Biomimetical catalytic activity of iron(III) porphyrins encapsulated in the zeolite X

The approach adopted for the obtention of zeolite-encapsulated FeP led to clean syntheses of biomimetical catalyst. The catalysts were obtained through the zeolite synthesis method, where NaX zeolite was synthesised around one of the cationic FePs: iron(III) 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (FeP1) or iron(III) 5-mono(2,6-dichloro-phenyl)10,15,20-tris(4-N-methylpyridyl)porphyrin (FeP2). The syntheses yielded pure FeP1NaX and FeP2NaX catalysts without any by-products blocking the zeolite nanopores. FeP1NaX and FeP2NaX efficiently catalysed the epoxidation of (Z)-cyclooctene by iodosylbenzene (PhIO) in DCE, giving rise to cis-epoxycyclooctane yields of 85% and 95%, respectively. Hydroxylation of adamantane shows a preferable alkane oxidation at the tertiary C---H bond, indicating a hydrogen abstraction through the Fe^IV(O)P^·+species in the initial step. The total adamantanol yields were 52% and 45% for FeP1NaX and FeP2NaX, respectively. Concerning selectivity, FeP1NaX and FeP2NaX gave an 1-adamantanol (Ad-1-ol)/2-adamantanol (Ad-2-ol) ratio of 20:1 and 11:1, respectively (after statistical correction). Therefore, these results indicate a free radical activation of the C---H bonds of adamantane as expected for P-450 models. In the cyclohexane oxidation catalysed by FeP1NaX in DCE, a cyclohexanol (C₆-ol) yield of 50% and an alcohol/ketone ratio of 10 was obtained. The hydroxylation occurs according to the so-called oxygen rebound mechanism, as expected for a P-450 model system. FeP2NaX is less selective (C₆-ol yield=25% and alcohol/ketone=1.2). One possible explanation is that a Russell-type mechanism involving O₂ imprisoned within the zeolite cages may be operating parallelly, generating both C₆-ol and cyclohexanone.     

Study of the Suppression of Porphyrin Emission upon Addition of Rare Earth Ions

A topic of constant investigation in recent decades has been the study of electron and/or energy transfer reactions in supramolecular systems. The energy transfer between donor-acceptor depends on the influence of the substituent in the intersystem crossing. The competition between the radiative and non-radiative processes also depends on other factors such as temperature, solvent and energy gap. In this work, we have studied the suppression of the emission of monocarboxyphenyl porphyrins after addition of rare earth ions (RE(III)). The porphyrin emission decreases with the addition of RE(III), no matter which ion is present. When Eu(III) was used, the emission of this ion was not observed either. This suppression happens due to the effect of the heavy atom and not due to the energy transfer through electronic levels between the porphyrin and the RE(III). After the addition of RE(III), the lifetime for MCTPPH₂ started to decay biexponentially, indicating the formation of a new species (MCTPPH₂-RE(III)) of a shorter lifetime. The presence of NO₂ groups in the ortho mesoaryl positions of MCTNPPH₂ and the presence of Zn(II) in Zn(MCTPP) decreased both the porphyrin lifetime and emission due to an increase in the spin-orbit coupling.     

Synthesis of new amphiphilic chlorin derivatives from protoporphyrin-IX dimethyl ester

A simple synthesis of new amphiphilic chlorin derivatives from protoporphyrin-IX dimethyl ester is reported. The preparation of such compounds is based in a straightforward methodology, which involves the Diels-Alder reaction of protoporphyrin-IX dimethyl ester with maleic anhydride followed by addition of nucleophilic species to the initially formed cycloadducts, a transformation, which is highly regioselective. Preliminary photophysical studies with the new compounds show that they meet adequate features for PDT applications.     

