While an excess of glucocorticoids is associated with hippocampal pathology in mood disorders, lithium exerts robust neuroprotective and neurotrophic effects. Here, 21 stably remitted bipolar I patients who had been on chronic lithium maintenance therapy, on average, for more than a decade, and 19 carefully matched healthy controls were studied using 3 T 1H-magnetic resonance spectroscopy of left and right hippocampus. Salivary cortisol samples were obtained to assess activity of the hypothalamus–pituitary–adrenal system. Absolute concentrations of N-acetylaspartate (NAA), choline-containing compounds and total creatine were similar in euthymic bipolar patients and healthy controls. Hippocampal glutamate concentrations were significantly increased as an effect of patient status (patients>controls) and laterality (left hippocampus>right hippocampus). Hippocampal glutamate content (Glu) was strongly correlated with NAA. Across groups and within the patient group, diurnal saliva cortisol levels showed a significant inverse relationship with both Glu and NAA. Taken together, these results add to the concept of bipolar disorder as an illness involving disturbed hippocampal structural plasticity under the opposing influences of lithium and glucocorticoids.

Aims: while lithium is accepted as the most widely used mood-stabilizer in the treatment of bipolar disorders, and even discussed as a candidate drug against cognitive deterioration, the mechanism of its action and its effect on the cognitive status remains largely speculative.

The complexation of uranium(VI) by humic acids (HAs) and fulvic acids (FAs) was studied to obtain information on the binding of uranium(VI) onto functional groups of humic substances. For this, various natural and synthetic HAs were chemically modified resulting in HAs with blocked phenolic OH groups. Both from the original and from the modified humic substances, solid uranyl humate complexes were prepared at pH 2. FTIR and extended X-ray absorption fine structure (EXAFS) spectroscopy were applied to study the chemical modification process of humic substances, to study the structure of uranyl humate complexes and to evaluate the effect of individual functional groups of humic substances (carboxylic and phenolic OH groups) on the complexation of uranyl ions. The results confirmed the predominant blocking of phenolic OH groups in the modified HAs. These modified HAs are suitable model substances to study the role of phenolic OH groups of HAs in dependence on pH. By EXAFS spectroscopy, identical structural parameters were determined for all uranyl humates. Axial UO bond distances of 1.78 Å were determined. In the equatorial plane approximately five oxygen atoms were found at a mean distance of 2.39 Å. The blocking of phenolic OH groups of HAs did not change the near-neighbor surrounding of uranium(VI) in uranyl humate complexes. Thus, the results confirmed that predominantly HA carboxylate groups are responsible for binding of uranyl ions and that the influence of phenolic OH groups is insignificant under the applied experimental conditions. The carboxylate groups are monodentate coordinated to uranyl ions.

Carbon-13 cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy ((13)C-CP/MAS-NMR) was applied to study the chemical modification process of humic acids (HA) with diazomethane and the subsequent alkaline hydrolysis of the methylated HA. This modification process results in HA with selectively blocked phenolic OH groups, which can be used for metal ion binding studies with humic substances. Different chemically modified and unmodified natural and synthetic HA with carbon-13 of natural abundance were investigated. In addition, carbon-13 labeled modified synthetic HA, that were synthesized with [(13)C]diazomethane as methylation reagent, were studied to confirm the assumed modification process and to determine the type of functional groups that have the highest affinity for methylation with diazomethane. The results of the NMR studies with carbon-13 labeled modified HA show that predominantly carboxyl and phenolic OH groups are methylated with diazomethane resulting in methyl ester and methyl ether groups, respectively. Due to the alkaline treatment of the methylated HA, the methyl esters of carboxyl groups are hydrolyzed, whereas methyl ethers of phenolic OH groups remain unchanged, which results in modified HA with blocked phenolic OH groups. From the spectra of the modified and unmodified HA with carbon-13 of natural abundance it can be concluded that the applied preparative modification procedure causes only the desired structural changes in HA.

