Radiochemical studies relevant to the separation of 68Ga and 68Ge

The radiochemical separation of radiogallium from radiogermanium was studied using ion-exchange chromatography (Amberlite IR-120) and solvent extraction (Aliquat 336 in o-xylene). Both Amberlite IR-120 and Aliquat 336 in o-xylene have been used for the first time in separations involving radiogallium and radiogermanium. For tracer studies the radionuclides ⁶⁸Ge (t _1/2 = 270.8 days), ⁶⁹Ge (t _1/2 = 39 h) and ⁶⁷Ga (t _1/2 = 78.3 h) were used. They were produced by the nuclear reactions ^natGa(p,xn)^68,69Ge and ^natZn(p,xn)⁶⁷Ga, respectively, and separated from their target materials in no-carrier-added form. Several factors affecting the separation of radiogallium from radiogermanium were studied and for each procedure the optimum conditions were determined. The solvent extraction using Aliquat 336 was found to be better. The separation yield of radiogallium was >95%, the time of separation short, the contamination from radiogermanium <0.008% and the final product was obtained in 0.5 M KOH. This method was adapted to the separation of n.c.a. ⁶⁸Ga from its parent n.c.a. ⁶⁸Ge. The quality of the product thus obtained is discussed.     

Tb4FeGe8 grown in liquid gallium: trans-cis chains from the distortion of a planar Ge square net

The ternary germanide Tb4FeGe8 was obtained from Ga flux reactions. The crystal structure studied with single-crystal X-ray diffraction revealed the existence of an orthorhombic average substructure (Cmcm, Z=1) with cell parameters a = 4.1118(14) A, b=15.844(5) A, and c=3.9885(15) A. The refinement [I > 2sigma(I)] converged to final residuals R1/wR2 = 0.0363/0.0893. The average structure (CeNiSi2-type) consists of a 3D [Fe1/4Ge2] framework where Ge atoms form a square net and Fe atoms reside alternatively above and below it with only 1/4 occupation probability. X-ray and electron diffraction studies showed a modulation in the Ge net. The modulated structure was refined based on a 4-fold monoclinic supercell (P2(1)/n) with parameters a = 5.7315(11) A, b = 15.842(3) A, c = 11.438(2) A, and beta = 91.724(4) degrees with R1/wR2 = 0.0643/0.1735 and uncovered a severe distortion of the Ge square net. The Ge atoms are displaced to form an array of cis-trans chains. The Ge-Ge distances within these chains are distinctively bonding, whereas those between the chains are nonbonding. Results of the electronic structure calculations and magnetic measurements are also reported. The structural distortions found in Tb4FeGe8 cast a doubt onto the correctness of many of the reported REM1-xGe2 disordered compounds and call for reinvestigation.     

Divergence in the behavior of the charge density wave in RETe3 (RE = rare-earth element) with temperature and RE element

Comparable changes in the volume of RETe3 materials caused by temperature and RE size have opposite trends to the incommensurate charge density wave modulation. This is unique behavior among all reported charge density wave materials.     

Intermetallics as zintl phases: Yb2Ga4Ge6 and RE3Ga4Ge6 (RE=Yb, Eu): structural response of a [Ga4Ge6]4- framework to reduction by two electrons

Two new intermetallic compounds, Yb(2)Ga(4)Ge(6) and Yb(3)Ga(4)Ge(6), were obtained from reactions in molten Ga. A third compound, Eu(3)Ga(4)Ge(6), was produced by direct combination of the elements. The crystal structures of these compounds were studied by single-crystal X-ray diffraction. Yb(2)Ga(4)Ge(6) crystallizes in an orthorhombic cell with a=4.1698(7), b=23.254(4), c=10.7299(18) A in the polar space group Cmc2(1). The structure of RE(3)Ga(4)Ge(6) is monoclinic, space group C2/m, with cell parameters a=23.941(6), b=4.1928(11), c=10.918(3) A, beta=91.426(4) degrees for RE=Yb, and a=24.136(2), b=4.3118(4), c=11.017(1) A, beta=91.683(2) degrees for RE=Eu. The refinement [I>2 sigma(I)] converged to the final residuals R(1)/wR(2)=0.0229/0.0589, 0.0411/0.1114, and 0.0342/0.0786 for Yb(2)Ga(4)Ge(6), Yb(3)Ga(4)Ge(6), and Eu(3)Ga(4)Ge(6), respectively. The structures of these two families of compounds can be described by a Zintl concept of bonding, in which the three-dimensional [Ga(4)Ge(6)](n-) framework serves as a host and electron sink for the electropositive RE atoms. The structural relation of RE(3)Ga(4)Ge(6) to of Yb(2)Ga(4)Ge(6) lies in a monoclinic distortion of the orthorhombic cell of Yb(2)Ga(4)Ge(6) and reduction of the [Ga(4)Ge(6)] network by two electrons per formula unit. The results of theoretical calculations of the electronic structure, electrical transport data, and thermochemical and magnetic measurements are also reported.     

