there was a decrease of particle size with increasing M W of PAC. Furthermore, it
should be noted that in our studies on PEI/PAC particle size parameters, the
smallest particle size of D H ¼ 80 nm was obtained for PEC-1.5, mixed at
pH ¼ 7/7 at PAC M w of 2,000 g/mol, which is evident from Fig. 10 (first open
square data point in bottom series).
3.1.3 PEL Topology: Linear Versus Branched
Imae and Miura reported complexation between fourth generation PAMAM
dendrimers (DEN) and poly(L-glutamic acid) (PLG) in 0.25 M NaCl [56]. They
observed a constant course for molecular DEN/PLG ratios X ( 300 but a steep
increases of the PEC particles from around R G ¼ 100 nm up to R G > 300 nm for
X > 300 (DEN and PLG concentration was 0.1% w/w) (see Fig. 11). This means
that DEN spheres bind to PLG chains like a loading process up to a certain
threshold value, but thereupon may act as crosslinkers for PLG chains, resulting
in larger aggregate-like PEC particles.
In principle, a similar behavior was found for cationic aromatic dendrimers
(excess component) complexed with DNA in studies by Shifrina and coworkers
aiming at positively charged DNA vectors [57].
400
300
0
500
1000
1000
0
500
1000
nm
500
1000
nm
500
200
100
Dimensions of conjugates (nm)
0
224 500
Poly(L)lysine (weight average molecular weight)
53 700
23 800
3 970
Fig. 9 Influence of poly(L-lysine) (PLL) molecular weight on the dimensions of PLL/DNA particles
obtained by SFM (see insets). (From [39] with kind permission of Nature Publishing Group)
210
M. M€ uller