Cage Window Research Articles

HP35 Protein in the Mesopore of MIL-101(Cr) MOF: A Model to Study Cotranslocational Unfolding.

The immobilization of enzymes in metal-organic framework (MOF) cages is important in biotechnology. In this context, the mechanism of translocation of proteins through the cavities of the MOF and the roles played by confinement and MOF chemistry in giving rise to stable protein intermediates that are otherwise transiently populated in the physiological environment are important questions to be addressed. These unexplored aspects are examined with villin headpiece (HP35) as a model protein confined within a mesopore of MIL-101(Cr) using molecular dynamics simulations. At equilibrium, the protein is located farther from the center of the cavity and closer to the MOF surface. Molecular interactions with the MOF partially unfold helix-1 at its N-terminus. Umbrella sampling simulations inform the range of conformations that HP35 undertakes during translocation from one cavity to another and associated changes in free energy. Relative to its equilibrium state within the cavity, the free energy barrier for the unfolded protein at the cage window is estimated to be 16 kcal/mol. This study of MOF-based protein conformation can also be a general approach to observing intermediates in folding-unfolding pathways.

Coral-like, self-assembled, and spatially bounded Ag nano-particles on franzinite zeolite composite sensor toward accurate, synergetic, and ultra-trace sulfadiazine detection

A coral-like Ag@FRA zeolite nanocomposite sensor reveals high sensitivity toward sulfadiazine (SDZ) in a dual detection of fluorescence and electrochemistry. The sensor has been as-synthesized in the hydrothermal condition through a one-pot self-assembly process in which the high crystalline Ag nanoparticles (NPs) are closely arranged and stacked on the nanosized surface cage window of the FRA (Franzinite) zeolite. Strong ultrasound can drive the coral-like composite release Ag nanoparticles whose distribution range mainly from 10 to 12 nm lead to the purple fluorescence in an emission spectrum. In sea water, the fluorescence increases linearly in the SDZ concentration range of 5 × 10−18-5 × 10−10 M. Furthermore, the LOD (limit of detection) reaches 1.4 × 10−22 M by the spatial confinement effect of the coral-liked FRA cage structure in CV (cyclic voltammetry) method at the characteristic potential peak position of 0.1 V vs. SCE. The theoretical calculation also confirms that the FRA cage structure matches well with the SDZ molecules. Further studies indicate the generation of a novel stable composite sensor with high specificity, good recovery and repeatability, which depends on the induction of silver ions upon the artificial synthesis of FRA.

Optimized Pore Nanospace through the Construction of a Cagelike Metal-Organic Framework for CO2/N2 Separation.

The development of metal-organic framework (MOF) adsorbents with a potential molecule sieving effect for CO2 capture and separation from flue gas is of critical importance for reducing the CO2 emissions to the atmosphere yet challenging. Herein, a cagelike MOF with a suitable cage window size falling between CO2 and N2 and the cavity has been constructed to evaluate its CO2/N2 separation performance. It is noteworthy that the introduction of coordinated dimethylamine (DMA) and N,N'-dimethylformamide (DMF) molecules not only significantly reduces the cage window size but also enhances the framework-CO2 interaction via C-H···O hydrogen bonds, as proven by molecular modeling, thus leading to an improved CO2 separation performance. Moreover, transient breakthrough experiments corroborate the efficient CO2/N2 separation, revealing that the introduction of DMA and DMF molecules plays a vital role in the separation of a CO2/N2 gas mixture.

Controlling Gas Selectivity in Molecular Porous Liquids by Tuning the Cage Window Size

Control of pore window size is the standard approach for tuning gas selectivity in porous solids. Here, we present the first example where this is translated into a molecular porous liquid formed from organic cage molecules. Reduction of the cage window size by chemical synthesis switches the selectivity from Xe-selective to CH4-selective, which is understood using 129Xe, 1H, and pulsed-field gradient NMR spectroscopy.

