Production Of Singlet Molecular Oxygen Research Articles

Porphyrin-polyethylenimine conjugates as photodynamic polymers to eliminate Staphylococcus aureus and Escherichia coli

The increase in bacteria resistant to antibiotics in clinical use has led to the establishment of new treatments for infections. One of the proposed therapies includes photodynamic inactivation (PDI) of microorganisms. In this context, two novel polymeric conjugates, PEI-TPPF10 and PEI-TPPF20, were synthesized by the aromatic nucleophilic substitution reaction between polyethylenimine (PEI) and 5,15-di(4-N,N-dimethylaminophenyl)-10,20-di(pentafluorophenyl)porphyrin (TPPF10) or 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TPPF20), respectively. The structures of these polymers were characterized by FTIR. UV–visible absorption and fluorescence studies indicated that the porphyrin units maintain their spectroscopic characteristics in the conjugates. The polymeric materials were able to produce singlet molecular oxygen and superoxide anion radical in solution. Furthermore, they were effective photosensitizers to photooxidize L-tryptophan and produce iodine in presence of iodide anions. The ability of these conjugates to photoinactivate bacteria was tested against Staphylococcus aureus and Escherichia coli. A reduction of 7 log (>99.9999 %) in cell survival was found after an irradiation with white light (90 mW/cm2) of 5 min (27 J/cm2) and 15 min (81 J/cm2), respectively. In these conjugates, the remaining amino groups are precursors of positive charges in the biological medium, favoring the interaction with microbial cells, which improves the photokilling activity. The results indicate that both conjugates are promising photosensitizing polymeric materials for the eradication of pathogens.

Photodynamic Polymers Constituted by Porphyrin Units as Antibacterial Materials

Photodynamic inactivation of microorganisms has emerged as a promising strategy to kill and eradicate pathogens. In this work, two polymers, TCP-P and ZnTCP-P, were synthesized by oxidative polymerization of 5,10,15,20-tetrakis [3-(N-ethylcarbazoyl)]porphyrin and its complex with Zn(II). Solid polymers consist of rods (diameter 100 nm, length ~100–500 nm) that form microporous structures on a surface. UV-visible absorption spectra in solution showed the Soret and Q bands characteristic of the corresponding constitutional porphyrins. In addition, the polymers presented two red emission bands with quantum yields ΦF = 0.11 for TCP-P and ΦF = 0.050 for ZnTCP-P. These compounds sensitized the production of singlet molecular oxygen with quantum yields of ΦΔ~0.3. Thus, the spectroscopic and photodynamic properties of the porphyrin units were maintained in the conjugates. The photodynamic activity induced by both polymers was tested to inactivate S. aureus. In cell suspensions, TCP-P was more effective than ZnTCP-P in killing bacteria. Viable S. aureus cells were not detected using 4 µM TCP-P after 20 min of irradiation. Moreover, both polymers showed a high photocytotoxic activity to eradicate S. aureus cells attached to a surface. The results indicate that these conjugated polymers can act as effective antimicrobial agents to photoinactivate pathogens.

Haloperoxidase-Catalyzed Luminol Luminescence

Common peroxidase action and haloperoxidase action are quantifiable as light emission from dioxygenation of luminol (5-amino-2,3-dihydrophthalazine-1,4-dione). The velocity of enzyme action is dependent on the concentration of reactants. Thus, the reaction order of each participant reactant in luminol luminescence was determined. Horseradish peroxidase (HRP)-catalyzed luminol luminescence is first order for hydrogen peroxide (H2O2), but myeloperoxidase (MPO) and eosinophil peroxidase (EPO) are second order for H2O2. For MPO, reaction is first order for chloride (Cl−) or bromide (Br−). For EPO, reaction is first order for Br−. HRP action has no halide requirement. For MPO and EPO, reaction is first order for luminol, but for HRP, reaction is greater than first order for luminol. Haloperoxidase-catalyzed luminol luminescence requires acidity, but HRP action requires alkalinity. Unlike the radical mechanism of common peroxidase, haloperoxidases (XPO) catalyze non-radical oxidation of halide to hypohalite. That reaction is second order for H2O2 is consistent with the non-enzymatic reaction of hypohalite with a second H2O2 to produce singlet molecular oxygen (1O2*) for luminol dioxygenation. Alternatively, luminol dehydrogenation by hypohalite followed by reaction with H2O2 yields dioxygenation consistent with the same reaction order. Haloperoxidase action, Cl−, and Br− are specifically quantifiable as luminol luminescence in an acidic milieu.

