Polyethylenimines Research Articles

Phenylene‐containing polyethylenimine‐like polymers absorb and release CO2 to blow biomass‐based polyurethanes

AbstractCO2 adducts of hydrophobically modified polyethylenimines (PEIs) are promising alternatives to global warming halogen‐containing blowing agents of polyurethanes (PUs), despite the high cost of the raw material PEIs. Herein, an economical synthesis of PEI‐like polymers was explored via condensation between pentaethylenehexamine and terephthalaldehyde, followed by chemical reduction of the as‐formed Schiff base linkages. The resultant p‐phenylene‐containing polyamine polymers (PEIPs) could be grafted with alkyl (Cn) side chains and adducted with CO2 to form a new type of CO2‐releasing blowing agents for PUs designated as yCn‐xPEIP‐CO2s, where x and y represent the backbone molecular weight and the side chain grafting rate, respectively. Among them, the specimen 10%C8−3.6 kPEIP‐CO2 was the most effective in terms of good dispersibility in PU raw materials, low foam density (about 51 kg/m3), and uniform pore morphology. Moreover, the phenylene linkages enhanced the hydrophobicity of the consequent CO2 adducts and weakened the intermolecular hydrogen bonding and ionic attraction, both facilitating the dispersion of the corresponding blowing agents into a castor oil‐derived polyol, Polycin M‐365. The specimen 10%C8−3.6 kPEIP‐CO2 could disperse as suspended fine floccules that finally aggregated into a flocculent, liquid‐like bottom layer, being easily redispersed into the bulk. The unique compatibility with plant oil‐derived polyols and the economic availability would make the PEIP‐based blowing agents suitable for the next generation of sustainable and biomass‐based PU foams.

Homogeneous polyurethane foaming systems containing polyester diol, ethylene glycol, and alkylated polyethylenimine‐CO2 adducts

AbstractCO2 adducts from alkylated polyethylenimines (PEIs) in powder form are newly developed blowing agents for polyurethanes (PUs) to replace the ozone‐depleting and/or global warming halogen‐containing blowing agents. However, they are difficult to disperse into the raw materials of PUs. Herein, we explored reactive solvents for alkyl‐grafted PEI‐based CO2 adducts (xCn‐PEI‐CO2s, whose alkyl carbon number n = 4, 8, or 12 and grafting rate x = 5%, 10%, or 15%) and found that the most effective solvent was ethylene glycol (EG), with solute mass concentrations exceeding 50%. According to this, we designed homogenous foaming systems for PUs, containing poly(ethylene‐co‐diethylene glycol adipate)diol, EG, and different xCn‐PEI‐CO2 blowing agents, with mass percentages of 85, 11.25, and 3.75, respectively. The xCn‐PEI‐CO2 blowing agents in the ternary mixture could effectively blow PUs, with densities ranging from 210 to 240 kg/m3. The addition of 0.1 g of water as an extra blowing agent reduced the densities down to 110 kg/m3, compared with the 140 kg/m3 density of the control foam blown solely by water. The liquid status of the ternary foaming mixtures and their cooperative performance with water to blow PUs could enhance the suitability of the climate‐friendly xCn‐PEI‐CO2 blowing agents in PU foam industry.

Polyurethane foams co-blown by water and alkylated polyethylenimine-CO2 adducts: An additive or antagonistic effect?

Recently developed CO2 adducts of alkylated polyethylenimines (PEIs) can replace traditional, ozone-depleting, and/or global warming halogen-containing blowing agents of polyurethanes (PUs). Meanwhile, water is the most common chemical blowing agent that is cheap and also environment neutral. Herein, the co-blowing performances of the two types of blowing agents were investigated. For the polyether polyol or castor oil derived polyol foaming systems, which were blended just before foaming, the consequent co-blown foams surprisingly did not possess lower densities than the control foams blown solely by water, showing an antagonistic effect in blowing performance. The relatively large particles (e.g. tens of micrometers) of the hydrophilic PEI-CO2 blowing agents absorbed water from the foaming mixtures, preventing the trapped water from chemically blowing PUs. After the foams were set, the absorbed water gradually diffused out to react with the residual isocyanate groups, which no longer contributed to PU foaming. Differently, after aging the castor oil derived polyol foaming mixtures (without water and isocyanate components that were added before PU foaming), the dispersed PEI-CO2 particles decreased in size down to nanoscale (about 20–180 nm). These nanoparticles were small enough for out-diffusion of the absorbed water, which generated foaming CO2 in time. The densities of the resultant foams could be lowered to the theoretical values. The additive effect with water could enhance the application freedom of the climate-friendly alkylated PEI-CO2 blowing agents.

