Anh P. Nguyen

Interpretation of Secondary Organic Aerosol Formation from Diesel Exhaust Photooxidation in an Environmental Chamber

Secondary organic aerosol (SOA) formation from diesel exhaust was investigated using an environmental chamber. Particle volume measurement based solely on mobility diameter underestimated the SOA formation from diesel exhaust due to the external void space of agglomerate particles. Therefore, particle mass concentration and fractal-like dimension was determined from the particle effective density as a function of particle mass using an aerosol particle mass analyzer and scanning mobility particle sizer (APM–SMPS). Continuous aging of aerosol measured by an increase of atomic ratio (O/C) underscored the importance of multigenerational oxidation of low-volatile organic vapors emitted from diesel engine as a possible significant source of ambient oxygenated SOA. Higher particle effective densities were observed when raw exhaust was injected into a full bag as opposed to filling a bag with diluted exhaust using an ejector diluter. This suggests that the dilution method, in addition to dilution ratio, may impact the evaporation of semivolatile species. This study demonstrates the critical need to evaluate particle mass when evaluating SOA formation onto fractal particles such as diesel exhaust.

Kinetics of soot oxidation by NO2.

Modern technologies use NO(2) to promote low-temperature soot oxidation for diesel particulate filter regeneration. In this study, the online aerosol technique of high-temperature oxidation tandem differential mobility analysis is used to study kinetics of soot oxidation by NO(2). Soot particles are exposed to varying temperature and NO(2) mixing ratio inside the furnace resulting from thermal decomposition of NO(2) to NO. This causes soot oxidation rates to vary throughout the furnace. Variations in temperatures and NO(2) mixing ratio are thoroughly accounted for the first time. Soot oxidation rates are calculated as a function of frequency factor A(soot), activation energy E(soot), and concentration of NO(2) within the furnace at temperatures ranging from 500 to 950 degrees C. Results suggest A(soot) and E(soot) values for soot oxidation of 2.4 x 10(-14) (nm K(-0.5) s(-1) cm(3) molecule(-1)) and 47.1 kJ mol(-1), respectively, when reaction order to NO(2) is assumed as unity. The activation energy for soot oxidation with NO(2) is significantly lower than oxidation with air. However, parts per million levels of NO(2) cause soot oxidation at low temperatures suggesting NO(2) is a stronger oxidant than O(2).

Separation of miRNA and its methylation products by capillary electrophoresis.

Methylation is a crucial step in plant microRNA biogenesis. To improve our understanding of the methylation process and its regulation, a rapid and convenient high-throughput method should be sought to help with the study of reaction kinetics and assist the search for chemical inhibitors of the methyltransferase, HEN1. In this short communication, we report a pioneering work that used capillary electrophoresis (CE) to separate the miRNA and its methylation product. Capillary zone electrophoresis (CZE) with UV-absorption detection and a reduced running temperature achieved good separation of miR173/miR173* and miR173-m/miR173*-m with a detection limit of around 1 microM. To enhance detection sensitivity, capillary gel electrophoresis (CGE) coupled with laser-induced fluorescence (LIF) detection was also tested, and base-line separation of nanomolar duplex RNA samples was achieved using 4% polyvinylpyrrolidone (PVP) as the sieving matrix and SYBR Green II RNA gel stain for on-column labeling. Although further study is needed to investigate if the separation is sequence dependent, our study demonstrated, for the first time, that CE could be an effective and rapid method in monitoring the miRNA methylation process.

Identification of Ligands to Manganese and Calcium in Photosystem II by Site-Directed Mutagenesis

The Mn and Ca ions in Photosystem II are believed to be located at the interface between the intrinsic and extrinsic polypeptides of the PSII core. The recent identification of YZ [1,2] and YD [3,4] as Tyr-161 and Tyr-160 of the D1 and D2 polypeptides, respectively, suggests that many of the ligands to Mn and Ca are likely to be contributed by the D1 and D2 polypeptides. From considerations of Mn coordination chemistry[5,6], and from recent EPR [7] and electron spin echo [8] measurements with 15N, the Mn ions are believed to be coordinated primarily by carboxyl residues. Carboxyl residues are also likely ligands for Ca. There are 27 carboxyl residues in the lumenally-exposed regions of the mature forms of the D1 and D2 polypeptides. Several models for Mn and Ca ligation have been advanced incorporating a number of these residues [9,10]. However, there appears to be no compelling reason for selecting any particular residue over any other; unlike the previous situation with YZ and YD, there is no apparent C2 symmetry between the D1 and D2 polypeptides in this region.

1,25-DIHYDROXYVITAMIN D3 REGULATES CALBINDIN-D28K EXPRESSION AT THE TRANSCRIPTIONAL LEVEL

This chapter presents the results of the study to analyze if 1,25-dihydroxyvitamin D 3 [l,25(OH) 2 D 3 ] regulates calbindin-D 28K expression at the transcriptional level. Vitamin D-deficient chicks (3–4 week old) were dosed intramuscularly with 6.5 nmoles l,25(OH) 2 D 3 . At various times, afterward nuclei were isolated from the duodenal mucosa to measure l,25(OH) 2 D 3 receptor occupancy levels by an exchange assay and calbindin-D 28K gene transcription by nuclear run-off. Steady-state levels of calbindin-D 28K gene transcription in vitamin D-deficient and vitamin D-replete chicks, and in vitamin D-replete chicks 1 hour following a dose of 600 μg cycloheximide, were also measured. The time course of l,25(OH) 2 D 3 receptor occupancy in vitamin D-deficient chicks following a dose of 6.5 nmoles of l,25(OH) 2 D 3 showed that binding of the hormone to its receptor occurred very quickly and reached a peak at l–2 h. A similar response profile was observed in the rate of calbindin-D 28K gene transcription following the same dose of l,25(OH) 2 D 3 . These data support the hypothesis that the mechanism of action of l,25(OH) 2 D 3 is like that of other classical steroid hormones, exerting its effects by the initiation of transcription of the calbindin-D 28K gene through a receptor-mediated mechanism.