protein molecules (system B) and one for incorporating positively charged protein
molecules (system A), were investigated to assess whether the order of mixing was
important. These systems were PAA 42 -PAAm 417 , PDMAEMA 150 and lysozyme
and PAA 139 (system A), and a-lactalbumin and quarternised poly(2-vinyl
pyridinium) 41 -block-poly(ethylene oxide) 205 (P2MVP 41 -PEO 205 ) (system B). The
two protein molecules lysozyme and a-lactalbumin are similar in size but oppositely charged at pH 7 [65]. The pH during these measurements was fixed at 7 using
a phosphate buffer [50]. First, light scattering titrations were performed, starting at
F
À
¼ 0 and F
À
¼ 1 (4). The results of these light scattering titrations [I(F
À ) and
R h (F
À ) ] are presented in Figs. 10 and 11.
One can directly see that the shapes of I(F
À ) are very different for the two
systems. The shape of the I(F
À
) curves in Fig. 10 for system A strongly resemble
the I(F
À ) curves presented in Fig. 9. This is no surprise because the same homopolymer and diblock copolymer were used. There is, however, a difference in the
position of the maximum light scattering intensity.
I(F
À ) for system B, containing the negatively charged protein molecule
(Fig. 11a, b), is not symmetrical, unlike the I(F
À
) of Fig. 10 and the schematic
representation of I(F
À ) proposed by Van der Burgh et al. [61]. Interestingly, an
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
F −
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
10
20
30
F −
a
b
I
R h
(a.u.)
(nm)
Fig. 10 Composition titrations of system A: (a) I(F
À ) and (b) R h (F
À ). Solid circles titrant is
PAA 42 -PAAm 417 ; open circles titrant is mixture of PDMAEMA 150 and lysozyme. The pH was
fixed at 7 using a phosphate buffer. Arrows indicate the direction of the titration. Reprinted from
[50] with permission. Copyright 2009, American Chemical Society
156
S. Lindhoud and M.A. Cohen Stuart