Synthesis and crystal structure of the thiophene-3-acetonitrile complex fac-[Mo(CO)3{NCCH2(C4 H 3S-3)}3]

Reaction of fac-[Mo(CO)₃(NCMe)₃] with three equivalents of NCCH₂(C₄ H ₃S-3) in acetonitrile gives the tris(thiophene-3-acetonitrile) complex, fac-[Mo(CO)₃{NCCH₂(C₄H₃S-3)}₃] (1) in 7% yield. Complex 1 crystallizes out in the orthorhombic space group Pnma with a = 12.714(17), b = 16.41(2), c = 11.304(16) Å, Z = 4. The structure has crystallographic m symmetry and the metal is in an almost perfect octahedral environment, with a facial arrangement of carbonyl and thiophene-3-acetonitrile groups. The thiophene rings are disordered.     

Crystal structure of chloro(dicarbonyl) bis(acetonitrile) (π-2-methallyl) molybdenum(II)

The title compound crystallizes in the monoclinic spacegroup P2₁/m with a = 6.796(9), b = 12.145(14), c = 7.749(8)Å, = 101.86(1)°, and Z = 2. The crystal structure consists of molecules of [MoCl(CO)₂(NCMe)₂(³-C₃H₄Me-2)] with crystallographically imposed C_s symmetry and has a pseudo-octahedral geometry, with the -allyl group trans- to the chloro group and the two cis-carbonyl and acetonitrile groups occupying the equatorial plane.     

Crystal structure of [WBr2(CO)(PPh2Cy)2(η2-MeC2Me)]·CH2Cl2 (Cy = cyclohexyl)

[WBr₂(Co)(PPh₂Cy)₂(²-MeC₂Me)]·CH₂Cl₂ (Cy = cyclohexyl) crystallizes in the monoclinic space group, P2₁/n, with a = 10.606(12), b = 23.11(3), c = 18.19(2) Å, = 106.070(10) D_calc = 1.610g cm^–3 for Z = 4. The tungsten coordination geometry can best be considered as a distorted octahedron, with the but-2-yne ligand occupying one coordination site, which has a trans-Br(2) group. The equatorial plane is made up of trans-PPh₂Cy groups, with the bromo and carbonyl ligands occupying the other two sites.     

Synthesis and structural studies of hydrophilic mesocyclic trithioethers

The functionalized mesocyclic trithioethers, 1,4,7-trithiacyclodecane-9,9-dimethanol (10S3-diMeOH), 9 -methyl-1, 4, 7 - trithiacyclodecane - 9 -carboxylic acid (Me-10S3-acid), 1,4,7-trithiacycloundecane-9,10-diol (dihydroxy-11S3), 1,5,9-trithiacyclododecane-3,3-dimethanol (12S3-diMeOH), 3-methyl-1,5,9-trithiacyclododecane-3-carboxylic acid (Me-12S3-acid), and 1 , 5 , 9 - trit hiacyclo tride cane -11 , 12 - diol ( dihydroxy - 13S3), have been synthesized using the cesium dithiolate technique. The single-crystal X-ray structure has been determined for 3-methyl-1,5,9-trithiacyclododecane-3-carboxylic acid. The compound crystallizes in the monoclinic space group P2₁/n, with a = 9.513(2) Å, b = 5.706(1) Å, c = 25.70(1) Å, β = 96.50(1)°, Z = 4, and R = 0.075. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:123–128, 1998     

MULTIDIMENSIONAL UPWIND RESIDUAL DISTRIBUTION SCHEMES FOR THE CONVECTION–DIFFUSION EQUATION

Multidimensional residual distribution schemes for the convection–diffusion equation are described. Compact upwind cell vertex schemes are used for the discretization of the convective term. For the diffusive term, two approaches are compared: the classical finite element Galerkin formulation, which preserves the compactness of the stencil used for the convective part, and various residual-based approaches in which the diffusive term, evaluated after a reconstruction step, is upwinded along with the convective term.     

Expression, Purification, Crystallization and Molecular Replacement Studies of TorI, an Inhibition Protein of Tor System

TorI, a Tor system inhibitor acting through protein-protein interaction with the TorR response regulator, is an excisionase that interacts with the integrase and DNA during prophage excision. It has been crystallized by the vapor-diffusion method using polyethylene glycol 3350 as a precipitant at pH 8.5. The X-ray diffraction data sets from the TorI crystal was collected at a resolution of 2.1 , using a synchrotron source. The crystal belongs to primitive monoclinic lattice with cell parameters of 46.210 × 53.992 × 73.561     

Metastability of native proteins and the phenomenon of amyloid formation

An experimental determination of the thermodynamic stabilities of a series of amyloid fibrils reveals that this structural form is likely to be the most stable one that protein molecules can adopt even under physiological conditions. This result challenges the conventional assumption that functional forms of proteins correspond to the global minima in their free energy surfaces and suggests that living systems are conformationally as well as chemically metastable.     

Stereoselective cycloaddition of 1,3-cyclohexadiene on Si(100): a simple algorithm for product identification based on secondary orbital interactions

We consider the reaction of 1,3-cyclohexadiene (1,3-CHD) on Si(100) and show that the observed reactivity and stereoselectivity cannot be explained on the basis of thermodynamics. We postulate the existence of secondary orbital interactions (SOIs) and introduce a simple algorithm that examines all possible secondary interactions between the frontier orbitals of the molecule and the surface. We demonstrate using an orbital symmetry-based algorithm supported by DFT calculations that SOIs favor a particular molecular configuration, consistent with the experimental observations. The potential role of SOIs in controlling surface chemical reactions is discussed.     

Degradation mechanism of poly(lactic-co-glycolic) acid block copolymer cast films in phosphate buffer solution

We have investigated the degradation of poly(lactic-co-glycolic) acid copolymer with a lactic to glycolic ratio of 50:50. Solvent-cast films were incubated at 37 °C in phosphate buffered saline solution and their degradation was followed using potentiometry, light microscopy, gravimetry, size exclusion chromatography, differential scanning calorimetry and infrared spectroscopy. The degradation process was found to have two main steps. The first step was observed from 0 to 7 days of degradation. During the first few days a soft layer formed at the surface of the film. As degradation time increased this soft surface layer was found to swell and wrinkle. The polymer molecular weight in the bulk was found to decrease as soon as the film was placed in the medium while the polymer present in the surface layer was found to degrade at a much slower rate. The second step of degradation was found to occur after 8 days. At this stage of the degradation process the molecular weight of the polymer in the bulk of the films was so low that the materials became liquid resulting in the detachment of the film from the glass slide. At this stage the mass loss and amount of acid released in the media were found to increase significantly.