ABSTRACT
In this work, pyrazine (A), aminopyrazine (B), quinoxaline (C), and 5,6,7,8-tetrahydroquinoxaline (D) have been screened out among a large number of pyrazine derivatives to construct Hofmann-type metal-organic frameworks (MOFs) Fe(L)[M(CN)4 ] (M=Pt, Pd) with similar 3D pillared-layer structures. X-ray single-crystal diffraction reveals that the alternate linkage between M and FeII ions through cyano bridges forms the 2D extended metal cyanide sheets, and ligands A-D acted as vertical columns to connect the 2D sheets to give 3D pillared-layer structures. Subsequently, a series of bivariate MOFs were constructed by pairwise combination of the four ligands A-D, which were confirmed by 1 Hâ NMR, PXRD, FTIR, and Raman spectroscopy. The results demonstrated that ligand size and crystallization rate play a dominant role in constructing bivariate Hofmann-type MOFs. More importantly, the spin-crossover (SCO) properties of the bivariate MOFs can be finely tuned by adjusting the proportion of the two pillared ligands in the 3D Hofmann-type structures. Remarkably, the spin transition temperatures, Tc ↑ and Tc ↓ of Fe(A)x (B)1-x [Pt(CN)4 ] (x=0 to 1) can be adjusted from 239 to 254â K and from 248 to 284â K, respectively. Meanwhile, the width of the hysteresis loops can be widened from 9 to 30â K. Changing Pt to Pd, the hysteresis loops of Fe(A)x (B)1-x [Pd(CN)4 ] can be tuned from 9 (Tc ↑=215â K, Tc ↓=206â K) to 24â K (Tc ↑=300â K, Tc ↓=276â K). This research provides wider implications in the development of advanced bistable materials, especially in precisely regulating SCO properties.
ABSTRACT
Two FeII8L12 cubic metal-organic cages were constructed with semi-rigid ligands and they further self-assembled into supramolecular assemblies with three different porous cavities. The supramolecular assemblies showed synergistic adsorption of I2 and TTF, and their solid state spin-crossover behaviors were influenced by the adsorbed guest molecules.
ABSTRACT
CO2 capture under a dynamical flow situation requires adsorbents possessing balanced proportion of macropores as diffusion path and micropores as adsorption reservoir. However, the construction of interconnected micro-/macropores structure coupled with abundant nitrogen species into one carbon skeleton remains a challenge. Here, we report a new approach to prepare sponge-like carbon with a well-developed micro-/macroporous structure and enriched nitrogen species through aqueous phase polymerization of acrylonitrile in the presence of graphene oxide. The tension stress caused by the uniform thermal shrinkage of polyacrylonitrile during the pyrolysis together with the favorable flexibility of graphene oxide sheets are responsible for the formation of the sponge-like morphology. The synergistic effect of micro-/macroporous framework and rich CO2 -philic site enables such carbon to decrease resistance to mass transfer and show high CO2 dynamic selectivity over N2 (454) and CH4 (11), as well as good CO2 capacity at 298â K under low CO2 partial pressure (0.17â bar, a typical CO2 partial pressure in flue gas). The above attributes make this porous carbon a promising candidate for CO2 capture from flue gas, methane sources and other relevant applications.
ABSTRACT
The development of highly selective, chemically stable and moisture-resistant adsorbents is a key milestone for gas separation. Porous carbons featured with random orientation and cross-linking of turbostratic nanodomains usually have a wide distribution of micropores. Here we have developed a thermoregulated phase-transition-assisted synthesis of carbon nanoplates with more than 80 % sp2 carbon, unimodal ultramicropore and a controllable thickness. The thin structure allows oriented growth of carbon crystallites, and stacking of crystallites in nearly parallel orientation are responsible for the single size of the micropores. When used for gas separation from CH4 , carbon nanoplates exhibit high uptakes (5.2, 5.3 and 5.1â mmol g-1 ) and selectivities (7, 71 and 386) for CO2 , C2 H6 and C3 H8 under ambient conditions. The dynamic adsorption capacities are close to equilibrium uptakes of single components, further demonstrating superiority of carbon nanoplates in terms of selectivity and sorption kinetics.
ABSTRACT
BACKGROUND: To test if the hypocretin (orexin) neuropeptide precursor (HCRT) gene, HCRT, mutations are implicated in the development of narcolepsy with cataplexy deficiency in young children. METHODS: The entire HCRT gene and ~2000 bp promoter region was first sequenced in 181 patients and 153 controls, and rare polymorphisms including three nonsynonymous amino acid changes were identified. Next the 557 bp region of exon 2 harboring the three nonsynonymous changes was sequenced in an additional 298 early-onset subjects and in 148 control samples. RESULTS: A previously known common polymorphism (rs760282) and nine rare novel polymorphisms were identified in subjects and controls without significant differences. Two nonsynonymous exon 2 substitutions (+977 H54A, +979 G55R) were detected in two subjects with early onset at 7 and 6 years, respectively, but were not found in any controls. These substitutions are not likely to vastly change peptide binding to hypocretin receptors. One additional exon 2 substitution (+1019, K68R) was found in two patients and one control. Additional sequencing that focused on exon 2 showed additional subjects and controls with the +1019 K68R polymorphism and without significant differences between the subjects and the control. Segregation of two of these three nonsynonymous single nucleotide polymorphisms (SNPs) were observed from unaffected parents to offspring. CONCLUSIONS: Sequencing of a large number of early-onset narcolepsy subjects revealed three novel nonsynonymous substitutions within the preprohypocretin protein, two of which were only found in patients with early-onset narcolepsy but are not likely to be functionally significant, especially in heterozygote subjects.
