Computational Exploration of the Water Concentration Dependence of the Proton Transport in the Porous UiO–66(Zr)–(CO₂H)₂ Metal–Organic Framework

The UiO–66­(Zr)–(CO₂H)₂ metal–organic framework (MOF) has been recently revealed as a promising proton conducting material under humidification. Here, aMS-EVB3 molecular dynamics simulations are performed to reveal at the molecular level the structure, thermodynamics, and dynamics of the hydrated proton in three-dimensional (3D)-cages MOF as a function of the water loading. It is found that the most stable proton solvation structure corresponds to a H₇O₃⁺ cation and that a transition between this complex and a Zundel cation likely governs the proton transport in this MOF occurring via a Grotthuss-type mechanism. It is further shown that the formation of a H₂O hydrogen-bonded bridge that connects the cages occurs only at high water concentration and this creates a path allowing the excess proton to jump from one cage to another. This leads to a faster self-diffusivity of proton at high water concentration, thereby supporting the increase of the proton conductivity with the water loading as experimentally evidenced

Confinement Effects on the Ionic Liquid Dynamics in Ionosilica Ionogels: Impact of the Ionosilica Nature and the Host/Guest Ratio

Ionosilica ionogels have been lately introduced as emerging all-ionic designer materials. They consist of an ionic liquid (IL) guest trapped within a solid ionosilica support host. In this work, we investigate the influence of the (i) ionosilica nature and (ii) the ionosilica/IL ratio on the mobility of the confined IL. We report the elaboration of various ionosilica ionogels via a nonhydrolytic sol–gel process, using namely tris­(3-(trimethoxysilyl)­propyl)­amine (TTA), methyl-tris­(3-(trimethoxysilyl)­propyl)­ammonium iodide (MTTA), and tetrakis­(3-(trimethoxysilyl)-propyl)­ammonium iodide (TKTA) as ionosilica precursors, with the IL butyl-methyl imidazolium bis­(trifluoromethanesulfonyl)­imide ([BMIM] TFSI). Various ionogels were prepared from different ratios between the ionosilica host and the IL guest. The host/guest interactions, i.e., the change in the conformational contribution of the IL counter-anion, were explored by means of Raman spectroscopy. In addition, the transport properties of the confined species were probed via spin echo solid-state NMR experiments and Complex Impedance Spectroscopy (CIS) measurements. Raman experiments revealed different conformational equilibrium for the TFSI anion in the various ionosilica ionogels, with an increase in the cisoid form compared to the bulk IL due to confinement effects. The TFSI anion seems to experience different degrees of confinement and thus different interactions with the ionosilica scaffold as a function of the investigated parameters. Concomitantly, the 1H spin echo NMR and CIS measurements revealed a significantly higher ionic mobility in the materials synthesized from the tris-trialkoxysilylated ammonium precursor compared to the one synthesized from the tetra-trialkoxysilylated ammonium precursor. These results may reflect stronger host–guest interactions in the latter case related to the higher degree of the network reticulation. All these techniques give concordant results and highlight an effect of the chemical constitution of the ionosilica scaffold and the amount of confined IL on its dynamics within the network

A Joint Experimental/Computational Exploration of the Dynamics of Confined Water/Zr-Based MOFs Systems

A joint modeling (molecular dynamics simulations)/​experimental (broadband dielectric spectroscopy) approach was conducted to investigate the water adsorption in the UiO-66­(Zr) MOF, and its functionalized versions bearing acidic polar groups (−COOH or 2-COOH per linker). It was first pointed out that the proton conduction measured at room temperature increases with (i) the water uptake and (ii) the concentration of the free acidic carboxylic functions. This trend was further analyzed in light of the preferential arrangements of water within the pores of each MOF as elucidated by molecular dynamics simulations. Indeed, it was revealed that the guest molecules preferentially (i) form interconnected clusters within the UiO-66­(Zr)­s cages and generate a H-bond network responsible for the proton propagation and (ii) strongly interact with the −COOH grafted functions, resulting in the creation of additional charge carriers in the case of the hydrated functionalized solids. Broadband dielectric spectroscopy shed light on how these water configurations impact the local dynamics of both the water molecules and the MOF frameworks. The dielectric relaxation investigation evidenced the existence of one or two relaxation processes, depending on the nature of the UiO-66­(Zr) framework and its hydration level. Compared to the dielectric behavior of water confined in a large variety of media, it was thus concluded that the fastest process corresponds to the dynamics of the water molecules forming clusters, while the slowest process is due to the concerted local motion of water/ligand entities

