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871.
Interpenetration as a Mechanism for Negative Thermal Expansion in the Metal–Organic Framework Cu3(btb)2 (MOF‐14) 下载免费PDF全文
Yue Wu Dr. Vanessa K. Peterson Emily Luks Dr. Tamim A. Darwish Prof. Cameron J. Kepert 《Angewandte Chemie (International ed. in English)》2014,53(20):5175-5178
Metal–organic framework materials (MOFs) have recently been shown in some cases to exhibit strong negative thermal expansion (NTE) behavior, while framework interpenetration has been found to reduce NTE in many materials. Using powder and single‐crystal diffraction methods we investigate the thermal expansion behavior of interpenetrated Cu3(btb)2 (MOF‐14) and find that it exhibits an anomalously large NTE effect. Temperature‐dependent structural analysis shows that, contrary to other interpenetrated materials, in MOF‐14 the large positive thermal expansion of weak interactions that hold the interpenetrating networks together results in a low‐energy contractive distortion of the overall framework structure, demonstrating a new mechanism for NTE. 相似文献
872.
Toroker MC Kanan DK Alidoust N Isseroff LY Liao P Carter EA 《Physical chemistry chemical physics : PCCP》2011,13(37):16644-16654
The positions of electronic band edges are one important metric for determining a material's capability to function in a solar energy conversion device that produces fuels from sunlight. In particular, the position of the valence band maximum (conduction band minimum) must lie lower (higher) in energy than the oxidation (reduction) reaction free energy in order for these reactions to be thermodynamically favorable. We present first principles quantum mechanics calculations of the band edge positions in five transition metal oxides and discuss the feasibility of using these materials in photoelectrochemical cells that produce fuels, including hydrogen, methane, methanol, and formic acid. The band gap center is determined within the framework of DFT+U theory. The valence band maximum (conduction band minimum) is found by subtracting (adding) half of the quasiparticle gap obtained from a non-self-consistent GW calculation. The calculations are validated against experimental data where possible; results for several materials including manganese(ii) oxide, iron(ii) oxide, iron(iii) oxide, copper(i) oxide and nickel(ii) oxide are presented. 相似文献
873.
Nechab M Besson E Campolo D Perfetti P Vanthuyne N Bloch E Denoyel R Bertrand MP 《Chemical communications (Cambridge, England)》2011,47(18):5286-5288
Mesoporous silica grafted with a tertiary amine was used as a basic nanocatalyst to promote in confined medium the enantioselective cascade rearrangement of enediynes based on the phenomenon of memory of chirality; the multi-substrates recyclable catalytic reagent could easily be recovered by simple filtration, and reused without any decrease in activity even when changing the solvent. 相似文献
874.
A method for the determination of penicillin V together with its impurities and by-products formed during biosynthesis, using capillary electrophoresis (CE) with UV and electrospray-mass spectrometric (ESI-MS) detection is presented. Aqueous and nonaqueous electrolytes containing 20 mM ammonium acetate were investigated to determine their suitability for the separation of these analytes. These carrier electrolytes were optimized with respect to the pH and the solvent/s used (water, methanol, acetonitrile, ethanol and isopropanol) and it was shown that although the nonaqueous electrolytes offered unique separation selectivities, the best results in terms of selectivity and sensitivity were obtained for the aqueous system. Finally, the applicability of this method for the analysis of a mixture representative of a real fermentation broth was demonstrated using an aqueous carrier electrolyte with both UV and ESI-MS detection. 相似文献
875.
Brett W. Boote Himashi P. Andaraarachchi Bryan A. Rosales Rafael Blome-Fernández Feng Zhu Malinda D. Reichert Kalyan Santra Jingzhe Li Jacob W. Petrich Javier Vela Emily A. Smith 《Chemphyschem》2019,20(20):2647-2656
Lead halide perovskites possess unique characteristics that are well-suited for optoelectronic and energy capture devices, however, concerns about their long-term stability remain. Limited stability is often linked to the methylammonium cation, and all-inorganic CsPbX3 (X=Cl, Br, I) perovskite nanocrystals have been reported with improved stability. In this work, the photostability and thermal stability properties of CsPbX3 (X=Cl, Br, I) nanocrystals were investigated by means of electron microscopy, X-ray diffraction, thermogravimetric analysis coupled with FTIR (TGA-FTIR), ensemble and single particle spectral characterization. CsPbBr3 was found to be stable under 1-sun illumination for 16 h in ambient conditions, although single crystal luminescence analysis after illumination using a solar simulator indicates that the luminescence states are changing over time. CsPbBr3 was also stable to heating to 250 °C. Large CsPbI3 crystals (34±5 nm) were shown to be the least stable composition under the same conditions as both XRD reflections and Raman bands diminish under irradiation; and with heating the γ (black) phase reverts to the non-luminescent δ phase. Smaller CsPbI3 nanocrystals (14±2 nm) purified by a different washing strategy exhibited improved photostability with no evidence of crystal growth but were still thermally unstable. Both CsPbCl3 and CsPbBr3 show crystal growth under irradiation or heat, likely with a preferential orientation based on XRD patterns. TGA-FTIR revealed nanocrystal mass loss was only from liberation and subsequent degradation of surface ligands. Encapsulation or other protective strategies should be employed for long-term stability of these materials under conditions of high irradiance or temperature. 相似文献
876.
