Origins of dihydrogen binding to metal-inserted porphyrins: Electric polarization and Kubas interaction

Quantum chemical modeling of hydrogen binding in metal-organic frameworks: validation, insight, predictions and challenges

A detailed chemical understanding of H2 interactions with binding sites in the nanoporous crystalline structure of metal-organic frameworks (MOFs) can lay a sound basis for the design of new sorbent materials. Computational quantum chemical calculations can aid in this quest. To set the stage, we review general thermodynamic considerations that control the usable storage capacity of a sorbent. We then discuss cluster modeling of H2 ligation at MOF binding sites using state-of-the-art density functional theory (DFT) calculations, and how the binding can be understood using energy decomposition analysis (EDA). Employing these tools, we illustrate the connections between the character of the MOF binding site and the associated adsorption thermodynamics using four experimentally characterized MOFs, highlighting the role of open metal sites (OMSs) in accessing binding strengths relevant to room temperature storage. The sorbents are MOF-5, with no open metal sites, Ni2(m-dobdc), containing Lewis acidic Ni(II) sites, Cu(I)-MFU-4l, containing π basic Cu(I) sites and V2Cl2.8(btdd), also containing π-basic V(II) sites. We next explore the potential for binding multiple H2 molecules at a single metal site, with thermodynamics useful for storage at ambient temperature; a materials design goal which has not yet been experimentally demonstrated. Computations on Ca2+ or Mg2+ bound to catecholate or Ca2+ bound to porphyrin show the potential for binding up to 4 H2; there is precedent for the inclusion of both catecholate and porphyrin motifs in MOFs. Turning to transition metals, we discuss the prediction that two H2 molecules can bind at V(II)-MFU-4l, a material that has been synthesized with solvent coordinated to the V(II) site. Additional calculations demonstrate binding three equivalents of hydrogen per OMS in Sc(I) or Ti(I)-exchanged MFU-4l. Overall, the results suggest promising prospects for experimentally realizing higher capacity hydrogen storage MOFs, if nontrivial synthetic and desolvation challenges can be overcome. Coupled with the unbounded chemical diversity of MOFs, there is ample scope for additional exploration and discovery.

Efficient delivery of anticancer 5-fluorouracil drug by alkaline earth metal functionalized porphyrin-like porous fullerenes: A DFT study

Finding and developing effective targeted drug delivery systems has emerged as an attractive approach for treating a wide range of diseases. In the present study, the potential of alkaline earth metal functionalized porphyrin-like porous C₂₄N₂₄ fullerenes for delivering 5-fluorouracil (5FU) anticancer drug is assessed using density functional theory calculations. The goal is to evaluate how the addition of alkaline earth metals to C₂₄N₂₄ enhances the adsorption capabilities of this system towards 5FU drug. The adsorption energies and charge transfers are determined in order to evaluate the strength of the interaction between the 5FU and fullerene surfaces. According to the results, adding alkaline earth metals increases the drug's adsorption energy on the C₂₄N₂₄ fullerene. In all cases, the drug molecule interacts with the metal atom through its CO group. Furthermore, the adsorption strength of the 5FU increases with metal atom size (Ca > Mg > Be), which is connected to the polarizability of these atoms. The adsorption energies of 5FU are shown to be highly sensitive on solvent effects and the acidity of the environment. The adsorption strength of 5FU decreases within the solvent (water), allowing it to be released more easily. The moderate adsorption energies and short desorption times of 5FU imply that it is reversibly adsorbed on the functionalized fullerenes.

Sc-functionalized porphyrin-like porous fullerene for CO2 storage and separation: A first-principles evaluation

In recent years, there has been a lot of interest in capturing and storing carbon dioxide (CO₂) on porous materials as an efficient method for decreasing the adverse effects of this greenhouse gas on the environment and climate change. The current work introduces a Sc-decorated porphyrin-like porous fullerene (Sc₆@C₂₄N₂₄) as an efficient material for CO₂ capture, storage, and separation using density functional theory calculations. While CO₂ is physisorbed over pristine C₂₄N₂₄, the addition of Sc atoms on the N₄ sites of C₂₄N₂₄ greatly enhances CO₂ adsorption energy. Each Sc atom in Sc₆@C₂₄N₂₄ may adsorb up to three CO₂ molecules, resulting in a gravimetric density of 48%. Moreover, temperature may be used to modulate CO₂ adsorption/desorption over the substrate. The Sc-decorated C₂₄N₂₄ fullerene exhibits a lower affinity for adsorbing N₂, CH₄, and H₂ molecules than CO₂. As a consequence, this material might be considered for purifying CO₂ molecules from CO₂/N₂, CO₂/CH₄, and CO₂/H₂ mixtures. This study also sheds light on the nature of the Sc-CO₂ interaction as well as the underlying mechanism of selective CO₂ adsorption on Sc decorated C₂₄N₂₄.

Density Functional Theory Study of Hydrogen Adsorption in a Ti-Decorated Mg-Based Metal-Organic Framework-74

The Ti-binding energy and hydrogen adsorption energy of a Ti-decorated Mg-based metal-organic framework-74 (Mg-MOF-74) were evaluated by using first-principles calculations. Our results revealed that only three Ti adsorption sites were found to be stable. The adsorption site near the metal oxide unit is the most stable. To investigate the hydrogen-adsorption properties of Ti-functionalized Mg-MOF-74, the hydrogen-binding energy was determined. For the most stable Ti adsorption site, we found that the hydrogen adsorption energy ranged from 0.26 to 0.48 eV H2 (-1) . This is within the desirable range for practical hydrogen-storage applications. Moreover, the hydrogen capacity was determined by using ab initio molecular dynamics simulations. Our results revealed that the hydrogen uptake by Ti-decorated Mg-MOF-74 at temperatures of 77, 150, and 298 K and ambient pressure were 1.81, 1.74, and 1.29 H2  wt %, respectively.