L2: Noncovalent Interactions

Intramolecular Force

Hold together the atoms making up a molecule. Strong interaction within the molecule.

Examples of Intramolecular Forces

Covalent bonds and ionic bonds

Intermolecular Force

Attraction or repulsion between neighboring particles (atoms, molecules or ions). Weaker than intramolecular force

Examples of Intermolecular Forces

ion-dipole, dipole-dipole interaction, hydrogen-bonding, van der Waals forces

substrate is to enzyme what receptor is to _______

ligand

what do ligands transmit

signals

Which bonds range from 150-400 kJ and are most biologically important

covalent

Biologically important noncovalent bonds are roughly

10 to 100 times weaker

noncovalent bonds being weaker allows

them to be continually broken and re-formed

interplay depends on

rapid exchanges of molecular partners

various noncovalent interactions are individually weak, but when many are present

their energies can sum to a total that is often several hundreds of kilojoules. This amount of energy is sufficient to provide stability to macromolecular structures

The variation in the dependence of bond energy on distance predicts that charge–charge interactions

are stronger over much longer distances than are van der Waals

interactions

All noncovalent interactions are _______ in nature;

electrostatic

The simplest electrostatic interactions are those between

a pair of charged particles, referred to as

ionic bonds

The attraction of the oppositely charged ions is

governed by ______. The law applies in a ________

Coulomb’s Law; vacuum

In a cell, charges are ____ in solution by the medium that exists between the charges

screened

The _______ of a medium is represented

by ε, the dielectric constant (water has a high

dielectric constant, 80) giving rise to the

equation:

screening effect

the vector sum, mu, represents

the net dipole moment

Benzene has neither a net charge nor a permanent dipole moment, but a nearby charge can induce a redistribution of electrons, producing an

induced dipole

Planar molecules like benzene have a strong tendency to stack because

fluctuations in the electron clouds of the stacked rings give rise to

mutually attractive induced dipoles (van der Waals interactions)

stacked benzene rings do not

Interpenetrate

At first the longer-range attraction dominates,

but then the repulsive energy increases so rapidly that it acts as a barrier

The repulsive energy barrier defines the distance of closest approach (rv) and

and the van der Waals radii