Selective Sieving Research Articles

Topological Sieving of Rings According to Their Rigidity.

We present a novel mechanism for resolving the mechanical rigidity of nanoscopic circular polymers that flow in a complex environment. The emergence of a regime of negative differential mobility induced by topological interactions between the rings and the substrate is the key mechanism for selective sieving of circular polymers with distinct flexibilities. A simple model accurately describes the sieving process observed in molecular dynamics simulations and yields experimentally verifiable analytical predictions, which can be used as a reference guide for improving filtration procedures of circular filaments. The topological sieving mechanism we propose ought to be relevant also in probing the microscopic details of complex substrates.

Metal-organic framework-based mixed matrix membranes: Synergetic effect of adsorption and diffusion for CO2/CH4 separation

ZIF-8 nanoparticles were doped into P84 polymer matrix to synthesize defect-free mixed matrix membranes (MMMs) for CO2/CH4 separation. A remarkable combination of gas permeability and separation factor appeared in MMMs with filler loading of 27 wt%. The permeability of CO2 achieved 10.92 Barrers along with CO2/CH4 separation factor of 92.6, separately corresponding to an increment of 339% and 35.7% compared with the pure P84 membrane, which breaks the trade-off between permeability and selectivity of polymer membranes. Adsorption and diffusion coefficient of CO2 and CH4 for ZIF-8/P84 MMMs as well as the apparent activation energy of the corresponding processes were quantitatively determined, indicative of a synergetic effect of the selective adsorption and molecular sieving property arising from ZIF-8 nanoparticle fillers on the significant improvement of separation performances.

SEED GERMINATION ECOLOGY AND SEEDLING EMERGENCE OF SIXTEEN TREE SPECIES AUTUMN SOWN

In nature, the regeneration and the seed germination ecology of tree species is varied due to divers’ environmental factors and evolution process. As a consequence, understanding the factors controlling the seed germination and seedling emergence in the time and the space. In most nurseries, tree seeds are usually sown in spring or rarely in autumn and, they are often pretreated to increase the seed germination where the germination timing is selective sieve that a plant experiences throughout its life history. However, in most nursery of Kurdistan region, the managers have not a good knowledge about the seeds sowing timing and seedling emergency of native tree species. Therefore, the main aim of this study is to investigate seed germination phenology with providing new data and determine optimal ways of seed sowing time that will permit a best seedling establishment of sixteen native and introduced tree species. The results showed, the seed sowing timing and seedling emergence of these tree species. In addition, these species exhibit significant divergence in term sowing timing and seedling establishment. Thereby, our results have a high value for managers of Kurdistan governmental and private nurseries as a suggestion which exact time is better for sowing seeds and which seeds need pre-treatment before sowing in order to obtain better regeneration.

Yolk-shell structured composite for fast and selective lithium ion sieving

Yolk-shell structured C@Li4Ti5O12 microspheres composed of carbon core (ca. 500 nm) and sea urchin-like Li4Ti5O12 shell (ca. 400–500 nm) are formed by hydrothermally treating the core–shell structured C@TiO2 in the EtOH/H2O solution of LiOH and calcining it in N2 atmosphere. Yolk-shell structured TiO2-type lithium ion sieve is further transformed from C@Li4Ti5O12 through the acid treatment, which have a high specific surface area of 201.74 m2/g. The composite shows adsorption capacity towards Li+ proportional to the pH value in the range of 7–13. The adsorption reaches equilibrium within 2 h with a high equilibrium adsorption capacity of 28.46 mg/g under alkaline conditions, which is ca. 8 times the value of ordinary TiO2 lithium ion sieve with comparable size and surface area, demonstrating the enhanced adsorption is attributed to the generation of more accessible surficial voids by replacing internal part with light carbon core. The adsorption follows Freundlich and pseudo-second-order kinetic models with a high rate constant of 0.015 g/(mg·min). The selective adsorption to Li+ is verified in the presence of K+, Na+, Ca2+ and Mg2+.

Selective constraint and adaptive potential of West Nile virus within and among naturally infected avian hosts and mosquito vectors.

