Guillaume Maurin

Effect of the organic functionalization of flexible MOFs on the adsorption of CO2

The adsorption of CO2 by a series of functionalized flexible MIL-53(Fe) solids has been evaluated through a combination of in situ X-ray power diffraction, adsorption calorimetry, IR spectroscopy and computer modelling. It appears that (i) strongly polar groups maintain the nonporous structure in its closed form due to strong intra-framework interactions and (ii) less polar functional groups allow only a modulation of the CO2–framework interactions, in some cases with a disappearance of the initial intra-framework μ2-OH⋯X hydrogen bonds, but do not interact directly with the CO2 molecules.

Adsorption of light hydrocarbons in the flexible MIL-53(Cr) and rigid MIL-47(V) metal–organic frameworks: a combination of molecular simulations and microcalorimetry/gravimetry measurements

The adsorption of short linear alkanes has been explored in the highly flexible MIL-53(Cr) porous metal-organic framework by means of molecular simulations based on configurational bias grand canonical Monte Carlo. The unusual shape of the adsorption isotherms with the existence of steps has been successfully modelled by creating a (narrow pore, large pore) phase mixture domain, the composition of which varies with pressure. A further step consisted of combining our computational approach with several experimental tools including microcalorimetry, gravimetry and in situ X-ray diffraction, to fully characterize the adsorption behaviour of the isostructural MIL-47(V) rigid MOF, i.e. the preferential arrangement of each type of alkane inside the pores and the resulting interaction energy. Finally, relationships are established between the adsorption enthalpies and both alkyl chain length and polarisability of the alkanes that can be further utilised to predict the energetics of the adsorption process for longer alkane chains.

Probing the adsorption performance of the hybrid porous MIL-68(Al): a synergic combination of experimental and modelling tools

A joint experimental/modelling approach has been conducted to get some insight into the microscopic mechanism in play for a series of small gas molecules including CH4, CO2, N2 and H2S in the porous aluminium-based (Al3+) terephthalate MIL-68 solid containing two distinct pore channels (MIL: Materials of Institute Lavoisier). A further step consisted of predicting the separation performances of this material for the CO2/CH4 and CO2/N2 mixtures that are compared to the other MOFs reported so far in the literature. The theoretical impact of the functionalization of the organic linker via amino groups on the selectivity of this hybrid material for these gas mixtures is then pointed out. Finally, the stability of the solid upon H2S adsorption which is commonly present in the raw natural gas is confirmed.

Acid-functionalized UiO-66(Zr) MOFs and their evolution after intra-framework cross-linking: structural features and sorption properties

The functionalization of metal–organic frameworks (MOFs) with free carboxylic groups is naturally difficult due to their potential coordination with metal ions. The impact of functionalizing the archetypical metal organic framework UiO-66(Zr) with free pending carboxylic groups was thus studied by a multi-technique approach. First, an environmentally friendly water synthesis route was developed to produce UiO-66(Zr)–(COOH)x (x = 1, 2) and the kinetics of crystallization was studied by in situ energy dispersive X-ray diffraction. In a second step, the structural features were studied by temperature-dependent X-ray diffractometry and further characterized by density functional theory calculations and solid-state nuclear magnetic resonance spectroscopy. The gas sorption properties, acidity and conductivity features were respectively assessed by gas isotherms and calorimetry, infrared spectroscopy and complex impedance spectroscopy. These data show the noticeable influence of the introduced acidic groups. Finally, it was shown that the thermal treatment of such solids leads to an intra-framework cross-linking associated with the formation of anhydride bridges, as evidenced by FTIR and solid-state NMR, and modelled by DFT simulations. These species have a strong impact on the acidity, but a limited effect on gas sorption properties at room temperature. The reversibility of the carboxylic acids to anhydride transformation was also assessed.

Design of Hydrophilic Metal Organic Framework Water Adsorbents for Heat Reallocation

A new hydrothermally stable Al polycarboxylate metal-organic framework (MOF) based on a heteroatom bio-derived aromatic spacer is designed through a template-free green synthesis process. It appears that in some test conditions this MOF outperforms the heat reallocation performances of commercial SAPO-34.

