THE EFFECT OF FLUORIDE ON BINDING and PHOTODYNAMIC ACTION OF PHTHALOCYANINES WITH PROTEINS

Fluoride inhibits chloroaluminum phthalocyanine tetrasulfonate (AlPcS)-induced photohemolysis when added to dye loaded cells prior to light exposure. The mechanism by which F- exerts this effect was studied by measuring the binding of phthalocyanine (Pc) to various proteins in the absence and presence of F-. Parallel measurements were made of the photodynamic action under these conditions. Fluoride reduced the binding to proteins of AlPcS and CoPcS. The binding of CuPcS, ZnPcS and H2PcS was not affected. When bound to bovine serum albumin and exposed to light, H2Pc, ZnPc and AlPcCl were bleached at a biphasic rate. Only the photobleaching of AlPcCl was affected by F-. The effect of F- was to inhibit the initial rapid phase without affecting the slower phase. In the presence of D2O only the second phase of photobleaching was enhanced, in the absence or presence of F-. No effect of F- was observed on tryptophan photooxidation or glyceraldehyde-3-phosphate dehydrogenase photoinactivation by AlPcS. Crosslinking of spectrin monomers photosensitized by AlPcS was inhibited by F- in parallel with the reduced binding of dye to the protein. It is concluded that F- exerts its effect by complexing with metal ligands of Pc. As a result, the dye may be released from the protein or the binding mode may be changed in such a way that effective photochemistry is prevented. Primary photophysical processes of Pc most probably are not affected by F-.     

Photodynamic efficacy of chlorin p6: a pH dependent study in aqueous and lipid environment

Photodynamic efficacy of chlorin p6, a potential candidate of photodynamic therapy (PDT), has been studied at pH 5.0, 6.0 and 7.6 in aqueous and lipid environment. Increased chlorin p6 mediated photodynamic bleaching of N,N-dimethyl-4-nitrosoaniline (RNO), a measure of singlet oxygen yield, was obtained at higher pH. Rate of photodynamic bleaching of RNO was also higher at higher pH and the rate decreased with lowering in pH of irradiated solution. Photodynamic oxidation of tryptophan was also found to be higher at higher pH. Diminished oxidation of RNO was obtained with decrease in pH of irradiated solution. Both, RNO bleaching and tryptophan oxidation was significantly reduced by sodium azide, a known quencher of singlet oxygen. At lower pH, chlorin p6 mediated photodynamic malondialdehyde (MDA) and lipid hydroperoxide formation in egg lecithin liposome was higher. At higher pH chlorin p6 was found to be photodynamically more effective in aqueous environment whereas at lower pH chlorin p6 was photodynamically more effective in hydrophobic environment.     

Photobleaching Kinetics and Effect of Solvent in the Photophysical Properties of Indocyanine Green for Photodynamic Therapy

Indocyanine green is an attractive molecule for photodynamic therapy due to its near infrared absorption, resulting in a higher tissue penetration. However, its quantum yields of the triplet and singlet state have been reported to be low and then, reactive oxygen species are unlikely to be formed. Aiming to understand the ICG role in photodynamic response, its photobleaching behavior in solution has been studied under distinct conditions of CW laser irradiation at 780 and 808 nm, oxygen saturations and solvents. Sensitizer bleaching and photoproduct formation were measured by absorption spectroscopy and analyzed using the PDT bleaching macroscopic model to extract physical parameters. ICG photobleaching occurs even at lower oxygen concentrations, indicating that the molecule presents more than one way of degradation. Photoproducts were produced even in solution of less than 4 % oxygen saturation for both solvents and excitation wavelengths. Also, the amplitude of absorption related to J-dimers was increased during irradiation, but only in 50 % PBS solution. The formation of photoproducts was enhanced in the presence of J-type dimers under low oxygen concentration, and the quantum yields of triplet and singlet states were one order of magnitude and two times higher, respectively, when compared to ICG in distilled H₂O.     

