Products active on mosquitoes,IV: Synthesis and biological activity of 8-propargyloxy-3,7-dimethyl-2,6-octadienyl/6-octenyl ethers

Summary A series of 8-proparglyoxy-3,7-dimethyl-2,6-octadienyl and 8-propargyloxy-3,7-dimethyl-6-octenyl ethers were prepared from 8-hydroxygeranyl and 8-hydroxycitronellyl ethers, respectively. Almost all compounds showed high toxicity toCulex quinquefaciatus larvae at 1 mgl^–1 dose level.

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Gegen Mücken aktive Produkte, 4. Mitt.: Synthese und biologische Aktivität von 8-Propargyloxy-3,7-dimethyl-2,6-octadienyl/6-octenyl-ethern

Zusammenfassung Eine Reihe von 8-Propargyloxy-3,7-dimethyl-2,6-octadienyl- und 8-propargyloxy-3,7-dimethyl-6-octenyl-ethern wurden aus 8-Hydroxygeranyl- bzw. 8-Hydroxycitronellyl-ethern hergestellt. Fast alle Verbindungen zeigten hoch Toxizität gegenüber Larven vonCulex quinquefaciatus in einer Dosierung von 1 mgl^–1.

     

An investigation of the properties of poly(dimethylsiloxane)-bioinspired silica hybrids

Elastomers typically require the incorporation of reinforcing fillers in order to improve their mechanical properties. For commercial silicone systems silica and titania are typically used as fillers. Fumed and precipitated silica are made on an industrial scale for many applications; however, we have shown recently that biological and synthetic macromolecules can generate new silica structures using a bioinspired route. Herein we have incorporated bioinspired silica fillers into poly(dimethylsiloxane) (PDMS) elastomers and investigated their mechanical, morphological and thermal properties as a function of filler loading. The equilibrium stress-strain characteristics of the PDMS-bioinspired silica hybrids were determined as a function of bioinspired filler loading and the Mooney-Rivlin constants (2C₁ and 2C₂) were calculated. The thermal characteristics, in particular glass transition temperatures (T_g) and melting points (T_m), of the PDMS-bioinspired silica hybrids were characterized using differential scanning calorimetry (DSC). The thermal stability of these hybrid materials were investigated using thermogravimetric analysis (TGA). The morphology of the samples was characterized using scanning electron microscopy (SEM), and the filler dispersion was characterized using ultra small angle X-ray scattering (USAXS) and scanning electron microscopy (SEM). Although spherical silica particles were used here, we have demonstrated elsewhere that this bioinspired synthetic route also enables highly asymmetric silica structures to be prepared such as fibres and sheets. This methodology therefore offers the interesting possibility of preparing new hybrid systems where the properties are highly anisotropic.     

Treatment of trigeminal ganglion neurons in vitro with NGF,GDNF or BDNF: effects on neuronal survival,neurochemical properties and TRPV1-mediated neuropeptide secretion

Background  

Nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) all play important roles in the development of the peripheral sensory nervous system. Additionally, these growth factors are proposed to modulate the properties of the sensory system in the adult under pathological conditions brought about by nerve injury or inflammation. We have examined the effects of NGF, GDNF and BDNF on adult rat trigeminal ganglion (TG) neurons in culture to gain a better understanding of how these growth factors alter the cytochemical and functional phenotype of these neurons, with special attention to properties associated with nociception.     

Novel ozone-mediated cleavage of the benzhydryl protecting group from aziridinyl esters

[reaction: see text]. N-Benzhydryl aziridines-2-carboxylates can be readily obtained from the catalytic asymmetric aziridination reaction from N-benzhydrylimines and ethyl diazoacetate. Cleavage of the benzhydryl group by hydrogenolysis leads to ring opening when R = aryl. Surprisingly, ozone will selectively oxidize the benhydryl group in these aziridines even when R is an aryl group. This allows for a new deprotection strategy for these aziridines whose generality is explored.     

