Synthesis and characterization of Di-π-cyclopentadienyl- metal pentasulfides of titanium(IV) and vanadium (IV):an operational test of the influence of an unpaired electron on the molecular geometry

Our preparation of Ti(h⁵?C₅H₅)₂ S₅ by the reaction of elemental sulfur with Ti(h⁵?C₅H₅)₂(CO)₂ in hexane and of V(h⁵?C₅H₅)₂S₅?$\text{1}\text{2}$ H₂O by the reacti of V(h⁵?C₅H₅)₂ Cl₂ with Na₂S₅ in THF and structural analyses by single crystal X-ray diffraction (together with infrared, solution EPR, and temperaturedependent magnetic susceptibility measurements) represent an extension of our previous work on M(h⁵?C₅H₅)₂ (SC₆H₅)₂ (M = Ti, V). The crystallographic results provide further support of our previous conclusions that the Ballhausen—Dahl model is not valid for M(h⁵?C₅H₅)₂L₂ systems. The structuralfeatures of the chair-like titanium and vanadium pentasulfide molecules are compared to the corresponding phenylmercapto analogs and to the chair-like cyclohexasulfur molecule in rhombohedral sulfur. Ti(h⁵?C₅H₅)₂S₅ was isolated as a mixture of monoclinic and orthorhombic Crystalline phases-which were both characterized by preliminary X-ray data. A complete Structural determination and refinement of the monoclinic phase, which contains two independent molecules in a cell of dimensions a 22.843(2), b 7.958(1), c 14.465(1) Å, β 90.074(4)° and symmetry P2₁/c, yielded R₁ 5.3 % and R₂ 5.9 % for 2168 independent diffractometry-collected data with I≥ 2.5o(I). V(h⁵?C₅H₅)₂S₅-$\text{1}\text{2}$ H₂O contains four V(h⁵?C₅H₅)₂S₅ molecules and two water molecules of hydration (of crystallographic site symmetry C₂-2) in onorthorhombic unit cell of symmetry P2₁2₁2 and of dimensions a 13.491(1), b 12.748(1), c 7.715(1) Å. Least-squares refinement of 750 diffractometry data with I≥2.0σ(I) gave R₁ 2.4% and R₂ 3.0% Both of these compounds were independently synthesized and Spectroscopically characterized by Köpf and co-workers, and-a Complete X-ray diffraction study was performed by Epstein and Bernal on a different monoclinic phase of Ti(h⁵?C₅H₅)₂S₅ (isolated by-Köpf). An extraction of V(h⁵?C₅H₅)₂S₅ with re fluxing benzene under nitrogen atmosphere in a Soxhlet apparatus led to the formation of the previously reported [V₂ (h⁵?C₅H₅)₂S₅]_n compound which was characterized by physical measurements including a preliminary X-ray diffraction study.     

Mass transfer and benzene removal from air using latex rubber tubing and a hollow-fiber membrane module

A dense-phase latex rubber tube and a polyporous propylene hollow-fiber membrane module (HFMM) were investigated for control of benzene-contaminated gas streams. The abiotic mass flux observed through the latex tube was 3.9–13 mg/(min·m²) for 150 ppm of benzene at various gas and liquid flow rates, while a 100-fold lower mass flux was observed in the HFMM. After seeding with an aromatic-degrading culture enriched from activated sludge, the observed removal was 80% of 150 ppm, corresponding toa mass flux of 45 mg/(min·m²). The observed mass flux through the HFMM during biofiltration also rose, to 0.4 mg/(min·m²). Because the HFMM had a 50-fold higher surface area than the latex tube, the observed ben zene removal was 99.8%. Compared to conventional biofilters, the two reactors had modest elimination capacities, 2.5–18 g/(m³·h) in the latex tube membrane bioreactor and 4.8–58 g/(m³·h) in the HFMM. Although the HFMM had a higher elimination capacity, the gas-phase pressure drop was much greater.     

