Simultaneous serum desalting and total protein determination by macroporous reversed-phase chromatography

Macroporous reversed-phase (mRP) chromatography was successfully used to develop an accurate and precise method for total protein in serum. The limits of detection (0.83 μg, LOD) and quantification (2.51 μg, LOQ) for the mRP method are comparable with those of the widely used micro BCA protein assay. The mRP method can be used to determine the total protein concentration across a wide dynamic range by detecting chromatographic peaks at 215 nm and 280 nm. The method has the added advantage of desalting and denaturing proteins, leading to more complete digestion by trypsin and to better LC–MS–MS identification in shotgun proteomics experiments.

Two molybdenum pentacarbonyl complexes with electroneutral phosphane ligands: [bis(morpholin‐4‐yl)(pentafluoroethyl)phosphane‐κP]pentacarbonylmolybdenum(0) and pentacarbonyl[(pentafluoroethyl)bis(piperidin‐1‐yl)phosphane‐κP]molybdenum(0)

The crystal structures of the title compounds, [Mo{(C₄H₈NO)₂P(C₂F₅)}(CO)₅], (1a), and [Mo{(C₅H₁₀N)₂P(C₂F₅)}(CO)₅], (2a), were determined as part of a larger project that focuses on the synthesis and coordination chemistry of phosphane ligands possessing moderate (electroneutral, i.e. neither electron‐rich nor electron‐deficient) electronic characteristics. Both complexes feature a slightly distorted octahedral geometry at the metal center, due to the electronic and steric repulsions between two of the four equatorial CO groups and the pentafluoroethyl group attached to the phosphane ligand. Bond length and angle data for (1a) and (2a) support the conclusion that the free phosphane ligands are electroneutral. For complex (1a), the Mo—P, Mo—C_ax and Mo—C_eq(ave) bond lengths are 2.5063 (5), 2.018 (2) and 2.048 (2) Å, respectively, and for complex (2a) these values are 2.5274 (5), 2.009 (3) and 2.050 (3) Å, respectively. Geometric data for (1a) and (2a) are compared with similar data reported for analogous Mo(CO)₅ complexes.     

Synthesis and structures of silicon-, germanium- and tin-containing tungsten imido alkyl complexes (ArN)2W(CH2EMe3)2 (E = Si, Ge, Sn)

The novel silicon-, germanium- and tin-containing imido alkyl complexes of tungsten of the type (ArN)₂W(CH₂EMe₃)₂ (; E = Si (1), Ge (2), Sn (3)) have been prepared by the reactions of (ArN)₂WCl₂(dme) (dme = 1,2-dimethoxyethane) with heteroelement-containing alkyllithium or Grignard reagents Me₃ECH₂Li (E = Si, Ge), Me₃ECH₂MgCl (E = Ge, Sn). The title compounds were isolated in high yields as crystalline solids and characterized by elemental analysis, IR, ¹H, ¹³C, ²⁹Si and ¹¹⁹Sn NMR spectroscopy and X-ray diffraction studies. The geometry of the W atoms in the compounds can be described as a distorted tetrahedron.     

Oligonucleotides containing new fluorescent 1-phenylethynylpyrene and 9,10-bis(phenylethynyl)anthracene uridine-2′-carbamates: synthesis and properties

The synthesis of two novel fluorescent uridine-2′-carbamate phosphoramidites is described. The reagents carrying fluorescent polyaromatic hydrocarbons 1-phenylethynylpyrene (PEPy) or 9,10-bis(phenylethynyl)anthracene (BPEA) are suitable for oligonucleotide synthesis. Prepared oligonucleotide conjugates show strong dye emissions at 401 and 485 nm, but low FRET rate when located in the oligonucleotide duplex. The dyes show considerable compensation of the usual carbamate duplex destabilization. The possible explanation of both effects is binding of PEPy and BPEA to the minor groove of the DNA duplex.     

Synthesis of hydroporphyrins based on comparative studies of palladium-catalyzed and non-catalyzed approaches

Hydroporphyrins have been synthesized using both Pd-catalyzed and non-catalyzed approaches. Comparative studies of the reaction of tetrasubstituted porphyrins with organolithium reagents in the presence of and without palladium catalysts showed that depending on reagents, the catalyst structure and reactivity of the corresponding porphyrins, chlorins (β-hydroporphyrins) and/or porphodimethenes (meso hydroporphyrins) of 5,10-type can be prepared in reasonable yields. In the absence of Pd catalysts, the formation of chlorins is predominant in the reactions with aliphatic RLi while porphodimethenes are the main products in reactions with PhLi. The use of a palladium catalyst resulted in the formation of both types of hydroporphyrins and the selective formation of either β-mono- or disubstituted chlorins. Of special interest was the reaction of octaethylporphyrin. Here, reaction with t-BuLi in the presence of Pd(PPh₃)₄/CuI proceeded with complete regioselectivity for 5,10-porphodimethenes.     

