The effects of selected solvents on allyltrimethoxysilane and chloropropyltrimethoxysilane and the role of these solvents in determining mutagenic potential in salmonella and Escherichia coli

Recently acquired bacterial mutagenicity test data (salmonella/Escherichia coli) indicated that allyltrimethoxysilane (ATMOS) showed mutagenic activit y when prepared as a solution in ethanol but was not mutagenic in the same test when prepared in dimethylsulfoxide (DMSO), methanol, or acetone. Chlor opropyltrimethoxysilane (CPTMOS) was positive in this assay whether ethanol , methanol, acetone, or DMSO was used as the solvent. A study was carried o ut to evaluate the effect of the solvent on each methoxysilane as it is pre pared for the mutagenicity test. A scheme was used for ATMOS and CPTMOS in which 6 samples were prepared as 10 wt% solutions of either silane in ethan ol, DMSO, or acetone (solvents commonly used in the bacterial mutagenicity test) and then analyzed by Si-29 NMR. The samples were then mixed 50:50 wit h pH 7 phosphate-buffered water and analyzed again over several hours. The solvent interaction with methanol was not investigated but is believed to b e unlikely since the only reaction expected would be exchange of methoxy gr oups between the silane and methanol. These experiments showed that CPTMOS and ATMOS are stable in ethanol, acetone, and DMSO prior to dilution with w ater. Subsequently aqueous dilutions of ethanol and acetone solutions of th e two silanes did not undergo observable hydrolysis under these conditions. However, both methoxysilanes began hydrolysis immediately when the DMSO so lutions were diluted with water Condensation products were subsequently obs erved within 40 min. These data together with the differing bacterial mutag enicity test results for ATMOS in ethanol vs. methanol or acetone suggest t hat (1) the use of DMSO as a solvent for the mutagenicity testing of some m ethoxysilanes may be inappropriate and (2) alkoxysilanes in general should be tested in the compatible alcohols or other suitable solvent to avoid pos sible transalkoxylation reactions.