Integrated Pharmacotherapy I: Acid-Base, pH, Ionization, Solubility & Partitioning Vocabulary

Vocabulary flashcards covering fundamental physical pharmacy and pharmacotherapy concepts including acid-base equilibria, pH, ionization constants, intermolecular forces, solubility parameters, and partition coefficients.

Non-electrolyte

A compound that does not dissociate into charged species when dissolved in water, remaining instead as neutral, uncharged molecules (e.g., ethanol).

Electrolyte

A compound that dissociates into charged species when added to water and therefore conducts electricity.

Strong Electrolyte

A compound that dissociates completely into charged species in water, including salts, strong acids, and strong bases.

Weak Electrolyte

A compound (either a weak acid or weak base) that only partially dissociates into charged molecules in solution.

Lewis Base

An atom or molecule that donates a lone pair of electrons (commonly referred to as a nucleophile in organic chemistry).

Lewis Acid

An atom or molecule that can accept a lone pair of electrons (commonly referred to as an electrophile in organic chemistry).

Bronstead - Lowry Acid

Any chemical species capable of donating a proton ($H^+$).

Bronstead - Lowry Base

Any chemical species capable of accepting a proton ($H^+$), typically by donating a lone pair of electrons from atoms such as oxygen, nitrogen, or sulfur.

Conjugate Acid

A species that possesses the exact same molecular structure as its conjugate base, but has one additional proton.

Conjugate Base

A species that possesses the exact same molecular structure as its conjugate acid, but has one less proton.

Amphoteric

The property of a substance or molecule (such as water) that enables it to act as both an acid and a base.

Equilibrium Constant ($K$)

The ratio of the concentration of products to the concentration of reactants at the point of chemical equilibrium.

Autoionization Constant of Water ($K_w$)

An equilibrium constant equal to $1.0 \times 10^{-14}$ at 25\,\text{^\circ C}, representing the product of proton and hydroxide ion concentrations ($[H^+][OH^-]$) with bulk solvent concentration built into it.

pH

A logarithmic measurement of proton concentration defined mathematically as $pH = -\log([H^+])$, where every 1-point change corresponds to a 10-fold change in proton concentration.

pKa

Mathematically defined as $pKa = -\log(K_a)$, and functionally defined as the $pH$ at which an aqueous solution yields an exactly equal mixture of conjugate acid and conjugate base.

Acid Dissociation Constant ($K_a$)

The equilibrium constant describing the dissociation of a specific conjugate acid-base pair in water, expressed as $K_a = \frac{[H^+][CB]}{[CA]}$.

Zwitterion

A molecule that contains both a positively charged and a negatively charged functional group simultaneously (e.g., phenylalanine).

Isoelectric Point ($pI$)

The $pH$ that yields the zwitterion as the predominant species in solution, calculated for a simple zwitterion as $pI = \frac{pKa_1 + pKa_2}{2}$.

Intrinsic Solubility ($S_0$)

The concentration of an uncharged solute in a saturated solution at a specific temperature.

Total Solubility ($S_t$)

The observed solubility of an ionizable drug, combining the intrinsic solubility of the uncharged species and the equilibrium concentration of the ionized species.

Partition Coefficient ($P$)

The ratio of a drug's solubility in n-octanol to its solubility in water ($P = \frac{C_{\text{octanol}}}{C_{\text{water}}}$), defined specifically for the unionized form of the molecule.

log P

The logarithm of the partition coefficient; values below 1 represent excessive hydrophilicity that limits membrane diffusion, while values above 3.5 indicate excessive lipophilicity that limits aqueous solubility.

Apparent Partition Coefficient ($P_{\text{app}}$)

The effective partition ratio for weak electrolytes defined as $P_{\text{app}} = \frac{C_o}{(C_u + C_i)_w}$, accounting for both unionized and ionized forms in the aqueous phase.

Ion-Ion Interaction

The strongest non-covalent intermolecular attractive force, occurring between an anion with a full formal negative charge and a cation with a full formal positive charge.

Ion-Dipole Interaction

A non-covalent electrostatic attraction between a full formal ionic charge and the partial opposite charge of a polar molecular dipole.

Dipole-Dipole Interaction

An electrostatic attraction occurring between the positive and negative ends of polar bonds in adjacent molecules.

Hydrogen Bond

A strong form of dipole-dipole interaction occurring when a lone pair on an oxygen or nitrogen atom interacts with a proton bound to another oxygen or nitrogen atom.

van der Waals Interactions

Transient, short-lived weak attractive forces created when spontaneous electron redistributions in a non-polar molecule induce dipoles in neighboring non-polar molecules.