pH-Dependent Conformations for Hyperbranched Poly(ethylenimine) from All-Atom Molecular Dynamics

Trends in the synthetic polymer delivery of RNA

Ribonucleic acid (RNA) has emerged as one of the most promising therapeutic payloads in the field of gene therapy. There are many unique types of RNA that allow for a range of applications including vaccination, protein replacement therapy, autoimmune disease treatment, gene knockdown and gene editing. However, RNA triggers the host immune system, is vulnerable to degradation and has a low proclivity to enter cells spontaneously. Therefore, a delivery vehicle is required to facilitate the protection and uptake of RNA therapeutics into the desired host cells. Lipid nanoparticles have emerged as one of the only clinically approved vehicles for genetic payloads, including in the COVID-19 messenger RNA vaccines. While lipid nanoparticles have distinct advantages, they also have drawbacks, including strong immune stimulation, complex manufacturing and formulation heterogeneity. In contrast, synthetic polymers are a widely studied group of gene delivery vehicles and boast distinct advantages, including biocompatibility, tunability, inexpensiveness, simple formulation and ease of modification. Some classes of polymers enhance efficient transfection efficiency, and lead to lower stimulation of the host immune system, making them more viable candidates for non-vaccine-related applications of RNA medicines. This review aims to identify the most promising classes of synthetic polymers, summarize recent research aimed at moving them into the clinic and postulate the future steps required for unlocking their full potential.

Branched polyethyleneimine: CHARMM force field and molecular dynamics simulations

Polyethyleneimine (PEI), one of the non-viral vectors of great interest for gene delivery, was investigated at all-atom level, with particular emphasis on its branched form. We report the extension of our previously published CHARMM force field (FF) for linear PEI, with parameters optimized specifically for branched configurations. A new residue type for the branch connector is introduced and the charges and bonded parameters are derived from ab initio calculations based on a model polymer. The new FF is validated by extensive molecular dynamics simulations of solvated branched PEIs of various protonation fractions and branch lengths. The gyration radii, end-to-end distances, and diffusion coefficients are compared with results for linear PEIs of similar molecular weights and protonation patterns. Solvated complexes of DNA with (linear/branched) PEI were also investigated to determine favorable attachment conformations. The parametrized atomistic force field is suitable for simulations of PEI with arbitrary branching pattern, protonation, and size, and is expected to provide relevant insights regarding optimal conditions for DNA-PEI complex formation.

Graphene Oxide/Polyethylenimine Aerogels for the Removal of Hg(II) from Water

This article reports the synthesis of an aerogel involving reduced graphene oxide (rGO) and polyethylenimine (PEI), and describes its potential application as an effective sorbent to treat Hg(II) contaminated water. The rGO/PEI sorbent was synthetized using a supercritical CO₂ method. N₂ physisorption, electron microscopy, and elemental mapping were applied to visualize the meso/macroporous morphology formed by the supercritical drying. The advantages of the synthetized materials are highlighted with respect to the larger exposed GO surface for the PEI grafting of aerogels vs. cryogels, homogeneous distribution of the nitrogenated amino groups in the former and, finally, high Hg(II) sorption capacities. Sorption tests were performed starting from water solutions involving traces of Hg(II). Even though, the designed sorbent was able to eliminate almost all of the metal from the water phase, attaining in very short periods of time residual Hg(II) values as low as 3.5 µg L⁻¹, which is close to the legal limits of drinking water of 1–2 µg L⁻¹. rGO/PEI exhibited a remarkably high value for the maximum sorption capacity of Hg(II), in the order of 219 mg g⁻¹. All of these factors indicate that the designed rGO/PEI aerogel can be considered as a promising candidate to treat Hg(II) contaminated wastewater.

Activated carbon fiber modified with hyperbranched polyethylenimine and phytic acid for the effective adsorption and separation of In(iii)

The PA–HPEI–OACF constructed with PA, HPEI, and ACF displays excellent performance in the adsorption and separation of In(iii).

99mTc radiolabeling of polyethylenimine capped carbon dots for tumor targeting: synthesis, characterization and biodistribution

PURPOSE

Due to the favorable physicochemical properties and the biocompatibility, carbon dots (CDs) have gained a great attention as a tumor targeting agent. This study investigates polyethylenimine capped CDs (PEI capped CDs) as a prospective nanocarrier of technetium-99m (99mTc) for tumor targeting. Technetium-labeled CDs could be introduced as a promising candidate for single photon emission tomography (SPECT) imaging.

MATERIALS AND METHODS

Polyethylenimine capped CDs were prepared by hydrothermal method using hyperbranched PEI and citric acid. For a purpose of comparison, citrate capped CDs were also prepared by microwave irradiation. Both types of CDs were characterized and radiolabeled with 99mTc using sodium borohydride (NaBH4) as a reducing agent. Biodistribution and tumor targeting efficiency of the produced radiolabeled CDs have been studied in Earlich ascites tumor mice model.

RESULTS

Citrate capped CDs and PEI capped CDs have been synthesized successfully and characterized. High radiochemical yield of 99mTc-citrate capped CDs 99mTc-PEI capped CDs was obtained (97 ± 0.7 and 90 ± 0.2, respectively). Biodistribution studies of 99mTc-labeled PEI capped CDs have shown a potential tumor uptake (10 ± 0.5% Radioactivity/gram tumor) with high target to non-target ratio (T/NT) around 7 at 1-h post injection. 99mTc-citrate capped CDs have achieved a lower tumor uptake level (3.8 ± 0.3% Radioactivity/gram tumor 1 h post injection).

CONCLUSION

This study introduces PEI capped CDs as a promising nanocarrier of 99mTc for efficient tumor targeting. Technetium-labeled PEI capped CDs could be utilized as a potential SPECT tumor imaging agent.

Effect of pH and Molecular Length on the Structure and Dynamics of Linear and Short-Chain Branched Poly(ethylene imine) in Dilute Solution: Scaling Laws from Detailed Molecular Dynamics Simulations

Atomistic molecular dynamics (MD) simulations are carried out to examine the effect of molecular weight M_w (= 0.6, 0.86, 1.12, and 2.15 kDa) and pH (or equivalently, degree of ionization, α⁺ = 0, 50, and 100%) on the structure, state of hydration, and dynamics of linear and branched poly(ethylene imine) (PEI) chains in infinitely dilute salt-free aqueous solutions. It is found that the degree of ionization is the key factor determining the type of molecular conformation adopted by PEI, regardless of molecular architecture and chain length, resulting in a stable trans conformation for fully ionized solutions and in a stable gauche⁺/gauche^- state for neutral or alternate ionized ones; in the latter case, a strong electrolyte behavior is verified for both linear and branched PEI. Linear PEI is observed to be significantly stiffer than branched PEI of the same molecular weight at 100% degree of ionization, but the effect subsides as the degree of ionization decreases. Also, linear PEI diffuses markedly slower than branched PEI of the same M_w. From the MD results, scaling exponents are deduced and reported for the conformation, solvent-accessible surface area, and dynamics of the two different PEI structures with M_w.