A3B Type Research Articles

Photoredox Catalysis by 21-Thiaporphyrins: A Green and Efficient Approach for C-N Borylation and C-H Arylation.

Photoredox catalysis provides a green and sustainable alternative for C-H activation of organic molecules that eludes harsh conditions and use of transition metals. The photocatalytic C-N borylation and C-H arylation mostly depend on the ruthenium and iridium complexes or eosin Y and the use of porphyrin catalysts is still in infancy. A series of novel 21-thiaporphyrins (A2B2 and A3B type) were synthesized having carbazole/phenothiazine moieties at their meso-positions and screened as catalysts for C-N borylation and C-H arylation. This paper demonstrates the 21-thiaporphyrin catalyzed C-N borylation and het-arylation of anilines under visible light. The method utilizes only 0.1 mol % of 21-thiaporphyrin catalyst under blue light for the direct C-N borylation and het-arylation reactions. A variety of substituted anilines were used as source for expensive and unstable aryl diazonium salts in the reactions. The heterobiaryls and aryl boronic esters were obtained in decent yields (up to 88 %). Versatility of the 21-thiaporphyrin catalyst was tested by thiolation and selenylation of anilines under similar conditions. Mechanistic insight was obtained from DFT studies, suggesting that 21-thiaporphyrin undergo an oxidative quenching pathway. The photoredox process catalyzed by 21-thiaporphyrins offers a mild, efficient and metal-free alternative for the formation of C-C, C-S, and C-Se bonds in aryl compounds; it can also be extended to borylation reaction.

Electrocatalysis Using Cobalt Porphyrin Covalently Linked with Multi-Walled Carbon Nanotubes: Hydrazine Sensing and Hydrazine-Assisted Green Hydrogen Synthesis.

Acid-treated multi-walled carbon nanotube (MWCNT) covalently functionalized with cobalt triphenothiazine porphyrin (CoTriPTZ-OH) A3B type porphyrin, containing three phenothiazine moieties (represented as MWCNT-CoTriPTZ) is synthesized and characterized by various spectroscopic and microscopic techniques. The nanoconjugate, MWCNT-CoTriPTZ, exhibits a pair of distinct redox peaks due to the Co2+/Co3+ redox process in 0.1M pH 7.0 phosphate buffer. Further, it electrocatalytically oxidizes hydrazine at a low overpotential with a high current. This property is advantageously utilized for the sensitive determination of hydrazine. The developed electrochemical sensor exhibits high sensitivity (0.99 µAµM-1cm-2), a low limit of detection (4.5 ppb), and a broad linear calibration range (0.1µM to 3.0mM) for the determination of hydrazine. Further, MWCNT-CoTriPTZ is exploited for hydrazine-assisted green hydrogen synthesis. The high efficiency of hydrazine oxidation is confirmed by the low onset potential (0.45V (vs RHE)) and 0.60V (vs RHE) at the current density of 10mA.cm-2. MWCNT-CoTriPTZ displays a high current density (77.29mA.cm-2) at 1.45V (vs RHE).

Rational design of bimetallic alloys for effective hydrodechlorination of 4-chlorophenol

A combined density functional theory (DFT) and microkinetic model (MKM)-based approach is applied to design Pd-based A3B type bimetallic alloys – Pd3Cu, Pd3Ag and Pd3Au for hydrodechlorination (HDC) reaction of 4-chlorophenol (4-CP).

A3B type asymmetric metallo phthalocyanines bearing carboxylic acid and tert-butyl groups: Photophysical, photochemical and aggregation properties

In this study, A3B type asymmetric magnesium(II), zinc(II) and indium(III)chloro phthalocyanine derivatives bearing carboxylic acid and tert-butyl groups were synthesized and their photochemical, photophysical and aggregation properties for photodynamic therapy (PDT) application were investigated. In the first part of the study; phthalonitriles, which are the starting materials, were synthesized and then different phthalocyanine compounds were obtained from the synthesized phthalonitriles in the second part. The synthesized compounds were characterized using different techniques. At the same time, the photophysical and photochemical properties of the synthesized compounds were also investigated. The calculated singlet oxygen quantum values in DMSO are 0.30 for MgPc, 0.72 for ZnPc, and 0.62 for InPc in and these values in DMF are 0.25 for MgPc, 0.68 for ZnPc, and 0.60 for InPc after photochemical studies. The obtained results proved that the contribution of the substituents increased the therapeutic efficacy. Finally, our results show that all Pc derivatives have displayed desirable singlet oxygen, photodegradation, fluorescence and aggregation properties for PDT studies.

