Crystal and molecular structure ofS-methyl(pentafluorosulfanyl)thiocarbamate

The X-ray structure of S-methyl(pentafluorosulfanyl)thiocarbamate, SF₅NHC(O)SCH₃, has been determined from three-dimensional diffractometer data and refined by full-matrix least-squares techniques. The crystals are monoclinic:P2₁/m,a=5.008 (5),b=7.811 (2),c=9.348 (4) Å, =99.08 (7)°, andZ=2; finalR=0.046 for 517 observed reflections. The structure comprises hydrogen-bonded (NHO) chains with the component monomers in thecis, cis-conformation, i.e., the arrangement of the nonhydrogen and nonfluorine atoms is nearly planar, the SF₅ group and the O are in acis position with respect to the C-NH bond, and the O and the CH₃ group are in acis position with respect to the C(O)-S bond. Theoretical methods including MNDO and molecular modeling were used to study the relative stabilities of the four possible conformations of SF₅NHC(O)SCH₃.     

Dynamic nature of the intramolecular electronic coupling mediated by a solvent molecule: a computational study

We present a combined Molecular Dynamics/Quantum Chemical study of the solvent-mediated electronic coupling between an electron donor and acceptor in a C-clamp molecule. We characterize the coupling fluctuations due to the solvent motion for different solvents (acetonitrile, benzene, 1,3-diisopropyl-benzene) for the charge separation and the charge recombination processes. The time scale for solvent-induced coupling fluctuation is approximately 0.1 ps. The effect of these fluctuations on the observed rate is discussed using a recently developed theoretical model. We show that, while the microscopic charge transfer process is very complicated and its computational modeling very subtle, the macroscopic phenomenology can be captured by the standard models. Analyzing the contribution to the coupling given by different solvent orbitals, we find that many solvent orbitals mediate the electron transfer and that paths through different solvent orbitals can interfere constructively or destructively. A relatively small subset of substrate-solvent configurations dominate contributions to solvent-mediated coupling. This subset of configurations is related to the electronic structure of the C-clamp molecule.     

Activation of alkenes and H2 by [Fe]-H2ase model complexes

The established ability of the Fe(II) bridging hydride species (micro-H)(micro-pdt)[Fe(CO)2(PMe3)]2+, 1-H+, to take-up and heterolytically activate dihydrogen, resulting in H/D scrambling of H2/D2 and H2/D2O mixtures (Zhao et al. Inorg. Chem. 2002, 41, 3917) has prompted a study of simultaneous alkene/H2 activation by such [Fe]H2ase model complexes. That the required photolysis produced an open site was substantiated by substitution of CO in 1-H+ by CH3CN with formation of structurally characterized [(micro-H)(micro-pdt)[Fe(CO)2(PMe3)][Fe(CO)(CH3CN)(PMe3)]]+[PF6]-. Under similar photolytic conditions, H/D exchange reactions between D2 and terminal alkenes (ethylene, propene and 1-butene), but not bulkier alkenes such as 2-butene or cyclohexene, were catalyzed by 1-H+ and the edt (SCH2CH2S) analogue, 2-H+. Substantial regioselectivity for H/D exchange at the internal vinylic hydrogen was observed. The extent to which the olefins were deuterium enriched vs deuterated was catalyst dependent. The stabilizing effect of the binuclear chelating ligands, SCH2CH2CH2S, pdt, and SCH2CH2S, edt, is required for the activity of binuclear catalysts, as the mono-dentate micro-SEt analogue decomposed to inactive products under the photolytic conditions of the catalysis. Reactions of 1 and 2 with EtOSO2CF3 yielded the S-alkylated products, [(micro-SCH2CH2CH2SEt)[Fe(CO)2(PMe3)]2]+[SO3CF3]- (1-Et+), and 2-Et+, rather than micro-C2H5 analogues to the micro-H of 1-H+. The stability and lack of reactivity toward H2 of 1-Et+ and 2-Et+, indicates they are not on the reaction path of the olefin/D2 H/D exchange process. A mechanism with olefin binding to an open site created by CO loss and formation of an Fe-(CH2CHDR) intermediate is indicated. A likely role of a binuclear chelate effect is implicated for the unique S-XXX-S cofactor in the active site of [Fe]H2ase.     

