ALBERT

Beschreibung: 0Genetic polymorphism by means of biochemical genetic markers using polyacrylamide gel electrophoresis system in four barbus fish species has been investigated. Species scientific name were Barbus sharpeyi ; Gunther, 1847 , Barbus grypus ; Heckel, 1843, Barbus xanthopterus ; Heckel, 1843 and Barbus esocinus ; Heckel, 1843.Sampling site and location were mainly in the rivers located in Khoozestan province such as Karoon and Karkheh rivers and the Dez dam. Different organs such as blood, muscle, kidney, eye and heart were sampled and analysed for the presence of tf, es, sod and pgm alleles. High polymorphism and presence of different alleles scored, but populations were not in the H-W equilibrium. Considring results, using current and avaiable genetic markers such as microsattelits is recommended for future works.

Beschreibung: Iranian Fisheries Science Research Institute

Beschreibung: Published

Beschreibung: Cheshmehkileh River and adjacent mountainous streams, play a strategic role as a historical axis for anthropogenic civilization, human welfare also habitat and migration pathway of commercial – biologic valuable fishes e.g. Caspian trout, Caspian kuttum, members of Cyprinidae family in south Caspian Sea drainage. Treats such as overfishing of Caspian trout and Red spotted trout stocks in mountainous headwaters, barriers construction and manipulations those are out of river carrying capacity developed by human activities, affected normal function of river as well. Sand mining big factories establishment next to the river, legal and illegal trade of river sediments, direct entry of Tonekabon landfill leakage into the river, development of Rainbow trout farms since 3 decades and huge effluents into the river containing dead fish and types of solids, escapement of cultured Rainbow trouts into the river, … are major minimum factors which needs basic information for integrating inclusively drainage management system. Cheshmehkileh River contains Headwaters of Dohezar (Daryasar & Nusha), Sehezar and Valamroud rivers during 13 monthly sampling phases between September 2009 and October 2010 based on macrozoobenthoses investigations by EPT, EPT/C EPA protocols, measurements of nominated physic-chemical and microbiologic parameters. Probability of Rainbow trouts escapement and invasion, existence, nutrition in Cheshmehkileh environment indeed investigated. Data analysis explained significant differences (P〈0.05) between groups of measured parameters in different sampling stations. Dendogram of clustered analysis based on consolidation of major biologic/ physic-chemical and microbiologic parameters, separated stations No. 1, 3, 2, 4 in one group and remained classified in different groups. Station 8 and 9 similarly separated which expressed general similarities according to Sehezar river environment which were differs in comparison with other stations. Station 11 separated according to its natural quality of water and environment. Similarities between station 10 to Sehezar river stations 8 and 9 expressed general influence of Sehezar River more than Dohezar River in Cheshmehkileh condition especially in station No. 10. High scores of EPT and EPT/C indices in upstream stations 1, 3 and 8 also low score of indices in stations 7, 13 and 6 expressed levels of environment quality between these groups of stations. Maximum average biomass of macroinvertebrates belongs to Trichoptera order in Cheshmehkileh River. Significant decrease of biomass in stations 11, 12 and 13 in comparison with other stations stated environment degradation in mentioned stations relevant to excessive sand mining as well. Pollution resistant groups of invertebrates significantly increased in downstreams against upstream stations. Also disappearing of Plecoptera order in station No. 7, 9, 10 and 13 stated low quality of environment in comparison with upstream stations. Confirmation of effects quality and quantity for point and non-point sources of imported pollutants require specific management considerations in order to present exploitations, pollutants control and emergencies for river monitoring in forthcoming years.

Beschreibung: Iranian Fisheries Science Research Institute

Beschreibung: Published

Beschreibung: 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 September 2018

Beschreibung: Many chemical constituents are removed from the ocean by attachment to settling particles, a process referred to as “scavenging.” Radioisotopes of thorium, a highly particle-reactive element, have been used extensively to study scavenging in the ocean. However, this process is complicated by the highly variable chemical composition and concentration of particles in oceanic waters. This thesis focuses on understanding the cycling of thorium as affected by particle concentration and particle composition in the North Atlantic. This objective is addressed using (i) the distributions 228,230,234Th, their radioactive parents, particle composition, and bulk particle concentration, as measured or estimated along the GEOTRACES North Atlantic Transect (GA03) and (ii) a model for the reversible exchange of thorium with particles. Model parameters are either estimated by inversion (chapter 2-4), or prescribed in order to simulate 230Th in a circulation model (chapter 5). The major findings of this thesis follow. In chapters 2 and 3, I find that the rate parameters of the reversible exchange model show systematic variations along GA03. In particular, 𝑘1, the apparent first-order rate "constant" of Th adsorption onto particles, generally presents maxima in the mesopelagic zone and minima below. A positive correlation between 𝑘1 and bulk particle concentration is found, consistent with the notion that the specific rate at which a metal in solution attaches to particles increases with the number of surface sites available for adsorption. In chapter 4, I show that Mn (oxyhydr)oxides and biogenic particles most strongly influence 𝑘1 west of the Mauritanian upwelling, but that biogenic particles dominate 𝑘1 in this region. In chapter 5, I find that dissolved 230Th data are best represented by a model that assumes enhanced values of 𝑘1 near the seafloor. Collectively, my findings suggest that spatial variations in Th radioisotope activities observed in the North Atlantic reflect at least partly variations in the rate at which Th is removed from the water column.

Beschreibung: This work was supported by the US National Science Foundation. Two US NSF grants have supported the research in this thesis (OCE-1232578 and OCE-155644).

