Cationic Polymer Chains Research Articles

Gas-Controlled Self-Assembly of Metallacycle-Cored Supramolecular Star Polymer with Tunable Antibacterial Activity.

Herein, a three-armed amphiphilic metallacycle-cored star supramolecular polymer (Por-MOM-PDMAEMA) has been designed and synthesized via highly efficient post-assembly polymerization. This star polymer is further self-assembled into nanoparticles of different sizes depending upon the experimental conditions. The gas-controlled morphology transformation and tunable antibacterial activities of Por-MOM-PDMAEMAis systematically investigated and compared with metallacycle (MOM). The superior antibacterial activity of Por-MOM-PDMAEMA against multidrug-resistant P. aeruginosa implies that the presence of photodynamic photosensitizer (Por) and cationic polymer chain will significantly enhance antibactericidal activity, which is mainly attributed to the synergistic effect of photosensitizer and polymer chain linked in one metallacycle core. By leveraging the unique properties of metallacycle and their dynamic response to gaseous stimuli, the antibacterial properties of the Por-MOM-PDMAEMA can be finely tuned in response to gas triggers.

Air-Stable Semiconducting Ionic Polymers for Thermoelectric Applications

Thermoelectric (TE) devices that interconvert heat and electricity are the promising tools to harvest waste heat and solve energy problems. The current TE market is dominated by inorganic materials such as Bi2Te3 due to their excellent TE performance; however, the issues of inorganics that involve material toxicity, rigidity, heavy weight and energy-intensive processing techniques are limiting the wide applications of TE devices. Choosing organic materials that are light weight, mechanically flexible, abundant and require low-temperature processing, as in our research focus, is paving the path to sustainability and opening up opportunities for a variety of applications such as electronic wearables and sensors.In our study, we aim to design and develop sensors that can detect high electric-field utilizing air-stable ionic polymer TE systems, a novel type of organic semiconductors, via a facile, solution-processing technique. We selected two n-type chloride-based ionic polymers, MADQUAT and PDADMAC as our starting materials because they have relatively low yet reliable ionic conductivities and intrinsically high Seebeck Coefficients under dry condition. The key challenge was that chloride-based polymers were extremely unstable due to their sensitivity to air/moisture and polymer relaxation. We adopted a solution-processable anion exchange technique and successfully created new systems with the same cationic polymer chain but various anions such as tetrafluoroborate (BF4 -) and hexafluorophosphate (PF6 -), that are more hydrophobic, increasing the system stability. Currently, we are investigating our stable ionic polymer TE performance by applying high voltages (500V-2000V) laterally across the samples through a pair of electrodes thermally evaporated on top. The change in TE properties after the high E-field application will help us probe further into the ionic movement of the polymeric systems thermodynamically and kinetically and understand what determines the p/n-type behavior. The thermoelectric sensor for high E-field detection can be incorporated into devices that can detect planetary objects in the outer space as well as microscale biological systems.

Multi‐Stimuli Responsive Thiazolothiazole Viologen‐Containing Poly(2‐Isopropyl‐2‐Oxazoline) and Its Multi‐Modal Thermochromism, Photochromism, Electrochromism, and Solvatofluorochromism Applications

AbstractSmart materials are highly desirable over the recent decade due to the growing demand on complicated nature. Smart materials with stable stimuli‐responsive properties are widely applied in sensors, smart windows, displays, and chemical valves, but they are relatively rare. Most of the current chromic materials are triggered by one or two external stimuli, and only a few multi‐stimuli responsive instances still suffer by their restricting functional states, such as solution or polymer. To address these challenges, researchers are focusing their efforts on developing a new generation of multi‐stimulus responsive chromic materials. In this article, our group has adopted a new strategy for the synthesis of the multi‐stimuli responsive single polymeric material, which can be useful for different applications (such as thermochromism, photochromism, electrochromism, and solvatofluorochromism). Thiazolothiazole viologen (TTv)‐containing poly(2‐isopropyl‐2‐oxazoline) (PiPO) was synthesized using a one‐pot reaction where the living cationic polymer chains were reacted with thiazolothiazole viologen to produce multi‐stimuli responsive PiPO‐TTv. PiPO‐TTv‐based device demonstrated multi‐responsive properties due to the thermoresponsive properties of PiPO segments and photo‐, electro‐responsive properties of TTv monomer, respectively. PiPO‐TTv material, additionally exhibits fluorescence characteristics that makes it appealing for environmental and molecular biological sensor applications.

