Guanosine and fullerene derived de-aggregation of a new phthalocyanine-linked cytidine derivative

Synthesis and Characterization of Bulky Substituted Hemihexaphyrazines Bearing 2,6-Diisopropylphenoxy Groups

New substituted [30]trithiadodecaazahexaphyrines (hemihexaphyrazines) were synthesized by a crossover condensation of 2,5-diamino-1,3,4-thiadiazole with 4-chloro-5-(2,6-diisopropylphenoxy)- or 4,5-bis-(2,6-diisopropylphenoxy)phthalonitriles. The compounds were characterized by 1H-, 13C-NMR, including COSY, HMBC, and HSQC spectroscopy, MALDI TOF spectrometry, elemental analysis, IR and UV-Vis absorbance and fluorescence techniques.

Photochemical and photophysical properties of tetracarboxylic acid phthalocyanines from glycolic and lactic acids in homogeneous and micro heterogeneous media

Glycolic acid and lactic acid substituted zinc phthalocyanines were studied concerning their photophysical and photochemical properties in eight organic solvents (homogeneous medium) and in aqueous media with the presence of CTAB and PVP 360 surfactants. Solvent effects were investigated according to several physical solvent parameters, including studies that used more than one parameter at a time, such as the E_T(30) scale and the Lippet-Mataga equation. Computational studies were realized and was found in good agreement with experimental data indicating J-type dimers' formation through hydrogen bonds, which may not affect the spectroscopic properties. Fluorescence lifetimes were recorded using a time-correlated single-photon counting setup (TCSPC) technique. The direct method (analyzing the phosphorescence decay curves of singlet oxygen at 1270 nm) was employed to study singlet oxygen quantum yields. Phthalocyanine macrocycle with lactic acid substituent showed better solvation arrangement than the glycolic derivative, which can be explained based on the presence of the methyl group bonded to the chain. The water solvation of Pc's in the presence of cationic surfactant (CTAB) and biocompatible polymer PVP 360 increses the importance of this study for appliance in photodynamic therapy (PDT).

Synthesis and Applications of Porphyrin-Biomacromolecule Conjugates

With potential applications in materials and especially in light-responsive biomedicine that targets cancer tissue selectively, much research has focused on developing covalent conjugation techniques to tether porphyrinoid units to various biomacromolecules. This review details the key synthetic approaches that have been employed in the recent decades to conjugate porphyrinoids with oligonucleotides and peptides/proteins. In addition, we provide succinct discussions on the subsequent applications of such hybrid systems and also give a brief overview of the rapidly progressing field of porphyrin-antibody conjugates. Since nucleic acid and peptide systems vary in structure, connectivity, functional group availability and placement, as well as stability and solubility, tailored synthetic approaches are needed for conjugating to each of these biomacromolecule types. In terms of tethering to ONs, porphyrins are typically attached by employing bioorthogonal chemistry (e.g., using phosphoramidites) that drive solid-phase ON synthesis or by conducting post-synthesis modifications and subsequent reactions (such as amide couplings, hydrazide-carbonyl reactions, and click chemistry). In contrast, peptides and proteins are typically conjugated to porphyrinoids using their native functional groups, especially the thiol and amine side chains. However, bioorthogonal reactions (e.g., Staudinger ligations, and copper or strain promoted alkyne-azide cycloadditions) that utilize de novo introduced functional groups onto peptides/proteins have seen vigorous development, especially for site-specific peptide-porphyrin tethering. While the ON-porphyrin conjugates have largely been explored for programmed nanostructure self-assembly and artificial light-harvesting applications, there are some reports of ON-porphyrin systems targeting clinically translational applications (e.g., antimicrobial biomaterials and site-specific nucleic acid cleavage). Conjugates of porphyrins with proteinaceous moieties, on the other hand, have been predominantly used for therapeutic and diagnostic applications (especially in photodynamic therapy, photodynamic antimicrobial chemotherapy, and photothermal therapy). The advancement of the field of porphyrinoid-bioconjugation chemistry from basic academic research to more clinically targeted applications require continuous fine-tuning in terms of synthetic strategies and hence there will continue to be much exciting work on porphyrinoid-biomacromolecule conjugation.

