Spinneret - Weaving the chemical web one molecule at a time...

Diamonds almost as old as the Earth itself have been found locked in ancient crystals of zircon from the Jack Hills region of Western Australia, according to scientists writing in Nature this week. The diamonds could provide unique insights into the early evolution of our planet’s crust.

Zircons are tough and resist heat and some samples have been shown to be several billion years old. As such, they retain vital clues about the Earth’s geological evolution, at least as far as the crust and mantle are concerned. Recent studies of these ancient crystals have suggested that the Earth may have cooled much faster than previously thought, with the continental crust and oceans forming some 4.4 billion years ago.

Now, Martina Menneken and colleagues at the Westfälische Wilhelms-Universität Muenster, in Germany, have investigated mineral inclusions within zircons and found that some of them contained small diamonds. The zircons have been dated using uranium and lead isotopes and found to be over four billion years old — almost one billion years older than the previous oldest-known terrestrial diamonds, and present in material that crystallized within 300 million years of the formation of the Earth itself.

The authors suggest that these diamond inclusions formed under ultrahigh-pressure conditions, which implies that the Earth had a relatively thick continental crust and crust–mantle interaction at least 4.25 billion years ago.

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Steve Ley and his team (some 40 PhD students over the last two decades) have finally cracked the total synthesis of the natural insecticide azadirachtin. This hugely complex natural product extracted from the Indian neem tree put up quite a struggle from the year it was isolated (1968) till its structure was unequivocally elucidated (seventeen years later) till the publication of Ley’s paper in Angewandte Chemie outlining the 64-step strategy for making it from standard starting materials. Check out the Angewandte press site for a more detailed write-up and the paper itself for full details of the completion of these chemical odyssey.

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A molecular Möbius strip that can flip between single-sided and double-sided modes has been synthesised by chemists in Poland without snapping the ring.

Lechoslaw Latos-Grazynski and his colleagues at the University of Wroclaw explain that for a molecule to be defined as aromatic it must exist as a near planar ring and have a pi electron system that allows for the free movement of electron pairs between alternating double and single bonds - the classic Hückel topology. Even rings that are twisted into a figure eight can have this topology. However, a molecule with a 180 degree twist has the Möbius topology and there is no distinction between the “upper and lower” pi electron cloud to give it the properties of aromaticity.

The team worked with an expanded porphyrin analogue - A,D-di-p-benzi[28]hexaphyrin(1.1.1.1.1.1) with a figure-of-eight shape having two phenylene six-membered carbon rings at the crossover point. Whether or not these rings are perpendicular or parallel dictates whether or not the molecule is Hückel or Möbius.

Finding molecules of this type are of fundamental importance to understanding molecular topology and aromaticity but the color change inherent in the flip might also allow the compound to be used as an indicator for the presence of other species in a solution, for instance.

You can read more about the study in the current issue of the SpectroscopyNOW.com ezine and see a blue-green morph of Prof Latos-Grazynski.

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