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  • Chemistry  (10,581)
  • General Chemistry  (1,786)
  • Fisheries
  • 2015-2019  (121)
  • 2000-2004
  • 1995-1999  (10,476)
  • 1945-1949
  • 1940-1944
  • 2017  (121)
  • 1996  (10,476)
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  • 2015-2019  (121)
  • 2000-2004
  • 1995-1999  (10,476)
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  • 1
    Publication Date: 2021-05-19
    Description: Status of fish consumption was analyzed by completing the 295 questionnaires in all 22 metropolitan regions of Tehran from different households in 2008. After reviewing the descriptive and statistics analysis along with the non-parametric statistics, the fish consumption per capita was extracted through formulas. The average and mode of purchasing of each household occurs 11 times per year with 5.1 Kg in each time. Considering the higher fish consumption growth rate in Iran, the sequence of interest in all kinds of protein is as follows: poultry, mutton, beef, Trout, wild fishes and Chinese carps. The highest interest of households to buy fish more than other protein resources is due to the nutrient value of it. An average of 33.2% purchasing is dedicated to the farmed fish. 59% of purchasers are interested to buy packed up fish products and pay attention to the label of nutrient values on the product package. Fish consumption per capita is 13.3 Kg, which is divided to 6.4 kg for farmed fishes, 5.8 Kg for wild fishes and 1.1 Kg for canned fish. The higher consumption per capita of Tehran citizens in comparison with other people from other cities, who are living in Tehran, is because of their tendency and freshness of farmed fishes. In contrast, the consumption of canned and wild fishes among people of littoral regions who live in Tehran is higher than others.
    Description: Published
    Keywords: Fish consumption per capita ; Fish ; Consumption ; Per capita ; Fisheries
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.546-556
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  • 2
    Publication Date: 2021-05-19
    Description: The purpose of the present research was to identify and rank the effective environmental (background) indices on OE process in Mazandaran Fisheries Organization. In terms of data collection, the method used in this study was the descriptive-survey method and in terms of research purposes, it was an applied research. Statistical population included experts and leading experts of Mazandaran fisheries organization in 2014. After literature review, the effective environmental (background) indices on OE were identified. Data were collected using Delphi and paired comparisons questionnaires, and analyzed using fuzzy Delphi method and FAHP. The results showed that the effective environmental (background) indices on OE, in order of priority, were the economic environments, legal-political environment, social-cultural environment, technological environment, administrative environment and international environment.
    Description: Published
    Keywords: Development ; Economic ; Environmental ; Organizational Entrepreneurship ; Fuzzy Delphi ; Fuzzy AHP ; Mazandaran Fisheries Organization ; Entrepreneurship ; Fisheries ; Explanation ; Ranking ; Factors
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.125-138
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  • 3
    Publication Date: 2021-05-19
    Description: Creating a database of affiliated laboratories of the institute is organized with the aim of integrating information related to laboratories of research centers and their subsidiaries. The main objective of conducting this project in this stage is to upgrade it, establish and running one software system based on up-to-date technology of networking. For this purpose organizing the centers database, a periodic report on various aspects can be done which help for implementing appropriate monitoring and management .Among the sectors that are designed and upgraded for this system include : Portal, bank of information, advanced possibilities for inputting data, searching and reporting on laboratory.The advantages of this precise and updated reports can be collected easily from the general information of research institutes and centers, reports of the number of lab experts with different educational levels in affiliated centers, awareness of numbers and status of the chemical materials in the laboratories of each center, and the significant and important point is about economizing equipment, chemical materials and on time calibration.
    Description: Published
    Keywords: Bank of information ; Laboratories ; Research institute ; Network ; Data ; Fisheries
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.149-153
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  • 4
    Publication Date: 2021-05-19
    Description: Caspian Sea, Persian Gulf and the natural aquatic environment, made Iran’s geo-strategic and socioeconomic situation of the fisheries and aquaculture sector unique. This sector in the three areas of “ecotourism”, “food production” and “social behavior” play a crucial role in achieving Iran's Vision Policy of 1404 goals. However, Iran's valuable position in ornamental fish farming industry has been less attention and several issues challenged its development trend. Markazi is one of the leading provinces in this industry. So the main purposes of research were to identify current situation and providing development strategies. This study was descriptive and data were collected by survey method. The Statistical population was ornamental fish’s Producers and experts in Markazi province which due to limit number, census sampling was applied. The main tool for gathering information was questionnaire which its face validity confirmed through educational specialist and expert’s viewpoint. Also, the reliability of research tool was evaluated by Coronbach Alfa Test. The results showed that "Employment and income" and "Interest in breeding ornamental fish" were two main reasons to attract practitioners to this industry. The respondents considered the current situation ornamental fish industry, undesirable (Score 1.17 out of 5). Factor analysis showed that five factors named; "Corporate management and food resources", "management of extension and informing about authentic breeding principles", "Care Management and Insurance", "imported fish quality management" and "technical and financial support" have explained about 80% of the variance of the current situation and barriers to the development of ornamental fish industry in Markazi Province. The most important strategies to reduce facing problem in mentioned industry were development priority belonged ornamental fish industry trade system and development of specialized human resources training.
    Description: Published
    Keywords: Ornamental fish industry ; ِDevelopment ; Ornamental ; Fish ; Industry ; Fisheries ; Aquaculture ; Quality
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.133-148
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  • 5
    Publication Date: 2021-05-19
    Description: Debido a la disminución de las poblaciones de Panulirus argus a nivel nacional, y al conocimiento limitado sobre su estado actual en la región noroccidental de Cuba, se realizó la evaluación de la pesquería de langosta en esta zona. Se aplicó un Modelo Dinámico de Biomasa basado en series de captura (t) y esfuerzo pesquero (días pesca) por temporadas de pesca entre 1955-2015. El modelo mostró buen ajuste a los datos de captura (R2 = 0,74). Los parámetros estimados fueron: coeficiente de capturabilidad (q = 6,08 x 10-5), tasa intrínseca de crecimiento de la población (r = 0,18) y capacidad de carga del ambiente (K = 5 621 t). La captura máxima sostenible (CMS) obtenida fue de 251 t con un esfuerzo (fCMS) de 1 469 días pesca, una tasa de mortalidad por pesca (FCMS) de 0,089 y una biomasa (BCMS) de 2 811 t. A partir de 2012 se observó un incremento en la captura por unidad de esfuerzo, lo cual puede reflejar una cierta recuperación de la abundancia de la especie, ya que la biomasa presenta una tendencia creciente desde 2005 aunque todavía se encuentra por debajo del límite de sostenibilidad (BCMS), por lo que el recurso se califica como agotado. Los resultados de la tasa de mortalidad por pesca (F) muestran que existieron niveles elevados de explotación en los períodos 1966-1978, 1982-1992 y 1994-2005, que contribuyeron con la disminución de la biomasa por debajo de su nivel sostenible desde 1972. Sin embargo, en los últimos años se observa una reducción de F por debajo del límite de FCMS, y por lo tanto la pesquería no se encuentra bajo efectos de sobrepesca desde 2005.
