Generation Of Singlet Molecular Oxygen Research Articles

Enhancement of the Photosensitizing Properties of 6-Carboxypterin through Covalent Binding to the pH-Responsive and Biocompatible Poly(allylamine Hydrochloride).

A polymeric photosensitizer was synthesized through covalent attachment of the natural photosensitizer 6-carboxypterin (Cap) to a poly(allylamine hydrochloride) (PAH) polymer. The optimization of the functionalization steps and purification procedure is described. The overall yield of the functionalization reaction was 67% to generate the modified polymer (PAH-Cap), featuring a Cap substitution degree of approximately 1% and advantageous spectroscopic properties. Photosensitizing properties of PAH-Cap were observed to occur via both photooxidation mechanisms, i.e., type I and type II. This feature was demonstrated using a biologically relevant target molecule, 2'-deoxyguanosine (dG). The spectroscopic, photophysical, and photochemical behaviors in aqueous environments were studied and compared to Cap. To explore possible further relevant biological applications, experiments with PAH-Cap and dG were carried out at physiological pH. PAH-Cap can generate singlet molecular oxygen and initiate an electron transfer process at pH 7 in air-saturated solutions upon UVA irradiation. Moreover, based on its spectroscopic features, visible light can be used to initiate the photooxidation of biological compounds in water, with many interesting advantages compared to free Cap and other related pteridines. These advantages include an enhancement of the photosensitizing effect at physiological pH and the potential of PAH-Cap for its use as a building block in supramolecular assemblies. The functionalization strategy hereby described can be employed for the preparation of robust photoactive polymers with great potential for its application in photodynamic therapy (PDT) and disinfection technologies.

Colloidal Quantum Dots as an Emerging Vast Platform and Versatile Sensitizer for Singlet Molecular Oxygen Generation.

Singlet molecular oxygen (1O2) has been reported in wide arrays of applications ranging from optoelectronic to photooxygenation reactions and therapy in biomedical proposals. It is also considered a major determinant of photodynamic therapy (PDT) efficacy. Since the direct excitation from the triplet ground state (3O2) of oxygen to the singlet excited state 1O2 is spin forbidden; therefore, a rational design and development of heterogeneous sensitizers is remarkably important for the efficient production of 1O2. For this purpose, quantum dots (QDs) have emerged as versatile candidates either by acting individually as sensitizers for 1O2 generation or by working in conjunction with other inorganic materials or organic sensitizers by providing them a vast platform. Thus, conjoining the photophysical properties of QDs with other materials, e.g., coupling/combining with other inorganic materials, doping with the transition metal ions or lanthanide ions, and conjugation with a molecular sensitizer provide the opportunity to achieve high-efficiency quantum yields of 1O2 which is not possible with either component separately. Hence, the current review has been focused on the recent advances made in the semiconductor QDs, perovskite QDs, and transition metal dichalcogenide QD-sensitized 1O2 generation in the context of ongoing and previously published research work (over the past eight years, from 2015 to 2023).

Visible light promoted and chlorophyll catalyzed α-oxidation of amines to amides under aerobic conditions: Synthesis of 3,4-dihydroisoquinolin-1(2H)-ones and N-phenyl oxalamides

A novel method for the metal-free synthesis of 3,4-dihydroisoquinolin-1(2H)-ones and N-phenyl oxalamides from 1,2,3,4-tetrahydronisoquinoline and N-phenyl glycine derivatives based on visible-light photoredox catalysis under aerobic conditions is reported. Natural pigment chlorophyll is used as photosensitizer to generate singlet molecular oxygen 1O2, which is involved in the aerobic α-oxidation of N-phenyl amines. The protocol provides amides in good yields at room temperature under mild conditions. Based on the experimental results, a plausible photoredox mechanism is proposed.

Biological Action of Singlet Molecular Oxygen from the Standpoint of Cell Signaling, Injury and Death.

