Association of similarly charged polyelectrolytes in dilute solution

Similarly charged species are seldom attractive. For e.g., colloids with similar charges on their surface can be assembled into colloidal crystals by optimizing the ionic strength, i.e., the concentration of counter-ions in the solution. Charged polymers are trickier to assemble in the sense that the conformational degrees of freedom are multi-fold.

In my talk, I would speak about pH assisted and light-responsive self-assembled microstructures of a cationic polymer, Polyethyleneimine (PEI), a well-known gold-standard non-viral vector for gene transfection. Generally, PEI is complexed with oppositely charged molecules to derive self-assembled polyplexes which are used for various drug delivery applications. However, our recent experimental observations suggest that at pH values between 2.5 to 4, neat PEI chains in explicit water undergo a completely unprecedented and never observed before kind of self- assembly process. ^[1] The self-assembly is extremely slow, irreversible, and occurs under quiescent conditions to form a 3-D fibrillar network comprising hollow fibrils (Figure 1). The transition of PEI {≈ O (nm)} chains into micron-sized fibrillar network follows coalescence of smaller PEI chains to form ≈ 100-200 nm spheroidal aggregates accompanied with conformational/ morphological transitions into anisotropic rod-like aggregates which assemble end-to-end to form a network structure. Further, it will be shown how these self-assembled structures show light responsiveness under similar pH conditions. ^[2] My lecture will mainly focus on our experimental results; however, some PMF calculations based on MD simulations will also be shown to support the experimental findings.^[3] We believe that our work will initiate to seek more understanding in the gene delivery through hyperbranched PEI-based polyplexes which encounter several levels of low pH conditions once transfected into cells. ^[4]

1. Jain M.; Seth J. R.; Hegde; L. H. R.; Sharma, K.P.; Macromolecules 2020, 53, 8974−8981
2. Sharma S.; Sharma, K. P.; Chem. Commun., 2022,58, 13779-13782
3. Singh, R.; Gade, H. M.; Sharma, K. P.; Seth, J. R. Macromolecules 2025, ASAP
4. Sharma S.; Mishra, M.; Kapoor, S.; Sharma, K. P. Small 2025 (Just Accepted)