A new tantalum dinitrogen complex and a parahydrogen-induced polarization study of its reaction with hydrogen

Reduction of Cp*(2)TaCl(2) with sodium amalgam in THF under a nitrogen atmosphere results in the formation of the novel complex (Cp*(2)TaCl)(2)(micro-N(2)). This dinuclear complex containing a micro-eta(1):eta(1) dinitrogen bridge has been characterized by NMR and X-ray crystallography. The complex possesses a C(2)-symmetric structure with each Ta bound to diastereotopic Cp* rings and chloride in addition to the micro-N(2) bridge. The Ta-N and N-N distances of 1.885(10) and 1.23(1) A, respectively, suggest modest reduction of the dinitrogen moiety. The two Cp* resonances on each Ta center remain inequivalent in solution, even up to 80 degrees C. Addition of hydrogen results in the formation of two isomers of the dihydride complex Cp*(2)TaH(2)Cl. Under parahydrogen, polarized resonances are observed for the unsymmetrical isomer with adjacent hydrides as the product of H(2) oxidative addition. The symmetric isomer of Cp*(2)TaH(2)Cl also forms, most likely by isomerization of the unsymmetrical kinetic isomer. The reactivity of (Cp*(2)TaCl)(2)(micro-N(2)) was compared to that of the related monomer, Cp*(2)TaCl(THF). The THF adduct yields the same hydrogen addition products, but the reaction is much more facile than for the nitrogen dimer, indicative of the structural integrity of the micro-N(2) complex.     

Separation of thorium from uranium ore

Thorium-230 has many research applications, but there is not a commercial source of this isotope. However, since ²³⁰Th is part of the ²³⁸U decay chain, it can be separated from naturally occurring uranium. In this work, a novel procedure was developed to separate thorium from uranium ore, consisting of leaching, liquid–liquid extraction, precipitations and ion exchange chromatography. The final product was 91.32?±?0.77 mg of thorium with a purity of 99.5?±?1.2 wt%. Of that, 7.65?±?0.10 mg was ²³⁰Th and the remainder ²³²Th. The total yield of ²³⁰Th was 71.1?±?5.4%. Ways to improve the yield by further processing the back-extraction solution are suggested.

     

Absolute quantitation of host cell proteins in recombinant human monoclonal antibodies with an automated CZE‐ESI‐MS/MS system

We report the first use of CZE for absolute characterization of host cell proteins (HCPs) in recombinant human monoclonal antibodies. An electrokinetically pumped nanoelectrospray interface was used to couple CZE with a tandem mass spectrometer. Three isotopic‐labeled peptides (LSFDKDAMVAR, VDIVENQAMDTR, and LVSDEMVVELIEK) were synthesized by direct incorporation of an isotope‐labeled lysine or arginine. The heavy‐labeled peptides were spiked in the HCP digests at known concentrations. After CZE‐ESI‐MS/MS analysis, the peaks of native and isotopic‐labeled peptides were extracted with mass tolerance ≤ 5 ppm from the electropherograms, and the ratios of peak area between native and isotopic‐labeled peptides pairs were calculated. Calibration curves (the ratios of peak area versus spiked peptide amount) with R² values of 0.999, 0.997, and 0.999 were obtained for the three HCP peptides, and the absolute amounts of the three proteins present were determined to be at the picomole level in a 20 μg sample of digested HCPs. The target proteins were present at the 7–30 ppt level in the purified HCP samples.     

NMR Characterization of Complex p‐Oligophenyl Scaffolds by Means of Aliasing Techniques to Obtain Resolution‐Enhanced Two‐Dimensional Spectra

The usefulness of computer‐assisted aliasing to secure maximal resolution of signal clusters in ¹H‐ and ¹³C‐NMR spectra (which is essential for structure determination by HMBC 2D NMR spectroscopy) in minimal acquisition time is exemplified by the complete characterization of the two complementary p‐octiphenyls 1 and 2 with complex substitution patterns. The need for digital resolution near 1 Hz/pt to dissect the extensive signal clusters in the NMR spectra of these refined oligomers excluded structure determination under routine conditions. High resolution was secured by exploiting the low signal density in the ¹³C dimension of HMBC spectra by using computer‐assisted aliasing to maximize signal density. Based on the observed shifts in DEPT and ¹H‐decoupled ¹³C‐NMR spectra of 1 and 2 , computer‐assisted aliasing allowed to reduce the number of required time increments by a factor of 20 to 30 compared to full‐width spectra with identical resolution. Without signal‐to‐noise constraints, this computer‐assisted aliasing reduced the acquisition time for high‐resolution NMR spectra needed for complete characterization of refined oligomers 1 and 2 by the same factor (e.g., from over a day to about an hour). With resolved signal clusters in fully aliased HSQC and HMBC spectra, unproblematic structure determination of 1 and 2 is demonstrated by unambiguous assignment of all C‐ and H‐atoms. These findings demonstrate that computer‐assisted aliasing of the underexploited ¹³C dimension makes extensive molecular complexity accessible by conventional multidimensional heteronuclear NMR experiments without extraordinary efforts.     

