In Vitro Demonstration of the Heavy-Atom Effect for Photodynamic Therapy

Red/near-infrared boron-dipyrromethene dyes as strongly emitting fluorophores

We present an overview of the state of the art in long-wavelength boron-dipyrromethene (BODIPY) fluorophores, focusing on strategies to shift the absorption and emission bands into the red/near-infrared (NIR) range of the spectrum. This report also discusses chemical modifications of the chromophoric core to obtain analyte-responsive fluorophores, including examples of pH and metal ion indicators. Finally, we present a new series of phenanthrene-fused BODIPY dyes, emitting with high efficiency in the red/NIR region of the spectrum, as well as discussing potential applications thereof as probes.

Functionalized BF(2) Chelated Azadipyrromethene Dyes

Fluorescent molecules that emit in the near infra-red are potentially useful as probes for biotechnology. A relatively under-explored design for probes of this type are the aza-BODIPY dyes; this study was performed to enhance our understanding of these materials and ways in which they may be used in dye cassette systems. Thus, the aza-BODIPY dyes 1a - g were prepared. An advanced intermediate towards an eighth compound in the series, 6h, was made but it could not be complexed with boron effectively to give 1h. Spectroscopic properties of these compounds were recorded, and correlations between substituent effects, UV absorbance, fluorescence emissions, and quantum yields were made. Compound 1a was coupled with a fluorescein-alkyne derivative to give the energy transfer cassettes 2 and 3. Both these compounds gave poor energy transfer, and the possible reasons for this were discussed.

The chemistry of fluorescent bodipy dyes: versatility unsurpassed

The world of organic luminophores has been confined for a long time to fairly standard biological labeling applications and to certain analytical tests. Recently, however, the field has undergone a major change of direction, driven by the dual needs to develop novel organic electronic materials and to fuel the rapidly emerging nanotechnologies. Among the many diverse fluorescent molecules, the Bodipy family, first developed as luminescent tags and laser dyes, has become a cornerstone for these new applications. The near future looks extremely bright for "porphyrin's little sister".

Synthesis, Photophysical Properties, and Laser Behavior of 3-Amino and 3-Acetamido BODIPY Dyes

The asymmetrically substituted BODIPY dyes 9a and 9b have been synthesized through a key redox step involving the alpha-nitroso derivative of the starting pyrrol. Both dyes emit fluorescence with quantum yields of ca. 0.7, but only 8b behaves as a good laser dye, with an efficiency of 48% in ethanol solution.

Luminescent, Three-Coordinate Azadipyrromethene Complexes of d10 Copper, Silver, and Gold

Boron azadipyrromethenes are red-light-absorbing dyes with chromophoric capabilities deriving from a conjugated, chelating framework. Reported here are tricoordinate copper(I), silver(I), and gold(I) complexes of a tetraphenylazadipyrromethene ligand. The new complexes are characterized by optical absorption and emission spectroscopy, multinuclear NMR, mass spectrometry, elemental analysis, and X-ray diffraction crystallography. Time-dependent density functional theory calculations indicate that the principal absorption features in azadipyrromethene complexes result from optically allowed intraligand transitions that undergo configuration interaction.

Near-infrared sensing properties of dimethlyamino-substituted BF2-azadipyrromethenes

[reaction: see text] The synthesis and sensing characteristics of a new class of organic colorimetric and fluorometric chemosensor which operates in the 850-650 nm spectral region is outlined. Judicious placing of amine substituents on the BF2-chelated tetraarylazadipyrromethene chromophore generates a triple absorption and emission responsive sensor. Dramatic pH responsive absorption and fluorescence changes can be observed across a broad acidity range, from pH 5 to 6 M HCl, in conjunction with a visible colorimetric change from red to purple to blue.

Structures and electronic absorption spectra of a recently synthesised class of photodynamic therapy agents

A theoretical study was performed on a novel class of boron-containing molecules (various substituted tetraarylazadipyrromethenes), which show in vitro activity for application in photodynamic therapy. Geometric optimisation of the structures for the singlet and triplet electronic states was carried out on compounds in vacuo at the density functional level of theory, by employing the PBE0 hybrid functional and the split-valence plus polarisation basis set. The absorbance properties in the UV-visible region were examined by means of time-dependent density functional response theory, using the same functional as mentioned above. To evaluate the influence of the solvent on the excitation energies, the continuum polarisable model was applied. Calculated electronic excitations, such as those regarding the Q-like band, were found to be in good agreement (within 0.01-0.1 eV) with experimental values and experimental trends on changing both the substituents and solvent.

Conformationally restricted aza-BODIPY: highly fluorescent, stable near-infrared absorbing dyes

Novel NIR fluorescent, conformational restricted aza-dipyrromethene boron difluoride (aza-BODIPY) dyes were prepared by an efficient process. Such conformational restricted aza-BODIPY dyes possess intense absorption, strong fluorescence, high chemical and photostability. Additionally, the sharp fluorescence of non-amine containing aza-BODIPY dyes is insensitive to solvent polarity.