Synthesis of novel zinc porphyrins with bioisosteric replacement of Sorafenib: Efficient theranostic agents for anti-cancer application

Novel zinc porphyrins (trans-A2B2 and A3B type) are reported containing pharmacophoric groups derived from Sorafenib at the meso-positions. The pharmacophoric and bioisosteric modification of Sorafenib was done with 2-methyl-4-nitro-N-phenylaniline. The in-vitro photo-cytotoxicity studies of zinc porphyrins on HeLa cells revealed excellent PDT based autophagy inhibition of cancer cells, with IC50 values between 6.2 to 15.4 μM. The trans-A2B2 type zinc porphyrin with two bioisosteric groups gave better cytotoxicity than A3B type. Molecular docking studies revealed excellent binding with mTOR protein kinase of the designed porphyrins. The confocal studies indicated significant ER localization of trans-A2B2 type zinc porphyrin in HeLa cells along with ROS generation. trans-A2B2 type zinc porphyrin induced ER stress in cancer cells, thereby causing elevation of Ca+2 ions in cytoplasm, which led to cancer cell death via autophagy pathway. The studies suggested that trans-A2B2 and A3B type zinc porphyrins can be developed as theranostic agents for anti-cancer applications.

Preliminary In Vitro Evaluation of Some Porphyrins Using Human Breast Tumor Cells

Background:: Tetrapyrrolic compounds, such as porphyrins and metalloporphyrins, are highly interesting for pharmaceutical chemistry designs considering their good biocompatibility and therapeutic potential. Objective:: The aim of the present work was a preliminary in vitro evaluation of some unsymmetrical porphyrins and the corresponding symmetrical structures as potential candidates for the photodynamic therapy of malignant tumors. Methods:: The biocompatibility of compounds was assessed in terms of their in vitro effect on the viability and proliferation of breast human carcinoma MCF-7 cells and human normal peripheral blood mononuclear cells. Results:: Results indicated that unsymmetrical and symmetrical porphyrins were non-toxic against tumor MCF-7 cells in the concentration range of 0.2–2μM, making them valuable candidates for further development as photosensitizers for PDT in tumors. Moreover, unsymmetrical compounds tended to restore the response of normal and tumor cells affected by the vehicle (dimethyl sulfoxide) used for the initial solubilization of porphyrins, while the symmetrical compounds were less active in this respect. Conclusion:: Unsymmetrical A3B type porphyrins prove enhanced capacity as potential theranostic agents in interaction with human carcinoma MCF-7 cells, despite reduced differences with the corresponding symmetrical form.

Synthesis of Conjugates of Cationic meso-Arylporphyrins with Substituted closo-Decaborate Anion Derivative [B10H9NH=C(CH3)CH2C≡CH

A click reaction-based approach to the synthesis of water-soluble conjugates of cationic meso-arylporphyrins of A3B type and closo-decaborate anion derivatives [B10H9NH=C(CH3)NHCH2C≡CH]– is presented. The structure of the conjugates was established by advanced methods of analysis. Their main absorption and luminescence characteristics were investigated.

DSSCs based on unsymmetrical A3B type Zn(II) and TiO(IV) naphthalenephthalocyanine/porphyrin cocktail dyes: A potential alternative for ruthenium based sensitizers

To increase the efficiency of dye-sensitized solar cells (DSSCs), there is still a need for alternative dyes that can absorb a broad spectrum of sunlight and maintain high conversion efficiencies. In order to meet these requirements, a cocktail dye made up of novel phthalocyanines together with a porphyrin have been designed. The novel unsymmetrical phthalocyanines are two ferrocenylphenoxy-naphthalenephthalocyanine (FPNPc) with Zn (ZnFPNPc) or TiO (TiOFPNPc) at the inner core and 4-ferrocenylphenoxy and 4-carboxybenzo substituents at peripheral positions. In order to increase their UV–Vis absorption capacity, cocktails have been prepared with the synthesized new dyes (ZnFPNPc or TiOFPNPc) and YD2 porphyrin dye. The full characterization of novel synthesized dyes has been performed by UV–Vis absorption, FTIR, H1-NMR, MALDI-TOF, electrochemical, TD-DFT techniques. In this work we have prepared DSSCs based on YD2 and phthalocyanine dye molecule with different cocktail ratio (YD2 + ZnFPNPc or YD2 + TiOFPNPc ratios: 1:1, 1:2, 2:1, 1:3, 3:1, 1:4 and 4:1). The best solar cell performance has been performed in the cases of YD2 + ZnFPNPc (3:1) (9.96%) and YD2 + TiOFPNPc (3:1) (10.72%) cocktail dyes. Due to the high efficiency values obtained, these new cocktail dyes are expected to be a good alternative to the ruthenium-based complex dyes used in DSSCs and pave the way for potential alternative dyes.

