"Can you hear it?"
Milia held an ice sample.
"Hear what?" Kana asked.
"Whispers of hydrogen bonds."
Rei laughed. "Poetic."
"But not metaphor. Hydrogen bonds are communicating."
Kana showed interest. "What do you mean?"
Milia explained. "Hydrogen bonds have directionality. Straight line."
"H-O-H... straight line?"
"Ideally. Weakens when angle deviates."
Rei drew a diagram. "Hydrogen bridges two atoms."
"One covalent bond, other hydrogen bond."
Kana wrote in notebook. "So, hydrogen?"
"Yes. Hydrogen is mediator."
Milia continued. "But hydrogen bonds are weak. Easily break and reform."
"Constantly changing?"
"Yes. Dynamic equilibrium. That's why whispers."
Rei explained. "Water is network of hydrogen bonds."
"One water molecule can make up to four hydrogen bonds."
Kana asked. "In ice?"
"Regular crystal structure. All water molecules make four bonds."
Milia showed the ice. "That's why ice is lighter than water."
"Lighter?" Kana was surprised.
"Hydrogen bonds create space. Density decreases."
Rei supplemented. "This is important for life."
"Why?"
"Lakes freeze from top. Organisms below can survive."
Kana understood. "If ice sank..."
"Lake would freeze from bottom, organisms would perish."
Milia drew another diagram. "In proteins, hydrogen bonds are also important."
"α-helix and β-sheet. Both stabilized by hydrogen bonds."
Rei explained. "Hydrogen bonds between backbone N-H and C=O."
"Regular pattern?"
"Yes. That's why specific structures form."
Kana asked. "DNA too?"
"Two hydrogen bonds between A-T, three between G-C," Milia answered.
"So higher GC content means more stable?"
"Correct. Three bonds are stronger."
Rei added. "But two bonds make A and T easily separate."
"During replication?"
"Yes. Balance is important."
Milia showed water sample. "Water's unique properties are also hydrogen bonds."
"High boiling point, high specific heat, high surface tension..."
Kana took notes. "All thanks to hydrogen bonds?"
"Yes. Despite small molecular weight, these values are high."
Rei compared. "Methane has molecular weight 16, boils at -164 degrees."
"Water is molecular weight 18, boils at 100."
"Power of hydrogen bonds."
Kana pondered. "Life is built on hydrogen bonds?"
"Mostly," Milia said.
"Water, proteins, DNA, all involve hydrogen bonds."
Rei organized. "Weak but numerous. Directional so specific."
"And reversible," Milia continued.
"So can flexibly change."
Kana touched the ice. "Cold..."
"Hydrogen bonds are taking heat."
"Water evaporation also requires breaking hydrogen bonds. That's why evaporation heat is high."
Rei explained. "Why sweat has cooling effect."
Kana asked. "How weak are hydrogen bonds?"
"About 20 kJ/mol. One-twentieth of covalent bonds," Milia answered.
"But easily break?"
"At room temperature, constantly breaking and forming."
Rei added. "Average lifetime is picosecond order."
"Short!"
"That's why whispers. Gone in instant."
Kana closed notebook. "But new voices always born."
Milia smiled. "Dynamic dialogue."
Rei said quietly. "Hydrogen bonds are language of life."
Kana murmured. "I feel I can hear."
"Hear what?"
"Whispers of molecules."
Milia opened window. "If you listen quietly, maybe you can."
The three fell silent. Invisible bonds keep whispering. While supporting life.
"Whispers of hydrogen bonds," Kana murmured. "Weak, gentle, but indispensable."
Rei nodded. "That's beauty of life."