Week 29 / Physical Stability- polymorphic forms Flashcards
Flashcard Front (Question):
What is the key structural feature of crystalline materials?
Flashcard Back (Answer):
Crystalline materials have atoms and molecules packed in a high degree of order, forming a regular, repeating lattice structure.
Flashcard Front (Question):
How do crystalline materials behave when heated?
Flashcard Front (Question):
Give two examples of crystalline substances in pharmaceuticals.
Flashcard Back (Answer):
Crystals exhibit a sharp transition from the solid to liquid state (melting point) at a specific temperature.
Flashcard Back (Answer):
Sodium chloride
Ibuprofen
Flashcard Front (Question):
What are polymorphic forms?
Flashcard Back (Answer):
Polymorphic forms are different crystalline forms of the same substance, with different arrangements of molecules in the solid state.
They can vary in melting point, solubility, and stability.
Flashcard Front (Question):
What is the structural arrangement of atoms in amorphous materials?
Flashcard Back (Answer):
In amorphous materials, atoms and molecules are arranged in a random, disordered fashion, lacking long-range order.
Flashcard Front (Question):
How do amorphous materials behave when heated?
Flashcard Back (Answer):
They soften gradually rather than melting sharply, eventually forming a highly viscous liquid.
Flashcard Front (Question):
Give two examples of amorphous substances in pharmaceuticals.
Flashcard Back (Answer):
Glass
Spray-dried lactose monohydrate
Flashcard Front (Question):
What is a unit cell in crystallography?
Flashcard Back (Answer):
A unit cell is the smallest repeating building block of a crystal lattice.
It defines the geometric structure of the crystal and repeats in three dimensions to form the full crystal.
Flashcard Front (Question):
How is the crystallographic structure of a crystal defined?
Flashcard Back (Answer):
Crystallographic structure is defined by the periodic arrangement of atoms or molecules in three dimensions, forming a 3D lattice.
Flashcard Front (Question):
Why is the unit cell important in describing crystallinity?
Flashcard Back (Answer):
Because it captures the essential geometry and symmetry of the crystal, allowing scientists to understand and predict the overall structure and properties of the material.
Flashcard Front (Question):
What determines the description of a unit cell?
Flashcard Back (Answer):
The geometry of the unit cell—its shape, angles, and dimensions—determines how it is described and how it repeats in space.
Flashcard Front (Question):
How is the unit cell described geometrically?
Flashcard Front (Question):
What do a, b, and c represent in the context of a unit cell?
Flashcard Front (Question):
What do α, β, and γ represent in the unit cell description?
Flashcard Back (Answer):
The unit cell is described by:
Three dimensions: the lengths of the axes (a, b, c)
Three angles: the angles between these axes (α, β, γ)
Flashcard Back (Answer):
a, b, and c represent the lengths of the axes of the unit cell.
Flashcard Back (Answer):
α, β, and γ represent the angles between the axes:
α is the angle between b and c
β is the angle between a and c
γ is the angle between a and b
Flashcard Front (Question):
How are crystal systems classified?
Flashcard Front (Question):
What are the seven basic crystal systems?
Flashcard Front (Question):
What are Bravais lattices in advanced crystallography?
Flashcard Front (Question):
How do the Bravais lattices differ from the basic crystal systems?
Flashcard Back (Answer):
Crystal systems are classified into seven basic crystal systems, based on their geometric description. These systems describe all possible degrees of atomic order with atoms at each corner of the unit cell.
Flashcard Back (Answer):
The seven basic crystal systems are:
Cubic
Tetragonal
Orthorhombic
Hexagonal
Rhombohedral (Trigonal)
Monoclinic
Triclinic
Flashcard Back (Answer):
Advanced crystallography classifies crystal systems into fourteen Bravais lattices, which consider the possibility of atoms inside the unit cell, or at edges or faces of the unit cell.
Flashcard Back (Answer):
The Bravais lattices take into account additional symmetry elements, such as the presence of atoms at centers of faces, edges, or within the unit cell, extending the basic seven systems to fourteen possible lattices.
Flashcard Front (Question):
What is crystal habit?
Flashcard Back (Answer):
Crystal habit describes the overall shape of a crystal, which results from different rates of growth in each dimension of the crystal.
Flashcard Front (Question):
Can two crystals with the same habit have the same combination of faces?
Flashcard Back (Answer):
No, two crystals with the same habit (e.g., orthorhombic) may have different combinations of faces.
Flashcard Front (Question):
Can crystals with the same crystallographic forms have the same habit?
Flashcard Back (Answer):
No, crystals with the same combinations of crystallographic forms can still have different crystal habits.
Flashcard Front (Question):
What are some common types of crystal habits?
Flashcard Back (Answer):
Prismatic: Crystals form elongated, prism-like shapes.
Isometric: Crystals have equal-length axes and symmetrical forms.
Tabular: Crystals form thin, flat shapes, like tablets.
Flashcard Front (Question):
How can crystal habit be modified?
Flashcard Back (Answer):
Crystal habit can be modified by adding impurities to the crystallisation solution. These impurities can alter the growth patterns of the crystal.
Flashcard Front (Question):
What role do surfactants play in modifying crystal habit?
Flashcard Back (Answer):
Surfactants can adsorb onto crystal faces during crystal growth, altering the rate of growth along different axes, thus changing the crystal habit.
Flashcard Front (Question):
What is the effect of a cationic surfactant on crystal habit?
Flashcard Back (Answer):
A cationic surfactant results in the formation of thin, flaky plate-shaped crystals.
Flashcard Front (Question):
What is the effect of an anionic surfactant on crystal habit?
Flashcard Back (Answer):
An anionic surfactant leads to the formation of thin, long needle-shaped crystals.
lashcard Front (Question):
What is polymorphism in crystallography?