Beschreibung: Seit einigen Jahren erfährt die Abfallwirtschaft unter dem Schlagwort "Kreislaufwirt­schaft" einen massiven Perspektivwech­sel: Nach den Vorstellungen der Europäischen Kommission, die 2015 ihren Aktionsplan Kreislaufwirtschaft vorgestellt hat, sollen Abfälle in Zukunft in erster Linie als potenzieller Rohstoff gesehen werden; sowohl die in einzelnen Produkten enthaltenen natürlichen Ressourcen als auch deren ökonomischer Wert sollen am Ende der Nutzungsphase möglichst optimal erhalten bleiben. Angesichts der Rohstoffarmut in Eu­ropa sollen die Abfälle recycelt und wieder in den Produktionsprozess zurückfließen, um so auch langfristig die europäische Wettbewerbsfä­higkeit sicherzustellen. Damit geraten jedoch auch neue Fragen in den Fokus: Was genau passiert eigentlich mit un­serem Müll? Wo bleibt er, und in welchen Teilen der Welt wird er recycelt? Und wer hat dann Zu­griff auf die Rohstoffe, die aus ihm zurückgewonnen werden?

Beschreibung: Germany's waste management system is one of the world's most advanced - its primary objective is to dispose of waste in a way that is safe for both people and the environ- ment. However, only about 14 per cent of the raw materials used in industry are derived from recycling processes; the remainder are still sourced from primary materials. The circular economy is not yet being implemented on a large enough scale. Recyclates or recycled materials, i.e. secondary raw materials recovered from waste, are being fed back into production and usage processes at volumes that are far below what is possible. If this system were to be improved, loss of value, dependence on volatile commodity markets, lower resource productivity, and externalities in the form of environmental pollution could be avoided. A drive towards digitalisation in industry and the waste management sector could make this happen. A study by the German Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB) indicates that no other lead market in the environmental sector stands to benefit from digitalisation more than the circular economy - and that, at the same time, no sector has ever been so poorly positioned.

Beschreibung: Eine Kosten-Nutzen-Analyse ist ein bewährtes Mittel, um die Rentabilität einer Energieeffizienzmaßnahme zu bewerten: Die Investitionskosten werden mit den eingesparten Energiekosten verglichen. Investitionsentscheidungen für Energieeffizienzmaßnahmen erfolgen allerdings häufig nicht nach einer reinen Erwägung der direkten Kosten und Nutzen. Gründe hierfür sind unter anderem "versteckte" Kosten und Risiken (z. B. Kosten für die Beschaffung von Informationen, Unsicherheiten über zukünftige Energiepreise und Einsparungen), aber auch nicht-monetäre Hemmnisse, die bei Entscheidungen eine Rolle spielen (z. B. beschränkte Rationalität, Präferenzen, Zeitverfügbarkeit). Vor diesem Hintergrund verfolgt der Bericht das Ziel, ein besseres Verständnis der Kosten-Nutzen-Erwägungen von Investoren und deren Entscheidungswirklichkeit zu erlangen. Die Untersuchung zeigt, dass Energieeffizienzdienstleistungen (EEDL) generell die versteckten Kosten - Transaktionskosten - reduzieren können. Das setzt aber voraus, dass EEDL sachgerecht durchgeführt werden. Transaktionskosten werden allerdings im Zusammenhang mit Energieeffizienzmaßnahmen von den Akteuren kaum wahrgenommen und entsprechend nicht quantifiziert. Des Weiteren zeigt sich, dass insbesondere bei Unternehmen die EEDL-Kosten für bestimmte Maßnahmen hoch sein können. Doch werden gerade in diesen Fällen die Transaktionskosten reduziert. Grundsätzlich erscheinen kostenaufwendigere EEDL, wie umfassendere Vor-Ort-Beratungen, im Gegensatz zu den preiswerteren Vor-Ort-Checks besser geeignet, um Transaktionskosten zu reduzieren.

Beschreibung: Mit dem Auslaufen vieler Konzessionsverträge im Strom- und Gasbereich auf der örtlichen Verteilnetzebene sind in Deutschland zahlreiche neue Stadtwerke entstanden. Die Bestandsaufnahmen der Autoren zeigen einen eindrucksvollen Sachstand: Durch Gründung von insgesamt 152 neuen Stadt-, Gemeinde- und Regionalwerken haben zahlreiche Kommunen zwischen 2005 und 2016 die Chance ergriffen, ihre Energieversorgung künftig mit eigenen Unternehmen stärker selbst gestalten zu wollen. Doch zum Ende dieser Periode lässt dieser Trend in Deutschland merklich nach. International hingegen mehren sich die Fälle kommunalwirtschaftlichen Engagements. Selbst im Mutterland des Kapitalismus, den USA, gibt es eine starke Bewegung zur Gründung von Stadtwerken. Insbesondere in den Kommunen werden die Auswirkungen verfehlter Privatisierungspolitik deutlich. Hier zeigten sich die negativen Auswirkungen einer am Shareholder Value ausgerichteten Versorgung am deutlichsten. Deshalb wird dort zunehmend nach Lösungen gesucht, die den Public Value steigern, dabei die Gemeinwohlinteressen der Kommunen in den Vordergrund stellen und die Qualität von Serviceleistungen der Daseinsvorsorge nachhaltig verbessern.

