CO2 Adsorption in a Robust Iron(III) Pyrazolate-Based MOF: Molecular-Level Details and Frameworks Dynamics From Powder X-ray Diffraction Adsorption Isotherms

Understanding adsorption processes at the molecular level, with multi-technique approaches, is nowadays at the frontier of porous materials research. In this work it is shown that with a proper data treatment, in situ high-resolution powder X-ray diffraction (HR-PXRD) at variable temperature and gas pressure can reveal atomic details of the accommodation sites, the framework dynamics as well as thermodynamic information (isosteric heat of adsorption) of the CO2 adsorption process in the robust iron(III) pyrazolate-based MOF Fe2(BDP)3 [H2BDP = 1,4-bis(1H-pyrazol-4-yl)benzene]. Highly reliable "HR-PXRD adsorption isotherms" can be constructed from occupancy values of CO2 molecules. The "HR-PXRD adsorption isotherms" accurately match the results of conventional static and dynamic gas sorption experiments and Monte Carlo simulations. These results are indicative of the impact of the molecular-level behavior on the bulk properties of the system under study and of the potential of the presented multi-technique approach to understand adsorption processes in metal-organic frameworks.

Scalable Synthesis and Electrocatalytic Performance of Highly Fluorinated Covalent Organic Frameworks for Oxygen Reduction

In this study, we present a novel approach for the synthesis of covalent organic frameworks (COFs) that overcomes the common limitations of non-scalable solvothermal procedures. Our method allows for the room-temperature and scalable synthesis of a highly fluorinated DFTAPB-TFTA-COF, which exhibits intrinsic hydrophobicity. We used DFT-based calculations to elucidate the role of the fluorine atoms in enhancing the crystallinity of the material through corrugation effects, resulting in maximized interlayer interactions, as disclosed both from PXRD structural resolution and theoretical simulations. We further investigated the electrocatalytic properties of this material towards the oxygen reduction reaction (ORR). Our results show that the fluorinated COF produces hydrogen peroxide selectively with low overpotential (0.062 V) and high turnover frequency (0.0757 s-1 ) without the addition of any conductive additives. These values are among the best reported for non-pyrolyzed and metal-free electrocatalysts. Finally, we employed DFT-based calculations to analyse the reaction mechanism, highlighting the crucial role of the fluorine atom in the active site assembly. Our findings shed light on the potential of fluorinated COFs as promising electrocatalysts for the ORR, as well as their potential applications in other fields.

Mercury Clathration-Driven Phase Transition in a Luminescent Bipyrazolate Metal-Organic Framework: A Multitechnique Investigation

Mercury is one of the most toxic heavy metals. By virtue of its triple bond, the novel ligand 1,2-bis(1H-pyrazol-4-yl)ethyne (H₂BPE) was expressly designed and synthesized to devise metal-organic frameworks (MOFs) exhibiting high chemical affinity for mercury. Two MOFs, Zn(BPE) and Zn(BPE)·nDMF [interpenetrated i-Zn and noninterpenetrated ni-Zn·S, respectively; DMF = dimethylformamide], were isolated as microcrystalline powders. While i-Zn is stable in water for at least 15 days, its suspension in HgCl₂ aqueous solutions prompts its conversion into HgCl₂@ni-Zn. A multitechnique approach allowed us to shed light onto the observed HgCl₂-triggered i-Zn-to-HgCl₂@ni-Zn transformation at the molecular level. Density functional theory calculations on model systems suggested that HgCl₂ interacts via the mercury atom with the carbon-carbon triple bond exclusively in ni-Zn. Powder X-ray diffraction enabled us to quantify the extent of the i-Zn-to-HgCl₂@ni-Zn transition in 100-5000 ppm HgCl_2 (aq) solutions, while X-ray fluorescence and inductively coupled plasma-mass spectrometry allowed us to demonstrate that HgCl₂ is quantitatively sequestered from the aqueous phase. Irradiating at 365 nm, an intense fluorescence is observed at 470 nm for ni-Zn·S, which is partially quenched for i-Zn. This spectral benchmark was exploited to monitor in real time the i-Zn-to-HgCl₂@ni-Zn conversion kinetics at different HgCl_2 (aq) concentrations. A sizeable fluorescence increase was observed, within a 1 h time lapse, even at a concentration of 5 ppb. Overall, this comprehensive investigation unraveled an intriguing molecular mechanism, featuring the disaggregation of a water-stable MOF in the presence of HgCl₂ and the self-assembly of a different crystalline phase around the pollutant, which is sequestered and simultaneously quantified by means of a luminescence change. Such a case study might open the way to new-conception strategies to achieve real-time sensing of mercury-containing pollutants in wastewaters and, eventually, pursue their straightforward and cost-effective purification.