Energy transfer to ground state triplet molecular oxygen results in the generation of singlet molecular oxygen (1O2), which has potent oxidizing ability. Irradiation of light, notably ultraviolet A, to a photosensitizing molecule results in the generation of 1O2, which is thought to play a role in causing skin damage and aging. It should also be noted that 1O2 is a dominant tumoricidal component that is generated during the photodynamic therapy (PDT). While type II photodynamic action generates not only 1O2 but also other reactive species, endoperoxides release pure 1O2 upon mild exposure to heat and, hence, are considered to be beneficial compounds for research purposes. Concerning target molecules, 1O2 preferentially reacts with unsaturated fatty acids to produce lipid peroxidation. Enzymes that contain a reactive cysteine group at the catalytic center are vulnerable to 1O2 exposure. Guanine base in nucleic acids is also susceptible to oxidative modification, and cells carrying DNA with oxidized guanine units may experience mutations. Since 1O2 is produced in various physiological reactions in addition to photodynamic reactions, overcoming technical challenges related to its detection and methods used for its generation would allow its potential functions in biological systems to be better understood.

Влияние центрального иона металла на люминесцентные и фотофизические параметры фталоцианинов

Based on the data on the spectral and photophysical parameters of the metal complexes of tetraazaporphyrins and phthalocyanines, the effect of the central metal ion on the manifestation of spin-orbit interaction is considered. For complexes of phthalocyanines with Mg(II), Zn(II), Pd(II), and Pt(II) ions, the absorption spectra, luminescence spectra, and luminescence excitation spectra were measured, and the lifetimes and quantum yields of luminescence were determined. It was shown that metal phthalocyanines with Mg(II) and Zn(II) ions, as well as Mg-tetaraazaporphyrin, exhibit intense fluorescence with high quantum yields. For single molecules of Mg-tetaraazaporphyrin in a polymer film at T=6 K, the fluorescence excitation spectra consisting both exclusively of zero-phonon lines and containing phonon wings were measured. A wide distribution of the measured zero-phonon line widths was observed. It is demonstrated, that the introduction of Pd(II) and Pt(II) ions into the center of phthalocyanine macrocycles leads to a decrease in fluorescence and the appearance of intense phosphorescence even at room temperature. Based on measurements of quantum yields of photosensitized generation of singlet molecular oxygen, the quantum yield of interconversion into triplet states for the compounds under study was defined. Deactivation of the lower triplet state of phthalocyanines with Pd(II) and Pt(II) ions indicates the influence of the internal heavy atom effect on the rate of triplet state deactivation at room temperature and at 77 K.

Singlet Molecular Oxygen Generation in the Reaction of Biological Haloamines of Amino Acids and Polyamines with Hydrogen Peroxide†.

Leucocytes generate hypohalous acids (HOCl and HOBr) to defend the host against pathogens. In cells, hypohalous acids react with amine-containing molecules, such as amino acids and polyamines, producing chloramines and bromamines, reservoirs of oxidizing power that can potentially damage host tissues at sites of inflammation. Hypohalous acids also react with H2 O2 to produce stoichiometric amounts of singlet molecular oxygen ( ), but its generation in leucocytes is still under debate. Additionally, it is unclear whether haloamines generate following a reaction with H2 O2 . Herein, we provide evidence of the generation of in the reactions between amino acid-derived (taurine, N-α-acetyl-Lysine and glycine) and polyamine-derived (spermine and spermidine) haloamines and H2 O2 in an aqueous solution. The unequivocal formation of was detected by monitoring its characteristic monomol light emission at 1270 nm in the near-infrared region. For amino acid-derived haloamines, the presence of was further confirmed by chemical trapping with anthracene-9,10-divinylsulfonate and HPLC-MS/MS detection. Altogether, photoemission and chemical trapping studies demonstrated that chloramines were less effective at producing than bromamines of amino acids and polyamines. Thus, formation via bromamines and H2 O2 may be a potential source of in nonilluminated biological systems.

Visible-light-promoted and chlorophyll-catalyzed aerobic desulfurization of thioamides to amides.

A novel method for the metal-free synthesis of amides from thioamides based on visible-light photoredox catalysis and in an air atmosphere is reported. Natural pigment chlorophyll is used as a photosensitizer to generate singlet molecular oxygen 1O2, which is involved in the aerobic desulfurization of thioamides. The protocol provides amides in good yields at room temperature under mild conditions. On the basis of experimental results, a plausible photoredox mechanism is proposed.