Lignin-Based Nonviral Gene Carriers Functionalized by Poly[2-(Dimethylamino)ethyl Methacrylate]: Effect of Grafting Degree and Cationic Chain Length on Transfection Efficiency.

Lignin is a natural renewable biomass resource with great potential for applications, while its development into high value-added molecules or materials is rare. The development of biomass lignin as potential nonviral gene delivery carriers was initiated by our group through the “grafting-from” approach. Firstly, the lignin was modified into macroinitiator using 2-bromoisobutyryl bromide. Then cationic polymer chains of poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) were grown from the lignin backbone using atom transfer radical polymerization (ATRP) to yield lignin-PDMAEMA graft copolymers (LPs) with branched structure. To gain a deep understanding of the relationship between the nonviral gene transfection efficiency of such copolymers and their structural and compositional factors, herein eight lignin-based macroinitiators with different modification degrees (MDs, from 3.0 to 100%) were synthesized. Initiated by them, a series of 20 LPs were synthesized with varied structural factors such as grafting degree (GD, which is equal to MD, determining the cationic chain number per lignin macromolecule), cationic chain length (represented by number of repeating DMAEMA units per grafted arm or degree of polymerization, DP) as well as the content of N element (N%) which is due to the grafted PDMAEMA chains and proportional to molecular weight of the LPs. The in vitro gene transfection capability of these graft copolymers was evaluated by luciferase assay in HeLa, COS7 and MDA-MB-231cell lines. Generally, the copolymers LP-12 (N% = 7.28, MD = 36.7%, DP = 13.6) and LP-14 (N% = 6.05, MD = 44.4%, DP = 5.5) showed good gene transfection capabilities in the cell lines tested. Overall, the performance of LP-12 was the best among all the LPs in the three cell lines at the N/P ratios from 10 to 30, which was usually several times higher than PEI standard. However, in MDA-MB-231 at N/P ratio of 30, LP-14 showed the best gene transfection performance among all the LPs. Its gene transfection efficiency was ca. 11 times higher than PEI standard at this N/P ratio. This work demonstrated that, although the content of N element (N%) which is due to the grafted PDMAEMA chains primarily determines the gene transfection efficiency of the LPs, it is not the only factor in explaining the performance of such copolymers with the branched structure. Structural factors of these copolymers such as grafting degree and cationic chain length could have a profound effect on the copolymer performance on gene transfection efficiency. Through carefully adjusting these factors, the gene transfection efficiency of the LPs could be modulated and optimized for different cell lines, which could make this new type of biomass-based biomaterial an attractive choice for various gene delivery applications.

Quaternization of Poly(2-diethyl aminoethyl methacrylate) Brush-Grafted Magnetic Mesoporous Nanoparticles Using 2-Iodoethanol for Removing Anionic Dyes

Magnetic mesoporous silica nanoparticles (Fe3O4-MSNs) were successfully synthesized with a relatively high surface area of 568 m2g−1. Fe3O4-MSNs were then modified with poly(2-diethyl aminoethyl methacrylate) (PDEAEMA) brushes using surface-initiated ARGET atom transfer radical polymerization (ATRP) (Fe3O4@MSN-PDMAEMA). Since the charge of PDEAEMA is externally regulated by solution pH, tertiary amines in the polymer chains were quaternized using 2-iodoethanol to obtain cationic polymer chains with a permanent positive charge (Fe3O4@MSN-QPDMAEMA). The intensity of the C−O peak in the C1s X-ray photoelectron spectrum increased after reaction with 2-iodoethanol, suggesting that the quaternization process was successful. The applicability of the synthesized materials on the removal of methyl orange (MO), and sunset yellow (E110) dyes from an aqueous solution was examined. The effects of pH, contact time, and initial dyes concentrations on the removal performance were investigated by batch experiments. The results showed that the Fe3O4@MSN-PDMAEMA sample exhibited a weak adsorption performance toward both MO and E110, compared with Fe3O4@MSN-QPDMAEMA at a pH level above 5. The maximum adsorption capacities of MO and E110 using Fe3O4@MSN-QPDMAEMA were 294 mg g−1 and 194.8 mg g−1, respectively.

