Analysis of Compacted Semiflexible Polyanions Visualized by Atomic Force Microscopy:  Influence of Chain Stiffness on the Morphologies of Polyelectrolyte Complexes

Abstract

The morphologies of the compacted semiflexible biological polyanions alginate, acetan, circular plasmid DNA, and xanthan were investigated using tapping mode atomic force microscopy followed by quantitative image analysis. A shape factor was calculated for each of the observed polyelectrolyte complexes and used as a basis for dividing the structures into ensembles of morphologically linear, toroidal, and globular structures for subsequent quantitative analysis. Compaction of polyanions with chitosan yielded a small fraction of the torus morphology when the persistence length, L p, of 25 nm (acetan) was reached. For both DNA, L p = 50 nm, and xanthan, L p = 120 nm, it was found that the toroids make up a substantial fraction of the complexed structures formed by the given chitosan and at room temperature. Rodlike complexes were additionally observed within DNA−chitosan complexes, whereas they do not appear as a significant fraction of chitosan-complexed high-molecular-weight xanthan. The average height of the condensates was observed to be ∼2 nm for the compacted xanthan toroids, while it was determined to be ∼5 nm for compacted DNA toroids. Reducing the degree of polymerization of xanthan yielded a decrease in the fraction of toroids. Compacted xanthan at room temperature displays a number of racquets and other morphologies similar to the reported intermediate, metastable states by simulations. The reduced abundance of such structures following annealing supports the interpretation of their metastable nature.

Isothermal titration calorimetry study of the polyelectrolyte complexation of xanthan and chitosan samples of different degree of polymerization

“…For the case of SX80 the first stage is a complexation of xanthan into well-defined structures (rods), similar to what has previously been observed for short-chained xanthan upon compaction with a different chitosan sample. 21 For the SX15 samples, complexes are observed in the AFM topographs from the first stage ( Figure 2B), which are then aggregating/clustering during the second stage.…”

“…4,20 Even though the polycation-polyanion self-assembly process is widely used, detailed molecular mechanisms can be specific to the molecular pairs investigated and therefore need specific elucidation in view of the general features. The interaction between xanthan and chitosan has previously been studied with regard to both polyelectrolyte complexes 21,22 and multilayers, 23 and these two polymers have also been used to form hydrogels, [24][25][26] for example, for the immobilization of enzymes. 27 Xanthan is a bacterial polysaccharide produced by strains of Xanthomonas, a family of plant pathogens.…”

Improved chitosan-mediated gene delivery based on easily dissociated chitosan polyplexes of highly defined chitosan oligomers

“…Based on the calculation of a shape factor for each polyplex structure, reflecting the symmetry of the structure about the three axis of rotation, the polyplexes were sorted into three different classes (toroidal, rod-like and spherical shapes). 47,48 In vitro gene transfer Most in vitro transfection studies were performed in the epithelial human embryonic kidney cell line 293. The cells (45 000 cells/cm 2 ) were seeded at 70% confluence in 96-well tissue culture plates (Costar, Cambridge, UK) 24 h before transfection.…”

Forming Highly Ordered Arrays of Functionalized Polymer Nanowires by Dewetting on Micropillars

“…Double-helix DNA has an L p of 50 nm. [23] In contrast, polylysine, NaPSS, and PEO have much smaller L p s of 1.8, [24] 3.2, [25] and 0.4 nm, [26] respectively. As a result, DNA forms much looser coils in water than the other three polymers.…”