical entities and the quality control of flavonoid containing natural products require easy-to-use but reliable and robust analytical methodologies. For structural elucidation of flavonoids and their glycosides, nuclear magnetic resonance (NMR) and mass spectroscopy (MS) are the generally used techniques. In phytochemical analyses, however, high amounts of flavonoids are difficult to isolate for NMR, thus low sample volume requiring MS based methods are emerging. This review summarizes and compares currently available methods for structural elucidation of flavonoids by LC-MS and LC-MSn, and focuses on the identification options of unknown flavonoid glycosides in complex samples (e.g., plant extracts) with the emphasis on the differentiation of isomeric compounds. © 2008 Wiley Periodicals, Inc.,.

Rainer M.,Institute for Radiochemistry | Qureshi M.N.,Institute for Radiochemistry | Bonn G.K.,Institute for Radiochemistry
Analytical and Bioanalytical Chemistry | Year: 2011

The application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) for the analysis of low molecular weight (LMW) compounds, such as pharmacologically active constituents or metabolites, is usually hampered by employing conventional MALDI matrices owing to interferences caused by matrix molecules below 700 Da. As a consequence, interpretation of mass spectra remains challenging, although matrix suppression can be achieved under certain conditions. Unlike the conventional MALDI methods which usually suffer from background signals, matrix-free techniques have become more and more popular for the analysis of LMW compounds. In this review we describe recently introduced materials for laser desorption/ionization (LDI) as alternatives to conventionally applied MALDI matrices. In particular, we want to highlight a new method for LDI which is referred to as matrix-free material-enhanced LDI (MELDI). In matrix-free MELDI it could be clearly shown, that besides chemical functionalities, the material's morphology plays a crucial role regarding energy-transfer capabilities. Therefore, it is of great interest to also investigate parameters such as particle size and porosity to study their impact on the LDI process. Especially nanomaterials such as diamond-like carbon, C 60 fullerenes and nanoparticulate silica beads were found to be excellent energy-absorbing materials in matrix-free MELDI. © 2010 Springer-Verlag.

Schmeide K.,Institute for Radiochemistry | Bernhard G.,Institute for Radiochemistry
Applied Geochemistry | Year: 2010

The sorption of Np(V) and Np(IV) onto kaolinite has been studied in the absence and presence of humic acid (HA) in a series of batch equilibrium experiments under different experimental conditions: [Np]0: 1.0×10-6 or 1.0×10-5M, [HA]0: 0 or 50mg/L, I: 0.01 or 0.1M NaClO4, solid to liquid ratio: 4g/L, pH: 6-11, anaerobic or aerobic conditions, without or with carbonate. The results showed that the Np(V) sorption onto kaolinite is affected by solution pH, ionic strength, Np concentration, presence of carbonate and HA. In the absence of carbonate, the Np(V) uptake increased with pH up to ∼96% at pH 11. HA further increased the Np(V) sorption between pH 6 and 9 but decreased the Np(V) sorption between pH 9 and 11. In the presence of carbonate, the Np(V) sorption increased with pH and reached a maximum of 54% between pH 8.5 and 9. At higher pH values, the Np(V) sorption decreased due to the presence of dissolved neptunyl carbonate species with a higher negative charge that were not sorbed onto the kaolinite surface which is negatively charged in this pH range. HA again decreased the Np(V) uptake in the near-neutral to alkaline pH range due to formation of aqueous neptunyl humate complexes. The decrease of the initial Np(V) concentration from 1.0×10-5M to 1.0×10-6M led to a shift of the Np(V) adsorption edge to lower pH values. A higher ionic strength increased the Np(V) uptake onto kaolinite in the presence of carbonate but had no effect on Np(V) uptake in the absence of carbonate.To the best of the authors' knowledge, this is the first study on the sorption of Np(IV) onto kaolinite in the presence of HA. For this, a synthetic HA with pronounced reducing properties was applied. This HA effectively reduced Np(V) to Np(IV) and stabilized the tetravalent oxidation state during sorption experiments over a wide pH range. The Np(IV) uptake onto kaolinite is strongly affected by HA. Especially in the near-neutral pH range the Np(IV) uptake was found to be very low in the presence of HA which was attributed to the strong Np(IV) humate complexation in solution. Thus, depending on the prevailing geochemical conditions, HA has an immobilizing as well as a mobilizing effect on Np(V). In the case of Np(IV), the mobilizing effect predominates. © 2010 Elsevier Ltd.

