Crystals Flashcards
Crystal with all lengths and angles = 90°
Cubic
Crystal with 2 lengths the same and all angles = 90°
Tetragonal
Crystal with all lengths different and all angles = 90°
Orthorhombic
Crystal with all lengths different and 2 angles = 90° and 1 angle not 90°
Rhombohedral
Crystal with 2 lengths the same and 2 angles = 90° and 1 angle = 120°
Hexagonal
Crystal with all lengths different and 2 angles = 90° and one doesn’t equal 90°
Monoclinic
All lengths different and all angles different
Triclinic
How many atoms are in primitive cubic cell?
1 (8 1/8ths)
How many atoms are in body-centred cubic cell?
2 (8 1/8ths + 1)
How many atoms are in face-centred cubic cell?
4 (8 1/8ths + 4 1/2s + 1)
What states does x-ray diffraction occur in?
Solid only
Bragg’s Law
nλ = 2d sinθ
What causes the scatter of x-rays in a crystal?
The electron cloud around the atoms
What does each diffraction spot correspond to?
A single point in the lattice
What is polymorphism?
When molecules are arranged in 2 or more different ways
In what ways can molecules be arranged differently?
- Differences in orientation or conformation of the molecules
How can polymorphism be detected?
- Differences in x-ray diffraction pattern
- Melting Point
- Solubility
What are 2 types of multi-component systems?
Solvates and hydrates
How are different polymorphs prepared?
Manipulating conditions of crystallisation such as solvent, temperature, pressure, cooling rate and stirring rate)
What processing process may cause polymorphic changes?
Milling, drying, compression and time
What pharmaceutical properties are affected by polymorphism?
Density, melting point, hygroscopicity, apparent solubility
What is bioavailability?
The rate and extent to which a substance is absorbed and circulated around the body
How can polymorphic forms be characterised?
X-ray diffraction, microscopy, thermal analysis and spectroscopy
What does DSC stand for and detect?
Differential Scanning Calorimetry can detect different melting points if they exist