Anticancer and Antioxidant Activities of the Peptide Fraction from Algae Protein Waste

Algae protein waste is a byproduct during production of algae essence from Chlorella vulgaris. There is no known report on the anticancer peptides derived from the microalgae protein waste. In this paper, the peptide fraction isolated from pepsin hydrolysate of algae protein waste had strong dose-dependent antiproliferation and induced a post-G1 cell cycle arrest in AGS cells; however, no cytotoxicity was observed in WI-38 lung fibroblasts cells in vitro. The peptide fraction also revealed much better antioxidant activity toward peroxyl radicals and LDL than those of Trolox. Among these peptides, a potent antiproliferative, antioxidant, and NO-production-inhibiting hendecapeptide was isolated, and its amino acid sequence was VECYGPNRPQF. These results demonstrate that inexpensive algae protein waste could be a new alternative to produce anticancer peptides

Caffeine Confinement into a Series of Functionalized Porous Zirconium MOFs: A Joint Experimental/Modeling Exploration

A multitechnique approach was conducted to investigate the confinement of caffeine in a series of UiO-66­(Zr)-type MOFs, functionalized with −H, −NH₂, −Br, and −2OH groups. DFT calculations were first undertaken to elucidate the preferential geometries of the drug within the pores and the resulting drug/host framework interactions. It was shown that the caffeine molecules are preferentially located in the smaller cages, giving rise to only weak interactions with the function groups grafted on the organic linker. These host/guest interactions were concomitantly probed by advanced 1D and 2D high-field/ultrafast MAS NMR and FTIR spectroscopies, which allowed us to not only validate the DFT predictions but also to bring complementary insight into the nature of the interacting sites of both the caffeine and the MOFs. Dielectric relaxation measurements further revealed significant modifications of the ligand dynamics upon the drug encapsulation for all UiO-66­(Zr) solids. It was demonstrated that the perturbation of the ligand flip strongly depends on the nature of the grafted function. While the dynamics of the ligand is slightly enhanced in the case of the −NH₂ form, it is significantly slower for the −Br analogue. Such specific behaviors were then interpreted in light of the conclusions drawn from the DFT calculations and NMR observations

Structure and Dynamics of the Functionalized MOF Type UiO-66(Zr): NMR and Dielectric Relaxation Spectroscopies Coupled with DFT Calculations

Advanced one- and two-dimensional high-field and ultrafast MAS NMR measurements have been conducted in tandem with DFT calculations for the NMR parameters to deeply characterize the local environment and the long-range structure order of the porous metal–organic framework (MOF) type UiO-66­(Zr) (UiO for University of Oslo) functionalized by a series of polar −Br, −2OH, and −NH₂ groups. Such an innovative combining approach applied to the complex architecture of MOFs has been revealed successful not only to unambiguously assign all the NMR signals to the corresponding crystallographic sites but also to validate the crystal structures for each functionalized material that were only predicted so far. A further step consisted of probing the impact of the grafted functions on the ligand dynamics of these MOFs by means of dielectric relaxation spectroscopy measurements. It has been evidenced that the rotational motion of the organic linker requires overpassing an energy barrier that strongly depends on the functional groups, the −NH₂ functionalized version implying the highest activation energy. Such a finding was further explained by the relatively strong intraframework interactions which take place between the grafted function and the inorganic node as suggested by the analysis of the corresponding simulated crystal structure