Imines supported on silica as CO2 capture selective adsorbents

CO2 capture technologies must be developed to reduce Green House Gas emissions in order to fulfill the Paris Agreement. Adsorption is considered one of the available technologies due to the mild conditions used in the process. Selective sorbents with high CO2 adsorption capacities are needed. In this work, several types of branched polyethylenimines (PEI), with different average molecular weight, are used agglomerated with silica at different amounts by weight. The adsorption has been measured and the kinetic parameters are estimated from breakthrough experiments in a fixed bed. The results showed that the materials produced were selective to CO2 and can be used in adsorption processes, the sample lowest average molecular weight had the higher adsorption capacity.

3D Graphene Oxide-Polyethylenimine Scaffolds for Cardiac Tissue Engineering.

The development of novel three-dimensional (3D) nanomaterials combining high biocompatibility, precise mechanical characteristics, electrical conductivity, and controlled pore size to enable cell and nutrient permeation is highly sought after for cardiac tissue engineering applications including repair of damaged heart tissues following myocardial infarction and heart failure. Such unique characteristics can collectively be found in hybrid, highly porous tridimensional scaffolds based on chemically functionalized graphene oxide (GO). By exploiting the rich reactivity of the GO's basal epoxydic and edge carboxylate moieties when interacting, respectively, with NH2 and NH3+ groups of linear polyethylenimines (PEIs), 3D architectures with variable thickness and porosity can be manufactured, making use of the layer-by-layer technique through the subsequent dipping in GO and PEI aqueous solutions, thereby attaining enhanced compositional and structural control. The elasticity modulus of the hybrid material is found to depend on scaffold's thickness, with the lowest value of 13 GPa obtained in samples containing the highest number of alternating layers. Thanks to the amino-rich composition of the hybrid and the established biocompatibility of GO, the scaffolds do not exhibit cytotoxicity; they promote cardiac muscle HL-1 cell adhesion and growth without interfering with the cell morphology and increasing cardiac markers such as Connexin-43 and Nkx 2.5. Our novel strategy for scaffold preparation thus overcomes the drawbacks associated with the limited processability of pristine graphene and low GO conductivity, and it enables the production of biocompatible 3D GO scaffolds covalently functionalized with amino-based spacers, which is advantageous for cardiac tissue engineering applications. In particular, they displayed a significant increase in the number of gap junctions compared to HL-1 cultured on CTRL substrates, which render them key components for repairing damaged heart tissues as well as being used for 3D in vitro cardiac modeling investigations.

Analysis of polymeric nanoparticle properties for siRNA/DNA delivery in a tumor xenograft tissue slice air-liquid interface model.

Classical two-dimensional (2D) cell culture as a drug or nanoparticle test system only poorly recapitulates in vivo conditions. Animal studies are costly, ethically controversial, and preclude large-scale testing. We established a three-dimensional (3D) tissue slice air-liquid interface (ALI) culture model for nanoparticle testing. We developed an optimized procedure for the reproducible generation of large sets of tissue slices from tumor xenografts that retain their tissue architecture. When used for the analysis of nanoparticles based on chemically modified polyethylenimines (PEIs) to deliver siRNA or DNA, differences in transfection efficacy and cytotoxicity between nanoparticles were observed more clearly than in 2D cell culture. While nanoparticle efficacies between cell culture and the tissue slice model overall correlated, the tissue slice model also identified particularly suitable candidates whose efficacy was underestimated in 2D cell culture and had already been shown in previous in vivo studies. The ex vivo 3D tissue slice ALI culture model is a powerful system that allows the effective evaluation of biological nanoparticle efficacy and biocompatibility in an intact tissue environment. It is comparably inexpensive, time-saving, and follows the 3R principle, while allowing the identification of critical nanoparticle properties and optimal candidates for in vivo applications.