Arthropod-borne viruses are among the most genetically constrained RNA viruses, yet they have a remarkable propensity to adapt and emerge. We studied wild birds and mosquitoes naturally infected with West Nile virus (WNV) in a ‘hot spot’ of virus transmission in Chicago, IL, USA. We generated full coding WNV genome sequences from spatiotemporally matched bird and mosquito samples using high-throughput sequencing, allowing a molecular evolutionary assessment with deep coverage. Mean FST among samples was 0.66 (±0.02 SE) and was bimodal, with mean nucleotide diversity being higher between samples (interhost πN = 0.001; πS = 0.024) than within them (intrahost πN < 0.0001; πS < 0.001). Eight genomic sites with FST > 1.01 (in the PrM, NS2a, NS3, NS4b, and 5'-noncoding genomic regions) showed bird versus mosquito variant frequency differences of >30 per cent and/or polymorphisms fixed in ≥5 host or vector individuals, suggesting host tropism for these variants. However, phylogenetic analyses demonstrated a lack of grouping by bird or mosquito, most inter-sample differences were synonymous (mean interhost πN/πS = 0.04), and there was no significant difference between hosts and vectors in either their nucleotide diversities or levels of purifying selection (mean intrahost πN/πS = 0.28 in birds and πN/πS = 0.21 in mosquitoes). This finding contrasts with the ‘trade-off’ and ‘selective sieve’ hypotheses that have been proposed and tested in the laboratory, which predict strong host versus vector effects on WNV genetic variation, with heightened selective constraint in birds alternating with heightened viral diversity in mosquitoes. Overall, our data show WNV to be highly selectively constrained within and between both hosts and vectors but still able to vary at a limited number of sites across the genome. Such site-specific plasticity in the face of overall selective constraint may offer a mechanism whereby highly constrained viruses such as WNV and its relatives can still adapt and emerge.

A two-dimensional cationic covalent organic framework membrane for selective molecular sieving

A two-dimensional cationic covalent organic framework membrane with extraordinary separation properties and high permeability.

Macromolecular Coating Enables Tunable Selectivity in a Porous PDMS Matrix.

Whether for laboratory use or clinical practice, many fields in Life Sciences require selective filtering. However, most existing filter systems lack the ability to easily tune their filtration behavior. Two key elements for efficient filtering are a high surface-to-volume ratio and the presence of suitable chemical groups which establish selectivity. In this study, an artificial PDMS-based capillary system with highly tunable selectivity properties is presented. The high surface-to-volume ratio of this filter system is generated by first embedding sugar fibers into a synthetic polymer matrix and then dissolving these fibers from the cured polymer. To functionalize this filter, the inner surface of the capillaries is coated with purified or synthetic macromolecules. Depending on the type of macromolecule used for filter functionalization, selective sieving is observed based on steric hindrance, electrostatic binding, electrostatic repulsion, or specific binding interactions. Furthermore, it is demonstrated that enzymes can be immobilized in the capillary system which allows for performing multiple cycles of enzymatic reactions with the same batch of enzymes and without the need to separate the enzymes from their reaction products. In addition to lab-scale filtration and enzyme immobilization applications demonstrated here, the functionalized porous PDMS matrix may also be used to test binding interactions between different molecules.

ZIF-8@DBzPBI-BuI composite membranes for olefin/paraffin separation

ZIF-8 is a member of Zeolitic Imidazole Framework family having high internal surface area, the high thermo-chemical stability and ease of synthesis gained immense attention for its highly selective sieving ability. Transforming it into a membrane form and practical utility remains a challenge. Any success towards this direction would radically reduce the cost of propylene/propane separation. Present study reports use of substituted polybenzimidazole (DBzPBI-BuI) for fabrication of flexible, thus scalable composite membranes with ZIF-8 (ZIF-8@DBzPBI-BuI) possessing host-guest compatibility. The membrane with 30% ZIF-8 loading showed promising propylene-propane separation (ideal selectivity of 32.7), coupled with propylene permeability of 12.13 Barrer. Analysis of sorption shed light on the high contribution of diffusivity on governing permeation properties of the composite membranes. The mixed gas analysis offered highly encouraging results in comparison to known composite membranes of different polymers with ZIF-8. Placement of present data on ‘upper-bound’ showed a rapid enhancement in selectivity by the addition of ZIF-8 in the polymer matrix, which seems to be a result of the elimination of inter-phase defects. It was made possible due to the functionality of host polymer.

