Polymorphic Forms

Question 1

List a key property of polymorphic forms

Answer 1

• atoms are packed in a high degree order

-

Question 2

List a key property of amorphous forms

Answer 2

• atoms are arranged in a random order

Question 3

Give an example of a polymorph

Answer 3

sodium chloride

Question 4

Give an example of an amorphous material

Answer 4

glass

Question 5

What can the crystallographic structure be described as?

Answer 5

3D lattice, in which the unit cell is the repeating unit

Question 6

What is the unit cell?

Answer 6

The building block of the crystal described by 3 dimensions

Question 7

What are the dimensions and angles describing a unit cell?

lengths of axes and angles

Answer 7

lengths - a, b, c

angles - α, β, γ

Question 8

How many basic crystal systems are there?

Answer 8

7 unit cells

Question 9

How many advanced crystallographic systems are there?

Answer 9

14 unit cells

Question 10

What do Bravais lattices consider the possibility of ?

Answer 10

The presence of centre atoms inside the cell or at edges of faces

Question 11

What are the 7 basic crystal lattice systems?

Answer 11

• cubic
• tetragonal
• orthorhombic
• monoclinic
• triclinic
• trigonal
• hexagonal

Question 12

What does crystal habit describe?

Answer 12

The overall shape of the crystal

Question 13

What is crystal habit a result of?

Answer 13

Different growth rates in each dimension

Question 14

Two crystals with same habit may have different combinations of faces/angles

Answer 14

faces

Question 15

How can crystal habit be modified?

Answer 15

Adding impurities

Question 16

What is produced as a result of crystal habit modification using an anionic surfactant on adipic acid?

Answer 16

Thin long needle

Question 17

What is produced as a result of crystal habit modification using an cationic surfactant on adipic acid?

Answer 17

thin flaky plates

Question 18

Presence of surfactants in crystallisation solution can change crystal habit by absorbing/adsorbing onto crystal faces during crystal growth

Answer 18

adsorbing

Question 19

Polymorphic forms can have the same type of crystal ____ but different proportions of axes and angles

Answer 19

lattice

Question 20

Give 3 ways in which polymorphs differ

Answer 20

• thermodynamic stability
• free energies
• physical properties e.g. m.p.

Question 21

How do polymorphs have an effect in pharmaceutics?

Answer 21

• manufacture of dosage form
• pharmacological activity
• bioavailability

Question 22

What is fuels the transition between polymorphic forms?

Answer 22

heat or pressure

Question 23

Describe enantropic transition

Answer 23

between all forms

Question 24

Describe monotropic transition

Answer 24

metastable form into stable form

Question 25

Metastable forms are higher/lower energy polymorphs

Answer 25

higher

Question 26

Give 3 characteristics of stable polymorphs in comparison to higher energy polymorphs

Answer 26

- lowest free energy - higher m.p. - lowest solubility

Question 27

Polymorphic form nomenclature use roman numerals in order of the highest _______ point

Answer 27

melting

Question 28

In drug delivery why is it better to have metastable forms?

Answer 28

- better solubility, dissolution, and bioavailability

Question 29

Describe crystal solvates

Answer 29

crystals contain solvent of crystallisation

Question 30

Describe crystal hydrates

Answer 30

Water is the solvent of crystallisation

Question 31

Describe crystal anhydrates

Answer 31

crystals with no water of crystallisation

Question 32

What is a polymorphic solvate?

Answer 32

solvent interacts with crystal, and when crystals lose the solvent a new crystal form will be produced

Question 33

What is a pseudopolymorphic solvate?

Answer 33

No interaction between solvent and crystal bonding, when crystal solvates lose the solvent the lattice is not destroyed

Question 34

Hydrates are more/less soluble than anhydrates and more/less thermodynamically stable

Answer 34

less | more

Question 35

Give a possible crystal defect

Answer 35

- missing atom | - impurity replacing the original atom

Question 36

How can defects influence crystals?

Answer 36

alter their physical properties