Photodamage in a Mitochondrial Membrane Model Modulated by the Topology of Cationic and Anionic Meso‐Tetrakis Porphyrin Free Bases

The photodynamic effects of the cationic TMPyP (meso‐tetrakis [N‐methyl‐4‐pyridyl]porphyrin) and the anionic TPPS4 (meso‐tetrakis[4‐sulfonatophenyl]porphyrin) against PC/CL phosphatidylcholine/cardiolipin (85/15%) membranes were probed to address the influence of phorphyrin binding on lipid damage. Electronic absorption spectroscopy and zeta potential measurements demonstrated that only TMPyP binds to PC/CL large unilamellar vesicles (LUVs). The photodamage after irradiation with visible light was analyzed by dosages of lipid peroxides (LOOH) and thiobarbituric reactive substance and by a contrast phase image of the giant unilamellar vesicles (GUVs). Damage to LUVs and GUVs promoted by TMPyP and TPPS4 were qualitatively and quantitatively different. The cationic porphyrin promoted damage more extensive and faster. The increase in LOOH was higher in the presence of D₂O, and was impaired by sodium azide and sorbic acid. The effect of D₂O was higher for TPPS4 as the photosensitizer. The use of DCFH demonstrated that liposomes prevent the photobleaching of TMPyP. The results are consistent with a more stable TMPyP that generates long‐lived singlet oxygen preferentially partitioned in the bilayer. Conversely, TPPS4 generates singlet oxygen in the bulk whose lifetime is increased in D₂O. Therefore, the affinity of the porphyrin to the membrane modulates the rate, type and degree of lipid damage.     

Photodynamic Therapy: Tumor Targeting with Adenoviral Proteins

A brief summary of the mechanisms involved in photodynamic therapy (PDT) and the role of delivery vehicles for photosensitizer targeting is addressed. Phthalocyanines (Pc) have been coupled to adenovirus type 2 capsid proteins including the hexon, the penton base and the fiber to enhance their target selectivity. Adenovirus penton base proteins contain the arginine-glycine-aspartic acid peptidic sequence (RGD) motif known to bind with great affinity and high specificity to integrin receptors, expressed by several types of cancer. Tetrasulfonated aluminum phthalocyanine (AlPcS4) was covalently coupled to the various capsid proteins via one or two caproic acid spacer chains (A1 or A2) in 7:1 up to 66:1 molar ratios. The capacity of the bioconjugates for singlet oxygen production, as measured by an L-tryptophan oxidation assay, was strongly reduced, likely reflecting scavenging by the carrier. Cell adsorption and in vitro photocytotoxicity assays were carried out using the A549 and HEp2 human cell lines expressing integrin receptors, and one murine, the EMT-6 cell line, which lacks receptors for the RGD sequence. The AlPcS4A2-protein complexes induced greater cytotoxicity as compared to the analogous AlPcS4A1 preparations. The penton base-AlPcS4A2 derivative was the more phototoxic for all cell lines tested. Tumor response studies using Balb/c mice with EMT-6 tumor implants demonstrated that the free AlPcS4A2 induced complete tumor regression at a dose of 1 mumol/kg and 400 J/cm2, which is comparable to the activity of the known AlPcS2adj. A mixture of adenovirus type 2 soluble proteins covalently labeled with AlPcS4A2 required 0.5 mumol/kg to induce the same response with the same light dose, suggesting that the high affinity RGD/receptor complex is able to target Pc for PDT.     

