Chemical Composition Of Membranes Research Articles

Toward in situ characterization for advancing membrane performance in water treatment processes

Membrane technology has significant potential for addressing global water crises because membranes, with precisely defined pore structures at the molecular level and multifunctional groups, serve as selective permeation barriers. Over the past few decades, ex situ characterization techniques (e.g., scanning electron microscopy) have been employed to examine the morphology and chemical composition of membranes. However, the rise of in situ characterization methods, such as in situ transmission electron microscopy, is a promising frontier. These techniques allow for the real-time investigation of membrane structure and performance on relevant temporal and spatial scales, with the potential to significantly enhance membrane efficiency. This study elucidates the challenges and opportunities associated with in situ characterization, which provides critical information on membranes within their actual operating environments, eliminating the need for dedicated sample preparation. By focusing on in situ characterization techniques, our goal is to substantially improve membrane performance through a deeper understanding and optimization of membrane fabrication, filtration, and cleaning processes, which can ultimately contribute to carbon footprint reduction.

Preparation of a fouling-resistant Teflon/PVDF composite membrane and its application to treat nanofiltration brine from landfill leachates

Landfill leachates (LFLs) pose a severe environmental threat given their high strength and the slow degradation nature of their organic and inorganic pollutants constituents. Hence, they are challenging to treat by conventional wastewater treatment methods. Although membrane distillation (MD) is promising for wastewater treatment, membrane wetting and scaling that lead to membrane fouling are the bottlenecks in applying this technology to LFLs. In this work, a commercial Teflon emulsion was used to modify the PVDF membrane via a simple dip-coating method, followed by depositing the PTFE particles onto the membrane surface via thermal curing crosslinking reaction. Hence, a Teflon/PVDF composite membrane was successfully prepared with resistance to sodium dodecyl sulfate wetting, CaSO4 scaling, and humic acid fouling. Effects of the Teflon emulsion concentration and dipping time on the composite membrane's chemical composition, surface characteristics, porosity, mechanical properties, liquid entry pressure (LEPW), and direct contact membrane distillation (DCMD) performance were systematically investigated. The results showed that Teflon emulsion modification could improve the membrane surface's hydrophobicity, reduce pore size, and increase mechanical strength. The Teflon/PVDF composite membrane with 100% Teflon emulsion and 10 min dipping time exhibited the highest hydrophobicity and 144.3º water contact angle. The M100-10 membrane also exhibited stable performance for treating nanofiltration (NF) brine collected from the LFL. When concentrating the NF brine, the M100-10 membrane achieved only a 7.1% flux decay rate. Hence, the Teflon/PVDF composite membrane demonstrated excellent wetting, scaling, and fouling resistance. This dip-coating method is simple, low cost, easy to scale up, and has potential in the large-scale production of hydrophobic porous membranes.

Effect of melatonin and cholesterol on the structure of DOPC and DPPC membranes

The cell membrane plays an important role in the molecular mechanism of amyloid toxicity associated with Alzheimer's disease. The membrane's chemical composition and the incorporation of small molecules, such as melatonin and cholesterol, can alter its structure and physical properties, thereby affecting its interaction with amyloid peptides. Both melatonin and cholesterol have been recently linked to amyloid toxicity. Melatonin has been shown to have a protective role against amyloid toxicity. However, the underlying molecular mechanism of this protection is still not well understood, and cholesterol's role remains controversial. We used small-angle neutron diffraction (SAND) from oriented lipid multi-layers, small-angle neutron scattering (SANS) from unilamellar vesicles experiments and Molecular Dynamics (MD) simulations to elucidate non-specific interactions of melatonin and cholesterol with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) model membranes. We conclude that melatonin decreases the thickness of both model membranes by disordering the lipid hydrocarbon chains, thus increasing membrane fluidity. This result is in stark contrast to the much accepted ordering effect induced by cholesterol, which causes membranes to thicken.

Polyamide thin film composite membranes prepared from 3,4′,5-biphenyl triacyl chloride, 3,3′,5,5′-biphenyl tetraacyl chloride and m-phenylenediamine

Two novel of tri- and tetra-functional biphenyl acid chloride: 3,4′,5-biphenyl triacyl chloride (BTRC) and 3,3′,5,5′-biphenyl tetraacyl chloride (BTEC), were synthesized, and used as new monomers for the preparations of the thin film composite (TFC) reverse osmosis (RO) membranes. The TFC RO membranes were prepared on a polysulfone supporting film through interfacial polymerization with the two new monomers and m-phenylenediamine (MPD). The membranes were characterized for the permeation properties, chemical composition, d-space between polymer chains, hydrophilicity, membrane morphology including top surface and cross-section. Permeation experiment was employed to evaluate the membranes performance including salt rejection and water flux. The surface structure and chemical composition of membranes were analyzed by attenuated total reflectance infrared (ATR-IR) and X-ray photoelectronic spectroscopy (XPS). The results revealed that the active layer of membranes was composed of highly cross-linked aromatic polyamide with the functional acylamide (–CONH–) bonds. The TFC membranes prepared from biphenyl acid chloride exhibit higher salt rejection compared with that prepared from trimesoyl chloride (TMC) at the expanse of some flux.