Sex-specific influences of mtDNA mitotype and diet on mitochondrial functions and physiological traits in Drosophila melanogaster.

Here we determine the sex-specific influence of mtDNA type (mitotype) and diet on mitochondrial functions and physiology in two Drosophila melanogaster lines. In many species, males and females differ in aspects of their energy production. These sex-specific influences may be caused by differences in evolutionary history and physiological functions. We predicted the influence of mtDNA mutations should be stronger in males than females as a result of the organelle’s maternal mode of inheritance in the majority of metazoans. In contrast, we predicted the influence of diet would be greater in females due to higher metabolic flexibility. We included four diets that differed in their protein: carbohydrate (P:C) ratios as they are the two-major energy-yielding macronutrients in the fly diet. We assayed four mitochondrial function traits (Complex I oxidative phosphorylation, reactive oxygen species production, superoxide dismutase activity, and mtDNA copy number) and four physiological traits (fecundity, longevity, lipid content, and starvation resistance). Traits were assayed at 11 d and 25 d of age. Consistent with predictions we observe that the mitotype influenced males more than females supporting the hypothesis of a sex-specific selective sieve in the mitochondrial genome caused by the maternal inheritance of mitochondria. Also, consistent with predictions, we found that the diet influenced females more than males.

Transcriptome predictors of coral survival and growth in a highly variable environment.

Concern over rapid environmental shifts associated with climate change has led to a search for molecular markers of environmental tolerance. Climate‐associated gene expression profiles exist for a number of systems, but have rarely been tied to fitness outcomes, especially in nonmodel organisms. We reciprocally transplanted corals between two backreef locations with more and less variable temperature regimes to disentangle effects of recent and native environment on survival and growth. Coral growth over 12 months was largely determined by local environment. Survival, however, was impacted by native environment; corals from the more variable environment had 22% higher survivorship. By contrast, corals native to the less variable environment had more variable survival. This might represent a “selective sieve” where poor survivors are filtered from the more stressful environment. We also find a potential fitness trade‐off—corals with high survival under stressful conditions grew less in the more benign environment. Transcriptome samples taken a year before transplantation were used to examine gene expression patterns that predicted transplant survival and growth. Two separate clusters of coexpressed genes were predictive of survival in the two locations. Genes from these clusters are candidate biomarkers for predicting persistence of corals under future climate change scenarios.

Techno-economic feasibility analysis on carbon membranes for hydrogen purification

Abstract H 2 production from a biomass fermentation process provides a great opportunity for green and sustainability economy compared to use fossil fuels (e.g., steam methane reforming process), but the process usually produces a humidified gas containing 35–65 (vol.%) H 2 and 40–50 (vol.%) CO 2 . A novel, energy efficient two-stage carbon membrane system for H 2 purification based on the combination of H 2 selective carbon molecular sieve membranes in the first stage and CO 2 selective carbon membranes in the second stage was proposed. The concept is the first unique technology providing a low H 2 purification cost 2 produced at a feed pressure of 20 bara based on process simulation and cost estimation. The produced high purity CO 2 (>95 vol.%) and H 2 (>99.5 vol.%) can be integrated into a gasification reformer and Fischer-Tropsch reactors to improve the biodiesel productivity from biomass.

Optimization of a Pressure Swing Adsorption Process for Nitrogen Rejection from Natural Gas

Nitrogen rejection from natural gas is a capital intensive process. The most widely used technology, cryogenic distillation, is uneconomical for gas wells in remote areas or with small production rate. In this work, a detailed simulation and optimization is carried out to explore the feasibility of pressure-vacuum swing adsorption (PVSA) technology for on-site nitrogen rejection at remote/low-throughput gas wells. The designed PVSA unit possesses high mobility at a cost that scales well with low throughput. A nonisothermal and nonisobaric simulation model including detailed description of both micropore and barrier resistances in a kinetically selective carbon molecular sieve adsorbent has been used for process optimization. The process parameters constitute the decision variables of the optimization problem, with recovery and productivity as the objective functions, and industrial pipeline purity specification as an inequality constraint. Starting with a 6-step PVSA cycle, it is shown that a modified 9-s...

