Solid-Liquid-Solution Phases in Poly(diallyldimethylammonium)/Poly(acrylic acid) Polyelectrolyte Complexes at Varying Temperatures

The coacervation and complexation of oppositely charged polyelectrolytes are dependent on numerous environmental and preparatory factors, but temperature is often overlooked. Temperature effects remain unclear because the temperature dependence of both the dielectric constant and polymer-solvent interaction parameter can yield lower and/or upper critical solution phase behaviors for PECs. Further, secondary interactions, such as hydrogen bonding, can affect the temperature response of a PEC. That is, mixtures of oppositely charged polyelectrolytes can exhibit phase separation upon lowering and/or increasing the mixture's temperature. Here, the phase behavior of poly(diallylmethylammonium)/poly(acrylic acid) (PDADMA/PAA) complexes under varying KBr ionic strengths, mixing ratios, and temperatures at a fixed pH (in which PAA hydrogen bonding can occur) is examined. At room temperature, the PDADMA/PAA PECs exhibit four different phase states: precipitate, coexisting precipitate and coacervate, solid-like gel, and coacervate. Variable-temperature optical microscopy reveals the upper critical solution temperature (UCST) at which each phase transitioned to a solution state. Interestingly, the UCST value is highly dependent on the original phase of the PEC, in which solid-like precipitates exhibit higher UCST values. Large-scale all-atom molecular dynamics (MD) simulations support that precipitates exhibit kinetic trapping, which may contribute to the higher UCST values observed in the experiment. Taken together, this study highlights the significance of temperature on the phase behavior of PECs, which may play a larger role in stimuli-responsive materials, membraneless organelles, and separations applications.

Mimicking Charged Host-Defense Peptides to Tune the Antifungal Activity and Biocompatibility of Amphiphilic Polymers

Invasive fungal infections impose a substantial global health burden. They cause more than 1.5 million deaths annually and are insufficiently met by the currently approved antifungal drugs. Antifungal peptides are a promising alternative to existing antifungal drugs; however, they can be challenging to synthesize, and are often susceptible to proteases in vivo. Synthetic polymers which mimic the properties of natural antifungal peptides can circumvent these limitations. In this study, we developed a library of 29 amphiphilic polyacrylamides with different charged units, namely, amines, guanidinium, imidazole, and carboxylic acid groups, representative of the natural amino acids lysine, arginine, histidine, and glutamic acid. Ternary polymers incorporating primary ammonium (lysine-like) or imidazole (histidine-like) groups demonstrated superior activity against Candida albicans and biocompatibility with mammalian cells compared to the polymers containing the other charged groups. Furthermore, a combination of primary ammonium, imidazole, and guanidinium (arginine-like) within the same polymer outperformed the antifungal drug amphotericin B in terms of therapeutic index and exhibited fast C. albicans-killing activity. The most promising polymer compositions showed synergistic effects in combination with caspofungin and fluconazole against C. albicans and additionally demonstrated activity against other clinically relevant fungi. Collectively, these results indicate the strong potential of these easily producible polymers to be used as antifungals.

Elucidation of Protonation Cooperativity of a STING-Activating Polymer

Stimuli-responsive nanomaterials have the potential to improve the performance and overcome existing barriers of conventional nanotherapeutics. Molecular cooperativity design in stimuli-responsive nanomedicine can amplify physiological signals, enabling a cooperative response for improved diagnostic and therapeutic precision. Previously, this work reported an ultra-pH-sensitive polymer, PEG-b-PC7A, that possesses innate immune activating properties by binding to the stimulator of interferon genes (STING) through polyvalent phase condensation. This interaction enhances STING activation and synergizes with the endogenous STING ligand for robust cancer immunotherapy. Despite its successes in innate immune activation, the fundamental physicochemical and pH-responsive properties of PC7A require further investigation. Here, this study elucidates the protonation cooperativity driven by the phase transition of PC7A copolymer. The highly cooperative system displays an "all-or-nothing" proton distribution between highly charged unimer (all) and neutral micelle (nothing) states without gradually protonated intermediates. The binary protonation behavior is further illustrated in pH-precision-controlled release of a representative anticancer drug, β-lapachone, by PC7A micelles over a noncooperative PE5A polymer. Furthermore, the bimodal distribution of protons is represented by a high Hill coefficient (nH  > 9), featuring strong positive cooperativity. This study highlights the nanoscale pH cooperativity of an immune activating polymer, providing insights into the physicochemical characterization and design parameters for future nanotherapeutics development.

