Polymorphic Forms Flashcards
List a key property of polymorphic forms
- atoms are packed in a high degree order
-
List a key property of amorphous forms
- atoms are arranged in a random order
Give an example of a polymorph
sodium chloride
Give an example of an amorphous material
glass
What can the crystallographic structure be described as?
3D lattice, in which the unit cell is the repeating unit
What is the unit cell?
The building block of the crystal described by 3 dimensions
What are the dimensions and angles describing a unit cell?
lengths of axes and angles
lengths - a, b, c
angles - α, β, γ
How many basic crystal systems are there?
7 unit cells
How many advanced crystallographic systems are there?
14 unit cells
What do Bravais lattices consider the possibility of ?
The presence of centre atoms inside the cell or at edges of faces
What are the 7 basic crystal lattice systems?
- cubic
- tetragonal
- orthorhombic
- monoclinic
- triclinic
- trigonal
- hexagonal
What does crystal habit describe?
The overall shape of the crystal
What is crystal habit a result of?
Different growth rates in each dimension
Two crystals with same habit may have different combinations of faces/angles
faces
How can crystal habit be modified?
Adding impurities
What is produced as a result of crystal habit modification using an anionic surfactant on adipic acid?
Thin long needle
What is produced as a result of crystal habit modification using an cationic surfactant on adipic acid?
thin flaky plates
Presence of surfactants in crystallisation solution can change crystal habit by absorbing/adsorbing onto crystal faces during crystal growth
adsorbing
Polymorphic forms can have the same type of crystal ____ but different proportions of axes and angles
lattice
Give 3 ways in which polymorphs differ
- thermodynamic stability
- free energies
- physical properties e.g. m.p.
How do polymorphs have an effect in pharmaceutics?
- manufacture of dosage form
- pharmacological activity
- bioavailability
What is fuels the transition between polymorphic forms?
heat or pressure
Describe enantropic transition
between all forms
Describe monotropic transition
metastable form into stable form
Metastable forms are higher/lower energy polymorphs
higher
Give 3 characteristics of stable polymorphs in comparison to higher energy polymorphs
- lowest free energy
- higher m.p.
- lowest solubility
Polymorphic form nomenclature use roman numerals in order of the highest _______ point
melting
In drug delivery why is it better to have metastable forms?
- better solubility, dissolution, and bioavailability
Describe crystal solvates
crystals contain solvent of crystallisation
Describe crystal hydrates
Water is the solvent of crystallisation
Describe crystal anhydrates
crystals with no water of crystallisation
What is a polymorphic solvate?
solvent interacts with crystal, and when crystals lose the solvent a new crystal form will be produced
What is a pseudopolymorphic solvate?
No interaction between solvent and crystal bonding, when crystal solvates lose the solvent the lattice is not destroyed
Hydrates are more/less soluble than anhydrates and more/less thermodynamically stable
less
more
Give a possible crystal defect
- missing atom
- impurity replacing the original atom
How can defects influence crystals?
alter their physical properties
