BackAqueous Chemistry: Water – Noncovalent Interactions and Hydrogen Bonding
Study Guide - Smart Notes
Tailored notes based on your materials, expanded with key definitions, examples, and context.
Noncovalent Interactions Define the Structure and Function of Biomolecules
Overview of Noncovalent Bonding
Noncovalent interactions are essential for the structure and function of biomolecules, such as proteins, nucleic acids, and hormones. These interactions are generally weaker than covalent bonds but are crucial for dynamic biological processes.
Noncovalent bonds include charge-charge, hydrogen bonding, van der Waals, and dipole interactions.
They allow biomolecules to interact, recognize, and bind to each other transiently.
Example: Human growth hormone binding to its cellular receptor is mediated by noncovalent interactions.
Covalent and Noncovalent Bond Energies
Relative Strengths of Bonds
Covalent bonds are much stronger than noncovalent bonds, which can be continually broken and reformed in biological systems.
Covalent bond energies are typically >300 kJ/mol.
Noncovalent bond energies range from 0.4 to 21 kJ/mol, depending on the type.
1 kcal = 4.184 J (energy conversion).
Type of Interaction | Approximate Energy (kJ/mol) |
|---|---|
Charge-Charge | 13 to 17 |
Hydrogen bond | 2 to 21 |
Van der Waals | 0.4 to 0.8 |
Types of Noncovalent Interactions
Classification and Examples
Noncovalent interactions are classified based on the nature of the interacting species. Each type plays a specific role in biomolecular structure and recognition.
Type of Interaction | Model | Example |
|---|---|---|
Charge-Charge | Electrostatic attraction/repulsion between ions | Na+ and Cl- |
Charge-Dipole | Ion interacting with a polar molecule | Na+ with H2O |
Dipole-Dipole | Interaction between two polar molecules | H2O with H2O |
Charge-Induced Dipole | Ion induces dipole in a nonpolar molecule | Na+ with benzene |
Dipole-Induced Dipole | Polar molecule induces dipole in a nonpolar molecule | H2O with benzene |
Dispersion (van der Waals) | Transient induced dipoles | Between nonpolar molecules |
Hydrogen bond | Donor and acceptor atoms | O-H...O in water |
Hydrogen Bonding
Nature and Importance of Hydrogen Bonds
Hydrogen bonds are a special type of dipole-dipole interaction, critical for the structure of water and biomolecules like proteins and nucleic acids.
Hydrogen bond forms when a hydrogen atom covalently bonded to an electronegative atom (such as O or N) interacts with another electronegative atom.
Creates a lower energy state and stabilizes molecular structures.
Hydrogen bonds are directional and have specific donor and acceptor atoms.
Donor → Acceptor | Distance (Å) | Comment |
|---|---|---|
O-H...O | 2.8 | H bond formed in water |
N-H...O | 2.9 | Bonding of water to other molecules |
N-H...N | 3.0 | Important in protein and nucleic acid structures |
O-H...N | 3.2 | Weaker than above |
C-H...O | 3.7 | Relatively weak |
Hydrogen Bonding in Biological Molecules
Hydrogen bonds are abundant in biomolecules, stabilizing secondary and tertiary structures.
Proteins: Hydrogen bonds between backbone amide and carbonyl groups stabilize alpha helices and beta sheets.
Nucleic acids: Hydrogen bonds between base pairs hold the double helix together.
H-bond donors: Typically N-H or O-H groups.
H-bond acceptors: Typically O or N atoms with lone pairs.
Additional info:
Noncovalent interactions are reversible and allow for dynamic biological processes such as enzyme-substrate binding and molecular recognition.
Hydrogen bonds are essential for the unique properties of water, including its high boiling point and surface tension.
