Archive for the ‘Interesting chemistry’ Category

Deltamethrin – a polymorphed insecticide.

Wednesday, March 24th, 2021

Deltamethin is a pyrethroid insecticide for control of malaria which has been used for a little while. Perhaps inevitably, mosquitoes are developing resistance to it. So what could be done about countering this? Well, perhaps surprisingly, form a polymorph![1] These crystal structure isomers are often highly undesirable; thus Ritonavir, which changed its polymorphic form during manufacture to become far less active (due it has to be said to insolubility). Now a polymorph of Deltamethin has been discovered, which when applied as a powder, increases its effectiveness more than 10 times against Anopheles mosquitoes and provides a potentially new affordable malaria control solution for countries that are loosing protection.

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References

  1. J. Yang, B. Erriah, C.T. Hu, E. Reiter, X. Zhu, V. López-Mejías, I.P. Carmona-Sepúlveda, M.D. Ward, and B. Kahr, "A deltamethrin crystal polymorph for more effective malaria control", Proceedings of the National Academy of Sciences, vol. 117, pp. 26633-26638, 2020. http://dx.doi.org/10.1073/pnas.2013390117

The small-molecule antiviral compound Molnupiravir: an exploration of its tautomers.

Sunday, March 14th, 2021

For obvious reasons, anti-viral molecules are very much in the news at the moment. Thus Derek Lowe highlights Molnupiravir which is shown as a hydroxylamine, the representation originating from the Wikipedia page on the molecule.

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Non-covalent-interaction (NCI) surfaces for two large annulenes (revisited).

Sunday, February 7th, 2021

The last post addressed the concept of “steric clashes” in a pericyclic reaction transition state as an extension of the time honoured practice of building molecular models to analyse reaction outcomes. A modern computer generated model might express this in terms of a NCI (non-covalent-interaction) surface. A few posts ago, I had looked at some “molecules of the year” for 2020, one of which was a “figure-eight” twisted dodecaporphyrin in which an aspect of the reported[1] geometry had struck me as potentially lacking features due to the so-called non-covalent dispersion or van der Waals attractions. So I am revisiting here by adding the NCI surface for this molecule and one other.

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References

  1. M. Rickhaus, M. Jirasek, L. Tejerina, H. Gotfredsen, M.D. Peeks, R. Haver, H. Jiang, T.D.W. Claridge, and H.L. Anderson, "Global aromaticity at the nanoscale", Nature Chemistry, vol. 12, pp. 236-241, 2020. http://dx.doi.org/10.1038/s41557-019-0398-3

The chemical synthesis of C2: another fascinating twist to the story.

Wednesday, January 20th, 2021

Last May, I wrote an update to the story sparked by the report of the chemical synthesis of C2.[1] This species has a long history of spectroscopic observation in the gas phase, resulting from its generation at high temperatures.[2] The chemical synthesis however was done in solution at ambient or low temperatures, a game-changer as they say. Here I give another update to this unfolding story.

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References

  1. K. Miyamoto, S. Narita, Y. Masumoto, T. Hashishin, T. Osawa, M. Kimura, M. Ochiai, and M. Uchiyama, "Room-temperature chemical synthesis of C2", Nature Communications, vol. 11, 2020. http://dx.doi.org/10.1038/s41467-020-16025-x
  2. T.W. Schmidt, "The Spectroscopy of C2: A Cosmic Beacon", Accounts of Chemical Research, vol. 54, pp. 481-489, 2021. http://dx.doi.org/10.1021/acs.accounts.0c00703

The thermal reactions … took precisely the opposite stereochemical course to that which we had predicted

Wednesday, January 20th, 2021

The quote of the post title comes from R. B. Woodward explaining the genesis of the discovery of what are now known as the Woodward-Hoffmann rules for pericyclic reactions.[1] I first wrote about this in 2012, noting that “for (that) blog, I do not want to investigate the transition states”. Here I take a closer look at this aspect.

