Interlayer interactions play an important role in the formation of two-dimensional covalent organic frameworks (2D COFs), yet the effects of monomer structure on COF formation, crystallinity, and ...susceptibility to exfoliation are not well understood. Here we probe these effects by studying the stacking behavior of imine-linked macrocycles that represent discrete models of 2D COFs. Specifically, macrocycles based on terephthaldehyde (PDA) or 2,5-dimethoxyterephthaldehyde (DMPDA) stack upon cooling molecularly dissolved solutions. Both macrocycles assemble cooperatively with similar ΔH e values of −97 kJ/mol and −101 kJ/mol, respectively, although the DMPDA macrocycle assembly process showed a more straightforward temperature dependence. Density functional theory calculations of the stacking of PDA macrocycles suggested two stable configurations that were close in energy. Circular dichroism spectroscopy performed on macrocycles bearing chiral side chains revealed a helix reversion process for the PDA macrocycles that was not observed for the DMPDA macrocycles. Given the structural similarity of these monomers, these findings demonstrate that the stacking processes associated with nanotubes derived from these macrocycles, as well as for the corresponding COFs, are complex and susceptible to kinetic traps, casting doubt on the relevance of thermodynamic arguments for improving materials quality. Rather, a deeper understanding of the mechanism of supramolecular polymerization and its interplay with polymerization and error correction during COF synthesis is needed for improved control of the crystallinity and morphology of these emerging materials.
A library of polymeric amphiphiles was prepared based on a one-pot methodology using reversible addition fragmentation chain transfer (RAFT) polymerization. These surfactants were then employed to ...disperse carbon nanotubes (CNTs) within water and an aqueous DMSO solution. All polymeric materials that were soluble in water were used to prepare dispersions of CNT. A range of experimental techniques including atomic force microscopy (AFM), fluorescence quenching experiments, UV/Vis absorbance measurements and 1H NOESY NMR spectroscopy were employed to probe the interactions between the CNT and the polymeric surfactant.
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•Synthesis of amphiphilic diblock copolymers via one-pot RAFT methodology.•Preparation of stable aqueous dispersions of carbon nanotubes.•Use of fluorescence to probe interactions between surfactant and carbon nanotubes.•Use of absorbance to probe interactions between surfactant and carbon nanotubes.
Nanotubes assembled from macrocyclic precursors offer a unique combination of low dimensionality, structural rigidity, and distinct interior and exterior microenvironments. Usually the weak stacking ...energies of macrocycles limit the length and mechanical strength of the resultant nanotubes. Imine‐linked macrocycles were recently found to assemble into high‐aspect ratio (>103), lyotropic nanotubes in the presence of excess acid. Yet these harsh conditions are incompatible with many functional groups and processing methods, and lower acid loadings instead catalyze macrocycle degradation. Here we report pyridine‐2,6‐diimine‐linked macrocycles that assemble into high‐aspect ratio nanotubes in the presence of less than 1 equiv of CF3CO2H per macrocycle. Analysis by gel permeation chromatography and fluorescence spectroscopy revealed a cooperative self‐assembly mechanism. The low acid concentrations needed to induce assembly enabled nanofibers to be obtained by touch‐spinning, which exhibit higher Young's moduli (1.33 GPa) than many synthetic polymers and biological filaments. These findings represent a breakthrough in the design of inverse chromonic liquid crystals, as assembly under such mild conditions will enable the design of structurally diverse and mechanically robust nanotubes from synthetically accessible macrocycles.
Mechanisch robuste Nanoröhren: Die Einführung einer Pyridineinheit in einen Imin‐verknüpften Makrocyclus ermöglicht dessen kooperative protonierungsgetriebene Anordnung zu Nanoröhren. Touch‐Spinning der Nanoröhren ergibt Nanofasern mit Young‐Moduli von 1.33 GPa – ein weit höherer Wert als für viele synthetische Polymere und biologische Filamente.
Macrocyclesbased on directional bonding and dynamic covalentbond exchange can be design ed with specificpore shapes, sizes, andfunctionality.These sys- tems retain many of the design criteria and ...desirableas- pects of two-dimensional (2D) covalent organic frame- works (COFs)but are more easily processed. Here we access discrete hexagonal imine-linked macrocycles by condensing atruncated analogueof1,3,5-tris(4-aminophe- nyl)benzene(TAPB) with terephthaldehyde (PDA). The monomers first condense into polymers buteventually convertinto hexagonal macrocycles in high yield. The high selectivity for hexagonal macrocycles is enforcedby their aggregation and crystallization into layered struc- tures with more sluggish imine exchange. Their formation and exchange processes provide new insight into how imine-linked 2D COF simultaneously polymerize and crys- tallize. Solutions of theseassembled macrocycles were cast into oriented, crystalline films, expanding the poten- tial routes to 2D materials.
