Overview of cationic phthalocyanines for effective photoinactivation of pathogenic microorganisms

Pivotal Role of the Intracellular Microenvironment in the High Photodynamic Activity of Cationic Phthalocyanines

To investigate the influence of phthalocyanine aggregation on their photodynamic activity, a series of six cationic water-soluble zinc(II) phthalocyanines bearing from four to sixteen 4-((diethylmethylammonium)methyl)phenoxy substituents was synthesized. Depending on their structure, the phthalocyanines have different aggregation behaviors in phosphate buffer solutions ranging from fully assembled to monomeric states. Remarkably, independent of aggregation in buffer, very high photodynamic efficiencies against the tumor cell lines MCF-7 and MDA-MB-231 in the nanomolar range were found for all investigated phthalocyanine, and the IC50(light) varied from 27 to 358 nM (3.5 J/cm2, 660 nm) with IC50(dark)/IC50(light) ratios up to ∼3700. This is due to the intracellular disassembly of aggregated phthalocyanines with the formation of monomeric photoactive forms, as demonstrated by fluorescence microscopy. Indeed, the interaction of aggregated phthalocyanines with serum proteins in a buffer resulted in the disassembly of nonluminescent aggregate species with the release of photoactive monomers bound to protein macromolecules.

Bacterial Photodynamic Inactivation: Eradication of Staphylococcus aureus and Escherichia coli Mediated by Pyridinium-Pyrazolyl Zinc(II) Phthalocyanines

Antimicrobial resistance remains an enduring global health issue, manifested when microorganisms, such as bacteria, lack responsiveness to antimicrobial treatments. Photodynamic inactivation (PDI) of microorganisms arises as a noninvasive, nontoxic, and repeatable alternative for the inactivation of a broad range of pathogens. So, this study reports the synthesis, structural characterization, and photophysical properties of a new tetra-β-substituted pyridinium-pyrazolyl zinc(II) phthalocyanine (ZnPc 1a) that was compared with two previously described pyridinium-pyrazolyl ZnPcs 2a and 3a. The PDI efficacy of these three ZnPcs (1a-3a) against a drug-resistant Gram-positive bacterium (as Staphylococcus aureus) and a Gram-negative bacterium (as Escherichia coli) is also reported. The PDI efficacy toward these bacteria was examined with ZnPcs 1a-3a in the 5.0-10.0 μM range using a white light source with an irradiance of 150 mW/cm2. All ZnPcs displayed a significant PDI activity against S. aureus, with reductions superior to 3 Log CFU/mL. Increasing the treatment time, the E. coli was inactivated until the detection limit of the method (>6.3 Log CFU/mL) using the quaternized ZnPcs 1a-3a (10.0 μM, 120 min) being the inactivation time was reduced when added the KI for ZnPcs 1a and 3a. These findings demonstrate the effective PDI performance of pyridinium-pyrazolyl group-bearing PSs, indicating their potential use as a versatile antimicrobial agent for managing infections induced by Gram-negative and Gram-positive bacteria.

Unveiling the potent antimicrobial photodynamic therapy in Gram-positive and Gram-negative bacteria - Water remediation with monocharged chlorins

Water pollution is a significant concern worldwide, and it includes contaminants such as antibiotic-resistant pathogens. Antimicrobial photodynamic therapy (aPDT) offers a non-invasive and non-toxic alternative for the inactivation of these microorganisms. So, this study reports the synthesis, structural characterisation, photophysical properties, and aPDT efficacy of cationic free-base and zinc(II) chlorin (Chl) derivatives bearing N,N-dimethylpyrrolydinium groups (H2Chl 1a and ZnChl 1b). The aPDT assays were performed against two bacterial models: Staphylococcus aureus (Gram-(+)) and Escherichia coli (Gram-(-)). The H2Chl 1a and ZnChl 1b distinct's solubility profile, coupled with their ability to generate singlet oxygen (1O2) under light exposure, (H2Chl 1a, ФΔ = 0.58 < TPP, ФΔ = 0.65 < ZnChl 1b, ФΔ = 0.83) opens up their potential application as photosensitizers (PS) in aPDT. The effectiveness of H2Chl 1a and ZnChl 1b at 1.0 and 5.0 μM in aPDT against S. aureus and E. coli at 500 W m-2 (total exposure time: 60-120 min) showed a viability reduction >6.0 log10 CFU mL-1. Additionally, KI was used as a coadjuvant to potentiate the photoinactivation of E. coli, reaching the method's detection limit (>4.0 log10 RLU). As most of the PS developed to inactivate Gram-negative bacteria are cationic with three or more charges, the fact that the H2Chl 1a and ZnChl 1b with only one cationic charge photoinactivate E. coli at low concentrations and with a reduced light dose, it is an importing discovery that deserves further exploration. These monocharged chlorin dyes have the potential for water remediation.

