Marine chemical ecology

This review covers the recent marine chemical ecology literature for benthic cyanobacteria, macroalgae, sponges, octocorals, molluscs, other benthic invertebrates, fish and seabirds.     

Computational model of photocatalytic water splitting

The photochemistry of a supramolecular system consisting of a (truncated) chlorophyll, benzoquinone and water has been explored with ab initio computational methods. It is shown that this photosynthetic model system can split a water molecule upon the absorption of a visible photon via an electron-driven proton-transfer process. It is suggested that the coupled transfer of an electron and a proton in hydrogen-bonded systems is mechanistically superior to electronic charge separation in covalently bonded donor-bridge-acceptor systems.     

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.     

On the nature and signatures of the solvated electron in water

The hydrated electron is one of the simplest chemical transients and has been the subject of intense investigation and speculation since its discovery in 1962 by Hart and Boag. Although extensive kinetic and spectroscopic research on this species has been reported for many decades, its structure, i.e., the dominant electron-water binding motif, and its binding energy remained uncertain. A recent milestone in the research on the hydrated electron was the determination of its binding energy by liquid-jet photoelectron spectroscopy. It turned out that the assumption of a single electron binding motif in liquid water is an oversimplification. In addition to different isomers in cluster spectroscopy and different transient species of unknown structure in ultrafast experiments, long-lived hydrated electrons near the surface of liquid water have recently been discovered. The present article gives an account of recent work on the topic "solvated electrons" from the perspectives of cluster spectroscopy, condensed-phase spectroscopy, as well as theory. It highlights and critically discusses recent findings and their implications for our understanding of electron solvation in aqueous environments.     

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.     

GIT-equivalence and semi-stable subcategories of quiver representations

In this paper, we answer the question of when the subcategory of semi-stable representations is the same for two rational vectors for an acyclic quiver. This question has been previously answered by Ingalls, Paquette, and Thomas in the tame case in [14]. Here we take a more invariant theoretic approach, to answer this question in general. We recover the known result in the tame case.