Rigid Pores Research Articles

Solvent-resistant isoporous membranes with tailored pore characteristics and on-demand sieving by site-selective hyper-crosslinking

Isoporous block copolymer membranes with high porosity and narrow pore size distribution have been viewed as ideal membrane platforms for precise separation of similarly sized particles or solutes. However, tailored made fabrication of solvent-resistant isoporous membranes with switchable pores and rigid pores for customizable sieving have been rarely reported. Herein, we show that site-selective hyper-crosslinking is effective and robust to prepare such membranes from polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP). The selective crosslinking in PS domains endows the membrane with excellent solvent resistance and structural stability. Since not participated in the crosslinking reaction, the P4VP brushes located in pore walls endow the crosslinked membranes with adaptive pore size, switchable permeance and tunable rejections that vary with Hansen solubility parameter of solvents. Moreover, by a facile while complete etching the P4VP from pores, the switchable performance is removed and resultant membranes show rigid pore characteristics and constant rejections. Crosslinked membranes with either switchable pores or rigid-likes pores exhibit superior long-term stability (30 days) in harsh solvents. This work presents a top-down method to construct highly stable isoporous membranes with both switchable and rigid pore characteristics from the same block copolymer, which will shed the light on precisely tailoring the pore size and pore rigidity for crosslinked isoporous membranes that will not only enable the tailored sieving but also the modelling of solvent flowing behaviours in nanopores.

Constricted Migration of Human Myoblasts Impairs Motility, Nuclear Integrity and Differentiation

Introduction: Upon injury, muscle stem cells (MuSCs) undergo activation, proliferation, migration, differentiation and fusion to regenerate muscle. MuSCs sense and respond to the mechanical microenvironment of the tissue while migrating through the interstitial matrix to the cell niche. In fibrosis, a common manifestation of injury, the mechanical microenvironment of the tissue is modified. The extracellular matrix (ECM) has increased stiffness and decreased porosity which may decrease the mobility and differentiation ability of MuSCs. The objective of this study was to determine the capacity of human myoblast to undergo constricted migration through small rigid pores and the deficits in their regenerative capacity following constricted migration. We hypothesized that fewer cells would undergo constricted migration and those that did would incur greater nuclear rupture, increased DNA damage, and impaired differentiation capacity. Methods: Immortalized human myoblasts were allowed to migrate through transwell inserts of pores with 3μm (constricted migration) and 8μm diameter (unconstricted migration) or in 2D conditions (control). Live cell imaging techniques over a period 24 hours were used to quantify relative cell migration. The extent of nuclear rupture and DNA damage were quantified using immunofluorescent imaging of cells on transwell inserts. Differentiation index was calculated by removing the cells from the transwell and placing in differentiation conditions prior to immunofluorescent imaging. Results: Cells migrated more rapidly through large pores than the constrictive pores. For 3μm protrusions through the pores resulted in migration in ~46 % cells compared to 68% for 8μm pores. Following migration through the pores there was no difference in 2D migration, but it was significantly slower than cells that remained in 2D conditions. Human myoblasts undergoing 3μm migration incurred nuclear rupture in ~85% of cells while cells migrating through 8μm or non-migrating cells rarely had ruptured nuclei (<2%). 3μm migration was also related to a significant ~80% increase in DNA damage from cells undergoing 8μm migration. The human myoblasts undergoing 3μm migration maintained impaired differentiation of ~30% compared to 8μm migration or non-migrating cells. Conclusions: The study results support the hypothesis that constricted environments impair migration, cause substantial nuclear rupture, induce DNA damage, and impair differentiation. The use of human myoblasts with different migration speeds than previously used mouse myoblasts had substantially more profound impacts on nuclear rupture and persistence of differentiation defects. Thus, the constrictive environment presented by muscle fibrosis could be a critical aspect of impaired regeneration in fibrotic conditions. Funding sources: This work was supported by grants from NIH NIAMS R01 AR079545 and R00 AR067867 to LRS. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

“Rigid-elastic chimera” pore skeleton model and overpressure porosity measurement method for shale: A case study of the deep overpressure siliceous shale of Silurian Longmaxi Formation in southern Sichuan Basin, SW China