Periodic projector augmented wave density functional calculations on the hexachlorobenzene crystal and comparison with the experimental multipolar charge density model

The projector augmented wave (PAW) methodology has been used to calculate a high precision electron density distribution ρ(r) for the hexachlorobenzene crystal phase. Implementing the calculation of the crystallographic structure factors in the VASP code has permitted one to obtain the theoretical multipolar ρ(r). This electron density is compared with both the DFT electron density and the experimental multipolar model obtained from high-resolution X-ray diffraction data. This comparison has been carried out in intra- and intermolecular regions within the framework of the quantum theory of atoms-in-molecules (QTAIM) developed by Bader and co-workers. The characterization of the electron density in both C-Cl and Cl···Cl regions, as well as within the atomic basins, shows similar features for the three models. As a consequence, the observation of charge depletion and charge concentration regions around the halogen nuclei (along the C-Cl bonding axis and in the perpendicular plane, respectively) underlines the nature of halogen bonding in terms of electrophilic and nucleophilic interactions.     

Molecularly imprinted polymer solid-phase extraction coupled to square wave voltammetry at carbon fibre microelectrodes for the determination of fenbendazole in beef liver

A molecularly imprinted polymer was developed and used for solid-phase extraction (MISPE) of the antihelmintic fenbendazole in beef liver samples. Detection of the analyte was accomplished using square wave voltammetry (SWV) at a cylindrical carbon fibre microelectrode (CFME). A mixture of MeOH/HAc (9:1) was employed both as eluent in the MISPE system and as working medium for electrochemical detection of fenbendazole. The limit of detection was 1.9 × 10⁻⁷ mol L⁻¹ (57 μg L⁻¹), which was appropriate for the determination of fenbendazole at the maximum residue level permitted by the European Commission (500 μg kg⁻¹ in liver). Given that the SW voltammetric analysis could not be directly performed in the sample extract as a consequence of interference from some sample components, a sample clean-up with a MIP for selectively retaining fenbendazole was performed. The MIP was synthesized using a 1:8:22 template/methacrylic acid/ethylene glycol dimethacrylate ratio. A Britton–Robinson Buffer of pH 9.0 was selected for retaining fenbendazole in the MIP cartridges, and an eluent volume of 5.0 mL at a flow rate of 2.0 mL min⁻¹ was chosen in the elution step. Cross-reactivity with the MIP was observed for other benzimidazoles. The synthesized MIP exhibited a good selectivity for benzimidazoles with respect to other veterinary drugs. The applicability of the MISPE-SWV method was tested with beef liver samples, spiked with fenbendazole at 5,000 and 500 μg kg⁻¹. Results obtained for ten different liver samples yielded mean recoveries of (95 ± 12)% and (96 ± 11)% for the upper and lower concentration level, respectively.     

High density gradients in the (square root 3 x square root 3)R30 degrees-CO layer on Ru(0001)

The coverage regime just beyond 0.33 ML, representative of a perfectly ordered (square root 3 x square root 3)R30 degrees-CO layer on Ru(0001), has been investigated using infrared-absorption spectroscopy. Different isotopic mixtures of CO have been employed to derive a profound understanding of structural properties of such layers. It is found that extra CO molecules incorporated into the (square root 3 x square root 3)R30 degrees-CO layer affect their nearest neighbor molecules only, and the associated density gradient extends over no more than a few angstroms. Contrary to existing belief, the model system CO on Ru(0001) does not represent a case of an unusually shallow adsorption potential corrugation. Rather, CO experiences an exceptionally strong site preference when adsorbed on Ru(0001). Annealing causes the local distortion of the overlattice to propagate laterally, most probably in a density wave-like manner. Incipient motion on the atomic scale thereby has been detected by means of isotopic labeling of inequivalent molecules within the high density areas. All major conclusions are based on observations of (isotopically labeled) minority CO species which feature negligible dynamical lateral coupling. The majority CO species, on the other hand, provide laterally averaged, unspecific information on the status of the layer.     

