Zwitterionic Membranes Research Articles

Week-Long Operation of Electrochemical Aptamer Sensors: New Insights into Self-Assembled Monolayer Degradation Mechanisms and Solutions for Stability in Serum at Body Temperature.

Conventional wisdom suggests that widely utilized self-assembled alkylthiolate monolayers on gold are too unstable to last more than several days when exposed to complex fluids such as raw serum at body temperature. Demonstrated here is that these monolayers can not only last at least 1 week under such harsh conditions but that significant applied value can be captured for continuous electrochemical aptamer biosensors. Electrochemical aptamer biosensors provide an ideal tool to investigate monolayer degradation, as aptamer sensors require a tightly packed monolayer to preserve sensor signal vs background current and readily reveal fouling by albumin and other solutes when operating in biofluids. Week-long operation in serum at 37 °C is achieved by (1) increasing van der Waals interactions between adjacent monolayer molecules to increase the activation energy required for desorption, (2) optimizing electrochemical measurement to decrease both alkylthiolate oxidation and electric-field-induced desorption, and (3) mitigating fouling using protective zwitterionic membranes and zwitterion-based blocking layers with antifouling properties. This work further proposes origins and mechanisms of monolayer degradation in a logical stepwise manner that was previously unobservable over multiday time scales. Several of the observed results are surprising, revealing that short-term improvements to sensor longevity (i.e., hours) actually increase sensor degradation in the longer term (i.e., days). The results and underlying insights on mechanisms not only push forward fundamental understanding of stability for self-assembled monolayers but also demonstrate an important milestone for continuous electrochemical aptamer biosensors.

Engineering a novel zwitterionic polyurethane nanofiltration membrane with enhanced fouling resistance for water reclamation

Design of zwitterionic polymers with feasible methods is rational for grafting membrane surface and enhancing its antifouling property. Herein, we propose a facile and scalable “one-pot” polymerization approach to synthesize a novel thiolated zwitterionic polyurethane (TZP) and graft it onto a polydopamine activated membrane surface via Michael addition for engineering antifouling nanofiltration (NF) membranes. The chemical structure of TZP was confirmed by the 1H nuclear magnetic resonance and it had a weight average molecular weight of 13,000 g mol−1. The Fourier transform infrared and X-ray photoelectron spectra confirm the successful introduction of sulfobetaine groups on membrane surfaces. The TZP grafting neutralized the negative charge of PDA interlayer and further improved membrane hydrophilicity. The pore size and ion selectivity of the NF membranes were optimized by tuning TZP concentrations. Satisfactory divalent anion retention along with a molecular weight cut-off of ∼800 Da was achieved at 30 g L−1 TZP concentration (i.e., TZP-30). During two cycles of synthetic wastewater filtration, the TZP-30 membrane exhibited excellent fouling resistance and satisfactory flux recovery rate compared with a benchmark commercial NF membrane. Our findings shed light on the future design of novel zwitterionic polymers and antifouling NF membranes for sustainable water reclamation.

Tyrocidine potentiates the pore-forming ability of the linear gramicidins.

Antimicrobial peptides (AMPs) play an essential role in the innate immune system. They alter lipid bilayer properties, but they have intracellular effects as well. While microbes may become resistant to AMPs, the mechanisms are likely to differ from those developed against more conventional antibiotics. Given the pressing nature of increasing antibiotic resistance, we explored physicochemical mechanisms by which AMPs alter bilayer properties, with the aim to optimize future drug design, including minimizing the acquisition of resistance. To this end, we focused on the antibiotics produced by Brevibacillus brevis, a Gram-positive soil bacterium, a mixture of cyclic decapeptides (the tyrocidines), and linear pentadecapeptides (the gramicidins). The tyrocidines tend to be cytotoxic, but the linear gramicidins were the first antibiotics to be used and continue to be used in topical medications. The bactericidal activity of gramicidin results from the formation of cation-selective pores, which are sensitive to the physicochemical properties of the bilayer in which they are embedded. We therefore explored whether the tyrocidines might potentiate gramicidin channel formation through perturbation of membrane properties. Indeed, the tyrocidines enhance the channel-forming potency of gramicidin in both zwitterionic membranes formed by 1,2-Dierucoyl-sn-Glycero-3-Phosphocholine (DEPC) and negatively charged membranes formed by a 3:1 mixture of DEPC and 1,2-Dierucoyl-sn-Glycero-3-Phosphoglycerol (DEPG). Using dynamic light scattering (DLS) and zeta potential measurements to assess the LUV size distributions and net charge, we conclude that tyrocidine binds with high affinity to negatively charged DEPC:DEPG vesicles. Yet, the potentiation of gramicidin activity was greater in DEPC than in DEPC:DEPG membranes, likely due to an organizing effect of the cationic tyrocidines. Compared to the cyclic decapeptide gramicidin S, the tyrocidines behave similarly but are more potent.