Functional Systems Derived from Nucleobase Self-assembly

Dynamic and reversible non-covalent interactions endow synthetic systems and materials with smart adaptive functions that allow them to response to diverse stimuli, interact with external agents, or repair structural defects. Inspired by the outstanding performance and selectivity of DNA in living systems, scientists are increasingly employing Watson-Crick nucleobase pairing to control the structure and properties of self-assembled materials. Two sets of complementary purine-pyrimidine pairs (guanine:cytosine and adenine:thymine(uracil)) are available that provide selective and directional H-bonding interactions, present multiple metal-coordination sites, and exhibit rich redox chemistry. In this review, we highlight several recent examples that profit from these features and employ nucleobase interactions in functional systems and materials, covering the fields of energy/electron transfer, charge transport, adaptive nanoparticles, porous materials, macromolecule self-assembly, or polymeric materials with adhesive or self-healing ability.

Synthesis, characterization of new phthalocyanines and investigation of photophysical, photochemical properties and theoretical studies

This work describes the synthesis, spectral, aggregation and fluorescence properties of bis 4-[(4-tert-butylbenzyl)oxy substituted metal free (2), magnesium (3), zinc (4) and nickel (5) phthalocyanines. The syntheses of the novel compounds were confirmed by FT-IR, UV-vis, mass and NMR spectroscopy techniques, as well as elemental analysis. The effects of the nature of the central metal on the photophysical parameters of the phthalocyanine complexes are reported in this study. The photochemical properties (singlet oxygen quantum yields and photodegradation quantum yields) and photophysical properties (fluorescence behavior and fluorescence quantum yield) of the complexes were reported in different solutions (dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF) and tetrahydrofuran (THF)). However, energy minimized structure, vibrational frequency, molecular orbital levels and electronic absorption spectra were obtained by DFT calculations which supported the experimental results.

Aldehyde Substituted Phthalocyanines: Synthesis, Characterization and Investigation of Photophysical and Photochemical Properties

The new free and nickel phthalocyanine derivatives, tetrakis [(2-formylphenoxy)-phthalocyanine (4), tetrakis [(2-formylphenoxy)-phthalocyaninato]nickel(II) (5) have been synthesized via de-protection of tetra acetal-substituted phthalocyanines in acetic acid/FeCl3 system. The starting phthalocyanines, tetrakis [(2-(1,3-dioxolan-2-yl)phenoxy)-phthalocyanine (2) and tetrakis [(2-(1,3-dioxolan-2-yl)phenoxy)-phthalocyaninato]nickel (3), were prepared by the tetramerization of 4-(2-(1,3-dioxolan-2-yl) phenoxy) phthalonitrile (1). The new compounds have been characterized by the combination of FT-IR, (1)H NMR, UV-Vis, Mass spectra and elemental analysis. Compound 1 crystallizes in the Orthorhombic, space group Pbca with a = 9.2542 (4) Å, b = 13.3299 (5) Å, c = 23.2333 (11) Å, and Z = 8. Compound 1 is built up from two planar groups (phthalonitrile and phenoxy), with a dihedral angle of 69.693(36)° between them and non-planar dioxolane group. We report a combined experimental and theoretical study on molecule 1, as well. Geometric, spectroscopic and electronic properties of compound 1 has been calculated using B3LYP method and 6-311++G(dp) basis set. Fluorescence spectroscopy was applied to record the photoluminescence spectra of the prepared phthalocyanines and the photophysical and photochemical properties were examined in DMSO.

Silicon(IV) phthalocyanines substituted axially with different nucleoside moieties. Effects of nucleoside type on the photosensitizing efficiencies and in vitro photodynamic activities

A series of new silicon(IV) phthalocyanines (SiPcs) di-substituted axially with different nucleoside moieties have been synthesized and evaluated for their singlet oxygen quantum yields (ΦΔ) and in vitro photodynamic activities. The adenosine-substituted SiPc shows a lower photosensitizing efficiency (ΦΔ=0.35) than the uridine- and cytidine-substituted analogs (ΦΔ=0.42-0.44), while the guanosine-substituted SiPc exhibits a weakest singlet oxygen generation efficiency with a ΦΔ value down to 0.03. On the other hand, replacing axial adenosines with chloro-modified adenosines and purines can result in the increase of photogenerating singlet oxygen efficiencies of SiPcs. The formed SiPcs 1 and 2, which contain monochloro-modified adenosines and dichloro-modified purines respectively, appear as efficient photosensitizers with ΦΔ of 0.42-0.44. Both compounds 1 and 2 present high photocytotoxicities against HepG2 and BGC823 cancer cells with IC50 values ranging from 9nM to 33nM. The photocytotoxicities of these two compounds are remarkably higher than the well-known anticancer photosensitizer, chlorin e6 (IC50=752nM against HepG2 cells) in the same condition. As revealed by confocal microscopy, for both cell lines, compound 1 can essentially bind to mitochondria, while compound 2 is just partially localized in mitochondria. In addition, the two compounds induce cell death of HepG2 cells likely through apoptosis.

