Size Exclusion Chromatography of Quaternized Poly(vinylpyrrolidone-co-dimethyl Amino Ethyl Methacrylate) Copolymer (PVPDMAEMA): Absolute Molecular Weights and Molecular Weight Distributions by Low Angle Laser Light Scattering and Universal Calibration

Abstract

In 0.1M tris. pH 7 buffer containing 0.5M LiNO₃, PVPDMAEMA (which exists as a cationic polyelectrolyte) was found to elute based on hydrodynamic volume on Waters Ultrahydrogel columns. Within the exclusion limit of the column set an accurate weight average molecular weight of PVPDMAEMA can be obtained by universal calibration which is in very good agreement with the SEC/LALLS result.     

Molecular structures of the 1,6-disubstituted triptycenes Sb2(C6F4)3 and Bi2(C6F4)3 using gas-phase electron diffraction and ab initio and DFT calculations

The structures of the D(3h)-symmetric molecules dodecafluoro-1,6-distibatriptycene and dodecafluoro-1,6-dibismatriptycene [Z2(C6F4)3 (Z = Sb, Bi)] have been determined in the gas phase by electron diffraction, using the SARACEN method, with restraints obtained from quantum chemical calculations. Several methods of ab initio and density functional theory geometry calculations have been performed and recommendations made as to their relative suitabilities for determining the structures of such species. Calculations using the MP2 method with a small-core pseudopotential (aug-cc-pVQZ-PP) on the Sb and Bi atoms and the 6-311G* basis set on the light atoms were found to give the closest correlation with the experimental results for both molecules. Differences in structure were found depending on whether a large-core or small-core pseudopotential was used on the heavy atoms.     

Molecular octopus: octa functionalized calix[4]resorcinarene-hydroxamic acid [C4RAHA] for selective extraction, separation and preconcentration of U(VI)

A solvent extraction separation of uranium, in the presence of thorium, cerium and lanthanides with a new calix[4]resorcinarene bearing eight hydroxamic acid groups (C4RAHA) is described. Quantitative extraction of uranium is possible in ethyl acetate solution of C4RAHA at pH 8.0. The lambda(max) and molar absorptivity (varepsilon) for uranium is 356nm and 8352Lmol(-1)cm(-1). The Binding ratio of uranium with C4RAHA as evaluated by Job's method is 4:1. The system obeys Beer's law over the range 0.075-6.0mugml(-1) of uranium with Sandell sensitivity 0.0284mugcm(-2). A preconcentration factor of 142 was achieved by directly aspirating the extract for GF-AAS measurements. The two-phase stability constant evaluated at 25 degrees C for uranium is 15.91. The complexation is characterized by favorable enthalpy and entropy changes. A liquid membrane transport study of uranium was carried out from source to the receiving phase under controlled conditions and a mechanism of transport is proposed. Uranium has been determined in standard and environmental samples.     

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS): comparison of different internal standardization methods using laser-induced plasma (LIP) emission and LA-ICP-MS signals.

The source of signal variations that governs the analytical performance of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was investigated in this study. In order to specify the source of signal variations of LA-ICP-MS, laser-induced plasma (LIP) Fe emission, LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals were used as internal standards for the determination of trace elements in low-alloy steel certified reference materials (BS 50D and JSS 1005-1008). Fe 1373.5 nm emission signals from LIP were measured, while trace element LA-ICP-MS signals were collected. After that, the LIP emission signals, LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals were used as internal standards, and the analytical performance was evaluated by the RSDs and the correlation coefficients (r) of the calibration curves. The improvement factors were dependent on the internal standardization methods. Analytical precisions (RSDs) of trace element LA-ICP-MS signals were improved by factors of 1.5-3.3 using LIP Fe emission signals as an internal standard. The improvement factors of 2.5 - 5.9 and 4.1 - 17 were obtained by using LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals as internal standards, respectively. Better correlation coefficients (r) were also obtained using the LA-ICP-MS signal compensation (0.9985 by LA-ICP-MS Fe+ and 0.9996 by LA-ICP-MS Ni+) rather than the LIP Fe emission compensation (0.9932). In this paper we compare and discuss the analytical performance achieved by LA-ICP-MS using LIP Fe emission, LA-ICP-MS Fe+ and LA-ICP-MS Ni+ signals as internal standards.     

