Page 265 - Advances in Textile Biotechnology

246 Advances in textile biotechnology

constants such as k a , k d , and K d are calculated based on the binding curves
of the peptides. Isothermal titration calorimetry (ITC) can also be used to
study the binding thermodynamics of peptides with their binding partners
and thermodynamic parameters such as the binding enthalpy, entropy and
free energy, and binding constant can be calculated from calorimetric data.
(Chow et al., 2008) For ELPs, the inverse temperature transition is often
determined by turbidity (optical density at 350 nm) as a function of tem-
perature or by differential scanning calorimetry (DSC) (Reguera et al., 2003).
Nuclear magnetic resonance (NMR) and x-ray crystallography are the
methods of choice for obtaining comprehensive structural information for
proteins. In addition, protein folding can be studied using circular dichroism

(CD), which defines the unfolding and folding transitions of peptides. Dif-
ferential scanning calorimetry (DSC) can be used to elucidate the folding
and refolding properties of peptides during cooling and heating. Dynamic
light scattering (DLS) also named photon correlation spectroscopy, can be
used to determine the hydrodynamic radius (R h ) of polypeptides in aqueous
solution, especially useful for examining the formation of self-assembled
polypeptide micelles (Chow et al., 2008). Fluorescence spectroscopy com-
bined with previous techniques can provide additional information about
the structural state of the proteins (Woestenenk et al., 2003).
Rheological properties: the relationship between the molecular structure
of a polypeptide and is rheological properties can be estimated by measur-
ing G′ elastic (storage) modulus, which represents the solid-like component
of a material, G″, viscous (loss) modulus, that represents the liquid-like
component, η*, dynamic (complex) viscosity, and δ, loss angle, that is a
measure of the dissipation of energy inherent in the material and is a useful
parameter for quantifying the viscoelasticity of a material, as a function of
strain, frequency, temperature, time and other parameters (Chow et al.,
2008). The sol–gel transition for a given polymer solution or gelation point
can be easily detected by a measurement of G′ and G″ and is defi ned as
the crossover between G′ and G″ as a function of the previous parameters
cited (Nagapudi et al., 2005).

The mechanical properties of fiber proteins are determined by stretching
them at a particular strain rate d(l/l 0 )/dt, and measuring the force required

to extend the fiber a certain length, defined as dl. The strain (ε) represents

the normalized deformation (elasticity), which is defined as the ratio of

change in length (dl) to the initial length (l 0 ) or (dl/dl 0 ). The stress (σ) is
defi ned as the force (F) divided by the cross-sectional area (A) of the fi ber
(σ = F/A). Young’s modulus (E), which can be obtained from the slope of
the stress–strain curve, is a measure of the stiffness of the fi ber. If the fi ber
breaks during extension, the area under the curve is a measure of the tough-
ness of the fiber, a parameter that indicates the amount of energy absorbed

by the fiber. During extension, stress–strain profiles can often display

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