Wet flue gas CO2 capture and utilization using one-dimensional metal-organic chains

Herein, we describe the use of an ultramicroporous metal-organic framework (MOF) with a composition of [Ni₃(pzdc)₂(ade)₂(H₂O)_1.5]·(H₂O)_1.3 (pzdc: 3,5-pyrazole dicarboxylic acid; ade: adenine), for the selective capture of carbon dioxide (CO₂) from wet flue gas followed by its conversion to value-added products. This MOF is comprised of one-dimensional Ni(II)-pyrazole dicarboxylate-adenine chains; through pi-pi stacking and H-bonding interactions, these one-dimensional chains stack into a three-dimensional supramolecular structure with a one-dimensional pore network. Upon heating, our MOF undergoes a color change from light blue to lavender, indicating a change in the coordination geometry of Ni(II). Variable temperature ultraviolet-visible (UV/vis) spectroscopy data revealed a blue shift of the d-d transitions, suggesting a change in the Ni-coordination geometry from octahedral to a mixture of square planar and square pyramidal. The removal of the water molecules coordinated to Ni(II) leads to the generation of a MOF with open Ni(II) sites. Nitrogen isotherms collected at 77 K and 1 bar revealed that this MOF is microporous with a pore volume of 0.130 cm³ g^-1. Carbon dioxide isotherms show a step in the uptake at low pressure, after which the CO₂ uptake is saturated. The step in the CO₂ uptake is likely attributable to the rearrangement of the three-dimensional supramolecular structure to accommodate CO₂ within its pores. The affinity of this MOF for CO₂ is 35.5 kJ mol^-1 at low loadings, and it increases to 41.9 kJ mol^-1 at high loadings. While our MOF is porous to CO₂ and water (H₂O) at 298 K, it is not porous to N₂, and the CO₂/N₂ selectivity increases from 28.5 to 31.5 as a function of pressure. Breakthrough experiments reveal that this MOF can capture CO₂ from dry and wet flue gas with uptake capacities of 1.48 ± 0.01 and 1.14 ± 0.06 mmol g^-1, respectively. The MOF can be regenerated and reused at least three times, demonstrating consistent CO₂ uptake capacities. Upon understanding the sorption behavior of this MOF, catalysis experiments show that the MOF is catalytically active in the fixation of CO₂ into an epoxide ring for the formation of a cyclic carbonate. The turnover frequency for this reaction is 21.95 ± 0.03 h^-1. The MOF showed no catalytic deterioration after two cycles and maintained comparable catalytic activity when dry and wet CO₂/N₂ mixtures were used. This highlights that both N₂ and H₂O do not dramatically affect the catalytic activity of our MOF toward CO₂ fixation.

Tetrazine Linkers as Plug-and-Play Tags for General Metal-Organic Framework Functionalization and C60 Conjugation

The value of covalent post-synthetic modification in expanding the chemistry and pore versatility of reticular solids is well documented. Here we use mesoporous crystals of the metal-organic framework (MOF) UiO-68-TZDC to demonstrate the value of tetrazine connectors for all-purpose inverse electron-demand Diels-Alder ligation chemistry. Our results suggest a positive effect of tetrazine reticulation over its reactivity for quantitative one-step functionalization with a broad scope of alkene or alkyne dienophiles into pyridazine and dihydropyridazine frameworks. This permits generating multiple pore environments with diverse chemical functionalities and the expected accessible porosities, that is also extended to the synthesis of crystalline fulleretic materials by covalent conjugation of fullerene molecules.

