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"All-in-one" strategy for metalla[3]catenanes, borromean rings and ring-in-ring complex – EurekAlert

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IMAGE: Single-crystal X-ray structures of ring-in-ring complex.
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Credit: ©Science China Press

Interlocked molecular species have received considerable attention recently, not only because of their intriguing structures and topological importance, but also because of their important applications as molecular machines and nanoscale devices. Benefiting from the reversible coordination bond, some complicated interlocked structure could be realized by high-yield, one-step processes, for example, [2]catenanes and Solomon knot. Molecular Borromean rings (BRs) are [3]catenanes topoisomers in which none of the component rings are linked, but also cannot be separated without breaking one of the rings (Fig. 1). Linear [3]catenanes is another fascinating interlocked three-ring motif (Fig. 1). Several effective methods for the construction of organic linear [3]catenanes have been presented. However, the feasible strategies for the synthesis of organometallic linear metalla[3]catenanes based on coordination-driven self-assembly are still very rare. Beyond linear [3]catenanes, ring-in-ring complex are also a very rare structural motif, which can be considered as substructures of BRs and key intermediates for the preparation of BRs (Fig. 1).

Recently, Ye Lu, Dong Liu, Yue-Jian Lin, Zhen-Hua Li and Guo-Xin Jin from Fudan University (Shanghai, China) made exciting progress and developed self-assembly of metalla[3]catenanes, Borromean rings and ring-in-ring complex using a simple π-donor unit.

Due to the large electron cloud of the sulfur atom, S-containing heterocyclic compounds usually present stronger stacking interactions than polycyclic aromatic compounds under similar conditions. In order to enhance the stacking interactions, bithiophenyl groups were used as building blocks to replace the widely used phenylene or polycyclic aromatic groups. Meantime, electrostatic interactions between electron-rich (π-donor, D) and electron-deficient (π-acceptor, A) aromatic groups are important driving forces in host-guest chemistry. Metallarectangles or cages based on coordination self-assembly commonly bear several positive charges. Due to Coulombic repulsion, this type of metallarectangles or cages is more suitable for combination with electroneutral or electron-rich guests than with electron-poor cations, and overcoming the Coulombic repulsion between a cationic guest and a cationic host is still a challenge. Bithiophenyl groups are strong D units, thus their introduction into metallarectangles could lead to strong interactions between D units and A units, which is a promising strategy to overcome the Coulombic repulsion and potentially allow introduction of a positively-charged cation inside a positively-charged cationic metallarectangle. Following this logic, if an electron-deficient cation could be introduced into a cationic metallarectangle by taking advantage of strong D-A interactions, it could also be possible to thread a cationic metallarectangle based on A units inside a metallarectangle based on D units, to obtain a heterogeneous D-A ring-in-ring complex.

In this work, a series of Cp*Rh-based (Cp* = pentamethylcyclopentadienyl) homogeneous metalls[2]catenanes, as well as linear metalla[3]catenanes and BRs structure were realized through the use of building blocks based on bithiophenyl groups, a simple π-donor unit (Fig. 2). Bithiophenyl groups play a crucial role in the formation of the homogeneous interlocked structures, namely enhancing the strength of the inter-ring interactions. By taking advantage of strong electrostatic interactions between D and A units, the electron-deficient methylviologen cation was used as a guest molecule to realize reversible conversion between a [2]catenanes and a monomeric rectangle. Furthermore, a cationic metallarectangle based on A units was threaded inside a metallarectangle based on bithiophenyl groups, leading to a heterogeneous ring-in-ring complex (Fig. 3). This method for forming ring-in-ring complex was extended by use of a metallarectangle based on pyrenyl group.

These findings will help the understanding of coordination self-assembly and advance the field of organometallic assemblies.

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See the article:

Self-assembly of metalla[3]catenanes, borromean rings and ring-in-ring complex using a simple π-donor unit

https://doi.org/10.1093/nsr/nwaa164

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.

