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

Modulating the anti-cancer photodynamic efficiency of molybdenum-iodide nanoclusters via ligand design

Ligand-stabilized metallic nanoclusters are emerging as promising agents for photodynamic therapy (PDT). This study explores how precisely tailored ligands can optimize the anti-cancer PDT efficiency of molybdenum-iodide nanoclusters. Utilizing click chemistry, we synthesized a series of triazolate-capped nanoclusters by reacting Na2[Mo6I8(N3)6] with dibenzo[a,e]cyclooctyne (DBCO) derivatives. Dynamic light scattering and luminescence measurements confirmed that the bulky DBCO moieties effectively stabilized the nanoclusters in aqueous media, while the appended side chains dictated their colloidal behavior and photosensitizing capabilities. In vitro experiments with HeLa cancer cells revealed that the side chain's nature critically influences cellular uptake and phototoxicity. Positively charged nanoclusters exhibited enhanced cell membrane interactions and potent phototoxic effects, whereas negatively charged counterparts displayed reduced internalization and diminished PDT efficacy. Notably, the nanoclusters maintained consistent phototoxicity even after prolonged exposure to aqueous media, demonstrating the robust stability conferred by the DBCO ligands. These results higlight the potential for fine-tuning molybdenum-iodide nanocluster properties to optimize PDT applications, achieving a delicate balance between water stability, cellular interaction, and phototoxicity, thereby isolating key parameters that govern PDT efficiency.

Alkyl-π Liquids as Condensed-State Singlet Oxygen Photosensitizers

Functional materials capable of generating singlet oxygen (1O2), a highly reactive but short-lived species used to destroy organic materials, including chemical pollutants and biological entities, typically incorporate a chromophore that acts as a photosensitizer into a tertiary scaffold. Current functional materials that produce 1O2 include metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), polymeric nanoparticles, modified glasses, and supramolecular assemblies. Whilst multi-component functional materials have been widely reported, producing functional materials using a single small molecule in a condensed state has hardly been reported. Herein, we report the first use of functional molecular liquids (alkyl-π liquids), non-volatile single-component condensed-state fluidic materials, as photosensitizers for the generation of 1O2 at an alkyl-π liquid-water interface. We investigate the incorporation of various chromophores into alkyl-π liquids that are suitable for 1O2 production and analyze the molecular structure required to produce efficient alkyl-π liquid photosensitizers. The alkyl-π liquids were studied, impregnated into porous membranes, and as thin films on quartz and Si wafers, the limitations of 1O2 production were investigated. A system was successfully fabricated that can generate 1O2 within an alkyl-π liquid impregnated membrane and migrate across a membrane-water interface to destroy small organic molecules, demonstrating the potential of these systems for water decontamination.

Advancements in photodynamic inactivation: A comprehensive review of photosensitizers, mechanisms, and applications in food area

Food microbial contamination results in serious food safety issues and numerous food loss and waste, presenting one of the most significant challenges facing the global food system. Photodynamic inactivation (PDI) technology, which combines light and photosensitizers (PS) to provide antimicrobial effects, is an ideal nonthermal antimicrobial technique for the food industry. This review provides a comprehensive overview of PDI technology, beginning with the fundamental photoactivation principles of PS and the pathways of photoinduced reactive oxygen species (ROS) generation. PS is the most critical factor affecting PDI efficiency, which is categorized into three types: organic, metal oxide-, and carbon-based. This review systemically summarizes the photophysical properties, in vitro PDI performances, potential enhancement strategies, and the advantages and limitations of each type of PS. Furthermore, the antimicrobial mechanisms of the PDI technologies are analyzed at both microscopic and molecular levels. Finally, the current applications of PDI in various food systems are discussed, along with the associated challenges and opportunities. Overall, this review offers crucial insights into optimizing and advancing PDI technology, highlighting key challenges and suggesting future research directions to enhance the effectiveness and scalability of PDI for diverse food applications.

Octahedral molybdenum iodide clusters with pyrazole or pyrazolate ligands

Due to the combination of useful physicochemical properties (luminescence, X-ray contrast, etc.), octahedral molybdenum halide cluster complexes [Mo6X8L6]n have been the subject of active investigation during the last decades. The most common methods for synthesizing new compounds with organic ligands involve the use of silver salts of organic acids or the substitution of terminal methylate ligands. However, these methods often necessitate the use of special conditions, such as an inert atmosphere, absolute solvents, and silver salts, which can be costly. In contrast, aqua-hydroxo complexes formed by hydrolysis of many complexes are considered final unreactive products, despite the tendency for them to form. This work proposes a simple and affordable method for the preparation of hexaaqua and hexahydroxo iodide clusters of molybdenum from [Mo6I14]2- in a single step. Furthermore, the possibility of using such compounds as starting complexes for the synthesis of clusters with organic ligands such as pyrazole is discussed. The paper presents synthetic approaches, detailed characterization both in solid and in solution, and a study of the reactivity and luminescence properties of the obtained compounds.