Quantitative description of the relation between protein net charge and protein adsorption to air-water interfaces

In this study a set of chemically engineered variants of ovalbumin was produced to study the effects of electrostatic charge on the adsorption kinetics and resulting surface pressure at the air-water interface. The modification itself was based on the coupling of succinic anhydride to lysine residues on the protein surface. After purification of the modified proteins, five homogeneous batches were obtained with increasing degrees of modification and zeta-potentials ranging from -19 to -26 mV (-17 mV for native ovalbumin). These batches showed no changes in secondary, tertiary, or quaternary structure compared to the native protein. However, the rate of adsorption as measured with ellipsometry was found to decrease with increasing net charge, even at the initial stages of adsorption. This indicates an energy barrier to adsorption. With the use of a model based on the random sequential adsorption model, the energy barrier for adsorption was calculated and found to increase from 4.7 kT to 6.1 kT when the protein net charge was increased from -12 to -26. A second effect was that the increased electrostatic repulsion resulted in a larger apparent size of the adsorbed proteins, which went from 19 to 31 nm2 (native and highest modification, respectively), corresponding to similar interaction energies at saturation. The interaction energy was found to determine not only the saturation surface load but also the surface pressure as a function of the surface load. This work shows that, in order to describe the functionality of proteins at interfaces, they can be described as hard colloidal particles. Further, it is shown that the build-up of protein surface layers can be described by the coulombic interactions, exposed protein hydrophobicity, and size.     

An optimized digestion method coupled to electrochemical sensor for the determination of Cd, Cu, Pb and Hg in fish by square wave anodic stripping voltammetry

An optimized digestion method coupled to electrochemical detection to monitor lead, copper, cadmium and mercury in fish tissues was developed. Square wave anodic stripping voltammetry (SWASV) coupled to disposable screen-printed electrodes (SPEs) was employed as fast and sensitive electroanalytical method for heavy metals detection. Different approaches in digestion protocols were assessed. The study was focused on Atlantic hake fillets because of their wide diffusion in the human nutrition. Best results were obtained by digesting fish tissue with hydrogen peroxide/hydrochloric acid mixture coupled to solid phase (SP) purification of the digested material. This combined treatment allowed quantitative extraction from fish tissue (muscle) of the target analytes, with fast execution times, high sensitivity and avoiding organic residues eventually affecting electrochemical measurements. Finally, the method has been validated with reference standard materials such as dogfish muscle (DORM-2) and mussel tissues (NIST 2977).     

A new method for the determination of the interstitial site occupancy of carbon atoms at trace levels in the MO-VPE Ga1−x Al x As lattice

The uptake and the long term behavior of Cs-137, Cs-134 and K-40 in the annual tree rings of spruce were examined. The youngest tree rings which are most active in water transport have higher activity concentrations, of K-40 and of radiocesium than the older ones. The activity concentration of Cs-137 in a water transporting tree ring can be well described as a function of the activity concentration of K-40. Furthermore a depth profile of the soil was taken and gives information, about the depth distribution of radiocesium and K-40.     

Relation of the charge and spin correlation functions to the structures of π electron wave functions in alternant hydrocarbons

We analyze, in the Pariser–Parr–Pople (PPP ) model of alternant hydrocarbons, how the charge and spin correlation functions (CF 's) are related to the structure of a CI wave function and the MO 's of the systems. The analysis is based on the fact that an uncorrelated electron present in an orbital does not contribute to the linked dynamically correlated parts of the CF 's. By using the fact, simple rules are deduced predicting the covalent or ionic nature of the correlation structure in a low-lying state with two correlated electrons. The rules predict that the singlet minus and triplet plus states are covalent, while singlet plus and triplet minus states are ionic, where the plus and minus mean the alternancy symmetry. The rules also give a prediction for the unknown charge and spin correlation structures between different sites.     

Determination of Ga, Ge, As, Se and Sb in fly ash samples by ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry

Ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS) has been applied to determine Ga, Ge, As, Se and Sb in fly ash samples. The influences of instrument operating conditions and slurry preparation on the ion signals were reported. Pd and ascorbic acid were used as the mixed modifiers to enhance the ion signals. This method has been applied to determine Ga, Ge, As, Se and Sb in NIST SRM 1633a and 1633b coal fly ash reference materials and a fly ash sample collected locally. Since the sensitivities of the elements studied in slurry solution and aqueous solution were different slightly, analyte addition technique was used for the determination of Ga, Ge, As, Se and Sb in these samples. The As and Se analysis results of the reference materials agreed with the certified values. The results for which no certified value was available were also found to be in good agreement between the ETV-ICP-MS results and the reference values. The reference value was obtained by digesting the samples and analyzing the digested sample solutions by pneumatic nebulization Dynamic Reaction Cell™ (DRC) ICP-MS. The method detection limits estimated from analyte addition curves were about 0.23, 0.13, 0.17, 0.25 and 0.11 μg g⁻¹ for Ga, Ge, As, Se and Sb, respectively, in original fly ash samples.     

