SO2 Capture at Low Pressure in a Prototypical MIL-53 Aluminum MOF Family: The Influence of Pore Expansion.

Not only is excellent performance in SO2 capture by porous materials (uptake above 17 mmol g-1) relevant, but also finding a correlation between the architecture changes into a family and their SO2 adsorption is very useful. In this contribution, we studied the SO2 adsorption behavior (at very low pressure) of an Al(III)-MOF family that shares the pore architecture of MIL-53. The results indicate an inversely proportional trend for the SO2 capture and pore expansion, since by increasing the length of the channel pore, the SO2 uptake gradually decreases. In addition, this trend is clearly observed in the heat of adsorption, which describes the interaction between the SO2 molecule and the µ-OH functional group. These finding are supported by experimental analysis and computational studies.

Synthesis of Pyrrolo[3,4-b]pyridin-5-ones via Ugi-Zhu Reaction and In Vitro-In Silico Studies against Breast Carcinoma.

An Ugi-Zhu three-component reaction (UZ-3CR) coupled in a one-pot manner to a cascade process (N-acylation/aza Diels-Alder cycloaddition/decarboxylation/dehydration) was performed to synthesize a series of pyrrolo[3,4-b]pyridin-5-ones in 20% to 92% overall yields using ytterbium triflate as a catalyst, toluene as a solvent, and microwaves as a heat source. The synthesized molecules were evaluated in vitro against breast cancer cell lines MDA-MB-231 and MCF-7, finding that compound 1f, at a concentration of 6.25 µM, exhibited a potential cytotoxic effect. Then, to understand the interactions between synthesized compounds and the main proteins related to the cancer cell lines, docking studies were performed on the serine/threonine kinase 1 (AKT1) and Orexetine type 2 receptor (Ox2R), finding moderate to strong binding energies, which matched accurately with the in vitro results. Additionally, molecular dynamics were performed between proteins related to the studied cell lines and the three best ligands.

Evaluation of the catalytic activity of Zn-MOF-74 for the alcoholysis of cyclohexene oxide.

In the present work, nanocrystalline Zn-MOF-74 is shown to be a heterogeneous catalyst for the acid-catalyzed ring-opening alcoholysis of cyclohexene oxide. The results corroborated that accessible open metal sites within the material are critical conditions (Zn(ii) Lewis acid sites) for this reaction. Zn-MOF-74 was tested at three different temperatures (30, 40, and 50 °C) for the alcoholysis reaction. Furthermore, the cyclohexene oxide conversion was 94% in less than two days. A comparison of the catalytic activity with different crystal sizes of Zn-MOF-74 and the homogenous phase, zinc acetate, was conducted. Zn-MOF-74 exhibited excellent catalytic cyclability for three cycles without losing its activity. The material showed chemical stability by retaining its crystalline structure after the reaction and cyclability process.

MFM-300(Sc): a chemically stable Sc(III)-based MOF material for multiple applications.

Developing robust multifunctional metal-organic frameworks (MOFs) is the key to advancing the further deployment of MOFs into relevant applications. Since the first report of MFM-300(Sc) (MFM = Manchester Framework Material, formerly known as NOTT-400), the development of applications of this robust microporous MOF has only grown. In this review, a summary of the applications of MFM-300(Sc), as well as some emerging advanced applications, have been discussed. The adsorption properties of MFM-300(Sc) are presented systematically. Particularly, this contribution is focused on acid and corrosive gas adsorption. In addition, recent applications for catalysis based on the outstanding hemilabile Sc-O bond character are highlighted. Finally, some new research areas are introduced, such as host-guest chemistry and biomedical applications. This highlight aims to showcase the recent advances and the potential for developing new applications of this promising material.

Pseudo-multicomponent reactions.

Classical multicomponent reactions (MCRs) are domino-type one-pot processes in which three or more different reactants are combined sequentially in the same reactor to synthesize compounds containing all or almost all atoms coming from the reactants. Besides, pseudo-MCRs are also domino-type one-pot processes involving combinations of at least three reactants but in which at least one of them takes part in two or more reaction steps. In consequence, the products synthesized through pseudo-MCRs contain also all or almost all atoms but coming from two or more identical reactants. Thus, pseudo-MCRs differ from classical MCRs because the first ones appear to involve an assembly of a higher number of different components than those that are being truly assembled. However, pseudo-MCRs are also useful synthetic tools to generate libraries of complex compounds in few experimental steps, and although the repeated reactants may make them appear less diverse than classical MCRs, this can be offset by the higher number of reactants that can participate in this type of reaction. Overall, there are two types of pseudo-MCRs. The first are those in which the duplicated reagents participate in different steps of the corresponding reaction mechanism. The second kind of pseudo-MCRs are those in which one or more components react simultaneously with a main reagent containing two or more identical functional groups. These latter are known as repetitive pseudo-MCRs. Thus, the aim of the present review is to cover for the first time selected works mainly published in the last two decades about pseudo-MCRs and their repetitive versions toward the synthesis of novel, complex, and highly symmetrical molecules, often including their interesting applications in various fields of science and technology. The manuscript has been categorized considering the number of reagents participating in the corresponding pseudo-MCRs, aiming to give readers novel insights for their future investigations.

