Catarina I. V. Ramos

Nonclassic Metallointercalators with Dipyridophenazine: DNA Interaction Studies and Leishmanicidal Activity

Complexes [Cu(CH3COO)(dppz)2]CH3COO (1) and [Zn(dppz)2](BF4)2 (2) with the intercalator dipyridophenazine (dppz) were prepared to obtain metallointercalators with increased geometrical flexibility compared to octahedral ones. Biophysical results (thermal denaturation, circular dichroism, rheometry, atomic force microscopy) indicate a strong interaction with DNA by intercalation and the existence of a positive cooperative effect with groove binding being preferred at low concentration of complexes. Induced circular dichroism (ICD) studies with DNA show that compounds 1 and 2 have a preferred orientation when binding to DNA. Since the compounds lack functional groups to permit hydrogen bonds, a combined intercalation/covalent binding mode is plausible. Further studies by QTof-ESI-MS and tandem experiments with GC oligonucleotides strongly support this dual-binding mode, since binding requires loss of one dppz unit with the copper center remaining attached to DNA even after another dppz loss. DNA saturation by the copper compound occurs at about one-half the concentration required for the zinc complex. Molecular modeling results suggest that it is caused by the increased ability of Cu(II) to distort to a more planar structure during interaction with DNA. Compounds 1 and 2 are active against a viscerotropic Leishmania infantum strain at submicromolar concentrations (IC50 = 0.57 and 0.46 μM, respectively), being more active than the reference drug miltefosine (M) (15.97 μM). They are also more cytotoxic than the control on human macrophages (MTD25 = 0.41 (1), 0.63 (2)). Besides miltefosine, the zinc compound is the only one with a MTD25/IC50 ratio above 1 on the promastigote phase (1.39) and was further studied on the amastigote form with a significant improvement in the therapeutic index (2.51). Combined analysis of DNA biophysical studies, parasite activity, and cytotoxicity measurements suggests that intercalation correlates with leishmanicidal activity, while cytotoxicity results are justified by a combination of DNA intercalation and possible radical formation in the case of Cu(II), most probably hydroxyl and/or singlet oxygen radicals.

Cationic β-vinyl substituted meso-tetraphenylporphyrins: synthesis and non-covalent interactions with a short poly(dGdC) duplex

Several cationic beta-vinyl-pyridinium and beta-vinyl-quinolinium-meso-tetraphenylporphyrin derivatives were synthesized starting from 2-formyl-meso-tetraphenylporphyrin, and the corresponding Zn(II) complex, and different N-alkyl derivatives of 2- and 4-methylpyridine and 2- and 4-methylquinoline. The new compounds were obtained in a one-step process via base catalyzed aldol-type condensation reactions. Electrospray ionization mass spectrometry (ESI-MS) and ultraviolet-visible (UV-vis) spectroscopy were used to investigate the binding mode of the synthesized cationic beta-vinyl-pyridinium and beta-vinyl-quinolinium-meso-tetraphenylporphyrin derivatives with a short GC duplex oligonucleotide. Analysis of the obtained mass spectrometry results indicates the probable occurrence of outside binding. UV-vis spectroscopy data also points to non-intercalation. The potential photosensitizing capacity of these compounds was also ascertained from preliminary photophysical studies.

Differentiation of aminomethyl corrole isomers by mass spectrometry

Two new isomeric aminomethyl corrole derivatives of [5,10,15-tris(pentafluorophenyl)corrolato]gallium(III) were synthesized with pyridine (py) molecules as axial ligands. When investigated by electrospray ionization mass spectrometry, in the positive and the negative ion modes, these compounds showed an unusual gas-phase behavior that could be used for their differentiation. In the positive ion mode, the differentiation was achieved through the formation of diagnostic fragment ions formed from [M-py + H](+) precursors, by (CH(3) )(2) NH and HF losses. An unusual addition of water to the main fragment ions provides an alternative route for isomer identification. Semi-empirical calculations were performed to elucidate the structures and stabilities of the main ionic species formed in the positive ion mode. In the negative ion mode isomer discrimination is accomplished via the fragmentation of the methoxide adduct ions [M-py + CH(3) O](-) through (CH(3) )(2)  N(.) and HF losses.

Imidazole and imidazolium porphyrins: gas-phase chemistry of multicharged ions.

Electrospray ionization mass spectrometry/mass spectrometry in the positive ion mode was used to investigate the gas-phase chemistry of multicharged ions from solutions of porphyrins with 1,3-dimethylimidazolium-2-yl (DMIM) and 1-methylimidazol-2-yl (MIm) meso-substituents. The studied compounds include two free bases and 12 complexes with transition metals (Cu(II), Zn(II), Mn(III), and Fe(III)). The observed multicharged ions are either preformed or formed during the electrospraying process by reduction or protonation and comprise closed-shell and hypervalent mono-radical and bi-radical ions. The observed extensive and abundant fragmentation of the DMIM and MIm meso-substituents is a characteristic feature of these porphyrins. Fragments with the same mass values can be lost from the meso-substituents either as charged or neutral species and from closed-shell and hypervalent radical ions. Reduction processes are observed for both the free bases and the metallated DMIM porphyrins and occur predominantly by formation of hypervalent radicals that fragment, at low energy collisions, by loss of methyl radicals with formation of the corresponding MIm functionalities. These findings confirm that, when using electrospray ionization, reduction is an important characteristic of cationic meso-substituted tetrapyrrolic macrocycles, always occurring when delocalization of the formed hypervalent radicals is possible. For the Fe(III) and Mn(III) complexes, reduction of the metal centers is also observed as the predominant fragmentation of the corresponding reduced ions through losses of charged fragments testifies. The fragmentation of the closed-shell ions formed by protonation of the MIm porphyrins mirrors the fragmentation of the closed-shell ions of their DMIM counterparts.