Physically based molecular device model in a transient circuit simulator

Two efficient, physically based models for the real-time simulation of molecular device characteristics of single molecules are developed. These models assume that through-molecule tunnelling creates a steady-state Lorentzian distribution of excess electron density on the molecule and provides for smooth transitions for the electronic degrees of freedom between the tunnelling, molecular-excitation, and charge-hopping transport regimes. They are implemented in the fREEDA™ transient circuit simulator to allow for the full integration of nanoscopic molecular devices in standard packages that simulate entire devices including CMOS circuitry. Methods are presented to estimate the parameters used in the models via either direct experimental measurement or density-functional calculations. The models require 6–8 orders of magnitude less computer time than do full a priori simulations of the properties of molecular components. Consequently, molecular components can be efficiently implemented in circuit simulators. The molecular-component models are tested by comparison with experimental results reported for 1,4-benzenedithiol.     

Fully automated micro- and nanoscale one- or two-dimensional high-performance liquid chromatography system for liquid chromatography-mass spectrometry compatible with non-volatile salts for ion exchange chromatography

A one- or two-dimensional high performance liquid chromatography system for electrospray ionization mass spectrometers has been developed that is optimized for ion exchange and reversed phase separations. A unique and simple valve configuration permits the use of a variety of non-volatile salts; ammonium sulfate was used in an example of strong cation exchange separations. The system was designed and evaluated for both micro- and nanoflow chromatography. The peptide detection limit was approximately 100 fmol for micro- and 20 fmol for nanoflow, demonstrating the concentration and mass sensitivity improvements expected with nanoelectrospray ionization. The 1D/2D-HPLC MS system is fully automated for routine peptide analyses, compatible with direct injection of proteolytic digests, and exhibits chromatographic reproducibility and sensitivity. Software permits operator selection of either a 1D or 2D configuration with corresponding system parameters as required for individual samples. The hardware elements and resulting performance are described in this paper.     

Facile construction and divergent transformation of polycyclic isoxazoles: direct access to polyketide architectures

[reaction: see text] Base-promoted cyclocondensation of C-chloro oximes with cyclic 1,3-diketones affords functionalized isoxazoles in good yield and under convenient reaction conditions. This process enables the synthesis of highly substituted products with notable functional group tolerance. The products obtained are directly converted to a variety of polyketide-derived polycyclic structures including xanthenes, anthracenes, and benzophenones.     

Improved preparation and new reactions of β -(1-phenylthio) cyclopropyl enones

β-(1-Phenylthio)cyclopropyl enones can be conveniently prepared via reaction of the lithium salts of α-hydroxymethylene ketones with 1-lithio-1-phenylthiocyclopropane and are converted efficiently by treatment with aqueous acid to γ-keto cyclobutanones and less successfully by thermolysis to -γ-keto phenylthiocyclopentenes.     

Preferential solubilization of dodecanol from dodecanol-limonene binary oil mixture in sodium dihexyl sulfosuccinate microemulsions: effect on optimum salinity and oil solubilization capacity

Solubilization of dodecanol-limonene binary oil mixtures has been studied in saturated Winsor type I and III sodium dihexyl sulfosuccinate microemulsions. The systems showed different oil solubilization behavior below and above dodecanol volume fraction 0.2. Below 0.2 dodecanol volume fraction regular Winsor type microemulsions formed. The oil solubilization was characterized in this concentration range by the optimum salinity and the maximum characteristic length. Dodecanol showed Langmuirian-type surface excess adsorption at the vicinity of the surfactant layer. Variation of the optimum salinity and middle phase characteristic length with increasing dodecanol concentration could be linked to changes in the dodecanol surface excess. These relationships were used to develop new mathematical models for the optimum salinity and characteristic length as a function of oil phase composition. Both models yield excellent agreement with the data. Above dodecanol volume fraction 0.2 regular Winsor type III microemulsions are not formed. Therefore our new models are not applicable in this concentration range.     

Automated multi-attribute method sample preparation using high-throughput buffer exchange tips

Rationale

The multi-attribute method (MAM) has become a valuable mass spectrometry (MS)-based tool that can identify and quantify the site-specific product attributes and purity information for biotherapeutics such as monoclonal antibodies (mAbs) and fusion molecules in recent years. As we expand the use of the MAM at various stages of drug development, it is critical to enhance the sample preparation throughput without additional chemical modifications and variability.

