Chemistry Reference
In-Depth Information
72.6
72.4
72.2
72.0
71.8
71.6
71.4
71.2
0.01
0.11
1
10
100
time, s
Figure 1 Dynamic surface tension of lysozyme from maximum bubble pressure method at
different bulk concentrations: ,10
6
mol L
1
;+,5
10
6
mol L
1
;
n
,10
5
mol L
1
;
J
,9
10
5
mol L
1
results have been reported for BSA.
36
On the basis of fluorescent images, Stebe
et al.
37
have concluded that the induction time of lysozyme is caused by a first-
order phase transition from gaseous to liquid-expanded state.
Figure 2 presents dynamic surface tension data of lysozyme determined from
the profile of a buoyant bubble recorded over 24 h. The decrease in surface
tension for various lysozyme concentrations as measured from pendant drops is
shown in Figure 3. The adsorption was followed over 12-15 h. It can be seen
that no equilibrium has been reached and the dynamic surface tension contin-
ues to decrease over a long period of time. In contrast to behaviour at the low
lysozyme concentrations measured with a buoyant bubble, no intermediate
increase in surface tension was observed.
The dynamic surface tension of mixtures of lysozyme (7
10
7
M) + SDS at
varying concentrations has been measured with buoyant bubbles. At pH
¼
7
the protein has a positive net charge (z-potential
5.7 mV) which favours
complexation with the anionic SDS. Figure 4 presents the decrease of surface
tension of lysozyme (7
10
7
M) mixed with various concentrations of SDS.
The pure lysozyme system and the lysozyme + SDS systems have been
studied ellipsometrically. The refractive index, the adsorption layer thickness
and the adsorbed amount (mg m
2
) have all been determined. The changes in
adsorbed layer thickness for lysozyme alone and of SDS in the presence of
lysozyme (7
10
7
M) are shown in Figure 5. For the single component system
at very low concentrations, the thickness of the adsorption layer seems to begin
from ca. 225 A
˚
, but apparently this is due to the very low difference between
refractive index of water (1.3334) and that of the adsorbed layer, which makes
B
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