Adsorption of Benzene in the Cation-Containing MOFs MIL-141

The adsorption of benzene in the cation-containing metal–organic framework (MOF) MIL-141­(Cs) was explored by manometry measurements coupled with Monte Carlo simulations. This joint experimental/modeling approach demonstrates that this solid shows a high affinity for benzene that does not result from a direct interaction between the guest molecules and the Cs⁺ cations, in contrast to what is commonly observed in zeolites. This behavior was attributed to the high degree of confinement of Cs⁺, which prevents any cation detrapping upon adsorption, as revealed by dielectric relaxation spectroscopy and molecular dynamics simulations. This peculiar adsorption behavior is further discussed in relation to that of other alkali extraframework cations including Li⁺, Na⁺, K⁺, and Rb⁺

Iodine Capture by Hofmann-Type Clathrate Ni^II(pz)[Ni^II(CN)₄]

The thermally stable Hofmann-type clathrate framework Ni^II(pz)­[Ni^II(CN)₄] (pz = pyrazine) was investigated for the efficient and reversible sorption of iodine (I₂) in the gaseous phase and in solution with a maximum adsorption capacity of 1 mol of I₂ per 1 mol of Ni^II(pz)­[Ni^II(CN)₄] in solution

Series of Porous 3-D Coordination Polymers Based on Iron(III) and Porphyrin Derivatives

A new series of 3-D coordination polymers based on iron(III) and nickel(II) tetracarboxylate porphyrin (Ni-TCPP) have been produced using solvothermal conditions. MIL-141(A) solids (MIL stands for Material from Institut Lavoisier), formulated Fe(Ni-TCPP)A•(DMF)_<i>x </i>(A = Li, Na, K, Rb, Cs, DMF = N,N-dimethylformamide, <i>x</i> ∼ 3), are built up from three anionic interpenetrated PtS-type networks charge-balanced by alkali cations (A) entrapped inside the pores. MIL-141(A) thus includes three types of cations, two of which may act as coordinatively unsaturated metal sites (Ni²⁺ and A⁺). These solids all present a permanent porosity with a reasonably high surface area (S_BET = 510–860 m² g^–1) as well as some structural flexibility toward adsorption/desorption processes, modulated in both cases by the nature of A. Thermally Stimulated Current (TSC) measurements indicated that alkali cations are rather homogeneously distributed within the pores, while their interaction with the framework is stronger in MIL-141(A) than in the analogous cation-containing Faujasites X and Y zeolites. Finally, high pressure adsorption isotherms of N₂ and O₂ were measured. Whereas alkali ion-containing zeolites adsorb selectively N₂ toward O₂, the opposite is observed for MIL-141(A). This result is interpreted in light of the TSC data and the possible preferential interaction of the porphyrinic linker with O₂

Series of Porous 3-D Coordination Polymers Based on Iron(III) and Porphyrin Derivatives

A new series of 3-D coordination polymers based on iron(III) and nickel(II) tetracarboxylate porphyrin (Ni-TCPP) have been produced using solvothermal conditions. MIL-141(A) solids (MIL stands for Material from Institut Lavoisier), formulated Fe(Ni-TCPP)A•(DMF)_<i>x </i>(A = Li, Na, K, Rb, Cs, DMF = N,N-dimethylformamide, <i>x</i> ∼ 3), are built up from three anionic interpenetrated PtS-type networks charge-balanced by alkali cations (A) entrapped inside the pores. MIL-141(A) thus includes three types of cations, two of which may act as coordinatively unsaturated metal sites (Ni²⁺ and A⁺). These solids all present a permanent porosity with a reasonably high surface area (S_BET = 510–860 m² g^–1) as well as some structural flexibility toward adsorption/desorption processes, modulated in both cases by the nature of A. Thermally Stimulated Current (TSC) measurements indicated that alkali cations are rather homogeneously distributed within the pores, while their interaction with the framework is stronger in MIL-141(A) than in the analogous cation-containing Faujasites X and Y zeolites. Finally, high pressure adsorption isotherms of N₂ and O₂ were measured. Whereas alkali ion-containing zeolites adsorb selectively N₂ toward O₂, the opposite is observed for MIL-141(A). This result is interpreted in light of the TSC data and the possible preferential interaction of the porphyrinic linker with O₂