Spectroscopic investigations of high-power laser-induced dielectric breakdown in gas mixtures containing carbon monoxide

Large-scale plasma was created in gas mixtures containing carbon monoxide by high-power laser-induced dielectric breakdown (LIDB). The composition of the mixtures used corresponded to a cometary and/or meteoritic impact into the Earth's early atmosphere. A multiple-centimeter-sized fireball was created by focusing a single 85 J, 450 ps near-infrared laser pulse into the center of a 15 L gas cell. The excited reaction intermediates that formed in various stages of the LIDB plasma chemical evolution were investigated by optical emission spectroscopy (OES) with temporal resolution. Special attention was paid to any OES signs of molecular ions. However, carbon monoxide cations were registered only if their production was enhanced by Penning ionization, i.e., excess He was added to the CO. The chemical consequences of laser-produced plasma generation in a CO-N 2-H 2O mixture were investigated using high resolution Fourier-transform infrared absorption spectroscopy (FTIR) and gas chromatography (GC). Several simple inorganic and organic compounds were identified in the reaction mixture exposed to ten laser sparks. H 2 (18)O was used to avoid possible contamination. The large laser spark triggered more complex reactivity originating in carbon monoxide than expected, when taking into account the strong triple bond of carbon monoxide causing typically inefficient dissociation of this molecule in electrical discharges.     

Specific anion effects on enzymatic activity in nonaqueous media

The present work shows that salt anions affect the activity of Pseudomonas cepacia lipase both in aqueous and in nonaqueous media (NAM) according to a Hofmeister series. The biocatalytic assay in water was the hydrolysis of p-nitrophenyl acetate, whereas the esterification between 1-hexyl-beta-D-galactopyranoside and palmitic acid was followed in an organic solvent. The solid lipase preparations to be used in NAM were obtained through lyophilization in the presence of concentrated solutions of Hofmeister salts (Na2SO4, NaH2PO4/Na2HPO4, NaCl, NaBr, NaI, NaSCN). Salts affect enzyme activity in organic media through two mechanisms: (1) enzyme protection during lyophilization; (2) enzyme activation during the reaction. At least in our case, the latter seems to be more important than the former. The decrease of the activation energy caused by the stabilization of the transition state due to "kosmotropic" anions might be the driving force of enzyme activation. According to the most recent findings, dispersion forces may be responsible of specific anion enzyme activation/deactivation in NAM.     

Combined microwave-assisted isolation and solid-phase purification procedures prior to the chromatographic determination of phenolic compounds in plant materials

A fast, sensitive and selective procedure employing a combination of microwave-assisted extraction (MAE) and solid phase extraction (SPE) was applied prior to liquid chromatographic identification and quantification of phenolic compounds in plant materials. MAE has been tested and optimized for the isolation of phenolic acids (gallic, protocatechuic, p-hydroxybenzoic, chlorogenic, vanilic, caffeic, syringic, p-coumaric, ferulic, sinapic, benzoic, m-coumaric, o-coumaric, rosmarinic, cinnamic acids) and 3,4-dihydroxybenzaldehyde, syringaldehyde, p-hydroxybenzaldehyde, and vanillin in various plants. The effects of experimental conditions on MAE efficiency, such as solvent composition, temperature, extraction time, have been studied. The extraction efficiencies were compared with those obtained by computer-controlled, two-step Soxhlet-like extractions. Plant extracts were purified and phenolic compounds were pre-concentrated using SPE on polymeric RP-105 SPE sorbent prior to HPLC analysis. Chromatographic separation was carried out on a Hypersil BDS C₁₈ column using a mobile phase consisted of 0.3% (v/v) acetic acid in water (solvent A) and methanol (solvent B) at flow rate 0.6 ml min⁻¹ and column temperature 30 °C with gradient elution.     

Phase separation and phase dissolution in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blend

A blend of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5 wt% of acrylonitrile having the critical composition (80/20 PCL/SAN) was studied. This PCL/SAN blend having a lower critical solution temperature (LCST) phase boundary at 122 °C offered an excellent opportunity to investigate, firstly the kinetics of phase separation above LCST (125-180 °C), and secondly the kinetics of phase dissolution below LCST (50-115 °C). The blend underwent a temperature-jump above LCST where spinodal decomposition (SD) proceeded, yielding a regularly phase-separated structure (SD structure). Then, it was quenched to the temperatures below LCST when the phase dissolution proceeded. Optical microscopy was used to observe the spinodal decomposition qualitatively while light scattering was used to characterize the phase separation and phase dissolution quantitatively. It was found that during phase dissolution the peak maximum moved towards a smaller angle (wavelength of concentration fluctuations increased) while the peak intensity decreased. This behavior was explained by a model. Also it was found that the fastest phase dissolution kinetics at 80 °C, which was characterized by an apparent diffusion coefficient, was about 10 times slower than the kinetics of phase separation at 180 °C.     

