Determination of ethylene glycol dinitrate in dynamites using HPLC: application to the plastic explosive Goma-2 ECO

In this study, a sequential extraction method using water and methanol to recover ethylene glycol dinitrate or nitroglycol (EGDN) contained in Goma-2 ECO dynamite was developed. After, an HPLC method was used for the determination of EGDN in the two extracted phases. The analytical method was validated by evaluating its selectivity, sensitivity, linearity, and linear working concentration range, limit of detection and quantitation, precision (as repeatability and intermediate precision), accuracy, and robustness, providing appropriate values (i.e. RSD values for precision about 6% and accuracy about 100%). Finally, the EGDN content of a sample of the Goma-2-ECO dynamite was determined obtaining a concentration of 30.29%, which is in accordance with the manufacturer's specifications for this dynamite (25.7-31.4%).     

Very long-distance magnetic coupling in a dicopper(II) metallacyclophane with extended π-conjugated diphenylethyne bridges

Self-assembly of the rigid rodlike ligand N,N'-4,4'-diphenylethynebis(oxamate) (dpeba) and Cu(2+) ions affords a novel dinuclear copper(II) metallacyclophane (nBu(4)N)(4)[Cu(2)(dpeba)(2)]·4MeOH·2Et(2)O (1) featuring a very long intermetallic distance (r = 15.0 ?). Magnetic susceptibility measurements for 1 reveal a moderately weak but nonnegligible intramolecular antiferromagnetic coupling between the two metal centers across the double para-substituted diphenylethynediamidate bridge (J = -3.9 cm(-1); H = -JS(1)S(2), where S(1) = S(2) = S(Cu) = (1)/(2)). Density functional electronic structure calculations on 1 support the occurrence of a spin polarization mechanism.     

Click assembly of dye-functionalized octasilsesquioxanes for highly efficient and photostable photonic systems

New hybrid organic–inorganic dyes based on an azide‐functionalized cubic octasilsesquioxane (POSS) as the inorganic part and a 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BDP) chromophore as the organic component have been synthesized by copper(I)‐catalyzed 1,3‐dipolar cycloaddition of azides to alkynes. We have studied the effects of the linkage group of BDP to the POSS unit and the degree of functionalization of this inorganic core on the ensuing optical properties by comparison with model dyes. The high fluorescence of the BDP dye is preserved in spite of the linked chain at its meso position, even after attaching one BDP moiety to the POSS core. The laser action of the new dyes has been analyzed under transversal pumping at 532 nm in both the liquid phase and when incorporated into solid polymeric matrices. The monosubstituted new hybrid dye exhibits high lasing efficiency of up to 56 % with high photostability, with its laser output remaining at the initial value after 4×10⁵ pump pulses in the same position of the sample at a repetition rate of 30 Hz. However, functionalization of the POSS core with eight fluorophores leads to dye aggregation, as quantum mechanical simulation has revealed, worsening the optical properties and extinguishing the laser action. The new hybrid systems based on dye‐linked POSS nanoparticles open up the possibility of using these new photonic materials as alternative sources for optoelectronic devices, competing with dendronized or grafted polymers.     

Nature of the intermediates in gold(I)-catalyzed cyclizations of 1,5-enynes

The carbene or carbocationic nature of the intermediates in the gold-catalyzed cycloisomerization of 1,5-enynes can be revealed, depending on the ligands on the gold catalysts. Gold complexes with highly electron-donating ligands promote reactions that proceed via intermediates with carbene-like character, leading to products with a bicyclo[3.1.0]hexene skeleton. The intermediate cyclopropyl endo-gold carbenes formed in this cyclization have been trapped, for the first time, to give biscyclopropane derivatives in a reaction that proceeds in a concerted fashion, according to DFT calculations.     

Estimation of Activation Energy from the Survival Yields: Fragmentation Study of Leucine Enkephalin and Polyethers by Tandem Mass Spectrometry

