Positively charged dendronized polymers with protonated amine groups at the periphery and different dendron generations are cylindrically shaped nanoobjects whose radii and linear charge densities can be varied systematically. These polyelectrolytes have been complexed with DNA and subsequently adsorbed on precoated mica substrates. The analysis of scanning force microscopy data indicates that DNA wraps around the dendronized polymers. The calculated pitch is 2.30 +/- 0.27 and 2.16 +/- 0.27 nm for DNA wrapped around dendronized polymers of generation two and four, respectively. The complex with the second generation has been shown to be negatively charged, which is consistent with the theory of spontaneous overcharging of macro-ion complexes, when the electrostatic contribution to the free energy dominates over the elastic energy. The complexes may be of interest for the development of nonviral gene delivery systems.

Exploiting tapping mode-scanning force microscopy (TM-SFM), we characterized single polymeric chains of poly(isocyanodipeptides) (PICs) equilibrated in quasi two-dimensions on the basal plane of mica surfaces. While the average contour length 〈L〉 of an acid-catalyzed PIC bearing L-alanine-D-alanine methyl ester groups was as high as 5.3 µm, the corresponding Ni-catalyzed product exhibited an 〈L〉 of 70 nm. With a newly devised method based on the statistical analysis of the curvature of polymeric chains on a length scale up to about 100 nm from SFM images, we determined their persistence length lp. The measured value of lp ) 76 ( 6 nm for both products, independent of the contour length, indicates that the single polymer molecules are very rigid, i.e., even more rigid than the double-stranded DNA. This rigidity is attributed to the helical structure of the polymer backbone and, in particular, to the hydrogen-bonded networks that are present between the alanine moieties in the side chains.

No abstract

No abstract

No abstract