PyC60-naphthacrown system: a new supramolecular recognition element

Fulleropyrrolidine (PyC60) and a binaphthyl bridged crown ether macrocyclic receptor (1) undergoes spontaneous self-assembly phenomenon in solution to generate a new supramolecular recognition element having binding constant value of ∼5.83×10(4)dm(3)mol(-1). Lifetime measurement reveals a static quenching mechanism behind the deactivation of photoexcited state of 1 in presence of PyC60. The results obtained from this work would definitely reinforce bridged cyclic crown ether as one of the most suitable fragments for the molecular recognition of various macrocyclic receptor(s) in near future.

Spectroscopic and structural insights on molecular assembly consisting high potential zinc phthalocyanine photosensitizer attached to PyC60 through non-covalent interaction

Efforts to improve the ease of self-assembly formation through non-covalent interaction has led to the development of zinc phthalocyanine (zinc-2,9,16,23-tetra-tert-butyl phthalocyanine, i.e., ZnPc) as a high potential photosensitizer molecule towards C60 pyrrolidine tris-acid ethyl ester (PyC60) in toluene and 1,2-dichlorobenzene (DCB). Steady state fluorescence experiment elicits efficient quenching of the fluorescence intensity of both H2- and ZnPc in presence of PyC60. The average value of binding constant for PyC60/H2-Pc and PyC60/ZnPc systems in toluene (DCB) are determined to be 9910 (13,460) and 12,710 (24,060) dm(3) mol(-1), respectively. Lifetime experiment yields ∼3 times larger magnitude of charge separated rate constant for the PyC60/ZnPc system compared to PyC60/H2-Pc in toluene. Photoinduced energy transfer between PyC60 and H2- (/ZnPc) has been evidenced with nanosecond laser photolysis method; transient absorption studies establish that energy transfer from (T)PyC60(∗) to H2- and ZnPc occurs predominantly, as confirmed by the consecutive appearance of the triplet states of PyC60.

Effects of position (α or β) and linker heteroatom (O or S) of substituent on the photophysicochemical behavior of poly(oxyethylene) substituted ZnPcs and assessment of J-aggregation or protonation using TD-DFT computations

A series of zinc phthalocyanines (ZnPcs) tetra-substituted with 1,3-di[2-(2-ethoxyethoxy)ethoxy]-2-propanol () or 1,3-di[2-(2-ethoxyethoxy)ethoxy]-2-propanethiol () at peripheral (β) () and non-peripheral (α) () positions have been synthesized and characterized. The spectroscopic, photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen generation and photodegradation) properties of these newly synthesized phthalocyanines have been investigated in DMSO. The effects of the position of the substituents on the phthalocyanine skeleton and the nature of the linker heteroatom on their spectroscopic, photophysical and photochemical properties have been determined. The quenching behavior of the zinc phthalocyanines by 1,4-benzoquinone has been studied in DMSO. All of the zinc(ii) Pc complexes ( and ) showed similar electronic absorption spectra in various solvents (chloroform, dichloromethane, DMF, DMSO, THF and toluene). However, complex gave an extra red-shifted band at 742 nm in chloroform and dichloromethane. DFT and TD-DFT computations were performed on the model structures (, and ) to find out the cause of the extra red-shifted Q band (J-type aggregation or protonation of the Pc ring). The computational results showed that monoprotonation of a meso nitrogen atom leads to the formation of this extra band. Photophysical and photochemical measurements indicated that these newly synthesized ZnPc derivatives are promising candidates for use as photosensitizers in the application of PDT.