A simple collision model for multiple collisions occurring in quadrupole type mass spectrometers was derived and tested with leucine enkaphalin a common mass spectrometric standard with well-characterized properties. Implementation of the collision model and Rice-Ramsperger-Kassel-Marcus (RRKM) algorithm into a spreadsheet software allowed a good fitting of the calculated data to the experimental survival yield (SY) versus collision energy curve. In addition, fitting also ensured to estimate the efficiencies of the kinetic to internal energy conversion for Leucine enkephalin in quadrupole-time-of-flight and triple quadrupole instruments. It was observed that the experimental SY versus collision energy curves for the leucine enkephalin can be described by the Rice-Ramsperger-Kassel (RRK) formalism by reducing the total degrees of freedom (DOF) to about one-fifth. Furthermore, this collision model with the RRK formalism was used to estimate the critical energy (E _o ) of lithiated polyethers, including polyethylene glycol (PEG), polypropylene glycol (PPG), and polytetrahydrofurane (PTHF) with degrees of freedom similar to that of leucine enkephalin. Applying polyethers with similar DOF provided the elimination of the effect of DOF on the unimolecular reaction rate constant. The estimated value of E _o for PEG showed a relatively good agreement with the value calculated by high-level quantum chemical calculations reported in the literature. Interestingly, it was also found that the E _o values for the studied polyethers were similar.

A Quality Assurance Study for the Analysis of Hydrocarbons in Sediments

Abstract

Two exercises (MEDCAL I and II) were conducted in our Department during November 1984 and October 1986, with participants from the Mediterranean region, for testing the IOC Manual for the determination of petroleum hydrocarbons in sediments (IOC, Manuals and Guides, No. 11).

The gas chromatographic analysis of the saturated hydrocarbon fraction provided, at the best, a precision of 60% (relative standard deviation RSD) for n-alkanes (mean conc. 0.89 μg/g) and 56 % for the unresolved complex mixture (UCM) (mean conc. 16μg/g). The CPI and the pristane/phytane ratio provided better results (13% RSD). The aromatic fractions, analysed by UV-fluorescence, yielded in total a mean concentration of 10μg/g of chrysene equivalents with a 49% RSD.

The extraction-partition step was confirmed to be the main source of error in the analysis because when the results were corrected for recoveries, the RSD were reduced to 17, 30 and 6% for n-alkanes, UCM and total aromatics, respectively. Our reference intra-laboratory precision was, respectively, 18, 14 and 14%.     

2-Phospha-Allylic Systems

Abstract

Phosphamethincyanines prepared in 1964 by Dimroth and Hoffmann were among the first compounds with two-coordinate phosphorus. They are special cases of 2-phospha-allylic cations. Simple representatives of this type become available from the reaction of imidoyl chlorides with tris(trimethylsily1)phosphane.     

Synthesis of Fully O-Benzylated N-Linked Core Pentasaccharide Glycosyl Azide

The fully O-benzylated pentasaccharide glycosyl azide representing the common core structure of N-glycans was synthesized. The β-mannosidic linkage was created by C-2 epimerization of the initially introduced β-d- gluco-unit via DMSO/Ac₂O oxidation followed by stereoselective reduction with tetrabutylammonium borohydride.     

Structural characterization and dielectric properties of the solid solutions AgPb(Sb,Bi)S3

The new solid solutions AgPbSb_1 − x Bi _x S₃ were prepared by solid state reactions. The phases were characterized by powder X-ray diffractions (XRD), scanning electron microscopy, and thermal analysis. The XRD patterns of different members (x = 0.5, 0.7, 0.8, and 1.0) are consistent with pure phases crystallizing in the cubic PbS-type structure. The electrical characterization was carried out using ac impedance spectroscopy and dc methods. The temperature dependence of the dc conductivity shows typical semiconductor Arrhenius behavior. The impedance measurements were performed in the frequency range of 0.1 Hz to 10 MHz and at the temperature range of 15 °C to 350 °C. The ac conductivity conforms to Jonscher’s universal power law. The frequency dependence of the dielectric permittivity follows the normal dielectric material behavior, and the relaxation is thermally activated. The frequency and temperature dependences of the electrical data are found to follow Summerfield scaling formalism.     

Studies on the synthesis of pentacyclic strychnos indole alkaloids. photocyclization of n-chloroacetyl-1,2,3,4,5,6-hexahydro-1,5-methanoazocino[4,3-b]indole derivatives

Photocyclization of 2-chloroacetyl-1,2,3,4,5,6-hexahydro-1, 5-methanoazocino[4,3-b]indole ($\text{5}$) takes place at the indole 4-position to give a 1 ,2 ,3 ,4 , 5 ,6-hexahydro-2 ,11-ethano-1 ,5-methanoazocino [4 , 3-6] indole system. Consequently, the method appears to be unsuitable for constructing the pyrrolidine ring of pentacyclic Strychnos indole alkaloids.