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排序方式: 共有268条查询结果,搜索用时 15 毫秒
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93.
Chung KC Cao L Dias AV Pickering IJ George GN Zamble DB 《Journal of the American Chemical Society》2008,130(43):14056-14057
The high-affinity nickel-binding site of the Escherichia coli [NiFe]-hydrogenase accessory protein HypB was localized to residues at the immediate N-terminus of the protein. Modification of a metal-binding fusion protein, site-directed mutagenesis experiments, and DFT calculations were used to identify the N-terminal amine as a ligand as well as the three cysteine residues in the CXXCGCXXX motif. This sequence can be removed from the protein and both a synthesized peptide and a protein fusion bind nickel with a similar affinity and the same structure as the parent metalloprotein, indicating the self-sufficiency of this high-affinity nickel-binding sequence. 相似文献
94.
Torgersen T Wilkins AL Rundberget T Miles CO 《Rapid communications in mass spectrometry : RCM》2008,22(8):1127-1136
Marine algal toxins of the okadaic acid group can occur as fatty acid esters in blue mussels, and are commonly determined indirectly by transformation to their parent toxins by alkaline hydrolysis. Some data are available regarding the identity of the fatty acid esters, mainly of palmitic acid (16:0) derivatives of okadaic acid (OA), dinophysistoxin-1 (DTX1) and dinophysistoxin-2 (DTX2). Other fatty acid derivatives have been described, but with limited mass spectral data. In this paper, the mass spectral characterization of the [M-H](-) and [M+Na](+) ions of 16 fatty acid derivatives of each of OA, DTX1 and DTX2 is presented. The characteristic fragmentation of [M+Na](+) ions of OA analogues provided a useful tool for identifying these, and has not been described previously. In addition, a set of negative ion multiple reaction monitoring (MRM) methods was developed for direct determination of 16 fatty acid esters of OA, 16 fatty acid esters of DTX1 and 16 fatty acid esters of DTX2 in shellfish extracts. The MRM methods were employed to study the profiles of fatty acid esters of OA analogues in blue mussels and to compare these with fatty acid ester profiles reported for other groups of marine algal toxins. 相似文献
95.
Fuchter MJ Smith CJ Tsang MW Boyer A Saubern S Ryan JH Holmes AB 《Chemical communications (Cambridge, England)》2008,(18):2152-2154
The synthesis of a family of O-silylcarbamates from the corresponding silylamines has been achieved simply by heating the silylamine in supercritical carbon dioxide (scCO2), and these O-silylcarbamates have been shown to be effective precursors for the synthesis of a range of symmetrical and unsymmetrical ureas. 相似文献
96.
Laura E. Bickerton Andrew Docker Alistair J. Sterling Heike Kuhn Prof. Fernanda Duarte Prof. Paul D. Beer Prof. Matthew J. Langton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(45):11738-11745
Synthetic anion transporters show much promise as potential anti-cancer agents and therapeutics for diseases associated with mis-regulation of protein anion channels. In such applications high activity and anion selectivity are crucial to overcome competing proton or hydroxide transport which dissipates cellular pH gradients. Here, highly active bidentate halogen bonding and chalcogen bonding anion carriers based on electron deficient iodo- and telluromethyl−triazole derivatives are reported. Anion transport experiments in lipid bilayer vesicles reveal record nanomolar chloride transport activity for the bidentate halogen bonding anion carrier, and remarkably high chloride over proton/hydroxide selectivity for the chalcogen bonding anionophore. Computational studies provide further insight into the role of sigma-hole mediated anion recognition and desolvation at the membrane interface. Comparison with hydrogen bonding analogues demonstrates the importance of employing sigma-hole donor motifs in synthetic anionophores for achieving both high transport activity and selectivity. 相似文献
97.
Slowinski F Ben Ayad O Vache J Saady M Leclerc O Lochead A 《The Journal of organic chemistry》2011,76(20):8336-8346
Azabicyclo[2.2.1]heptane and -[3.3.1]nonane scaffolds (X = Cl, Br) containing a pyridinyl substituent at the bridgehead position were prepared via two complementary chemical pathways, either by the transformation of a methoxy group into a synthetically valuable chlorine atom at the C-6 position of the pyridine moiety or by means of a regioselective C-6 deprotonation/halogenation process of the pyridine moiety exemplified by chlorination or bromination. These newly generated scaffolds were then engaged in Suzuki-Miyaura coupling reactions to provide α7 nicotinic ligands. Both chemical series were evaluated in vitro for their affinity at α7 nicotinic receptors, revealing nanomolar potency with significant selectivity over the α4β2 nicotinic subtype. These approaches offer a general access to these α7 nicotinic scaffolds and ligands. 相似文献
98.
Nessvi S Johansson L Jopson J Stewart A Reeder A McKenzie R Scragg RK 《Photochemistry and photobiology》2011,87(5):1173-1178
The study aim was to determine the contribution of ethnicity, objectively measured skin color and skin reaction-to-sun exposure to variations in 25-hydroxyvitamin D(3) [25(OH)D(3) ]. A multiethnic sample (European, Maori, Pacific and Asian) of 503 adult volunteers aged 18-85 years, recruited from Auckland and Dunedin in New Zealand, answered a questionnaire on sun exposure and self-defined ethnicity. Skin color was measured using a spectrophotometer and the Individual Typology Angle (ITA) calculated. A blood sample was collected 4 weeks later to measure 25(OH)D(3). 25(OH)D(3) was associated with ethnicity, but not self-reported skin reaction-to-sun exposure. Amongst the ethnic groups, Asians had the lowest mean 25(OH)D level (37.0 nmol L(-1)) and Europeans with lighter colored skin had the highest (57.9 nmol L(-1)). An association also was seen between 25(OH)D(3) and skin color, with an increase of 2-3 nmol L(-1) per 10° increase in ITA value, indicating higher 25(OH)D(3) with lighter skin color; but much of this association disappeared after adjusting for ethnicity. In contrast, ethnicity remained associated with 25(OH)D(3) after adjusting for ITA skin color and skin reaction-to-sun exposure. These results indicate that self-defined ethnicity was a major determinant of variations in serum 25(OH)D(3), while objective measures of skin color explained relatively little additional variation. 相似文献
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100.
McKay D Frey AS Green JC Cloke FG Maron L 《Chemical communications (Cambridge, England)》2012,48(34):4118-4120
Calculations reveal a multistep pathway towards formation of linear [U](2)-(μ-η(1):η(1)-C(2)O(2)); [U] = U(η-C(8)H(6){SiH(3)-1,4}(2))(η-Cp). However formation of deltate-bridged [U](2)-(μ-η(1):η(2)-C(3)O(3)) requires an alternative mechanism, involving a side-on [U](2)-(μ-η(2):η(2)-CO) complex and whereby the bridging units of [U](2)-(μ-η(2):η(2)-C(n)O(n)) intermediates (n = 1, 2) react directly with free CO. 相似文献