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Colloid chemistry for pharmacists
Interparticle interaction
Berka Márta,
Bányai István
associate professor
professor
Dep. of Colloid- and Environmental Chemistry
http://dragon.unideb.hu/~kolloid/
2. lecture
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Characterization of colloids
Buzágh:
gh colloidal state parameters
1. Dispersity (or size distribution)
2. Morphology (shape, inner structure)
3. Spatial distribution
4. Interparticle interaction
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4. Molecular interactions
• The origin of interactions between colloidal particles.
The interactions between individual molecules.
– Ion1 - ion2
– Ion1 - permanent dipole2
– permanent dipole1 - permanent dipole2
– permanent dipole1 - Induced dipole2
– instantaneous dipole1 - Induced dipole2
– Hydrogen-bonding interaction
– Repulsion
• Hydrophilic and Hydrophobic interaction
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Molecular interactions
Sign: attraction (-), repulsion (+)
Coulomb: ion-ion
ECoul
Ei1d2
( ze)1 ( ze) 2 1
=
4πε 0 r
( ze)1 μ2 cos θ 1
=
4πε 0
r2
Acting
range~50nm
Range~1.5nm
ion-dipole
a) T low
dipole-dipole
Orientation effect
b) T high
r~ distance
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Molecular interactions
dipole-dipole
a) T low, the constant gives the sign: +2 parallel, -2 antiparallel
oriientation
Ed1d2
konst. μ1μ2 1
=
4πε 0
r3
range~1.5nm
At low temperature the orientation
effect yields an ordering!
b) T high, freely rotating dipoles, always attraction:
Ed1d2
2
μ12 μ22
1
=−
3 (4πε 0 ) 2 k BT r 6
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Molecular interactions
induced dipole- dipole
Dipólmomentum
molekula
Ei1d2
α μ
(
~−
)
Debye
molekula
HF
HCl
HBr
H2O
1.91
1.05
0.79
1.85
H2S
0.93
NH3
1.46
Debye
SO2
CO
CO2
molekula
1.6
0.1
0
1D= 3.33 ×10
-30
Debye
Metanol
Etanol
Aceton
Fenol
1.7
1.7
2.86
1.45
Cm
2
+
α
μ
1 Induction effect
1
2 1
r6
(4πε 0 ) 2
α, polarizability,
Polarizálhatóság
2
2
He
μ, Dipolmomentum, in Debye
H2
α, polarizability,
Ar
Xe
NH3
CH4
0.2
0.81
1.63
4
2.3
2.6
CO
H2O
O2
Cl2
CCl4
1.65
1.44
1.6
4.6
10.5
CH2=CH2
C 2 H6
C6 H6
4.3
4.5
10.3
α
× 10−30 , m3
4πε 0
The polarizability increases with volume (mass).
Induced dipoles are responsible for the London dispersion forces. The heavier the molecule, the larger the
induced dipole will be. Thus, London dispersion forces are strong for heavy molecules
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London dispersion interactions
Et1i2
3 ν 1ν 2 α1α 2 1
~− =
2 ν 1 + ν 2 (4πε 0 ) 2 r 6
instantaneous dipole- induced dipole
ν the characteristic frequency of
vibration of electron
Range~0.4nm
Dispersion forces are weak, short-lived
forces, which are experienced by all
molecules. They operate over very short
distances.
saturated vapour pressure:
CH3Cl <CH2Cl2< CHCl3 <CCl4
London dispersion
interactions (London forces tend
to increase with molecular weight,
some properties of liquid are
approximately proportional to the
energy of intermolecular attraction:
melting point, boiling point, vapor
pressure, surface tension, viscosity)
Additive!
London forces depend on the shape;
evaporation heat: pentane> isopentane>
neopentane
http://cost.georgiasouthern.edu/chemistry/general/molecule/forces.htm
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Summarizing of induction, orientation and dispersion to
the same type of molecules: β
E A ~ − β11r −6 , J
Boer and Hamaker for macroscopic phases:
A: Hamaker constant, q: pcs
atoms /volume,
A~q β
2
Compound μ Debye α
CCl4
0
Ethanol
1.73
Benzene
0
Water
1.82
β 11 ×10
CCl4
Etanol
Benzol
Cl-benzol
F-benzol
Toluol
víz
77
Jm
6
4.41
3.4
4.29
7.57
5.09
5.16
1.82
%
10.7
5.49
10.5
1.44
orientation induction dispersion
0
0
100
42.6
9.7
47.6
0
0
100
84.8
4.5
10.5
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Attraction- repulsion
between molecules
repulsion
konst. β11
Etot ~ 12 − 6 , J
r
r
attraction
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Hydrogen-bonding interaction
H-bonding interactions a donor acceptor interaction involving H atoms.