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Shrinking ice sheets could add 15 inches to sea level rise by 2100, study finds – Niagara Frontier Publications

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Ice shelves in Antarctica, such as the Getz Ice Shelf seen here, are sensitive to warming ocean temperatures. Ocean and atmospheric conditions are some of the drivers of ice sheet loss that scientists considered in a new study estimating additional global sea level rise by 2100. (Credit: Jeremy Harbeck / NASA; provided by the University at Buffalo)

Tue, Sep 22nd 2020 09:25 am

International effort leveraged UB’s supercomputing facilities for data storage

By the University at Buffalo

An international effort that brought together more than 60 ice, ocean and atmosphere scientists from three-dozen international institutions has generated new estimates of how much of an impact Earth’s melting ice sheets could have on global sea levels by 2100.

The research, led by NASA and supported by the University at Buffalo’s supercomputing facilities, finds that if greenhouse gas emissions continue apace, Greenland and Antarctica’s ice sheets could together contribute more than 15 inches (38 centimeters) of global sea level rise – and that’s beyond the amount that has already been set in motion by Earth’s warming climate.

Findings from this effort are in line with projections in the Intergovernmental Panel on Climate Change’s (IPCC) 2019 special report on oceans and the cryosphere. Meltwater from ice sheets contribute about a third of the total global sea level rise. The IPCC report projected Greenland would contribute 3.1 to 10.6 inches (8 to 27 cm) to global sea level rise between 2000-2100 and Antarctica could contribute 1.2 to 11 inches (3 to 28 cm).

These new results, published this week in a special issue of the journal The Cryosphere, come from the Ice Sheet Model Intercomparison Project (ISMIP6) led by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The study is one of many efforts scientists are involved in to project the impact of a warming climate on melting ice sheets, understand its causes and track sea level rise.

“One of the biggest uncertainties when it comes to how much sea level will rise in the future is how much the ice sheets will contribute. And how much the ice sheets contribute is really dependent on what the climate will do,” said project leader and ice scientist Sophie Nowicki, Ph.D., formerly at NASA Goddard, who joined the University at Buffalo this semester as Empire Innovation Professor in the department of geology in the UB College of Arts and Sciences, and in the UB RENEW Institute.

“The strength of ISMIP6 was to bring together most of the ice sheet modeling groups around the world, and then connect with other communities of ocean and atmospheric modelers as well, to better understand what could happen to the ice sheets,” said Heiko Goelzer, Ph.D., a scientist from Utrecht University in the Netherlands, now at NORCE Norwegian Research Centre in Norway. Goelzer led the Greenland ice sheet ISMIP6 effort.

UB helped to facilitate the research by enabling the team to transfer, store and process huge amounts of data at the university’s Center for Computational Research (CCR) as part of a pilot project to leverage the facility’s capabilities to support ice sheet research. The UB effort is led by Jason Briner, Ph.D., UB professor of geology; Jeanette Sperhac, scientific programmer at CCR; Beata Csatho, Ph.D., professor of geology; Kristin Poinar, Ph.D., assistant professor of geology; Nowicki; and Abani Patra, Ph.D., a former UB faculty member who is now at Tufts University, where he is the Stern Family Professor of Computer Science and Mathematics and director of the Data Intensive Studies Center.

With warming air temperatures melting the surface of the ice sheet, and warming ocean temperatures causing ocean-terminating glaciers to retreat, Greenland’s ice sheet is a significant contributor to sea level rise. The ISMIP6 team investigated two different scenarios the IPCC has set for future climate to predict sea level rise between 2015 and 2100: one with carbon emissions increasing rapidly and another with lower emissions.

In the high emissions scenario, they found the Greenland ice sheet would lead to an additional global sea level rise of about 3.5 inches (9 cm) by 2100. In the lower emissions scenario, the loss from the ice sheet would raise global sea level by about 1.3 inches (3 cm). This is beyond what is already destined to be lost from the ice sheet due to warming temperatures between preindustrial times and now; previous studies have estimated contribution to global sea level rise by 2100 to be about a quarter-inch (6 millimeters) for the Greenland ice sheet.

The ISMIP6 team also analyzed the Antarctic ice sheet to understand how much ice melt from future climate change would add to sea level rise, beyond what recent warming temperatures have already put in motion. Ice loss from the Antarctic ice sheet is more difficult to predict: In the west, warm ocean currents erode the bottom of large floating ice shelves, causing loss; while the vast East Antarctic ice sheet can gain mass, as warmer temperatures cause increased snowfall.