Multimodal integrated and broadband light-driven antibacterial cellulose fabric based on π-π coupling enhanced intermolecular FRET

Fabrication of antimicrobial photodynamic therapy (aPDT) materials based on organic photosensitizers has garnered considerable attention within functional textiles. However, the UV- or narrow-band absorption range of the photosensitizers results in poor photon utilization of the fabrics, limiting the photodynamic efficiency and wasting solar energy. In this study, a broadband light-driven antibacterial cellulose fabric (CF-ZnPc/NAD) was developed by loading carboxyl-modified zinc(II) phthalocyanine photosensitizer (CAZnPc) and cationic 1,8-naphthalimide fluorescent molecule (NAD) on the fabric via covalent binding and electrostatic adsorption assembly, facilitating the intermolecular π-π coupling and fluorescence resonance energy transfer (FRET) process. There is a 2.54-fold increase in photo-induced ROS generation capacity of CF-ZnPc/NAD via the FRET process compared to that of CF-ZnPc, and it also exhibited a strong photothermal effect (PTT), wherein the temperature of the fabric increased from 24.5 to 53.5 °C within 80 s of illumination (λ > 400 nm, 75 mW/cm2). CF-ZnPc/NAD exhibited strong light-harvesting capacity and a combination of aPDT and PTT, achieving excellent antibacterial performance against Staphylococcus aureus (Gram-positive, S. aureus) and Escherichia coli (Gram-negative, E.coli) with 99.99 % bacterial reduction under 90 min of illumination (λ > 400 nm, 10 ± 1 mW/cm2). This study demonstrates a novel and facile strategy for successfully fabricating high-performance antibacterial cellulose fabrics with potential biomedical prospects.

Editorial: Photodynamic Therapy as an Important Tool for Biological Breakthroughs-Photoactive Photosensitizers Applied from Cancer to Microbial Targets

Photodynamic therapy (PDT) stands as an approved clinical treatment for both oncologic and nononcologic disorders [...].

Light-Driven Tetra- and Octa-β-substituted Cationic Zinc(II) Phthalocyanines for Eradicating Fusarium oxysporum Conidia

Photodynamic inactivation (PDI) is an emerging therapeutic approach that can effectively inactivate diverse microbial forms, including vegetative forms and spores, while preserving host tissues and avoiding the development of resistance to the photosensitization procedure. This study evaluates the antifungal and sporicidal photodynamic activity of two water-soluble amphiphilic tetra- and octa-β-substituted zinc(II) phthalocyanine (ZnPc) dyes with dimethylaminopyridinium groups at the periphery (ZnPcs 1, 2) and their quaternized derivatives (ZnPcs 1a, 2a). Tetra(1, 1a)- and octa(2, 2a)-β-substituted zinc(II) phthalocyanines were prepared and assessed as photosensitizers (PSs) for their effects on Fusarium oxysporum conidia. Antimicrobial photoinactivation experiments were performed with each PS at 0.1, 1, 10, and 20 µM under white light irradiation at an irradiance of 135 mW·cm-2, for 60 min (light dose of 486 J·cm-2). High PDI efficiency was observed for PSs 1a, 2, and 2a (10 µM), corresponding to inactivation until the method's detection limit. PS 1 (20 µM) also achieved a considerable reduction of >5 log10 in the concentration of viable conidia. The quaternized PSs (1a, 2a) showed better PDI performance than the non-quaternized ones (1, 2), even at the low concentration of 1 µM, and a light dose of 486 J·cm-2. These cationic phthalocyanines are potent photodynamic drugs for antifungal applications due to their ability to effectively inactivate resistant forms, like conidia, with low concentrations and reasonable energy doses.