Physicochemical characterization and flocculation performance evaluation ofPAC/PMAPTACcomposite flocculant

AbstractA novel inorganic–organic composite flocculant was prepared with polyaluminum chloride (PAC) and poly(methacrylamido propyl trimethyl ammonium chloride) (PMAPTAC). To understand the physicochemical characterization of PAC/PMAPTAC and evaluate its flocculation efficiency, the interactions of PAC and cationic polymer were investigated, then the characterization and flocculation performance of PAC/PMAPTAC and PAC/Poly‐dimethyldiallylammonium chloride (PDMDAAC) were compared. The results showed that there were obvious interactions between PAC and cationic polymer in composite flocculant. The cationic polymer chain exhibited a coiled state in PAC solution, and the curly degree of PMAPTAC chain was lower than that of PDMDAAC due to the intermolecular association of methyl of PMAPTAC. The cationic polymer enhanced the charge neutralization ability of PAC and changed the aluminum hydrolysis polymerization species of PAC from low and medium polymeric species to high‐polymeric species. The flocculation sedimentation experiments turned out that the charge neutralization and bridging ability of PAC/PMAPTAC was higher than that of PAC/PDMDAAC, and the increase of molecular weight or content of PMAPTAC in PAC/PMAPTAC could enhance the charge neutralization and adsorption bridging ability simultaneously. The enhanced effects may come from the exist of polymer and the interactions between PAC and cationic polymer in composite flocculant.

Floating Magnetic Membrane for Rapid Enrichment of Pathogenic Bacteria

Efficient separation and enrichment of pathogenic bacteria from complex matrices are crucial for the detection and downstream biomedical investigations. Herein, we report a floating magnetic membrane comprised of superparamagnetic nanoparticles and cationic polymer chains for rapid capture and enrichment of pathogenic bacteria under continuous flow. Magnetic nanoparticles combined with polymeric chains have shown affordable features to capture, release, and concentrate the pathogens by applying an external magnetic field. We have verified the modulated porous characteristics of the floating magnetic membrane depending on the molecular weight of cationic polymer chains and demonstrated rapid enrichment of pathogenic bacteria from aqueous fluid in the capillary glass tube (> 50-fold). Structural flexibility of the magnetic membrane allows the liquid and smaller species to pass through but efficiently induces binding of the bacteria on the antibody-functionalized magnetic nanoparticles of the floating virtual web. The magnetic membrane enables size-selective filtration and target-specific trapping through ionic exchange and immunomagnetic isolation. This study implies that spatiotemporal application of the magnetic membrane for rapid enrichment of biological targets in a large volume of continuous flow using microfluidic devices and biochips.

Protein adsorption to (3-acrylamido propyl) trimethyl ammonium chloride-grafted Sepharose gel: Charge density reduction via copolymerizing with electroneutral monomer drastically increases uptake rate.