Beschreibung: In addition to the expansion of renewable energies, the efficient use of energy is crucial in order to ensure energy transition successful. The Federal Government of Germany has therefore set itself clear objectives with the National Energy Efficiency Action Plan (NAPE), which aims to reduce the primary energy consumption in Germany - compared to 2008 levels - by 20 per cent until 2020, and by 50 per cent until 2050. In addition, greenhouse gas emissions should fall by 40 per cent compared to 1990. To reach this goal, the German Federal Ministry of Economic Affairs and Energy (BMWi) inter alia launched the "National Top Runner Initiative (NTRI)" in January 2016. It is an important component and concerns private homes, as well as industry, retail and services. The NTRI is intended to bring energy efficient and high-quality appliances (so called Top Runners) onto the market more quickly, thus accelerate market replacement. For this purpose, motivation, knowledge and competence in product-related energy efficiency is to be strengthened and expanded along the whole value chain - from the appliance manufacturer to the retailer and the consumer. Manufacturers are pushed to develop more efficient products and consumers get valuable information about Top-Runner products and how they can benefit. In this context, retailers are especially relevant as they act as "gatekeeper" between manufacturers and consumers. They play a key role in advancing an energy efficient production and consumption. They do not only select the products but they also have a direct contact to consumers and influence the purchase decision. In this paper, special emphasis will be put on the role of retailers and the efforts of the National Top Runner Initiative will be illustrated. Barriers and incentives to motivate this target group will be elaborated.

Beschreibung: Dieses Inputpapier soll für japanische Entscheidungsträgerinnen und -träger aufzeigen, was die Hintergründe der in Deutschland zu beobachtenden Welle an Stadtwerke-Neugründungen und Rekommunalisierungen sind. Dabei wird auf aktuelle energiewirtschaftliche Entwicklungen und Rahmenbedingungen in Deutschland eingegangen, die ein besseres Verständnis vermitteln werden. Das Inputpapier soll vor allem japanische Kommunalpolitikerinnen und -politiker in die Lage versetzen, in ihren eigenen Gemeinden fundierte Diskussionen über eine mögliche Stadtwerkegründung zu führen und Entscheidungen vorzubereiten. Dies können sie auf Basis wichtiger Grundkenntnisse und Erfahrungen deutscher Städte und Gemeinden initiieren. Im Laufe des Gesamtprojektes wird im Herbst 2018 ein Werkzeugkasten entwickelt, der zur Unternehmens-Neugründung in Japan wichtige Hilfestellungen wird leisten können. Ergänzend dazu bleiben juristische und energiewirtschaftliche Fachberatungen unerlässlich, um einen erfolgreichen Start der neuen kommunalwirtschaftlichen Unternehmen zu gewährleisten. Dieses Inputpapier versteht sich daher als erste Handreichung und Hilfestellung für kommunale Entscheidungsträgerinnen und -träger in Japan, damit dort ein Grundverständnis des "Stadtwerkeprinzips" entstehen kann.

Beschreibung: Die sog. Klimapfadestudie und ihre Szenarien haben in der Öffentlichkeit ein breites Echo gefunden, nicht zuletzt weil der BDI damit erstmals eine eigene detaillierte Untersuchung der Machbarkeit der deutschen Klimaschutzziele vorlegt und offensiv in die Diskussionen um die langfristige Transformation des Energiesystems einsteigt. Während der BDI in der Mai-Ausgabe der "et" bereits wesentliche Ergebnisse vorgestellt hat, werden die Szenarien der Studie in diesem Artikel mit anderen vorliegenden Klimaschutzszenarien verglichen.

Beschreibung: Digital platforms may yield a host of advantages in putting circular economy into effect. This paper analyses the related chances and discusses requirements of digital platforms for the realization of a circular economy. It specifically points to potential solutions offered by digital platforms for existing barriers. From there it identifies issues that need specific attendance to create economically and ecologically functional platforms. Three economically relevant perspectives are discussed for this: a management perspective, a legislative perspective and a social/systems perspective.

Beschreibung: Stadtwerke spielen für die Energiewende eine zentrale Rolle. Zum einen stellen sie in Deutschland weit über die Hälfte der Versorgung an Strom, Gas und Wärme sicher, zum anderen haben Stadtwerke aufgrund ihrer kommunalen Verankerung eine besondere Position im Spannungsgefüge von Politik, Wirtschaft und Privathaushalten. Wenn es aber um die Frage geht, was den Erfolg von neugegründeten Stadtwerken ausmacht, besteht in der Literatur in gewissem Maße eine Forschungslücke. Die vorliegende Studie, die vom Wuppertal Institut und der BLUBERRIES GmbH gemeinsam erstellt wurde, behandelt ausgewählte Handlungsfelder, bei denen ein Einfluss auf den Unternehmenserfolg von neugegründeten Stadtwerken zu vermuten ist. Dabei werden als Rahmen die Ziele der Rekommunalisierung herangezogen und konkret vier Handlungsfelder in den Vordergrund gerückt. Der Fokus der Studie liegt auf Fragestellungen nach dem wirtschaftlichen Erfolg neugegründeter Stadtwerke sowie deren Zielerreichung. Dabei wird auf den klassischen Ansatz der Erfolgsfaktorenforschung zurückgegriffen. Ziel dieser Studie ist die Formulierung erster Aussagen darüber, wie einerseits die unterstellten Handlungsfelder in ihrer Ausgestaltung, andererseits die Erfolgsmaße durch neugegründete Stadtwerke beurteilt werden. Aufgrund der im Rahmen dieser Untersuchung vorgenommenen Online-Befragung lassen sich für die in den Focus genommenen vier Handlungsfelder (Kooperationen, Digitalisierung, Resilienz und Soziale Verantwortung) die wichtigsten Ergebnisse wie folgt zusammenfassen: Kooperationen und verschiedene Formen der Zusammenarbeit in der Gründungsphase spielen für den Erfolg neu gegründeter Stadtwerke eine sehr große Rolle. Neu gegründete Stadtwerke legen meist großen Wert auf nachhaltige Geschäftsbeziehungen zu örtlichen Unternehmen, was einen wesentlichen Beitrag zum Public Value darstellt. Insbesondere gut ausgearbeitete Geschäftsstrategien in den Bereichen Erneuerbare Energien, Verteilnetzbetrieb, Vertrieb und Diversifikation unterstützen die Umsetzung der Unternehmensziele in Bezug auf Resilienz und Nachhaltigkeit. Die eher durchschnittliche Bewertung der Resilienz-Relevanz für den Ausbau eines Smart Grids im Verteilnetzbereich ist ein Indiz dafür, dass der Ordnungsrahmen so geändert werden müsste, dass Investitionen in diesem Bereich attraktiver werden. Aufgrund des explorativen Charakters der vorgelegten Studie, der keine repräsentativen Aussagen über die Erfolgsfaktoren von neugegründeten Stadtwerken zulässt, werden folgende vier Hypothesen abgeleitet: 1. Der Einsatz von horizontal-kooperativen Ansätzen in der Gründungsphase als ein spezifisches Wesensmerkmal der deutschen Stadtwerkelandschaft hat positive Auswirkungen auf die Verbesserung des wirtschaftlichen Erfolgs und der Rentabilität. 2. Der Fokus auf Resilienz, Nachhaltigkeit und Klimaschutz als zentrale Werte des Stadtwerks und als integrale Bestandteile des Unternehmensleitbildes unterstützt die Erreichung der strategischen Ziele des neugegründeten Stadtwerks. 3. Das Anbieten von Smart Metern zur Erhöhung der Kundentransparenz, zur Verbesserung des Kundennutzens und zur Optimierung des Verteilnetzmanagements kann als Erfolgsfaktor eingestuft werden und unterstützt seitens der Stadtwerke eine positive Unternehmensentwicklung nicht nur in der Startphase. 4. Die explizite Wahrnehmung von sozialer Verantwortung wirkt sich positiv auf den Unternehmenserfolg aus. Es müsste nun anschließend auf der Basis einer größeren Grundgesamtheit geprüft werden, ob und inwieweit die beschriebenen Tendenzen (die sich aus der Online-Befragung ergeben) und die explorativen Hypothesen im Rahmen eines konfirmatorischen Untersuchungsansatzes wissenschaftlich verifiziert werden können.