Advances in photocatalytic degradation of organic pollutants in wastewaters: harnessing the power of phthalocyanines and phthalocyanine-containing materials

Access to clean water is increasingly challenging worldwide due to human activities and climate change. Wastewater treatment and utilization offer a promising solution by reducing the reliance on pure underground water. However, it is crucial to develop efficient and sustainable methods for wastewater purification. Among the emerging wastewater treatment strategies, photocatalysis has gained significant attention for decomposing organic pollutants in water, especially when combined with sunlight and a recoverable photocatalyst. Heterogeneous photocatalysts have distinct advantages, as they can be recovered and reused without significant loss of activity over multiple cycles. Phthalocyanine dyes, with their exceptional photophysical properties, are particularly valuable for homogeneous and heterogeneous photocatalysis. By immobilizing these photosensitizers in various supports, hybrid materials extend their light absorption into the visible spectrum, complementing most supports' limited UV light absorption. The novelty and research importance of this review stems from its discussion of the multifaceted approach to treating contaminated wastewater with phthalocyanines and materials containing phthalocyanines. It highlights key aspects of each study, including photocatalytic efficiency, recyclability characteristics, investigation of the generation of oxygen species responsible for degradation, identification of the major degradation byproducts for each pollutant, and others. Moreover, the review includes tables that illustrate and compare the various phthalocyanines and supporting materials employed in each study for pollutant degradation. Additionally, almost all photocatalysts mentioned in this review could degrade at least 5% of the pollutant, and more than 50 photocatalysts showed photocatalytic rates above 50%. When immobilized in some support, the synergistic effect of the phthalocyanine was visible in the photocatalytic rate of the studied pollutant. However, when performing these types of works, it is necessary to understand the degradation products of each pollutant and their relative toxicities. Along with this, recyclability and stability studies are also necessary. Despite the good results presented in this review, some of the works lack those studies. Moreover, none of the works mentions any study in wastewater.

A Photochemical Study of Photo-Induced Electron Transfer from DNAs to a Cationic Phthalocyanine Derivative

Water-soluble cationic gallium(III)-Pc complex (GaPc) is capable of photogenerating ROSs but does not exhibit photocytotoxicity in vivo. GaPc binds selectively, through a π-π stacking interaction, to the 5'-terminal G-quartet of a G-quadruplex DNA. The photo-excited state of GaPc of the complex is effectively quenched through electron transfer (ET) from the ground state of DNA guanine (G) bases to the photo-excited state of GaPc (ET(G-GaPc)). Hence the loss of the photocytotoxicity of GaPc in vivo is most likely to be due to the effective quenching of its photo-excited state through ET(G-GaPc). In this study, we investigated the photochemical properties of GaPc in the presence of duplex DNAs formed from a series of sequences to elucidate the nature of ET(G-GaPc). We found that ET(G-GaPc) is allowed in electrostatic complexes between GaPc and G-containing duplex DNAs and that the rate of ET(G-GaPc) (kET(G-GaPc)) can be reasonably interpreted in terms of the distance between Pc moiety of GaPc and DNA G base in the complex. We also found that the quantum yields of singlet oxygen (1O2) generation (ΦΔs) determined for the GaPc-duplex DNA complexes were similar to the value reported for free GaPc (Fujishiro R, Sonoyama H, Ide Y, et al (2019) J Inorg Biochem 192:7-16), indicating that ET(G-GaPc) in the complex is rather limited. These results clearly demonstrated that photocytotoxicity of GaPc is crucially affected by ET(G-GaPc). Thus elucidation of interaction of a photosensitizer with biomolecules, i.e., an initial process in PDT, would be helpful to understand its subsequent photochemical processes.

Phthalocyanine aggregates in the photodynamic therapy: dogmas, controversies, and future prospects

Photodynamic therapy (PDT), a rapidly developing method for the treatment of cancer and bacterial diseases, is based on the photosensitization of oxygen to generate reactive oxygen species (ROS) that destroy specific biological targets. Among the various photosensitizers, phthalocyanines (Pc) have attracted particular attention due to their excellent photophysical properties, most of which meet the therapeutic requirements. The statement that aggregation of Pc-based photosensitizers is undesirable because it suppresses ROS generation has become commonplace in PDT. In this review, we have collected and discussed a number of works whose results refute this well-established axiom and show that aggregated forms of phthalocyanines can still exhibit photodynamic activity, in some cases in synergy with the photothermal and optoacoustic effects. In addition, ROS generation can be induced by aggregates under the conditions of sonodynamic therapy.

