Multi-scale computational investigation of Ag-doped two-dimensional Zn-based MOFs for storage and release of small NO and CO bioactive molecules.

Nitric oxide (NO) and carbon monoxide (CO) are two important gasotransmitters with critical biological roles in the human body. Due to their short lifetime and dangerous side effects at high concentrations, it is essential to find safe storage and slow release methods of these two gases. Herein, we report the multi-scale simulations of two-dimensional (Zn)MOF-470 doped with antimicrobial Ag atoms to evaluate the degree of enhancement of adsorption and dynamics of NO and CO. The results show that NO binds to Ag stronger than CO. In addition, the decoration of the benzene ring with Ag atoms on both sides has led to the effective adsorption of NO and CO with binding energies of -26.34 and -21.71 kcal mol-1, respectively. The GCMC results show that Ag can significantly improve NO and CO storage capacity, especially in low-pressure ranges. The storage capacity of NO in (Zn)MOF-470 and Ag-doped MOFs is 6.12 and 7.21 mol kg-1, respectively. This storage capacity for CO is 4.09 and 5.48 mol kg-1, respectively. The heat of adsorption for NO and CO was obtained to be 31.72 and 25.64 kJ mol-1 for (Zn)MOF-470, and 36.5 and 31.12 kJ mol-1 for Ag-(Zn)MOF-470 at 298 K and 1 bar. Besides, the MD results indicate that when Ag is doped into the structure of MOFs, the dynamics of gases within the pores of MOFs significantly decrease. When Ag atoms are considered mobile, the dynamics of guest molecules increase and it shows that the structural and dynamical behavior of NO and CO strongly depends on the mobility or immobility of doped Ag atoms. The result from the MSD directions (x, y, and z components) indicates that the diffusion of NO and CO within the pores of (Zn)MOF-470 is anisotropic and this may be due to the 2D structural characteristics of the MOF, the dipolar nature of NO and CO molecules, and the very narrow and layered pores of (Zn)MOF-470. These promising results from the simulations suggest that (Zn)MOF-470 and doping Ag atoms into this MOF can improve the storage capacity and slow release of bioactive NO and CO along with utilization of the antimicrobial nature of Ag atoms in medical applications.

Tuning the Selectivity between C2H2 and CO2 in Molecular Porous Materials.

A combined experimental and theoretical study of C2H2 and CO2 adsorption and separation was performed in two isostructural molecular porous materials (MPMs): MPM-1-Cl ([Cu2(adenine)4Cl2]Cl2) and MPM-1-TIFSIX ([Cu2(adenine)4(TiF6)2]). It was revealed that MPM-1-Cl displayed higher low-pressure uptake, isosteric heat of adsorption (Qst), and selectivity for C2H2 than CO2, whereas the opposite was observed for MPM-1-TIFSIX. While MPM-1-Cl contains only one type of accessible channel, which has a greater preference toward C2H2, MPM-1-TIFSIX contains three distinct accessible channels, one of which is a confined region between two large channels that represents the primary binding site for both adsorbates. According to molecular simulations, the initial adsorption site in MPM-1-TIFSIX interacts more strongly with CO2 than C2H2, thus explaining the inversion of adsorbate selectivity relative to MPM-1-Cl.

Trace CO2 capture by an ultramicroporous physisorbent with low water affinity.

CO2 accumulation in confined spaces represents an increasing environmental and health problem. Trace CO2 capture remains an unmet challenge because human health risks can occur at 1000 parts per million (ppm), a level that challenges current generations of chemisorbents (high energy footprint and slow kinetics) and physisorbents (poor selectivity for CO2, especially versus water vapor, and/or poor hydrolytic stability). Here, dynamic breakthrough gas experiments conducted upon the ultramicroporous material SIFSIX-18-Ni-ß reveal trace (1000 to 10,000 ppm) CO2 removal from humid air. We attribute the performance of SIFSIX-18-Ni-ß to two factors that are usually mutually exclusive: a new type of strong CO2 binding site and hydrophobicity similar to ZIF-8. SIFSIX-18-Ni-ß also offers fast sorption kinetics to enable selective capture of CO2 over both N2 (S CN) and H2O (S CW), making it prototypal for a previously unknown class of physisorbents that exhibit effective trace CO2 capture under both dry and humid conditions.

