Synergistic photogeneration of nitric oxide and singlet oxygen by nanofiber membranes via blue and/or red-light irradiation: Strong antibacterial action.

New functionalities were added to biocompatible polycaprolactone nanofiber materials through the co-encapsulation of chlorin e6 trimethyl ester (Ce6) photogenerating singlet oxygen and absorbing light both in the blue and red regions, and using 4-(N-(aminopropyl)-3-(trifluoromethyl)-4-nitrobenzenamine)-7-nitrobenzofurazan, NO-photodonor (NOP), absorbing light in the blue region of visible light. Time-resolved and steady-state luminescence, as well as absorption spectroscopy, were used to monitor both photoactive compounds. The nanofiber material exhibited photogeneration of antibacterial species, specifically nitric oxide and singlet oxygen, upon visible light excitation. This process resulted in the efficient photodynamic inactivation of E. coli not only close to nanofiber material surfaces due to short-lived singlet oxygen, but even at longer distances due to diffusion of longer-lived nitric oxide. Interestingly, nitric oxide was also formed by processes involving photosensitization of Ce6 during irradiation by red light. This is promising for numerous applications, especially in the biomedical field, where strictly local photogeneration of NO and its therapeutic benefits can be applied using excitation in the "human body phototherapeutic window" (600-850 nm). Generally, due to the high permeability of red light, the photogeneration of NO can be achieved in any aqueous environment where direct excitation of NOP to its absorbance in the blue region is limited.

Organization of Cooperating Aluminum Pairs in Ferrierite Evidenced by Luminescence Quenching.

We show that four cooperating Al atoms located at the two neighboring six-membered (6-MR) rings in the ferrierite framework can be readily discerned by luminescence studies. Thus, luminescent Zn(II) cations accommodated by one aluminum pair of the 6-MR ring can be effectively quenched by neighboring Co(II) ions stabilized by the second ring. Quenching occurs via the energy transfer mechanism and allows estimation of the critical radius of Zn(II)-Co(II) interactions. This points to the appropriate geometry and distance of the transition metal ions accommodated within zeolite, providing direct evidence of the four-aluminum atom arrangement in the ferrierite framework.

Structural, optical, and bioimaging characterization of carbon quantum dots solvothermally synthesized from o-phenylenediamine.

Carbon quantum dots as a novel type of carbon nanomaterials have attracted the attention of many researchers because of their unique optical, antibacterial, and anticancer properties as well as their biocompatibility. In this study, for the first time, carbon quantum dots were prepared from o-phenylenediamine dissolved in toluene by a solvothermal route. Subsequently, the prepared carbon quantum dots were encapsulated into polyurethane films by a swelling-encapsulation-shrink method. Analyses of the results obtained by different characterization methods (AFM, TEM, EDS, FTIR, photoluminescence, and EPR) indicate the significant influence of the precursor on structural, chemical, and optical properties. Antibacterial and cytotoxicity tests showed that these dots did not have any antibacterial potential, because of the low extent of reactive oxygen species production, and showed low dark cytotoxicity. By investigating the cellular uptake, it was established that these dots penetrated the HeLa cells and could be used as probes for bioimaging.

Highly Efficient Antibacterial Polymer Composites Based on Hydrophobic Riboflavin Carbon Polymerized Dots.

Development of new types of antimicrobial coatings is of utmost importance due to increasing problems with pathogen transmission from various infectious surfaces to human beings. In this study, new types of highly potent antimicrobial polyurethane composite films encapsulated by hydrophobic riboflavin-based carbon polymer dots are presented. Detailed structural, optical, antimicrobial, and cytotoxic investigations of these composites were conducted. Low-power blue light triggered the composites to eradicate Escherichia coli in 30 min, whereas the same effect toward Staphylococcus aureus was reached after 60 min. These composites also show low toxicity against MRC-5 cells. In this way, RF-CPD composites can be used for sterilization of highly touched objects in the healthcare industry.

