Configuration assignments of yrare high-spin structures in 126Cs

High-spin states in ¹²⁶Cs were populated in the reaction ¹¹⁶Cd(¹⁴N, 4n) at a beam energy of 65 MeV. About 50 new transitions were placed in a level scheme that consists of six rotational structures, three of which have been observed for the first time. The newly observed bands and a previously reported but uninterpreted band were assigned configurations based on their population, aligned angular momentum, energy signature splitting and B(M1)/B(E2) ratios (for the strongly coupled bands).Received: 16 September 2002, Revised: 10 March 2003, Published online: 1 July 2003PACS: 21.10.Re Collective levels - 27.60.+j      

The cyclic fixation and reduction of molecular nitrogen with [WH4(Ph2PCH2CH2PPh2)2] in γ-irradiated solutions

Yields of NH₃ and N₂H₄ in radiation-catalytic reduction of N₂ by means of a hydride complex of W^IV with dppe in thf solution and in mixtures of thf with other solvents have been estimated. A mechanism proposed earlier of reduction of coordinated N₂ has been confirmed and the role of solvent in reduction of N₂ to NH₃ and amines has been explained.     

Hydrogen adsorption in a highly stable porous rare-earth metal-organic framework: sorption properties and neutron diffraction studies

A highly stable porous lanthanide metal-organic framework, Y(BTC)(H2O).4.3H2O (BTC = 1,3,5-benzenetricarboxylate), with pore size of 5.8 A has been constructed and investigated for hydrogen storage. Gas sorption measurements show that this porous MOF exhibits highly selective sorption behaviors of hydrogen over nitrogen gas molecules and can take up hydrogen of about 2.1 wt % at 77 K and 10 bar. Difference Fourier analysis of neutron powder diffraction data revealed four distinct D2 sites that are progressively filled within the nanoporous framework. Interestingly, the strongest adsorption sites identified are associated with the aromatic organic linkers rather than the open metal sites, as occurred in previously reported MOFs. Our results provide for the first time direct structural evidence demonstrating that optimal pore size (around 6 A, twice the kinetic diameter of hydrogen) strengthens the interactions between H2 molecules and pore walls and increases the heat of adsorption, which thus allows for enhancing hydrogen adsorption from the interaction between hydrogen molecules with the pore walls rather than with the normally stronger adsorption sites (the open metal sites) within the framework. At high concentration H2 loadings (5.5 H2 molecules (3.7 wt %) per Y(BTC) formula), H2 molecules form highly symmetric novel nanoclusters with relatively short H2-H2 distances compared to solid H2. These observations are important and hold the key to optimizing this new class of rare metal-organic framework (RMOF) materials for practical hydrogen storage applications.     

Analysis of dinitro- and amino-nitro-toluenesulfonic acids in groundwater by solid-phase extraction and liquid chromatography–mass spectrometry

A reversed-phase LC–MS method with quadrupole-time of flight (QTOF) detection has been developed for the determination of four dinitro-toluenesulfonic acids and two amino-nitro-toluenesulfonic acids in groundwater. The analytes were separated by HPLC with 0.1% (v/v) formic acid as mobile phase modifier compatible with mass spectrometric detection. QTOF-MS analysis with negative ion electrospray ionization afforded good selectivity and sensitivity for analysis of the dinitro- and amino-nitro-toluenesulfonic acids. Structure elucidation and confirmation were accomplished by tandem mass spectrometry. Characteristic ions resulting from the loss of NO, NO₂, and SO₂ from the [M–H]^– ions were detected. An intense fragment ion at m/z 80 representing the [SO₃]^– ion was detected for all dinitro- and amino-nitro-toluenesulfonic acids. Solid-phase extraction using a co-polymer cartridge was developed for preconcentration of the analytes from water. Good recovery (>85%) was achieved when 0.1% formic acid was added into the water samples before extraction. Method detection limits ranged from 10 to 76 ng L^–1 for the targeted compounds when 10 mL water was analyzed. Groundwater samples collected from wells close to a former ammunition plant in Stadtallendorf, Germany, were analyzed for the dinitro- and amino-nitro-toluenesulfonic acids.     

Study of multiple binding constants of dexamethasone with human serum albumin by capillary electrophoresis–frontal analysis and multivariate regression

Studies into the interactions between drugs and human serum albumin (HSA) are extremely important for drug discovery, since HSA behaves as a carrier for external drugs and internal biological molecules. In this paper, to evaluate the pharmacokinetic and pharmacodynamic properties of dexamethasone (DXM), the interaction between DXM and HSA was studied by capillary electrophoresis–frontal analysis (CE-FA). According to the Klotz equation, four binding sites between DXM and HSA were obtained, and the average binding constant was 1.05 × 10³ M⁻¹. Furthermore, according to multiple equilibrium theory, based on the assumption that there are two types of binding site, the binding constant at one site was calculated to be 3.539 × 10³ M⁻¹, and the average of the other three was 1.234 × 10³ M⁻¹. In addition, to obtain the detailed binding information at each binding site, new equations were deduced by multivariate regression. The four binding constants of DXM and HSA were calculated to be 5.558 × 10¹ M⁻¹, 2.158 × 10⁴ M⁻¹, 7.312 × 10³ M⁻¹ and 2.043 × 10³ M⁻¹, respectively, which is helpful for detailed studies into the interactions between drugs and proteins with multiple binding sites. Figure Electropherograms of DXM sodium phosphate and HAS mixtures for different protein to drug concentration ratios, obtained by CE-FA     

