Introduction to Properties of Solids

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Introduction to Properties of Solids

• Kausar Ahmad
• Kulliyyah of Pharmacy
• http//staff.iiu.edu.my/akausar

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Contents

• General properties
• Intermolecular forces
• Types of solids
• Amorphous
• Crystalline
• Crystal structure
• Crystallisation
• Crystal growth

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What is solid..to pharmacy?

• Majority of drugs and excipients exist as solids
• Various dosage forms are preparede.g. tablets,
  emulsions

4
General Properties

• Maintain shape
• Not fluid
• Molecules/atoms/ions are held closely by
• intermolecular
• interatomic
• ionic forces

5
Intermolecular forces

• Van der Waals forces
• Dipole-dipole (Keesom)
• Dipole-induced dipole (Debye)
• Induced dipole-induced dipole (London)
• Ion dipole and ion-induced dipole forces
• Hydrogen bonds

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Classification of Solids

• Amorphous
• Crystalline

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Amorphous Solids

• E.g. silica gel, synthetic plastics/polymers
• Irregular shape - molecules are arranged in a
  random manner
• No definite melting point- no crystal lattice to
  break
• Exhibit characteristic glass transition
  temperature, Tg
• Flow when subject to pressure over time
• Isotropic i.e. same properties in all direction
• Affect therapeutic activity e.g. amorphous
  antibiotic novobiocin is readily absorbed and
  therapeutically active compared to the
  crystalline form

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Crystalline Solids

• E.g. diamond, graphite
• Regular shape i.e. fixed geometric patterns
• Incompressible
• Definite /specific boiling points
• Diffract X-rays

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Crystal Structure

• Crystals contain highly ordered molecules or
  atoms held together by non-covalent interactions
• E.g. NaCl has the cubic structure

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Types of Crystal Structure

1. Cubic- sodium chloride
2. Tetragonal- urea
3. Hexagonal - iodoform

1. Rhombic- iodine
2. Monoclinic- sucrose
3. Triclinic- boric acid
4. Trigonal

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            CrystalSites CrystalHome
StrukturberichtDesignation PearsonSymbol
SpaceGroup PrototypeIndex FAQ References
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Crystal Lattice Structures Reference Date  1 Jan 1998
Crystal Lattice Structures Last Modified 18 Jan 2003
Index by Space Group
Space groups are listed in the order they appear
in the Crystallographic Tables. Where it
conflicts with the Crystallographic Tables we use
the notation in Pearson's Handbook. Space Group
generators, Wyckoff positions, etc., are
available online via the very useful Bilbao
Crystallographic Server, and at the National
Research Council of Canada's Generation of
standard and alternate settings of the 230 Space
Groups page. The easiest way to find information
about a given space group is to use the Table of
Space Group Symbols. We also have more
information on how space groups are presented
here. Each class of space groups corresponds to
certain Pearson Symbols. Clicking on the
appropriate symbol will take you to that part of
the Pearson Symbol Index,
Space Group Classes
Class Class Pearson Symbols
                  Triclinic Structures(1-2) aPn
                  Monoclinic Structures(3-15)    mPn    mCn   
                 Orthorhombic Structures(16-74)    oPn    oFn    oIn    oCn   
                  Tetragonal Structures(75-142)    tPn    tIn   
                 Trigonal Structures(143-167)    hPn    hRn
                   Hexagonal Structures(168-194)    hPn   
                 Cubic Structures(195-230)    cPn    cFn    cIn   
Go back to Crystal Lattice Structure page.
Structures indexed by Strukturbericht Designation Pearson Symbol Prototype Current URL http//cst-www.nrl.navy.mil/lattice/spcgrp/index.htmlThis page was created at theNaval Research LaboratoryCenter for Computational Materials ScienceSend comments and corrections to mehl_at_dave.nrl.navy.mil (Privacy Advisory)  
TRICLINIC
MONOCLINIC
ORTHOROMBIC
HEXAGONAL
TETRAGONAL
TRIGONAL
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Bravais Lattices

• End-centred
• Monoclinic
• orthorombic
• Face-centred
• Cubic (NaCl)
• Orthorombic
• Body-centred
• Cubic tetragonal
• Orthorombic

• Total of 14 possible types of unit cells
• For drugs, only 3 types
• Triclinic
• Monoclinic
• Orthorombic

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FCC Structure of NaCl

• Small spheres represent Na ions, large spheres
  represent Cl- ions.
• Each sodium ion is octahedrally surrounded by six
  chloride ions and vice versa.

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Binding Forces
Solid Type Binding force
NaCl cubic Electrostatic attraction
diamond tetragonal Covalent
graphite hexagonal Covalent
fatty acids ? Van der Waals hydrogen bonding
metallic ? ?
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Crystallisation

• Crystallisation steps from solution-
• Supersaturation of the solutione.g. cooling,
  evaporation, addition of precipitant or chemical
  reaction
• Formation of crystal nucleie.g. collision of
  molecules, deliberate seeding
• Crystal growth around the nuclei

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Crystal Growth

• Steps involved
• Transport of molecules to the surface
• Arrangement in the lattice
• Degree of agitation in the system affects the
  diffusion coefficient, thus affects crystal
  growth.

