# A Chemist’s Centenary Celebration of Pi

Today is Pi Day; a day where mathematicians celebrate the mathematical constant π.  This year is extra special, since at the exact second this post was published time lines up with π to an amazing 9 decimal places (3.14.15 9:26:53) and this will only happen once a century.

A quick recap of π… It is the number obtained when dividing the circumference of any circle by its diameter. It is therefore a very useful little number in the world of Chemistry where we are very much concerned with circular and spherical shapes. So today let’s join the mathematicians in their celebration. Here are 3 (π to 0 decimal places) areas where π is used in chemistry with examples of how these areas have impacted our daily lives.

1)  Atomic and molecular orbitals.  π helps us calculate how the electron clouds in atoms interact to form molecules.  Let’s introduce the π orbital (a coincidental name).  These special π systems are pivotal to dyes and plastics.  Putting the colour in your jumper and making drink bottles and parts of your car.  Sometimes when electrons get excited and jump into higher energy orbitals we get fluorescence or phosphorescence.  Keeping you safe on your bike at night after partying with glow sticks.

2)  Formation of droplets, bubbles and micelles in surface chemistry.  Concerned with the favourable spherical arrangements made to best separate hydrophobic from hydrophilic.  The pop in your champagne, the moisturisers you put on your face, the soap powder you use to clean your clothes and how best to deal with oil spillages in the sea.

3)  Predicting protein-drug binding.  π is used in the calculation of  binding scores for possible conformations (shapes) of potential drug molecules in the binding pocket of a protein.  By predicting how drugs bind to their targets we can design effective new pharmaceutical treatments as well as understand how chemicals behave in our body.

Of course let’s not forget that, as well as being a numeric constant, there are many other amazing things that this greek letter is used to represent in science. Examples include: osmotic pressure (how plants take up nutrients), nucleotide diversity (a topic from molecular genetics) and the Pion (an important subatomic particle).

We have certainly covered a broad array of chemistry applications, so a big thank you to 3.141592653 and however many further decimal places you require.