PEGylated Molybdenum-Iodine Nanocluster as a Promising Radiodynamic Agent against Prostatic Adenocarcinoma

The combination of photodynamic therapy and radiotherapy has given rise to a modality called radiodynamic therapy (RDT), based on reactive oxygen species-producing radiosensitizers. The production of singlet oxygen, O2(1Δg), by octahedral molybdenum (Mo6) clusters upon X-ray irradiation allows for simplification of the architecture of radiosensitizing systems. In this context, we prepared a radiosensitizing system using copper-free click chemistry between a Mo6 cluster bearing azido ligands and the homo-bifunctional linker bis-dPEG11-DBCO. The resulting compound formed nanoparticles, which featured production of O2(1Δg) and efficient cellular uptake, leading to remarkable photo- and radiotoxic effects against the prostatic adenocarcinoma TRAMP-C2 cell line. Spheroids of TRAMP-C2 cells were also used for evaluation of toxicity and phototoxicity. In vivo experiments on a mouse model demonstrated that subcutaneous injection of the nanoparticles is a safe administration mode at a dose of up to 0.08 g kg-1. The reported results confirm the relevancy of Mo6-based radiosensitizing nanosystems for RDT.

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

Phosphorescence, characterized by luminescent lifetimes significantly longer than that of biological autofluorescence under ambient environment, is of great value for biomedical applications. Academic evidence of fluorescence imaging indicates that virtually all imaging metrics (sensitivity, resolution, and penetration depths) are improved when progressing into longer wavelength regions, especially the recently reported second near-infrared (NIR-II, 1000-1700 nm) window. Although the emission wavelength of probes does matter, it is not clear whether the guideline of "the longer the wavelength, the better the imaging effect" is still suitable for developing phosphorescent probes. For tissue-specific bioimaging, long-lived probes, even if they emit visible phosphorescence, enable accurate visualization of large deep tissues. For studies dealing with bioimaging of tiny biological architectures or dynamic physiopathological activities, the prerequisite is rigorous planning of long-wavelength phosphorescence, being aware of the cooperative contribution of long wavelengths and long lifetimes for improving the spatiotemporal resolution, penetration depth, and sensitivity of bioimaging. In this Review, emerging molecular engineering methods of room-temperature phosphorescence are discussed through the lens of photophysical mechanisms. We highlight the roles of phosphorescence with emission from visible to NIR-II windows toward bioapplications. To appreciate such advances, challenges and prospects in rapidly growing studies of room-temperature phosphorescence are described.

Graphene Oxide Sheets Decorated with Octahedral Molybdenum Cluster Complexes for Enhanced Photoinactivation of Staphylococcus aureus

The emergence of multidrug-resistant microbial pathogens poses a significant threat, severely limiting the options for effective antibiotic therapy. This challenge can be overcome through the photoinactivation of pathogenic bacteria using materials generating reactive oxygen species upon exposure to visible light. These species target vital components of living cells, significantly reducing the likelihood of resistance development by the targeted pathogens. In our research, we have developed a nanocomposite material consisting of an aqueous colloidal suspension of graphene oxide sheets adorned with nanoaggregates of octahedral molybdenum cluster complexes. The negative charge of the graphene oxide and the positive charge of the nanoaggregates promoted their electrostatic interaction in aqueous medium and close cohesion between the colloids. Upon illumination with blue light, the colloidal system exerted a potent antibacterial effect against planktonic cultures of Staphylococcus aureus largely surpassing the individual contributions of the components. The underlying mechanism behind this phenomenon lies in the photoinduced electron transfer from the nanoaggregates of the cluster complexes to the graphene oxide sheets, which triggers the generation of reactive oxygen species. Thus, leveraging the unique properties of graphene oxide and light-harvesting octahedral molybdenum cluster complexes can open more effective and resilient antibacterial strategies.

A Neutral Heteroleptic Molybdenum Cluster trans-[{Mo6I8}(py)2I4]

Despite that the chemistry of octahedral cluster complexes has been actively developed recently, there are still a lot of unexplored areas. For example, to date, only a few halide M6-clusters with N-heterocycles are known. Here, we obtained an apically heteroleptic octahedral iodide molybdenum cluster complex with pyridine ligands—trans-[{Mo6I8}(py)2I4] by the direct substitution of iodide apical ligands of [{Mo6I8}I6]2– in a pyridine solution. The compound co-crystalized with a monosubstituted form [{Mo6I8}(py)I5]– in the ratio of 1:4, and thus, can be described by the formula (pyH)0.2[{Mo6I8}(py)1.8I4.2]·1.8py. The composition was studied using XRPD, elemental analyses, and 1H-NMR and IR spectroscopies. According to the absorption and luminescence data, the partial substitution of apical ligands weakly affects optical properties.