Computational study of the halogen atom-benzene complexes

The structures of halogen atom-benzene complexes were investigated by modern DFT and ab initio computational methods. The spectroscopic properties of the complexes are also predicted and are in good agreement with experiment where such data have been reported. The fluorine atom-benzene complex is predicted to be a sigma complex due to the strength of a C-F bond. The chlorine atom-benzene complex is predicted to have an eta(1) pi complex structure, which is only slightly more favorable (1.1 kcal/mol with the BH&HLYP/6-311++G method including the ZPE correction) than a sigma complex but is significantly more stable (4.4 kcal/mol with the BH&HLYP/6-311++G method including the ZPE correction) than the eta(6) pi complex. The bromine and iodine benzene complexes are also predicted to prefer an eta(1) pi complex structure.     

Total synthesis of lucilactaene, a cell cycle inhibitor active in p53-inactive cells

Hetero-bis-metalated 1,3-butadiene is employed in the lynchpin coupling of synthetic fragments of the side chain of the antitumor agent, lucilactaene. Sequential Stille and Suzuki-Miyaura couplings interpolate this unique boron/tin diene into the pentaene chain. The total synthesis of lucilactaene was accomplished efficiently, in just eight linear steps.     

Iron(III) p-toluenesulfonate catalyzed synthesis of homoallyl ethers from acetals and aldehydes

Iron(III) p-toluenesulfonate, Fe(OTs)₃·6H₂O, is an inexpensive, versatile and commercially available catalyst for the allylation of acetals using allyltrimethylsilane to yield homoallyl ethers in moderate to good yields. The one-pot conversion of aldehydes to homoallyl ethers using alkoxysilanes has also been accomplished using Fe(OTs)₃·6H₂O as a catalyst. The use of mild reaction conditions and a relatively non-corrosive catalyst make this method an attractive option for the synthesis of a range of homoallyl ethers.     

Gold nanoparticles as a colorimetric sensor for protein conformational changes

Spherical gold nanoparticles and flat gold films are prepared in which yeast iso-1-cytochrome c (Cyt c) is covalently bound to the gold surface by a thiol group in the cystein 102 residue. Upon exposure to solutions of different pH, bound Cyt c unfolds at low pH and refolds at high pH. This conformational change causes measurable shifts in the color of the coated nanoparticle solutions detected by UV-VIS absorption spectroscopy and in the refractive index (RI) of the flat gold films detected by surface plasmon resonance (SPR) spectroscopy. Both experiments demonstrate the same trend with pH, suggesting the use of protein-covered gold nanoparticles as a simple colorimetric sensor for conformational change.     

Ti(III)-Mediated reductions of N-hydroxy imidazoles to 1-protio-2,4(5)-disubstituted derivatives

N-hydroxy imidazoles are converted $\text{via}$ TiCl₃ in MeOH/H₂O to N-protio derivatives, useful precursors of chiral amino acids.     

Dendritic nanowire ultraviolet laser array

Self-organized dendritic crystal growth is explored to assemble uniform semiconductor nanowires into highly ordered one-dimensional microscale arrays that resemble comb structures. The individual ZnO nanowires have uniform diameters ranging from 10 to 300 nm. They are evenly spaced on a stem with a regular periodicity of 0.1-2 micrometer. Under optical excitation, each individual ZnO nanowire serves as a Fabry-Perot optical cavity, and together they form a highly ordered nanowire ultraviolet laser array.     

Metabonomics: the use of electrospray mass spectrometry coupled to reversed-phase liquid chromatography shows potential for the screening of rat urine in drug development

The application of liquid chromatography/mass spectrometry (LC/MS) followed by principal components analysis (PCA) has been successfully applied to the screening of rat urine following the administration of three candidate pharmaceuticals. With this methodology it was possible to differentiate the control samples from the dosed samples and to identify the components of the mass spectrum responsible for the separation. These data clearly show that LC/MS is a viable alternative, or complementary, technique to proton NMR for metabonomics applications in drug discovery and development.