Impact of Pore Flexibility in Imine-Linked Covalent Organic Frameworks on Benzene and Cyclohexane Adsorption

This work focuses on the impact of covalent organic frameworks' (COFs) pore flexibility in the adsorption and separation of benzene and cyclohexane. With this aim, we have selected the imine-linked 3D COFs COF-300 and LZU-111 as examples of flexible and rigid frameworks, respectively. Optimized syntheses at room temperature or in solvothermal conditions enabled us to selectively isolate the narrow-pore form of COF-300 (COF-300-rt) or a mixture of the narrow-pore and a larger-pore form (COF-300-st), respectively, with different textural properties (BET specific surface area = 39 or 1270 m²/g, respectively, from N₂ adsorption at 77 K). In the case of LZU-111, only the room temperature route was successful, leading to the known microporous framework. COF-300-rt, COF-300-st, and LZU-111 were studied for benzene and cyclohexane adsorption and separation in static and dynamic conditions. At 298 K and 1 bar, these COFs adsorb more benzene (251, 221, and 214 cm³/g STP, respectively) than cyclohexane (175, 133, and 164 cm³/g STP, respectively). Moreover, the benzene and cyclohexane isotherms of COF-300-rt and COF-300-st are characterized by steps, as expected with a flexible material. Indeed, in situ powder X-ray diffraction experiments on benzene- and cyclohexane-impregnated batches enabled us to trap, for the first time, a sequence of forms of COF-300 with different pore aperture, rationalizing the stepped hysteretic isotherms. Finally, benzene/cyclohexane separation was evaluated using a benzene/cyclohexane 50:50 v/v flow at different temperatures (T = 298, 323, and 348 K): LZU-111 does not selectively retain any of the two components, while COF-300 exhibits stronger benzene-COF interactions also in dynamic conditions.

Zirconium Metal-Organic Polyhedra with Dual Behavior for Organophosphate Poisoning Treatment

Organophosphate nerve agents and pesticides are extremely toxic compounds because they result in acetylcholinesterase (AChE) inhibition and concomitant nerve system damage. Herein, we report the synthesis, structural characterization, and proof-of-concept utility of zirconium metal-organic polyhedra (Zr-MOPs) for organophosphate poisoning treatment. The results show the formation of robust tetrahedral cages [((n-butylCpZr)3(OH)3O)4L6]Cl6 (Zr-MOP-1; L = benzene-1,4-dicarboxylate, n-butylCp = n-butylcyclopentadienyl, Zr-MOP-10, and L = 4,4'-biphenyldicarboxylate) decorated with lipophilic alkyl residues and possessing accessible cavities of ∼9.8 and ∼10.7 Å inner diameters, respectively. These systems are able to both capture the organophosphate model compound diisopropylfluorophosphate (DIFP) and host and release the AChE reactivator drug pralidoxime (2-PAM). The resulting 2-PAM@Zr-MOP-1(0) host-guest assemblies feature a sustained delivery of 2-PAM under simulated biological conditions, with a concomitant reactivation of DIFP-inhibited AChE. Finally, 2-PAM@Zr-MOP systems have been incorporated into biocompatible phosphatidylcholine liposomes with the resulting assemblies being non-neurotoxic, as proven using neuroblastoma cell viability assays.

High-Throughput Discovery of a Rhombohedral Twelve-Connected Zirconium-Based Metal-Organic Framework with Ordered Terephthalate and Fumarate Linkers

We report a metal‐organic framework where an ordered array of two linkers with differing length and geometry connect [Zr₆(OH)₄O₄]¹²⁺ clusters into a twelve‐connected fcu net that is rhombohedrally distorted from cubic symmetry. The ordered binding of equal numbers of terephthalate and fumarate ditopic carboxylate linkers at the trigonal antiprismatic Zr₆ core creates close‐packed layers of fumarate‐connected clusters that are connected along the single remaining threefold axis by terephthalates. This well‐defined linker arrangement retains the three‐dimensional porosity of the Zr cluster‐based UiO family while creating two distinct windows within the channels that define two distinct guest diffusion paths. The ordered material is accessed by a restricted combination of composition and process parameters that were identified by high‐throughput synthesis.