Reactions of 4-substituted 5H-1,2,3-dithiazoles with primary and secondary amines: fast and convenient synthesis of 1,2,5-thiadiazoles, 2-iminothioacetamides and 2-oxoacetamides

The treatment of 5H-1,2,3-dithiazole-5-thiones 1 in chloroform under reflux and 5H-1,2,3-dithiazol-5-ones 2 in THF at room temperature with primary aliphatic amines and benzylamine afforded 1,2,5-thiadiazole-3(2H)-thiones 3 and 1,2,5-thiadiazol-3(2H)-ones 6, respectively. The structure of dithiazolone 3f was confirmed by X-ray diffraction analysis. The reaction of dithiazolone 2e bearing an electron-donating methyl group in the 4-position gave 2-oxoacetamide 7e in high yield. The reaction of thiones 1 with secondary aliphatic amines in DMSO yielded 2-iminothioacetamides 8 in moderate yields together with elemental sulfur. Interestingly, the treatment of dithiazolones 2 with secondary amines under the same conditions afforded 2-oxoacetamides 9—the products of the hydrolysis of corresponding imino derivatives 10, which was isolated as 10b. A general mechanism was proposed for the formation of the products.     

Measurements of temperature and heat of phase transformation of pure silicon by using differential scanning calorimetry

Differential scanning calorimetry (DSC) technique has been applied for the experimental determination of temperature and heat of phase transition of pure silicon (7 N) during heating and cooling cycles at the rate of 10 K min^?1. The measurements were carried out in the temperature range of 25–1450 °C in a flow gas atmosphere (Ar, 99.9992%) using three types of crucibles made of alumina, h-BN and alumina covered with h-BN coating. The following characteristics were estimated from DSC curves: melting point of silicon—1414 °C, the heat of fusion—1826 J g^?1 and the heat of solidification—1654 J g^?1. It was found that the silicon evaporation phenomenon accompanying the tests had no effect on the measurements of temperature during solid-to-liquid and liquid-to-solid transformations and on the measurement of the latent heat of fusion. The effect of crucible type on the DSC measurements is discussed.

     

Microwave‐Assisted Solid‐Phase Synthesis of a 1,2‐Disubstituted Benzimidazole Library by Using a Phosphonium Linker

An efficient and rapid microwave‐assisted solid‐phase method for the synthesis of 5‐methyl‐1,2‐disubstituted benzimidazoles derivatives has been developed. The phosphonium linker, obtained by reaction between polymer‐supported triphenylphosphine and 4‐fluoro‐3‐nitrobenzyl iodide, underwent aromatic substitution with primary amines, followed by one‐pot reaction with aldehydes in the presence of SnCl₂·2H₂O, yielded the benzimidazole system under microwave irradiation. The final products were released from the resin with NaOH under microwave irradiation and were obtained in high purity and good overall yield.     

Determination of volatile nitrosamines in meat products by microwave-assisted extraction and dispersive liquid-liquid microextraction coupled to gas chromatography-mass spectrometry

Microwave-assisted extraction (MAE) and dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-mass spectrometry (GC-MS) were evaluated for use in the extraction and preconcentration of volatile nitrosamines in meat products. Parameters affecting MAE, such as the extraction solvent used, and DLLME, including the nature and volume of the extracting and disperser solvents, extraction time, salt addition and centrifugation time, were optimized. In the MAE method, 0.25g of sample mass was extracted in 10mL NaOH (0.05M) in a closed-vessel system. For DLLME, 1.5mL of methanol (disperser solvent) containing 20μL of carbon tetrachloride (extraction solvent) was rapidly injected by syringe into 5mL of the sample extract solution (previously adjusted to pH 6), thereby forming a cloudy solution. Phase separation was performed by centrifugation, and a volume of 3μL of the sedimented phase was analyzed by GC-MS. The enrichment factors provided by DLLME varied from 220 to 342 for N-nitrosodiethylamine and N-nitrosopiperidine, respectively. The matrix effect was evaluated for different samples, and it was concluded that sample quantification can be carried out by aqueous calibration. Under the optimized conditions, detection limits ranged from 0.003 to 0.014ngmL(-1) for NPIP and NMEA, respectively (0.12-0.56ngg(-1) in the meat products).     

Dielectric study of the slow motional processes in the polymorphic States of anhydrous caffeine

Molecular mobility in crystalline anhydrous caffeine was studied by the dielectric technique of thermally stimulated depolarization currents (TSDC). Two relaxational processes were found, one appearing at approximately -10 degrees C that is ascribed to a reorientational glass transition, and a higher temperature one that probably arises from local molecular motions that are precursors of diffusion and sublimation. The experimental results suggest that both crystalline phases II and I of caffeine, that have distinct crystal structures, are solid rotator phases. Furthermore, this dynamic reorientational disorder shows a reorientational glass transition at the same temperature in phase II and in metastable phase I.