Transcript protein interactions ch9

Protein Interactions
with Biomaterials
Topics:
•Thermodynamics of Protein
Adsorption
•Protein Structure
•Protein Transport and
Adsorption Kinetics
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Thermodynamics
For a reaction to spontaneously occur, the change
in Gibbs free energy, DG, must be <0:
DG  DH  TDS
DGads  DG prot  DGsol  DGSurf
G = Gibbs free energy
H = enthalpy (energy available to do work)
S = entropy (disorder)
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Thermodynamics of Protein Adsorption
Hydrophobicity: Hydrophobic
areas attract hydrophobic areas
Charge: Opposite charges attract
Size: Larger molecules have more
active sites
Structure: the stability (strength of
intramolecular bonds) and molecule
unfolding rate
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Surface features and their
interactions with proteins:
•
Topography: greater texture means
greater interaction
•
Composition: Chemistry governs
types of interactions
•
Hydrophobicity: hydrophobic
surfaces bind more protein
•
Heterogeneity: non-uniform
surfaces have many different types
of domains to interact with proteins
•
Potential: surface charge affects
charge distributions of ions in
solution and proteins
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Protein Structure
Proteins are
polymeric chains of
amino acids.
Each of the 20 standard
amino acids have a oneletter symbol. A sequence
of three symbols, as shown
for RNA (right) is called a
Amino acids have a central
codon
carbon atom attached to a
hydrogen, a carboxyl group
(COOH) and an amine
group (NH2)
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The pK value is related to the pH of the
amino acid. Higher values are more
acidic (lower pH)
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Proteins
(polypeptides) are
formed from
condensation
reactions between
amino acids
(peptide bonds).
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Secondary Structures
a-helix
b pleated structure
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Tertiary and Quaternary Structures
Interactions between side
chains control how the protein
folds in three and four
dimensions. These
interactions include:
•Covalent bonding
•Ionic interactions
•Hydrogen bonding
•Hydrophobic interactions
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Protein Transport and Adsorption
Kinetics
Four main types of
protein transport:
1. Diffusion
2. Thermal convection
3. Flow (convective
transport)
4. Coupled transport
(combinations of 1-3)
A concentration gradient
drives diffusion, while a
temperature gradient creates
thermal convection
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Diffusion is Fick’s 2nd
law, with the addition of
a contribution from flow:
dC
dC
1   C 
V
D
r

dt
dz
r r  r 
The velocity profile is given by:
2

2Q   r  
V
1  
2 
R   R  
V = velocity
 = viscosity
Here in cylindrical
coordinates
C = concentration
D = diffusivity
Q = volumetric flow rate
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Initial absorption rate is high
on a clean surface
Rate slows as surface
becomes covered
Further absorption occurs as
molecules rearrange to create
new free surface
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Protein exchange on a
material surface.
The initial protein (light
gray) is wedged out of
the way by the newer
proteins (dark gray),
which have a greater
affinity for the material
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