Nonclassical hydrides of Ni+ in ZSM-5 zeolite structures : a hybrid DFT study

We have studied the reactivity towards dihydrogen of Ni2+-Ni+ reduced ions, residing above two framework oxygen atoms, using a 18 SiO4 tetrahedrals (18T) model cluster representing the intersection of the straight and the sinusoidal channels in ZSM-5 zeolite. Reported are a detailed analysis of the Ni+-H-2 orbital interactions, the thermodynamic stability, and characteristic spectral signatures of the predicted Ni+(H-2)(n) nonclassical hydrides for n = 1 and 2, at the B3LYP level of theory. Comparison is made to existing spectroscopy data for a Ni+(H-2) complex formed in Ni-exchanged ZSM-5 zeolite [11]. (C) 2012 Elsevier B.V. All rights reserved

Dihydrogen in zeolite CaX: an inelastic neutron scattering study

We report an inelastic neutron scattering (INS) study of the rotational–vibrational spectrum of dihydrogen sorbed by zeolite CaX. In the low energy (<200 cm−1) INS spectrum of adsorbed H2 we observe the rotational–vibrational spectrum of H2, where the vibration is that of the H2 molecule against the binding site (i.e. H2–X, not H–H). We have observed for the first time the vibrational overtones of the hydrogen molecule against the adsorption surface up to sixth order. These vibrations are usually forbidden in INS spectroscopy because of the selection rules imposed by the spin flip event required. In our case we are able to observe such a vibration because the rotational transition J(1 ← 0) convolutes the vibrational spectrum. This paper reports the effect for the first time

On the effect of thermal treatment and hydrogen vibrational dynamics in sodium alanates : an inelastic neutron scattering study

We have measured inelastic neutron scattering (INS) spectra from Ti-doped polycrystalline alanates (NaAlH4 and Na3AlH6), at low temperature, in the energy transfer range 3-500 meV, both for thermally treated and untreated samples. From the spectral range corresponding to the fundamental vibrational bands of these aluminohydrides, accurate one-phonon spectra and hydrogen-projected densities of phonon states have been extracted and analyzed using ab initio lattice dynamics calculations. Satisfactory agreement has been found for the untreated samples. In the case of thermally treated samples, due to thermal decomposition, different ionic species are present and the sample composition could be quantitatively evaluated. No evidence for the existence of intermediate species such as AlH3 or AlH52- has been found

On the elusive nature of oxygen binding at coordinatively unsaturated 3d transition metal centers in metal organic frameworks

Using gas sorption measurements at ambient temperatures and in situ neutron powder diffraction methods, we have studied the interaction strengths and coordination geometries of O2 and N2 near the non occupied coordination site open metal site in the isostructural MOF structures of the CPO 27 M M MOF 74 series with M Co, Ni, Mn and Cu . Our experimental observations are compared to periodic quantum chemical model calculations. Contrary to recent computational studies, our results, both experimental and theoretical, unequivocally suggest rather weak interactions between the M II coordinatively unsatured centers and the adsorbate molecules, being mainly dispersive and electrostatic in nature. As a consequence, they exclude significant orbital charge transfer effects that could lead to superoxide peroxide formation. Calculated binding energies appear in good agreement with the measured isosteric heats of adsorption in the range of 10 20 kJ mol 1. These, relatively weak host guest interactions, lead to a tilted end on geometry in all of the investigated M II guest molecule adduct

Serotonin mediates oxidative stress and mitochondrial toxicity in a murine model of nonalcoholic steatohepatitis

BACKGROUND AND AIMS: Nonalcoholic steatohepatitis (NASH) is one of the most common causes of liver enzyme elevation in the West. Its prevalence is likely to increase further, paralleling the epidemic increase of the metabolic syndrome. Serotonin degradation by monoamine oxidase A (MAO-A) was recently implicated as an important source of reactive oxygen species. We therefore tested the pathogenetic role of serotonin in a murine model of diet-induced steatohepatitis. METHODS: Wild-type and serotonin-deficient mice, tryptophan hydroxylase 1 (Tph1(-/-)) were fed a choline-methionine-deficient diet for 2 and 6 weeks. MAO-A was inhibited with clorgyline. Steatosis, hepatocyte injury, and hepatic inflammation were assessed by histology, immunohistochemistry, and biochemical analysis. Expression levels of MAO-A and serotonin transporter were analyzed by reverse-transcription polymerase chain reaction and Western blot. Oxidative stress was detected by measuring lipid peroxidation. Mitochondrial damage was determined by electron microscopy and quantification of cytochrome c release. RESULTS: After choline-methionine-deficient diet, Tph1(-/-) mice displayed an equal degree of steatosis, yet reduced hepatocellular injury and less severe inflammation. The difference in these NASH-defining features could be attributed to an increased uptake and catabolism of serotonin, yielding enhanced levels of reactive oxygen species and lipid peroxides, which mediated hepatocellular injury by mitochondrial damage and inflammation. Inhibition of MAO-A reduced hepatocellular damage in wild-type mice. Correspondingly, MAO-A expression was up-regulated significantly in human NASH. CONCLUSIONS: This study provides evidence that serotonin plays a role in the pathogenesis of steatohepatitis, and therefore might represent a novel target for the prevention and treatment of NASH