    Description: Due to the declining populations of Panulirus argus nation wide, and the limited knowledge about its current status in the northwestern region of Cuba, an assessment of the spiny lobster fishery in this area was conducted. A biomass dynamic model was applied, based on catch series (t) and fishing effort (fishing days) by fishing seasons between years 1955-2015.The model showed good fit to the data catch (R2 = 0,74).The estimated parameters were: catchability coefficient (q = 6,08 x 10-5), population growth intrinsic rate (r = 0,18) and environment carrying capacity (K = 5 621 t). The maximum sustainable yield (MSY) obtained was 251 t, with an effort (fMSY) of 1 469 fishing days, a fishing mortality rate (FMSY) of 0.089 and a biomass (BMSY) of 2811 t. From 2012 an increase in catch per unit effort was observed, which may reflect a recovery in the abundance of the species. The biomass also shows a rebuilding from 2005, but remains depleted below the limit of BMSY. The fishing mortality rate (F) was high in the periods 1966-1978, 1982-1992 and 1994-2005, which contributed to the decline of the biomass below its sustainable level since 1972. In recent years F decreased bellow FMSY and therefore there is not overfishing since 2005.
    Description: Published
    Keywords: Langosta ; Modelo dinámico de biomasa ; Panulirus argus ; Pesquería ; Región noroccidental ; Lobster ; Biomass dynamic model ; Fisheries ; Northwestern region
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.24-29
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  • 6
    Publication Date: 2021-05-19
    Description: Thunnus tonggol is one of the most important large pelagic fish species in Hormuzgan province waters. Nominal catch of T. tonggol in 2010 was 32405 tones comprising 65% of total catch of large pelagic fishes. For sustainable exploitation of the resources of this fish, we need to identify its fishing pattern, maximum constant yield and recruitment pattern. Hence, length and weight data were collected randomly from 6 major artisanal fish-landing sites Hassineh, Kong, Bandar Abbas, Salakh, Sirik and Jask in Hormuzgan province, starting in April 2010 over one year. Growth parameters L∞ and K were estimated at 112.23cm 0.3 and (1/year), respectively. Hence, the natural mortality was calculated at 0.43 (1/year) and the maximum constant yield was computed at 11880 tones. Length-weight power relationship, W= aFLb , was W= 3×10-05FL2.82 that showed T. tonggol have isometric growth. Fishing pattern indicated that almost 85% of the catch was under the size at first maturity. Maximum recruitment pattern was in November with average fork length being 27cm. For optimum exploitation of T. tonggol stocks, we suggest two approaches including fishing ban in the maximum recruitment time and gear (Drift gillnet) modification.
    Description: Published
    Keywords: Mackerels ; Thunnus tonggol ; MCY ; Fishing ; Pattern ; Fisheries ; Fish ; Fish stocks
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.129-138
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  • 7
    Publication Date: 2021-05-19
    Description: Published
    Keywords: Establishment ; Streblospio gynobranchiata ; Cerastoderma glaucum ; Fish cage culture ; Structure ; Macrobenthic ; Invertebrate ; Population ; Culture ; Fish ; Biomass ; Abundance ; Feeding ; Fisheries
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed
    Format: pp.23-40
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  • 8
    Publication Date: 2022-05-25
    Description: Despite an absence of freshwater exploitation, the adult salmon run in the Matamek River, Quebec, declined during 1975-1980 to 〈23% of the level thought to occur there prior to 1967. Returns in 1979 and 1980 of adults tagged as smolts were 1.0% and 0.9%, respectively. Numbers of emigrating smolts and their corresponding adult returns are not significantly correlated, although we observed a trend towards more salmon (2 sea year fish) returning with larger numbers of migrating smolts. Since 1967 there is noted a decrease in the age at which returning adults smolted and females appear to now constitute a larger percentage of returning grilse and salmon. These, and other changes in life history characteristics, appear to be caused solely by commercial exploitation.
    Description: Prepared by the Woods Hole Oceanographic Institution and the Department of Recreation, Fish and Game of the Province of Quebec.
    Keywords: Atlantic salmon ; Fish populations ; Atlantic salmon ; Fisheries
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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  • 9
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2017
    Description: This thesis documents the origin, distribution, and fate of methane and several of its isotopic forms on Earth. Using observational, experimental, and theoretical approaches, I illustrate how the relative abundances of 12CH4, 13CH4, 12CH3D, and 13CH3D record the formation, transport, and breakdown of methane in selected settings. Chapter 2 reports precise determinations of 13CH3D, a “clumped” isotopologue of methane, in samples collected from various settings representing many of the major sources and reservoirs of methane on Earth. The results show that the information encoded by the abundance of 13CH3D enables differentiation of methane generated by microbial, thermogenic, and abiogenic processes. A strong correlation between clumped- and hydrogen-isotope signatures in microbial methane is identified and quantitatively linked to the availability of H2 and the reversibility of microbially-mediated methanogenesis in the environment. Determination of 13CH3D in combination with hydrogen-isotope ratios of methane and water provides a sensitive indicator of the extent of C–H bond equilibration, enables fingerprinting of methane-generating mechanisms, and in some cases, supplies direct constraints for locating the waters from which migrated gases were sourced. Chapter 3 applies this concept to constrain the origin of methane in hydrothermal fluids from sediment-poor vent fields hosted in mafic and ultramafic rocks on slow- and ultraslow-spreading mid-ocean ridges. The data support a hypogene model whereby methane forms abiotically within plutonic rocks of the oceanic crust at temperatures above ca. 300 C during respeciation of magmatic volatiles, and is subsequently extracted during active, convective hydrothermal circulation. Chapter 4 presents the results of culture experiments in which methane is oxidized in the presence of O2 by the bacterium Methylococcus capsulatus strain Bath. The results show that the clumped isotopologue abundances of partially-oxidized methane can be predicted from knowledge of 13C/12C and D/H isotope fractionation factors alone.
    Description: The research activities documented in this thesis were made possible by grants to my advisor from the U.S. National Science Foundation (NSF award EAR-1250394), the National Aeronautics and Space Administration (NASA) Astrobiology Institute (NAI, University of Colorado, Boulder, CAN 7 under Cooperative Agreement NNA15BB02A), the Department of Energy (DOE, Small Business Innovation Research program, contract DE-SC0004575), the Alfred P. Sloan Foundation via the Deep Carbon Observatory, and a Shell Graduate Fellowship through the MIT Energy Initiative. I completed the bulk of the work in this thesis while being supported by a National Defense Science and Engineering Graduate (NDSEG) Fellowship awarded through the Office of Naval Research of the U.S. Department of Defense. The StanleyW.Watson Fellowship Fund provided support during my first summer term at WHOI.The Charles M. Vest Presidential Fellowship at MIT supported me in the first year of my Ph.D. studies. I received additional support that year through NSF award EAR-1159318 (to S. Ono and T. Bosak) and theWalter & Adel Hohenstein Graduate Fellowship of Phi Kappa Phi. The MIT Earth Resources Laboratory and PAOC Houghton Fund funded my attendance at several conferences.
