Reference spectra of important adsorbed organic and inorganic phosphate binding forms for soil P speciation using synchrotron‐based K‐edge XANES spectroscopy

Direct speciation of soil phosphorus (P) by linear combination fitting (LCF) of P K‐edge XANES spectra requires a standard set of spectra representing all major P species supposed to be present in the investigated soil. Here, available spectra of free‐ and cation‐bound inositol hexakisphosphate (IHP), representing organic P, and of Fe, Al and Ca phosphate minerals are supplemented with spectra of adsorbed P binding forms. First, various soil constituents assumed to be potentially relevant for P sorption were compared with respect to their retention efficiency for orthophosphate and IHP at P levels typical for soils. Then, P K‐edge XANES spectra for orthophosphate and IHP retained by the most relevant constituents were acquired. The spectra were compared with each other as well as with spectra of Ca, Al or Fe orthophosphate and IHP precipitates. Orthophosphate and IHP were retained particularly efficiently by ferrihydrite, boehmite, Al‐saturated montmorillonite and Al‐saturated soil organic matter (SOM), but far less efficiently by hematite, Ca‐saturated montmorillonite and Ca‐saturated SOM. P retention by dolomite was negligible. Calcite retained a large portion of the applied IHP, but no orthophosphate. The respective P K‐edge XANES spectra of orthophosphate and IHP adsorbed to ferrihydrite, boehmite, Al‐saturated montmorillonite and Al‐saturated SOM differ from each other. They also are different from the spectra of amorphous FePO₄, amorphous or crystalline AlPO₄, Ca phosphates and free IHP. Inclusion of reference spectra of orthophosphate as well as IHP adsorbed to P‐retaining soil minerals in addition to spectra of free or cation‐bound IHP, AlPO₄, FePO₄ and Ca phosphate minerals in linear combination fitting exercises results in improved fit quality and a more realistic soil P speciation. A standard set of P K‐edge XANES spectra of the most relevant adsorbed P binding forms in soils is presented.     

Hierarchical Layer Engineering Using Supramolecular Double‐Comb Diblock Copolymers

The formation of unusual multilayered parallel lamellae‐in‐lamellae in symmetric supramolecular double‐comb diblock copolymers is presented. While keeping the concentration of surfactant fixed, the number of internal layers was found to increase with molecular weight M up to 34 for the largest block copolymer. The number of internal structures n was established to scale as M^0.67 and therefore enables easy design of such structures with great precision.     

Uptake of silver nanoparticles by monocytic THP-1 cells depends on particle size and presence of serum proteins

Human health risks by silver nanoparticle (AgNP) exposure are likely to increase due to the increasing number of NP-containing products and demonstrated adverse effects in various cell lines. Unfortunately, results from (toxicity) studies are often based on exposure dose and are often measured only at a fixed time point. NP uptake kinetics and the time-dependent internal cellular concentration are often not considered. Macrophages are the first line of defense against invading foreign agents including NPs. How macrophages deal with the particles is essential for potential toxicity of the NPs. However, there is a considerable lack of uptake studies of particles in the nanometer range and macrophage-like cells. Therefore, uptake rates were determined over 24 h for three different AgNPs sizes (20, 50 and 75 nm) in medium with and without fetal calf serum. Non-toxic concentrations of 10 ng Ag/mL for monocytic THP-1 cells, representing realistic exposure concentration for short-term exposures, were chosen. The uptake of Ag was higher in medium without fetal calf serum and showed increasing uptake for decreasing NP sizes, both on NP mass and on number basis. Internal cellular concentrations reached roughly 32/10 %, 25/18 % and 21/15 % of the nominal concentration in the absence of fetal calf serum/with fetal calf serum for 20-, 50- and 75-nm NPs, respectively. Our research shows that uptake kinetics in macrophages differ for various NP sizes. To increase the understanding of the mechanism of NP toxicity in cells, the process of uptake (timing) should be considered.     

Infrared spectrum of 4-methoxypicolinic acid N-oxide: computation of asymmetric O-H stretching band

In this article we studied the strong intramolecularly hydrogen-bonded system 4-methoxypicolinic acid N-oxide. The potential energy surface V = V(rOH,rOO) and the corresponding dipole moment function were calculated using the DFT B3LYP/6-31+G(d,p) level of approximation. The time-independent vibrational Schr?dinger equation was solved using a rectangular grid basis set and shifted Gaussian basis set. The vibrational spectrum and metric parameters were also calculated. Effects of deuteration were considered. The calculated vibrational spectra were compared with the experimental spectra. The vibrational transition corresponding to asymmetric O-H stretching that occurs at about 1400 cm-1 compares well with the experimentally assigned O-H asymmetric stretching band centered at 1380 cm-1. The corresponding asymmetric O-D stretching band was predicted to be at 1154 cm-1, while the experimental O-D band was not assigned due to its very low intensity. Several overtones and hot transitions of significant intensities were located in the vicinity of the fundamental O-H stretching frequency, effectively broadening the infrared absorption attributed to the O-H stretching mode. This is in a good agreement with the observed broad protonic absorptions found in the infrared spectra of the title compound and its analogs. We have shown that the Gaussian basis set is the method of choice for a two-dimensional vibrational problem that requires several hundreds of vibrational basis functions and when high accuracy of the eigenvalues is required or when extending the calculations to more vibrational degrees of freedom. We have also demonstrated that for a large number of basis functions the Gramm-Schmidt orthogonalization procedure outperforms symmetric and canonical orthogonalization schemes.     

