Measurements of side-chain 13C-13C residual dipolar couplings in uniformly deuterated proteins

13C-only spectroscopy was used to measure multiple residual (13)C-(13)C dipolar couplings (RDCs) in uniformly deuterated and (13)C-labeled proteins. We demonstrate that (13)C-start and (13)C-observe spectra can be routinely used to measure an extensive set of the side-chain residual (13)C-(13)C dipolar couplings upon partial alignment of human ubiquitin in the presence of bacteriophages Pf1. We establish that, among different broadband polarization transfer schemes, the FLOPSY family can be used to exchange magnetization between a J coupled network of spins while largely decoupling dipolar interactions between these spins. An excellent correlation between measured RDCs and the 3D structure of the protein was observed, indicating a potential use of the (13)C-(13)C RDCs in the structure determination of perdeuterated proteins.     

Stereochemie von Metallocenen, 8. Mitt.: Die Absolute Konfiguration von Optisch Aktiven Benzol-chromtricarbonyl-derivaten; Asymmetrische Synthese und Kinetische Racematspaltung von Chiralen Metallocenen

Zusammenfassung Es wird über die Synthese und Racematspaltung von drei Benzol-chromtricarbonyl-derivaten sowie der -Methyl-ferrocen-carbonsäure berichtet. Die Absolutkonfiguration von (+)-(1-Tetralon)-Cr(CO)₃ konnte als (1S) ermittelt werden. Bei den beiden isomeren Säuren (+)- bzw. (–)-(o- bzw. m-Tolylsäure)-Cr(CO)₃ gelang erstmalig die konfigurative Korrelation eines -mit einem -disubstituierten Metallocen. Die Absolutkonfiguration des auch durch asymmetrische Synthese zugänglichen (+)-(o-Tolylsäure)-Cr(CO)₃ ließ sich auf Grund der Ergebnisse der kinetischen Racematspaltung der Anhydride der beiden racem. -Methyl-metallocen-carbonsäuren mit (–)-Menthol und (–)--Phenäthylamin als (1 S) bestimmen, da die Konfiguration der Methyl-ferrocencarbonsäure (nach chemischer Korrelation) bekannt war.

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The synthesis and optical resolution of three benzene chromium tricarbonyl derivatives and of -methyl ferrocene carboxylic acid are reported. The absolute configuration of (+)-1-tetralone)-Cr(CO)₃ was established as (1S). In the case of the isomeric acids (+)-(o-toluic acid)- and (–)-(m-toluic acid)-Cr(CO)₃ resp. a configurational correlation of - and -disubstituted metallocenes was possible for the first time. The absolute configuration of (+)-(o-toluic acid)-Cr(CO)₃ (which is also accessible by asymmetric synthesis) could be established as (1S) by kinetic resolutions of the anhydrides of the two racemic -methyl metallocene carboxylic acids with (–)-menthol and (–)--phenethylamine, since (after chemical correlation) the configuration of methyl ferrocene carboxylic acid was known.

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Mit 1 Abbildung

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7. Mitt.:H. Falk undK. Schlögl, Tetrahedron [London], im Druck.     

13-Acetoxy-heptadecadien-(8, 10)-ol-(1), Octadien-(3, 5)-ol-(1)-Isomere und verwandte Verbindungen

Zusammenfassung Es werden diecis,cis- undtrans,trans-Isomeren der primären Alkohole Octadien-(3,5)-ol-(1) (I), 15-Acetoxy-nonadeca-dien-(10,12)-ol-(1) (IV), 17-Acetoxy-heneikosa-dien-(10,12)-ol-(1) (V), 12-Acetoxy-pentadeca-dien-(8,10)-ol-(1) (VII) und 13-Acetoxy-heptadeca-dien-(8,10)-ol-(1) (VI) synthetisiert und zusammen mit einigen Zwischenprodukten und Analogen unter Verwendung des Seidenspinners (Bombyx mori L.) und des Schwammspinners (Lymantria dispar L.) auf Attraktivität getestet. DieL. E.-Werte der synthetisierten cis,cis-VI-Präparate liegen in der Größenordnung von 10^–9 g/ml.

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Thecis, cis- andtrans, trans-isomere of the primary alcohols octadien-(3,5)-ol-(1) (I), 15-acetoxy-nonadecadien-(10,12)-ol-(1) (IV), 17-acetoxy-heneicosadien-(10,12)-ol-(1) (V), 12-acetoxypentadecadien-(8,10)-ol-(1) (VI) have been synthesized and tested for effectiveness as attractant together with several intermediates and analogues using the Silk Moth (Bombyx mori L.) and the Gipsy Moth (Lymantria dispar L.) The values of the attractant units of the cis, cis-VI-compounds synthesized are of the order 10^–9 g/ml.

