The cuticle

The nematode cuticle is an extremely flexible and resilient exoskeleton that permits locomotion via attachment to muscle, confers environmental protection and allows growth by molting. It is synthesised five times, once in the embryo and subsequently at the end of each larval stage prior to molting. It is a highly structured extra-cellular matrix (ECM), composed predominantly of cross-linked collagens, additional insoluble proteins termed cuticlins, associated glycoproteins and lipids. The cuticle collagens are encoded by a large gene family that are subject to strict patterns of temporal regulation. Cuticle collagen biosynthesis involves numerous co- and post-translational modification, processing, secretion and cross-linking steps that in turn are catalysed by specific enzymes and chaperones. Mutations in individual collagen genes and their biosynthetic pathway components can result in a range of defects from abnormal morphology (dumpy and blister) to embryonic and larval death, confirming an essential role for this structure and highlighting its potential as an ECM experimental model system

The ammonolysis of esters in liquid ammonia

The rates of ammonolysis of alkyl benzoate and phenylacetate esters in liquid ammonia increase with the acidity of the leaving group alcohol and show relatively large Brønsted βlg values of −1.18 and −1.34, respectively, when plotted against the aqueous pKa of the alcohol. The Brønsted βlg obtained using the pKa of the leaving group alcohol in liquid ammonia is significantly reduced to ~ −0.7, which indicates that the rate-limiting step involves a reaction of the tetrahedral intermediate with little C–OR bond fission in the transition state. The solvolysis reaction is subject to significant catalysis by ammonium ion, which, surprisingly, generates a similar Brønsted βlg indicating little interaction between the ammonium ion and the leaving group. It is concluded that the rate-limiting step for the ammonium-ion-catalysed solvolysis of alkyl esters in liquid ammonia is the diffusion-controlled protonation of the zwitterionic tetrahedral intermediate T+- to give T+, which is rapidly deprotonated to give T0 which is compatible with the rate-limiting step for the uncatalysed reaction being the formation of the neutral T0 by a ‘proton switc

Understanding the impact of Cotton Subsidies on developing countries

Models developed to investigate the impact of cotton subsidies have found that US support, by virtue of its absolute magnitude, is particularly damaging and responsible for most of the reduction in cotton-earning potential in developing countries. This has been used as an argument for reducing or postponing cuts in subsidies to European farmers, as these appear to have less impact on developing countries. Our results, through a careful examination of the nature of the cotton market, agree but suggest that under certain assumptions subsidies by smaller subsidisers (such as the EU) may be disproportionately harmful to some suppliers, notably to West and Central African countries. This is especially damaging to them since they have the potential to increase supply.Cotton, Subsidies, Development

Mechanism and Catalysis in the Hydrolysis of Some Acetals and Esters

Recent advances in the study of acetal hydrolysis and the effect of neighbouring hydroxyl groups on ester hydrolysis are reviewed. Some of the criteria used to elucidate the mechanism of such reactions are discussed. The enhanced rates of intra-molecular reactions over their inter-molecular counterparts are suggested to be due to factors other than just a 'concentration' effect, product stability reflected in the transition state may be important. Intra-molecular and inter-molecular general-acid catalysis have been detected in the hydrolysis of benzyli-dene 2,3-dioxy benzoic acid and benzylidene catechol, respectively. Several kinetic parameters of these reactions have been determined and are discussed. An example of nucleophilic catalysis by a carboxyl group has been found in the hydrolysis of o-carboxy benzylidene catechol. o-carboxy benzylidene 2,3-dioxy benzoic acid, a system which apparently contains suitably disposed carboxyl groups to act as general-acid and nucleophilic catalysts, was synthesised. However, the hydrolysis of this acetal showed no evidence of bifunctional catalysis. Ring opening during the acid catalysed hydrolysis of benzaldehyde acetals of 2,3-exo-norbornanediol is shown to be reversible. An A-2 mechanism is suggested to be the pathway of hydrolysis of these 1,3-dioxolanes. The facilitated rate of hydrolysis of beta-hydroxy esters, in particular beta-hydroxy butyrates and 2-hydroxy cyclopentane carboxylates, has been shown not to be due to any direct interaction between the two functional groups. 'Solvent sorting' is tentatively suggested to account for the observed phenomenon

The XMM-Newton spectral-fit database

The XMM-Newton spectral-fit database is an ongoing ESA funded project aimed to construct a catalogue of spectral-fitting results for all the sources within the XMM-Newton serendipitous source catalogue for which spectral data products have been pipeline-extracted (~ 120,000 X-ray source detections). The fundamental goal of this project is to provide the astronomical community with a tool to construct large and representative samples of X-ray sources by allowing source selection according to spectral properties.Comment: Conference proceedings of IAU Symposium 304: Multiwavelength AGN surveys and studie

Imide and isatin derivatives as β-lactam mimics of β-lactam antibiotics

Activated γ-lactams, which are derivatives of succinimide, phthalimide and isatin with suitable elements of molecular recognition, have been synthesised as mimics of the ß-lactam antibiotics and their chemical and biological reactivity determined

A deep Giant Metre-wave Radio Telescope 610-MHz survey of the 1^HXMM–Newton/Chandra survey field

We present the results of a deep 610-MHz survey of the 1^HXMM–Newton/Chandra survey area with the Giant Metre-wave Radio Telescope. The resulting maps have a resolution of ~7 arcsec and an rms noise limit of 60 μJy. To a 5σ detection limit of 300 μJy, we detect 223 sources within a survey area of 64 arcmin in diameter. We compute the 610-MHz source counts and compare them to those measured at other radio wavelengths. The well-known flattening of the Euclidean-normalized 1.4-GHz source counts below ~2 mJy, usually explained by a population of starburst galaxies undergoing luminosity evolution, is seen at 610 MHz. The 610-MHz source counts can be modelled by the same populations that explain the 1.4-GHz source counts, assuming a spectral index of −0.7 for the starburst galaxies and the steep spectrum active galactic nucleus (AGN) population. We find a similar dependence of luminosity evolution on redshift for the starburst galaxies at 610 MHz as is found at 1.4 GHz (i.e. 'Q'= 2.45^(+0.3)_(−0.4))

Gravitational Theory with a Dynamical Time

A gravitational theory involving a vector field $\chi^{\mu}$, whose zero component has the properties of a dynamical time, is studied. The variation of the action with respect to $\chi^{\mu}$ gives the covariant conservation of an energy momentum tensor $T^{\mu \nu}_{(\chi)}$. Studying the theory in a background which has killing vectors and killing tensors we find appropriate shift symmetries of the field $\chi^{\mu}$ which lead to conservation laws. The energy momentum that is the source of gravity $T^{\mu \nu}_{(G)}$ is different but related to $T^{\mu \nu}_{(\chi)}$ and the covariant conservation of $T^{\mu \nu}_{(G)}$ determines in general the vector field $\chi^{\mu}$. When $T^{\mu \nu}_{(\chi)}$ is chosen to be proportional to the metric, the theory coincides with the Two Measures Theory, which has been studied before in relation to the Cosmological Constant Problem. When the matter model consists of point particles, or strings, the form of $T^{\mu \nu}_{(G)}$, solutions for $\chi^{\mu}$ are found. For the case of a string gas cosmology, we find that the Milne Universe can be a solution, where the gas of strings does not curve the spacetime since although $T^{\mu \nu}_{(\chi)} \neq 0$, $T^{\mu \nu}_{(G)}= 0$, as a model for the early universe, this solution is also free of the horizon problem. There may be also an application to the "time problem" of quantum cosmology.Comment: 21 pages, discussions extended, some more explicit proofs included, more references include