"Are radicals lonely?"
Kana was reading a chemistry book.
Rei answered. "Isolated electrons. No pair."
"Pair?"
"Electrons usually pair up. But radicals have unpaired electrons."
Milia supplemented. "That loneliness makes radicals dangerous."
"Dangerous?"
"Very high reactivity. Try to find a partner."
Rei drew a diagram. "・OH hydroxyl radical. The dot is unpaired electron."
"Missing just one electron."
Kana understood. "So they steal from others?"
"Yes. Steal electrons. That's oxidation."
Milia explained. "In organisms, superoxide, hydrogen peroxide, hydroxyl radical."
"These cause oxidative stress."
"Oxidative stress?" Kana asked.
"Cell components get oxidized. DNA, proteins, lipids."
Rei gave a specific example. "Lipid peroxidation. Membrane fatty acids attacked by radicals."
"When one fatty acid becomes radical, chain reaction occurs."
"Chain?"
"Radical steals electron from neighboring molecule. That molecule also becomes radical."
Milia drew a diagram. "ROO・→ ROO・→ ROO・..."
"Spreads like an avalanche."
Kana got scared. "Can't it be stopped?"
"Antioxidants," Rei answered. "Vitamin C, vitamin E, glutathione."
"These capture radicals."
"Capture?"
Milia explained. "Give electrons to stabilize radicals."
"For example, vitamin E is fat-soluble. Captures radicals in membranes."
Rei wrote the formula. "E-OH + ROO・→ E-O・+ ROOH"
"Vitamin E itself becomes radical. But a stable radical."
"Stable?" Kana was surprised.
"Resonance structure. Unpaired electron is delocalized."
Milia supplemented. "That's why it can stop chain reactions."
"And vitamin C regenerates vitamin E."
Kana asked. "Why do radicals form?"
Rei answered. "Metabolic byproducts. In electron transport chain, oxygen is incompletely reduced."
"O2 → O2・- superoxide radical"
"Superoxide dismutase processes this."
Milia continued. "SOD. Enzyme converts superoxide to hydrogen peroxide."
"Then catalase converts hydrogen peroxide to water."
"2 H2O2 → 2 H2O + O2"
Kana summarized. "Organisms make radicals and process them?"
"Yes. It's a balance issue," Rei acknowledged.
"But when balance breaks?"
"Aging, cancer, neurodegenerative diseases," Milia said seriously.
"Radicals damage cells."
Rei added. "UV light, radiation, smoking. Radicals also arise from external sources."
Kana asked. "Are radicals only villains?"
"No," Milia denied. "Immune cells kill bacteria with radicals."
"Neutrophils weaponize superoxide."
Rei explained. "Respiratory burst. Release massive superoxide."
"That destroys pathogen DNA and proteins."
Kana understood. "Radicals are also tools."
"Depends on usage," Milia acknowledged.
"But control is important. Running wild damages own cells too."
Rei looked out the window. "Because there's oxygen, radicals are born."
"Oxygen has duality."
Milia continued. "Essential for life but also dangerous."
"Oxygen toxicity. Why deep-sea creatures avoid it."
Kana murmured. "Radicals react because they're lonely."
"Searching for electron pairs."
Rei said quietly. "Isolation means instability."
"For molecules and humans."
Milia smiled. "But isolation is temporary. A partner is always found."
"And becomes stable."
Kana closed her notebook. "Radicals seek peace too."
"Peace of electron pairing."
The three fell silent. Invisible radicals are born and disappear inside cells. Endless cycle of isolation and stability.