Simulations of hydrogen, carbon dioxide, and small hydrocarbon sorption in a nitrogen-rich rht-metal-organic framework.

Grand canonical Monte Carlo (GCMC) simulations of gas sorption were performed in Cu-TDPAH, also known as rht-MOF-9, hereafter [1], a metal-organic framework (MOF) with rht topology consisting of Cu2+ ions coordinated to 2,5,8-tris(3,5-dicarboxyphenylamino)-1,3,4,6,7,9,9b-heptaazaphenalene (TDPAH) ligands. This MOF is notable for the presence of open-metal copper sites and high nitrogen content on the linkers. [1] Exhibits one of the highest experimental H2 uptakes at 77 K/1 atm within the extant rht-MOF family (ca. 2.72 wt%) and also has strong affinity for CO2 (5.83 mmol g-1 at 298 K/1 atm). Our simulations, which include explicit many-body polarization interactions, accurately modeled macroscopic thermodynamic properties (e.g., sorption isotherms and isosteric heats of adsorption (Qst)) as well as the binding sites for H2, CO2, CH4, C2H2, C2H4, and C2H6 in the MOF. Four different binding sites were observed through analysis of the radial distribution function (g(r)) about the two chemically distinct Cu2+ ions, simulated annealing calculations, and examination of the three-dimensional histogram showing the sites of occupancy: (1) at the Cu2+ ion facing toward the center of the linker (CuL), (2) at the Cu2+ ion facing away from the center of linker (CuC), (3) nestled between three [Cu2(O2CR)4] units in the corner of the truncated tetrahedral (T-Td) cage and (4) straddling the copper nuclei parallel to the axis of the Cu-Cu bond within the T-Td cage. The low-loading (initial) binding site in the MOF is highly sensitive to the partial charges of the Cu2+ ions that were used for parametrization. It was discovered that most sorbates prefer to sorb onto or near the Cu2+ ions that exhibit the greater partial positive charge (i.e., at site 1). The simulated H2 and CO2 sorption results obtained using a polarizable potential for the respective sorbates are in good agreement with the corresponding experimental data, especially near ambient pressure. Simulations of gas sorption were also performed in [1] using nonpolarizable potentials for the individual sorbates; these include potentials from the TraPPE force field for most sorbates.

Predictive models of gas sorption in a metal-organic framework with open-metal sites and small pore sizes.

Simulations of CO2 and H2 sorption were performed in UTSA-20, a metal-organic framework (MOF) having zyg topology and composed of Cu2+ ions coordinated to 3,3',3'',5,5',5''-benzene-1,3,5-triyl-hexabenzoate (BHB) linkers. Previous experimental studies have shown that this MOF displays remarkable CO2 sorption properties and exhibits one of the highest gravimetric H2 uptakes at 77 K/1.0 atm (2.9 wt%) [Z. Guo, et al. Angew. Chem., Int. Ed., 2011, 50, 3178-3181]. For both sorbates, the simulations were executed with the inclusion of explicit many-body polarization interactions, which was necessary to reproduce sorption onto the open-metal sites. Non-polarizable potentials were also utilized for simulations of CO2 sorption as a control. The simulated excess sorption isotherms for both CO2 and H2 are in very good agreement with the corresponding experimental data over a wide range of temperatures and pressures, thus demonstrating the accuracy and predictive power of the polarizable potentials used herein. The theoretical isosteric heat of adsorption (Qst) values are also in good agreement with the newly reported experimental Qst values for the respective sorbates in UTSA-20. Sorption onto the more positively charged Cu2+ ion of the [Cu2(O2CR)4] cluster was observed for both CO2 and H2. However, a binding site with energetics comparable to that for an open-metal site was also discovered for both sorbates. A radial distribution function (g(r)) analysis about the preferential Cu2+ ions for CO2 and H2 revealed that both sorbates display different trends for the relative occupancy about such sites upon increasing/decreasing the pressure in the MOF. Overall, this study provides insights into the CO2 and H2 sorption mechanisms in this MOF containing open-metal sites and small pore sizes for the first time through a classical polarizable force field.

