Synthesis of tetrasubstituted Zn(II)-phthalocyanines carrying four carboranyl-units as potential BNCT and PDT agents

Synthesis, characterization, and DFT study of novel metallo phtalocyanines with four carboranyl clusters as photosensitisers for the photodynamic therapy of breast cancer cells

The synthesis and characterization of novel Zn(II) and Co(II) phthalocyanines 4 and 5, respectively containing four o-carboranyl units (40 boron atoms, 32.5% boron by weight) at the peripheral positions are described. The phthalocyanines (Pcs) were synthesized by cyclotetramerization of the previously prepared precursor 4‑(2‑thiol‑o‑carboranyl)thiolato‑phthalonitrile 3 with the presence of metal salt in boiling dry DMF under a dry nitrogen atmosphere. They were characterized by elemental analysis, UV-Vis, FT-IR, MALDI-TOF mass and ¹H NMR spectrometry. To elucidate the structural, spectroscopic and bonding properties of the obtained compounds, calculations with DFT/TD-DFT(Density Functional Theory/Time Dependent-Density Functional Theory) were performed. The cytotoxic effects of 4 and 5 on cancer cells and epithelial cells were determined. The targeted cytotoxicities of both compounds against cancer cells were analyzed with the cell viability test. Although, 4 caused less PDT (Photodynamic therapy) based decrease in cell viability of cancer cell line in comparison to 5, it showed comparatively high cytotoxicity against cancer cells but not epithelial cells. The IC₅₀ (half maximal inhibitory concentration) values indicate that 4 with PDT shows 17.3 fold more cytotoxicity to breast cancer cells than epithelial cells. The selectivity in cytotoxicity of 4 makes it a good candidate for cancer treatment. Interestingly, 5 was found to be highly cytotoxic for both cancer and epithelial cell lines. Considerably, 5 might be used as a cancer drug when combined with targeting agents such as antibodies and aptamers.

Carborane-layered double hydroxide nanohybrids for potential targeted- and magnetically targeted-BNCT applications

Carborane-intercalated layered double hydroxide nanohybrids (CB-LDH) and a magnesium ferrite (MF) supported-CB-LDH core–shell nanocomposite (CB-LDH@MF) are reported.

Novel axially carborane-cage substituted silicon phthalocyanine photosensitizer; synthesis, characterization and photophysicochemical properties

The novel axially dicarborane substituted silicon (IV) (SiPc-DC) phthalocyanine was synthesized by treating silicon phthalocyanine dichloride SiPc(Cl)2 (SiPc) with o-Carborane monool. The compound was characterized by mass spectrometry, UV-Vis, FT-IR, (1)H and (11)B Nuclear Magnetic Resonance Spectroscopy (NMR). Spectral, photophysical (fluorescence quantum yield) and photochemical (singlet oxygen (ΦΔ) and photodegradation quantum yield (Φd)) properties of the complex were reported in different solutions (Dimethyl sulfoxide (DMSO), Dimethylformamide (DMF) and Toluene). The results of spectral measurements showed that both SiPc and carborane cage can have potential to be used as sensitizers in photodynamic therapy (PDT) and boron neutron capture therapy (BNCT) by their singlet oxygen efficiencies (ΦΔ=0.41, 0.39).

Preliminary anti-cancer photodynamic therapeutic in vitro studies with mixed-metal binuclear ruthenium(II)-vanadium(IV) complexes