Photooxidation of Tetrahydrobiopterin under UV Irradiation: Possible Pathways and Mechanisms

Tetrahydrobiopterin (H₄Bip) is a cofactor for several key enzymes, including NO synthases and aromatic amino acid hydroxylases (AAHs). Normal functioning of the H₄Bip regeneration cycle is extremely important for the work of AAHs. Oxidized pterins may accumulate if the H₄Bip regeneration cycle is disrupted or if H₄Bip autoxidation occurs. These oxidized pterins can photosensitize the production of singlet molecular oxygen ¹O₂ and thus cause oxidative stress. In this context, we studied the photooxidation of H₄Bip in phosphate buffer at pH 7.2. We found that UV irradiation of H₄Bip affected its oxidation rate (quantum yield Φ₃₀₀ = (2.7 ± 0.4) × 10^?3). The effect of UV irradiation at λ = 350 nm on H₄Bip oxidation was stronger, especially in the presence of biopterin (Bip) (Φ₃₅₀ = (9.7 ± 1.5) × 10^?3). We showed that the rate of H₄Bip oxidation linearly depends on Bip concentration. Experiments with KI, a selective quencher of triplet pterins at micromolar concentrations, demonstrated that the oxidation is sensitized by the triplet state biopterin ³Bip. Apparently, electron transfer sensitization (Type‐I mechanism) is dominant. Energy transfer (Type‐II mechanism) and singlet oxygen generation play only a secondary role. The mechanisms of H₄Bip photooxidation and their biological meaning are discussed.     

Investigation of photobleaching of hypocrellin B in non-polar organic solvent and in liposome suspension

Hypocrellin B (HB) is a natural pigment with a promising application in the photodynamic therapy (PDT) for anticancer treatment. The photobleaching of HB in non-polar organic solvents and in liposomes in aqueous solution were investigated by the measurements of absorption spectra, quenching experiments and determination of photoproducts. Control experiments indicated that the sensitizer, oxygen and light were all essential for the photobleaching of HB, which suggested that it was mainly self-sensitized photooxidation. The illumination of HB with visible light in aerobic non-polar solvent generated singlet oxygen efficiently [Phi(1O(2))=0.76] which then attacked the sensitizer HB with formation of an endoperoxide product. The endoperoxide of HB was unstable at room temperature and underwent predominantly loss of singlet oxygen with regeneration of parent HB. The singlet oxygen released from the endoperoxide of HB was detected with chemical trapping experiments. When HB was embedded in EPC liposomes, no endoperoxide product and no singlet oxygen release from the photobleaching process of HB were detected. The quenching experiments indicated that the singlet oxygen mechanism (type II) played an important role in the non-polar solvent and the free radical mechanism (type I) was predominant in liposomal aqueous solution for the photobleaching of HB.     

Studies on the photooxidation mechanism of polymers. V. Oxidation of polybutadienes by singlet oxygen from microwave discharge and in dye-photosensitized reactions

The singlet oxygen oxidation of cis- and trans- 1,4-polybutadienes was studied by using singlet oxygen generated in a microwave generator and in dye-photosensitized reactions of these polymers in the solid state and in solution. It was shown that the reactions of singlet oxygen result in formation of hydroperoxide groups, whereas ultraviolet oxidation by molecular oxygen in addition leads to formation of carbonyl groups. During dye-photosensitized oxidation of polydienes in benzene solution, a very rapid decrease in the molecular weight was observed.     

The Triplet State of 6‐thio‐2′‐deoxyguanosine: Intrinsic Properties and Reactivity Toward Molecular Oxygen

Thiopurine prodrugs are currently among the leading treatment options for leukemia, immunosuppression, and arthritis. Patients undergoing long‐term thiopurine treatment are at a higher risk of developing sunlight‐induced skin cancers than the general population. This side effect originates from the cellular metabolization of thiopurine prodrugs to form 6‐thio‐2′‐deoxyguanosine, which can absorb UVA radiation, populating its reactive triplet state and leading to oxidatively generated damage. However, the photo‐oxidation mechanism is not fully understood. In this contribution, the oxidation potential and the adiabatic triplet energy of 6‐thio‐2′‐deoxyguanosine are estimated computationally, whereas the intrinsic rate of triple‐state decay and the rate constant for triplet quenching by molecular oxygen are determined using time‐resolved spectroscopic techniques. A singlet oxygen quantum yield of 0.24 ± 0.02 is measured in aqueous solution (0.29 ± 0.02 in acetonitrile). Its magnitude correlates with the relatively low percentage of triplet‐O₂ collision events that generate singlet oxygen (S_Δ = 37%). This behavior is rationalized as being due to the exergonic driving force for electron transfer between the triplet state of 6‐thio‐2′‐deoxyguanosine and molecular oxygen (ΔG_ET = ?69.7 kJ mol^?1), resulting in the formation of a charge‐transfer complex that favors nonradiative decay to the ground state over triplet energy transfer.     