Photoinduced bleaching in an efficient singlet oxygen photosensitizing protein: Identifying a culprit in the flavin-binding LOV-based protein SOPP3

Light-oxygen-voltage (LOV) proteins that bind flavin mononucleotide (FMN) have received attention as optogenetic systems that can photosensitize the production of singlet molecular oxygen, O2(a1Δg). Although the seminal compound in this family, mini singlet oxygen generator (miniSOG), does not make O2(a1Δg) in appreciable yield, it is a convenient standard against which other singlet oxygen photosensitizing proteins (SOPPs) can be judged. SOPP3 is a re-engineered version of miniSOG that selectively produces O2(a1Δg) in high yield but, when localized in a cell, the protein-encased FMN readily bleaches upon irradiation. In contrast, the bleaching of FMN in miniSOG is slow under the same conditions. The available evidence indicates that O2(a1Δg) is not directly involved in the bleaching reaction. Rather, electron-transfer reactions between FMN and molecules in the surrounding medium, likely mediated by residues in the LOV protein, accelerate FMN bleaching. In this regard, and identifying a culprit, replacing a glutamine that H-bonds to FMN in miniSOG with either leucine (Q103L) or valine (Q103V) increases the 3FMN lifetime and, thereby, increases both the O2(a1Δg) yield and the bleaching rate. Although the same electron transfer reactions likely influence these respective observations, the O2(a1Δg) yield principally reflects the kinetic competition between two processes that remove/deactivate 3FMN: (1) quenching by ground state oxygen, O2(X3Σg-), to produce O2(a1Δg), and (2) electron transfer to produce the FMN radical anion. Photobleaching principally reflects the accumulated electron-transfer-mediated depletion of ground state FMN, which, over time in the dark, is partly regenerated by compensating redox reactions. Despite the bleaching, irradiation of SOPP3 induces morphological change in a cell. This result, which contradicts conclusions from previous experiments with a lower light dose, indicates that SOPP3 may indeed be a viable optogenetic actuator.

Antimicrobial Photosensitizing Material Based on Conjugated Zn(II) Porphyrins.

The widespread use of antibiotics has led to a considerable increase in the resistance of microorganisms to these agents. Consequently, it is imminent to establish new strategies to combat pathogens. An alternative involves the development of photoactive polymers that represent an interesting strategy to kill microbes and maintain aseptic surfaces. In this sense, a conjugated polymer (PZnTEP) based on Zn(II) 5,10,15,20-tetrakis-[4-(ethynyl)phenyl]porphyrin (ZnTEP) was obtained by the homocoupling reaction of terminal alkyne groups. PZnTEP exhibits a microporous structure with high surface areas allowing better interaction with bacteria. The UV-visible absorption spectra show the Soret and Q bands of PZnTEP red-shifted by about 18 nm compared to those of the monomer. Also, the conjugate presents the two red emission bands, characteristic of porphyrins. This polymer was able to produce singlet molecular oxygen and superoxide radical anion in the presence of NADH. Photocytotoxic activity sensitized by PZnTEP was investigated in bacterial suspensions. No viable Staphylococcus aureus cells were detected using 0.5 µM PZnTEP and 15 min irradiation. Under these conditions, complete photoinactivation of Escherichia coli was observed in the presence of 100 mM KI. Likewise, no survival was detected for E. coli incubated with 1.0 µM PZnTEP after 30 min irradiation. Furthermore, polylactic acid surfaces coated with PZnTEP were able to kill efficiently these bacteria. This surface can be reused for at least three photoinactivation cycles. Therefore, this conjugated photodynamic polymer is an interesting antimicrobial photoactive material for designing and developing self-sterilizing surfaces.

