Infusion of Silver–Polydopamine Particles into Polyethersulfone Matrix to Improve the Membrane’s Dye Desalination Performance and Antibacterial Property

The advancement in membrane science and technology, particularly in nanofiltration applications, involves the blending of functional nanocomposites into the membranes to improve the membrane property. In this study, Ag-polydopamine (Ag-PDA) particles were synthesized through in situ PDA-mediated reduction of AgNO3 to silver. Infusing Ag-PDA particles into polyethersulfone (PES) matrix affects the membrane property and performance. X-ray photoelectron spectroscopy (XPS) analyses confirmed the presence of Ag-PDA particles on the membrane surface. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) describe the morphology of the membranes. At an optimum concentration of Ag-PDA particles (0.3 wt % based on the concentration of PES), the modified membrane exhibited high water flux 13.33 L∙m−2∙h−1 at 4 bar with high rejection for various dyes of >99%. The PESAg-PDA0.3 membrane had a pure water flux more than 5.4 times higher than that of a pristine membrane. Furthermore, in bacterial attachment using Escherichia coli, the modified membrane displayed less bacterial attachment compared with the pristine membrane. Therefore, immobilizing Ag-PDA particles into the PES matrix enhanced the membrane performance and antibacterial property.

Lipid interactions of an actinoporin pore-forming oligomer

ABSTRACTThe actinoporins are cytolytic toxins produced by sea anemones. Upon encountering a membrane, preferably containing sphingomyelin, they oligomerize and insert their N-terminal helix into the membrane, forming a pore. Whether sphingomyelin is specifically recognized by the protein or simply induces phase coexistence in the membrane has been debated. Here, we perform multimicrosecond molecular dynamics simulations of an octamer of fragaceatoxin C, a member of the actinoporin family, in lipid bilayers containing either pure 1,2-Dioleoyl-sn-Glycero-3-Phosphocholine (DOPC) or a 1:1 mixture of DOPC and palmitoyl sphingomyelin (PSM). The complex is highly stable in both environments, with only slight fraying of the inserted helices near their N-termini. Analyzing the structural parameters of the mixed membrane in the course of the simulation we see signs of a phase transition for PSM in the inner leaflet of the bilayer. In both leaflets, cross-interactions between lipids of different type decrease over time. Surprisingly, the aromatic loop thought to be responsible for sphingomyelin recognition interacts more with DOPC than PSM by the end of the simulation. These results support the notion that the key membrane property that actinoporins recognize is lipid phase coexistence.SIGNIFICANCE STATEMENTThe mechanism of selectivity of naturally produced toxins for their target membranes is not well understood. For example, actinoporins, toxins produced by sea anemones, have been reported to selectively target sphingomyelin-containing membranes. Whether they bind this lipid preferentially or recognize the phase coexistence that sphingomyelin induces is not clear. This work examines this issue by long computer simulations of an actinoporin oligomer embedded in lipid bilayers and finds no preferential interactions of the protein with sphingomyelin. Instead, the simulations show signs of phase separation, suggesting that phase coexistence is the key property that actinoporins recognize.

Analysis of the Influence of Pore-Forming Agent and Coagulation Bath on the Preparation of PES Hollow Fiber Membrane

PES is used as raw material for the preparation of membrane in this paper. Through gas-assisted-phase separation and synergetic pore-forming technology, the influence of the content of CaCO3 in foaming pore-forming agent and the content of N,N-DMAc in coagulation bath on membrane property is studied. The results indicate that this method prepares PES hollow fiber membrane with uniform macroporous structure in which the cross section is wedge-shaped and running through internal and external surface. The addition of CaCO3 can improve membrane property and the increase in the content of DMAc also has a great positive influence on membrane property.

Hopanoid lipids may facilitate aerobic nitrogen fixation in the ocean

Cyanobacterial diazotrophs are considered to be the most important source of fixed N2in the open ocean. Biological N2fixation is catalyzed by the extremely O2-sensitive nitrogenase enzyme. In cyanobacteria without specialized N2-fixing cells (heterocysts), mechanisms such as decoupling photosynthesis from N2fixation in space or time are involved in protecting nitrogenase from the intracellular O2evolved by photosynthesis. However, it is not known how cyanobacterial cells limit O2diffusion across their membranes to protect nitrogenase in ambient O2-saturated surface ocean waters. Here, we explored all known genomes of the major marine cyanobacterial lineages for the presence of hopanoid synthesis genes, since hopanoids are a class of lipids that might act as an O2diffusion barrier. We found that, whereas all non−heterocyst-forming cyanobacterial diazotrophs had hopanoid synthesis genes, none of the marineSynechococcus,Prochlorococcus(non−N2-fixing), and marine heterocyst-forming (N2-fixing) cyanobacteria did. Finally, we conclude that hopanoid-enriched membranes are a conserved trait in non−heterocyst-forming cyanobacterial diazotrophs that might lower the permeability to extracellular O2. This membrane property coupled with high respiration rates to decrease intracellular O2concentration may therefore explain how non−heterocyst-forming cyanobacterial diazotrophs can fix N2in the fully oxic surface ocean.