Velocity measurements in liquid sodium by means of ultrasound Doppler velocimetry

A successful application of ultrasound Doppler velocimetry in liquid sodium flows is described. To obtain sufficient Doppler signals, different problems had to be solved: the transmission of the ultrasonic beam through the channel wall made of stainless steel, the acoustic coupling between the transducer and the channel wall, and the wetting of the inner surface of the wall by the liquid metal, respectively. A sodium flow in a square duct exposed to a transverse magnetic field is investigated. In accordance with the existing knowledge about MHD channel flows, we found that the velocity profiles modified to a M-shape owing to the effect of an inhomogeneous magnetic field. Received: 12 June 2001/Accepted: 27 October 2001     

Symbolic squares in regular local rings

In this paper we prove for several classes of ideals in regular local rings of equicharacteristic 0 that the symbolic square of the ideal contains no minimal generator of the ideal. Our techniques come from residual intersections, integral closures of ideals, and differentials. Received January 14, 1997; in final form March 20, 1997     

COSMO-RS: A novel view to physiological solvation and partition questions

Both, dielectric continuum solvation models as well as surface or group based methods using polarity and lipophilicity parameters have been proven to be useful tools for the analysis of solvation and partition questions. For the first time, COSMO-RS provides an integrated theory, which combines the aspects of continuum solvation and surface interactions, and which ends up with chemical potentials of molecules in almost arbitrary solvents and mixtures. Due to its sound theoretical basis, COSMO-RS does not only provide a new quantitative access to solvation and partition properties in well defined solvents, but it also opens a novel view and gives a better understanding of the general problem of solvation. Finally, this allows for a generalisation of COSMO-RS to sophisticatedphysiological partition problems involving as complex phases as blood, brain, or cell membranes. The use of COSMO-RS for drug discovery and design is demonstrated by applications to blood-brain partition coefficients, and water solubility.     

PHOTOCHEMISTRY OF THE REACTION CENTERS OF SYSTEM II UNDER REPETITIVE FLASH GROUP EXCITATION IN ISOLATED CHLOROPLASTS

Abstract— Absorption changes induced in isolated chloroplasts by excitation with repetitive flash groups have been measured at 690 nm, indicating the photochemical turnover of chlorophyll-a_II (Chl-αn), and at 480 nm and 513 nm respectively, reflecting via electrochromic effect the formation of a transmembrane electric field. The data are compared with measurements of oxygen evolution. In chloroplasts with practically fully intact oxygen evolving capacity it was found: 1. The initial amplitude of the 690 nm absorption change induced by the second flash as a function of the time t_v between the first and second flash of a group increases with a half life of about 35 µs. On the other hand, the average oxygen yield due to the second flash as a function of the time t_v rises with a half life of about 600 µs (and a kinetics in the ms-range of minor extent), confirming the data of Vater et al. (1968). 2. Under far red background illumination, where contributions due to PS I in the µs-range can be excluded, the difference spectrum in the red of the absorption changes induced by the first flash corresponds with that of the absorption changes induced by the second flash fired 200 µ after the first flash. 3. The pattern of the absorption changes at 690 nm induced by repetitive double flash groups at t_v= 200 µs does not markedly change in normal chloroplasts by the presence of DBMIB?. Similar 690 nm absorption changes occur in trypsin treated chloroplasts, independent of the presence of DCMU. 4. The fast regeneration in the µs-range of Chl-a_n is also observed in the third flash of a triple flash group at a time t_v= 200 µs between the flashes of the group. 5. The initial amplitudes of the absorption changes with a decay kinetics slower than 100 µs induced by the second flash at 480 nm and 513 nm, respectively, as a function of the time t, between the first and second flash of a group, are characterized by a recovery half-time of about 600 µs, confirming earlier measurements at 520 nm (Witt and Zickler, 1974). On the basis of these results it is inferred that there does exist a photoreaction of Chl-α_n., with an electron acceptor, referred to as X_a, other than the ‘primary’ plastoquinone acceptor X320, if X320 persists in its reduced state. Under conditions of X320 being in the reduced state, this photochemical reaction was shown to be highly dissipative with respect to charging up the watersplitting enzyme system Y. Furthermore, this Chl-a_n-photoreaction with X_a does not lead to a vectorial transmembrane charge separation, which is stable for more than a few microseconds. Different models for the functional and structural organization of PS II are discussed.     

Simultaneous determination of alkylphenol ethoxylates and their biotransformation products by liquid chromatography/electrospray ionisation tandem mass spectrometry

Reversed-phase LC-MS/MS is used to determine major estrogenic alkylphenol ethoxylates (APEOs) and their biotransformation products. It allows the simultaneous analysis of eight APEOs, alkylphenoxy carboxylates (APECs) and alkylphenols (APs) in sewage treatment plant (STP) effluents in the same extract after solid-phase enrichment on polymeric Oasis HLB. As precursor ions, [APEO + NH4]+, [APEC - H]- and [AP - H]- were monitored. Instrumental limits of detection (LOD) were 2-600 pg, corresponding to sample concentrations of 0.04-12 ng l(-1), without correction for overall method recoveries. Matrix-induced signal suppression during electrospray ionisation (ESI) and extraction as well as overall method recoveries were assessed and the suitability of deuterated surrogates as internal standards was evaluated.     

Prediction of aqueous solubility of drugs and pesticides with COSMO-RS

The COSMO-RS method, originally developed for the prediction of liquid-liquid and liquid-vapor equilibrium constants based on quantum chemical calculations, has been extended to solid compounds by addition of a heuristic expression for the Gibbs free energy of fusion. By this addition, COSMO-RS is now capable of a priori prediction of aqueous solubilities of a wide range of typical neutral drug and pesticide compounds. Only three parameters in the heuristic expression have been fitted on a data set of 150 drug-like compounds. On these data an rms deviation of 0.66 log-units was achieved. Later, the model was tested on a set of 107 pesticides, which have been critically selected based on two experimental data sources and by a crosscheck with an independent HQSAR model. On this data set an rms of 0.61 log-units was achieved, without any adjustments to the structurally extremely diverse pesticides. This result verifies the ability of this extended COSMO-RS to predict aqueous solubilities of drugs and pesticides of almost arbitrary structural classes. The new method is COSMO-RSol.     

Vanadium(V) environments in bismuth vanadates: A structural investigation using Raman spectroscopy and solid state V NMR

The Bi₂O₃---V₂O₅ system was examined using Raman spectroscopy and solid state ⁵¹V wideline, magic-angle spinning (MAS), and nutation NMR spectroscopy. The methods are shown to be complementary in the identification of the various phases and in the characterization of their vanadium site symmetries. Most of the compositions examined (1:1 ≤ Bi:V ≤ 60:1) are multiphasic. Depending on the Bi:V ratio, the following phases have been identified: BiVO₄, Bi₄V₂O₁₁, a triclinic type-II phase, a cubic type-I phase, γ-Bi₂O₃ doped with V(V) (sillenite), and β-Bi₂O₃. Detailed spectroscopic characterization reveals that vanadium is tetrahedrally coordinated in all these compounds, and that the degree of symmetry increases with increasing Bi:V ratio. At the highest Bi:V ratios, the combined interpretation of the Raman and NMR data provides strong evidence for the presence of Bi⁵⁺O₄ tetrahedra.