Multiple Interface Reactions Enabled Zwitterionic Polyamide Composite Reverse Osmosis Membrane for Enhanced Permeability and Antifouling Property

Membrane fouling for polyamide composite reverse osmosis (RO) membranes is always one of the main bottleneck problems that limit its practical application. Herein, a novel zwitterionic polyamide composite membrane was prepared with a stepwise multiple interface reaction strategy, which combined the interfacial polymerization process with an interfacial grafting process to tailor an antifouling membrane surface. First, the polyamide composite membrane was prepared by conventional polyamide interface polymerization, and then N,N-dimethylethylenediamine was grafted to the polyamide composite layer via liquid interfacial amidation reaction to impart tertiary amine reactive sites, and finally 1,3-propane sultone underwent a vapor interfacial ring-opening reaction to induce quaternization of the tertiary amine reactive site and generate zwitterionic groups. Zwitterionic polyamide composite membrane showed higher hydrophilicity and lower surface roughness, which can facilitate water permeation and improve antifouling property. Compared to pristine RO membrane, the water flux of the zwitterionic RO membrane is promoted by ∼100%, and the NaCl rejection rate is maintained at 99%. Also note that the zwitterionic polyamide composite membrane exhibits outstanding antifouling property, compared to typical surfactants. The durability of the zwitterionic polyamide composite membrane during long-term operation was also demonstrated. This study provides a simple, effective, and novel method for the rational design and fabrication of antifouling RO membranes with excellent comprehensive separation performance.

High flux zwitterionic hybrid cellulose acetate desalination membranes: Formation of permeability-effective macropores by self-organizing zwitterionic silanes

Zwitterionic hybrid cellulose acetate membranes with improved flux and antifouling performance were produced by a modified non-solvent induced phase separation (NIPS) process in which a zwitterionic trimethoxysilane compound, (3-sulfopropylbetaine-propyl)-trimethoxysilane (SPPT), was added to the casting solutions at 1.0, 2.0, and 3.0 wt%. The successful incorporation of SPPT into cellulose acetate (CA) membranes was proved by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and thermal gravimetric analysis (TGA). Permeate fluxes of the hybrid membranes increased significantly compared to the control cellulose acetate membrane prepared without the addition of SPPT (15 bar pressure; 2000 ppm NaCl or MgSO4 aqueous solution filtration). The hybrid membranes exhibited an increase in permeate flux up to 87 % while their salt rejections slightly decreased in NaCl solution filtration. In MgSO4 solution filtration, the flux was increased by 61 % without sacrificing salt rejection. The reason for the enhancement in the flux was the formation of macropores in the membrane bulk structures by self-organizing zwitterionic silane groups. The highest resistance to bovine serum albumin (BSA) or xanthan gum as a foulant was observed in the hybrid membranes produced with 1.0 wt% of SPPT.

Triethanolamine-based zwitterionic polyester thin-film composite nanofiltration membranes with excellent fouling-resistance for efficient dye and antibiotic separation

Water pollution and scarcity caused by small organic compounds (dyes and antibiotics) have attracted considerable attention due to their potential adverse effects on ecological environment and human body. Nanofiltration membranes with high performance, such as high rejection and fouling resistance, are expected to address these challenges. Herein, a new zwitterionic triethanolamine-based (Z-TEOA) monomer is proposed for the fabrication of zwitterionic polyester thin-film composite nanofiltration (ZNF) membranes. Z-TEOA is successfully synthesized via the ring-open reaction between TEOA and 1,3-propane sultone. ZNF membranes are fabricated via the interfacial polymerization under alkaline conditions. All fabricated membranes exhibit enhanced hydrophilicity and permeability due to the introduction of the zwitterionic functionality in the thin film layers. Specifically, the optimum membrane (ZNF1.5-5) shows an ultralow water contact angle (WCA) of 20.2°, high rejections to Congo red (CR, 99.9%), methyl blue (MB, 99.7%), orange G (OG, 95.9%), and tetracycline (TC, 96.7%). The uncompromised MB rejection of the ZNF membrane after a chlorine exposure (10,000 ppm.h) indicates its excellent chlorine resistance. Furthermore, the achieved ultrahigh flux recovery ratio (FRR, 97.8%) for MB demonstrates its outstanding fouling-resistant performance. All results reveal its potential for applications in the treatment of wastewaters from textile and pharmaceutical industries.

