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
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It’s hard to know exactly why the relatives of today’s sockeye went extinct
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Published Apr 24, 2024 • Last updated 17 hours ago • 3 minute read
The artwork and publicity materials showcasing a giant salmon that lived five million years ago were ready to go to promote a new exhibit, when the discovery of two fossilized skulls immediately changed what researchers knew about the fish.
Initial fossil discoveries of the 2.7-metre-long salmon in Oregon in the 1970s were incomplete and had led researchers to mistakenly suggest the fish had fang-like teeth.
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It was dubbed the “sabre-toothed salmon” and became a kind of mascot for the Museum of Natural and Cultural History at the University of Oregon, says researcher Edward Davis.
But then came discovery of two skulls in 2014.
Davis, a member of the team that found the skulls, says it wasn’t until they got back to the lab that he realized the significance of the discovery that has led to the renaming of the fish in a new, peer-reviewed study.
“There were these two skulls staring at me with sideways teeth,” says Davis, an associate professor in the department of earth sciences at the university.
In that position, the tusk-like teeth could not have been used for biting, he says.
“That was definitely a surprising moment,” says Davis, who serves as director of the Condon Fossil Collection at the university’s Museum of Natural and Cultural History.
“I realized that all of the artwork and all of the publicity materials and bumper stickers and buttons and T-shirts we had just made two months prior, for the new exhibit, were all out of date,” he says with a laugh.
Davis is co-author of the new study in the journal PLOS One, which renames the giant fish the “spike-toothed salmon.”
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It says the salmon used the tusk-like spikes for building nests to spawn, and as defence mechanisms against predators and other salmon.
The salmon lived about five million years ago at a time when Earth was transitioning from warmer to relatively cooler conditions, Davis says.
It’s hard to know exactly why the relatives of today’s sockeye went extinct, but Davis says the cooler conditions would have affected the productivity of the Pacific Ocean and the amount of rain feeding rivers that served as their spawning areas.
Another co-author, Brian Sidlauskas, says a fish the size of the spike-toothed salmon must have been targeted by predators such as killer whales or sharks.
“I like to think … it’s almost like a sledgehammer, these salmon swinging their head back and forth in order to fend off things that might want to feast on them,” he says.
Sidlauskas says analysis by the lead author of the paper, Kerin Claeson, found both male and female salmon had the “multi-functional” spike-tooth feature.
“That’s part of our reason for hypothesizing that this tooth is multi-functional … It could easily be for digging out nests,” he says.
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“Think about how big the (nest) would have to be for an animal of this size, and then carving it out in what’s probably pretty shallow water; and so having an extra digging tool attached to your head could be really useful.”
Sidlauskas says the giant salmon help researchers understand the boundaries of what’s possible with the evolution of salmon, but they also capture the human imagination and a sense of wonder about what’s possible on Earth.
“I think it helps us value a little more what we do still have, or I hope that it does. That animal is no longer with us, but it is a product of the same biosphere that sustains us.”
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Arachnophobes need not fear: A new European Space Agency (ESA) image of Martian “spiders” actually shows seasonal eruptions of carbon dioxide gas on the Red Planet.
The dark, spindly formations were spotted in a formation known as Inca City in Mars‘ southern polar region. Images taken by ESA’s Mars Express orbiter and ExoMars Trace Gas Orbiter show dark clusters of dots that appear to have teeny little legs, not unlike baby spiderlings huddling together.
The formations are actually channels of gas measuring 0.03 to 0.6 miles (45 meters to 1 kilometer) across. They originate when the weather starts to warm in the southern hemisphere during Martian spring, melting layers of carbon dioxide ice. The warmth causes the lowest layers of ice to turn to gas, or sublimate.
As the gas expands and rises, it explodes out of the overlying ice layers, carrying with it dark dust from the solid surface. This dust geysers out of the ice before showering down onto the top layer, creating the cracked, spidery pattern seen here. In some places, the geysers burst through ice up to 3.3 feet (1 m) thick, according to ESA.
Related: Single enormous object left 2 billion craters on Mars, scientists discover
Inca City is also known as Angustus Labyrinthus. It’s named for its linear, ruin-like ridgelines, which were once thought to be petrified sand dunes or perhaps remnants of ancient Martian glaciers, which could have left high walls of sediment behind as they retreated.
In 2002, however, the Mars Orbiter revealed that Inca City is part of a circular feature approximately 53 miles (86 km) wide. This feature may be an old impact crater — suggesting that the geometric ridges may be magma intrusions that rose through the cracked, heated crust of Mars after it was hit by a renegade space rock. The crater would have then filled with sediment, which has since eroded, partially revealing the magma formations reminiscent of ancient ruins.
(CNN) — The Hubble Space Telescope has captured a stunning new image of the glowing gas ejected from a dying star, which in this case happens to resemble a “cosmic dumbbell.”
The portrait may also include evidence that the star gobbled up another star, in a form of stellar cannibalism, before it collapsed.
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