Chemistry Reference
In-Depth Information
Figure 3 Dynamic surface tension of lysozyme from pendant drop at different bulk
concentrations:
,
,1
10
6
mol L
1
;
n
,2
10
6
mol L
1
;
x
,5
10
6
mol
L
1
;
%
,7
10
6
mol L
1
;
v
,1
10
5
mol L
1
;
B
,2
10
5
mol L
1
;-,5
10
5
mol L
1
;
$
,7
10
5
mol L
1
; ,1
10
4
mol L
1
explain the subsequent increase in surface pressure and film thickness. In their
radio-labelling studies, Graham and Phillips
40
observed the same behaviour for
lysozyme adsorption and its surface pressure isotherms, although their plateau
in the surface pressure isotherm was between
5.6
10
6
M.
The surface pressure isotherm for lysozyme has been calculated from the model
and the theoretical parameters summarized in Table 1. The theory describes the
experimental data reasonably well with the listed set of parameters down to a
concentration of 10
7
M. Nevertheless, in the region of low bulk concentra-
tions, and hence low surface coverage, the theoretical predictions deviate
somewhat from the experimental points. In order to improve the agreement,
another set of parameters for the low concentrations would be required. The
difference between the sets involves the area parameters
o
0
and
o
max
. This
result is not surprising. When the concentration is very low the molecules
adsorb in their completely unfolded state, and so the value of
o
max
is higher.
The area parameter
o
min
(
o
1
) does not play a role in this low protein concen-
tration region, as it accounts for the completely folded state, and hence the
lowest surface area state of the adsorbed molecules, which is the case at high
concentrations. In order to fit the experimental data better, the value for the
other area parameter
o
0
(the area of one segment of an adsorbed protein
molecule) should be increased as well. Finally, the parameters a and b are taken
as fitting parameters, and best fit values are reported.
7
10
8
and
B
B
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