Local structure and NO adsorption/desorption property of Pd2+ cations at different paired Al sites in CHA zeolite.

Recently, Pd-exchanged CHA zeolites (Pd-CHA) have attracted attention as promising passive NOx adsorbers (PNAs) for reducing NOx emissions during the cold start period of a vehicle engine. In this work, the relationship between the local structures and the NO adsorption/desorption properties of the Pd cations in CHA zeolites was investigated. Pd cation formation and NO adsorption were theoretically explored by density functional theory (DFT) calculations for different paired Al sites in six-/eight-membered rings (6MR/8MR). Furthermore, we prepared a series of Pd-CHAs with different Pd loadings (0.5-5.4 wt%) and evaluated their NO adsorption/desorption properties by in situ infrared (IR) spectroscopy and temperature-programmed desorption (TPD) measurements. The increase in the Pd loading resulted in a shift in the NO desorption temperature toward a higher temperature regime. This phenomenon was ascribed to the increase in the proportion of less stable Pd cations, resulting in improved NO adsorption. Furthermore, the effect of Al distribution on the NO adsorption property of Pd-CHA was examined using CHA zeolites containing different proportions of paired Al sites in 6MR while maintaining similar Si/Al ratios (Si/Al = 12.0-16.5). The present study, based on a combination of theoretical and experimental techniques, shows that the NO adsorption/desorption properties over Pd-CHA can be tuned by controlling the Pd loading amount and the type of paired Al sites.

Transformation of Bulk Pd to Pd Cations in Small-Pore CHA Zeolites Facilitated by NO.

Atomic dispersion of metal species has attracted attention as a unique phenomenon that affects adsorption properties and catalytic activities and that can be used to design so-called single atom materials. In this work, we describe atomic dispersion of bulk Pd into small pores of CHA zeolites. Under 4% NO flow at 600 °C, bulk Pd metal on the outside of CHA zeolites effectively disperses, affording Pd2+ cations on Al sites with concomitant formation of N2O, as revealed by microscopic and spectroscopic characterizations combined with mass spectroscopy. In the present method, even commercially available submicrosized Pd black can be used as a Pd source, and importantly, 4.1 wt % of atomic Pd2+ cations, which is the highest loading amount reported so far, can be introduced into CHA zeolites. The structural evolution of bulk Pd metal is also investigated by in situ X-ray absorption spectroscopy (XAS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), as well as ab initio thermodynamic analysis using density functional theory (DFT) calculations.

An improved HPLC assay for phosphatidylcholine hydroperoxides (PCOOH) in human plasma with synthetic PCOOH as internal standard.

Quantitative and qualitative analyses of 1-palmitoyl-2-linoleoyl-phosphatidylcholine monohydroperoxide [PC 16:0/18:2-OOH] and 1-stearoyl-2-linoleoyl-phosphatidylcholine monohydroperoxide [PC 18:0/18:2-OOH] in human plasma were improved by chemiluminescence HPLC using synthetic 1-stearoyl-2-erucoyl-phosphatidylcholine monohydroperoxide (PC 18:0/22:1-OOH) as internal standard. The calibration curves of synthetic PC 16:0/18:2-OOH and PC 18:0/18:2-OOH, obtained by their direct injections with the IS into the HPLC system, were linear throughout the calibration range (10-1000 pmol). Within-day and between-day coefficients of variation were below 8%, and the recoveries were between 84% and 101%. Plasma concentrations of PC 16:0/18:2-OOH and PC 18:0/18:2-OOH were 102+/-59 nM (mean+/-SD) and 36+/-20 nM, respectively, in the 33 healthy volunteers. The present method might help understanding incompletely understood pathway of plasma phosphatidylcholine hydroperoxides.

A sandwich enzyme-linked immunosorbent assay for human plasma apolipoprotein A-V concentration.

Apolipoprotein A-V (apoA-V) is a recently discovered apolipoprotein that appears to have a role in plasma triglyceride (TG) transport. We have developed an ELISA for apoA-V using monoclonal antibodies that has a lower limit of detection of 0.3 ng/ml and linearity up to 20 ng/ml. The ELISA was then used to quantify plasma apoA-V in 196 healthy subjects and 106 patients with insulin-resistant diabetes mellitus. In the healthy subjects, total apoA-V concentration was 179.2 +/- 74.8 ng/ml, and it was greater in females than in males (P < 0.005). It was correlated positively with the plasma HDL cholesterol (r = 0.32, P < 0.0001), apoA-I (r = 0.27, P = 0.0001), and apoE (r = 0.18, P = 0.011) concentrations and negatively with plasma TG concentration (r = -0.22, P = 0.021). In relation to single nucleotide polymorphism 3 (-1131C/T) of the apoA-V gene, apoA-V concentration was higher in the T/T type than in the C/C type (P < 0.01). Plasma TG concentration was lower in the T/T type than in the C/C or C/T type (P < 0.05). ApoA-V concentration was lower in the diabetic patients (69.4 +/- 44.3 ng/ml; P < 0.01) than in the healthy controls.

Troglitazone ameliorates abnormal activity of protein tyrosine phosphatase in adipose tissues of Otsuka Long-Evans Tokushima Fatty rats.

Protein tyrosine phosphatases (PTPases) play an essential role in the regulation of steady-state phosphorylation of the insulin receptor and other proteins in the insulin signaling pathway. To determine the role of PTPases in adipose tissue in the development into an insulin-resistant state, we examined PTPase activities and protein levels of three major candidate PTPases in adipose tissues of 26-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Particulate PTPase activities in visceral and epididymal adipose tissues of OLETF rats were increased compared to those in Long-Evans Tokushima Otsuka (LETO) rats, non-insulin-resistant controls. Cytosolic PTPase activities in these tissues were conversely decreased in OLETF rats. In subcutaneous adipose tissues, those changes were not observed. Western blot analysis showed that the amounts of leukocyte antigen-related PTPase (LAR), PTPase 1B (PTP1B), and src homology 2-containing PTPase (SH-PTP2) were increased in particulate fractions of visceral and epididymal fat of OLETF rats. On the other hand, those in the cytosolic fractions were slightly decreased. Troglitazone was administered to OLETF rats to examine the effect of the drug on the changes in PTPase activity and distribution. Troglitazone treatment restored those alterations in PTPase activity in the particulate fraction and the amounts of LAR, PTP1B and SH-PTP2 in both fractions of visceral and epididymal adipose tissues of OLETF rats. Although it remains unknown whether such effects of troglitazone are mediated by peroxisome proliferator-activated receptor y, these data provide useful information for understanding the significance of PTPase in insulin-resistant rats and the molecular mechanism of troglitazone action.