They exist between electronegative atoms such as O, N, F, with H atoms
covalently bound to similar electronegative atoms.
Hydrophobic interaction
Hydrophobic interaction describes the
strong interaction between hydrophobic
molecules or surface in water. This is often
stronger than their attraction in free space.
Hydrophilic molecules are mostly
polar and have a H-bonding capacity
Why are non-polar molecules hydrophobic? Non-polar molecules share a
common characteristic: practically no intermolecular forces can form between them and
water (only dispersion forces). For a molecule to be water-soluble it must be able to
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experience dipolar interactions, or form hydrogen bonds, with water.
Hydrophobic, hydrophilic interaction
Hydrophobic and hydrophilic interactions: Some molecules such as hydrocarbons, oil, fats, inert atoms,
fluorocarbons and some polymers that are incapable of forming H-bonds and do not like to interact with
water, are called hydrophobic molecules. Hydrophobic means water-fearing or water-repelling. The
more general name lyophobic , which means solvent repelling. Hydrophilic molecules are mostly
polar and have a high H-bonding capacity.
In practice, hydrophobic molecules , in contact with water, prefer to interact with each other instead of the
water and try to minimize their total surface area and form a water immiscible phase. Hydrophobic
interaction describes the strong interaction between hydrophobic molecules or surface in water. This is
often stronger than their attraction in free space. This is contradicted by the prediction of a decrease in
the van der Waals attraction in water medium.
The interaction between a hydrophobic molecule and water is actually attractive , due to dispersion
interactions. However, the interactions between water and with itself is much more attractive due to Hbonding interactions, and water then has the effect of squeezing the hydrophobic molecules to attract
each other to form a larger aggregate, reducing the total free energy of the system.
Hydrophilic interaction is generally polar and capable of H-bonding.
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Summary of the interactions
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http://www.science.uwaterloo.ca/~cchieh/cact/c123/intermol.html
Samples
There comes a chain
length above which
the hydrophobic
nature of a hydroxyl
group because it
disrupts the hydrogen
bonding in water too
greatly. Alcohols
whose alkyl groups
are above a certain
size are therefore
insoluble in water*.
*Crowe, J.:Chemistry for the Biosciences Oxford UP. ISBN 0-19-928097-5, 2006
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Molecules of a water-soluble compound
and molecules of water mingle freely
with each other: the two types of
molecules are able to mix completely.
If a compound is insoluble in water, its
molecules cannot mix freely with
molecules of water.: instead, the two
types of molecule remain completely
separate. Occasionally, a small amount
of the solute dissolves, while the majority
floats on top of the solution.
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ion-dipole
The hydration of ions by water
molecules. The interaction of
ions by water molecules, is a
dipolar interaction, which exists
between the charge of the ion
and the partial charge on the
polar water molecule.
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Samples
A summary of how an
electronegative atom
can influence the
physical properties of
a molecule of which it
is part*.
*Crowe, J.:Chemistry for the Biosciences Oxford UP. ISBN 0-19-928097-5, 2006
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Samples
The alcohols are polar molecules.
Electrons are withdrawn towards
the highly electronegative oxygen
atom, distorting the distribution of
electrons throughout the molecule
as a whole. Consequently, the
molecule is polar.
Molecules of an alcohol can form
hydrogen bonds with water, and
with each other.
*Crowe, J.:Chemistry for the Biosciences Oxford UP. ISBN 0-19-928097-5, 2006
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Samples
Glycerolphospholipids
arrange themselves
in two sheets, each
with a hydrophilic and
a hydrophobic face.
The hydrophobic faces
of the two sheets lie
against one another,
forming a sealed,
water-free layer.
*Crowe, J.:Chemistry for the Biosciences Oxford UP. ISBN 0-19-928097-5, 2006
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Samples
The folding of a polypeptide
possessing hydrophobic and
hydrophilic portions. The
darker hydrophobic
portions fold away from
the aqueous surroundings;
this arrangement is stabilized
by dispersion forces which
operate between the tightly
packed hydrophobic
portions.
*Crowe, J.:Chemistry for the Biosciences Oxford UP. ISBN 0-19-928097-5, 2006
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Samples
The sequence of monomers within a polymer.
Side chains that are in close proximity when a polypeptide chain adopts its three-dimensional, folded
structure may be some distance apart in the polypeptide chain itself.. Look at this polypeptide chain, and
notice how amino acids A and B are some distance apart in the sequence of the polypeptide chain, but
actually come into close proximity when the chain is folded
*Crowe, J.:Chemistry for the Biosciences Oxford UP. ISBN 0-19-928097-5, 2006
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Samples
The various non-covalent
forces that can operate in
a biological molecule,
such as a polypeptide
*Crowe, J.:Chemistry for the Biosciences Oxford UP. ISBN 0-19-928097-5, 2006
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