Mechanistic Information on Cu<sup>II</sup> Metalation and Transmetalation of Chlorophylls

Orzeł, Łukasz; Eldik, Rudi van; Fiedor, Leszek; Stochel, Grażyna

doi:10.1002/ejic.200800662

Cited by 11 publications

(26 citation statements)

References 60 publications

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“…These results are in line with previous studies which showed that the solvent is a key factor controlling the rates of metal exchange in porphyrinoids, mostly via the solvation of metal ions [30, 36, 61]. Yet, specific solvent–macrocyclic ligand interactions also play a role [29], and because the degree of macrocycle distortion is directly related to the value of Δ H ≠ of metalation [18, 29, 62], one should consider the geometrical factor in solvent–porphyrinoid systems.…”

Section: Discussionsupporting

confidence: 93%

Factors controlling the reactivity of divalent metal ions towards pheophytin a

et al. 2017

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In this study, we evaluate the factors which determine the reactivity of divalent metal ions in the spontaneous formation of metallochlorophylls, using experimental and computational approaches. Kinetic studies were carried out using pheophytin a in reactions with various divalent metal ions combined with non- or weakly-coordinative counter ions in a series of organic solvents. To obtain detailed insights into the solvent effect, the metalations with the whole set of cations were investigated in three solvents and with Zn2+ in seven solvents. The reactions were monitored using electronic absorption spectroscopy and the stopped-flow technique. DFT calculations were employed to shed light on the role of solvent in activating the metal ions towards porphyrinoids. This experimental and computational analysis gives detailed information regarding how the solvent and the counter ion assist/hinder the metalation reaction as activators/inhibitors. The metalation course is dictated to a large extent by the reaction medium, via either the activation or deactivation of the incoming metal ion. The solvent may affect the metalation in several ways, mainly via H-bonding with pyrrolenine nitrogens and the activation/deactivation of the incoming cation. It also seems to affect the activation enthalpy by causing slight conformational changes in the macrocyclic ligand. These new mechanistic insights contribute to a better understanding of the “metal–counterion–solvent” interplay in the metalation of porphyrinoids. In addition, they are highly relevant to the mechanisms of metalation reactions catalyzed by chelatases and explain the differences between the insertion of Mg2+ and other divalent cations.Electronic supplementary materialThe online version of this article (doi:10.1007/s00775-017-1472-1) contains supplementary material, which is available to authorized users.

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Section: Discussionsupporting

confidence: 93%

Factors controlling the reactivity of divalent metal ions towards pheophytin a

et al. 2017

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“…All the features observed in Fig. 2D indicate formation of a typical Cu-Pheoa complex with a single central ion, Cu 2+ , placed in the cavity (compare our previous report 12 ). Its breakdown and release of Mg 2+ requires application of specific conditions, such as the presence of excess acetate, acting as a specific "pulling" ligand.…”

Section: Resultssupporting

confidence: 79%

“…In the presence of certain metal ions, such as Cu 2+ , two types of electron transfer processes can be distinguished in the formation of new metallo derivatives. 12 Whereas the one-electron oxidation of the tetrapyrrolic ring appears to be reversible, thus not preventing further central ion substitution, the multi-electron process leads directly to the degradation of the macrocyclic system. …”

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confidence: 99%

Fine tuning of copper(ii)–chlorophyll interactions in organic media. Metalation versus oxidation of the macrocycle