Enhanced removal of aqueous BPA model compounds using Metalloligs.

A model compound, 4-(t-butyl)phenol, was used as a substitute for BPA (bisphenol acetone or Bisphenol A) a material used for the production of a large volume of common plastics. Unfortunately, BPA is suspected to have estrogenic properties, and there is a suspicion that even small amounts can have a deleterious effect against humans, especially female infants. The model compound has some similarities to BPA, but lacks some of the serious properties of BPA dust. Since other workers have demonstrated the capability of removing BPA from plastics by extraction with saline or alcohol, we studied whether Octolig, a polyethylenediimine supported on silica gel, or transition metal derivatives of Octolig could be used to remove concentrations for model compounds from aqueous solution. Octolig gave modest results 20%, the manganese (II) and iron (III) derivatives gave poor results, Cuprilig was an improvement over those two Metalloligs, but the cobalt(II) derivative was able to remove up to 56% of the model compound. Two methods were studied, batch and column chromatography. Under the conditions used in this study, the batch method was superior.

Comparison of anion removal capacities of Octolig and Cuprilig.

Mixtures of sodium salts of phosphate, arsenate, and fluoride were used in chromatography and batch experiments to compare the capacity of two immobilized ligands (IMLIGs) to remove these anions: Octolig and its copper (II)-based metallolig, Cuprilig. The focus of this study was twofold. First, to find out which material, Octolig or Cuprilig, would remove these anions most effectively; and secondly to determine the optimal capacity for removal of representative anions. Removal capacity was evaluated by two methods: by chromatography and by a batch method. The methods gave identical results, but the batch method was more convenient. Cuprilig had a lower capacity for removal of phosphate than Octolig. The capability of Octolig for removing anions was: phosphate > arsenate > fluoride >>> chloride >>>> bromide. Replication of phosphate removal was good for a given batch of Octolig. Of three different samples of Octolig, two seemed to be alike based on the phosphate- removal capacity; the third was different on the basis of a Student's t-test. This distinction indicates the batch procedure could serve as a quality control/assurance technique.

Necroinflammatory liver disease in BALB/c background, TGF-beta 1-deficient mice requires CD4+ T cells.

The etiology of autoimmune liver disease is poorly understood. BALB/c mice deficient in the immunoregulatory cytokine TGF-beta1 spontaneously develop necroinflammatory liver disease, but the immune basis for the development of this pathology has not been demonstrated. Here, we show that BALB/c-TGF-beta1(-/-) mice exhibit abnormal expansion in hepatic mononuclear cells (MNCs) compared with wild-type littermate control mice, particularly in the T cell and macrophage lineages. To test whether lymphocytes of the adaptive immune system are required for the spontaneous development of necroinflammatory liver disease, BALB/c-TGF-beta1(-/-) mice were rendered deficient in B and T cells by crossing them with BALB/c-recombinase-activating gene 1(-/-) mice. BALB/c-TGF-beta1(-/-)/recombinase-activating gene 1(-/-) double-knockout mice showed extended survival and did not develop necroinflammatory liver disease. The cytolytic activity of BALB/c-TGF-beta1(-/-) hepatic lymphocytes was assessed using an in vitro CTL assay. CTL activity was much higher in BALB/c-TGF-beta1(-/-) hepatic MNCs compared with littermate control hepatic MNCs and was particularly pronounced in the CD4(+) T cell subset. Experimental depletion of CD4(+) T cells in young BALB/c-TGF-beta1(-/-) mice prevented the subsequent development of necroinflammatory liver disease, indicating that CD4(+) T cells are essential for disease pathogenesis in vivo. These data definitively establish an immune-mediated etiology for necroinflammatory liver disease in BALB/c-TGF-beta1(-/-) mice and demonstrate the importance of CD4(+) T cells in disease pathogenesis in vivo. Furthermore, TGF-beta1 has a critical role in homeostatic regulation of the hepatic immune system, inhibiting the development or expansion of hepatic cytolytic CD4(+) T cells.