FREQUENTLY ASKED TECHNICAL QUESTION
QUESTION: You say that the sulfurizing reagent, 40-4036, is stable for 1 month in solution "under ideal conditions". What are ideal conditions?
RESPONSE:The sulfurizing reagent, developed by Beaucage, is a very reactive product. In solution in acetonitrile, it must be stored in plastic or silanized glass containers. Solutions in sealed bottles are stable for periods of months, turning cloudy and finally precipitating as decomposition occurs.
On most synthesizers, the sulfurizing reagent must be installed on the port previously used for the iodine oxidizing solution. In this situation, the reagent will decompose quite rapidly over 24 to 48 hours. Indeed, we recommend weighing out the required amount of dry reagent into the silanized bottle provided. The recommended concentration for use is 1g/100mL So, if 40mL of solution is desired, weigh 0.4g of reagent into the silanized bottle and add 40mL of acetonitrile. It is important to flush the synthesizer line liberally first with acetonitrile then with the sulfurizing solution to remove traces of the previous solution from the line. After synthesis, we recommend removing the solution from the instrument immediately and discarding the remaining amount.
On synthesizers which have a spare port to accommodate an additional liquid reagent, the stability of the sulfurizing solution will progressively improve until the solution can be left on the machine for at least 1 month.
R.P. Iyer, W. Egan, J.B. Regan, and S.L. Beaucage, J. Amer. Chem. Soc., 1990, 112, 1253-1254.
QUESTION: Why can't I see my phosphorothioate oligo when I stain the gel with ethidium bromide?
RESPONSE:It appears that the sulfur of the phosphorothioate linkage can quench the fluorescence of ethidium bromide. I know researchers who could see their phosphorothioate oligo by UV shadowing but when stained with EtBr, no bands were observed, while on the same gel, normal phosphodiester oligos stained perfectly.
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