Journal of Porphyrins and Phthalocyanines

The binding and acid-base equilibria of the two novel mesoporphyrin derivatives, PB07 and PB109 (quino[4,4a,5,6-efg]- annulated 7-demethyl-8-deethylmesoporphyrin and 2'-cyano-8'-formyl-N'-methyl-1',1a',5a',6'-tetrahydroacrido [4,5,5a,6-bcd]- annulated 2,3-dihydromesoporphyrin, resp.), which are promising agents for photodynamic therapy (PDT), were studied in aqueous solutions of different surfactants (Triton X-100 (TX-100), dodecyl maltoside (DDM), cetyltrimethylammonium bromide (CTAB), lithium dodecyl sulfate (LDS)) and phosphatidyl choline (PC) liposomes. In all cases, the porphyrins are solubilized at neutral/alkaline pH in monomeric form and remain micelle/liposome-bound independently of their ionization state. The dissociation constants of the solubilized porphyrins are found to be influenced by the charge of the surface groups of the carrier. The protonation of pyrrole/quinoline nitrogens of the studied porphyrins is facilitated in the following order: LDS ≫TX-100 (DDM, PC liposomes) > CTAB. The dissociation constants of PB07 carboxylic groups are similar in neutral/cationic micellar and liposome solutions and are significantly decreased for LDS-bound pigment. The results provide necessary information for the optimization of delivery systems for PB07 and PB109 when applied as sensitizers in PDT.

Different meso-functionalized porphyrins were conveniently synthesized by direct reactions of meso-porphyrincatechols with 2-phenyl-1,3-indandione and 2-mercaptobenzothiazole as nucleophiles in relatively high yields via practical and efficient electrooxidation in aqueous solution, using cyclic voltammetry and controlled-potential coulometry. The results indicate that O-benzoquinone generated by electrochemically driven oxidation of the meso-porphyrincatechols is scavenged by nucleophiles to give related products via an EEEECCCC electrochemical pathway. Spectroscopic and molecular modeling studies show that there is no indication of atropoisomers in our isolated products.

Efficient selective oxidation of ketones to lactones by molecular oxygen with benzaldehyde as an oxygen acceptor, in the presence of metalloporphyrins, has been reported. Iron(III) meso-tetraphenylporphyrin chloride (Fe(TPP)Cl) showed excellent activity and selectivity for oxidation of cyclohexanones under mild conditions. Moreover, different factors influencing ketones oxidation, e.g. catalyst, solvent, temperature and additive, have been investigated. The turnover number (TON) of the Fe(TPP)Cl catalyst could reach up to 71000 in a large scale oxidation of cyclohexanone. A plausible mechanism of ketone oxidation by molecular oxygen in the presence of metalloporphyrins and benzaldehyde was proposed.

The interactions of two amphiphilic porphyrins with anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in aqueous solutions were studied by UV-vis absorption spectroscopy, fluorescence spectroscopy, resonance light scattering technique, fluorescence anisotropy and surface tension measurements. The two porphyrins, meso-tetra(4-hydroxyphenyl)porphyrin (THPP) and meso-tetra(3,5-dibromo-4-hydroxylphenyl)porphyrin (T(DBHP)P), exist as irregular aggregates in aqueous solutions with a broad and low absorption peak near the maximum of monomer peak. The interaction of THPP with AOT leads to the formation of a fluorescent aggregate of porphyrin which was assigned as J-type aggregate according to exciton theory. A long red-shifted Soret band together with a new strong Q-band, a broad emission peak and a sharply peaked resonance light scattering signal are observed for this J-aggregate. The formation of J-aggregate is independent of the initial THPP concentration and can be influenced greatly by ionic strength. The aggregation kinetics has been investigated by UV-vis absorption spectroscopy and fluorescence anisotropy. Conversion of the porphyrin monomers to J-aggregate is observed. The addition of THPP increases the surface tension of solution and changes the critical micelle concentration of AOT. J-aggregate was not observed for T(DBHP)P in AOT solutions which only shows solubilization. The mechanism of aggregation was discussed.

