Rate of Hydrogen-deuterium exchange in crystals?

Question

H-D exchange of peptide in D2O is rapid and the reaction is quenched with pH 2.2. What would happen if we use acetronitrile solution at pH 2.2 then dry the mixture say within 10 sec? Will this reaction stop? What is the known rate of H-D exchange in crystal at room temperature?

Answer 1

Wow, you're asking about 12 different questions in there.

First, "pH" means nothing in acetonitrile, because pH measures the concentration of H+, and almost no acid dissociates to form H+ in acetonitrile, which is not an a hydrogen-bonding solvent.

Second, unless you're talking about maybe one microliter or so in volume (max maybe 10 microliters), there's essentially no chance of drying any mixture within 10 seconds.

Third, if you want to figure out a rate of H-D exchange in crystals, good luck. Maybe someone out there has looked at it, but when people do H-D exchange they look at it through NMR or MS--liquid or gas. Not solid. Diffusion in crystals is not good and dependent on way too many factors that are not easy to control.

Fourth, you realize that when you have water-acetonitrile mixtures your proteins get denatured, right? It's really time to rethink your experiment, even if it's hypothetical.