A soap is a long chain molecule with a small head, the long chain is compatible with grease and the head is compatible with water.
Soap is ionized, this means, the long chain and a small ion separates and remains with electrical charges.
In a common household soap, the long chain remains negatively charged (anionic) and the small ion, usually sodium, remains positively charged (Na+).
In a quaternary ammonium soap, the reverse happens, the long chain remains positively charged (cationic) and the small ion, usually chloride, remains negatively charged (Cl-).
The great advantage of ammonium quaternaries is that the positive charge is more compatible with grease and is surrounded by several long chains that make this part more compatible with grease than a common soap. For this reason with much less quantity of cationic quaternary ammonium soap the fat dissolves.
Here's how soaps deactivate viruses.
Credit for the image : BBC
The fundamental conclusion is that any substance that attacks the fat layer deactivates viruses, for example the chlorine that comes in liquids such as Chloralex, alcohol, which is a very common grease solvent, and soaps as just explained.
It is said to deactivate a virus, because the scientific community considers that a virus is not alive, it is simply an advanced chemical structure that replicates.
This structure is made up of a layer of fat that protects a mixture of RNA and proteins that do not perform any vital function.
In contact with abundant organic material, such as that found inside a cell, these RNA molecules generate chemical reactions that replicate their RNA structure, that is, they duplicate them over and over again, killing cells and causing severe damage to the body in which they are housed, by destroying cell tissue.
However, to apply on human skin, not any substance that deactivates a virus is suitable, as it can damage the skin. The soda, strong toilet and drain cleaner deactivates viruses, but damages the skin by severe chemical burns.
With less intensity, Chlorine does the same, while alcohol, as it is a degreaser, removes the natural fat from the skin by drying it out, and its continuous use causes cracks due to excessive dryness.
The 4th and 5th generation ammonium quaternaries were created to be gentle with human skin. The first three generations were used and are still used to sanitize, but they are not recommended for continuous use and their common application is only on surfaces such as walls and operating room tables, surgical instruments, catheters, laryngoscopes etc.
Regarding effectiveness, alcohol works while it is present, in a hand gel for 10 to 20 seconds at most, when it evaporates all its action is lost, it destroys viruses and bacteria while it was present, but when it is lost it stops acting and does not give rear protection.
The quaternaries of ammonium, on the other hand, do not evaporate because they have very high boiling points, and being compatible with the skin, they remain there for up to 2 hours if there is no activity with the hands, if objects are touched and manipulated time is reduced to a minimum of 10 minutes.
For all that was just exposed, the ideal products to apply on human skin for sanitation are 4th. or, better, 5th. generation ammonium quaternaries, substances created specifically for this, either in gel, in liquid or in aerosol forms.
Links of interest :
Why Soap Works - The New York Times