Axially chiral biaryls, as exemplified by 1,1'-bi-2-naphthol (BINOL), are key components of catalysts, natural products and medicines. These materials are synthesized conventionally in ...enantioenriched form through metal-mediated cross coupling, de novo construction of an aromatic ring, point-to-axial chirality transfer or an atropselective transformation of an existing biaryl. Here, we report a highly enantioselective organocatalytic method for the synthesis of atropisomeric biaryls by a cation-directed O-alkylation. Treatment of racemic 1-aryl-2-tetralones with a chiral quinidine-derived ammonium salt under basic conditions in the presence of an alkylating agent leads to atropselective O-alkylation with e.r. up to 98:2. Oxidation with DDQ gives access to C
-symmetric and non-symmetric BINOL derivatives without compromising e.r. We propose that the chiral ammonium counterion differentiates between rapidly equilibrating atropisomeric enolates, leading to highly atropselective O-alkylation. This dynamic kinetic resolution process offers a general approach to the synthesis of enantioenriched atropisomeric materials.
Some classical economists, most notably Malthus, predicted that scarcity would undermine long-term human well-being. John Stuart Mill, in contrast, predicted that the threat of scarcity creates ...incentives for innovation that help to avoid some of the worst outcomes. Popular claims of marine ecologists often apply the Malthusian narrative to supplies of seafood, yet global supplies have continued to grow. We examine the modern seafood industry and evaluate Mill’s claims about innovation. We argue that the mechanisms that Mill discusses–innovation in response to and in anticipation of scarcity–account for much of what we see. Scarcities induce technological, policy, and market innovations that enable seafood supplies to grow, and these innovations can build on each other. The challenge for policy makers is to avoid knee-jerk responses to Malthusian narratives and craft policy responses that encourage innovation while recognizing physical limits of ocean resources.
A novel strategy for the recognition of anions in water using charge-neutral σ-hole halogen and chalcogen bonding acyclic hosts is demonstrated for the first time. Exploiting the intrinsic ...hydrophobicity of halogen and chalcogen bond donor atoms integrated into a foldamer structural molecular framework containing hydrophilic functionalities, a series of water-soluble receptors was constructed for an anion recognition investigation. Isothermal titration calorimetry (ITC) binding studies with a range of anions revealed the receptors to display very strong and selective binding of large, weakly hydrated anions such as I– and ReO4 –. This is achieved through the formation of 2:1 host–guest stoichiometric complex assemblies, resulting in an encapsulated anion stabilized by cooperative, multidentate, convergent σ-hole donors, as shown by molecular dynamics simulations carried out in water. Importantly, the combination of multiple σ-hole–anion interactions and hydrophobic collapse results in I– affinities in water that exceed all known σ-hole receptors, including cationic systems (β2 up to 1.68 × 1011 M–2). Furthermore, the anion binding affinities and selectivity trends of the first example of an all-chalcogen bonding anion receptor in pure water are compared with halogen bonding and hydrogen bonding receptor analogues. These results further advance and establish halogen and chalcogen bond donor functions as new tools for overcoming the challenging goal of anion recognition in pure water.
World food prices hit an all-time high in February 2011 and are still almost two and a half times those of 2000. Although three billion people worldwide use seafood as a key source of animal protein, ...the Food and Agriculture Organization (FAO) of the United Nations-which compiles prices for other major food categories-has not tracked seafood prices. We fill this gap by developing an index of global seafood prices that can help to understand food crises and may assist in averting them. The fish price index (FPI) relies on trade statistics because seafood is heavily traded internationally, exposing non-traded seafood to price competition from imports and exports. Easily updated trade data can thus proxy for domestic seafood prices that are difficult to observe in many regions and costly to update with global coverage. Calculations of the extent of price competition in different countries support the plausibility of reliance on trade data. Overall, the FPI shows less volatility and fewer price spikes than other food price indices including oils, cereals, and dairy. The FPI generally reflects seafood scarcity, but it can also be separated into indices by production technology, fish species, or region. Splitting FPI into capture fisheries and aquaculture suggests increased scarcity of capture fishery resources in recent years, but also growth in aquaculture that is keeping pace with demand. Regionally, seafood price volatility varies, and some prices are negatively correlated. These patterns hint that regional supply shocks are consequential for seafood prices in spite of the high degree of seafood tradability.
Does international trade make all parties better off? We study the relationship between food security and the international trade of fish and seafood between developing and developed countries. ...Specifically, we look at and discuss the evolution of trade flows – values, quantities, and prices – between developing and developed countries. The picture that emerges suggests that the quantity of seafood exported from developing countries to developed countries is close to the quantity of seafood imported by developing countries from developed countries. What takes place is a quality exchange: developing countries export high-quality seafood in exchange for lower quality seafood.