The results point to a greater range of possibilities, from ice sheet change that decreases sea level by 3.1 inches (7.8 cm), to increasing it by 12 inches (30 cm) by 2100, with different climate scenarios and climate model inputs. The regional projections show the greatest loss in West Antarctica, responsible for up to 7.1 inches (18 cm) of sea level rise by 2100 in the warmest conditions, according to the research.

“The Amundsen Sea region in West Antarctica and Wilkes Land in East Antarctica are the two regions most sensitive to warming ocean temperatures and changing currents, and will continue to lose large amounts of ice,” said Hélène Seroussi, Ph.D., an ice scientist at NASA’s Jet Propulsion Laboratory in Southern California who led the Antarctic ice sheet modeling in the ISMIP6 effort. “With these new results, we can focus our efforts in the correct direction and know what needs to be worked on to continue improving the projections.”

Different groups within the ISMIP6 community are working on various aspects of the ice sheet modeling effort. All are designed to better understand why the ice sheets are changing and to improve estimates of how much ice sheets will contribute to sea level rise.

“It took over six years of workshops and teleconferences with scientists from around the world working on ice sheet, atmosphere and ocean modeling to build a community that was able to ultimately improve our sea level rise projections,” Nowicki said. “The reason it worked is because the polar community is small, and we’re all very keen on getting this problem of future sea level right. We need to know these numbers.”

The new results will help inform the sixth IPCC report scheduled for release in 2022.

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New freshwater database tells water quality story for 12K lakes globally – Phys.org

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A sunset caught over Boundary Lake in Ontario’s Killarney Provincial Park. Credit: Amanda Liczner

Although less than one per cent of all water in the world is freshwater, it is what we drink and use for agriculture. In other words, it’s vital to human survival. York University researchers have just created a publicly available water quality database for close to 12,000 freshwater lakes globally—almost half of the world’s freshwater supply—that will help scientists monitor and manage the health of these lakes.

The study, led by Faculty of Science Postdoctoral Fellow Alessandro Filazzola and Master’s student Octavia Mahdiyan, collected data for lakes in 72 countries, from Antarctica to the United States and Canada. Hundreds of the lakes are in Ontario.

“The database can be used by scientists to answer questions about what lakes or regions may be faring worse than others, how has changed over the years and which environmental stressors are most important in driving changes in water quality,” says Filazzola.

The team included a host of graduate and undergraduate students working in the laboratory of Associate Professor Sapna Sharma in addition to a collaboration with Assistant Professor Derek Gray of Wilfrid Laurier University, Associate Professor Catherine O’Reilly of Illinois State University and York University Associate Professor Roberto Quinlan.

The researchers reviewed 3,322 studies from as far back as the 1950s along with online data repositories to collect data on chlorophyll levels, a commonly used marker to determine and ecosystem health. Chlorophyll is a predictor of the amount of vegetation and algae in lakes, known as primary production, including invasive species such as milfoil.

York University researchers have created a publicly available water quality database for close to 12,000 freshwater lakes globally – almost half of the world’s freshwater supply – that will help scientists monitor and manage the health of these lakes. Credit: York University

“Human activity, , agricultural, urban runoff and phosphorus from can all increase the level of chlorophyll in lakes. The primary production is most represented by the amount of chlorophyll in the lake, which has a cascading impact on the phytoplankton that eat the algae and the fish that eat the phytoplankton and the fish that eat those fish,” says Filazzola. “If the chlorophyll is too low, it can have cascading negative effects on the entire ecosystem, while too much can cause an abundance of algae growth, which is not always good.”

Warming summer temperatures and increased solar radiation from decreased cloud cover in the northern hemisphere also contributes to an increase in chlorophyll, while more storm events caused by contribute to degraded water quality, says Sharma. “Agricultural areas and urban watersheds are more associated with degraded water quality conditions because of the amount of nutrients input into these lakes.”

The researchers also gathered data on phosphorous and nitrogen levels—often a predictor of chlorophyll—as well as lake characteristics, land use variables, and climate data for each lake. Freshwater lakes are particularly vulnerable to changes in nutrient levels, climate, land use and pollution.

