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排序方式: 共有450条查询结果,搜索用时 281 毫秒
71.
Caitlin E. Shields Dr. Xue Wang Dr. Thomas Fellowes Rob Clowes Dr. Linjiang Chen Prof. Graeme M. Day Prof. Anna G. Slater Dr. John W. Ward Dr. Marc A. Little Prof. Andrew I. Cooper 《Angewandte Chemie (International ed. in English)》2023,62(34):e202303167
Hydrogen-bonded organic frameworks (HOFs) with low densities and high porosities are rare and challenging to design because most molecules have a strong energetic preference for close packing. Crystal structure prediction (CSP) can rank the crystal packings available to an organic molecule based on their relative lattice energies. This has become a powerful tool for the a priori design of porous molecular crystals. Previously, we combined CSP with structure-property predictions to generate energy-structure-function (ESF) maps for a series of triptycene-based molecules with quinoxaline groups. From these ESF maps, triptycene trisquinoxalinedione (TH5) was predicted to form a previously unknown low-energy HOF (TH5-A) with a remarkably low density of 0.374 g cm−3 and three-dimensional (3D) pores. Here, we demonstrate the reliability of those ESF maps by discovering this TH5-A polymorph experimentally. This material has a high accessible surface area of 3,284 m2 g−1, as measured by nitrogen adsorption, making it one of the most porous HOFs reported to date. 相似文献
72.
73.
Raghavendra Kumar P. Ajai K. Singh J. E. Drake M. B. Hursthouse M. E. Little 《Structural chemistry》2007,18(2):203-207
A non-Schiff base (Te, N, O) ligand MeOC6 H4TeCH2CH2NHCH(CH3)C6H4–2–OH (LH) having a chiral center and its palladium(II) complex [PdClL]·CH2Cl2 (1) have been synthesized. Both have characteristic 1H and 13C NMR spectra. The single crystal structure of the complex 1 has been determined by X-ray diffraction methods. The monoclinic crystals of 1 (space group P21/n) have a=14.581(5) Å, b=13.160(5) Å and c=20.249(5) Å, β=99.398(5)°. The Te $\cdots A non-Schiff base (Te, N, O) ligand MeOC6 H4TeCH2CH2NHCH(CH3)C6H4–2–OH (LH) having a chiral center and its palladium(II) complex [PdClL]·CH2Cl2 (1) have been synthesized. Both have characteristic 1H and 13C NMR spectra. The single crystal structure of the complex 1 has been determined by X-ray diffraction methods. The monoclinic crystals of 1 (space group P21/n) have a=14.581(5) ?, b=13.160(5) ? and c=20.249(5) ?, β=99.398(5)°. The TeCl secondary interactions [3.303(2)–3.352(2) ?] between two nearly square planar palladium complex molecules results in a
bimolecular aggregate having a PdPd distance 3.203(1) ?. The Pd–Te, Pd–N and Pd–O bond lengths are 2.5005(7)/2.4914(7), 2.060(4)/2.061(4) and 2.054(3)/2.044(3) ?,
respectively. 相似文献
74.
75.
76.
Roger G. Little Michael J. Nowlan 《Progress in Photovoltaics: Research and Applications》1997,5(5):309-315
The dominant photovoltaic (PV) technology today is crystalline silicon, used in 85% of the terrestrial modules shipped in 1996. Thin-film PV technologies promise to allow significant reductions in the cost per watt of electricity generated by PV modules. However, thin films must meet or exceed the standards for performance, reliability, and cost set by crystalline silicon in order to successfully penetrate the market. This paper reports the results of a detailed economic analysis done for a 25 MW year−1 multi-crystalline silicon production facility, including crystal growth, water slicing, solar cell fabrication and module assembly. The module manufacturing cost is projected to be $1·78 W−1. The sensitivity of module cost to polysilicon cost and cell efficiency were determined. This analysis provides a near-term (1998–2000) cost/performance benchmark against which thin-film technologies can be compared. © 1997 John Wiley & Sons, Ltd. 相似文献
77.
Poly(?-caprolactone) (PCL) has many favourable attributes for tissue engineering scaffold applications. A major drawback, however, is its slow degradation rate, typically greater than 3 years. In this study PCL was melt blended with a small percentage of poly(aspartic acid-co-lactide) (PAL) and the degradation behaviour was evaluated in phosphate buffer solution (PBS) at 37 °C. The addition of PAL was found to significantly enhance the degradation profile of PCL. Subsequent degradation behaviour was investigated in terms of the polymer's mechanical properties, molecular weight (Mw), mass changes and thermal characteristics. The results indicate that the addition of PAL accelerates the degradation of PCL, with 20% mass loss recorded after just 7 months in vitro for samples containing 8 wt% PAL. The corresponding pure PCL samples exhibited no mass loss over the same time period. In vitro assessment of PCL and PCL/PAL composites in tissue culture medium in the absence of cells revealed stable pH readings with time. SEM studies of cell/biomaterial interactions demonstrated biocompatibility of C3H10T1/2 cells with PCL and PCL/PAL composites at all concentrations of PAL additive. 相似文献
78.
