Richardson–Lucy deconvolution of reflection electron energy loss spectra

A procedure for deconvolving the energy spread introduced by the primary beam and the analyzer in a reflection electron energy loss spectrum (REELS) has been developed. The procedure is based on the Richardson–Lucy (RL) algorithm. The approach has been successfully tested on experimental spectra by comparison with spectra with an inherent high‐energy resolution. As a typical result, it was found that the effective energy resolution of spectra with a full width half maximum (FWHM) of the elastic peak of ～1.5 eV in the raw experimental data can be reduced to ～0.7 eV in the deconvoluted spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Pyrolysis—field ionization mass spetrometric investigation of polymeric heterocycles: I. polyquinolines and polyquinoxalines

Pyrolysis—field ionization mass spectrometry was used for the investigation of the mechanism of the thermal degradation of polymeric heterocycles. Heat-resistant polymers containing aromatic and heterocyclic units such as polyquinolines and polyquinoxalines have a strong tendency to form large condensed systems during pyrolysis, and finally will carbonize. In the course of this process, side-groups (phenyl) and small fragments (NH₃, HCN, acetonitrile, acrylonitrile, etc.) are split off. In addition, large heteroatom-containing fragments such as nitriles can be identified. These, together with some fragments that contain the complete heterocyclic ring, are characteristic of the chain building units (“key fragments”). Furthermore, compounds generated by recombination reactions and intramolecular cyclization are constituents of the pyrolysate.     

Alkylations of tricyclo[5.2.1.0]deca-4,8-dien-3-one by a cuprate reaction

Alkylation at C₆ of tricyclo[5.2.1.0^2,6]deca-4,8-dien-3-one (R=H) was achieved by treatment of 6-bromotricyclo[5.2.1.0^2,6]deca-4,8-dien-3-one with lithium dimethylcuprate and subsequently with an appropriate electrophile. The best results were obtained in THF as the solvent. A wide range of alkyl halides, bromo ketones and esters, and acetyl chloride resulted in C₆-tricyclo[5.2.1.0^2,6]deca-4,8-dien-3-ones in moderate to good yields. This alkylation reaction proceeds via a C₆-carbanionic Cu intermediate, which is likely stabilized by the enone olefinic bond. 6-Bromo-endo-tricyclo[5.2.1.0^2,6]dec-8-en-3-one, which lacks this double bond, behaves differently. Treatment with lithium dimethylcuprate leads to dehydrobromination to give tricyclo[5.2.1.0^2,6]deca-2(6),8-dien-3-one in high yield.     

Zur Protonierung und Methylierung des 1, 1-Dicyanoethylen-2, 2-dithiolat Dianions: Präparative und strukturelle Untersuchungen

Protonation and Methylation of 1, 1-Dicyanoethylene-2, 2-dithiolate Dianion. Preparative and Structural Investigations Protonation of alkaline metal salts of [S₂C = C(CN)₂]^2? ( I ) in water yields a product of composition H₂S₂C₄N₂ ( II ). The species has to be formulated as dimere and crystallizes with two moles DMSO from DMSO solution with space group C2/c and a = 20.611(3), b = 4.800(1), c = 20.638(3) Å, β = 103.3(1)°, Z = 4. The X-ray structural analysis shows II to be a centrosymmetric 1, 3-Dithiacyclobutane system. On methylation of I with CH₃I in the molar ratio 1:1, the monomethylated anion III can be isolated as AsPh₄ salt. The compound crystallizes in the monoclinic space group P2₁/c, with a = 23.632(2), b = 14.304(1), c = 7.989(1) Å, β = 100.1(8)° and Z = 4. There are nearly planar anions [MeS(S)C?C(CN)₂]^? with an anti-conformation of the MeS group.     

Determination of Aqueous Nickel-Carbonate and Nickel-Oxalate Complexation Constants

An ion-exchange method was used to determine complexation constants for the Ni-oxalate and Ni-carbonate systems in a NaClO₄ background electrolyte. The Ni-oxalate data were interpreted in terms of a single Niox(aq) complex having log K ₁ values for Ni²⁺ + ox^2– Niox(aq) of 3.9 ± 0.1 (I.S. = 0.5 mol-L^–1 p[H] = 7.1) and 4.4 ± 0.1 (I.S. = 0.1 mol-L^–1 p[H] = 8.6) at 22 ± 1C. Specific ion-interaction theory (SIT) was used to obtain log K ₁ = 5.17 ± 0.05 (95% confidence level and = –0.23 ± 0.15) at I.S. = 0. The Ni-carbonate studies were carried out at p[H] values of 7.5, 8.5, and 9.6 in 0.5 mol-L^–1 NaClO₄/NaHCO₃ solutions. The NiCO₃(aq) species was the dominant complex in the [CO₃ ^2–] concentration ranges studied at all three p[H] values. A log K ₁ value for Ni²⁺ + CO₃ ^2– NiCO₃(aq) of 2.9 ± 0.3 was deduced at I.S. = 0.5 mol-L^–1. Extrapolating this value to zero ionic strength using the SIT approach yielded log K ₁ = 4.2 ± 0.3 (95% confidence level and = –0.26 ± 0.04). The data allowed upper bound values for the complexation constants for NiHCO₃ ⁺ and Ni(CO₃)₂ ^2– to be estimated, i.e., log K < 1.4 for Ni²⁺ + HCO₃ ^– NiHCO₃ ⁺, and log K ₂ < 2 for NiCO₃(aq) + CO₃ ^2– Ni(CO₃)₂ ^2–, respectively.     