A convenient method for the determination of the absolute configuration of chiral amines 总被引:1,自引:0,他引:1
A highly useful methodology that allows the determination of the absolute configuration of aliphatic and aromatic chiral amines based on the rationalization of stereoselective three-point interactions during chromatography on a rationally designed chiral stationary phase and conformational analysis of the elutes was developed. This approach is based on the broadly accepted chiral recognition mechanism of the Whelk-O 1 CSP and requires a facile derivatization of the amine and the determination of the lowest energy conformation of the corresponding t-Boc- or Z-derived carbamates. The absolute configuration determined by employing chiral structure activity relationships in HPLC analysis was verified by single-crystal X-ray analysis or studies with carbamoyl derivatives of amines of known configuration. The general validity and applicability of this methodology was demonstrated by analysis of seven carbamates derived from aliphatic and aromatic amines. Due to its simplicity and time-efficiency, i.e., ease of derivatization of amines and fast HPLC method development, this approach can be considered a useful supplement to established techniques such as NMR spectroscopy. 相似文献
877.
Kylie M. Wilson John W. Swartout Henry A. Touchton Erica N. Lambert James E. Johnstone Ashley K. Archambeau David M. Marolf Emily R. Mikeska Vincent M. Lynch Vladimir N. Nesterov Eric W. Reinheimer Gregory L. Powell Cynthia B. Powell 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(5):529-537
Three asymmetric diosmium(I) carbonyl sawhorse complexes have been prepared by microwave heating. One of these complexes is of the type Os2(μ‐O2CR)(μ‐O2CR′)(CO)4L2, with two different bridging carboxylate ligands, while the other two complexes are of the type Os2(μ‐O2CR)2(CO)5L, with one axial CO ligand and one axial phosphane ligand. The mixed carboxylate complex Os2(μ‐acetate)(μ‐propionate)(CO)4[P(p‐tolyl)3]2, ( 1 ), was prepared by heating Os3(CO)12 with a mixture of acetic and propionic acids, isolating Os2(μ‐acetate)(μ‐propionate)(CO)6, and then replacing two CO ligands with two phosphane ligands. This is the first example of an Os2 sawhorse complex with two different carboxylate bridges. The syntheses of Os2(μ‐acetate)2(CO)5[P(p‐tolyl)3], ( 3 ), and Os2(μ‐propionate)2(CO)5[P(p‐tolyl)3], ( 6 ), involved the reaction of Os3(CO)12 with the appropriate carboxylic acid to initially produce Os2(μ‐carboxylate)2(CO)6, followed by treatment with refluxing tetrahydrofuran (THF) to form Os2(μ‐carboxylate)2(CO)5(THF), and finally addition of tri‐p‐tolylphosphane to replace the THF ligand with the P(p‐tolyl)3 ligand. Neutral complexes of the type Os2(μ‐O2CR)2(CO)5L had not previously been subjected to X‐ray crystallographic analysis. The more symmetrical disubstituted complexes, i.e. Os2(μ‐formate)2(CO)4[P(p‐tolyl)3]2, ( 8 ), Os2(μ‐acetate)2(CO)4[P(p‐tolyl)3]2, ( 4 ), and Os2(μ‐propionate)2(CO)4[P(p‐tolyl)3]2, ( 7 ), as well as the previously reported symmetrical unsubstituted complexes Os2(μ‐acetate)2(CO)6, ( 2 ), and Os2(μ‐propionate)2(CO)6, ( 5 ), were also prepared in order to examine the influence of axial ligand substitution on the Os—Os bond distance in these sawhorse molecules. Eight crystal structures have been determined and studied, namely μ‐acetato‐1κO:2κO′‐μ‐propanoato‐1κO:2κO′‐bis[tris(4‐methylphenyl)phosphane]‐1κP,2κP′‐bis(dicarbonylosmium)(Os—Os) dichloromethane monosolvate, [Os2(C2H3O2)(C3H5O2)(C21H21P)2(CO)4]·CH2Cl2, ( 1 ), bis(μ‐acetato‐1κO:2κO′)bis(tricarbonylosmium)(Os—Os), [Os2(C2H3O2)2(CO)6], ( 2 ) (redetermined structure), bis(μ‐acetato‐1κO:2κO′)pentacarbonyl‐1κ2C,2κ3C‐[tris(4‐methylphenyl)phosphane‐1κP]diosmium(Os—Os), [Os2(C2H3O2)2(C21H21P)(CO)5], ( 3 ), bis(μ‐acetato‐1κO:2κO′)bis[tris(4‐methylphenyl)phosphane]‐1κP,2κP‐bis(dicarbonylosmium)(Os—Os) p‐xylene sesquisolvate, [Os2(C2H3O2)2(C21H21P)2(CO)4]·1.5C8H10, ( 4 ), bis(μ‐propanoato‐1κO:2κO′)bis(tricarbonylosmium)(Os—Os), [Os2(C3H5O2)2(CO)6], ( 5 ), pentacarbonyl‐1κ2C,2κ3C‐bis(μ‐propanoato‐1κO:2κO′)[tris(4‐methylphenyl)phosphane‐1κP]diosmium(Os—Os), [Os2(C3H5O2)2(C21H21P)(CO)5], ( 6 ), bis(μ‐propanoato‐1κO:2κO′)bis[tris(4‐methylphenyl)phosphane]‐1κP,2κP‐bis(dicarbonylosmium)(Os—Os) dichloromethane monosolvate, [Os2(C3H5O2)2(C21H21P)2(CO)4]·CH2Cl2, ( 7 ), and bis(μ‐formato‐1κO:2κO′)bis[tris(4‐methylphenyl)phosphane]‐1κP,2κP‐bis(dicarbonylosmium)(Os—Os), [Os2(CHO2)2(C21H21P)2(CO)4], ( 8 ). 相似文献
