1,675 research outputs found
Photochemical Reductive trans-Elimination from trans-Diacidotetracyanoplatinate(IV) Complexes
Abstract
Upon CT excitation the complex ions trans-[Pt(CN)4N3X]2- and trans-[Pt(CN)4X2]2- (X = Cl and Br) undergo a reductive trans-elimination with formation of [Pt(CN)4]2- and two ligand radicals in the photoprimary step. The formation of a Pt(III) intermediate is not observed. Due to the stability of [Pt(CN)4]2-, recombination reactions regenerating the starting complex are efficient if the ligand radicals are not scavenged. For the azide complexes the high quantum yields for the production of [Pt(CN)4]2- are explained by the instability of azide radicals. For trans-[Pt(CN)4X2]2-, the recombination is efficient in aqueous solution, while in ethanol the halogen atoms are scavenged by hydrogen abstraction. The sequence of steps following CT excitation can be explained by a potential energy diagram.</jats:p
Correlative Microscopy of Morphology and Luminescence of Cu porphyrin aggregates
Transfer of energy and information through molecule aggregates requires as
one important building block anisotropic, cable-like structures. Knowledge on
the spatial correlation of luminescence and morphology represents a
prerequisite in the understanding of internal processes and will be important
for architecting suitable landscapes. In this context we study the morphology,
fluorescence and phosphorescence of molecule aggregate structures on surfaces
in a spatially correlative way. We consider as two morphologies, lengthy
strands and isotropic islands. It turns out that phosphorescence is quite
strong compared to fluorescence and the spatial variation of the observed
intensities is largely in line with the amount of dye. However in proportion,
the strands exhibit more fluorescence than the isotropic islands suggesting
weaker non-radiative channels. The ratio fluorescence to phosphorescence
appears to be correlated with the degree of aggregation or internal order. The
heights at which luminescence saturates is explained in the context of
attenuation and emission multireflection, inside the dye. This is supported by
correlative photoemission electron microscopy which is more sensitive to the
surface region. The lengthy structures exhibit a pronounced polarization
dependence of the luminescence with a relative dichroism up to about 60%,
revealing substantial perpendicular orientation preference of the molecules
with respect to the substrate and parallel with respect to the strands
Millimeter wave satellite concepts. Volume 1: Executive summary
The objectives of the program were: (1) development of methodology based on the technical requirements of potential services that might be assigned to millimeter wave bands for identifying the viable and appropriate technologies for future NASA millimeter research and development programs, and (2) testing of this methodology with user applications and services. The scope of the program included the entire communications network, both ground and space subsystems. The reports include: (1) cost, weight, and performance models for the subsystems, (2) conceptual design for point-to-point and broadcast communications satellites, (3) analytic relationships between subsystem parameters and an overall link performance, (4) baseline conceptual systems, (5) sensitivity studies, (6) model adjustment analyses, (7) identification of critical technologies and their risks, (8) brief R&D program scenarios for the technologies judged to be moderate or extensive risks
Calculation of coercivity of magnetic nanostructures at finite temperatures
We report a finite temperature micromagnetic method (FTM) that allows for the
calculation of the coercive field of arbitrary shaped magnetic nanostructures
at time scales of nanoseconds to years. Instead of directly solving the
Landau-Lifshitz-Gilbert equation, the coercive field is obtained without any
free parameter by solving a non linear equation, which arises from the
transition state theory. The method is applicable to magnetic structures where
coercivity is determined by one thermally activated reversal or nucleation
process. The method shows excellent agreement with experimentally obtained
coercive fields of magnetic nanostructures and provides a deeper understanding
of the mechanism of coercivity.Comment: submitted to Phys. Rev.
Inhibition of protein kinase C, (sodium plus potassium)-activated adenosine triphosphatase, and sodium pump by synthetic phospholipid analogues.
Inhibition of protein kinase C, (sodium plus potassium)-activated adenosine triphosphatase, and sodium pump by synthetic phospholipid analogues.
Delivery of sTRAIL variants by MSCs in combination with cytotoxic drug treatment leads to p53-independent enhanced antitumor effects
Mesenchymal stem cells (MSCs) are able to infiltrate tumor tissues and thereby effectively deliver gene therapeutic payloads. Here, we engineered murine MSCs (mMSCs) to express a secreted form of the TNF-related apoptosis-inducing ligand (TRAIL), which is a potent inducer of apoptosis in tumor cells, and tested these MSCs, termed MSC.sTRAIL, in combination with conventional chemotherapeutic drug treatment in colon cancer models. When we pretreated human colorectal cancer HCT116 cells with low doses of 5-fluorouracil (5-FU) and added MSC.sTRAIL, we found significantly increased apoptosis as compared with single-agent treatment. Moreover, HCT116 xenografts, which were cotreated with 5-FU and systemically delivered MSC.sTRAIL, went into remission. Noteworthy, this effect was protein 53 (p53) independent and was mediated by TRAIL-receptor 2 (TRAIL-R2) upregulation, demonstrating the applicability of this approach in p53-defective tumors. Consequently, when we generated MSCs that secreted TRAIL-R2-specific variants of soluble TRAIL (sTRAIL), we found that such engineered MSCs, labeled MSC.sTRAIL DR5, had enhanced antitumor activity in combination with 5-FU when compared with MSC.sTRAIL. In contrast, TRAIL-resistant pancreatic carcinoma PancTu1 cells responded better to MSC.sTRAIL DR4 when the antiapoptotic protein XIAP (X-linked inhibitor of apoptosis protein) was silenced concomitantly. Taken together, our results demonstrate that TRAIL-receptor selective variants can potentially enhance the therapeutic efficacy of MSC-delivered TRAIL as part of individualized and tumor-specific combination treatments. © 2013 Macmillan Publishers Limited All rights reserved
The BeppoSAX view of the X-ray active nucleus of NGC4258
BeppoSAX observed NGC4258 on December 1998, when its 2-10 keV luminosity was
\~1E41 erg/s. 100% variability is observed in the 3-10 keV band on timescales
of a half a day while 20% variability is observed on timescales of one hour.