Synthesis of New Polyheterocyclic Pyrrolo[3,4-b]pyridin-5-ones via an Ugi-Zhu/Cascade/Click Strategy.

A diversity-oriented synthesis (DOS) of two new polyheterocyclic compounds was performed via an Ugi-Zhu/cascade (N-acylation/aza Diels-Alder cycloaddition/decarboxylation/dehydration)/click strategy, both step-by-step to optimize all involved experimental stages, and in one pot manner to evaluate the scope and sustainability of this polyheterocyclic-focused synthetic strategy. In both ways, the yields were excellent, considering the high number of bonds formed with release of only one carbon dioxide and two molecules of water. The Ugi-Zhu reaction was carried out using the 4-formylbenzonitrile as orthogonal reagent, where the formyl group was first transformed into the pyrrolo[3,4-b]pyridin-5-one core, and then the remaining nitrile group was further converted into two different nitrogen-containing polyheterocycles, both via click-type cycloadditions. The first one used sodium azide to obtain the corresponding 5-substituted-1H-tetrazolyl-pyrrolo[3,4-b]pyridin-5-one, and the second one with dicyandiamide to synthesize the 2,4-diamino-1,3,5-triazine-pyrrolo[3,4-b]pyridin-5-one. Both synthesized compounds may be used for further in vitro and in silico studies because they contain more than two heterocyclic moieties of high interest in medicinal chemistry, as well as in optics due to their high π-conjugation.

Synthesis of bis-furyl-pyrrolo[3,4-b]pyridin-5-ones via Ugi-Zhu reaction and in vitro activity assays against human SARS-CoV-2 and in silico studies on its main proteins.

An Ugi-Zhu three-component reaction (UZ-3CR) coupled in one pot manner to a cascade process (N-acylation/aza Diels-Alder cycloaddition/decarboxylation/dehydration) was performed to synthesize a series of bis-furyl-pyrrolo[3,4-b]pyridin-5-ones in 45 to 82% overall yields using ytterbium triflate as a catalyst, toluene as a solvent, and microwaves as a heat source. The synthesized molecules were evaluated in vitro against human SARS-CoV-2 through a time-of-addition approach, finding that compound 1e, at a concentration of 10.0 µM, exhibited a significant reduction at the initial infection stages, thus showing prophylactic potential. On the other hand, it was found that compound 1d, at the same concentration, was significantly active when applied post-infection, thus exhibiting a therapeutic profile. Moreover, compound 1f showed both, prophylactic and therapeutic activity. Then, to understand interactions between synthesized compounds and the main proteins related to the virus, docking studies were performed on spike-glycoprotein, main-protease, and Nsp3 protein, finding moderate to strong binding energies, matching accurately with the in vitro results. Additionally, a pharmacophore model was computed behind further rational drug design.

SO2 capture enhancement due to confined methanol within MIL-53(Al)-TDC.

The SO2 capture performance of MIL-53(Al)-TDC was optimised by confining a small amount of MeOH within its pores (MeOH@MIL-53(Al)-TDC). In comparison with fully activated MIL-53(Al)-TDC, MeOH@MIL-53(Al)-TDC shows a 39% higher SO2 capture capacity. Monte Carlo simulations revealed that such an enhancement is associated with an increase in the degree of confinement via the SO2 molecules resulting from the formation of a lump (MeOH molecules) in the vicinity of the µ-OH groups.

Sulfur Dioxide Capture in Metal-Organic Frameworks, Metal-Organic Cages, and Porous Organic Cages.