Novel photosensitizing nanoparticles for PDT and biosensing applications

Loading of photosensitizing dyes into polymer beads is a meaningful strategy to improve their performance in photodynamic therapies (PDTs) or in sensing applications. In this work we describe a straightforward method for doping 390 nm and 26 nm carboxylated polystyrene nanoparticles with the hydrophobic tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) (RD3) complex. This Ru(II) photosensitizer (PS) efficiently generates singlet molecular oxygen (1O2) upon illumination with blue-green light and displays residual μs-lived red luminescence. its entrapment in the nanoparticles facilitates its use in water and opens up the possibility for bioconjugation without functionalization of the PS dye. After optimization of the doping protocol, we have carried out a photophysical (absorption, steady-state and time-resolved luminescence) and photochemical characterization of the photoactive nanoparticles by investigating the effect of the O2 concentration in water on the RD3 emission features. No leaching of the dye from the nanoparticles was observed. The 1O2 production quantum yield of the encapsulated PS (ΦΔ = 0.50), measured by monitoring the 1O2 emission decay at 1270 nm in D2O, is comparable to that of the free Ru(II) dye in the same solvent (0.49).

Sensitized photooxidation of triclosan pesticide. A kinetic study in presence of vitamin B2

Kinetic and mechanistic aspects of Riboflavin (Rf, vitamin B2)-sensitized photochemical degradation of Triclosan (TCS) have been studied by time-resolved and stationary techniques. TCS is a broadly-used biocide, also employed in a series of industrial products as a multifunctional additive. Rf, in the presence of light and oxygen, generates singlet molecular oxygen (O2(1Δg)) and superoxide radical anion (O2–).Results indicate that TCS quenches the triplet excited state of Rf (3Rf*), O2(1Δg), and O2–. The reactive rate constant for the interaction TCS-O2(1Δg) is 62-faster in alkaline medium with respect to pH 7. Photosensitized degradation of TCS by Rf was much faster than for phenol, a model pollutant, in similar conditions of pH. Kinetic analysis indicated that the reaction of TCS with 3Rf* and/or O2– is the prevailing oxidative route. Based on the environmental importance of the TCS, the products were determined by UHPLC-MS / MS analysis.

Methods to Unravel Pathways of Reactive Oxygen Species in the Photodynamic Inactivation of Bacteria.

Different experimental conditions can be used to detect the presence of reactive oxygen species (ROS) in the photodynamic inactivation of microorganisms. Here, we describe the effect of the media and the addition of ROS scavengers to obtain insight about the oxidative processes that take place during the photokilling of bacteria. In addition, 9,10-dimethylanthracene was used to sense the generation of singlet molecular oxygen, O2(1Δg), in microbial cells. Thus, the contribution of type I or type II pathways in the photocytotoxicity action can be rapidly detected and compared between different photosensitizers.

Generation of Singlet Molecular Oxygen by Lipid Hydroperoxides and Nitronium Ion†.

Singlet molecular oxygen is a reactive species involved in biological oxidative processes. The major cellular targets of singlet molecular oxygen are unsaturated fatty acids in the membrane, as well as nucleic acids and proteins. The aim of this study was to investigate whether lipids and commercial hydroperoxides generate singlet molecular oxygen, in presence of nitronium and activated nitronium ion. For this purpose, monomol light emitted in the near-infrared region (λ=1270nm) was used to monitor singlet molecular oxygen decay in different solvents, with different hydroperoxides and in the presence of azide. Direct measurements of the singlet molecular oxygen spectrum at 1270nm recorded during the reaction between lipids and commercial hydroperoxides and nitronium ions unequivocally demonstrated the formation of this excited species.

The Processes of Zinc Phosphoryl-Substituted Phthalocyaninate Dissolution in Water in the Presence of Tetradecyltrimethylammonium Bromide within a pH Range of 4–9