Gaining Insights on the H2 Sorbent Interactions Robust soc MOF Platform as a Case Study

We report on the synthesis and gas adsorption properties i.e., Ar and H2 of four robust 3 periodic metal organic frameworks MOFs having the targeted soc topology. These cationic MOFs are isostructural to the parent indium based MOF, In soc MOF 1a for NO3 , previously reported by us, and likewise are constructed from the assembly of rigid amp; 956;3 oxygen centered trinuclear metal carboxylate clusters, [M3O O2C amp; 8722; 6], where M In3 or Fe3 . Each inorganic trinuclear molecular building block MBB , generated in situ, is bridged by six 3,3 amp; 8242;,5,5 amp; 8242; azobenzenetetracarboxylate ABTC4 ligands to give the extended 4,6 connected MOF, soc MOF. In our previous work, we confirmed that the parent soc MOF, i.e., In soc MOF 1a, possesses unique structural characteristics e.g., vacant In binding sites and narrow pores with higher localized charge density , which led to exceptional hydrogen H2 storage capabilities. Therefore, charged MOFs with soc topology can be viewed collectively as an ideal prototypical platform to examine the impact of specific structural parameters on H2 MOF interactions via systematic gas adsorption studies. We infer that enhanced binding of molecular H2 is primarily governed by the presence and type of vacant metal centers i.e., Fe was shown to exhibit stronger H2 MOF interactions at low H2 loading compared to the In analogues . These findings are evident from the associated isosteric heat of adsorption Qst at low loadings and inelastic neutron scattering INS experiments of the rotational transitions of sorbed H2, as well as, temperature programmed desorption TPD studies for a select compound . The importance of localized charge density is also highlighted, where the extra framework nitrate anions in the Fe soc MOF 1a for NO3 facilitate enhanced binding affinities as compared to the chloride analogu

Investigating H2 Adsorption in Isostructural Metal Organic Frameworks M CUK 1 M Co and Mg through Experimental and Theoretical Studies

A combined experimental and theoretical study of H2 adsorption was carried out in Co CUK 1 and Mg CUK 1, two isostructural metal organic frameworks MOFs that consist of M2 ions M Co and Mg coordinated to pyridine 2,4 dicarboxylate pdc2 and OH ligands. These MOFs possess saturated metal centers in distorted octahedral environments and narrow pore sizes and display high chemical and thermal stability. Previous experimental studies revealed that Co CUK 1 exhibits a H2 uptake of 183 cm3 g 1 at 77 K 1.0 atm [ Angew. Chem., Int. Ed. 2007, 46, 272 amp; 8722;275, DOI 10.1002 anie.200601627], while that for Mg CUK 1 under the same conditions is 240 cm3 g 1 on the basis of the experimental measurements carried out herein. The theoretical H2 adsorption isotherms are in close agreement with the corresponding experimental measurements for simulations using electrostatic and polarizable potentials of the adsorbate. Through simulated annealing calculations, it was found that the primary binding site for H2 in both isostructural analogues is localized proximal to the center of the aromatic rings belonging to the pdc2 linkers. Inelastic neutron scattering INS spectroscopic studies of H2 adsorbed in both MOFs revealed a rotational tunnelling transition occurring at around 8 meV in the corresponding spectra; this peak represents H2 adsorbed at the primary binding site. Two dimensional quantum rotation calculations for H2 localized at the primary and secondary binding sites in both MOFs yielded rotational energy levels that are in agreement with the transitions observed in the INS spectra. Even though both M CUK 1 analogues possess different metal ions, they exhibit similar electrostatic environments, modeled structures at H2 saturation, and rotational potentials for H2 adsorbed at the most favorable adsorption site. Overall, this study demonstrates how important molecular level details of the H2 adsorption mechanism inside MOF micropores can be derived from a combination of experimental measurements and theoretical calculations using two stable and isostructural MOFs with saturated metal centers and small pore windows as model system