Controlling Gas Selectivity in Molecular Porous Liquids by Tuning the Cage Window Size

AbstractControl of pore window size is the standard approach for tuning gas selectivity in porous solids. Here, we present the first example where this is translated into a molecular porous liquid formed from organic cage molecules. Reduction of the cage window size by chemical synthesis switches the selectivity from Xe‐selective to CH4‐selective, which is understood using 129Xe, 1H, and pulsed‐field gradient NMR spectroscopy.

The Dimensional Precision of Forming Windows in Bearing Cages

In the case of double row tapered roller bearings, the windows found in bearing cages could be obtained using various machining methods. Some such machining methods are based on the cold forming process. There are many factors that are able to affect the machining accuracy of the windows that exist in bearing cages. On the dimensional precision of windows, the clearance between punches and die, the work stroke length, and the workpiece thickness could exert influence. To evaluate this influence, experimental research was developed taking into consideration the height and the length of the cage window and the distance between the contact elements of the cage. By mathematical processing of the experimental results, empirical mathematical models were determined and analyzed. The empirical models highlighted the intensity of the influence exerted by the considered forming process input factors on the dimensional precision of the windows obtained in bearing cages.

Kinematics and dynamics models of cylindrical roller bearing of railway transport

Purpose. Lack of kinematics models and imperfection of the known dynamics models of the roller bearings of railway rolling stock axle-boxes do not allow designing the optimal structure of bearing cages, providing the required service life and reliability of bearing units of wheel sets for cars and locomotives. The studies of kinematics and dynamics of roller bearings of axle boxes for cars and locomotives and modeling of their parts interaction to create the analytical method of bearing cages calculation are necessary. Methodology. This purpose has been achieved due to the modeling of kinematics of the ideal (without gaps) and real (taking account the gaps, manufacturing and installation errors) bearings, substantiation of the transfer mechanism of motion from the rollers to bearing cage, modeling the dynamics of rolling, research of interaction forces of the rollers with bearing cage. Findings. It is established that the kinematics of ideal bearing is determined by the contact deformations of the rollers and rings, when the kinematics of real bearing depends mainly on the side gaps in the windows of the bearing cage. On the basis of studies of the real bearing kinematics the dynamics models of the rollers and bearing cage interaction were constructed. The conducted studies of kinematics and dynamics of rolling bearings have changed our view of them as of the planetary mechanism, explained the reason of bearing cage loading, and confirmed the possibility of destruction during operation. Originality. It was first proposed a mechanism for motion transfer from the rollers to the bearing cage of roller bearings, consisting in that the side gap in the bearing cage window is reduced gradually multiple of the number of rollers of radial loading area according to the bearing cage motion. The models of roller bearing dynamics, which allow calculating the interaction forces of parts for all modes of operation, were improved. Practical value. Use of the offered models of kinematics and dynamics of the roller bearings will develop analytical calculation method of the bearing cage for the choice of its optimal design according to criterion of maximum service life and reliability of the bearing unit of wheel sets of the railway rolling stock.

Insight into the mechanism of CO2 adsorption on Cu–BTC and its composites with graphite oxide or aminated graphite oxide

CO2 adsorption on Cu–BTC and its composites with graphite oxide or aminated graphite oxide was evaluated at 273K and 295K under the pressure up to ∼0.1MPa. The samples before and after CO2 adsorption were characterized using X-ray diffraction, FT-IR spectroscopy and thermal analysis. The isosteric heats of adsorption were calculated from the experimental adsorption isotherms. The results indicate that CO2 is physically adsorbed on Cu–BTC and its composites with graphite oxide or aminated graphite oxide. The primary adsorption sites are open copper centers and cage window sites. The composite of Cu–BTC and modified graphite oxide with the highest degree of structural and chemical heterogeneity (MOF/GO-U3) shows the highest CO2 capacity (8.45mmol/g at 273K and 4.78mmol/g at 295K) and excellent regenerability with a relatively low and constant over a broad range of surface coverage isosteric heat of adsorption (average value ∼24.8kJ/mol).

Peer attachment formation by systemic redox regulation with social training after a sensitive period.

