Archive for December, 2021

Molecule of the year 2021: Infinitene.

Thursday, December 16th, 2021

The annual “molecule of the year” results for 2021 are now available … and the winner is Infinitene.[1],[2] This is a benzocirculene in the form of a figure eight loop (the infinity symbol), a shape which is also called a lemniscate [3] after the mathematical (2D) function due to Bernoulli. The most common class of molecule which exhibits this (well known) motif are hexaphyrins (hexaporphyrins; porphyrin is a tetraphyrin)[4],[5],[6], many of which exhibit lemniscular topology as determined from a crystal structure. Straightforward annulenes have also been noted to display this[7] (as first suggested here for a [14]annulene[8]) and other molecules show higher-order Möbius forms such as trefoil knots.[9],[10] This new example uses twelve benzo groups instead of six porphyrin units to construct the lemniscate. So the motif is not new, but this is the first time it has been constructed purely from benzene rings. (more…)


  1. K. Itami, M. Krzeszewski, and H. Ito, "Infinitene: A Helically Twisted Figure-Eight [12]Circulene Topoisomer", 2021.
  2. M. Krzeszewski, H. Ito, and K. Itami, "Infinitene: A Helically Twisted Figure-Eight [12]Circulene Topoisomer", Journal of the American Chemical Society, vol. 144, pp. 862-871, 2021.
  3. C.S.M. Allan, and H.S. Rzepa, "Chiral Aromaticities. AIM and ELF Critical Point and NICS Magnetic Analyses of Möbius-Type Aromaticity and Homoaromaticity in Lemniscular Annulenes and Hexaphyrins", The Journal of Organic Chemistry, vol. 73, pp. 6615-6622, 2008.
  4. H. Rath, J. Sankar, V. PrabhuRaja, T.K. ChandrashekarPresent address: The D, B.S. Joshi, and R. Roy, "Figure-eight aromatic core-modified octaphyrins with six meso links: syntheses and structural characterization", Chemical Communications, pp. 3343, 2005.
  5. H. Rath, J. Sankar, V. PrabhuRaja, T.K. Chandrashekar, and B.S. Joshi, "Aromatic Core-Modified Twisted Heptaphyrins[]:  Syntheses and Structural Characterization", Organic Letters, vol. 7, pp. 5445-5448, 2005.
  6. S. Shimizu, N. Aratani, and A. Osuka, "meso-Trifluoromethyl-Substituted Expanded Porphyrins", Chemistry - A European Journal, vol. 12, pp. 4909-4918, 2006.
  7. T. Perera, F.R. Fronczek, and S.F. Watkins, "2,9,16,23-Tetrakis(1-methylethyl)-5,6,11,12,13,14,19,20,25,26,27,28-dodecadehydrotetrabenzo[a,e,k,o]cycloeicosene", Acta Crystallographica Section E Structure Reports Online, vol. 67, pp. o3493-o3493, 2011.
  8. H.S. Rzepa, "A Double-Twist Möbius-Aromatic Conformation of [14]Annulene", Organic Letters, vol. 7, pp. 4637-4639, 2005.
  9. G.R. Schaller, F. Topić, K. Rissanen, Y. Okamoto, J. Shen, and R. Herges, "Design and synthesis of the first triply twisted Möbius annulene", Nature Chemistry, vol. 6, pp. 608-613, 2014.
  10. S.M. Bachrach, and H.S. Rzepa, "Cycloparaphenylene Möbius trefoils", Chemical Communications, vol. 56, pp. 13567-13570, 2020.

Protein-Biotin complexes. Crystal structure mining.

Sunday, December 12th, 2021

In the previous post, I showed some of the diverse “non-classical”interactions between Biotin and a protein where it binds very strongly. Here I take a look at two of these interactions to discover how common they are in small molecule structures.