Lateral diffusion of lipids in the DMPG membrane across the anomalous melting regime: effects of NaCl.

The anionic dimyristoyl phosphatidylglycerol (DMPG) membrane in solvents with a low ionic strength is known to exhibit an unusually wide melting regime between the gel and fluid phase characterized by various anomalous macroscopic characteristics, such as low turbidity and high electrical conductivity and viscosity. A recent neutron spin echo study [Kelley, E. G. et al., Struct. Dyn., 7 (2020) 054704] revealed that during the extended melting phase transition the DMPG membrane becomes softer and exhibits faster collective bending fluctuation compared to the higher temperature fluid phase. In contrast, in the present work, using incoherent quasielastic neutron scattering through the anomalous phase transition regime we find that single-particle lateral and internal lipid motions in the DMPG membrane show regular temperature dependence, with no enhanced dynamics evident in the anomalous melting regime. Further, we find that incorporation of NaCl in DMPG suppresses the anomalous extended melting regime, concurrently enhancing the single-particle lipid dynamics, both the lateral diffusivity and (to a lesser extent) the internal lipid motion. This seems rather counterintuitive and in variance with the dynamic suppression effect exerted by a salt on a zwitterionic membrane. However, since incorporation of a salt in anionic DMPG leads to enhanced cooperativity, the disrupted cooperativity in the salt-free DMPG is associated with the baseline lipid dynamics that is suppressed to begin with, whereas addition of salt partially restores the cooperativity, thus enhancing lipid dynamics compared to the salt-free baseline DMPG membrane state. These results provide new insights into the ion-membrane interaction and divulge a correlation between microscopic dynamics and the structure of the lipid bilayer.

Fabrication of novel zwitterionic copolymer high performance membrane applied for oil/water mixtures and emulsions separation

The separation of oily wastewater is important for the ecological environment. Due to all kinds of defects in traditional methods, membrane technology shows outstanding merit for separating oil contaminants from water. In this work, a novel zwitterionic monomer 2-(3-carboxyacryloyloxy)-N-(Carboxyethyl)-N, N-dimethyl ethanaminium (DMAAA) was synthesized and characterized. Then, a novel zwitterionic copolymer, poly(2-(3-carboxyacryloyloxy)-N-(Carboxyethyl)-N, N-dimethyl ethanaminium-co-2-hydroxyethyl acrylate) (P(DMAAA-co-HEA)) was prepared by free radical polymerization. The superhydrophilic and underwater-superoleophobic membranes were prepared using stainless steel mesh (SSM) with different pore sizes as substrate, P(DMAAA-co-HEA) as superhydrophilic component, nano-silica (SiO2) as micro-nano porous structure, and tetraethyl orthosilicate (TEOS) as cross-linking agent by the one-step dip-coating method. P(DMAAA-co-HEA)-TEOS-SiO2 coated 400 mesh SSM(PTS-SSM400) exhibits ultra-high separation flux (243,600 L·m−2·h−1) and separation efficiency (>99.88%) in separating oil/water mixtures. And the coated 2000 mesh SSM (PTS-SSM2000) can separate various surfactant-stabilized emulsions with high water flux and efficiency only under gravity. Moreover, the membranes have excellent chemical stability and wear resistance. Even having been successively immersed for seven days in acidic, alkaline, and saline environments, respectively, and after 50 wear resistance cycle tests, the coated membranes can still effectively separate oil/water mixtures. The simple and facile preparation method is especially suitable for large-scale practical industrial applications.