Quantitative study of interactions between oxygen lone pair and aromatic rings: substituent effect and the importance of closeness of contact

Current models describe aromatic rings as polar groups based on the fact that benzene and hexafluorobenzene are known to have large and permanent quadrupole moments. This report describes a quantitative study of the interactions between oxygen lone pair and aromatic rings. We found that even electron-rich aromatic rings and oxygen lone pairs exhibit attractive interactions. Free energies of interactions are determined using the triptycene scaffold and the equilibrium constants were determined by low-temperature 1H NMR spectroscopy. An X-ray structure analysis for one of the model compounds confirms the close proximity between the oxygen and the center of the aromatic ring. Theoretical calculations at the MP2/aug-cc-pVTZ level corroborate the experimental results. The origin of attractive interactions was explored by using aromatic rings with a wide range of substituents. The interactions between an oxygen lone pair and an aromatic ring are attractive at van der Waals' distance even with electron-donating substituents. Electron-withdrawing groups increase the strength of the attractive interactions. The results from this study can be only partly rationalized by using the current models of aromatic system. Electrostatic-based models are consistent with the fact that stronger electron-withdrawing groups lead to stronger attractions, but fail to predict or rationalize the fact that weak attractions even exist between electron-rich arenes and oxygen lone pairs. The conclusion from this study is that aromatic rings cannot be treated as a simple quadrupolar functional group at van der Waals' distance. Dispersion forces and local dipole should also be considered.     

Study on two coordination compounds using semicarbazide (SCZ) as bidentate ligand: {[\hbox{Ni}(\hbox{SCZ})_{3}](\hbox{NO}_{3})_{2}} and {\hbox{Cu}(\hbox{SCZ})_{2}\hbox{Cl}_{2}}

Two coordination compounds have been synthesized using semicarbazide as ligand- ${[\hbox{Ni}(\hbox{SCZ})_{3}](\hbox{NO}_{3})_{2}}$ (1) and ${\hbox{Cu}(\hbox{SCZ})_{2}\hbox{Cl}_{2}}$ (2). (1) crystallized as the monoclinic, P2(1)/c space group, a = 10.832(2) Å, b = 9.980(2) Å, c = 13.801(3) Å, β = 102.89(3)°; (2) crystallized as the monoclinic, P2(1)/c space group, a = 7.541(1) Å, b = 9.275(1) Å, c = 6.875(1) Å, β = 101.48(1)°. In both compounds, semicarbazides coordinate to nickel(II) or copper(II) centers to form the 5-member ring system. With the intermolecular hydrogen bonds, molecules are linked together to form the three-dimensional packing diagrams. Thermal decomposition mechanisms of both compounds were predicted based on DSC, TG-DTG and FTIR analyses.     

Experiment investigation of La(1-x)SrxMnO3 by high-resolution X-ray emission and spin-polarized X-ray absorption spectroscopy

Big changes in resistivity along with the changing of local structure in some oxide systems, such as high-temperature superconductors and colossal magnetoresistance system, strongly suggest the need of a systematic investigation of their local electronic and atomic structures. In this work we present the high-resolution X-ray emission spectra and the spin-polarized X-ray absorption near-edge spectroscopy (SPXANES) data at the Mn K-edge in the La(1-x)Sr(x)MnO(3). This experiment is based on a high-resolution large-acceptance crystal analyzer based on Si (111) and optimized for X-ray fluorescence spectroscopy. With a spherical bent crystal monochromator, a Mn Kbeta emission spectra with high resolution was obtained with a short collection time and SPXANES spectra of La(1-x)Sr(x)MnO(3) at room temperature were also measured at high temperature.     

Voltammetry and electrocatalytic properties of cobalt (1,4,8,12-tetraazacyclopentadecane) in aqueous solution

Summary The spectrochemical, electrochemical and electrocatalytic properties of Co[15]aneN₄ ([15]aneN₄ = 1,4,8,12-tetraazacyclopentadecane) have been investigated. The results show that, in aqueous solution, this compound mainly exists as three species whose axial coordination positions are occupied by water and/or hydroxy ligands; it is marginal whether other substrates such as Cl^– and NO _inf3 ^sup– interact with the central ion in acid-base solutions. The approximate Pourbaix diagram of Co^III/II[15]ane N₄ was determined. There is an electrochemically-induced isomerization between two trans conformational isomers of the Co[15]aneN₄ complexes in acid and netural solutions. The Co[15]aneN₄ complex has electrocatalytic properties for reduction of nitrate and nitrite only in strong alkaline solution.     

Carbon-assisted morphological manipulation of CdS nanostructures and their cathodoluminescence properties

CdS nanostructures with different morphologies and sizes were successfully fabricated through a facile and effective carbon-assisted thermal evaporation method. Through simply changing the positions of silicon substrates, the temperatures and the effects of carbon in different zones were modified, and thus the morphologies of CdS nanostructures were varied from multipods to nanobrushes to nanocups. These nanostructures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDS), X-ray powder diffraction (XRD) and Raman spectroscopy. Cathodoluminescence (CL) measurement shows that the as-grown CdS nanostructures display different luminescent properties. CdS multipods and nanocups show mainly green emission centered at 496 nm. However, nanobrushes exhibit predominant red emission band peaking at 711 nm. These interesting results show that carbon not only affected the growth process but also influenced the properties of CdS nanostructures.