New freshwater database tells water quality story for 12K lakes globally
Postdoctoral Fellow Alessandro Filazzola standing at the edge of David Lake in Ontario’s Killarney Provincial Park. Credit: Amanda Liczner

“In addition to drinking water, freshwater is important for transportation, agriculture, and recreation, and provides habitats for more than 100,000 species of invertebrates, insects, animals and plants,” says Sharma. “The database can be used to improve our understanding of how levels respond to global environmental change and it provides baseline comparisons for environmental managers responsible for maintaining quality in lakes.”

The researchers started looking only at Ontario lakes, but quickly expanded it globally as although there are thousands of lakes in Ontario a lot of the data is not as readily available as it is in other regions of the world.

“The creation of this database is a feat typically only accomplished by very large teams with millions of dollars, not by a single lab with a few small grants, which is why I am especially proud of this research,” says Sharma.

The research is published in Nature’s Scientific Data journal.


Explore further

More nutrient reduction still needed to save lakes in China


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Scientific Data, DOI: 10.1038/s41597-020-00648-2

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Citation:
New freshwater database tells water quality story for 12K lakes globally (2020, September 22)
retrieved 22 September 2020
from https://phys.org/news/2020-09-freshwater-database-quality-story-12k.html

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Nasa outlines plan for first woman on Moon by 2024 – BBC News

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The US space agency (Nasa) has formally outlined its $28bn (£22bn) plan to return to the Moon by 2024.

As part of a programme called Artemis, Nasa will send a man and a woman to the lunar surface in the first landing with humans since 1972.

But the agency’s timeline is contingent on Congress releasing $3.2bn for building a landing system.

Astronauts will travel in an Apollo-like capsule called Orion that will launch on a powerful rocket called SLS.

Speaking on Monday afternoon (US time), Nasa administrator Jim Bridenstine said: “The $28bn represents the costs associated for the next four years in the Artemis programme to land on the Moon. SLS funding, Orion funding, the human landing system and of course the spacesuits – all of those things that are part of the Artemis programme are included.”

But he explained: “The budget request that we have before the House and the Senate right now includes $3.2bn for 2021 for the human landing system. It is critically important that we get that $3.2bn.”

Artemis: To the Moon and Beyond

The US House of Representatives has already passed a Bill allocating $600m towards the lunar lander. But Nasa will need more funds to develop the vehicle in full.

Mr Bridenstine added: “I want to be clear, we are exceptionally grateful to the House of Representatives that, in a bipartisan way, they have determined that funding a human landing system is important – that’s what that $600m represents. It is also true that we are asking for the full $3.2bn.”

The new document outlines Phase 1 of the plan, which includes an uncrewed test flight around the Moon – called Artemis-1 – in the autumn of 2021.

Nasa’s human spaceflight chief Kathy Lueders said that Artemis-1 would last for about a month to test out all the critical systems.

She said that demonstration flight would reduce the risk for Artemis-2, which will repeat the trip around the Moon with astronauts.

A new test has been added to this mission – a proximity operations demonstration. Shortly after Orion separates from the upper-stage of the SLS rocket – known as the interim cryogenic propulsion stage – astronauts will manually pilot the spacecraft as they approach and back away from the stage.

This will assess Orion’s handling qualities, along with the performance of the spacecraft’s hardware and software.

Artemis-3 will become the first mission to send astronauts to the lunar surface since Apollo 17 some 48 years ago.

Nasa has provided $967m (£763m) to several companies to work on designs for the landing vehicle that will take them there.

Later in the decade, the plan calls for Nasa to establish a base for humans, called Artemis Base Camp, that would include the infrastructure needed for long-term exploration of the Moon.

Scientists would like to extract water-ice from the lunar South Pole, because it could potentially be used to make rocket fuel on the Moon, at a lower cost than carrying it from Earth.

By comparison with Artemis, the Apollo programme in the 1960s and 70s cost upwards of $250bn in inflation-adjusted US dollars.

However, the $28bn for this new plan does not include money already spent developing the Orion spacecraft and Space Launch System (SLS) rocket.

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