Analytical pyrolysis of polyethyleneimines

Poly(ethylene imine) is a family of polymers with a high content of amine groups employed in various applications and widely investigated as CO2 adsorbents in carbon capture and sequestration. In this study, five branched polyethylenimines (PEIs) of different molecular weights were analysed by Py-GC-MS to gather information on the chemical structure of the principal thermal degradation products. All the PEIs produced pyrolysates with a similar chemical composition characterised by the occurrence of ethylenediamine, diethylenetriamine, piperazine, N-ethylaminepiperazine, pyrazine, 2-methylpyrazine, 2,3-dimethylpyrazine, 2-ethylpyrazine. Oligomeric ethylene polyamines were volatilised or evolved after chain scission of the PEI backbone. Pyrolysates also contained minor amounts of alkylated pyrroles, imidazoles, pyridines and other compounds that could not be identified. Pyrolysis products were formed at 300 °C, and their abundance increased markedly from 400° to 600°C. Pyrolysis of PEIs at 500 °C in the presence of mesoporous silica favoured cyclisation and aromatisation, enhancing the production of alkylated pyrazines. These compounds are of potential interest in the food industry as flavour-enhancing additives.

Comparison of tyrosine-modified low molecular weight branched and linear polyethylenimines for siRNA delivery

Polyethylenimines (PEIs) have been previously introduced for siRNA delivery. In particular, in the case of higher molecular weight PEIs, this is associated with toxicity, while low molecular weight PEIs are often insufficient for siRNA complexation. The tyrosine-modification of PEIs has been shown to enhance PEI efficacy and biocompatibility. This paper evaluates a set of tyrosine-modified low molecular weight linear or branched polyethylenimines as efficient carriers of siRNA. Complexation efficacies and biophysical complex properties were analyzed by zeta potential, dynamic light scattering and circular dichroism measurements as well as gel electrophoresis. Biological knockdown was studied in 2 D cell culture and 3 D ex vivo tissue slice air-liquid interface culture. The results demonstrate that siRNAs were able to form stable complexes with all tested polymers. Complexation was able to protect siRNA from degradation by RNase and to mediate target gene knockdown, as determined on the mRNA level and in PC3-Luc3/EGFP and HCT116-Luc3/EGFP expressing reporter cells on the protein level, using flow cytometry and confocal microscopy. The direct comparison of the studied polymers revealed differences in biological efficacies. Moreover, the tyrosine-modified PEIs showed high biocompatibility, as determined by LDH release and mitochondria integrity (J-aggregate assay) as well as caspase 3/7 (apoptosis) and H2O2 levels (ROS). In 3 D tissue slices, complexes based on LP10Y proved to be most efficient, by combining tissue penetration with efficient gene expression knockdown.

Polyethylenimine Increases Antibacterial Efficiency of Chlorophyllin.

Polyethylenimines (PEIs), a group of polycationic molecules, are known to impair the outer membrane of Gram-negative bacteria and exhibit antimicrobial activity. The outer membrane of Gram-negative strains hinders the uptake of photosensitizer chlorophyllin. In this study, we report chlorophyllin and branched PEI combinations’ activity against Escherichia coli strains DH5α and RB791, Salmonella enterica sv. Typhimurium LT2, and Bacillus subtilis 168. The minimal bactericidal concentration (MBC) was determined by plating cells treated with different concentrations of PEI and chlorophyllin on agar and monitoring their growth after 24 h. All tested combinations of PEI and chlorophyllin were lethal for S. enterica after 240 min of incubation in light, whereas PEI alone (<100 µg mL−1) was ineffective. In the darkness, complete inhibition was noted with a combination of ≥2.5 µg mL−1 chlorophyllin and 50 µg mL−1 PEI. If applied alone, PEI alone of ≥800 µg mL−1 of PEI was required to completely inactivate E. coli DH5α cells in light, whereas with ≥5 µg mL−1 chlorophyllin, only ≥100 µg mL−1 PEI was needed. No effect was detected in darkness with PEI alone. However, 1600 µg mL−1 PEI in combination with 2.5 µg mL−1 resulted in complete inactivation after 4 h dark incubation. PEI alone did not inhibit E. coli strain RB791, while cells were inactivated when treated with 10 µg mL−1 chlorophyllin in combination with ≥100 µg mL−1 (in light) or ≥800 µg mL−1 PEI (in darkness). Under illumination, B. subtilis was inactivated at all tested concentrations. In the darkness, 1 µg mL−1 chlorophyllin and 12.5 µg mL−1 PEI were lethal for B. subtilis. Overall, PEI can be used as an antimicrobial agent or potentiating agent for ameliorating the antimicrobial activity of chlorophyllin.