Towards an Improved anti-HIV Activity of NRTI via Metal–Organic Frameworks Nanoparticles

Nanoscale mesoporous iron carboxylates metal-organic frameworks (nanoMOFs) have recently emerged as promising platforms for drug delivery, showing biodegradability, biocompatibility and important loading capability of challenging highly water-soluble drugs such as azidothymidine tryphosphate (AZT-TP). In this study, nanoMOFs made of iron trimesate (MIL-100) were able to act as efficient molecular sponges, quickly adsorbing up to 24 wt% AZT-TP with entrapment efficiencies close to 100%, without perturbation of the supramolecular crystalline organization. These data are in agreement with molecular modelling predictions, indicating maximal loadings of 33 wt% and preferential location of the drug in the large cages. Spectrophotometry, isothermal titration calorimetry, and solid state NMR investigations enable to gain insight on the mechanism of interaction of AZT and AZT-TP with the nanoMOFs, pointing out the crucial role of phosphates strongly coordinating with the unsaturated iron(III) sites. Finally, contrarily to the free AZT-TP, the loaded nanoparticles efficiently penetrate and release their cargo of active triphosphorylated AZT inside major HIV target cells, efficiently protecting against HIV infection.

Estimation of the breathing energy of flexible MOFs by combining TGA and DSC techniques.

The energetics of the breathing phenomenon of MIL-53(Cr) have been estimated through a combined TGA and DSC water desorption analysis of the rigid MIL-47(V) and flexible MIL-53(Cr) and MIL-53(Fe) systems.

WATER AND ETHANOL DESORPTION IN THE FLEXIBLE METAL ORGANIC FRAMEWORKS, MIL-53 (Cr, Fe), INVESTIGATED BY COMPLEX IMPEDANCE SPECTROCOPY AND DENSITY FUNCTIONAL THEORY CALCULATIONS

The breathing behaviour of MIL-53(Cr) and MIL-53(Fe) upon water and ethanol desorption has been investigated by combining complementary experimental techniques including ThermoGravimetry Analysis (TGA), Differential Scanning Calorimetry (DSC) and Complex Impedance Spectroscopy (CIS). It was shown that two stages of solvent departure are involved in the desorption process, as revealed by (i) a change of the weight loss gradient in the TGA curve, (ii) the existence of a second endothermic peak in the DSC signal and (iii) a sudden drop and/or profile change of the ac conductivity in CIS. All these features are observed around a typical temperature T(c), for which the framework contractions, caused by the solvent desorption, occur. Moreover, it is shown that these modifications are more pronounced when the magnitude of the breathing is higher, as illustrated by the comparison of the water/MIL-53(Cr), ethanol/MIL-53(Cr) and water/MIL-53(Fe) systems. CIS data were further analyzed in the light of DFT calculations which provided the preferential arrangements of the molecules within the pores and the resulting host/guest interactions. It could then be proposed that (i) the polarization conductivity results from the local re-orientation of the μ(2)-OH dipoles bonded to the metal atom from the hybrid solid, i.e. Fe or Cr, and (ii) that dc conductivity, which can be ascribed to a proton propagation via a Grotthus mechanism, is favoured when the solvent molecules form strong hydrogen bonds between each other.

Impact of phosphorylation on the encapsulation of nucleoside analogues within porous iron(III) metal–organic framework MIL-100(Fe) nanoparticles

Encapsulation of azidothymidine (AZT) or its phosphorylated derivatives (AZT-MP and AZT-TP) has been performed using nanoparticles of the porous crystalline iron(iii) trimesate metal-organic framework MIL-100(Fe). The number of phosphate groups per nucleoside analogue has a high impact on the drug loading capacity, and their interaction with the Lewis acid sites from the nanoMOFs is also discussed through a combination of techniques such as UV-vis absorption, circular dichroism, isothermal titration calorimetry, HPLC and molecular simulations. Finally, the effect of the differences in terms of host-guest interactions is discussed through the release in physiological buffers of AZT, AZT-MP and AZT-TP. New perspectives for the nanoencapsulation of monophosphorylated nucleoside analogues for effective anti-cancer and anti-viral therapies are then discussed.

Selective nitrogen capture by porous hybrid materials containing accessible transition metal ion sites

Selective dinitrogen binding to transition metal ions mainly covers two strategic domains: biological nitrogen fixation catalysed by metalloenzyme nitrogenases, and adsorptive purification of natural gas and air. Many transition metal-dinitrogen complexes have been envisaged for biomimetic nitrogen fixation to produce ammonia. Inspired by this concept, here we report mesoporous metal-organic framework materials containing accessible Cr(III) sites, able to thermodynamically capture N2 over CH4 and O2. This fundamental study integrating advanced experimental and computational tools confirmed that the separation mechanism for both N2/CH4 and N2/O2 gas mixtures is driven by the presence of these unsaturated Cr(III) sites that allows a much stronger binding of N2 over the two other gases. Besides the potential breakthrough in adsorption-based technologies, this proof of concept could open new horizons to address several challenges in chemistry, including the design of heterogeneous biomimetic catalysts through nitrogen fixation.