One class classification as a practical approach for accelerating π-π co-crystal discovery

The implementation of machine learning models has brought major changes in the decision-making process for materials design. One matter of concern for the data-driven approaches is the lack of negative data from unsuccessful synthetic attempts, which might generate inherently imbalanced datasets. We propose the application of the one-class classification methodology as an effective tool for tackling these limitations on the materials design problems. This is a concept of learning based only on a well-defined class without counter examples. An extensive study on the different one-class classification algorithms is performed until the most appropriate workflow is identified for guiding the discovery of emerging materials belonging to a relatively small class, that being the weakly bound polyaromatic hydrocarbon co-crystals. The two-step approach presented in this study first trains the model using all the known molecular combinations that form this class of co-crystals extracted from the Cambridge Structural Database (1722 molecular combinations), followed by scoring possible yet unknown pairs from the ZINC15 database (21 736 possible molecular combinations). Focusing on the highest-ranking pairs predicted to have higher probability of forming co-crystals, materials discovery can be accelerated by reducing the vast molecular space and directing the synthetic efforts of chemists. Further on, using interpretability techniques a more detailed understanding of the molecular properties causing co-crystallization is sought after. The applicability of the current methodology is demonstrated with the discovery of two novel co-crystals, namely pyrene-6H-benzo[c]chromen-6-one (1) and pyrene-9,10-dicyanoanthracene (2).

Machine learning using one class classification on a database of existing co-crystals enables the identification of co-formers which are likely to form stable co-crystals, resulting in the synthesis of two co-crystals of polyaromatic hydrocarbons.

Investigation on the interconversion from DMF-solvated to unsolvated copper(ii) pyrazolate coordination polymers

Enlarging the family of CPs with the {Cu(μ-pz)₂} building unit: synthesis, thermal behaviour, crystal structure and spectroscopic properties of [Cu(μ-4-Xpz)₂(μ-DMF)]_n (4-Xpz = 4-Xpyrazolate, X = H, Cl, Br, I) and the non-solvated counterparts.

Tuning Carbon Dioxide Adsorption Affinity of Zinc(II) MOFs by Mixing Bis(pyrazolate) Ligands with N-Containing Tags

The four zinc(II) mixed-ligand metal-organic frameworks (MIXMOFs) Zn(BPZ)_x(BPZNO₂)_1-x, Zn(BPZ)_x(BPZNH₂)_1-x, Zn(BPZNO₂)_x(BPZNH₂)_1-x, and Zn(BPZ)_x(BPZNO₂)_y(BPZNH₂)_1-x-y (H₂BPZ = 4,4'-bipyrazole; H₂BPZNO₂ = 3-nitro-4,4'-bipyrazole; H₂BPZNH₂ = 3-amino-4,4'-bipyrazole) were prepared through solvothermal routes and fully investigated in the solid state. Isoreticular to the end members Zn(BPZ) and Zn(BPZX) (X = NO₂, NH₂), they are the first examples ever reported of (pyr)azolate MIXMOFs. Their crystal structure is characterized by a three-dimensional open framework with one-dimensional square or rhombic channels decorated by the functional groups. Accurate information about ligand stoichiometric ratio was determined (for the first time on MIXMOFs) through integration of selected ligands skeleton resonances from ¹³C cross polarized magic angle spinning solid-state NMR spectra collected on the as-synthesized materials. Like other poly(pyrazolate) MOFs, the four MIXMOFs are thermally stable, with decomposition temperatures between 708 and 726 K. As disclosed by N₂ adsorption at 77 K, they are micro-mesoporous materials with Brunauer-Emmett-Teller specific surface areas in the range 400-600 m²/g. A comparative study (involving also the single-ligand analogues) of CO₂ adsorption capacity, CO₂ isosteric heat of adsorption (Q_st), and CO₂/N₂ selectivity in equimolar mixtures at p = 1 bar and T = 298 K cast light on interesting trends, depending on ligand tag nature or ligand stoichiometric ratio. In particular, the amino-decorated compounds show higher Q_st values and CO₂/N₂ selectivity vs the nitro-functionalized analogues; in addition, tag "dilution" [upon passing from Zn(BPZX) to Zn(BPZ)_x(BPZX)_1-x] increases CO₂ adsorption selectivity over N₂. The simultaneous presence of amino and nitro groups is not beneficial for CO₂ uptake. Among the compounds studied, the best compromise among uptake capacity, Q_st, and CO₂/N₂ selectivity is represented by Zn(BPZ)_x(BPZNH₂)_1-x.