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References

  1. R.B. Woodward, and R. Hoffmann, "Stereochemistry of Electrocyclic Reactions", Journal of the American Chemical Society, vol. 87, pp. 395-397, 1965. http://dx.doi.org/10.1021/ja01080a054

Dispersion attraction effects on the computed geometry of a leminscular dodecaporphyrin.

Friday, January 1st, 2021

In the previous post, I showed the geometries of three large cyclic porphyrins, as part of an article[1] on exploring the aromaticity of large 4n+2 cyclic rings. One of them had been induced into a “figure-eight” or lemniscular conformation, as shown below.

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References

  1. M. Rickhaus, M. Jirasek, L. Tejerina, H. Gotfredsen, M.D. Peeks, R. Haver, H. Jiang, T.D.W. Claridge, and H.L. Anderson, "Global aromaticity at the nanoscale", Nature Chemistry, vol. 12, pp. 236-241, 2020. http://dx.doi.org/10.1038/s41557-019-0398-3

Global aromaticity at the nanoscale.

Thursday, December 31st, 2020

Here is another of the “large” molecules in the c&e news shortlist for molecule-of-the-year, 2020. This one is testing the Hückel 4n+2 rule out to a value never before seen (n = 40, or 162 π-electrons).[1] The take-home message is that this rule seems to behave well in predicting global aromaticity even at this sort of scale!

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References

  1. M. Rickhaus, M. Jirasek, L. Tejerina, H. Gotfredsen, M.D. Peeks, R. Haver, H. Jiang, T.D.W. Claridge, and H.L. Anderson, "Global aromaticity at the nanoscale", Nature Chemistry, vol. 12, pp. 236-241, 2020. http://dx.doi.org/10.1038/s41557-019-0398-3

Tying different knots in a molecular strand.

Wednesday, December 30th, 2020

The title derives from an article[1] which was shortlisted for the annual c&en molecule of the year 2020 awards (and which I occasionally cover here). In fact this year’s overall theme is certainly large molecules, the one exception being a smaller molecule with a quadruple bond to boron, a theme I have already covered here.

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References

  1. D.A. Leigh, F. Schaufelberger, L. Pirvu, J.H. Stenlid, D.P. August, and J. Segard, "Tying different knots in a molecular strand", Nature, vol. 584, pp. 562-568, 2020. http://dx.doi.org/10.1038/s41586-020-2614-0

An interesting aromatic molecule found in Titan’s atmosphere: cyclopropylidene.

Saturday, November 7th, 2020

Cyclopropylidene must be the smallest molecule to be aromatic due to π-electrons, with just three carbon atoms and two hydrogen atoms. It has now been detected in the atmosphere of Titan, one of Saturn’s moons[1] and joining benzene, another aromatic molecule and the protonated version C3H3+ there.

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References

  1. C.A. Nixon, A.E. Thelen, M.A. Cordiner, Z. Kisiel, S.B. Charnley, E.M. Molter, J. Serigano, P.G.J. Irwin, N.A. Teanby, and Y. Kuan, "Detection of Cyclopropenylidene on Titan with ALMA", The Astronomical Journal, vol. 160, pp. 205, 2020. http://dx.doi.org/10.3847/1538-3881/abb679

A new example of a quadruple bond from carbon – to Fe.

Saturday, November 7th, 2020

Way back in 2010, I was writing about an experience I had just had during an organic chemistry tutorial, which morphed into speculation as to whether a carbon atom might sustain a quadruple bond to nitrogen. A decade on, and possibly approaching 100 articles by many authors on the topic, quadruple bonds to carbon continue to fascinate. Now an article as appeared[1] repeating this speculation for a carbon to iron quadruple bond, in the very simple species C⩸Fe(CO)3. This is particularly exciting because of the very real prospect of synthesising this species and perchance getting a crystal structure (something not possible with most of the other quadruply bonded carbon systems studied to date).

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References

  1. A.J. Kalita, S.S. Rohman, C. Kashyap, S.S. Ullah, and A.K. Guha, "Transition metal carbon quadruple bond: viability through single electron transmutation", Physical Chemistry Chemical Physics, vol. 22, pp. 24178-24180, 2020. http://dx.doi.org/10.1039/d0cp03436c