Beschreibung: Seit Mitte der 2000er Jahre ist in Deutschland ein Großteil der Konzessionsverträge für örtliche Strom-Verteilnetze ausgelaufen. Dies eröffnete den Kommunen vielerorts die Möglichkeit ihre bis dahin in privatem Besitz befindlichen Strom-Verteilnetze zu rekommunalisieren. Vor dem Hintergrund der Energiewende und dem damit einhergehenden Umbau der deutschen Energielandschaft hin zu dezentralen Versorgungsstrukturen eröffnete sich kommunalen Verantwortlichen so die Möglichkeit die Umsetzung energiepolitischer Ziele der Bundesregierung auf kommunaler Ebene aktiv mitzugestalten. Eine im Jahr 2013 durch das Wuppertal Institut durchgeführte Sondierungsstudie erfasste für den Zeitraum 2005 bis 2016 zahlreiche Stadtwerke-Neugründungen, welche einen Trend zur Rekommunalisierung im Bereich der Energieversorgung andeutete. Darüber hinaus versuchen sich Institutionen wie das Deutsche Institut für Urbanistik (Difu) und der Verband kommunaler Unternehmen e.V. (VKU) bereits seit Jahren einen Überblick über die Entwicklung von Rekommunalisierungen zu verschaffen. Trotzdem existiert bis heute keine flächendeckende Erhebung über Rekommunalisierungen in Deutschland. Ziel dieser Arbeit war es daher eine Bestandsaufnahme über die Rekommunalisierung von Strom-Verteilnetzkonzessionen im Untersuchungsraum Nordrhein-Westfalen zwischen 2005 und 2016 vorzunehmen. In diesem Zeitraum konnten für den Untersuchungsraum insgesamt 119 Rekommunalisierungen festgestellt werden. Damit lagen bis Ende 2016 bereits zwei Drittel aller nordrhein-westfälischen Strom-Verteilnetzkonzessionen in kommunaler Hand, womit der Trend zur Rekommunalisierung eindeutig belegt werden konnte.

Beschreibung: Deutschland verfügt über eines der weltweit führenden Systeme im Bereich der Abfallwirtschaft - vorrangiges Ziel ist es, Abfall sicher und umweltschonend zu entsorgen. Allerdings kommen nur ca. 14 Prozent der in der Industrie eingesetzten Rohstoffe aus dem Recycling, der Rest sind noch immer Primärmaterialien. Kreislaufwirtschaft findet noch nicht ausreichend statt: Rezyklate, aus Abfällen gewonnene Sekundärrohstoffe, werden noch weit unterhalb der möglichen Mengen in Produktions- und Nutzungsprozesse zurückführt. Werteverlust, Abhängigkeit von volatilen Rohstoffmärkten, geringere Ressourcenproduktivität und Externalitäten in Form von Umweltverschmutzung ließen sich damit vermeiden. Eine Digitalisierungsoffensive in Industrie und Abfallwirtschaft könnte dies bewirken. Eine Studie des Bundesministeriums für Umwelt, Naturschutz, Bau und Reaktorsicherheit (BMUB) verweist darauf, dass kein Umweltleitmarkt so stark von der Digitalisierung profitieren könnte wie die Kreislaufwirtschaft - und dass gleichzeitig kein Sektor bisher so schlecht aufgestellt ist.

Beschreibung: The comment and response concerning the report of oxidation of methane to methanol by water (Reports, 5 May 2017, p. 523) do not fully capture the implications of thermodynamic limitations. A nonisothermal process in which each cycle requires a large temperature swing and permits only substoichiometric methane conversion surely could not be carried out on any practical scale.

Beschreibung: Labinger argues that stepwise reaction of methane with water to produce methanol and hydrogen will never be commercially feasible because of its substoichiometric basis with respect to the active site and the requirement of a large temperature swing. This comment is not touching any new ground, beyond describing the thermodynamic feasibility, thermal cycling, and the role of water as discussed previously. Most important, it does not have a solid numerical basis.