Dipole excitations in the semimagic N=50 nucleus Rb-87 were investigated at the Stuttgart Dynamitron facility using bremsstrahlung with an end-point energy of 4.0 MeV. The widths Gamma or the reduced excitation probabilities B(Pi1)up arrow of 18 states were determined for the first time. The magnetic dipole excitations are well reproduced in the framework of the shell model, however, these calculations cannot describe the observed electric dipole excitations. The 1/2(+) state at 3060 keV is proposed to be the weak coupling of an f(5/2) proton hole to the 3(-) octupole vibrational state in the N=50 core Sr-88. The relatively strong E1 transition from that state to the ground state is explained as mainly the neutron h(11/2)-->g(9/2) transition. The breakup of the N=50 core and neutron excitations into the h(11/2) shell are essential to describe electric dipole excitations, but neutron-core excitations do not play an important role for the structure of magnetic dipole excitations.

[1,2-14C]TCA of a high specific activity (3.7 GBq/mmol) and appropriate radioindicator techniques were used, to study the effect of trichloroacetic acid (TCA) on conifers. Easy uptake of TCA from soil through spruce roots and its further translocation by the transpiration stream up to the needles (where damage of the photosynthetic apparatus occurs) has been proved. During the growth period, after one-shot load of TCA, the uptake was most intensive in current-year needles at first; over an extended period a decrease in the level of [1,2-14C]TCA-derived radioactivity was found in the current-year needles while in older needles (C + 2), the level rose. Symptoms of TCA biodegradation and/or metabolism were found in the plant/soil system under study. During an eight-week exposure significant losses of radioactivity into the atmosphere were noticed, at least a part of them in the form of carbondioxide. The results of these more or less preliminary experiments demonstrated the suitability and advantages of the radioisotopic technique used.

The cation exchange in uranyl (UO22+) and iron (Fe3+) humates is studied. At large Fe3+ concentrations, these ions are not exchanged for uranyl ions. However, even at large uranyl concentrations, Fe3+ ions can substitute for uranyl in its complexes with natural humic acid (NHA). X-ray photoelectron spectroscopy evidence shows that Fe3+ ions are more prone to complex formation at the surface of NHA grains than uranyl ions. This prevents the diffusion of uranyl ions into NHA grains and, hence, the formation of uranyl complexes with NHA.

A growing interest in the phytotoxic effects of trichloroacetic acid (TCA) has led us to develop a small-scale (< 1 mmol) one-pot synthesis of [1,2-C-14]TCA with > 70% yield and specific activity of 3.7 GBq/mmol. Copyright (C) 2001 John Wiley & Sons, Ltd.

We studied the influence of humic acid (HA) on the uranium(VI) sorption onto the rock material phyllite and onto its main mineral constituents quartz, muscovite, chlorite, and albite at an ionic strength of 0.1 M in the pH range of 3.5 to 9.5 under aerobic conditions. The uranium(VI) concentration was 1 × 10-6M and the HA concentration was 5 and 60 mg/L, respectively. The solid/solution ratio was 12.5 g/L. Furthermore, we studied the uranium and HA sorption on ferrihydrite (3 × 10-4M Fe) and compared the results to the sorption behavior of phyllite. The study showed that the uranium sorption onto phyllite and onto its mineral constituents is influenced by the pH-dependent sorption behavior of the HA. Due to high HA sorption onto the solids in the acidic pH range the uranium uptake is enhanced compared to the uranium uptake in the absence of HA. A high concentration of dissolved HA in the near-neutral pH range reduces the uranium sorption due to formation of aqueous uranyl humate complexes. Furthermore, we could show that the high uranium and HA sorption on phyllite is primarily caused by minor amounts of the secondary mineral ferrihydrite that is formed due to weathering of phyllite. Thus, the ferrihydrite predominates the contributions of the main minerals quartz, muscovite, chlorite, and albite, that are naturally present in the rock material phyllite.

