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-] = K w = 1 x 10-4 M2

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

> > pH = -log[H+]

> Weak Acid and Base Equilibria

> > K a and pK a (Equation 2.8)
> > Polyprotic Acids

> A Closer Look at pK a 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 pK a

> > 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