Separation and characterization of humic acids from Antarctica by capillary electrophoresis and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Inclusion complexes of humic acids with cyclodextrins

A new capillary electrophoresis procedure based on micellar electrokinetic capillary chromatography for the separation of humic acids (HAs) isolated from Antarctica soil was developed. The HAs were separated and characterized using a background electrolyte containing 0.09 M borate+0.09 M Tris+0.001 M EDTA (BTE) of pH 8.3, modified with alpha-, beta-, or gamma-cyclodextrins (CDs) and sodium dodecyl sulfate. It was found that from alkaline solution of HAs in the presence of CDs, the HAs are not completely precipitated with a strong acid and a certain part (some fractions) remains soluble. Mass spectrometry shows that HAs contain 15-25 simple low-Mr compounds and several families of compounds with similar structure (m/z approximately 800-1200). Comparison of HA analysis from Antarctica soil with those of soil HAs from the American continent show a high similarity between the samples and confirm several identical compounds and some with very similar structural units.     

Solvatochromic azamethine dyes for probing the polarity of gold-cluster-functionalized silica particles

Azamethine dyes of the merocyanine type [4-(N,N-di-n-butylamino)-2-methylphenyl][2,4-di-keto-3-[N'-(n-hexyl)]-5-cyano-6-methyl-3-pyridinio]-1-azamethine (1) and [4-(N,N-diethylamino)-2-(N'-tert-butylcarboxy)-amidophenyl]-[2,4-diketo-3-[N"-(n-hexyl)]-5-cyano-6-methyl-3-pyridinio]-1-azamethine (2) have been used as surface-polarity indicators for gold-cluster-functionalized silica particles. Their UV/Vis absorption maxima range from about lambda=600 to 700 nm as a function of solvent polarity and are clearly separated from the surface plasmon UV/Vis absorption band of gold (lambda approximately 520-540 nm). Solvatochromism of both dyes has been investigated in 26 solvents of different polarity. The positive solvatochromic band shifts of 1 and 2 can be well expressed in terms of the empirical Kamlet-Taft solvent polarity parameters alpha and pi*. They are mainly sensitive to the dipolarity/polarizability (pi* term; 70-75 %) and HBD (hydrogen-bond donating) acidity (alpha term) of the solvent. Both dyes adsorb readily on functionalized silica samples from solutions in 1,2-dichloroethane or cyclohexane. The surface polarities of gold-cluster-functionalized silica particles, with and without co-adsorbed L-cysteine and poly(ethylenimine), have been investigated by using these solvatochromic dyes. The specific interaction of dye 2 with cysteine has been examined independently by quantum-chemical calculations by using the AM1 and PM3 methods.     

Unmittelbare photometrische Bestimmung des Antimongehaltes von legierten St?hlen mit Jodid

Zusammenfassung Das photometrische Verfahren von Ploum [1,2] zur Antimonbestimmung mit Jodid in nichtlegierten Stählen wurde so modifiziert, daß einerseits die Arbeitszeit durch Vereinfachung der Methode herabgesetzt wird und es andererseits zur Untersuchung hochlegierter Stähle herangezogen werden kann. 20% Cr, 12% Ni, 3% Mo, 4% W, 2% Mn, 3% V, 1% Ti, 0,4% Si, 0,8% Nb, 0,04% Ta, 0,1% Co, 0,05% Al, 0,05% As, 0,014% Sn und 0,004% B haben keinen Einfluß. Cu > 0,2% stört. Es können Antimongehalte von 0,001–0,025% bestimmt werden.

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Direct photometric determination of antimony in alloy steels with iodide

The method of Ploum [1,2] for the direct determination of antimony in plain steels has been modified. It has been possible to reduce the working time in simplifying the method and to apply the procedure to the investigation of high-alloy steels. 20% Cr, 12% Ni, 3% Mo, 4% W, 2% Mn, 3% V, 1% Ti, 0.4% Si, 0.8% Nb, 0.04% Ta, 0.1% Co, 0.05% Al, 0.05% As, 0.014% Sn and 0.004% B have no effect. Cu >0.2% interferes. Sb contents from 0.001 to 0.025% can be determined.

