Medicine formulations 1 Wk4

What is the primary difference between intermolecular and intramolecular forces?

Intermolecular forces are between molecules (no covalency), while intramolecular forces are within molecules (covalency is established).

List the types of intramolecular forces.

Ionic bonds, covalent bonds, and metallic bonds.

Why are intermolecular forces relevant to medicine?

They are responsible for the coherence of matter (gas, liquid, and solid), interfacial phenomena, stability of disperse systems, powder compaction, drug action in vivo, etc.

Describe the nature of repulsive forces between molecules.

Electrostatic repulsion increases exponentially as separation decreases. When electron clouds touch, they repel.

What happens at the equilibrium distance (re) between molecules?

Attractive and repulsive forces are equal, creating a stable state.

List the types of intermolecular forces.

Van der Waals forces and hydrogen bonding.

What are the subtypes of Van der Waals forces?

Dipole-dipole interactions (Keesom forces), dipole-induced dipole interactions (Debye forces), and induced dipole-induced dipole interactions (London forces).

Describe Keesom forces.

These are dipole-dipole interactions resulting from electronegativity imbalances in molecules.

What is hydrogen bonding?

The interaction between a molecule containing a hydrogen atom and a strongly electronegative atom such as fluorine, oxygen, or nitrogen. It is a special type of dipole-dipole force.

Describe London dispersion forces.

They occur between two apolar molecules, inducing temporary dipoles as they approach each other.

How do gases differ from solids and liquids in terms of molecular forces?

Gases have the weakest intermolecular forces.

State the ideal gas law.

P = (nRT)/V, where P is pressure, n is the number of moles, R is the ideal gas constant, T is temperature, and V is volume.

What assumptions are made in the "ideal" gas law?

There is no interaction between gas molecules, and gas molecules bounce off one another as perfectly elastic small balls.

How does temperature affect the kinetic energy and velocity of gas molecules?

The kinetic energy and the velocity of the molecules increase with temperature.

What happens when pressure is applied to a gas?

The molecules are brought within the sphere of the van der Waals interaction forces and pass into the liquid state.

Describe the dynamic equilibrium of vapor pressure.

At a constant temperature, molecules with the highest energies break away from the surface of the liquid and pass into the gaseous state (evaporate), and some molecules return to the liquid state (condense). When the rate of condensation equals the rate of vaporization, a dynamic equilibrium is established.

What is boiling point?

The temperature at which the vapor pressure of the liquid equals the external or atmospheric pressure.

What is an aerosol?

A suspension of small particles of solid or liquid in a gas.

Describe freeze-drying (lyophilization).

A process where a drug suspended in water is frozen and then dried by a sublimation process.

List the basic properties of solids.

Solids keep their original shape, have molecules/atoms/ions in close proximity, exhibit strong molecular forces, and are practically incompressible.

What is latent heat of fusion?

The energy required to change a substance from the solid to the liquid state without a change in temperature.

List the types of solids.

Crystalline, amorphous, and polycrystals (mixture of both).

Describe crystalline solids.

Arranged in highly ordered microscopic structures (lattices) and show definite melting points.

Describe amorphous solids.

Arranged in a random manner, with no repeating long-range order, and have a melting range (no definitive MP).

Describe crystallization.

A process where crystals are produced by inducing a change from the liquid state to the solid state.

What are the methods of crystallization?

Cooling molten material, adding a salt, adding a non-solvent, and evaporation.

What is polymorphism?

A substance exists in more than one crystalline form.

What are hydrates and solvates?

Crystalline forms containing either water or solvent, respectively.

How does polymorphism affect solubility?

Different polymorphs have different energy states and therefore, different solubilities.

What is a "metastable" polymorph?

A crystalline form that is thermodynamically unstable relative to other polymorphs of the same compound at a given temperature and pressure. It will eventually convert to the more stable form.

Why are metastable forms sometimes used in formulations?

Because they generally have higher solubility than stable forms, which can lead to better bioavailability.

What is a "monotropic" system in polymorphism?

A system where only ONE polymorph is stable at ALL temperatures below the melting point. All other forms are metastable.

n a monotropic system, which polymorph has the highest melting point?

The stable form.

In a monotropic system, which polymorph has the lowest melting point?

The polymorph that is least stable.

What is the key difference between a monotropic and an enantiotropic system?

Monotropic systems have only one stable form at all temperatures below the melting point, while enantiotropic systems have a transition temperature where the stability of two polymorphs inverts.

How can polymorphism affect a drug's properties?

It can affect a drug's solubility, dissolution rate, stability, and bioavailability.

What is an "enantiotropic" system?

A system where one polymorph is stable at one temperature, and another polymorph is stable at a different temperature. There is a transition temperature at which the two forms are in equilibrium.

Define "pseudopolymorphism."

When the crystal lattice contains solvent molecules, it is referred to as pseudopolymorphism (e.g., hydrates and solvates).

What is a "hydrate"?

A crystalline solid containing water molecules in its crystal lattice.

What is a "solvate"?

A crystalline solid containing solvent molecules (other than water) in its crystal lattice.