In Silico Evaluation of Oligomeric Representations for Molecularly Imprinted Polymer Modeling Using a Biological Template

Molecularly imprinted polymers (MIPs) have significant relevance to analytical sensing due to their functionalized and template-specific structurally complementary cavities, providing increased sensibility and specificity for instrumental analyses, thereby enabling a wide variety of applications, especially for biological processes. Designing and developing MIPs entirely by experimental approaches are time-consuming and costly processes; thus, computational tools are used to assess some of the most critical parameters for imprinting, such as ligand screening. A typical practice is to model functional ligands as monomers; however, this representation fails to predict how ligand-template interactions evolve during polymer growth. In this context, this work aims to evaluate whether additional oligomeric representations affect the formation of noncovalent complexes between typical ligands and the P31 Asian lineage Zika virus epitope, using classical molecular dynamics. The ligands 2-vinylpyridine, 4-vinylaniline, acrylic acid, acrylamide, and 2-hidroxyethyl methacrylate were simulated as monomers, trimers, pentamers, and decamers, and their influence on the epitope structural conservation and ligand-template interactions were evaluated. Analyses of root-mean-square deviation, fluctuation, radius of gyration, pair correlation function, and number of hydrogen bonding-type interactions were conducted, showing the ligand chain size had an influence on the complex formation. However, this influence had no discernible pattern, exhibiting better performance in some cases while noninfluential in others. Of particular significance, in terms of epitope structural conservation, distinct oligomeric chains led to the selection of the distinct most interactive ligands. This observation raises important questions regarding the use of oligomeric chains in MIP simulations, thus prompting the need for further investigations of this subject.

PEG-Free Polyion Complex Nanocarriers for Brain-Derived Neurotrophic Factor

Many therapeutic formulations incorporate poly(ethylene glycol) (PEG) as a stealth component to minimize early clearance. However, PEG is immunogenic and susceptible to accelerated clearance after multiple administrations. Here, we present two novel reformulations of a polyion complex (PIC), originally composed of poly(ethylene glycol)₁₁₃-b-poly(glutamic acid)₅₀ (PEG-PLE) and brain-derived neurotrophic factor (BDNF), termed Nano-BDNF (Nano-BDNF PEG-PLE). We replace the PEG based block copolymer with two new polymers, poly(sarcosine)₁₂₇-b-poly(glutamic acid)₅₀ (PSR-PLE) and poly(methyl-2-oxazolines)₃₈-b-poly(oxazolepropanoic acid)₂₇-b-poly(methyl-2-oxazoline)₃₈ (PMeOx-PPaOx-PMeOx), which are driven to association with BDNF via electrostatic interactions and hydrogen bonding to form a PIC. Formulation using a microfluidic mixer yields small and narrowly disperse nanoparticles which associate following similar principles. Additionally, we demonstrate that encapsulation does not inhibit access by the receptor kinase, which affects BDNF’s physiologic benefits. Finally, we investigate the formation of nascent nanoparticles through a series of characterization experiments and isothermal titration experiments which show the effects of pH in the context of particle self-assembly. Our findings indicate that thoughtful reformulation of PEG based, therapeutic PICs with non-PEG alternatives can be accomplished without compromising the self-assembly of the PIC.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Computational and experimental approaches for chitosan-based nano PECs design: Insights on a deeper comprehension of nanostructure formation

Nanostructured polyelectrolyte complexes (nano PECs) based on biopolymers are an important technological strategy to target drugs to the action and/or absorption site in a more effective way. In this work, computational studies were performed to predict the ionization, spatial arrangement and interaction energies of chitosan (CS), hyaluronic acid (HA), and hypromellose phthalate (HP), for the design of nano PEC carriers for methotrexate (MTX). The optimal pH range (5.0-5.5) for preparing nano PECs was selected by experimental and computational methodologies, favoring the polymers interactions. CS, HA, HP and MTX addition order was also rationalized, maximizing their interactions and MTX entrapment. Spherical nano-sized particles (256-575 nm, by dynamic light scattering measurement) with positive surface charge (+25.5 to +29.2 mV) were successfully prepared. The MTX association efficiency ranged from 20 to 32 %. XRD analyses evidenced the formation of a new material with an organized structure, in relation to raw polymers.

