Self-assembly and salt-induced thermoresponsive properties of amphiphilic PEG/cation random terpolymers in water

Herein, we report the self-assembly and salt-induced thermoresponsive properties of amphiphilic random terpolymers consisting of hydrophilic poly(ethylene glycol) (PEG) and quaternary ammonium cations, and hydrophobic dodecyl groups in water. The random terpolymers self-assembled into size-controlled multichain micelles in pure water or in water containing NaCl. The micelle size increased upon increasing the content of the cationic groups in the total hydrophilic monomer units (∼50 mol%) and turned larger in the presence of NaCl than that in pure water. More uniquely, the random terpolymer micelles showed lower critical solution temperature-type solubility in water containing salts such as NaCl, while the solutions of the polymer micelles in pure water were transparent even upon heating to over 90 °C. The cloud point (Cp) temperature of the aqueous polymer micelle solution was controlled by the concentration of NaCl or the composition of the terpolymers. The critical concentration of NaCl for thermoresponsive solubility depended on the PEG/cation composition of the terpolymers. For example, a PEG/cation/dodecyl (1/1/2) random terpolymer micelle exhibited thermoresponse in water containing more than 0.5 M NaCl; the Cp of the aqueous solution decreased from 86 °C to 59 °C upon increasing the concentration of NaCl from 0.5 M to 2.0 M. The Cp of their terpolymers increased upon increasing the content of quaternary ammonium cations

Hydration State on Poly(ethylene glycol)-Bearing Homopolymers and Random Copolymer Micelles: In Relation to the Thermoresponsive Property and Micellar Structure

Poly(ethylene glycol) (PEG)-bearing (co)polymers often show lower critical solution temperature-type solubility in water; the aqueous solution becomes clouded and/or phase-separated upon heating to a certain temperature (cloud-point temperature). In general, it has been interpreted that the thermoresponsive properties of (co)polymers in water originate from the dehydration of the polymer chains, whereas the hydration state of these polymers has not yet been evaluated. Herein, we report the amount of hydration water on PEG-bearing homopolymers and random copolymer micelles in water, analyzed by terahertz time-domain spectroscopy, and micellar structures (molecular packing in the hydrophilic layer) determined by small-angle X-ray scattering. Systematic investigation by changing the ratio of PEG side chains and alkyl side chains revealed a clear correlation between the thermoresponsive properties, molecular and micellar structures, and the amount of hydration water. The random copolymers induce self-folding or intermolecular self-assembly to form unimer or multichain micelles in water; the size of the micelles increases with an increasing number of hydrophobic monomer units. As the micelle size increases, the PEG chains tend to be densely packed in the hydrophilic shell layers, leading to a reduction in the amount of hydration water per ethylene glycol unit of PEG. Thus, the dehydration of the PEG chain likely becomes easier, and the cloud-point temperatures decrease with increasing hydrophobic monomer content

Synthesis of Amphiphilic Three-Armed Star Random Copolymers via Living Radical Polymerization and their Unimolecular Folding Properties in Water

Amphiphilic three-armed star random copolymers were synthesized by ruthenium-catalyzed living radical copolymerization of hydrophilic poly(ethylene glycol) methyl ether methacrylate (PEGMA) and hydrophobic dodecyl methacrylate (DMA). Their amphiphilic star random copolymers with 10-50 mol% DMA efficiently self-folded in water with intramolecular hydrophobic interaction to form compact unimolecular micelles. Owing to PEG segments, star copolymers were thermoresponsive to induce lower critical solution temperature-type phase separation in water

Polymeric pseudo-crown ether for cation recognition via cation template-assisted cyclopolymerization.