Kinetic, Isotherm, and Equilibrium Investigation of Cr(VI) Ion Adsorption on Amine-Functionalized Porous Silica Beads.

The hexavalent chromium (Cr(VI)) ion adsorption properties were conferred to porous silica beads by introducing alkylamine chains through functionalization with an aminosilane coupling agent, [3-(2-aminoethylamino)propyl]triethoxysilane (AEAPTES), or with an epoxysilane coupling agent, (3-glycidyloxypropyl)triethoxysilane (GOPTES), and polyfunctional amine compounds or poly-ethylenimines (PEIs). The presence of amino groups on the silica beads was confirmed by XPS and the amount of amino groups increased to 0.270 mmol/g by increasing the AEAPTES concentration and/or reaction time. The adsorption capacity of the silica beads functionalized with AEAPTES was the maximum at the initial pH value of 3.0 and the initial adsorption rate increased with an increase in the temperature. The adsorption capacity increased with an increase in the amount of amino groups at pH 3.0 and 30 °C. The adsorption behavior obeyed the pseudo-second order kinetic model and was well expressed by the Langmuir isotherm. These results support that Cr(VI) ion adsorption is accomplished through the electrostatic interaction between protonated amino groups and HCrO4− ions. In addition, the adsorption capacity further increased to 0.192–0.320 mmol/g by treating the GOPTES-treated silica beads with triethylenetetramine, pentaethylenehexamine, or PEI. These empirical, equilibria, and kinetic aspects obtained in this study support that the porous silica-based adsorbents prepared in this study can be applied to the removal of Cr(VI) ions.

Polyethylenimine-Coated Ultrasmall Holmium Oxide Nanoparticles: Synthesis, Characterization, Cytotoxicities, and Water Proton Spin Relaxivities.

Water proton spin relaxivities, colloidal stability, and biocompatibility of nanoparticle magnetic resonance imaging (MRI) contrast agents depend on surface-coating ligands. In this study, hydrophilic and biocompatible polyethylenimines (PEIs) of different sizes (Mn = 1200 and 60,000 amu) were used as surface-coating ligands for ultrasmall holmium oxide (Ho2O3) nanoparticles. The synthesized PEI1200- and PEI60000-coated ultrasmall Ho2O3 nanoparticles, with an average particle diameter of 2.05 and 1.90 nm, respectively, demonstrated low cellular cytotoxicities, good colloidal stability, and appreciable transverse water proton spin relaxivities (r2) of 13.1 and 9.9 s−1mM−1, respectively, in a 3.0 T MR field with negligible longitudinal water proton spin relaxivities (r1) (i.e., 0.1 s−1mM−1) for both samples. Consequently, for both samples, the dose-dependent contrast changes in the longitudinal (R1) and transverse (R2) relaxation rate map images were negligible and appreciable, respectively, indicating their potential as efficient transverse T2 MRI contrast agents in vitro.

Branched versus Linear Structure: Lowering the CO2 Desorption Temperature of Polyethylenimine-Functionalized Silica Adsorbents

Lowering the regeneration temperature for solid CO2-capture materials is one of the critical tasks for economizing CO2-capturing processes. Based on reported pKa values and nucleophilicity, we compared two different polyethylenimines (PEIs): branched PEI (BPEI) and linear PEI (LPEI). LPEI outperformed BPEI in terms of adsorption and desorption properties. Because LPEI is a solid below 73–75 °C, even a high loading amount of LPEI can effectively adsorb CO2 without diffusive barriers. Temperature-programmed desorption (TPD) demonstrated that the desorption peak top dropped to 50.8 °C for LPEI, compared to 78.0 °C for BPEI. We also revisited the classical adsorption model of CO2 on secondary amines by using in situ modulation excitation IR spectroscopy, and proposed a new adsorption configuration, R1(R2)-NCOOH. Even though LPEI is more expensive than BPEI, considering the long-term operation of a CO2-capturing system, the low regeneration temperature makes LPEI attractive for industrial applications.