    Keywords: Methane ; Chemistry ; Isotopes ; Oxidation
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 10
    Publication Date: 2022-05-25
    Description: The United States Congressional Serial Set contains a wide variety of historical documents relating to natural resources and their history in the United States. It is an excellent resource for those researching historical data concerning fisheries, from extant species and ecology to economic issues. Information on resources outside the United States is also available due to the U.S. history of explorations and expansions. Charts, maps and tables are found within many of the papers and reports. There are also numerous scientific illustrations.
    Keywords: Fisheries ; fisheries data ; historical account ; United States government data ; United States Serial Set
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 11
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    University of Tehran , Kish International Campus | Iran, Kish Island
    Publication Date: 2021-05-19
    Description: Unpublished
    Keywords: Lutjanus ehrenbergii ; Fish ; Fisheries
    Repository Name: AquaDocs
    Type: Images/Video , Non Refereed
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  • 12
    Publication Date: 2021-05-19
    Description: The Deepwater Horizon accident and oil spill in the Gulf of Mexico from the Macondo well began on April 20, 2010. Oil flowed into the Gulf for 87 days until the well was capped on July 15, 2010, and declared sealed on September 19, 2010. The United States (USA) Government initially estimated that a total oil discharge into the Gulf of 4.9 million barrels (210 million U.S. gallons) resulted from the spill; however, the estimate was challenged in litigation, reduced to 3.19 million barrels by a trial court, and remains in dispute. A massive cleanup, restoration, and research program followed and continues to the present, mostly funded by BP Exploration & Production Inc. (BP).
    Description: Published
    Keywords: Deepwater Horizon Oil Rig ; Pollution effects ; Fish ; Fisheries ; Oil spills ; Marine mammals ; Birds ; Turtles ; Diseases
    Repository Name: AquaDocs
    Type: Book/Monograph/Conference Proceedings , Refereed
    Format: lxv, pp.869-1757
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  • 13
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    University of Tehran , Kish International Campus | Iran, Kish Island
    Publication Date: 2021-05-19
    Description: Unpublished
    Keywords: Ecsenius pulcher ; Blenny ; Fish ; Fisheries ; Coral reef ; Benthic
    Repository Name: AquaDocs
    Type: Images/Video , Non Refereed
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  • 14
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    Universidade Estadual de Maringá. Departamento de Biologia. Programa de Pós-Graduação em Ecologia de Ambientes Aquáticos Continentais.
    Publication Date: 2022-07-12
    Description: The promotion of mega-constructions, as reservoirs of Itaipu and Yacyretá, are based in ideas of development and progress. However, the report showed by the World Commission on Dams (WCD) in November of 2000, made responsible to the big reservoirs, the projects on Sustainable Regional Development (SRD), as generating of social and environmental damages. Thus, the main goal of the present study is to investigate the social and cultural transformations in the communities of the islanders and riparian people from Ituzaingó and Porto Rico with the constructions of the hydroelectric power plants of Itaipu (Brazil), Porto Primavera (Brazil) and Yacyretá (Argentina). Are analyzed many factors that allowed the built of those reservoirs and their principal actors. Also, the contradictions more visible verified in the social community and environmental of Ituzaingó and Porto Rico. The three reservoirs are located on the Paraná River basin, because the exploration of there hidroelectrical potential and promote of development of the different regions. Although, the reservoirs of Itaipu and Yacyretá, as projects of DRS, not allowed better social conditions for the traditional communities of Porto Rico and Ituzaingó, and they were made loose their significance when they are compare with the damages caused. In the other hand, its main beneficiaries are the multilateral financiers agencies and the economical trusts with distant headquarters from the south of Brazil and the northeast of Argentina.
    Description: A aceitação e promoção de megaobras, como as barragens de Itaipu e Yacyretá, são baseadas em idéias de desenvolvimento e de progresso. Contudo, o informe apresentado pela Comissão Mundial de Represas (CMR) em novembro de 2000, responsabilizou às grandes represas, os projetos de Desenvolvimento Regional Sustentável (DRS) por excelência, como geradoras de uma série de danos sociais e ambientais. Destarte, o objetivo do presente trabalho foi o estudo das transformações sociais ocorridas nas comunidades de ilhéus e ribeirinhos de Ituzaingó e Porto Rico a partir das mudanças na paisagem ecológica decorrentes das construções das usinas hidrelétricas de Itaipu (Brasil), Porto Primavera (Brasil) e Yacyretá (Argentina). Com essa finalidade foram analisados alguns dos fatores que possibilitaram a concretização desses projetos assim como a identificação dos seus principais protagonistas. O trabalho também contemplou o resgate das vozes dos pescadores-lavradores da região. As três usinas assentam-se sobre o rio Paraná com o propósito de explorar o seu potencial hidrelétrico e estimular o desenvolvimento das respectivas regiões. Porém, as represas de Itaipu, Porto Primavera e Yacyretá, como projetos de DRS, não promoveram, até hoje, melhoras significativas para as comunidades tradicionais de Porto Rico e Ituzaingó. O desenvolvimento alcançado perde toda importância quando comparado aos prejuízos ocasionados. Paradoxalmente, os seus principais beneficiários são as agências financiadoras multilaterais e os consórcios econômicos com sedes distantes do sul brasileiro e do nordeste argentino.
    Description: PhD
    Keywords: Hydroelectric ; Impact environment ; Fisheries ; Paraná River ; Environment police ; Ciências Ambientais ; Brazil ; Comunidades ; Pescadores ; Política ambiental ; Exclusão social ; Ecologia humana ; Usinas hidrelétricas ; Impacto socioambiental ; Human ecology ; Brasil ; Comunity ; Paraná, Rio
    Repository Name: AquaDocs
    Type: Thesis/Dissertation
    Format: 137pp.
