Covid-19 have you losing your sanity trying to find hand sanitizer? Well, if soap & sink are available, that’d be wiser, but you can also go all MacGyver! Turns out you only need a few things to make an alcohol-based hand sanitizer… WHO knew – and so can you!  

Covid-19 is the disease sometimes referred to as the “novel coronavirus” that’s caused by a virus named SARS-Cov-2. If that “SARS” in the name freaks you out and/or confuses you, relax (but not totally) – it’s similar genetically to the SARS (Severe Acute Respiratory Syndrome) virus that caused an epidemic in 2003, but this new SARS is less deadly – but more easily transmitted – and still more deadly than the flu, so you really should take it seriously (but try to avoid panicking). 

The best weapon we have against it is prevention. If you’re able to, stay home. And, as people keep telling you – wash your hands! The BEST BEST BEST way to do this is with soap and water – with 20s of some nice scrubbing action to really dislodge gunk. But, you’re not always near a sink, so alcohol-based hand sanitizers can serve as a back-up. Both can “kill” SARS-Cov-2 (I put kill in quotations because viruses aren’t typically considered living things although we talk of live and dead virus so go figure…). Anyways, soap and hand sanitizer can both destroy SARS-Cov-2, but hand washing goes a step further – it also physically removes dirt and grime, whereas hand sanitizers don’t. It’s kinda like if there’s a bunch of ants on your counter and you just spray some ant-killer on them and leave the dead ants there vs killing them and wiping them off onto a paper towel you toss in the trash. 

Both soap and sanitizer can disrupt the virus’ membrane (oily coating), getting it to spill out its guts (which, by themselves, are harmless). SARS-Cov-2’s main “gut component” is a single strand of RNA holding its genetic blueprint (genome) – note that this is opposed to the double-stranded DNA genome we have. Within its genome are instructions for hijacking the host cell to make more copies of that genome which it can then use to make more “viral particles” to bud out and infect new cells. 

These “viral particles” are the genome packed in a “suitcase” with the least amount of stuff it needs. To keep its RNA safe on the journey, it winds it up around “nucleocapsid proteins” and packages it all in a lipid (fatty) membrane coat. Within that membrane are embedded proteins, including the “crown-like” “spike proteins” that jut out and let it dock onto receptors on our cells. If we can disrupt that membrane and those proteins, we can disarm the virus so it can’t do any damage. So, how can we do this?

Yesterday we saw how soaps and detergents (artificial soaps) work:

Here’s an overview: soaps and detergents (artificial soaps) are amphiphilic – they have a hydrophilic (water-loving) head and a hydrophobic (water-avoided) tail. When in a watery environment, in order to maximize head exposure and minimize tail exposure, they form spheres called micelles, with heads on the outs, and they can trap hydrophobic gunk like dirt and grime inside of them, dislodging the gunk & making it easy to wash off. 

The soap & detergent molecules are similar enough to the lipids making up the membrane to wedge their way in between them, allowing them to break the membranes apart, then surround all the pieces in micelles which, since they have those water-loving heads on the surface, can get rinsed off. 

How about alcohols? Alcohols come in and destroy things, even the proteins inside the viral envelope they dissolve, but they don’t clean up after themselves. Chemically-speaking, an alcohol is just something with a hydroxyl (-OH) group. The alcohol most people are most familiar with is the one that’s in “alcoholic beverages” – ethanol (CH₃CH₂OH). Another common one is isopropanol (aka isopropyl alcohol aka rubbing alcohol). Similarly to soaps, these alcohols can disrupt the viral membrane because they have an amphiphilic nature. And Once they’ve dissolved the membrane by breaking up the lipid-lipid bonds, they go to work disrupting the bonds keeping proteins folded, denaturing the proteins so they couldn’t work even if the membrane were intact. 

Unlike soap, it doesn’t need to rinsed off. Instead, it evaporates. There’s been a lot of talk about stock market volatility – but less talk about chemical volatility. So let’s change that… Volatility in the chemical sense refers to how easy it is for something to evaporate (go from liquid to gas). In order for something to evaporate, the molecules in it need to have enough energy to break free of their attractions to one another. So, the tighter the attractions (more self-sticky the molecule) the harder this is, and the more energy (in the form of heat) you need.

Water is really sticky, so it’s NOT very volatile. This comes from water’s strong polarity (unequal charge distribution) – water is, molecularly speaking, H₂O (2 hydrogens sharing electrons with an oxygen). They don’t share these electrons fairly – O hogs the shared electrons, making it partly negative and leaving the H’s partly positive. So, even though water is neutral overall, there are partial charges in the different parts, so all parts of the molecule are attractive to some “opposite” part in another copy of the molecule, like 2 pieces of tape – making it quite hard to escape!

