Synthesis of Novel Sulfobetaine Polymers with Differing Dipole Orientations in Their Side Chains, and Their Effects on the Antifouling Properties

A novel avenue in the successful synthesis of Schiff base macromolecules via innovative plasma and classical approaches

Schiff base macromolecules have been successfully synthesized, utilizing a classical chemistry route and a dielectric barrier discharge (DBD) plasma technique. The synthesis of monomeric units has been accomplished through typical reactions of aldehyde and amine functional molecules. The condensation polymerization of the Schiff base molecules has been instigated chemically, using p-toluene sulfonyl chloride in refluxed ethanol. The molecular weight of the obtained polymers was discovered to be 524, 664 and 1,503,228 for Schiff base polymers 4a and 4b, respectively. Additionally, the polymerization reactions were prompted, employing a Dielectric Barrier Discharge (DBD) atmospheric pressure air plasma technique. The DBD plasma demonstrated a very powerful routine to produce high molecular weights macromolecules with optimum condition at 5 min. duration time, which could be an ecofriendly strategy to acquire this class of materials. The new polymeric materials have been characterized utilizing FTIR and NMR spectroscopy. Moreover, the complexation of polymer 4b with various metal moieties, Ru (II), Co (II), Cu (II), and Ni (II), has been executed in order to have a comparative study of their antitumor activity against MCF-7, HCT-116, and HepG-2 cell lines. Furthermore, the density functional theory was exploited to optimize the polymers and their complexes, and their HOMO-LUMO and energy gap were calculated, which was utilized to examine the inter/intra molecular charge transfer. The molecular electrostatic potential map was similarly quantified to investigate the reactive sites that are present in the investigated molecules. The result for the docking study confirmed that these complexed polymers adopted numerous important interactions with the amino acid of the targeted enzyme.

Effect of Interfacial Charge Distribution in Mixed Charge-Equilibrated SAMs on the Attachment of Pathogens

Zwitterions consisting of positively and negatively charged groups confer hydrophilicity while retaining overall charge neutrality. Both properties were identified as decisive prerequisites for protein-resistant coatings. In this work, we studied the electrostatic contributions to the bacterial attachment process by altering the interfacial charge distribution of the two charges and correlated the results with bacterial adhesion data. Therefore, we generated a set of well-defined, quasi-zwitterionic, charge-equilibrated self-assembled monolayers on gold-coated substrates. As cationic component (11-mercaptoundecyl)-N,N,N-trimethylammonium was combined in a 1:1 ratio with anionic thiols of varying alkyl spacer lengths. By embedding 8-mercaptooctanoic acid, 12-mercaptododecanoic acid, or 16-mercaptohexadecanoic acid, the distance of the anionic moiety to the surface could be varied while maintaining the distance of the cationic moiety to the substrate. Thereby, the interfacial charge distribution and thus the average orientation of the zwitterionic dipoles of the charge-equilibrated mixed self-assembled monolayers have been systematically varied. The resistance against the nonspecific adsorption of the blood-related proteins human serum albumin and fibronectin as well as the attachment-inhibiting effect against the pathogenic bacteria Escherichia coli, Pseudomonas fluorescens, and Bacillus subtilis was tested. It turned out that the change in dipole orientation affected the proteins and the bacteria in different ways with an equilibrated charge distribution within the surface plane being in total the superior one. The results are further discussed based on streaming current data revealing net surface charge of the self-assembled monolayers and the apparent zeta potential of the bacteria to understand to what degree electrostatic interactions contribute to the attachment process.

Enhanced Resistance of Zwitterionic Hydrogels against Marine Fouling Using a Zwitterionic Photo Cross-Linker

Polyzwitterions have great potential as fouling-resistant materials for biomedical and environmental products, in particular, in the form of hydrogel coatings. While typically these are soft materials, for many applications it is also necessary to achieve sufficient mechanical stability. This may be accomplished by high degrees of cross-linking, which, however, will impair the overall hydrophilicity of the gels for the commonly used hydrophobic cross-linkers. To mitigate this dilemma, a zwitterionic methacrylate monomer was developed that contains a benzophenone moiety as a photo-cross-linkable unit and a hydrophilic zwitterionic sulfobetaine moiety. Copolymers of the standard sulfobetaine methacrylate 3-[N-(2'-methacryloyloxyethyl)-N,N-dimethylammonio] propane-1-sulfonate (SPe) with contents of the new photo cross-linker of up to about 50 mol % were realized, and their films were photocured and analyzed. Subsequently, the resistance against the nonspecific adsorption of model proteins was determined in laboratory assays by surface plasmon resonance spectroscopy. Moreover, the attachment of marine fouling organisms was investigated in laboratory assays under dynamic conditions as well as in short-term field exposures in the sea. Copolymers with sufficiently high cross-linker contents of about 30 mol % were able to maintain a high hydration capability and to substantially reduce marine biofouling even in field tests in the ocean.