Flashcard Back (Answer):
Polymorphism occurs when a substance can form multiple crystal forms with different arrangements of molecules or atoms, while maintaining the same crystal shape.
Flashcard Front (Question):
Do polymorphic forms affect the inner order or crystal shape?
Flashcard Back (Answer):
Polymorphic forms affect the inner order (the arrangement of molecules or atoms within the crystal), not the crystal shape.
Flashcard Front (Question):
Can polymorphic forms have the same type of crystal lattice?
Flashcard Back (Answer):
Yes, polymorphic forms can have the same type of crystal lattice (e.g., triclinic), but with different proportions of axes and angles.
Flashcard Front (Question):
Why do different polymorphs have distinct properties?
Flashcard Back (Answer):
Different polymorphs have different internal arrangements of molecules, which results in varying forces of attraction between the molecules. This leads to different physical and chemical properties, such as melting point, solubility, and stability.
Flashcard Front (Question):
What are the thermodynamic differences between polymorphs?
Flashcard Back (Answer):
Polymorphs have different thermodynamic stabilities and different free energies. The more stable polymorph has the lowest free energy.
Flashcard Front (Question):
How do polymorphs affect fundamental physical properties?
Flashcard Back (Answer):
Polymorphs have different physical properties, such as:
Melting point
Vapor pressure
Solubility
Flashcard Front (Question):
What is the impact of polymorphism on the manufacture of dosage forms?
Flashcard Back (Answer):
Polymorphism can affect the manufacture of dosage forms, as different polymorphs may have different flow properties, compaction characteristics, and dissolution rates, which can influence the production process.
Flashcard Front (Question):
How does polymorphism affect the pharmacological activity of dosage forms?
Flashcard Back (Answer):
Polymorphism can impact the pharmacological activity of a drug, as different polymorphs may have different rates of dissolution, leading to varying drug absorption and efficacy.
Flashcard Front (Question):
How does polymorphism affect drug bioavailability?
Flashcard Back (Answer):
Polymorphism can significantly influence drug bioavailability, as the solubility and dissolution rate of different polymorphs can affect how quickly and effectively the drug is absorbed into the body.
Flashcard Front (Question):
How can polymorphic forms transition between each other?
Flashcard Back (Answer):
Polymorphic forms can transition by heat or pressure.
Flashcard Front (Question):
What is an “enantropic transition”?
Flashcard Back (Answer):
An enantropic transition is the transition between all polymorphic forms of a substance, meaning the substance can switch between different forms in either direction.
Flashcard Front (Question):
What is a “monotropic transition”?
Flashcard Back (Answer):
A monotropic transition is the transition from one form to another where the transition is irreversible—the metastable form transitions to a stable form, and the reverse transition does not occur.
Flashcard Front (Question):
What are the characteristics of a stable polymorphic form?
Flashcard Back (Answer):
A stable polymorphic form has:
Lowest free energy
Highest melting point
Usually, lowest solubility
Flashcard Front (Question):
How are polymorphic forms named?
Flashcard Back (Answer):
Polymorphic forms are named using Roman numerals (I, II, III, etc.), in order of their melting point, with form I being the most stable.
Flashcard Front (Question):
What is the stable and metastable polymorphic forms of testosterone?
Flashcard Back (Answer):
Polymorphic form I: Stable form (MP = 155°C)
Polymorphic forms II-IV: Metastable forms (MP = 148°C, 144°C, and 143°C, respectively)
Flashcard Front (Question):
Why are metastable polymorphic forms preferred in drug delivery?
Flashcard Back (Answer):
Metastable polymorphic forms are preferred because they typically have better solubility, faster dissolution, and higher bioavailability, improving the drug’s effectiveness.
Flashcard Front (Question):
What are crystal solvates?
Flashcard Back (Answer):
Crystal solvates are crystals that contain solvent molecules as part of their crystallisation process.
Flashcard Front (Question):
What are crystal hydrates?
Flashcard Back (Answer):
Crystal hydrates are a specific type of solvate, where water is the solvent involved in the crystallisation process.
Flashcard Front (Question):
What are anhydrates?
Flashcard Back (Answer):
Anhydrates are crystals that have no water of crystallisation. They are the dry form of the crystal.
Flashcard Front (Question):
What is a polymorphic solvate?
Flashcard Back (Answer):
A polymorphic solvate is when a solvent interacts with the crystal structure (through bonding). If the crystal loses the solvent, a new crystal form will be created.
Flashcard Front (Question):
What is a pseudopolymorphic solvate?
Flashcard Back (Answer):
A pseudopolymorphic solvate is when no bonding interaction exists between the solvent and the crystal. When the crystal loses the solvent, the crystal lattice remains intact.
Flashcard Front (Question):
How do crystal hydrates and anhydrates differ in pharmaceutical properties?
Flashcard Back (Answer):
Crystal hydrates and anhydrates have different solubility and melting points, leading to distinct pharmaceutical properties.
Flashcard Front (Question):
Are hydrates or anhydrates more soluble?
Flashcard Back (Answer):
Hydrates are generally less soluble than anhydrates and are thermodynamically more stable.
Flashcard Front (Question):
What are point defects in crystals?
Flashcard Front (Question):
What can cause point defects in crystals?
Flashcard Front (Question):
How do point defects affect the crystal?
Flashcard Back (Answer):
Point defects are missing atoms or irregularities at specific points in the crystal lattice.
Flashcard Back (Answer):
Point defects can be caused by:
Impurities replacing the original atom in the lattice.
Flashcard Back (Answer):
Point defects can influence the physical properties of the crystals, such as their strength, conductivity, and dissolution rate.