We report the synthesis and characterisation of mixed-metal binuclear ruthenium(II)-vanadium(IV) complexes, which were used as potential photodynamic therapeutic agents for melanoma cell growth inhibition. The novel complexes, [Ru(pbt)2(phen2DTT)](PF6)2·1.5H2O 1 (where phen2DTT = 1,4-bis(1,10-phenanthrolin-5-ylsulfanyl)butane-2,3-diol and pbt = 2-(2'-pyridyl)benzothiazole) and [Ru(pbt)2(tpphz)](PF6)2·3H2O 2 (where tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine) were synthesised and characterised. Compound 1 was reacted with [VO(sal-L-tryp)(H2O)] (where sal-L-tryp = N-salicylidene-L-tryptophanate) to produce [Ru(pbt)2(phen2DTT)VO(sal-L-tryp)](PF6)2·5H2O 4; while [VO(sal-L-tryp)(H2O)] was reacted with compound 2 to produce [Ru(pbt)2(tpphz)VO(sal-L-tryp)](PF6)2·6H2O 3. All complexes were characterised by elemental analysis, HRMS, ESI MS, UV-visible absorption, ESR spectroscopy, and cyclic voltammetry, where appropriate. In vitro cell toxicity studies (with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay) via dark and light reaction conditions were carried out with sodium diaqua-4,4',4'',4''' tetrasulfophthalocyaninecobaltate(II) (Na4[Co(tspc)(H2O)2]), [VO(sal-L-tryp)(phen)]·H2O, and the chloride salts of complexes 3 and 4. Such studies involved A431, human epidermoid carcinoma cells; human amelanotic malignant melanoma cells; and HFF, non-cancerous human skin fibroblast cells. Both chloride salts of complexes 3 and 4 were found to be more toxic to melanoma cells than to non-cancerous fibroblast cells, and preferentially led to apoptosis of the melanoma cells over non-cancerous skin cells. The anti-cancer property of the chloride salts of complexes 3 and 4 was further enhanced when treated cells were exposed to light, while no such effect was observed on non-cancerous skin fibroblast cells. ESR and (51)V NMR spectroscopic studies were also used to assess the stability of the chloride salts of complexes 3 and 4 in aqueous media at pH 7.19. This research illustrates the potential for using mixed-metal binuclear ruthenium(II)-vanadium(IV) complexes to fight skin cancer.

Syntheses of near infrared absorbed phthalocyanines to utilize photosensitizers

Phthalocyanines have become of major interest as functional colorants for various applications. In order to use various applications especially photosensitizers, the absorption maxima called Q-band of phthalocyanines are required to be shifted to the near infrared region. Substituted phthalocyanine analog alkylbenzopiridoporphyrazins, especially zinc bis(1,4-didecylbenzo)-bis(3,4-pyrido)porphyrazine, and toroidal-shaped phthalocyanines having aminoamine dendric side chains such as toroidal zinc poly(aminoamine)phthalocyanine dendrons were synthesized. Phthalocyanines of two types reportedly use photosensitizers for photodynamic therapy of cancer. The respective efficacies of photodynamic therapy of cancer for zinc bis(1,4-didecylbenzo)-bis(3,4-pyrido)porphyrazine and its regioisomers were estimated using laser-flash photolysis. The capability of using photodynamic therapy for toroidal zinc poly(aminoamine)phthalocyanine dendrons was assessed using a cancer cell culture. Both phthalocyanines were suitable for the use as a photosensitizer as photodynamic therapy of cancer. Then, non-peripheral thioaryl substituted phthalocyanines, 1,4,8,11,15,18,22,25-octakis(thioaryl)phthalocyanines, such as 1,4,8,11,15,18,22,25-octakis(thiophenylmethyl)phthalocyanines, 1,4,8,11,15,18,22,25-octakis(thiophenylmethoxy)phthalocyanines, and 1,4,8,11,15,18,22,25-octakis(thiophenyl tert-butyl)phthalocyanines were also synthesized in order to develop next- generation photovoltaic cells and/or dye-sensitized solar cells. Non-peripheral substituted 1,4,8,11,15,18,22,25-octakis(thioaryl)phthalocyanines exhibited a Q-band in the near infrared region. Electrochemical measurements were performed on the above-mentioned 1,4,8,11,15,18,22,25-octakis(thioaryl)phthalocyanines described above to examine their electron transfer abilities and electrochemical mechanisms. The compounds 1,4,8,11,15,18,22,25-octakis(thioaryl)phthalocyanines are anticipated to be appropriate materials for use in the next generation of photovoltaic cells.

Electrochemical evidence of intramolecular electronic communication in Zr and Hf phthalocyanines bearing ferrocene-containing β-diketonato axial ligands: structure of [PcHf(FcCOCHCOC6H5)2]