Electronic absorption spectroscopy and fluorescence spectroscopy have been employed to analyze the aggregation of zinc phosphoryl-substituted phthalocyaninate by the example of zinc 2,(3),9,(10),16,(17),23,(24)-tetra(2-phosphoryl)phenoxyphthalocyaninate ([ZnPc(PO(OH)2)4]) in dimethyl sulfoxide and water at different pH values. It has been found that, in aqueous systems with pH 4–9, this compound exists in an aggregated state, while it forms a molecular solution in dimethyl sulfoxide. Moreover, ZnPc(PO(OH)2)4 is in fact insoluble in water at pH < 5.7. The addition of tetradecyltrimethylammonium bromide as a cationic surfactant to an aqueous ZnPc(PO(OH)2)4 solution leads to the complete disaggregation of the dye into individual molecules within a wide pH range (from 4 to 9.18) and a marked increase in the solubility of ZnPc(PO(OH)2)4 in strongly acidic media. Analysis of the fluorescent properties of surfactant micellar solutions containing ZnPc(PO(OH)2)4 has shown that such systems can generate singlet molecular oxygen. At the same time, the high intensity of ZnPc(PO(OH)2)4 fluorescence in micellar solutions makes it possible to visually observe the distribution of micelles that carry nonaggregated dye molecules in living tissues.

Bacteriochlorin-bis(spermine) conjugate affords an effective photodynamic action to eradicate microorganisms.

A novel bacteriochlorin bearing two spermine units (BCS) was synthesized from 3,13-dibromo-8,8,18,18-tetramethylbacteriochlorin (BC-Br 3,13 ). The synthesis involved the Suzuki coupling of BC-Br 3,13 to obtain a bacteriochlorin-dibenzaldehyde (BCA), which was subjected to reductive amination with spermine. The resulting bacteriochlorin BCS presents a strong near-infrared absorption band at 747 nm, emits at 750 nm with fluorescence quantum yield of 0.14, and generates singlet molecular oxygen, O2 (1 Δg ), with a quantum yield of 0.27. Photokilling capacities mediated by BCS were evaluated in microbial cells. The viability of Staphylococcus aureus decreased 7 logs when cells were incubated with 1 μM BCS and irradiated for 15 minutes. Comparable photocytotoxic effect was obtained with Escherichia coli, when cells were treated for 30 minutes with visible light. BCS was also an effective photosensitizer to inactivate Candida albicans. In addition, this bacteriochlorin was able to eradicate bacteria at short incubation times. The structure of BCS contains eight basic amino groups that, when protonated in water, increase the binding to the cell envelope. In summary, the readily accessible bacteriochlorin BCS was highly effective at low concentrations as a broad-spectrum antimicrobial photosensitizer.

Disaggregation of Zinc Tetra(4-Carboxyphenoxy) Phthalocyaninate in Aqueous Solutions of Dodecyl-, Tetradecyl-, and Hexadecyltrimethylammonium Bromides at pH 6–9

The aggregation of zinc tetra(4-carboxyphenoxy) phthalocyaninate, ZnPc(COOH)4, in organic solvents and water at different pH values has been analyzed using electronic absorption and luminescence spectroscopies. It has been found that, in aqueous systems at pH 6–9, ZnPc(COOH)4 exists in an aggregated state, while it forms molecular solutions in dimethylformamide and dimethyl sulfoxide. The use of cationic surfactants (dodecyl-, tetradecyl-, and hexadecyltrimethylammonium bromides) causes the disaggregation of ZnPc(COOH)4 into individual molecules in aqueous solutions at pH ≥ 6. This opens up possibilities of applying ZnPc(COOH)4 as a preparation for photodynamic therapy in physiological solutions, because each molecule of this compound may participate in the generation of singlet molecular oxygen.

Characteristics of the excited triplet states of thiolated guanosine derivatives and singlet oxygen generation.

Thioguanine is sensitive to UVA light and generates singlet molecular oxygen (1O2*) when exposed to UVA. Three thioguanosine derivatives, 2',3',5'-tri-O-acetyl-6-thioguanosine (ta6TGuo), 2',3',5'-tri-O-acetyl-8-thioguanosine (ta8TGuo), and 2',3',5'-tri-O-acetyl-6,8-dithioguanosine (taDTGuo) were explored photophysically and photochemically. Nanosecond transient absorption and time-resolved near-infrared emission measurements were carried out to investigate the characteristics of their excited triplet states in acetonitrile solution. The quantum yield of intersystem crossing (ΦISC), the intrinsic decay rate constant (k0), the quenching rate constant by 3O2 (kq) and the self-quenching rate constant (kSQ) of their triplet states were all determined. From the precise analysis of the quantum yield of 1O2* generation (ΦΔ) against the concentration of dissolved molecular oxygen, the fraction of the triplet states quenched by dissolved oxygen which gives rise to 1O2* formation (SΔ) was successfully obtained with high accuracy. The ΦΔ values at low oxygen concentrations reveal that these thioguanosines, particularly taDTGuo, can still effectively generate 1O2* at low molecular oxygen concentrations like carcinomatous microenvironments. These findings indicate that taDTGuo would perform well as a potential agent for photo-induced cancer therapies.