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4. Mitt. der Reihe Synthese und Wirksamkeit von Sexualduftstoff-Analogen; 3. Mitt.:R. Riemschneider, A. Kühnl undK. Brockmeyer, unveröffentlichte Versuche; 2. Mitt.:R. Riemschneider undG. Kasang, Z. Naturforschg.18 b, 646 (1963); 1. Mitt.:R. Riemschneider, Vortrag vom 1. 9. 1962 in S. Paolo.     

Röntgenkristallstruktur-analyse eines 3β,20-dihydroxylierten 22,26-epimino-5α-cholestan-derivats

By X-ray analysis of the hydroiodide of the 22,26-epimino-5α-cholestan-3β,20-diol (1), the constitution and configuration has been established and the side chain stereochemistry determined as 20R : 22S : 25S. The final discrepancy R was 0·167.     

Low-dimensional Compounds Containing Cyano Groups. XIII. Structural–spectral Correlation of Copper Dicyanoargentates

The new mixed-valence mixed-metal complex Cu(py)₆Cu₂Ag₂(CN)₆ (py = pyridine) possesses a three dimensional polymeric crystal structure. The Cu(I) atom is tetrahedrally coordinated by two nitrogen atoms of pyridine molecules, by one nitrogen atom of the dicyanoargentate anion and by one carbon atom of the cyano group. Both the dicyanoargentate anion and the cyano group bridge the Cu(I) atom with neighboring Cu(II) atoms. These are hexacoordinated in the form of an elongated tetragonal bipyramid. The equatorial plane is formed by two nitrogen atoms from two pyridine molecules and two nitrogen atoms from bridging cyano groups. Axial positions are occupied by nitrogen atoms of the bridging [Ag(CN₂]⁻ anions. Correlation between structures of the title compound and seven other dicyanoargentates with their i.r. spectra has been studied. The coordination mode of [Ag(CN₂]⁻ anions in compounds Cu_8-xAg_x(tn)₃(CN)₁₀ x = 0.25, Cu(3-Mepy)₂Ag₂(CN)₄, Cu(py)₂Ag₂(CN)₄ and Cu(py)₄Ag₂(CN)₄ (tn is 1,3-diaminopropane, 3-Mepy is 3-methylpyridine) is predicted based on this correlation.     

Benefits of X-Ray Spectrum Simulation at low Energies

 There are particular benefits in spectrum simulation for the interpretation of characteristic X-ray peaks below about 2 keV in energy, where peak overlaps, a sloping background and changing detector efficiency make it difficult to measure true peak intensities. Despite these difficulties, we have shown that a useful accuracy of simulation is possible without major revision of the existing theory, allowing the electron microprobe user to compare on-line a measured spectrum with one synthesised from an assumed sample composition. As part of a wider study, we have used a database of X-ray spectra from 150 samples of known composition to confirm the accuracy of simulation over the energy range from 0.28–1.9 keV, finding an RMS error of better than 8%. The database included 181 Kα, Lα and Mα peaks from elements of atomic number 6–77, excited by beam voltages from 5–30 kV. Central to the method is the use of the ratio of (Peak Intensity)/(Total Background Intensity), which allows spectra to be compared from instruments of differing collection efficiency, thereby easing the collection of data over a wide range of conditions. Examples are given to illustrate the use of the simulator in helping to choose the best conditions for analysis, and as an aid in interpreting the spectra so obtained. Both modes of operation are iterative in nature and require a fast and accurate simulator that is easy to use. Further development will be guided by experience in its use.     

Structure and properties of the dendron-encapsulated polyoxometalate (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], a first generation dendrizyme

