Photochemical reactivity of aqueous fullerene clusters: C60 versus C70

Photoactive conjugated microporous polymer@C60 with quencher on tailed Y-triangular DNA structure for high-performance signal-off photoelectrochemical biosensing

Herein, we synthesized a conjugated microporous polymer (CMP) decorated C₆₀ (CMP@C₆₀) with high photoelectric conversion efficiency, in which continuously repeated donor-acceptor (D-A) π electron unit within one molecule of CMP on C₆₀ could not only effectively increase the mobility of photogenerated carriers with improved electron transmission, but also constitute the cascade energy band matching with reduced electron-hole recombination. Based on the high-performance of CMP@C₆₀ for producing exciting initial photoelectrochemical (PEC) signal, a sensitive signal-off sensing platform was designed for lead ion (Pb²⁺) assay by coupling with quencher methylene blue (MB) interacting on efficient long tailed Y-triangular DNA structure (LYTD). The proposed LYTD with a tripod structure could generate six long tails in situ on its side at the same time via a simple hybridization chain reaction (HCR), providing notably grooves on electrode to accommodate quencher MB to significantly depress the signal for sensitive detection of Pb²⁺. As a result, the proposed PEC biosensor revealed excellent analysis capability with a low detection limit of 0.3 fM (S/N = 3). Additionally, it also showed satisfactory stability in the detection of tap water samples, lake water samples and clinical serum samples, manifesting great application prospect in the areas of environmental pollutant detection.

The occurrence of pristine and functionalized fullerenes as constituents of airborne aerosols

We investigated if pristine and functionalized fullerenes could be actual constituents of fine atmospheric aerosols. Comprehensive profiles of fullerenes from 1 µL extracts were made through matrix laser desorption ionization Time-of-Flight Mass Spectrometry (MALDI-MS) within a few minutes. The ion with m/z 720, corresponding to [C₆₀]^-•, was identified as fullerene after 1 µL of α-cyano-4-hydroxycinnamic acid matrix solution was spotted over the dried extracts. The ions with the m/z corresponding to C₇₀, C₇₆, C₈₄, C₁₀₀, C₁₁₈, C₁₂₈, and C₁₃₀ were also attributed to other fullerene species detected within the samples. The ion m/z 878 was found to be the fullerene derivative diethyl methano[60]fullerene dicarboxylate. Since ions of fragmented fullerene molecules were not detected even at high laser energies, we considered the fullerenes' occurring as original constituents of real atmospheric particle matrices instead of being formed as artifacts of the laser action on samples. Therefore, this protocol would be helpful in the understanding of the distribution of either pristine or functionalized fullerenes in the environment and their participation in atmospheric chemistry under typical conditions, as well as its application in vitro and in vivo (eco)toxicity studies.

Graphitic carbon nitride embedded with graphene materials towards photocatalysis of bisphenol A: The role of graphene and mediation of superoxide and singlet oxygen

Composite photocatalysts comprising graphitic carbon nitride (g-C₃N₄) and graphene materials were synthesized and evaluated in the photocatalysis of bisphenol A (BPA) with a focus on elucidating the reaction mechanism. Embedding reduced graphene oxide (rGO) to g-C₃N₄ significantly accelerated the photocatalysis rate of BPA by three folds under visible light irradiation at neutral pH. We showed that rGO synthesized in intimate contact with g-C₃N₄ increased the surface areas and electrical conductivity of the g-C₃N₄ composites and promoted the electron-hole pair separation. The BPA photodegradation mechanism involved selective oxidants as superoxide (O₂^•-) and singlet oxygen (¹O₂) that were formed through one-electron reduction of O₂ and the unique oxidation of O₂^•- by photogenerated hole (h⁺), respectively. The synthesized photocatalyst exhibited superior visible light photoreactivity to that of N-doped P25 TiO₂, good photo-stability and reuse potential, and was operative in complex wastewater. rGO embedded g-C₃N₄ achieved good photomineralization of BPA at 80% in 4 h compared to 40% of bare g-C₃N₄. This study sheds light on the photocatalysis mechanism of BPA with a metal-free, promising rGO/g-C₃N₄ photocatalyst.

