Unexpected Disparity in Photoinduced Reactions of C60 and C70 in Water with the Generation of O2 •- or 1O2

Enhancement of photoinduced reactive oxygen species generation in open-cage fullerenes

Photodynamic therapy is an important tool in modern medicine due to its effectiveness, safety, and the ability to provide targeted treatment for a range of diseases. Photodynamic therapy utilizes photosensitizers to generate reactive oxygen species (ROS). Fullerenes can be used as photosensitizers to produce ROS in high quantum yields. Open-cage fullerenes are a subclass of fullerenes characterized by a partially open structure, with one or more openings or apertures. The promising electrochemical properties of open-cage fullerenes motivated us to investigate their use for DNA-cleavage and ROS generation under visible light irradiation through type I electron transfer and type II energy transfer reactions. Our results show that open-cage C60 fullerenes are more efficient for photoinduced cleavage of DNA and ROS generation via both the type I electron transfer and type II energy transfer pathways than pristine C60 or a C60 pyrrolidine derivative without open-cage. The greater efficiency of ROS generation by open-cage C60 fullerene in type I and type II reactions can be attributed to the increased rate of the initial intersystem crossing process, resulting from larger total reorganization energies, as indicated by computationally calculated relative rates using the Marcus equation, and the lower reduction potential of the open-cage derivative 3, as determined by CV, which facilitates a more efficient generation of the corresponding radical anion (C60˙-).

Interaction of a pyrene derivative with cationic [60]fullerene in phospholipid membranes and its effects on photodynamic actions

We have reported that upon visible light irradiation, ferrocene-porphyrin-[60]fullerene triad molecules yield long-lived charge-separated states, enabling the control of the plasma membrane potential (V m) in living cells. These previous studies indicated that the localization of the triad molecules in a specific intra-membrane orientation and the suppression of the photodynamic actions of the [60]fullerene (C60) moiety are likely important to achieve fast and safe control of V m, respectively. In this study, by mimicking our previous system of triad molecules and living cells, we report a simplified model system with a cationic C60 derivative (catC60) and a liposome with embedded 1-pyrenebutyric acid (PyBA) to demonstrate that the addition of PyBA was important to achieve fast and safer control of V m.

Pioneering the Photoactive Relevance of Quinazolinone-Fullereropyrrolidine Nanohybrids To Address Chemotherapeutic Resistance in Cancer

This study investigates the impact of C70 and C60 fullerenes on quinazolinone, specifically in quinazolinone-fulleropyrrolidine nanohybrids. The nanohybrids Q 3 C 70 M and Q 3 C 60 M exhibit distinct spectral shifts and have significant photobiological antineoplastic properties. Q 3 C 60 M enhances apoptosis, while Q 3 C 70 M reduces Cyclin A levels and counteracts oncogenic effects by promoting cell differentiation. Q 3 C 70 M demonstrates heightened cytotoxicity by overcoming chemotherapy resistance by modulating BAX and BCL-2 levels. This innovative approach, distinguishing between C70 and C60, represents a novel contribution to the existing scientific literature.

Synthesis and characterization of water-soluble C60-peptide conjugates

With the aim of developing biocompatible and water-soluble C60 derivatives, three types of C60-peptide conjugates consisting of hydrophilic oligopeptide anchors (oligo-Lys, oligo-Glu, and oligo-Arg) were synthesized. A previously reported Prato reaction adduct of a biscarboxylic acid-substituted C60 derivative was subjected to a solid phase synthesis for amide formation with N-terminal amines of peptides on resin to successfully provide C60-peptide conjugates with one C60 and two peptide anchors as water-soluble moieties. Among three C60-peptide conjugates prepared, C60-oligo-Lys was soluble in water at neutral pH, and C60-oligo-Glu was soluble in buffer with a higher pH value, but C60-oligo-Arg was insoluble in water and most other solvents. C60-oligo-Lys and C60-oligo-Glu were characterized by 1H and 13C NMR. Photoinduced 1O2 generation was observed in the most soluble C60-oligo-Lys conjugate under visible light irradiation (527 nm) to show the potential of this highly water-soluble molecule in biological systems, for example, as a photosensitizer in photodynamic therapy.

Water-Soluble Fullerene Monoderivatives for Biomedical Applications

Monoderivatives of fullerenes functionalized with hydrophilic groups make them water soluble, while preserving the hydrophobic fullerene cage. This class of molecules have intriguing biomedical applications, including drug delivery, photodynamic therapy (PDT), antiviral and antimicrobial activity and reactive oxygen species (ROS)-scavenging abilities. In this Concept we discuss the synthesis and biomedical applications of water-soluble fullerene monoderivatives and their biological behavior based on their structures.