Alpha-substituted organic peroxides: synthetic strategies for a biologically important class of gem-dihydroperoxide and perketal derivatives

In this paper we review the recent developments in the synthesis of alpha-substituted hydroperoxides. Alpha-substituted hydroperoxides are interesting compounds due to their chemistry and bioactivity and as intermediates for the synthesis of other peroxides, of which cyclic peroxides are of major importance. Although the emphasis of this report will be on the derivatives of gem-dihydroperoxides, perketals, as well as the less studied nitrogen and sulfur derivatives, will also be covered.     

Virtually epimerization-free synthesis of peptide-alpha-thioesters

Under slightly basic or neutral reaction conditions peptide-alpha-thioesters are photochemically synthesized from peptide-alpha-nitroindoline precursors, either in solution, or by direct photorelease from a solid support.     

Crystal structure, electronic structure, and physical properties of Ti1-deltaMo1+deltaAs4 and Ti1-deltaMo1+deltaSb4

The new ternary pnictides, Ti(1-delta)Mo(1+delta)Pn4 (Pn = As, Sb), were uncovered during our search for novel thermoelectric materials. Both compounds crystallize in the OsGe2 type in the monoclinic space group C2/m, with lattice dimensions of a = 10.1222(9) A, b = 3.6080(3) A, c = 8.1884(8) A, beta = 120.230(2) degrees , and V = 258.38(7) A3 (Z = 2) for Ti(0.79(1))Mo(1.21)Sb4 and a = 9.1580(2) A, b = 3.3172(1) A, c = 7.6666(1) A, beta = 119.496(1) degrees , and V = 202.720(4) A3 (Z = 2) for Ti(0.86(2))Mo(1.14)As4. The electronic structure calculations predicted metallic behavior for these compounds, which was in agreement with the measured temperature dependence of the electrical conductivity and Seebeck coefficient.     

Influence of the methacrylate monolith structure on genomic DNA mechanical degradation, enzymes activity and clogging

The chromatography of mechanically sensitive macromolecules still represents a challenge. While larger pores can reduce the mechanically induced cleavage of large macromolecules and column clogging, the column performance inevitably decreases. To investigate the effect of pore size on the mechanical degradation of DNA, column permeability and enzyme biological activity, methacrylate monoliths with different pore sizes were tested. Monolith with a 143 nm pore radius mechanically damaged the DNA and was clogged at flow rates above 0.5 ml min(-1) (26 cm h(-1)). For monoliths with a pore radius of 634 nm and 2900 nm, no mechanical degradation of DNA was observed up to 5 ml min(-1) (265 cm h(-1)) above which the HPLC itself became the main source of damage. A decrease of a permeability appeared at flow rate 1.8 ml min(-1) (95 cm h(-1)) and 2.3 ml min(-1) (122 cm h(-1)), respectively. The effect of the pore size on enzyme biological activity was tested with immobilized DNase and trypsin on all three monoliths. Although the highest amount of enzyme was immobilized on the monolith with the smallest pores, monolith with the pore radius 634 nm exhibited the highest DNase biological activity probably due to restricted access for DNA molecules into the small pores. Interestingly, specific biological activity was increasing with a pore size decrease. This was attributed to higher number of contacts between a substrate and immobilized ligand.     

Trace analysis of surfactants using chromatographic and electrophoretic techniques

Because of the widespread use, increased application of new formulations and immense impact on organisms and ecology surfactants are still in the focus of analytical chemistry. The development of methods with higher selectivity and lower detection limits is important to meet the requirements of greater responsibility for health of people and environment. Efficient separation methods, like HPLC, GC and CE, in combination with sensitive detection, like MS, are to be preferred over collective techniques which can suffer from interfering components. A review on trace analysis of ionic and neutral surfactants including sample preparation steps is presented, considering especially those methods which provide information about homologous and isomeric distribution of surfactant mixtures. Examples for the determination of linear alkylbenzene sulfonates in river water by HPLC and CE are discussed to show the capability of these methods for environmental analyses. As future trends increased applications of LC/MS (very high sensitivity) and also of CE (robustness and possibility for rapid method development) can be predicted. Received: 30 July 1998 / Revised: 28 October 1998 / Accetped: 1 November 1998     

Mevalonate-Independent Biosynthesis of Terpenoid Volatiles in Plants: Induced and Constitutive Emission of Volatiles

Terpenoids from flower and leaf volatiles are predominantly synthesized along the mevalonate-independent pathway, as shown by administration of [D₂]deoxy-D -xylulose and [D₅]mevalolactone. The parallel use of two pathways for the biosynthesis of the sesquiterpenoid-derived 4,8-dimethylnona-1,3,7-triene (DMNT, see picture) may be important to ensure the synthesis of the volatile alarm codes of plants.