Bioinspired synthesis of new silica structures

Silicon and oxygen are the two most abundant elements in the Earth's crust but despite the vast scientific literature on crystalline and amorphous silica, new chemistries, structures and applications continue to be discovered for compounds formed from these elements--thus we present here for the first time the formation of new amorphous silica structures that were uniquely synthesized by a bioinspired synthetic system.     

Prediction of thermodynamic properties of polymer solutions by a group-contribution method

The Flory–Huggins lattice-theory expression for solvent activity in a polymer-solution is commonly used to calculate the thermodynamic interaction parameter χ with the aid of experimental data from vapor pressure osmometry. This expression assumes that χ is independent of composition. However, experimental data for a variety of polymer-solvent mixtures indicate that χ exhibits an appreciable concentration dependence. A group contribution method, UNIFAC (UNIQUAC Functional-Group Activity Coefficients) incorporating the free-volume correction of Oishi and Prausnitz is used to predict the dependence of χ on solvent concentration. Agreement with previously reported experimental data is within 15%. Calculated values of χ obtained from the Flory–Huggins expression for solvent activity and from the corresponding Gibbs free energy of mixing (which does not assume that χ is independent of composition) are compared. Calculations based on the Gibbs free energy of mixing predict a somewhat larger value of χ relative to those based on solvent activity. The specific Gibbs free energy of mixing for polystyrene-solvent mixtures is calculated using the UNIFAC model, and is found to represent qualitatively the phase equilibrium behavior. Quantitative discrepancies are observed, however, for the polystyrene-acetone system in light of the actual experimental solubility reported by Suh and Clark (20). Most of the thermodynamic predictions for polymer-solvent systems investigated herein are correlated qualitatively with the relative mismatch between solubility parameters of both components.     

Influence of charge and structure on the coordination chemistry of copper aminoglycosides

Aminoglycosides are a family of molecules based on a 2-deoxystreptamine ring that is functionalized with a variety of sugar units that contain vicinal amine and hydroxyl functionality. These positively-charged amines promote selective high affinity binding to bacterial 16 s rRNA with resultant antibacterial activity. Aminoglycosides have also been shown to selectively target a variety of therapeutically relevant RNA motifs, and in combination with copper to promote irreversible degradation of the RNA target. The presence of multiple hydroxyl and amine groups on multiple rings creates many potential copper coordination sites. However, only a small subset of these sites actually bind copper, which have not been clearly defined experimentally, Herein we describe a more extensive structural characterization of the complexes of six aminoglycosides (kanamycin A, kanamycin B, neomycin B, neamine, tobramycin and paromomycin) that provide insights on the factors contributing to the coordination selectivity of aminoglycosides toward divalent copper. The presence of vicinal ligand donors capable of chelating the copper ion appears to be a prerequisite for stable metal binding, with charge density providing further tuning of the K(D). A possible role for metal coordination in antibacterial activity is also considered.     

Biomimetic and bioinspired silica: recent developments and applications

In a previous review of biological and bioinspired silica formation (S. V. Patwardhan et al., Chem. Commun., 2005, 1113 [ref. 1]), we have identified and discussed the roles that organic molecules (additives) play in silica formation in vitro. Tremendous progress has been made in this field since and this review attempts to capture, with selected examples from the literature, the key advances in synthesising and controlling properties of silica-based materials using bioinspired approaches, i.e. conditions of near-neutral pH, all aqueous environments and room temperature. One important reason to investigate biosilicifying systems is to be able to develop novel materials and/or technologies suitable for a wide range of applications. Therefore, this review will also focus on applications arising from research on biological and bioinspired silica. A range of applications such as in the areas of sensors, coatings, hybrid materials, catalysis and biocatalysis and drug delivery have started appearing. Furthermore, scale-up of this technology suitable for large-scale manufacturing has proven the potential of biologically inspired synthesis.