Polyzwitterions: controlled synthesis, soft materials and applications

Polyzwitterions refer to polymers containing both positive and negative charged groups in one side chain, which have shown unique physicochemical properties and significant potential in diverse applications due to their amphiphilic and net-neutral charged properties. This review aims to highlight the recent advances in the design and synthesis of polyzwitterions including direct polymerization of zwitterionic monomers and deionization of polymers. Furthermore, the formation of polyzwitterion based soft materials such as nanoparticles by self-assembly, hydrogels, coatings and polyzwitterion brushes, as well as the influence of the microstructure on their properties and applications are discussed. The potential applications of polyzwitterions in drug delivery, antifouling, lubrication, energy storage and antibacterial are also summarized. Finally, the prospects of polyzwitterions are proposed.

Unveiling the Preference for a Carbon Spacer Length of Three in Zwitterionic Sulfobetaines: Insights from DFT Calculations

Zwitterionic sulfobetaines (SBs) have shown excellent performance in biological and chemical applications. The carbon spacer lengths (CSLs) between oppositely charged groups are crucial for the properties of SBs. However, most reported studies naturally selected the SB molecule with a CSL of three, although the underlying reason for this choice remains unclear. In this work, using DFT calculations, we systemically investigated the effect of CSL on the molecular properties of SB molecules, including optimized confirmations, electrostatic potentials, atomic charges, dipole moments, and their self-association behaviors in both the gas phase and water solvent. The solvation free energies of SB molecules with various CSLs were calculated to evaluate the hydrophilicity of SBs. The results of our calculations demonstrated that a CSL of three is a critical length for optimal molecular properties, offering the strongest charge separation and the best hydrophilicity. While all SB molecules can form stable dimers through strong intermolecular electrostatic interactions, the dimers become unstable in water due to electrostatic shielding by water molecules. These findings shed light on the preference for a CSL of three in zwitterionic SBs and provide guidance for the rational design of SB-based materials.

Anti-polyelectrolyte effect of zwitterions containing (meth)acrylic waterborne polymer chains as tool for colloidal stabilization and polymer reinforcement

The anti-polyelectrolyte effect, a characteristic unique to polymer chains containing zwitterions, was investigated for its impact on colloidal stabilization during emulsion polymerization and on the resulting polymer characteristics. The zwitterionic monomer (ZM) 3-[(3-Acrylamidopropyl)dimethylammonio]propane-1-sulfonate (A3361) was selected for the synthesis of 30 wt% emulsifier-free methyl methacrylate/n-butyl acrylate (MMA/n-BA) polymer latex. Three pH conditions were examined: neutral, where the zwitterionic chains are in a collapsed state, and acidic and basic, where these chains adopt an extended conformation, leading to the anti-polyelectrolyte effect. The study of the anti-polyelectrolyte phenomenon on colloidal stability was challenging due to the increased ionic strength in the dispersions. Nevertheless, films cast from the acidic latex demonstrated enhanced mechanical properties, water resistance, and humidity barrier compared to films produced at neutral pH. This improvement is attributed to the anti-polyelectrolyte phenomenon, where the extended polymer chains rich in zwitterions offer enhanced ionic complexation, resulting in a denser and thicker ionic complexed network within the MMA/n-BA matrix. Under basic pH conditions, these improvements were modest, indicating that the anti-polyelectrolyte mechanism is influenced by pH. Furthermore, the high incorporation of A3361 facilitated, for the first time, the synthesis of 50% solids content emulsifier-free latexes, highlighting practical importance of this technology.