A review on functional nanoarchitectonics nanocomposites based on octahedral metal atom clusters (Nb6, Mo6, Ta6, W6, Re6): inorganic 0D and 2D powders and films

This review is dedicated to various functional nanoarchitectonic nanocomposites based on molecular octahedral metal atom clusters (Nb₆, Mo₆, Ta₆, W₆, Re₆). Powder and film nanocomposites with two-dimensional, one-dimensional and zero-dimensional morphologies are presented, as well as film matrices from organic polymers to inorganic layered oxides. The high potential and synergetic effects of these nanocomposites for biotechnology applications, photovoltaic, solar control, catalytic, photonic and sensor applications are demonstrated. This review also provides a basic level of understanding how nanocomposites are characterized and processed using different techniques and methods. The main objective of this review would be to provide guiding significance for the design of new high-performance nanocomposites based on transition metal atom clusters.

Octahedral Molybdenum Cluster-Based Nanomaterials for Potential Photodynamic Therapy

Photo/radiosensitizers, such as octahedral molybdenum clusters (Mo₆), have been intensively studied for photodynamic applications to treat various diseases. However, their delivery to the desired target can be hampered by its limited solubility, low stability in physiological conditions, and inappropriate biodistribution, thus limiting the therapeutic effect and increasing the side effects of the therapy. To overcome such obstacles and to prepare photofunctional nanomaterials, we employed biocompatible and water-soluble copolymers based on N-(2-hydroxypropyl)methacrylamide (pHPMA) as carriers of Mo₆ clusters. Several strategies based on electrostatic, hydrophobic, or covalent interactions were employed for the formation of polymer-cluster constructs. Importantly, the luminescent properties of the Mo₆ clusters were preserved upon association with the polymers: all polymer-cluster constructs exhibited an effective quenching of their excited states, suggesting a production of singlet oxygen (O₂(¹Δ_g)) species which is a major factor for a successful photodynamic treatment. Even though the colloidal stability of all polymer-cluster constructs was satisfactory in deionized water, the complexes prepared by electrostatic and hydrophobic interactions underwent severe aggregation in phosphate buffer saline (PBS) accompanied by the disruption of the cohesive forces between the cluster and polymer molecules. On the contrary, the conjugates prepared by covalent interactions notably displayed colloidal stability in PBS in addition to high luminescence quantum yields, suggesting that pHPMA is a suitable nanocarrier for molybdenum cluster-based photosensitizers intended for photodynamic applications.

Hafnium Oxide Nanostructured Thin Films: Electrophoretic Deposition Process and DUV Photolithography Patterning

In the frame of the nanoarchitectonic concept, the objective of this study was to develop simple and easy methods to ensure the preparation of polymorphic HfO2 thin film materials (<200 nm) having the best balance of patterning potential, reproducibility and stability to be used in optical, sensing or electronic fields. The nanostructured HfO2 thin films with micropatterns or continuous morphologies were synthesized by two different methods, i.e., the micropatterning of sol-gel solutions by deep ultraviolet (DUV) photolithography or the electrophoretic deposition (EPD) of HfO2 nanoparticles (HfO2-NPs). Amorphous and monoclinic HfO2 micropatterned nanostructured thin films (HfO2-DUV) were prepared by using a sol-gel solution precursor (HfO2-SG) and spin-coating process following by DUV photolithography, whereas continuous and dense monoclinic HfO2 nanostructured thin films (HfO2-EPD) were prepared by the direct EPD of HfO2-NPs. The HfO2-NPs were prepared by a hydrothermal route and studied through the changing aging temperature, pH and reaction time parameters to produce nanocrystalline particles. Subsequently, based on the colloidal stability study, suspensions of the monoclinic HfO2-NPs with morphologies near spherical, spindle- and rice-like shapes were used to prepare HfO2-EPD thin films on conductive indium-tin oxide-coated glass substrates. Morphology, composition and crystallinity of the HfO2-NPs and thin films were investigated by powder and grazing incidence X-ray diffraction, scanning electron microscopy, transmission electron microscopy and UV-visible spectrophotometry. The EPD and DUV photolithography performances were explored and, in this study, it was clearly demonstrated that these two complementary methods are suitable, simple and effective processes to prepare controllable and tunable HfO2 nanostructures as with homogeneous, dense or micropatterned structures.