Determination of vitamin A (retinol) in infant formula and adult nutritionals by liquid chromatography: First Action 2011.15

During the "Standards Development and International Harmonization: AOAC INTERNATIONAL Mid-Year Meeting," held on June 29, 2011, an Expert Review Panel (ERP) reviewed the method for the "Determination of Vitamins A (Retinol) and E (alpha-Tocopherol) in Foods by Liquid Chromatography: Collaborative Study," published by Jonathan W. DeVries and Karlene R. Silvera in J. AOAC Int. in 2002. After evaluation of the original validation data, an ERP agreed in June 2011 that the method meets standard method performance requirements (SMPRs) for vitamin A, as articulated by the Stakeholder Panel on Infant Formula and Adult Nutritionals. The ERP granted the method First Action status, applicable to determining vitamin A in ready-to-eat infant and adult nutritional formula. In an effort to achieve Final Action status, it was recommended that additional information be generated for different types of infant and adult nutritional formula matrixes at varied concentration levels as indicated in the vitamin A (retinol) SMPR. Existing AOAC LC methods are suited for specific vitamin A analytical applications. The original method differs from existing methods in that it can be used to assay samples in all nine sectors of the food matrix. One sector of the food matrix was powdered infant formula and gave support for the First Action approval for vitamin A in infant and adult nutritional formula. In this method, standards and test samples are saponified in basic ethanol-water solution, neutralized, and diluted, converting fats to fatty acids and retinol esters to retinol. Retinol is quantitated by an LC method, using UV detection at 313 or 328 nm for retinol. Vitamin concentration is calculated by comparison of the peak heights or peak areas of retinol in test samples with those of standards.     

Modification of the BAX System PCR assay for detecting Salmonella in beef, produce, and soy protein isolate. Performance Tested Method 100201

The BAX System PCR assay for Salmonella detection in foods was previously validated as AOAC Research Institute (RI) Performance Tested Method (PTM) 100201. New studies were conducted on beef and produce using the same media and protocol currently approved for the BAX System PCR assay for E. coli O157:H7 multiplex (MP). Additionally, soy protein isolate was tested for matrix extension using the U.S. Food and Drug Administration-Bacteriological Analytical Manual (FDA-BAM) enrichment protocols. The studies compared the BAX System method to the U.S. Department of Agriculture culture method for detecting Salmonella in beef and the FDA-BAM culture method for detecting Salmonella in produce and soy protein isolate. Method comparison studies on low-level inoculates showed that the BAX System assay for Salmonella performed as well as or better than the reference method for detecting Salmonella in beef and produce in 8-24 h enrichment when the BAX System E. coli O157:H7 MP media was used, and soy protein isolate in 20 h enrichment with lactose broth followed by 3 h regrowth in brain heart infusion broth. An inclusivity panel of 104 Salmonella strains with diverse serotypes was tested by the BAX System using the proprietary BAX System media and returned all positive results. Ruggedness factors involved in the enrichment phase were also evaluated by testing outside the specified parameters, and none of the factors examined affected the performance of the assay.     

Diels-alder reactions of 3-(2-nitrovinyl)indoles: Formation of carbazoles and bridged carbazoles

The Diels-Alder reactions of 1-substituted-3-(2-nitrovinyl)indoles 3 with quinones and acetylenes give aromatized 1:1 adducts (- nitrous acid) ( 1 ) or (- nitrous acid, -2 hydrogens) 2,5 . Likewise, dimerization (-2 nitrous acids) of 3 gives aromatized 2-(3-indolyl)carbazoles 4 . In contrast, 3 reacts with maleimides 6 to give 1:2 adducts (- nitrous acid or -2 hydrogens) 10 and 11 , respectively, along with smaller amounts of 1:1 adducts (- nitrous acid, -2 hydrogens; or -4 hydrogens) 12 and 13 , respectively. A mechanism for formation of the nitro products 11 and 13 is discussed. A 1:2 adduct (-2 hydrogens) 19 was also obtained from a Diels-Alder reaction between maleimide and the vinylindole produced in situ by condensing 1-methylindole with acetone. The stereochemisty of this 1:2 adduct has been determined by X-ray crystallography.