Have photosynthetic pigments been formulated for chemical stability? A cursory insight into the reactivity of magnesium porphyrinoids

Magnesium complexes with reduced tetrapyrrolic ligands are active compounds of plant and bacteria photosystems. However, also the porphyrin complex appears as an intermediate on the biosynthetic pathway of the photosynthetic pigments. Its transformations, in particular the reduction of pyrrole rings...

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Bibliographic Details
Published in:Journal of coordination chemistry 2018-07, Vol.71 (11-13), p.1837-1851
Main Authors: Orzeł, Łukasz, Rutkowska-Zbik, Dorota, Świrski, Mateusz, Stochel, Grażyna
Format: Article
Language:English
Subjects:
Acetic acid
Chlorophyll
Coordination compounds
demetalation
Density functional theory
Electronic structure
Ligands
Magnesium
Metal ions
Organic chemistry
Photosynthesis
photosynthetic pigments
Pigments
Porphyrinoids
Spectroscopic analysis
Stability
stability of complexes
Substitution reactions
transmetalation
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Summary:Magnesium complexes with reduced tetrapyrrolic ligands are active compounds of plant and bacteria photosystems. However, also the porphyrin complex appears as an intermediate on the biosynthetic pathway of the photosynthetic pigments. Its transformations, in particular the reduction of pyrrole rings, lead to the acquisition of the properties that are primary for activity in antenna systems and reaction centers. On the other hand, modifications of the porphyrin system must affect the resistance to destructive processes, such as loss of metal ion and its substitution. In order to compare the stability of three natural Mg complexes, namely Mg protoporphyrin IX, chlorophyll a, and bacteriochlorophyll a, spectroscopic studies in solution were performed. The difference in the electronic structure of the macrocyclic ligand was the basic variable in testing the action against d-electron metal salts and acetic acid. The spectroscopic studies were supplemented with calculations using the Density Functional Theory which provided insight into the stability of M(II)-N bonds depending on the dimension of the delocalized electron system. The results indicate the decreasing stability of Mg(II) complexes on the biosynthetic pathway, thereby providing an additional justification for incorporation of the metal ion into porphyrin prior to the electronic modifications of the tetrapyrrolic system.
ISSN:0095-8972
1029-0389
DOI:10.1080/00958972.2018.1484915