Journal of Porphyrins and Phthalocyanines

This short review highlights the author’s group research on modified vitamin B${}_{12}$ derivatives with a peptide backbone as (1) inhibitors of B${}_{12}$-dependent enzymes and as (2) models of cofactor B${}_{12}$-protein complexes.

The synthesis and optical, electrochemical, and magnetic properties of nickel(II) complexes of 5,10,20-triaryl-5,15-diazaporphyrin (TriADAP) are reported. Metal-templated cyclization of unsymmetrically substituted nickel(II)–bis(1-amino-9-chloro-5-mesityldipyrrin; mesityl = 2,4,6-trimethylphenyl) complexes afforded the corresponding TriADAPs or 5-aryl-15-benzyl-10,20-dimesityl-5,15-diazaporphyrin, depending on the combination of base and solvent. The latter macrocycle was converted to TriADAP by deprotection of the $N$-benzyl group through Pd/C-promoted hydrogenation. TriADAPs were isolated in both 18$\pi$ (cation) and 19$\pi$ (neutral) forms. The interconversion between these two oxidation states resulted in a distinct change in the optical properties of the DAP $\pi$-system. NMR spectroscopy of the 18$\pi$ TriADAP cations showed that they had aromatic character, whereas EPR spectroscopy of the 19$\pi$ TriADAP showed a highly delocalized electron spin of the $\pi$-radical. The para substituents of the $N$-aryl groups of TriADAPs had a small but distinct impact on their HOMO and LUMO energies. The change in the net charge of one electron was directly reflected in the redox properties of the DAP ring; TriADAP was more easily reduced and less easily oxidized than DAP. The difference in the net charge was also reflected by the shielding of the pyrrolic $\beta$-protons observed in the ${}^{\mathrm{\text{1}}}$H NMR spectra. The present results confirm that TriADAP is a highly promising framework for constructing a new class of azaporphyrin-based materials with 18$\pi$–19$\pi$ redox-switchable optical and magnetic properties.

In line with current efforts to direct PDT photosensitizers to specific organelles such as mitochondria, a triphenylphosphonium-tetrasubstituted Zn phthalocyanine was designed, taking into account synthetic constraints. Triphenylphosphonium moieties were successfully introduced on alkyl bromide substituents on a pre-formed phthalocyanine. Photophysical and photochemical measurements showed that the photoproperties of the Zn phthalocyanine core were not affected by the triphenylphosphonium groups. Biological investigations demonstrated the dark innocuousness of the phthalocyanine up to 1 $\mu$M, a concentration that exhibited a powerful phototoxicity. Cell death was confirmed to be photodynamically induced thanks to reactive oxygen species detection experiments. Nonetheless, the triphenylphosphonium moieties did not promote the accumulation of the phthalocyanine in mitochondria as significantly as expected.

We describe the oxidative ring opening of octaethyl-2-oxochlorin using two different oxidation methods, both providing a mixture of all possible regioisomeric products (8-$\alpha$ through 8-$\delta )$. While isomers 8-$\alpha$, 8-$\gamma$, and 8-$\delta$ formed in isolable yields and relative ratios that varied with the oxidation method used, isomer 8-$\beta$ was invariably formed in trace amounts only. The three major products were spectroscopically characterized (IR, MS, 1D- and 2D NMR spectroscopy) and their configurations were deduced by NMR spectroscopy. The spectroscopic findings correlated well with the single crystal X-ray structure of the novel cleavage product 8-$\alpha$ and the known compound of 8-$\gamma$. The work broadens the number of octaethylporphyrin-derived biliverdin derivatives available and presents a methodology of controlling the biliverdin backbone configuration by introduction of a $\beta$-ketone functionality into select positions.

A series of zinc porphyrins, namely ZnPa and ZnPb, which exist predominantly as aggregates, are utilized in a top-down preparation of individualized and stabilized single wall carbon nanotubes (SWCNTs). Sizable interactions in the ground state of the corresponding SWCNT/ZnPa and SWCNT/ZnPb electron donor–acceptor systems lead to charge transfer in the excited state. The product includes the simultaneous reduction of the electron-accepting SWCNTs and the oxidation of the electron-donating ZnPa and ZnPb.

