Post #2309756

2026-05-06 14:31 UTC

Some questions for people into #cryoEM and #biochemistry All pKa values vary with temperature. This is especially apparent with Tris buffer: change of ~ +0.5 pH unit going from room temp to 4°C. Proton transfers in acid/base equilibria are very fast. Are they faster than vitrification? In other words, does a change of pKa (due to a rapid drop in temperature) of the buffer compound have the time to change the pH of the solution before it is fully vitrified? There are pH-sensitive fluorophores. Has anyone vitrified and imaged them in a cryo-confocal microscope to determine whether vitrification changed the pH?

Replies (2)

@cpr320@frontrange.co 2026-05-06 15:05

@Guillawme@fediscience.org That's an interesting question because near pH 7, H+ and OH- ions are fairly far apart: almost 1000 times the intermolecular spacing. So you might think it would take a while for them to find each other and recombine...

Open ##2336605
@GetzlerChem@mstdn.science 2026-05-06 16:31

@Guillawme@fediscience.org this is a *FANTASTIC* fundamental question!! I don't know if your proposed method would work since I think fluorophore response might be temperature dependent as well. I am not a kineticist or a physical chemist, but I generally thing of proton transfers in water between things that have pKa in the 0-14 range to be borderline barrierless, so I kinda think maybe? how big are the things being vitrified? I don't know cryoEM #chemistry #pH

Open ##2336606