In Vitro Photoinactivation of Fusarium oxysporum Conidia with Light-Activated Ammonium Phthalocyanines

Antimicrobial photodynamic therapy (aPDT) has been explored as an innovative therapeutic approach because it can be used to inactivate a variety of microbial forms (vegetative forms and spores) without causing significant damage to host tissues, and without the development of resistance to the photosensitization process. This study assesses the photodynamic antifungal/sporicidal activity of tetra- and octasubstituted phthalocyanine (Pc) dyes with ammonium groups. Tetra- and octasubstituted zinc(II) phthalocyanines (1 and 2) were prepared and tested as photosensitizers (PSs) on Fusarium oxysporum conidia. Photoinactivation (PDI) tests were conducted with photosensitizer (PS) concentrations of 20, 40, and 60 µM under white-light exposure at an irradiance of 135 mW·cm^-2, applied during 30 and 60 min (light doses of 243 and 486 J·cm^-2). High PDI efficiency corresponding to the inactivation process until the detection limit was observed for both PSs. The tetrasubstituted PS was the most effective, requiring the lowest concentration and the shortest irradiation time for the complete inactivation of conidia (40 µM, 30 min, 243 J·cm^-2). Complete inactivation was also achieved with PS 2, but a longer irradiation time and a higher concentration (60 µM, 60 min, 486 J·cm^-2) were necessary. Because of the low concentrations and moderate energy doses required to inactivate resistant biological forms such as fungal conidia, these phthalocyanines can be considered potent antifungal photodynamic drugs.

Anti-Viral Photodynamic Inactivation of T4-like Bacteriophage as a Mammalian Virus Model in Blood

The laboratorial available methods applied in plasma disinfection can induce damage in other blood components. Antimicrobial photodynamic therapy (aPDT) represents a promising approach and is approved for plasma and platelet disinfection using non-porphyrinic photosensitizers (PSs), such as methylene blue (MB). In this study, the photodynamic action of three cationic porphyrins (Tri-Py(+)-Me, Tetra-Py(+)-Me and Tetra-S-Py(+)-Me) towards viruses was evaluated under white light irradiation at an irradiance of 25 and 150 mW·cm^−2, and the results were compared with the efficacy of the approved MB. None of the PSs caused hemolysis at the isotonic conditions, using a T4-like phage as a model of mammalian viruses. All porphyrins were more effective than MB in the photoinactivation of the T4-like phage in plasma. Moreover, the most efficient PS promoted a moderate inactivation rate of the T4-like phage in whole blood. Nevertheless, these porphyrins, such as MB, can be considered promising and safe PSs to photoinactivate viruses in blood plasma.

Photodynamic inactivation of pathogenic Gram-negative and Gram-positive bacteria mediated by Si(IV) phthalocyanines bearing axial ammonium units

The photodynamic inactivation (PDI) of microorganisms has gained interest as an efficient option for conventional antibiotic treatments. Recently, Si(IV) phthalocyanines (SiPcs) have been highlighted as promising photosensitizers (PSs) to the PDI of microorganisms due to their remarkable absorption and emission features. To increase the potential of cationic SiPcs as PS drugs, one novel (1a) and two previously described (2a and 3a) axially substituted PSs with di-, tetra-, and hexa-ammonium units, respectively, were synthesized and characterized. Their PDI effect was evaluated for the first time against Escherichia coli and Staphylococcus aureus, a Gram-negative and a Gram-positive bacterium, respectively. The photodynamic treatments were conducted with PS concentrations of 3.0 and 6.0 μM under 60 min of white light irradiation (150 mW.cm^-2). The biological results show high photodynamic efficiency for di- and tetra-cationic PSs 1a and 2a (6.0 μM), reducing the E. coli viability in 5.2 and 3.9 log, respectively (after 15 min of dark incubation before irradiation). For PS 3a, a similar bacterial reduction (3.6 log) was achieved but only with an extended dark incubation period (30 min). Under the same experimental conditions, the photodynamic effect of cationic PSs 1a-3a on S. aureus was even more promising, with abundance reductions of ca. 8.0 log after 45-60 min of PDI treatment. These results reveal the high PDI efficiency of PSs bearing ammonium groups and suggest their promising application as a broad-spectrum antimicrobial to control infections caused by Gram-negative and Gram-positive bacteria.

