Selective methylative homologation: an alternate route to alkane upgrading

InI3 catalyzes the reaction of branched alkanes with methanol to produce heavier and more highly branched alkanes, which are more valuable fuels. The reaction of 2,3-dimethylbutane with methanol in the presence of InI3 at 180-200 degrees C affords the maximally branched C7 alkane, 2,2,3-trimethylbutane (triptane). With the addition of catalytic amounts of adamantane the selectivity of this transformation can be increased up to 60%. The lighter branched alkanes isobutane and isopentane also react with methanol to generate triptane, while 2-methylpentane is converted into 2,3-dimethylpentane and other more highly branched species. Observations implicate a chain mechanism in which InI3 activates branched alkanes to produce tertiary carbocations which are in equilibrium with olefins. The latter react with a methylating species generated from methanol and InI3 to give the next-higher carbocation, which accepts a hydride from the starting alkane to form the homologated alkane and regenerate the original carbocation. Adamantane functions as a hydride transfer agent and thus helps to minimize competing side reactions, such as isomerization and cracking, that are detrimental to selectivity.     

Ultrasonic wave propagation in concentrated slurries – The modelling problem

The suspended particle size distribution in slurries can, in principle, be estimated from measured ultrasonic wave attenuation across a frequency band in the 10s of MHz range. The procedure requires a computational model of wave propagation which incorporates scattering phenomena. These models fail at high particle concentrations due to hydrodynamic effects which they do not incorporate. This work seeks an effective viscosity and density for the medium surrounding the particles, which would enable the scattering model predictions to match experimental data for high solids loading. It is found that the required viscosity model has unphysical characteristics leading to the conclusion that a simple effective medium modification to the ECAH/LB is not possible. The paper confirms the successful results which can be obtained using core–shell scattering models, for smaller particles than had previously been studied, and outlines modifications to these which would permit rapid computation of sufficient stability to support fast particle sizing procedures.     

Lipid metabolite profiling identifies desmosterol metabolism as a new antiviral target for hepatitis C virus

Hepatitis C virus (HCV) infection has been clinically associated with serum lipid abnormalities, yet our understanding of the effects of HCV on host lipid metabolism and conversely the function of individual lipids in HCV replication remains incomplete. Using liquid chromatography-mass spectrometry metabolite profiling of the HCV JFH1 cell culture infection model, we identified a significant steady-state accumulation of desmosterol, an immediate precursor to cholesterol. Pharmacological inhibition or RNAi-mediated depletion of DHCR7 significantly reduced steady-state HCV protein expression and viral genomic RNA. Moreover, this effect was reversed when cultures were supplemented with exogenous desmosterol. Together, these observations suggest an intimate connection between HCV replication and desmosterol homeostasis and that the enzymes responsible for synthesis of desmosterol may be novel targets for antiviral design.     

A short path synthesis of [13C/15N] multilabeled pyrimidine nucleosides starting from glucopyranose nucleosides

The synthesis of fully [13C/15N] labeled pyrimidine nucleosides has been achieved from 13C-glucose and labeled nucleobases. The reaction scheme leads directly to the protected nucleosides without the need for the inversion of configuration of C-3 of 13C-glucose. This was achieved by an oxitative ring-opening reaction removing the carbon with the wrong configuration.     

Phosphine‐Stabilized Diiododiborenes: Isolable Diborenes with Six Labile Bonds

The lability of B=B, B?P, and B–halide bonds is combined in the syntheses of the first diiododiborenes. In a series of reactivity tests, these diiododiborenes undergo cleavage of all six of their central bonds in different ways, leading to products of B=B hydrogenation and dihalogenation as well as halide exchange.     

Threshold photoelectron study of naphthalene, anthracene, pyrene, 1,2-dihydronaphthalene, and 9,10-dihydroanthracene

Threshold photoelectron spectra (TPESs) were obtained for naphthalene, anthracene, pyrene, 1,2-dihydronaphthalene, and 9,10-dihydroanthracene using imaging photoelectron photoion coincidence spectroscopy, from threshold to a photon energy of ～20 eV. Outer valence Green's function calculations at the OVGF∕cc-pVTZ level of theory were used to assign molecular orbitals to the observed TPES features. There is generally good agreement between the predicted and observed bands. Threshold regions for each molecule exhibit vibrational structure which is readily assigned based on previous PES studies. While the measured adiabatic ionization energies (IE(a)) for naphthalene, anthracene, and pyrene are in good agreement with previous works, new values are reported for the two dihydro species (1,2-dihydronaphthalene, 8.010 ± 0.010 eV and 9,10-dihydroanthracene, 8.335 ± 0.010 eV). A comparison is also made with the G3∕∕B3LYP composite method, which consistently overestimates the IE values by 0.06-0.09 eV. The double ionization energies for anthracene and pyrene have been measured to be 19.3 ± 0.2 and 19.8 ± 0.2 eV, respectively.     

Synthesis, crystal structures, and electronic properties of nonlinear fused thienoacene semiconductors

Two fused thienoacene compounds with two-dimensional ring connectivity were synthesized, and their semiconducting properties were characterized. Both compounds have a crystal structure comprised of herringbone arrays of tight π-π stacks. Strong π-π interactions lead to self-assembly into well-defined crystalline thin films from the vapor phase for both compounds. Field effect transistors were fabricated, affording identical hole mobilities of 3.0 × 10(-3) cm(2)/(V s) and I(on/off) > 10(5).     

Competing Effects of Chlorination on the Strength of Te⋅⋅⋅O Chalcogen Bonds Select the Structure of Mixed Supramolecular Macrocyclic Aggregates of Iso-Tellurazole N-Oxides

Chlorination of 3-methyl-5-phenyl-1,2-tellurazole-2-oxide yielded the λ⁴Te dichloro derivative. Its crystal structure demonstrates that the heterocycle retains its ability to autoassociate by chalcogen bonding (ChB) forming macrocyclic tetramers. The corresponding Te⋅⋅⋅O ChB distances are 2.062 Å, the shortest observed to date in aggregates of this type. DFT−D3 calculations indicate that while the halogenated molecule is stronger as a ChB donor it also is a weaker ChB acceptor; the overall effect is that the ChBs in the chlorinated homotetramer are not significantly stronger. However, partial halogenation or scrambling selectively yield the 2 : 2 heterotetramer with alternating λ⁴Te and λ²Te centers, which calculations identified as the thermodynamically preferred arrangement.