Universal "Three-in-One" Matrix to Maximize Reactive Oxygen Species Generation from Food and Drug Administration-Approved Photosensitizers for Photodynamic Inactivation of Biofilms

Biofilms, an accumulation of microorganisms, cause persistent bacterial infection and low cure rate due to the remarkable drug resistance. Photodynamic inactivation (PDI) is a promising treatment modality for bacterial infections, but the formation of biofilms raises new challenges for photosensitizers (PSs), particularly the reactive oxygen species (ROS) generation efficiency. Herein, through targeting the Jablonski energy diagram, we proposed a universal "three-in-one" matrix of Gd³⁺-ADP assembly for encapsulation and fixing of PSs to inhibit non-radiative transitions and promoting intersystem crossing (ISC) by the heavy atom and paramagnetic effects of Gd³⁺, eventually resulted in boosted ROS generation from the existing PSs (1.5-9.0-fold). Particularly, photophysical studies indicated that the matrix resulted in simultaneous ISC promotion and triplet-state lifetime lengthening, which is essential for ROS boosting. The PDI performance of the matrix was confirmed through fast and effective elimination of bacterial biofilms in 10-30 min. Moreover, successful therapy of a Pseudomonas aeruginosa biofilm-infected all-thickness third-degree burn wound was achieved within 11 days with Ce 6@CNs (matrix) but not feasible for matrix-free PSs (Ce 6 only), which highlighted the role of "three-in-one" matrix in ROS boosting.

Violet-blue Light Induces "Natural" Photodynamic Plasma Disinfection with Endogenous Sensitizers

Naturally, endogenous porphyrins can provide sensitized disinfection power, and to photobiologists' delight, violet-blue light has potential virtues. But progress is needed before violet-blue light treatment can used for microbe treatment of blood samples, and yet safeguard against plasma protein photooxidation. A report by Maclean et al. in this issue of Photochemistry & Photobiology on microbe reduction of blood samples showing negligible competing protein photooxidation may bring that goal a step closer.

Synthesis of novel hexamolybdenum cluster-functionalized copper hydroxide nanocomposites and its catalytic activity for organic molecule degradation

A novel heterogeneous catalytic nanomaterial based on a molybdenum cluster-based halide (MC) and a single-layered copper hydroxynitrate (CHN) was first prepared by colloidal processing under ambient conditions. The results of the elemental composition and crystalline pattern indicated that CHN was comprehensively synthesized with the support of the MC compound. The absorbing characteristic in the ultraviolet and near-infrared regions was promoted by both of the ingredients. The proper chemical interaction between the materials is a crucial reason to modify the structure of the MCs and only a small decrease in the magnetic susceptibility of CHN. The heterogeneous catalytic activity of the obtained MC@CHN material was found to have a high efficiency and excellent reuse when it is activated by hydrogen peroxide (H₂O₂) for the degrading reaction of the organic pollutant at room temperature. A reasonable catalytic mechanism was proposed to explain the distinct role of the copper compound, Mo₆ compound, and H₂O₂ in the production of the radical hydroxyl ion. This novel nanomaterial will be an environmentally promising candidate for dye removal.

Surface modification of silica nanoparticles by hexarhenium anionic cluster complexes for pH-sensing and staining of cell nuclei

The surface deposition of luminescent anionic cluster complex [{Re₆S₈}(OH)₆]^4- advantages to the design and synthesis of composite luminescent silica nanoparticles (SNs) for intracellular imaging and sensing, while the encapsulation of the cluster units into SNs lacks for efficient luminescence. The deposition of the Re₆ clusters resulted from their assembly at the silica surface functionalized by amino-groups provides the synthetic route for the composite SNs with bright cluster-centered luminescence invariable in pH range from 4.0 to 12.0. The pH-dependent supramolecular assembly of the cluster units with polyethyleneimine (PEI) at the silica surface is an alternative route for the synthesis of the composite SNs with high cluster-centered luminescence sensitive to pH-changes within 4.0-6.0. The sensitivity derives from the pH-driven conformational changes of PEI chains resulting in the release of the clusters from the PEI-based confinement under the acidification within pH 6.0-4.0. The potential of the composite SNs in cellular contrasting has been also revealed by the cell viability and flow cytometry measurements. It has been found that the PEI-supported embedding of the cluster units facilitates cell internalization of the composite SNs as well as results in specific intracellular distribution manifested by efficient staining of the cell nuclei in the confocal images.

The role of gold nanoparticles' aspect ratio in plasmon-enhanced luminescence and the singlet oxygen generation rate of Mo6 clusters

Here we present a study on the effect of the aspect ratio (AR) of gold nanoparticles on the emission intensity and singlet oxygen production rate of hexamolybdenum cluster-doped silica particles. It was shown that these parameters can be enhanced gradually up to 6.7- and 13-fold with the AR.

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.