A Simple Method of Synthesis of 3-Carboxy-2,2,5,5-Tetraethylpyrrolidine-1-oxyl and Preparation of Reduction-Resistant Spin Labels and Probes of Pyrrolidine Series

Stable free radicals are widely used as molecular probes and labels in various biophysical and biomedical research applications of magnetic resonance spectroscopy and imaging. Among these radicals, sterically shielded nitroxides of pyrrolidine series demonstrate the highest stability in biological systems. Here, we suggest new convenient procedure for preparation of 3-carboxy-2,2,5,5-tetraethylpyrrolidine-1-oxyl, a reduction-resistant analog of widely used carboxy-Proxyl, from cheap commercially available reagents with the yield exceeding the most optimistic literature data. Several new spin labels and probes of 2,2,5,5-tetraethylpyrrolidine-1-oxyl series were prepared and reduction of these radicals in ascorbate solutions, mice blood and tissue homogenates was studied.     

Laser ablation of paper: Raman identification of products

Old paper samples are bleached using pulsed laser radiation with a wavelength of 532 nm. The ablation products of five paper samples that differ by composition and production dates are studied using Raman microspectroscopy. Cellulose, protein, calcite, titanium dioxide (anatase, rutile, and brookite), quartz, lazurite, bonattite, and dolomite are identified as ablation products.     

High-temperature fluorescence of low- and high concentration aqueous ATP solution

Abstract

The results of an experimental study of luminescence of an aqueous solution of adenosine triphosphate (ATP) at room temperature are presented. High-temperature fluorescence of low- and high-concentrated solution was experimentally detected and analyzed. The shape of the fluorescence spectrum, the excited state lifetime and the temperature behavior of the emission intensity indicate the formation in the high-concentrated solution of rather stable dimer-like complexes, which can form excimer states.     

A Self‐Sorting Scheme Based on Tetra‐Urea Calix[4]arenes

Size and shape do matter : When dimerized in nonpolar solvents, an equimolar mixture of eleven tetra‐urea calix[4]arenes with different wide‐rim substituents self‐sorts into only six out of 35 different homo‐ and heterodimers (see picture). Since the calixarene scaffold and the four urea units are the same in all cases, the self‐sorting process is driven only by the cooperative action of steric requirements and stoichiometry.

     

Determination of association constants of inclusion complexes of steroid hormones and cyclodextrins from their electrophoretic mobility

CE estimation of the association constants of several steroid hormones with beta-CD and gamma-CD and their hydroxypropyl derivative is presented. Estriol, 17beta-estradiol, ethynylestradiol, estrone, progesterone, mestranol and norethindrone are among the target analytes. The calculation of the cyclodextrin:analyte association constants were performed from the electrophoretic mobility values of steroids at different concentration of CDs in the run buffer. The reliability of the final data was ensured by employing three different linearisation plots (double reciprocal fit, Y-reciprocal fit and X-reciprocal fit). The highest inclusion affinity of target analytes was observed towards gamma-CD and its hydroxypropyl derivative, which is demonstrated by high association constant values and corresponding good linearity of the plots. The affinity of steroids towards a particular CD type based on physical and structural characteristics is explored.     

Hilic MS/MS determination of amino acids in herbs of Fumaria schleicheri L., Ocimum basilicum L., and leaves of Corylus avellana L.

The aim of research was to study the content of amino acids using in extracts of Fumaria schleicheri L., Ocimum basilicum L., and Corylus avellana L. by HILIC MS/MS method. Separation of amino acids in the samples was carried out with Acquity H-class UPLC system (Waters, Milford, USA) equipped with SeQuant ZIC-Hilic collumn (2.1 × 150 mm, 3.5 μm) (Merck Millipore, Darmstadt, Germany). The MS/MS fragment ion chromatograms of the test solutions established the presence of 19 amino acids. The obtained results have shown that O. basilicum L. characterized the highest concentrations of different neurogenic amino acids (128.1 mg/kg), comparing with F. schleicheri L. and C. avellana L. (57.72 and 52.91 mg/kg, respectively).     

