Attack of the Killer Water Molecule (AKA hydrolysis)

Water fills our oceans, lakes, rivers and streams. It comes out of our taps. We swim in the stuff, and we drink it. For these reasons we tend to think of water as being inert. It isn’t. Water is an aggressively reactive molecule. Consider what happens when you stir salt into water: the water destroys the salt crystals. But why is water so ferocious? Read on to find out.

The Nature of Water 

In a molecule of water (H2O), two hydrogen atoms are attached to an oxygen atom. Oxygen has a much greater pull on electrons, or electronegativity, than hydrogen. In part this is because the oxygen atom has eight positively charged protons in its nucleus, and hydrogen only has one. Oxygen’s highly charged nucleus tugs electrons away from hydrogen, resulting in a partial negative charge (δ-) on the oxygen and a partial positive charge (δ+) on each hydrogen.

Figure 1 shows two views of a water molecule. Notice that the oxygen atom is surrounded by four pairs of electrons: two bonding pairs and two nonbonding, or lone pairs (Figure 1, left). The four electron pairs, which have a negative charge, repel each other and exist as far apart as possible around the spherical oxygen atom. In effect, to two bonding pairs are pushed to one side by the lone pairs, giving water a bent, or V shape (Figure 1, right).

Figure 1. Water has a bent shape

A partial negative charge exists at the point of the V and a partial positive charge exists at each tip. As a result, each water molecule behaves like a tiny magnet and is attracted to other charged particles. In some cases this attraction is so strong that water is able to break the bonds that hold other particles together. A reaction in which water attacks another compound is called hydrolysis. Hydro means “water” and lysis means “to unbind”, so hydrolysis literally means “to unbind with water”.

Hydrolysis Reactions

Hydrolysis of salt Consider a crystal of table salt (NaCl). The crystal contains positively charged sodium (Na+) ions and negatively charged chlorine (Cl-) ions. These charged particles interact with each other, holding the crystal together. Water, which is attracted to the charged particles, can disrupt this interaction and cause the salt crystal to dissolve (Figure 2).

Figure 2. Salt dissolving in water

Our oceans are salty because water attacks salt, but salt isn’t the only compound that water attacks. Water can also attack certain molecules.

Hydrolysis of molecules We have already established that oxygen is an electron bully. But oxygen doesn’t just tug electrons away from hydrogen. It tugs electrons away from other atoms as well, including carbon. A bond between oxygen and carbon possesses a dipole moment that can attract molecules of water. In some cases water attacks the molecule, causing it to split apart.

If you’ve eaten recently, hydrolysis is occurring right now, in your stomach and intestines. Digestion of fats, carbohydrates, and proteins is a hydrolysis reaction. Figure 3 shows hydrolysis of the ester bond in a fat.

Figure 3. Hydrolysis of the ester bond in a fat.

Of course, our bodies don’t just break down fats, carbohydrates, and proteins; they build new ones, too. To build new molecules water must be added in a type of reaction called dehydration. Dehydration is the reverse of hydrolysis.

So it turns out that water is a very good solvent for life, not because it is inert, but because it is highly reactive. Our very clever cells have learned to harness this reactivity so that they can build or break molecules on an as-needed basis.



How stinky socks launched the biotech revolution

Actually, there were two biotech revolutions. I will only argue that the second biotech revolution, which took place in the twentieth century, was launched by stinky socks. The first biotech revolution, which took place some 6,000 years before in the neolithic period, was arguably launched by beer. 

Biotechnology is, quite simply, the manipulation of living organisms or their components to make a desired product. (10) Beer is brewed with a living organism (yeast), and as such brewing is considered a form of biotechnology. Selective breeding, another form of biotechnology, was introduced around the same time as brewing, possibly to produce a more reliable source of grains for the beer. (4)

Thanks to the skills developed by early biotechnologists, humankind was able to develop a plethora of unique products and pets, from cheese to chihuahuas. (5) But the results weren’t always reproducible and the process was often less than desirable.

Take leather tanning, a process that involves removing flesh and hair from animal skin. Historically, tanning was done using urine, feces, and brain.(1) Urine, feces, and brains are all component of a living organism, so this qualifies as biotechnology.

Fortunately for tanners everywhere, in 1907 a sharp chemist named Otto Rohm had a better idea. Flesh and hair, Rohm reasoned, are biological in origin, and mammalian digestive system very good at breaking down biological molecules. Why not use digestive juices to tan leather? Rohm made an extract of digestive juice from cow pancreas and tested whether it could tan leather. It could. (2)

Meanwhile, Rohm’s wife, Elisabeth reasoned that digestive juice could also be used to remove stains from laundry. Think about it: most clothing stains are biological in origin–coffee, ketchup, blood–so it makes sense that they could be removed by digestive juice, right? Rohm tested whether his digestive juice extract could remove stains from laundry. It could. (2)

Digestive juice digests because it contains a special class of molecules, called enzymes, which are able to speed up a reaction.  Rohm partly purified a digestive enzyme called trypsin that is able to speed up the breakdown of protein, and in 1913 patented trypsin-containing laundry presoak solution called BURNUS. (2, 11)

It would be nice to say that BURNUS was a big success, but it wasn’t. It was expensive to produce and had a short shelf life. BURNUS was important, however, in that it was the first commercial product to utilize partly purified enzyme. (9) In other words, it launched the second biotech revolution: one in which purified biological components and isolated organisms are used to make a desired product.

At the time Rohm conducted his research the biological nature of enzymes was largely unknown. But shortly thereafter scientists demonstrated that certain enzymes, including trypsin and other digestive enzymes, are composed of protein. (7) And shortly thereafter this, scientists demonstrated that instructions for making proteins are encoded on DNA. (3) With this knowledge came the ability to engineer custom-designed proteins, a process called genetic engineering.

And what is one of the most successful products of genetic engineering? Laundry detergent! Modern laundry detergent, as well as dishwasher detergent, contains digestive enzymes from bacteria, some of which have been genetically modified to increase yield, or to improve stability or performance. (5) These enzymes are completely biodegradable, (9) and enable you to get the stink our of your socks at a lower temperature and with less harsh chemicals than laundry detergents of old. (8)


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(5) A. Kirk, O., Borchert, T. V., & Fuglsang, C. C. (2002). Industrial enzyme applications. Current opinion in biotechnology, 13(4), 345-351.

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    (7) J The Nobel prize in chemistry 1946. (2016, July 29) Retrieved from

    (8) C. Olsen, H. S., & Falholt, P. (1998). The role of enzymes in modern detergency. Journal of Surfactants and Detergents, 1(4), 555-567.

    (9) B Schäfer, T., Kirk, O., Borchert, T. V., Fuglsang, C. C., Pedersen, S., Salmon, S., … & Lund, H. (2005). Enzymes for technical applications. Biopolymers Online.

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