Scaling behaviour for the water transport in nanoconfined geometries

The transport of water in nanoconfined geometries is different from bulk phase and has tremendous implications in nanotechnology and biotechnology. Here molecular dynamics is used to compute the self-diffusion coefficient D of water within nanopores, around nanoparticles, carbon nanotubes and proteins. For almost 60 different cases, D is found to scale linearly with the sole parameter theta as D(theta)=DB[1+(DC/DB-1)theta], with DB and DC the bulk and totally confined diffusion of water, respectively. The parameter theta is primarily influenced by geometry and represents the ratio between the confined and total water volumes. The D(theta) relationship is interpreted within the thermodynamics of supercooled water. As an example, such relationship is shown to accurately predict the relaxometric response of contrast agents for magnetic resonance imaging. The D(theta) relationship can help in interpreting the transport of water molecules under nanoconfined conditions and tailoring nanostructures with precise modulation of water mobility

The cyclic keto-enol insecticide spirotetramat inhibits insect and spider mite acetyl-CoA carboxylases by interfering with the carboxyltransferase partial reaction

Acetyl-CoA carboxylase (ACC) catalyzes the committed and rate-limiting step in fatty acid biosynthesis. The two partial reactions, carboxylation of biotin followed by carboxyl transfer to the acceptor acetyl-CoA, are performed by two separate domains in animal ACCs.The cyclic keto-enol insecticides and acaricides have been proposed to inhibit insect ACCs. In this communication, we show that the enol derivative of the cylic keto-enol insecticide spirotetramat inhibited ACCs partially purified from the insect species Myzus persicae and Spodoptera frugiperda, as well as the spider mite (Tetranychus urticae) ACC which was expressed in insect cells using a recombinant baculovirus. Steady-state kinetic analysis revealed competitive inhibition with respect to the carboxyl acceptor, acetyl-CoA, indicating that spirotetramat-enol bound to the carboxyltransferase domain of ACC. Interestingly, inhibition with respect to the biotin carboxylase substrate ATP was uncompetitive.Amino acid residues in the carboxyltransferase domains of plant ACCs are important for binding of established herbicidal inhibitors. Mutating the spider mite ACC at the homologous positions, for example L1736 to either isoleucine or alanine, and A1739 to either valine or serine, did not affect the inhibition of the spider mite ACC by spirotetramat-enol. These results indicated different binding modes of the keto-enols and the herbicidal chemical families

On the mode of action of bifenazate: New evidence for a mitochondrial target-site

Bifenazate is one the most frequently used acaricides to control spider mites. Although first thought to be a neurotoxin, genetic evidence has pointed towards a mitochondrial target site, in particular the Qo site of mitochondrially encoded cytochrome b. In this study, we present the first biochemical evidence for a physical interaction between [14C] bifenazate and mitochondrial complex III of Tetranychus urticae. We further show that bifenazate is differentially metabolized in insects and mites, possibly underlying the high selectivity of the compound. In contrast to the proposed mitochondrial mode of action, it was recently shown that bifenazate can act as a synergist or allosteric modulator of functionally expressed T. urticae GABA receptor homologues. We therefore sequenced and determined the expression level of all three T. urticae GABA receptors in bifenazate susceptible and highly resistant strains. We found no mutations linked with resistance in these receptors, and their expression level was not overall changed between strains. We finally summarize all available evidence and argue for a mitochondrial mode of action via inhibition of complex III at the cytochrome b Qo site