# User:Andy Maloney/Notebook/Lab Notebook of Andy Maloney/2009/12/07/Effect of Sodium Chloride on the Solubility of Caseins

## Disclaimer

This is my review and notes on the paper. If you read this notebook, then you should read the paper before you read what I put here.

## Review

So the important thing I took from this paper was that the isoelectric point of casein is 4.6.

Now the isoelectric point is the pH at which a molecule in solution has no net charge. This has some important consequences

• Minimum solubility of molecules or proteins occur when the pH = pI.
• pH > pI $\implies$ protein has a net negative charge in solution
• pH < pI $\implies$ protein has a net positive charge in solution

Also, they say that casein binds Na+ and K+ ions at neutral pH. I don't really know what this means but it may be important.

Another interesting thing is that they show casein's solubility decreases as you increase the concentration of NaCl. I'm interpreting this as meaning the solubility of casein decreases as you increase ionic strength. This could mean that the way I make PEM-C is totally wrong. I'm stirring 0.5 mg/mL casein right now in the nano pure water so we will see if it goes into solution.

• Update: It would appear that the answer to this is no. I would like to note that there are gigantic globs of the casein in solution right now. I have no clue what is going on but they are a lot larger than the specs I put into the water. I wonder if the micelles have a hydrated center.

Well, another odd thing is that if you have casein in solution and you add NaCl, the pH will drop.