Based on analysis of pore features and pore skeleton composition of shale, a “rigid elastic chimeric” pore skeleton model of shale gas reservoir was built. Pore deformation mechanisms leading to increase of shale porosity due to the pore skeleton deformation under overpressure were sorted out through analysis of stress on the shale pore and skeleton. After reviewing the difficulties and defects of existent porosity measurement methods, a dynamic deformed porosity measurement method was worked out and used to measure the porosity of overpressure Silurian Longmaxi Formation shale under real formation conditions in southern Sichuan Basin. The results show: (1) The shale reservoir is a mixture of inorganic rock particles and organic matter, which contains inorganic pores supported by rigid skeleton particles and organic pores supported by elastic-plastic particles, and thus has a special “rigid elastic chimeric” pore structure. (2) Under the action of formation overpressure, the inorganic pores have tiny changes that can be assumed that they don't change in porosity, while the organic pores may have large deformation due to skeleton compression, leading to the increase of radius, connectivity and ultimately porosity of these pores. (3) The “dynamic” deformation porosity measurement method combining high injection pressure helium porosity measurement and kerosene porosity measurement method under ultra-high variable pressure can accurately measure porosity of unconnected micro-pores under normal pressure conditions, and also the porosity increment caused by plastic skeleton compression deformation. (4) The pore deformation mechanism of shale may result in the “abnormal” phenomenon that the shale under formation conditions has higher porosity than that under normal pressure, so the overpressure shale reservoir is not necessarily “ultra-low in porosity”, and can have porosity over 10%. Application of this method in Well L210 in southern Sichuan has confirmed its practicality and reliability.

An aliphatic MOF with a molecular sieving effect for efficient C2H2/C2H4 separation.

A metal-organic framework, SDMOF-1, with rigid pores of about 3.4 Å, which is appropriate for accommodating C2H2 molecules, exhibits high C2H2 adsorption capacity and great separation capability of the C2H2/C2H4 mixture. This work provides a new method to design aliphatic MOFs with a molecular sieving effect to realize efficient gas separation.

Hetero-Polycrystalline Membranes with Narrow and Rigid Pores for Molecular Sieving.

Molecular sieving membranes have great potential for energy-saving separations, but they suffer from permeability-selectivity trade-off limitation. In this report, simultaneous hetero-crystallization and hetero-linker coordination of metal-organic framework (MOF) hollow fiber membranes through one-pot synthesis for precise gas separation is reported. It is found that the hetero-polycrystalline membranes consist of 2D and 3D MOF phases and are defect-free and roughly orientated, hetero-linker exchange of 3D phase by larger geometric ones can narrow transport pathway, and framework rigidification occurs and thus fixes MOF channels. The prepared membranes are robust and reproducible, and exhibit substantially improved performance, with H2 /CO2 , H2 /N2 , and H2 /CH4 selectivities up to 361, 482, and 541, respectively, accompanied by high H2 permeance over 1100gas permeation units, which can easily outclass trade-off upper bounds of state-of-the-art membranes.

An enhancement of CO2 capture in a type-III porous liquid by 2-Methylimidazole zinc salt (ZIF-8)

Porous liquids (PLs) with porosity and fluidity have shown great potential in gas separation. In this work, a type-III PLs were synthesized by mixing 2-Methylimidazole zinc salt (ZIF-8) nanoparticles as the main units and 1-Ethyl-3-methylimidazolium Bis(trifluoro-methanesulfonyl)-imide ([EMlm][NTf2]) as the solvent. Molecular dynamics simulation evidenced the permanent, vacant, rigid pores of PLs. The prepared PLs were characterized, and their CO2 uptake performances were obtained using a CO2 static absorption system. ZIF-8 could significantly increase the CO2 absorption capacity of the porous liquid, and when the mass fraction of ZIF-8 inside PLs was 10 wt%, the CO2 absorption capacity increased by 143 %. Then, the CO2 absorption characteristics of porous liquids were studied in different conditions, including temperature, pressure, and concentration of the ZIF-8. The CO2 adsorption heat calculated by the Clausius–Clapeyron relation is −6.5 kJ/mol. The absorption rate of PLs was studied using the damping film theory. The CO2 uptake capacity of the PLs decreased with temperature but increased with pressure and CO2 concentration. Subsequently, the absorption-adsorption model was established to predict the CO2 uptake capacity of PLs. The theoretical values agree with the experimental values, indicating that the developed absorption-adsorption model can predict the CO2 uptake properties of PLs. Finally, analysis of the CO2 cyclic performance of the PLs showed the PLs could be regenerated under negative pressure, and the CO2 uptake capacity remained stable after five cycles, indicating the [EMIm][NTf2]/ZIF-8 PLs could be applied in CO2 capture.