2(3), 9(10), 16(17), 23(24)-tetrakis[(3-mercapto)propoxy] phthalocyaninate zinc (II)/gold nanoparticle conjugates: Synthesis and photophysical properties

Novel stable zinc (II) thiol-phthalocyaninate gold nanoparticle nanoconjugates (PcS-AuNP) with a reproducible and homogeneous distribution size of 16 ± 4 nm were efficiently prepared by means of a ligand exchange reaction. The nanoconjugates were characterized by TEM, DLS, FT-IR and UV–vis. PcS-AuNP were a stable system at least for two months in darkness. Singlet molecular oxygen generation was observed when gold plasmon and phthalocyanine were independently excited at 510 nm and 610 nm, respectively. The PcS-AuNP system obtained is a photosensitive material in a wide range of the UV–vis spectrum (300–400 nm, 500–530 nm and 610–799 nm).

Photodynamic Inhibition of Biofilm Forming Microorganisms on Surfaces

Microorganisms play an important role in our everyday life and in an ecological context. While a great number of species provide a benefit to humans, some of them can be terribly harmful due to the diseases they trigger. To remove or hinder those unwanted microorganisms has been a goal since their discovery. There are classical approaches to accomplish that, but the adaptability of microorganisms – especially the alarming development of antibiotic resistant strains - always calls for new methods. Once microorganisms grow in biofilms they are hard to come by and inadvertently spread infections are a fatal risk for immunodeficient people. Photodynamic Inactivation (PDI) has good potential as antimicrobial agent, which avoids most of aforementioned problems. Singlet oxygen is a highly reactive molecule against which there has been no development of countermeasures in biological systems besides provision of quenching molecules inside the cells. Therefore there is also little to no risk of resistance development when using PDI against microorganisms. Easy availability of light and oxygen in many of the potential target sites are just some advantages of PDI. Even though much less often associated with maladies, fungi can be similarly harmful. Due to their asexual life cycle and sporulation they are more robust against changes in environmental conditions. Their high robustness requires highly toxic biocides which in turn come with the risk of damaging the environment. Even seemingly, harmless microorganisms like algae and cyanobacteria show increasing tendencies to harm humans directly or indirectly and in symbiosis with fungi, they form even more resistant lichen, which pose new challenges concerning their removal. Biofilms on outdoor walls cause aesthetic problems and economic damage. Therefore, wall colors are often mixed with conventional biocides. However, biocides are increasingly designed towards higher efficacy while remaining environmentally persistent. This combination implies serious toxicity problems for all living organisms and whole ecosystems. Thus, an eco-friendly and non-harmful to human health alternative to conventional biocides in wall color is strongly recommended. The well-known photosensitizer TMPyP was used as an additive in commercially available facade paint. The generation of singlet molecular oxygen was shown using time resolved 2D measurements of the singlet oxygen luminescence. The photodynamic activity of the photosensitizer in the facade paint was demonstrated by phototoxicity tests with defined mold fungi and a mixture of microorganisms harvested from native outdoor biofilms as model organisms. Phototrophic biofilms are an important factor in biofouling and biodeterioration of building materials. The aim of this study was to examine the potential of PDI through generation of singlet oxygen as a possible alternative to biocides preventing the growth and formation of biofilms of these phototrophic organisms. Four photosensitizers were investigated according to their photoinhibitive effect on two strains of green algae using visible light for photoexcitation. The two anionic photosensitizers showed no significant phototoxicity whereas the two cationic photosensitizers caused a drastic reduction of biomass on a short time scale and also displayed long term inhibition of algae growth. Furthermore, to investigate the intrinsic mechanisms of PDI we studied the singlet oxygen luminescence kinetics - a method that proved to be a very effective approach towards understanding mechanisms on a cellular level. Here we present the first two-dimensional measurement of singlet oxygen kinetics in phototrophic microorganisms on surfaces during PDI. We established a system of reproducible algae samples on surfaces, incubated with two different cationic, antimicrobial potent photosensitizers. Fluorescence microscopy images indicate that one photosensitizer localizes inside the green algae while the other accumulates along the outer algae cell wall. A newly developed setup allows for the measurement of singlet oxygen luminescence on the green algae sample surfaces over several days. The kinetics of the singlet oxygen luminescence of both photosensitizers show different developments and a distinct change over time, corresponding with the differences in their localization as well as their photosensitization potential. While the complexity of the signal reveals a challenge for the future, this study incontrovertibly marks a crucial, inevitable step in the investigation of photodynamic inactivation of biofilms: it shows the feasibility of using the singlet oxygen luminescence kinetics to investigate photodynamic effects on surfaces and thus opens a field for numerous investigations. Figure 1

