A Pyridine–Pyridine Cross‐Coupling Reaction via Dearomatized Radical Intermediates

A pyridine–pyridine coupling reaction has been developed between pyridyl phosphonium salts and cyanopyridines using B₂pin₂ as an electron‐transfer reagent. Complete regio‐ and cross‐selectivity are observed when forming a range of valuable 2,4′‐bipyridines. Phosphonium salts were found to be the only viable radical precursors in this process, and mechanistic studies indicate that the process does not proceed through a Minisci‐type coupling involving a pyridyl radical. Instead, a radical–radical coupling process between a boryl phosphonium pyridyl radical and a boryl‐stabilized cyanopyridine radical explains the C?C bond‐forming step.     

The effect of microstructural representation on simulations of microplastic ratcheting

This paper assesses the sensitivity of cyclic plasticity to microstructure morphology by examining and comparing the microplastic ratcheting behavior of different idealized microstructures (square, hexagonal, tessellated, and digitized from experimental data). This analysis demonstrates the sensitivity of computational accuracy to the various approximations in microstructural representation. The methodology used to perform this study relies on a coupling between microstructural characterization, mechanical testing and numerical simulations to investigate the influence of the microstructure on the purely tensile uniaxial microplastic ratcheting behavior of pure nickel polycrystals. The morphology and deformation behavior of polycrystals were characterized using electron back-scatter diffraction (EBSD), while a finite element model (FEM) of crystal plasticity was used in a computational framework. The predicted cyclic behavior is compared to experimental results both at the macroscopic and microstructural scales. The stress–strain response is less sensitive to the details of the microstructural representation than might be expected with all representations displaying similar macroscopic constitutive response. However, the details of the plastic strain distribution at the microstructural scale and the related estimations of damage mechanics vary substantially from one microstructural representation to another.     

Pi-complex structure of gaseous benzene-NO cations assayed by IR multiple photon dissociation spectroscopy

[C(6)H(6)NO](+) ions, in two isomeric forms involved as key intermediates in the aromatic nitrosation reaction, have been produced in the gas phase and analyzed by IR multiple photon dissociation (IRMPD) spectroscopy in the 800-2200 cm(-)(1) fingerprint wavenumber range, exploiting the high fluence and wide tunability of a free electron laser (FEL) source. The IRMPD spectra were compared with the IR absorption spectra calculated for the optimized structures of potential isomers, thus allowing structural information on the absorbing species. [C(6)H(6)NO](+) ions were obtained by two routes, taking advantage of the FEL coupling to two different ion traps. In the first one, an FT-ICR mass spectrometer, a sequence of ion-molecule reactions was allowed to occur, ultimately leading to an NO(+) transfer process to benzene. The so-formed ions displayed IRMPD features characteristic of a [benzene,NO](+) pi-complex structure, including a prominent band at 1963 cm(-)(1), within the range for the N-O bond stretching vibration of NO (1876 cm(-)(1)) and NO(+) (2344 cm(-)(1)). A quite distinct species is formed by electrospray ionization (ESI) of a methanol solution of nitrosobenzene. The ions transferred and stored in a Paul ion trap showed the IRMPD features of substituent protonated nitrosobenzene, the most stable among conceivable [C(6)H(6)NO](+) isomers according to computations. It is noteworthy that IRMPD is successful in allowing a discrimination between isomeric [C(6)H(6)NO](+) species, whereas high-energy collision-induced dissociation fails in this task. The [benzene,NO](+) pi-complex is characterized by IRMPD spectroscopy as an exemplary noncovalent ionic adduct between two important biomolecular moieties.     

On the theory of the temperature dependence of the refractive index of insulators and semi-conductors

A theory of the temperature dependence of the refractive index of insulators and semi-conductors was elaborated on the basis of the Lorentz theory of absorption and dispersion of insulators, which holds in a wide region of the spectrum including the region of intrinsic absorption. On Ge, ZnSand SiO₂ it is shown that the theoretical results agree with the experimental results at least qualitatively, and with Gealso quantitatively to a satisfactory degree.     