Unmodified and tyrosine-modified polyethylenimines as potential carriers for siRNA: Biophysical characterization and toxicity

Polyethylenimines (PEIs) are being explored as efficient non-viral nanocarriers for nucleic acid delivery in vitro and in vivo. To address limitations regarding PEI efficacy and biocompatibility, modifications of the chemical structure of linear and branched PEIs have been introduced, including grafting with tyrosine. The aim has been to compare linear and branched polyethylenimines of a wider range of different molecular mass with their tyrosine-modified derivatives. To do so, physico-chemical and biological properties of the polymers were investigated.Even in the absence of a negatively charged nucleic acid counterpart, PEIs form particle structures with defined size and surface potential. Tyrosine modification of PEI led to significantly reduced toxicity, while simultaneously increasing interaction with cellular membranes. All the effects were also dependent on the PEI molecular weight and structure (i.e., linear vs. branched). Especially in the case of linear PEIs, the improved membrane interaction also translated into slightly enhanced hemolysis, whereas their genotoxic potential was essentially abolished. Due to the improvement of properties critical for nano-vector efficacy and biocompatibility, our data demonstrate that tyrosine-modified PEIs are very promising and safe nanocarriers for the delivery of small RNAs, like siRNAs and miRNAs.

Non-viral siRNA transfection of primary mesenchymal stromal cells (MSCs): Assessment of tyrosine-modified PEI and PPI efficacy and biocompatibility

Mesenchymal stromal cells (MSCs) are multipotent cells derived from different sources and able to differentiate into distinct cell lineages. For their possible biomedical application, the “tuning” of MSCs also involves the specific knockdown of defined target genes. A major limitation, however, is the notoriously low transfection efficacy especially of primary MSCs.In this paper, we systemically analyze a large set of tyrosine-modified linear or branched low molecular weight polyethylenimines (PEIs) of different sizes, as well as the tyrosine-modified polypropylenimine dendrimer PPI-G4, for their capacity of non-viral siRNA transfection into umbilical cord-derived MSCs from two different donors. Knockdown efficacies are determined on the molecular level and confirmed in functional assays. Beyond the determination of cell viabilities, acute cytotoxicity, induction of apoptosis/necrosis and mitochondrial membrane alterations are also studied. On the molecular level, caspase activation, ROS induction and genotoxic effects are analyzed.Major differences are observed between the various tyrosine-modified PEIs, with some candidates showing high knockdown efficacy and biocompatibility. PPI-G4-Y dendrimers, however, are identified as most efficient for siRNA transfection into MSCs. PPI-G4-Y/siRNA nanoparticles lead to particularly high gene knockdown, without cytotoxic and genotoxic effects on the cellular and molecular level, and are thus particularly well-suited for the tuning of MSCs.

Therapeutic delivery of siRNA with polymeric carriers to down-regulate STAT5A expression in high-risk B-cell acute lymphoblastic leukemia (B-ALL).

Overexpression and persistent activation of STAT5 play an important role in the development and progression of acute lymphoblastic leukemia (ALL), the most common pediatric cancer. Small interfering RNA (siRNA)-mediated downregulation of STAT5 represents a promising therapeutic approach for ALL to overcome the limitations of current treatment modalities such as high relapse rates and poor prognosis. However, to effectively transport siRNA molecules to target cells, development of potent carriers is of utmost importance to surpass hurdles of delivery. In this study, we investigated the use of lipopolymers as non-viral delivery systems derived from low molecular weight polyethylenimines (PEI) substituted with lauric acid (Lau), linoleic acid (LA) and stearic acid (StA) to deliver siRNA molecules to ALL cell lines and primary samples. Among the lipid-substituted polymers explored, Lau- and LA-substituted PEI displayed excellent siRNA delivery to SUP-B15 and RS4;11 cells. STAT5A gene expression was downregulated (36–92%) in SUP-B15 and (32%) in RS4;11 cells using the polymeric delivery systems, which consequently reduced cell growth and inhibited the formation of colonies in ALL cells. With regard to ALL primary cells, siRNA-mediated STAT5A gene silencing was observed in four of eight patient cells using our leading polymeric delivery system, 1.2PEI-Lau8, accompanied by the significant reduction in colony formation in three of eight patients. In both BCR-ABL positive and negative groups, three of five patients demonstrated marked cell growth inhibition in both MTT and trypan blue exclusion assays using 1.2PEI-Lau8/siRNA complexes in comparison with their control siRNA groups. Three patient samples did not show any positive results with our delivery systems. Differential therapeutic responses to siRNA therapy observed in different patients could result from variable genetic profiles and patient-to-patient variability in delivery. This study supports the potential of siRNA therapy and the designed lipopolymers as a delivery system in ALL therapy.