Highly Photocytotoxic Glucosylated Silicon(IV) Phthalocyanines. Effects of Peripheral Chloro Substitution on the Photophysical and Photodynamic Properties

Two novel glucoconjugated silicon(IV) phthalocyanines (compounds 3 and 4) have been prepared and examined for their photophysical and biological properties. With two axial 1,2:5,6-di-O-isopropylidene-alpha-d-glucofuranose substituents linked to the silicon center through the tetraethylene glycol chain, both compounds are highly soluble and remain nonaggregated in N,N-dimethylformamide. The dichloro-substituted phthalocyanine 4 exhibits a weaker fluorescence emission and higher efficiency to generate singlet oxygen compared with the nonchlorinated counterpart 3 as a result of the heavy atom effect. Both compounds are highly photocytotoxic against HT29 human colorectal carcinoma and HepG2 human hepatocarcinoma cells, particularly the nonchlorinated phthalocyanine 3, of which the IC50 values are as low as 6 nM. The lower photodynamic activity of the chlorinated derivative (IC50 = 17-21 nM) can be attributed to its higher aggregation tendency in the biological media, leading to a lower efficiency to generate reactive oxygen species inside the cells. Fluorescence microscopic studies have also revealed that compound 3 has a high and selective affinity to the lysosomes, but not the mitochondria, of HT29 cells.

Bis(2-pyridyl)-substituted boratriazaindacene as an NIR-emitting chemosensor for Hg(II)

Aryl-substituted boratriazaindacenes (Aza-Bodipy's) are a new class of dyes with long wavelength absorption and emissions. We now report the first application of these dyes in metal ion sensing. 2-Pyridyl substituents at positions 1 and 7 create a well-defined pocket for metal ion binding. The chemosensor described here is selective for Hg(II) ions, and both absorption and emission spectra display large changes that would allow ratiometric sensing. [reaction: see text].

Avaliação da atividade fotodinâmica de porfirinas para uso em terapia fotodinâmica através da fotoxidação de triptofano

Neste trabalho investigou-se a atividade fotodinâmica de octaetilporfirina (OEP), octaetilporfirina de vanadil (VOOEP) e meso-tetramesitilporfirina (m-TMP). Este estudo foi realizado através da determinação da constante da velocidade de fotoxidação (k f) do aminoácido triptofano (Trp). A participação do oxigênio singlete nesta fotoxidação foi determinada através da adição de azida de sódio e água deuterada no meio de reação. Os valores de k f/10-4s-1 para a fotoxidação de Trp demonstraram que OEP (2,80 ± 0.05) é mais eficiente do que m-TMP (1,62 ± 0,07) e VOOEP (0,81 ± 0,08). Os valores de k f foram menores na presença de azida de sódio e maiores na presença de água deuterada, sugerindo que o oxigênio singlete é o responsável pela atividade fotodinâmica de OEP, VOOEP e m-TMP. Estes resultados sugerem também que as diferenças na atividade fotodinâmica entre as porfirinas podem ser associadas com as diferenças na estrutura molecular das mesmas. A presença do grupo vanadil (V=O) interfere claramente na atividade fotodinâmica de OEP causando considerável redução na sua eficiência.

Enhancement of Two-Photon Absorption Cross-Section and Singlet-Oxygen Generation in Porphyrins upon β-Functionalization with Donor−Acceptor Substituents

The microwave-enhanced synthesis, comparative singlet oxygen sensitization efficiency, and nonlinear optical characterization of a new beta-functionalized porphyrin and its copper complex are described. We show that the introduction of a donor-acceptor push-pull conjugated fragment in the beta position strongly perturbs the porphyrin electronic structure leading to a remarkable one- and two-photon NIR absorption enhancement.

2-Amino-3,4-diethylpyrrole derivatives: new building blocks for coiled structures

The synthesis of a multicomponent, mixed oligomer containing alpha-aminopyrrole is described; this system adopts a coiled structure in the solid state and serves as a prototype of a possible new class of hydrogen bond based helicates.

Supramolecular photonic therapeutic agents

A new approach to achieving selectivity for photodynamic therapy based upon the reversible off/on switching of the key therapeutic property (singlet oxygen generation) of a supramolecular photonic therapeutic agent (SPTA) in response to an external stimulus in the surrounding microenvironment is described. A series of SPTA analogues with pH responsive receptors of varying pKa are presented, in which the generation of singlet oxygen is shown to be dependent upon a proton source. For example, systems have been constructed such that the excited state energy of the photosensitizer can be decayed by a rapid photoinduced electron transfer (PET) mechanism, resulting in virtually no singlet oxygen being generated, but when the amine receptor is protonated the PET mechanism does not operate and singlet oxygen is produced. In vitro efficacy demonstrated that the SPTA derivatives can be activated within cells and one analogue is measured to have an EC50 value of 5.8 nM when assayed in the MRC5 cell line.

