Molecular Lefties and Righties: A Handy Peek into Chirality

by Flora Guo

Have you ever tried wearing a right-handed shoe on your left foot? Or vice versa? From personal experience, I know that this is definitely a frustrating experience. However, this everyday occurrence demonstrates an interesting property of the molecules around you.

As a right-handed person, I often take everyday things for granted. Left-handed people are more likely to injure themselves while using tools designed without their best interests at heart (or on hand). In fact, over 90% of the world population is right-handed, meaning that you, dear reader, probably share my sentiments. In addition, did you know that certain molecules can also display handedness? This phenomenon is called chirality, which originates from the Greek word for hand. Whether you’ve known it or not, these chiral molecules play an important role in your life.

I was first introduced to chiral molecules at a Metro Vancouver Physics Circle session last year. These bi-weekly sessions take place at UBC, where students in grades 10-12 can delve into the curious worlds of physics and astronomy. There, Professor Valery Milner showed us his research on optical centrifuges. By manipulating pulses of light, he can essentially rotate molecules in a synchronized manner. This light is a controlled oscillation in the electromagnetic field, the electric component of which causes a molecule’s light electrons electrons to move. Due to electrostatic attraction, the heavier protons follow this moving electron cloud. This allows the whole molecule to spin. Intrigued by his lecture, I asked about potential applications of this research. Curiously enough, the rotation of these molecules can actually identify the handedness, or chirality of species.

What is Chirality?

You can visualize chirality by looking at both of your hands. Due to the distinct nature of your pinky and thumb as well as your palm and back of the hand, you cannot superimpose your hands onto each other. In other words, it’s impossible to position your hands on top of each other such that they’re oriented in exactly the same way. This is precisely the reason why your right foot doesn’t quite fit into your left shoe. In chemistry, this property is seen in enantiomers, which are molecules with non-imposable mirror images of each other. Enantiomers can be formed whenever a carbon centre has four distinct groups attached to it.

How do chiral molecules influence our everyday lives?

Interestingly, even though chiral molecules share the exact same atoms and bonds, they can have much different properties. Although this distinct behaviour only occurs when the chiral molecules react with another chiral species, it can be the difference between a sweet (d-amino acids) and a bitter (l-amino acids) taste. In fact, the chiral nature of a molecule called limonene is the reason why we can differentiate between the citrus scents of orange and lemon is due to . The limonene enantiomers actually react with chiral receptors in our nose and mouth, creating different tastes.

The next time you mix up your mittens or see your mirror reflection, remember that this curious behaviour is one that occurs even on the smallest scale. Even when we aren’t aware of the fact, scientific phenomena surround our everyday lives. Though it might not seem like a drastic difference, these mirror reflections sure make the world a sweeter (like d-amino acids!) place.

Written by: Flora Guo