The Molecular Butterfly Effect: Intermolecular Forces and Drug Stability

Vocabulary flashcards covering intermolecular forces, solid-state architecture, polymorphism, and clinical case studies involving drug stability and solubility.

Intermolecular Forces

The forces of attraction and repulsion between molecules that dictate the state of matter (gas, liquid, or solid) and pharmaceutical properties like solubility and stability.

Van der Waals Forces

Weak intermolecular modulators existing between all molecules with an energy range of $0.5-10\,kcal/mole$, including Keesom, Debye, and London forces.

Keesom Forces

Dipole-Dipole interactions between permanent dipoles; categorized as the strongest of the Van der Waals forces.

Debye Forces

Dipole-Induced Dipole interactions where a permanent dipole induces a dipole in a neutral molecule.

London Forces

Dispersion forces occurring between induced dipoles caused by random electron shifts; they are the weakest Van der Waals forces.

Ion-Dipole Forces

Attractive forces that account for the aqueous solubility of ionic crystalline substances.

Covalent Bonds

Intramolecular bonds with a baseline energy of $50-100\,kcal/mole$.

Ionic Bonds

Intramolecular bonds with a baseline energy of $100-1000\,kcal/mole$.

Cohesion

Attractive intermolecular forces between like molecules.

Adhesion

Attractive intermolecular forces between different molecules.

Crystalline Solids

Solids characterized by long-range order and a highly structured crystal lattice, resulting in lower solubility/bioavailability but higher stability.

Amorphous Solids

Solids with random, chaotic molecular arrangements and no long-range order, leading to higher solubility and bioavailability but lower stability.

Sharp Melting Point

A characteristic of crystalline solids where all bonds break simultaneously at a specific energy threshold due to uniform lattice environments.

Broad Melting Range

A characteristic of amorphous solids where varied bond strengths result in connections breaking at different temperatures as heat is applied.

Polymorphism

A phenomenon where a single chemical entity exists in more than one crystalline form, possessing identical chemistry but different physical properties.

The Golden Rule of Polymorphism

The principle stating that the most thermodynamically stable polymorph is inherently the least water-soluble.

Ritonavir Form I

The originally approved monoclinic crystalline form of the HIV medication that relied on specific intermolecular packing for solubility.

Ritonavir Form II

A spontaneous orthorhombic polymorph that is thermodynamically more stable but severely less water-soluble, leading to product dissolution failure.

Molecular Hinge

The short-chain alkane in Abilify that provides conformational flexibility, allowing the molecule to lock into various crystalline lattices.

Seesaw Principle

The inverse relationship between thermodynamic stability (melting point) and aqueous solubility, observed among polymorphs like those of Abilify.

PEG (Polyethylene Glycol)

A polymeric structure used in products like MiraLAX where chain length and specific intermolecular forces bind water in the gut to act as an osmotic laxative.