Using Catechol and Zwitterion-Functionalized Copolymers to Prevent Dental Bacterial Adhesion

In this manuscript, we report the synthesis of zwitterionic copolymers and their ability to form antifouling coatings on porous hydroxyapatite as a mimic of dental coatings. Specifically, we systematically investigated how altering the composition of copolymers of catechol methacrylate (Cat-MA or 2) and methacryloyloxyethyl phosphorylcholine (2-MPC) with varying catechol-to-zwitterion ratios impacted their adhesive and antifouling properties, allowing for the rational design of functional coatings. Characterization by ellipsometry, contact angle goniometry, and X-ray photoelectron spectroscopy revealed the presence of hydrophilic copolymer coatings of ∼10 nm thickness. Notably, these copolymers adhered to hydroxyapatite and reduced the level of attachment of both Gram-negative Escherichia coli and Gram-positive Streptococcus oralis. Additionally, in vitro experiments that mimicked the complex mouth environment (i.e., swallowing and using mouthwash) were employed to evaluate S. oralis adhesion, finding that the copolymer coatings reduced the quantity of adhered bacteria. We suggest that these copolymers provide insights into the design of antifouling coatings that are appropriate for use in oral care.

Albumin/Thiacalix[4]arene Nanoparticles as Potential Therapeutic Systems: Role of the Macrocycle for Stabilization of Monomeric Protein and Self-Assembly with Ciprofloxacin

The therapeutic application of serum albumin is determined by the relative content of the monomeric form compared to dimers, tetramers, hexamers, etc. In this paper, we propose and develop an approach to synthesize the cone stereoisomer of p-tert-butylthiacalix[4]arene with sulfobetaine fragments stabilization of monomeric bovine serum albumin and preventing aggregation. Spectral methods (UV-vis, CD, fluorescent spectroscopy, and dynamic light scattering) established the influence of the synthesized compounds on the content of monomeric and aggregated forms of BSA even without the formation of stable thiacalixarene/protein associates. The effect of thiacalixarenes on the efficiency of protein binding with the antibiotic ciprofloxacin was shown by fluorescence spectroscopy. The binding constant increases in the presence of the macrocycles, likely due to the stabilization of monomeric forms of BSA. Our study clearly shows the potential of this macrocycle design as a platform for the development of the fundamentally new approaches for preventing aggregation.

Low Fouling Polysulfobetaines with Variable Hydrophobic Content

Amphiphilic polymer coatings combining hydrophilic elements, in particular zwitterionic groups, and hydrophobic elements comprise a promising strategy to decrease biofouling. However, the influence of the content of the hydrophobic component in zwitterionic coatings on the interfacial molecular reorganization dynamics and the anti-fouling performance is not well understood. Therefore, coatings of amphiphilic copolymers of sulfobetaine methacrylate 3-[N-2'-(methacryloyloxy)ethyl-N,N-dimethyl]-ammonio propane-1-sulfonate (SPE) are prepared which contain increasing amounts of hydrophobic n-butyl methacrylate (BMA). Their fouling resistance is compared to that of their homopolymers PSPE and PBMA. The photo-crosslinked coatings form hydrogel films with a hydrophilic surface. Fouling by the proteins fibrinogen and lysozyme as well as by the diatom Navicula perminuta and the green algae Ulva linza is assessed in laboratory assays. While biofouling is strongly reduced by all zwitterionic coatings, the best fouling resistance is obtained for the amphiphilic copolymers. Also in preliminary field tests, the anti-fouling performance of the amphiphilic copolymer films is superior to that of both homopolymers. When the coatings are exposed to a marine environment, the reduced susceptibility to silt incorporation, in particular compared to the most hydrophilic polyzwitterion PSPE, likely contributes to the improved fouling resistance.

Polyelectrolytes as Building Blocks for Next-Generation Membranes with Advanced Functionalities

The global society is in a transition, where dealing with climate change and water scarcity are important challenges. More efficient separations of chemical species are essential to reduce energy consumption and to provide more reliable access to clean water. Here, membranes with advanced functionalities that go beyond standard separation properties can play a key role. This includes relevant functionalities, such as stimuli-responsiveness, fouling control, stability, specific selectivity, sustainability, and antimicrobial activity. Polyelectrolytes and their complexes are an especially promising system to provide advanced membrane functionalities. Here, we have reviewed recent work where advanced membrane properties stem directly from the material properties provided by polyelectrolytes. This work highlights the versatility of polyelectrolyte-based membrane modifications, where polyelectrolytes are not only applied as single layers, including brushes, but also as more complex polyelectrolyte multilayers on both porous membrane supports and dense membranes. Moreover, free-standing membranes can also be produced completely from aqueous polyelectrolyte solutions allowing much more sustainable approaches to membrane fabrication. The Review demonstrates the promise that polyelectrolytes and their complexes hold for next-generation membranes with advanced properties, while it also provides a clear outlook on the future of this promising field.