Antibacterial Nanoparticles with Natural Photosensitizers Extracted from Spinach Leaves.

We prepared antibacterial polystyrene nanoparticles (NPs) with natural photosensitizers from chlorophyll (Chl) extract via a simple nanoprecipitation method using the same solvent for dissolution of the polystyrene matrix and extraction of Chls from spinach leaves. A high photo-oxidation and antibacterial effect was demonstrated on Escherichia coli and was based on the photogeneration of singlet oxygen O2(1Δg), which was directly monitored by NIR luminescence measurements and indirectly verified using a chemical trap. The photoactivity of NPs was triggered by visible light, with enhanced red absorption by Chls. To reduce the quenching effect of carotenoids (ß-carotene, lutein, etc.) in the Chl extract, diluted and/or preirradiated samples, in which the photo-oxidized carotenoids lose their quenching effect, were used for preparation of the NPs. For enhanced photo-oxidation and antibacterial effects, a sulfonated polystyrene matrix was used for preparation of a stable dispersion of sulfonated NPs, with the quenching effect of carotenoids being suppressed.

Magnetically Separable Photoactive Nanofiber Membranes for Photocatalytic and Antibacterial Applications.

We have prepared photoactive multifunctional nanofiber membranes via the simple electrospinning method. The antibacterial and photocatalytic properties of these materials are based on the generation of singlet oxygen formed by processes photosensitized by the tetraphenylporphyrin encapsulated in the nanofibers. The addition of magnetic features in the form of magnetic maghemite (γ-Fe2O3) nanoparticles stabilized by polyethylenimine enables additional functionalities, namely, the postirradiation formation of hydrogen peroxide and improved photothermal properties. This hybrid material allows for remote manipulation by a magnetic field, even in hazardous and/or highly microbial contaminant environments.

Water-soluble sulfonated phosphorus(V) corrolazines and porphyrazines: the effect of macrocycle contraction and pyrazine ring fusion on spectral, acid-base and photophysical properties.

Novel water-soluble dihydroxophosphorus(V) complexes of sulphophenyl substituted porphyrazine (6), corrolazine (7) and its pyrazine fused derivative (8) were prepared and their spectral, acid-base and photophysical properties in aqueous solutions were studied. Due to the presence of eight SO3H groups, the compounds were fully monomeric (7 and 8) or only slightly aggregated (6) in water. Spectrophotometric titration revealed that the two stage deprotonation of axially bonded hydroxy groups can be achieved for porphyrazine 6 (pKa1 = 5.62, pKa2 = 9.13) and pyrazine fused corrolazine 8 (pKa1 = 6.5, pKa2 = 11.7), while only the first dissociation stage could be observed for corrolazine 7 (pKa1 = 9.94). The fluorescence emission of the corrolazines 7, 8 and especially porphyrazine 6 was low in water (ΦF = 0.086, 0.18, and 0.014, respectively) and completely quenched under basic conditions due to photoinduced electron transfer. In comparison with porphyrazine 6, the contraction of the macrocycle in the corrolazines 7 and 8 induced significant improvement of singlet oxygen production in water reaching values of ΦΔ = 0.56 and 0.43, respectively, which makes the corrolazines promising photosensitizers for photodynamic therapy. The observed evolution of the electronic absorption spectra and fluorescence quenching observed in a basic medium was explained using the model DFT calculations (cc-pvtz basis set) performed for the dihydroxophosphorus(V) complexes of unsubstituted porphyrazine and corrolazine and their mono- and doubly deprotonated forms.

Heterogeneous photoactive antimicrobial coatings based on a fluoroplastic doped with an octahedral molybdenum cluster compound.

