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Surface tension is the force per unit length that must be applied perpendicular to the surface to counterbalance the net inward pull.
Surface tension is the force per unit length that must be applied perpendicular to the surface to counterbalance the net inward pull.
False
Interfacial tension is generally stronger than surface tension due to the adhesive forces between two liquid phases.
Interfacial tension is generally stronger than surface tension due to the adhesive forces between two liquid phases.
False
Mercury has a surface tension of 476 dynes/cm.
Mercury has a surface tension of 476 dynes/cm.
True
Surface free energy increases when the surface of the liquid decreases.
Surface free energy increases when the surface of the liquid decreases.
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The capillary rise method is one technique for measuring surface and interfacial tension.
The capillary rise method is one technique for measuring surface and interfacial tension.
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Interfacial tensions are measured in dynes/m but surface tensions are measured in dynes/cm.
Interfacial tensions are measured in dynes/m but surface tensions are measured in dynes/cm.
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The choice of method for measuring tensions solely depends on the size of the sample available.
The choice of method for measuring tensions solely depends on the size of the sample available.
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In the bulk of the liquid, each molecule is pulled equally in all directions by neighboring liquid molecules, resulting in a net force of zero.
In the bulk of the liquid, each molecule is pulled equally in all directions by neighboring liquid molecules, resulting in a net force of zero.
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Micellar solubilization occurs below the CMC.
Micellar solubilization occurs below the CMC.
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The maximum additive concentration of a solubilizate (MAC) is defined as the concentration of a solubilizate that can be incorporated at a fixed surfactant concentration below the CMC.
The maximum additive concentration of a solubilizate (MAC) is defined as the concentration of a solubilizate that can be incorporated at a fixed surfactant concentration below the CMC.
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As the number of micelles increases, the extent of solubilization decreases.
As the number of micelles increases, the extent of solubilization decreases.
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Smaller molecules tend to have worse absorption and distribution.
Smaller molecules tend to have worse absorption and distribution.
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Particle size reduction of poorly soluble drugs decreases surface area, leading to decreased dissolution rate and absorption.
Particle size reduction of poorly soluble drugs decreases surface area, leading to decreased dissolution rate and absorption.
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Hydrophobic substances that need increased solubility are known as solubilizates.
Hydrophobic substances that need increased solubility are known as solubilizates.
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Solubility is unaffected by the pH of the environment.
Solubility is unaffected by the pH of the environment.
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The turbidity of a solution indicates that the maximum additive concentration (MAC) has been exceeded.
The turbidity of a solution indicates that the maximum additive concentration (MAC) has been exceeded.
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Iodine's solubility in water cannot be increased by using surfactants like tween.
Iodine's solubility in water cannot be increased by using surfactants like tween.
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The partition coefficient (o/w) indicates a drug's ability to penetrate biological membranes.
The partition coefficient (o/w) indicates a drug's ability to penetrate biological membranes.
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The unionized form of a drug has a lower partition coefficient than the ionized form.
The unionized form of a drug has a lower partition coefficient than the ionized form.
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The solubilizing agent in micellar solubilization is the hydrophobic substance.
The solubilizing agent in micellar solubilization is the hydrophobic substance.
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Cresol and chlorocresol can have their solubility increased in water by using triethanolamine oleate.
Cresol and chlorocresol can have their solubility increased in water by using triethanolamine oleate.
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Dissolution rate is not important for drug absorption.
Dissolution rate is not important for drug absorption.
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The molecular weight of a drug influences its pharmacokinetics in terms of absorption, distribution, metabolism, and excretion.
The molecular weight of a drug influences its pharmacokinetics in terms of absorption, distribution, metabolism, and excretion.
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Very fine powders can lead to stability issues such as wetting or agglomeration problems due to increased air adsorption.
Very fine powders can lead to stability issues such as wetting or agglomeration problems due to increased air adsorption.
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In the equation log x/m = log k + 1/n log P, the variable x represents the mass of the adsorbent.
In the equation log x/m = log k + 1/n log P, the variable x represents the mass of the adsorbent.
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The Freundlich isotherm can be validated by plotting log x/m on the x-axis and log P on the y-axis.
The Freundlich isotherm can be validated by plotting log x/m on the x-axis and log P on the y-axis.
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The slope of the linear plot obtained from the Freundlich isotherm gives the value of 1/n.
The slope of the linear plot obtained from the Freundlich isotherm gives the value of 1/n.
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The Langmuir adsorption isotherm represents the relationship between the amount of adsorbate adsorbed and the unabsorbed adsorbate concentration at variable temperatures.
The Langmuir adsorption isotherm represents the relationship between the amount of adsorbate adsorbed and the unabsorbed adsorbate concentration at variable temperatures.
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At higher pressures, the experimental isotherms always approach saturation.
At higher pressures, the experimental isotherms always approach saturation.
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The factor 1/n in the adsorption equation can take values greater than 1.
The factor 1/n in the adsorption equation can take values greater than 1.
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The relationship described by the adsorption isotherm shows that physical adsorption decreases with an increase in pressure at fixed temperatures.
