Electric Field and Electrophoresis

[DoctorCakes]

I am confused as to how an electric field affects a pH gradient. Normally in electrophoresis a positively charged amino acid would migrate towards anode and vice-versa. So what is the relationship between an electric field and pH gradient? I am assuming this is related to a galvanic cell but the amino acids are not being oxidized/reduced.

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[wizzed101]

Fields don't affect pH gradient. The field is there for charged molecules to gravitate toward: positively charged to cathode and negatively charged to anode.

 

[theonlytycrane]

Electrophoresis uses an electromotive force so think of it like an electrolytic cell where the cathode is (-) and the anode is (+).

The pH just changes protonation states, affecting the net charge on the molecule.

 

[DoctorCakes]

Makes sense, so putting pH aside, why would we consider this a electrolytic cell and not a galvanic cell?

 

[wizzed101]

I don't follow... What cell?

 

[DoctorCakes]

The only way to logically think of a cathode and anode is part of a cell, no?

 

[wizzed101]

You can induce charges on any surface without setting up a cell.

Think about capacitance.

You just need a field to orient the molecules within the pH gradient. Just think of anode as where negative charges migrate to and vice versa.

 

[aldol16]

Think about capacitance.

Good. This is an excellent characterization of electrophoresis. One could even draw analogies between the gel and migrating molecules as a dielectric.

 

[DoctorCakes]

Got it thank you!