What’s the one true gift pi-electrons give we can celebrate as chromatographers? Color, or in chemistry talk, chromophores.
Pi day is one of the few holidays that unites us self-proclaimed nerds around the world. People flood social media pages with π pride, proudly wearing t-shirts with catchy phrases like “cutie π” and mouth-watering images of every pie known to humans.
Mmmmm, pumpkin pie.
What you never see, though, are people celebrating pi-electrons. Sure, π is integral for calculations in industries like construction, quantum physics, and space flights. But when pi-electrons transition from excited to ground states, they emit light in the process, giving rise to illuminating properties like fluorescence and bioluminescence.
Perhaps it’s the spectroscopy lover in me but I’d like to put a spin on pi day and shine some light on electrons. In honor of chromophores and chromatography, this blog is dedicated to pi-electrons because, let's be honest, chemists’ electrons are far more exciting and excitable than circles (pun intended)!
What’s in a chromophore?
Simply put, a chromophore is the structural part of a molecule giving color. In chemistry, color comes in two main ways: through conjugation in organic compounds or through ligand-metal complexes. Conjugated systems come from the connection of double bonds with extensive delocalization of pi-electrons which undergo electronic transitions and give off energy in the form of visible light.
Types of chromophores
Chromophores come in all type of sizes and color and there are three distinct classes:
Organic chromophores like the orange pigmented beta-carotene found in carrots and the red pigment lycopene found in tomatoes. For organic chromophores, atoms like carbon and nitrogen usually make up the conjugated system.
Inorganic chromophores such as the bright green of nickel(II) sulfate and brilliant blue of copper(II) sulfate. The key feature here is the metal-based chromophores aren’t conjugated or free of carbon and nitrogen.
Ligand-metal complexes, like the pigments of hemoglobin and chlorophyll, are my favorite because they are a combination of organic and inorganic chromophores. Hemoglobin contains nitrogen and iron to give the red color, while the green of chlorophyll comes from a nitrogen and magnesium complex.
Chromophores and chromatography
The literal translation of chromatography means “color writing.” The foundations of this chemical technique date back to the 18th century and used to separate plant carotenoids and chlorophylls.
As science advanced, the 20th century saw the birth of liquid chromatography coupled with UV and fluorescence HPLC detectors, which are perfectly suited for the detection of molecules with pi-electrons and chromophores. These inventions changed the game for analytical chemistry, allowing for the separation and analysis of peptides and proteins.
Fast forward to the 21st century where the applications of liquid chromatography are vital to pharmaceutical manufacturing, drug discovery, food testing, and toxicology industries.
Chromatography beyond chromophores
Can you imagine what the founders of chromatography would say if they were alive today? I bet they’d ooh and ahh at the field’s advancements and accomplishments—we’re certainly honored that the Thermo Scientific Vanquish Core HLPC System won the Select Scientist’s Award for Best Separation Product of 2020!
What was once a science used to identify plant chromophores is now a discipline extended to detecting all types of compounds, even those without double bonds or any absorption in the UV or visible spectrum, thanks to technology like charged aerosol detection and mass spectrometry.
I’m excited to see what the future of liquid chromatography holds. What do you think the next big milestone for this field is? Drop a comment below with your future predictions for chromatography.