Radical (NO) and nonradical (N(2)O) reagents convert a ruthenium(IV) nitride to the same nitrosyl complex

The ruthenium(IV) nitride complex (PNP)RuN (PNP = (tBu2PCH2-SiMe2)2N-) reacts rapidly with 2NO to form (PNP)Ru(NO) and N2O, via no detectable intermediate. The linear nitrosyl complex has a planar structure. In a slower reaction, (PNP)RuN reacts with N2O by O-atom transfer (established by 15N labeling) to give the same nitrosyl complex and N2. Density functional theory (B3LYP) calculations show both reactions to be very thermodynamically favorable. Analysis of possible intermediates in each reaction shows that radical (PNP)RuN(NO) has much spin density on nitride N (hence, N2-), while one 2 + 3 metallacycle, (PNP)RuN3O, has the wrong connectivity to form a product. Instead, an intermediate with a doubly bent N2O (hence, a two-electron reduced N-nitrosoimide form) brings the O atom in proximity to the nitride N on the path to a product.     

Vapor-liquid coexistence of patchy models: relevance to protein phase behavior

The vapor-liquid coexistence boundaries of fluids composed of particles interacting with highly directional patchy interactions, in addition to an isotropic square well potential, are evaluated using grand canonical Monte Carlo simulations combined with the histogram reweighting and finite size scaling methods. We are motivated to study this more complicated model for two reasons. First, it is established that the reduced widths of the metastable vapor-liquid coexistence curve predicted by a model with only isotropic interparticle interactions are much too narrow when compared to the experimental phase behavior of protein solutions. Second, interprotein interactions are well known to be "patchy." Our results show that at a constant total areal density of patches, the critical temperature and the critical density increase monotonically with an increasing number of uniformly spaced patches. The vapor-liquid coexistence curves plotted in reduced coordinates (i.e., the temperature and the density scaled by their respective critical values) are found to be effectively independent of the number of patches, but are much broader than those found for the isotropic models. Our findings for the reduced width of the coexistence curve are almost in quantitative agreement with the available experimental data for protein solutions, stressing the importance of patchiness in this context.     

Uniform blow-up rate for diffusion equations with nonlocal nonlinear source

In this paper, we investigate the blow-up rate of solutions of diffusion equations with nonlocal nonlinear reaction terms. For large classes of equations, we prove that the solutions have global blow-up and that the rate of blow-up is uniform in all compact subsets of the domain. In each case, the blow-up rate of _|u(t)|∞${\left|u\left(t\right)\right|}_{\infty }$ is precisely determined.     

Total synthesis of (+/-)-strychnine via a [4 + 2]-cycloaddition/rearrangement cascade

A new strategy for the synthesis of the Strychnos alkaloid (+/-)-strychnine has been developed and is based on an intramolecular [4 + 2]-cycloaddition/rearrangement cascade of an indolyl-substituted amidofuran. The critical D-ring was assembled by an intramolecular palladium-catalyzed enolate-driven cross-coupling of an N-tethered vinyl iodide. [reaction: see text].     

Predicting two-dimensional boron-carbon compounds by the global optimization method

We adopt a global optimization method to predict two-dimensional (2D) nanostructures through the particle-swarm optimization (PSO) algorithm. By performing PSO simulations, we predict new stable structures of 2D boron-carbon (B-C) compounds for a wide range of boron concentrations. Our calculations show that: (1) All 2D B-C compounds are metallic except for BC(3) which is a magic case where the isolation of carbon six-membered ring by boron atoms results in a semi-conducting behavior. (2) For C-rich B-C compounds, the most stable 2D structures can be viewed as boron doped graphene structures, where boron atoms typically form 1D zigzag chains except for BC(3) in which boron atoms are uniformly distributed. (3) The most stable 2D structure of BC has alternative carbon and boron ribbons with strong in-between B-C bonds, which possesses a high thermal stability above 2000 K. (4) For B-rich 2D B-C compounds, there is a novel planar-tetracoordinate carbon motif with an approximate C(2)(v) symmetry.     

Theoretical studies on the intra- and intermolecular C-H activation by T-shaped pincer complexes

Three coordinated, T-shaped (PNP)M^I (M = Co, Ru, Rh, Os and Ir) and [(PCP)Pt⁰]⁻, as well as their reactivities for intra- and intermolecular C-H activation have been studied by DFT methods. The experimental observed reactivities were well reproduced. The calculation also generated structural and energetic information which the experimental values were not yet available. We found that the intramolecular C-H activation is in general possible for the low spin (PNP)M^I. Intermolecular C-H activation is not preferred either thermodynamically or kinetically, but could be in competition if the intramolecular activation is reversible. Using model compounds, we found that the intramolecular C-H activation reactivity is not sensitive to steric effects of the bulky ligands. However, the strain of the four-membered ring in the product significantly reduces the reactivity, and the driving force increases by 4.51-12.95 kcal/mol if the strain was largely removed by changing from a four-membered ring to a five-membered ring. The C-H activation step is quite difficult for metals with a d¹⁰ configuration. Part of the reason is that one phosphine ligand dissociates during the reaction because the product has a d⁸ configuration and prefers a square planar structure.     

Highly enantio- and diastereoselective synthesis of β-methyl-γ-monofluoromethyl-substituted alcohols

Enanatiopure β-methyl-γ-monofluoromethyl alcohols were prepared from the allylic alkylation between fluorobis(phenylsulfonyl)methane with Morita-Baylis-Hillman carbonates. The reaction was catalyzed by using the Cinchona alkaloid derivative, (DHQD)(2)AQN. The origin of the stereoselectivity was verified by DFT methods. Calculated geometries and relative energies of various transition states strongly support the observed stereoselectivity.     

Self-assembly of disk-like multiring ZnO-SnO2 colloidal nanoparticles

ZnO-SnO(2) colloidal nanoparticles have been successfully synthesized by using the composite of ZnCl(2) and Sn(OC(4)H(9))(4) as inorganic precursor and dodecylbenzenesulfonic acid (DBSA) as an organic template. The assembled nanostructures of ZnO-SnO(2) products have been carefully investigated by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). It is found that ZnO-SnO(2) colloidal nanoparticles take a disk-like multiring nanostructure. This interesting structure is predominantly determined by the tenacity for ZnO-SnO(2) mixtures to stabilize lamellae. A mechanism based on electrostatic interactions between the precursor and template has been proposed to illustrate the resulting nanoparticle structure.