Efficient Polymer-Mediated Delivery of Gene-Editing Ribonucleoprotein Payloads through Combinatorial Design, Parallelized Experimentation, and Machine Learning

Chemically defined vectors such as cationic polymers are versatile alternatives to engineered viruses for the delivery of genome-editing payloads. However, their clinical translation hinges on rapidly exploring vast chemical design spaces and deriving structure-function relationships governing delivery performance. Here, we discovered a polymer for efficient intracellular ribonucleoprotein (RNP) delivery through combinatorial polymer design and parallelized experimental workflows. A chemically diverse library of 43 statistical copolymers was synthesized via combinatorial RAFT polymerization, realizing systematic variations in physicochemical properties. We selected cationic monomers that varied in their pK_a values (8.1-9.2), steric bulk, and lipophilicity of their alkyl substituents. Co-monomers of varying hydrophilicity were also incorporated, enabling elucidation of the roles of protonation equilibria and hydrophobic-hydrophilic balance in vehicular properties and performance. We screened our multiparametric vector library through image cytometry and rapidly uncovered a hit polymer (P38), which outperforms state-of-the-art commercial transfection reagents, achieving nearly 60% editing efficiency via nonhomologous end-joining. Structure-function correlations underlying editing efficiency, cellular toxicity, and RNP uptake were probed through machine learning approaches to uncover the physicochemical basis of P38's performance. Although cellular toxicity and RNP uptake were solely determined by polyplex size distribution and protonation degree, respectively, these two polyplex design parameters were found to be inconsequential for enhancing editing efficiency. Instead, polymer hydrophobicity and the Hill coefficient, a parameter describing cooperativity-enhanced polymer deprotonation, were identified as the critical determinants of editing efficiency. Combinatorial synthesis and high-throughput characterization methodologies coupled with data science approaches enabled the rapid discovery of a polymeric vehicle that would have otherwise remained inaccessible to chemical intuition. The statistically derived design rules elucidated herein will guide the synthesis and optimization of future polymer libraries tailored for therapeutic applications of RNP-based genome editing.

Surface Modification of Cellulose Nanocrystals via RAFT Polymerization of CO2-Responsive Monomer-Tuning Hydrophobicity

Cellulose nanocrystals (CNCs) were converted into a CO₂-responsive composite nanomaterial by grafting poly(dimethylaminoethyl methacrylate) (PDMAEMA), poly(diethylaminoethyl methacrylate) (PDEAEMA), and poly(diisopropylaminoethyl methacrylate) (PDPAEMA) onto its surface using both grafting-to and grafting-from approaches. The zeta potential (ζ) of the graft-modified CNC could be reversibly switched by protonation/deprotonation of the tertiary amine groups simply by sparging with CO₂ and N₂, respectively. Depending on the grafting density and the molecular weight of the polymer grafts, CNC can form stable aqueous dispersions at either mildly acidic pH (under CO₂) or mildly basic (under N₂) conditions. Moreover, it was also determined that the CNC hydrophobicity, assessed using phase-shuttling experiments at different pH values, was also dependent on both the grafting density and molecular weight of the polymer grafts, thereby making it possible to easily tune CNC dispersibility and/or hydrophobicity.

pH-Induced Changes in Polypeptide Conformation: Force-Field Comparison with Experimental Validation

Microsecond-long all-atom molecular dynamics (MD) simulations, circular dichroism, laser Doppler velocimetry, and dynamic light-scattering techniques have been used to investigate pH-induced changes in the secondary structure, charge, and conformation of poly l-lysine (PLL) and poly l-glutamic acid (PGA). The employed combination of the experimental methods reveals for both PLL and PGA a narrow pH range at which they are charged enough to form stable colloidal suspensions, maintaining their α-helix content above 60%; an elevated charge state of the peptides required for colloidal stability promotes the peptide solvation as a random coil. To obtain a more microscopic view on the conformations and to verify the modeling performance, peptide secondary structure and conformations rising in MD simulations are also examined using three different force fields, i.e., OPLS-AA, CHARMM27, and AMBER99SB*-ILDNP. Ramachandran plots reveal that in the examined setup the α-helix content is systematically overestimated in CHARMM27, while OPLS-AA overestimates the β-sheet fraction at lower ionization degrees. At high ionization degrees, the OPLS-AA force-field-predicted secondary structure fractions match the experimentally measured distribution most closely. However, the pH-induced changes in PLL and PGA secondary structure are reasonably captured only by the AMBER99SB*-ILDNP force field, with the exception of the fully charged PGA in which the α-helix content is overestimated. The comparison to simulations results shows that the examined force fields involve significant deviations in their predictions for charged homopolypeptides. The detailed mapping of secondary structure dependency on pH for the polypeptides, especially finding the stable colloidal α-helical regime for both examined peptides, has significant potential for practical applications of the charged homopolypeptides. The findings raise attention especially to the pH fine tuning as an underappreciated control factor in surface modification and self-assembly.