A facile synthesis to Zn(2)SiO(4):Mn(2+) phosphor with controllable size and morphology at low temperature

Sphere- and rod-shaped Zn(2)SiO(4):Mn(2+) phosphor nanocrystals were synthesized at 230 degrees C. The process consists of tuning the surfactant concentration in the oil/surfactant/ethanol system. Powder X-ray (XRD) and transmission electron microscopy (TEM) were used to characterize the phase purity, size and morphology. Photoluminescent (PL) spectra were collected and analyzed. Fourier transform infrared (FT-IR) spectra of the samples indicate the removal of surfactant in the phosphor nanoparticles. As a result, the sphere-shaped phosphor nanoparticles of 100 nm in size can be redispersed in ethanol ultrasonically. The suspension maintain stable for over 48 h.     

Molecular structure of 2-Amino-5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazol (Megazol) and related compounds: A concerted study using X-ray crystallography,molecular mechanics,and semiempirical methods

A structural study of three nitroimidazoles was carried out using molecular mechanics, semiempirical methods, and X-ray crystallography. Structural features which might account for the high efficiency of1 (Megazol) as an antiparasitic drug and its opposite, the inactivity of its regiomers2 and3 were examined, i.e., coplanarity of the two rings, preferred conformations, and rotational barriers around the pivot bond between the two rings. For the three compounds an antiperiplanar conformation is preferred for the N(CH₃) and C-S bonds. For compounds1 and3, the rings are coplanar, with2 being somewhat twisted. The geometry obtained by molecular mechanics for compound1 is in excellent agreement with the X-ray structure, and greater confidence can be placed in this method than in semiempirical ones. Similarities observed on the LUMO positions, as well as rotational barriers lead to the conclusion that the differences in biological activity of these compounds do not rely on their ground state properties but rather on their subsequent reactions with oxygen. In addition, the calculations revealed significant structural information of a family of biological importance (nitroimidazoles) and constitute a comparative test for the MM2, AM1, and PM3 methods.     

Size and concentration determination of (functionalised) fullerenes in surface and sewage water matrices using field flow fractionation coupled to an online accurate mass spectrometer: Method development and validation

In order to assess the environmental risks of a compound it is imperative to have suitable and reliable techniques for its determination in environmental matrices. In this paper, we focused on a method development for the recently introduced online coupling of a field flow fractionation (FFF) system to an Orbitrap-HRMS, that allows the simultaneous size and concentration determination of different aqueous fullerene aggregates and their concentrations in different size fractions. A 0.05% NH₄OH solution in water was identified as the best carrier liquid for the analysis of the three different aqueous fullerene suspensions (C₆₀ [60], [6,6]-phenyl-C₆₁ butyric acid methyl ester ([60]PCBM) and [6,6]-(bis)phenyl-C₆₁ butyric acid methyl ester ([60]bisPCBM)). The multi-angle light scattering (MALS) data received after employing the ammonia solution was consistent with both the theory and calibration using well defined Au and latex particles. The LODs obtained using Orbitrap HRMS detection were 0.1 μg L⁻¹ for an injection volume of 100 μL which are significantly better than the LODs obtained by using UV (20 μg L⁻¹) and MALS detectors (5 μg L⁻¹). However, these LODs can be further improved as in theory there is no limit to the amount of sample that can be injected into the FFF. Environmental samples (river and sewage water) were spiked with fullerenes and the fractograms obtained for these samples revealed that the matrix does affect the size of fullerene aggregates. Information on the size distribution can be useful for the risk assessment of these particles.     

Trace element analysis of geological glasses by laser plasma ionization mass spectrometry (LIMS): A comparison with other multielement and microanalytical methods

Laser plasma ionization mass spectrometry (LIMS) is used in our laboratory as an in-situ microanalytical method for the investigation of solids, especially of rocks and minerals. To demonstrate the accuracy of this method we have analyzed homogeneous geological glass samples. The results are compared with data obtained from other analytical techniques. The performance of the LIMS method for geochemical investigations is discussed. Received: 2 December 1996 / Revised: 21 February 1997 / Accepted: 26 February 1997     

Molecular Structure of (1-Benzyl-4-phenyl-1H-1,2,3-triazol-5-yl)(4-bromophenyl) methanone: A Combined Experimental and Theoretical Study

One-pot three component reaction was used to synthesize 1,4,5-trisubstituted 1,2,3-triazole(A) from the corresponding acid chloride, benzyl azide and 1-copper(I) phenylethyne. The molecular structure was determined by single-crystal X-ray analysis. The compound crystallizes in the orthorhombic space group Pbca, a = 14.9815(14), b = 9.6496(10), c = 25.528(2) A, Z = 8. Furthermore, crystal packing demonstrated a molecular wall-like structure based on supramolecular chains of A, stabilized by CH···O, CH···Br, N···C and CH···π interactions. Molecular geometry in the ground state has been determined by density functional theory(DFT) by B3LYP/6-311G* basis set and compared with the experimental data. The computed vibrational frequencies are compared with the experimental FT-IR data and frontier molecular orbital analyses were performed at the same level of theory. Theoretical parameters are in good agreement with the corresponding X-ray diffraction values.     