New insights into the role of system sealing capacity in shale evolution under conditions analogous to geology: Implications for nanopore evolution

Closed and semi-closed pyrolysis of a lacustrine shale sample was conducted using the same instrument characterized by lithostatic pressure and limited reactive space in order to unravel the impacts of the system sealing capacity on organic matter occurrence and nanopore development in shales under conditions analogous to natural processes. The solid residues were subjected to organic geochemical measurements, low-pressure gas (N2 and CO2) adsorption tests, and field emission-scatter electrical microscope analysis. The results revealed that solvent extraction played positive and negative roles in the pore development of solid residues from both systems at different thermal maturities. Inorganic and organic pores were primarily filled or shielded by soluble bitumen at low and high temperatures, respectively. The occurrences of organic matter in solid residues from the two systems were different at lower temperatures but gradually evolved similarly at higher temperatures and were dominated by nanoscale interparticle organic matter. Organic pore occurrence in solid residues from the two systems was approximately comparable. However, differences in pore volume and specific surface area of solid residues from the closed and semi-closed systems increased measurably below 550 °C. At 550 °C, a strong mechanical compaction and overpressure environment caused deformation and closure of pores surrounding rigid minerals and pores associated with ductile minerals surrounding organic matter in solid residue from the closed system, while only a few pores surrounding rigid minerals from the semi-closed system deformed. Consequently, similar pore parameters of solid residues from the two systems were obtained at this temperature. Additionally, the variation in organic porosity of solid residues from the two systems has obvious stages based on mass balance calculation. The organic porosity evolution is collectively affected by system sealing capacity and thermal maturity at lower matured stages. In contrast, organic porosity evolution in solid residues is independent of system sealing capacity at high- and overmatured stages. Although the depositional environment is different, this study provides direct evidence that the difference in system sealing capacity is not the predominant factor leading to different organic pore developments in the Silurian and Cambrian shales in South China.

Designing heterogeneous MOF-on-MOF membrane with hierarchical pores for effective water treatment

Rationally regulating the separation pores is an effective way to achieve efficient separation membrane. However, the developed metal-organic framework (MOF) membranes for water treatment are all formed by one kind of MOF, which can only provide rigid pores, makes it difficult to achieve high flux and excellent rejection ratio simultaneity. Here, we proposed a facile strategy for the synthesis of heterogeneous MOF-on-MOF membrane with hierarchical pores, by site-specific grown ZIF-8 layer on UiO-66-NH2 layer. Thus unique architecture of the obtained double-layered MOF membrane (UiO-66-NH2@ZIF-8) endows multidimensional separation pores: (i) the large pores of UiO-66-NH2 can facilitate water transportation, (ii) the molecular-sieving pores of ZIF-8 can intercept dyes, (iii) UiO-66-NH2 acting as active sites can promote the growth of ZIF-8. As a result, the optimized UiO-66-NH2@ZIF-8 membrane exhibits high flux (36.7 L m−2 h−1 bar−1) and excellent dye rejections (>97.0%). Through analysis and comparison, the regulated multi-type pores play an important role in membrane performance. Coupled with the facile membrane preparing method, this work can used as a potential approach of designing other advanced MOF membrane for water treatment.

Tailoring the Structure of Carbon Molecular Sieves Derived from an Aromatic Polyamide

Energy-efficient and selective separation technologies are required to reclaim aqueous waste streams for reuse. Carbon molecular sieves (CMS) are one material capable of separating organic solvent and gaseous mixtures due to the presence of permanent, rigid, and molecular sieving pores and could potentially be used in aqueous separations. Here, a novel CMS material is derived from an aromatic polyamide precursor with tailored fabrication techniques. Structural characteristics of this CMS have been probed with various analyses and are potentially ideal for selective separations as adsorbents. Elemental analyses provide insight about the potential chemical structures of CMS materials that result from degradation mechanisms. Gravimetric sorption data is used to estimate sorption, diffusion, and permeability selectivity with water and N, N-dimethylformamide. While challenges to the development and implementation of such carbonaceous materials remain, highly selective materials are critical starting points for enabling ultra-challenging separation processes of the future.

