Assignment 1: Dissolution, Solubility, and Diffusion PDF

[Assignment 1 ] [Dissolution, solubility, and diffusion -- specific aims] 1\. Be able to define dissolution and to describe the two stages of dissolution of a solid in a liquid. Answer: Dissolution is the process of transferring molecules or ions from a solid state into a solution. The two stages...

[Assignment 1 ] [Dissolution, solubility, and diffusion -- specific aims] 1\. Be able to define dissolution and to describe the two stages of dissolution of a solid in a liquid. Answer: Dissolution is the process of transferring molecules or ions from a solid state into a solution. The two stages of dissolution from a solid into a liquid are: 1) the liberation of solute molecules from the solid phase to the liquid phase, and 2) the migration of solute molecules through the boundary layer surrounding the crystal to the bulk of the solution. 2\. Be able to define solubility and miscibility, and to describe the difference between saturated and unsaturated solutions. What is the most likely result of a solid that is added to a solution beyond its solubility limit? Answer: Solubility refers to the concentration of solute in a saturated solution at a specific temperature (and pressure). Miscibility describes liquids that can mix together in any proportion. A saturated solution contains a solute at the maximum limit of its solubility at any given temperature and pressure, while an unsaturated solution holds the dissolved solute at a concentration below what is required for complete saturation at a specific temperature. The most likely outcome of adding a solid to a solution beyond its solubility limit is a saturated solution. 3\. Be able to describe classification of solvents based on their intermolecular forces, and to provide major examples to polar, semipolar, and nonpolar solvents. Answer: Based on intermolecular forces, solvents are classified into three major categories: polar, semipolar, and nonpolar. Water is a polar solvent. Examples of semipolar solvents include glycerin, propylene glycol, methyl alcohol, ethyl alcohol, acetone, and aniline. Examples of nonpolar solvents include chloroform, ethyl ether, octyl alcohol, benzene, and carbon tetrachloride. 4\. Be able to define diffusion. Is diffusion a relatively fast or slow process? Be able to provide examples of processes in the pharmaceutical sciences that involve diffusion. Answer: The process through which a concentration is decreased by a spontaneous flow of matter. Diffusion is a relatively slow phenomenon. It is particularly relevant because drugs released from tablets, powders, granules, ointments, and suppository bases depend on diffusion to function effectively. 5\. Be able to explain regarding diffusion whether the passage of matter through a solid barrier can occur by simple molecular diffusion, by movement through solvent-filled pores, or both. Answer: Molecules can diffuse through both a solid barrier via simple molecular diffusion and through solvent-filled pores. 6\. Be able to explain regarding diffusion through a nonporous media whether it depends on the solubility of the permeating molecules in the bulk membrane, or not. Is the following statement: "The diffusion of a drug through a polymeric membrane involves dissolution of the drug in the matrix of the membrane" true or false? Answer: Molecular diffusion through nonporous media relies on the solubility of the permeating molecules within the bulk membrane. The assertion that "the diffusion of a drug through a polymeric membrane involves the dissolution of the drug in the matrix of the membrane" is a TRUE statement. 7\. Be able to explain regarding diffusion through solvent-filled pores whether it is mostly influenced by relative size of the penetrating molecules, diameter and shape of the pores, or both. Answer: Diffusion through pores filled with solvent is primarily influenced by the relative size of the penetrating molecules and the diameter and shape of the pores. 8\. Be able to describe regarding a membrane that has polymeric strands with branching and intersecting channels, whether the diffusing molecules (diffusants) pass through the tortuous pores formed by the overlapping strands of the polymer, or dissolve in the polymer matrix and pass through the film by simple diffusion? Answer: The diffusing molecules may pass through the complex pores created by the overlapping strands of the polymer and dissolve in the polymer matrix or pass through the film via simple diffusion. 9\. Be able to describe mechanisms of diffusion through biological membranes, including transcellular and paracellular diffusion and diffusion using membrane transporters. Answer: Transcellular diffusion happens through the lipoidal bilayer of cells, while paracellular diffusion takes place through the spaces between adjacent cells. Diffusion that utilizes a membrane transporter can involve both energy-dependent and energy-independent carrier-mediated transport. 