My Work at a Concordia’s Chemistry Department For 10 Weeks
This summer, I got to have a truly incredible experience working inside Concordia University’s research lab, and I learned things beyond what I had originally known, all revolving around a tiny, but packed, word called chirality. For those of you who have taken chemistry NYA, you may know that “chirality’’ (meaning handedness in Latin) is the property of a molecule that has a non-superimposable mirror image. It is a property centered around the orientation of the molecule’s structure and its asymmetry. A chiral molecule and its mirror image are called enantiomers. This is not just a concept for molecules, but other things in the macroscopic world. Think about your hands, your feet, or your shoes. These are all examples of chiral objects. That’s as far as I got into chirality during the semester, but there is so much more behind that word that I only found out about during the summer. Chiral molecules are extremely interesting. Because of their asymmetry, chiral molecules are optically active, meaning they can rotate plane-polarized light. However, because enantiomers are oriented differently, enantiomers rotate plane-polarized light in different directions, but by the same amount. This is not the only thing that differs between enantiomers. In truth, enantiomers can react very differently in biological species, despite having the same molecular formula, because of their different orientation. The drug thalidomide is an example of how enantiomers can differ so much. Thalidomide was meant to act as an analgesic in the 1960s, but instead caused birth defects because of its other handedness. As a result, finding ways to produce molecules of one handedness, homochiral molecules, has been of large interest to researchers involved in pharmaceuticals and other industries. The obstacle with this is that some molecules come in racemic forms when crystallized; in other words, they have equal amounts of both enantiomers. This makes it hard to isolate just one. However, many methods have been produced in order to find a solution, and the one I worked with was called Viedma Ripening.
Viedma Ripening is a fascinating process that actually converts the chirality of crystal using a solid to solution equilibrium. Simply put, it takes a racemic crystal mixture and transforms it into a crystal of one enantiomer, making the other enantiomer vanish in solution. Viedma Ripening uses multiple concepts including the Gibbs-Thomson Effect, where small particles dissolve more easily than large ones, and Ostwald Ripening, where smaller crystals dissolve to re-attach to larger crystals. During Viedma Ripening, the solution of the molecule and its racemic crystals are grinded by beads rotating at a high rpm. As the crystals are grinded in solution, both enantiomers start to dissolve into solution, and new crystals crystallize and reattach to larger ones. Whichever enantiomer is more present in crystal form will ultimately lead the crystallization of the molecules in solution. That is, the molecules that recrystallize will form the crystals of the same enantiomer as that of the majority because of the enantioselectivity of the molecules (molecules of the same enantiomer attach to each other). This process continues till the one enantiomer remains present in crystal form and you have your homochiral crystal. Of course, there are many more conditions to this type of experiment, varying between what type of crystals you are working with. I worked with Valine (an essential amino acid) which is chiral and 1-(p-toluenesulfonyl)uracil which is an achiral molecule in solution, but a chiral crystal because of the way it crystallizes; therefore, the procedures for those molecules were different.
Regardless, the concept is the same, and it is truly an interesting experiment which I encourage you all to look into more detail with!