Fatty Acid solubility in water

[laczlacylaci]

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I read that free fatty acid is soluble in water due to deprotonation.
When I hear deprotonation, my mind think the free FA was deprotonated by a strong base (NaOH) to make a salt, so then its soluble in water? despite the long non-polar chain? Is this true?

I understand that triacyl glyceride would be not soluble. They need an emulsifier to be digested.

 

[theonlytycrane]

If the carbon tail is really short then maybe, but fatty acids are transported around the body by chylomicrons and albumin protein because these are usually not water-soluble.

 

[drsmurf]

+1

 

[aldol16]

I read that free fatty acid is soluble in water due to deprotonation.
When I hear deprotonation, my mind think the free FA was deprotonated by a strong base (NaOH) to make a salt, so then its soluble in water? despite the long non-polar chain? Is this true?

The carboxylic acid head group might be solvated by water but the long acyl tail will not. This is the basis for formation of vesicles when you drop oil in water and shake the container up.

It doesn't need to be deprotonated by a strong base. In some instances, even water is strong enough to deprotonate something that's acidic enough and there's certainly enough water around in a biological system. Keep in mind that the pKa of water is 14.0. In any case, a strong base is not necessarily needed to deprotonate molecules at the microscopic level.

But even so, most fatty acids will not be soluble in water because the solvation shell required around the long acyl tail groups is so unfavorable that it overshadows whatever small gain you get from solvation of the charged head group. However, there will obviously be a spectrum of solubilities depending on how long the acyl tail is, whether there's branching, etc. This gives rise to the so-called logD and logP values that one can determine for almost any molecule.