Porphyrinoids are ideal compounds to be incorporated into DNA due to their peculiar spectroscopic characteristics, fascinating photochemistry and synthetic versatility. The ability to act as photosensitizers in the presence of oxygen promoted interest of the scientific community to study the non-covalent binding of porphyrins with DNA in order to use them in photodynamic therapy. Thus, the understanding of the mechanisms involved in the binding of porphyrins with DNA can help to find a porphyrin with specific base degradation activity. In this work we characterized the binding modes of spermine derivative porphyrin with three different polynucleotides: ct-DNA, poly(dG-dC)${}_{\mathrm{\text{2}}}$ in both B- and Z-conformation using several spectroscopic techniques (UV-vis, Electronic Circular Dichroism and Resonance Light Scattering).

The molecular structures of three porphyrinate derivatives have been determined by X-ray studies. Two derivatives, [Fe(TTP)(1-MeIm)${}_{\mathrm{\text{2}}}$] · 2C${}_{\mathrm{\text{7}}}$H${}_{\mathrm{\text{8}}}$ and [Fe(T-$p$-OCH${}_{\mathrm{\text{3}}}$PP)(BzHIm)${}_{\mathrm{\text{2}}}$] are iron(II) derivatives, whereas the third, [Fe(TMP)(BzHIm)${}_{\mathrm{\text{2}}}$]ClO${}_{\mathrm{\text{4}}}$ · 2CHCl${}_{\mathrm{\text{3}}}$, is an iron(III) species. The structure determinations provide evidence of the importance of steric effects, either from the axial ligand or the porphyrin ligand, in defining the overall stereochemistry.

X-ray structures of gold corroles, which are still rather uncommon, afford significant insights into intermolecular interactions involving Au(III), a subject that has been much less studied than aurophilic and metallophilic interactions involving Au(I). The X-ray structure of gold $\beta$-octabromo-meso-tris(para-pentafluorosulfanylphenyl)corrole, reported herein, has revealed two Au···Br interactions (∼4.2 Å) per Au atom. We suggest that analogous but somewhat stronger Au···Br interactions are a key factor underlying the remarkable insolubility of gold octabromocorrole derivatives.

Pd(II)-catalyzed C–H phosphonation with diethyl phosphite in the meso positions of mesityl-substituted porphyrins taken either as free base or Ni(II) and Zn(II) complexes has been investigated and the reaction conditions have been optimized. Ni(II) porphyrinates have been found to be advantageous over free porphyrins and their Zn(II) complexes. The possibility of diphosphonation was shown using 5,15-dimesityl porphyrin.

Phthalocyanines (Pcs) have been known for excellent electron transfer properties owing to their extended $\pi$-conjugated structures. In addition, functionalized iron oxide nanoparticles (Fe${}_{\mathrm{\text{3}}}$O${}_{\mathrm{\text{4}}}$ NPs) have attracted considerable interest owing to their unique spectral and electronic properties. Hence, it can be reasonably expected that Fe${}_{\mathrm{\text{3}}}$O${}_{\mathrm{\text{4}}}$ NPs decorated with Pc molecules could provide a useful electrocatalytic system. Herein, we present the preparation and electrochemical properties of cobalt-phthalocyanine (CoPc)-decorated Fe${}_{\mathrm{\text{3}}}$O${}_{\mathrm{\text{4}}}$ NPs (CoPc@Fe${}_{\mathrm{\text{3}}}$O${}_{\mathrm{\text{4}}})$. The Fe${}_{\mathrm{\text{3}}}$O${}_{\mathrm{\text{4}}}$ NPs were first coated with a silica layer to produce SiO${}_{\mathrm{\text{2}}}$@Fe${}_{\mathrm{\text{3}}}$O${}_{\mathrm{\text{4}}}$. Subsequently, CoPc with a siloxane end group (CoPc-TEOS) was anchored to the outer surface of the SiO${}_{\mathrm{\text{2}}}$@Fe${}_{\mathrm{\text{3}}}$O${}_{\mathrm{\text{4}}}$. The CoPc@Fe${}_{\mathrm{\text{3}}}$O${}_{\mathrm{\text{4}}}$ thus prepared was fully analyzed using various characterization methods. Distinctive electrochemical responses of CoPc and CoPc@Fe${}_{\mathrm{\text{3}}}$O${}_{\mathrm{\text{4}}}$ in the presence of picric acid were observed, demonstrating the potential application of the current approach to electrochemical catalysis.