Impact of a conformationally restricted receptor on the BF2 chelated azadipyrromethene fluorosensing platform

Conformational control of the receptor-fluorophore orientation of BF2 chelated azadipyrromethene sensors reveals two photophysically different modes of analyte triggered fluorescence switching both of which exhibit large off-on fluorescence intensity responses to the light input-output of the sensors in the visible red spectral region.

Water soluble distyryl-boradiazaindacenes as efficient photosensitizers for photodynamic therapy

We introduce a novel class of water soluble, extended conjugation boradiazaindacene dyes which are efficient singlet oxygen generators and have spectacular photoinduced cytotoxicity when excited in the "therapeutic window" of the electromagnetic spectrum.

PET modulated fluorescent sensing from the BF2 chelated azadipyrromethene platform

A convergent building block synthesis has been applied to new off/on photoinduced electron transfer (PET) modulated fluorescent sensors which are based on a BF(2) chelated tetraarylazadipyrromethene platform and operate in the biomedically important red region of the visible spectrum. Incorporation of diethylamine and morpholine receptors facilitates off/on microenvironment polarity and pH sensing. Aqueous formulation and in vitro cellular imaging demonstrates their potential for intracellular sensing.

A modular synthesis of unsymmetrical tetraarylazadipyrromethenes

[reaction: see text] A stepwise route to unsymmetrical tetraarylazadipyrromethenes by a condensation of 2,4-diaryl-5-nitroso-pyrroles with 2,4-diarylpyrroles is described. This modular building-block approach allows for the introduction of up to four different aryl substituents on the azadipyrromethene and is tolerant of a varied substituent set. An efficient synthesis of the 2,4-diarylpyrroles building blocks from 1,3-diaryl-4-nitro-butan-1-ones by nitro hydrolysis to a keto-aldehyde and subsequent ammonia condensation reaction has been achieved. The facile conversion of 2,4-diarylpyrroles into their alpha-nitroso analogues by their reaction with sodium nitrite generated the second building block required for the synthesis.

New π-Extended Water-Soluble Squaraines as Singlet Oxygen Generators

[graph: see text] Condensation of squaric acid with a number of differently substituted 2-pyrrolyl derivatives afforded three new classes of squaraines. Their sharp and intense absorption bands in the biological window (700-900 nm), inherent singlet oxygen generation capabilities, together with proper functionalization allowing good water solubility make them suitable candidates as new non-porphyrinic singlet oxygen photosensitizers for photodynamic therapy (PDT).

Water-Soluble Green Perylenediimide (PDI) Dyes as Potential Sensitizers for Photodynamic Therapy

[reaction: see text] A series of water-soluble green perylenediimide (PDI) dyes have been synthesized. On red light excitation, these dyes were shown to be efficient generators of singlet oxygen, and in cell culture media, they were shown to display significant light-induced cytotoxic effects on the human erythroleukemia cell line (K-562). It appears that highly versatile PDI dyes are likely to find new applications in photodynamic therapy.

Two-photon absorption in solution by means of time-dependent density-functional theory and the polarizable continuum model

We present the first study of two-photon absorption (TPA) of solvated molecules based on direct evaluation of TPA cross sections from the quadratic response of time-dependent perturbations. A set of prototypical two-photon (TP) chromophores has been selected and analyzed: a pure pi system (t-stilbene) and its substituted homologs obtained employing a donor (D) and an acceptor (A) group to probe the solvent effects along the series pi, D-pi-D, A-pi-D, and A-pi-A. For the selected systems we have calculated the TPA cross sections in different environments by means of the polarizable continuum model. The data have been analyzed to evaluate how the structural and environmental parameters contribute to the final two-photon absorption cross section. These include molecular structure, geometry relaxation in solution, polarity, and refractive index of the solvent. The performances of the three common functionals SVWN, BLYP, and B3LYP have been compared. The results show a significant solvent dependence of the TPA cross section and an unusual trend when passing from cyclohexane to water. The data have also been rationalized in terms of the main orbital excitations leading to the transitions. Finally, trends along the series have been described and comparison with experiments and previous calculations has been drawn.

A potent nonporphyrin class of photodynamic therapeutic agent: cellular localisation, cytotoxic potential and influence of hypoxia

We have developed a totally new class of nonporphyrin photodynamic therapeutic agents with a specific focus on two lead candidates azadipyrromethene (ADPM)01 and ADPM06. Confocal laser scanning microscopy imaging showed that these compounds are exclusively localised to the cytosolic compartment, with specific accumulation in the endoplasmic reticulum and to a lesser extent in the mitochondria. Light-induced toxicity assays, carried out over a broad range of human tumour cell lines, displayed EC₅₀ values in the micro-molar range for ADPM01 and nano-molar range for ADPM06, with no discernable activity bias for a specific cell type. Strikingly, the more active agent, ADPM06, even retained significant activity under hypoxic conditions. Both photosensitisers showed low to nondeterminable dark toxicity. Flow cytometric analysis revealed that ADPM01 and ADPM06 were highly effective at inducing apoptosis as a mode of cell death. The photophysical and biological characteristics of these PDT agents suggest that they have potential for the development of new anticancer therapeutics.