Reaction mechanism of porphyrin metallation studied by theoretical methods
Shen, Yong LU and Ryde, Ulf LU
(2005)
In Chemistry: A European Journal
11(5).
p.1549-1564
- Abstract
- We have studied the reaction mechanism for the insertion of Mg2+ and Fe2+ into a porphyrin ring with density functional calculations with large basis set and including solvation, zero-point and thermal effects. We have followed the reaction from the outer-sphere complex, in which the metal is coordinated with six water molecules and the porphyrin is doubly protonated, until the metal ion is inserted into the deprotonated porphyrin ring with only one water ligand remaining. This reaction involves the stepwise displacement of five water molecules and the removal of two protons from the porphyrin ring. In addition, a step seems to be necessary in which a porphyrin pyrrolenine nitrogen atom changes its interaction from a hydrogen bond to a... (More)
- We have studied the reaction mechanism for the insertion of Mg2+ and Fe2+ into a porphyrin ring with density functional calculations with large basis set and including solvation, zero-point and thermal effects. We have followed the reaction from the outer-sphere complex, in which the metal is coordinated with six water molecules and the porphyrin is doubly protonated, until the metal ion is inserted into the deprotonated porphyrin ring with only one water ligand remaining. This reaction involves the stepwise displacement of five water molecules and the removal of two protons from the porphyrin ring. In addition, a step seems to be necessary in which a porphyrin pyrrolenine nitrogen atom changes its interaction from a hydrogen bond to a metal-bound solvent molecule to a direct coordination to the metal ion. If the protons are taken up by a neutral imidazole molecule, the deprotonation reactions are exothermic with minimal barriers. However, with a water molecule as an acceptor, they are endothermic. The ligand exchange reactions were approximately thermoneutral ( +/- 20 kJ mol(-1), with one exception) with barriers of up to 72 kJ mol(-1) for Mg and 51 kJ mol(-1) for Fe. For Mg, the highest barrier was found for the formation of the first bond to the porphyrin ring. For Fe, a higher barrier was found for the formation of the second bond to the porphyrin ring, but this barrier is probably lower in solution. No evidence was found for an initial pre-equilibrium between a planar and a distorted porphyrin ring. Instead, the porphyrin becomes more and more distorted as the number of metal-porphyrin bonds increase (by up to 191 kJ mol(-1)). This strain is released when the porphyrin becomes deprotonated and the metal moves into the ring plane. Implications of these findings for the chelatase enzymes are discussed. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/152739
- author
- Shen, Yong
LU
and Ryde, Ulf
LU
- organization
- publishing date
- 2005
- type
- Contribution to journal
- publication status
- published
- subject
- in
- Chemistry: A European Journal
- volume
- 11
- issue
- 5
- pages
- 1549 - 1564
- publisher
- Wiley-Blackwell
- external identifiers
-
- pmid:15662683
- wos:000227262000019
- scopus:14844323140
- pmid:15662683
- ISSN
- 1521-3765
- DOI
- 10.1002/chem.200400298
- language
- English
- LU publication?
- yes
- additional info
- The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Theoretical Chemistry (S) (011001039)
- id
- 084faa45-fe15-44b1-88ce-86b0d0d1f40c (old id 152739)
- date added to LUP
- 2016-04-01 16:28:18
- date last changed
- 2023-01-24 02:30:25
@article{084faa45-fe15-44b1-88ce-86b0d0d1f40c,
abstract = {{We have studied the reaction mechanism for the insertion of Mg2+ and Fe2+ into a porphyrin ring with density functional calculations with large basis set and including solvation, zero-point and thermal effects. We have followed the reaction from the outer-sphere complex, in which the metal is coordinated with six water molecules and the porphyrin is doubly protonated, until the metal ion is inserted into the deprotonated porphyrin ring with only one water ligand remaining. This reaction involves the stepwise displacement of five water molecules and the removal of two protons from the porphyrin ring. In addition, a step seems to be necessary in which a porphyrin pyrrolenine nitrogen atom changes its interaction from a hydrogen bond to a metal-bound solvent molecule to a direct coordination to the metal ion. If the protons are taken up by a neutral imidazole molecule, the deprotonation reactions are exothermic with minimal barriers. However, with a water molecule as an acceptor, they are endothermic. The ligand exchange reactions were approximately thermoneutral ( +/- 20 kJ mol(-1), with one exception) with barriers of up to 72 kJ mol(-1) for Mg and 51 kJ mol(-1) for Fe. For Mg, the highest barrier was found for the formation of the first bond to the porphyrin ring. For Fe, a higher barrier was found for the formation of the second bond to the porphyrin ring, but this barrier is probably lower in solution. No evidence was found for an initial pre-equilibrium between a planar and a distorted porphyrin ring. Instead, the porphyrin becomes more and more distorted as the number of metal-porphyrin bonds increase (by up to 191 kJ mol(-1)). This strain is released when the porphyrin becomes deprotonated and the metal moves into the ring plane. Implications of these findings for the chelatase enzymes are discussed.}},
author = {{Shen, Yong and Ryde, Ulf}},
issn = {{1521-3765}},
language = {{eng}},
number = {{5}},
pages = {{1549--1564}},
publisher = {{Wiley-Blackwell}},
series = {{Chemistry: A European Journal}},
title = {{Reaction mechanism of porphyrin metallation studied by theoretical methods}},
url = {{https://lup.lub.lu.se/search/files/135492918/72_fc_react.pdf}},
doi = {{10.1002/chem.200400298}},
volume = {{11}},
year = {{2005}},
}