Regulation of vascular tone and blood pressure by singlet molecular oxygen in inflammation.

The principle aim of this review is to prompt vascular researchers interested in vascular inflammation and oxidative stress to consider singlet molecular oxygen (1O2) as a potentially relevant contributor. A secondary goal is to propose novel treatment strategies to address haemodynamic complications associated with septic shock. Increased inflammation and oxidative stress are hallmarks of a range of vascular diseases. We recently showed that in systemic inflammation and oxidative stress associated with models of inflammation including sepsis, the tryptophan catabolizing enzyme indoleamine 2,3-dioxygenase-1 (Ido1) contributes to hypotension and decreased blood pressure through production of singlet molecular oxygen (1O2). Once formed, 1O2 converts tryptophan bound to Ido1 to a vasoactive hydroperoxide which decreases arterial tone and blood pressure via oxidation of a specific cysteine residue of protein kinase G1α. These works show, for the first time, that 1O2 contributes to arterial redox signalling and that Ido1 contributes to the regulation of blood pressure through production of a novel tryptophan-derived hydroperoxide, thus presenting a new signalling pathway as novel target in the treatment of blood pressure disorders such as sepsis.

A General Method to Establish the Relative Efficiency of Different Sonosensitizers to Generate ROS for SDT.

The most common way to demonstrate the reactive oxygen species (ROS)-mediated pathways in photodynamic therapy (PDT) and in sonodynamic therapy (SDT) is the use of specific ROS inhibitors. We present a general method to establish the relative efficiency of different sonosensitizers which produce the same ROS. To demonstrate it, we use peroxides as sonosensitizers which produce singlet molecular oxygen. The method is easily generalized by all types of ROS.

Oxygen-dependent photophysics and photochemistry of prototypical compounds for organic photovoltaics: inhibiting degradation initiated by singlet oxygen at a molecular level

Photo-initiated, oxygen-mediated degradation of the molecules in the active layer of organic photovoltaic, OPV, devices currently limits advances in the development of solar cells. To address this problem systematically and at a molecular level, it is informative to quantify the kinetics of the pertinent processes, both in solution phase and in solid films. To this end, we examined the oxygen-dependent photophysics and photochemistry of selected functionalized fullerenes, thiophene derivatives, and a subphthalocyanine commonly used in OPV devices. We find that the photosensitized production of singlet molecular oxygen, O2(a1Δg), by these molecules is a key step in the degradation process. We demonstrate that the addition of either β-carotene or astaxanthin as antioxidants can inhibit degradation by a combination of three processes: (a) deactivation of O2(a1Δg) to the oxygen ground state, O2(X3Σg−), (b) quenching of the O2(a1Δg) precursor, and (c) sacrificial reactions of the carotenoid with free radicals formed in the photo-initiated reactions. For OPV systems in which reaction with O2(a1Δg) contributes to the degradation, the first two of these processes are desired and should have appreciable impact in prolonging the longevity of OPV devices because they do not result in a chemical change of the system.

Antimicrobial Photodynamic Polymeric Films Bearing Biscarbazol Triphenylamine End-Capped Dendrimeric Zn(II) Porphyrin.

