[jeffmoonchop]

Hi, I'm currently in the work of making lipid nanoparticles where I'm using cationic lipid molecules to attract anionic mRNA to make the particles. Currently, the mixture is acidic when I make the particles, however, to remove ethanol, the pH needs to be adjusted to 7 before I can use a buffer exchange system at larger scales. When I adjust to pH 7, the ethanol concentration is reduced, but the particle size increases.

My question is regarding the effect of ethanol on the 'apparent' pH.

After I make the particles, the pH is around 6.6, but the ethanol concentration is 25%, I've found that ethanol increases the apparent pH so I'm assuming the true pH is lower, perhaps 6-6.2.
The pKa of the mRNA is 6.4, I'm thinking that due to the effect of ethanol on the pH reading, when I adjust to pH 7, the actual pH is 6.4, and I'm seeing particle growth due to the maximum number of mRNA molecules attaching to the lipid.

Does anyone have any insight on this?

thanks

[Babcock_Hall]

I do not understand what you mean when you say that the pK_a of the mRNA is 6.4.  Is there some group on the mRNA with that value?

I know just enough about mixed solvents and pH to be dangerous.  However, I found this quote from a Beckman handbook on applied electrochemistry to be helpful:  "Three non aqueous buffers containing 50% methanol in water, which are defined by NBS, gave higher pH values than totally aqueous solutions of the same solutes and molalities."  The Orion Guide to pH measurement stated, "Some work has been done on methanol and ethanol mixtures."