Disaccharide-polyethylenimine organic nanoparticles as non-toxic in vitro gene transporters and their anticancer potential

Polyethylenimines (PEIs) have been shown as efficient gene delivery vectors due to their unique properties, however, toxicity as well as non-specific interactions with the tissues/cells because of high charge density have hampered their use in clinical applications. To counter these concerns, here, we have prepared disachharide-PEI organic nanoparticles by mixing PEIs with non-reducing disaccharides, i.e. trehalose (TPONs) and sucrose (SPONs), under mild conditions. The fabricated nanoparticles were complexed with pDNA and size of these complexes was found in the range of ~130–162 nm with zeta potential ~ +8–25 mV. Further evaluation of these nanoparticles revealed that substitution of disaccharides on PEIs successfully augmented cell viability. Transfection efficiency exhibited by these complexes was significantly higher than the unmodified polymer and the standard, Lipofectamine, complexes. Fabrication of organic nanoparticles did not alter the buffering capacity considerably which was found to be instrumental during endosomal escape of the complexes. Among both the series of nanoparticles, trehalose-PEI organic nanoparticles (TPONs) exhibited greater pDNA transportation potential than sucrose-PEI organic nanoparticles (SPONs) which was also established by flow cytometric data, wherein percent cells expressing GFP was higher in case of TP/pDNA complexes as compared to SP/pDNA complexes. Interestingly, TPONs also showed promising anticancer activity on cancer cell lines i.e. Mg63, MCF-7 and HepG2. Overall, the results advocate promising potential of disaccharide-PEI organic nanoparticles as efficient gene delivery agents which can be used effectively in future gene therapy applications along with anti-cancer competence of TPONs.

Carbon dioxide adducts from DOPO‐grafted polyethylenimines as both blowing agents and flame retardants for polyurethanes

AbstractThe high risk of flammability of polyurethane foams (PUFs) and the high global warming potentials of polyurethane (PU) blowing agents rank key problems to be solved in PUF industry. Herein, 9,10‐dihydro‐9‐oxa‐10‐phosphenanthrene‐10‐oxide (DOPO)‐grafted polyethylenimines (PEIs) are synthesized via Atherton–Todd reaction, with grafting rate ranging from 13.3% to 28.3%. The grafted PEIs further react with CO2 to obtain corresponding CO2 adducts (DOPO‐PEI‐CO2s). On the one hand, these CO2 adducts can disperse into PU foaming mixture to release CO2 as a climate‐friendly blowing agent. The resultant PUFs possess a density about 56 kg m−3 and a compressive strength over 200 kPa, suitable for some industrial applications. On the other hand, the DOPO grafting endows the PUFs with moderate flame retardancy, increasing the PUFs' limiting oxygen index value from 19.7 to 25 vol%, and decreasing the horizontal burning speed from about 360 mm min−1 down to 130 mm min−1. This study for the first time provides a type of polyurethane (PU) raw material that can serve as both blowing agents and flame retardants.

In situ synthesis of CO2 adducts of modified polyethylenimines in polyether polyols for polyurethane foaming