The series of zirconium(IV) and hafnium(IV) phthalocyanine complexes [PcM(FcCOCHCOR)2] (Pc = phthalocyaninato; M = Zr; R = CF3 (1), CH3 (2), C6H5 (3), Fc ((C5H5)Fe(C5H4), 4), as well as M = Hf ; R = CF3 (5), CH3 (6), C6H5 (7), and Fc (8)) were synthesized. A single-crystal X-ray diffraction analysis of the structure of [PcHf(FcCOCHCOC6H5)2], 7 (Z = 2, space group P1), showed the two axial β-diketonato ligands were orientated in such a way that the ferrocenyl groups were positioned diagonally opposite each other. From the structural determination of 7 it was clear that these complexes have a distorted D4h symmetry at the coordination site of the metal centers, which explains a splitting of the UV-vis Q band into Qx and Qy components with 3 ≤ Δλ(max,Q) ≤ 10 nm. Cyclic and square wave voltammetric studies in CH2Cl2/[N((n)Bu)4][B(C6F5)4] allowed observation of at least three phthalocyaninato macrocycle-based redox couples as well as all (i.e., two or four) well-resolved ferrocenyl couples in 1-8. For M = Zr and R = Fc, formal reduction potentials of the four ferrocenyl groups were found to be E°' = 296, 386, 538, and 687 mV versus free ferrocene. Spectroelectrochemical evidence, UV-vis Q-band maximum wavelengths, and HOMO-LUMO energy gaps as expressed by ΔE°'I-III = ΔE°'wave I - ΔE°'wave III were mutually consistent, indicating that the first phthalocyaninato ring-based oxidation occurs before ferrocenyl oxidations take place. The potential for each redox process was found to be dependent on the sum of β-diketonato R-group group electronegativities, ΣχR. Mathematical relationships for the dependency of E°' on ΣχR for all four observed ring-based redox processes as well as for the ferrocenyl-based redox processes were determined. This allowed prediction of potentials for redox processes that fall outside the workable potential window of the solvent. No significant differences were found between the corresponding redox potentials of zirconium and hafnium analogues bearing the same axial ligands.

Synthesis and characterization of nanosized polycarboranyl-porphyrazine conjugates

The synthesis and characterization of a highly boronated porphyrazine, 2,3,7,8,12,13,17,18-octakis-[6-(2-(1′-methyl-1′,2′-dicarba-closo-dodecaboran-2′ -yl)hexyl)-1,2-dicarba-closo-dodecaboran-1-yl)hexylthio] 5,10,15,20 (21H, 23H) porphyrazine (H2(MCHE)CHESPz), is reported. This nanosized molecule bears eight dicarboranyl-substituted carborarod-like alkyl pendants and, as such, represents a rare example, if any, of a tetrapyrolic system bearing 160 boron atoms per molecule, corresponding to 40% boron content by weight.

Reactions of oxonium derivatives of (B12H12)2- with phenoles, and synthesis and photochemical properties of a phthalocyanine containing four (B12H12)2- groups

The reactions of dodecahydro-closo-dodecaborate oxonium derivatives with various phenols resulted in phenoxy-undecahydro-closo-dodecaborates in high yields. Using this method, a phthalocyanine zinc(II) complex containing four ( B 12 H 12)2- species was prepared in high yield. The compound shows good photocatalytic activity. The combination of boron cages and phthalocyanines makes this compound useful for boron neutron capture therapy for cancer and photodynamic tumor therapy.

Synthesis, properties and photodynamic activities of some zinc(II) phthalocyanines against Escherichia coli and Staphylococcus aureus

Two new zinc phthalocyanine derivatives bearing four 3,5-di-tert-butyl-4-hydroxyphenyl (ZnPc1) and 3,5-dimethylphenoxy (ZnPc2) have been synthesized and proved by elemental analyses and UV-vis, 1H NMR, FTIR and MALDI-TOF mass spectra as spectroscopic determination. Thermal stabilities of these neutral Zn -phthalocyanines were performed by thermal gravimetric analysis and, significantly, were found stable up to 373 °C for ZnPc1 and 550 °C for ZnPc2. In addition, the photostability of the sensitizers was quite successful within 240 min. Furthermore, photodynamic therapy has been investigated using these neutral phthalocyanines. Singlet oxygen generation capacities of ZnPc1 and ZnPc2 were studied using 1,3-diphenyl-iso-benzofuran (50.0 μM) as a selective singlet oxygen trap in DMSO and both of them demonstrated very high singlet oxygen generation capacity. Photodynamic therapy is of considerable interest for its potential as an antimicrobial therapy on the grounds that the photodynamic activity of these compounds was tested against a Gram-negative bacteria, Escherichia coli and a Gram-positive bacteria, Staphylococcus aureus. Suspensions of the microorganisms were irradiated for 240 min in the presence of ZnPc1 (with hydrophilic group) and ZnPc2 phthalocyanines. In order to simulate solar radiation, we used a 750 W xenon lamp. Minimum photosensitizer concentration was used as 0.1 mg.10 mL-1 in 1% dimethylsulfoxide/phosphate buffer saline solution (DMSO/PBS). Moreover, the photostability of these compounds has been investigated and the effect of the amount of DMSO tested against selected bacteria. In the dark, with and without Pcs, bacterial inactivation did not occur. Bacterial inactivation by light with ZnPc1 was observed in response to Gram-negative bacteria E. coli and Gram-positive bacteria S. aureus, whereas the photoinactivation studies with ZnPc2 have revealed that the lack of its activity is due to its poor affinity for either of the organisms. These results suggest that a neutral amphiphilic photosensitizer may be easily used in an application concerning photoinactivation of bacterial cells as well as ionic photosensitizers.