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  • 15
    Publication Date: 2022-05-26
    Description: This report represents a first step at considering the potential for the use of market-based incentives to aid in the resolution of fishery bycatch problems. Market-based incentives have several advantages over more traditional command-and-control approaches, including cost-effective allocations of environmental controls; incentives for firms to seek technological solutions; flexibility; returns to the public for the use of its resources; and lower administrative costs in some cases. Notwithstanding these advantages and with several notable exceptions, market-based incentives are almost never employed in the management of fishery bycatch problems. There may be several reasons why this is the case, including significant distributional effects, high costs of monitoring and enforcement, difficulties in educating consumers about product attributes, administrative and transactions costs, or merely oversight. We consider this report to be an "advanced outline" of the issues surrounding the consideration of market-based incentives. We begin first by developing in Section 2 a definition of bycatch, including a "typology" of bycatch types. Next, we compile available public information on bycatch in U.S. fisheries, as defined by target species, location, and gear type (Section 3 and Appendix 1). We then review, in Section 4, two potentially relevant strands of literature, the economic theory of multispecies fisheries and studies from other social sciences of how small-scale fisheries deal with problems of bycatch. In Section 5, we describe, in general, the kinds of market-based policy instruments that may be of use in managing bycatch problems. Following this evaluation, we identify and discuss, as case studies; three priority fisheries: th~ northeastern groundfish fishery; the Gulf of Mexico shrimp fishery; and the eastern tropical Pacific yellowfin tuna fishery (Section 6). Finally, in Section 7, we outline approaches to identifying appropriate policy instruments, including a qualitative comparison of market-based approaches, an examination of the effect of specific types of uncertainty on the choice between taxes and ITQs, and the development of a "proposal" for a bycatch management "policy package." This section concludes with a proposal for a set of priority market-based approaches to bycatch management in the three cases discussed in Section 6.
    Description: NOAA Contract No. 50-DGNF-5-00172
    Keywords: Bycatch ; Fisheries
    Repository Name: Woods Hole Open Access Server
    Type: Working Paper
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  • 16
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2017
    Description: Salt marshes are physically, chemically, and biologically dynamic environments found globally at temperate latitudes. Tidal creeks and marshtop ponds may expand at the expense of productive grass-covered marsh platform. It is therefore important to understand the present magnitude and drivers of production and respiration in these submerged environments in order to evaluate the future role of salt marshes as a carbon sink. This thesis describes new methods to apply the triple oxygen isotope tracer of photosynthetic production in a salt marsh. Additionally, noble gases are applied to constrain air-water exchange processes which affect metabolism tracers. These stable, natural abundance tracers complement traditional techniques for measuring metabolism. In particular, they highlight the potential importance of daytime oxygen sinks besides aerobic respiration, such as rising bubbles. In tidal creeks, increasing nutrients may increase both production and respiration, without any apparent change in the net metabolism. In ponds, daytime production and respiration are also tightly coupled, but there is high background respiration regardless of changes in daytime production. Both tidal creeks and ponds have higher respiration rates and lower production rates than the marsh platform, suggesting that expansion of these submerged environments could limit the ability of salt marshes to sequester carbon.
    Description: Financial support for my doctoral research was provided by the United States Department of Defense through the National Defense Science and Engineering Graduate Fellowship Program, the National Science Foundation under grant OCE-1233678, and the Woods Hole Oceanographic Institution (WHOI) under grants from the WHOI Coastal Ocean Institute, Ocean and Climate Change Institute, and Ocean Life Institute. WHOI Academic Programs Office also provided funding support for research, through the Ocean Ventures Fund, and for my stipend, as graduate research assistantships including an assistantship from the United States Geological Survey administered by WHOI.
    Keywords: Marshes ; Chemistry ; Metabolism ; Knorr (Ship : 1970-) Cruise KN210-04
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 17
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-11
    Description: Vicinal diamines are a common structural motif in bioactive natural products, therapeutic agents, and molecular catalysts, motivating the continuing development of efficient, selective, and sustainable technologies for their preparation. We report an operationally simple and environmentally friendly protocol that converts alkenes and sodium azide—both readily available feedstocks—to 1,2-diazides. Powered by electricity and catalyzed by Earth-abundant manganese, this transformation proceeds under mild conditions and exhibits exceptional substrate generality and functional group compatibility. Using standard protocols, the resultant 1,2-diazides can be smoothly reduced to vicinal diamines in a single step, with high chemoselectivity. Mechanistic studies are consistent with metal-mediated azidyl radical transfer as the predominant pathway, enabling dual carbon-nitrogen bond formation.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 18
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-18
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 19
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-18
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 20
    Publication Date: 2017-08-18
    Description: In methanogenic archaea, the carbon dioxide (CO 2 ) fixation and methane-forming steps are linked through the heterodisulfide reductase (HdrABC)–[NiFe]-hydrogenase (MvhAGD) complex that uses flavin-based electron bifurcation to reduce ferredoxin and the heterodisulfide of coenzymes M and B. Here, we present the structure of the native heterododecameric HdrABC-MvhAGD complex at 2.15-angstrom resolution. HdrB contains two noncubane [4Fe-4S] clusters composed of fused [3Fe-4S]-[2Fe-2S] units sharing 1 iron (Fe) and 1 sulfur (S), which were coordinated at the CCG motifs. Soaking experiments showed that the heterodisulfide is clamped between the two noncubane [4Fe-4S] clusters and homolytically cleaved, forming coenzyme M and B bound to each iron. Coenzymes are consecutively released upon one-by-one electron transfer. The HdrABC-MvhAGD atomic model serves as a structural template for numerous HdrABC homologs involved in diverse microbial metabolic pathways.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 21
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-25
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 22
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-09-01
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
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  • 23
    Publication Date: 2017-08-25
    Description: Current catalytic processes involving carbon-carbon bond activation rely on -unsaturated coupling partners. Exploiting the concept of transfer hydrogenative coupling, we report a ruthenium(0)-catalyzed cycloaddition of benzocyclobutenones that functionalizes two adjacent saturated diol carbon-hydrogen bonds. These regio- and diastereoselective processes enable convergent construction of type II polyketide substructures.
    Keywords: Chemistry
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  • 24
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-25
    Keywords: Chemistry
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  • 25
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-25
    Description: We imaged the interfacial structure and dynamics of water in a microscopically confined geometry, in three dimensions and on millisecond time scales, with a structurally illuminated wide-field second harmonic microscope. The second harmonic images reported on the orientational order of interfacial water, induced by charge-dipole interactions between water molecules and surface charges. The images were converted into surface potential maps. Spatially resolved surface acid dissociation constant (p K a,s ) values were determined for the silica deprotonation reaction by following pH-induced chemical changes on the curved and confined surfaces of a glass microcapillary immersed in aqueous solutions. These values ranged from 2.3 to 10.7 along the wall of a single capillary because of surface heterogeneities. Water molecules that rotate along an oscillating external electric field were also imaged.
    Keywords: Chemistry
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  • 26
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-25
    Keywords: Chemistry
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  • 27
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-09-01
    Keywords: Chemistry
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  • 28
    Publication Date: 2017-09-01
    Description: Copper ions exchanged into zeolites are active for the selective catalytic reduction (SCR) of nitrogen oxides (NO x ) with ammonia (NH 3 ), but the low-temperature rate dependence on copper (Cu) volumetric density is inconsistent with reaction at single sites. We combine steady-state and transient kinetic measurements, x-ray absorption spectroscopy, and first-principles calculations to demonstrate that under reaction conditions, mobilized Cu ions can travel through zeolite windows and form transient ion pairs that participate in an oxygen (O 2 )–mediated Cu I -〉Cu II redox step integral to SCR. Electrostatic tethering to framework aluminum centers limits the volume that each ion can explore and thus its capacity to form an ion pair. The dynamic, reversible formation of multinuclear sites from mobilized single atoms represents a distinct phenomenon that falls outside the conventional boundaries of a heterogeneous or homogeneous catalyst.
