Publications: Article 1 (2022)
A crystal is like a three-dimensional grid of the same chunk of material (called a unit cell) repeated through space in the same pattern, in the same structure, again and again. Some crystals you might know are salt (sodium chloride), diamond (carbon), and ruby (aluminum oxide). Cocrystals are a special type of crystal, where that unit cell is comprised of two or more molecules that aren't quite bound to each other—it's sort of like they're cuddling, and that cuddle-bundle repeats over and over in space.
What's cool is that a cocrystal acts like a whole new substance with different properties from its cuddlers coformers. This is great for medicine, because an ibuprofen cocrystal might have a much later expiration date, or an aspirin cocrystal could reach its destination in the body much faster. Now the weird part. Some cocrystals form spontaneously in the solid state. Imagine if you were doing laundry and found that all your shirts and pants had fused to form jumpsuits, but washing them separated them again—and this was repeatable. That's kind of like what's going on at the molecular level with these cocrystals. But why? How?! That's what we're trying to figure out.
My responsibility in this lab was to research some of the key chemistry underlying these spontaneous solid-state reactions, namely kinetics and thermodynamics. For kinetics tracking, we used solid-state nuclear magnetic resonance spectroscopy (ssNMR), powder x-ray diffractometry (PXRD), and a couple of other methods to track the rate of cocrystallization under different environmental conditions. For the thermodynamics approach, we used bomb calorimetry (BC) and differential scanning calorimetry (DSC) to derive Gibbs free energy change for a second set of reactions.
Kinetics is the study of reaction rates. It's what happens along the way from point A to point B—the journey, not the destination. I tracked the reactions of 15 unique combinations of coformers from among the following chemicals: caffeine, theophylline, nicotinamide, oxalic acid, malonic acid, maleic acid, fumaric acid, succinic acid, and glutaric acid. I followed each system for as long as a month under four levels of relative humidity: 0% (bone dry), 50% (temperate climate), 75% (gross), and ambient conditions (whatever the air was like in the lab that day). These systems were tracked by PXRD with follow-up by ssNMR, gravimetry, and optical microscopy.
Thermodynamics is the study of reaction states. It's the difference between point A and point B, regardless of how you got there. A seven-hour drive for my parents is only five hours when I'm behind the wheel? Don't ask how. Just appreciate that we were at home this morning, and now we're on vacation. Thermodynamics. Anyway, I used BC and DSC to study a smaller set of cocrystals. BC is burning stuff to study enthalpy, DSC is freezing stuff to study entropy. Enthalpy and entropy combine to give us the free energy change of the reaction. Now we know the energetics from point A to point B for a reaction—from separate coformers to cuddling in a cocrystal.
Publications: Article 1 (2020); Article 2 (2023)
Positron Emission Tomography (PET) is an imaging technique used in hospitals, like CT or MRI. Doctors cram you in one of those off-white plastic tubes full of expensive machinery and look at your brain with magic. The magic here is positrons. They're like electrons, but positive instead of negative, and they are emitted by radioactive materials. These positrons almost immediately crash into nearby electrons to make photons, which are so small that they pass through your body like wind through a screen door.
So a doctor will put a tiny amount of radioactive stuff in you, which is designed to target something in your body, like an enzyme or receptor. Positrons smash into electrons at that site, photons fly out of your body and hit the big plastic tube machine, the machine backtraces the path of these photons to exactly where the crash happened in your body, and a computer creates a chart from the data. It's an extremely precise technique which can find health problems before you even notice them, so you can get treatment for a disease before it starts having a negative effect on your life. In this lab, we make and study new radioactive materials that help with early diagnosis for brain conditions, such as stroke, dementia, and schizophrenia.
My responsibility in this lab was to synthesize non-radioactive versions of experimental materials and optimize their production, so that we can make more of them with fewer ingredients. I worked on two projects: one synthesizing ligands for NR2B, and one synthesizing ligands for COX-2.
NR2B is part of a big protein blob called NMDA, which is found all over the brain. NR2B in particular is found most often in parts of the brain having to do with learning and memory. When NR2B isn't working properly, it can lead to awful conditions like schizophrenia and neuropain. With the right PET radioligand, we could identify and act on these conditions before they become severe. I synthesized, purified, and characterized 13 new ligands, then improved our process for greater efficiency. One of these materials is showing great promise, and a medical team at NIMH is continuing to study its efficacy.
Cyclooxygenase is an enzyme responsible for production of prostaglandins. These have to do with the inflammatory response, so when you need to take aspirin or ibuprofen, prostaglandins are probably involved. Normally, the human body has a bunch of one version of cyclooxygenase throughout the body, called COX-1. This one is around for normal prostaglandin needs. COX-2 is another version that shows up in much smaller quantities. When the body suffers from an inflammatory illness, COX-2 production ramps up and it becomes way overexpressed. When we find a lot of COX-2 in the brain, it usually means neuroinflammation, which is indicative of neurodegenerative diseases. This whole thing is obviously bad news, so if we can find a PET radioligand that is highly selective for COX-2 over COX-1 in the brain, we will make great strides in research and treatment for problems like dementia. My job on this project was to increase both the quantity and efficiency of production for a promising COX-2 ligand candidate.