Methods

In this study, a fully automated MAM sample preparation protocol is presented, where rapid desalting in less than 15 minutes is achieved using miniaturized size-exclusion chromatography columns in pipette tips on an automated liquid handler. The peptide samples were analyzed using an electrospray ionization (ESI) orbitrap mass spectrometer coupled to an ultra-high-performance liquid chromatography (UHPLC) system with a dual column switching system.

Results

No significant change was observed in product attributes and their quantities compared with manual, low-artifact sample preparation. The sample recovery using the buffer exchange tips was greatly enhanced over the manual spin cartridges while still demonstrating excellent reproducibility for a wide variety of starting sample concentrations. Unlike a plate desalting system, the individual columns provide flexibility in the number of samples prepared at a time and sample locations within plates.

Conclusions

This automated protocol enables the preparation of up to 96 samples with less “at-bench” time than the manual preparation of a smaller batch of samples, thereby greatly facilitating support of process development and the use of the MAM in quality control.

     

Differential expression of the skeletal muscle proteome in mdx mice at different ages

The mdx mouse is the most commonly used animal model for Duchenne muscular dystrophy (DMD), a disease caused by the absence of dystrophin. Although much has been done to elucidate the structure and function of dystrophin and the dystrophin-associated glycoprotein complex (DGC), little is known about the cascade of molecular events triggered by the absence of dystrophin that lead to muscle degeneration. To study the molecular basis of DMD, we decided to systematically study the skeletal muscle proteome in mdx mice at different ages. By using two-dimensional (2-D) gel electrophoresis, we defined changes in the protein expression pattern between mdx and control muscles. Approximately 46 differentially expressed proteins from the cytosolic fraction of mdx hindlimb muscles at three months of age were detected by 2-D gel analysis, of which 24 were identified by matrix assisted laser desorption/ionization- mass spectrometry. Most of the proteins fell into five groups of functionally related proteins. These functional categories are (i) metabolism and energy production, (ii) serine protease inhibitor family, (iii) growth and differentiation, (iv) calcium homeostasis, and (v) cytoskeletal reorganization and biogenesis. The potential roles of the differentially expressed proteins are discussed in the context of the mdx phenotype. Finally, we analyzed alterations of protein expression in mdx mice at one and six months of age to determine how protein expression changes with disease progression.     

Cellulase retention and sugar removal by membrane ultrafiltration during lignocellulosic biomass hydrolysis

Technologies suitable for the separation and reuse of cellulase enzymes during the enzymatic saccharification of pretreated corn stover are investigated to examine the economic and technical viability of processes that promote cellulase reuse while removing inhibitory reaction products such as glucose and cellobiose. The simplest and most suitable separation is a filter with relatively large pores on the order of 20–25 mm that retains residual corn stover solids while passing reaction products such as glucose and cellobiose to form a sugar stream for a variety of end uses. Such a simple separation is effective because cellulase remains bound to the residual solids. Ultrafiltration using 50-kDa polyethersulfone membranes to recover cellulase enzymes in solution was shown not to enhance further the saccharification rate or overall conversion. Instead, it appears that the necessary cellulase enzymes, including β-glucosidase, are tightly bound to the substrate; when fresh corn stover is contacted with highly washed residual solids, without the addition of fresh enzymes, glucose is generated at a high rate. When filtration was applied multiple times, the concentration of inhibitory reaction products such as glucose and cellobiose was reduced from 70 to 10 g/L. However, an enhanced saccharification performance was not observed, most likely because the concentration of the inhibitory products remained too high. Further reduction in the product concentration was not investigated, because it would make the reaction unnecessarily complex and result in a product stream that is much too dilute to be useful. Finally, an economic analysis shows that reuse of cellulase can reduce glucose production costs, especially when the enzyme price is high. The most economic performance is shown to occur when the cellulase enzyme is reused and a small amount of fresh enzyme is added after each separation step to replace lost or deactivated enzyme.