Osmoadaptation in halophilic and alkaliphilic methanotrophs

By using (1)H- and (13)C-NMR spectroscopy, an accumulation of sucrose and two cyclic amino acids [ectoine (1,4,5, 6-tetrahydro-2-methyl-4-pyrimidine carboxylic acid) and 5-oxoproline (pyrrolidone carboxylic acid)] was detected in the halotolerant methanotrophs Methylobacter alcaliphilus 20Z and Methylobacter modestohalophilus 10S. The organic solute pool was found to increase upon raising the NaCl concentration. In M. alcaliphilus 20Z, the intracellular level of the total solutes was shown to be sufficient to balance the osmotic pressure of the medium, whereas in M. modestohalophilus 10S their content was several times lower. Additionally, phosphatidylglycerol and phosphatidylcholine were predominant cell phospholipids in salt-adapted M. alcaliphilus 20Z. However, no phosphatidylcholine was found in M. modestohalophilus 10S, and the portion of phosphatidylglycerol increased while phosphatidylethanolamine decreased upon elevated external NaCl concentrations. Regularly arranged glycoprotein surface layers (S-layers) of hexagonal and linear (p2) symmetry were observed on the outer cell walls of M. alcaliphilus 20Z and M. modestohalophilus 10S. The S-layer in M alcaliphilus 20Z consisting of tightly packed, cup-shaped subunits was lost during growth at pH 7.2 (the lowest possible pH) in the absence of NaCl. Hence, osmoadaptation in the methanotrophs studied involves structure/function alterations of cell envelopes and changes in the chemical composition of membranes as well as de novo synthesis of compatible solutes.

Diversity, adaptation and activity of the bacterial flora in saline environments

Saline environments have a natural bacterial flora, which may play a significant role in the economy of these habitats. The natural saline environments (usually containing salinity equivalent to 4–30% NaCl) are aquatic (e.g. salt marshes) or terrestrial (e.g. saline lands). Saline environments include an increasing area of salt-affected cultivated soils throughout the world. These environments contain various ions which may interfere with uptake of water and which may be toxic to a large number of organisms. Saline environments harbour taxonomically diverse bacterial groups, which exhibit modified physiological and structural characteristics under the prevailing saline conditions. The majority of these bacteria can osmoregulate by synthesizing specific compatible organic osmolytes such as glutamine, proline and glycine betaine and a few of them accumulate inorganic solutes such as Na+, K+ and Mg2+. The morphology of the bacteria is usually modified, cells are usually elongated, swollen and showing shrinkage, in addition to changes in the cell and cytoplasmic volume. The chemical composition of membranes may also occasionally be modified, and the synthesis pattern of proteins, lipids, fatty acids and polysaccharides may change with a moderate increase in salinity. However, ultrastructural alterations in cells of halophilic bacteria have not been reported, and profound changes in cellular properties of these bacteria only occur at concentrations above 2MNaCl. Evidence has accumulated that the bacteria are essential elements in the saline environment because of their activity such as degradation of plant remains, nitrogen fixation and production of active metabolites.

Development of rat jejunum: lipid permeability, physical properties, and chemical composition

This study reports the correlation between jejunal microvillus membrane's chemical composition, physical properties, and lipid permeability over the age range of 9-25 days in the rat. During this period of time the diet varies from entirely maternal milk (9 days, suckling) to milk plus chow (18 days, weaning) to finally predominantly chow (25 days, weaned). Lipid permeability was found to be greatest during the suckling period but decreased rapidly over the subsequent 2 wk of life. Alterations in lipid permeability were correlated with maturation of the microvillus membrane, both in terms of its lipid fluidity and chemical composition. The static component of membrane fluidity did not vary significantly over this time period, in agreement with a constant molar ratio of cholesterol-to-phospholipid (0.87 +/- 0.08, 0.94 +/- 0.07, and 0.84 +/- 0.04 at ages 9, 18, and 25 days, respectively). However, decreasing membrane lipid permeability correlated with decreasing lipid fluidity assessed by probes sensitive to the dynamic component of membrane lipid fluidity within the superficial regions of the bilayer. Furthermore, by measurement of the incremental change in free energy associated with a methylene group partitioning into the microvillus membrane, the hydrophobicity of the membrane could be assessed in vivo. These data demonstrate that suckling rats have the most hydrophobic microvillus membrane (-459 +/- 30 cal/mol), but with maturation a decline in membrane hydrophobicity occurred (-358 +/- 60 cal/mol). The results suggest that during the first 3 wk of life the jejunal microvillus membrane of the rat undergoes a maturation process that is well suited to the change in dietary nutrients ingested. Furthermore, changes in lipid permeability, in vivo properties of the microvillus membrane, and the associated change in lipid fluidity are similar to associations recently recognized in the adult animal.