A novel biscarbazol triphenylamine end-capped dendrimeric zinc(II) porphyrin (DP 5) was synthesized by click chemistry. This compound is a cruciform dendrimer that bears a nucleus of zinc(II) tetrapyrrolic macrocycle substituted at the meso positions by four identical substituents. These are formed by a tetrafluorophenyl group that possesses a triazole unit in the para position. This nitrogenous heterocyclic is connected to a 4,4'-di(N-carbazolyl)triphenylamine group by means of a phenylenevinylene bridge, which allows the conjugation between the nucleus and this external electropolymerizable carbazoyl group. In this structure, dendrimeric arms act as light-harvesting antennas, increasing the absorption of blue light, and as electroactive moieties. The electrochemical oxidation of the carbazole groups contained in the terminal arms of the DP 5 was used to obtain novel, stable, and reproducible fully π-conjugated photoactive polymeric films (FDP 5). First, the spectroscopic characteristics and photodynamic properties of DP 5 were compared with its constitutional components derived of porphyrin P 6 and carbazole D 7 moieties in solution. The fluorescence emissions of the dendrimeric units in DP 5 were more strongly quenched by the tetrapyrrolic macrocycle, indicating photoinduced energy transfer. In addition, FDP 5 film showed the Soret and Q absorption bands and red fluorescence emission of the corresponding zinc(II) porphyrin. Also, FDP 5 film was highly stable to photobleaching, and it was able to produce singlet molecular oxygen in both N,N-dimethylformamide (DMF) and water. Therefore, the porphyrin units embedded in the polymeric matrix of FDP 5 film mainly retain the photochemical properties. Photodynamic inactivation mediated by FDP 5 film was investigated in Staphylococcus aureus and Escherichia coli. When a cell suspension was deposited on the surface, complete eradication of S. aureus and a 99% reduction in E. coli survival were found after 15 and 30 min of irradiation, respectively. Also, FDP 5 film was highly effective to eliminate individual bacteria attached to the surface. In addition, photodynamic inactivation (PDI) sensitized by FDP 5 film produced >99.99% bacterial killing in biofilms formed on the surface after 60 min irradiation. The results indicate that FDP 5 film represents an interesting and versatile photodynamic active material to eradicate bacteria as planktonic cells, individual attached microbes, or biofilms.

Light-Harvesting Antenna and Proton-Activated Photodynamic Effect of a Novel BODIPY-Fullerene C60 Dyad as Potential Antimicrobial Agent.

A covalently linked BODIPY-fullerene C60 dyad (BDP-C60 ) was synthesized as a two-segment structure, which consists of a visible light-harvesting antenna attached to an energy or electron acceptor moiety. This structure was designed to improve the photodynamic action of fullerene C60 to inactivate bacteria. The absorption spectrum of BDP-C60 was found to be a superposition of the spectra of its constitutional moieties, whereas the fluorescence emission of the BODIPY unit was strongly quenched by the fullerene C60 . Spectroscopic, calculations, and redox studies indicate a competence between photoinduced energy and electron transfer. Protonating the dimethylaminophenyl substituent through addition of an acidic medium led to a substantial increase in the fluorescence emission, triplet excited state formation, and singlet molecular oxygen production. At physiological pH, photosensitized inactivation of Staphylococcus aureus mediated by 1 μM BDP-C60 exhibited a 4.5 log decrease of cell survival (>99.997 %) after 15 min irradiation. A similar result was obtained with Escherichia coli using 30 min irradiation. Moreover, proton-activated photodynamic action of BDP-C60 turned this dyad into a highly effective photosensitizer to eradicate E. coli. Therefore, BDP-C60 is an interesting photosensitizing structure in which the light-harvesting antenna effect of the BODIPY unit combined with the protonation of dimethylaminophenyl group can be used to improve the photoinactivation of bacteria.

Porphyrins containing basic aliphatic amino groups as potential broad-spectrum antimicrobial agents.

