I use to monomerize my Abeta 42 (Anaspec) in HFIP, dry to a peptide film and store it at -20C.  To prepare for an experiment I would dissolve in NaOH.  I would see a lag period doing ThT assays that slowly increased until the growth phase.  I found literature stating HFIP actually forms complex aggregates and is difficult to completely remove from the dried peptide film.  

I then tried monomerizing using 10% NH4OH at room temperature for 10 mins, then sonicate for 5 min, aliquot into tubes, snap freeze and lyophilize.  I then stored the lyophilized Abeta at -20C.  To use, I dissolved the lyophilized peptide in 60mM NaOH.  Even after an hour there was still obvious cloudiness to the solution and I can see precipitate.  I centrifuge 5min at 16,000 x g and there is an obvious pellet.  TEM also showed sort of clumpy aggregates and ThT has no lag phase, it begins aggregating immediately.

I need to start with monomers for my experiments, does anyone have any advice?