Excess partial molar enthalpies,entropies, Gibbs energies,and volumes in aqueous dimethylsulfoxide

The excess partial molar enthalpies, the vapor pressures, and the densities of dimethylsulfoxide (DMSO)–H₂O mixtures were measured and the excess partial molar Gibbs energies and the partial molar volumes were calculated for DMSO and for H₂O. The values of the excess partial molar Gibbs energies for both DMSO and H₂O are negative over the entire composition range. The results for the water-rich region indicated that the presence of DMSO enhances the hydrogen bond network of H₂O. Unlike monohydric alcohols, however, the solute-solute interaction is repulsive in terms of the Gibbs energy. This was a result of the fact that the repulsion among solutes in terms of enthalpy surpassed the attraction in terms of entropy. The data in the DMSO-rich region suggest that DMSO molecules form clusters which protect H₂O molecules from exposure to the nonpolar alkyl groups of DMSO.     

Quantification of veterinary antibiotics (sulfonamides and trimethoprim) in animal manure by liquid chromatography-mass spectrometry

A fast and cost effective method was developed to extract and quantify residues of veterinary antimicrobial agents (antibiotics) in animal manure by liquid-liquid extraction and liquid chromatography-mass spectrometry. The compounds investigated include six sulfonamides, one metabolite, and trimethoprim. The method was performed without sample clean up. Recoveries from spiked manure slurry samples (spike level = 1 mg/kg) were as follows: sulfaguanidine (52%), sulfadiazine (47%), sulfathiazole (64%), sulfamethazine (89%), its metabolite N4-acetyl-sulfamethazine (88%), sulfamethoxazole (84%), sulfadimethoxine (51%), and trimethoprim (64%). Relative standard deviations of the recoveries were less than 5% within the same day and less than 20% between days. The limit of quantification was below 0.1 mg/kg liquid manure slurry for all compounds and calibration curves obtained from extracts of spiked samples were linear up to a level of 5 mg/kg liquid manure, except for trimethoprim (0.01-0.5 mg/kg). Analysis of six grab samples taken in Switzerland from manure pits on farms where medicinal feed had been applied revealed total sulfonamide concentrations of up to 20 mg/kg liquid manure.     

Stereoselective Synthesis of Isomers of the Naturally Occurring 13-Hydroxy-2,4,9-tetradecatrienoic Acid. Part II [1]

The stereoselective syntheses of four unsaturated hydroxy fatty acids 13S,2E,4E,9E)- 13-hydroxy-2,4,9-tetradecatrienoic acid, (13S,9Z,11E)-13-hydroxy-9,11-tetradecadienoic acid, (13S,9E, 11E)-13-hydroxy-9,11-tetradecadienoic acid, and (13S,2E,4E,9E)-13-hydroxy-2,4,9,11-tetradecatrienoic acid, are described. Wittig reactions, regioselective oxidation of dialcohol 3, and diastereomerization were used.     

Photochemical investigation of Roussin's red salt esters: Fe2(mu-SR)2(NO)4

The photochemistry of various Roussin's red ester compounds of the general formula Fe(2)(SR)(2)(NO)(4), where R = CH(3), CH(2)CH(3), CH(2)C(6)H(5), CH(2)CH(2)OH, and CH(2)CH(2)SO(3)(-), were investigated. Continuous photolyses of these ester compounds in aerated solutions led to the release of NO with moderate quantum yields for the photodecomposition of the ester (Phi(RSE) = 0.02-0.13). Electrochemical studies using an NO electrode demonstrated that 4 mol of NO are generated for each mole of ester undergoing photodecomposition. Nanosecond flash photolysis studies of Fe(2)(SR)(2)(NO)(4) (where R = CH(2)CH(2)OH and CH(2)CH(2)SO(3)(-)) indicate that the initial photoreaction is the reversible dissociation of NO. In the absence of oxygen, the presumed intermediate, Fe(2)(SR)(2)(NO)(3), undergoes second-order reaction with NO to regenerate the parent cluster with a rate constant of k(NO) = 1.1 x 10(9) M(-1) s(-1) for R = CH(2)CH(2)OH. Under aerated conditions the intermediate reacts with oxygen to give permanent photochemistry.     