Attachment formation is the most pivotal factor for humans and animals in the growth and development of social relationships. However, the developmental processes of attachment formation mediated by sensory-motor, emotional, and cognitive integration remain obscure. Here we developed an animal model to understand the types of social interactions that lead to peer-social attachment formation. We found that the social interaction in a sensitive period was essential to stabilise or overwrite the initially imprinted peer affiliation state and that synchronised behaviour with others based on common motivations could be a driver of peer social attachment formation. Furthermore, feeding experience with supplementation of ubiquinol conferred peer social attachment formation even after the sensitive period. Surprisingly, the experience of feeding beyond the cage window was also effective to reduce the required amount ubiquinol, suggesting that peri-personal space modulation may affect socio-emotional cognition and there by lead to attachment formation.

Superior Performance of Copper Based MOF and Aminated Graphite Oxide Composites as CO2 Adsorbents at Room Temperature

New composites Cu-BTC MOF and graphite oxide modified with urea (GO-U) are developed and tested as CO2 adsorbents at room temperature. The composite containing GO-U with the highest nitrogen content exhibits an excellent CO2 uptake (4.23 mmol/g) at dynamic conditions. The incorporation of GO-U into MOF changes the chemistry and microstructure of the parent MOF and results in synergistic features beneficial for CO2 retention on the surface. To identify these features the initial and exhausted materials were extensively characterized from the points of view of their porosity and chemistry. Although the adsorption forces are relatively strong, the results indicate that CO2 is mainly physisorbed on the composites at dry dynamic conditions at ambient temperature and pressure. The primary adsorption sites include small micropores specific for the composites, open Cu sites, and cage window sites.

Adsorption of Propane and Propylene on CuBTC Metal–Organic Framework: Combined Theoretical and Experimental Investigation

A combined experimental and theoretical investigation of propane and propylene adsorption in the metal–organic framework CuBTC is presented. The dependence of adsorption enthalpies on the adsorbed amount was determined by microcalorimetry up to 8 mmol g–1 coverage (roughly C3Hn/Cu2+ ratio of 1.5). Trends observed experimentally were interpreted on the basis of accurate calculations carried out at the hybrid DFT–ab initio level. Three types of adsorption sites were identified; however, qualitatively different results were obtained for propane and propylene. Propane preferentially adsorbs at the cage center sites (−ΔH° = 43 kJ mol–1), followed by adsorption at the cage window sites (31 kJ mol–1), while the interaction with the coordinatively unsaturated sites (CUS) is relatively weak (24 kJ mol–1). On the contrary, propylene preferentially interacts with the CUS (56 kJ mol–1), while the adsorption at the cage center and cage window sites was found to be only 45 and 34 kJ mol–1, respectively. Due to the topology of CuBTC, lateral interactions are significantly more important among the adsorbates located at the cage center and cage window sites (populated in the case of propane) than among adsorbates at the CUS and cage center sites (populated in the case of propylene). Therefore, adsorption energies obtained for coverages above 6 mmol g–1 of adsorbed amount were larger for propane than for propylene. Consequently, the presence of small cages makes the CuBTC MOF less suitable for propane/propylene separation than MOFs having the Cu2+ CUS but without small cages (e.g., CPO-27).

Understanding CO2 Adsorption in CuBTC MOF: Comparing Combined DFT–ab Initio Calculations with Microcalorimetry Experiments

A combined experimental and theoretical investigation of CO2 adsorption in the metal–organic framework CuBTC is presented. Adsorption enthalpies were measured as a function of coverage up to 13 mmol g–1 adsorbed amount (corresponding roughly to CO2/Cu = 5:2) by a Tian–Calvet-type microcalorimeter. Experimetal data are interpreted based on accurate calculations employing a combined DFT–ab initio computational scheme. CO2 molecules adsorb preferentially on coordinatively unsaturated sites for coverages below CO2/Cu = 1:1; at higher coverages (up to CO2/Cu = 5:3), CO2 adsorbs in cage window sites; and at higher coverages, the sites in cage centers and in large cages start to be occupied. Experimental adsorption enthalpies are almost constant (−29 kJ mol–1) up to the CO2/Cu = 5:3 coverage, suggesting a homogeneity of adsorption sites. However, calculations clearly show that adsorption sites in CuBTC are rather heterogeneous. The experimentally observed independence of adsorption enthalpies with respect to coverage is due to the cancellation of two effects: the decrease in the adsorbate–adsorbent interaction is compensated by an increase in the lateral interactions.