Fibrous aggregates: Amplifying aggregation-induced emission to boost health protection

Environmental monitoring and personal protection are critical for preventing and for protecting human health during all infectious disease outbreaks (including COVID-19). Fluorescent probes combining sensing, imaging and therapy functions, could not only afford direct visualizing existence of biotargets and monitoring their dynamic information, but also provide therapeutic functions for killing various bacteria or viruses. Luminogens with aggregation-induced emission (AIE) could be well suited for above requirements because of their typical photophysical properties and therapeutic functions. Integration of these molecules with fibers or textiles is of great interest for developing flexible devices and wearable systems. In this review, we mainly focus on how fibers and AIEgens to be combined for health protection based on the latest advances in biosensing and bioprotection. We first discuss the construction of fibrous sensors for visualization of biomolecules. Next recent advances in therapeutic fabrics for individual protection are introduced. Finally, the current challenges and future opportunities for "AIE + Fiber" in sensing and therapeutic applications are presented.

Thiopyridinium phthalocyanine for improved photodynamic efficiency against pathogenic fungi

The emergence of opportunistic pathogens and the selection of resistant strains have created a grim scenario for conventional antimicrobials. Consequently, there is an ongoing search for alternative techniques to control these microorganisms. One such technique is antimicrobial photodynamic therapy (aPDT), which combines photosensitizers, light, and molecular oxygen to produce reactive oxygen species and kill the target pathogen. Here, the in vitro susceptibilities of three fungal pathogens, namely Candida albicans, Aspergillus nidulans, and Colletotrichum abscissum to aPDT with zinc(II) phthalocyanine (ZnPc) derivative complexes were investigated. Three ZnPc bearing thiopyridinium substituents were synthesized and characterized by several spectroscopic techniques. The Q-band showed sensitivity to the substituent with high absorptivity coefficient in the 680-720 nm region. Derivatization and position of the rings with thiopyridinium units led to high antifungal efficiency of the cationic phthalocyanines, which could be correlated with singlet oxygen quantum yield, subcellular localization, and cellular uptake. The minimum inhibitory concentrations (MIC) of the investigated ZnPc-R complexes against the studied microorganisms were 2.5 μM (C. albicans) and 5 μM (A. nidulans and C. abscissum). One ZnPc derivative achieved complete photokilling of C. albicans and, furthermore, yielded low MIC values when used against the tolerant plant-pathogen C. abscissum. Our results show that chemical modification is an important step in producing better photosensitizers for aPDT against fungal pathogens.

Graphene Quantum Dots and Phthalocyanines Turn-OFF-ON Photoluminescence Nanosensor for ds-DNA

Supramolecular hybrids of graphene quantum dots (GQDs) and phthalocyanine (Pc) dyes were studied as turn-OFF-ON photoluminescence nanosensors for detection of ds-DNA. Pcs with four (Pc4) and eight (Pc8) positive charges were selected to interact with negatively charged GQDs. The photoluminescence of the GQDs was quenched upon interaction with the Pcs, due to the formation of non-emissive complexes. In the presence of ds-DNA, the Pcs interacted preferentially with the negatively charged ds-DNA, lifting the quenching effect over the photoluminescence of the GQDs and restoring their emission intensity. The best performance as a sensor of ds-DNA was registered for the GQD-Pc8, with a limit of detection (LOD) in the picomolar range. The LOD for GQD-Pc8 was more than one order of magnitude lower and its sensitivity was about a factor of three higher than that of the analogue GQD-Pc4 nanosensor. The sensitivity and selectivity of this simple GQD-Pc8 nanosensor is comparable to those of the more sophisticated carbon-based nanosensors for DNA reported previously.

Palladium Phthalocyanines Varying in Substituents Position for Photodynamic Inactivation of Flavobacterium hydatis as Sensitive and Resistant Species

