In embalming chemistry, the cross-linking of proteins by formaldehyde primarily yields which small molecule?

• A. Hydrogen gas
• B. Ammonia
• C. Carbon dioxide
• D. Water

Answer: (D)

Formaldehyde preserves and stiffens tissue by forming links between protein amino groups. It first reacts with amino groups on proteins to form a hydroxymethyl intermediate, which can then combine with a second amino group to create a methylene bridge between the proteins. That condensation releases a molecule of water, so the small molecule produced in this cross-linking process is water. The other options don’t come from this cross-linking mechanism.