Redox Properties of the Iron Complexes of Orally Active Iron Chelators CP20, CP502, CP509, and ICL670

Redox cycling of iron is a critical aspect of iron toxicity. Reduction of a low‐molecular‐weight iron(III)‐complex followed by oxidation of the iron(II)‐complex by hydrogen peroxide may yield the reactive hydroxyl radical (OH^.) or an oxoiron(IV) species (the Fenton reaction). Complexation of iron by a ligand that shifts the electrode potential of the complex to either to far below ?350 mV (dioxygen/superoxide, pH=7) or to far above +320 mV (H₂O₂/HO^., H₂O pH=7) is essential for limitting Fenton reactivity. The oral chelating agents CP20, CP502, CP509, and ICL670 effectively remove iron from patients suffering from iron overload. We measured the electrode potentials of the iron(III) complexes of these drugs by cyclic voltammetry with a mercury electrode and determined the dependence on concentration, pH, and stoichiometry. The standard electrode potentials measured are ?620 mV, ?600 mV, ?535 mV, and ?535 mV with iron bound to CP20, ICL670, CP502, and CP509, respectively, but, at lower chelator concentrations, electrode potentials are significantly higher.     

Photosensitized oxidation of hypoxanthine and xanthine by aluminum phthalocyanine tetrasulfonate. Role of the alkylating quinone 2,5-dichloro-diaziridinyl-1,4-benzoquinone

Photoirradiation of nitrogen-saturated aqueous solutions containing aluminum phthalocyanine tetrasulfonate (AlPcS4) at 675 nm in the presence of 2,5-dichloro-diaziridinyl-1,4-benzoquinone (AZDClQ) and hypoxanthine (HX) produces the oxidized HX derivatives, xanthine (X) and uric acid (UA). Concentrations of the AZDClQ semiquinone, X and UA increase at the expense of HX with an increase in irradiation time. Almost negligible decomposition of HX, as well as very low amounts of X, are detected if photolysis occurs under identical conditions but in the absence of AZDClQ. Addition of calf-thymus DNA produces quinone-DNA covalent adducts after photolysis of anaerobic samples containing quinone, DNA and AlPcS4, in the presence or absence of HX and at pH 5.5. However, larger amounts of quinone-DNA adducts are detected if HX is present. The results presented here could have applications in the photodynamic treatment of hypoxic tissues such as solid tumors, under conditions of high HX concentration, where Type-I pathways could be more important than singlet oxygen generation.     

Effects of the Oxygenation Level on Formation of Different Reactive Oxygen Species During Photodynamic Therapy

We examined the effect of the oxygenation level on efficacy of two photosensitizing agents, both of which target lysosomes for photodamage, but via different photochemical pathways. Upon irradiation, the chlorin termed NPe6 forms singlet oxygen in high yield while the bacteriopheophorbide WST11 forms only oxygen radicals (in an aqueous environment). Photokilling efficacy by WST11 in cell culture was impaired when the atmospheric oxygen concentration was reduced from 20% to 1%, while photokilling by NPe6 was unaffected. Studies in a cell‐free system revealed that the rates of photobleaching of these agents, as a function of the oxygenation level, were correlated with results described above. Moreover, the rate of formation of oxygen radicals by either agent was more sensitive to the level of oxygenation than was singlet oxygen formation by NPe6. These data indicate that the photochemical process that leads to oxygen radical formation is more dependent on the oxygenation level than is the pathway leading to formation of singlet oxygen.     

