=biology =medicine


Bleach is the most common disinfectant today. That's sodium hypochlorite, made by absorbing Cl2 into NaOH. It's generally considered to kill bacteria by disrupting cell membranes by oxidizing double bonds in fatty acids, but like chlorine, it can also chlorinate tyrosine and amines. It's cheap and works fairly well, but it releases chlorine gas, and can take a little while to kill viruses.

Immune cells can also produce hypochlorite to kill bacteria they've "eaten". This is done by reacting H2O2 with Cl-. A little bit of the hypochlorite can escape, and even that can cause serious side effects.

That being the case, peroxyacids also oxidize double bonds in fatty acids, so they should also work for disinfection. And they do. Peroxyacetic acid, which you can get by just mixing H2O2 and acetic acid, has occasionally been used as a disinfectant. But it's volatile and smells even worse than bleach.

OK, so what if you use a non-volatile acid instead? It also needs to be nontoxic and cheap, of course. And it can't be too big, because it needs to be able to diffuse into the bacterial cell membrane to some extent. Perhaps citric acid, or phthalic acid?

And yes, peroxycitric acid works fine as a disinfectant. But this is such "advanced technology" that it was only figured out a few decades ago, and bleach production and usage is apparently too entrenched for something that merely doesn't release chlorine gas to compete. And the stability isn't bad; hydrogen peroxide is normally more stable in acidic solutions anyway. This is less storable than bleach powder in a sealed container, but bleach solution in a plastic bottle doesn't last forever either, and refrigeration is fairly effective at slowing peroxide solution decomposition.

Direct sunlight is pretty good at killing most infectious bacteria. Pure blue light can also kill bacteria without being particularly harmful to humans, by catalytic production of radicals inside bacteria. "High Intensity Narrow Spectrum light" disinfection with bright 405nm blue light from LEDs is now being considered for use in some hospital rooms. You could either pulse it, turning it on for a few seconds every few minutes with a ramp up so people could close their eyes, or you could give people blue-filtering glasses and run it continuously at the cost of more heat generation and electricity usage, or you could control it manually. But this does not kill viruses effectively; that basically requires UV light.

If you just want to kill viruses, a saturated solution of CaCl2 should be highly effective at denaturing proteins. That has some obvious disadvantages when used like most disinfectants:
- it will damage skin by drying it
- if wiped on surfaces, it doesn't go away; it will instead stay as a liquid or white powder, depending on conditions

However, it might make sense to use a bowl of saturated CaCl2 solution to kill viruses on the outside of rubber gloves being worn.
- It should quickly denature virus proteins.
- It's completely nontoxic in small amounts.
- CaCl2 is very cheap. (~$0.14/kg)
- It's nonvolatile, so it could be kept in an open bowl.

CaCl2 is also somewhat soluble in ethanol; it could potentially increase the disinfection effectiveness of ethanol, and make denaturing it with methanol to prevent people from drinking it unnecessary. There is some evidence of CaCl2 increasing disinfection effectiveness but it really hasn't been studied much.



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