ADSORPTION BEHAVIOUR OF 5-METHYLRESORCINOL AND ITS MIXTURES WITH LYSOZYME AT AIR-WATER INTERFACE - Biochemistry and Biotechnology: Research and Development - page 102

Adsorption of Methylresorcinol in the Presence of Lysozyme
Several authors reported changes in adsorption kinetics for the mixtures of proteins and
surfactants [Alahverdjieva et al., 2008; Maldonado-Valderrama et al., 2007; Wu et al., 2006].
For protein/ non-ionic surfactant mixtures there is a competitive adsorption [Alahverdjieva et
al., 2008] from the very first addition of surfactant which increases with the surfactant
concentration at a fixed protein contents and leads to a gradual displacement of the protein
from the interface. From a certain surfactant concentration on the two isotherms, the mixture
and the pure surfactant, overlap indicating a surface layer covered essentially by free
surfactant molecules. The dynamic surface tension measurements performed in phosphate
buffer solutions (pH 7.4, I = 0.05 M) at constant lysozyme concentration, 3.4 10 -6 M, and
varying concentrations of MR, show that the LYS-MR mixture is more surface active than the
pure MR in concentration < CMC mix . Moreover, adsorption rate is enhanced with respect to
that of pure MR at the same concentration (Figure 4, 5). The Lys-MR mixtures are slightly
more surface active than its both components alone at MR concentration > CMC mix . (64.6
mM).
Figure 5. Dynamic curves of adsorption of MR in mixture with lysozyme at air/water interface at 25 O C;
MR concentrations 0.16-128.2 mM and constant lysozyme concentration 3.4 10 -6 M.
The interaction in the mixture may be of either synergistic or antagonistic. The synergism
leads to the enhancement of the surface activity of the mixture which in turn lowers the CMC
of the mixed system compared to the individual components. Antagonism is a result of
competition of surfactants in adsorption process due to difference in their hydrophobicity and
possible unfavorable sterical effects of their structure. Consequently, micelle formation takes
place at higher concentrations.
As concerning the effect of MR on the surface activity of lysozyme, it is seen from figure
4 that MR decreases the surface activity of lysozyme at concentration < CMC mix and