    Keywords: Chemistry
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  • 29
    Publication Date: 2017-09-01
    Description: All-c is -multifluorinated cycloalkanes exhibit intriguing electronic properties. In particular, they display extremely high dipole moments perpendicular to the aliphatic ring, making them highly desired motifs in material science. Very few such motifs have been prepared, as their syntheses require multistep sequences from diastereoselectively prefunctionalized precursors. Herein we report a synthetic strategy to access these valuable materials via the rhodium–cyclic (alkyl)(amino)carbene (CAAC)–catalyzed hydrogenation of readily available fluorinated arenes in hexane. This route enables the scalable single-step preparation of an abundance of multisubstituted and multifluorinated cycloalkanes, including all- cis -1,2,3,4,5,6-hexafluorocyclohexane as well as cis-configured fluorinated aliphatic heterocycles.
    Keywords: Chemistry
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  • 30
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-11
    Keywords: Chemistry
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  • 31
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-09-01
    Keywords: Chemistry
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  • 32
    Publication Date: 2017-06-02
    Description: Biological molecular motors translate their local directional motion into ordered movement of other parts of the system to empower controlled mechanical functions. The design of analogous geared systems that couple motion in a directional manner, which is pivotal for molecular machinery operating at the nanoscale, remains highly challenging. Here, we report a molecular rotary motor that translates light-driven unidirectional rotary motion to controlled movement of a connected biaryl rotor. Achieving coupled motion of the distinct parts of this multicomponent mechanical system required precise control of multiple kinetic barriers for isomerization and synchronous motion, resulting in sliding and rotation during a full rotary cycle, with the motor always facing the same face of the rotor.
    Keywords: Chemistry
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  • 33
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-06-02
    Description: The tricyclic diterpene fungal metabolite (+)-pleuromutilin has served as a starting point for antibiotic development. Semisynthetic modification of its glycolic acid subunit at C14 provided the first analogs fit for human use, and derivatization at C12 led to 12- epi -pleuromutilins with extended-spectrum antibacterial activity, including activity against Gram-negative pathogens. Given the inherent limitations of semisynthesis, however, accessing derivatives of (+)-pleuromutilin with full control over their structure presents an opportunity to develop derivatives with improved antibacterial activities. Here we disclose a modular synthesis of pleuromutilins by the convergent union of an enimide with a bifunctional iodoether. We illustrate our approach through synthesis of (+)-12- epi -mutilin, (+)-11,12-di- epi -mutilin, (+)-12- epi -pleuromutilin, (+)-11,12-di- epi -pleuromutilin, and (+)-pleuromutilin itself in 17 to 20 steps.
    Keywords: Chemistry
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  • 34
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-06-02
    Keywords: Chemistry
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  • 35
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-06-02
    Keywords: Chemistry
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  • 36
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-06-16
    Keywords: Chemistry
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  • 37
    Publication Date: 2017-06-16
    Description: Dual-comb spectroscopy offers the potential for high accuracy combined with fast data acquisition. Applications are often limited, however, by the complexity of optical comb systems. Here we present dual-comb spectroscopy of water vapor using a substantially simplified single-laser system. Very good spectroscopy measurements with fast sampling rates are achieved with a free-running dual-comb mode-locked semiconductor disk laser. The absolute stability of the optical comb modes is characterized both for free-running operation and with simple microwave stabilization. This approach drastically reduces the complexity for dual-comb spectroscopy. Band-gap engineering to tune the center wavelength from the ultraviolet to the mid-infrared could optimize frequency combs for specific gas targets, further enabling dual-comb spectroscopy for a wider range of industrial applications.
    Keywords: Chemistry
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  • 38
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-06-23
    Keywords: Chemistry
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  • 39
    Publication Date: 2017-06-23
    Description: The biological properties of trifluoromethyl compounds have led to their ubiquity in pharmaceuticals, yet their chemical properties have made their preparation a substantial challenge, necessitating innovative chemical solutions. We report the serendipitous discovery of a borane-catalyzed formal C(sp 3 )-CF 3 reductive elimination from Au(III) that accesses these compounds by a distinct mechanism proceeding via fluoride abstraction, migratory insertion, and C-F reductive elimination to achieve a net C-C bond construction. The parent bis(trifluoromethyl)Au(III) complexes tolerate a surprising breadth of synthetic protocols, enabling the synthesis of complex organic derivatives without cleavage of the Au-C bond. This feature, combined with the "fluoride-rebound" mechanism, was translated into a protocol for the synthesis of 18 F-radiolabeled aliphatic CF 3 -containing compounds, enabling the preparation of potential tracers for use in positron emission tomography.
    Keywords: Chemistry
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  • 40
    Publication Date: 2017-06-30
    Description: The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and mixed halide anions. The concentration of defect states, which reduce a cell’s performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.
    Keywords: Chemistry
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  • 41
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-07-21
    Keywords: Chemistry
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  • 42
    Publication Date: 2017-07-21
    Description: The conversion of widely available carboxylic acids into versatile boronic esters would be highly enabling for synthesis. We found that this transformation can be effected by illuminating the N -hydroxyphthalimide ester derivative of the carboxylic acid under visible light at room temperature in the presence of the diboron reagent bis(catecholato)diboron. A simple workup allows isolation of the pinacol boronic ester. Experimental evidence suggests that boryl radical intermediates are involved in the process. The methodology is illustrated by the transformation of primary, secondary, and tertiary alkyl carboxylic acids as well as a diverse range of natural-product carboxylic acids, thereby demonstrating its broad utility and functional group tolerance.
    Keywords: Chemistry
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  • 43
    Publication Date: 2017-07-21
    Description: Lithium-ion batteries with ever-increasing energy densities are needed for batteries for advanced devices and all-electric vehicles. Silicon has been highlighted as a promising anode material because of its superior specific capacity. During repeated charge-discharge cycles, silicon undergoes huge volume changes. This limits cycle life via particle pulverization and an unstable electrode-electrolyte interface, especially when the particle sizes are in the micrometer range. We show that the incorporation of 5 weight % polyrotaxane to conventional polyacrylic acid binder imparts extraordinary elasticity to the polymer network originating from the ring sliding motion of polyrotaxane. This binder combination keeps even pulverized silicon particles coalesced without disintegration, enabling stable cycle life for silicon microparticle anodes at commercial-level areal capacities.
