Archive for the ‘Interesting chemistry’ Category

London: set to become a National Park City in 2019.

Friday, February 9th, 2018
No Gravatar

Last year, I showed photos of wildflower meadows in west London close to where we live, evolving as the seasons changed. Today we hear the announcement that London itself is set be declared the world’s first National Park City in 2019.

(more…)

Multispectral Chiral Imaging with a Metalens.

Saturday, January 6th, 2018
No Gravatar

The title here is from an article on metalenses[1] which caught my eye.

(more…)

References

  1. M. Khorasaninejad, W.T. Chen, A.Y. Zhu, J. Oh, R.C. Devlin, D. Rousso, and F. Capasso, "Multispectral Chiral Imaging with a Metalens", Nano Letters, vol. 16, pp. 4595-4600, 2016. http://dx.doi.org/10.1021/acs.nanolett.6b01897

Can any hypervalence in diazomethanes be amplified?

Saturday, December 23rd, 2017
No Gravatar

In the previous post, I referred to a recently published review on hypervalency[1] which introduced a very simple way (the valence electron equivalent γ) of quantifying the effect. Diazomethane was cited as one example of a small molecule exhibiting hypervalency (on nitrogen) by this measure. Here I explore the effect of substituting diazomethane with cyano and nitro groups.

(more…)

References

  1. M.C. Durrant, "A quantitative definition of hypervalency", Chemical Science, vol. 6, pp. 6614-6623, 2015. http://dx.doi.org/10.1039/C5SC02076J

Are diazomethanes hypervalent molecules? Probably, but in an unexpected way!

Saturday, December 23rd, 2017
No Gravatar

A recently published review on hypervalency[1] introduced a very simple way of quantifying the effect. One of the molecules which was suggested to be hypervalent using this method was diazomethane. Here I take a closer look.

(more…)

References

  1. M.C. Durrant, "A quantitative definition of hypervalency", Chemical Science, vol. 6, pp. 6614-6623, 2015. http://dx.doi.org/10.1039/C5SC02076J

A form of life that can stably store genetic information using a six-letter, three-base-pair alphabet?

Saturday, December 2nd, 2017
No Gravatar

For around 16 years, Floyd Romesberg’s group has been exploring un-natural alternatives (UBPs) to the Watson-Crick base pairs (C-G and A-T) that form part of the genetic code in DNA. Recently they have had remarkable success with one such base pair, called X and Y (for the press) and dNaMTP and d5SICSTP (in scholarly articles).[1],[2] This extends the genetic coding from the standard 20 amino acids to the possibility of up to 172 amino acids. Already, organisms engineered to contain X-Y pairs in their DNA have been shown to express entirely new (and un-natural) proteins.

(more…)

References

  1. A.W. Feldman, M.P. Ledbetter, Y. Zhang, and F.E. Romesberg, "Reply to Hettinger: Hydrophobic unnatural base pairs and the expansion of the genetic alphabet", Proceedings of the National Academy of Sciences, vol. 114, pp. E6478-E6479, 2017. http://dx.doi.org/10.1073/pnas.1708259114
  2. D.A. Malyshev, K. Dhami, H.T. Quach, T. Lavergne, P. Ordoukhanian, A. Torkamani, and F.E. Romesberg, "Efficient and sequence-independent replication of DNA containing a third base pair establishes a functional six-letter genetic alphabet", Proceedings of the National Academy of Sciences, vol. 109, pp. 12005-12010, 2012. http://dx.doi.org/10.1073/pnas.1205176109

The di-anion of dilithium (not the Star Trek variety): Another “Hyper-bond”?

Saturday, September 16th, 2017
No Gravatar

Early in 2011, I wrote about how the diatomic molecule Be2 might be persuaded to improve upon its normal unbound state (bond order ~zero) by a double electronic excitation to a strongly bound species. I yesterday updated this post with further suggestions and one of these inspired this follow-up.

(more…)

Two new types in the chemical bonding zoo: exo-bonds and hyper-bonds?

Wednesday, September 6th, 2017
No Gravatar

The chemical bond zoo is relatively small (the bond being a somewhat fuzzy concept, I am not sure there is an actual count of occupants). So when two new candidates come along, it is worth taking notice. I have previously noted the Chemical Bonds at the 21st Century-2017: CB2017 Aachen conference, where both were discussed.

(more…)

One more WATOC 2017 Report.

Thursday, August 31st, 2017
No Gravatar

Conferences can be intense, and this one is no exception. After five days, saturation is in danger of setting in. But before it does, I include two more (very) brief things I have learnt.

(more…)

(another) WATOC 2017 report.

Tuesday, August 29th, 2017
No Gravatar

Another selection (based on my interests, I have to repeat) from WATOC 2017 in Munich.

  1. Odile Eisenstein gave a talk about predicted 13C chemical shifts in transition metal (and often transient) complexes, with the focus on metallacyclobutanes. These calculations include full spin-orbit/relativistic corrections, essential when the carbon is attached to an even slightly relativistic element. She noted that the 13C shifts of the carbons attached to the metal fall into two camps, those with δ ~+80 ppm and those with values around -8 ppm. These clusters are associated with quite different reactivities, and also seem to cluster according to the planarity or non-planarity of the 4-membered ring. There followed some very nice orbital explanations which I cannot reproduce here because my note taking was incomplete, including discussion of the anisotropy of the solid state spectra. A fascinating story, which I add to here in a minor aspect. Here is a plot of the geometries of the 52 metallacyclobutanes found in the Cambridge structure database. The 4-ring can be twisted by up to 60° around either of the C-C bonds in the ring, and rather less about the M-C bonds. There is a clear cluster (red spot) for entirely flat rings, and perhaps another at around 20° for bent ones, but of interest is that it does form something of a continuum. What is needed is to correlate these geometries with the observed 13C chemical shifts to see if the two sets of clusters match. I include this here because in part such a search can be done in “real-time” whilst the speaker is presenting, and can then be offered as part of the discussion afterwards. It did not happen here because I was chairing the meeting, and hence concentrating entirely on proceedings!

    (more…)

WATOC 2017 report.

Tuesday, August 29th, 2017
No Gravatar

The triennial conference is this year located in Munich. With 1500 participants and six parallel sessions, this report can give only a flavour of proceedings.

(more…)