Antimicrobial photodynamic therapy (aPDT) has been considered as a promising methodology to fight the multidrug resistance of pathogenic bacteria. The procedure involves a photoactive compound (photosensitizer), the red or near infrared spectrum for its activation, and an oxygen environment. In general, reactive oxygen species are toxic to biomolecules which feature a mechanism of photodynamic action. The present study evaluates two clinical isolates of Gram-negative Flavobacteriumhydatis (F. hydatis): a multidrug resistant (R) and a sensitive (S) strain. Both occur in farmed fish, leading to the big production losses because of the inefficacy of antibiotics. Palladium phthalocyanines (PdPcs) with methylpyridiloxy groups linked peripherally (pPdPc) or non-peripherally (nPdPc) were studied with full photodynamic inactivation for 5.0 µM nPdPc toward both F. hydatis, R and S strains (6 log), but with a half of this value (3 log) for 5.0 µM pPdPc and only for F. hydatis, S. In addition to the newly synthesized PdPcs as a "positive control" was applied a well-known highly effective zinc phthalocyanine (ZnPcMe). ZnPcMe showed optimal photocytotoxicity for inactivation of both F. hydatis R and S. The present study is encouraging for a further development of aPDT with phthalocyanines as an alternative method to antibiotic medication to keep under control the harmful pathogens in aquacultures' farms.

Promising Photocytotoxicity of Water-Soluble Phtalocyanine against Planktonic and Biofilm Pseudomonas aeruginosa Isolates from Lower Respiratory Tract and Chronic Wounds

Alternative methods of killing microbes have been extensively researched in connection with the widespread appearance of antibiotic resistance among pathogenic bacteria. In this study, we report on in vitro antimicrobial phototoxicity research of cationic phthalocyanine with 2-(4-N-methylmorpholin-4-ium-4-yl)ethoxy substituents against selected clinical strains of Pseudomonas aeruginosa isolated from the lower respiratory tract and chronic wounds. The microorganisms tested in the research were analyzed in terms of drug resistance and biofilm formation. The photocytotoxic effect of phthalocyanine was determined by the reduction factor of bacteria. The studied cationic phthalocyanine at a concentration of 1.0 × 10−4 M, when activated by light, revealed a significant reduction factor, ranging from nearly 4 to 6 log, of P. aeruginosa cells when compared to the untreated control group. After single irradiation, a decrease in the number of bacteria in biofilm ranging from 1.3 to 4.2 log was observed, whereas the second treatment significantly improved the bacterial reduction factor from 3.4 to 5.5 log. It is worth mentioning that a boosted cell-death response was observed after the third irradiation, with a bacterial reduction factor ranging from 4.6 to 6.4 log. According to the obtained results, the tested photosensitizer can be considered as a potential antimicrobial photodynamic therapy against multidrug-resistant P. aeruginosa.

The Antimicrobial Photoinactivation Effect on Escherichia coli through the Action of Inverted Cationic Porphyrin-Cyclodextrin Conjugates

Photodynamic action has been used for diverse biomedical applications, such as treating a broad range of bacterial infections. Based on the combination of light, dioxygen, and photosensitizer (PS), the photodynamic inactivation (PDI) approach led to the formation of reactive oxygen species (ROS) and represented a non-invasive, non-toxic, repeatable procedure for pathogen photoinactivation. To this end, different tetrapyrrolic macrocycles, such as porphyrin (Por) dyes, have been used as PSs for PDI against microorganisms, mainly bacteria. Still, there is significant room for improvement, especially new PS molecules. Herein, unsymmetrical new pyridinone (3−5) and thiopyridyl Pors (7) were prepared with α-, β-, or γ-cyclodextrin (CD) units, following their quaternization to perform the corresponding free-base Pors (3a−5a and 7a), and were compared with the already-known Pors 6a and 8a, both bearing thiopyridinium and CD units. These water-soluble porphyrins were evaluated as PSs, and their photophysical and photochemical properties and photodynamic effects on E. coli were assessed. The presence of one CD unit and three positive charges on the Por structure (3a−5a and 7a) enhanced their aqueous solubility. The photoactivity of the cationic Pors 3a−5a and 6a−8a ensured their potential against the Gram-negative bacterium E. coli. Within each series of methoxypyridinium vs thiopyridinium dyes, the best PDI efficiency was achieved for 5a with a bacterial viability reduction of 3.5 log10 (50 mW cm−2, 60 min of light irradiation) and for 8a with a total bacterial viability reduction (>8 log10, 25 mW cm−2, 30 min of light irradiation). Here, the presence of the methoxypyridinium units is less effective against E. coli when compared with the thiopyridinium moieties. This study allows for the conclusion that the peripheral charge position, quaternized substituent type/CD unit, and affinity to the outer bacterial structures play an important role in the photoinactivation efficiency of E. coli, evidencing that these features should be further addressed in the pursuit for optimised PS for the antimicrobial PDI of pathogenic microorganisms.