Beschreibung: Vinyl carbocations have been the subject of extensive experimental and theoretical studies over the past five decades. Despite this long history in chemistry, the utility of vinyl cations in chemical synthesis has been limited, with most reactivity studies focusing on solvolysis reactions or intramolecular processes. Here we report synthetic and mechanistic studies of vinyl cations generated through silylium–weakly coordinating anion catalysis. We find that these reactive intermediates undergo mild intermolecular carbon-carbon bond–forming reactions, including carbon-hydrogen (C–H) insertion into unactivated sp 3 C–H bonds and reductive Friedel-Crafts reactions with arenes. Moreover, we conducted computational studies of these alkane C–H functionalization reactions and discovered that they proceed through nonclassical, ambimodal transition structures. This reaction manifold provides a framework for the catalytic functionalization of hydrocarbons using simple ketone derivatives.

Beschreibung: It is commonly assumed that recognition and discrimination of chirality, both in nature and in artificial systems, depend solely on spatial effects. However, recent studies have suggested that charge redistribution in chiral molecules manifests an enantiospecific preference in electron spin orientation. We therefore reasoned that the induced spin polarization may affect enantiorecognition through exchange interactions. Here we show experimentally that the interaction of chiral molecules with a perpendicularly magnetized substrate is enantiospecific. Thus, one enantiomer adsorbs preferentially when the magnetic dipole is pointing up, whereas the other adsorbs faster for the opposite alignment of the magnetization. The interaction is not controlled by the magnetic field per se, but rather by the electron spin orientations, and opens prospects for a distinct approach to enantiomeric separations.

Beschreibung: Theory has established the importance of geometric phase (GP) effects in the adiabatic dynamics of molecular systems with a conical intersection connecting the ground- and excited-state potential energy surfaces, but direct observation of their manifestation in chemical reactions remains a major challenge. Here, we report a high-resolution crossed molecular beams study of the H + HD -〉 H 2 + D reaction at a collision energy slightly above the conical intersection. Velocity map ion imaging revealed fast angular oscillations in product quantum state–resolved differential cross sections in the forward scattering direction for H 2 products at specific rovibrational levels. The experimental results agree with adiabatic quantum dynamical calculations only when the GP effect is included.

Beschreibung: The chemistry of the carbonyl group is essential to modern organic synthesis. The preparation of substituted, enantioenriched 1,3- or 1,5-dicarbonyls is well developed, as their disconnection naturally follows from the intrinsic polarity of the carbonyl group. By contrast, a general enantioselective access to quaternary stereocenters in acyclic 1,4-dicarbonyl systems remains an unresolved problem, despite the tremendous importance of 2,3-substituted 1,4-dicarbonyl motifs in natural products and drug scaffolds. Here we present a broad enantioselective and stereodivergent strategy to access acyclic, polysubstituted 1,4-dicarbonyls via acid-catalyzed [3,3]-sulfonium rearrangement starting from vinyl sulfoxides and ynamides. The stereochemistry at sulfur governs the absolute sense of chiral induction, whereas the double bond geometry dictates the relative configuration of the final products.

Beschreibung: With the recent soaring production of natural gas, the use of methane and other light hydrocarbon feedstocks as starting materials in synthetic transformations is becoming increasingly economically attractive, although it remains chemically challenging. We report the development of photocatalytic C–H amination, alkylation, and arylation of methane, ethane, and higher alkanes under visible light irradiation at ambient temperature. High catalytic efficiency (turnover numbers up to 2900 for methane and 9700 for ethane) and selectivity were achieved using abundant, inexpensive cerium salts as photocatalysts. Ligand-to-metal charge transfer excitation generated alkoxy radicals from simple alcohols that in turn acted as hydrogen atom transfer catalysts. The mixed-phase gas/liquid reaction was adapted to continuous flow, enabling the efficient use of gaseous feedstocks in scalable photocatalytic transformations.

Beschreibung: Intrigued by the potential of nanoscale machines, scientists have long attempted to control molecular motion. We monitored the individual 0.7-nanometer steps of a single molecular hopper as it moved in an electric field along a track in a nanopore controlled by a chemical ratchet. The hopper demonstrated characteristics desired in a moving molecule: defined start and end points, processivity, no chemical fuel requirement, directional motion, and external control. The hopper was readily functionalized to carry cargos. For example, a DNA molecule could be ratcheted along the track in either direction, a prerequisite for nanopore sequencing.

Beschreibung: Phosphorothioate nucleotides have emerged as powerful pharmacological substitutes of their native phosphodiester analogs with important translational applications in antisense oligonucleotide (ASO) therapeutics and cyclic dinucleotide (CDN) synthesis. Stereocontrolled installation of this chiral motif has long been hampered by the systemic use of phosphorus(III) [P(III)]–based reagent systems as the sole practical means of oligonucleotide assembly. A fundamentally different approach is described herein: the invention of a P(V)-based reagent platform for programmable, traceless, diastereoselective phosphorus-sulfur incorporation. The power of this reagent system is demonstrated through the robust and stereocontrolled synthesis of various nucleotidic architectures, including ASOs and CDNs, via an efficient, inexpensive, and operationally simple protocol.

Beschreibung: Here we report an anomalous porous molecular crystal built of C–H···N-bonded double-layered roof-floor components and wall components of a segregatively interdigitated architecture. This complicated porous structure consists of only one type of fully aromatic multijoint molecule carrying three identical dipyridylphenyl wedges. Despite its high symmetry, this molecule accomplishes difficult tasks by using two of its three wedges for roof-floor formation and using its other wedge for wall formation. Although a C–H···N bond is extremely labile, the porous crystal maintains its porosity until thermal breakdown of the C–H···N bonds at 202°C occurs, affording a nonporous polymorph. Though this nonporous crystal survives even at 325°C, it can retrieve the parent porosity under acetonitrile vapor. These findings show how one can translate simplicity into ultrahigh complexity.

