Effect of Mn and Fe on the reactivity of sulfated zirconia toward H2 and n-butane: a diffuse reflectance IR spectroscopic investigation

Sulfated zirconia (SZ) and sulfated zirconia promoted with 2 wt % manganese (MnSZ) or iron (FeSZ), all active in n-butane isomerization, were investigated using diffuse reflectance Fourier transform IR spectroscopy (DRIFTS). By adsorption of H(2) at 77 K or of n-butane at room temperature, it was found that the promoters neither enhance the Lewis nor the Br?nsted acid strength. SZ and promoted SZ do not exhibit higher acid strength than zeolites. In a batch experiment using 70 hPa of H(2), SZ did not react at 473 K. Reaction of H(2) with MnSZ produced water (band at 5242 cm(-1)) and a decrease in the sulfate groups (multiple bands). Heating of SZ in 10 hPa n-butane to 573 K caused total reduction of sulfate to H(2)S (2583, 2570 cm(-1)) and partial and total oxidation of butane to olefinic species (3062 cm(-1)), CO(2), and water. MnSZ and FeSZ reacted with n-butane already at 373 K; products of skeletal isomerization (methyne CH vibration at 2910 cm(-1)) were detected and sulfate groups were consumed. Rather than increasing the acidity, the promoters enhance the oxidation potential of sulfate and facilitate alkane activation via oxidative dehydrogenation.     

Elimination of residual lipid contamination in single volume proton MR spectra of human brain.

Short echo time 1H NMR spectra of the human brain reveal signals from various metabolites. In addition, resonances from macromolecules are present that may provide further useful information in several brain diseases. The detection of all these signals is possible if excellent volume selection is obtained; even small lipid contamination from surrounding fat tissue leads to strong spectral contamination. It affects the macromolecule resonances in the 0.5 to 2.0 ppm region and some adjacent metabolite signals and jeopardizes their quantitative analysis. This paper demonstrates how spatial contamination from insufficiently dephased signals can be recognized, analysed, and removed in localized STEAM spectroscopy of the brain.     

Synthesis and Characterisation of Luminescent [CrIII2L(μ-carboxylato)]3+ Complexes with High-Spin S=3 Ground States (L=N6S2 donor ligand)

The synthesis, structure, magnetic, and photophysical properties of two dinuclear, luminescent, mixed-ligand [Cr^III₂L(O₂CR)]³⁺ complexes (R=CH₃ ( 1 ), Ph ( 2 )) of a 24-membered binucleating hexa-aza-dithiophenolate macrocycle (L)²⁻ are presented. X-ray crystallographic analysis reveals an edge-sharing bioctahedral N₃Cr(μ-SR)₂(μ_1,3-O₂CR)CrN₃ core structure with μ_1,3-bridging carboxylate groups. A ferromagnetic superexchange interaction between the electron spins of the Cr³⁺ ions leads to a high-spin (S=3) ground state. The coupling constants (J=+24.2(1) cm⁻¹ ( 1 ), +34.8(4) cm⁻¹ ( 2 ), H=−2JS₁S₂) are significantly larger than in related bis-μ-alkoxido-μ-carboxylato structures. DFT calculations performed on both complexes reproduce both the sign and strength of the exchange interactions found experimentally. Frozen methanol-dichloromethane 1 : 1 solutions of 1 and 2 luminesce at 750 nm when excited into the ⁴LMCT state on the ⁴A₂ → ²T₁ (ν₂) bands (λ_exc=405 nm). The absolute quantum yields (Φ_L) for 1 and 2 were found to be strongly temperature dependent. At 77 K in frozen MeOH/CH₂Cl₂ glasses, Φ_L=0.44±0.02 (for 1 ), Φ_L=0.45±0.02 (for 2 ).     