Polybetaines in Biomedical Applications

Polybetaines, that have moieties bearing both cationic (quaternary ammonium group) and anionic groups (carboxylate, sulfonate, phosphate/phosphinate/phosphonate groups) situated in the same structural unit represent an important class of smart polymers with unique and specific properties, belonging to the family of zwitterionic materials. According to the anionic groups, polybetaines can be divided into three major classes: poly(carboxybetaines), poly(sulfobetaines) and poly(phosphobetaines). The structural diversity of polybetaines and their special properties such as, antifouling, antimicrobial, strong hydration properties and good biocompatibility lead to their use in nanotechnology, biological and medical fields, water remediation, hydrometallurgy and the oil industry. In this review we aimed to highlight the recent developments achieved in the field of biomedical applications of polybetaines such as: antifouling, antimicrobial and implant coatings, wound healing and drug delivery systems.

Amphiphilic Zwitterionic Acrylate/Methacrylate Copolymers for Marine Fouling-Release Coatings

Methacrylate and acrylate monomers are popular building blocks for antifouling (AF) and fouling-release (FR) coatings to counteract marine biofouling. They are used in various combinations and often combined into amphiphilic materials. This study investigated the FR properties of amphiphilic ethylene glycol dicyclopentenyl ether acrylate (DCPEA) and the corresponding methacrylate (DCPEMA) blended with 5 wt % zwitterionic carboxybetaine acrylate (CBA) and the corresponding methacrylate (CBMA). A series of (co)polymers with different acrylate/methacrylate compositions were synthesized and tested against the attachment of the diatom Navicula perminuta and in short-term dynamic field exposure experiments. The more hydrophobic methacrylate DCPEMA homopolymer outperformed its acrylate counterpart DCPEA. Incorporated zwitterionic functionality of both CBMA and CBA imparted ultralow fouling capability in the amphiphilic polymers toward diatom attachment, whereas in the real ocean environment, only the employment of CBMA reduced marine biofouling. Moreover, it was observed that CBA-containing coatings showed different surface morphologies and roughnesses compared to the CBMA analogues. Particularly, a high impact was found when acrylic CBA was mixed with methacrylic DCPEMA. While the wettability of the coatings was comparable, investigated methacrylates in general exhibited superior fouling resistance compared to the acrylates.

Biomimetic surface coatings for marine antifouling: Natural antifoulants, synthetic polymers and surface microtopography

Marine biofouling is a ubiquitous problem that accompanies human marine activities and marine industries. It exerts detrimental impacts on the economy, environment, ecology, and safety. Traditionally, mainstream approaches utilize metal ions to prevent biological contamination, but this also leads to environmental pollution and damage to the ecosystem. Efficient and environmentally friendly coatings are urgently needed to prevent marine devices from biofouling. Since nature is always the best teacher for humans, it offers us delightful thoughts on the research and development of high-efficiency, broad-spectrum and eco-friendly antifouling coatings. In this work, we focus on the research frontier of marine antifouling coatings from a bionic perspective. Enlightened by three distinctive dimensions of bionics: chemical molecule bionic, physiological mechanism bionic, and physical structure bionic, the research status of three main bioinspired strategies, which are natural antifoulants, bioinspired polymeric antifouling coatings, and biomimetic surface microtopographies, respectively, are demonstrated. The antifouling mechanisms are further interpreted based on biomimetic comprehension. The main fabrication methods and antifouling performances of these coatings are presented along with their advantages and drawbacks. Finally, the challenges are summarized, and future research prospects are proposed. It is believed that biomimetic antifouling strategies will contribute to the development of nontoxic antifouling techniques with exceptional repellency and stability.

Sulfobetaine Methacrylate Polymers of Unconventional Polyzwitterion Architecture and Their Antifouling Properties

Combining high hydrophilicity with charge neutrality, polyzwitterions are intensely explored for their high biocompatibility and low-fouling properties. Recent reports indicated that in addition to charge neutrality, the zwitterion's segmental dipole orientation is an important factor for interacting with the environment. Accordingly, a series of polysulfobetaines with a novel architecture was designed, in which the cationic and anionic groups of the zwitterionic moiety are placed at equal distances from the backbone. They were investigated by in vitro biofouling assays, covering proteins of different charges and model marine organisms. All polyzwitterion coatings reduced the fouling effectively compared to model polymer surfaces of poly(butyl methacrylate), with a nearly equally good performance as the reference polybetaine poly(3-(N-(2-(methacryloyloxy)ethyl)-N,N-dimethylammonio)propanesulfonate). The specific fouling resistance depended on the detailed chemical structure of the polyzwitterions. Still, while clearly affecting the performance, the precise dipole orientation of the sulfobetaine group in the polyzwitterions seems overall to be only of secondary importance for their antifouling behavior.