Beschreibung: Some of the simplest and most powerful carbon-carbon bond forming strategies take advantage of readily accessible ubiquitous motifs: carbonyls and olefins. Here we report a fundamentally distinct mode of reactivity between carbonyls and olefins that differs from established acid-catalyzed carbonyl-ene, Prins, and carbonyl-olefin metathesis reaction paths. A range of epsilon, zeta-unsaturated ketones undergo Brønsted acid–catalyzed intramolecular cyclization to provide tetrahydrofluorene products via the formation of two new carbon-carbon bonds. Theoretical calculations and accompanying mechanistic studies suggest that this carbocyclization reaction proceeds through the intermediacy of a transient oxetane formed by oxygen atom transfer. The complex polycyclic frameworks in this product class appear as common substructures in organic materials, bioactive natural products, and recently developed pharmaceuticals.

Beschreibung: Alkene aminoarylation with a single, bifunctional reagent is a concise synthetic strategy. We report a catalytic protocol for the addition of arylsulfonylacetamides across electron-rich alkenes with complete anti-Markovnikov regioselectivity and excellent diastereoselectivity to provide 2,2-diarylethylamines. In this process, single-electron alkene oxidation enables carbon-nitrogen bond formation to provide a key benzylic radical poised for a Smiles-Truce 1,5-aryl shift. This reaction is redox-neutral, exhibits broad functional group compatibility, and occurs at room temperature with loss of sulfur dioxide. As this process is driven by visible light, uses readily available starting materials, and demonstrates convergent synthesis, it is well suited for use in a variety of synthetic endeavors.

Beschreibung: Photocatalysis based on optically active, "plasmonic" metal nanoparticles has emerged as a promising approach to facilitate light-driven chemical conversions under far milder conditions than thermal catalysis. However, an understanding of the relation between thermal and electronic excitations has been lacking. We report the substantial light-induced reduction of the thermal activation barrier for ammonia decomposition on a plasmonic photocatalyst. We introduce the concept of a light-dependent activation barrier to account for the effect of light illumination on electronic and thermal excitations in a single unified picture. This framework provides insight into the specific role of hot carriers in plasmon-mediated photochemistry, which is critically important for designing energy-efficient plasmonic photocatalysts.

Beschreibung: Single-electron reduction of a carbonyl to a ketyl enables access to a polarity-reversed platform of reactivity for this cornerstone functional group. However, the synthetic utility of the ketyl radical is hindered by the strong reductants necessary for its generation, which also limit its reactivity to net reductive mechanisms. We report a strategy for net redox-neutral generation and reaction of ketyl radicals. The in situ conversion of aldehydes to α-acetoxy iodides lowers their reduction potential by more than 1 volt, allowing for milder access to the corresponding ketyl radicals and an oxidative termination event. Upon subjecting these iodides to a dimanganese decacarbonyl precatalyst and visible light irradiation, an atom transfer radical addition (ATRA) mechanism affords a broad scope of vinyl iodide products with high Z -selectivity.

Beschreibung: Reactions that form a product with the same reactive functionality as that of one of the starting compounds frequently end in oligomerization. As a salient example, selective aldol coupling of the smallest, though arguably most useful, enolizable aldehyde, acetaldehyde, with just one partner substrate has proven to be extremely challenging. Here, we report a highly enantioselective Mukaiyama aldol reaction with the simple triethylsilyl (TES) and tert -butyldimethylsilyl (TBS) enolates of acetaldehyde and various aliphatic and aromatic acceptor aldehydes. The reaction is catalyzed by recently developed, strongly acidic imidodiphosphorimidates (IDPi), which, like enzymes, display a confined active site but, like small-molecule catalysts, have a broad substrate scope. The process is scalable, fast, efficient (0.5 to 1.5 mole % catalyst loading), and greatly simplifies access to highly valuable silylated acetaldehyde aldols.

Beschreibung: Single-molecule magnets (SMMs) containing only one metal center may represent the lower size limit for molecule-based magnetic information storage materials. Their current drawback is that all SMMs require liquid-helium cooling to show magnetic memory effects. We now report a chemical strategy to access the dysprosium metallocene cation [(Cp i Pr5 )Dy(Cp*)] + (Cp i Pr5 , penta-iso-propylcyclopentadienyl; Cp *, pentamethylcyclopentadienyl), which displays magnetic hysteresis above liquid-nitrogen temperatures. An effective energy barrier to reversal of the magnetization of U eff = 1541 wave number is also measured. The magnetic blocking temperature of T B = 80 kelvin for this cation overcomes an essential barrier toward the development of nanomagnet devices that function at practical temperatures.

Beschreibung: The development of highly reactive and stereoselective catalytic systems is required not only to improve existing synthetic methods but also to invent distinct chemical reactions. Herein, a homogenized combination of nickel-based Lewis acid–surfactant-combined catalysts and single-walled carbon nanotubes is shown to exhibit substantial activity in water. In addition to the enhanced reactivity, stereoselective performance and long-term stability were demonstrated in asymmetric conjugate addition reactions of aldoximes to furnish chiral nitrones in high yields with excellent selectivities. The practical and straightforward application of the designed catalysts in water provides an expedient, environmentally benign, and highly efficient pathway to access optically active compounds.