Die chemische Verschiebung der Exomethylenprotonen von α-Methylen-cycloketonen,Konformation der Keto-Exomethylengruppe

Die durch die Anisotropie der Bindungen bedingte innere chemische Verschiebung der Exomethylenprotonen wurde in Abhängigkeit vom Rotationswinkel zwischen der Keto- und Exomethylengruppe in Dipolnäherung berechnet. Aus dem Vergleich der theoretischen Werte mit den für eine Reihe von α-Methylen-cycloketonen und 16) experimentell erhaltenen folgt, daß die Keto-Exomethylengruppe bei den Verbindungen mit n = 5, 6, 7 und 8 in einer s-cis-Konformation und bei denen mit n = 9 und 10 in einer s-trans-Konformation vorliegt. Beim α-Methylen-cyclohexadecanon (n = 16) findet eine teilweise freie Rotation statt.     

Self-Assembly and Phase Behavior of Short Chain Phosphonic Acid-Water Systems in a Wide Concentration Range Microscopic,NMR, and X-ray Diffraction Studies

The phase behavior of n-octane and n-hexane phosphonic acid-D₂O systems was studied in the concentration range from 0.1 to 90 wt.% and in a temperature range from 10° to 130°C by polarizing and dark field microscopy and by ¹H, ²D and, ³¹P NMR. Further, electron microscopy, X-ray diffraction and surface tension measurements were performed. For the first time, a widely spaced lamellar phase was observed over large concentration and temperature ranges in an essentially two-component system. By using the sonication or injection methods, unilamellar liposomes were obtained below 1 wt.%. At high temperatures, the clouding phenomenon was observed. The importance of hydrogen bond formation between polar groups for building up stable lamellae even at high dilution is stressed. The results are discussed with respect to some existing points of view concerning the possibility of lamellar structure formation from single short chain amphiphilic compounds including lipids.     

Optimization of spin-triplet supercurrent in ferromagnetic Josephson junctions

We have observed long-range spin-triplet supercurrents in Josephson junctions containing ferromagnetic (F) materials, which are generated by noncollinear magnetizations between a central Co/Ru/Co synthetic antiferromagnet and two outer thin F layers. Here we show that the spin-triplet supercurrent is enhanced up to 20 times after our samples are subject to a large in-plane field. This occurs because the synthetic antiferromagnet undergoes a "spin-flop" transition, whereby the two Co layer magnetizations end up nearly perpendicular to the magnetizations of the two thin F layers. We report direct experimental evidence for the spin-flop transition from scanning electron microscopy with polarization analysis and from spin-polarized neutron reflectometry. These results represent a first step toward experimental control of spin-triplet supercurrents.     

Analysis of some greedy algorithms for the single-sink fixed-charge transportation problem

The single-sink fixed-charge transportation problem (SSFCTP) consists of finding a minimum cost flow from a number of nodes to a single sink. Beside a cost proportional to the amount shipped, the flow cost encompass a fixed charge. The SSFCTP is an important subproblem of the well-known fixed-charge transportation problem. Nevertheless, just a few methods for solving this problem have been proposed in the literature. In this paper, some greedy heuristic solutions methods for the SSFCTP are investigated. It is shown that two greedy approaches for the SSFCTP known from the literature can be arbitrarily bad, whereas an approximation algorithm proposed in the literature for the binary min-knapsack problem has a guaranteed worst case bound if adapted accordingly to the case of the SSFCTP.     

Tissue specific resonance frequencies of water and metabolites within the human brain

Chemical shift imaging (CSI) without water suppression was used to examine tissue-specific resonance frequencies of water and metabolites within the human brain. The aim was to verify if there are any regional differences in those frequencies and to determine the influence of chemical shift displacement in slice-selection direction. Unsuppressed spectra were acquired at 3T from nine subjects. Resonance frequencies of water and after water signal removal of total choline, total creatine and NAA were estimated. Furthermore, frequency distances between the water and those resonances were calculated. Results were corrected for chemical shift displacement. Frequency distances between water and metabolites were consistent and greater for GM than for WM. The highest value of WM to GM difference (14ppb) was observed for water to NAA frequency distance. This study demonstrates that there are tissue-specific differences between frequency distances of water and metabolites. Moreover, the influence of chemical shift displacement in slice-selection direction is showed to be negligible.