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Transition metal complexes of phyllobilins - a new realm of bioinorganic chemistry.

Li C, Kräutler B - Dalton Trans (2015)

Bottom Line: Some linear tetrapyrroles are, however, effective multi-dentate ligands and their transition metal complexes have remarkable chemical properties.YCCs and PiCCs are ligands for various biologically relevant transition metal-ions, such as Zn(ii)-, Ni(ii)- and Cu(ii)-ions.Thanks to their capacity for metal-ion coordination, phyllobilins could, e.g., be involved in heavy-metal transport and detoxification, and some of their metal-complexes could act as sensitizers for singlet oxygen or as plant toxins against pathogens.

View Article: PubMed Central - PubMed

Affiliation: Institute of Organic Chemistry & Centre of Molecular Biosciences, University of Innsbruck, Innrain 80/82, A-6020 Innsbruck, Austria. bernhard.kraeutler@uibk.ac.at.

ABSTRACT
Natural cyclic tetrapyrroles feature outstanding capacity for binding transition metal ions, furnishing Nature with the important metallo-porphyrinoid 'Pigments of Life', such as heme, chlorophyll (Chl) and vitamin B12. In contrast, linear tetrapyrroles are not generally ascribed a biologically relevant ability for metal-binding. Indeed, when heme or Chl are degraded to natural linear tetrapyrroles, their central Fe- or Mg-ions are set free. Some linear tetrapyrroles are, however, effective multi-dentate ligands and their transition metal complexes have remarkable chemical properties. The focus of this short review is centred on such complexes of the linear tetrapyrroles derived from natural Chl-breakdown, called phyllobilins. These natural bilin-type compounds are massively produced in Nature and in highly visible processes. Colourless non-fluorescing Chl-catabolites (NCCs) and the related dioxobilin-type NCCs, which typically accumulate in leaves as 'final' products of Chl-breakdown, show low affinity for transition metal-ions. However, NCCs are oxidized in leaves to give less saturated coloured phyllobilins, such as yellow or pink Chl-catabolites (YCCs or PiCCs). YCCs and PiCCs are ligands for various biologically relevant transition metal-ions, such as Zn(ii)-, Ni(ii)- and Cu(ii)-ions. Complexation of Zn(ii)- and Cd(ii)-ions by the effectively tridentate PiCC produces blue metal-complexes that exhibit an intense red fluorescence, thus providing a tool for the sensitive detection of these metal ions. Outlined here are fundamental aspects of structure and metal coordination of phyllobilins, including a comparison with the corresponding properties of bilins. This knowledge may be valuable in the quest of finding possible biological roles of the phyllobilins. Thanks to their capacity for metal-ion coordination, phyllobilins could, e.g., be involved in heavy-metal transport and detoxification, and some of their metal-complexes could act as sensitizers for singlet oxygen or as plant toxins against pathogens.

No MeSH data available.


Related in: MedlinePlus

Formula of a model Zn(ii)-1-formylbiliverdinate, in which the Zn(ii)-ion is pentacoordinate due to ligation of a water molecule (structure derived from X-ray crystal analysis).
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fig13: Formula of a model Zn(ii)-1-formylbiliverdinate, in which the Zn(ii)-ion is pentacoordinate due to ligation of a water molecule (structure derived from X-ray crystal analysis).

Mentions: An early study reported a solution of meso-biliverdin (mBV) to change colour from blue to green upon addition of a solution of Zn(OAc)2 in MeOH under N2, due to formation of the Zn(ii)-complex of mBV.77 Analysis of the crystal structures of the Zn-complex of an ‘octaethyl-formylbiliverdinate’ (prepared from photo-oxidation of Zn-octaethylporphyrin) revealed the presence of a monomeric penta-coordinate Zn-complex as mono-hydrate (with four N and one axial H2O coordinating to Zn, see Fig. 13), as well as a dimer involving alternative bonding to two tetra-coordinate Zn-ions by two pairs of N-atoms from each ligand.78 A Zn-1,19-dideoxy-1,2,3,7,8,12,13,17,18,19-decamethylbiladiene-a,c featured a similar dimeric structure.79 In water or DMSO and in the absence of O2, binding of BV to Zn-, Cd- and Cu-ions was observed in a 1 : 1 stoichiometry. In aqueous solution, further oxidation reactions of various BV-metal complexes were observed.24,74,80


Transition metal complexes of phyllobilins - a new realm of bioinorganic chemistry.

