Studium des gegenseitigen Einflusses der Bindungen in Thiocyanat-Kupfer(II)-Komplexen mit Methyl- und Dimethylpyridinen mittels Infrarotspektroskopie

The infrared spectra of thiocyanato-copper(II) complexes of the type Cu(NCS)₂ L ₂ with all isomeric picolines and lutidines (L) as well as those of the type Cu(NCS)₂ L ₃ withL=3- and 4-picoline, 3,4- and 3,5-lutidine were measured. The behaviour of the (CN) stretching vibrations of the Cu(NCS)₂ L ₂ complexes led to conclusions on the different kind of coordination of the NCS groups in dependence on the ligandL. The mutually conditioned strength of the Cu–NCS and Cu–N(L) bonds in the equatorial plane, especially in the presence of ligandsL with the steric effect, was determined from the frequency shift of the Cu–NCS and Cu–N(L) stretching vibrations with regard to the vibrations for Cu(NCS)₂(pyridine)₂.

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Ligandenfeldspektren einiger Cyanato-Kupfer(II)-Komplexe des Typs Cu(NCO)2 L 2 mit Liganden aus der Chinolin- und Isochinolingruppe Cyanato-Kupfer(II)-Komplexe mit organischen Liganden, 7. Mitt.

Zusammenfassung Die Ligandenfeldspektren der Komplexe des Typs Cu(NCO)₂ L ₂ (L=Ligand der Chinolin- bzw. Isochinolingruppe) im festen Zustand wurden aufgenommen. Das Spektrum des Komplexes Cu(NCO)₂(Chin)₂ weist eine einzige Bande auf und deutet auf eine pseudooktaedrische Struktur. Die Spektren der übrigen Komplexe enthalten hingegen neben den Hauptbanden auch Schultern bzw. ist die anwesende Bande zusammengesetzt, so daß diese Spektren mit einer planaren Struktur im Einklang sind. Die annähernden Werte für den Parameter 10Dq wurden berechnet; sie liegen im Bereich von 7,1 bis 7,8 kK.

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Ligand field spectra of some cyanato-copper(II) complexes with ligands from the quinoline- and isoquinoline group

The ligand field spectra of complexes of the type Cu(NCO)₂ L ₂ (L=ligand from the quinoline or isoquinoline group) in the solid state were recorded. Only the spectrum of Cu(NCO)₂(Quin)₂ exhibits a single band and indicates a pseudooctahedral structure, while the spectra of the remaining complexes also contain shoulders in addition to the main band, or this band is composite, thus being in accordance with a planar structure. The approximate values of the parameter 10Dq were calculated and found to be in the range of 7.1 to 7.8 kK.

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6. Mitt.:M. Quastlerová-Hvastijová, J. Kohout undJ. Gao, Z. anorg. allgem. Chem., im Druck.     

A New Alkylation-Elimination Method for Synthesis of Antiviral Fluoromethylenecyclopropane Analogues of Nucleosides

A new method for the synthesis of fluoromethylenecyclopropane nucleosides by alkylation-elimination procedure is described. Fluorination of methylenecyclopropane carboxylate 6 gave fluoroester 7. Treatment of 7 with phenylselenenyl bromide afforded the desired ethyl (E)-2-bromomethyl-1-fluoro-2-phenylselenenylcyclopropane-1-carboxylate 11 in 85% yield. DIBALH reduction of 11 gave 13, which after acetylation to 14 was reacted with 2-amino-6-chloropurine to give the 9-alkylated product 15 in 87% yield. Se-oxidation of 15 with hydrogen peroxide afforded 16, which underwent smooth elimination in a mixture of THF-DMF at 60 °C giving rise to a Z,E mixture of protected nucleosides 17. Deacetylation gave Z-1a and E-1a which were separated on a silica gel column. Both Z-1a and E-1a were converted into the respective guanine analogues Z-1b and E-1b.     

An investigation into the initial degradation steps of four major dye chromophores: study of their one-electron oxidation and reduction by EPR, ENDOR, cyclic voltammetry, and theoretical calculations

The degradation of dyes is frequently initiated by one-electron oxidation or reduction; however, relatively little is known about the initially formed radicals. Acid Green 25 (AG25), Crystal Violet (CVI), Methylene Blue (MB), and Acid Orange 7 (AO7), representing paradigms of four types of commercial organic dyes, were therefore investigated in terms of their redox behavior. Their redox potentials in MeCN and buffered aqueous solutions were determined by cyclic voltammetry. The structures of the one-electron reduced and oxidized dyes were established by EPR spectroscopy and by theoretical calculations on the density functional level of theory.     