We investigated the influence of phenolic OH groups on the complexation behavior of humic acid (HA) with UO22+ions at pH 4. Starting from synthetic HA type M1, natural HA Aldrich, and natural HA Kranichsee, we synthesized modified HAs with blocked phenolic OH groups by derivatization with diazomethane. The partial blocking of phenolic OH groups was confirmed by a radiometric method which quantitatively determined the functional groups and by FTIR spectroscopy. The complexation behavior of the chemically modified and unmodified HAs with UO22+ions was investigated by time-resolved laser-induced fluorescence spectroscopy. The experimental data were evaluated with the metal ion charge neutralization model. We determined comparable complexation constants for all HAs. Two modified HAs (type M1 and Aldrich) had significantly lower loading capacities for UO22+ions (10.5 ± 0.9% and 9.7 ± 1.6%, respectively) than the corresponding unmodified HAs 18.0 ± 2.0% and 17.5 ± 1.6%, respectively). This indicates that the blocking of the phenolic OH groups changes the complexation behavior of HAs.

Complexes of U(VI) and Fe(III) with natural humic acid (NHA) were studied by X-ray photoelectron spectroscopy (XPS). It follows from the analysis of the uranium and iron concentrations at the surface and in the bulk of the humates that the reaction in solution is heterogeneous. The NHA reacts as a particle. In solutions containing either U(VI) or Fe(III), NHA reacts similar with Fe(III) and U(VI). However, in a mixed solution of Fe(III) and U(VI), NHA reacts predominantly with iron. In comparison to Fe(III) complexes, the complexes with U(VI) are formed mostly in the inner of the NHA particle. Therefore, the concentration ratio U/Fe as measured by XPS increases by powdering of the particles. Salts of Fe(III) can be used to inhibit the uranium migration in form of its soluble humates.

Complexes of uranyl UO(2)(2+) and Fe(III) with natural humic acid (NHA) were synthesized. The reaction is heterogeneous, the NHA reacting as a particle. The concentrations of the elements on the surface and inside this particle are different. In the absence of iron, uranyl reacts with NHA more completely than Fe(III) with NHA in the absence of uranyl. However, in the joint reaction of NHA with Fe(III) and uranyl, the NHA preferentially forms complexes with Fe(III). The UO(2)(2+) complexes in comparison with the Fe(III) complexes are preferentially formed inside the NHA; consequently, when the particles are ground, the U/Fe concentration ratio is increased. Accordingly, Fe(III) salts may be used to prevent migration of uranyl in the form of soluble complexes with NHA. Natural humic acid and its complexes also contain small amounts of sulfate and RSH-type groups, the sulfate/sulfide ratio on the surface being 0.5, but the ratio decreases by a factor of two after grinding the particles. The NR(2) group in the complex is found mainly in the ionic form HN R(2)(+).

Natural humic acids, HA`s, having varying amounts of their proton exchange capacities, PEC`s, loaded with uranyl ions and synthetic HA loaded with 14% PEC were prepared either from solution or from suspension. The interaction of uranium with the humates was studied using U L{sub III}-edge extended X-ray absorption fine structure, EXAFS, and infrared, IR, spectroscopy. IR results indicate a direct complexation of the uranyl ions onto the HA`s. The spectral positions of the asymmetric and symmetric IR stretching frequencies for COO{sup -} in the complex suggest monodentate coordination of HA carboxylate groups onto the uranyl cation. In all samples studied, the EXAFS analysis yielded axial uranium-oxygen distances of 1.77-1.78 A and five oxygen atoms in the plane equatorial to the uranyl unit at distances of 2.37-2.39 A. The bond distances determined from the EXAFS are the same, within the experimental error, for both synthetic and two different natural uranyl humates, for samples with large loadings and samples with relatively low uranyl loadings, as well as for dry and wet paste samples. Comparison of the EXAFS from the uranyl humates with that observed for two crystalline uranyl carboxylate complexes indicates that the HA carboxylate groups act predominantly as monodentate ligands when bound to the uranyl unit. Additional, neutral ligands must also be coordinated to the uranyl ion in order to satisfy the uranyl cation coordination number determined as 5 {+-} 0.7. (orig.)