Application of a Deconvolutive Procedure to Analyze Several Chlorophenol Species in Natural Waters by Square‐Wave Voltammetry on the Boron‐Doped Diamond Electrode

Abstract

The anodic voltammetric behavior of 4‐chlorophenol (4‐CP) on a boron‐doped diamond electrode (BDD) in aqueous solution was studied by square‐wave voltammetry. After optimization of the experimental conditions, 4‐CP was determined in a Britton‐Robinson buffer solution with pH 6.0, prepared with pure water. Moreover, mixtures of some different chlorophenols were also investigated and an analytical method was developed for the simultaneous determination of these compounds in natural waters. The oxidation of 4‐CP on BDD was used for analytical purposes and quantification limits as low as 9.2 µg L^?1 were obtained. This result illustrates the advantage of using oxidation process currents on BDD electrodes as the analytical signal, even in contaminated matrices. In order to compare the results found here with the conventional methodology to determine chlorophenols, HPLC‐UV‐vis measurements were also performed and were in good agreement with the analytical values obtained by SWV.     

QUANTUM YIELDS AND KINETICS OF THE PHOTOBLEACHING OF HEMATOPORPHYRIN, PHOTOFRIN II, TETRA(4-SULFONATOPHENYL)-PORPHINE AND UROPORPHYRIN

Abstract Porphyrins used as sensitizers for the photodynamic therapy (PDT) of tumors are progressively destroyed (photobleached) during illumination. If the porphyrin bleaches too rapidly, tumor destruction will not be complete. However, with appropriate sensitizer dosages and bleaching rates, irreversible photodynamic injury to the normal tissues surrounding the tumor, which retain less sensitizer, may be significantly decreased. This paper surveys the quantum yields and kinetics of the photobleaching of four porphyrins: hematoporphyrin (HP), Photofrin II (PF II), tetra(4-sulfonatophenyOporphine (TSPP) and uroporphyrin I (URO). The initial quantum yields of photobleaching, as measured in pH 7.4 phosphate buffer in air, were: 4.7 × 10^-5, 5.4 × 10^-5, 9.8 × 10^-5, and 2.8 × 10^-5 for HP, PF II, TSPP and URO respectively; thus, the rates of photobleaching are rather slow. Low oxygen concentration (2 μM) significantly reduced the photobleaching yields. However, D₂O increased the yields only slightly, and the singlet oxygen quencher, azide, had no effect, even at 0.1 M. Photosensitizing porphyrins in body fluids, cells and tissues may be closely associated with various photooxidizable molecules and electron acceptors and donors. Therefore, selected model compounds in these categories were examined for their effects on porphyrin photobleaching. A number inhibited and/or accelerated photobleaching, depending on the compound, the porphyrin and the reaction conditions. For example, 1.0 mM furfuryl alcohol increased the photobleaching yields of HP and URO more than 5-fold, with little effect on PF II or TSPP. In contrast, the electron acceptor, methyl viologen, increased the photobleaching yield of TSPP more than 10-fold, with little accelerating effect on the other porphyrins. These results suggest that the mechanism(s) of the photobleaching of porphyrin photosensitizers in cells and tissues during PDT may be complex.     

Oxygen dependence of two-photon activation of zinc and copper phthalocyanine tetrasulfonate in Jurkat cells