     

Neue Koordinationsverbindungen aus Triorganylzinn(IV)-dimesylamiden und Neutralliganden: Einkern- und Mehrkernkomplexe mit molekularer oder ionischer Kristallstruktur

Polysulfonylamines. CII. New Coordination Compounds Derived from Triorganyltin(IV) Dimesylamides and Uncharged Ligands: Mononuclear and Polynuclear Complexes with Molecular or Ionic Crystal Structures The purpose of this report is to draw attention to the remarkable versatility of the dimesylamides R₃SnA [A^– = (MeSO₂)₂N^–; R = Me ( 1 a ) or Ph ( 1 b )] as precursors for pentacoordinate triorganyltin(IV) complexes belonging to four distinct structural types. Representative complexes were prepared by treating 1 a or 1 b in the appropriate molar ratios with unidentate thiourea or urea-type ligands or with the bidentate ligand [Ph₂P(O)CH₂]₂ (DPPOE). The following compounds were characterized by X-ray analysis: [Me₃Sn(A)(thiourea)] ( 2 a ; monoclinic, space group P2₁/n), [Ph₃Sn(A)(tetramethylthiourea)] ( 2 b ; monoclinic, P2₁, two independent formula units), [Me₃Sn(1-methylurea)₂]⁺ · A^– ( 3 a ; monoclinic, P2₁/c), [Ph₃Sn(1,1-dimethylurea)₂]⁺ · A^– ( 3 c ; triclinic, P1), [{Ph₃Sn(A)}₂(μ-dppoe)] ( 4 ; triclinic, P1), [Ph₃Sn(μ-dppoe)]_nⁿ⁺ · n A^– · n MeCN ( 5 ; monoclinic, P2₁/c). The lattices of 2 a , 2 b and 4 contain discrete uncharged formula units which are mononuclear for 2 a and 2 b or dinuclear for 4 , whereas 3 a , 3 c and 5 have ionic structures featuring mononuclear cations for 3 a and 3 c or an infinite linear-polymeric cation for 5 . In all the structures, the tin atoms adopt trigonal-bipyramidal geometries, the apical positions being occupied in 2 a and 2 b by the S atom of the thiourea and one O atom of A^–, in 3 a and 3 c by the O atoms of two urea-type ligands, in 4 by an O atom of the bridging DPPOE molecule and one O atom of A^–, and in 5 by two phosphoryl O atoms from different bridging DPPOE ligands. In the structures of 2 a , 3 a and 3 c , the (thio)urea NH functions are connected to A^– via intermolecular or interionic N–H … O and N–H … N hydrogen bonds. Crystals of [{Me₃Sn(bipyH⁺ … A^–)}₂(μ-bipy)]²⁺ · 2 A^– ( 6 ; monoclinic, C2/c) formed adventitiously in a reaction mixture containing 1 a and 4,4′-bipyridine. The rod-like supramolecular cation of 6 (length ca. 4 nm) is built up from two Me₃Sn⁺ units bridged through bipy and unidentally coordinated by a monoprotonated bipy (= bipyH⁺), resulting in a trigonal-bipyramidal geometry around tin (N atoms apical); each of the terminal bipyH⁺ ligands forms an ⁺N–H … N^– hydrogen bond with one A^–.     

Mediation of metal chelation in cysteine-derived tetramate systems

A study of bicyclic tetramates modified with a bulky ester, which leads to steric hindrance of distal chelating atoms as a route for the alteration of metal binding ability is reported. This approach required the development of a direct method for the synthesis of different esters of cysteine from cystine, which then provided access to bicyclic tetramates by Dieckmann cyclisation. Further derivation to ketones and carboxamides by Grignard addition and transamination reactions respectively provided rapid access to a chemical library of tetramates with diverse substitution. Of interest is that bicyclic tetramate ketones and carboxamides showed different tautomeric and metal binding behaviour in solution. Significantly, in both systems, the incorporation of bulky C-5 esters at the bridging position not only reduced metal binding, but also enhanced antibacterial potencies against Gram-positive MRSA bacteria. Those tetramates with antibacterial activity which was not metal dependent showed physiochemical properties of MSA of 559–737 Ų, MW of 427–577 Da, clogP of 1.8–6.1, clogD_7.4 of −1.7 to 3.7, PSA of 83–109 Ų and relative PSA of 12–15% and were generally Lipinski rule compliant. A subset of tetramates exhibited good selectivity towards prokaryotic bacterial cells. Given that the work reported herein is synthesis-led, without the underpinning detailed mechanistic understanding of biological/biochemical mechanism, that the most active compounds occupy a small region of chemical space as defined by MW, clogP, PSA and %PSA is of interest. Overall, the bicyclic tetramate template is a promising structural motif for the development of novel antibacterial drugs, with good anti-MRSA potencies and appropriate drug-like physiochemical properties, coupled with a potential for multi-targeting mechanisms and low eukaryotic cytotoxicity.

A study of bicyclic tetramates modified with a bulky ester, which leads to steric hindrance of distal chelating atoms, is used as a route for the alteration of metal binding ability.