Polycation-Anionic Lipid Membrane Interactions.

Natural or synthetic polycations are used as biocides or as drug/gene carriers. Understanding the interactions between these macromolecules and cell membranes at the molecular level is therefore of great importance for the design of effective polymer biocides or biocompatible polycation-based delivery systems. Until now, details of the processes at the interface between polycations and biological systems have not been fully recognized. In this study, we consider the effect of strong polycations with quaternary ammonium groups on the properties of anionic lipid membranes that we use as a model system for protein-free cell membranes. For this purpose, we employed experimental measurements and atomic-scale molecular dynamics (MD) simulations. MD simulations reveal that the polycations are strongly hydrated in the aqueous phase and do not lose the water shell after adsorption at the bilayer surface. As a result of strong hydration, the polymer chains reside at the phospholipid headgroup and do not penetrate to the acyl chain region. The polycation adsorption involves the formation of anionic lipid-rich domains, and the density of anionic lipids in these domains depends on the length of the polycation chain. We observed the accumulation of anionic lipids only in the leaflet interacting with the polymer, which leads to the formation of compositionally asymmetric domains. Asymmetric adsorption of the polycation on only one leaflet of the anionic membrane strongly affects the membrane properties in the polycation-membrane contact areas: (i) anionic lipid accumulates in the region near the adsorbed polymer, (ii) acyl chain ordering and lipid packing are reduced, which results in a decrease in the thickness of the bilayer, and (iii) polycation-anionic membrane interactions are strongly influenced by the presence and concentration of salt. Our results provide an atomic-scale description of the interactions of polycations with anionic lipid bilayers and are fully supported by the experimental data. The outcomes are important for understanding the correlation of the structure of polycations with their activity on biomembranes.

Solution Properties of Amphoteric Random Copolymers Bearing Pendant Sulfonate and Quaternary Ammonium Groups with Controlled Structures.

Amphoteric random copolymers P(AMPS/APTAC50) x, where x = 41, 89, and 117, composed of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) and 3-acrylamidopropyltrimethylammonium chloride (APTAC) were prepared via reversible addition-fragmentation chain transfer radical polymerization. P(AMPS/APTAC50) x can dissolve in pure water to form small interpolymer aggregates. In aqueous solutions of NaCl, P(AMPS/APTAC50) x can dissolve in the unimer state. Amphoteric random copolymer P(AMPS/APTAC50)c with high molecular weight was prepared via conventional free-radical polymerization. Although P(AMPS/APTAC50)c cannot dissolve in pure water, it can dissolve in aqueous solutions of NaCl. In amphoteric random copolymers with high molecular weight, the possibility of continuous sequences of monomers with the same charge may increase, which may cause strong interactions between polymer chains. When fetal bovine serum (FBS) and polyelectrolytes were mixed in phosphate-buffered saline, the hydrodynamic radius and light-scattering intensity increased. There was no interaction between P(AMPS/APTAC50) x and FBS because corresponding increases could not be observed.

Preparation of Water-soluble Polyion Complex (PIC) Micelles Covered with Amphoteric Random Copolymer Shells with Pendant Sulfonate and Quaternary Amino Groups.

An amphoteric random copolymer (P(SA)91) composed of anionic sodium 2-acrylamido-2-methylpropanesulfonate (AMPS, S) and cationic 3-acrylamidopropyl trimethylammonium chloride (APTAC, A) was prepared via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. The subscripts in the abbreviations indicate the degree of polymerization (DP). Furthermore, AMPS and APTAC were polymerized using a P(SA)91 macro-chain transfer agent to prepare an anionic diblock copolymer (P(SA)91S67) and a cationic diblock copolymer (P(SA)91A88), respectively. The DP was estimated from quantitative 13C NMR measurements. A stoichiometrically charge neutralized mixture of the aqueous P(SA)91S67 and P(SA)91A88 formed water-soluble polyion complex (PIC) micelles comprising PIC cores and amphoteric random copolymer shells. The PIC micelles were in a dynamic equilibrium state between PIC micelles and charge neutralized small aggregates composed of a P(SA)91S67/P(SA)91A88 pair. Interactions between PIC micelles and fetal bovine serum (FBS) in phosphate buffered saline (PBS) were evaluated by changing the hydrodynamic radius (Rh) and light scattering intensity (LSI). Increases in Rh and LSI were not observed for the mixture of PIC micelles and FBS in PBS for one day. This observation suggests that there is no interaction between PIC micelles and proteins, because the PIC micelle surfaces were covered with amphoteric random copolymer shells. However, with increasing time, the diblock copolymer chains that were dissociated from PIC micelles interacted with proteins.