Role of charge transfer interaction and the chemical physics behind effective fulleropyrrolidine/porphyrin non-covalent interaction in solution

The present paper reports the photophysical insights on supramolecular interaction of a monoporphyrin derivative, namely, 1, with C60 pyrrolidine tris-acid ethyl ester (PyC60) in toluene and benzonitrile. The ground state interaction between PyC60 and 1 is facilitated through charge transfer interaction. Both UV-Vis and steady state measurements elicit almost similar magnitude of binding constant for the PyC60/1 complex in toluene and benzonitrile, viz., 6825 and 6540 dm(3 )mol(-1), respectively. Life time measurement evokes that rate of charge separation is fast in benzonitrile. Both hybrid-DFT and DFT calculations provide very good support in favor of electronic charge-separation in PyC60/1 system in vacuo.

Photophysical investigations on determination of molecular structure and binding strength of supramolecular complexation between fulleropyrrolidine and a designed bisporphyrin in solution

The present article reports, for the first time, the photophysical aspects of non-covalent interaction of a fullerene derivative, namely, C60 pyrrolidine tris-acid ethyl ester (PyC60) with a designed bisporphyrin (1) (having carbazole spacer unit) in toluene. Absorption spectrophotometric studies reveal that decrease in the absorption intensity of the Soret absorption band of 1 takes in presence of PyC60 in the solvent studied. Steady state fluorescence studies reveal efficient quenching of fluorescence intensity of 1 in presence of PyC60. Static quenching model explores a binding constant (KS) value of 2,910 dm(3) mol(-1) in toluene. Time resolved emission study establishes static quenching mechanism for the investigated supramolecule in non-polar solvent. Molecular mechanics calculations in vacuo evoke the single projection structure of the PyC60-1 complex and interpret the geometrical arrangement of both PyC60 and 1 during non-covalent complexation.

A series of asymmetrical phthalocyanines: synthesis and near infrared properties

We report here the preparation of asymmetrical phthalocyanine dimers 1a–3a, which are endowed with novel charge transfer bands at 1,151–1,154 nm and strong NIR luminescences at 840–860 nm and 1,600–1,650 nm. Through H-bonding interaction, 1a–3a are inclined to self-assemble into hexrod nanotubes at the interface of CHCl₃ and CH₃OH. Our results provide further insights into the interaction in molecular dimers, and suggest that 1a–3a have potential application in magnets and supramolecular architectures.

Fully protected glycosylated zinc (II) phthalocyanine shows high uptake and photodynamic cytotoxicity in MCF-7 cancer cells

Phthalocyanine photosensitizers are effective in anticancer photodynamic therapy (PDT) but suffer from limited solubility, limited cellular uptake and limited selectivity for cancer cells. To improve these characteristics, we synthesized isopropylidene-protected and partially deprotected tetra β-glycosylated zinc (II) phthalocyanines and compared their uptake and accumulation kinetics, subcellular localization, in vitro photocytotoxicity and reactive oxygen species generation with those of disulfonated aluminum phthalocyanine. In MCF-7 cancer cells, one of the compounds, zinc phthalocyanine {4}, demonstrated 10-fold higher uptake, 5-fold greater PDT-induced cellular reactive oxygen species concentration and 2-fold greater phototoxicity than equimolar (9 μm) disulfonated aluminum phthalocyanine. Thus, isopropylidene-protected β-glycosylation of phthalocyanines provides a simple method of improving the efficacy of PDT.

A comparative study on photophysical and photochemical properties of zinc phthalocyanines with different molecular symmetries

The five possible non-peripherally substituted zinc(II) phthalocyanines with different molecular symmetries (Pc1–Pc5) were synthesized from statistical condensation of the phthalonitrile derivatives (A and B). 2-[2-(2-ethoxyethoxy)ethoxy]-1-[2-((2-ethoxyethoxy)-ethoxy)ethoxymethyl]ethyloxy and 2′-[(tert-butoxycarbonyl)amino]ethoxy groups were used as substituents. The structures of the new compounds were characterized using elemental analysis and spectroscopic data including IR, 1H and 13C NMR, electronic absorption and mass spectra. The photophysical and photochemical properties of these new compounds were investigated in DMSO. The effect of the molecular symmetry of phthalocyanine molecules on the photophysical and photochemical properties was compared in this study.