Hexagonal mesoporous silica modified with copper phthalocyanine as a photocatalyst for pesticide 2,4-dichlorophenoxiacetic acid degradation

A new mesoporous catalyst was prepared by the reaction between 3-aminopropyltrimethoxisylane and Cu(II)-hexadecafluorophthalocyanine, followed by co-condensation of tetraethylorthosilicate around a micelle formed by n-dodecylamine. The surfactant was removed from the pores by continuous extraction with ethanol, giving the Si-CuF16Pc catalyst. This catalyst was characterized by SEM, FTIR, TGA, 29Si NMR, N2 adsorption and X-ray diffraction. SEM images confirmed that the catalyst material is formed by nanoaggregates with a diameter of 100 nm. N2 adsorption isotherms showed that Si-CuF16Pc has a surface area of approximately 200 m2 g(-1) and a porous diameter of 7.7 nm, characterizing the mesoporosity of this product. This novel material shows an excellent photocatalytic activity, degrading almost 90% of 2,4-dichlorophenoxyacetic acid (2,4-D) up to 30 min, while only approximately 40% of photodegradation was obtained in its absence.     

Chlorin photosensitizers sterically designed to prevent self-aggregation

The synthesis and photophysical evaluation of new chlorin derivatives are described. The Diels-Alder reaction between protoporphyrin IX dimethyl ester and substituted maleimides furnishes endo-adducts that completely prevent the self-aggregation of the chlorins. Fluorescence, resonant light scattering (RLS) and (1)H NMR experiments, as well as X-ray crystallographic have demonstrated that the configurational arrangement of the synthesized chlorins prevent π-stacking interactions between macrocycles, thus indicating that it is a nonaggregating photosensitizer with high singlet oxygen (Φ(Δ)) and fluorescence (Φ(f)) quantum yields. Our results show that this type of synthetic strategy may provide the lead to a new generation of PDT photosensitizers.     

The use of electrospray ionization tandem mass spectrometry on the structural characterization of novel asymmetric metallo-organic supermolecules,based on pentafluorophenylporphyrins and ruthenium complexes

The novel asymmetric metallo-organic triads cis- and trans-[B(4-py)BPFPH₂{Ru₃O(Ac)₆(py)₂}{Ru(bpy)₂Cl}](PF₆)₂ (5a,b) for which cis- and trans-B(4-py)BPFPH₂ = 5,10-bis(pentafluorophenyl)-15,20-bis(4-pyridyl)porphyrin and 5,15-bis(pentafluorophenyl)-10,20-bis(4-pyridyl)porphyrin, respectively; Ac = acetate; py = pyridine and bpy = 2,2′-bipyridine, as well as their corresponding monosubstituted dyads cis- and trans-[B(4-py)BPFPH₂{Ru₃O(Ac)₆(py)₂}]PF₆ (4a,b) have been structurally characterized via electrospray ionization mass spectrometry (ESI-MS and ESI-MS/MS). The ESI-MS of dyads 4a,b display two characteristic Ru-multicomponent clusters of isotopologue ions corresponding to singly charged ions 4a,b⁺ of m/z 1629 and doubly charged ions [4a,b+H]²⁺ of m/z 815 and the triads 5a,b are detected by ESI-MS as the intact doubly charged cluster of isotopologue ions of m/z 1039 [5a,b]²⁺. The ESI-MS/MS of 4a,b⁺, [4a,b+H]²⁺ and [5a,b]²⁺ reveal characteristic dissociation pathways, which confirm the structural assignments providing additional information on the intrinsic binding strengths of the gaseous ions. Although the gas-phase behavior of each pair of isomers was rather similar, the less symmetric dyads 4a,b are distinguished via the ¹H NMR spectral profile of the pyrrolic signals. Exploratory photophysical assays have shown that both modifying motifs alter the porphyrinic core emission profile, opening the possibility to use these asymmetric systems as photophysical devices.     

Characterization of cationic glycoporphyrins by electrospray tandem mass spectrometry

Novel cationic porphyrin derivatives having a galactose or a bis(isopropylidene)galactose unit linked directly to a pyridine or to an aminophenyl group were characterized by electrospray tandem mass spectrometry (ESI-MS/MS). The electrospray mass spectra (ESI-MS) show the M(+) ions, since these porphyrins are already monocharged in solution. The fragmentation of these ions under ESI-MS/MS conditions was studied and it was found that elimination of the sugar residue as a radical (-163 or -243 Da) is a common fragmentation pathway. Loss of the sugar unit as a neutral fragment (-162 or -242 Da) and cross-ring fragmentations typical of glyco-derivatives are also observed for the pyridinium glycoporphyrins, but they are absent in the case of ammonium glycoporphyrins. The cationic beta-pyridiniumvinyl porphyrins show an atypical fragmentation due to the cleavage of the C(5)-C(6) bond of the sugar unit. Overall, the different patterns of fragmentation observed in the ESI-MS/MS spectra of the sugar pyridinium porphyrins and of the sugar ammonium phenyl porphyrins can give important information about the type of spacer between the porphyrin and the sugar unit.     