Despite the wide variety of strategies developed to combat pathogenic microorganisms, the infectious diseases they cause remain a worldwide health issue. Hence, the search for new disinfectants, which prevent infection spread, constitutes an extremely urgent task. One of the most promising methods is the use of photoactive compounds - photosensitizers, capable of generating reactive oxygen species, in particular, singlet oxygen (O2(1Δg)), which causes rapid and effective death of microorganisms of all types. In this work, we propose the utilization of the powdered cluster complex (Bu4N)2[{Mo6I8}(OTs)6] as a photoactive additive to commercially available fluoroplastic lacquer F-32L to create heterogeneous self-sterilizing coatings. We show that soaking of the prepared films in water for 60 days did not lead to a decrease in their photosensitization properties indicating their excellent stability. Moreover, the use of the cluster complex in the solid state allowed significant expansion of the operating wavelength range, which covers the UV region and a large part of the visible region (250-650 nm). The films displayed high photoantimicrobial activity against five common pathogens (bacteria and fungi) under white-light irradiation. Overall, the properties demonstrated make these materials promising for practical use in everyday outdoor and indoor disinfection since they are active under both sunlight and artificial lighting.

Luminescent Cationic Group 4 Metallocene Complexes Stabilized by Pendant N-Donor Groups.

Cationic group 4 metallocene complexes with pendant imine and pyridine donor groups were prepared as stable crystalline [B(C6F5)4]- salts either by protonation of the intramolecularly bound ketimide moiety in neutral complexes [(η5-C5Me5){η5-C5H4CMe2CMe2C(R)═N-κN}MCl] (M = Ti, Zr, Hf; R = t-Bu, Ph) by PhNMe2H+[B(C6F5)4]- to give [(η5-C5Me5){η5-C5H4CMe2CMe2C(R)═NH-κN}MCl]+[B(C6F5)4]- or by chloride ligand abstraction from the complexes [(η5-C5Me5)(η5-C5H4CMe2CH2C5H4N)MCl2] (M = Ti, Zr) by Li[B(C6F5)4]·2.5Et2O to give [(η5-C5Me5)(η5-C5H4CMe2CH2C5H4N-κN)MCl]+[B(C6F5)4]-. Solid state structures of the new compounds were established by X-ray diffraction analysis, and their electrochemical behavior was studied by cyclic voltammetry. The cationic complexes of Zr and Hf, compared to the corresponding neutral species, exhibited significantly enhanced luminescence predominantly from triplet ligand-to-metal (3LMCT) excited states with lifetimes up to 62 µs and quantum yields up to 58% in the solid state. DFT calculations were performed to explain the structural features and optical and electrochemical properties of the complexes.

Electrophoretically Deposited Layers of Octahedral Molybdenum Cluster Complexes: A Promising Coating for Mitigation of Pathogenic Bacterial Biofilms under Blue Light.

The fight against infective microorganisms is becoming a worldwide priority due to serious concerns about the rising numbers of drug-resistant pathogenic bacteria. In this context, the inactivation of pathogens by singlet oxygen, O2(1Δg), produced by photosensitizers upon light irradiation has become an attractive strategy to combat drug-resistant microbes. To achieve this goal, we electrophoretically deposited O2(1Δg)-photosensitizing octahedral molybdenum cluster complexes on indium-tin oxide-coated glass plates. This procedure led to the first example of molecular photosensitizer layers able to photoinactivate bacterial biofilms. We delineated the morphology, composition, luminescence, and singlet oxygen formation of these layers and correlated these features with their antibacterial activity. Clearly, continuous 460 nm light irradiation imparted the layers with strong antibacterial properties, and the activity of these layers inhibited the biofilm formation and eradicated mature biofilms of Gram-positive Staphylococcus aureus and Enterococcus faecalis, as well as, Gram-negative Pseudomonas aeruginosa and Escherichia coli bacterial strains. Overall, the microstructure-related oxygen diffusivity of the layers and the water stability of the complexes were the most critical parameters for the efficient and durable use. These photoactive layers are attractive for the design of antibacterial surfaces activated by visible light and include additional functionalities such as the conversion of harmful UV/blue light to red light or oxygen sensing.