The role of physical and chemical properties of Pd nanostructured materials immobilized on inorganic carriers on ion formation in atmospheric pressure laser desorption/ionization mass spectrometry

Fundamental parameters influencing the ion‐producing efficiency of palladium nanostructures (nanoparticles [Pd‐NP], nanoflowers, nanofilms) during laser irradiation were studied in this paper. The nanostructures were immobilized on the surface of different solid inorganic carrier materials (porous and mono‐crystalline silicon, anodic porous aluminum oxide, glass and polished steel) by using classical galvanic deposition, electroless local deposition and sputtering. It was the goal of this study to investigate the influence of both the nanoparticular layer as well as the carrier material on ion production for selected analyte molecules. Our experiments demonstrated that the dimensions of the synthesized nanostructures, the thickness of the active layers, surface disorders, thermal conductivity and physically or chemically adsorbed water influenced signal intensities of analyte ions during surface‐assisted laser desorption/ionization (SALDI) while no effects such as plasmon resonance, photoelectric effect or catalytic activity were expected to occur. Excellent LDI abilities were seen for Pd‐NPs immobilized on steel, while Pd nanoflowers on porous silicon exhibited several disadvantages; viz, strong memory effects, dependency of the analytical signal on amount of physically and chemically adsorbed water inside porous carrier, reduced SALDI activity from unstable connections between Pd and semiconductor material, decrease of the melting point of pure silicon after Pd immobilization and resulting strong laser ablation of metal/semiconductor complex, as well as significantly changed surface morphology after laser irradiation. The analytical performance of Pd‐NP/steel was further improved by applying a hydrophobic coating to the steel surface before galvanic deposition. This procedure increased the distance between Pd‐NPs, thus reducing thermal stress upon LDI; it simultaneously decreased spot sizes of deposited sample solutions. Copyright © 2014 John Wiley & Sons, Ltd.     

Electronic, Magnetic, and Magnetoresistance Properties of the n=2 Ruddlesden-Popper Phases Sr3Fe2−xCoxO7−δ (0.25≤x≤1.75)

A series of oxygen-deficient n=2 Ruddlesden-Popper phases, Sr₃Fe_2−xCo_xO_7−δ (0.25≤x≤1.75), were prepared by solid-state reactions. Temperature-dependent susceptibility and field-dependent magnetization data indicate that for x≥0.25 the dominant magnetic interactions are ferromagnetic. The onset of strong ferromagnetic interactions is evident at ∼200 K, and a transition to a cluster-glass state is observed for all compositions below ∼45 K. The temperature variation of resistivity for all the compounds shows variable-range hopping behavior with two different localization energy scales: one for T<40 K and another for T>80 K. Large negative magnetoresistance (the largest MR ∼−65% for x=0.25) is observed for all phases. The magnetic susceptibility, Mössbauer and X-ray absorption near-edge spectroscopy data indicate that the formal oxidation state of Fe is close to 4+. The key role of d delocalization in the Sr₃Fe_2−xCo_xO_7−δ system is compared to the Sr₃Fe_2−xMn_xO_7−δ series, where d localization dominates the properties.     

Synthesis and Comparison of the Reactivity of 3,4,5‐1H‐Trinitropyrazole and Its N‐Methyl Derivative

3,4,5‐Trinitro‐1H‐pyrazole ( 1 ) has been obtained via nitration of 3,5‐dinitropyrazole with mixture of sulfuric and nitric acids. Compound 1 reacts with excess ammonia and aliphatic amines, in the presence of bases with NH‐azoles, phenols, thiols, and triflouroethanol at mild conditions in water. All these reactions occur as the nucleophilic substitution of the nitro‐group at position 4 in 1 affording 4‐R‐3,5‐dinitropyrazoles. The product of methylation of 1 , N‐methyl‐3,4,5‐trinitropyrazole ( 4 ), also reacts with thiols, phenols, oximes, ammonia, amines, and NH‐azoles. The reactions proceed with high yields but nucleophilic substitutions in these cases occur regioselectively at position 5 in 4 to afford 5‐R‐3,4‐dinitropyrazoles.     

Tris(Trimethylsilyl)Phosphine in Reaction with Bis(Phenylenedioxa)Chlorophosphorane. The Way to Phosphoranylphosphines

Abstract

Tris(trimethy1silyl)phosphine (1) is the key reagent in the synthesis of one- and two-coordinated phosphorus compounds. Its characteristic features are extreme reactivity, high nucleophility of phosphorus atom and the P-Si bonds lability. The interaction of phosphine (1) with bis(catecho1)chlorophosphome (2) has been studied by dynamic ³¹P NMR method. On the reagents ratio 1:1 at first the nucleophilic substitution of chlorine occurs leading to formation of phosphome (3) with P^III-P^v bond (σ_P(III) -117.0, σ^P(V) 17.4 ppm, ¹J_pp 305.0 Hz) which converts then into more stable 2-(trimethylsiloxyphenyloxy)-4,5-bem- 1,3,2-dioxaphospholane (4).