Physical Pharmacy I - Lecture Notes PDF

Physical Pharmacy I Lec. 1 States of Matter Introduction The importance of physical pharmacy: ✓Physical pharmacy integrates knowledge of mathematics, physics, and chemistry and applies them to the pharmaceutical dosage form What is physical deve...

Physical Pharmacy I Lec. 1 States of Matter Introduction The importance of physical pharmacy: ✓Physical pharmacy integrates knowledge of mathematics, physics, and chemistry and applies them to the pharmaceutical dosage form What is physical development. pharmacy and Why it is ✓It provides the important for usbasis physicochemical as for rational formulation, pharmacists? manufacturing, compounding, drug delivery, product selection, and product usage. ✓It focus on the theories behind the phenomena needed for dosage form design.  Binding Forces Between Molecules o Bonding forces are forces of attraction or repulsion which act between neighboring particles such as atoms, molecules, or ions. o For molecules to exist as aggregates in gases, liquids, and solids, intermolecular forces must exist. o Cohesion, or the attraction of like molecules, and Adhesive adhesion, or the attraction of unlike molecules, are manifestations of intermolecular forces.  Repulsive and Attractive Forces o When molecules interact, both repulsive and attractive forces are involved. o The opposite charge will initiate binding forces and bring them closer than similarly charged molecules. o The attractive forces are necessary for molecules to cohere while repulsive forces act to prevent the molecules from interpenetrating and destroying each other. o The repulsion is due to the interpenetration of the electronic clouds of molecules and increases exponentially with a decrease in the distance between molecules. ❑ Intramolecular forces: are the forces that hold atoms together within a molecule. Types: Ionic bonding. Covalent bonding. Metallic bonding. water Adhesive Ionic bond ( electrovalent bond) Covalent bond Metallic bond of sodium ❑ Intermolecular forces (secondary forces): are the forces that exist between molecules. o Intermolecular attractions are not nearly as strong as the intramolecular attractions that hold compounds together (covalent or ionic bonds). Types: Adhesive Van der Waals forces Ion-dipole and ion-induced dipole forces Cohesive Ion-ion interactions Hydrogen bonds 1. Van der Waals Forces o They are weak forces that involve the dispersion of charge across a molecule called a dipole. o The forces are due to the attractions between the partial positive and partial negative electrical charges between molecules. o They are nonionic interactions. o In general, the van der Waals forces arise from three different contributions: ‫توجيهي‬ ✓Orientation or Keesom interaction ‫اسحثاثي‬ ✓Induction or Debye interaction ‫تشتتي‬ ✓Dispersion or London interaction Dipole (An electric dipole is a separation of positive and negative charges).  London forces ( Dispersion Forces): o Occur between two nonpolar molecules (neutral) in which the molecules can induce the polarity on each other ( induce dipole – induce dipole). o For example, octane and methane are both nonpolar molecules, so they have only London dispersion forces. o The London dispersion force is the weakest intermolecular force.  Keesom forces: o Occur between polar molecules in which the permanent dipoles interact with one another (dipole–dipole interaction) because the charges are partial, the strength of bonding is much weaker. o An aqueous solution that contains electrolytes, does not have Keesom interaction. o Molecules that possess permanent dipoles include water, hydrochloric acid, alcohol, acetone, and phenol.  Debye forces: o Occur between a polar and nonpolar molecule in which the permanent dipole in the polar molecule induce an electrical dipole in the nonpolar one ( dipole- induce dipole). o These forces do not depend on temperature as much as that of Keesom forces. o An example of a Debye interaction would be forces between water molecules and those of oxygen.  