Zwitterionic forward osmosis membrane with low structural parameter based on highly porous polyvinylidene fluoride substrate for desalination

Polyamide thin-film composites (PA-TFC) forward osmosis (FO) membranes have great potential in wastewater treatment and desalination. However, they are continuously studied to further enhance the FO performances from the improvement of the PA layer and the substrate individually. Here, a polyvinylidene fluoride/poly(hydroxyethyl methacrylate) (PVDF/PHEMA) membrane with a highly porous surface was fabricated and used as the substrate to engineer a thin and rough PA layer. After being post-modified by zwitterionic groups, the resulting membrane (namely TFC90-Z) has a much lower structure parameter ( S , 216 ± 12 µm) in comparison to common FO membranes in literature, thus decreasing internal concentration polarization and increasing FO performances. Specific salt flux ( J s /J w ) and water flux ( J w ) of TFC90-Z are 0.03 ± 0.01 g/L and 18.5 ± 0.4 L m -2 h -1 under the active layer-facing draw solution (AL-DS) orientation using 1.0 M NaCl as the draw solution and deionized water as the feed solution. Meanwhile, NaCl rejection is 91.6 ± 0.1%. This work offers an efficient way to engineer excellent PA-TFC FO membranes for aqueous separation and desalination. • PA-TFC FO membranes were fabricated on highly porous PVDF/PHEMA substrates via IP. • The PA layer was post-modified by zwitterionic groups via co-deposition of TA and AEPPS. • ICP is weakened due to the low structure parameter of the zwitterionic PA-TFC FO membrane. • The as-prepared FO membrane has excellent FO performances especially specific salt flux ( J s /J w ).

Ruscogenin interacts with DPPC and DPPG model membranes and increases the membrane fluidity: FTIR and DSC studies

Ruscogenin, a kind of steroid saponin, has been shown to have significant anti-oxidant, anti-inflammatory, and anti-thrombotic characteristics. Furthermore, it has the potential to be employed as a medicinal medication to treat a variety of acute and chronic disorders. The interaction of a drug molecule with cell membranes can help to elucidate its system-wide protective and therapeutic effects, and it's also important for its pharmacological activity. The molecular mechanism by which ruscogenin affects membrane architecture is still a mystery. Ruscogenin's interaction with zwitterionic dipalmitoyl phosphatidylcholine (DPPC) and anionic dipalmitoyl phosphatidylglycerol (DPPG) multilamellar vesicles (MLVs) was studied utilizing two non-invasive approaches, including: Fourier Transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry. Ruscogenin caused considerable alterations in the phase transition profile, order, dynamics and hydration state of head groups and glycerol backbone of DPPC and DPPG MLVs at all concentrations. The DSC results indicated that the presence of ruscogenin decreased the main phase transition temperature (Tm) and enthalpy (ΔH) values of both membranes and increased half height width of the main transition (ΔT1/2). The FTIR results demonstrated that all concentrations (1, 3, 6, 9, 15, 24 and 30 mol percent) of ruscogenin disordered the DPPC MLVs both in the gel and liquid crystalline phases while it increased the order of DPPG MLVs in the liquid crystalline phase. Moreover, ruscogenin caused an increase in the dynamics of DPPC and DPPG MLVs in both phases. Additionally, it enhanced the hydration of the head groups of lipids and the surrounding water molecules implying ruscogenin to interact strongly with both zwitterionic and charged model membranes.

Efficacy of Electrospun Nanofiber Membranes on Fouling Mitigation: A Review.

Despite the advantages of high contaminant removal, operational flexibility, and technical advancements offered, the undesirable fouling property of membranes limits their durability, thus posing restrictions on their usage. An enormous struggle is underway to conquer this major challenge. Most of the earlier reviews include the basic concepts of fouling and antifouling, with respect to particular separation processes such as ultrafiltration, nanofiltration, reverse osmosis and membrane bioreactors, graphene-based membranes, zwitterionic membranes, and so on. As per our knowledge, the importance of nanofiber membranes in challenging the fouling process has not been included in any record to date. Nanofibers with the ability to be embedded in any medium with a high surface to volume ratio play a key role in mitigating the fouling of membranes, and it is important for these studies to be critically analyzed and reported. Our Review hence intends to focus on nanofiber membranes developed with enhanced antifouling and biofouling properties with a brief introduction on fabrication processes and surface and chemical modifications. A summary on surface modifications of preformed nanofibers is given along with different nanofiller combinations used and blend fabrication with efficacy in wastewater treatment and antifouling abilities. In addition, future prospects and advancements are discussed.

