I used FITC Isomer I and ethanol and APTES under argon. The precipitate is bright orange. I want to use this for synthesis of nanoparticles (dye conjugated) and the precipitate will not help in this case.
Amine reactive probes are typically dissolved in anhydrous dimethylformamide (DMF) and may not be stable in alcohols for very long.They are considered unstable once in solution even in DMF. APTES is also very reactive with water, which is required for the ethoxysilane to react, but can form precipitates in just a few hours depending on the water concentration. Because EtOH is somewhat hygroscopic and hard to keep anhydrous, it may not be the best solvent if you want to make a stable solution. Since the ethoxysilane reaction is both a hydrolysis and a condensation reaction, the water content remains the same and the reaction continues until all of the silanes are reacted.
Ron Reiserer Thank you for the answer. The problem seems to be the APTES which was old (there were precipitates at the bottom of the APTES bottle). I tried the same reaction again with fresh APTES and it seemed to work (no precipitate now). But I do agree with your view that they are not long term stable in EtOH.
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