Molecular size-dependent subcontinuum solvent permeation and ultrafast nanofiltration across nanoporous graphene membranes.

Selective solvent and solute transport across nanopores is fundamental to membrane separations, yet it remains poorly understood, especially for non-aqueous systems. Here, we design a chemically robust nanoporous graphene membrane and study molecular transport in various organic liquids under subnanometre confinement. We show that the nature of the solvent can modulate solute diffusion across graphene nanopores, and that breakdown of continuum flow occurs when pore size approaches the solvent's smallest molecular cross-section. By holistically engineering membrane support, modelling pore creation and defect management, high rejection and ultrafast organic solvent nanofiltration of dye molecules and separation of hexane isomers are achieved. The membranes exhibit stable fluxes across a range of solvents, consistent with flow across rigid pores whose size is independent of the solvent. These results demonstrate that nanoporous graphene is a rich materials system for controlling subcontinuum flow that could enable new membranes for a range of challenging separation needs.

Nonlinear material and ionic transport through membrane nanotubes

Membrane nanotubes (NTs) and their networks play an important role in intracellular membrane transport and intercellular communications. The transport characteristics of the NT lumen resemble those of conventional solid-state nanopores. However, unlike the rigid pores, the soft membrane wall of the NT can be deformed by forces driving the transport through the NT lumen. This intrinsic coupling between the NT geometry and transport properties remains poorly explored. Using synchronized fluorescence microscopy and conductance measurements, we revealed that the NT shape was changed by both electric and hydrostatic forces driving the ionic and solute fluxes through the NT lumen. Far from the shape instability, the strength of the force effect is determined by the lateral membrane tension and is scaled with membrane elasticity so that the NT can be operated as a linear elastic sensor. Near shape instabilities, the transport forces triggered large-scale shape transformations, both stochastic and periodic. The periodic oscillations were coupled to a vesicle passage along the NT axis, resembling peristaltic transport. The oscillations were parametrically controlled by the electric field, making NT a highly nonlinear nanofluidic circuitry element with biological and technological implications.

Cellulose Acetate Hollow Fiber Membranes from Banana Stem Fibers Coated by TiO2 for Degradation of Waste Textile Dye

Cellulose acetate hollow fiber membrane from banana stem fibers coated by TiO2 (CAHFMT) was prepared and characterized as an alternative material for degradation of waste textile dye. Its applicability was demonstrated by mechanical properties, FTIR, SEM, thermal resistance, performance, and degradation efficiency. Cellulose acetate (CA) was synthesized from banana stem fibers by swelling stage, acetylation reaction, and hydrolysis reaction. CA was modified using TiO2 of various concentrations. CAHFMT with 22 % w/v dope concentration has the optimum mechanical properties (stress, strain and Young’s modulus), as well as hydrophilic properties. The performances of CAHFMT with Congo red were determined. The SEM results showed that the membrane had rigid pores. Moreover, this research stated that CAHFMT could be a solution to overcome economical and effective problems.

Reduced Lamin A/C Does Not Facilitate Cancer Cell Transendothelial Migration but Compromises Lung Metastasis.

Simple SummaryThe nucleus is the largest and stiffest organelle of tumor cells. Cancer metastasis depends on the ability of cancer cells circulating in the blood to exit blood vessels and survive in target organs. The roles of the shell (lamina) of the nucleus in cancer cell migration and survival in distinct organs of metastasis are still unclear. A-type lamins are key lamina components that increase nuclear stiffness and reduce squeezing capacity through highly rigid barriers. We addressed how reduced expression of A-lamins (lamin A/C) affects cancer cell survival and crossing of endothelial barriers and lung capillaries and found that reduced lamin A/C expression impairs cancer growth in spheroids and restricts cancer metastasis to lungs without improving cancer cell squeezing and extravasation from lung vessels, the key platform for cancer entry into lungs.The mechanisms by which the nuclear lamina of tumor cells influences tumor growth and migration are highly disputed. Lamin A and its variant lamin C are key lamina proteins that control nucleus stiffness and chromatin conformation. Downregulation of lamin A/C in two prototypic metastatic lines, B16F10 melanoma and E0771 breast carcinoma, facilitated cell squeezing through rigid pores, and reduced heterochromatin content. Surprisingly, both lamin A/C knockdown cells grew poorly in 3D spheroids within soft agar, and lamin A/C deficient cells derived from spheroids transcribed lower levels of the growth regulator Yap1. Unexpectedly, the transendothelial migration of both cancer cells in vitro and in vivo, through lung capillaries, was not elevated by lamin A/C knockdown and their metastasis in lungs was even dramatically reduced. Our results are the first indication that reduced lamin A/C content in distinct types of highly metastatic cancer cells does not elevate their transendothelial migration (TEM) capacity and diapedesis through lung vessels but can compromise lung metastasis at a post extravasation level.

