Mimicking the two-dimensional spectrochemical series using density functional computations

With tetragonal distortions of tetrahedral d2 complexes as examples, nonadditive and additive ligand fields are compared computationally, using Kohn-Sham density functional theory (KS-DFT) and ligand-field theory to obtain 45 linear, parametrical equations. For each complex, a "data" reduction from three nonadditive-field parameters to two parameters of the additive field occurs. The complexes V and CrX4- (where X=F, Cl, Br, I) provide the two-dimensional spectrochemical series of the sigma and pi AOM parameters, which are known semiempirically for the halide ligands. The same parametrical results can be obtained from the Kohn-Sham orbital energies of the "average of configuration" computation.     

Characterization and application of supported metal catalysts with well-tailored pore systems and metal dispersions

Silica supported silver catalysts were prepared by sol-gel techniques and characterized by physisorption, in-situ ESCA measurements and transmission electron microscopy. Compared to conventional supported group VIII metal catalysts, these Ag/SiO₂ catalysts exhibited a superior performance for the selective hydrogenation of α,β-unsaturated aldehydes to allylic alcohols.     

On-line enzymatic reaction,extraction, and chromatography of fatty acids and triglycerides with supercritical carbon dioxide

Supercritical carbon dioxide can be utilized both as an introduction solvent in capillary SFC and as a reaction medium; both possibilities are illustrated in this study. An off-line SFE unit was modified for on-line SFE-SFC. To facilitate rapid depressurization of the extraction cell and to prevent memory effects, a 6-port valve was installed at the outlet line of the extraction unit. An increased background signal was obtained when PEEK polymer was used in the construction of the extraction vessel; when stainless steel was used, the blanks improved. The synthesis of methyl esters and butyl esters of fatty acids from triglycerides in edible fat was examined using an immobilized lipase as a catalyst in on-line SFE-SFC. As a result of 30 minutes reaction – extraction time, high yields of fatty acid esters were obtained at a pressure of 150 bar and a temperature of 50°C.     

Über die Darstellung von Arsendichloridtrifluorid,AsCl2F3

On the Preparation of Arsenic Dichloride Trifluoride, AsCl₂F₃ AsCl₂F₃ is prepared by pyrolysis of [AsCl₄]⁺ [AsF₆]^?. The vibrational spectra of the new low temperature compound are reported and the valence force constants are calculated. The formation of AsCl₂F₃ by ligand exchange reactions is discussed.     

Configurationally and conformationally homogeneous cyclicN-aryl sulfimides. II.13C-and1H NMR spectra

The configuration and (in case of mobile ring systems) the preferred conformation in a series of thiane- and ofcis-andtrans-1-thiadecalin-1-N-4-chlorophenyl imides were assigned by means of¹³C- and¹H nmr spectroscopy.¹H nmr criteria known to be valid for determination of the stereochemistry of cyclic sulfoxides may be applied (with limitations) to cyclicN-aryl sulfimides, if both isomers (S–N bond equatorial and axial, respectively) are known. The assignments are easier, and unambiguous for single isomers, by comparison of¹³C nmr chemical shifts of ring carbon atoms of sulfimides and sulfides. The influence of equatorially and axially oriented sulfimide groups on the chemical shifts of neighbouring protons, and on the carbon atoms of the heterocyclic rings are discussed in detail.

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Konfigurativ und konformationell einheitliche cyclische N-Aryl-sulfimide. II.¹³C- und¹H-NMR-Spektroskopie

Zusammenfassung Die Konfiguration und (bei beweglichen Ringsystemen) die bevorzugte Konformation einer Reihe von Thian- und voncis- undtrans-1-Thiadekalin-1-N-4-chlorophenylimiden wurde durch¹³C- und¹H-NMR-Spektroskopie bestimmt. Bekannte¹H-NMR-Kriterien zur Festlegung der Stereochemie cyclischer Sulfoxide sind (mit Einschränkungen) auch bei cyclischenN-Arylsulfimiden anwendbar, wenn beide Isomere (S–N-Bindung äquatorial bzw. axial) bekannt sind. Leichter, und auch bei Vorliegen von nur einem Isomeren eindeutig, gelingt die Zuordnung durch Vergleich der¹³C-NMR-Verschiebungen der Ringkohlenstoffatome von Sulfimiden und Sulfiden. Die Einflüsse äquatorial oder axial orientierter Sulfimidgruppen auf die chemischen Verschiebungen benachbarter Wasserstoffe und der Kohlenstoffe des Heterorings werden diskutiert.

     

Synthesis of 5,6-dihydro-4H-thiopyran-4-ones

The anions of 1,4-diaryl-3-buten-2-ones 1 reacts with arylisothiocyanates, yielding intermediates 4 which can ring close to 5,6-dihydro-4H-thiopyran-4-ones 5 . Under similar reaction conditions ethyl 3-oxo-4-pentenoates 7 gives the 6-spiropyrans 9 . Methylation of 3 gives the S-methylated open form 6 .     