Removal of sulfonamide antibiotics from water: Evidence of adsorption into an organophilic zeolite Y by its structural modifications

Sulfonamide antibiotics are persistent pollutants of aquatic bodies, known to induce high levels of bacterial resistance. We investigated the adsorption of sulfadiazine, sulfamethazine, and sulfachloropyridazine sulfonamides into a highly dealuminated faujasite zeolite (Y) with cage window sizes comparable to sulfonamide dimensions. At maximal solubility the antibiotics were almost completely (>90%) and quickly (t<1min) removed from the water by zeolite. The maximal amount of sulfonamides adsorbed was 18-26% DW of dry zeolite weight, as evidenced by thermogravimetric analyses and accounted for about one antibiotic molecule per zeolitic cage. The presence of this organic inside the cage was revealed by unit cell parameter variations and structural deformations obtained by X-ray structure analyses carried out using the Rietveld method on exhausted zeolite. The most evident deformation effects were the lowering of the Fd-3m real symmetry in the parent zeolite to Fd-3 and the remarkable deformations which occurred in the 12-membered ring cage window after sulfadiazine or sulfachloropyridazine adsorption. After sulfamethazine adsorption, zeolite deformation caused a lowering in symmetry up to the monoclinic P2/m space group. The effective and irreversible adsorption of sulfonamides into organophylic Y zeolite makes this cheap and environmentally friendly material a suitable candidate for removing sulfonamides from water.

Nanoclusters in Nanocages: Platinum Clusters and Platinum Complexes in Zeolite LTL Probed by 129Xe NMR Spectroscopy

Platinum nanoclusters and mononuclear platinum complexes in zeolite KLTL were characterized by 129Xe NMR spectroscopy at temperatures from 100 to 296 K; the chemical shift increased with decreasing temperature, consistent with xenon's increasingly strong interactions with the platinum. The room-temperature chemical shift of xenon characterizing the zeolite containing the platinum clusters was 148.7 ppm, but that of the zeolite containing the platinum complexes was only 98.3 ppm, slightly greater than the value representing the bare zeolite, 95.4 ppm. These data, combined with literature data characterizing similar samples, indicate that the 129Xe chemical shift increases with the size of the metal species in the zeolite, up to the point at which entry of the Xe atom into the space containing the metal is constrained by the geometry of the metal species and the zeolite cage; in the limiting case, the chemical shift is substantially reduced because a Xe atom interacts with an encaged nanocluster only through a cage window.

Zeolite-supported transition metal catalysts by design

Zeolite supported metal Catalysts are prepared by ion exchange or incipient wetness impregnation, or by deposition of metal complexes, followed by calcination and reduction. Hydrogen reduction of encaged transition metal ions yields metal dusters or isolated atoms and protons of high Brønsted acidity. The elementary steps in the genesis of mono- and bimetallic metal dusters have been unravelled by a combination of dynamic and spectroscopic methods. Small metal clusters can be anchored to zeolite cage walls by transition metal ions or protons; however, adsorption of a CO which can displace the protons from the metal, initiates migration of the primary carbonyl dusters leading to their coalescence. At low temperature, this process is limited by the geometry of the metal core vis-à-vis the cage window. Protons of high Brensted acidity can reoxidize metals at elevated temperature, even selectively “leach” the less noble metal atoms out of bimetal clusters. Large metal particles, present in zeolite voids or at the external surface, can be transformed into small particles, exposing virtually all their metal atoms, by either of two novel in situ techniques which are based on oxidative dispersion with oxygen or chlorine gas.