New porphyrin derivatives bearing basic aliphatic amino groups were synthesized from the condensation of meso-4-[(3-N,N-dimethylaminopropoxy)phenyl]dipyrromethane, pentafluorobenzaldehyde and 4-(3-N,N-dimethylaminopropoxy)benzaldehyde. The reaction was catalyzed by trifluoroacetic acid in acetonitrile. This approach was used to obtain porphyrins with different patterns of substitution, of which three of them were isolated: 5,15-di(4-pentafluorophenyl)-10,20-di[4-(3-N,N-dimethylaminopropoxy)phenyl]porphyrin (F10APP), 5-(4-pentafluorophenyl)-10,15,20-tris[4-(3-N,N-dimethylaminopropoxy)phenyl]porphyrin (F5APP) and 5,10,15,20-tetrakis[4-(3-N,N-dimethylaminopropoxy)phenyl]porphyrin (TAPP). The UV-vis spectroscopic characterizations and the photodynamic effect of these compounds were compared in N,N-dimethylformamide. These porphyrins showed red fluorescence emission with quantum yields of 0.09-0.15. Moreover, they sensitized the production of singlet molecular oxygen, reaching quantum yields values of 0.33-0.53. Photodynamic inactivation was studied in two bacteria, Staphylococcus aureus and Escherichia coli, and a yeast Candida albicans. High amount of cell-bound porphyrin was obtained at short times (<2 min) of incubation. After 15 min irradiation, a 7 log reduction of S. aureus was found for cells treated with 1 μM F5APP. Similar photokilling was obtained in E. coli, but using 7.5 μM F5APP and 30 min irradiation. Under these conditions, a decrease of 5 log was observed in C. albicans cells. An increase in cell survival was observed by addition of sodium azide, whereas a slight protective effect was found in the presence of D-mannitol. Moreover, the photoinactivation mediated by these porphyrins was higher in D2O than in water. Thus, these porphyrins induced the photodynamic activity mainly through the intermediacy of O2(1Δg). In particular, F5APP was a highly effective photosensitizer with application as a broad-spectrum antimicrobial. This porphyrin contains three basic aliphatic amino groups that may be protonated at physiological pH. In addition, it is substituted by a lipophilic pentafluorophenyl group, which confers an amphiphilic character to the tetrapyrrolic macrocycle. This effect can increase the interaction with the cell envelopment, improving the photocytotoxic activity against the microorganisms.

Photophysical and Photochemical Properties of 3-methylpterin as a New and More Stable Pterin-type Photosensitizer.

Pterin derivatives are heterocyclic compounds which are present in different biological systems. Neutral aqueous solutions of pterins present acid-base and keto-enol equilibria. These compounds, under UV-A radiation fluoresce, undergo photooxidation, generate reactive oxygen species and photoinduce the oxidation of biological substrates. As photosensitizers, they may act through different mechanisms, mainly through an electron transfer-initiated process (type-I mechanism), but they also produce singlet molecular oxygen (1 O2 ) upon irradiation (type-II mechanism). In general, upon UV-A excitation two triplet states, corresponding to the lactim and lactam tautomers, are formed, but only the last one is the responsible for the photosensitized reactions of biomolecules. We present a study of the photochemical properties of 3-methylpterin (3-Mep) which, in contrast to most pterin derivatives, exists only in the lactam form. Also an improvement in the synthesis of 3-Mep is reported. The spectroscopic properties 3-Mep in aqueous solution were similar to those of the unsubstituted pterin derivative (Ptr) in its acid form, such as absorption, fluorescent and phosphorescent emission spectra. Experiments using 2'-deoxyguanosine 5'-monophosphate (dGMP) as oxidizable target demonstrated that methylation at C-3 position of the pterin moiety does not affect significantly the efficiency of photosensitization, but results in a more photostable sensitizer.

Proton-Dependent Switching of a Novel Amino Chlorin Derivative as a Fluorescent Probe and Photosensitizer for Acidic Media.

A novel chlorin derivative (TPCF20 -NMe2 ) has been synthesized as a syn adduct of a pyrrolidine-fused chlorin bearing a C-linked N,N-dimethylaminophenyl residue. The absorption spectrum of TPCF20 -NMe2 is essentially identical to that of TPCF20 in N,N-dimethylformamide, indicating a very weak interaction between the chlorin macrocycle and the amine group in the ground state. However, the fluorescence emission of the chlorin moiety in TPCF20 -NMe2 is effectively quenched by the attached amine unit. Moreover, TPCF20 -NMe2 is unable to attain a triplet excited state or to photosensitize singlet molecular oxygen. Spectroscopic and redox properties indicate that intramolecular photoinduced electron transfer can take place from the N,N-dimethylaminophenyl group to the chlorin macrocycle. Thus, in an acid medium, protonation of the amino group leads to a considerable increase in the fluorescence emission, triplet excited-state formation, and singlet molecular oxygen production. Photodynamic inactivation of Escherichia coli sensitized by TPCF20 -NMe2 is negligible at neutral pH. However, this chlorin becomes highly effective in inactivating E. coli cells under acidic conditions. Therefore, these results indicate that TPCF20 -NMe2 is an interesting molecular structure, in which protonation of the amino group can be used as an off/on molecular switch activating red fluorescence emission and photodynamic activity capable of eradicating bacteria.