    Keywords: Chemistry
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  • 44
    Publication Date: 2017-07-21
    Description: Stretching polymer chains accelerates dissociation of a variety of internal covalent bonds, to an extent that correlates well with the force experienced by the scissile bond. Recent theory has also predicted scenarios in which applied force accelerates dissociation of unloaded bonds and kinetically strengthens strained bonds. We report here unambiguous experimental validation of this hypothesis: Detailed kinetic measurements demonstrate that stretching phosphotriesters accelerates dissociation of the unloaded phosphorus-oxygen bond orthogonal to the pulling axis, whereas stretching organosiloxanes inhibits dissociation of the aligned loaded silicon-oxygen bonds. Qualitatively, the outcome is determined by phosphoester elongation and siloxane contraction along the pulling axis in the respective rate-determining transition states. Quantitatively, the results agree with a simple mechanochemical kinetics model.
    Keywords: Chemistry
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  • 45
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-07-28
    Keywords: Chemistry
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  • 46
    Publication Date: 2017-07-28
    Description: The water-gas shift (WGS) reaction (where carbon monoxide plus water yields dihydrogen and carbon dioxide) is an essential process for hydrogen generation and carbon monoxide removal in various energy-related chemical operations. This equilibrium-limited reaction is favored at a low working temperature. Potential application in fuel cells also requires a WGS catalyst to be highly active, stable, and energy-efficient and to match the working temperature of on-site hydrogen generation and consumption units. We synthesized layered gold (Au) clusters on a molybdenum carbide (α-MoC) substrate to create an interfacial catalyst system for the ultralow-temperature WGS reaction. Water was activated over α-MoC at 303 kelvin, whereas carbon monoxide adsorbed on adjacent Au sites was apt to react with surface hydroxyl groups formed from water splitting, leading to a high WGS activity at low temperatures.
    Keywords: Chemistry
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  • 47
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-04
    Keywords: Chemistry
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  • 48
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-08-04
    Keywords: Chemistry
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  • 49
    Publication Date: 2017-08-04
    Description: Biological systems sense and respond to mechanical stimuli in a complex manner. In an effort to develop synthetic materials that transduce mechanical force into multifold changes in their intrinsic properties, we report on a mechanochemically responsive nonconjugated polymer that converts to a conjugated polymer via an extensive rearrangement of the macromolecular structure in response to force. Our design is based on the facile mechanochemical unzipping of polyladderene, a polymer inspired by a lipid natural product structure and prepared via direct metathesis polymerization. The resultant polyacetylene block copolymers exhibit long conjugation length and uniform trans-configuration and self-assemble into semiconducting nanowires. Calculations support a tandem unzipping mechanism of the ladderene units.
    Keywords: Chemistry
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  • 50
    Publication Date: 2017-08-04
    Description: Solvation and transport of excess protons in aqueous systems play a fundamental role in acid-base chemistry and biochemical processes. We mapped ultrafast proton excursions along the proton transfer coordinate by means of two-dimensional infrared spectroscopy, both in bulk water and in a Zundel cation (H 5 O 2 ) + motif selectively prepared in acetonitrile. Electric fields from the environment and stochastic hydrogen bond motions induce fluctuations of the proton double-minimum potential. Within the lifetime of a particular hydration geometry, the proton explores a multitude of positions on a sub-100-femtosecond time scale. The proton transfer vibration is strongly damped by its 20- to 40-femtosecond population decay. Our results suggest a central role of Zundel-like geometries in aqueous proton solvation and transport.
    Keywords: Chemistry
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  • 51
    Publication Date: 2017-09-30
    Description: Hypermetallic alkaline earth (M) oxides of formula MOM have been studied under plasma conditions that preclude insight into their formation mechanism. We present here the application of emerging techniques in ultracold physics to the synthesis of a mixed hypermetallic oxide, BaOCa + . These methods, augmented by high-level electronic structure calculations, permit detailed investigation of the bonding and structure as well as the mechanism of its formation via the barrierless reaction of Ca ( 3 P J ) with BaOCH 3 + . Further investigations of the reaction kinetics as a function of collision energy over the range 0.005 kelvin (K) to 30 K and of individual Ca fine-structure levels compare favorably with calculations based on long-range capture theory.
    Keywords: Chemistry
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  • 52
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-09-30
    Keywords: Chemistry
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  • 53
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-10-13
    Keywords: Chemistry
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  • 54
    Publication Date: 2017-10-13
    Description: The selective oxidation of methane, the primary component of natural gas, remains an important challenge in catalysis. We used colloidal gold-palladium nanoparticles, rather than the same nanoparticles supported on titanium oxide, to oxidize methane to methanol with high selectivity (92%) in aqueous solution at mild temperatures. Then, using isotopically labeled oxygen (O 2 ) as an oxidant in the presence of hydrogen peroxide (H 2 O 2 ) , we demonstrated that the resulting methanol incorporated a substantial fraction (70%) of gas-phase O 2 . More oxygenated products were formed than the amount of H 2 O 2 consumed, suggesting that the controlled breakdown of H 2 O 2 activates methane, which subsequently incorporates molecular oxygen through a radical process. If a source of methyl radicals can be established, then the selective oxidation of methane to methanol using molecular oxygen is possible.
    Keywords: Chemistry
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  • 55
    Publication Date: 2017-10-13
    Description: Halogens are among the most electronegative elements, and the variations in size and polarizability of halogens require different descriptions of the intermolecular bonds they form. Here we use the inelastic tunneling probe (itProbe) to acquire real-space imaging of intermolecular-bonding structures in the two-dimensional self-assembly of halogenbenzene molecules on a metal surface. Direct visualization is obtained for the intermolecular attraction and the "windmill" pattern of bonding among the fully halogenated molecules. Our results provide a hitherto missing understanding of the nature of the halogen bond.
    Keywords: Chemistry
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  • 56
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-10-13
    Keywords: Chemistry
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  • 57
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-10-13
    Keywords: Chemistry
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  • 58
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-10-13
    Keywords: Chemistry
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  • 59
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-11-17
    Keywords: Chemistry
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  • 60
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-11-24
    Keywords: Chemistry
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  • 61
    Publication Date: 2017-11-24
    Description: The discovery of new materials for separating ethylene from ethane by adsorption, instead of using cryogenic distillation, is a key milestone for molecular separations because of the multiple and widely extended uses of these molecules in industry. This technique has the potential to provide tremendous energy savings when compared with the currently used cryogenic distillation process for ethylene produced through steam cracking. Here we describe the synthesis and structural determination of a flexible pure silica zeolite (ITQ-55). This material can kinetically separate ethylene from ethane with an unprecedented selectivity of ~100, owing to its distinctive pore topology with large heart-shaped cages and framework flexibility. Control of such properties extends the boundaries for applicability of zeolites to challenging separations.