Alcohols, on the other hand, have that -OH which offers attraction opportunities, but they also have that “boring” hydrocarbon part (e.g. CH₃CH₂- in the case of ethanol). So it’s more like a post-it note – the sticky part is only in one place, so it’s easier to pull copies of them apart. As a result, alcohols are volatile – they evaporate “easily”

So, if you were to have 100% alcohol, it would evaporate really quickly, before it could do any harm, and wouldn’t make for a very effective sanitizer – and it would super dry out your skin. To prevent this, you add some water (but not too much!) – dilute the alcohol typically to 60-80%. Not only does this help keep your product from going bye-bye – it helps microbes go bye-bye! A virus is used to being surrounded by watery stuff, not alcoholly stuff, so the water can kinda help the alcohol sneak in

Even with the water, hand sanitizers are skin-drying – when ethanol mixes with water, it makes it easier for water to evaporate too because it breaks up the water’s sticky network so it takes less energy for a water molecule to break free and make a gassy run for it. So hand sanitizers can kinda take evaporating too far and pull water out of your skin. And this can make your skin crack, providing avenues for other microbes to sneak in – not good. So, to help counteract the dry-out-ness, hand sanitizers often contain other additives like tocopherol acetate (looks a lot like vitamin E), aloe vera, or glycerol (glycerin) which serve as humectants to help your skin retain its moisture and/or emollients, which help keep things smooth. 

An added benefit to some of these, like the aloe and glycerol is that they thicken your water/alcohol mixture up into a gel that’s easier to use (and harder to spill). As the -ol in the name suggests, glycerol technically is an alcohol (it has -OH’s), but it’s here for goopiness, not germicidalness. In fact, we often use glycerol in the lab to protect cells and proteins when we freeze them (use it as a cryoprotectant). Unlike the alcohols commonly used in hand sanitizers (ethanol, isopropanol, or plain propanol (the non-branched version of isopropanol), glycerol is big and bulky and has multiple OH’s on it so it doesn’t have that lipid-fakability-ness needed to break in. 

Commercial makers often add a couple of other things:

  • scent – this is my least favorite part – my skin’s really sensitive 
  • bad-tasting thing to prevent people from drinking it. 

Speaking of drinking, some people always want to know if you can just like use vodka? Well, since you need to get to at least 60% alcohol, and you’re mixing the alcohol with stuff, that alcohol needs to be high enough proof that it’ll still be at least 60% alcohol once you’ve diluted it – for example, 120 proof liquor only has 60% alcohol to begin with.

But you CAN make your own hand sanitizer (assuming you can find the ingredients) A general formula you can use is 2 parts rubbing alcohol, 1 part aloe. I didn’t have aloe, so I went with the WHO’s recipe I. 

The WHO provides a couple recipes (1 with ethanol and one with isopropanol) – but these recipes are for making a lot of it (the recipes are geared towards developing countries with larger-scale public health aims in mind). So, instead of making a whole liter, I divided everything by 10 and made 100mL. This meant ~83mL of ethanol, 1.45mL glycerol (I “cheated” and used 2.9mL of 50 glycerol which is wayyyyy easier to pipet because this stuff really is goopy!), 4.2mL hydrogen peroxide, filled too 100mL with super-pure water. 

If you’re wondering about the hydrogen peroxide (H₂O₂), it isn’t an active ingredient in this – it’s not there to clean your hands – instead, it’s there to kill off any spores that might be in your sanitizer – the protocol actually calls for you to “quarantine” your sanitizer after its made for several days to allow the hydrogen peroxide time to work first. You can learn a lot more about hydrogen peroxide here: but it’s what’s called an “oxidant” – it can donate electrons leading to the generation of energetic things called reactive oxygen species (ROS) which can attack spore walls. 

And if you thought I was joking about “quarantining” it, that’s literally the term they use! “The bottles should be kept in quarantine for 72 hours. This allows time for any spores present in the alcohol or the new or re-used bottles to be eliminated by H₂O₂”

But, whatever you do, don’t quarantine it near a flame – it’s highly flammable! 

Another benefit of soap and water over hand sanitizer is that soap & water is more “one size kills all” – hand sanitizer doesn’t work on all viruses or bacteria – but thankfully it works on SARS-Cov-2. But it still can’t do all that de-gunking. So, if you can, think sink!

Hope this helps! And sincerely hope you’re all staying happy and healthy. 

Best wishes,

the bumbling biochemist

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