Capture, storage and subsequent controlled release or transformation of sulfur dioxide (SO2 ) in mild conditions is still a challenge in the material science field. Recent advances in the use of porous materials have demonstrated good SO2 capture, particularly in metal-organic frameworks (MOFs), metal-organic cages (MOCs), and porous organic cages (POCs). The striking feature of these porous materials is the high SO2 uptake capacity in reversible settings. A partially fluorinated MIL-101(Cr) is stand-alone material with the highest SO2 uptake in chemically stable MOFs. Likewise, metal-free adsorbents like POCs exhibits a reversible SO2 uptake behavior. The SO2 adsorption characteristics of these three structurally and functionally unique adsorbent systems are highly dependent on the binding sites and mode of binding of SO2 molecules. This Review has highlighted the preferential binding sites in these materials to give a full perspective on the field. We anticipate that it will offer valuable information on the progress made towards improving SO2 capture by hybrid systems.

Fluorometric detection of iodine by MIL-53(Al)-TDC.

The fluorescent properties of MIL-53(Al)-TDC are drastically changed due to the presence of iodine, even in small quantities, as a result of an energy transfer process from the host material (MIL-53(Al)-TDC) to the guest molecule (I2). While MIL-53(Al)-TDC's emission spectrum shows a weak and broad band, after I2 adsorption, it exhibits well-resolved and long-lasting emission lines, which could be exploited for iodine detection. Density Functional Theory periodical calculations demonstrated that in the most stable MIL-53(Al)-TDCI2 configuration, the I2 molecule is bonded mainly by an O-HI hydrogen bond. The QTAIM showed that other non-covalent interactions also provided stability to MIL-53(Al)-TDCI2. The electrostatic potential analysis indicated that the I2 molecule adsorption occurs by a combination of specific interactions with a strong electrostatic contribution and weak interactions. These results postulate fluorescent MIL-53(Al)-TDC as an efficient I2 detector (potentially for radioactive I2), using a simple fluorimetric test.

Bottleneck Effect Explained by Le Bail Refinements: Structure Transformation of Mg-CUK-1 by Confining H2O Molecules.

The structure transformation of Mg-CUK-1 due to the confinement of H2O molecules was investigated. Powder X-ray diffraction (PXRD) patterns were collected at different H2O loadings and the cell parameters of the H2O-loaded Mg-CUK-1 material were determined by the Le Bail strategy refinements. A bottleneck effect was observed when one hydrogen-bonded H2O molecule per unit cell (18% relative humidity (RH)) was confined within Mg-CUK-1, confirming the increase in the CO2 capture for Mg-CUK-1.

Partially Reversible H2S Adsorption by MFM-300(Sc): Formation of Polysulfides.

The metal-organic framework (MOF)-type MFM-300(Sc) exhibits a combined physisorption and chemisorption capture of H2S, leading to a high uptake (16.55 mmol g-1) associated with high structural stability. The irreversible chemisorbed sulfur species were identified as low-order polysulfide (n = 2) species. The isostructural MFM-300(In) was demonstrated to promote the formation of different polysulfide species, paving the way toward a new methodology to incorporate polysulfides within MOFs for the generation of novel MOF-lithium/sulfur batteries.

Confined benzene within InOF-1: contrasting CO2 and SO2 capture behaviours.

The confinement of small amounts of benzene in InOF-1 (Bz@InOF-1) shows a contradictory behavior in the capture of CO2 and SO2. While the capture of CO2 is increased 1.6 times, compared to the pristine material, the capture of SO2 shows a considerable decrease. To elucidate these behaviors, the interactions of CO2 and SO2 with Bz@InOF-1 were studied by DFT periodical calculations postulating a plausible explanation: (a) in the case of benzene and CO2, these molecules do not compete for the preferential adsorption sites within InOF-1, providing a cooperative CO2 capture enhancement and (b) benzene and SO2 strongly compete for these preferential adsorption sites inside the MOF material, reducing the total SO2 capture.

Sulfadiazine hosted in MIL-53(Al) as a biocide topical delivery system.

Sulfadiazine (SDZ), a bacteriostatic agent, was hosted in a metal-organic framework, specifically in MIL-53(Al) and modified-zinc MIL-53(Al,Zn). Materials were characterized structural, and texturally. Both hosts loaded sulfadiazine but they were differenced regarding the release of sulfadiazine. The presence of zinc plays a significant role to the modulation of sulfadiazine-MOF interactions. Release of sulfadiazine from sulfadiazine@MOFs was monitored in vitro and ex vivo conditions. A kinetic release model is proposed for in vitro sulfadiazine release. Remarkably, the materials did not show cytotoxicity against eukaryote cells.

Synthesis of Pyrrolo[3,4-b]pyridin-5-ones via Multicomponent Reactions and In Vitro-In Silico Studies Against SiHa, HeLa, and CaSki Human Cervical Carcinoma Cell Lines.