Efficient ethylene/ethane separation by zwitterionic deep eutectic solvent membranes

Zwitterionic deep eutectic solvent membranes (ZDESMs) hold great promise in molecular separations yet have rarely been reported. Herein, for the first time, ZDESMs are constructed by zwitterionic deep eutectic solvent (ZDES) and ethylene-transport carrier (silver salt) for ethylene/ethane separation. Experiments and simulations reveal that the ZDESMs possess structural nano-heterogeneity with discrete zwitterionic nanodomains and interconnected carrier channels, thus flexibly regulating the carrier spatial distribution as well as promoting carrier activity and stability synchronously. The ZDESMs acquires high ethylene permeability, ethylene/ethane selectivity at low carrier concentration, and long-term stability, which is superior to most of the-state-of-the-art ethylene/ethane separation membranes. The proposed ZDESMs expand the membrane family, and the nano-heterogeneity design and visualization of membrane structure will offer valuable guidance on developing advanced membranes for energy-intensive gas separations.

Inorganic salt regulated zwitterionic nanofiltration membranes for antibiotic/monovalent salt separation

Zwitterionic nanofiltration membranes (ZNFMs) are conducive to achieve efficient antibiotic/monovalent salt separation. However, preparation of ZNFMs through interfacial polymerization is limited by electrostatic interaction between zwitterions. In this study, inorganic salts were applied to regulate reactions in interfacial polymerization, such as interfacial reaction and thermal cross-linking reaction. The electrostatic interaction between zwitterions was broken by the inorganic salts to promote cross-linking of zwitterionic polyamide networks. Therefore, an intact and ultrathin separation layer was formed on substrates. The obtained ZNFMs exhibited a high permeance of 21.6 L m−2 h−1 bar−1, while the rejections for erythromycin (ERY) and NaCl were 97.5% and 8.5%, respectively. Moreover, the ZNFMs also had an exceptional anti-fouling property, which showed a great potential in antibiotic/monovalent salt separation.

Acyl chain length tuning improves antimicrobial potency and biocompatibility of short designed lipopeptides

HypothesisDesigned antimicrobial lipopeptides (ALPs) offer the attractive benefits of short peptide sequences and flexible tuning of amphiphilicity by altering the acyl chain length. These lipopeptides kill microbes by forming intriguing in-membrane nanostructures and causing the leakage of internal contents. However, how subtle differences in the molecular structures of the lipopeptides affect their antimicrobial efficacy and biocompatibility to host cells is still under-investigated. ExperimentsThis work focuses on assessing changes in the acyl chain length of CH3(CH2)n-2CO-KKKIII-NH2 (n = 10, 12 and 14, K = lysine, I = isoleucine, denoted as CnKI3) on the antimicrobial potency and cytotoxicity by combining biological assays with physical measurements. Aggregation properties were characterized by changes in critical aggregation concentration (CAC) from surface tension measurements. Antimicrobial susceptibility tests, cytotoxic MTT assays, haemolytic tests, and dynamic bactericidal experiments were employed to reveal their bioactive potency toward different types of cells. To further investigate lipopeptides’ underlying antimicrobial and cytotoxic mechanisms, lipid monolayer and lipid small unilamellar vesicle (SUV) models were established and biophysically characterized. FindingsAn increase in n led to the decrease in the CAC of CnKI3, showing a rising membrane-lytic power. Subsequent bioactive measurements revealed the optimal performance of C12KI3 from this series of lipopeptides. The selective membrane binding behaviour was well supported by neutron reflection data from charged lipid monolayer models, revealing membrane-supported nanostructures of ALPs. However, increased membrane-lytic actions in C14KI3 led to notably increased toxicity and reduced selectivity. On the other hand, C14KI3 can impose faster dynamic killing than natural lipopeptide polymyxin B, showing the distinct impact of the amphiphilic balance from the designed lipopeptide. In contrast, the distinctly weaker binding to zwitterionic membrane models (monolayers and SUVs) provided direct nanoscale structural evidence to the mildness of the designed ALPs on host cells. This work demonstrates the high selectivity and fast killing of rationally designed short ALPs to microbes via in-membrane nanostructuring.