Luminescence temperature antiquenching of water-soluble CdTe quantum dots: role of the solvent

Luminescence temperature antiquenching (LTAQ) is observed for water-soluble CdTe quantum dots (QDs) capped with aminoethanethiol (AET). The efficient exciton emission (quantum efficiency of approximately 40% at 300 K) is quenched almost completely as the QD solutions are cooled to below 230 K and is fully recovered around 270 K upon warming up to room temperature (LTAQ). Temperature-dependent lifetime measurements show that the quenching rate is high, resulting in an on/off behavior. No LTAQ is observed for CdTe QDs capped with aminoundecanethiol (AUT). The LTAQ is explained by the influence of solvent freezing on the surface of the QD core. Freezing of the solvation water molecules surrounding the QD will induce strain in the capping shell, due to the interaction between water and the charged heads of the capping molecules. Short carbon chains (AET) will propagate the strain to the QD surface, creating surface quenching states, whereas long and flexible chains (AUT) will dissipate the strain, thus avoiding surface distortion. Freezing-point depression by the addition of methanol results in a lowering of the transition temperature. Additional support is provided by the size dependence of the LTAQ: smaller particles, with higher local ionic strength due to a higher density of charged NH(3)(+) surface groups, experience a lower transition temperature due to stronger local freezing-point depression.     

Residual lignin inhibits thermal degradation of cellulosic fiber sheets

The market for cellulosic fiber based food packaging applications is growing together with the importance of improving the thermal durability of these fibers. To shed light on this, we investigated the role of residual lignin in pulp on the thermal stability of refined pulp sheets. The unbleached, oxygen delignified, and fully bleached pulp sheets were studied after four separate refining degrees. Comparison by Gurley air resistance, Bendtsen porosity, and the oxygen transmission rate tests showed that lignin containing sheets had better air and oxygen barrier properties than fully bleached sheets. Sheet density and light scattering coefficient measurements further confirmed that the lignin containing pulps underwent more intense fibrillation upon refining that changed the barrier properties of the sheets. Thermal treatments (at 225 °C, 20 and 60 min, in water vapor atmospheres of 1 and 75 v/v %) were applied to determine the thermal durability of the sheets. The results revealed that the residual lignin in pulps improved the thermal stability of the pulp sheets in the hot humid conditions. This effect was systematically studied by tensile strength, brightness, and light absorption coefficient measurements. The intrinsic viscosity results support the findings and suggest that lignin is able to hinder the thermal degradation of pulp polysaccharides. In spite of the fact that lignin is known to enhance the thermal yellowing of paper, no significant discoloration of the pulp sheets containing residual lignin was observed in the hot humid conditions (75 v/v %). Our results support the idea of lignin strengthening the thermal durability of paper.     

Quantification of allantoin and other metabolites of the purine degradation pathway in human plasma samples using a newly developed HILIC-LC-MS/MS method

The development of a simple HILIC-LC-MS/MS method to quantify the plasma levels of allantoin, inosine, hypoxanthine, and adenosine, using stripped plasma for the bioanalytical method validation, was the purpose of this study. Chromatographic separation conducted using an XBridge BEH Amide column (2.1 × 150 mm, 3.5 μm) was achieved under gradient elution with two mobile phases: 0.1% formic acid–ACN (5:95) and 0.1% formic acid–ACN (50:50). Multiple reaction monitoring MS detection was performed using a triple quadrupole. The method validation experiments were performed according to the European Medicines Agency and the U.S. Food and Drug Administration guidelines. The lower LOQ was 50 nM, 5 nM, 20 nM, and 2 nM for allantoin, inosine, hypoxanthine, and adenosine, respectively. The recovery was repeatable and stable. The intraday precision ranged from 1.6% to 6.5%, while the interday precision ranged from 3.4% to 58.7%. Therefore, it is necessary to make a matrix-matched calibration curve each day to overcome this issue. Since the quality control samples’ stability did not always comply with the guidelines, the samples need to be analyzed soon after collection.