A Reversible Proton Generator with On/Off Thermoswitch

A reversible polymer photoacid with a thermal on/off switch at physiological temperature able to trigger a large pH modulation of its environment is prepared. Light is used to control the acidity of the solution. Additionally, the temperature could be used to modulate the photoacid efficiency, practically turning on and off the ability of the polymer to produce protons. The behavior of this thermoresponsive photoacid copolymer is the result of the combined action of the temperature-responsive N-isopropylacrylamide and of a reversible photoacid monomer based on a spiropyran derivative. The acidification of the aqueous medium is activated by irradiation at λ = 460 nm. The reverse reaction is achieved by removing the light stimuli or by exposing the solution to UV-light. Increasing the temperature above the lower critical solution temperature of the copolymer deactivates the photoacid and irradiation at λ = 460 nm does not lead to the generation of protons or to any detectable change in the pH value of the solution. Hence, the addition of N-isopropylacrylamide as a comonomer acts as a thermal on/off switch for the photoacid and the coupling of temperature-and light-responsiveness in the polyphotoacids yields a "thermophotoacid".

Scope of sulfur dioxide incorporation into alkyldiallylamine-maleic acid-SO2 tercyclopolymer

Alternate copolymerization of diallylamine derivatives [(CH₂CH Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CH₂)₂NR; R = Me, (CH₂)₃PO(OEt)₂, and CH₂PO(OEt)₂] (I)–maleic acid (MA) and (I·HCl)–SO₂ pairs have been carried out thermally using ammonium persulfate initiator as well as UV radiation at a λ of 365 nm. The reactivity ratios of ≈0 for the monomers in each pair I–MA and I·HCl–SO₂ ensured their alternation in each copolymer. However, numerous attempted terpolymerizations of I–MA–SO₂ failed to entice MA to participate to any meaningful extent. In contrast to reported literature, only 1–2 mol% of MA was incorporated into the polymer chain mainly consisting of poly(I-alt-SO₂). Quaternary diallyldialkylammonium chloride [(CH₂CH–CH₂)₂N⁺R₂Cl⁻; R = Me, Et] (II) also, did not participate in II–MA–SO₂ terpolymerizations. Poly((I, R = Me)-alt-SO₂) III is a stimuli-responsive polyampholyte; its transformation under pH-induced changes to cationic, polyampholyte-anionic, and dianionic polyelectrolytes has been examined by viscosity measurements. The pK_a of two carboxylic acid groups and NH⁺ in III has been determined to be 2.62, 5.59, and 10.1. PA III, evaluated as a potential antiscalant in reverse osmosis plants, at the concentrations of 5 and 20 ppm, imparted ≈100% efficiency for CaSO₄ scale inhibition from its supersaturated solution for over 50 and 500 min, respectively, at 40 °C. The synthesis of PA III in excellent yields from cheap starting materials and its very impressive performance may grant PA III a prestigious place as an environment-friendly phosphate-free antiscalant.

Alternate copolymerization of diallylamine derivatives [(CH₂=CH–CH₂)₂NR; R = Me, (CH₂)_nPO(OEt)₂] (I)–maleic acid (MA) and (I·HCl)–SO₂ pairs have been carried out thermally using ammonium persulfate initiator as well as UV radiation at λ of 365 nm.

Synthesis and application of polyzwitterionic and polyampholytic maleic acid-alt-(diallylamino)propylphosphonates

Ammonium persulfate-initiated alternate copolymerization of maleic acid with phosphonate ester monomer [(CH₂CH–CH₂)₂NH⁺(CH₂)₃PO₃Et₂Cl⁻] gave polyzwitterion A which upon ester hydrolysis afforded antiscalant polyampholyte B.