Cyclopolymerization is a chain polymerization of bifunctional monomers via alternating processes of intramolecular cyclization and intermolecular addition, to give soluble linear polymers consisting of in-chain cyclic structures. Though cyclopolymers comprising in-chain multiple large rings potentially show unique functionality, they generally require the elaborate design of bifunctional monomers. Here we report cation template-assisted cyclopolymerization of poly(ethylene glycol) dimethacrylates as an efficient strategy directly yielding polymeric pseudo-crown ethers with large in-chain cavities (up to 30-membered rings) for selective molecular recognition. The key is to select a size-fit metal cation for the spacer unit of the divinyl monomers to form a pseudo-cyclic conformation, where the two vinyl groups are suitably positioned for intramolecular cyclization. The marriage of supramolecular chemistry and polymer chemistry affords efficient, one-pot chemical transformation from common chemical reagents with simple templates to functional cyclopolymers

The ASTRO-H X-ray Observatory

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV. These instruments include a high-resolution, high-throughput spectrometer sensitive over 0.3-2 keV with high spectral resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers covering 5-80 keV, located in the focal plane of multilayer-coated, focusing hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12 keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the 40-600 keV band. The simultaneous broad bandpass, coupled with high spectral resolution, will enable the pursuit of a wide variety of important science themes.Comment: 22 pages, 17 figures, Proceedings of the SPIE Astronomical Instrumentation "Space Telescopes and Instrumentation 2012: Ultraviolet to Gamma Ray

The Quiescent Intracluster Medium in the Core of the Perseus Cluster

Clusters of galaxies are the most massive gravitationally-bound objects in the Universe and are still forming. They are thus important probes of cosmological parameters and a host of astrophysical processes. Knowledge of the dynamics of the pervasive hot gas, which dominates in mass over stars in a cluster, is a crucial missing ingredient. It can enable new insights into mechanical energy injection by the central supermassive black hole and the use of hydrostatic equilibrium for the determination of cluster masses. X-rays from the core of the Perseus cluster are emitted by the 50 million K diffuse hot plasma filling its gravitational potential well. The Active Galactic Nucleus of the central galaxy NGC1275 is pumping jetted energy into the surrounding intracluster medium, creating buoyant bubbles filled with relativistic plasma. These likely induce motions in the intracluster medium and heat the inner gas preventing runaway radiative cooling; a process known as Active Galactic Nucleus Feedback. Here we report on Hitomi X-ray observations of the Perseus cluster core, which reveal a remarkably quiescent atmosphere where the gas has a line-of-sight velocity dispersion of 164+/-10 km/s in a region 30-60 kpc from the central nucleus. A gradient in the line-of-sight velocity of 150+/-70 km/s is found across the 60 kpc image of the cluster core. Turbulent pressure support in the gas is 4% or less of the thermodynamic pressure, with large scale shear at most doubling that estimate. We infer that total cluster masses determined from hydrostatic equilibrium in the central regions need little correction for turbulent pressure.Comment: 31 pages, 11 Figs, published in Nature July

Hitomi (ASTRO-H) X-ray Astronomy Satellite

The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E  >  2  keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month

Hitomi X-Ray Studies of Giant Radio Pulses from the Crab Pulsar

To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2300 keV band and the Kashima NICT radio telescope in the 1.41.7 GHz band with a net exposure of about 2 ks on 2016 March 25, just before the loss of the Hitomi mission. The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1000 and 100 GRPs were simultaneously observed at the main pulse and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main pulse or inter-pulse phase. All variations are within the 2 fluctuations of the X-ray fluxes at the pulse peaks, and the 3 upper limits of variations of main pulse or inter-pulse GRPs are 22% or 80% of the peak flux in a 0.20 phase width, respectively, in the 2300 keV band. The values for main pulse or inter-pulse GRPs become 25% or 110%, respectively, when the phase width is restricted to the 0.03 phase. Among the upper limits from the Hitomi satellite, those in the 4.510 keV and 70300 keV bands are obtained for the first time, and those in other bands are consistent with previous reports. Numerically, the upper limits of the main pulse and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) 10(exp 11) erg cm(exp 2), respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magnetosphere. Although the number of photon-emitting particles should temporarily increase to account for the brightening of the radio emission, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a >0.02% brightening of the pulse-peak flux under such conditions