et al. 2015

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The nature of chlorophyll interactions with copper(II) ions varies considerably in organic solvents, depending on the dominant coordinative form. Besides formation of the metallo tetrapyrrolic complex, Cu(II) ions can cause oxidation of the pigment, reversible or irreversible, which can lead to the destruction of the macrocyclic structure. All these reaction types can be distinguished within a quite narrow range of reaction conditions. The ability to form new metallo derivatives in either metalation or transmetalation reactions is obviously limited by the concentration of the potential oxidant, but can be secured below this level via suitable composition of the reaction system. The decisive factor in the selection of a specific reaction pathway is the presence of a potential ligand that can affect the reactivity of Cu(II) for example by shifting its redox potential. Spectroscopic and electrochemical studies were performed in order to determine the predominant species of Cu(II) in methanol, nitromethane and acetonitrile in the presence of chloride and acetate ions, as well as to assign their appropriate oxidizing ability. This allowed us to estimate the boundary conditions for the electron transfer processes in chlorophyll-Cu(II) systems. Chlorophyll and its free base can undergo both types of electron transfer processes, however, they reveal different susceptibilities that make this class of ligands quite versatile markers in tuning the reactivity of metal ions in solutions. IntroductionInteractions of chlorophylls (Chls; including chlorophyll a, Chla, its free base pheophytin a, Pheoa, and other derivatives) with metal ions, although not strictly related to their basic biological functions, are important for proper metabolism of the photosynthetic pigment. They are decisive not only in biosynthesis of Chla (Fig. 1) at the stage of enzyme-driven Mg 2+ incorporation into protoporphyrin IX (3,7,12,17-tetramethyl-8,13-divinyl-2,18-porphinedipropionic acid), [1][2][3][4] but also in the spontaneous substitution of metal ions occurring in plants growing on soils contaminated by heavy metals. 5 The latter effect, observed clearly for Cu 2+ , Zn 2+ , Cd 2+ and Hg 2+ , results in the irreversible loss of photosynthetic abilities. [5][6][7] In recent years, deeper insight into the mechanisms of metal ion -Chl interactions has become important also for the development of procedures for modification and synthesis of new tetrapyrrolic complexes in terms of their potential biomedical applications. [8][9][10] Although the primary function of chlorophylls is related to electron transfer processes, their occurrence in biological systems is not due to pigment interactions with redox-active metal ions. Properties of natural photosystems, View Article OnlineView Journal | View Issue including the composition of endogenous ligands, prevent degradation of the pigment's macrocyclic structure in the presence of Cu 2+ and other potential metallic oxidants.Displacement of the chlorophyllic central ion in vivo is limited to a few me...

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“…The analysis of the collected data reveals that the native central atom of bacteriochlorophyll, magnesium, is not stable in the macrocycle cavity. This observation is not surprising, as the low stability of magnesium porphyrins, chlorins and bacteriochlorins is a well-known fact [8, 45, 46], further reflected by the high cost of these synthetic materials.…”

Section: Resultsmentioning

confidence: 99%

Metallobacteriochlorophylls as potential dual agents for photodynamic therapy and chemotherapy

Rutkowska‐Zbik

Witko

2013

J Mol Model

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A theoretical analysis of bacteriochlorophyll a containing its non-native divalent metal ions: Co, Ni, Cu, Zn, Ru, Rh, Pd, and Pt, has been carried out by means of density functional theory (DFT) calculations. The main stress was put on the derivatives with metals, which already found applications as coordination compounds in anti-tumor therapy (Ru, Pt, Pd, and Rh). The idea was to combine their cytotoxic properties with the known suitability of bacteriochlorophylls macrocycle for photodynamic therapy. The geometries of the studied systems are compared and reveal a number of similarities. The cores of the modified bacteriochlorophylls are flat, and the introduced metal ions lie in plane of the macrocycle, showing its large ability to accommodate metal ions of different sizes. However, four metal–nitrogen bonds, linking the central ions with the macrocycle ligand, are not equivalent. Metals are the strongest attached to nitrogens, which come from the pyrrole, which is fused with isocyclic ring. Based on the known spectroscopic data, the absorption properties of the proposed systems are predicted. Finally, it is found that all studied metal–macrocycle adducts are stable in aqueous media. The only exceptions are Mg-BChla (the finding is reflected by experimental facts) and Zn-BChla. The predicted high stability of Ru-, Rh-, Pt- and Pd-bacteriochlorophylls might turn out beneficial for therapeutic purposes.Electronic supplementary materialThe online version of this article (doi:10.1007/s00894-012-1747-y) contains supplementary material, which is available to authorized users.

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Mechanistic Information on Cu^II Metalation and Transmetalation of Chlorophylls

Cited by 11 publications

References 60 publications

Factors controlling the reactivity of divalent metal ions towards pheophytin a

Factors controlling the reactivity of divalent metal ions towards pheophytin a

Fine tuning of copper(ii)–chlorophyll interactions in organic media. Metalation versus oxidation of the macrocycle

Metallobacteriochlorophylls as potential dual agents for photodynamic therapy and chemotherapy

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Mechanistic Information on CuII Metalation and Transmetalation of Chlorophylls

Cited by 11 publications

References 60 publications

Factors controlling the reactivity of divalent metal ions towards pheophytin a

Factors controlling the reactivity of divalent metal ions towards pheophytin a

Fine tuning of copper(ii)–chlorophyll interactions in organic media. Metalation versus oxidation of the macrocycle

Metallobacteriochlorophylls as potential dual agents for photodynamic therapy and chemotherapy

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Mechanistic Information on Cu^II Metalation and Transmetalation of Chlorophylls