3.3. Thermodynamic parameters of interaction between Tbz and Hb
Thermodynamic parameters related to the decrease of the fluorescence
intensity in the drug upon the addition of different amounts of
protein immobilized GPTS–SPIONs were described by Maltas et al.
[21] and determined by using the following Stern–Volmer equation
(Eq. (1)):
Fo=F ¼ 1 þ Kqτ0½ ¼ Q 1 þ KSV½ ð Q 1Þ
where Fo and F are the fluorescence intensity of the drug before and
after the addition of the quencher, respectively; KSV is the Stern–Volmer
quenching constant which can be calculated by the slopes of the Stern–
Volmer equation (Fo/F vs. log [Q]) curves; [Q] is the concentration of the
quencher; and τ0 is the fluorescence lifetime of the biomolecule in the
absence of the quencher, which is assumed to be 10−8 s [21].
The equilibrium between binding constant (Kb) and the number of
binding sites (n) are given by the following equation [24]:
log½ ¼ ð Þ Fo−F =F logKb þ n log½ ð Q 2Þ
where Kb is the binding constant, n is the number of binding sites, [Q] is
the concentration of the quencher.
Kb values are estimated as 2.18, 3.23 and 4.35 L mol−1 and the binding
sites (n) are 0.14, 0.20 and 0.27 at different temperatures (298, 301
and 304 K) in order to determine the binding force of the reaction,
respectively. The values of Kb increased with an increase in the temperature
which was assumed to increase the stability of Tbz–Hb
immobilized nanoparticles. The values of n also increased with an increase
in temperature. This suggests that the changes in the protein
structure on the nanoparticles may occur with temperature [25].