Photodynamic-active smart biocompatible material for an antibacterial surface coating.

Here we present a new effective antibacterial material suitable for a coating, e.g., surface treatment of textiles, which is also time and financially undemanding. The most important role is played by hydrophobic carbon quantum dots, as a new type of photosensitizer, produced by carbonization of different carbon precursors, which are incorporated by swelling from solution into various polymer matrices in the form of thin films, in particular polyurethanes, which are currently commercially used for industrial surface treatment of textiles. The role of hydrophobic carbon quantum dots is to work as photosensitizers upon irradiation and produce reactive oxygen species, namely singlet oxygen, which is already known as the most effective radical for elimination different kinds of bacteria on the surface or in close proximity to such modified material. Therefore, we have mainly studied the effect of hydrophobic carbon quantum dots on Staphylococcus aureus and the cytotoxicity tests, which are essential for the safe handling of such material. Also, the production of singlet oxygen by several methods (electron paramagnetic spectroscopy, time-resolved near-infrared spectroscopy), surface structures (atomic force microscopy and contact angle measurement), and the effect of radiation on polymer matrices were studied. The prepared material is easily modulated by end-user requirements.

Dually directional glycosylated phthalocyanines as extracellular red-emitting fluorescent probes.

The development of new non-aggregated phthalocyanines bearing multivalent saccharide moieties on their macrocyclic rims is of great interest. Many characteristics, including water-solubility, non-toxicity and others, can be feasibly obtained by these amphiphiles which can be considered as a key solution for demonstrating highly efficient photoactive materials in water. Herein, a family of five newly prepared dually directional Zn(ii) containing phthalocyanines (PcG1-4) and azaphthalocyanine (AzaPcG1) glycoconjugates is described. The unique spatial arrangement of the glucoside units based on peripherally hexadeca-(PcG1) and nonperipherally octa-(PcG4) macrocycles provides a fully monomeric behaviour along with a high fluorescence (ΦF∼ 0.21) in aqueous solution. These amphiphiles were characterized by low toxicity, and an extremely low cellular uptake was obtained due to the highly polar nature of the glucoside substituents. Accordingly, their potential as suitable photoactive chromophores for red-emitting extracellular fluorescent probes has been confirmed upon the evaluation of paracellular transport using a layer of MDCKII cells with the permeability coefficient fully comparable with an established evaluator of the integrity of the monolayer.

Multifunctional Photosensitizing and Biotinylated Polystyrene Nanofiber Membranes/Composites for Binding of Biologically Active Compounds.

A three-step postprocessing functionalization of pristine electrospun polystyrene nanofiber membranes was used for the preparation of nanostructured biotinylated materials with an externally bonded porphyrin photosensitizer. Subsequently, the material was able to strongly bind biologically active streptavidin derivatives while keeping its photosensitizing and antibacterial properties due to the generation of singlet oxygen under the exclusive control of visible light. The resulting multifunctional materials functionalized by a streptavidin-horseradish peroxidase conjugate as a model bioactive compound preserved its enzymatic activity even in the presence of a porphyrin photosensitizer with some quenching effect on the activity of the photosensitizer. Prolonged kinetics of both singlet oxygen luminescence and singlet oxygen-sensitized delayed fluorescence (SODF) were found after irradiation by visible light. The above results reflected less effective quenching of the porphyrin photosensitizer triplet state by ground state oxygen and indicated hindered oxygen transport (diffusion) due to surface functionalization. We found that SODF could be used as a valuable tool for optimizing photosensitizing efficiency as well as a tool for confirming surface functionalization. Full photosensitizing and enzyme activity could be achieved by a space separation of photosensitizers and enzyme/biomolecules in the nanofiber composites consisting of two layers. The upper layer contained a photosensitizer that generated antibacterial singlet oxygen upon irradiation by light, and the bottom layer retained enzymatic activity for biochemical reactions.

