Unprecedented Self-Assembly in Dilute Aqueous Solution of Polyethyleneimine: Formation of Fibrillar Network

Abstract

Polyethyleneimine (PEI), a cationic polyelectrolyte, finds great utility as a nonviral gene transfection vector. The mechanism of gene delivery process across the cell membrane through PEI-based polyplexes is still much debated; however, a general consensus is that the proton binding-based PEI conformational changes occur as the pH alters during the process. Taking a step back, even the understanding of wide pH range (from 1 to 10) dependent conformational changes for neat PEI in explicit water remains elusive. In pursuit of this objective, using a combination of optical and electron microscopy, we observed that a dilute aqueous solution of linear or branched PEI (M w ranging from 0.8 to 750 kDa) at room temperature and having pH in the range 2.5–4 undergoes a completely novel and highly unprecedented slow self-assembly process to form a micrometer-sized thick fibrillar network. These self-assembled structures are highly robust, irreversible, and interestingly, generic for PEI and form over 24–72 h in a dilute aqueous solution irrespective of the molecular weight and configuration of PEI. A combination of turbidity and acid titration experiments on PEI aqueous solutions having different pH values reveal that the mechanism of this hierarchical self-assembly (between pH 2.5-4) can be explained by the unique protonation behavior of PEI chains and their ability to undergo conformational/morphological transitions.

The Ph as a Tool to Tailor the Performance of Symmetric and Asymmetric Layer-by-Layer Nanofiltration Membranes

“…This is in accordance with trends reported earlier in literature [40]. However, due to the buffer capacities of PEI, it is disputable whether at pH 4 all available charges are indeed ionized [32,41,42]. Nevertheless, this leaves unchanged that PEI at pH 4 has a significantly higher charge density than PEI at pH 8 or 9.…”

The Adsorption Structure of Polyethylene Imine on Copper Surfaces for Electrodeposition

“…This observation is in line with experimental findings for PEI in acidic aqueous solutions, which revealed increasing hydrodynamic radius with decreasing pH. [26] This effect was explained by the high degree of protonated amines at low pH values and electrostatic repulsion between the protonated groups. Figure 1 shows the effect of cuprous ions is small, but an increase in the degree of trans character with protonation is detectable.…”

Mechanistic Insights into Selective Sensing of Pb2+ in Water by Photoluminescent CdS Quantum Dots

“…The first method involves high temperatures, complicated synthetic methodologies, and hazardous organic solvents and capping agents. The second approach involves direct synthesis of NCs in aqueous phase, and is thus a greener alternative that makes use of biocompatible capping reagents, e.g., thioglycolic acid, cysteine, glutathione, or polyethyleneimine (PEI). − Aqueous QDs are characterized by the abundance of trap states, which quench band edge emission and are often associated with significantly red-shifted (∼0.2 to 0.7 eV) PL and low photoluminescence quantum yield (PLQY).…”