Combining analytical and theoretical methods, we present a detailed study of a heteropolytungstate cluster encapsulated in a shell of dendritically branching surfactants, namely (C(52)H(60)NO(12))(12)[(Mn(H(2)O))(3)(SbW(9)O(33))(2)], 3. This novel surfactant-encapsulated cluster (SEC) self-assembles spontaneously from polyoxometalate-containing solutions treated with a stoichiometric amount of dendrons. Compound 3 exhibits a discrete supramolecular architecture in which a single polyoxometalate anion resides in a compact shell of dendrons. Our approach attempts to combine the catalytic activity of polyoxometalates with the steric properties of tailored dendritic surfactants into size-selective catalytic systems. The structural characterization of the SEC is based on analytical ultracentrifugation (AUC) and small-angle neutron scattering (SANS). The packing arrangement of dendrons at the cluster surface is gleaned from molecular dynamics (MD) simulations, which suggests a highly porous shell structure due to the dynamic formation of internal clefts and cavities. From analysis of the MD trajectory of 3, a theoretical neutron-scattering function is derived that is in good agreement with experimental SANS data. Force field parameters used in MD simulations are partially derived from a quantum mechanical geometry optimization of [(Zn(H(2)O))(3)(SbW(9)O(33))(2)](12)(-), 2b, at the density functional theory (DFT) level. DFT calculations are corroborated by X-ray structure analysis of Na(6)K(6)[(Zn(H(2)O))(3)(SbW(9)O(33))(2)].23H(2)O, which is isostructural with the catalytically active Mn derivative 2a. The combined use of theoretical and analytical methods aims at rapidly prototyping smart catalysts ("dendrizymes"), which are structurally related to naturally occurring metalloproteins.     

Effects of temperature on the triplet behavior of the styrylphenanthrene isomers

The properties of the triplet state of five styrylphenanthrene (StPh) trans isomers were studied in 2-methyltetrahydrofuran (MTHF) as a function of temperature. At room temperature the T-T absorption was observed only for 4- and 9-StPh, while under these conditions 1-, 2-, and 3-StPh have too low a quantum yield of triplet formation (Φ_T <0.02); their T-T absorption spectra were obtained at low temperature. Φ_T of 1- and 2-StPh increases more than tenfold on going from 293 to 77 K, and the triplet lifetime (τ_T) increases by four orders of magnitude and approaches values of 5–40 ms at 77 K. The change in τ_T is explained in terms of an equilibrium between trans and perpendicular (perp) conformations of the lowest triplet state in fluid solution and temperature and viscosity effects on the trans → perp rotation. Evidence is presented for the existence of two conformeric trans triplet states of 3-StPh at 77 K. Semi-empirical calculations were performed to obtain the energy of the triplet state, the wavelengths of several T-T absorption maxima (λ_T), and the oscillator strength. The calculated λ_T values coincide with those measured in n-hexane.     

Some Tris[(triorganophosphine)gold(I)]-oxonium and -Organoimonium Tetrafluoroborates with Bulky Substituents

Tris{[tri(2-methylphenyl)phosphine]gold(I)}-, tris{[tri(2,4,6-trimethylphenyl)phosphine]gold(I)}- and tris{[tri(cyclohexyl)phosphine]gold(I)}-oxonium tetra-fluoroborate ( 1?3 ) have been prepared from the corresponding (phosphine)gold(I) chlorides, silver oxide, and sodium tetrafluoroborate in acetone. These oxonium salts are excellent aurating agents for primary amines. Thus in the reaction with 1, t -butylamine ^tBuNH₂ and aniline PhNH₂ are readily converted into the tri nuclear imino complexes {[(2-MeC₆H₄)₃P]Au}₃N^tBu⁺BF₄^? ( 4 ) and {[(2-MeC₆H₄)₃P]Au}₃NPh⁺BF ( 5 ) in high yields. With 3 , both aniline and 8-amino-quinoline also give the tri nuclear complexes, i.e. {[(c-C₆H₁₁)₃P]Au}₃ NPh⁺BF ( 6 ) and {[(c-C₆H₁₁)₃P]Au}₃N(C₉H₆N)⁺BF ( 7 ). Auration of aniline with the most sterically hindered reagent 2 yields only the bi nuclear complex {[2,4,6-Me₃C₆H₂)₃P] · Au}₂N(Ph)H⁺BF ( 8 ). The reagents 1?3 and the Products 4 – 8 have been characterized by analytical and NMR spectroscopic data, and the crystal structures of compounds 4 and 6 have been determined by single crystal x-ray diffraction. In the cations of 4 , a triangle of gold atoms with short Au — Au contacts [3.036(1), 3.107(1), and 3.214(1) Å] forms a steep pyramid with the nitrogen atom, in which the angles Au? N? Au are all much smaller than the tetrahedral standard of 109.7°: 94.8(4), 98.1(4), and 103.0(4)°. This triangular Au₃ unit is staggered relative to the three methyl groups of the ^tBu substituent at nitrogen. The results for 6 are similar [Au — Au: 3.037(1), 3.071(1), and 3.222(1) Å; Au? N? Au: 95.3(3), 96.5(3), and 103.6(3)°]. Variable temperature NMR studies of compounds 3 and 8 show hindered rotation of the mesityl groups about the P? C bonds of the ligands originating from the steric congestion within each tertiary phosphine.