Amino-decorated bis(pyrazolate) metal–organic frameworks for carbon dioxide capture and green conversion into cyclic carbonates

The amino-tagged bis(pyrazolate) MOF Zn(BPZNH2) is an excellent CO₂ adsorbent and CO₂ epoxidation catalyst under green conditions.

Distinguishing Fabry-Perot from guided resonances in thin periodically-textured silicon absorbers

Periodic texturing is one of the main techniques for light-trapping in thin-film solar cells. Periodicity allows for the excitation of guided modes in the structure and, thus, largely enhances absorption. Understanding how much a guided resonance can increase the absorption is therefore of great importance. There is a common method to understand if an absorption peak is due to the excitation of a guided mode, using dispersion diagrams. In such graphs, a resonance is identified as the intersection of a guided-mode-line of a uniform waveguide (with the same optical thickness as the grating structure) with the center of a Brillouin zone of the grating. This method is unfortunately not reliable when the grating height is comparable with the thickness of the wave-guide, or when the thickness of the wave-guide is much larger than the wavelength. In this work, we provide a novel approach to calculate the contribution of a guided resonance to the total absorption in a periodic waveguide, without using the dispersion diagram. In this method, the total electric field in the periodic structure is described by its spatial frequencies, using a Fourier expansion. Fourier coefficients of the electric field were used to calculate the absorption of each diffraction order of the grating. Rigorous numerical calculations are provided to support our theoretical approach. This work paves the way for a deeper understanding of light behavior inside a periodic structure and, consequently, for developing more efficient light-trapping techniques for solar cells applications.

A Mechanical Model Lung for Hydraulic Testing of Total Liquid Ventilation Circuits

A new model lung (ML), designed to reproduce the tracheal pressure vs. fluid flow relationship in animals undergoing total liquid ventilation (TLV) trials, was developed to be used as a mock bench test for neonatal TLV circuits.

The ML is based on a linear inertance-resistance-compliance (LRC) lumped-parameter model of the respiratory system with different resistance values for inspiration (Rinsp) or expiration (Rexp). The resistant element was set up using polypropylene hollow fibres packed inside a tube. A passive oneway valve was used to control the resistance cross-section area provided for the liquid to generate different values for Rinsp or Rexp, each adjustable by regulating the active length of the respective fibre pack. The compliant element consists of a cylindrical column reservoir, in which bars of different diameter were inserted to adjust compliance (C). The inertial phenomena occurring in the central airways during TLV were reproduced by specifically dimensioned conduits into which the endotracheal tube connecting the TLV circuit to the ML was inserted. A number of elements with different inertances (L) were used to simulate different sized airways.

A linear pressure drop-to-flow rate relationship was obtained for flow rates up to 5 l/min. The measured C (0.8 to 1.3 mL cmH2O−1 kg−1), Rinsp (90 to 850 cmH2O s l−1), and Rexp (50 to 400 cmH2O s l −1) were in agreement with the literature concerning animals weighing from 1 to 12 kg. Moreover, features observed in data acquired during in vivo TLV sessions, such as pressure oscillations due to fluid inertia in the upper airways, were similarly obtained in vitro thanks to the inertial element in the ML.

A novel passive left heart platform for device testing and research

Integration of biological samples into in vitro mock loops is fundamental to simulate real device's operating conditions. We developed an in vitro platform capable of simulating the pumping function of the heart through the external pressurization of the ventricle. The system consists of a fluid-filled chamber, in which the ventricles are housed and sealed to exclude the atria from external loads. The chamber is connected to a pump that drives the motion of the ventricular walls. The aorta is connected to a systemic impedance simulator, and the left atrium to an adjustable preload. The platform reproduced physiologic hemodynamics, i.e. aortic pressures of 120/80 mmHg with 5 L/min of cardiac output, and allowed for intracardiac endoscopy. A pilot study with a left ventricular assist device (LVAD) was also performed. The LVAD was connected to the heart to investigate aortic valve functioning at different levels of support. Results were consistent with the literature, and high speed video recordings of the aortic valve allowed for the visualization of the transition between a fully opening valve and a permanently closed configuration. In conclusion, the system showed to be an effective tool for the hemodynamic assessment of devices, the simulation of surgical or transcatheter procedures and for visualization studies.