Reduction and adduct formation from electrosprayed solutions of porphyrin salts

The solutions of four meso-tetrakis(N-alkylpyridinium-4-yl)porphyrin salts and of the p-toluenesulfonate salt of meso-tetrakis(4-trimethylammoniumphenyl)porphyrin, in methanol, were studied by electrospray mass spectrometry, in order to investigate the influence of the type of counter ion, the length of the substituent N-alkyl groups of the four (N-alkylpyridinium-4-yl)porphyrins and the presence of an aromatic (alkylpyridinium) or aliphatic (trimethylammonium) nitrogen, in ion formation. In our experimental conditions, adducts with the counter ions were formed only for the meso-tetrakis(4-trimethylammoniumphenyl)porphyrin and were not observed for the other porphyrins, even when the counter ion was the same. In contrast, formation of reduced species, such as the [M(4+) + e(-)]3+, [M(4+) + 2e(-)]2+, [M(4+) + 4e(-) + 2H(+)]2+, and [M(4+) + 5e(-) + 2H(+)]+ ions was observed only for the (N-alkylpyridinium-4-yl)porphyrins and the appearance of these species is apparently solvent related and may occur via counter ion/solvent adducts.

Synthesis, characterization and biological evaluation of cationic porphyrin–terpyridine derivatives

A simple access to a new series of cationic porphyrin–terpyridine derivatives is described. The key step to obtain the required neutral precursors as major products involved a Krohnke type approach. The methodology allowed also the isolation of the respective benzoporphyrins and porphyrin–chalcone type derivatives, and in one case a new 2-(2,4-terpyridin-6-yl)-porphyrin. The quaternization of the pyridyl groups was performed in the presence of the adequate alkyl iodide affording the dicationic derivatives in excellent yields. All the new conjugates were fully characterised and it was found that the cationic isomers can be efficiently differentiated by ESI-MS, as their behaviour can be intensively studied by mass spectrometry. The new methylated cationic porphyrin–terpyridine derivatives demonstrate an ability to generate singlet oxygen and their efficacy to photoinactivate bioluminescent Gram-negative E. coli was evaluated. A reduction in the bioluminescence signal, up to 5.4 log, was obtained with the most efficient photosensitiser.

Electrospray mass spectrometry for the study of the non-covalent interactions of porphyrins and duplex desoxyribonucleotides

An overview of the use of electrospray mass spectrometry for the study of non-covalent interactions of cationic porphyrins and small DNA duplexes, highlighting the work developed in the Mass Spectrometry Laboratory of the University of Aveiro, is presented here.

ESI-MS/MS of expanded porphyrins: a look into their structure and aromaticity

Electrospray mass spectrometry/mass spectrometry was used to investigate the gas-phase properties of protonated expanded porphyrins, in order to correlate those with their structure and conformation. We have selected five expanded meso-pentafluorophenyl porphyrins, respectively, a pair of oxidized/reduced fused pentaphyrins (22 and 24 π electrons), a pair of oxidized/reduced regular hexaphyrins (26 and 28 π electrons) and a regular doubly N-fused hexaphyrin (28 π electrons). The gas-phase behavior of the protonated species of oxidized and reduced expanded porphyrins is different. The oxidized species (aromatic Hückel systems) fragment more extensively, mainly by the loss of two HF molecules. The reduced species (Möbius aromatic or Möbius-like aromatic systems) fragment less than their oxidized counterparts because of their increased flexibility. The protonated regular doubly fused hexaphyrin (non-aromatic Hückel system) shows the least fragmentation even at higher collision energies. In general, cyclization through losses of HF molecules decreases from the aromatic Hückel systems to Möbius aromatic or Möbius-like aromatic systems to non-aromatic Hückel systems and is related to an increase in conformational distortion. Copyright

Hybrids Based on Graphene Oxide and Porphyrin as Tools for Detection and Stabilization of DNA G-Quadruplexes

Telomerase inhibition has been an important strategy in cancer therapies, but for which effective drugs are still required. Here, noncovalent hybrid nanoplatforms containing the tetracationic 5,10,15,20-tetrakis(1-methyl-pyridinium-4-yl)porphyrin (TMPyP) and graphene oxide (GO) were prepared for promoting telomerase inhibition through the selective detection and stabilization of DNA guanine-quadruplex (G-Q) structures. Upon binding TMPyP to the GO sheets, the typical absorption bands of porphyrin have been red-shifted and the fluorescence emission was quenched. Raman mapping was used for the first time to provide new insights into the role of the electrostatic and π–π stacking interactions in the formation of such hybrids. The selective recovery of fluorescence observed during the titration of TMPyP@GO with G-Q, resembles a selective “turn-off–on” fluorescence sensor for the detection of G-Q, paving the way for a new class of antitumor drugs.

Adventures in corrole features by electrospray ionization mass spectrometry studies

In this short review the importance of electrospray mass spectrometry in corrole chemistry is highlighted. ESI-MS and ESI-MS/MS are depicted as important tools for the identification and characterization of novel corrole derivatives. Metallocorrole chemistry and differentiation of corrole isomers via ESI-MS/MS and/or TWIM-MS were chosen as two focal points.