Low-Dose Near-Infrared Light-Activated Mitochondria-Targeting Photosensitizers for PDT Cancer Therapy.

Phthalocyanines (Pcs) are promising candidates for photodynamic therapy (PDT) due to their absorption in the phototherapeutic window. However, the highly aromatic Pc core leads to undesired aggregation and decreased reactive oxygen species (ROS) production. Therefore, short PEG chain functionalized A3B type asymmetric Pc photosensitizers (PSs) were designed in order to decrease aggregation and increase the aqueous solubility. Here we report the synthesis, characterization, optical properties, cellular localization, and cytotoxicity of three novel Pc-based agents (LC31, MLC31, and DMLC31Pt). The stepwise functionalization of the peripheral moieties has a strong effect on the distribution coefficient (logP), cellular uptake, and localization, as well as photocytotoxicity. Additional experiments have revealed that the presence of the malonic ester moiety in the reported agent series is indispensable in order to induce photocytotoxicity. The best-performing agent, MLC31, showed mitochondrial targeting and an impressive phototoxic index (p.i.) of 748 in the cisplatin-resistant A2780/CP70 cell line, after a low-dose irradiation of 6.95 J/cm2. This is the result of a high photocytotoxicity (IC50 = 157 nM) upon irradiation with near-infrared (NIR) light, and virtually no toxicity in the dark (IC50 = 117 μM). Photocytotoxicity was subsequently determined under hypoxic conditions. Additionally, a preliminarily pathway investigation of the mitochondrial membrane potential (MMP) disruption and induction of apoptosis by MLC31 was carried out. Our results underline how agent design involving both hydrophilic and lipophilic peripheral groups may serve as an effective way to improve the PDT efficiency of highly aromatic PSs for NIR light-mediated cancer therapy.

Clamshell‐type Bis‐phthalocyanine with Tetrachlorocyclotriphosphazene Intramolecular Bridge: Synthesis and Structural Evaluation by DFT, NMR and Optical Spectroscopy

AbstractAn interaction of 2‐hydroxy‐9(10),16(17),23(24)‐tri‐tert‐butyl‐29H,31H‐ phthalocyanine (1) with hexachlorocyclotriphosphazene (phosphonitrilic chloride trimer) produced, along with the A3B type low‐symmetry monophthalocyanine (monomer 2), a bis‐derivative 3 with spectral characteristics such as that of most clamshell‐type phthalocyanines (typically, H‐dimers). The reaction can be considered conditionally selective. DFT calculations showed the possibility of the existence of several isomers. Based on the UV‐Vis, fluorescent and NMR studies, we found that 3 was obtained as an inseparable mixture of three diastereomers‐achiral cis‐isomer and two chiral trans‐isomers. DFT analysis has also shown that cis‐isomer can exist as two rotamers‐parallel and oblique, by an analogy with the cofacial J‐type dimers that we obtained earlier.

Meso-Carbazole substituted palladium porphyrins: Efficient catalysts for visible light induced oxidation of aldehydes

The A3B and A2B2 type porphyrins having [Formula: see text]-butylcarbazole and [Formula: see text]-cyanophenyl groups are synthesized and characterized. Their palladium complexes have also been prepared and utilized as catalysts for the photo-oxidation reactions of aromatic aldehydes in good yields. Pd(II)porphyrins displayed decent phosphorescence at [Formula: see text]670 nm and were able to generate singlet oxygen upon light irradiation. The calculated singlet oxygen quantum yields for Pd(II)porphyrins were between 57% and 73%. The photo-catalytic application of Pd(II)porphyrins for aerobic oxidation of aromatic aldehydes is demonstrated.

Tuning the Acceptor Unit of Push-Pull Porphyrazines for Dye-Sensitized Solar Cells.

