Phosphonium-borate zwitterions, anionic phosphines, and dianionic phosphonium-dialkoxides via tetrahydrofuran ring-opening reactions

Sterically demanding secondary phosphines and phosphides react with (THF)B(C(6)F(5))(3) (THF = tetrahydrofuran) to give the THF ring-opened compounds [R(2)PHC(4)H(8)OB(C(6)F(5))(3)] and [Mes(2)PC(4)H(8)OB(C(6)F(5))(3)Li(THF)(2)] (Mes = C(6)H(2)Me-2,4,6). These reactions also occur consecutively to give the double THF ring-opened compounds [Mes(2)P(C(4)H(8)OB(C(6)F(5))(3))(2)][Li(THF)(4)] and [t-Bu(2)P(C(4)H(8)OB(C(6)F(5))(3))(2)Li].     

Ultrafast ring-closure reaction of photochromic indolylfulgimides studied with UV-pump-IR-probe spectroscopy

The ring-opening and ring-closure reactions of a photochromic indolylfulgimide are investigated with femtosecond vibrational spectroscopy. Spectral signatures due to excited-state decay and vibrational cooling are seen in the mid-IR region. For the ring-opening reaction triggered with visible pulses, a lifetime of the excited electronic state of 4 ps was obtained in polar solution. In a nonpolar solvent, this time constant is reduced to 2 ps. The ring-closure reaction induced with UV pulses displays an excited-state lifetime and thus a building of the photoproduct of roughly 0.5 ps. For all processes, the subsequent cooling occurs on a 15-ps time scale lasting up to approximately 50 ps. The time-resolved IR measurements do not support the existence of any long-living intermediate states.     

Influence of Process Parameters on the Reaction Kinetics of the Chromium‐Catalyzed Trimerization of Ethylene

In this paper we report the results of an extensive experimental kinetic study carried out on the novel ethylene trimerization catalyst system, comprising the chromium source [CrCl₃(thf)₃] (thf=tetrahydrofuran), a Ph₂P‐N(iPr)‐P(Ph)‐N(iPr)H (PNPNH) ligand (Ph=phenyl, iPr=isopropyl), and triethylaluminum (AlEt₃) as activator. It could be shown that the initial activity shows a first‐order dependency on the ethylene concentration. Also, a first‐order dependency was found for the catalyst concentration. The initial activity follows a typical Arrhenius behavior with an experimentally determined activation energy of 52.6 kJ mol^?1. At elevated temperatures (ca. 80 °C), a significant deactivation was observed, which can be tentatively traced back to a ligand rearrangement in the presence of AlEt₃. After a fast initial phase, a pronounced ‘kink’ in the ethylene‐uptake curve is observed, followed by a slow, almost linear, further increase of the total ethylene consumption. The catalyst composition, in particular the ligand/chromium and the cocatalyst/chromium molar ratio, has a strong impact on the catalytic performance of the trimerization of ethylene.     

Quantitative determination of tolazoline in serum and urine

A high-performance liquid chromatographic procedure is described for the analysis of tolazoline in serum and urine. This assay procedure is suitable for the analysis of micro-samples (50 or 100 microliters serum and 100 microliters urine). Samples are extracted in a single step and injected into a reversed-phase high-performance liquid chromatography system for detection at 210 nm. The clinical applicability of this assay is demonstrated by the determination of tolazoline serum and urine concentrations in neonates. In addition, the presence of urine conjugates and the extent of serum protein binding were investigated. This assay procedure has the required sensitivity (0.1 microgram/ml), accuracy and precision for both routine monitoring and pharmacokinetic characterization of tolazoline in neonates and adults.     

Hydrosilylation of alkynes by Ni(CO)3-stabilized silicon(II) hydride

Not copy and paste: Although β-diketiminato ligands have been employed for the stabilization of Ge(II) and Sn(II) hydrides, the corresponding Si(II) hydride is not accessible. However, coordination of silicon(II) to a {Ni(CO)(3)} fragment allowed the isolation of the first Si(II) hydride metal complex 1. This complex was used for the first silicon(II)-based and Ni(0)-mediated, stereoselective hydrosilylation of alkynes. R = phenyl, tolyl.     

Synthesis,crystal and molecular structures of the octanuclear cationic mixed-valence cobalt acetate complex

A new octanuclear mixed-valence cobalt acetate complex of the cationic type [Co₄ ^IICo₄ ^III(μ₄-O)₄(μ₃-OMe)₄(μ-OAc)₆(H₂O)₈]F₂ · 10H₂O ([I]F₂ · 10H₂O) was prepared by crystallization from a solution of ‘cobalt(III) acetate’ in a Me₂CO-MeOH-H₂O-HF mixture and studied by X-ray diffraction. The crystals are monoclinic: space group C2/c, a = 17.222 Å, b = 16.836 Å, c = 16.586 Å, β = 94.902°, Z = 4, R = 4.37% (I > 2σ(I)). In the crystal, the I²⁺ complex cations, fluoride anions, and solvate water molecules form a three-dimensional (3D) coordination supermolecular system.     

Characterization of protein-ligand interactions by high-resolution solid-state NMR spectroscopy

A novel approach for detection of ligand binding to a protein in solid samples is described. Hydrated precipitates of the anti-apoptotic protein Bcl-xL show well-resolved (13)C-(13)C 2D solid-state NMR spectra that allow site-specific assignment of resonances for many residues in uniformly (13)C-enriched samples. Binding of a small peptide or drug-like organic molecule leads to changes in the chemical shift of resonances from multiple residues in the protein that can be monitored to characterize binding. Differential chemical shifts can be used to distinguish between direct protein-ligand contacts and small conformational changes of the protein induced by ligand binding. The agreement with prior solution-state NMR results indicates that the binding pocket in solid and liquid samples is similar for this protein. Advantages of different labeling schemes involving selective (13)C enrichment of methyl groups of Ala, Val, Leu, and Ile (Cdelta1) for characterizing protein-ligand interactions are also discussed. It is demonstrated that high-resolution solid-state NMR spectroscopy on uniformly or extensively (13)C-enriched samples has the potential to screen proteins of moderate size ( approximately 20 kDa) for ligand binding as hydrated solids. The results presented here suggest the possibility of using solid-state NMR to study ligand binding in proteins not amenable to solution NMR.     

Investigation of gaseous metabolites from moulds by Ion Mobility Spectrometry (IMS) and Gas Chromatography-Mass Spectrometry (GC-MS)

The metabolism of moulds results in the formation of various microbial volatile organic compounds (MVOCs). These substances can be used as an indicator for the presence of moulds in the indoor environment. Three different mould strains were cultivated on culture media and IMS spectra of gaseous mould metabolites were recorded using a portable mini system with a tritium source and a 5 cm drift cell. The headspace spectra are characteristic for mould species and their age. Typical gaseous components of the metabolites were identified and compared with results obtained from gas chromatography using a mass spectrometer detector. It was observed that the MVOCs formation depends on mould species and their growing stage with a maximum of MVOCs emission occurring during the first 10 days. These preliminary results show that IMS can be applied to detect MVOCs in indoor environment and indicate hidden mould growth.