We synthesized an uncharged water-soluble porphyrin, meso-tetrakis-(3,4,5-tri-{2-[2-(2-methoxy-ethoxy)-ethoxy]-ethoxy}-phenyl)-porphyrin, to solubilize single-walled carbon nanotubes (SWNTs) in aqueous solutions through supramolecular interactions. The porphyrin-SWNTs composites in aqueous solution are stable for several weeks. The porphyrin-SWNTs composites in aqueous solution have been characterized by UV-vis absorption and fluorescence spectroscopy and with atomic force microscope (AFM). The fluorescence emitted from the porphyrin ring in the aqueous solution of the porphyrin-SWNTs composite is highly quenched, evidently implying the presence of strong electronic interactions between the SWNTs and the porphyrin molecules in aqueous solution. The AFM investigation furthermore supports that the porphyrin molecules are complexed on the SWNTs side wall through π-π interaction.

Magnesium porphyrazinates substituted with eight (p-tolyl) and (o-tolyl) units on the peripheral positions have been synthesized for the first time by cyclotetramerization of 1,2-bis(p-tolyl)maleonitrile and 1,2-bis(o-tolyl)maleonitrile in the presence of magnesium butanolate. Their demetalation by the treatment with trifluoroacetic acid resulted in partially oxidized products, namely, octakis(p-tolyl)-2-seco-porphyrazine-2,3-dione and octakis(o-tolyl)-2-seco-porphyrazine-2,3-dione. Further reactions of these products with copper(II) acetate, zinc(II) acetate and cobalt(II) acetate have led to the metallo derivatives, [octakis(p-tolyl)-2-seco-2,3-dioxoporphyrazinato]M(II) and [octakis(o-tolyl)-2-seco-2,3-dioxoporphyrazinato]M(II) (M = Cu, Zn, Co). These novel compounds have been characterized by elemental analysis, together with FT-IR, ¹H NMR, UV-vis and mass spectral data.

Novel 2,3,9,10,16,17,23,24-octaamino substituted Ni(II) phthalocyanine (2) was synthesized from tosylamido (tosyl: toluene-p-sulphonyl) derivative by the cleavage of tosyl groups in the presence of 90% sulfuric acid. Octa-hexanoylamido Ni(II) phthalocyanine (3a) and octa-lauroylamido Ni(II) phthalocyanine (3b) were obtained by reacting of octa-amino Ni(II) phthalocyanine (2) with hexanoyl chloride and lauroyl chloride, respectively. The new compounds have been characterized by elemental analysis, FT-IR, NMR and UV-vis spectroscopy and mass spectrometry. The aggregation behaviors of new compounds were investigated by UV-vis spectroscopy.

A series of N-substituted porphyrins were synthesized either by direct alkylation of the symmetrical porphyrins or from the unsymmetrical porphyrins obtained via MacDonald's procedure using the appropriate N-substituted dipyrromethanes. Depending upon the nature of the peripheral substitutions in the porphyrin system, the nickel(II)-promoted rearrangement of these compounds gave either meso-substituted or unsubstituted Ni(II) porphyrins or chlorins. The chlorins and meso-substituted porphyrins were formed via the intramolecular migration of the N-substituent to carbon. This approach provides easy access for the synthesis of chlorins and the meso-substituted porphyrins, which are otherwise difficult to synthesize.

HemAT is a signal transducer protein responsible for aerotaxis control of some bacteria and archaea, which contains a heme-containing globin domain as the sensor of its physiological effector, O₂. The interaction between the heme-bound ligand and the surrounding amino acid residue(s) plays a crucial role for selective sensing of O₂ and signal transduction by HemAT. In this work, we have elucidated by resonance Raman spectroscopy how O₂ and CO interact with HemAT-Hs and HemAT-Rr, HemAT from Halobacterium salinarum and Rhodospirillum rubrum, respectively. HemAT-Hs and HemAT-Rr showed three conformers in the O₂-bound form, as is the case of HemAT-Bs, HemAT from Bacillus subtilis. Though the hydrogen bonding patterns observed in the three conformers were the same for HemAT-Bs, HemAT-Hs, and HemAT-Rr, the involved residues for the hydrogen bonding interaction were different from one another.