Polystyrene and Poly(ethylene glycol)-b-Poly(ε-caprolactone) Nanoparticles with Porphyrins: Structure, Size, and Photooxidation Properties.

The transport of a photosensitizer to target biological structures followed by the release of singlet oxygen is a critical step in photodynamic therapy. We compared the (photo)physical properties of polystyrene nanoparticles (TPP@PS) of different sizes and self-assembled poly(ethylene glycol)-b-poly(ε-caprolactone) core/shell nanoparticles (TPP@PEG-PCL) with different lengths of copolymer blocks, both suitable for the transport of the tetraphenylporphyrin (TPP) photosensitizer. The singlet oxygen was formed inside both nanoparticles after irradiation with visible light. Its kinetics was controlled by the size of TPP@PS; its lifetime (τΔ) increased with increasing nanoparticle size (from 6.5 to 16 µs) because of hindered diffusion into the external aqueous environment, where it was quickly deactivated. Accordingly, the prolongation of the singlet oxygen-sensitized delayed fluorescence kinetics was found for TPP@PS of high size. The TPP@PEG-PCL self-assemblies allowed for enhanced oxygen diffusion, and the estimated low values of τΔ ≈ 3.7 µs were independent of the size of building blocks. The delayed fluorescence in oxygen-free conditions originating from triplet-triplet annihilation indicated a high mobility of TPP in the PCL core in comparison with fixed molecules in the PS matrix. Photooxidation of uric acid revealed the highest efficacy for TPP@PS of small sizes, whereas the largest TPP@PS exhibited the lowest activity, and the efficacy of TPP@PEG-PCL remained independent of the sizes of the building blocks.

Effect of Iodination on the Photophysics of the Laser Borane anti-B18H22: Generation of Efficient Photosensitizers of Oxygen.

Treatment of the laser borane anti-B18H22 (compound 1) with iodine in ethanol gives the monoiodinated derivative 7-I-anti-B18H21 (compound 2) in 67% yield, or, by reaction with iodine or ICl in the presence of AlCl3 in dichloromethane, the diiodinated derivative 4,4'-I2-anti-B18H20 (compound 3) in 85% yield. On excitation with 360 nm light, both compounds 2 and 3 give strong green phosphorescent emissions (λmax = 525 nm, ΦL = 0.41 and λmax = 545 nm, ΦL = 0.71 respectively) that are quenched by dioxygen to produce O2(1Δg) singlet oxygen with quantum yields of ΦΔ = 0.52 and 0.36 respectively. Similarly strong emissions can be stimulated via the nonlinear process of two-photon absorption when exciting with 720 or 800 nm light. The high quantum yields of singlet-oxygen production, coupled with the option of two-photon excitation, make compounds 2 and 3 promising O2(1Δg) photosensitizers. The molecular structures of compounds 2 and 3 were determined by single-crystal X-ray crystallographic studies as well as multinuclear NMR spectroscopy and mass spectrometry. Time-resolved UV-vis spectroscopy was used to delineate their photophysical properties, and the electronic-structure properties of the emitting species were determined by means of multiconfigurational quantum-chemistry computations.

Antibacterial photodynamic activity of carbon quantum dots/polydimethylsiloxane nanocomposites against Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae.

Despite great efforts, the design of antibacterial surfaces is still a challenge. In this work, results of structural, mechanical, cytotoxic and antibacterial activities of hydrophobic carbon quantum dots/polydimethylsiloxane surfaces are presented. Antibacterial action of this surface is based on the generation of reactive oxygen species which cause bacteria damage by oxidative stress. At the same time, this surface was not cytotoxic towards the NIH/3T3 cells. Swelling-encapsulation-shrink method is applied for encapsulation of hydrophobic carbon quantum dots in medical grade silicone-polydimethylsiloxane. XPS and photoluminescence spectroscopy analyses confirm that hydrophobic carbon quantum dots have been encapsulated successfully into polydimethylsiloxane polymer matrix. Based on stress-strain test the improvement of mechanical properties of these nanocomposites is established. It is shown by electron paramagnetic resonance spectroscopy and luminescence method that nanocomposite generates singlet oxygen initiated by 470 nm blue light irradiation. Antibacterial testing shows the nanocomposite in the form of foil kills Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae and is very effective after only a 15 min irradiation.