Beschreibung: Exploration of intermediates that enable chemoselective cycloaddition reactions and expeditious construction of fused- or bridged-ring systems is a continuous challenge for organic synthesis. As an intermediate of interest, the oxyallyl cation has been harnessed to synthesize architectures containing seven-membered rings via (4+3) cycloaddition. However, its potential to access five-membered skeletons is underdeveloped, largely due to the thermally forbidden (3+2) pathway. Here, the combination of a tailored precursor and a Pd(0) catalyst generates a Pd-oxyallyl intermediate that cyclizes with conjugated dienes to produce a diverse array of tetrahydrofuran skeletons. The cycloaddition overrides conventional (4+3) selectivity by proceeding through a stepwise pathway involving a Pd-allyl transfer and ring closure sequence. Subsequent treatment of the (3+2) adducts with a palladium catalyst converts the heterocycles to the carbocyclic cyclopentanones.

Beschreibung: Understanding the practical limitations of chemical reactions is critically important for efficiently planning the synthesis of compounds in pharmaceutical, agrochemical, and specialty chemical research and development. However, literature reports of the scope of new reactions are often cursory and biased toward successful results, severely limiting the ability to predict reaction outcomes for untested substrates. We herein illustrate strategies for carrying out large-scale surveys of chemical reactivity by using a material-sparing nanomole-scale automated synthesis platform with greatly expanded synthetic scope combined with ultrahigh-throughput matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry (MALDI-TOF MS).

Beschreibung: Researchers around the world have observed the formation of molecularly ordered structures of unknown origin on the surface of titanium dioxide (TiO 2 ) photocatalysts exposed to air and solution. Using a combination of atomic-scale microscopy and spectroscopy, we show that TiO 2 selectively adsorbs atmospheric carboxylic acids that are typically present in parts-per-billion concentrations while effectively repelling other adsorbates, such as alcohols, that are present in much higher concentrations. The high affinity of the surface for carboxylic acids is attributed to their bidentate binding. These self-assembled monolayers have the unusual property of being both hydrophobic and highly water-soluble, which may contribute to the self-cleaning properties of TiO 2 . This finding is relevant to TiO 2 photocatalysis, because the self-assembled carboxylate monolayers block the undercoordinated surface cation sites typically implicated in photocatalysis.

Beschreibung: The alkaline earth metals calcium (Ca), strontium (Sr), and barium (Ba) typically engage in chemical bonding as classical main-group elements through their n s and n p valence orbitals, where n is the principal quantum number. Here we report the isolation and spectroscopic characterization of eight-coordinate carbonyl complexes M(CO) 8 (where M = Ca, Sr, or Ba) in a low-temperature neon matrix. Analysis of the electronic structure of these cubic O h -symmetric complexes reveals that the metal–carbon monoxide (CO) bonds arise mainly from [M(d )] -〉 (CO) 8 backdonation, which explains the strong observed red shift of the C-O stretching frequencies. The corresponding radical cation complexes were also prepared in gas phase and characterized by mass-selected infrared photodissociation spectroscopy, confirming adherence to the 18-electron rule more conventionally associated with transition metal chemistry.

Beschreibung: Mystery surrounds the transition from gas-phase hydrocarbon precursors to terrestrial soot and interstellar dust, which are carbonaceous particles formed under similar conditions. Although polycyclic aromatic hydrocarbons (PAHs) are known precursors to high-temperature carbonaceous-particle formation, the molecular pathways that initiate particle formation are unknown. We present experimental and theoretical evidence for rapid molecular clustering–reaction pathways involving radicals with extended conjugation. These radicals react with other hydrocarbon species to form covalently bound complexes that promote further growth and clustering by regenerating resonance-stabilized radicals through low-barrier hydrogen-abstraction and hydrogen-ejection reactions. Such radical–chain reaction pathways may lead to covalently bound clusters of PAHs and other hydrocarbons that would otherwise be too small to condense at high temperatures, thus providing the key mechanistic steps for rapid particle formation and surface growth by hydrocarbon chemisorption.

Beschreibung: Basic heteroarenes are a ubiquitous feature of pharmaceuticals and bioactive molecules, and Minisci-type additions of radical nucleophiles are a leading method for their elaboration. Despite many Minisci-type protocols that result in the formation of stereocenters, exerting control over the absolute stereochemistry at these centers remains an unmet challenge. We report a process for addition of prochiral radicals, generated from amino acid derivatives, to pyridines and quinolines. Our method offers excellent control of both enantioselectivity and regioselectivity. An enantiopure chiral Brønsted acid catalyst serves both to activate the substrate and induce asymmetry, while an iridium photocatalyst mediates the required electron transfer processes. We anticipate that this method will expedite access to enantioenriched small-molecule building blocks bearing versatile basic heterocycles.

Beschreibung: Primary amines are essential constituents of biologically active molecules and versatile intermediates in the synthesis of drugs and agrochemicals. However, their preparation from easily accessible alkenes remains challenging. Here, we report a general strategy to access primary amines from alkenes through an operationally simple iron-catalyzed aminochlorination reaction. A stable hydroxylamine derivative and benign sodium chloride act as the respective nitrogen and chlorine sources. The reaction proceeds at room temperature under air; tolerates a large scope of aliphatic and conjugated alkenes, including densely functionalized substrates; and provides excellent anti-Markovnikov regioselectivity with respect to the amino group. The reactivity of the 2-chloroalkylamine products, an understudied class of amphoteric molecules, enables facile access to linear or branched aliphatic amines, aziridines, aminonitriles, azido amines, and homoallylic amines.