Abstract 2726: Nuclear checkpoints for melanoma and breast cancer lung metastasis

Abstract Introduction Metastasis involves cancer cell intravasation and extravasation from blood vessels at target organs. The mechanisms by which the nuclei of metastatic tumor cells squeeze through different vascular and epithelial barriers are poorly understood. The nuclear lamina attaches chromatin domains to the nuclear periphery and controls the mechanical properties of the nucleus and its crosstalk with the cell cytoskeleton. A-type lamins, lamin A and its splice variant lamin C, are key nuclear lamina proteins that control nucleus stiffness and regulate chromatin conformation. Reduced lamin A was reported in some aggressive cancers. Results and Discussion Using a new in vitro transendothelial migration (TEM) assay we found that melanoma and breast cancer cells slowly squeeze their nuclei and complete TEM through endothelial junctions irrespective of their relative lamin A/C levels, suggesting that lamin A/C dependent nuclear stiffening is not a rate-limiting step for cancer cell squeezing through endothelial cells in vitro. In contrast, reduced lamin A/C enhanced cancer cell squeezing through rigid pores. Tumor emigration analysis across blood vessels in vivo was performed by new 3D imaging of fluorescently labeled cancer cells with high and low lamin A/C levels. This imaging was based on light sheet microscopy of lipid-cleared lungs of recipient mice in situ labeled with anti-vascular CD31 mAb. Using this technology, we found that reduced lamin A/C expression did not enhance the emigration of circulating murine melanoma and breast cancer cells across lung capillaries in vivo. Lower lamin A/C levels reduced the constitutive, transcriptionally repressed, heterochromatin in both melanoma and breast cancer cells. Decreased lamin A/C expression did not enhance however, nuclear rupture in the tumor cells that entered the lung parenchyma. The outcomes of the epigenetic and mechanical changes resulting of lamin A/C suppression on tumor growth and metastasis are under current investigation. Conclusions Our results suggest that subsets of tumor cells may benefit from reducing their nuclear content of lamin A/C mainly at the level of rigid barrier crossing (e.g. dense interstitial spaces), but not at the level of extravasation or post extravasation survival at target organs. How alterations in lamin A/C content contribute to tumor heterogeneity and metastatic potential of singular cancer cells remains an open question. Citation Format: Francesco Roncato, Ofer Regev, Nehora Levi, Sara W. Feigelson, Gabi Gerlitz, Ronen Alon. Nuclear checkpoints for melanoma and breast cancer lung metastasis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2726.

Micromechanics-based assessment of the effective viscosity of suspensions of generalized-Newtonian fluids embedding noncolloidal angular/spheroidal pores and particles

The viscosity of suspensions depends on the properties of the fluid, i.e., the matrix material as well as on the volume fraction and shape of embedded inclusions. Regarding this dependence, a micromechanics-based homogenization approach is presented, giving access to the resulting effective viscous properties, starting from well established homogenization schemes originally proposed for the linear-elastic material response. In order to incorporate nonlinear matrix behavior, i.e., non-Newtonian fluids, the secant method of nonlinear homogenization is employed. The effect of nonsphericity of inclusions is considered by substituting the Eshelby tensor by a replacement tensor (replacement Eshelby tensor) determined by linear-elastic finite element simulations in Traxl and Lackner [Mech. Mater. 126, 126–139 (2018)]. In total, suspensions consisting of four different types of matrix materials, namely, (i) Newtonian, (ii) shear thickening, (iii) shear thinning power-law fluids, and (iv) Bingham or Herschel–Bulkley yield-stress fluids are considered embedding spherical, cubical, and tetrahedral inclusions (rigid particles and pores). The performance of the model is assessed by finite element simulations of respective representative volume elements, showing good agreement between model predictions and numerical results for small and moderate inclusion volume fractions.