Huck C.W.,Institute for Radiochemistry
Journal of Pharmaceutical and Biomedical Analysis | Year: 2014

During the last couple of years great advances in vibrational spectroscopy including near-infrared (NIR), mid-infrared (MIR), attenuated total reflection (ATR) and imaging and also mapping techniques could be achieved. On the other hand spectral treatment features have improved dramatically allowing filtering out relevant information from spectral data much more efficiently and providing new insights into the biochemical composition. These advances offer new possible quality control strategies in phytomics and enable to get deeper insights into biochemical background in terms of medicinal relevant questions. It is the aim of the present article pointing out the technical and methodological advancements in the NIR and MIR field and to demonstrate the individual methods efficiency by discussing distinct selected applications. © 2013 Elsevier B.V.

Humic acid (HA) model substances with pronounced redox functionality were synthesized by oxidation of hydroquinone or catechol in the presence of glycine or glutamic acid and characterized concerning their elemental, structural and functional properties. In order to characterize the redox properties of the synthetic products, formal redox potentials and Fe(III) reducing capacities were determined and compared to purified Aldrich HA (AHA). Furthermore, the reduction of U(VI) in the presence of HA was studied.The synthetic products show elemental, functional and structural properties comparable to natural HA, however, they are characterized by high amounts of phenolic/acidic OH groups (5.3-6.6meq/g). Furthermore, the synthetic HA show significantly higher reducing capacities for Fe3+ and [Fe(CN)6]3- at pH 3.0 (8.8-14.5meq/g) and at pH 9.2 (27.5-36.9meq/g), respectively, than AHA (pH 3.0: 1.2±0.1meq/g; pH 9.2: 7.2±1.9meq/g). The highest reducing capacities were obtained for HA Cat-Gly (pH 3.0: 14.5±1.6meq/g; pH 9.2: 36.9±0.2meq/g), an oxidation product from catechol and glycine, which is characterized by the lowest formal redox potential (E0*=517±12mV) of all studied HA (E0*=517-571mV). Indications for a slight reduction of U(VI) in the presence of HA were observed, whereby, HA Cat-Gly exhibits again the highest reducing capacity (pH 6: 0.065±0.002meq/g). Using modified HA with blocked phenolic/acidic OH groups the importance of these functional groups for the redox behavior of HA was confirmed.Synthetic HA with pronounced redox functionality can be used to study the redox behavior of HA and the redox stability of metal ions in the presence of HA and furthermore, to stabilize redox-sensitive metal ions against oxidation in complexation and transport studies with HA. This contributes to a better understanding of interaction processes of metal ions with humic substances in soils, sediments and waters. © 2011 Elsevier B.V.

Starting from known structures of the modifications of As2O5 we investigate the results of relaxations in DFT calculations performed at different fixed volumes per formula unit on keeping the axis relations and the symmetry of the original space group. We analyse the correlation between the topology of a structure, i.e. the co-ordination geometry and the distances observed, with the charges of the atoms as derived form a Bader analysis of the electron distribution resulting from a DFT relaxation. A similar study is done on the changes of the structure and the charges as a result of a relaxation without such a symmetry bias giving a new hitherto unknown possible high pressure structure. © 2015 Elsevier Masson SAS. All rights reserved.