    Keywords: Chemistry
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  • 62
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-12-01
    Keywords: Chemistry
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  • 63
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-12-01
    Keywords: Chemistry
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  • 64
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-12-01
    Keywords: Chemistry
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  • 65
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-12-01
    Keywords: Chemistry
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  • 66
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-12-01
    Description: The electrophilic aromatic substitution of a C–H bond of benzene is one of the archetypal transformations of organic chemistry. In contrast, the electron-rich -system of benzene is highly resistant to reactions with electron-rich and negatively charged organic nucleophiles. Here, we report that this previously insurmountable electronic repulsion may be overcome through the use of sufficiently potent organocalcium nucleophiles. Calcium n -alkyl derivatives—synthesized by reaction of ethene, but-1-ene, and hex-1-ene with a dimeric calcium hydride—react with protio and deutero benzene at 60°C through nucleophilic substitution of an aromatic C–D/H bond. These reactions produce the n- alkyl benzenes with regeneration of the calcium hydride. Density functional theory calculations implicate an unstabilized Meisenheimer complex in the C–H activation transition state.
    Keywords: Chemistry
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  • 67
    Publication Date: 2017-12-01
    Description: Altering a material’s catalytic properties requires identifying structural features that give rise to active surfaces. Grain boundaries create strained regions in polycrystalline materials by stabilizing dislocations and may provide a way to create high-energy surfaces for catalysis that are kinetically trapped. Although grain-boundary density has previously been correlated with catalytic activity for some reactions, direct evidence that grain boundaries create surfaces with enhanced activity is lacking. We used a combination of bulk electrochemical measurements and scanning electrochemical cell microscopy with submicrometer resolution to show that grain-boundary surface terminations in gold electrodes are more active than grain surfaces for electrochemical carbon dioxide (CO 2 ) reduction to carbon monoxide (CO) but not for the competing hydrogen (H 2 ) evolution reaction. The catalytic footprint of the grain boundary is commensurate with its dislocation-induced strain field, providing a strategy for broader exploitation of grain-boundary effects in heterogeneous catalysis.
    Keywords: Chemistry
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  • 68
    Publication Date: 2017-11-17
    Description: Metals that are active catalysts for methane (Ni, Pt, Pd), when dissolved in inactive low–melting temperature metals (In, Ga, Sn, Pb), produce stable molten metal alloy catalysts for pyrolysis of methane into hydrogen and carbon. All solid catalysts previously used for this reaction have been deactivated by carbon deposition. In the molten alloy system, the insoluble carbon floats to the surface where it can be skimmed off. A 27% Ni–73% Bi alloy achieved 95% methane conversion at 1065°C in a 1.1-meter bubble column and produced pure hydrogen without CO 2 or other by-products. Calculations show that the active metals in the molten alloys are atomically dispersed and negatively charged. There is a correlation between the amount of charge on the atoms and their catalytic activity.
    Keywords: Chemistry
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  • 69
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-11-17
    Keywords: Chemistry
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  • 70
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-11-17
    Keywords: Chemistry
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  • 71
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-11-17
    Keywords: Chemistry
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  • 72
    Publication Date: 2017-12-01
    Description: Deuterium- and tritium-labeled pharmaceutical compounds are pivotal diagnostic tools in drug discovery research, providing vital information about the biological fate of drugs and drug metabolites. Herein we demonstrate that a photoredox-mediated hydrogen atom transfer protocol can efficiently and selectively install deuterium (D) and tritium (T) at α-amino sp 3 carbon-hydrogen bonds in a single step, using isotopically labeled water (D 2 O or T 2 O) as the source of hydrogen isotope. In this context, we also report a convenient synthesis of T 2 O from T 2 , providing access to high-specific-activity T 2 O. This protocol has been successfully applied to the high incorporation of deuterium and tritium in 18 drug molecules, which meet the requirements for use in ligand-binding assays and absorption, distribution, metabolism, and excretion studies.
    Keywords: Chemistry
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  • 73
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-10-27
    Keywords: Chemistry
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  • 74
    Publication Date: 2017-11-03
    Description: The irradiation of gold nanorod colloids with a femtosecond laser can be tuned to induce controlled nanorod reshaping, yielding colloids with exceptionally narrow localized surface plasmon resonance bands. The process relies on a regime characterized by a gentle multishot reduction of the aspect ratio, whereas the rod shape and volume are barely affected. Successful reshaping can only occur within a narrow window of the heat dissipation rate: Low cooling rates lead to drastic morphological changes, and fast cooling has nearly no effect. Hence, a delicate balance must be achieved between irradiation fluence and surface density of the surfactant on the nanorods. This perfection process is appealing because it provides a simple, fast, reproducible, and scalable route toward gold nanorods with an optical response of exceptional quality, near the theoretical limit.
    Keywords: Chemistry
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  • 75
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-11-03
    Keywords: Chemistry
    Print ISSN: 0036-8075
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  • 76
    Publication Date: 2017-10-27
    Description: Whereas standard transmission electron microscopy studies are unable to preserve the native state of chemically reactive and beam-sensitive battery materials after operation, such materials remain pristine at cryogenic conditions. It is then possible to atomically resolve individual lithium metal atoms and their interface with the solid electrolyte interphase (SEI). We observe that dendrites in carbonate-based electrolytes grow along the 〈111〉 (preferred), 〈110〉, or 〈211〉 directions as faceted, single-crystalline nanowires. These growth directions can change at kinks with no observable crystallographic defect. Furthermore, we reveal distinct SEI nanostructures formed in different electrolytes.
    Keywords: Chemistry
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  • 77
    Publication Date: 2017-05-12
    Description: Nanostructured materials have shown extraordinary promise for electrochemical energy storage but are usually limited to electrodes with rather low mass loading (~1 milligram per square centimeter) because of the increasing ion diffusion limitations in thicker electrodes. We report the design of a three-dimensional (3D) holey-graphene/niobia (Nb 2 O 5 ) composite for ultrahigh-rate energy storage at practical levels of mass loading (〉10 milligrams per square centimeter). The highly interconnected graphene network in the 3D architecture provides excellent electron transport properties, and its hierarchical porous structure facilitates rapid ion transport. By systematically tailoring the porosity in the holey graphene backbone, charge transport in the composite architecture is optimized to deliver high areal capacity and high-rate capability at high mass loading, which represents a critical step forward toward practical applications.
    Keywords: Chemistry
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  • 78
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-05-12
    Keywords: Chemistry
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  • 79
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-05-12
    Keywords: Chemistry
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  • 80
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-21
    Keywords: Chemistry
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  • 81
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-28
    Keywords: Chemistry
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  • 82
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-28
    Keywords: Chemistry
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  • 83
    Publication Date: 2017-04-28
    Description: The next generation of high-performance batteries should include alternative chemistries that are inherently safer to operate than nonaqueous lithium-based batteries. Aqueous zinc-based batteries can answer that challenge because monolithic zinc sponge anodes can be cycled in nickel–zinc alkaline cells hundreds to thousands of times without undergoing passivation or macroscale dendrite formation. We demonstrate that the three-dimensional (3D) zinc form-factor elevates the performance of nickel–zinc alkaline cells in three fields of use: (i) 〉90% theoretical depth of discharge (DOD Zn ) in primary (single-use) cells, (ii) 〉100 high-rate cycles at 40% DOD Zn at lithium-ion–commensurate specific energy, and (iii) the tens of thousands of power-demanding duty cycles required for start-stop microhybrid vehicles.
