Study of molar response of dextrans in electrochemical detection

In this work, a methodological approach is reported, aimed at assessing the electrochemical response of some model gluco-oligosaccharides (dextrans). Such strategy is based on the complementary use of both anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and capillary zone electrophoresis coupled with UV detection (CZE-UV). Unlike HPAEC-PAD, CZE-UV required derivatization with a chromophoric dye (i.e., 8-aminonaphtalene-1,3,6-trisulphonic acid, ANTS) to enhance UV response and separation selectivity. From the comparison between chromophore response and PAD signal, the reliability of HPAEC-PAD for quantitative evaluation of dextran mixtures containing mainly oligomers with polymerization degree (DP) up to 18 could be proved, due to the fairly constant molar response. For higher DPs (up to 41), a maximum in the trend of the molar responses was observed followed by a steep decrease for DPs higher than about 30-35; indeed, an underestimation of weight-average molecular weight of dextran mixtures containing such oligomers was noticed.     

Ising phases of Heisenberg ladders in a magnetic field

We show that Dzyaloshinskii-Moriya (DM) interactions can substantially modify the phase diagram of spin-1/2 Heisenberg ladders in a magnetic field provided they compete with exchange. For nonfrustrated ladders, they induce a local magnetization along the DM vector that turns the gapless intermediate phase into an Ising phase with broken translational symmetry, while for frustrated ladders, they extend the Ising order of the half-integer plateau to the surrounding gapless phases of the purely Heisenberg case. Implications for experimental ladder and dimer systems are discussed.     

Electrospray mass spectrometric studies of a potential antitumor drug and its analogous platinum(II) and platinum(IV) complexes with the ethylenediamine-N,N′-di-3-propanoato ligand and its dibutyl ester

Abstract  The electrospray mass spectrometric (ESI–MS) behavior of the complexes trans-dichloro(ethylenediamine-N,N′-di-3-propionato)platinum(IV), trans-dibromo(ethylenediamine-N,N′-di-3-propionato)platinum(IV), dichloro(ethylenediamine-N,N′-di-3-propionic acid)platinum(II), tetrachloro(O,O′-di-n-butyl-ethylenediamine-N,N′-di-3-propanoate)platinum(IV), chlorotribromo(O,O′-di-n-butyl-ethylenediamine-N,N′-di-3-propanoate)platinum(IV), and dichloro(O,O′-di-n-butyl-ethylenediamine-N,N′-di-3-propanoate)platinum(II), with the formulae trans-[PtCl₂(eddp)] (1), trans-[PtBr₂(eddp)] (2), [PtCl₂(H₂eddp)] (3), [PtCl₄(Bu₂eddp)] (4), [PtBr₃Cl(Bu₂eddp)] (5), and [PtCl₂(Bu₂eddp)]·H₂O (6), is reported. The deprotonated molecular ions or halide adducts are usually observed. ESI–MS data demonstrate the usefulness of the method for efficient characterization of metal complexes in solution. Graphical Abstract        

Three-sublattice ordering of the SU(3) Heisenberg model of three-flavor fermions on the square and cubic lattices

Combining a semiclassical analysis with exact diagonalizations, we show that the ground state of the SU(3) Heisenberg model on the square lattice develops three-sublattice long-range order. This surprising pattern for a bipartite lattice with only nearest-neighbor interactions is shown to be the consequence of a subtle quantum order-by-disorder mechanism. By contrast, thermal fluctuations favor two-sublattice configurations via entropic selection. These results are shown to extend to the cubic lattice, and experimental implications for the Mott-insulating states of three-flavor fermionic atoms in optical lattices are discussed.     

Optical conductivity of the Bechgaard salts: the sum rules revisited

The validity of the optical sum rules has been addressed eversince and was always matter of debate. Particularly controversial is the proof that the partial sum rules can be extended to both optical conductivity and energy loss function. We show in this paper that for both transverse (optical conductivity) and longitudinal (energy loss function) absorption processes the corresponding sum rule can be theoretically established and through appropriate conditions for the integration limits exactly verified. We also focus our attention on the one-dimensional case within the microscopic Hubbard model. An application of these concepts to the quasi one-dimensional systems, for which we have chosen the organic (TMTSF)₂PF₆ material, will also be presented. Received: 19 December 1997 / Received in final form: 9 March 1998 / Accepted: 23 March 1998     

Spectral function and self-energy of the one-dimensional Hubbard model in the U →∞ limit

The interpretation of the k dependent spectral functions of the one-dimensional, infinite U Hubbard model obtained by using the factorized wave-function of Ogata and Shiba is revisited. The well defined feature which appears in addition to low energy features typical of Luttinger liquids, and which, close to the Fermi energy, can be interpreted as the shadow band resulting from 2k _F spin fluctuations, is further investigated. A calculation of the self-energy shows that, not too close to the Fermi energy, this feature corresponds to a band, i.e. to a solution of the Dyson equation ω-ε(k)-ReΣ(k,ω) = 0.     