Water-Soluble Gd(III)-Porphyrin Complexes Capable of Both Photosensitization and Relaxation Enhancement

With the aim of developing more stable Gd(III)-porphyrin complexes, two types of ligands 1 and 2 with carboxylic acid anchors were synthesized. Due to the N-substituted pyridyl cation attached to the porphyrin core, these porphyrin ligands were highly water-soluble and formed the corresponding Gd(III) chelates, Gd-1 and Gd-2. Gd-1 was sufficiently stable in neutral buffer, presumably due to the preferred conformation of the carboxylate-terminated anchors connected to nitrogen in the meta position of the pyridyl group helping to stabilize Gd(III) complexation by the porphyrin center. ¹H NMRD (nuclear magnetic relaxation dispersion) measurements on Gd-1 revealed high longitudinal water proton relaxivity (r₁ = 21.2 mM^-1 s^-1 at 60 MHz and 25 °C), which originates from slow rotational motion resulting from aggregation in aqueous solution. Under visible light irradiation, Gd-1 showed extensive photoinduced DNA cleavage in line with efficient photoinduced singlet oxygen generation. Cell-based assays revealed no significant dark cytotoxicity of Gd-1, while it showed sufficient photocytotoxicity on cancer cell lines under visible light irradiation. These results indicate the potential of this Gd(III)-porphyrin complex (Gd-1) as a core for the development of bifunctional systems acting as an efficient photodynamic therapy photosensitizer (PDT-PS) with magnetic resonance imaging (MRI) detection capabilities.

Structurally Defined Water-Soluble Metallofullerene Derivatives towards Biomedical Applications

Endohedral metallofullerenes (EMFs) are excellent carriers of rare-earth element (REE) ions in biomedical applications because they preclude the release of toxic metal ions. However, existing approaches to synthesize water-soluble EMF derivatives yield mixtures that inhibit precise drug design. Here we report the synthesis of metallobuckytrio (MBT), a three-buckyball system, as a modular platform to develop structurally defined water-soluble EMF derivatives with ligands by choice. Demonstrated with PEG ligands, the resulting water-soluble MBTs show superb biocompatibility. The Gd MBTs exhibit superior T1 relaxivity than typical Gd complexes, potentially superseding current clinical MRI contrast agents in both safety and efficiency. The Lu MBTs generated reactive oxygen species upon light irradiation, showing promise as photosensitizers. With their modular nature to incorporate other ligands, we anticipate the MBT platform to open new paths towards bio-specific REE drugs.

Facile construction of fluorescent C70-COOH nanoparticles with advanced antibacterial and anti-biofilm photodynamic activity

Photodynamic antibacterial therapy has been considered as one of the most promising treatments to alleviate the spread of multidrug resistant bacterial pathogens. Given the hypoxic environment of infectious tissues, photosensitizers with reduced oxygen-demand could exhibit superiority upon irradiation. Herein reported is a novel C₇₀-based photosensitizers synthesized by the facile one-step thiol-ene reaction. Various characterization techniques were employed to confirm the structural, photoluminescent properties, photostability and biocompatibility of the as-synthesized C₇₀-COOH nanoparticles. Furthermore, they were capable of efficiently producing reactive oxygen species following both the type I and II mechanistic pathways, thus still generating adequate free radicals under hypoxic condition. Therefore, they could approach and destroy the bacterial cell membrane in the presence of visible light, thereby causing cytoplasmic leakage and eventually achieving broad-spectrum inactivation of four representative bacterial strains. Especially, methicillin-resistant Staphylococcus aureus (MRSA) were completely eliminated after merely 10 minutes irradiation, and the formation of its corresponding biofilm were also greatly inhibited by C₇₀-COOH nanoparticles. These results provide new insights and opportunities for the development of hypoxia-tolerant fullerene-based photosensitizers to combat multidrug resistant bacterial and related infections.

Reactive-Oxygen-Species-Mediated Surface Oxidation of Single-Molecule DNA Origami by an Atomic Force Microscope Tip-Mounted C60 Photocatalyst

A tripod molecule incorporating a C₆₀ photocatalyst into a rigid scaffold with disulfide legs was designed and synthesized for the stable and robust attachment of C₆₀ onto an Au-coated atomic force microscope (AFM) tip. The "tripod-C₆₀" was immobilized onto the tip by forming S-Au bonds in the desired orientation and a dispersed manner, rendering it suitable for the oxidation and scission of single molecules on a countersurface, thereby functioning as "molecular shears". A DNA origami with a well-defined structure was chosen as the substrate for the tip-induced oxidation. The gold-coated, C₆₀-functionalized AFM tip was used for both AFM imaging and oxidation of DNA origami upon visible-light irradiation. The localized and temporally controlled oxidative damage of DNA origami was successfully performed at the single-molecule level via singlet-oxygen (¹O₂) generation from the immobilized C₆₀ on the AFM tip. This oxidative damage to DNA origami can be carried out under ambient conditions in a fluid cell at room temperature, rendering it well-suited for the manipulation of a variety of species on surfaces via a spatially and temporally controlled oxidation reaction triggered by ¹O₂ locally generated from the immobilized C₆₀ on the AFM tip.