No abstract

The Fermi Large Area Telescope (LAT) has opened the way for comparative studies of cosmic rays (CRs) and high-energy objects in the Milky Way (MW) and in other, external, star-forming galaxies. Using 2 yr of observations with the Fermi LAT, Local Group galaxy M31 was detected as a marginally extended gamma-ray source, while only an upper limit has been derived for the other nearby galaxy M33. We revisited the gamma-ray emission in the direction of M31 and M33 using more than 7 yr of LAT Pass 8 data in the energy range -0.1 100 GeV, presenting detailed morphological and spectral analyses. M33 remains undetected, and we computed an upper limit of´---2.0 10 erg cm s 12 2 1 on the -0.1 100 GeV energy flux (95% confidence level). This revised upper limit remains consistent with the observed correlation between gamma-ray luminosity and star formation rate tracers and implies an average CR density in M33 that is at most half of that of the MW. M31 is detected with a significance of nearly s 10 . Its spectrum is consistent with a power law with photon index G =  + 2.4 0.1 stat syst and a -0.1 100 GeV energy flux of ( ) + ---5.6 0.6 10 erg cm s stat syst 12 21 . M31 is detected to be extended with a s 4 significance. The spatial distribution of the emission is consistent with a uniform-brightness disk with a radius of 0°. 4 and no offset from the center of the galaxy, but nonuniform intensity distributions cannot be excluded. The flux from M31 appears confined to the inner regions of the galaxy and does not fill the disk of the galaxy or extend far from it. The gamma-ray signal is not correlated with regions rich in gas or star formation activity, which suggests that the emission is not interstellar in origin, unless the energetic particles radiating in gamma rays do not originate in recent star formation. Alternative and nonexclusive interpretations are that the emission results from a population of millisecond pulsars dispersed in the bulge and disk of M31 by disrupted globular clusters or from the decay or annihilation of dark matter particles, similar to what has been proposed to account for the so-called Galactic center excess found in Fermi-LAT observations of the MW.

The cellular behavior and toxicity effect of organometallic complexes depend largely on their peripheral ligands. In this study, we have synthesized a series of novel luminescent cationic iridium(III) complexes by tuning the ancillary N(∧)N ligand based on a structure [Ir(ppy)2(N(∧)N)](+) (ppy = 1-phenyl-pyridine; N(∧)N = 2,2'-bipyridine (bpy, 1) or phenanthroline (phen, 2) or 4,7-diphenyl-1,10- phenanthroline (DIP, 3)). As the size of coordinated N(∧)N ligand increases, absorbance/emission efficiency, quantum yields, lipophilicity, and cell uptake rates of the complexes also increase, in a general order: 3 > 2 > 1. All three complexes display anticancer activity, with 3 exhibiting the highest cellular uptake efficiency and the greatest cytotoxic activities in several cancer cell lines with IC50s lower than that of cisplatin. Because of its strong hydrophobic nature, the death inducer 3 was found to accumulate favorably to endoplasmic reticulum (ER) and to cause ER stress in cells. The fast cytosolic release of calcium from stressed ER disturbed the morphology and function of mitochondria, initiating an intrinsic apoptotic pathway. Understanding of the cell death mechanism would help further structure-activity optimization on these novel Ir(III) complexes as emerging cancer therapeutics.

Under well-controlled conditions, different polypyrrole variants can be galvanostatically prepared in acetonitrile + 1% H2O by changing the current density. At current densities down to 0.25 mA/cm2, PPy(I) is electrosynthesized; at lower current densities, a mixture of PPy(I) and PPy(II) is generated. In the presence of a small amount of acid (∼1 × 10-5 M), PPy(II) is exclusively formed. The availability of well-defined materials enables us to perform further reliable characterization by EQCM. The results reveale different natures of ionic transport when different PPy variants are switched between oxidized and neutral states. When doped with PF6 -, PPy(I) and PPy(III) show only anionic movement upon redox, whereas PPy(II) exhibits the transport of both anion and cation. The structural diversity of PPy explains some controversial results that were obtained in the past. The mechanistic analysis offers new insight into the formation paths of conducting polymers. Of particular interest is the electrochemical solid-state transition from PPy(II) to PPy(I) in pyrrole-free solution when a higher potential (>1.4 V) is applied to the PPy(II)-coated electrode. Repetitive potential scans transform PPy(II) completely into PPy(I). The transition is clearly evidenced by voltammograms. EQCM demonstrated a consistent change in ionic movement. In situ conductivity measurements indicate different types of charge carriers generated during the charging of PPy(I) and PPy(II).