K. Srilatha L. Pavić A. Moguš-Milanković Ch. Srinivasa Rao G. Little Flower V. Ravi Kumar N. Veeraiah 《Journal of Non》2011,357(19-20):3538-3547
LiI–AgI–B2O3 glasses mixed with different concentrations of V2O5 (ranging from 0 to 1.0 mol%) were prepared. Electrical and dielectric properties over wide ranges of frequency (10?2–107 Hz) and temperature (173–523 K) have been studied. Additionally spectroscopic properties viz., optical absorption and ESR spectra have been investigated. The optical absorption and ESR studies have revealed that vanadium ions do exist in both V4+ and V5+ states and the redox ratio is the highest in the glasses containing 0.8 mol% of V2O5. The results of conductivity measurements have indicated that there is a mixed conduction (both ionic and electronic). The ionic conduction seems to be dominant over polaron hopping only in the glasses containing V2O5 more than 0.8 mol% of V2O5. The impedance spectra have also indicated that the conduction is predominantly polaronic in nature. The frequency and temperature dependence of the electrical moduli as well as dielectric loss parameters have exhibited relaxation character attributed to the vanadyl complexes. The relaxation effects have been analyzed by the graphical method and from this analysis it has been established that there is a spreading of relaxation times. The results have been further discussed quantitatively in the light of different valance states of vanadium ions with the aid of the data on spectroscopic properties. 相似文献
79.
Binding of muscimol-conjugated quantum dots to GABAC receptors 总被引:1,自引:0,他引:1
Gussin HA Tomlinson ID Little DM Warnement MR Qian H Rosenthal SJ Pepperberg DR 《Journal of the American Chemical Society》2006,128(49):15701-15713
Functionalization of highly fluorescent CdSe/ZnS core-shell nanocrystals (quantum dots, qdots) is an emerging technology for labeling cell surface proteins. We have synthesized a conjugate consisting of approximately 150-200 muscimols (a GABA receptor agonist) covalently joined to the qdot via a poly(ethylene glycol) (PEG) linker (approximately 78 ethylene glycol units) and investigated the binding of this muscimol-PEG-qdot conjugate to homomeric rho1 GABAC receptors expressed in Xenopus oocytes. GABAC receptors mediate inhibitory synaptic signaling at multiple locations in the central nervous system (CNS). Binding of the conjugate was analyzed quantitatively by determining the fluorescence intensity of the oocyte surface membrane in relation to that of the surrounding incubation medium. Upon 5- to 10-min incubation with muscimol-PEG-qdots (34 nM in qdot concentration), GABAC-expressing oocytes exhibited a fluorescent halo at the surface membrane that significantly exceeded the fluorescence of the incubation medium. This halo was absent following muscimol-PEG-qdot treatment of oocytes lacking GABAC receptors. Incubation of the oocyte with free muscimol (100 microM-5 mM), PEG-muscimol (500 microM), or GABA (100 microM - 5 mM) substantially reduced or eliminated the fluorescence halo produced by muscimol-PEG-qdots, and the removal of GABA or free muscimol led to a recovery of muscimol-PEG-qdot binding. Unconjugated qdots and PEG-qdots that lacked conjugated muscimol neither exhibited significant binding activity nor diminished the subsequent binding of muscimol-PEG-qdots. The results indicate that muscimol joined to qdots via a long-chain PEG linker exhibits specific binding activity at the ligand-binding pocket of expressed GABAC receptors, despite the presence of both the long PEG linker and the sterically bulky qdot. 相似文献
80.
Zugates GT Anderson DG Little SR Lawhorn IE Langer R 《Journal of the American Chemical Society》2006,128(39):12726-12734
The safe and efficient delivery of DNA remains the major barrier to the clinical application of non-viral gene therapy. Here, we present novel, biodegradable polymers for gene delivery that are capable of simple graft modification and demonstrate the ability to respond to intracellular conditions. We synthesized poly(beta-amino ester)s using a new amine monomer, 2-(pyridyldithio)-ethylamine (PDA). These cationic, degradable polymers contain pyridyldithio functionalities in the side chains that react with high specificity toward thiol ligands. This reactivity is demonstrated using both mercaptoethylamine (MEA) and the thiol peptide RGDC, a ligand that binds with high affinity to certain integrin receptors. These two polymer derivatives displayed strong DNA binding as determined using electrophoresis and dye exclusion assays. In addition, the MEA-based polymer and plasmid DNA were shown to self-assemble into cationic complexes with effective diameters as low as 100 nm. Furthermore, this DNA binding ability was substantially reduced in response to intracellular glutathione concentrations, which may aid in DNA unpackaging inside the cell. These complexes also displayed low cellular toxicity and were able to mediate transfection at levels comparable to PEI in human hepatocellular carcinoma cells. These results suggest that PDA-based poly(beta-amino ester)s may serve as a modular platform for polymer-mediated gene delivery. 相似文献