Beck H.P.,Institute for Radiochemistry
Zeitschrift fur Kristallographie | Year: 2012

The crystal chemistry of many AB2O6 compounds is summarized in family trees comparing the crystal symmetry of several structures in group-subgroup relations. In this second part of a series the largest family derived from a hexagonally close packed arrangement of anions is described. On reducing the symmetry, different choices of octahedral sites for A and B cations and voids lead to four branches - the Rosiaite-, the ZnTa2O 6-, the columbite- and the rutile-branch. We trace the reasons for the specific distribution patterns of the cations in the individual compounds by comparing long range contributions, i.e. the Madelung Part of Lattice Energy (MAPLE), and local effects represented by bond valence calculations according to I. D. Brown. Long range effects largely determine the choice of sites in the respective space groups, however, small local adjustments play a decisive role for the stability of a specific structural modification. Such mechanismsultimately impose how the structure of an individual compound deviates from an ideally packed arrangement. We discuss the difference between the ideal structures and the real examples given in the family tree by defining a sort of deformation tensor and a measure of similarity, and we describe and depict the anisotropic deformation by a strain tensor. © by Oldenbourg Wissenschaftsverlag, Müchen.

Viehweger K.,Institute for Radiochemistry | Geipel G.,Institute for Radiochemistry
Environmental and Experimental Botany | Year: 2010

Comparisons of uranium (U) accumulation and tolerance were conducted in terrestrial versus laboratory trials using an endemic, on a former U mining site growing Arabidopsis halleri. Sequential extractions of soil samples pointed out a correlation between the low bioavailability of the micronutrient iron and the uptake of the non-essential U. A prerequisite for the uptake of iron occurring mostly as Fe(III) oxides and hydroxides in this habitat is the reduction to Fe(II) at the root surface. This could be accompanied by a reduction of U because a similar reduction of U(VI) to U(IV) took place as it was shown by photoacoustic measurements. Arabidopsis plants growing in their native habitat accumulated ∼35 mg kg-1 (dry weight) U in roots and ∼17 mg kg-1 (dry weight) U in shoots. Concerning only the probable bioavailable U, the soil-to-plant transfer factor (TF) was around 1.2 for roots and 0.6 for shoots, respectively However, the uptake of hydroponically grown plants (laboratory trials) were 100-fold more in roots and 10-fold more in shoots compared with the native grown plants. This drastic increased U accumulation could be attributed to iron deficiency of hydroponically grown plants. To get more insights in mechanisms of U tolerance the tolerance index (TI) was calculated using root elongation measurements. In addition to this some impacts on basic photosynthetic traits, e.g. the chlorophyll content, were investigated. The chlorophyll a/b ratio was around 7 in native grown plants whereas the ratio of hydroponically grown dropped during the growth cycle due to the above mentioned lack of iron. Fluorescence spectra of chlorophyll extracts from U containing leaves revealed an additional peak assignable to a flavonoid. Thus, the reported data are a further indication that a deficiency of an essential metal can facilitate the uptake of non-essential metal. © 2010 Elsevier B.V. All rights reserved.

Kautenburger R.,Institute for Radiochemistry
Journal of Analytical Atomic Spectrometry | Year: 2011

Geological clay formations are often considered as a host rock for a future waste repository. Many studies concerning sorption or desorption experiments of radionuclides or other toxic metals onto/from geological samples like clay are performed with batch techniques where only small amounts of the homogenised clay samples are in contact with the appropriate metals diluted in high volumes of aqueous solutions. This can lead to a high leaching of metal ions originating from the clay. The leached elements can considerably increase the background concentration of many isotopes, and they may also influence the results of the sorption/desorption experiments due to their competition with the used metal ions. This study focuses on this problem by analysing element leaching of clay during the batch procedure. After characterisation of the used Opalinus clay (OPA), element leaching was performed by extraction of homogenised clay samples from a bore hole with two different leaching solutions, Milli-Q water and, in contrast, synthetic porewater (PW) with a high ionic strength. After centrifugation, the leached elements in the supernatant were analysed by inductively coupled plasma-mass spectrometry (ICP-MS). Depending on the used extraction solution different elemental compositions in the leachate can be determined. The leaching of OPA with Milli-Q water leads to a dissolution of mainly anionic element species, whereas the use of PW leads to a release of mainly cationic metal ions. In particular, metals like Al, Fe, V, Cr, Co, Ni, Sr, Ba and U (beside the present PW ions) can be found in the leachates. © 2011 The Royal Society of Chemistry.

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