The key role of peripheral substituents in the chemistry of phthalocyanines and their analogs

The preparation and optical properties of peripherally substituted phthalocyanines and their analogs (i.e. naphthalocyanines, anthracyanines, aza-analogs of phthalocyanines, and tetraazaporphyrins) have been widely discussed. This review highlights methodologies that have been published in poorly known and mostly unavailable Russian journals.

Cobaltacarborane-phthalocyanine conjugates: Syntheses and photophysical properties

Syntheses of two new cobaltacarborane-phthalocyanine conjugates, one anionic (Pc 6) and one zwitterionic (Pc 7), were accomplished via cyclotetramerization of the corresponding cobaltacarborane-substituted phthalonitriles (4 or 5) with excess phthalonitrile in quinoline. X-ray structures of two phthalonitrile precursors (2 and 3) were obtained and are discussed, and the absorption and emission properties of the two cobaltacarborane-phthalocyanine conjugates in several solvents were investigated. The anionic conjugate 6 exists mainly as a monomer in polar organic solvents and has fluorescence quantum yields in the region 0.2-0.3. The zwitterionic conjugate 7 aggregates in solution and displays lower quantum yields ~0.1 in organic solvents.

Neutral and polyanionic carboranylporphyrazines: synthesis and physico-chemical properties

Among the challenges precluding the widespread use of boron neutron capture therapy (BNCT) has been the difficulty in achieving selective delivery of large quantities of boron to malignant cells. In an attempt to address this issue we have recently developed an effective strategy to synthesize a new family of boronated porphyrazines to be delivered through the membrane of cancerous tissues as such or with the help of liposomes. Herein we describe the synthesis and the basic physico-chemical properties of neutral octa-closo-carboranyl-alkylthio-porphyrazines as well as of their water-soluble counterparts obtained by mild deboronation of the closo-polyedra. Preliminary studies indicate that these compounds show negligible cell toxicity and, compared with BPA, good cellular uptake. This encourages further studies for their evaluation as potential BNCT agents.

Enhanced cellular uptake with a cobaltacarborane-porphyrin-HIV-1 Tat 48-60 conjugate

A series of four porphyrin-cobaltacarborane conjugates have been synthesized, containing three or four cobaltabisdicarbollide anions linked by O(CH(2)CH(2)O)(2) groups to the porphyrin macrocycle and one of them containing a HIV-1 Tat 48-60 peptide sequence linked via a low molecular weight poly(ethylene glycol) (PEG) spacer. The cellular uptake, cytotoxicity, and preferential sites of intracellular localization of the conjugates were evaluated in human HEp2 cells. All conjugates are nontoxic in the dark at the concentrations studied. Upon exposure to low light dose (1 J cm(-)(2)) only the porphyrin-cobaltacarborane-HIV-1 Tat 48-60 conjugate showed 30% inhibition of cell proliferation at a concentration of 10 microM. The cellular uptake was dependent on the number of carborane cages and was significantly enhanced by the presence of the cell penetrating peptide sequence HIV-1 Tat 48-60. All conjugates preferentially localized in the cell lysosomes.

Synthesis and cellular studies of a carboranylchlorin for the PDT and BNCT of tumors

The syntheses of closo- and nido-carboranylchlorins 4 and 5 from a known carboranylporphyrin are described. Water-soluble nido-carboranylporphyrin 5 was found to have very low dark cytotoxicity (IC50 > 500 microM using a MTT-based assay) but to be toxic in the presence of red light (IC50 = 80 microM at 0.55 J/cm2 light dose). Under the same experimental conditions, carboranylchlorin 5 was taken up by human glioma T98G cells to a significantly higher extent than chlorin e6, a chlorophyll degradation product. The preferred sites of subcellular localization of carboranylchlorin 5 were found to be the cell lysosomes. Our results suggest that carboranylchlorin 5 is a promising new dual sensitizer for the PDT and BNCT treatment of tumors.

