Naseem A. Ramsahye

Flexible Porous Metal-Organic Frameworks for a Controlled Drug Delivery

Flexible nanoporous chromium or iron terephtalates (BDC) MIL-53(Cr, Fe) or M(OH)[BDC] have been used as matrices for the adsorption and in vitro drug delivery of Ibuprofen (or alpha- p-isobutylphenylpropionic acid). Both MIL-53(Cr) and MIL-53(Fe) solids adsorb around 20 wt % of Ibuprofen (Ibuprofen/dehydrated MIL-53 molar ratio = 0.22(1)), indicating that the amount of inserted drug does not depend on the metal (Cr, Fe) constitutive of the hybrid framework. Structural and spectroscopic characterizations are provided for the solid filled with Ibuprofen. In each case, the very slow and complete delivery of Ibuprofen was achieved under physiological conditions after 3 weeks with a predictable zero-order kinetics, which highlights the unique properties of flexible hybrid solids for adapting their pore opening to optimize the drug-matrix interactions.

The Structure of the Aluminum Fumarate Metal–Organic Framework A520

The synthesis of the commercially available aluminum fumarate sample A520 has been optimized and its structure analyzed through a combination of powder diffraction, solid-state NMR spectroscopy, molecular simulation, IR spectroscopy, and thermal analysis. A520 is an analogue of the MIL-53(Al)-BDC solid, but with a more rigid behavior. The differences between the commercial and the optimized samples in terms of defects have been investigated by in situ IR spectroscopy and correlated to their catalytic activity for ethanol dehydration.

Microscopic Model of the Metal-Organic Framework/Polymer Interface: A First Step toward Understanding the Compatibility in Mixed Matrix Membranes

An innovative computational methodology integrating density functional theory calculations and force field-based molecular dynamics simulations was developed to provide a first microscopic model of the interactions at the metal-organic framework (MOF) surface/polymer interface. This was applied to the case of the composite formed by the polymer of intrinsic microporosity, PIM-1, and the zeolitic imidazolate framework, ZIF-8, as a model system. We found that the structure of the composite at the interface is the result of both the chemical affinity between PIM-1 and ZIF-8 and the rigidity of the polymer. Specifically, there is a preferential interaction between the -CN groups of PIM-1 and the NH terminal functions of the organic linker at the ZIF-8 surface. Additionally, the resulting conformation of the polymer gives rise to interfacial microvoids at the vicinity of the MOF surface. The porosity, rigidity, and density of the interfacial polymer were analyzed and compared to those for the bulk polymer. It was shown that the polymer still feels the impact of the MOF surface even at long distances above 15-20 Å. Further, both the polydispersity of the polymer and the flexibility of the MOF surface were revealed to only slightly affect the properties of the MOF/interface. This work, which delivers a microscopic picture of the MOF surface/polymer interactions at the interface, would lead, in turn, to the understanding of the compatibility in MOF-based mixed-matrix membranes.

On the breathing effect of a metal–organic framework upon CO2 adsorption: Monte Carlo compared to microcalorimetry experiments

Grand Canonical Monte Carlo simulations have explained the breathing of a metal-organic framework upon CO(2) adsorption, first suggested by microcalorimetry.

A phase transformable ultrastable titanium-carboxylate framework for photoconduction

Porous titanium oxide materials are attractive for energy-related applications. However, many suffer from poor stability and crystallinity. Here we present a robust nanoporous metal–organic framework (MOF), comprising a Ti12O15 oxocluster and a tetracarboxylate ligand, achieved through a scalable synthesis. This material undergoes an unusual irreversible thermally induced phase transformation that generates a highly crystalline porous product with an infinite inorganic moiety of a very high condensation degree. Preliminary photophysical experiments indicate that the product after phase transformation exhibits photoconductive behavior, highlighting the impact of inorganic unit dimensionality on the alteration of physical properties. Introduction of a conductive polymer into its pores leads to a significant increase of the charge separation lifetime under irradiation. Additionally, the inorganic unit of this Ti-MOF can be easily modified via doping with other metal elements. The combined advantages of this compound make it a promising functional scaffold for practical applications.Porous TiO2 materials are attractive for energy-related applications owing to their accessible active sites, but suffer from poor stability. Here the authors synthesize a highly stable and porous metal–organic framework containing polymeric 1D Ti–O subunits, which displays a high condensation degree and high photoconductivity.

A multidisciplinary approach to understanding sorption induced breathing in the metal organic framework MIL53(Cr)

Abstract A combination of methods (microcalorimetry, FTIR, Synchrotron XRD and molecular modelling) have been used to understand the sorption induced breathing with in the chromium metal organic framework MIL53. Strongly polar probes such as CO 2 and H 2 O induce such breathing whereas non-polar molecules such as CH 4 do not. In this system the breathing is strongly related to specific interactions between surface hydroxyls and the probe gas/vapour.

Diffusion of Carbon Dioxide and Nitrogen in the Small‐Pore Titanium Bis(phosphonate) Metal–Organic Framework MIL‐91 (Ti): A Combination of Quasielastic Neutron Scattering Measurements and Molecular Dynamics Simulations

The diffusivity of CO2 and N2 in the small-pore titanium-based bis(phosphonate) metal-organic framework MIL-91(Ti) was explored by using a combination of quasielastic neutron scattering measurements and molecular dynamics simulations. These two techniques were used to determine the loading dependence of the self-diffusivity, corrected and transport diffusivities of these two gases to complement our previously reported thermodynamics study, which revealed that this material was a promising candidate for CO2 /N2 separation. The calculated and measured diffusivities of both gases were shown to be of an order of magnitude sufficiently high, from 10-9 to 10-10  m2  s-1 , and N2 diffused faster than CO2 through the small channel of MIL-91(Ti). Consequently, the separation process does not involve any kinetic-driven limitations. This study further revealed that the global diffusion mechanism involves motions of gases along the channels by a jump sequence, and the residence times for CO2 in the region close to the specific PO⋅⋅⋅H⋅⋅⋅N zwitterionic sites are much higher than those for N2 , which explains the faster diffusivity observed for N2 .

Derivation of new interatomic potential for flexible metal-organic frameworks: a pre-requisite for understanding swelling under adsorption conditions.

Abstract A new force field for describing flexible metal-organic framework and host-guest interactions with CO 2 has been developed. Further insights into the key features of this class of materials are gleaned from constant pressure energy minimizations and canonical Monte Carlo simulations on CO 2 adsorption in the chromium terephthalate, MIL-53.

Modeling of Diffusion in MOFs

Abstract Metal-organic frameworks (MOFs) have emerged as materials of great potential in the fields of gas adsorption, storage, and separation. This has led to a boom in computational studies in order to explore and characterize the properties of the thousands of existing frameworks, with regard to storage/separation ability and transport properties. The large diversity of structures can give rise to different structural phenomena upon the introduction of guest molecules, as well as dictating the behavior of guests within the pore system, leading to some unusual diffusion mechanisms. Molecular dynamics has long provided unique insights into diffusion in porous materials, and force field parameters have been developed and refined for a reliable description of the MOFs. In this chapter we describe the computational tools available and illustrate how they have been deployed over the last 10 years for the prediction and understanding of the diffusion phenomena in this class of hybrid materials.