A Computational Way To Achieve More Effective Candidates for Photodynamic Therapy.

The purpose of the work described herein is to design highly efficient photosensitizers (PS) for photodynamic therapy (PDT) in theory. A series of expanded Zn porphyrins have been studied as light-activated PS. Their main photophysical properties are systematically calculated by using density functional theory and its time-dependent extension. The mechanisms of PDT are discussed. All the considered candidates exhibit intense absorption in the therapeutic window (600-800 nm), efficient intersystem crossing, and sufficient energy for singlet molecular oxygen production. Accordingly, the designed Zn pentaphyrins and sapphyrins would be proposed as potential PS for PDT. Moreover, the therapeutic effects of Zn pentaphyrins and sapphyrins are better than those of the referenced Zn iso-pentaphyrin. It is expected that the results could provide a new way to design and develop PS for PDT application.

Generation of ROS mediated by mechanical waves (ultrasound) and its possible applications

The thermal decomposition of 9,10 diphenylanthracene peroxide (DPAO2) generates DPA and a mix of triplet and singlet molecular oxygen. For DPAO2 the efficiency to produce singlet molecular oxygen is 0.35. On the other hand, it has shown that many thermal reactions can be carried out through the interaction of molecules with ultrasound. Ultrasound irradiation can create hydrodynamic stress (sonomechanical process), inertial cavitation (pyrolitic process) and long range effects mediated by radicals or ROS. Sonochemical reactions can be originated by pyrolytic like process, shock mechanical waves, thermal reactions and radical and ROS mediated reactions. Sonolysis of pure water can yield hydrogen or hydroxyl radicals and hydrogen peroxide (ROS). When DPAO2 in 1,4 dioxane solution is treated with 20 or 24kHz and different power intensity the production of molecular singlet oxygen is observed. Specific scavengers like tetracyclone (TC) are used to demonstrate it. The efficiency now is 0.85 showing that the sonochemical process is much more efficient that the thermal one. Another endoperoxide, artemisinin was also studied. Unlike the concept of photosensitizer of photodynamic therapy, in spite of large amount of reported results in literature, the term sonosensitizer and the sonosensitization process are not well defined. We define sonosensitized reaction as one in which a chemical species decompose as consequence of cavitation phenomena producing ROS or other radicals and some other target species does undergo a chemical reaction. The concept could be reach rapidly other peroxides which are now under experimental studies. For artemisinin, an important antimalarian and anticancer drug, was established that ultrasound irradiation increases the effectiveness of the treatment but without any explanation. We show that artemisinin is an endoperoxide and behaves as a sonosensitizer in the sense of our definition.

Nanoenvironmental effect in AOT reverse micelles on the triplet excited state properties of flavins and quenching by molecular oxygen

AbstractThe triplet quantum yield (ΦT) and lifetime (τT) of the lowest excited triplet state of the flavins (3F*), for example, lumiflavin, riboflavin, flavin mononucleotide, and flavin adenine dinucleotide were determined by laser‐flash photolysis experiments in Aerosol‐OT reverse micelles (AOT RM) dispersed in n‐hexane as function of the amount of water dissolved w0 = [H2O]/[AOT]. The energy‐transfer quenching of 3F* by triplet molecular oxygen 3O2 to produce singlet molecular oxygen (1O2) was also evaluated by applying a simple pseudophase model for the 3O2 partition between the organic solvent and the AOT RM. The quantum yield of 1O2 generation by the flavins was also calculated. The results are discussed as a function of the nanoenvironmental changes produced in the constrained aqueous interior of the AOT RM as the amount of dispersed water increases. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Synthesis, crystal structure and physicochemical characterization of a Hg(II) complex with 6-methoxyquinoline as ligand