We have investigated the complexation behavior of natural humic acids (HA) with model substances. Our synthetic HA model substance, prepared from glutamic acid and xylose, shows operational properties comparable to those of natural HA in terms of water solubility at different pH and in the type and number of its functional groups. We investigated its complexation behavior with the U O r ion by time-resolved laser-induced fluorescence spectroscopy. For comparison, we used purified natural HA from Fluka and Aldrich. The experimental data were evaluated applying the metal ion charge neutralization model developed by Kim and Czerwinski. For our synthetic product, we determined a loading capacity of 23 ± 4% and a complexation constant of log β = 6.16 ± 0.22 (pH 3.90 ± 0.05; / : 0.1 Μ NaC104). The obtained values are comparable with experimental results determined for Fluka and Aldrich HA. These results lead to the conclusion that our synthetic product appropriately models the functionality of natural HA.

Two compounds of known crystal structure, sodium triacetatodioxouranium(VI), Na[UO2(CH3COO)3], and dibenzoatodioxouranium(VI), UO2[C6H5(COO)]2, were studied by uranium LIII-edge extended X-ray absorption fine structure, EXAFS, spectroscopy to differentiate between bidentate and monodentate coordination of carboxylate ions on the basis of the uranium–equatorial oxygen, Oeq, bond lengths. Bidentate coordination can be verified by detecting carboxyl carbon atoms and the neighboring distal carbon atom of the organic rest. In contrast, EXAFS spectra for monodentate carboxylate complexes show no evidence of carbon atoms beyond the Oeq coordination shell. The mode of coordination was determined by EXAFS analysis for solid uranyl complexes with humic, methoxybenzoic, and salicylic acids. A correlation between the U LIII-edge X-ray absorption near-edge structure, XANES, and the U–Oeq bond distance according to the relationship ΔE·R(Oeq)2=constant was observed. For the samples studied, the constant was determined to be 197±8 eV Å2.

Surface complexes of uranyl and calcium ions with solid humic acid were studied by electron spectroscopy for chemical analysis (ESCA). Uranyl-, calcium-, and mixed uranyl-calcium-humates were prepared. The uranium and calcium concentrations were determined both in the bulk and at the surface of the humates. The atomic ratio U/Ca is larger at the surface than in the bulk. The interatomic distances (U—O)ax and (U—O)cq around the uranium atom in humates were determined. The differences in the concentration of functional groups and in complexation are discussed for two types of humic acid.

Fluka humic acid having 87, 35, 10, and 8 percent of its proton exchange capacity, % PEC, loaded with uranyl ions and synthetic humic acid loaded with 14% PEC were prepared either from solution or from suspension. The interaction of uranium with the humic acids was studied using U L-m-edge extended X-ray absorption fine structure, EXAFS, and infrared, IR, spectroscopy. IR results indicate complexation of the uranyl ions onto the humic acid carboxylic groups. The uranium-oxygen (U-O) bond distances determined from the EXAFS analysis are the same, within the experimental error, for both synthetic and natural uranyl humates, for samples with large loadings and samples with relatively low uranyl loadings, as well as for dry and wet paste samples. In all samples studied, axial U-O distances of 1.77-1.78 Angstrom and five equatorial oxygen atoms at distances of 2.37-2.39 Angstrom were found. Comparison of the equatorial bond distances to those for Various uranyl carboxylates reported in the literature indicates that the humic acid carboxylate groups act predominantly as monodentate ligands when bound to the uranyl unit. Additional, neutral ligands must also be coordinated to the uranyl ion in order to satisfy the uranyl cation coordination number determined as five.

We have investigated the U L-III-edge EXAFS of two carboxylato uranyl complexes of known structure to explore the possibilty of differentiating between monodentate and bidentate coordinated carboxylate ions. The interpretation of EXAFS results from uranyl complexes with carboxylate ions based solely on axial and equatorial bond lengths can be inconclusive; information from further-distant shells is often needed. Multiple scattering (MS) pathways along the O=U=O unit and in coordinating chelating or monodentate carboxylate groups can make substantial contributions to the EXAFS. Therefore, MS pathways were calculated using FEFF6 [1] and considered in the data analysis. EXAFS results are compared to XRD data reported in the literature.