CO2 adducts from hydrophobically-modified polyethylenimines (PEIs) in powder form are newly-developed environment-friendly blowing agents for polyurethanes (PUs). However, they are difficult to disperse into foaming systems that usually contain polyether polyols as the PU soft segments. Herein, we employ mixtures of di(propylene glycol) monomethyl ether-grafted polyethylenimines (DPG-PEIs) and poly(propylene glycol) (PPG) polyols to absorb CO2, with in situ formation of the CO2 adduct particles as PU blowing agents. Their CO2 saturation degrees, revealed by thermogravimetry, scatter in the range of 93–98%. The DPG side chains tend to be exposed at the particle–matrix interface to stabilize the particles. In addition, some PPG oligomers in the matrix might entangle with the CO2 adduct macromolecules during the in situ particle formation. The entangled PPG chains could further stabilize the suspending particles. The high grafting rate and high molecular weight of the PEI backbones could result in small particles, which largely thicken the foaming systems. The optimized blowing agents, with grafting rates between 5% and 8% and PEI backbone molecular weights not higher than 10k Da, show particle sizes from several hundreds of nanometers to ∼1 μm. The resultant foams demonstrate densities below 50 kg/m3 and compressive strengths over 200 kPa, comparable to the values from industrial foams. This in situ CO2 adduction has potential as a universal method suitable for PU foaming at an industrial scale.

Supramolecular self-assemblies of engineered polyethylenimines as multifunctional nanostructures for DNA transportation with excellent antimicrobial activity

In this study, indole-3-butanoic acid (IBA), a biologically and environmentally safe entity, has been grafted onto low and high molecular weight (1.8 and 25 kDa) polyethylenimines (PEI) mainly through primary amines to obtain amphiphilic indole-3-butanoyl-polyethylenimines (IBPs). Two series of IBPs (IBP1.8 and IBP25) were prepared which, on self-assembly in aqueous medium, yielded multifunctional nanomicellar structures (IBP1.8 and IBP25) capable of transporting genetic material in vitro and exhibiting other biological activities. Physicochemical characterization showed the size of IBP1.8 and IBP25 nanostructures in the range of ~332–234 nm and ~283–166 nm, respectively, with zeta potential varying from ~+29–17 mV and ~+37–25 mV. DNA release assay demonstrated higher release of plasmid DNA from IBP nanostructures as compared to native PEIs. Cytotoxicity showed a decreasing pattern with increasing degree of grafting of IBA onto PEIs making these nanostructures non-toxic. pDNA complexes of these nanostructures (both IBPs1.8 and IBPs25) displayed considerably higher transfection efficiency, however, IBP1.8/pDNA complexes performed much better (~7–9 folds) as compared to native PEI/pDNA and Lipofectamine/pDNA complexes on mammalian cells. CLSM analysis revealed that these complexes entered nucleus in sufficient amounts suggesting higher uptake and efficient internalization of the complexes. Besides, these supramolecular nanostructures not only exhibited excellent antimicrobial potential (MIC ~49–100 µg/ml) against clinical as well as resistant pathogenic strains but also found to possess antioxidant property. Overall, the projected low molecular weight PEI-based vectors could serve as more effective multifunctional nanomaterials having promising potential for future gene therapy applications with capability to provide protection against other bacterial infections.

Rational design of silicas with meso-macroporosity as supports for high-performance solid amine CO2 adsorbents

Silica-supported amine adsorbents are extensively studied for CO2 capture. However, rational design of silica materials with specific pore structures as amine supports for large CO2 adsorption capacity, fast adsorption-desorption kinetics, easy regeneration, and good cyclic performance, still remains a challenge. Herein, we synthesize a series of ordered silicas with either bimodal or trimodal meso-macro porosities through a single- or double-templating route as supports for polyethylenimines (PEI) to make solid amine CO2 adsorbents. Bimodal silicas with textural mesopores and interconnected macropores are ideal supports at medium amine loading, illustrated by significantly high amine efficiencies, e.g., 50BPEI (800)/PS-80-00 achieves a CO2 uptake of 350 mg g−1 PEI at 75 °C, 1 bar, which is the one of the highest values among PEI/silica composites reported so far; however, further increase of amine loading leads to severe amine efficiency fading. In comparison, trimodal silicas with internal mesopores, textural mesopores, and interconnected macropores show outstanding performance at high amine loading, e.g., 70BPEI (800)/PS-80-187 exhibits a CO2 adsorption capacity of 215 mg g−1 adsorbent at 75 °C, 1 bar, which is one of the highest values among reported PEI/silica composites. Moreover, we also study the correlations of the CO2 adsorption capacity and kinetics, regeneration of adsorbent, and cyclic CO2 adsorption-desorption performance with the PEI type, PEI loading amount, and operation temperatures. This work brings insight into factors affecting the CO2 capture performance for amine-impregnated silica composites, providing an important guidance to design high-performance solid amine CO2 adsorbents in the near future.