Bimetallic Nanoparticles-Stabilized Conductive Metal-Organic Frameworks for Superior Chemiresistors

Introduction Recently, conductive metal-organic frameworks (cMOFs), having electrical conductivity with ultra-high specific surface area, have attracted much attention in diverse applications. In particular, cMOFs are promising materials for gas sensors, because their high surface area facilitates surface reactions of gas molecules, which can be transduced by electrical signals. However, cMOFs-based gas sensors are still suffering from some challenges, such as low response and poor detection limits [1]. On the other hand, bimetallic nanoparticles (BNPs) are known to have superior activities for surface reactions than single-elemental counterparts. In this regard, we envisioned that ultra-small BNPs can be encapsulated in the cavities of cMOFs and these BNPs-decorated cMOFs (BNP@cMOFs) can exhibit exceptionally high surface reactivity with efficient electrical responses. Here, for the first time, we report the combination of cMOFs with ultra-small BNPs in order to translate bimetallic synergies for surface reactions into cMOFs-based chemiresistors. As a proof of our concept, we fabricated 2 nm-sized Pt–Ru BNPs encapsulated in cMOFs (PtRu@cMOFs). PtRu@cMOFs-based sensors show hugely improved NO2 sensing performances at room temperature in air, in terms of response, cross-selectivity, and detection limits. Method Cu3(HHTP)2, a typical cMOF, is prepared by hydrothermal method using copper(II) acetate and HHTP. The Cu3(HHTP)2 has numerous rigid pores with a diameter of 2 nm, which act as an encapsulation site for BNPs. Two kinds of metal precursors, RuCl3 and K2PtCl4, are added in the suspension of Cu3(HHTP)2 in deionized water. Then, the suspension is stirred for 30 min to bind heterogeneous metal ions with the cavities of Cu3(HHTP)2. The metal ions are electrostatically bound to oxygen groups in HHTP of Cu3(HHTP)2. Subsequently, the metal precursors are reduced with sodium borohydride (NaBH4), resulting in ultra-small (~2 nm) PtRu BNPs encapsulated in the cavities of Cu3(HHTP)2. The prepared PtRu@cMOFs are used as a chemiresistor for NO2 detection, in order to utilize bimetallic synergies in Pt–Ru nanocatalysts for chemiresistive sensing. Results and Conclusions We investigated the morphology of PtRu NPs in PtRu@cMOFs by using transmission electron microscopy (TEM) analysis. TEM image showed that ~2 nm PtRu NPs were well dispersed in the cMOF-matrix. X-ray photoelectron spectroscopy (XPS) analysis was conducted to confirm the formation of Pt–Ru BNPs. In the region of Pt and Ru spectra, PtRu@cMOFs display shifts of Pt0 4f and Ru0 3p peaks compared to monometallic counterparts. As reported in previous literature, these peak shifts indicate the interaction between atomic Pt and Ru in bimetallic Pt–Ru, demonstrating the formation of Pt–Ru BNPs in cMOFs. To investigate bimetallic synergy of Pt–Ru BNPs in cMOFs-based chemiresistive sensing, the resistance changes (ΔR/R0) of PtRu@cMOFs in response to exposures of NO2 2 ppm are compared with those of pristine cMOFs, Ru@cMOFs, and Pt@cMOFs. Importantly, PtRu@cMOFs showed hugely improved NO2 responses compared to pristine cMOFs, Pt@cMOFs, and Ru@cMOFs, demonstrating the superior catalytic effect of Pt–Ru BNPs on NO2 sensing. Responses of PtRu@cMOFs-based sensors were measured in 0.2–3 ppm of NO2. The sensors showed high responses of 46.8% to 1 ppm, which is the regulatory permissible NO2 exposure limit designated by the occupational safety and health administration (OSHA) in U.S.A. Moreover, PtRu@cMOFs exhibited 8-fold higher responses to NO2 than other analytes, demonstrating the ultrahigh cross-selectivity. Furthermore, PtRu@cMOFs showed superior sensing response compared to the state-of-art NO2 sensors in air at room temperature. In conclusion, we have demonstrated the synthesis of BNPs embedded in cMOFs, which have superior NO2 sensing performances. The cavities of cMOFs do not only act as a binding site of metal precursors but also suppress the growth of BNPs during the chemical reduction, generating ultra-small (~ 2nm) PtRu BNPs in cMOFs. PtRu@cMOFs exhibit greater NO2 responses compared to their monometallic counterparts. These outstanding sensing performances are attributed to the bimetallic synergies of Pt and Ru in Pt–Ru BNPs with highly porous and conductive matrix. Our approaches provide general and facile methods to create various beneficial BNPs in versatile cMOFs [2].