A series of 12 polysubstituted pyrrolo[3,4-b]pyridin-5-ones were synthesized via a one-pot cascade process (Ugi-3CR/aza Diels-Alder/N-acylation/decarboxylation/dehydration) and studied in vitro using human epithelial cervical carcinoma SiHa, HeLa, and CaSki cell line cultures. Three compounds of the series exhibited significative cytotoxicity against the three cell lines, with HeLa being the most sensitive one. Then, based on these results, in silico studies by docking techniques were performed using Paclitaxel as a reference and αß-tubulin as the selected biological target. Worth highlighting is that strong hydrophobic interactions were observed between the three active molecules and the reference drug Paclitaxel, to the αß-tubulin. In consequence, it was determined that hydrophobic-aromatic moieties of bioactive compounds and Paclitaxel play a key role in making stronger interactions to the ligand-target complex. A quantitative structure activity relationship (QSAR) study revealed that the six membered rings are the most significant molecular frameworks, being present in all proposed models for the in vitro-studied cell lines. Finally, also from the docking interpretation, a ligand-based pharmacophore model is proposed in order to find further potential polyheterocyclic candidates to bind stronger to the αß-tubulin.

Relevance of hydrogen bonding in CO2 capture enhancement within InOF-1: an energy and vibrational analysis.

The enhancement of CO2 capture due to the confinement of polar molecules within InOF-1 was previously demonstrated. In particular, the presence of MeOH produced 1.30-fold increase in the total CO2 capture. This was explained before with the presence of hydrogen bonds. However, a detailed analysis of the hydrogen bonds among µ2-OH functional groups, MeOH molecules and CO2 molecules was not elucidated; moreover, the possible mechanisms that could explain the enhancement of the capture were also not explained. In this investigation, the density functional theory (DFT) periodic calculations and experimental in situ DRIFTS results allowed us to postulate four plausible CO2 adsorption mechanisms for MeOH-functionalised InOF-1, which described the hydrogen bonds and rationalised the nature of the CO2 capture enhancement.

CO2 capture enhancement for InOF-1: confinement of 2-propanol.

The 2-propanol (i-PrOH) adsorption properties of InOF-1 are investigated along with the confinement of small amounts of this alcohol to enhance the CO2 capture for i-PrOH@InOF-1 (1.25-fold improvement compared to pristine InOF-1). InOF-1 exhibited a high affinity towards i-PrOH, experimentally quantified by ΔHads (-55 kJ mol-1), and DFT geometry optimisations showed strong hydrogen bonding between O(i-PrOH) and H(µ2-OH). Quantum chemical models demonstrated that the CO2 capture increase for i-PrOH@InOF-1 was due to a decrease in the void surface of InOF-1 (bottleneck effect), and the formation of essential hydrogen bonds of CO2 with i-PrOH and with the hydroxo functional group (µ2-OH) of InOF-1.

Outstanding reversible H2S capture by an Al(iii)-based MOF.

The MOF-type MIL-53(Al)-TDC was demonstrated to be an optimal adsorbent for H2S capture combining an unprecedented uptake at room temperature, excellent cyclability and low-temperature regeneration.

Confined toluene within InOF-1: CO2 capture enhancement.

The toluene adsorption properties of InOF-1 are studied along with the confinement of small amounts of this non-polar molecule revealing a 1.38-fold increase in CO2 capture, from 5.26 wt% under anhydrous conditions to 7.28 wt% with a 1.5 wt% of pre-confined toluene at 298 K. The InOF-1 affinity towards toluene was experimentally quantified by ΔH ads (-46.81 kJ mol-1). InOF-1 is shown to be a promising material for CO2 capture under industrial conditions. Computational calculations (DFT and QTAIM) and DRIFTs in situ experiments provided a possible explanation for the experimental CO2 capture enhancement by showing how the toluene molecule is confined within InOF-1, which constructed a "bottleneck effect".

Humidity-induced CO2 capture enhancement in Mg-CUK-1.

Kinetic CO2 adsorption measurements in the water-stable and permanently microporous Metal-organic framework material, Mg-CUK-1, reveal a 1.8-fold increase in CO2 capture from 4.6 wt% to 8.5 wt% in the presence of 18% relative humidity. Thermodynamic CO2 uptake experiments corroborate this enhancement effect, while grand canonical Monte Carlo simulations also support the phenomenon of a humidity-induced increase in the CO2 sorption capacity in Mg-CUK-1. Molecular simulations were implemented to gain insight into the microscopic adsorption mechanism responsible for the observed CO2 sorption enhancement. These simulations indicate that the cause of increasing CO2 adsorption enthalpy in the presence of H2O is due to favorable intermolecular interactions between the co-adsorbates confined within the micropores of Mg-CUK-1.