Rheology of asphalts modified with glycidylmethacrylate functionalized polymers

Asphalt is known to be a colloidal suspension in which asphaltenes are covered by a stabilizing phase of polar resins and form complex micelles that are dispersed in the oily maltenic phase. In order to enhance its mechanical properties (e.g., in road paving), asphalts are often loaded with polymeric materials, thereby obtaining blends that can have different physical or chemical structures, depending on the composition of the added polymer. Asphalts modified by the addition of reactive ethylene terpolymers were prepared and their dielectric and rheological properties were measured both before and after a cure at high temperature. Even if it is not possible to determine the exact nature of the chemical interactions between asphalt and polymer, master curves obtained from dynamic data clearly show that during the cure the material tends to the behavior of a cross-linked network.     

Decoding the intricate network of molecular interactions of a hyperstable engineered biocatalyst

Computational design of protein catalysts with enhanced stabilities for use in research and enzyme technologies is a challenging task. Using force-field calculations and phylogenetic analysis, we previously designed the haloalkane dehalogenase DhaA115 which contains 11 mutations that confer upon it outstanding thermostability (T_m = 73.5 °C; ΔT_m > 23 °C). An understanding of the structural basis of this hyperstabilization is required in order to develop computer algorithms and predictive tools. Here, we report X-ray structures of DhaA115 at 1.55 Å and 1.6 Å resolutions and their molecular dynamics trajectories, which unravel the intricate network of interactions that reinforce the αβα-sandwich architecture. Unexpectedly, mutations toward bulky aromatic amino acids at the protein surface triggered long-distance (∼27 Å) backbone changes due to cooperative effects. These cooperative interactions produced an unprecedented double-lock system that: (i) induced backbone changes, (ii) closed the molecular gates to the active site, (iii) reduced the volumes of the main and slot access tunnels, and (iv) occluded the active site. Despite these spatial restrictions, experimental tracing of the access tunnels using krypton derivative crystals demonstrates that transport of ligands is still effective. Our findings highlight key thermostabilization effects and provide a structural basis for designing new thermostable protein catalysts.

Illustration of cooperative thermostabilization effects of the double-lock system that: (i) induced backbone changes, (ii) closed the molecular gates, (iii) reduced the volumes of the main and slot access tunnels, and (iv) occluded the active site.     

4‐Acetamido‐3,3,5,5‐[2H4]‐2,2,6,6‐tetra­([2H3]methyl)piperidin‐1‐yloxyl 0.33‐hydrate

The asymmetric unit of the title compound, C₁₁H₅D₁₆N₂O₂·0.33H₂O, is formed by three crystallographically independent piperidin‐1‐yloxyl mol­ecules and a mol­ecule of water. The mol­ecules are crosslinked by nine hydrogen bonds into layers parallel with the ac plane. The water mol­ecule contributes to the stability of the low‐symmetry arrangement by four hydrogen bonds.     

Multi-element characterization of silicon nitride powders by atomic and mass spectrometric solution methods

A sample pretreatment technique for silicon nitride involving digestion and matrix/traces separation was developed by means of radiotracers and applied to analysis of this material by inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry and graphite furnace atomic absorption spectrometry. The results obtained for a high purity silicon nitride material by these methods are compared each with the other and with those obtained by neutron activation analysis. The limits of detection and the capabilities of the methods are compared and discussed.     

An automated method for the analysis of stable isotope labeling data in proteomics

An algorithm is presented for the generation of a reliable peptide component peak table from liquid chromatography-mass spectrometry (LC-MS) and subsequent quantitative analysis of stable isotope coded peptide samples. The method uses chemical noise filtering, charge state fitting, and deisotoping toward improved analysis of complex peptide samples. Overlapping peptide signals in mass spectra were deconvoluted by correlation with modeled peptide isotopic peak profiles. Isotopic peak profiles for peptides were generated in silico from a protein database producing reference model distributions. Doublets of heavy and light labeled peak clusters were identified and compared to provide differential quantification of pairs of stable isotope coded peptides. Algorithms were evaluated using peptides from digests of a single protein and a seven-protein mixture that had been differentially coded with stable isotope labeling agents and mixed in known ratios. The experimental results correlated well with known mixing ratios.     

Generalized reinhardt domains

In this paper we investigate a class of Lie group actions on , the so-calledpolar actions, that naturally generalize the standard actions. For a domain invariant under such an action (i.e., a generalized Reinhardt domain) we characterize the invariant plurisubharmonic functions and determine the envelope of holomorphy in geometric terms. For a generalized Reinhardt domain containing the origin of we also compute its automorphism group. Supported in part by NSF Grant 8602020