Trimethylamine N-oxide-derived zwitterionic polyamide thin-film composite nanofiltration membranes with enhanced anti-dye deposition ability for efficient dye separation and recovery

Organic dyes from textile industries are becoming the second largest pollutants in the world. In this study, inspired by the seawater fish, a new diamine monomer, N,N-bis(3-aminopropyl)methylamine N-oxide (DNMAO) with a trimethylamine N-oxide (TMAO)-derived “N+─O−” zwitterionic functionality, has been designed for the fabrication of polyamide thin-film composite (TFC) membranes to purify dye-contaminated water and recover organic dyes. The fabricated membranes show enhanced permeability and improved anti-dye-deposition performance. The optimum membrane fabricated at 0.5 wt% of DNMAO feed solution exhibits an ultrahigh pure water permeability (PWP) of 37.5 LMH bar−1, a superior Congo red (CR) rejection of 99.93%, and a low sodium chloride (NaCl) rejection of 9.3%, indicating its outstanding performance for dye/salt separation. It can also achieve the complete CR removal from a feed with a low CR concentration of 1 ppm, demonstrating its superior separation performance for the production of clean potable water. In addition, the low dye loss rate (6.22%) and high salt removal rate (85.6%) are achieved during the purification and recovery test with CR/NaCl mixtures. Furthermore, the optimum membrane possesses an excellent anti-dye-deposition performance with a flux recovery ratio (FRR) of 92.1%. All these results demonstrate its potential for applications in not only textile wastewater treatment but also organic dye purification and recovery.

Molecular mechanisms of direct and indirect interplay between amyloid β42 oligomer and characteristic lipids

Accumulating evidence suggests that toxicity in patients with Alzheimer's disease originates from the deposition of Aβ42 aggregates on the neuronal cell membrane. However, the molecular mechanism underlying Aβ42 aggregation on the surface of different lipids is poorly understood. In this study, coarse-grained and all-atomic molecular dynamics (MD) simulations were used to characterize the assembly process of two Aβ42 pentameric oligomers and the perturbation “footprints” of three characteristic lipid constitute bilayer membranes: POPC, POPG, and their hybrid PcPg composed of POPG and POPC in a 1:3 ratio. Our results revealed that the Aβ decamer was first formed in the water phase prior to its contact with the lipid surface, indicating that the water phase plays an incubation role in Aβ42 oligomer aggregation. Moreover, the presence of any of the three lipids accelerated the assembly process of the two Aβ42 pentameric. The aggregation rate and aggregate conformation were strictly dependent on lipid charge, oligomer size, and degree of aggregation. In turn, the presence of oligomer impacted the surface of the lipid, generating a clear perturbation “footprint”, regardless of whether the interplay was direct or indirect, revealing for the first time that the indirect interaction is not seamless and can be detected clearly at the molecular level. Indirect interplay stands for the non-contacting interaction interfaced by the water phase, indicating a metastable state with long-range interaction under non-shaking conditions. Our results reveal the crucial role of non-contacting interactions in determining the phase status of zwitterionic membranes.

Reduction of nanoscopic dynamics in the zwitterionic membrane by salt

The effect of addition of lithium chloride on the lateral diffusivity and internal motion of lipid in unilamellar dimyristoylphosphatidylcholine (DMPC) vesicles was investigated using elastic incoherent neutron scattering, quasielastic incoherent neutron scattering, and differential scanning calorimetry. A shift of the main phase transition to a higher temperature indicated a broader temperature range of the thermodynamic stability of the ordered phase resulting from the salt addition. A universal stiffening effect exerted by lithium chloride on the lipid membrane manifested itself in (1) lower mean-square displacement and (2) decreasing diffusivities, both lateral and localized, in both the ordered gel and the disordered fluid phase state. A strong reduction in the lateral lipid diffusivity was likely primarily due to the strong interaction of Li+ ions with the head group of the zwitterionic DMPC lipid and was consistent with the previous reports of the effect of a salt addition on the self-diffusivity of zwitterionic lipids in a membrane. Besides the whole lipid long-range diffusivity, quasielastic neutron scattering allowed measurements of the local internal motion of the lipid. Despite the weak interaction between the ions and the uncharged lipid tails, in both the ordered and the disordered phase states, the local diffusivity of the lipid tails decreased by a factor of 2.2 in the presence of the salt, which closely correlates with the decrease in the diffusivity (that is, an increase in viscosity) of water in the LiCl salt solution by a factor of 2.4. Regardless of the phase state of the membrane, the decrease in the local diffusivity of the lipid seems to mimic the decrease in the diffusivity (which is inverse of the increase of viscosity) of the solvents.