Characterisation by X-ray photoelectron spectroscopy of surface layers of poly(vinyl alcohol) on particles formed by dispersion polymerisation of divinylbenzene

Well-defined dispersions of polydivinylbenzene in methanol and a binary liquid mixture of methanol and water were stabilised by samples of partially hydrolysed poly(vinyl alcohol) (PVOH). Mean particle diameters in the range 0.3–1.0 m were produced in dispersion polymerisations. In order to assess surface coverage by PVOH, alcohol groups in the stabilising surface layer were derivatised with trifluoroacetic anhydride. Characterisation of trifluoroacetate groups by X-ray photoelectron spectroscopy permits the quantitative determination of atomic fluorine. The relative concentrations of surface fluorine are in agreement with expectation based on the degrees of hydrolysis of 35 mol% and 72.5 mol% of the PVOH stabilisers. Treatments based on broadscan and high-resolution spectra permit reasonable estimates of the layer thickness for PVOH chains collapsed onto the surface of dry particles. Calculations of the area occupied per PVOH chain are consistent with estimates for other stabilising chains in hydrocarbon media.     

Silicon-based nanowires from silicon wafers catalyzed by cobalt nanoparticles in a hydrogen environment

We present here the synthesis of silicon-based nanowires directly from silicon wafers at high temperatures and in the presence of cobalt nanoparticles and hydrogen gas. All three ingredients were critical to the growth of Si-based nanowires, which were between 5-60 nm in diameter and microm-mm long. Both heavily coiled and straight Si-based nanowires were made. Experimental evidence suggested that the sources of silicon for the nanowires growth were in the gas phase.     

Synthesis of the beta-hydroxydopa-gamma-hydroxy-delta-sulfinylnorvaline component of ustiloxins A and B

The dopa-sulfinylnorvaline component of ustiloxins A and B has been prepared using an Evans salen-Al-catalysed aldol reaction with a 6-mercaptoisovanillin derivative, followed by incorporation of the norvaline group and asymmetric oxidation of the resulting sulfide to give the corresponding sulfoxide.     

Synthesis and characterization of an air-stable gallium hydride, [t-Bu(H)Ga(mu-NEt(2))](2), and related chloride derivatives

The synthesis of [t-Bu(H)Ga(mu-NEt(2))](2) (1) was accomplished by the addition of 4 t-BuLi to [Cl(2)Ga(mu-NEt(2))](2). Evidence suggests that two tert-butyl groups are lost as isobutylene and result in Ga-H bond formation. The gallium hydride 1 is remarkably stable toward ambient air, oxygen, photolysis, and moderate heating; however, in CHCl(3) the hydride is replaced by chloride, producing [t-Bu(Cl)Ga(mu-NEt(2))](2) (2). Compound 1 may also be synthesized by sequential tert-butyl additions to [Cl(2)Ga(mu-NEt(2))](2). A singly substituted tert-butyl dimer, t-Bu(Cl)Ga(mu-NEt(2))(2)GaCl(2) (3), was also isolated, and interconversions between 1, 2, and 3 are described. Compound 1 was tested for utility in the chemical vapor deposition of GaN and produced gallium-rich films at low temperatures (<250 degrees C) with limited nitrogen incorporation due to facile Et(2)NH elimination.     

Osteoblast and Chrondrocyte Proliferation in the Presence of Alumina And Titania Nanoparticles

Proliferation of osteoblasts (bone-forming cells) and chondrocytes (cartilage-synthesizing cells) exposed to different sizes of alumina as well as titania particles at various concentrations (from 10,000 to 100g/ml of culture media) was investigated in the present in vitro study. Compared to respective conventional (i.e., micron) particle size ceramics, results provided the first evidence of increased osteoblast and chondrocyte proliferation in the presence of nanoparticles. Material characterization studies revealed that the only difference between respective ceramic particles was nano- and conventional-dimensions; specifically, phase, charge, and chemical properties were similar between different size alumina and titania particles, respectively. Thus, the present study provided the first evidence of a less detrimental effect of nano- as compared to conventional-dimension wear debris on cell function; such wear debris may result from friction between articulating components of orthopedic implants composed of novel nanophase ceramic materials. In this manner, results provided additional evidence to the literature that nanophase ceramics may become the next generation of bone prosthetic materials with improved osseointegrative (i.e., ability to bond to juxtaposed bone in situ) properties.