John P. Smart

Fast atom bombardment mass spectrometry as a tool for the rapid determination of enantioselective binding of methylated cyclodextrins

The first FABMS study of the enantioselectivity shown during complex formation between per-methylated cyclodextrins and pairs of enantiomeric guest molecules is described. The 1:1 mixtures of the cyclodextrins, both α- and β-, with the guests, the methyl esters of the amino acids tryptophan and phenylalanine, were studied in a 100:50:1 glycerol-thioglycerol-trifluoro-acetic acid matrix. The uncomplexed cyclodextrin peaks were then used as internal standards to determine the preference of the cavity for one or other of the enantiomers. A clear trend for the preferential binding, greater than 5:1 in each case, of the d-enantiomers of the amino acid esters was observed in agreement with literature 1H NMR experiments. This methodology provides a rapid route to assessing the enantioselectivity shown by the widely used cyclodextrins towards pairs of enantiomeric guests.

Determining failure laws for ceramic materials

For determining the failure probability of ceramic components in a varying stress field, there are many theories which are based on the Weibull “weakest-link” ideas. However, the difference between the predictions for many stress systems is small and because of the scatter in the failure loads for ceramic materials and the inevitable experimental errors, it has been difficult to decide which is most suitable.In this paper, a testing regime is described which spreads the predictions from the various theories to allow the most suitable theory for a given material to be chosen. This will give more confidence when designing with ceramics.Tests are also described on a reactor grade graphite and it is shown that of the theories examined the maximum non-coplanar strain energy release rate is the most suitable criterion although the results indicate that current ‘weakest-link’ ideas may not be suitable to describe all loading situations. Reasons for this are discussed.Copyright

Kinetically controlled regiospecific silylation of polyols via dibutylstannanediyl acetals

A general procedure is described whereby the tert-butyldimethylsilylation of unsymmetrical 1,2- and 1,3-diols via their dibutylstannanediyl derivatives occurs regiospecifically at the primary hydroxy group under neutral conditions; six-membered ring acetals (derived from 1,3-diols) are found to react in preference to five-membered ring acetals (derived from 1,2-diols), the reverse of stannanediyl-mediated acylation, tosylation and alkylation procedures, leading to kinetically controlled discrimination between the different primary hydroxy groups of polyol systems such as butane-1,2,4-triol and lactose.