A family of four push–pull porphyrazines of A3B type, where each unit A contains two peripheral propyl chains and the unit B is endowed with a carboxylic acid, were prepared. The carboxylic acid was attached to the β-position of the pyrrolic unit, either directly (Pz 10), or through cyanovinyl (Pz 11) and phenyl (Pz 7) groups. The fourth Pz (14) consisted in a pyrazinoporphyrazine wherein the dinitrogenated heterocycle provided intrinsic donor–acceptor character to the macrocycle and contained a carboxyphenyl substituent. The direct attachment of the carboxylic acid functions and their linkers to the porphyrazine core produces stronger perturbation on the electronic properties of the macrocycle, with respect to their connection through fused benzene or pyrazine rings in TT112 and 14, respectively. The HOMO and LUMO energies of the Pzs, which were estimated with DFT calculations, show little variation within the series, except upon introduction of the cyanovinyl spacer, which produces a decrease in both frontier orbital energetic levels. This effective interaction of cyanovinyl substitution with the macrocycle is also evidenced in UV/Vis spectroscopy, where a large splitting of the Q-band indicates strong desymmetrization of the Pz. The performance of the four Pzs as photosensitizers in DSSCs were also investigated.

Pd(II) porphyrins: Synthesis, singlet oxygen generation and photoassisted oxidation of aldehydes to carboxilic acids

The synthesis and spectral studies of A3B and A2B2 type porphyrins and their Pd(II) complexes are reported. The meso-positions on porphyrin macrocycle are substituted with pentafluorophenyl and N-butylcarbazole or triphenylamine groups. Pd(II) porphyrins displayed decent phosphorescence ∼670 nm and are able to produce singlet oxygen by type II pathway, after photoirradiation. The calculated singlet oxygen quantum yields for Pd(II) porphyrins are (ΦΔ = 30%–63%). The catalytic application of Pd(II) porphyrins towards photoassisted aerobic oxidation of aromatic aldehydes to carboxylic acids is demonstrated.

Low-symmetry A3B type pentachlorocyclotriphosphazene substituted phthalocyanine with improved nonlinear optical properties: Synthesis, spectroscopic and ab initio/(TD)DFT study

In the present work, we performed structural modification of 2-hydroxy-9(10),16(17),23(24)-tri-tert-butyl-29H,31H-phthalocyanine (1) using phosphonitrilic chloride trimer (hexachlorocyclotriphosphazene). Despite the wide availability of phosphazenes and their derivatives, including polymeric materials based on them, this is one of the few examples of the introduction of an active phosphazene cycle into the structure of a macroheterocyclic compound. Target free-base ligand 2 was characterized by the MALDI-TOF/TOF mass spectrometry, as well as the 1H, 31P NMR and FT-IR spectroscopy. Also, a tendency towards H-aggregation in polar media was demonstrated. Theoretical calculations based on time-dependent Hartree-Fock approach for nonlinear optical properties have allowed revealing a self-defocusing effect in the case of phthalocyanine 2, which makes it an interesting candidate for all-optical switching, two-photon imaging, and optical power limiting applications.

A3B type unsymmetrical and amphiphilic phthalocyanines: Synthesis, characterization, thermal stability and aggregation studies.

This study reports the preparation, analysis, aggregation statuses and thermal properties of five phthalocyanines. The preparation of all molecules includes two steps: the first step is the preparation of phthalocyanine precursor molecules (A and B coded phthalonitriles); the second step is the synthesis of one metal-free and four metalled phthalocyanines (A3B-Co, A3B-Cu, A3B-H, A3B-Ni, and A3B-Zn coded compounds). Compound A holds a hydrophobic chain (cetyl alcohol); compound B holds a hydrophilic chain (tetraethylene glycol). Phthalocyanines include three hydrophobic chains and one hydrophilic chain (A3B type phthalocyanine). Characterization methods which were used to determine the structure of these compounds are Fourier Transform Infrared (FTIR), Proton Nuclear Magnetic Resonance (1H NMR), Carbon-13 Nuclear Magnetic Resonance (13C NMR), and Ultraviolet Visible (UV Vis) spectroscopies and elemental analysis. The phthalocyanines have high stability up to 260 °C as a minimum value. Aggregation statuses of the phthalocyanines change to the metal from the metal or to the solvent from the solvent.

Asymmetric phthalocyanines (A3B type) containing aminophenoxy and hydroxyphenyl-diazenyl-phenoxy substituents

In this research new asymmetric metal-phthalocyanine complexes (A3B-type), with Zn2+, Co2+ and Ru2+, bearing aminophenoxy and hydroxyphenyl-diazenyl-phenoxy substituents, were synthetized. The synthetic route to asymmetric Pcs (A3B-type), based on ring expansion method is refined. The photophysical and electrochemical properties of the new phthalocyanines were investigated. In addition to this investigation, a comparative study took place on the effect of the expansion of conjunction on properties of the MPc compound. Moreover, the effect of pH to the ground state electronic absorption spectra of compounds bearing hydroxyphenyl-diazenyl-phenoxy substituents was also studied. Theoretical studies (DFT) were also carried out in order to support the corresponding experimental results.

