Hi,
I am doing some single molecule experiments using T7 phage DNA molecules (40 Kb). I tried to add polystyrene sulfonate [poly(sodium 4-styrenesulfonate)] solution (prepared by adding 50 mg powder to 0.5X TBE buffer which is my experiment buffer) for some experiments. polystyrene sulfonate is a polyanion, very much like DNA. But, I see that DNA molecules start to aggregate as soon as I add polystyrene sulfonate to the DNA solution.
I tried two different polystyrene sulfonate concentrations (2.5 and 0.25 mg/ml) and both showed serious aggregation. All experiments were done in 0.5X TBE buffer.
Not sure why aggregation happens when both DNA and polystyrene sulfonate are polyanions. Any suggestions on why would be very helpful.
Poly(sodium 4-styrenesulfonate) average Mw ~70,000, powder - See more at: http://www.sigmaaldrich.com/materials-science/material-science-products.html?TablePage=112436133#sthash.E0rM0jQf.dpuf Poly(sodium 4-styrenesulfonate) average Mw ~70,000, powder - See more at: http://www.sigmaaldrich.com/materials-science/material-science-products.html?TablePage=112436133#sthash.E0rM0jQf.dpuf
@Ojeiru Ezomo: Thanks for the reference. But, I understand that this work actually talks about condensation of DNA and polystyrene sulfonate in presence of polyethylenimine. That is because one (DNA or polystyrene sulfonate) is a polyanion and the other (polyethylenimine) is a polycation. But, this reference does not show what happens when one puts two polyanions together. Please correct me if I am wrong.
Have a good day!!!
I would assume the problem is depletion flocculation, which then should be observed above a certain polymer concentration.
@Titus Sobisch: Thanks. I indeed came across a paper that shows polyelectrolyte aggregation in polystyrene sulfonate solutions when ionic-strength of buffer is low. I understand that similarly charged polyelectrolytes could still attract each other in presence of counter-ions. Aggregate formation is indeed concentration dependent from my own experimental observations, as well as the data provided in the attached reference.
Hi Sriram, could you please give more references to this problem of aggregation when DNA interacts with small molecules in general? More specifically on how to overcome this problem without loosing activity of the small molecule in question.
Please help.
Thank You.
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