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Inside or outside the box? Effect of substrate location on coordination-cage based catalysis
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Solea, Atena B., Sudittapong, Burin, Taylor, Christopher G. P. and Ward, Michael D. (2022) Inside or outside the box? Effect of substrate location on coordination-cage based catalysis. Dalton Transactions, 51 (30). pp. 11277-11285. doi:10.1039/d2dt01713j ISSN 1477-9226.
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Official URL: https://doi.org/10.1039/d2dt01713j
Abstract
In this work we compare and contrast the hydrolysis of two different aromatic esters using an octanuclear cubic Co8 coordination cage host as the catalyst. Diacetyl fluorescein (DAF) is too large to bind inside the cage cavity, but in aqueous solution it interacts with the exterior surface of the cage via a hydrophobic interaction with K = 1.5(2) × 104 M−1. This is sufficient to bring it into close proximity to the layer of hydroxide ions which also surrounds the 16+ cage surface even at modest pH values, accelerating the hydrolysis of DAF to fluorescein with kcat/kuncat (the rate acceleration for that fraction of DAF in contact with the cage surface in the equilibrium) ≈50. This is far smaller than many known examples of catalysis inside a cage cavity, but at the exterior surface it is potentially general with no cavity-imposed size/shape limitations for guest binding. In contrast 4-nitrophenyl acetate (4NPA) binds inside the cage cavity with K = 3.5(3) × 103 M−1 and as such is surrounded in solution by the hydroxide ions which accumulate around the cage surface. However its hydrolysis is actually inhibited: either because of a geometrically unfavourable geometry of the bound substrate which makes it inaccessible to surface-bound hydroxide, or because the necessary volume expansion/geometry change associated with formation of a tetrahedral intermediate cannot be accommodated inside the cavity. Any 4NPA that is free in solution as part of the equilibrium undergoes catalysed hydrolysis at the cage exterior surface in the same way as DAF, but the effect is limited by the low affinity of 4NPA for the exterior surface. We conclude that exterior-surface catalysis can be effective and potentially general; and that cavity-binding of guests can result in negative, rather than positive, catalysis.
Item Type: | Journal Article | |||||||||
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Subjects: | Q Science > QD Chemistry | |||||||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Chemistry | |||||||||
SWORD Depositor: | Library Publications Router | |||||||||
Library of Congress Subject Headings (LCSH): | Chemistry, Inorganic, Hydrolysis, Esters, Catalysis | |||||||||
Journal or Publication Title: | Dalton Transactions | |||||||||
Publisher: | Royal Society of Chemistry | |||||||||
ISSN: | 1477-9226 | |||||||||
Official Date: | 14 August 2022 | |||||||||
Dates: |
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Volume: | 51 | |||||||||
Number: | 30 | |||||||||
Page Range: | pp. 11277-11285 | |||||||||
DOI: | 10.1039/d2dt01713j | |||||||||
Status: | Peer Reviewed | |||||||||
Publication Status: | Published | |||||||||
Access rights to Published version: | Open Access (Creative Commons) | |||||||||
Date of first compliant deposit: | 12 August 2022 | |||||||||
Date of first compliant Open Access: | 24 August 2022 | |||||||||
RIOXX Funder/Project Grant: |
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