Triethylphosphanimin-Komplexe der Acetate von Kupfer(II) und Zink. Kristallstrukturen von [Zn(O2C–CH3)2(HNPEt3)], [Cu5(O2C–CH3)10(HNPEt3)2] und [Cu(O2C–CH3)2(HNPEt3)2]

Triethylphosphanimine Complexes of the Acetates of Copper(II) and Zinc. Crystal Structures of [Zn(O₂C–CH₃)₂(HNPEt₃)], [Cu₅(O₂C–CH₃)₁₀(HNPEt₃)₂], and [Cu(O₂C–CH₃)₂(HNPEt₃)₂] The title compounds originate from the anhydrous acetates of zinc and copper(II) with trimethylsilyl-triethylphosphanimine, Me₃SiNPEt₃, in the presence of water in dichloromethane. They form colourless ( 1 ), bluish-green ( 2 ), and blue ( 3 ), respectively, single crystals, which were characterized by IR spectroscopy and by crystal structure analyses. [Zn(O₂C–CH₃)₂(HNPEt₃)] ( 1 ): Space group P 4 2₁c, Z = 8, lattice dimensions at –83 °C: a = b = 1709.6(2), c = 982.4(1) pm, R = 0.0551. 1 has a polymeric chain structure in which the zinc atoms are μ₂-bridged via the oxygen atoms of one of the two acetato groups, while the second acetato group and the phosphanimine are bonded terminally. [Cu₅(O₂C–CH₃)₁₀(HNPEt₃)₂]( 2 · 4 CH₂Cl₂): Space group P2₁/c, Z = 8, lattice dimensions at –80 °C: a = 1761.18(13), b = 4074.5(2), c = 1733.34(15) pm, β = 91.383(10)°, R = 0.0413. 2 consists of the two structural units [Cu₂(O₂C–CH₃)₄] and [Cu₃(O₂C–CH₃)₆(HNPEt₃)₂], which are connected via two of the acetato groups of the Cu₃-unit along the crystallographic a-axis to form three crystallographically independent polymeric strands. [Cu(O₂C–CH₃)₂(HNPEt₃)₂] ( 3 ): Space group P2₁/n, Z = 2, lattice dimensions at 20 °C: a = 695.49(8), b = 1217.85(10), c = 1380.05(7) pm, β = 96.451(7)°, R = 0.0291. 3 forms monomeric, centrosymmetric molecules with a square planar environment at the Cu atoms.     

Planar-Tetracoordinate Carbon in a Neutral Saturated Hydrocarbon: Theoretical Design and Characterization

Exact planarity at the central carbon atom is achieved, according to molecular orbital calculations, in the strained polycyclic cage hydrocarbon dimethanospiro[2.2]octaplane (see structure). There are no glaringly long C−C bonds, which might have reflected inherent instability in this molecule that is yet to be synthesized.     

Long-range electronic interactions in androstanediones

The results of MNDO SCF MO calculations on 5α-androstane (1), androstan-3-one (2), androstan-16-one (3), androstan-17-one (4), androstane-3,16-dione (5), and androstane-3,17-dione (6) and the experimental ¹³C-NMR chemical shifts observed in various solvents (C₆D₁₂, CDCl₃, CD₃CO₂D, CD₂Cl₂, CD₃COCD₃, CD₃OD, CD₃CN) were used to assess the nature of long-range interactions between 3,16- and 3,17-carbonyl groups in androstanediones. The ¹³C-NMR results appear to confirm the proposition that the interactions in androstane-3,16-dione are stronger. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 797–803, 1997     

MBO(N)D: A multibody method for long‐time molecular dynamics simulations

A modeling approach that can significantly speed up the dynamics simulation of large molecular systems is presented herein. A multigranular modeling approach, whereby different parts of the molecule are modeled at different levels of detail, is enabled by substructuring. Substructuring the molecular system is accomplished by collecting groups of atoms into rigid or flexible bodies. Body flexibility is modeled by a truncated set of body‐based modes. This approach allows for the elimination of the high‐frequency harmonic motion while capturing the low‐frequency anharmonic motion of interest. This results in the use of larger integration step sizes, substantially reducing the computational time required for a given dynamic simulation. The method also includes the use of a multiple time scale (MTS) integration scheme. Speed increases of 5‐ to 30‐fold over atomistic simulations have been realized in various applications of the method. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 159–184, 2000     

(E)‐5‐[Hydroxyimino(phenyl)methyl]‐1‐methyl‐3,4‐dihydro‐2H‐pyrrolium trifluoromethanesulfonate

The cation of the title compound, C₁₂H₁₅N₂O⁺·CF₃SO₃^?, exists as an E‐configured hydroxy­imino derivative conjugated with a nearly planar iminium system. The twist angle between the phenyl ring and the oxime group is 72.2 (2)°. An O—H?O hydrogen bond links the oxime group of the cation to the anion.     

Identifying key electrostatic interactions in Rhizomucor miehei lipase: the influence of solvent dielectric

The conformational change associated with the interfacial activation of Rhizomucor miehei lipase involves the displacement of an α-helical lid (residues 82–96) away from the active site on moving from water (high dielectric) to lipid (low dielectric). The presence of two media of very different dielectric properties suggests that electrostatic interactions play an important role in this process. We have used linearized Poisson–Boltzmann calculations to examine the key electrostatic interactions which contribute to lid stability in the closed and open states. It is the two charged residues of the lid, Arg86 and Asp91, that form the strongest electrostatic interactions with the rest of the protein. We identify key residues whose interactions with the lid are significantly perturbed by the change in the dielectric of the medium: Asp61, Arg80, Lys109, Glu117 and the active-site residues Asp203 and Asp256, all of which lie within approximately 20 ? of the lid. We suggest that these residues are good candidates for site-specific mutation studies, which could help elucidate their role in the lipase activation mechanism. Received: 27 May 1998 / Accepted: 17 September 1998 / Published online: 7 December 1998