A New Method of Calculating Pore Size Distribution: Analysis of Adsorption Isotherms of N(2) and CCl(4) for a Series of MCM-41 Mesoporous Silicas

The adsorption isotherms of N(2) gas at 77 K and CCl(4) vapor at 283.1(5), 298.1(5), and 308.1(5) K were measured for six samples of the mesoporous silicas having uniform cylindrical pores (MCM-41). The pore radii of the six samples (r(p)), which were evaluated from the alpha(s) plots of the N(2) isotherms, were 1.13, 1.29, 1.50, 1.65, 1.90, and 2.53 nm. The CCl(4) adsorption isotherms show that the capillary condensation occurs at the very narrow P/P(0) range. The core radii of the six adsorbents (r(c)), which were estimated from a comparison plot of the CCl(4) isotherm, were 0.90, 1.01, 1.28, 1.37, 1.60, and 2.17 nm. In the comparison plot, the standard CCl(4) isotherm for nonporous silica was used as the reference isotherm. It has been clarified that the Polanyi adsorption potential of capillary condensation is proportional to the reciprocal of the core radii: RT ln(P(0)/P)=5.37r(c)(-1) nm(-1), ln(P(0)/P)=2.17r(c)(-1) nm(-1) at 298.1(5) K, [A]. The statistical thickness of adsorbed CCl(4) on the curved surface (t((pore))), which was estimated from the difference between the pore radii and the core radii, was given by Eq. [B]: t((pore))=0.188+0.336(P/P(0))+0.382(P/P(0))(2) nm [B], (0.08

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Optical dimer excitations and exchange parameters in (Et4N)3Cr2F9: first observation of the 4A2 --> 2A1 transition

The synthesis, crystal growth, and polarized optical absorption spectra in the visible and near-UV of (Et4N)3Cr2F9 are reported. In the energy range 25800-27700 cm(-1) the 4A2 --> 2A1 (O notation) ligand field transition can be resolved in detail for the first time in any Cr3+ compound. This allows the determination of the antiferromagnetic ground-state exchange splitting with great accuracy: J = 25.9 cm(-1) and j = 0.27 cm(-1) using the Hamiltonian H = J(S(A).S(B)) - j(S(A).S(B))2, where j leads to deviations from the regular Landé pattern. The temperature dependence of the magnetic susceptibility is nicely reproduced by these parameters. A comparison with Cs3Cr2Cl9 and Cs3Cr2Br9 reveals an exponential dependence of the ground-state splitting upon the Cr-Cr distance in the [Cr2X9]3- dimers. This is the result of a dominant sigma-type orbital exchange pathway along the Cr-Cr axis.     

New designer drug 4-iodo-2,5-dimethoxy-beta-phenethylamine (2C-I): studies on its metabolism and toxicological detection in rat urine using gas chromatographic/mass spectrometric and capillary electrophoretic/mass spectrometric techniques

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A truncated version of reduced multireference coupled-cluster method with singles and doubles and noniterative triples: application to F2 and Ni(CO)n (n=1, 2, and 4)

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New layered uranium phosphate fluorides: syntheses, structures, characterizations, and ion-exchange properties of A(UO2)F(HPO4).xH2O (A = Cs+, Rb+, K+; x = 0-1)

Single crystals of three new layered uranium phosphate fluorides, A(UO2)F(HPO4).xH2O (A = Cs+, Rb+, and K+; x = 0-1) have been synthesized by hydrothermal reactions using UO3, H3PO4, HF, and corresponding alkali metal halides as reagents. Although all three new materials have layered structures, each of them contains different structural motifs within the layer. While Cs(UO2)F(HPO4).0.5H2O and Rb(UO2)F(HPO4) reveal noncentrosymmetric crystal structures, K(UO2)F(HPO4).H2O crystallizes in a centrosymmetric space group. In addition, the ion-exchanged phases for all three materials are highly crystalline. Crystal data: Cs(UO2)F(HPO4).0.5H2O, orthorhombic, space group Pca21 (No. 29), with a = 25.656(5) A, b = 6.0394(12) A, c = 9.2072(18) A, and Z = 4; Rb(UO2)F(HPO4), orthorhombic, space group Cmc21 (No. 36), with a = 17.719(4) A, b = 6.8771(14) A, c = 12.139(2) A, and Z = 8; K(UO2)F(HPO4).H2O, monoclinic, P21/n (No. 14), with a = 6.7885(14) A, b = 8.7024(17) A, c = 12.020(2) A, beta = 94.09(3), and Z = 4.