The nuclear component is visible above 2 keV only, being obscured by a column
density of (9.5+/-1.2)E22 cm-2; this component is detected up to 70 keV with
S/N>=3 and with the steep power law energy index of 1.11+/-0.14. Bremsstrahlung
emission for the 2-70 keV X-ray luminosity, as expected in ADAF models with
strong winds, is ruled out by the data. The ratio between the nuclear radio and
the X-ray luminosities is <=1E-5, similar to that of radio quiet AGN. X-ray
variability and spectral shape, radio to X-ray and NIR to X-ray luminosity
ratios suggest that the nucleus of NGC4258 could be a scaled-down version of a
Seyfert nucleus. The soft (E<=2keV) X-ray emission is complex. There are at
least two thermal-like components, with T1=0.6+/-0.1 keV and T2>=1.3 keV. The
cooler (L(0.1-2.4keV)=1E40 erg/s) component is probably associated with the
jet, resolved in X-rays by the ROSAT HRI. The second component, which can be
modeled equally well by an unobscured power law model, has L(0.1-2.4keV)~7E39
erg/s, consistent with that expected from discrete X-ray sources in the host
galaxy. NGC4258 and other maser AGNs show strong nuclear X-ray absorption. We
propose that this large column of gas might be responsible for shielding the
regions of maser emission from X-ray illumination. So a large column density
gas may be a necessary property of masing AGNs.Comment: ApJ in pres
ROSAT Blank Field Sources I: Sample Selection and Archival Data
We have identified a population of blank field sources (or `blanks') among
the ROSAT bright unidentified X-ray sources with faint optical counterparts.
The extreme X-ray over optical flux ratio of blanks is not compatible with the
main classes of X-ray emitters except for extreme BL Lacertae objects. From the
analysis of ROSAT archival data we found no indication of variability and
evidence for only three sources, out of 16, needing absorption in excess of the
Galactic value. We also found evidence for an extended nature for only one of
the 5 blanks with a serendipitous HRI detection; this source (1WGAJ1226.9+3332)
was confirmed as a z=0.89 cluster of galaxies. Palomar images reveal the
presence of a red (O-E~2) counterpart in the X-ray error circle for 6 blanks.
The identification process brought to the discovery of another high z cluster
of galaxies, one (possibly extreme) BL Lac, two ultraluminous X-ray sources in
nearby galaxies and two apparently normal type1 AGNs. These AGNs, together with
4 more AGN-like objects seem to form a well defined group: they present
unabsorbed X-ray spectra but red Palomar counterparts. We discuss the possible
explanations for the discrepancy between the X-ray and optical data, among
which: a suppressed big blue bump emission, an extreme dust to gas (~40-60 the
Galactic ratio), a high redshift (z>3.5) QSO nature, an atypical dust grain
size distribution and a dusty warm absorber. These AGN-like blanks seem to be
the bright (and easier to study) analogs of the sources which are found in deep
Chandra observations. Three more blanks have a still unknown nature.Comment: 23 pages, 8 figures, accepted by ApJ main journa
FACT -- The G-APD revolution in Cherenkov astronomy
Since two years, the FACT telescope is operating on the Canary Island of La
Palma. Apart from its purpose to serve as a monitoring facility for the
brightest TeV blazars, it was built as a major step to establish solid state
photon counters as detectors in Cherenkov astronomy. The camera of the First
G-APD Cherenkov Telesope comprises 1440 Geiger-mode avalanche photo diodes
(G-APD), equipped with solid light guides to increase the effective light
collection area of each sensor. Since no sense-line is available, a special
challenge is to keep the applied voltage stable although the current drawn by
the G-APD depends on the flux of night-sky background photons significantly
varying with ambient light conditions. Methods have been developed to keep the
temperature and voltage dependent response of the G-APDs stable during
operation. As a cross-check, dark count spectra with high statistics have been
taken under different environmental conditions. In this presentation, the
project, the developed methods and the experience from two years of operation
of the first G-APD based camera in Cherenkov astronomy under changing
environmental conditions will be presented.Comment: Proceedings of the Nuclear Science Symposium and Medical Imaging
Conference (IEEE-NSS/MIC), 201
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