44,305 research outputs found
Metal-Oxo Photo-oxidants, Photochemistry and Photophysics of trans-[Os^(VI)(tmc)(O)_2]^(2+)(tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane) and trans-[Os^(VI)(CN)_4(O)_2]^(2-)
trans-[Os^(VI)(tmc)(O)_2]^(2+)(tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane) and trans-[Os^(VI)(CN)_4(O)_2]^(2-) are emissive in the solid state and in fluid solutions at room temperature (τ~ 1.0–1.5 µs); the (^3)E_g state of trans-[Os^(VI)(tmc)(O)_2]^(2+) is a powerful one-electron oxidant {[Os^(VI)(O)_2]^(2+) + e^– → [Os^V (O)_2]+, E^0_f > 2.0 V vs. normal hydrogen electrode} in aqueous solution, reacting with PPh3 and ((PhCH_2)_2)S to give O=PPh_3 and ((PhCH_2)_2)S=O, respectively
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Preparation of multiblock copolymers via step-wise addition of l-lactide and trimethylene carbonate.
Poly(l-lactide) (PLA) is a bioderived and biodegradable polymer that has limited applications due to its hard and brittle nature. Incorporation of 1,3-trimethylene carbonate into PLA, in a block copolymer fashion, improves the mechanical properties, while retaining the biodegradability of the polymer, and broadens its range of applications. However, the preparation of 1,3-trimethylene carbonate (TMC)/l-lactide (LA) copolymers beyond diblock and triblock structures has not been reported, with explanations focusing mostly on thermodynamic reasons that impede the copolymerization of TMC after lactide. We discuss the preparation of multiblock copolymers via the ring opening polymerization (ROP) of LA and TMC, in a step-wise addition, by a ferrocene-chelating heteroscorpionate zinc complex, {[fc(PPh2)(BH[(3,5-Me)2pz]2)]Zn(ÎĽ-OCH2Ph)}2 ([(fcP,B)Zn(ÎĽ-OCH2Ph)]2, fc = 1,1'-ferrocenediyl, pz = pyrazole). The synthesis of up to pentablock copolymers, from various combinations of LA and TMC, was accomplished and the physical, thermal, and mechanical properties of the resulting copolymers evaluated
A Search for Interstellar Carbon Chain Alcohol HC4OH in Star-Forming Region L1527 and Dark Cloud TMC-1
We report a sensitive search for the rotational transitions of the carbon
chain alcohol HC4OH in the frequency range of 21.2-46.7 GHz in the star-forming
region L1527 and the dark cloud TMC-1. The motivation was laboratory detection
of HC4OH by microwave spectroscopy. Despite achieving rms noise levels of
several millikelvin in the antenna temperature using the 45 m telescope at
Nobeyama Radio Observatory, the detection was not successful, leading to 3
sigma upper limits corresponding to the column densities of 2.0 \times 1012 and
5.6 \times 1012 cm-2 in L1527 and TMC-1, respectively. These upper limits
indicate that [HC4OH]/[HC5N] ratios are less than 0.3 and 0.1 in L1527 and
TMC-1, respectively, where HC5N is an HC4-chain cyanide and HC4OH is a
hydroxide. These ratios suggest that the cyano carbon chain molecule dominates
the hydroxyl carbon chain molecule in L1527 and TMC-1. This is contrary to the
case of saturated compounds in hot cores, e.g., CH3OH and CH3CN, and can be a
chemical feature of carbon chain molecules in L1527 and TMC-1. In addition, the
column densities of the "unsubstituted" carbon chain molecule C4H and the
sulfur-bearing molecules SO and HCS+ were determined from detected lines in
L1527.Comment: Astrophysical Journal, in pres
The Dust Emissivity Spectral Index in the Starless Core TMC-1C
In this paper we present a dust emission map of the starless core TMC-1C
taken at 2100 microns. Along with maps at 160, 450, 850 and 1200 microns, we
study the dust emissivity spectral index from the (sub)millimeter spectral
energy distribution, and find that it is close to the typically assumed value
of beta = 2. We also map the dust temperature and column density in TMC-1C, and
find that at the position of the dust peak (A_V ~ 50), the
line-of-sight-averaged temperature is ~7 K. Employing simple Monte Carlo
modeling, we show that the data are consistent with a constant value for the
emissivity spectral index over the whole map of TMC-1C.Comment: 11 pages, including 5 pages of figures. Accepted to Ap
Limits on chemical complexity in diffuse clouds: search for CH3OH and HC5N absorption
Context: An unexpectedly complex polyatomic chemistry exists in diffuse
clouds, allowing detection of species such as C2H, C3H2, H2CO and NH3 which
have relative abundances that are strikingly similar to those inferred toward
the dark cloud TMC-1
Aims: We probe the limits of complexity of diffuse cloud polyatomic
chemistry.
Methods: We used the IRAM Plateau de Bure Interferometer to search for
galactic absorption from low-lying J=2-1 rotational transitions of A- and
E-CH3OH near 96.740 GHz and used the VLA to search for the J=8-7 transition of
HC5N at 21.3 GHz.
Results: Neither CH3OH nor HC5N were detected at column densities well below
those of all polyatomics known in diffuse clouds and somewhat below the levels
expected from comparison with TMC-1. The HCN/HC5N ratio is at least 3-10 times
higher in diffuse gas than toward TMC-1.
Conclusions: It is possible to go to the well once (or more) too ofte
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