Static headspace versus head space solid-phase microextraction (HS-SPME) for the determination of volatile organochlorine compounds in landfill leachates by gas chromatography

The determination of five volatile organochlorine compounds, VOX (chloroform, 1,1,1-trichloroethane, carbon tetrachloride, trichloroethene and tetrachloroethene) in raw landfill leachates and biologically cleansed leachates by GC-MS is investigated. Two extraction and preconcentration procedures were evaluated for recovery of such analies from the samples, including static headspace (HS) and solid phase microextraction by sampling the headspace above the sample (HS-SPME). Optimisation of operating parameters for the best performance of both, sampling and preconcentration techniques was described. Detection limits, time of analysis, precision and linear ranges of both introduction techniques have been established. Application of proposed methods to the determination of the five VOX under study in the above referred samples revealed the absence of such analytes in both leachates. Then both methods were applied to the determination to the five organochlorine compounds under study on spiked leachates samples. While HS-GC-MS offered better analytical precision than HS-SPME-GC-MS, this last technique gave a faster analytical response because no dilution must be done for a reliable VOX determination in landfill leachates. In any case, both sample introduction techniques tested provides excellent recoveries and good analytical precision (ranged from 1 to 3%).     

Mononuclear Tricoordinate Copper(I) and Silver(I) Halide Complexes of a Sterically Bulky Thiourea Ligand and a Computational Insight of Their Interaction with Human Insulin

Reaction of two equivalents of the bulky 1,3-bis(2,6-diethylphenyl)thiourea ligand (L) with MX (being M = Cu⁺, Ag+; and X = Cl⁻, Br⁻, I⁻) in acetonitrile afforded neutral complexes of the type [MXL₂] [CuClL₂].2CH₃CN (1a); [CuBrL₂].2CH₃CN (1b); [CuIL₂] (1c): [AgClL₂] (2a); [AgBrL₂] (2b) and [AgIL₂] (2c). The two aromatic groups in free ligand were found to be trans with respect to the thiourea unit, which was a reason to link the ligand molecules via intermolecular hydrogen bonding. Intramolecular hydrogen bonding was observed in all metal complexes. The copper complexes 1a and 1b are acetonitrile solvated and show not only intra- but also intermolecular hydrogen bonding between the coordinated thiourea and the solvated acetonitrile molecules. Silver complexes reported here are the first examples of structurally characterized tricoordinated thiourea-stabilized monomeric silver(I) halides. Molecular docking studies were carried out to analyze the binding modes of the metal complexes inside the active site of the human insulin (HI) protein. Analysis of the docked conformations revealed that the electrostatic and aromatic interactions of the protein N-terminal residues (i.e., Phe and His) may assist in anchoring and stabilizing the metal complexes inside the active site. According to the results of docking studies, the silver complexes exhibited the strongest inhibitory capability against the HI protein, which possesses a deactivating group, directly bonded to silver. All compounds were fully characterized by elemental analysis, NMR spectroscopy, and molecular structures of the ligand, and five out of six metal complexes were also confirmed by single-crystal X-ray diffraction.     

Thermodynamic characteristics and the temperatures of relaxation transitions of poly(methacrylic acid)

The heat capacity of poly(methacrylic acid) containing 2.5 wt % water was measured in a vacuum adiabatic calorimeter at temperatures between 80 and 325 K. The heat capacity of anhydrous poly(methacrylic acid) was calculated, and its standard enthalpies of combustion and formation were determined. On the basis of the enthalpy of melting of the “free”-water phase, the limit of water solubility in the polymer was found calorimetrically at 273 K. The temperatures of relaxation transitions (the glass transition and the β and γ transitions) of poly(methacrylic acid) mixtures with water were determined via differential thermal analysis in the region 80–550 K. In addition, the determination of the temperatures of transitions of anhydrous poly(methacrylic acid) was performed via extrapolation to zero water content of the concentration dependences of the relaxation-transition temperatures.     

Acceleration Modes in Fermi Accelerator

We explain Fermi acceleration of particles bouncing in a gravitational field and experiencing a force due to a modulated evanescent laser field. The acceleration strongly depends upon the initial conditions in the phase space and certain modulation amplitude. We study the accelerated modes by the Poincaré surface of sections and Lyapunov exponents. Furthermore, we identify the initial areas of the phase space that support accelerated dynamics and write a mapping for accelerated dynamics. We show that a distinction between accelerated and chaotic evolutions can be made with the help of the aspect ratio. The Lyapunov exponent shows that the accelerated mode supports ordered evolution.     

Suppression of band crossing in the neutron-rich nuclei 172, 173Yb due to the absence of a static pair field

High-spin states in the neutron-rich nuclei ^172,173Yb have been populated in a ¹⁷⁰Er(⁷Li,(p,d,t)xn) incomplete-fusion reaction and the emitted γ-radiation was detected with the GASP array. The signature partners of the 7/2⁺[633] rotational band of the odd-N ¹⁷³Yb isotope have been newly established and were observed up to spin values of (45/2⁺) and (43/2⁺), respectively. The ground-state band of the even-even nucleus ¹⁷²Yb has been observed up to a spin value of (22⁺). No band crossings were found in these bands. To explain this observation, it is proposed that the static pair field is absent, considering that the neutron odd-even mass differences reach for these nuclei very small values and that the band crossing is absent in cranked shell modell calculations without pairing. The results indicate, however, that strong dynamic correlations are still present.     

Lifetime measurements in 148Gd

Lifetimes of excited states in ¹⁴⁸Gd were measured using the recoil distance method with a plunger device coupled to the EUROBALL Ge detector array. The differential decay curve method in coincidence mode allowed the unambiguous determination of lifetimes of more than 20 excited states. The obtained transition strengths are in good agreement with the shell model calculations. The effect of the Z = 64 subshell closure on the B(E2 : 2⁺ → 0⁺) reduced strengths above the N = 82 magic number is discussed.-1 Received: 14 November 2002 / Accepted: 4 February 2003 / Published online: 29 April 2003     

Bacterial Constituents CXIII Structure Revision of Several Pyoverdins Produced by Plant-Growth Promoting and Plant-Deleterious Pseudomonas Species

The structural revision on the basis of spectroscopic and degradation results of several pyoverdins from Pseudomonas spp. is reported. Siderotyping studies by the isoelectrofocusing technique and by ferri-pyoverdin uptake experiments had prompted a re-investigation of some structures proposed in the literature.     

The radioprotective and prophylactic properties of biologically active substances prepared by supercritical fluid extraction from pine shoots

The radioprotective properties of a substance from pine shoots prepared by supercritical fluid extraction with carbon dioxide were studied for a model of an experimental bone-marrow radiation sickness form. Experiments were performed for white nonlinear mice. The CO₂ extract of pine shoots was shown to possess radioprotective properties. The extract was subjected to pre-clinical tests for Wistar line male rats with respect to its antiatherogenic and antioxidative action in the creation of experimental hyperlipemia.