"Look, this enzyme reaction changes with a magnetic field."
Kana pointed to the lab notebook. By the window in the club room, Toma was playing with a small magnet.
"Magnetic field? Chemical reactions?" Kana tilted her head.
Rei answered quietly. "If radical pairs are involved, the reaction is affected by magnetic fields. It's an electron spin issue."
"Electron... spin?"
"Electrons are like tiny magnets. They have a property called spin." Rei began drawing a diagram.
Toma brought the magnet closer. "Even with such a small magnet?"
"Theoretically. But to observe effects in experiments, more special conditions are needed."
Kana pondered. "What are radical pairs?"
"A pair of molecules with unpaired electrons. Normally, electrons pair up for stability. But during chemical reactions, unpaired electrons temporarily form."
Rei wrote a reaction scheme on the whiteboard.
"The electron spins of these radical pairs change orientation due to magnetic fields. This changes reaction rates and product ratios."
"Mysterious," Kana's eyes lit up. "Invisible magnetic fields change molecular fates."
Toma suddenly thought of something. "Then, the magnetic sense of migratory birds too?"
"Good insight. Indeed, a protein called cryptochrome in bird retinas is thought to detect magnetic fields through a radical pair mechanism."
Kana was surprised. "Organisms use quantum effects?"
"There's a field called quantum biology. Superposition states of electron spins influence biological reactions."
Rei continued. "The spins of two electrons can be either parallel (triplet state) or antiparallel (singlet state). With a magnetic field, the conversion rate between these two states changes."
"Spin states... change?"
"Yes. Singlet and triplet have different chemical reactivity. Singlets tend to pair up and form bonds. Triplets move separately."
Toma asked while moving the magnet. "So stronger magnetic fields have bigger effects?"
"Not linear. Even weak magnetic fields like Earth's can have effects with appropriate molecular systems. That's the secret of biological magnetoreception."
Kana looked back at the notebook. "This paper writes about flavin radicals."
"Flavin is a coenzyme involved in electron transfer. When it absorbs light, it enters an excited state and forms radical pairs."
"And that senses magnetic fields?"
"Probably. The spin state of flavin radicals changes with magnetic fields, which is transmitted to nerves through some signal transduction system."
Toma placed the magnet on the lab bench. "Can we experiment with this?"
"Difficult with household magnets. Precise control and detection systems are needed."
"But I understand the principle," Kana said. "When electron spins, an invisible property, align, the pathway of chemical reactions changes."
Rei smiled. "The intersection of quantum mechanics and biochemistry. Electrons are both particles and waves, and also tiny magnets."
"A mysterious world," Kana looked out the window. "Inside our bodies too, electrons are quietly spinning."
"More like having intrinsic angular momentum than spinning," Rei corrected. "But as a poetic expression, it's not bad."
Toma said while putting away the magnet. "Invisible things move visible things."
"That's the charm of quantum biology," Rei concluded.
The three quietly contemplated how electrons, the smallest existence, are involved in life, the greatest mystery.