Synthesis, cellular uptake and animal toxicity of a tetra(carboranylphenyl)-tetrabenzoporphyrin

A water-soluble nido-carboranyl-tetrabenzoporphyrin has been synthesized in 43% overall yield, by condensation of butanopyrrole with a carboranylbenzaldehyde, followed by metal insertion, oxidation, demetallation and deboronation reactions. This compound accumulated within human glioblastoma T98G cells to a significant higher extent than a structurally related nido-carboranylporphyrin, and localized preferentially in the cell lysosomes. Animal toxicity studies using male and female BALB/c mice revealed that both compounds are non-toxic even at a dose of 160 mg/kg, administered intraperitoneally as a single injection at a concentration of 4 mg/mL. It is concluded that the tetra(carboranylphenyl)-tetrabenzoporphyrin is a promising new sensitizer for the treatment of malignant tumors.

A novel10B-enriched carboranyl-containing phthalocyanine as a radio- and photo-sensitising agent for boron neutron capture therapy and photodynamic therapy of tumours: in vitro and in vivo studies

The synthesis of a Zn(ii)-phthalocyanine derivative bearing four 10B-enriched o-carboranyl units (10B-ZnB4Pc) and its natural isotopic abundance analogue (ZnB4Pc) in the peripheral positions of the tetraazaisoindole macrocycle is presented. The photophysical properties of ZnB4Pc, as tested against model biological systems, were found to be similar with those typical of other photodynamically active porphyrin-type photosensitisers, including a singlet oxygen quantum yield of 0.67. The carboranyl-carrying phthalocyanine was efficiently accumulated by B16F1 melanotic melanoma cells in vitro, appeared to be partitioned in at least some subcellular organelles and, upon red light irradiation, induced extensive cell mortality. Moreover, ZnB4Pc, once i.v.-injected to C57BL/6 mice bearing a subcutaneously transplanted pigmented melanoma, photosensitised an important tumour response, provided that the irradiation at 600-700 nm was performed 3 h after the phthalocyanine administration, when appreciable concentrations of ZnB4Pc were still present in the serum. Analogously, irradiation of the 10B-ZnB4Pc-loaded pigmented melanoma with thermal neutrons 24 h after injection led to a 4 day delay in tumour growth as compared with control untreated mice. These results open the possibility to use one chemical compound as both a photosensitising and a radiosensitising agent for the treatment of tumours by the combined application of photodynamic therapy and boron neutron capture therapy.

Synthesis and Structural Characterization of Carborane-Containing Neutral, Self-Assembled Pt-Metallacycles

[structure: see text] We have combined carborane chemistry with the newly developed directional bonding strategy to synthesize neutral macrocycles. The m- and p-carborane dicarboxylates were utilized as the donor linkers in conjunction with 1,8-bis[trans-Pt(PEt3)2NO3]anthracene 3, 2,9-bis[trans-Pt(PEt3)2NO3]phenanthrene 5, and cis-Pt(PEt3)2(NO3)2 unit 6. Three new platinum-based macrocycles, 4, 7, and 8, were thus synthesized. 31P{1H} NMR as well as the X-ray characterization of Pt-metallacycles reveal the formation of single highly symmetrical neutral species.

Coordination-Driven Self-Assemblies with a Carborane Backbone

The design and self-assembly of five new supramolecular complexes (a rectangle, a triangle, a hexagon, and two squares) are described. These assemblies incorporate carborane building blocks and were prepared in excellent yields (>85%). The assemblies and building blocks were characterized with multinuclear NMR spectroscopy, electrospray ionization mass spectrometry, and elemental analysis. Isotopically resolved mass spectrometry data confirm the existence of the rectangle, triangle, and hexagon, and NMR data are consistent with the formation of all five assemblies. The X-ray structures of two linear carborane building blocks, 1,12-(4-CC(C(5)H(4)N)(2)-p-C(2)B(10)H(10) (1) and 1,12-(trans-(Pt(PEt(3))(2)I)CC)(2)-p-C(2)B(10)H(10) (2), are reported: 1 is monoclinic, P2(1)/c, a = 10.6791(4) A, b = 8.0091(14) A, c = 11.6796(4) A, beta = 107.8461(15) degrees , V = 950.89(5) A(3), Z = 2; 2 is monoclinic, C2/c, a = 62.1128(10) A, b = 22.0071(3) A, c = 14.0494(2) A, beta = 89.9411(8) degrees , V = 19204.4(5) A(3), Z = 16. Crystals of the linear linker 1 exhibit close pi-pi pyridine and pyridine-B(carborane) interactions, which are discussed.