878.
Emily Dalton Qinyuan Chai Molly W. Shaw Tucker J. McKenzie Eric S. Mullins Neil Ayres 《Journal of polymer science. Part A, Polymer chemistry》2019,57(13):1389-1395
Shape memory polymers (SMPs) are a class of responsive polymers that have attracted attention in designing biomedical devices because of their potential to improve minimally invasive surgeries. Use of porous SMPs in vascular grafts has been proposed because porosity aids in transfer of fluids through the graft and growth of vascular tissue. However, porosity also allows blood to leak through grafts so preclotting the materials is necessary. Here hydrogels have been synthesized from acrylic acid and N‐hydroxyethyl acrylamide and coated around a porous SMP produced from lactose functionalized polyurea‐urethanes. The biocompatibility of the polymers used to prepare the cross‐linked shape memory material is demonstrated using an in vitro cell assay. As expected, the hydrogel coating enhanced fluid uptake abilities without hindering the shape memory properties. These results indicate that hydrogels can be used in porous SMP materials without inhibiting the shape recovery of the material. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1389–1395 相似文献
879.
Brigita Darminto Dr. Gregory J. Rees John Cattermull Dr. Kenjiro Hashi Dr. Maria Diaz-Lopez Dr. Naoaki Kuwata Dr. Stephen J. Turrell Emily Milan Yvonne Chart Dr. Camilla Di Mino Prof. Hyeon Jeong Lee Prof. Andrew L. Goodwin Prof. Mauro Pasta 《Angewandte Chemie (International ed. in English)》2023,62(51):e202314444
The sodium-rich antiperovskites (NaRAPs) with composition Na3OB (B=Br, Cl, I, BH4, etc.) are a family of materials that has recently attracted great interest for application as solid electrolytes in sodium metal batteries. Non-Arrhenius ionic conductivities have been reported for these materials, the origin of which is poorly understood. In this work, we combined temperature-resolved bulk and local characterisation methods to gain an insight into the origin of this unusual behaviour using Na3OBr as a model system. We first excluded crystallographic disorder on the anion sites as the cause of the change in activation energy; then identified the presence of a poorly crystalline impurities, not detectable by XRD, and elucidated their effect on ionic conductivity. These findings improve understanding of the processing-structure-properties relationships pertaining to NaRAPs and highlight the need to determine these relationships in other materials systems, which will accelerate the development of high-performance solid electrolytes. 相似文献
880.
Polymer monolithic stationary phases are designed as a continuous interconnected globular material perfused by macropores. Like packed column, where separation efficiency is related to particle diameter, the efficiency of monoliths can be enhanced by tuning the size of both the microglobules and macropores. This protocol described the synthesis of poly(styrene-co-divinylbenzene) monolithic stationary phases in capillary column formats. Moreover, guidelines are provided to tune the macropore structure targeting high-throughput and high-resolution monolith chromatography. The versatility of these columns is exemplified by their ability to separate tryptic digests, intact proteins, and oligonucleotides under a variety of chromatographic conditions. The repeatability of the presented column fabrication process is demonstrated by the successful creation of 12 columns in three different column batches, as evidenced by the consistency of retention times (coefficients of variance [c.v.] = 0.9%), peak widths (c.v. = 4.7%), and column pressures (c.v. = 3.1%) across the batches. 相似文献