The Surprisingly Positive Effect of Zinc-Phthalocyanines With High Photodynamic Therapy Efficacy of Melanoma Cancer

Phthalocyanine (Pc) dyes are photoactive molecules that can absorb and emit light in the visible spectrum, especially in the red region of the spectrum, with great potential for biological scopes. For this target, it is important to guarantee a high Pc solubility, and the use of suitable pyridinium units on their structure can be a good strategy to use effective photosensitizers (PSs) for photodynamic therapy (PDT) against cancer cells. Zn(II) phthalocyanines (ZnPcs) conjugated with thiopyridinium units (1–3) were evaluated as PS drugs against B16F10 melanoma cells, and their photophysical, photochemical, and in vitro photobiological properties were determined. The photodynamic efficiency of the tetra- and octa-cationic ZnPcs 1–3 was studied and compared at 1, 2, 5, 10, and 20 µM. The different number of charge units, and the presence/absence of a-F atoms on the Pc structure, contributes for their PDT efficacy. The 3-(4′,5′-dimethylthiazol-2′-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays on B16F10 melanoma cells show a moderate to high capacity to be photoinactivated by ZnPcs 1–3 (ZnPc 1 > ZnPc 2 > ZnPc 3). The best PDT conditions were found at a Pc concentration of 20 μM, under red light (λ = 660 ± 20 nm) at an irradiance of 4.5 mW/cm² for 667 s (light dose of 3 J/cm²). In these conditions, it is noteworthy that the cationic ZnPc 1 shows a promising photoinactivation ratio, reaching the detection limit of the MTT method. Moreover, these results are comparable to the better ones in the literature.

Photodynamic Inactivation of Antibiotic-Resistant and Sensitive Aeromonas hydrophila with Peripheral Pd(II)- vs. Zn(II)-Phthalocyanines

The antimicrobial multidrug resistance (AMR) of pathogenic bacteria towards currently used antibiotics has a remarkable impact on the quality and prolongation of human lives. An effective strategy to fight AMR is the method PhotoDynamic Therapy (PDT). PDT is based on a joint action of a photosensitizer, oxygen, and light within a specific spectrum. This results in the generation of singlet oxygen and other reactive oxygen species that can inactivate the pathogenic cells without further regrowth. This study presents the efficacy of a new Pd(II)- versus Zn(II)-phthalocyanine complexes with peripheral positions of methylpyridiloxy substitution groups (pPdPc and ZnPcMe) towards Gram-negative bacteria Aeromonas hydrophila (A.hydrophila). Zn(II)-phthalocyanine, ZnPcMe was used as a reference compound for in vitro studies, bacause it is well-known with a high photodynamic inactivation ability for different pathogenic microorganisms. The studied new isolates of A.hydrophila were antibiotic-resistant (R) and sensitive (S) strains. The photoinactivation results showed a full effect with 8 µM pPdPc for S strain and with 5 µM ZnPcMe for both R and S strains. Comparison between both new isolates of A.hydrophila (S and R) suggests that the uptakes and more likely photoinactivation efficacy of the applied phthalocyanines are independent of the drug sensitivity of the studied strains.

The application of photodynamic inactivation to microorganisms in food

Nowadays, food safety issues have drawn increased attention due to the continual occurrence of infectious diseases caused by foodborne pathogens, which is an important factor causing food safety hazard. Meanwhile, the emergence of an increasing number of antibiotic-resistant pathogens is a worrisome phenomenon. Therefore, it is imperative to find new technologies with low-cost to inactivate pathogenic microorganisms and prevent cross-contamination. Compared with traditional preservatives, photodynamic inactivation (PDI) has emerged as a novel and promising strategy to eliminate foodborne pathogens with advantages such as non-toxic and low microbial resistance, which also meets the demand of current consumers for green treatment. Over the past few years, reports of using this technology for food safety have increased rapidly. This review summarizes recent progresses in the development of photodynamic inactivation of foodborne microorganisms. The mechanisms, factors influencing PDI and the application of different photosensitizers (PSs) in different food substrates are reviewed.