2. Ionic Interactions /Ion-Ion Interactions o They are formed between two counter ions. o Ion–ion interactions can also be repulsive when two ions of like charge are brought closely together. o Ion–ion interactions may be intermolecular (e.g., a hydrochloride salt of a drug) or intramolecular (e.g., a salt-bridge interaction between counter ions in proteins). o It is important to keep in mind that ion–ion interactions are considerably stronger than many of the forces described in this section and can even be stronger than covalent bonding when an ionic bond is formed.  3. Ion-Dipole and Ion-Induced Dipole Forces o Attraction between polar or nonpolar molecules and ions. o This effect can clearly influence the solubility of a solute and may be important in the dissolution process. o In the polar molecule and ionic compound ( water and potassium chloride), ion-dipole forces exist between them. o These are the strongest intermolecular forces, generally. δ- O H H Na+Cl- δ+ δ+ Induced dipole Water molecule dipole  4. Hydrogen Bonding o Interaction between a molecule containing a hydrogen atom and a strongly electronegative atom such as fluorine, oxygen, or nitrogen. o Because of the small size of the hydrogen atom and its large electrostatic field, it can move in close to an electronegative atom and form an electrostatic type of union known as a hydrogen bond or hydrogen bridge. o It exists in ice and in liquid water and accounts for many of the unusual properties of water including its high dielectric constant, abnormally low vapor pressure, and high boiling point. o Hydrogen bonds can also exist between alcohol molecules, carboxylic acids, aldehydes, esters, and polypeptides. o The two polar molecules (ethanol and ammonia), have dipole-dipole forces, but more importantly, they are both capable of hydrogen bonding, which is stronger than ordinary dipole-dipole interactions. o while the other polar molecules (chloroform and acetone) cannot engage in hydrogen bonding, they have dipole-dipole interactions.  States of Matter Matter is anything that has mass and takes up space. Matter can be classified into different states such as crystalline solid, liquid, and gas (primary states or phases of matter ) on the basis of intermolecular forces and the arrangement of particles. Temperature and pressure are the two important factors determining whether a substance exists in a gaseous, liquid, or solid state.  ❑ Gaseous State o The molecular forces in the gaseous state are much weaker. Hence, due to possible random motion in all directions, gases have no bounding surface and fill completely any available space. o The gases thus have neither definite shape nor definite volume. o Hence, they exert a pressure—a force per unit area— expressed in dynes/cm2. o Pressure is also recorded in atmospheres or in millimeters of mercury. o Another important characteristic of a gas, its volume, is usually expressed in liters or cubic centimeters (1 cm3 = 1 mL). o The temperature involved in the gas equations is given according to the absolute or Kelvin scale ( 0°C is equal to 273.15 kelvins ).  The Ideal Gas Laws ✓ No intermolecular interactions exist and collisions are perfectly elastic, and thus no energy is exchanged upon collision. Boyle’s Law At constant temperature (absolute or kelvin) Gay-Lussac and Charles law EXAMPLE 2-1 The Effect of Pressure Changes on the Volume of an Ideal Gas In the assay of ethyl nitrite spirit, the nitric oXide gas that is liberated from a definite quantity of spirit and collected in a gas burette occupies a volume of 30.0 mL at a temperature of 20 °C and a pressure of 740 mm Hg. Assuming the gas is ideal, what is the volume at 0° C and 760 mm Hg?  P.V = R This equation is PV is always constant Or P.V = RT correct only for 1 T T mole of gas. While for n moles it becomes PV= nRT general ideal gas law EXAMPLE 2-2 Calculation of Volume Using the Ideal Gas Law What is the volume of 2 moles of an ideal gas at 25°C and 780 mm Hg? PV= nRT EXAMPLE 2-3 Molecular Weight Determination by the Ideal Gas Law If 0.30 g of ethyl alcohol in the vapor state occupies 200 mL at a pressure of 1 atm and a temperature of 100°C, what is the molecular weight of ethyl alcohol? Assume that the vapor behaves as an ideal gas. Kinetic Molecular Theory o Gas particles are far apart (at low P and high T). o No interaction between gas particles (at low P) but move with complete independence. o Gas particles move due to internal kinetic energy (continuous random motion ). o Gas particles have perfect elasticity.