Chemists Just Tied the Tiniest Knot Ever—Even Smaller Than a Cell
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For decades chemists have tried to make smaller and smaller molecular knots in an attempt to potentially create and understand more complex structures.
University of Western Ontario in Canada and the Chinese Academy of Sciences just tied the world’s tightest knot with a trefoil knot composed only 54 atoms.
This is close to the quantum theoretical limit of how small a trefoil knot can be.
Knots come in all shapes and sizes, and each is perfectly suited for its own task—but you’ve likely never seen a knot quite like this. Scientists from the University of Western Ontario in Canada and the Chinese Academy of Sciences accidentally created the world’s tightest knot. Containing only 54 atoms, it’s also the world’s smallest knot. It takes the form of a trefoil knot, twisting three times in an interlacing loop with no loose ends.
This supplants previous pint-sized knots created by scientists in 2017 and 2020, earning this trefoil creation a hollowed spot in the Guinness Book of World Records. But pursuing this obscure world record isn’t the goal of this complicated case of knot-tying—the researchers hope that figuring out how this knot forms could lead to the creation of more complex structures. The results of this happy accident were published in the journal Nature Communications earlier this month.
Originally, the research team was working on metal acetylides—a type of hydrocarbon used in organic chemical reactions—according to ScienceAlert. However, when connecting gold acetylide with diphosphine ligand (you know…as you do), it created a gold-carbon-phosphorus formula described as [Au6{1,2-C6H4(OCH2CC)2}3{Ph2P(CH2)4PPh2}3], or simply just Au6. The result was a 54-atom trefoil knot, which the researchers did not expect.
“There is no absolute way to estimate the tightness of a knot,” the paper reads. “However, for a given knot type, they can be ranked according to the number of atoms in the shortest path along the knotted strand or, more generally for all knots, by this number divided by the number of crossings (the backbone crossing ratio or BCR).”
This BCR figure is found by taking the number of atoms in the knot divided by the number of crossings. According to this metric, the lower the number, the tighter the knot. The 2017 knot contained 192 atoms and had a BCR of 24, and the 2020 record-breaking knot had a BCR of 23.
This knot? Try 18 on for size.
“We hadn’t predicted that this would happen in this case, so it was serendipity.” University of Western Ontario’s Richard Puddephatt, a co-author on the study, told New Scientist. “It’s quite a complicated system and, honestly, we don’t know how it happens.”
So with two world records supplanted in just seven years, could there be a tighter knot out there? Well, theoretically yes. Quantum chemical calculations suggest that the minimum number of atoms in a trefoil structure is around 50, meaning this new knot is pretty much as tight as it gets.
Au6 isn’t exactly your trusty clove hitch, figure 8, or even square knot, but like these more traditional knots, it certainly gets its job done.
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