Selective flow injection analysis of ultra-trace amounts of Cr(VI), preconcentration of it by solvent extraction, and determination by electrothermal atomic absorption spectrometry (ETAAS)

A rapid, robust, sensitive and selective time-based flow injection (FI) on-line solvent extraction system interfaced with electrothermal atomic absorption spectrometry (ETAAS) is described for analyzing ultra-trace amounts of Cr(VI). The sample is initially mixed on-line with isobutyl methyl ketone (IBMK). The Cr(VI) is complexed by reaction with ammonium pyrrolidine dithiocarbamate (APDC), and the non-charged Cr(VI)–PDC chelate formed is extracted into IBMK in a knotted reactor made from PTFE tubing. The organic extractant is separated from the aqueous phase by a gravity phase separator with a small conical cavity and delivered into a collector tube, from which 55 μl organic concentrate is subsequently introduced via an air flow into the graphite tube of the ETAAS instrument. The operations of the FI-system and the ETAAS detector are synchronously coupled. A significant advantage of the approach is that matrix constituents, such as high salt contents, effectively are eliminated. The extraction procedure was optimized by a simplex approach. A central composite design was subsequently employed to verify the estimated operational optimum. An 18-fold enhancement in sensitivity of Cr(VI) was achieved after preconcentration for 99 s at a sample flow rate of 5.5 ml min⁻¹, as compared to direct introduction of 55 μl of sample, yielding a detection limit (3σ) of 3.3 ng l⁻¹. The sampling frequency was 24.2 samples h⁻¹. The proposed method was successfully evaluated by analyzing a NIST Cr(VI)-reference material, synthetic seawater and waste waters, and waste water samples from an incineration plant and a desulphurization plant, respectively.     

An approach to sequence-specific antibody proteases

We describe here a novel strategy for the isolation of antibodies with sequence-specific protease activity: the synthesis of dipeptide haptens in which the targeted peptide bond has been replaced by a ring-strained or torsionally strained hydroxyethylene transition-state analog. Thus, the analogs mimic both a peptide bond in a distorted, reactive conformation and the transition state for peptide bond hydrolysis. In order to obtain sequence-specific antibody proteases, these analogs have been flanked with additional amino acid residues in preparation for immunization. In particular, we have synthesized peptides containing analogs such as 2-cis-amino-3-cis-hydroxycyclobutane carboxylic acid andendo-(3-amino-2-hydroxy)bicyclo[2.2.1]heptane-7-anti-carboxylic acid. We have also prepared a series of peptide derivatives containing analogs, such as 2-[3-amino-2-oxo-1-azetidinyl]-3-methylbutanoic acid, in which the targeted peptide bond has been incorporated into a β-lactam ring. Since the “peptide bond” has been left intact, these species mimic only a distorted ground state. At present, antibodies are being elicited against a number of the above peptide derivatives.     

Half-life measurement of <Superscript>126</Superscript>Sn isolated from Hanford nuclear defense waste

Summary Long-term risk assessment of residual and disposed nuclear fuel reprocessing waste requires good knowledge of component isotopes with long half-lives. For example, the accuracy of the accepted ¹²⁶Sn half-life of approximately 100,000 years is insufficient for desired risk assessments. From modeling and sampling, ¹²⁶Sn is known to exist in Hanford nuclear waste. Excess portions of waste characterization samples were used to isolate ¹²⁶Sn for measurement of its half-life. Isolation was performed with ion-exchange resins. The resulting ¹²⁶Sn was gamma-assayed with a hyperpure germanium spectrometer for decay photon identification and activity values. An inductively coupled plasma/mass spectrometer was used to measure the atom quantity of the isolated ¹²⁶Sn. The separation chemistry, observed gamma energies, and calculated half-life are presented. The half-life of ¹²⁶Sn estimated in this work is (2.33±0.10) ^. 10⁵ years.     

Die gravimetrische Phosphorbestimmung in wolframhaltigen St?hlen

Zusammenfassung Einige der üblichen Methoden zur Phosphorbestimmung in wolframlegierten Stählen werden unter Anwendung von ¹⁸⁵W und ³²P einer Nachprüfung unterzogen. Dabei erweisen sich die Phosphorverluste durch Adsorption an dem Wolframsäureniederschlag als gering, so daß sie bei weniger anspruchsvollen Bestimmungen unberücksichtigt bleiben können. Erheblich größer sind dagegen die Fehler, die durch Mitfällung von Wolframsäure mit dem Ammoniummolybdatophosphatniederschlag entstehen können. Es werden zwei Methoden angegeben, nach denen eine quantitative Abtrennung des Wolframs und damit eine sichere Bestimmung des Phosphors möglich ist.Herr Prof. Dr.-Ing. K. Schwabe ermöglichte es uns freundlicherweise, die Untersuchungen mit radioaktivem Wolfram und Phosphor im Zentralinstitut für Kernphysik Rossendorf, Bereich Radiochemie, durchzuführen. Ihm sei auch an dieser Stelle herzlichst gedankt.