Some terpenoid and steroid derivatives from echinoderms and sponges

Abstract

Isolation, characterization and chemical composition of the membrane from sheep platelets

A procedure of the isolation of platelets from the blood of adult sheep ( Ovis aries L. var domestica) is reported. This procedure is based on differential centrifugation and a specific lysis for elimination of erythrocytes. We have obtained platelets with a purity at least 99% and a relative high yield (2.3 ± 0.4 g wet/1 whole blood = 235 ± 40 mg platelet proteins/1 whole blood). After disruption, homogenisation and ultracentrifugation onto a discontinuous sucrose gradient (1.6 M, 1.1 M, 1.0 M and 0.6 M sucrose), four fractions were obtained. We have separated, for the first time, a particulate preparation enriched in the whole sheep plasma membrane. This fraction was characterized by: (i) the typical membrane morphology as shown by electron micrographs; (ii) the highest activities in membrane marker enzymes such as bis( p-nitrophenyl)phosphate phosphodiesterase (EC 3.1.16.1) and 5′-dTMP- p-nitrophenyl ester phosphodiesterase (EC 3.1.3.35), and the relatively low activity for marker enzymes associated to other subcellular fractions; (iii) the highest sialic acid; cholesterol and phospholipid concentrations. The chemical composition of the platelet membrane isolated is: total proteins, 49%; lipids, 47%; carbohydrates, ≅3.4% (the content of hexoses is twice as high as that of hexosamines and sialic acid). The similarities and differences of this preparation with others from several sources are discussed.

Change in chemical composition of membrane of Bacillus caldotenax after shifting the growth temperature.

Membranes from Bacillus caldotenax contain neutral lipids and phospholipids such as phosphatidyl-ethanolamine, phosphatidyl glycerol and cardiolipin. Each of the lipids has almost the same fatty acid composition. When the growth temperature decreases, not only the fatty acid composition but also the lipid composition changes such that the membrane fluidity increases, and the composition of membrane-bound proteins also changes. On shifting the growth temperature from 65 degrees to 45 degress C, the bacterium grows immediately with a doubling time at 45 degrees C, but the compositions of proteins and lipids in membranes gradually change and reach the compositions typical of cells growing at 45 degrees C one doubling time after the temperature shift, respectively. It is concluded that the change in chemical composition of membrane of the bacterium on the temperature shift from 65 degrees to 45 degrees C is not prerequisite for growth at 45 degrees C.

Vascular basement membranes: preparation and properties of material isolated with the use of detergents.

During the past few years, work in our laboratories has been directed toward the isolation and chemical characterization of vascular basement membranes obtained from several organs. The chemical composition of these membranes, isolated in a pure form, can be related to changes in structure that occur in disease. We are particularly interested in those changes associated with diabetes mellitus (1–7). The nondisruptive detergent solubilization techniques used in these procedures permit the preparation of vascular basement membranes which are morphologically intact and which retain their histoarchitecture. With these preparations, the permeability of the basement membranes themselves, divorced from the contribution of the adjacent cell layers, was studied (3,5). Using this approach one can attempt to define the role which vascular basement membranes may play in the permeation of macromolecules through capillary walls, an area of some controversy (8–11). The findings that vascular basement membranes isolated by our techniques retained not only their morphologic and chemical properties (1–5), but also their immunologic characteristics (12), and their binding characteristics of cationic probes (13,14) further support the usefulness of this procedure in the study of basement membrane permeability. Modification of our technique has also been found useful in the isolation and examination of the pericellular matrix of human fibroblast cultures, a primary component of which is the cell adhesion protein fibronectin (15). In this chapter, we describe a method for isolation of vascular basement membranes, and compare permeability and chemical composition of membranes isolated from the central nervous system with those isolated from renal glomeruli. The method was first developed for study of renal glomeruli and these experiments will be described first.

SUBJECT: MEMBRANE TECHNOLOGY: BASIC PRINCIPLES OF REVERSE OSMOSIS AND ULTRAFILTRATION

Theories of the process of ultrafiltration and reverse osmosis, that involve permeation of solvent through a membrane in a sense opposite to that which obtains in osmosis, are considered. Factors that affect rates of permeation of solute and of solvent, and hence the selectivity of the membrane, are discussed.The physical structure and chemical composition of membranes are discussed, and the effect of processing variables on structure and composition, and hence on permeation rates and selectivity, are considered. The formation of boundary layers of high solute concentration at the surface of the membrane exposed to the solution has an appreciable effect on permeation; techniques for preventing their formation are mentioned. Some basic considerations relating to the power requirements of membrane processes are defined.