Carbon molecular sieve membrane from a microporous spirobisindane-based polyimide precursor with enhanced ethylene/ethane mixed-gas selectivity

A highly selective carbon molecular sieve (CMS) membrane derived from a novel spirobisindane-based polyimide was synthesized. The mixed-gas ethylene/ethane selectivity of 15.6 at 20 bar is the highest reported value for CMS-type membranes to date.

The Membrane Steps of Bacterial Cell Wall Synthesis as Antibiotic Targets.

Peptidoglycan is the major component of the cell envelope of virtually all bacteria. It has structural roles and acts as a selective sieve for molecules from the outer environment. Peptidoglycan synthesis is therefore one of the most important biogenesis pathways in bacteria and has been studied extensively over the last twenty years. The pathway starts in the cytoplasm, continues in the cytoplasmic membrane and finishes in the periplasmic space, where the precursor is polymerized into the peptidoglycan layer. A number of proteins involved in this pathway, such as the Mur enzymes and the penicillin binding proteins (PBPs), have been studied and regarded as good targets for antibiotics. The present review focuses on the membrane steps of peptidoglycan synthesis that involve two enzymes, MraY and MurG, the inhibitors of these enzymes and the inhibition mechanisms. We also discuss the challenges of targeting these two cytoplasmic membrane (associated) proteins in bacterial cells and the perspectives on how to overcome the issues.

Regeneration of used turbine oils using molecular sieves as sorbents

ABSTRACTThe quality of used turbine oils plays an important role on safe and smooth operation of turbine generator sets. Microporous molecular sieves are investigated as effective, environmentally safe, and cost-effective materials for purification and regeneration of turbine oils in late stages of oxidation to prolong its lifetime. Molecular sieve crystals with microporous structure and high selectivity are used to trap oxidation by-products. It has been found that selective molecular sieves can effectively remove oxidation products due to a high affinity of strong Brønsted acid sites to polar groups, thus quality indexes of turbine oil in service could be kept in high level during operation by purification with molecular sieve such as acid number, clemulsibility, rotating pressure vessel value. The mechanism of regeneration of used turbine oil using the microporous molecular sieves was also discussed.

Sampling From the Proteome to the Human Leukocyte Antigen-DR (HLA-DR) Ligandome Proceeds Via High Specificity

Comprehensive analysis of the complex nature of the Human Leukocyte Antigen (HLA) class II ligandome is of utmost importance to understand the basis for CD4+ T cell mediated immunity and tolerance. Here, we implemented important improvements in the analysis of the repertoire of HLA-DR-presented peptides, using hybrid mass spectrometry-based peptide fragmentation techniques on a ligandome sample isolated from matured human monocyte-derived dendritic cells (DC). The reported data set constitutes nearly 14 thousand unique high-confident peptides, i.e. the largest single inventory of human DC derived HLA-DR ligands to date. From a technical viewpoint the most prominent finding is that no single peptide fragmentation technique could elucidate the majority of HLA-DR ligands, because of the wide range of physical chemical properties displayed by the HLA-DR ligandome. Our in-depth profiling allowed us to reveal a strikingly poor correlation between the source proteins identified in the HLA class II ligandome and the DC cellular proteome. Important selective sieving from the sampled proteome to the ligandome was evidenced by specificity in the sequences of the core regions both at their N- and C- termini, hence not only reflecting binding motifs but also dominant protease activity associated to the endolysosomal compartments. Moreover, we demonstrate that the HLA-DR ligandome reflects a surface representation of cell-compartments specific for biological events linked to the maturation of monocytes into antigen presenting cells. Our results present new perspectives into the complex nature of the HLA class II system and will aid future immunological studies in characterizing the full breadth of potential CD4+ T cell epitopes relevant in health and disease.