Polymer-grafting to porous materials is an effective way to create protein ion-exchangers of high capacity and uptake rate because the 3D architecture of the polymeric ion exchange groups provides high binding space and facilitated transport of the bound protein. Herein, a new anion exchanger was fabricated by grafting (3-acrylamide propyl) trimethyl ammonium chloride (APTAC) onto Sepharose FF gel for protein adsorption and chromatography. The ion exchanger, denoted as FF-pAPTAC, presented high capacity but limited uptake rate in bovine serum albumin (BSA) adsorption due to the high charge density of the cationic polymer chains. To solve the problem, we proposed to copolymerize APTAC with an electroneutral monomer, acrylamide (AM), onto Sepharose FF to modulate the charge density of the grafted polymer chains. By decreasing the feeding molar ratio of APTAC to AM, the ionic capacity (IC) of the copolymerized resins, FF-p(AM-APTAC)n (n denotes IC in mmol/L), decreased, but the chain length could be remained almost unchanged due to the similar reactivity ratios of the two monomers. With decreasing IC, the static adsorption capacity (qm) of FF-p(AM-APTAC)n decreased gradually because of the decline of protein binding sites. The uptake rate, however, represented by the ratio of effective pore diffusivity to the free solution diffusivity (De/D0), exhibited a strong uptrend with decreasing IC, reaching ~2.5-fold of the maximum observed with FF-pAPTACn. It is considered that the decrease of charge density weakened protein binding strength to the chains and increased the chain flexibility, which consequently facilitated the transport of bound proteins on the chains. Moreover, at the same IC, each FF-p(AM-APTAC)n displayed similar adsorption capacity but high uptake rate as compared with its FF-pAPTACn counterpart mainly due to the longer chain length of the copolymer. Particularly, ~6.5-fold enhancement of De/D0 was observed at IC=50±2mmol/L. Both high adsorption capacity and uptake rate made FF-p(AM-APTAC)n exhibit superior dynamic binding performance. The findings proved that reducing chain charge density by copolymerizing an electroneutral monomer was promising for fabrication of high-performance protein ion exchangers.

Tuning of particle indentation by surface modification of polymer particles and substrates

We studied the influence of the chemical properties of the polymer particle and the polymer substrate on particle indentation. The polymer particles were arrayed over the polymer substrate and heat treatment (annealing) was conducted above the glass transition temperature (Tg) of bulk polymer to indent polymer particles into the polymer substrate. Surface topologies of particle-indented surfaces were observed with a field-emission scanning electron microscope (FE-SEM) and the degree of particle indentation (DI) was evaluated with a scanning probe microscope (SPM). The particle-arrayed substrate was placed upside down and then heat treatment was carried out. It was found that there was no effect of gravity on particle indentation. To prepare polymer particles with different chemical properties, surface grafting of hydrophobic, hydrophilic, cationic and anionic polymer chains was carried out by iniferter-initiated living radical polymerization. We found that the indentation of these particles was influenced by the outermost surface of the particle. Next, to investigate the effect of the substrate surface on particle indentation, sulfonation of the polystyrene (PS) substrate was carried out with concentrated sulfuric acid. We found that the surface property of the substrate also influenced particle indentation. From these results, we concluded that particle indentation would be determined by the interaction between the particle surface and the substrate surface. Finally, we intended to analyze the viscoelastic property of the substrate surface by particle indentation. We could estimate Tg values of PS and polyvinyl chloride (PVC) substrates by observing the particle indentation at the different annealing temperatures.

Double Pseudo-Polymeric Gold(III)-Mercury(II) Complexes [Au(S2CNR2)2]nX [R2 = (CH2)6, (CH2)4O] Containing ([HgCl3]−)n, [HgCl4]2− and [Hg2Cl6]2− Anions: Chemisorption Synthesis, Principles of Supramolecular Self-Assembly, and Thermal Behavior

Novel pseudo-polymeric complexes of gold(III)-mercury(II) with cyclic alkylene dithiocarbamate ligands: ([Au{S2CN(CH2)6}2][HgCl3])n, ([Au{S2CN(CH2)6}2]2[HgCl4]·H2O)n, and ([Au{S2CN(CH2)4O}2]2[Hg2Cl6])n have been obtained and structurally characterized. The sophisticated supramolecular structure of the obtained compounds is realized due to secondary non-valent Au⋯S interactions and includes mononuclear and binuclear cations and anions as structural units as well as cationic and anionic polymer chains. The thermal behavior of the obtained complexes has been studied by means of simultaneous thermal analysis. The products of thermal transformations of the complexes are reduced elemental gold and HgCl2.