Latest trends on photodynamic disinfection of Gram-negative bacteria: photosensitizer's structure and delivery systems

Antimicrobial resistance is threatening to overshadow last century's medical advances. Etiological agents of previously eradicated infectious diseases are now resurgent as multidrug-resistant strains, especially for Gram-negative strains. Finding new therapeutic solutions is a real challenge for our society. In this framework, Photodynamic Antimicrobial ChemoTherapy relies on the generation of toxic reactive oxygen species in the presence of light, oxygen, and a photosensitizer molecule. The use of reactive oxygen species is common for disinfection processes, using chemical agents, such as chlorine and hydrogen peroxide, and as they do not have a specific molecular target, it decreases the potential of tolerance to the antimicrobial treatment. However, light-driven generated reactive species result in an interesting alternative, as reactive species generation can be easily tuned with light irradiation and several PSs are known for their low environmental impact. Over the past few years, this topic has been thoroughly studied, exploring strategies based on single-molecule PSs (tetrapyrrolic compounds, dipyrrinate derivatives, metal complexes, etc.) or on conjunction with delivery systems. The present work describes some of the most relevant advances of the last 6 years, focusing on photosensitizers design, formulation, and potentiation, aiming for the disinfection of Gram-negative bacteria.

Photodynamic therapy for leishmaniasis: Recent advances and future trends

Leishmaniasis has infected more than 12 million people worldwide. This neglected tropical disease, causing 20,000-30,000 deaths per year, is a global health problem. The emergence of resistant parasites and serious side effects of conventional therapies has led to the search for less toxic and non-invasive alternative treatments. Photodynamic therapy is a promising therapeutic strategy to produce reactive oxygen species for the treatment of leishmaniasis. In this regard, natural and synthetic photosensitizers such as curcumin, hypericin, 5-aminolevulinic acid, phthalocyanines, phenothiazines, porphyrins, chlorins and nanoparticles have been applied. In this review, the recent advances on using photodynamic therapy for treating Leishmania species have been reviewed.

Photodynamic disinfection and its role in controlling infectious diseases

Photodynamic therapy is witnessing a revival of its origins as a response to the rise of multi-drug resistant infections and the shortage of new classes of antibiotics. Photodynamic disinfection (PDDI) of microorganisms is making progresses in preclinical models and in clinical cases, and the perception of its role in the clinical armamentarium for the management of infectious diseases is changing. We review the positioning of PDDI from the perspective of its ability to respond to clinical needs. Emphasis is placed on the pipeline of photosensitizers that proved effective to inactivate biofilms, showed efficacy in animal models of infectious diseases or reached clinical trials. Novel opportunities resulting from the COVID-19 pandemic are briefly discussed. The molecular features of promising photosensitizers are emphasized and contrasted with those of photosensitizers used in the treatment of solid tumors. The development of photosensitizers has been accompanied by the fabrication of a variety of affordable and customizable light sources. We critically discuss the combination between photosensitizer and light source properties that may leverage PDDI and expand its applications to wider markets. The success of PDDI in the management of infectious diseases will ultimately depend on the efficacy of photosensitizers, affordability of the light sources, simplicity of the procedures, and availability of fast and efficient treatments.

Porphyrin-Schiff Base Conjugates Bearing Basic Amino Groups as Antimicrobial Phototherapeutic Agents

New porphyrin–Schiff base conjugates bearing one (6) and two (7) basic amino groups were synthesized by condensation between tetrapyrrolic macrocycle-containing amine functions and 4-(3-(N,N-dimethylamino)propoxy)benzaldehyde. This approach allowed us to easily obtain porphyrins substituted by positive charge precursor groups in aqueous media. These compounds showed the typical Soret and four Q absorption bands with red fluorescence emission (Φ_F ~ 0.12) in N,N-dimethylformamide. Porphyrins 6 and 7 photosensitized the generation of O₂(¹Δ_g) (Φ_Δ ~ 0.44) and the photo-oxidation of L-tryptophan. The decomposition of this amino acid was mainly mediated by a type II photoprocess. Moreover, the addition of KI strongly quenched the photodynamic action through a reaction with O₂(¹Δ_g) to produce iodine. The photodynamic inactivation capacity induced by porphyrins 6 and 7 was evaluated in Staphylococcus aureus, Escherichia coli, and Candida albicans. Furthermore, the photoinactivation of these microorganisms was improved using potentiation with iodide anions. These porphyrins containing basic aliphatic amino groups can be protonated in biological systems, which provides an amphiphilic character to the tetrapyrrolic macrocycle. This effect allows one to increase the interaction with the cell wall, thus improving photocytotoxic activity against microorganisms.