14-Cmethionine uptake as a potential marker of inflammatory processes after myocardial ischemia and reperfusion

A relationship between L-[methyl-11C]methionine (11C-methionine) uptake and angiogenesis has been suggested in gliomas. However, methionine uptake in myocardial ischemia and reperfusion has received little attention. We investigated the serial changes and mechanisms of 14-Cmethionine uptake in a rat model of myocardial ischemia and reperfusion. Methods: The left coronary artery was occluded for 30 min, followed by reperfusion for 1-28 d. At the time of the study, 14-Cmethionine (0.74 MBq) and 201Tl (14.8 MBq) were injected intravenously at 20 and 10 min before sacrifice, respectively. One minute before sacrifice, the left coronary artery was reoccluded, and 99mTc-hexakis-2-methoxyisobutylisonitrile (150-180 MBq) was injected to verify the area at risk. Histologic sections of the heart were immunohistochemically analyzed using anti-CD68, anti-smooth-muscle a-actin (SMA), and antitroponin I and compared with the autoradiography findings. Results: Both 14Cmethionine (uptake ratio, 0.71 ± 0.13) and 201Tl uptake were reduced in the area at risk at 1 d after reperfusion. However, 3 d after reperfusion, an increased 14-Cmethionine uptake (1.79 ± 0.23) was observed corresponding to the area of still-reduced 201Tl uptake, and the 14-Cmethionine uptake gradually declined until 28 d. The increased 14-Cmethionine uptake area at 3 and 7 d corresponded well to the macrophage infiltrations demonstrated by positive CD68 staining. Anti-SMA staining appeared at 7 d, after which CD68 staining was gradually replaced by the SMA staining, suggesting that methionine uptake in the early phase after ischemia and reperfusion might reflect inflammatory activity. Conclusion: 14-Cmethionine accumulated in the infarcted area, and its uptake corresponded closely to macrophage infiltration at 3-7 d after reperfusion. Methionine imaging may be useful for inflammatory imaging early after myocardial infarction. COPYRIGHT © 2013 by the Society of Nuclear Medicine and Molecular Imaging, Inc

Mechanistic insights into the oxidation of copper(i) species during NH3-SCR over Cu-CHA zeolites : a DFT study

Selective catalytic reduction of nitrogen oxides using ammonia (NH3-SCR) over Cu-exchanged zeolites proceeds via reduction of Cu(ii) to Cu(i) and subsequent reoxidation of Cu(i) to Cu(ii). Although the mechanism of reduction half cycle has been relatively well established, reoxidation pathways of Cu(i) to form the original Cu(ii) species are highly complicated and remain unclear. Herein, oxidation mechanisms of Cu(i) to Cu(ii) species in CHA zeolites during the NH3-SCR process were investigated by periodic DFT calculations. The NH3-solvated Cu(i) and Cu(ii) species were considered for exploring the oxidative activation reaction pathways. The results show that, with O-2 as the sole oxidant, Cu(i) can be effectively oxidized to Cu(ii) via multinuclear Cu-oxo intermediates with moderate reaction barriers. The NO-assisted oxidation of Cu(i) was found to favor the formation of Cu nitrate/nitrite species, which seem to only act as off-cycle resting states. We propose that reoxidation of Cu(i) to Cu(ii) with O-2 as the sole oxidant plays a key role in the oxidation half cycle under standard NH3-SCR conditions

Formation and Reactions of NH4NO3 during Transient and Steady-State NH3-SCR of NOx, over H-AFX Zeolites: Spectroscopic and Theoretical Studies

Operando infrared (IR) spectroscopy and density functional theory (DFT) calculations were combined to investigate the selective catalytic reduction (SCR) of NOx by NH3 over H-AFX zeolites. The steady-state kinetics shows that SCR reactions involving NO2 proceed much more rapidly than those of NO. Data from in situ IR combined with online mass spectrometry under transient conditions demonstrate that Bronsted acid sites (BASs) promote the reaction of NO2 with NH3 to form N-2, H2O, and NH4NO3 at low temperatures (50-150 degrees C). In combination with DFT results, these data suggest that NO promotes the reduction of NH4NO3 to NRINO2, which then decomposes into N-2 and H2O. Therefore, the accumulation of NH4NO3 in the zeolite is inhibited by NO. Furthermore, when NO is absent, NH4NO3 decomposition into N2O and H2O occurs only at high temperatures (>200 degrees C). A comparison of H-AFX and Cu-AFX implies that Cu sites are not active for the reduction of NO2 by NH3 and that BASs are responsible for the NH3-SCR reactions involving NO2

Regeneration of atomic Ag sites over commercial gamma-aluminas by oxidative dispersion of Ag metal particles

Ag(3 wt%)-loaded gamma-Al2O3 (Ag/Al2O3) catalysts were prepared using four types of commercially available alumina powders (CTB, PUR, VGL, and CFF). Based on the support, the activity of these catalysts for the H-2-assisted selective catalytic reduction (SCR) of NO by NH3 or C3H6 decreased in the order CTB > PUR > VGL > CFF. After sintering treatment (H-2 reduction at 800 degrees C), the particle size of the Ag metal nanoparticles (NPs) changed and was found to be correlated with the catalytic activity (CTB PUR > VGL > CFF. IR study of pyridine adsorbed on Ag-free gamma-Al2O3 showed that the number of strong Lewis acid sites (unsaturated Al-IV(3+)) increased in the same order, CTB > PUR > VGL > CFF, and the number of strong Lewis acid sites decreased when Ag was loaded on the supports. In situ X-ray absorption near-edge structure (XANES) and UV-vis studies of Ag/Al2O3 sintered under NO + O-2 at 400 degrees C showed oxidative redispersion of the Ag metal NPs to regenerate atomic Ag(i) sites. The amount of redispersed Ag metal and the initial rates of redispersion estimated from the in situ UV-vis results changed in the following order: CTB > PUR > VGL > CFF. These results suggest that the HO-mu(1)-Al-VI site adjacent to the unsaturated Al-IV(3+) site on gamma-Al2O3 is the anchoring site of the atomic Ag species, and the sintering resistance of Ag/Al2O3 increases with the number of HO-mu(1)-Al-VI sites. During H-2-assisted SCR, where both H-2 and NO + O-2 were co-fed to the catalysts, the number of highly dispersed Ag species (active sites) increased with the number of HO-mu(1)-Al-VI sites; hence, NO conversion increased with the number of HO-mu(1)-Al-VI sites on the support. The present results provide molecular-level insights into the design of sintering-resistant Ag/Al2O3 catalysts for SCR

In situ/operando spectroscopic studies on NH3-SCR reactions catalyzed by a phosphorus-modified Cu-CHA zeolite

The modification of Cu-exchanged zeolites with phosphorus represents a promising method to enhance their hydrothermal stability, which is of pivotal importance for catalysts that promote the selective catalytic reduction of NO with ammonia (NH3-SCR). In this study, we investigated the reaction mechanism of NH3-SCR catalyzed by a phosphorus-modified CHA zeolite that contains active Cu species (Cu-P-CHA), and assessed the effect of the phosphorus modification on the hydrothermal stability of the catalyst by employing in situ/operando spectroscopic methods. In their entirety, the combined results from in situ/operando IR, UV-vis, and XANES experiments revealed that the NH3-SCR process over Cu-P-CHA proceeds via the reduction of Cu(II) to Cu(I) followed by a reoxidation of Cu(I) to Cu(II). In addition, we found that the phosphorus modification improved the hydro thermal durability of the catalyst by retaining a higher amount of the redox-active Cu species and the zeolite framework