Molecular-Level Insight into the Interactions of DNA/Polycation Complexes with Model Cell Membranes.

The interactions of DNA/polycation complexes (polyplexes) with cell membranes are crucial for understanding the molecular mechanisms behind polycation-mediated delivery of nucleic acid therapeutics into the target cells. In this study, we employed both biased and unbiased atomic-scale computer simulations to get an insight into such interactions. To this end, we considered complexes of DNA with linear polyethylenimine (PEI) with various polycation contents, ranging from an almost fully neutralized DNA to a highly overcharged polyplex. Our findings clearly show that the free energy gradually increases when a polyplex approaches the surface of a zwitterionic (neutral) phospholipid membrane from bulk water, implying the lack of attractive polyplex/membrane interactions. Remarkably, overcharging of DNA molecules by polycations enhances the repulsion between the polyplex and the zwitterionic lipid membrane. The observed repulsion is most likely driven by the dehydration of a polyplex upon its partitioning into the zwitterionic lipid membrane as well as by the loss of conformational entropy of PEI chains. We also demonstrate that cationic polymer chains are able to protect DNA from the dehydration as well as from contacts with lipid molecules. Interestingly, the absence of local minima in the free energy profiles does not exclude transient weak adsorption of a polyplex on the zwitterionic membrane surface. We show that such spontaneous adsorption can indeed be initiated by the interactions of loose polycation chains of the polyplex with polar head groups of lipids. Overall, our computational findings contribute considerably to the understanding of the initial stages in polycation-mediated DNA transfection. In particular, we demonstrate that a zwitterionic lipid bilayer represents an energetic barrier for polyplexes, so that a proper model of the cell membrane should account for the anionic surface charge of the membrane (e.g., due to the presence of proteoglycans).

Hybrid Mesoporous Nanoparticles for pH-Actuated Controlled Release.

Among a variety of inorganic-based nanomaterials, mesoporous silica nanoparticles (MSNs) have several attractive features for application as a delivery system, due to their high surface areas, large pore volumes, uniform and tunable pore sizes, high mechanical stability, and a great diversity of surface functionalization options. We developed novel hybrid MSNs composed of a mesoporous silica nanostructure core and a pH-responsive polymer shell. The polymer shell was prepared by RAFT polymerization of 2-(diisopropylamino)ethyl methacrylate (pKa ~6.5), using a hybrid grafting approach. The hybrid nanoparticles have diameters of ca. 100 nm at pH < 6.5 and ca. 60 nm at pH > 6.5. An excellent control of cargo release is achieved by the combined effect of electrostatic interaction of the cargo with the charged silica and the extended cationic polymer chains at low pH, and the reduction of electrostatic attraction with a simultaneous collapse of the polymer chains to a globular conformation at higher pH. The system presents a very low (almost null) release rate at acidic pH values and a large release rate at basic pH, resulting from the squeezing-out effect of the coil-to-globule transition in the polymer shell.

Super-resolution Imaging of Proton Sponge-Triggered Rupture of Endosomes and Cytosolic Release of Small Interfering RNA.

The intracellular delivery of nucleic acids and proteins remains a key challenge in the development of biological therapeutics. In gene therapy, the inefficient delivery of small interfering RNA (siRNA) to the cytosol by lipoplexes or polyplexes is often ascribed to the entrapment and degradation of siRNA payload in the endosomal compartments. A possible mechanism by which polyplexes rupture the endosomal membrane and release their nucleic acid cargo is commonly defined as the "proton sponge effect". This is an osmosis-driven process triggered by the proton buffering capacityof polyplexes. Herein, we investigate the molecular basis of the "proton sponge effect" through direct visualization of the siRNA trafficking process, including analysis of individual polyplexes and endosomes, using stochastic optical reconstruction microscopy. We probe the sequential siRNA trafficking steps through single molecule super-resolution analysis of subcellular structures, polyplexes, and silencing RNA molecules. Specifically, individual intact polyplexes released in the cytosol upon rupture of the endosomes, the damaged endosomal vesicles, and the disassembly of the polyplexes in the cytosol areexamined. We findthat the architecture of the polyplex and the rigidity of the cationic polymer chains are crucial parameters that control the mechanism of endosomal escape driven by the proton sponge effect. We provide evidence that in highly branched and rigid cationic polymers, such as glycogen or polyethylenimine, immobilized on silica nanoparticles, the proton sponge effect is effective in inducing osmotic swelling and rupture of endosomes.