Background The regional impact of care at a National Cancer Institute Comprehensive Cancer Center (NCI-CCC) on adherence to National Comprehensive Cancer Network (NCCN) ovarian cancer treatment ...guidelines and survival is unclear. Study Design We performed a retrospective population-based study of consecutive patients diagnosed with epithelial ovarian cancer between January 1, 1996 and December 31, 2006 in southern California. Patients were stratified according to care at an NCI-CCC (n = 5), non-NCI high-volume hospital (≥10 cases/year, HVH, n = 29), or low-volume hospital (<10 cases/year, LVH, n = 158). Multivariable logistic regression and Cox-proportional hazards models were used to examine the effect of NCI-CCC status on treatment guideline adherence and ovarian cancer-specific survival. Results A total of 9,933 patients were identified (stage I, 22.8%; stage II, 7.9%; stage III, 45.1%; stage IV, 24.2%), and 8.1% of patients were treated at NCI-CCCs. Overall, 35.7% of patients received NCCN guideline adherent care, and NCI-CCC status (odds ratio OR 1.00) was an independent predictor of adherence to treatment guidelines compared with HVHs (OR 0.83, 95% CI 0.70 to 0.99) and LVHs (OR 0.56, 95% CI 0.47 to 0.67). The median ovarian cancer-specific survivals according to hospital type were: NCI-CCC 77.9 (95% CI 61.4 to 92.9) months, HVH 51.9 (95% CI 49.2 to 55.7) months, and LVH 43.4 (95% CI 39.9 to 47.2) months (p < 0.0001). National Cancer Institute Comprehensive Cancer Center status (hazard ratio HR 1.00) was a statistically significant and independent predictor of improved survival compared with HVH (HR 1.18, 95% CI 1.04 to 1.33) and LVH (HR 1.30, 95% CI 1.15 to 1.47). Conclusions National Cancer Institute Comprehensive Cancer Center status is an independent predictor of adherence to ovarian cancer treatment guidelines and improved ovarian cancer-specific survival. These data validate NCI-CCC status as a structural health care characteristic correlated with superior ovarian cancer quality measure performance. Increased access to NCI-CCCs through regional concentration of care may be a mechanism to improve clinical outcomes.
We use the one-dimensional TRISTAN-MP particle-in-cell code to model the nonlinear evolution of the whistler heat flux instability (WHFI) that was proposed by Gary et al. and Gary & Li to regulate ...the electron heat flux in the solar wind and astrophysical plasmas. The simulations are initialized with electron velocity distribution functions typical for the solar wind. We perform a set of simulations at various initial values of the electron heat flux and βe. The simulations show that parallel whistler waves produced by the WHFI saturate at amplitudes consistent with the spacecraft measurements. The simulations also reproduce the correlations of the saturated whistler wave amplitude with the electron heat flux and βe revealed in the spacecraft measurements. The major result is that parallel whistler waves produced by the WHFI do not significantly suppress the electron heat flux. The presented simulations indicate that coherent parallel whistler waves observed in the solar wind are unlikely to regulate the heat flux of solar wind electrons.
COSMOS-Web: An Overview of the JWST Cosmic Origins Survey Casey, Caitlin M.; Kartaltepe, Jeyhan S.; Drakos, Nicole E. ...
Astrophysical journal/The Astrophysical journal,
09/2023, Volume:
954, Issue:
1
Journal Article, Web Resource
Peer reviewed
Open access
Abstract
We present the survey design, implementation, and outlook for COSMOS-Web, a 255 hr treasury program conducted by the James Webb Space Telescope in its first cycle of observations. COSMOS-Web ...is a contiguous 0.54 deg
2
NIRCam imaging survey in four filters (F115W, F150W, F277W, and F444W) that will reach 5
σ
point-source depths ranging ∼27.5–28.2 mag. In parallel, we will obtain 0.19 deg
2
of MIRI imaging in one filter (F770W) reaching 5
σ
point-source depths of ∼25.3–26.0 mag. COSMOS-Web will build on the rich heritage of multiwavelength observations and data products available in the COSMOS field. The design of COSMOS-Web is motivated by three primary science goals: (1) to discover thousands of galaxies in the Epoch of Reionization (6 ≲
z
≲ 11) and map reionization’s spatial distribution, environments, and drivers on scales sufficiently large to mitigate cosmic variance, (2) to identify hundreds of rare quiescent galaxies at
z
> 4 and place constraints on the formation of the universe’s most-massive galaxies (
M
⋆
> 10
10
M
⊙
), and (3) directly measure the evolution of the stellar-mass-to-halo-mass relation using weak gravitational lensing out to
z
∼ 2.5 and measure its variance with galaxies’ star formation histories and morphologies. In addition, we anticipate COSMOS-Web’s legacy value to reach far beyond these scientific goals, touching many other areas of astrophysics, such as the identification of the first direct collapse black hole candidates, ultracool subdwarf stars in the Galactic halo, and possibly the identification of
z
> 10 pair-instability supernovae. In this paper we provide an overview of the survey’s key measurements, specifications, goals, and prospects for new discovery.
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