Journal of Porphyrins and Phthalocyanines

The present work demonstrates a simple and elegant strategy by which synthetically simple porphyrins are grafted on solid polymer support to generate porphyrin pairs held together by strong coulombic forces. Metalloporphyrins of tetra(4-pyridyl)porphyrins (MTPyP) were reacted with chloromethylated polystyrene (PS) beads to get covalently bound monocationic porphyrins on the polymer support (PS–MTPyP⁺). These were then converted to their tetracationic species (PS–MTMe₃PyP⁴⁺) by exhaustive quaternisation, using CH₃I. These polymer-grafted cationic porphyrins were made to react with tetraanionic p-sulphonated phenylporphyrins (MTPPS^4-) in aqueous conditions. Analysis showed that the PS–MTMe₃PyP⁴⁺ take up MTPPS^4- in exactly 1:1 stoichiometry to form strongly bound (ionically) porphyrin pairs. A variety of homo- and hetero-porphyrin pairs involving central metal ions like Mn, Co, Cu, Zn and Ag and also free-base porphyrins are generated by this strategy.

The synthesis of compounds containing polyhedral boron cages and porphyrin or phthalocyanine units connected covalently in one molecule is reviewed. The importance of these compounds arises, on the one hand, from the use of polyhedral boron derivatives in neutron capture therapy for cancer; on the other hand, porphyrins and phthalocyanines are known as photosensitizers in photodynamic tumor therapy. Current interest in the binding of polyhedral boron compounds to porphyrins and phthalocyanines is due to the observation that porphyrins and phthalocyanines show improved uptake and good persistence in tissues. Medical applications of compounds containing polyhedral boron cages and porphyrin or phthalocyanine units in one molecule are briefly discussed.

In this work a selection of octasubstituted phthalocyaninato zinc complexes were synthesized and their photochemistry studied. The substituents included cholesterol (3a), estrone (3b), naphthol (3c) and phenoxy groups substituted with CH₃ (3d), C(CH₃)₃ (at two positions, 3e), C(CH₃)₃ (3f), NO₂ (3g), NH₂ (3h), COH (3i), COOH (3j), and H (3k). In general, complexes containing electron-donating groups attached to the phenoxy ring (e.g. 3e and 3f) were found to be photochemically unstable with photobleaching quantum yields of the order of 10^-3. In the presence of electron-withdrawing groups (3g, 3i, and 3j) the photobleaching quantum yields were of the order of 10^-6 to 10^-5. Singlet oxygen quantum yields (Φ_Δ) ranged from 0.01 to 0.73. The lowest Φ_Δ was observed for the highly aggregated complex 3c. All the complexes showed aggregation at high concentrations. Electrochemical reduction using a thin-layer spectroelectrochemistry cell showed that the complexes become more monomeric following reduction.

Exhaustive electro-oxidation of ZnOEP in the presence of pyridine and Et₄NPF₆ affords in high yield the new tetracationic porphyrin in which the four meso protons of ZnOEP are replaced by four pyridinium groups linked via their nitrogens: [Zn-5,10,15,20-tetrakis(N-pyridiniumyl)-2,3,7,8,12,13,17,18-octaethylporphyrin]⁴⁺, 1. The compound has been characterized by elemental analysis, ¹H NMR, and crystallography. The latter confirms the preparative electrosynthetic methodology and molecular structure of 1, and shows the porphyrin skeleton to adopt a severely nonplanar saddle conformation which minimizes steric crowding between the 12 peripheral substituents. As a consequence of the nonplanarity (and the high charge) of the complex, 1 exhibits significant red-shifts of the visible and Soret bands as well as a considerable broadening and loss of intensity of the latter. 1 first undergoes four one-electron reduction steps at the four pyridinium sites before the normal one-electron reduction of the porphyrin π-system.

Cytotoxicity induced by photodynamic therapy (PDT) is connected with the phenomena of photo-oxidation. Generation of singlet oxygen and free radicals (superoxide or hydroxide) is accepted as a mechanism for the photo-oxidation action of PDT. Very little is however known about the validity of metabolitic and biochemical events observed in cell culture systems to in vivo tumor shrinkage following PDT. In the present work using the well-studied tetrabenzamido-substituted zinc (II)-naphthalocyanine (ZnNc) including towards pigmented melanoma, we accessed its efficacy for apoptotic processes during PDT of Lewis lung carcinoma (LLC) in mice in dependence on light intensity. Early photodynamic therapy responses were examined at 1, 3, 6, 10 and 24 h after coherent 774 nm illumination of the tumors applied 24 h after intraperitoneal (i.p.) injection of dipalmitoylphosphatidylcholine (DPPC)-liposome-incorporated 0.5 mg kg^-1 b.w. ZnNc. Fluence rates of 260, 380 and 500 mW cm^-2 at a fluence of 360 J cm^-2 were used. Macroscopic observations showed that tumor reduction (and its eventual elimination) depends on optimal conditions for the occurring of photochemical reaction during PDT. At the same time, electron microscopy (EM) assays demonstrated strongly expressed dependence of apoptotic processes on the applied light intensities. Features of apoptotic processes were most clearly expressed at the highest used fluence rate.

The preparation of a new zinc(II) metalloporphyrin, substituted with four alkylated carbazole moieties, by reaction of pyrrole and 3-formyl-9-hexylcarbazole is reported. The substitution pattern negatively shifts the redox potentials of the macrocycle and leads to a material that emits green light at 615 nm when photo-excited at 554 nm.

We report a fast, simple, safe, and effective procedure for the synthesis of several soluble metal tetrakis(tert-butyl)phthalocyaninates, M(TBPc) (M = Zn, Mg, Co, Cu) and M(TBPc)₂ (M = Tb, La), from the respective metal-free phthalocyanine by microwave irradiation. Metal chlorides and acetates are used as metal sources.