In vitro hemodynamics and valve imaging in passive beating hearts

Due to their high complexity, surgical approaches to valve repair may benefit from the use of in vitro simulators both for training and for the investigation of those measures which can lead to better clinical results. In vitro tests are intrinsically more effective when all the anatomical substructures of the valvular complexes are preserved. In this work, a mock apparatus able to house an entire explanted porcine heart and subject it to pulsatile fluid-dynamic conditions was developed, in order to enable the hemodynamic analysis of simulated surgical procedures and the imaging of the valvular structures. The mock loop's hydrodynamic design was based on an ad-hoc defined lumped-parameter model. The left ventricle of an entire swine heart was dynamically pressurized by an external computer-controlled pulse duplicator. The ascending aorta was connected to a hydraulic circuit which simulated the input impedance of the systemic circulation; a reservoir passively filled the left atrium. Accesses for endoscopic imaging were located in the apex of the left ventricle and in the aortic root. The experimental pressure and flow tracings were comparable with the typical in vivo curves; a mean flow of 3.5±0.1l pm and a mean arterial pressure of 101±2 mmHg was obtained. High-quality echographic and endoscopic video recordings demonstrated the system's excellent potential in the observation of the cardiac structures dynamics. The proposed mock loop represents a suitable in vitro system for the testing of minimally-invasive cardiovascular devices and surgical procedures for heart valve repair.

Combined use of the EPA-QUAL2E simulation model and factor analysis to assess the source apportionment of point and non point loads of nutrients to surface waters

Diffuse pollution is generally indirectly estimated by area and specific emission factors as function of land use. However in many cases these estimates were proven to be remarkably inaccurate. Aim of this study was to combine a water quality simulation model, (USEPA-QUAL2E) and Factor Analysis to increase the understanding of the water pollutants source apportionment. The study concerned two different watersheds, an upland area characterised by a very scarce agricultural use, and another area covering both the upland and the lowland physiographic regions. Particularly the lowland region is included in one of the most productive agricultural areas in Italy. By comparing instream measurements with QUAL2E simulations during dry and wet weather conditions, a good fit (errors +/-20%) was found for the dry weather scenario, whereas very poor was the model performance on the wet weather scenario. This was in the same way expected since the rainfall-driven pollutants scenario deviates significantly from QUAL2E general assumptions of constant emissions in steady state streamflow conditions. However the poor fit was also due to the scarcer reliability of the adopted non point emission estimates. Despite of approximations the model wet weather simulations enabled to estimate the non point contribution to the instream load at the rainfall event scale resolution. Such diffuse sources contribution was found around 80% in the area of extensive agricultural land use, and around 40% in the upland region. Factor Analysis applied to the instream measurements data shed light on the exchange from the groundwater to the surface water system that occurred in the upland region. The hypothesis of a groundwater contribution to the instream total load of nitrates was also supported by QUAL2E simulations that, when considering only the point loads, systematically underestimate the dry weather nitrate concentrations. The same pattern was not observed for the lowland region.

First identification and localization of a visual pigment in Hydra (Cnidaria, Hydrozoa)

The cnidarian Hydra does not possess identified photoreceptive structures or specialized cells for light detection; nevertheless, it shows a marked photosensitivity. So far no evidence has been previously reported about the localization of the proteins involved in the photoresponse. We used polyclonal antibodies and immunofluorescence microscopy on whole-mount Hydra to identify a putative rhodopsin-like protein. Our results show an immunoreactivity in the ectodermal layer of Hydra, which corresponds in position to the nervous epidermal sensory cells. These data provide the first identification of a rhodopsin-like protein in a phylogenetically old invertebrate and give a new insight into the Hydra photoreceptive response.

Ultrastructure of the pellicle of Euglena gracilis

Deep-etching technique was used to investigate the organization of the pellicle complex of Euglena gracilis. The interpretation of the images was further supported by SEM and TEM investigations. Our results mainly validate data obtained by previous freeze-fracture studies on the E and P faces of the outer cortical membrane. At the level of the ridges, the outer E fracture face is highly organized in a regular striated pattern, whereas the P inner face shows a particulate structure. However, our images reveal that this particulate organization of the P face is not limited to the ridges, but it is displayed also by the grooves. Moreover, this face shows two distinct layers, a particulate layer facing the cytoplasm and a striated layer facing the E face; these layers represent different true fracture levels of the same P face.