Research progress of environmentally friendly marine antifouling coatings

The antifouling mechanisms and research progress in the past three years of environmentally friendly marine antifouling coatings are introduced in this work.

Effect of Dipole Orientation in Mixed, Charge-Equilibrated Self-assembled Monolayers on Protein Adsorption and Marine Biofouling

While zwitterionic interfaces are known for their excellent low-fouling properties, the underlying molecular principles are still under debate. In particular, the role of the zwitterion orientation at the interface has been discussed recently. For elucidation of the effect of this parameter, self-assembled monolayers (SAMs) on gold were prepared from stoichiometric mixtures of oppositely charged alkyl thiols bearing either a quaternary ammonium or a carboxylate moiety. The alkyl chain length of the cationic component (11-mercaptoundecyl)-N,N,N-trimethylammonium, which controls the distance of the positively charged end group from the substrate's surface, was kept constant. In contrast, the anionic component and, correspondingly, the distance of the negatively charged carboxylate groups from the surface was varied by changing the alkyl chain length in the thiol molecules from 7 (8-mercaptooctanoic acid) to 11 (12-mercaptododecanoic acid) to 15 (16-mercaptohexadecanoic acid). In this way, the charge neutrality of the coating was maintained, but the charged groups exposed at the interface to water were varied, and thus, the orientation of the dipoles in the SAMs was altered. In model biofouling studies, protein adsorption, diatom accumulation, and the settlement of zoospores were all affected by the altered charge distribution. This demonstrates the importance of the dipole orientation in mixed-charged SAMs for their inertness to nonspecific protein adsorption and the accumulation of marine organisms. Overall, biofouling was lowest when both the anionic and the cationic groups were placed at the same distance from the substrate's surface.

Effects of crosslink density in zwitterionic hydrogel coatings on their antifouling performance and susceptibility to silt uptake

Hydrogel coatings effectively reduce the attachment of proteins and organisms in laboratory assays, in particular when made from zwitterionic monomers. In field experiments with multiple species and non-living material, such coatings suffer from adsorption of particulate matter. In this study, the zwitterionic monomer 3-[N-(2-methacryloyloxyethyl)-N,N-dimethylammonio] propanesulfonate (SPE) was copolymerized with increasing amounts of the photo-crosslinker benzophenon-4-yloxyethyl methacrylate (BPEMA) to systematically alter the density of crosslinks between the polymer chains. The effect of increasing crosslink density on the antifouling (AF) performance of the coatings was investigated in laboratory assays and fields tests. In both cases, the AF performance was improved by increasing the crosslinker content. The coatings reduced protein, diatom, and barnacle accumulation, and showed better resistance to biomass accumulation. The findings underline that the marine AF performance of hydrogel coatings does not only depend on the specific chemical structure of the polymers, but also on their physico-chemical properties such as rigidity and swelling.

Polymeric Coatings Based on Water-Soluble Trimethylammonium Copolymers for Antifouling Applications

Crosslinked polymeric materials based on a quaternary trimethylammonium compound were developed and evaluated as potential antifouling coatings. For this purpose, two water-soluble random copolymers, poly(4-vinylbenzyltrimethylammonium chloride-co-acrylic acid) P(VBCTMAM-co-AAx) and poly(N,N-dimethylacrylamide-co-glycidylmethacrylate) P(DMAm-co-GMAx), were synthesized via free radical polymerization. A water based approach for the synthesis of P(VBCTMAM-co-AAx) copolymer was used. Coatings of the complementary reactive copolymers in different compositions were obtained by curing at 120 °C for one day and were used to coat aquaculture nets. These nets were evaluated in respect to their release rate using Total Organic Carbon (TOC) and Total Nitrogen (TN) measurements. Finally, the antifouling efficacy of these newly-composed durable coatings was investigated for 14 days in accelerated conditions. The results showed that this novel polymeric material provides contact-killing antifouling activity for a short time period, whereas it functions efficiently in biofouling removal after high-pressure cleaning.