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Probing Halogen Bonding via Paramagnetic Ligand Tagging
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry. (Erdélyi Group)ORCID iD: 0000-0002-7945-5504
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Organic Chemistry. (Erdélyi Group)
2018 (English)In: EMBO Course: Multidimensional NMR in Structural Biology, Joachimsthal, 12-17 Aug, 2018, 2018Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

Halogen Bonding is a spectacle that has recently received widespread attention, despite the fact that it was discovered over 200 years ago. This fundamental interaction is vastly abundant in today’s world, and a better understanding of it would enable us to both design and improve upon existing drugs, materials and catalysts, to name a few. Halogen bonds (XB) are roughly 180°, non-covalent interactions that exploit the anisotropic electron density of a halogen atom. Analogous to hydrogen bonding, a halogen bond acceptor (being an electron donor in the form of a Lewis base (LB)) and a halogen bond donor (being an electron acceptor consisting of a halogen with a σ-hole) must exist. σ-Holes are electrophilic regions that arise on the opposite tip of an R-X bond in the anti-bonding orbital and to maximise these holes, one can make ‘R’ more electron withdrawing and/or ‘X’ larger with a more diffuse outer electron shell (I > Br > Cl > F).

Halogen bonding, like many other weak bonding interactions, is incredibly difficult to measure accurately in solution. Thus, we hypothesize that paramagnetic NMR techniques are potentially useful for their detection and characterization. This involves the use of a compound containing free electrons, and when these are subjected to the large magnetic field of an NMR spectrometer, they exhibit unique qualities that one can fruitfully exploit. In these studies, we mainly focus on measuring Pseudocontact Shifts (PCS) that arise from vast spectral broadening due to the free electrons. With this technique, we are able to assess very weak bonding interactions by the detection of small chemical shift differences due to a much larger spectral window than commonly detected.

In this work, building upon previous studies carried out within the group,[1] we synthesise cyclen-based organic ligands which complex a paramagnetic lanthanide (Ln3+) species. Attached to one amine in the cyclen core, via a linker, is a Lewis Base (or halogen bond acceptor) which is utilised in probing halogen bonding between itself and a free halogen bond donor in solution. Expected PCS measurements will give an accurate value of the weak bonding interaction between donor and acceptor in solution- the resolution of which is something that is simply not possible via classical NMR studies.

Place, publisher, year, edition, pages
2018.
National Category
Chemical Sciences
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-357807OAI: oai:DiVA.org:uu-357807DiVA, id: diva2:1240481
Conference
EMBO Course: Multidimensional NMR in Structural Biology, Joachimsthal, August 12-17, 2018.
Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2018-08-21

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