Flocculation of a suspension of quartz in the presence of super flocculants of different charge

The influence of cationic and anionic superprocesses and their binary mixtures on the degree of aggregation and the charge of particles of a suspension of quartz. Varied the amount entered in the suspension of the specified reagents, the charge density of the flocculants, the order of introduction of mixture components in the system. The addition of anionic flocculant causes a twofold increase in the potential due to adsorption of negatively charged ions of polymer segments on the negatively charged surface of quartz particles due to non-Coulomb forces. It is shown that the addition of cationic flocculant leads to a significant decrease in the negative values of the particles and a change in the sign of their charge. In the presence of mixtures of anionic and cationic flocculants, regardless of their composition and the order of introduction of the components into the suspension, the particles acquire a negative potential characteristic of the particles adsorbing only anionic flocculant. With an increase in the amount of the added mixture, the flocculation rate and the size of the resulting floccules increase, while a further increase in the concentration of these mixtures causes a decrease in the size of the aggregates. For mixtures of charged anionic and cationic flocculants, the synergism of flocculant action is observed. This effect was observed even for mixtures with multiple excess of negatively charged segments compared to positively charged ones. The observed regularities are explained by the peculiarities of the structure of adsorption layers of flocculant mixtures by the coexistence of a thin layer of adsorbed cationic polymer chains with a large number of contacts with the surface and an extended layer of anionic flocculant (long loops and tails of macromolecules), in which a layer of cationic polymer is “hidden”. The electrokinetic potential and the ability of particles to aggregate (by the mechanism of formation of polymer bridges) in solutions of mixtures of anionic and cationic polyelectrolytes is determined, first of all, by the adsorption value of anionic polymer.

(Invited) A Thermo-Responsive Cationic Comb-Type Copolymer Enhances Membrane Permeabilizing Activity of an Amphiphilic Peptide

Amphiphilic peptides are great focus owing to potential applications including drug delivery systems and antimicrobials. E5 peptide, one of amphiphilic peptides, forms amphiphilic α-helix at low pH, and exhibits membrane permeabilizing activity.1,2) However, the activity of E5 peptide is low attributed to low solubility in aqueous media. In the previous paper, we showed that the cationic comb-type copolymer, poly(allylamine)-graft-dextrane (PAA-g-Dex) formed soluble inter-polyelectrolyte complex (sIPEC) with E5 peptide at both low and natural pH, and E5/PAA-g-Dex exhibited strong membrane disruptive activity.3) In this study, we designed a novel comb-type cationic copolymer composed of a PAA main chain and thermoresponsive poly(N-isopropylacrylamide) graft chains (PAA-g-PNIPAAm). We hypothesized that the thermoresponsive hydrophilic/hydrophobic transition of the grafted polymer would regulate the membrane disruption activity of E5 peptide. The target copolymer was prepared by activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). The ratio of AA units to Initiator to NIPAAm units was estimated to be 100:9:421 by 1H NMR. Thus, the number-averaged molecular weight (M n) of PNIPAAm and the PNIPAAm contents were 1.0 × 104 and 94.3 wt %, respectively. Circular dichroism (CD) spectra measurement revealed that PAA-g-PNIPAAm formed sIPEC with E5 peptide, resulting in α-helix formation of E5 peptide. Furthermore, the complex formation of E5 and PAA-g-PNIPAAm was investigated by measuring the fluorescence spectra of triptophan residure in E5 peptide. From these investigations, we found that the interaction between E5 peptide and PAA-g-PNIPAAm at 35 °C (above LCST) was stronger than that at 25 °C (below LCST). These results suggest that the hydrophobicity of the environment around the cationic polymer chain influences complex formation. E5 peptide in the presence of PAA-g-PNIPAAm induced the leakage from liposomes, whereas E5 peptide alone did not. Importantly, E5/PAA-g-PNIPAAm induced more significant leakage at 35 °C than at 25 °C. Thus, membrane disruptive activity of E5/PAA-g-PNIPAAm sIPEC was regulated in response to temperature coupled with the phase transition of the thermo-responsive grafted chain.4)

