Journal of Porphyrins and Phthalocyanines

Cavitands and porphyrinoids are two major groups of molecules. If cyclodextrins are maybe the most famous type of cavitands, the properties of resorcinarenes are now well known and rise rapidly increasing attention. This mini-review aims at detailing all the combinations of resorcinarenes with porphyrinoids reported so far, evidencing the bright future of such combos. In addition, two newly synthesized porphyrins-resorcinarene hybrids are reported.

The $N$-methylated 25-oxasmaragdyrins were synthesized by reacting 25-oxasmaragdyrins with CH₃I in presence of KOH in THF at reflux temperature. Although the reactions were carried out in presence of excess CH₃I, we obtained only dimethyl-25-oxasma ragdyrins, where $N$-methylations occurred at 24 and 26 “N”s of pyrrole rings of tripyrrane moiety of smaragdyrin core as confirmed by X-ray crystallography. The $N$-methylated-25-oxasmaragdyrins were characterized in detail by 1D and 2D NMR spectroscopy, absorption, fluorescence and electrochemical techniques. The effect of distortion induced by methylation, clearly reflected in structural and electronic properties of the macrocycle. All the pyrrole and furan protons experienced upfield shifts in the ¹H NMR and maximum upfield shifts were noted for the $N$-methylated pyrrole ring protons. The absorption spectra showed broad Soret band and four ill-defined Q-bands with significant reduction in extinction coefficients. The $N$-methylated 25-oxasmaragdyrins were comparatively less fluorescent. The redox studies indicated that they are difficult to oxidize and easier to reduce.

Using the sterically hindered base, 1,8-diazabicyclo[5.4.0]undec-7-ene, for enolization and tert-butyldimethylsilyl-trifluoromethanesulfonate for silylation, chlorophyll (Chl) $a$ produced after 15 min at 0 $°$C in deaerated pyridine solution under argon, after work-up and chromatographic purification on a sucrose column, tert-butyldimethylsilyl-enol ether of Chl $a$ in a yield of 77%. The 13¹-deoxo-13¹,13²-didehydro-chlorophyll $a$, was obtained in a yield of 23% through a reaction sequence, where Chl $a$ was first reduced with sodium borohydride to 13${}^1(R,S)$-hydroxy-Chl $a$, which via demetalation yielded 13${}^1(R,S)$-hydroxypheophytin $a$. In the presence of the sterically hindered base, 1,8-bis(dimethylamino)naphthalene, trifluoroacetylimidazole dehydrated 13${}^1(R,S)$-hydroxypheophytin $a$ to 13¹-deoxo-13¹,13²-didehydro-pheophytin $a$, which after metalation yielded 13¹-deoxo-13¹,13²-didehydro-Chl $a$. Using 1,8-bis(dimethylamino)naphthalene and trifluoroacetylimidazole, the straight conversion of 13${}^1(R,S)$-hydroxy-Chl $a$ to 13¹-deoxo-13¹,13²-didehydro-Chl $a$ was found unsuccessful. The major products were characterized by electronic absorption spectra (UV-vis) and practically completely assigned ¹H and ${}^{13}$C NMR spectra. Some intermediates of the syntheses were also characterized by ESI-TOF mass spectra. Compared with Chl $a$, the macrocyclic ring-current in the synthesized Chl $a$ enol derivatives was found weakened by the expansion of the $\pi$-system to include the isocyclic ring E. Nevertheless, these enol derivatives were still considered to be diamagnetic and aromatic. The possibility of the functional role of the enol derivatives of chlorophyll in photosynthesis is discussed.

Amino group modified phthalocyanines (Pcs) and their derivatives have attracted great attention in the field of photodynamic therapy (PDT) because of their satisfied anticancer activity. The existence of N atoms in these Pcs is very important because they not only provide water solubility of Pcs, but also greatly affect their PDT activity. To clear the influence of N atoms number on PDT activity of amino group modified Pcs and their derivatives, in this manuscript, two series of amine modified Pcs with different N atom number and their water soluble derivatives, hydrochloride and quaternizing derivatives were synthesized. Their photochemical and photobiology properties were studied and compared. The results indicated that with increasing the number on N atom, the reactive oxygen species (ROSs) generation ability, cancer cell uptaken ability and photoinduced anticancer activity were all increased in these ZnPcs.

The investigation of electrochemical properties of active layers containing 5,15-bis(pyrid-3-yl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphine, [5,15-bis(pyrid-3-yl)-3,7,13,17-tetramethyl-2,8,12, 18-tetraethylporphinato]cobalt(II), bispyridine[5,15-bis(pyrid-3-yl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphinato]cobalt(III), [5,15-bis(pyrid-4-yl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphinato]cobalt(II) and bispyridine[5,15-bis(pyrid-4-yl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphinato]cobalt(III) in 0.1 M KOH aqueous solution has been carried out by cyclic voltammetry. The potential ranges of redox processes related to the transformation of the porphyrin macrocycle, pyridyl substituents and central metal have been established. The electrochemical parameters of oxygen electroreduction reaction (the half-wave potential — E${}_{1/2}$(O${}_2$), the maximum potential — E${}_p$(O${}_2$), the current density — j, the activation energy — E_act) have been determined. It was shown that all porphyrins exhibit the catalytic activity. The electroreduction process of oxygen on electrode with the porphyrin-ligand occurs via 2-electron mechanism to give hydrogen peroxide ion HO₂^-, and on ones with the cobalt porphyrins — via parallel-sequential pathway including 2-electron and 4-electron processes to give HO₂^-, OH^-. The presence of pyridine axial ligands in Co-complexes leads to a significant increase of the electrocatalytic activity in molecular oxygen reduction reaction.

