Week 29 / Physical Stability- polymorphic forms

Question 1

Flashcard Front (Question):
What is the key structural feature of crystalline materials?

Answer 1

Flashcard Back (Answer):
Crystalline materials have atoms and molecules packed in a high degree of order, forming a regular, repeating lattice structure.

Question 2

Flashcard Front (Question):
How do crystalline materials behave when heated?

Flashcard Front (Question):
Give two examples of crystalline substances in pharmaceuticals.

Answer 2

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

Question 3

Flashcard Front (Question):
What are polymorphic forms?

Answer 3

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.

Question 4

Flashcard Front (Question):
What is the structural arrangement of atoms in amorphous materials?

Answer 4

Flashcard Back (Answer):
In amorphous materials, atoms and molecules are arranged in a random, disordered fashion, lacking long-range order.

Question 5

Flashcard Front (Question):
How do amorphous materials behave when heated?

Answer 5

Flashcard Back (Answer):
They soften gradually rather than melting sharply, eventually forming a highly viscous liquid.

Question 6

Flashcard Front (Question):
Give two examples of amorphous substances in pharmaceuticals.

Answer 6

Flashcard Back (Answer):

Glass

Spray-dried lactose monohydrate

Question 7

Flashcard Front (Question):
What is a unit cell in crystallography?

Answer 7

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.

Question 8

Flashcard Front (Question):
How is the crystallographic structure of a crystal defined?

Answer 8

Flashcard Back (Answer):
Crystallographic structure is defined by the periodic arrangement of atoms or molecules in three dimensions, forming a 3D lattice.

Question 9

Flashcard Front (Question):
Why is the unit cell important in describing crystallinity?

Answer 9

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.

Question 10

Flashcard Front (Question):
What determines the description of a unit cell?

Answer 10

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.

Question 11

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?

Answer 11

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

Question 12

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?

Answer 12

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.

Question 13

Flashcard Front (Question):
What is crystal habit?

Answer 13

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.

Question 14

Flashcard Front (Question):
Can two crystals with the same habit have the same combination of faces?

Answer 14

Flashcard Back (Answer):
No, two crystals with the same habit (e.g., orthorhombic) may have different combinations of faces.

Question 15

Flashcard Front (Question):
Can crystals with the same crystallographic forms have the same habit?

Answer 15

Flashcard Back (Answer):
No, crystals with the same combinations of crystallographic forms can still have different crystal habits.

Question 16

Flashcard Front (Question):
What are some common types of crystal habits?

Answer 16

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.

Question 17

Flashcard Front (Question):
How can crystal habit be modified?

Answer 17

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.

Question 18

Flashcard Front (Question):
What role do surfactants play in modifying crystal habit?

Answer 18

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.

Question 19

Flashcard Front (Question):
What is the effect of a cationic surfactant on crystal habit?

Answer 19

Flashcard Back (Answer):
A cationic surfactant results in the formation of thin, flaky plate-shaped crystals.

Question 19

Flashcard Front (Question):
What is the effect of an anionic surfactant on crystal habit?

Answer 19

Flashcard Back (Answer):
An anionic surfactant leads to the formation of thin, long needle-shaped crystals.

Question 20

lashcard Front (Question):
What is polymorphism in crystallography?

Answer 20

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.

Question 21

Flashcard Front (Question):
Do polymorphic forms affect the inner order or crystal shape?

Answer 21

Flashcard Back (Answer):
Polymorphic forms affect the inner order (the arrangement of molecules or atoms within the crystal), not the crystal shape.

Question 22

Flashcard Front (Question):
Can polymorphic forms have the same type of crystal lattice?

Answer 22

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.

Question 23

Flashcard Front (Question):
Why do different polymorphs have distinct properties?

Answer 23

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.

Question 24

Flashcard Front (Question): What are the thermodynamic differences between polymorphs?

Answer 24

Flashcard Back (Answer): Polymorphs have different thermodynamic stabilities and different free energies. The more stable polymorph has the lowest free energy.

Question 25

Flashcard Front (Question): How do polymorphs affect fundamental physical properties?

Answer 25

Flashcard Back (Answer): Polymorphs have different physical properties, such as: Melting point Vapor pressure Solubility

Question 26

Flashcard Front (Question): What is the impact of polymorphism on the manufacture of dosage forms?

Answer 26

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.

Question 27

Flashcard Front (Question): How does polymorphism affect the pharmacological activity of dosage forms?

Answer 27

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.

Question 28

Flashcard Front (Question): How does polymorphism affect drug bioavailability?

Answer 28

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.

Question 29

Flashcard Front (Question): How can polymorphic forms transition between each other?

Answer 29

Flashcard Back (Answer): Polymorphic forms can transition by heat or pressure.

Question 30

Flashcard Front (Question): What is an "enantropic transition"?

Answer 30

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.

Question 31

Flashcard Front (Question): What is a "monotropic transition"?

Answer 31

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.

Question 32

Flashcard Front (Question): What are the characteristics of a stable polymorphic form?

Answer 32

Flashcard Back (Answer): A stable polymorphic form has: Lowest free energy Highest melting point Usually, lowest solubility

Question 33

Flashcard Front (Question): How are polymorphic forms named?

Answer 33

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.

Question 34

Flashcard Front (Question): What is the stable and metastable polymorphic forms of testosterone?

Answer 34

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)

Question 35

Flashcard Front (Question): Why are metastable polymorphic forms preferred in drug delivery?

Answer 35

Flashcard Back (Answer): Metastable polymorphic forms are preferred because they typically have better solubility, faster dissolution, and higher bioavailability, improving the drug’s effectiveness.

Question 36

Flashcard Front (Question): What are crystal solvates?

Answer 36

Flashcard Back (Answer): Crystal solvates are crystals that contain solvent molecules as part of their crystallisation process.

Question 37

Flashcard Front (Question): What are crystal hydrates?

Answer 37

Flashcard Back (Answer): Crystal hydrates are a specific type of solvate, where water is the solvent involved in the crystallisation process.

Question 38

Flashcard Front (Question): What are anhydrates?

Answer 38

Flashcard Back (Answer): Anhydrates are crystals that have no water of crystallisation. They are the dry form of the crystal.

Question 39

Flashcard Front (Question): What is a polymorphic solvate?

Answer 39

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.

Question 40

Flashcard Front (Question): What is a pseudopolymorphic solvate?

Answer 40

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.

Question 41

Flashcard Front (Question): How do crystal hydrates and anhydrates differ in pharmaceutical properties?

Answer 41

Flashcard Back (Answer): Crystal hydrates and anhydrates have different solubility and melting points, leading to distinct pharmaceutical properties.

Question 42

Flashcard Front (Question): Are hydrates or anhydrates more soluble?

Answer 42

Flashcard Back (Answer): Hydrates are generally less soluble than anhydrates and are thermodynamically more stable.

Question 43

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?

Answer 43

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.