A Thermoresponsive Cationic Comb-Type Copolymer Enhances Membrane Disruption Activity of an Amphiphilic Peptide.

Membrane active peptides (MAPs) have potential applications in drug delivery systems and as antimicrobials. We previously showed that a cationic comb-type copolymer, poly(allylamine)- graft-dextran (PAA- g-Dex), forms a soluble inter-polyelectrolyte complex with an anionic MAP, the E5 peptide, resulting in significant enhancement of the membrane disruption activity of E5. In this study, we designed a novel comb-type cationic copolymer composed of a PAA main chain and thermoresponsive poly( N-isopropylacrylamide) graft chains (PAA- g-PNIPAAm). We hypothesized that the thermoresponsive hydrophilic/hydrophobic transition of the grafted polymer would regulate the membrane disruption activity of E5 peptide. Both the binding affinity of the complex and the membrane disruption activity of E5/PAA- g-PNIPAAm were found to be enhanced above the phase transition temperature of the grafted chain. Our analysis suggests that the hydrophilic/hydrophobic environment around the cationic polymer chain plays important roles in the enhancement of the activity of the anionic peptide.

Design of Free Triblock Polylysine- b-Polyleucine- b-Polylysine Chains for Gene Delivery.

Mixing cationic polymer chains with anionic DNA chains in solution results in the polymer/DNA complexes (also known as polyplexes). We recently confirmed that it is those noncomplexed cationic chains free in the mixture that promote the gene transfection, leading to a hypothesis: free cationic chains adsorbed on various anionic membranes interfere with the signal protein interaction, disrupt the intervesicular fusion, and block the endolysosome pathway so that the plasmid DNA (pDNA) chains have a higher chance to enter the nucleus. Accordingly, we design and synthesize linear cationic-hydrophobic-cationic triblock polylysine (K)- b-polyleucine (L)- b-polylysine (K) as free cationic chains by using natural protamine to condense the pDNA. The hydrophobic middle L-block helps its insertion into the membrane, while the interaction of the two cationic side K-blocks with the signal proteins helps the escape of the polyplexes from the lysosome entrapment. We studied the transfection efficiency of these copolymers with different block lengths. We found the optimal length of blocks K and L that allows the free triblock cationic copolymer chains to effectively enhance the gene transfection process. A combination of copolypeptides and protamine provides a new kind of biocompatible and nontoxic gene vectors made of only nontoxic peptides.

Elaboration on the Distribution of Hydrophobic Segments in the Chains of Amphiphilic Cationic Polymers for Small Interfering RNA Delivery.