Absorption Characteristics and Quantum Yields of Singlet Oxygen Generation of Thioguanosine Derivatives

6-Thioguanine (1a) is considered to be photochemotherapeutic due to its specific characteristics of photosensitivity to UVA light and singlet molecular oxygen generation. To extend its phototherapeutic ability, two related thioguanines, 8-thioguanine (2a) and 6,8-dithioguanine (3a), have been designed and explored. Since the solubility of these thioguanines in dehydrated organic solvents is too poor to study, their triacetyl-protected ribonucleosides, that is, 2',3',5'-tri-O-acetyl-6-thioguanosine (1c), 2',3',5'-tri-O-acetyl-8-thioguanosine (2c) and 2',3',5'-tri-O-acetyl-6,8-dithioguanosine (3c) were prepared and investigated. The absorption maxima of 1c, 2c and 3c in acetonitrile were found at longer wavelengths than that of unthiolated guanosine (4c). Especially, 3c has the longest wavelength for absorption maximum and the highest value in terms of molar absorption coefficient among all thionucleobases and thionucleosides reported. These absorption properties were also well reproduced by quantum chemical calculations. Quantum yields of singlet oxygen generation of 2c and 3c were determined by near-infrared emission measurements to be as large as that of 1c. These results suggest that the newly synthesized thioguanosines, in particular 3c, can be further developed as a potential photosensitive agent for light-induced therapies.

Acid Dissociation Equilibrium and Singlet Molecular Oxygen Quantum Yield of Acetylated 6,8-Dithioguanosine in Aqueous Buffer Solution.

2',3',5'-Tri- O-acetyl-6,8-dithioguanosine (taDTGuo) is a nucleoside derivative of drug 6-thioguanine and under further development as a potential photochemotherapeutic agent due to its desirable properties of photosensitivity to UVA light and singlet molecular oxygen generation. The photochemical characteristics of taDTGuo under biological conditions (namely in aqueous solution) were intensively investigated by the steady-state absorption and emission, time-resolved near-infrared emission measurements, and quantum chemical calculations. taDTGuo was found to be held in sequential acid dissociation equilibria within pH 3.79-11.93. With the global fitting analysis of the absorption spectra at various pHs, two p Ka values of the equilibria were determined to be 7.02 ± 0.01 and 9.79 ± 0.01. Quantum chemical calculations suggested that its mono- and dianionic species in the ground state should be 1-imide anionic form (N1-taDTGuo-) and 1,7-di-imide anionic form (taDTGuo2-). taDTGuo generates a singlet molecular oxygen effectively and has pH-dependent quantum yields. In conclusion, taDTGuo would be very useful as a potent agent for photochemotherapy under certain carcinomatous pH conditions.

Singlet oxygen generation from poly[4-diacetoxyiodo]styrene and hydrogen peroxide

Treatment of hydrogen peroxide with a polymer-supported hypervalent iodine compound, poly[4-diacetoxyiodo] styrene (PDAIS), generates singlet molecular oxygen ($^{1}$O$_{2})$. Singlet oxygen generation was proved by trapping with typical organic compounds such as conjugated dienes, aromatic dienes, and electron-rich alkene. When compared to monomer analogue, the use of PDAIS in peroxidation of substrates gave slightly better yields (45%-96%). Regeneration and reuse of PDAIS showed similar activity. The mechanism underlying generation of singlet oxygen and reaction scope was examined.