The chemical reaction that turns soapy water into the most effective weapon against coronavirus
In 1817, the Royal Printing Office of Madrid published the Memoir on the Barrel Plants of Spain, by the eminent botanist and doctor Mariano Lagasca. This work, two hundred years later, continues to be a mandatory reference with regard to those plants that, when burned, produce “barrilla”: ashes rich in soda.
Don Mariano says that the invention of soap probably began with an accident thousands of years ago. According to legend, the rain washed the fat and ashes from frequent animal sacrifices into a nearby river, where they formed a foam with a surprising ability to clean skin and clothing. The essential elements of soap: the fat and ash from the firewood of certain plants, are a combination that altered human history and that, although no one could have foreseen it, would eventually become one of our most effective defenses against viruses. pathogenic microbes.
The plants that produce barbell, the barbell plants, live in saline environments, so they anchor their roots in soils rich in salts, so rich that they are sometimes true brines. Salt water is harmful to most plants. Just as we become dehydrated by ingesting salt (which quickly manifests itself in the cracking of the lip mucous membranes), plants also become dehydrated.
Salt dehydrates plants and causes serious metabolic problems.
What do barrel plants do to survive in soil that is practically brine? They achieve this by osmotically accumulating more salt (sodium and potassium chlorides) inside them than in the soil that supports them. It was in these plants that, in 1807, Sir Humphry Davy isolated sodium for the first time, and they are popularly said to contain soda, although in addition to sodium they also accumulate potassium.
The scientific names offer a clue: Salsola soda, Salsola kali, Suaeda vera, Salicornia ramosissima, while the common names end up raising our expectations: soda, alkali soda, barrel soda, salicor.
The chemical reaction that produces ashes rich in soda and fat is called saponification (from the Latin sapo, “soap” and ficar, “to make”). Soda (or potash) breaks down the triglycerides that form fats, forming the sodium salt of the fatty acid and releasing glycerin. The fatty acid has a nonpolar body (fatty part formed by carbons and hydrogens) and a head (formed by the COOH acid) which, having oxygen, is polar.
The fatty acid forms micelles, which constitute the mechanism by which soap solubilizes water-insoluble fat molecules, cleaning fats (from the non-polar part) and dirt (from the polar part).
The chemical reaction of saponification is this:
Fat + soda = soap + glycerin
We usually think of soap as something gentle and relaxing, but from the perspective of microorganisms it is extremely destructive. A drop of regular soap diluted in water is enough to break down and kill many types of bacteria and viruses, including the new coronavirus. The secret of soap’s impressive power is its bipolarity.
Soap is made of pin-shaped molecules, each of which has a hydrophilic head (binds easily with water) and a hydrophobic tail, which shies away from water and easily adheres to oils and greases. Soap molecules, when suspended in water, float randomly alone, interact with other molecules in the solution and assemble themselves into small bubbles called micelles with heads that point outward and tails that stay inside.
Some bacteria and viruses, including the SARS-CoV-2 coronavirus, have proteinaceous and fatty (lipid) membranes that resemble double-layered micelles with two bands of hydrophobic tails sandwiched between two rings of hydrophilic heads. These membranes bristle with spikes made of proteins that allow viruses to infect cells and bacteria to perform vital tasks that keep them alive. Pathogens enveloped in lipid membranes include coronaviruses, HIV, as well as viruses that cause hepatitis B and C, herpes, Ebola, Zika, dengue, and numerous bacteria that attack the intestines and respiratory tract.
When we wash our hands with soap and water, we surround any microorganisms on our skin with soap molecules. The hydrophobic tails of free-floating soap molecules shun water. In doing so, they enter the lipid envelopes of bacteria and viruses and force them open, acting as wedges that leverage and destabilize the entire membrane protective system. The proteins break off from the broken membranes and enter the surrounding water, killing bacteria and rendering viruses useless.
The process is twofold. Some soap molecules break the chemical bonds that allow bacteria, viruses and grime to stick to surfaces, pulling them away from the skin. The micelles that form around the grimy particles and the fragments of viruses and bacteria trap each other, suspending them in a kind of floating cages. When you rinse your hands, all the microorganisms that have been killed, injured and trapped by the soap molecules are washed away by the water.
Therefore, those who compulsively buy alcoholic hand sanitizers are not making a mistake, they are simply using less effective mechanisms than conventional soap.
Disinfectants with at least 60% ethanol act in a similar way, because they kill bacteria and viruses by destabilizing their lipid membranes. However, they do not prevent the microorganisms and their remains from detaching from the skin. Therefore, alcohol-based sanitizer is only useful when soap and water are not available.
Not suitable for all pathogens
In any case, neither soaps nor disinfectants are Fierabrás’ cure-all balm. There are viruses that do not depend on lipid membranes to infect cells and bacteria that protect their delicate membranes with resistant armor of proteins and sugars. Examples of such pathogens include bacteria that cause meningitis, pneumonia, diarrhea, and skin infections, and hepatitis A, polio, rhinovirus, and adenovirus.
These more resistant pathogens are less susceptible to the destructive chemical attack of both ethanol and soap. However, even in these cases, soap wins on points. Vigorous cleaning with soap and water can remove germs from the skin, so handwashing is more effective than disinfectant.
In the 21st century, the era of 5G robotic surgery and gene therapy, it is wonderful that a little soapy water, a recipe that the Phoenicians already knew, continues to be one of the most effective hygienic-sanitary actions. All kinds of viruses and microorganisms stick to our skin in our daily activities. When we touch our eyes, nose or mouth – a habit, one study indicates, that occurs every two and a half minutes – we widen the doors of our internal organs to millions of potentially dangerous microbes.
As Ignacio Felipe Semmelweis discovered exactly a century and a half ago, washing with water (warm or hot) and soap is one of the key public health practices that can significantly slow the contagion rate of a pandemic and limit the number of infected, which prevents overloading of hospitals, clinics and health centers. However, the technique only works if each of us washes our hands with the frequency and vigor of a surgeon.
Soap is more than a personal protector. When used appropriately, it joins the social safety net. At the molecular level, soap disintegrates, at the social level it integrates. Let’s remember that the next time we pass the bathroom: other people’s lives are in our hands.
Article published in The Conversation.