Abstract Photodynamic therapy (PDT), the use of light-activated drugs, is a promising treatment of cancer as well as several nonmalignant conditions. However, the efficacy of one-photon (1-gamma) PDT is limited by hypoxia, which can prevent the production of the cytotoxic singlet oxygen ((1)O(2)) species, leading to tumor resistance to PDT. To solve this problem, we propose an irradiation protocol based on a simultaneous, two-photon (2-gamma) excitation of the photosensitizer (Ps). Excitation of the Ps triplet state leads to an upper excited triplet state T(n) with distinct photochemical properties, which could inflict biologic damage independent of the presence of molecular oxygen. To determine the potential of a 2-gamma excitation process, Jurkat cells were incubated with zinc or copper phthalocyanine tetrasulfonate (ZnPcS(4) or CuPcS(4)). ZnPcS(4) is a potent (1)O(2) generator in 1-gamma PDT, while CuPcS(4) is inactive under these conditions. Jurkat cells incubated with either ZnPcS(4) or CuPcS(4) were exposed to a 670 nm continuous laser (1-gamma PDT), 532 nm pulsed-laser light (2-gamma PDT), or a combination of 532 and 670 nm (2-gamma PDT). The efficacy of ZnPcS(4) to photoinactivate the Jurkat cells decreased as the concentration of oxygen decreased for both the 1-gamma and 2-gamma protocols. In the case of CuPcS(4), cell phototoxicity was measured only following 2-gamma irradiation, and its efficacy also decreased at a lower oxygen concentration. Our results suggest that for CuPcS(4) the T(n) excited state can be populated after 2-gamma irradiation at 532 nm or the combination of 532 and 670 nm light. Dependency of phototoxicity upon aerobic conditions for both 1-gamma and 2-gamma PDT suggests that reactive oxygen species play an important role in 1-gamma and 2-gamma PDT.     

Photosensitised oxidation of a water pollutant using sulphonated porphyrin

Photodegradation of endocrine disrupting butylparaben (BP) in aerated aqueous solutions was studied using 4,4′,4″,4‴-(porphine-5,10,15,20-tetrayl)tetrakis(benzenesulphonic acid) (TPPS₄), as a sensitiser. Influence of various parameters, such as initial sensitiser and BP concentration, pH of the reaction solution and oxygen content in the reaction solution, on the photosensitised oxidation was examined. It was found that the dominant pathway of BP degradation occurred in the reaction with molecular singlet oxygen ¹O₂, i.e. via photosensitised oxidation mechanism of type II. Kinetic parameters of the BP reaction with ¹O₂ were estimated.     

Spectroscopic Properties of 4‐Pyridoxic Acid as a Function of pH and Solvent

The photophysical properties and acid/base equilibria of 4‐pyridoxic acid (=3‐hydroxy‐5‐(hydroxymethyl)‐2‐methylpyridine‐4‐carboxylic acid), the final product of the catabolism of vitamin B₆, have been studied in aqueous solutions. The ground state of 4‐pyridoxic acid exhibits the different protonated forms A – D in the range of H₀=?6 to pH 11.5. HMQC‐ and HMBC‐NMR Studies allowed the pH‐dependent assignment of the different C‐atoms, and the evaluation of the deprotonation sequence. The 3‐OH group in the ground state has a ‘pK_a’ of H₀=?0.64, which is much lower than that found for other vitamin B₆ related compounds. The pK_a value of the 4‐COOH group is 5.4. Fluorescence studies showed that the same species exist at the lowest excited singlet state, but in different pH ranges. The 3‐OH group is four pH units more acidic in the lowest excited singlet state than in the ground state. Excitation spectra and emission decays in the pH range of 8 to 11.5 indicate that the pyridine N‐atom is more basic in the excited singlet state than in the ground state. The emission spectra are red‐shifted in protic solvents, in agreement with an intramolecular H‐bond between the ionized 3‐OH group and the nonionized 4‐COOH group.     