The first oxidative cleavage of DNA by manganese $N$-confused porphyrin [chloro(2-aza-2-methyl-5,10,15,20-tetrakis($p$-chlorophenyl)-21-carbaporphyrin)manganese(III), 1] using H₂O₂ as oxidant agent and its magnetic, calf thymus DNA(ct-DNA)- and human serum albumin (HSA) binding properties were investigated. The magnitude of the axial (D) zero-field splitting for the mononuclear Mn(III) center in 1 was determined to be approximately 2.71 cm${}^{-1}$ by paramagnetic susceptibility measurements. The DNA- and HSA binding experimental results showed that 1 bound to ct-DNA via an outside groove binding mode and the hydrophobic cavity located in subdomain IIA of HSA with the binding constant of 4.144 × 10⁵ M${}^{-1}$ and $\sim$ 10⁶ M${}^{-1}$, respectively. Thermodynamic parameters revealed that both DNA- and HSA binding were spontaneous process. The main driven forces were the hydrogen bond and van der Waals for the former, but hydrophobic interaction for the latter, which were further confirmed by molecular docking modeling. Manganese $N$-confused porphyrin 1 could cleave the supercoiled plasmid DNA efficiently in the presence of hydrogen peroxide. Hydroxyl radical (${}^{•}$OH) was found the active species for oxidative damage of DNA.

The interaction of (chloro)-$\mu$-nitrido-bis[(tetra-tert-butyl-phthalocyaninato)iron(IV)] Cl(FePc)₂N with organic $N$-bases L as electron–donors (L $=$ diethylamine, imidazole, 1-methylimidazole, 2-methylimidazole) with the formation of one-electron reduced species (L)PcFe${}^{\text{III}}$–N$=$Fe${}^{\text{IV}}$Pc(L) was investigated in benzene at 298 K by UV-visible spectroscopy. The reaction was established to be stepwise process including fast reversible axial binding of two substrate molecules onto iron cations followed by slow one-electron metal-centered reduction. The results of IR, ESI-MS and EPR study support the formation of final product with Fe${}^{+3}$–N$=$Fe${}^{+4}$ unit and two substrate molecules in the first coordination sphere. The reaction kinetics was studied, the pre-equilibrium constants $K_{\text{eq}}$ and rate constants $k$ were obtained. The $K_{\text{eq}}$ and $k$ values were found to be linearly correlated with basicity of substrates p$K_{\text{a}}$. The possibility of the transition Fe${}^{4+}\to$ Fe${}^{3+}$ is promoted by electron–donor properties of substrate combined with the presence of both electron-rich macrocycle and $\pi$-backdonation Fe $\leftarrow$ N${}_{\text{Pc}}$.

An in-depth study of the electronic structure of a 1,4-diazabicyclo[2.2.2]octane (DABCO) induced molecular self-assembled xanthene-bridged and amide-bonded porphyrin dimer is reported. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations are used to identify trends in the optical spectroscopic properties. B3LYP geometry optimization predicts the formation of an almost perfectly eclipsed structure with respect to the two porphyrin rings with the analogous pyrrole nitrogens separated by 7.7–8.1 Å. The observed distinctive derivative-shaped band morphology of the pseudo-Faraday-A${}_1$ terms in the MCD spectra has been used to identify the main electronic Q and B-bands and to validate the TD-DFT calculations. The absence of a discernible splitting of the redox steps or a quenching of the fluorescence demonstrates that there is no significant exciton coupling between the two porphyrin rings.

A novel one-step strategy for the synthesis of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin using Ag^IIOBP is described. Ag^IIOBP was synthesized and was. Bromination of Ag^IITPP was carried out in a one-step reaction by varying the subsequently demetalated using H₂S time interval and stoichiometric addition of Br₂. The molecular weight of the halogenated porphyrin was confirmed by MALDI-TOF mass spectrometry. The synthesis of Ag(II) 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin was followed by demetalation of Ag(II) ion from the halogenated porphyrin. The demetalation of was carried out under mild conditions using sodium sulphide in trifluoroacetic acid. The time taken for the demetalation was considerably lesser than previously reported and which facilitated a simple way for the isolation of the final product in good yield. The yield of the free base was 98%. The formation of the product and purity was confirmed by ¹H NMR, Mass spectrometry. UV-visible spectrophotometer clearly showed the appearance of a characteristic Q-band of the octa-brominated porphyrin.