Facile plasma grafting of zwitterions onto nanofibrous membrane surface for improved antifouling properties and filtration performance

To improve the permeability and antifouling properties of filtration membrane, zwitterionic sulfobetaine methacrylate (SBMA) was introduced onto the surface of ethylene vinyl alcohol copolymer (EVOH) nanofibrous membrane (NFM) via facile spray-coating followed by plasma treatment method. Surface chemical compositions, morphology, pore size distribution, roughness, zeta potential, hydrophilicity, permeability, separation performance, antifouling and mechanical properties of the pristine EVOH nanofibrous membrane, plasma treated membrane (PNFM) and the SBMA modified membrane (PZNFM) were systematically characterized and compared. Due to the improved hydrophilicity and antifouling properties, PZNFM showed higher water permeability (i.e. 9426.7 L h−1 m−2, 0.2 MPa), lower bovine serum albumin (BSA) adsorption (i.e. 0.15%), and higher flux recovery ratio (i.e. 95.65%) compared with the original NFM. Meanwhile, the newly prepared zwitterionic membrane can separate and intercept of E. coli, S. aureus and Brevundimonas dimimuta absolutely. The mutiphysical-chemical properties of the membrane allow it to function with synergy between permeability and sterile filtration efficiency for further bacterial separation and interception application. Our work provides a simple and scalable method to fabricate sterile membrane with outstanding performance, highlighting its great potential in sterile filtration.

A dual-biomimetic strategy to construct zwitterionic anti-fouling membrane with superior emulsion separation performance

Developing efficient polymeric membranes for the purification of emulsified oily wastewater is of great significance but still challenging, restricted by low flux and severe membrane fouling. Endowing the intrinsically hydrophobic membranes with excellent hydrophilicity thus robust oil-fouling resistance in a facile and universal manner is highly desired. Herein, inspired by saltwater fish and mussel, we report a delicate zwitterionic surface design via co-assembly of 3-aminopropyldimethylamine oxide (APDMAO) and dopamine. Taking advantage of the direct connected positively charged and negatively charged moieties (N+-O-), APDMAO could strongly interact with water molecules via hydrogen bonds thus form a robust hydration barrier as revealed by molecular dynamics (MD) simulations and sum frequency generation (SFG) vibrational spectroscopy. Besides, APDMAO could bond with dopamine via both covalent and noncovalent interactions to regulate coating behavior and improve coating stability. Owing to the superhydrophilicity of APDMAO and the distinct adhesion of polydopamine, the modified membrane exhibits robust superhydrophilicity, underwater superoleophobicity and anti-oil-fouling capability. Consequently, the resultant membrane achieves an ultra-high water permeability of 5163 L m−2 h−1 bar−1 accompanied with an excellent oil rejection of 99.7% for the separation of mineral oil-in-water emulsion. Additionally, the separation performance remains rather stable during 20 cycles of emulsion filtration. The modified membrane also exhibits desired durability and antibacterial property, demonstrating its great promise in practical oily sewage remediation.

Membrane-Catalyzed Aggregation of Islet Amyloid Polypeptide Is Dominated by Secondary Nucleation.

Type II diabetes is characterized by the loss of pancreatic β-cells. This loss is thought to be a consequence of membrane disruption, caused by the aggregation of islet amyloid polypeptide (IAPP) into amyloid fibrils. However, the molecular mechanisms of IAPP aggregation in the presence of membranes have remained unclear. Here, we use kinetic analysis to elucidate the aggregation mechanism of IAPP in the presence of mixed zwitterionic and anionic lipid membranes. The results converge to a model in which aggregation on the membrane is strongly dominated by secondary nucleation, that is, the formation of new nuclei on the surface of existing fibrils. The critical nucleus consists of a single IAPP molecule, and anionic lipids catalyze both primary and secondary nucleation, but not elongation. The fact that anionic lipids promote secondary nucleation implies that these events take place at the interface between the membrane and existing fibrils, demonstrating that fibril growth occurs at least to some extent on the membrane surface. These new insights into the mechanism of IAPP aggregation on membranes may help to understand IAPP toxicity and will be important for the development of therapeutics to prevent β-cell death in type II diabetes.