electrophoresis and acidity

[Captain Sisko]

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if I'm electrophoresing a protein in acidic solution, say at a ph of 4, will the ph increase with the application of current? so add electrons, they combine with protons and produce hydrogen gas? does this make sense? if not, why?

 

[Trayshawn]

You mean gel electrophoresis?

I don't think you use an acidic solution with those. I believe you use a buffer. You denature all the proteins with SDS (a surfactant) and thus make all proteins highly negatively charged. That charge is what attracts them to the positively charged anode (anode = where anions go (+) / cathode = where cations go(-)) at the bottom of the gel. I believe the pH is held relatively constant due to the buffer.

 

[Captain Sisko]

You mean gel electrophoresis?

I don't think you use an acidic solution with those. I believe you use a buffer. You denature all the proteins with SDS (a surfactant) and thus make all proteins highly negatively charged. That charge is what attracts them to the positively charged anode (anode = where anions go (+) / cathode = where cations go(-)) at the bottom of the gel. I believe the pH is held relatively constant due to the buffer.

say the experiment is to determine the isoelectric point of the protein. you use gel electrophoresis on whole protein using buffers at various phs. my question pertains to the acidic buffer case.

 

[FeinMS]

If you're talking about using gel electrophoresis to separate proteins by their pI. The set up is so that the "pool" is composed of gradient of pH buffers. Proteins are then loaded at one end, and they will keep traveling toward the opposite end until their pI=pH of the buffer. pH of the buffer does not increase as current is applied, but as current is applied, proteins start moving toward the opposite end. For example, if they're loaded at pH=0 end, all proteins will be + charged, so when current is applied, they will go toward - end (cathode, where cations go) When proteins are at the pI, the charge is 0, so current applied can't move the proteins, that's where they stop and we use that to separate proteins.

 

[Captain Sisko]

If you're talking about using gel electrophoresis to separate proteins by their pI. The set up is so that the "pool" is composed of gradient of pH buffers. Proteins are then loaded at one end, and they will keep traveling toward the opposite end until their pI=pH of the buffer. pH of the buffer does not increase as current is applied, but as current is applied, proteins start moving toward the opposite end. For example, if they're loaded at pH=0 end, all proteins will be + charged, so when current is applied, they will go toward - end (cathode, where cations go) When proteins are at the pI, the charge is 0, so current applied can't move the proteins, that's where they stop and we use that to separate proteins.

OK that's not what I'm talking about.

Forget about electrophoresis. Let's simplify what I'm asking:

What happens if you have an acidic solution, and you apply a current across it?

Do free electrons combine with excess protons in the acidic solution to form hydrogen gas?

 

[FeinMS]

Hmm, I'm not too sure about that, but I can tell you that acidic solution can conduct electricity because of their dissociated ions. If electrons (currents) combined with free protons and formed H2 gas, the electrons (currents) will be lost, so the solution will not be conducting material anymore.

 

[JingleChips]

OK that's not what I'm talking about.

Forget about electrophoresis. Let's simplify what I'm asking:

What happens if you have an acidic solution, and you apply a current across it?

Do free electrons combine with excess protons in the acidic solution to form hydrogen gas?

Assuming you have the correct battery set-up, I believe the answer is yes, but I'm not sure if this answer is the one your looking for.

Applying a current across a solution of pure water will probably not result in the release of hydrogen gas - pure water (DI water) is very unconductive (due to the low auto-ionization of water) and you will need a huge input of current in order to generate any substantial amount of hydrogen gas.

However, the conductivity of an acidic solution is much greater than that of a DI water solution - and hydrogen gas will be produced much more readily than in a solution of DI water. This is not limited to acidic solutions - using soluble salts having a cation with lower reduction potentials than H+ (aka a negative reduction potential, http://dl.clackamas.cc.or.us/ch105-09/standard1.htm ) can also be used - and strong bases (again as long as the cation reduction potential is less favorable than that of H+) can be used to produce more hydrogen gas.

Read more on "electrolyte selection" here
http://en.wikipedia.org/wiki/Electrolysis_of_water