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The structure-reactivity relationships in metalation reactions of porphyrinoids have been studied using experimental
and theoretical methods. A series of eight porphyrinoic ligands, derivatives of chlorophylls, was prepared in which both
the peripheral groups and the degrees of saturation of the macrocycle were systematically varied. To reveal the solvent
and structural factors which control the interactions of these macroligands with metal centers, their interactions with
reactive $Zn^{2+}$
and inert $Pt^{2+}$
ions were investigated using absorption spectroscopy. In parallel, quantum chemical
calculations
(
density functional theory, DFT
)
were performed for the same set of molecules to examine the influence of
structural and electronic factors on the energy of the frontier orbitals, the nucleophilicity/electronegativity of the
macrocycle, its hardness, and conformation. These static descriptors of chemical reactivity, relevant to metalation
reactions, were verified against the results obtained in the experimental model. The experimentally obtained kinetic
data clearly show that the solvent has a crucial role in the activation of the incoming metal center. In terms of chelator
structure, the largest effects concern the size of the delocalized $\pi$-electron system and the presence of side groups.
Both the DFT calculations and experimental results show the strong influence of the macrocycle rigidity and of the
peripheral groups on the chelating ability of porphyrinoids. In particular, the peripheral functionalization of the
macrocyclic system seems to drastically reduce its reactivity toward metal ions. The effect of peripheral groups is two-
fold:
(
i
)
a lower electron density on the core nitrogens, and
(
ii
)
increased rigidity of the macrocycle.The outcomes of the
theoretical and experimental analyses are discussed also in terms of their relevance to the mechanism of biological
metal insertion in the biosynthesis of heme and chlorophyll.
wydział: instytut / zakład / katedra:
Wydział Biochemii, Biofizyki i Biotechnologii : Zakład Fizjologii i Biochemii Roślin, Wydział Chemii : Zakład Chemii Nieorganicznej
typ:
artykuł w czasopiśmie
podtyp:
artykuł
punktacja MEiN [2010 A]: 32
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