Posts Tagged ‘spectroscopy’

Multispectral Chiral Imaging with a Metalens.

Saturday, January 6th, 2018
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The title here is from an article on metalenses[1] which caught my eye.

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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

MOLinsight: A web portal for the processing of molecular structures by blind students.

Friday, March 31st, 2017
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Occasionally one comes across a web site that manages to combine being unusual, interesting and also useful. Thus www.molinsight.net is I think a unique chemistry resource for blind and visually impaired students.

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George Olah and the norbornyl cation.

Friday, March 10th, 2017
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George Olah passed away on March 8th. He was part of the generation of scientists in the post-war 1950s who had access to chemical instrumentation that truly revolutionised chemistry. In particular he showed how the then newly available NMR spectroscopy illuminated structures of cations in solvents such “Magic acid“. The obituaries will probably mention his famous “feud” with H. C. Brown over the structure of the norbornyl cation (X=CH2+), implicated in the mechanism of many a solvolysis reaction that characterised the golden period of physical organic chemistry just before and after WWII. 

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Braiding a molecular knot with eight crossings.

Friday, January 20th, 2017
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This is one of those posts of a molecule whose very structure is interesting enough to merit a picture and a 3D model. The study[1] reports a molecular knot with the remarkable number of eight crossings.

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References

  1. J.J. Danon, A. Krüger, D.A. Leigh, J. Lemonnier, A.J. Stephens, I.J. Vitorica-Yrezabal, and S.L. Woltering, "Braiding a molecular knot with eight crossings", Science, vol. 355, pp. 159-162, 2017. http://dx.doi.org/10.1126/science.aal1619

Hydrogen bonding to chloroform.

Monday, November 14th, 2016
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Chloroform, often in the deuterated form CDCl3, is a very common solvent for NMR and other types of spectroscopy. Quantum mechanics is increasingly used to calculate such spectra to aid assignment and the solvent is here normally simulated as a continuum rather than by explicit inclusion of one or more chloroform molecules. But what are the features of the hydrogen bonds that form from chloroform to other acceptors? Here I do a quick search for the common characteristics of such interactions.

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Managing (open) NMR data: a working example using Mpublish.

Monday, August 1st, 2016
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In March, I posted from the ACS meeting in San Diego on the topic of Research data: Managing spectroscopy-NMR, and noted a talk by MestreLab Research on how a tool called Mpublish in the forthcoming release of their NMR analysis software Mestrenova could help. With that release now out, the opportunity arose to test the system.

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Research data: Managing spectroscopy-NMR.

Wednesday, March 16th, 2016
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At the ACS conference, I have attended many talks these last four days, but one made some “connections” which intrigued me. I tell its story (or a part of it) here.

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Chiroptical spectroscopy of the natural product Steganone.

Tuesday, February 10th, 2015
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Steganone is an unusual natural product, known for about 40 years now. The assignment of its absolute configurations makes for an interesting, on occasion rather confusing, and perhaps not entirely atypical story. I will start with the modern accepted stereochemical structure of this molecule, which comes in the form of two separately isolable atropisomers.
steganone
The first reported synthesis of this system in 1977 was racemic, and no stereochemistry is shown in the article (structure 2).[1] Three years later an “Asymmetric total synthesis of (-)steganone and revision of its absolute configuration” shows how the then accepted configuration (structure 1 in this article) needs to be revised to the enantiomer shown as structure 12 in the article[2] and matching the above representation. The system has continued to attract interest ever since[3],[4],[5],[6], not least because of the presence of axial chirality in the form of atropisomerism. Thus early on it was shown that the alternative atropisomer, the (aS,R,R) configuration initially emerges out of several syntheses, and has to be converted to the (aR,R,R) configuration by heating[3]. One could easily be fooled by such isomerism!

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References

  1. D. Becker, L.R. Hughes, and R.A. Raphael, "Total synthesis of the antileukaemic lignan (±)-steganacin", J. Chem. Soc., Perkin Trans. 1, pp. 1674-1681, 1977. http://dx.doi.org/10.1039/P19770001674
  2. J. Robin, O. Gringore, and E. Brown, "Asymmetric total synthesis of the antileukaemic lignan precursor (-)steganone and revision of its absolute configuration", Tetrahedron Letters, vol. 21, pp. 2709-2712, 1980. http://dx.doi.org/10.1016/S0040-4039(00)78586-8
  3. E.R. Larson, and R.A. Raphael, "Synthesis of (–)-steganone", J. Chem. Soc., Perkin Trans. 1, pp. 521-525, 1982. http://dx.doi.org/10.1039/P19820000521
  4. A. Bradley, W.B. Motherwell, and F. Ujjainwalla, "A concise approach towards the synthesis of steganone analogues", Chemical Communications, pp. 917-918, 1999. http://dx.doi.org/10.1039/A900743A
  5. M. Uemura, A. Daimon, and Y. Hayashi, "An asymmetric synthesis of an axially chiral biaryl via an (arene)chromium complex: formal synthesis of (–)-steganone", J. Chem. Soc., Chem. Commun., vol. 0, pp. 1943-1944, 1995. http://dx.doi.org/10.1039/C39950001943
  6. B. Yalcouye, S. Choppin, A. Panossian, F.R. Leroux, and F. Colobert, "A Concise Atroposelective Formal Synthesis of (-)-Steganone", European Journal of Organic Chemistry, vol. 2014, pp. 6285-6294, 2014. http://dx.doi.org/10.1002/ejoc.201402761

Blasts from the past. A personal Web presence: 1993-1996.

Saturday, November 1st, 2014
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Egon Willighagen recently gave a presentation at the RSC entitled “The Web – what is the issue” where he laments how little uptake of web technologies as a “channel for communication of scientific knowledge and data” there is in chemistry after twenty years or more. It caused me to ponder what we were doing with the web twenty years ago. Our HTTP server started in August 1993, and to my knowledge very little content there has been deleted (it’s mostly now just hidden). So here are some ancient pages which whilst certainly not examples of how it should be done nowadays, give an interesting historical perspective. In truth, there is not much stuff that is older out there!

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