We were about to change topics @IowaBiochem class from lipids to N metabolism when we were rudely interrupted by #COVID19 -- I think we need to provide a service to explain what soap is and how it inactivates viruses. We'll also explain what detergents are including bile acids /1
Students will recall that the bulk of animal & plant fats are triglycerides (3 fatty acids esterified to glycerol) & that when TAGs are digested by us, lipases hydrolyse the FAs from glycerol so that they can be beta oxidized /2
Most animal fat has long chain saturated FAs--saturated FA can pack closely & are thus solid at room temp. Different plants make different lengths of FAs based on the plant's FA synthase (how many 2C units it adds before the FA is hydrolyzed off) and its desaturases /3
The olive has a FAS that makes a lot of C18 FA with one C=C bond. We call that oleic acid. Olive oil TAG also has about 10% each of regular old palmitic acid and 10% of a C18 with two C=C bonds. Of course, there's 1 glycerol for every 3 FA /4
Why and how would you make soap out of olive oil or any other TAG? /5
Well, I better tell you what soap is first! /6
Soap are the salts of FAs. The simplest Na salts of FA are generally solid soaps with a stoichiometry of 1 Na per FA. Ca is a divalent cation and coordinates 2 FA /7
By forming ionic bonds between the FA carboxylic acid & the cation, soaps are water soluble. Their acyl groups interact with any other lipid & allow them to emulsify anything greasy. Of course, that includes viruses and bacteria /8
Our ancestors figured out that lye (eg, NaOH) converts fats to soaps. The -OH group attacks FA-glycerol linkages releasing 3 Na-FA plus glycerol. Oops, you just figured out why olive oil soap contains glycerine as an ingredient & that you can make it at home (wear gloves!) /9
If you add NaOH to olive oil, you get a lovely green solid consisting of ~8 parts Na oleate, 1 part Na palmitate, 1 part Na linoleate and 3 parts glycerine (not by weight but mole) /10
Do that with coconut fat & you get a coconut soap with the characteristic medium chain FA content of coconut. Do that with lard or schmaltz & you get soaps with the FA content of animals fats. They all emulsify viruses by disrupting membranes. Next lesson will be detergents🙏