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Precipitation

• Induced by altering pH of solution to reach
  saturation solubility.
• By chemical reaction to produce precipitate from
  a homogeneous solution.
• The rate of reaction is important in determining
  habit.

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Crystallization from Supersaturated Solutions of
Sodium Acetate end lecture here

• Description A supersaturated solution of sodium
  acetate is crystallized by pouring it onto a seed
  crystal, forming a stalagmite-like solid. Heat is
  radiated from the solid.
• Source Shakhashiri, B.Z. Chemical
  Demonstrations A Handbook for Teachers of
  Chemistry

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• End of lecture 1 of 2

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Crystallisation
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Contents - 2

• Properties of solids and implications
• Crystal habits
• Types of crystal habit
• Factors affecting habits
• Polymorphism
• Methods to characterise solids

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Crystal Habits

• Variation in size
• Number of faces
• Kind of faces
• Habits describe the overall shape of the crystal
  e.g. acicular (needle), prismatic, pyramidal,
  tabular, equant, columnar lamellar types.

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Factors affecting types of habits

• Temperature
• Solvent
• Crystal growth ratee.g. at high rate, acicular
  form of phenylsalicylate is formed
• Viscositye.g. less viscous media favours coarse
  and equidimensional forms of minerals
• Addition of impuritiese.g.sulfonic acid dyes
  alter habits of ammonium, sodium and potassium
  nitrates
• Presence of surfactantse.g. anionic cationic
  surfactants on adipic acid crystals

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EQUANT Any three perpendicular axis through the
crystal are more or less equal. Can be used to
describe rounded as well as angular crystals.
Fluorite forms crystals that are a good example
of equant crystals.
ACICULAR Long and needle-like, thinner than
prismatic but thicker than fibrous. Natrolite
crystals can be good examples of acicular
crystals.
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PRISMATIC One of the most common of crystal
habits. Prismatic crystals are "pencil-like",
elongated crystals that are thicker than needles
(see acicular). Indicolite (a variety of elbaite)
forms good examples of prismatic crystals.
TABULAR Book-like (tablets) that are thicker than
platy but not as elongated as bladed. Wulfenite
forms crystals that are a good example of tabular
crystals.
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Sodium Chloride Class Halides Uses Major
source of salt and as mineral specimens.
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Exercise

• How many forms of
• Adipic acid crystals
• exist?
• Refer Florence Attwood

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Polymorphisms

• When compounds crystallise as different
  polymorphs, properties change.
• Molecules arrange in two or more ways in the
  crystal packed differently in crystal lattice,
  different orientation, different in conformation
  of molecules at lattice site.
• X-ray diffraction patterns change.

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ExamplePolymorphism of Spironolactone

• A diuretic (no potassium loss)
• 2 polymorphic forms and 4 solvated crystalline
• Form 1 spironolactone powder is dissolved in
  acetone at a temperature near boiling point and
  cooled to 0 deg. C within a few hours
  needle-like
• Form 2 powder dissolved in acetone or dioxane or
  chloroform at RT and acetone allowed to evaporate
  for several weeks - prism

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Polymorphs of spironolactone
1
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Properties of Spironolactone Polymorphs
Parameters Form 1 Form 2
Unit cell orthorombic orthorombic
Dimension of a, b, c axes 0.998, 3.557, 0.623 1.058, 1.900, 1.101
Crystal habit Needle-like prisms
Melting point 205 deg. C 210 deg. C
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Polymorphism in Pharmaceutical compounds
drugs polymorphs amorphous pseudo
ampicillin 1 0 0
cortisone acetate 8 0 0
chloramphenicol palmitate 3 1 0
erythromycin 2 0 0
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Solubility of chloramphenicol palmitate
Form B
1 1
Form A
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Characterisation of Solids

1. Microscopy polarised light
2. X-ray crystallography - single crystal- on the
   basis that crystals can diffract X-rays-
   wavelengths same magnitude as distance between
   atoms/molecules in crystal- enable the
   determination of the distances of various planes
   in crystals. Thus, structures.- e.g. penicillin
3. X-ray diffraction powder sample gtgtpolymorphic
   state

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Continue characterisation of solids

• Differential scanning calorimetry Tg, Tc and Tm
• Infrared spectrometry
• Melting point pure solid liquid in
  equilibrium normal at 1 atm
• Heat of fusion ( Hf) heat required to melt
  (increase intermolecular distance) 1 g of solid
• Solubility

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References

• AT Florence D AttwoodPhysicochemical
  Principles of Pharmacy 3rd. Ed, Macmillan (1998)
  Chapter 1
• EA Rawlins, Bentleys Textbook of Pharmaceutics
• ME Aulton, Pharmaceutics The Science of Dosage
  Form Design
• JT Cartensen, Advance Pharmaceutical Solids,
  Marcel Dekker, New York (2001)
• BD Cullity SR Stock, Elements of x-ray
  diffraction 3rd Ed., Prentice Hall, New Jersey
  (2001)