Determination of the chromophore structures in the photoinduced reaction cycle of phytochrome

The chromophore structures in the parent states Pr and Pfr as well as in the photocycle intermediate Lumi-R of oat phytochrome phyA are determined by comparison of the experimental resonance Raman spectra with calculated Raman spectra that have been obtained by density functional theory calculations (B3LYP) using scaled force fields. The spectra were calculated for various tetrapyrrole geometries including more than twenty different methine bridge isomers. For the parent states Pr and Pfr the best agreement in terms of vibrational frequencies, isotopic shifts, and Raman intensities was achieved with the ZZZasa and ZZEssa geometry, respectively. For the first intermediate Lumi-R, the chromophore geometry is concluded to be the ZZEasa configuration. These finding imply that the primary step of the photoactivation of phytochrome is the Z/E isomerization of the C-D methine bridge double bond, whereas the single bond remains in the anti conformation. The subsequent transition to the physiologically active state Pfr includes a (partial) single bond rotation of the A-B methine bridge.     

Wismutmonojodid BiJ,eine Verbindung mit Bi(O) und Bi(II)

Bismuth Monoiodide, a Compound with Bi(O) and Bi(II) Bismuth monoiodide was synthesized in closed tubes from the elements as well as from Bi and HgI₂ as a black coloured crystalline compound. With increasing temperature BiI passes two transitions. α-BiI is stable below 370 K and changes to β-BiI by a martensitic transition. γ-BiI is the stable modification above 564 K and decomposes at 585 K peritectically to BiI₃ and a lower iodide. All three modification crystallize in the monoclinic space group C2/m. The structures (single crystal studies) of α-BiI and β-BiI are characterized by onedimensional infinite chains [Bi₄I₄] with covalent bonds but only weak interactions in between. The [Bi₄I₄]-chains are built up by two completely different Bi atoms. Bi(A) is only bonded to three Bi whereas Bi(B) has bonds to one Bi and four I. The average bond lengths are Bi? Bi = 304.5 pm and Bi? I = 313.7 pm respectively. The configuration of the Bi(A) atoms is typical for Bi^O and that one of the Bi(B) atoms is characteristic for Bi²⁺ with the electron configuration s²p¹. Therefore, α-BiI and β-BiI are mixed valence compounds [Bi^OBi²⁺I₄]. The structures are variants of the simple cubic polonium type of structure and differ in the stacking of connected units. The structures and their transitions, the possible configurations for monohalides BiX on principle as well as the energy balances of the disproportionation of Bi⁺ are discussed together in detail.     

Reversed-phase high-performance liquid chromatographic separation of epimeric alkaloid N-oxides from Thalictrum simplex L.

A simple and precise method was developed for the analytical and preparative reversed-phase HPLC separation of a mixture of epimeric pavine N-oxides containing 49.1% of (−)-thalimonine N-oxide A and 50.1% of (−)-thalimonine N-oxide B isolated from Thalictrum simplex L. (Ranunculaceae). A reversed-phase system with Nucleosil C₁₈ analytical and preparative columns and ethanol-1.5% aqueous orthophosphoric acid (15:85) as the mobile phase was used. The epimeric pavine N-oxides were completely separated within 50 min.     

Metallosupramolecular Chemistry in Two Dimensions

Ultrathin films of metallosupramolecular coordination polyelectrolytes (MEPEs) on planar solid substrates assembled by electrostatic layer-by-layer self-assembly (ELSA) are characterized with UV-vis spectroscopy, optical ellipsometry, and X-ray reflectometry. MEPEs based on different ditopic ligands and transition metal ions are employed and shown to form regular ELSA multilayers. A quantitative analysis is in agreement with a surface coverage of approximately two MEPE monolayers per deposition step. In addition, we demonstrate that multilayers of MEPEs with different transition metal ions can be assembled. Even with kinetically labile metal ions, there is no metal ion exchange in these multilayers. Absorption spectra of multilayers on silicon show a band inversion of the MLCT band, which is rationalized in terms of optical effects.