Beschreibung: Despite the enormous potential for the use of stereospecific cross-coupling reactions to rationally manipulate the three-dimensional structure of organic molecules, the factors that control the transfer of stereochemistry in these reactions remain poorly understood. Here we report a mechanistic and synthetic investigation into the use of enantioenriched alkylboron nucleophiles in stereospecific Pd-catalyzed Suzuki cross-coupling reactions. By developing a suite of molecular descriptors of phosphine ligands, we could apply predictive statistical models to select or design distinct ligands that respectively promoted stereoinvertive and stereoretentive cross-coupling reactions. Stereodefined branched structures were thereby accessed through the predictable manipulation of absolute stereochemistry, and a general model for the mechanism of alkylboron transmetallation was proposed.

Beschreibung: Heterobiaryls composed of pyridine and diazine rings are key components of pharmaceuticals and are often central to pharmacological function. We present an alternative approach to metal-catalyzed cross-coupling to make heterobiaryls using contractive phosphorus C–C couplings, also termed phosphorus ligand coupling reactions. The process starts by regioselective phosphorus substitution of the C–H bonds para to nitrogen in two successive heterocycles; ligand coupling is then triggered via acidic alcohol solutions to form the heterobiaryl bond. Mechanistic studies imply that ligand coupling is an asynchronous process involving migration of one heterocycle to the ipso position of the other around a central pentacoordinate P(V) atom. The strategy can be applied to complex drug-like molecules containing multiple reactive sites and polar functional groups, and also enables convergent coupling of drug fragments and late-stage heteroarylation of pharmaceuticals.

Beschreibung: Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF 3 I molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF 3 fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations.

Beschreibung: Common anionic nucleophiles such as those derived from inorganic salts have not been used for enantioselective catalysis because of their insolubility. Here, we report that merging hydrogen bonding and phase-transfer catalysis provides an effective mode of activation for nucleophiles that are insoluble in organic solvents. This catalytic manifold relies on hydrogen bonding complexation to render nucleophiles soluble and reactive, while simultaneously inducing asymmetry in the ensuing transformation. We demonstrate the concept using a chiral bis-urea catalyst to form a tridentate hydrogen bonding complex with fluoride from its cesium salt, thereby enabling highly efficient enantioselective ring opening of episulfonium ion. This fluorination method is synthetically valuable considering the scarcity of alternative protocols and points the way to wider application of the catalytic approach with diverse anionic nucleophiles.

Beschreibung: Carbon dioxide (CO 2 ) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO 2 to ethylene with 70% faradaic efficiency at a potential of –0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO 2 reduction and carbon monoxide (CO)–CO coupling activation energy barriers; as a result, onset of ethylene evolution at –0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.

Beschreibung: White phosphorus, generated in the legacy thermal process for phosphate rock upgrading, has long been the key industrial intermediate for the synthesis of phosphorus-containing chemicals, including herbicides, flame-retardants, catalyst ligands, battery electrolytes, pharmaceuticals, and detergents. In contrast, phosphate fertilizers are made on a much larger scale from phosphoric acid, obtained by treating phosphate rock with sulfuric acid. Dehydration of phosphoric acid using sodium chloride gives trimetaphosphate, and here we report that trichlorosilane, primarily used for the production of high-purity silicon, reduces trimetaphosphate to the previously unknown bis(trichlorosilyl)phosphide anion. This anion offers an entry point to value-added organophosphorus chemicals such as primary and secondary alkyl phosphines, and thus to organophosphinates, and can also be used to prepare phosphine gas and the hexafluorophosphate anion, all previously available only downstream from white phosphorus.

Beschreibung: Cross-coupling chemistry is widely applied to carbon-carbon bond formation in the synthesis of medicines, agrochemicals, and other functional materials. Recently, single-electron–induced variants of this reaction class have proven particularly useful in the formation of C(sp 2 )–C(sp 3 ) linkages, although certain compound classes have remained a challenge. Here, we report the use of sulfones to activate the alkyl coupling partner in nickel-catalyzed radical cross-coupling with aryl zinc reagents. This method’s tolerance of fluoroalkyl substituents proved particularly advantageous for the streamlined preparation of pharmaceutically oriented fluorinated scaffolds that previously required multiple steps, toxic reagents, and nonmodular retrosynthetic blueprints. Five specific sulfone reagents facilitate the rapid assembly of a vast set of compounds, many of which contain challenging fluorination patterns.

Beschreibung: Plasmon-induced chemical reactions of molecules adsorbed on metal nanostructures are attracting increased attention for photocatalytic reactions. However, the mechanism remains controversial because of the difficulty of direct observation of the chemical reactions in the plasmonic field, which is strongly localized near the metal surface. We used a scanning tunneling microscope (STM) to achieve real-space and real-time observation of a plasmon-induced chemical reaction at the single-molecule level. A single dimethyl disulfide molecule on silver and copper surfaces was dissociated by the optically excited plasmon at the STM junction. The STM study combined with theoretical calculations shows that this plasmon-induced chemical reaction occurred by a direct intramolecular excitation mechanism.

Beschreibung: Identifying catalyst activation modes that exploit one-electron chemistry and overcome associated deactivation pathways will be transformative for developing first-row transition metal catalysts with performance equal or, ideally, superior to precious metals. Here we describe a zinc-activation method compatible with high-throughput reaction discovery that identified scores of cobalt-phosphine combinations for the asymmetric hydrogenation of functionalized alkenes. An optimized catalyst prepared from ( R , R )-Ph-BPE {Ph-BPE, 1,2-bis[(2 R ,5 R )-2,5-diphenylphospholano]ethane} and cobalt chloride [CoCl 2 ·6H 2 O] exhibited high activity and enantioselectivity in protic media and enabled the asymmetric synthesis of the epilepsy medication levetiracetam at 200-gram scale with 0.08 mole % catalyst loading. Stoichiometric studies established that the cobalt (II) catalyst precursor ( R , R )-Ph-BPECoCl 2 underwent ligand displacement by methanol, and zinc promoted facile one-electron reduction to cobalt (I), which more stably bound the phosphine.