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831.
Boday Dylan J. Stover Robert J. Muriithi Beatrice Loy Douglas A. 《Journal of Sol-Gel Science and Technology》2012,61(1):144-150
Bridged polysilsesquioxanes are increasingly used to prepare protective coatings, particulate chromatographic materials, and
adsorbents. However, little is known about the mechanical properties of the materials and how they are influenced by the nature
of the bridging group. In this paper, we have prepared monolithic xerogels and aerogels of hexylene- and phenylene-bridged
polysilsesquioxanes and have measured their flexural strength and modulus. Consistent with their compact structure, the porous,
glassy phenylene- and hexylene-bridged xerogels were hundreds of stronger than the analogous aerogels. The nature of the bridging
group did not appear to affect the mechanical properties of the xerogels, in contrast, it presented a profound effect on the
mechanical properties of the aerogels. Phenylene-bridged aerogels were brittle and 30% stronger than silica aerogels of the
same density. However, the opaque hexylene-bridged aerogels were found to be elastic and appreciably weaker than the phenylene-bridged
or silica aerogels. 相似文献
832.
Georgia M. Arvanitis Michael E. Berardini Douglas M. Ho 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(3):m126-m128
The title complex [systematic name: trans‐bis(3‐isopropyl‐7‐oxocyclohepta‐1,3,5‐trienolato)copper(II)], [Cu(C10H11O2)2],is a substance possessing antimicrobial activity. The compound crystallizes in a number of polymorphic forms, the structures for two of which are reported here. Stacks of square‐planar molecules exhibiting weak intermolecular copper–olefin π interactions (not observed in earlier reports on this substance) are described. The molecules have crystallographically imposed inversion symmetry, with stacking and copper–olefin π distances ranging from 3.226 (2) to 3.336 (1) Å. 相似文献
833.
M. Liezers S. A. Lehn K. B. Olsen O. T. FarmerIII Douglas C. Duckworth 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(1):299-304
Electrochemically modulated separations (EMS) are shown to be a rapid and selective means of extracting and concentrating
Pu from complex solutions prior to isotopic analysis by inductively coupled plasma mass spectrometry (ICP‐MS). This separation
is performed in a flow injection mode, on‐line with the ICP‐MS. A three‐electrode, flow‐by electrochemical cell is used to
accumulate Pu at an anodized glassy carbon electrode by redox conversion of Pu(III) to Pu (IV&VI). The entire process takes
place in 2% (v/v) (0.46 M) HNO3. No redox chemicals or acid concentration changes are required. Plutonium accumulation and release is redox dependent and
controlled by the applied cell potential. Large transient volumetric concentration enhancements can be achieved. Based on
more negative U(IV) potentials relative to Pu(IV), separation of Pu from uranium is efficient, thereby eliminating uranium
hydride interferences. EMS‐ICP‐MS isotope ratio measurement performance will be presented for femtogram to attogram level
plutonium isotope injections. 相似文献
834.
Douglas Du Boulay Khozirah Shaari Brian W. Skelton Peter G. Waterman Allan H. White 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(2):199-200
A room‐temperature single‐crystal X‐ray structure determination of the title compound, C21H20O8, confirms the stereochemical assignment made previously on the basis of spectroscopic studies [Shaari & Waterman (1994). J. Nat. Prod. 57 , 720–724]. 相似文献
835.
Judith L. Kissick Douglas A. Keszler 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(6):631-632
The structure of rubidium dilithium digallium tris(borate), RbLi2Ga2(BO3)3, contains two‐dimensional sheets of open‐branched rings of GaO4 tetrahedra and planar BO3 triangles that are joined by LiO4 tetrahedra to form a three‐dimensional framework. Ten‐coordinate Rb atoms lie on twofold axes and occupy channels within the framework that extend along the b axis. 相似文献
836.
A new class of tetraamide macrocyclic receptors for anions with two quaternized amine functionalities exhibited higher affinities for anions compared with the corresponding neutral amides. In two crystal structures of halide complexes of the prototypes with phenyl and pyridine spacers, the anions are held by hydrogen bonding with the amide hydrogens. The pyridine analogues display higher affinities in general than the phenyl systems, a phenomenon which is attributed to the anion version of the chelate effect. 相似文献
837.