Photodynamic properties of amphiphilic derivatives of aluminum tetrasulfophthalocyanine

Photodynamic therapy (PDT) is a promising treatment modality that has recently been accepted in clinics as a curative or palliative therapy for cancer and other nonmalignant conditions. Phthalocyanines (Pc) are attractive photosensitizers for PDT because of their enhanced photophysical and photochemical properties. The overall charge and solubility of Pc play a major role in their potential usefulness for PDT. A series of amphiphilic derivatives of tetrasulfonated aluminum Pc (AlPcS4) was prepared by substituting one of the four sulfonate groups with aliphatic side chains of 4, 8, 12 and 16 carbon atoms. The photodynamic properties of the derivatives were compared with those of AlPcS4 and the adjacent disulfonated aluminum Pc. Parameters studied included reversed-phase high-performance liquid chromatography (HPLC) retention times, capacity to generate singlet oxygen (1O2), in vitro cell uptake and phototoxicity, as well as PDT response of transplantable EMT-6 tumors in mice. The monomerized AlPcS4 derivatives showed similar or higher capacities to generate 1O2 as compared with the parent AlPcS4 as measured from relative L-tryptophan photooxidation yields. A549 cell uptake of the AlPcS4 derivatives decreased in the following order: AlPcS4(C16) > AlPcS4(C12) > AlPcS4(C8) > AlPcS4(C4). Human low-density lipoprotein at high concentrations (40 micrograms/mL) completely prevented uptake, whereas at 4 micrograms/mL uptake was decreased for the more lipophilic compounds and yet remained unaffected for the more hydrophilic dyes. Using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, A549 cell survival was assessed; it showed that photocytotoxic activity varied directly with the HPLC retention times, i.e. more hydrophilic compounds were less phototoxic. As 1O2 yields were similar for the four substituted AlPcS4 derivatives, it was postulated that the increased cytotoxic activity was caused by enhanced subcellular localization as a result of the long aliphatic side chains. These amphiphilic compounds proved to be photodynamically potent against the EMT-6 mouse mammary tumor model implanted in Balb/c mice. At dye doses of 0.2 mumol/kg and a fluence of 400 J/cm2 complete tumor regression was observed with no morbidity. The substitution of AlPcS4 with long aliphatic chains on the macrocycle greatly enhances its photodynamic efficacy both in vitro and in vivo.     

The embedding of meta-tetra(hydroxyphenyl)-chlorin into silica nanoparticle platforms for photodynamic therapy and their singlet oxygen production and pH-dependent optical properties

This study relates to nanoparticle (NP) platforms that attach to tumor cells externally and only deliver singlet oxygen for photodynamic therapy (PDT) while conserving the embedded photosensitizers (PS). As a model, we demonstrate the successful embedding of the PS meta‐tetra(hydroxyphenyl)‐chlorin (m‐THPC) in NP that are based on a sol–gel silica matrix and also show its positive effect on the singlet oxygen production. The embedding of m‐THPC inside silica NP is accomplished by a modified Stöber sol–gel process, in which (3‐aminopropyl)‐triethoxysilane is introduced during the reaction. Singlet oxygen delivery by the targetable photodynamic NP exceeds that from free PS molecules. In the physiological pH range, there is no significant pH‐induced decrease in the fluorescence of m‐THPC embedded in silica NP, which might otherwise affect the efficiency of PDT.     

Photophysical properties of diphenyl-2,3-dihydroxychlorin and diphenylchlorin

The photophysical properties of 5,15-diphenyl-2,3-dihydroxychlorin (DPCOH) and 5,15-diphenyl-chlorin (DPC) in organic solution were studied. Absorption, fluorescence, triplet state and photobleaching experiments are reported. The ground states of both compounds show strong absorbance in red region (lambda = 638 nm, epsilon = 35,000 M(-1) cm(-1) and lambda = 645 nm, epsilon = 42,000 M(-1) cm(-1), respectively) and the singlet excited states show low fluorescence quantum yields of 0.0802 and 0.150 in benzene and the lifetimes are 7.38 and 10.18 ns, respectively. Absorption spectra of the triplet states were also measured and they have nearly the same triplet state lifetimes of 53 micros (DPCOH) and 50 micros (DPC). The triplet quantum yields are 0.82 and 0.75, respectively. The data of photobleaching quantum yields show that the presence of oxygen does not significantly affect the photobleaching. All the results demonstrate that both diphenylchlorines are good candidates for second-generation photosensitizer in photodynamic therapy.