Overview
This lecture discusses non-covalent molecular interactions—specifically hydrophobic interactions and hydrogen bonds—and their relevance in biological systems, focusing on how molecules interact without electron exchange.
Types of Molecular Interactions
- Not all molecular interactions are true chemical bonds; some do not involve electron sharing or exchange.
- These interactions are weaker than chemical bonds and can be broken without chemical reactions.
- Key types: hydrophobic interactions and hydrogen (H) bonds.
Hydrophobic Interactions
- Occur when nonpolar molecules cluster together in watery (aqueous) environments.
- "Hydrophobic" means "water-fearing"; such molecules do not mix with water.
- Hydrophilic means "water-loving."
- Nonpolar molecules (often with many C-H or C-C bonds) are typically hydrophobic.
- In water, hydrophobic molecules group together, being pushed aside by water molecules.
Hydrogen Bonds
- Hydrogen bonds are not true chemical bonds; they mostly involve attraction between polar regions of different molecules.
- Often (but not always) involve hydrogen atoms.
- Result from polar covalent bonds within molecules, creating partial positive and negative charges.
- These bonds are intermolecular (between molecules) and reversible.
- In water, the oxygen atom (slightly negative) is attracted to a hydrogen atom (slightly positive) on another molecule.
- These interactions help explain many properties of water.
- Hydrogen bonding can occur wherever there are opposite partial charges, such as between water and other polar molecules.
Key Terms & Definitions
- Hydrophobic — Molecules that avoid or repel water, usually nonpolar.
- Hydrophilic — Molecules that interact well with water, usually polar.
- Polar Covalent Bond — A bond where electrons are shared unequally, causing partial charges.
- Hydrogen Bond (H bond) — A weak attraction between a slightly positive hydrogen atom and a slightly negative atom (often oxygen or nitrogen) in another molecule.
- Intermolecular — Occurring between different molecules.
Action Items / Next Steps
- Review polar vs. nonpolar molecules and practice identifying partial charges.
- Prepare for next chapter on water properties, focusing on hydrogen bonding and hydrophobic effects.