The relationship described by the adsorption isotherm shows that physical adsorption decreases with an increase in pressure at fixed temperatures.
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When 1/n = 0, the adsorption is independent of pressure.
When 1/n = 0, the adsorption is independent of pressure.
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Different polymorphs of a drug can exhibit different solubilities.
Different polymorphs of a drug can exhibit different solubilities.
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Only one polymorphic form of a drug is therapeutically active.
Only one polymorphic form of a drug is therapeutically active.
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Polymorphs with higher solubility are always less stable compared to those with lower solubility.
Polymorphs with higher solubility are always less stable compared to those with lower solubility.
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Crystal hydrates are crystals that contain a solvent of crystallization, specifically water.
Crystal hydrates are crystals that contain a solvent of crystallization, specifically water.
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Anhydrous forms of crystals generally have a slower dissolution rate than their hydrated counterparts.
Anhydrous forms of crystals generally have a slower dissolution rate than their hydrated counterparts.
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Different polymorphs can affect the shelf life of a drug due to variations in physical properties.
Different polymorphs can affect the shelf life of a drug due to variations in physical properties.
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Solvated forms of a drug will always have the same bioavailability as their anhydrous form.
Solvated forms of a drug will always have the same bioavailability as their anhydrous form.
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Polymorphs of a drug may have different degradation rates that can impact potency.
Polymorphs of a drug may have different degradation rates that can impact potency.
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Study Notes
Physicochemical Properties of Drugs
- Understanding physicochemical properties is essential for drug formulation, development, optimization of delivery systems, and predicting drug behavior in the body.
Molecular Weight
- Molecular weight influences pharmacokinetics, including absorption, distribution, metabolism, and excretion.
- Smaller molecules generally exhibit improved absorption and distribution.
Particle Size and Surface Area
- Reducing particle size of poorly soluble drugs enhances dissolution rate and absorption by increasing surface area.
- Inhalation aerosols are optimally absorbed when particle size is between 1-6 µm.
- Very fine powders can lead to stability issues such as air adsorption and wetting problems.
- Size reduction may alter crystallinity, potentially impacting chemical stability.
Solubility
- Solubility is the capacity of a drug to dissolve in a solvent, crucial for absorption, distribution, and bioavailability.
- Poor aqueous solubility results in incomplete absorption.
- Weak acidic or basic drugs have pH-dependent solubility; enhancing solubility can be achieved through:
- Size reduction
- Formation of complexes
- Use of solubilizing excipients, like surface-active agents.
Partition Coefficient (o/w)
- The partition coefficient indicates a drug's distribution between oil and water phases.
- Higher lipid solubility correlates with greater membrane permeability.
Ionization Constant (pKa)
- Influences the degree of ionization at various pH levels, impacting solubility, permeability, and receptor binding.
- Unionized forms of drugs generally have higher lipid solubility and absorption compared to ionized forms.
Surface and Interfacial Tensions
- Surface tension is the inward force on molecules at a liquid's surface, measured in dynes/cm or N/m.
- Interfacial tension describes forces at interfaces between two immiscible phases, typically lower than surface tension.
Surface Free Energy
- Surface molecules possess additional energy compared to bulk molecules.
- Increasing the liquid surface (e.g., fine sprays) raises the surface free energy.
Measurement of Tensions
- Commonly used methods include:
- Capillary rise method
- Ring method
- Drop weight method
- Drop count method
- Selection depends on tensions to be measured and desired accuracy.
Micellar Solubilization
- Micelles enhance solubility of hydrophobic materials in dispersion media.
- The process is effective above the critical micelle concentration (CMC).
- Increased micelle concentration correlates with enhanced solubilization of the solubilizate.
Maximum Additive Concentration (MAC)
- Definition: Maximum concentration of solubilizate that can be integrated into a solubilization system at fixed surfactant concentration beyond CMC.
- Determined by adding increasing solubilizate concentrations until turbidity appears.
Adsorption Isotherm
- Describes the relationship between the mass of gas adsorbed and pressure, expressed as log x/m = log k + 1/n log P.
- At fixed pressures, physical adsorption generally decreases with temperature and approaches saturation at high pressures.
Freundlich and Langmuir Isotherms
- Freundlich isotherm can be valid if plotting log x/m against log P yields a straight line.
- Langmuir isotherm represents adsorption relationship at constant temperature with varying initial concentrations.
Significance of Polymorphism
- Different polymorphs show varying solubilities and therapeutic effects on bioavailability.
- Polymorph stability (both chemical and physical):
- Chemical stability varies with solubility and degradation rates.
- Physical stability influences melting point, density, hardness, and moisture absorption.
Solvation
- Solvation involves crystalline solids trapping solvents during crystallization, forming solvates or hydrates.
- Solvated forms generally exhibit varied solubility and dissolution rates compared to anhydrous forms.
- Anhydrates typically dissolve faster than their hydrated counterparts.
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Description
This quiz examines the physicochemical properties that are crucial in drug formulation and delivery. It covers key concepts such as molecular weight, particle size, surface area, and solubility, emphasizing their impact on drug behavior in the body. Understand how these factors influence absorption, distribution, metabolism, and excretion of drugs.
