Hydrogen-bonding interactions in crown-(thio)urea complexes with anions,chemical warfare agents and simulants

ABSTRACT

Benzocrown ethers incorporating phenyl and nitrophenyl urea and thiourea moieties were synthesised. Both the nitrophenyl urea and thiourea derivative gave a fluoride-specific colorimetric response but only the urea derivative bound the organophosphonate nerve agent simulants dimethyl methylphosphonate (DMMP) and diisopropyl methylphosphonate (DIMP). This suggested an application as sensors for the nerve agents sarin, soman and cyclosarin which release fluoride upon hydrolysis. Although no fluoride-induced response was observed in the UV-visible spectrum, binding to soman was determined by ¹H NMR. DFT computational simulations suggested that the two crowns adopt different conformations in which both can bind fluoride but only the urea derivative can bind DMMP, DIMP and soman. The results show that, for this system, simulant- and soman-binding behaviours are in good agreement.     

The Effect of Cations on Uranyl Transport and Fluorescence in Mesoporous Silica Gel

The fluorescence intensity and transport kinetics of uranyl into mesoporous silica gel was measured in the presence of six naturally occurring cations. It was shown that the presence of the cations can reduce the fluorescence intensity of the uranyl through collision quenching and through competition for the silica gel surface sites. Stern-Volmer quenching coefficients were obtained by measuring the uranyl fluorescence as a function of cation concentration. The cations compete with uranyl to occupy silica gel surface sites and cause a decrease in uranyl fluorescence intensity and a reduction in the uranyl saturation time constant. Energy-dispersive x-ray spectroscopy (EDS) was used to measure the weight percentage of uranium and the cations in the silica gel samples and these results correlated well with the results of the saturation time constant measurements. The results of this study show that, at high concentrations, the presence of cations in water can influence the fluorescence intensity and transport kinetics of uranyl into mesoporous silica gel.     

Vacuum moulding of a superplastic in two dimensions

A mathematical model is proposed for the process of vacuum superplasticforming. The model exploits the fact that in most industrialapplications the sheet aspect ratio (thickness/sheet width)is small. After an initial consideration of some of the moregeneral properties and the literature of superplastic materials,the elastic/plastic deformation of an internally-inflated thin-walledcylinder is examined. Plates of arbitrary geometry are thenconsidered. A quasisteady model in which the sheet moves througha sequence of steady states is developed. Some simplified closed-formsolutions are examined, but for general cases a system of nonlinearpartial differential equations must be solved numerically. Anefficient and accurate semi-explicit numerical scheme is proposedand a simplified stability analysis is presented; the methodis then used to compute properties of superplastic vacuum mouldedsheets in a number of practically motivated cases.