Influence of strong electron donating nature of phenothiazine on A3B- type porphyrin based dye sensitized solar cells

Structural modifications of porphyrin sensitizers have shown significant impact on incident photon to current generation whilst applied into dye sensitized solar cells. Nevertheless, various positional alterations of donor/acceptors attached porphyrin dyes reported until now in which A3B based sensitizers received much attention in DSSCs. Herein, we reported A3B type hexyl-phenothiazine appended porphyrins (G10 and G11) utilized as sensitizer with liquid redox electrolyte results the efficiency of 5.4% which is highest performance amongst A3B type sensitizers reported. Optical and electrochemical properties of G10 and G11 suggested that photoinduced intramolecular electron transfer mechanism occurred from donor hexyl-phenothiazine to acceptor acetic acid via porphyrin macrocycle. Density functional theory calculations revealed that lowest occupied molecular orbital of dyes close to the conduction band of TiO2 facilitates efficient electron injection from dye to nanoparticles. Incident photon to electron conversion efficiency (IPCE) spectra and J-V curve of dyesdepict broad band from 350 to 750 nm in the range of >50–55% as a result power conversion efficiency (η) of 5.11–5.40%. Therefore, design of diverse molecular structures pave the way for improved efficiency and durability of photovoltaic devices.

Synthesis and Spectral Properties of Nickel Complexes with Low-Symmetry Phenoxy- and Phenylsulfanyl-Substituted and 1,4-Naphthoquinone-Annulated Phthalocyanines

Cross-coupling of 4,5-diphenoxyphthalonitrile or 4,5-bis(phenylsulfanyl)phthalonitrile (component A) with imide of anthraquinone-2,3-dicarboxylic acid (component B) in the presence of urea, nickel acetate, ammonium chloride, and molybdate has afforded metal complexes of the corresponding low-symmetry phthalocyanines of the A3B, AABB, and ABAB type. Investigation of their spectral properties has shown that the complexes are associated in chloroform, the type of association depending on the dipole moment of the molecule.

Low‐Symmetry Phthalocyanine Cobalt Bis(dicarbollide) Conjugate for Hydrogen Reduction

The synthesis and characterization of two new A3B type unsymmetrical zinc phthalocyanines, one bearing a hydroxyl group and the other bearing a cobalt bis(dicarbollide) unit, are reported here. The introduction of diethylaminophenoxy moieties to the phthalocyanine fragments yields outstanding solubilities in organic solvents, as well as providing electropolymerization on the surface of the electrode. These modified electrodes are found to be effective for the electrocatalytic reduction of hydrogen ions in acidic media. The enhanced hydrogen‐evolution reaction (HER) performance for the bis(dicarballide)‐functionalized phthalocyanine‐modified electrode can be simultaneously observed. This is attributed to its redox‐active metal center of cobalt bis(dicarbollide), creating a synergistic effect, to facilitate many more electrocatalytic active sites, resulting in improved HER performance. The catalyst shows an onset potential of 163 mV at a current density of 8.79 µA cm–2, and a Tafel slope as low as 28 mV dec–1.

Mesomorphic structure peculiarities of two mix-substituted phthalocyanines of the A3B type

ABSTRACTMesomorphic properties and structures of two mix-substituted lipophilic phthalocyanine derivatives of the A3B type, with a different ratio of electron-donating (hexadecyloxy-) and electron-withdrawing (Cl-) substituents on the isoindol fragments ‘A’ and ‘B’, correspondingly, were studied by polarising optical microscopy, differential scanning calorimetry and small-angle X-ray scattering. Both compounds display columnar mesophases, and the type of organisation of the columns in the mesomorphic state was found to strongly depend on the number of peripheral chlorine substituents in the molecule. The di-chloro-substituted phthalocyanine forms a solid pasty lamellar phase at room temperature, which on heating undergoes successive transitions to two large-lattice columnar mesophases (2D-Colh and 3D-MCol) arising from the aggregation of several phthalocyanine-containing piles. On the contrary, aggregation of columns does not occur for the tetra-chloro-substituted phthalocyanine, which forms a nematic columnar mesophase of single phthalocyanine piles (1D-NCol). While the di-chloro-compound partly crystallises on cooling, the nematic phase of the tetra-chloro-compound freezes at room temperature. The reasons for this different self-organisation behaviour are not yet fully understood, but some hints may be deduced from the proposed supramolecular models.