The Remarkable Structure of Lithium Cyanide/Isocyanide

Electron correlation corrections have a considerable influence on the relative stabilities of lithium isocyanide ( 1 ), lithium cyanide ( 2 ), and the bridged form, 3 . While Hartree-Fock theory finds 1 to be most stable and 3 not to be a minimum, MP2/6-31G* optimization indicates 3 to be the global minimum. At higher levels employing full fourth-order Møller-Plesset theory and a quadruply split valence and polarized basis set (MP4STDQ/6-311+G*), 2 is only about 2 kcal/mol less stable than 1 and 3 , which are indicated to have nearly the same energy. LiNC thus is similar to C(Na)N and C(K)N, both of which are known to prefer T-shaped (bridged) structures in the gas phase. However, to an even greater extent than formerly realized, rotation of the lithium cation around the cyanide anion nucleus should be practically free. ΔH (LiCN) = 32.8 kcal/mol is estimated from the calculated lithium cation affinity of 151.2 kcal/mol. In addition, we find at the MP4SDTQ/6-31+G*//MP2/6-31G* level that the bridged form of NaCN is favored by 2–3 kcal/mol over the corresponding linear forms, which have nearly the same energy.     

Optisch aktive β(alkoxy)ethyl-phosphonsäureester, β(alkoxy)ethyl-phenyl-phosphinsäureester, β(alkoxy)ethyl-diphenylphosphinoxide und β(alkoxy)ethyl-diphenylphosphine

The title compounds are synthesized by Michael-type additions of optically active alcohols to the corresponding PO-activated vinylderivatives.     

Reaktionen mit phosphororganischen Verbindungen, 49. Synthese und 1H-NMR-Spektren von (3-Acylbicyclo[2.2.1]hept-5-en-2-yl)phosphonsäureestern

Reactions with Organophosphorus Compounds, 49. Synthesis and ¹H NMR Spectra of (3-Acylbicyclo[2.2.1]hept-5-en-2-yl)phosphonates Reaction of the (E)-(β-acylvinyl)phosphonates 1 with cyclopentadiene yields the isomeric norbornylphosphonates 2 (endo-acyl, exo-P) and 3 (exo-acyl, endo-P) in a 7:3 ratio. With 1,3-cyclohexadiene the corresponding bicyclooctenyl derivatives 7 and 8 are obtained from 1a . The (Z)-phosphinylacrylate 4 gives with cyclopentadiene the isomers 5 (exo-CO₂Me, exo-P) and 6 (endo-CO₂Me, endo-P) in nearly equal amounts. The configuration of the cycloadducts has been proved by ¹H NMR spectroscopy.     

The baculovirus expression system as a tool for generating diversity by viral surface display

It has become a major goal of molecular biologists, biochemists, and immunologists to be able to modulate the structure of proteins, in order to increase their antigenicity, alter their biological properties and/or explore their function. Based on the concept of bacterial phage display, by which proteins are being selected and analyzed in conjunction with their genetic information, eukaryotic systems have been investigated for their use in generating biomolecular diversity. The advantage of posttranslational modification and the possible harbouring of structural complex proteins has lead scientists to include eukaryotic systems in the wide field of molecular design. The ideal expression vectors for surface display are eukaryotic viruses, that allow large gene insertions, efficiently present foreign proteins on the particle surface, are easy to propagate and, if possible, not pathogenic to humans. By inserting peptides into a native virus coat protein or by expressing foreign proteins as coat protein fusion proteins or linked to specific anchor domains it becomes possible to display polypeptides of interest on the surface of replicating particles. A variety of different strategies are currently under investigation in order to utilize the baculovirus insect cell expression system for efficient display on the surface of virus particles as well as on the surface of virally infected insect cells. Increasing the transfection efficiency, optimizing cloning procedures, and establishing applicable selection methods have lead to the development of a powerful tool for drug screening and ligand screening.     

Beitrag zur Trennung des Urans von Thorium mittels Ionenaustausches und zur fluorimetrischen Uranbestimmung

Zusammenfassung Es wird eine Uran-Thoriumtrennung mittels des stark basischen Anionenaustauschers Amberlite IRA 400 beschrieben. Uran(VI) läßt sich von Thorium und einer Reihe anderer Kationen dadurch trennen, daß es mit 6,5n Salzsäure einen negativ geladenen Komplex bildet, der am Austauscherharz sorbiert wird, während Thorium keinen Komplex bildet und daher nicht sorbiert wird. Uran wird mit 1 n Salzsäure eluiert.Zur Bestimmung des Urans wird eine genaue und empfindliche fluorimetrische Bestimmung angewendet, die durch Einfachheit und Billigkeit der dazu verwendeten Apparate gekennzeichnet ist.Das Verhalten anderer Kationen unter den Bedingungen der Trennung wurde qualitativ studiert und die Möglichkeit der Trennung des Urans und Thoriums von den erwähnten Kationen diskutiert.Herrn Prof. Dr. L. Schmid, Wien, zum 60. Geburtstag gewidmet.Für die Gewährung eines Stipendiums zur Ausführung der vorliegenden Arbeit an eine von uns (M. P.), sei der Österreichischen Gesellschaft für Mikrochemie der beste Dank ausgesprochen.Herrn Prof. Dr. F. Hecht, der diese Arbeit ermöglichte, sei für seine stete Hilfe herzlich gedankt.     