Principles and applications of high temperature ion conducting ceramic in power generation - fuel cells and oxygen membranes

High temperature membranes can be used in numerous applications including ceramic filters, selective sieves, removal of impurities, oxygen and hydrogen separation, electrochemical devices such as solid oxide fuel cells and solid oxide electrolysers. The fabrication process is oriented at achieving desired properties of the final product, including proper conductivity, size and density of pores, tortuosity, mechanical stability in high operating temperatures and others. Among the mentioned applications, solid oxide fuel cells and oxygen separation membranes represent materials with mixed ionic and electronic conductivity (MIEC) which will be further discussed in the lecture. Such material are often referred as membranes designed specifically for transport of ions and electrons.

Subnanometer Two-Dimensional Graphene Oxide Channels for Ultrafast Gas Sieving

Two-dimensional (2D) materials with atomic thickness and extraordinary physicochemical properties exhibit unique mass transport behaviors, enabling them as emerging nanobuilding blocks for separation membranes. Engineering 2D materials into membrane with subnanometer apertures for precise molecular sieving remains a great challenge. Here, we report rational-designing external forces to precisely manipulate nanoarchitecture of graphene oxide (GO)-assembled 2D channels with interlayer height of ∼0.4 nm for fast transporting and selective sieving gases. The external forces are synergistic to direct the GO nanosheets stacking so as to realize delicate size-tailoring of in-plane slit-like pores and plane-to-plane interlayer-galleries. The 2D channels endow GO membrane with excellent molecular-sieving characteristics that offer 2-3 orders of magnitude higher H2 permeability and 3-fold enhancement in H2/CO2 selectivity compared with commercial membranes. Formation mechanism of 2D channels is proposed on the basis of the driving forces, nanostructures, and transport behaviors.

Impaired Albumin Uptake and Processing Promote Albuminuria in OVE26 Diabetic Mice.

The importance of proximal tubules dysfunction to diabetic albuminuria is uncertain. OVE26 mice have the most severe albuminuria of all diabetic mouse models but it is not known if impaired tubule uptake and processing are contributing factors. In the current study fluorescent albumin was used to follow the fate of albumin in OVE26 and normal mice. Compared to normal urine, OVE26 urine contained at least 23 times more intact fluorescent albumin but only 3-fold more 70 kD fluorescent dextran. This indicated that a function other than size selective glomerular sieving contributed to OVE26 albuminuria. Imaging of albumin was similar in normal and diabetic tubules for 3 hrs after injection. However 3 days after injection a subset of OVE26 tubules retained strong albumin fluorescence, which was never observed in normal mice. OVE26 tubules with prolonged retention of injected albumin lost the capacity to take up albumin and there was a significant correlation between tubules unable to eliminate fluorescent albumin and total albuminuria. TUNEL staining revealed a 76-fold increase in cell death in OVE26 tubules that retained fluorescent albumin. These results indicate that failure to process and dispose of internalized albumin leads to impaired albumin uptake, increased albuminuria, and tubule cell apoptosis.

Prediction of gas transport across amine mixed matrix membranes with ideal morphologies based on the Maxwell model

The incorporation of highly selective molecular sieve such as carbon molecular sieve (CMS) and highly affinitive solvent such as diethanolamine (DEA) into polyethersulfone (PES) have been implemented to synthesize amine mixed matrix membranes (MMMs) with an enhanced gas performance. Synergetic effect of CMS and DEA has caused the improvement of carbon dioxide (CO2) permeability and ideal CO2/CH4 selectivity. While existing theoretical models define the relative permeability well for binary mixed matrix membranes they fail to predict the relative permeability of amine mixed matrix membranes. In fact, the degree of deviation from the simple model predictions provides understanding into the detailed properties of the third component, which has been neglected in previous analyses of these models. Modification of an existing model, namely the Maxwell model, provides an outline to analyze the gas permeation properties of model systems with CMS and DEA in glassy polymer phase. The new model is developed by modifying the basic Maxwell MMMs model. The modification also includes the optimization of λdm, which is defined as the ratio of dispersed phase permeability to matrix permeability, and the determination of permeability of the dispersed phase. Furthermore, this Maxwell model has been extended to model the performance of amine mixed matrix membranes by incorporation of combined volume fraction of filler and amine φ*ad. The proposed approach can predict the permeability of CO2 through amine MMMs and also lowers the AARE % value.