    Keywords: Chemistry
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  • 84
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-21
    Keywords: Chemistry
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  • 85
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-21
    Keywords: Chemistry
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  • 86
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-21
    Description: Methane undergoes highly facile C–H bond cleavage on the stoichiometric IrO 2 (110) surface. From temperature-programmed reaction spectroscopy experiments, we found that methane molecularly adsorbed as a strongly bound complex on IrO 2 (110) and that a large fraction of the adsorbed complexes underwent C–H bond cleavage at temperatures as low as 150 kelvin (K). The initial dissociation probability of methane on IrO 2 (110) decreased from 80 to 20% with increasing surface temperature from 175 to 300 K. We estimate that the activation energy for methane C–H bond cleavage is 9.5 kilojoule per mole (kJ/mol) lower than the binding energy of the adsorbed precursor on IrO 2 (110), and equal to a value of ~28.5 kJ/mol. Low-temperature activation may avoid unwanted side reactions in the development of catalytic processes to selectively convert methane to value-added products.
    Keywords: Chemistry
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  • 87
    Publication Date: 2017-04-21
    Description: Real-time tracking of the three-dimensional (3D) evolution of colloidal nanoparticles in solution is essential for understanding complex mechanisms involved in nanoparticle growth and transformation. We used time-resolved small-angle and wide-angle x-ray scattering simultaneously to monitor oxidation of highly uniform colloidal iron nanoparticles, enabling the reconstruction of intermediate 3D morphologies of the nanoparticles with a spatial resolution of ~ 5 angstroms. The in situ observations, combined with large-scale reactive molecular dynamics simulations, reveal the details of the transformation from solid metal nanoparticles to hollow metal oxide nanoshells via a nanoscale Kirkendall process—for example, coalescence of voids as they grow and reversal of mass diffusion direction depending on crystallinity. Our results highlight the complex interplay between defect chemistry and defect dynamics in determining nanoparticle transformation and formation.
    Keywords: Chemistry
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  • 88
    Publication Date: 2017-04-28
    Description: The catalytic stereoselective synthesis of compounds with chiral phosphorus centers remains an unsolved problem. State-of-the-art methods rely on resolution or stoichiometric chiral auxiliaries. Phosphoramidate prodrugs are a critical component of pronucleotide (ProTide) therapies used in the treatment of viral disease and cancer. Here we describe the development of a catalytic stereoselective method for the installation of phosphorus-stereogenic phosphoramidates to nucleosides through a dynamic stereoselective process. Detailed mechanistic studies and computational modeling led to the rational design of a multifunctional catalyst that enables stereoselectivity as high as 99:1.
    Keywords: Chemistry
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  • 89
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-05-05
    Description: Medvedev et al . (Reports, 6 January 2017, p. 49) argue that recent density functionals stray from the path toward exactness. This conclusion rests on very compact 1s 2 and 1s 2 2s 2 systems favored by the Hartree-Fock picture. Comparison to actual energies for the same systems indicates that the "straying" is not chemically relevant and is at best specific to the studied dense systems.
    Keywords: Chemistry
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  • 90
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-05-05
    Keywords: Chemistry
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  • 91
    Publication Date: 2017-05-05
    Description: Direct functionalization of methane in natural gas remains a key challenge. We present a direct stepwise method for converting methane into methanol with high selectivity (~97%) over a copper-containing zeolite, based on partial oxidation with water. The activation in helium at 673 kelvin (K), followed by consecutive catalyst exposures to 7 bars of methane and then water at 473 K, consistently produced 0.204 mole of CH 3 OH per mole of copper in zeolite. Isotopic labeling confirmed water as the source of oxygen to regenerate the zeolite active centers and renders methanol desorption energetically favorable. On the basis of in situ x-ray absorption spectroscopy, infrared spectroscopy, and density functional theory calculations, we propose a mechanism involving methane oxidation at Cu II oxide active centers, followed by Cu I reoxidation by water with concurrent formation of hydrogen.
    Keywords: Chemistry
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  • 92
    Publication Date: 2017-05-05
    Description: Kepp argues in his Comment, among other concerns, that the atomic densities we have considered are not relevant to molecular bonding. However, this does not change the main conclusion of our study, that unconstrained fitting of flexible functional forms can make a density functional more interpolative but less widely predictive.
    Keywords: Chemistry
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  • 93
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-15
    Keywords: Chemistry
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  • 94
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-15
    Keywords: Chemistry
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  • 95
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-15
    Keywords: Chemistry
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  • 96
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-15
    Description: The synthesis of a carbon nanobelt, comprising a closed loop of fully fused edge-sharing benzene rings, has been an elusive goal in organic chemistry for more than 60 years. Here we report the synthesis of one such compound through iterative Wittig reactions followed by a nickel-mediated aryl-aryl coupling reaction. The cylindrical shape of its belt structure was confirmed by x-ray crystallography, and its fundamental optoelectronic properties were elucidated by ultraviolet-visible absorption, fluorescence, and Raman spectroscopic studies, as well as theoretical calculations. This molecule could potentially serve as a seed for the preparation of structurally well-defined carbon nanotubes.
    Keywords: Chemistry
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  • 97
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-01-06
    Description: Computational modeling of molecules and materials is now an essential part of the scientific endeavor in chemistry, physics, and biology. A widely used methods is density functional theory (DFT), which provides energies and electron densities of molecular systems in a computationally tractable manner. However, as Medvedev et al. show on page 49 of this issue (1), recent developments in DFT have improved the energies while not always concurrently improving the electron densities, suggesting a departure from the theoretical principles underlying DFT. Author: Sharon Hammes-Schiffer
    Keywords: Chemistry
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  • 98
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-03-03
    Description: Although methane is a volatile gas, it can be efficiently trapped in ice, which can then be readily set on fire. Beyond the curiosity of this “burning ice,” caged methane is of great importance as one of the world's largest natural gas resources (1). In these materials, known as clathrates, methane molecules are tightly bound in nanometer-sized, regularly interspaced cages. Other inorganic materials, such as the silica mineral chibaite, can similarly encapsulate methane and higher hydrocarbons (2). Simple organic compounds have also been found to trap various organic molecules upon crystallization (3). On page 931 of this issue, Lin et al. (4) show that bipyramidal gold nanocrystals can be programmed to assemble into colloidal crystals with structures that resemble those of molecular clathrates, but on a much higher length scale. Authors: Dipak Samanta, Rafal Klajn
    Keywords: Chemistry
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  • 99
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-10-20
    Keywords: Chemistry
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  • 100
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-10-20
    Keywords: Chemistry
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