Hydrophobization of cationic polymers, as an efficient strategy, had been widely developed in the structure of cationic polymer micelles to improve the delivery efficiency of nucleic acids. However, the distribution of hydrophobic segments in the polymer chains is rarely considered. Here, we have elaborated three types of hydrophobized polyethylene glycol (PEG)-blocked cationic polymers with different distributions of the hydrophobic segments in the polymer chains PEG-PAM-PDP (E-A-D), PEG-PDP-PAM (E-D-A), and PEG-P(AM/DP) (E-(A/D)), which were synthesized by reversible addition-fragmentation chain transfer polymerization of methoxy PEG, cationic monomer aminoethyl methacrylate, and pH-sensitive hydrophobic monomer 2-diisopropylaminoethyl methacrylate, respectively. In aqueous solution, all of the three copolymers, E-A-D, E-D-A, and E-(A/D), were able to spontaneously form nanosized micelles (100-150 nm) (ME-A-D, ME-D-A, and ME-(A/D)) and well-incorporated small interfering RNA (siRNA) into complex micelles (CMs). The effect of distributions of the hydrophobic segments on siRNA delivery had been evaluated in vitro and in vivo. Compared with ME-D-A and ME-(A/D), ME-A-D showed the best siRNA binding capacity to form stable ME-A-D/siRNA CMs less than 100 nm, mediated the best gene-silencing efficiency and inhibition effect of tumor cell growth in vitro, and showed better liver gene-silencing effect in vivo. In the case of ME-(A/D) with a random distribution of cationic and hydrophobic segments, a gene-silencing efficiency higher than Lipo2000 but lesser than ME-A-D and ME-D-A was obtained. As the mole ratio of positive and negative charges increased, ME-D-A/siRNA and ME-A-D/siRNA showed similar performances in size, zeta potential, cell uptake, and gene silencing, but ME-(A/D)/siRNA showed reversed performances. In addition, ME-A-D as the best siRNA carrier was evaluated in the tumor tissue in the xenograft murine model and showed good anticancer capacity. Obviously, the distribution of the hydrophobic segments in the amphiphilic cationic polymer chains should be seriously considered in the design of siRNA vectors.

Analysis of blinking from multicoloured SERS‐active Ag colloidal nanoaggregates with poly‐L‐lysine via truncated power law

Silver colloidal nanoaggregates have been widely used for surface‐enhanced Raman scattering (SERS) measurements. SERS‐active nanoaggregates generally show monotone colors, although multicoloured‐blinking emissions, which occur at the single‐molecule level, have been observed from each Ag colloidal nanoaggregate with poly‐L‐lysine. For the same single nanoaggregates, SERS peaks of poly‐L‐lysine were observed at shorter wavelengths than those of the background emission band; thus, their blinking can be measured separately. The background emission is attributed to fluorescence from an Ag atomic cluster. This may be modulated by the surface plasmon enhancement of each Ag nanoaggregate and is the likely cause of multicoloured background emission. Notably, the probability distributions as a function of time for not only the dark events of SERS but also those of the background emission were reproduced via a truncated power law, indicating the same random‐walk mechanism for their blinking despite the different illuminants. The power law for the dark background emission events was truncated at a shorter tail than that for the dark SERS events. This result suggests that the fluorescent Ag cluster reaches a junction of the Ag nanoaggregate covered with citrate anions more quickly than the cationic polymer chain. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Quantitative study of effects of free cationic chains on gene transfection in different intracellular stages

Previously, we revealed that in the application of using cationic polymer chains, polyethylenimine (PEI), to condense anionic plasmid DNA chains (pDNA) to form the DNA/polymer polyplexes, after all the pDNAs are complexed with PEI, further added PEIs exist individual chains and free in the solution mixture. It is those uncomplexed polycation chains that dramatically promote the gene transfection. In the current study, we studied how those free cationic chains with different lengths and topologies affect the intracellular trafficking of the polyplexes, the translocation of pDNA through the nuclear membrane, the transcription of pDNA to mRNA and the translocation of mRNA from nucleus to cytosol in HepG2 cells by using a combination of the three-dimensional confocal microscope and TaqMan real-time PCR. We found that free branched PEI chains with a molar mass of 25,000g/mol and a total concentration of 1.8×10−6g/mL promote the overall gene transfection efficiency by a factor of ~500 times. Our results quantitatively reveal that free chains help little in the cellular uptake, but clearly reduce the lysosomal entrapment of those internalized polyplexes (2–3 folds); assist the translocation of pDNA through nuclear membrane after it is released from the polyplexes in the cytosol (~5 folds); enhance the pDNA-to-mRNA transcription efficiency (~4 folds); and facilitate the nucleus-to-cytosol translocation of mRNA (7–8 folds). The total enhancement of those steps agrees well with the overall efficiency, demonstrating, for the first time, how free cationic polymer chains quantitatively promote the gene transfection in each step in the intracellular space.