Nanohoop Rotaxanes from Active Metal Template Syntheses and Their Potential in Sensing Applications.

The unique optoelectronic properties and smooth, rigid pores of macrocycles with radially oriented π systems render them fascinating candidates for the design of novel mechanically interlocked molecules with new properties. Two high-yielding strategies are used to prepare nanohoop [2]rotaxanes, which owing to the π-rich macrocycle are highly emissive. Then, metal coordination, an intrinsic property afforded by the resulting mechanical bond, can lead to molecular shuttling as well as modulate the observed fluorescence in both organic and aqueous conditions. Inspired by these findings, a self-immolative [2]rotaxane was then designed that self-destructs in the presence of an analyte, eliciting a strong fluorescent turn-on response, serving as proof-of-concept for a new type of molecular sensing material. More broadly, this work highlights the conceptual advantages of combining compact π-rich macrocyclic frameworks with mechanical bonds formed via active-template syntheses.

Nanohoop Rotaxanes from Active Metal Template Syntheses and Their Potential in Sensing Applications

AbstractThe unique optoelectronic properties and smooth, rigid pores of macrocycles with radially oriented π systems render them fascinating candidates for the design of novel mechanically interlocked molecules with new properties. Two high‐yielding strategies are used to prepare nanohoop [2]rotaxanes, which owing to the π‐rich macrocycle are highly emissive. Then, metal coordination, an intrinsic property afforded by the resulting mechanical bond, can lead to molecular shuttling as well as modulate the observed fluorescence in both organic and aqueous conditions. Inspired by these findings, a self‐immolative [2]rotaxane was then designed that self‐destructs in the presence of an analyte, eliciting a strong fluorescent turn‐on response, serving as proof‐of‐concept for a new type of molecular sensing material. More broadly, this work highlights the conceptual advantages of combining compact π‐rich macrocyclic frameworks with mechanical bonds formed via active‐template syntheses.

Tunable nanochannels enable selective gas adsorption

Typical gas separation nanomaterials such as zeolites and microporous carbon have rigid pores, making it difficult to control gas diffusion within the material. Now, researchers led by Kyoto University’s Susumu Kitagawa have designed a nanoporous soft crystal that can selectively adsorb and store various gas molecules (Science 2019, DOI: 10.1126/science.aar6833). The material consists of a copper-based porous coordination polymer with metal centers linked by butterfly-shaped ligands made from isophthalic acid and phenothiazine 5,5-dioxide (OPTz). This structure forms an array of nanocages connected by diffusion channels. At low temperatures, the entrances to the nanocages are so small that gas molecules can’t fit through. But with increased temperature, the wing tips of the OPTz units flip up, enlarging the nanocage entrances and allowing the gas molecules to move from one nanocage to another. By varying the temperature, researchers can control the size of the cage entrances so that they selectively adsor...

Molecular sieving of ethylene from ethane using a rigid metal-organic framework.

There are great challenges in developing efficient adsorbents to replace the currently used and energy-intensive cryogenic distillation processes for olefin/paraffin separation, owing to the similar physical properties of the two molecules. Here we report an ultramicroporous metal-organic framework [Ca(C4O4)(H2O)], synthesized from calcium nitrate and squaric acid, that possesses rigid one-dimensional channels. These apertures are of a similar size to ethylene molecules, but owing to the size, shape and rigidity of the pores, act as molecular sieves to prevent the transport of ethane. The efficiency of this molecular sieve for the separation of ethylene/ethane mixtures is validated by breakthrough experiments with high ethylene productivity under ambient conditions. This material can be easily synthesized at the kilogram scale using an environmentally friendly method and is water-stable, which is important for potential industrial implementation. The strategy of using highly rigid metal-organic frameworks with well defined and rigid pores could also be extended to other porous materials for chemical separation processes.