Determination of Cr(VI) in welding fumes by anion-exchange fast protein liquid chromatography with electrothermal atomic absorption spectrometric detection

The applicability of an anion-exchange fast protein liquid chromatographic-electrothermal atomic absorption spectrometric procedure (FPLC-ETAAS) was investigated for the determination of Cr(VI) in welding fumes after alkaline extraction of aerosols loaded on filters. Gas tungsten arc welding (GTAW) of stainless steel was applied. Samples of welding fumes were collected during regular welding on polycarbonate membrane filters of 8 microm and 0.4 microm pore size (inhalable and respirable aerosols). Alkaline extraction (2% NaOH-3% Na2CO3) of filters in a heated ultrasonic bath was applied to leach Cr from the airborne particulate matter. 0.5 cm3 of sample extract was then injected onto an anion-exchange FPLC column. Tris-HCl buffer (0.005 mol dm(-3), pH 8.0) and the same buffer with NaCl (0.5 mol dm(-3)) were employed in gradient elution (15 min, flow rate 1 cm3 min(-1)). The separated Cr species were determined "off line" by ETAAS in 0.5 cm3 fractions. Cr(VI) was reproducibly and quantitatively eluted from 12.0 to 13.0 min with a maximum peak at 12.5 min. Good repeatability of measurement (+/-3.0%) of alkaline extracts was obtained for Cr(VI). The LOD (3s) was found to be 0.035 microg m(-3) Cr(VI), when 2 m3 of aerosols were collected on the filter. Validation of the procedure was performed by spiking alkaline extracts and by the analysis of standard reference material CRM 545, Cr(VI) in welding dust loaded on a filter. The technique was successfully applied for the determination of Cr(VI) in welding fumes.     

Efficient methods for isolating five phytochemicals from Gentiana macrophylla using high‐performance countercurrent chromatography

Efficient high‐performance countercurrent chromatography methods were developed to isolate five typical compounds from the extracts of Gentiana macrophylla. n‐Butanol‐soluble extract of G. macrophylla contained three hydrophilic iridoids, loganic acid ( 1 ), swertiamarin ( 2 ) and gentiopicroside ( 3 ), and a chromene derivative, macrophylloside D ( 4 ) which were successfully isolated by flow rate gradient (1.5 mL/min in 0–60 min, 5.0 mL/min in 60–120 min), and consecutive flow rate gradient HPCCC using n‐butanol/0.1% aqueous trifluoroacetic acid (1:1, v/v, normal phase mode) system. The yields of 1 – 4 were 22, 16, 122, and 6 mg, respectively, with purities over 97% in a flow rate gradient high‐performance countercurrent chromatography, and consecutive flow rate gradient high‐performance countercurrent chromatography gave 1 , 2 , 3 (54, 41, 348 mg, respectively, purities over 97%) and 4 (13 mg, purity at 95%) from 750 mg of sample. The main compound in methylene chloride soluble extract, 2‐methoxyanofinic acid, was successfully separated by n‐hexane/ethyl acetate/methanol/water (4:6:4:6, v/v/v/v, flow‐rate: 4 mL/min, reversed phase mode) condition. The structures of five isolates were elucidated by ¹H, ¹³C NMR and ESI‐Q‐TOF‐MS spectroscopic data which were compared with previously reported values.     

Eu3+、Ga3+共掺杂SiO2基质材料的制备及其发光性质

通过溶胶-凝胶方法制备了稀土离子Eu³⁺和Ga³⁺共掺杂的SiO₂材料;利用IR、XRD等研究了材料的结构,结果表明材料属于非晶态,800 ℃退火后样品的主要结构仍为SiO₂的网状结构。400 ℃退火的样品在393 nm激发下发射光谱显示了Eu³⁺的特征发射光谱,产生3条明显谱带,分别是576 nm(⁵D₀-⁷F     

Dynamic spin Jahn-Teller effect in small magnetic clusters

We study the effect of spin-phonon coupling in small magnetic clusters, concentrating on a S=1/2 ring of 4 spins coupled antiferromagnetically. If the phonons are treated as classical variables, there is a critical value of the spin-phonon coupling above which a static distortion occurs. This is a good approximation if the zero point energy is small compared to the energy gain due to the distortion, which is true for large exchange interactions compared to the phonon energy (J≫ħω). In the opposite limit, one can integrate out the phonon degrees of freedom and get an effective spin Hamiltonian. Using exact diagonalizations to include the quantum nature of both spins and phonons, we obtain the spectrum in the whole range of parameters and explicit the crossover between the classical and quantum regimes. We then establish quantitatively the limits of validity of two widely used approaches (one in the quantum and one in the classical limits) and show that they are quite poor for small magnetic clusters. We also show that upon reducing ħω/J the first excitation of a 4-site cluster becomes a singlet, a result that could be relevant for Cu₂Te₂O₅Br₂.