Interactions between sulfobetaine-based polyzwitterions and polyelectrolytes

Dipole-driven interlude of mesomorphism in polyelectrolyte solutions

Uniformly charged polyelectrolyte molecules disperse uniformly in aqueous electrolyte solutions, due to electrostatic repulsion between them. In stark contrast to this well-established result of homogeneous polyelectrolyte solutions, we report a phenomenon where an aqueous solution of positively charged poly(L-lysine) (PLL) exhibits precipitation of similarly charged macromolecules at low ionic strength and a homogeneous solution at very high ionic strength, with a stable mesomorphic state of spherical aggregates as an interlude between these two limits. The precipitation at lower ionic strengths that is orthogonal to the standard polyelectrolyte behavior and the emergence of the mesomorphic state are triggered by the presence of a monovalent small organic anion, acrylate, in the electrolyte solution. Using light scattering, we find that the hydrodynamic radius R_h of isolated PLL chains shrinks upon a decrease in electrolyte (NaBr) concentration, exhibiting the "anti-polyelectrolyte effect." In addition, R_h of the aggregates in the mesomorphic state depends on PLL concentration c_p according to the scaling law, [Formula: see text]. Furthermore, at higher PLL concentration, the mesomorphic aggregates disassemble by a self-poisoning mechanism. We conjecture that all these findings can be attributed to both intra- and interchain dipolar interactions arising from the transformation of polycationic PLL into a physical polyzwitterionic PLL at higher concentrations of acrylate. The reported phenomenon of PLL exhibiting dipole-directed assembly of mesomorphic states and the anti-polyelectrolyte effect are of vital importance toward understanding more complex situations such as coacervation and formation of biomolecular condensates.

Interpolymer Complexes of Poly(methacryloyloxyethyl phosphorylcholine) and Polyacids

It has been shown that macromolecules of poly(methacryloyloxyethyl phosphorylcholine) can form hydrogen bonded interpolymer complexes with homo- and copolymers of carboxylic acids and with poly(vinylphosphonic) acid in aqueous solutions. Polarized luminescence and IR spectroscopy were applied in the investigation. Nanosecond relaxation times characterizing the mobility of the chain fragments for the initial luminescent labeled polymers were determined and their changes by a factor of 2-50 were established during the formation of an interpolymer complex. Hydrogen bonds play a dominant role in the formation of these complexes. Hydrophobic interactions serve as an additional stabilizing factor. It is established that poly(methacryloyloxyethyl phosphorylcholine)/poly(vinylphosphonic acid) complex forms a looser structure in comparison with those for polycarboxylic acids as result of electrostatic repulsion between charged groups.

Multiscale simulations of polyzwitterions in aqueous bulk solutions and brush array configurations

Zwitterionic polymers are very promising candidates for antifouling materials that exhibit high chemical stability as compared to polyethylene glycol-based systems. A number of simulation and experimental studies have emerged over recent years for the investigation of sulfobetaine-based zwitterionic polymers. Investigating the structural and thermodynamic properties of such polymers requires access to broad time and length regimes, thus necessitating the development of multiscale simulation strategies. The present article advocates a mesoscopic dissipative particle dynamics (DPD) model capable of addressing a wide range of time and length scales. The mesoscopic force field was developed hand-in-hand with atomistic simulations based on the OPLS force field through a bottom-up parameterization procedure that matches the atomistically calculated strand-length, strand-angle and pair distribution functions. The DPD model is validated against atomistic simulations conducted in this work, and against relevant atomistic simulation studies, theoretical predictions and experimental correlations from the literature. Properties examined include the conformations of SPE polymers in dilute bulk aqueous solution, the density profile and thickness of brush arrays as functions of the grafting density and chain length. In addition, we compute the potential of mean force of an approaching hydrophilic or hydrophobic foulant via umbrella sampling as a function of its position relative to the poly-zwitterion-covered surface. The aforementioned observables lead to important insights regarding the conformational tendencies of grafted polyzwitterions and their antifouling properties.