Mesoporous Iron Oxide Synthesized Using Poly(styrene-b-acrylic acid-b-ethylene glycol) Block Copolymer Micelles as Templates for Colorimetric and Electrochemical Detection of Glucose.

Herein, we report the soft-templated preparation of mesoporous iron oxide using an asymmetric poly(styrene-b-acrylic acid-b-ethylene glycol) (PS-b-PAA-b-PEG) triblock copolymer. This polymer forms a micelle consisting of a PS core, a PAA shell, and a PEG corona in aqueous solutions, which can serve as a soft template. The mesoporous iron oxide obtained at an optimized calcination temperature of 400 °C exhibited an average pore diameter of 39 nm, with large specific surface area and pore volume of 86.9 m2 g-1 and 0.218 cm3 g-1, respectively. The as-prepared mesoporous iron oxide materials showed intrinsic peroxidase-like activities toward the catalytic oxidation of 3,3',5,5'-tertamethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). This mimetic feature was further exploited to develop a simple colorimetric (naked-eye) and electrochemical assay for the detection of glucose. Both our colorimetric (naked-eye and UV-vis) and electrochemical assays estimated the glucose concentration to be in the linear range from 1.0 µM to 100 µM with a detection limit of 1.0 µM. We envisage that our integrated detection platform for H2O2 and glucose will find a wide range of applications in developing various biosensors in the field of personalized medicine, food-safety detection, environmental-pollution control, and agro-biotechnology.

pH-Induced Association and Dissociation of Intermolecular Complexes Formed by Hydrogen Bonding between Diblock Copolymers.

Poly(sodium styrenesulfonate)⁻block⁻poly(acrylic acid) (PNaSS⁻b⁻PAA) and poly(sodium styrenesulfonate)⁻block⁻poly(N-isopropylacrylamide) (PNaSS⁻b⁻PNIPAM) were prepared via reversible addition⁻fragmentation chain transfer (RAFT) radical polymerization using a PNaSS-based macro-chain transfer agent. The molecular weight distributions (Mw/Mn) of PNaSS⁻b⁻PAA and PNaSS⁻b⁻PNIPAM were 1.18 and 1.39, respectively, suggesting that these polymers have controlled structures. When aqueous solutions of PNaSS⁻b⁻PAA and PNaSS⁻b⁻PNIPAM were mixed under acidic conditions, water-soluble PNaSS⁻b⁻PAA/PNaSS⁻b⁻PNIPAM complexes were formed as a result of hydrogen bonding interactions between the pendant carboxylic acids in the PAA block and the pendant amide groups in the PNIPAM block. The complex was characterized by ¹H NMR, dynamic light scattering, static light scattering, and transmission electron microscope measurements. The light scattering intensity of the complex depended on the mixing ratio of PNaSS⁻b⁻PAA and PNaSS⁻b⁻PNIPAM. When the molar ratio of the N-isopropylacrylamide (NIPAM) and acrylic acid (AA) units was near unity, the light scattering intensity reached a maximum, indicating stoichiometric complex formation. The complex dissociated at a pH higher than 4.0 because the hydrogen bonding interactions disappeared due to deprotonation of the pendant carboxylic acids in the PAA block.