A catalytic enantioselective nucleophilic aromatic substitution reaction which yields axially chiral biaryl derivatives in excellent yields with e.r. values of up to 97:3 has been developed. This ...process uses a chiral counterion to direct the addition of thiophenolate to a prochiral dichloropyrimidine by a tandem desymmetrization/kinetic resolution mechanism. The products can be derivatized to a range of atropisomeric structures without any reduction in enantioenrichment, thus offering access to unexplored chiral biaryl architectures.
Asymm‐Desymm: A catalytic asymmetric nucleophilic aromatic substitution reaction which yields axially chiral biaryls in excellent yields with e.r. values of up to 97:3 has been developed. This process uses a chiral counterion to direct the addition of thiophenolate to an achiral dichloropyrimidine by a tandem desymmetrization/kinetic resolution mechanism. The products can be derivatized, thus offering access to unexplored chiral biaryl architectures.
Causal inference in coupled human and natural systems Ferraro, Paul J.; Sanchirico, James N.; Smith, Martin D.
Proceedings of the National Academy of Sciences - PNAS,
03/2019, Volume:
116, Issue:
12
Journal Article
Peer reviewed
Open access
Coupled human and natural systems (CHANS) are complex, dynamic, interconnected systems with feedback across social and environmental dimensions. This feedback leads to formidable challenges for ...causal inference. Two significant challenges involve assumptions about excludability and the absence of interference. These two assumptions have been largely unexplored in the CHANS literature, but when either is violated, causal inferences from observable data are difficult to interpret. To explore their plausibility, structural knowledge of the system is requisite, as is an explicit recognition that most causal variables in CHANS affect a coupled pairing of environmental and human elements. In a large CHANS literature that evaluates marine protected areas, nearly 200 studies attempt to make causal claims, but few address the excludability assumption. To examine the relevance of interference in CHANS, we develop a stylized simulation of a marine CHANS with shocks that can represent policy interventions, ecological disturbances, and technological disasters. Human and capital mobility in CHANS is both a cause of interference, which biases inferences about causal effects, and a moderator of the causal effects themselves. No perfect solutions exist for satisfying excludability and interference assumptions in CHANS. To elucidate causal relationships in CHANS, multiple approaches will be needed for a given causal question, with the aim of identifying sources of bias in each approach and then triangulating on credible inferences. Within CHANS research, and sustainability science more generally, the path to accumulating an evidence base on causal relationships requires skills and knowledge from many disciplines and effective academic-practitioner collaborations.
As sea level rises and storm frequency and severity increase, communities worldwide are investing in coastline management projects to maintain beach widths and dunes that support recreational ...amenities and mitigate storm risks. These projects are costly, and differences in property owners’ returns from maintaining wide beaches will influence community-level support for investment in shoreline defense. One way to account for these differences is by funding the project through a tax instrument that imposes the heaviest cost on residents who benefit most from beach nourishment. Some communities along the US east coast have adopted this approach. We use an agent-based model to evaluate how the imposition of project costs affects coastline management over the long-term. Charging higher tax rates on oceanfront properties reduces desired beach width among those owners but increases desired width for owners of inland properties. The aggregate impact on beach width depends on coastline shape and development patterns that determine the balance between these two groups, heterogeneity of beach width preferences and climate change beliefs, and levels of participation in local politics. Overall, requiring property owners who benefit most from beach nourishment to bear the highest cost results in wider beaches. The result suggests that delineating tax rates to account for unequal benefits of local public goods across taxpayers could facilitate local investment in climate change adaptation.
Over the past two decades, comparative sequence analysis using codon-substitution models has been honed into a powerful and popular approach for detecting signatures of natural selection from ...molecular data. A substantial body of work has focused on developing a class of "branch-site" models which permit selective pressures on sequences, quantified by the ω ratio, to vary among both codon sites and individual branches in the phylogeny. We develop and present a method in this class, adaptive branch-site random effects likelihood (aBSREL), whose key innovation is variable parametric complexity chosen with an information theoretic criterion. By applying models of different complexity to different branches in the phylogeny, aBSREL delivers statistical performance matching or exceeding best-in-class existing approaches, while running an order of magnitude faster. Based on simulated data analysis, we offer guidelines for what extent and strength of diversifying positive selection can be detected reliably and suggest that there is a natural limit on the optimal parametric complexity for "branch-site" models. An aBSREL analysis of 8,893 Euteleostomes gene alignments demonstrates that over 80% of branches in typical gene phylogenies can be adequately modeled with a single ω ratio model, that is, current models are unnecessarily complicated. However, there are a relatively small number of key branches, whose identities are derived from the data using a model selection procedure, for which it is essential to accurately model evolutionary complexity.
We conduct the first empirical investigation of common-pool resource users' dynamic and strategic behavior at the micro level using real-world data. Fishermen's strategies in a fully dynamic game ...account for latent resource dynamics and other players' actions, revealing the profit structure of the fishery. We compare the fishermen's actual and socially optimal exploitation paths under a time-specific vessel allocation policy and find a sizable dynamic externality. Individual fishermen respond to other users by exerting effort above the optimal level early in the season. Congestion is costly instantaneously but is beneficial in the long run because it partially offsets dynamic inefficiencies.
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