Exploring the conformation,charge density distribution and the electrostatic properties of galanthamine molecule in the active site of AChE using DFT and AIM theory

Quantum chemical calculations and charge density analysis were carried out to understand the geometry, charge density distribution and the electrostatic properties of isolated galanthamine molecule (form I) and for the same lifted out from the active site (form II) of AChE. The optimized geometry of isolated galanthamine was obtained from a hybrid density functional theory (B3LYP/6‐311G**) calculation. A docking analysis on galanthamine with AChE was performed, and the lowest docked energy structure was selected from the active site of AChE for the further study. A single point energy quantum chemical calculation (B3LYP/6‐311G**) was carried out for the lowest energy structure, which was lifted from the galanthamine–AChE complex from molecular docking analysis. The structural comparison between (I) and (II) helps to understand the conformational modification of the galanthamine molecule in the active site. When the molecule present in the active site, the molecular geometry is seen to be significantly altered, specifically, large changes were observed in the outer core of the molecule while the inner core geometry is intact. The bond topological and electrostatic properties of (I) and (II) were calculated. The dipole moment of the galanthamine molecule also increases from 2.09 to 2.67 D in the process. A large negative electrostatic potential region is found at the vicinity of oxygen and nitrogen atoms of the molecule, which predominantly involve strong hydrophobic and electrostatic interactions with the amino acid residues TRP84, PHE330, GLY118, TYR70, and SER122 present in the active site of AChE. © 2013 Wiley Periodicals, Inc.     

REMGa3Ge and RE3Ni3Ga8Ge3 (M = Ni, Co; RE = rare-earth element): new intermetallics synthesized in liquid gallium. X-ray, electron, and neutron structure determination and magnetism

New quaternary intermetallic phases REMGa(3)Ge (1) (RE = Y, Sm, Tb, Gd, Er, Tm; M = Ni, Co) and RE(3)Ni(3)Ga(8)Ge(3) (2) (RE = Sm, Gd) were obtained from exploratory reactions involving rare-earth elements (RE), transition metal (M), Ge, and excess liquid Ga the reactive solvent. The crystal structures were solved with single-crystal X-ray and electron diffraction. The crystals of 1 and 2 are tetragonal. Single-crystal X-ray data: YNiGa(3)Ge, a = 4.1748(10) A, c = 23.710(8) A, V = 413.24(2) A(3), I4/mmm, Z = 4; Gd(3)Ni(3)Ga(8)Ge(3), a = 4.1809(18) A, c = 17.035(11) A, V = 297.8(3) A(3), P4/mmm, Z = 1. Both compounds feature square nets of Ga atoms. The distribution of Ga and Ge atoms in the REMGa(3)Ge was determined with neutron diffraction. The neutron experiments revealed that in 1 the Ge atoms are specifically located at the 4e crystallographic site, while Ga atoms are at 4d and 8g. The crystal structures of these compounds are related and could be derived from the consecutive stacking of disordered [MGa](2) puckered layers, monatomic RE-Ge planes and [MGa(4)Ge(2)] slabs. Complex superstructures with modulations occurring in the ab-plane and believed to be associated with the square nets of Ga atoms were found by electron diffraction. The magnetic measurements show antiferromagnetic ordering of the moments located on the RE atoms at low temperature, and Curie-Weiss behavior at higher temperatures with the values of mu(eff) close to those expected for RE(3+) free ions.     

Orbital contributions to the molecular charge and energy density distributions in Co2(CO)8

For Co2(CO)8, the representative of a whole class of bridged cobalt complexes, the 18-electron rule predicts a direct metal-metal bond in addition to the metal-bridge bonds. By intuition, this bond should have bent-bond character. However, it is well-known from charge density analyses that no bond critical point exists in the corresponding spatial region. Otherwise, the energy density distribution points to a certain stabilizing contribution of this local area to the total molecular energy. It is shown that a partitioning of the total charge and energy densities into orbital contributions can lead to a deeper insight into complex bonding properties.