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Selectivity

About: Selectivity is a(n) research topic. Over the lifetime, 9445 publication(s) have been published within this topic receiving 227360 citation(s).

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Journal ArticleDOI
03 Apr 1998-Science
TL;DR: The architecture of the pore establishes the physical principles underlying selective K+ conduction, which promotes ion conduction by exploiting electrostatic repulsive forces to overcome attractive forces between K+ ions and the selectivity filter.

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Abstract: The potassium channel from Streptomyces lividans is an integral membrane protein with sequence similarity to all known K+ channels, particularly in the pore region. X-ray analysis with data to 3.2 angstroms reveals that four identical subunits create an inverted teepee, or cone, cradling the selectivity filter of the pore in its outer end. The narrow selectivity filter is only 12 angstroms long, whereas the remainder of the pore is wider and lined with hydrophobic amino acids. A large water-filled cavity and helix dipoles are positioned so as to overcome electrostatic destabilization of an ion in the pore at the center of the bilayer. Main chain carbonyl oxygen atoms from the K+ channel signature sequence line the selectivity filter, which is held open by structural constraints to coordinate K+ ions but not smaller Na+ ions. The selectivity filter contains two K+ ions about 7.5 angstroms apart. This configuration promotes ion conduction by exploiting electrostatic repulsive forces to overcome attractive forces between K+ ions and the selectivity filter. The architecture of the pore establishes the physical principles underlying selective K+ conduction.

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6,217 citations


5


Journal ArticleDOI
Shengwei Liu1, Jiaguo Yu1, Mietek Jaroniec1Institutions (1)
TL;DR: The surface chemistry and the surface structure at the atomic level are key factors in tuning the adsorption selectivity and, consequently, photocatalytic selectivity of HTS toward azo dyes.

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Abstract: A fluoride mediated self-transformation method is proposed for the synthesis of hollow TiO2 microspheres (HTS) composed of anatase polyhedra with exposed ca. 20% {001} facets. Importantly, HTS exhibit tunable photocatalytic selectivity in decomposing azo dyes in water. The fluorinated HTS show preferential decomposition of methyl orange (MO) in comparison to methylene blue (MB). In contrast, the surface-modified HTS by either NaOH washing or calcinations at 600 °C favor decomposition of MB over MO. The surface chemistry and the surface structure at the atomic level are key factors in tuning the adsorption selectivity and, consequently, photocatalytic selectivity of HTS toward azo dyes.

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933 citations


Journal ArticleDOI
TL;DR: The presented activity-selectivity-size relations provide novel insights in the CO2 electroreduction reaction on nanoscale surfaces and lend themselves well to density functional theory (DFT) evaluation and reaction mechanism verification.

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Abstract: A study of particle size effects during the catalytic CO2 electroreduction on size-controlled Cu nanoparticles (NPs) is presented. Cu NP catalysts in the 2–15 nm mean size range were prepared, and their catalytic activity and selectivity during CO2 electroreduction were analyzed and compared to a bulk Cu electrode. A dramatic increase in the catalytic activity and selectivity for H2 and CO was observed with decreasing Cu particle size, in particular, for NPs below 5 nm. Hydrocarbon (methane and ethylene) selectivity was increasingly suppressed for nanoscale Cu surfaces. The size dependence of the surface atomic coordination of model spherical Cu particles was used to rationalize the experimental results. Changes in the population of low-coordinated surface sites and their stronger chemisorption were linked to surging H2 and CO selectivities, higher catalytic activity, and smaller hydrocarbon selectivity. The presented activity–selectivity–size relations provide novel insights in the CO2 electroreduction r...

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773 citations


Journal ArticleDOI
02 Apr 1992-Nature
TL;DR: The effects on ion selectivity of replacing lysine at position 1,422 in repeat III and/or alanine in repeat IV of rat sodium channel II are reported, suggesting that these residues constitute part of the selectivity filter of the channel.

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Abstract: THE sodium channel, one of the family of structurally homologous voltage-gated ion channels1, differs from other members, such as the calcium and the potassium channels, in its high selectivity for Na+. This selectivity presumably reflects a distinct structure of its ion-conducting pore. We have recently identified two clusters of predominantly negatively charged amino-acid residues, located at equivalent positions in the four internal repeats of the sodium channel as the main determinants of sensitivity to the blockers tetrodotoxin and saxitoxin2. All site-directed mutations reducing net negative charge at these positions also caused a marked decrease in single-channel conductance2. Thus these two amino-acid clusters probably form part of the extracellular mouth and/or the pore wall of the sodium channel. We report here the effects on ion selectivity of replacing lysine at position 1,422 in repeat III and/or alanine at position 1,714 in repeat IV of rat sodium channel II (ref. 3), each located in one of the two clusters, by glutamic acid, which ccurs at the equivalent positions in calcium channels. These amino-acid substitutions, unlike other substitutions in the adjacent regions, alter ion-selection properties of the sodium channel to resemble those of calcium channels. This result indicates that lysine 1,422 and alanine 1,714 are critical in deter mining the ion selectivity of the sodium channel, suggesting that these residues constitute part of the selectivity filter of the channel.

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742 citations


Journal ArticleDOI
Abstract: The epoxidation of propylene with hydrogen peroxide in the liquid phase, in the presence of titanium silicalite catalyst (TS-1), is described. The best solvents are methanol and methanol/ water mixtures. The temperature is normally between room temperature and 60°C. Under these conditions, reaction rates are fast, yields on H2O2 are quantitative, and selectivity to propylene oxide is very high. Propylene glycol and its monomethyl ethers and trace amounts of formaldehyde are the only by-products formed. Selectivity is further improved and the hydrolysis of the epoxide is almost suppressed when the residual acidity of the catalyst is completely neutralized. The activity of spent catalyst is recovered by calcining at 550°C or, more simply, by washing with solvents. Complete activity recovery shows that Ti is not removed from the crystalline framework during the epoxidation reactions.

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649 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202220
2021482
2020459
2019436
2018438
2017413

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Topic's top 5 most impactful authors

Graham J. Hutchings

23 papers, 888 citations

Avelino Corma

13 papers, 875 citations

Libor Červený

11 papers, 83 citations

Hirotaka Ihara

11 papers, 245 citations

Alfons Baiker

10 papers, 357 citations