Outline

Introduction (Figure 2.1)

Non-Covalent Interactions (2-40 kJ/mol)

Hydrogen Bonds
Charge-charge interactions
Other non-covalent interactions

Covalent Bonds (300-400 kJ/mol)

The Nature of Noncovalent Interactions (Figure 2.2)

Charge-Charge Interactions

Coulomb's Law

The force is inversely proportional to r²

Dielectric Medium, Dielectric Constant

The medium shields charges

Energy of Interaction

The force is non-directional and inversely proportional to 'r'

Permanent and Induced Dipole Interactions (Figure 2.4, Table 2.1)

Permanent Dipole
Permanent Dipole Interactions (Figure 2.2)
Induced Dipole Interactions
Dispersion Forces (Figure 2.5)

Molecular Repulsion at Extreme Close Approach: Figure 2.6, Table 2.2

van der Waals Radius

Hydrogen Bonds (Figure 2.7)

Donors/Acceptors (Table 2.3)

The Role of Water in Biological Processes (Figure 2.8)

The Structure and Properties of Water (Table 2.4, 2.5, Figure 2.9, Figure 2.10)

-OH groups are strong hydrogen bond donors

Non-bonded electron pairs on oxygen excellent hydrogen bond acceptors.

Hydrogen bonds most clearly defined when water freezes

Unusual properties of water

High viscosity
High surface tension
Density decreases on freezing
High heat of vaporization
High boiling point

Water as a Solvent

Hydrophilic molecules in Aqueous Solution (Figure 2.11)

Hydration shells (Figure 2.12)

Hydrophobic molecules in Aqueous Solution

Clathrate cages (Figure 2.13)

Amphipathic molecules in Aqueous Solution (Figure 2.14)

Examples = fatty acids, detergents

Structures formed

Monolayer
Micelles
Bilar vesicles

Ionic Equilibria

Acids and Bases: Proton Donors and Acceptors

Strong/Weak Acids/Bases (Table 2.6)

Ionization of Water and the Ion Product

[H⁺][OH-] = Kw = 1 x 10^-4 M²

The pH Scale and the Physiologic pH Range (Figure 2.16)

pH = -log[H⁺]

Weak Acid and Base Equilibria

Ka and pKa (Equation 2.8)
Polyprotic Acids

A Closer Look at pKa Values: Factors Affecting Acid Dissociation

Hydration favors

Electrostatic attraction opposes

Titration of Weak Acids: The Henderson-Hasselbalch Equation

Buffer Solutions (Figure 2.17, Table 2.7)

Buffers work within 1 pH unit of pKa

Buffer calculation

Molecules with Multiple Ionizing Groups: Ampholytes, Polyampholytes, and Polyelectrolytes (Figure 2.18, Figure 2.19, Diagram

pI

Isoelectric focusing

Interactions Between Macroions in Solution

Solubility of Macroions and pH (Figure 2.20, Figure 2.21)

Repulsive effects (nucleic acids)

Attractive effects (histones to DNA)

Minimum solubility at isoelectric point

Influence of Small Ions: Ionic Strength (Figure 2.22)

Debye-Huckel Theory

Salting In - adding counterions to a point increases protein solubility

Salting Out - adding very large amounts of counterions decreases protein solubility