It’s been 96 days since my last post, roughly the period since the new revolution in U.S. health policies. I won’t make excuses. Ironically, since before any of this started, I’ve been trying to find a literary agent for my debut novel (upmarket thriller) about a race-to-the-cure for a pandemic, by a drug developer who must also come to terms with personal responsibility. If you know of an agent who may be interested, please leave their name in a comment on this blog.
Meanwhile I’ve been busy. One project supported work for an anti-COVID mask and filter technology that is ready for prime time. That device is more than anti-viral – it’s also antibacterial, antiprotozoan, etc. It turns out that disinfectants are simultaneously elegant and crude. I’ll talk about bacteria first.
Bacterial cells have an outer wall that is roughly 100 to 400 chemical bonds thick. It’s made of linear proteins that look somewhat like centipedes at the molecular level, with branches out to the sides of a long spine. The branches, in turn, have plus- and minus-charged groups at their ends. When the polymers are laid out in an array, the charged groups overlap, forming an elegant and very tough protein network. What do I mean by tough? Think of a cross between nylon and the rubbery covering on a golf ball. Chemically, that’s pretty close to the reality.
Now, that wall can be cracked by exposure to plus and minus charges (they always come paired) in water. Traditional soaps work that way, as do ammonium salts and related disinfectants. Charges in liquid will drill down through the wall, or make it bubble up like solvent does when stripping a layer of paint. Then a combination of leaking and charge-gelling of the guts kills the micro-beastie. My back-of-the-envelope math on the ratio of outside charges to germ cells at the lower effective concentrations finds about a billion to one – comparable to covering the outer surface of every pathogen cell with disinfectant molecules. It’s a massacre.
Of course, not every charge in that solution will find its way to a bacterial surface. Also, many charges will diffuse away and cripple additional germ cells after the kills. Still, seeing that billion-to-one ratio changed my thinking about how disinfectants work.
Yet that isn’t the main point. So, first, more context. As a virus, COVID-19 is unusual in having only a fatty double layer as shielding, and the layers are borrowed from humans. They’re destroyed by soap or disinfectants, in fact COVID-19 is *very* easy to kill in the open. Sadly, the same conditions could harm internal human cells, so drinking soap is not an advisable cure.
Moving on, most other viruses have a shell called a capsid instead of – or sometimes inside of – that soft double layer. Capsids are still mysterious. They’re tough and made of protein. Famously, they have polygon shapes, and each side is formed from a panel. We know a bit about protein composition in the panels, and a lot less about how panels are held together at edges and corners. Now I come to a personal epiphany, after reading lists of which disinfectants work for what. Certain ammonium salts devastate capsid viruses as readily as they knock out bacteria. So, if I speculate / hypothesize wildly, capsid shells *might* form by the same strategy as for bacterial cell walls – by clicking centipede structures into place at their charge points.
It gets better. The centipede shape is often referred to as a bottle-brush structure, and has some opposite applications at the microbial level. For instance, some bacteriophages – which are viruses that attack bacteria – have the same centipede-like shape and charge arrangements. Meaning, centipedes gather as walls, yet centipedes can also storm the walls.
A recent study mimicked the centipede paradigm with a cellulose backbone and acrylic branches (terminated with charges). That was extremely effective at killing bacteria. But unlike traditional disinfectants, this one was broken down by enzymes that are ubiquitous in the outdoors. And the decomposition products were no longer antibiotic, making them ecologically friendly. Yet I don’t know what the fate would be for nano-acrylic residues in the environment. Possibly further innovation may be needed, but the disinfectant proof of concept is exquisite.
Food for Thought
W. Zheng, M. Anzaldua, A. Arora, et al., “Environmentally benign nanoantibiotics with a built-in deactivation switch responsive to natural habitats,” Biomacromolecules, open-access preprint (April 7, 2020) posted in full at:
Circling-V ™ 