Mehrfachbindungen zwischen hauptgruppenelementen und übergangsmetallen: VII. Oxidative decarbonylierungsprozessein der photochemie von tricarbonyl(η5-pentamethylcyclopentadienyl)rhenium: Neue oxo—rhenium-komplexe

Short-wavelength photolysis of tricarbonyl(η⁵-pentamethylcyclopentadienyl)rhenium (1) (λ < 300 nm, quartz-glass) in tetrahydrofuran yields under partial or complete decarbonylation three novel organorhenium compounds, with the relative yields depending upon the irradiation time. Formed by exhaustive oxidative decarbonylation, the complex trioxo(η⁵-pentamethylcyclopentadienyl)rhenium(VII) (5) represents the first example of the new class of oxo half-sandwich complexes. The derivatives (μ-O)[(η⁵-C₅Me₅)Re(CO)₂]₂ (2; Me = CH₃) and (η⁵-C₅Me₅)₂Re₂(CO)₂O₂ (3; Me = CH₃) containing both oxo and carbonyl ligands are formed from 1 at shorter irradiation times. Both compounds are isolable intermediates along the mechanistically not yet fully established sequence 1 → → 5 as they are degraded to 5 under CO₂ elimination in the presence of air and/or light. The mixed oxo carbonyl complex 2 has been characterized by means of single-crystal X-ray diffraction techniques (triclinic, space group P$\text{1}$-C_i¹; a 907.4(2), b 1040.2(3), c 1414.3(4) pm; α 79.99(2), β 88.42(2), γ 66.18(2)°; R_iso = 0.068, R_aniso = 0.037, R_w = 0.031). The molecular structure centres around an isosceles Re₂O triangle whose metal centres exhibit a strongly distorted square-pyramidal geometry; the metal-metal distance recorded at 281.7(1) pm is in agreement with a single bond by the EAN rule. The centrically coordinated, planar five-membered ring ligands are parallel to each other (interplanar angle 2°) and occupy trans-positions with respect to the central Re₂O geometry.     

Atropisomerism of phosphorus-containing N-aryl carbamates. Experimental and computational data

Studies by ¹H NMR spectroscopy and X-ray diffraction analysis revealed hindered rotation of the aromatic substituent about the C_Ar—N bond in ortho-substituted (except for o-fluorine-substituted) phosphorus-containing carbamates. The energy barriers to rotation (G _c ) and coalescence temperatures (T _c) determined by the coalescence method increase with increasing volume of the ortho substituent. Conformations resulting from rotation of the ortho-substituted aryl group about the C_Ar—N bond were analyzed by quantum-chemical methods, potential curves were constructed, and differences between the conformational energies and the heights of rotation barriers were estimated. The theoretical rotation barriers change in parallel with the experimental values of G _c ; however, the theoretical values are much smaller in magnitude.     

Anwendung von 2D-NMR-Techniken zur Analyse komplexer Spektren. Maleopimarsäuremethylester

A combination of 2D-NMR-techniques including 2D-J-resolved spectroscopy, SECSY and¹H-¹³C-shift correlation is used to assign the¹H- and¹³C-spectrum of Maleopimaric acid methylester [17,19-Dinoratis-15-ene-4,13,14-tricarboxylic acid 4-methylester, 16-(1-methylethyl)cyclic-13,14-anhydrid (4, 8, 12)] (1).

     

Application of significant structures theory to amorphous polyethylene

The thermodynamic properties of amorphous polyethylene are calculated from a model based on the method of significant structures. The motion of a molecule as a whole is described by the motion of segments, each segment moving independently of all others. It is assumed that on melting, holes appear in the solid lattice and the segments can move into these vacancies, obtaining some gaslike degrees of freedom. The complete frequency distribution for polyethylene is used for the solidlike degrees of freedom, while a corrected classical partition function is used for the gaslike degrees of freedom. The calculated thermodynamic properties are in reasonable agreement with experimentally determined values, assuming each gaslike segment to consist of 20 CH₂ groups.     

Intensity analysis of f-f transitions and correlation with conductivity and ultrasonic absorption for holmium solvates

Absorption spectra of holmium nitrate in MFA and DMF have been measured in the range 8000–42000 cm^?1. The τ_λ parameters were evaluated from the experimental oscillator strengths using the Judd equation. For Ho(NO₃)₃ in DMF a considerable increase in τ₂ was observed, suggesting the existence of inner-sphere species in this system. This suggestion was verified by ultrasonic absorption and conductivity measurements.