The Photodynamic Properties and the Genotoxicity of Heat-Treated Silicalite-1 Films.

We investigated the use of a supported silicalite-1 film (SF) as a promising coating for metallic materials used in the fabrication of prostheses. The role of carbonaceous residua present on high-temperature calcined-SF in generating singlet oxygen for future use as a sterilization method has also been addressed, and the potential genotoxicity of these residua in osteoblast-like cells has been investigated. Calcination of as-synthesized SF induced the appearance of a rather complicated mixture of aliphatic and aromatic species on its outer surface. A series of variously volatile polycyclic aromatic hydrocarbons (PAH), including naphthalene, fluorene, phenanthrene, anthracene, fluoranthene, and pyrene, were identified in micromole concentrations. Irradiation of these PAHs on calcined-SF immersed in air-saturated chloroform led to the formation of very low concentrations of singlet oxygen. However, an increased level of DNA damage was observed on calcined-SF by immunofluorescence staining of phosphorylated histone H2AX analyzed by flow cytometry.

The effect of iodide and temperature on enhancing antibacterial properties of nanoparticles with an encapsulated photosensitizer.

Aqueous dispersions of sulfonated polystyrene nanoparticles (average diameter: 30 ± 14 nm) with encapsulated 5,10,15,20-tetraphenylporphyrin (TPP) are promising candidates for antibacterial treatments due to the photogeneration of cytotoxic singlet oxygen species O2(1Δg) under physiological conditions using visible light. The antibacterial effect on gram-negative Escherichia coli was significantly enhanced after the addition of nontoxic potassium iodide (0.001-0.01 M) because photogenerated O2(1Δg) oxidized iodide to I2/I3-, which is another antibacterial species. The improved antibacterial properties were predicted using luminescence measurements of O2(1Δg), transient absorption of TPP triplets and singlet oxygen-sensitized delayed fluorescence (SODF). In contrast to a solution of free photosensitizers, the aqueous dispersion of photoactive nanoparticles did not exhibit any quenching of the excited states after the addition of iodide or any tendency toward aggregation and/or I3--induced photo-aggregation. We also observed a decrease in the lifetime of O2(1Δg) and a significant increase in SODF intensity at higher temperatures, due to the increased oxygen diffusion coefficient in nanoparticles and aqueous surroundings. This effect corresponds with the significantly stronger antibacterial effect of nanoparticles at physiological temperature (37 °C) in comparison with that at room temperature (25 °C).

Phosphinatophenylporphyrins tailored for high photodynamic efficacy.

The development of effective photosensitizers is particularly attractive for photodynamic therapy of cancer. Three novel porphyrin photosensitizers functionalized with phosphinic groups were synthesized and their physicochemical, photophysical, and photobiological properties were collected. Phosphinic acid groups (R1R2POOH) attached to the porphyrin moiety (R1) contain different R2 substituents (methyl, isopropyl, phenyl in this study). The presence of phosphinic groups does not influence absorption and photophysical properties of the porphyrin units, including the O2(1Δg) productivity. In vitro studies show that these porphyrins accumulate in cancer cells, are inherently nontoxic, however, exhibit high phototoxicity upon irradiation with visible light with their phototoxic efficacy tuned by R2 substituents on the phosphorus centre. Thus, phosphinatophenylporphyrin with isopropyl substituents has the strongest photodynamic efficacy due to the most efficient cellular uptake. We demonstrate that these porphyrins are attractive candidates for photodynamic applications since their photodynamic efficacy can be easily tuned by the R2 substituent.