Yulin Ren Esperanza J. Carcache de Blanco Leonardus B.S. Kardono Heebyung Chai Norman R. Farnsworth Steven M. Swanson Yuanqing Ding Jannie P.J. Marais A. Douglas Kinghorn 《Tetrahedron》2010,66(29):5311-5320
A new biflavonoid (1), a new xanthone enantiomer (2), five new caged xanthones (3-7), and several known compounds were isolated from the stem bark of Garcinia lateriflora, collected in Indonesia. The structures of the new compounds were determined by analysis of spectroscopic data, and the absolute configuration of the caged xanthones was shown for the first time at carbons 5, 7, 8, 8a, 10a, and 27, by analysis of COSY and NOESY NMR and ECD spectra. The biflavonoids exhibited proteasome-inhibitory activity, and the known compound, morelloflavone (8) was found to have the greatest potency (IC50=1.3 μM). The caged xanthones were cytotoxic toward HT-29 cells, with the known compound, morellic acid (10) being the most active (ED50=0.36 μM). However, when tested in an in vivo hollow fiber assay, it was inactive at the highest dose tested (20 mg/kg). 相似文献
838.
Godlewski G Alapafuja SO Bátkai S Nikas SP Cinar R Offertáler L Osei-Hyiaman D Liu J Mukhopadhyay B Harvey-White J Tam J Pacak K Blankman JL Cravatt BF Makriyannis A Kunos G 《Chemistry & biology》2010,17(11):1256-1266
The enzyme fatty acid amide hydrolase (FAAH) catalyzes the in vivo degradation of the endocannabinoid anandamide, thus controlling its action at receptors. A novel FAAH inhibitor, AM3506, normalizes the elevated blood pressure and cardiac contractility of spontaneously hypertensive rats (SHR) without affecting these parameters in normotensive rats. These effects are due to blockade of FAAH and a corresponding rise in brain anandamide levels, resulting in CB? receptor-mediated decrease in sympathetic tone. The supersensitivity of SHR to CB? receptor-mediated cardiovascular depression is related to increased G protein coupling of CB? receptors. Importantly, AM3506 does not elicit hyperglycemia and insulin resistance seen with other FAAH inhibitors or in FAAH?/? mice, which is related to its inability to inhibit FAAH in the liver due to rapid hepatic uptake and metabolism. This unique activity profile offers improved therapeutic value in hypertension. 相似文献
839.
840.
Jorge P. López‐Alonso Dr. Miguel A. Pardo‐Cea Irene Gómez‐Pinto Dr. Irene Fernández Dr. Avijit Chakrabartty Prof. Enrique Pedroso Prof. Carlos González Prof. Douglas V. Laurents Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(18):5314-5323
KIA7, a peptide with a highly restricted set of amino acids (Lys, Ile, Ala, Gly and Tyr), adopts a specifically folded structure. Some amino acids, including Lys, Ile, Ala, Gly and His, form under the same putative prebiotic conditions, whereas different conditions are needed for producing Tyr, Phe and Trp. Herein, we report the 3D structure and conformational stability of the peptide KIA7H, which is composed of only Lys, Ile, Ala, Gly and His. When the imidazole group is neutral, this 20‐mer peptide adopts a four‐helix bundle with a specifically packed hydrophobic core. Therefore, one‐pot prebiotic proteins with well‐defined structures might have arisen early in chemical evolution. The Trp variant, KIA7W, was also studied. It adopts a 3D structure similar to that of KIA7H and its previously studied Tyr and Phe variants, but is remarkably more stable. When tested for ribonucleolytic activity, KIA7H, KIA7W and even short, unstructured peptides rich in His and Lys, in combination with Mg++, Mn++ or Ni++ (but not Cu++, Zn++ or EDTA) specifically cleave the single‐stranded region in an RNA stem–loop. This suggests that prebiotic peptide–divalent cation complexes with ribonucleolytic activity might have co‐inhabited the RNA world. 相似文献