Temperature-Responsive Behavior of Double Hydrophilic Carboxy-Sulfobetaine Block Copolymers and Their Self-Assemblies in Water

The block copolymer poly(2-((2-(methacryloyloxy)ethyl)dimethylammonio)acetate)- b-poly(3-( N-(2-metharyloylethyl)- N, N-dimethylammonio)propanesulfonate) (PGLBT- b-PSPE) was synthesized by reversible addition-fragmentation chain transfer (RAFT) technique under precise control. The PGLBT- b-PSPE block copolymers showed upper critical solution temperature (UCST) behavior originating from PSPE moieties. Unlike PSPE homopolymers, the transmittance change with temperature was gradual, and unexpected retardation or slight changes in a reverse direction were found at the intermediate stage. Light scattering and ¹H NMR studies proved that the block copolymers formed spherical micelles that were composed of a PSPE core and PGLBT shell around room temperature and lower temperatures, and slowly disassociated with temperature increase. During the transition, fast (small particle) and slow (large particle) diffusive modes were detected by dynamic light scattering (DLS), which implied that the unimers were escaping from the self-assembled structure and swollen micelles, respectively. At sufficiently high temperatures where the solutions became almost transparent, the slow mode eventually disappeared, and only the fast mode remained. In addition, once the polymeric particles are formed, the size did not vary much with additional cooling. The transition point and the pattern of transmittance alteration were dependent on the degree of polymerization and the [PGLBT]:[PSPE] ratios; more PGLBT made the block copolymer less responsive to temperature and led the cloud point to lower degrees. However, random copolymers PGLBT- r-PSPE did not show any temperature-responsivity, and even small amount of GLBTs (10%) distributed in a PSPE chain significantly suppressed the transition.

Synthesis and characterization of a novel antibacterial material containing poly(sulfobetaine) using reverse atom transfer radical polymerization

A novel antibacterial agent was synthesized using 2-(dimethylamino)ethyl methacrylate (DM) and sodium 3-chloro-2-hydroxypropane sulfonate (CHPS). It was characterized by Fourier transform infrared spectroscopy (FTIR), NMR Spectroscopy (¹H NMR), and X-ray photoelectron spectroscopy (XPS). This new agent DMCHPS was then grafted onto a polyurethane (PU) substrate via surface-initiated reverse atom transfer radical polymerization (SI-RATRP). The modified PU was characterized by FTIR and XPS. The hydrophilic properties of the PU surface before and after the incorporation of DMCHPS were determined by static contact angle (SCA) measurements. The results showed that the hydrophilicity of the PU surface after the modification was remarkably improved. MIC tests and bacterial adhesion confirmed that modified PU has good antibacterial properties. Protein adsorption experiments show that the material has a certain ability to resist pollution. Furthermore, the high survival rate of HEK293 human embryonic kidney cells shows that the modified PU has a potential use as a medicinal material.

A novel antibacterial agent was synthesized using 2-(dimethylamino)ethyl methacrylate (DM) and sodium 3-chloro-2-hydroxypropane sulfonate (CHPS).

Modulating the solubility of zwitterionic poly((3-methacrylamidopropyl)ammonioalkane sulfonate)s in water and aqueous salt solutions via the spacer group separating the cationic and the anionic moieties

Even small variations of the spacer group between the anionic and the cationic moieties of poly(sulfobetaine)s strongly affect their aqueous phase behaviour.

Highly Stable, Protein-Resistant Surfaces via the Layer-by-Layer Assembly of Poly(sulfobetaine methacrylate) and Tannic Acid