Characterization and catalytic activity of iron(III) mono(4-N-methyl pyridyl)-tris(halophenyl) porphyrins in homogeneous and heterogeneous systems

The synthesis, characterization and catalytic activity of the cationic iron porphyrins Fe[M(4-N-MePy)TDCPP]Cl₂ and Fe[M(4-N-MePy)TFPP]Cl₂ in the epoxidation of (Z)-cyclooctene by PhIO in homogeneous solution and supported on silica gel (SG), imidazole propyl gel (IPG) or SG modified with 2-(4-sulfonatophenyl)ethyl groups (SiSO₃) have been accomplished. When supported on IPG, both cationic FeP bind to the support via Fe–imidazole coordination. Fe[M(4-N-MePy)TDCPP]IPG contains a mixture of low-spin bis-coordinated Fe^IIIP and high-spin mono-coordinated Fe^IIIP species, whereas Fe[M(4-N-MePy)TFPP]IPG only contains high-spin mono-coordinated Fe^IIIP. These FePIPG catalysts also contain Fe^IIP species, whose presence was confirmed by EPR spectroscopy using NO as a paramagnetic probe. Both cationic FePs coordinate to SG through Fe–O ligation and they are present as high-spin Fe^IIIP species. The cationic FePs supported on SiSO₃⁻ are also high-spin Fe^IIIP species and they bind to the support via electrostatic interaction between the 4-N-methylpyridyl groups and the SO₃⁻ groups present on the matrix. In homogeneous solution, both Fe[M(4-N-MePy)TDCPP]Cl₂ and Fe[M(4-N-MePy)TFPP]Cl₂ have similar catalytic activity to Fe(TDCPP)Cl and Fe(TFPP)Cl, leading to cis-epoxycyclooctane yields of 92%. When supported on inorganic matrices, both FePs lead to epoxide yields comparable to their homogeneous analogues and their anchoring enables catalyst recovery and re-use. Recycling of Fe[M(4-N-MePy)TDCPP]SiSO₃⁻ shows that this FeP maintains its activity in a second reaction.     

Mechanism and efficiency of cell death of type II photosensitizers: effect of zinc chelation

A series of meso-substituted tetra-cationic porphyrins, which have methyl and octyl substituents, was studied in order to understand the effect of zinc chelation and photosensitizer subcellular localization in the mechanism of cell death. Zinc chelation does not change the photophysical properties of the photosensitizers (all molecules studied are type II photosensitizers) but affects considerably the interaction of the porphyrins with membranes, reducing mitochondrial accumulation. The total amount of intracellular reactive species induced by treating cells with photosensitizer and light is similar for zinc-chelated and free-base porphyrins that have the same alkyl substituent. Zinc-chelated porphyrins, which are poorly accumulated in mitochondria, show higher efficiency of cell death with features of apoptosis (higher MTT response compared with trypan blue staining, specific acridine orange/ethidium bromide staining, loss of mitochondrial transmembrane potential, stronger cytochrome c release and larger sub-G1 cell population), whereas nonchelated porphyrins, which are considerably more concentrated in mitochondria, triggered mainly necrotic cell death. We hypothesized that zinc-chelation protects the photoinduced properties of the porphyrins in the mitochondrial environment.     

[1,2,3,4-Tetrakis(α/β-d-galactopyranos-6-yl)phthalocyaninato]zinc(II): a water-soluble phthalocyanine

A novel water-soluble asymmetrical sugar-phthalocyanine was prepared via a statistical cross-condensation of tetrakis(1,2:3,4-di-O-isopropylidene-α-d-galactopyranos-6-yl)phthalonitrile with phthalonitrile. The new compound, with amphiphilic character, can be useful as a selective photosensitizer in photodynamic therapy, as well as for constructing phthalocyanine-based supramolecular systems.