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How to make a porphyrin flip: dynamics of asymmetric porphyrin oligomers.


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Article

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Authors

Shang, Cheng 
Philpott, Julian M 
Bampos, Nick 
Barker, Paul D 
Wales, David J 

Abstract

We present the first predictions of meso-aryl flipping pathways in porphyrin oligomers. In the context of cyclic oligoporphyrins this flipping results in a paddle rotation of each porphyrin monomer in the oligomeric ring. If the monomer porphyrin units are asymmetric, this flipping will have consequences for their supramolecular behaviour. Desymmetrisation of synthetic porphyrins leads to synthetic challenges, and hence these species are not as well studied as the more accessible, symmetric counterparts. We have both simulated and synthesized novel, desymmetrised monomeric and cyclic trimeric porphyrins and we predict that the flipping barrier for a porphyrin monomer within the trimer is 36.7 kJ mol(-1) higher than that for meso-aryl flipping in the monomer. The flipping rates estimated from Variable temperature NMR data are consistent with these results. We have also carried out a systematic investigation of how porphyrinic substituents will affect the dynamics, revealing that adding steric bulk in the right place can facilitate meso-aryl flipping. While supramolecular chemistry often focuses on highly symmetric assemblies, evolution can break molecular symmetry in subtle ways, leading to many pseudosymmetric assemblies in biology, especially protein-porphyrinic complexes that are important for energy harvesting and electron transport systems. The dynamic behaviour we have characterized can be critical for the design and function of these molecules, and hence our results will help inform future efforts in the synthesis of asymmetric porphyrinic assemblies that interact with biomolecules.

Description

Keywords

porphyrin, flipping, energy landscape, NMR

Journal Title

Phys Chem Chem Phys

Conference Name

Journal ISSN

1463-9076
1463-9084

Volume Title

Publisher

Royal Society of Chemistry (RSC)
Sponsorship
European Research Council (267369)
Engineering and Physical Sciences Research Council (EP/I001352/1)
This work was supported by the ERC [grant number EP/I001352/1] and [grant number EP/G0606491/1].
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