Zwitterionic materials have received great attention because of the non-fouling property. As a result of the electric neutrality of zwitterionic polymers, their layer-by-layer (LBL) assembly is generally conducted under specific conditions, such as very low pH values or ionic strength. The formed multilayers are unstable at high pH or in a high ionic strength environment. Therefore, the formation of highly stable multilayers of zwitterionic polymers via the LBL assembly process is still challenging. Here, we report the LBL assembly of poly(sulfobetaine methacrylate) (PSBMA) with a polyphenol, tannic acid (TA), for protein-resistant surfaces. The assembly process was monitored by a quartz crystal microbalance (QCM) and variable-angle spectroscopic ellipsometry (VASE), which confirms the formation of thin multilayer films. We found that the (TA/PSBMA)n multilayers are stable over a wide pH range of 4-10 and in saline, such as 1 M NaCl or urea solution. The surface morphology and chemical composition were characterized by specular reflectance Fourier transform infrared spectroscopy (FTIR/SR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Furthermore, (TA/PSBMA)n multilayers show high hydrophilicity, with a water contact angle lower than 15°. A QCM was used to record the dynamic protein adsorption process. Adsorption amounts of bovine serum albumin (BSA), lysozyme (Lys), and hemoglobin (Hgb) on (TA/PSBMA)20 multilayers decreased to 0.42, 52.9, and 37.9 ng/cm(2) from 328, 357, and 509 ng/cm(2) on a bare gold chip surface, respectively. In addition, the protein-resistance property depends upon the outmost layer. This work provides new insights into the LBL assembly of zwitterionic polymers.

Charged micropollutant removal with hollow fiber nanofiltration membranes based on polycation/polyzwitterion/polyanion multilayers

Hollow fiber nanofiltration membranes can withstand much higher foulant concentrations than their spiral wound counterparts and can be used in water purification without pretreatment. Still, the preparation of hollow fiber nanofiltration membranes is much less established. In this work, we demonstrate the design of a hollow fiber nanofiltration membrane with excellent rejection properties by alternatively coating a porous ultrafiltration membrane with a polycation, a polyzwitterion, and a polyanion. On model surfaces, we show, for the first time, that the polyzwitterion poly N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethylammonium betaine (PSBMA) can be incorporated into traditional polyelectrolyte multilayers based on poly(styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC). Furthermore, work on model surfaces allows a good characterization of, and insight into, the layer build-up and helps to establish the optimal membrane coating conditions. Membranes coated with these multilayers have high salt rejection of up to 42% NaCl, 72% CaCl2, and 98% Na2SO4 with permeabilities of 3.7-4.5 l·m(-2)·h(-1)·bar(-1). In addition to the salt rejections, the rejection of six distinctively different micropollutants, with molecular weights between 215 and 362 g·mol(-1), was investigated. Depending on the terminating layer, the incorporation of the polyzwitterion in the multilayer results in nanofiltration membranes that show excellent retentions for both positively and negatively charged micropollutants, a behavior that is attributed to dielectric exclusion of the solutes. Our approach of combining model surfaces with membrane performance measurements provides unique insights into the properties of polyzwitterion-containing multilayers and their applications.

Zwitteration: coating surfaces with zwitterionic functionality to reduce nonspecific adsorption

Coating surfaces with thin or thick films of zwitterionic material is an effective way to reduce or eliminate nonspecific adsorption to the solid/liquid interface. This review tracks the various approaches to zwitteration, such as monolayer assemblies and polymeric brush coatings, on micro- to macroscopic surfaces. A critical summary of the mechanisms responsible for antifouling shows how zwitterions are ideally suited to this task.

Building polyzwitterion-based multilayers for responsive membranes

We systematically investigate the assembly of multilayers based on a polyzwitterion (PSBMA) and a polycation (PDADMAC) for the development of ionic strength responsive membranes. Although the polyzwitterion is essentially charge neutral, we show that specific electrostatic interactions with the PDADMAC allow for the formation of stable multilayers. The growth of this LbL system is monitored on model surfaces (silica) via optical reflectometry for different pH values and ionic strengths. While no effect of pH on the layer growth is observed, we did observe a strong dependence on the ionic strength. Upon increasing the ionic strength during deposition from 0.005 to 0.5 M NaCl, the adsorbed amount is significantly decreased, a behavior that is opposite to classical LbL systems. Similar results to those obtained on silica are also observed on top of classical LbL systems and on polymeric membranes. This demonstrates that the growth of the polyzwitterion multilayers is independent of the substrate. Coating these polyzwitterion multilayers on hollow fiber membranes via dip-coating yields membranes that are stimuli responsive toward the ionic strength of the filtration solution, with an increase in permeability of up to 108% from 0 to 1.5 M NaCl. We show that the fabrication of the polyzwitterion multilayers is an easy and controlled way to provide surfaces, such as membranes, with the specific functionalities of polyzwitterions.