10\. Be able to describe Fick's first law of diffusion and the factors that may influence flux according to this law. When will the diffusion stop? Why is there a negative sign in this equation? What are the main factors that affect the diffusion coefficient? Answer: Fick's law of diffusion is used to determine the flux ("J"), which represents the rate of diffusion through a unit area. The formula for Fick's law involves the negative diffusion coefficient ("D") multiplied by the concentration ("C") and divided by the distance of movement perpendicular to the surface of the barrier ("X"). Diffusion ceases when the concentration gradient no longer exists. The negative sign in this equation indicates that diffusion occurs in the direction of decreasing concentration of the diffusant. The primary factors influencing the diffusion coefficient include concentration, temperature, pressure, solvent properties, and the chemical nature of the diffusant. [Interfacial phenomena -- specific aims] 11\. Be able to describe to which dosage forms is interfacial phenomena relevant. Answer: Interfacial phenomena are relevant for powders, suspensions, emulsions, colloidal dispersions, and other semisolid dosage forms. 12\. Be able to describe interface, surface and the main difference between them. Can two gases form an interface? Is every surface an interface? Is every interface a surface? Answer: An interface is the boundary between two distinct (immiscible) phases within a system. The term surface refers to the outer boundary of a material. The primary difference between a surface and an interface is that a surface involves a single phase, whereas an interface involves two different phases. Two gases cannot create an interface; every surface is an interface, but not every interface qualifies as a surface. 13\. Be able to describe surface- and interfacial tension. Answer: Surface tension refers to the unequal attractive forces acting on molecules at the surface of the vapor compared to the molecular forces in the bulk of the liquid. Interfacial tension describes the attractive force between two liquids and is also pertinent to solid-liquid interfaces. Surface tension specifically applies to liquid-vapor and solid-vapor tensions. 14\. Be able to define surfactants, and describe their unique feature and their orientation at interfaces; what is the main action of surfactants? \[answer: reduce the interfacial tension by their presence in the interface\] Why is it important that the molecule has both a hydrophilic and a hydrophobic portion? Answer: Surfactants are molecules that are adsorbed at interfaces and orient themselves to reduce interfacial tension through their presence at the interface. A unique feature of surfactants is that they contain both hydrophilic and hydrophobic portions, which is essential because these properties enable the orientation of molecules at an interface. The primary function of surfactants is to decrease interfacial tension by being present at the interface. 15\. Be familiar with the characteristics of the (4) main classes of surfactants. In which dosage forms can anionic surfactants be used? Which type of surfactants can be used as disinfectants and preservatives? Are cationic surfactants compatible with anionic agents? Which group of compounds is the most important among cationic surfactants? Which types of surfactants are sodium lauryl sulfate and benzalkonium chloride? Answer: The four main classes of surfactants are anionic, cationic, non-ionic, and amphoteric. Anionic surfactants can be found in dosage forms such as carboxylate ions (like soaps), sulfonate ions, and sulfate ions. Cationic surfactants serve as disinfectants and preservatives but are incompatible with anionic surfactants. Among the cationic surfactants, quaternary ammonium compounds are particularly notable. For instance, sodium lauryl sulfate is an anionic surfactant, while benzalkonium chloride is a cationic surfactant. 16\. Be able to describe the main difference between the chemical compositions of tweens and spans, which of them is more hydrophilic and which is more hydrophobic? Are tweens and spans anionic, cationic, non-ionic or amphoteric surfactants? What are the advantages and disadvantages of non-ionic surfactants, and in particular of tweens? Answer: Tweens are more hydrophilic than spans. Both tweens and spans are non-ionic surfactants. The advantages of non-ionic surfactants, particularly tweens, include their reduced sensitivity to pH changes and electrolytes, enhanced compatibility with other materials, and low toxicity and irritancy. However, non-ionic surfactants, especially tweens, also have a few disadvantages. These can include an unpleasant taste and potential interactions with parabens, which form insoluble complexes. 17\. Be able to describe regarding surfactants, which type of surfactants is the most commonly used in pharmaceutical dosage forms, and which type of surfactants is the most appropriate for dosage forms used orally and through parenteral administration? Are amphoteric surfactants used in many products? Answer: Non-ionic surfactants are the most commonly used surfactants in pharmaceutical dosage forms and are the most suitable type for oral and parenteral formulations. Amphoteric surfactants are not commonly found in many products.