Alkynyl-substituted phthalocyanines: versatile building blocks for molecular materials synthesis

Phthalocyanines are an interesting class of aromatic macrocycles which possess unique physical and chemical properties that make them excellent building blocks for the construction of molecular materials. Among the different functional groups that can be incorporated into the phthalocyanine's skeleton, the alkynyl group is one of the most interesting; this is confirmed by the large number of organic synthetic materials constructed from acetylene-based scaffolds due its rigidity and linearity, allowing high exciton and electron coupling between chromophore units. Additionally, these systems are particularly important, considering the wide range of functional group interconversions that the triple bond may permit. This account represents a concise overview of the most important contributions on the synthesis and applications of mono- and poly-alkynyl-substituted phthalocyanine-based molecular systems, towards the development of new functional molecular materials.

Synthesis and optical properties of tetrapyrazino-porphyrazines containing camphorquinone group

2,3-dicyanopyrazine and metallophthalocyanines were synthesized with magnesium containing (±)camphorquinone substituent. 2,3-dicyanopyrazine was prepared by condensation reaction of diaminomaleonitrile (DAMN) with 1,7,7-trimethylbicyclo[2.2.1]heptane-2,3-dione (1). The tetrapyrazinoporphyrazine was characterized by a combination of UV-visible spectroscopy, fluorescence spectroscopy, infrared radiation, elemental analysis, MALDI-TOF-MS and 1H NMR spectroscopy.

Photocontrollable J-aggregation of a diarylethene-phthalocyanine hybrid and its aggregation-stabilized photochromic behavior

The photocontrollable J-aggregation of a diarylethene-phthalocyanine hybrid (T-ZnPc) and its aggregation-stabilized photochromic behavior were investigated by various techniques. T-ZnPc initially exhibited slight J-aggregation tendency in solvents such as chloroform and toluene through conformational planarization effect, but formed much stronger J-aggregates upon the illumination of 254 nm UV light. In darkness, the UV-irradiated solutions gradually returned to their initial state. These phenomena can be explained by the pronounced change in molecular planarity accompanying the reversible isomerization of the diarylethene units of T-ZnPc. Besides, we have found that the thermal stability of the closed-ring diarylethene isomers in molecularly dispersed T-ZnPc is much poorer than that in aggregates. As long as the aggregates were broken, they converted to corresponding open-ring form instantly. This study provided an example of fully photocontrollable aggregation of phthalocyanines and paved a new way for improving the stability of the photochromic systems.

Electrochemical and in situ Spectroelectrochemical Properties of Phthalocyanines Bearing N-Benzyl-4-Phenyloxyacetamide Moieties

The general redox behaviour of phthalocyanines bearing N-benzyl-4-phenyloxyacetamide moieties (H2Pc, ZnPc, NiPc, CuPc, and CoPc) has been identified by cyclic voltammetry and differential pulse voltammetry on Pt in dimethylsulfoxide/tetrabutylammonium perchlorate. These measurements showed that the complexes indicate subsequent one-electron reduction and oxidation processes. Although the voltammetric measurements implied the association of the redox processes of some complexes with aggregation phenomenon, the complete evaluation of the aggregation effects by only these measurements was not possible. In situ UV-Vis spectroelectrochemical measurements enabled us to assign the ligand- and metal-based redox processes, and identify if the aggregation affects these processes. These measurements suggested that the redox processes of H2Pc, NiPc, and CuPc are coupled by aggregation phenomenon, while those of ZnPc and especially CoPc are not, probably due to the difference in their axial coordinating properties.

Interactions of cytidine with N2-functionalized guanosines and cytidine – cytidine exchange involving a GC pair — NMR and fluorescence spectroscopic study

Two N2-functionalized guanosines by diphenylaminobiphenyl and di(2-pyridyl)aminobiphenyl have been found to act as the effective probes for G–C interactions in organic media. Because of the highly emissive nature of the N2-functionalized guanosines in the visible region, the GC base pair formation event accompanied by distinct fluorescence quenching can be readily monitored by fluorescence spectroscopy. NMR and fluorescence results confirm that the N2-arylguanosines form H-bonded pairs with cytidine, selectively. An unusual exchange pathway between non-bound cytidine and bound cytidine, in the GC pair, has been identified and extensively studied by NMR methods.