Li C, Kräutler B - Dalton Trans (2015)

Formula of a model Zn(ii)-1-formylbiliverdinate, in which the Zn(ii)-ion is pentacoordinate due to ligation of a water molecule (structure derived from X-ray crystal analysis).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4447063&req=5

fig13: Formula of a model Zn(ii)-1-formylbiliverdinate, in which the Zn(ii)-ion is pentacoordinate due to ligation of a water molecule (structure derived from X-ray crystal analysis).
Mentions: An early study reported a solution of meso-biliverdin (mBV) to change colour from blue to green upon addition of a solution of Zn(OAc)2 in MeOH under N2, due to formation of the Zn(ii)-complex of mBV.77 Analysis of the crystal structures of the Zn-complex of an ‘octaethyl-formylbiliverdinate’ (prepared from photo-oxidation of Zn-octaethylporphyrin) revealed the presence of a monomeric penta-coordinate Zn-complex as mono-hydrate (with four N and one axial H2O coordinating to Zn, see Fig. 13), as well as a dimer involving alternative bonding to two tetra-coordinate Zn-ions by two pairs of N-atoms from each ligand.78 A Zn-1,19-dideoxy-1,2,3,7,8,12,13,17,18,19-decamethylbiladiene-a,c featured a similar dimeric structure.79 In water or DMSO and in the absence of O2, binding of BV to Zn-, Cd- and Cu-ions was observed in a 1 : 1 stoichiometry. In aqueous solution, further oxidation reactions of various BV-metal complexes were observed.24,74,80

Bottom Line: Some linear tetrapyrroles are, however, effective multi-dentate ligands and their transition metal complexes have remarkable chemical properties.YCCs and PiCCs are ligands for various biologically relevant transition metal-ions, such as Zn(ii)-, Ni(ii)- and Cu(ii)-ions.Thanks to their capacity for metal-ion coordination, phyllobilins could, e.g., be involved in heavy-metal transport and detoxification, and some of their metal-complexes could act as sensitizers for singlet oxygen or as plant toxins against pathogens.

View Article: PubMed Central - PubMed

Affiliation: Institute of Organic Chemistry & Centre of Molecular Biosciences, University of Innsbruck, Innrain 80/82, A-6020 Innsbruck, Austria. bernhard.kraeutler@uibk.ac.at.

ABSTRACT
Natural cyclic tetrapyrroles feature outstanding capacity for binding transition metal ions, furnishing Nature with the important metallo-porphyrinoid 'Pigments of Life', such as heme, chlorophyll (Chl) and vitamin B12. In contrast, linear tetrapyrroles are not generally ascribed a biologically relevant ability for metal-binding. Indeed, when heme or Chl are degraded to natural linear tetrapyrroles, their central Fe- or Mg-ions are set free. Some linear tetrapyrroles are, however, effective multi-dentate ligands and their transition metal complexes have remarkable chemical properties. The focus of this short review is centred on such complexes of the linear tetrapyrroles derived from natural Chl-breakdown, called phyllobilins. These natural bilin-type compounds are massively produced in Nature and in highly visible processes. Colourless non-fluorescing Chl-catabolites (NCCs) and the related dioxobilin-type NCCs, which typically accumulate in leaves as 'final' products of Chl-breakdown, show low affinity for transition metal-ions. However, NCCs are oxidized in leaves to give less saturated coloured phyllobilins, such as yellow or pink Chl-catabolites (YCCs or PiCCs). YCCs and PiCCs are ligands for various biologically relevant transition metal-ions, such as Zn(ii)-, Ni(ii)- and Cu(ii)-ions. Complexation of Zn(ii)- and Cd(ii)-ions by the effectively tridentate PiCC produces blue metal-complexes that exhibit an intense red fluorescence, thus providing a tool for the sensitive detection of these metal ions. Outlined here are fundamental aspects of structure and metal coordination of phyllobilins, including a comparison with the corresponding properties of bilins. This knowledge may be valuable in the quest of finding possible biological roles of the phyllobilins. Thanks to their capacity for metal-ion coordination, phyllobilins could, e.g., be involved in heavy-metal transport and detoxification, and some of their metal-complexes could act as sensitizers for singlet oxygen or as plant toxins against pathogens.

No MeSH data available.


Related in: MedlinePlus