Abstract A new complex of Hg(II) with 6-methoxyquinoline (C10H9NO-6MQ) has been synthesized and characterized. The structure of the complex Hg(6MQ)Cl2 was determined by single crystal X-ray diffraction. It crystallizes in the monoclinic space group P21/c with a = 3.9139(3), b = 26.3400(2), c = 10.9090(9) Å, β = 89.833(6)°, V = 1124.6(1) Å3 and Z = 4 molecules per unit cell. The coordination geometry of the mercury(II) center can be described as a distorted square pyramid formed by one nitrogen atom of the 6MQ and four chlorine atoms. Fourier transform infrared, Raman and UV/Vis spectroscopic studies have been carried out to characterize the compound, using theoretical calculations for the assignment of the experimentally observed bands. The thermal behavior was investigated by thermogravimetric analysis. The quantum yield of singlet molecular oxygen production ΦΔ was measured with steady-state methods in ethanol, using 9,10-dimethylanthracene (DMA) as actinometer and Bengal rose as reference photosensitizer. The resultant singlet molecular oxygen was detected indirectly by photooxidation reactions of DMA. The luminescence properties have also been studied.

Subtle structural changes in octupolar merocyanine dyes influence the photosensitized production of singlet oxygen.

The photophysical properties of two indoline-based octupolar merocyanine dyes and of the corresponding quinoline-based dyes were examined. This seemingly subtle structural change in the chromophore of these molecules has an appreciable effect on the yields with which these respective compounds sensitize the production of singlet molecular oxygen, O2(a(1)Δg). The indoline-based dyes are reasonably efficient O2(a(1)Δg) sensitizers (ϕΔ ∼ 0.35), whereas the quinoline-based dyes are poor O2(a(1)Δg) sensitizers (ϕΔ ∼ 0.005). A series of experiments, including Laser-Induced Optoacoustic Calorimetric (LIOAC) measurements, reveal that this difference principally reflects the fact that the excited singlet state of the quinoline-based dyes rapidly and efficiently decays via nonradiative channels to regenerate the ground state molecule. It is likely that a charge-transfer state mediates this efficient coupling between the excited and ground states. Such subtle, structure-dependent effects are important in elucidating and ultimately understanding phenomena that influence the efficiency of photosensitized O2(a(1)Δg) production. In turn, the knowledge gained facilitates the rational design and preparation of O2(a(1)Δg) sensitizers with explicitly controlled properties.

New azine compounds as photoantimicrobial agents against Staphylococcus aureus

Aggregation phenomena of Neutral Red and a new derivative monobrominated Neutral Red were examined in different buffer solutions as a function of dye concentration. The dyes were chemically and photochemically stable and the lipophilicity of the new bromo-compound was characterized by experimental and computer prediction data. In addition, the acid dissociation constant and the singlet molecular oxygen production were determined spectrophotometrically yielding values of 1.16 and 3.14 for Neutral Red and the monobrominated derivative, respectively.The effect of photosensitizer concentration, visible irradiation time and cellular density on lethal photosensitization against Staphylococcus aureus were investigated. The improved physicochemical and photophysical properties of monobrominated Neutral Red were accompanied by a significant increase in the photoantimicrobial action, in conventional-sensitive and -resistant isolates.Based on these results, the dyes exhibited favorable properties; therefore, the new derivative compound could be a promising sensitizer with applications in the photoinactivation of S. aureus.

Riboflavin derivatives for enhanced photodynamic activity against Leishmania parasites

Riboflavin derivatives with various substituents (O-acyl, N-methyl, N-alkylcarboxyalkyl or N-alkyl(trialkyl)ammonium) have been prepared and spectroscopically characterized (absorption, emission and fluorescence quantum yields). Their quantum yields of photosensitized singlet molecular oxygen production (ΦΔ 0.24–0.58) and octanol/water partition coefficients (Pow ≤0.01–11) were measured. Preliminary studies indicate that all derivatives display higher phototoxicity against the human protozoan parasite Leishmania than the parent riboflavin, with negligible toxicity in the absence of light. Their photodynamic action shows a higher correlation with Pow than with ΦΔ, opening up their potential application to cutaneous diseases treatment.