A Review on the Environmental Fate Models for Predicting the Distribution of Engineered Nanomaterials in Surface Waters

Exposure assessment is a key component in the risk assessment of engineered nanomaterials (ENMs). While direct and quantitative measurements of ENMs in complex environmental matrices remain challenging, environmental fate models (EFMs) can be used alternatively for estimating ENMs' distributions in the environment. This review describes and assesses the development and capability of EFMs, focusing on surface waters. Our review finds that current engineered nanomaterial (ENM) exposure models can be largely classified into three types: material flow analysis models (MFAMs), multimedia compartmental models (MCMs), and spatial river/watershed models (SRWMs). MFAMs, which is already used to derive predicted environmental concentrations (PECs), can be used to estimate the releases of ENMs as inputs to EFMs. Both MCMs and SRWMs belong to EFMs. MCMs are spatially and/or temporally averaged models, which describe ENM fate processes as intermedia transfer of well-mixed environmental compartments. SRWMs are spatiotemporally resolved models, which consider the variability in watershed and/or stream hydrology, morphology, and sediment transport of river networks. As the foundation of EFMs, we also review the existing and emerging ENM fate processes and their inclusion in recent EFMs. We find that while ENM fate processes, such as heteroaggregation and dissolution, are commonly included in current EFMs, few models consider photoreaction and sulfidation, evaluation of the relative importance of fate processes, and the fate of weathered/transformed ENMs. We conclude the review by identifying the opportunities and challenges in using EFMs for ENMs.

Wavelength-Dependent Efficiency of Sequential Photooxygenation: C=C Bond Cleavage on Open-Cage C60 Derivatives

We have studied the efficiency of the C=C double bond cleavage on open-cage fullerene C₆₀ derivatives by singlet oxygen using four different LED lamps including UV, blue, green, and red radiation. The results indicate that red radiation is the most efficient for this photochemical oxidation owing to the sufficient penetration of the longer-wavelength light. By applying this method to a 2-methoxyethoxymethyl-substituted azafulleroid derivative, we demonstrated the sequential double photooxygenation which provides a symmetric diketo imide derivative having a 15-membered-ring opening via stepwise cleavage of two C=C double bonds. Using a H₂ -encapsulating derivative, we further examined the size of the opening by comparison with the structural isomer, based on H₂ -release experiments and theoretical calculations.

Water disinfection processes change the cytotoxicity of C60 fullerene: Reactions at the nano-bio interface

The environmental transformation of nanoparticles results in significant changes in their structure, properties, and toxicity, which are imperative for assessing their environmental impact and health risks. Little is known about the toxicity alteration of fullerene nanoparticles (C₆₀) after water disinfection processes considering their potential application in antimicrobial control in water treatment ultimately ending in sewage treatment plants. We showed that C₆₀ aggregates (nC₆₀) were converted to more oxidized forms via commonly used water disinfection processes (i.e., phototransformation and photochlorination treatment). The light-irradiated nanoparticles (UV_nC₆₀) exhibited mitigated cytotoxicity relative to nC₆₀, whereas photochlorinated nC₆₀ (UV/Cl_nC₆₀) showed an exacerbated outcome. We revealed a distinct toxic mechanism occurring at the nano-bio interface, for which electrons were shuttled by C₆₀ nanoparticles from membrane-bound NADPH oxidase to extracellular molecular oxygen, resulting in the production of various extracellular reactive oxygen species (ROS). UV/Cl_nC₆₀ showed the highest electron-shuttling activity due to its high carbonyl content, and more than 2.4-fold higher level of extracellular hydroxyl radicals were detected relative to that in untreated cells. Although UV_nC₆₀ possessed a somewhat higher carbonyl content than nC₆₀, it showed a weaker adhesion to the cell membrane, which compromised the electron-transfer process. The intrinsic ROS generation/quenching capabilities and oxidative potentials of the various nanoparticles were also systematically compared. Overall, this report highlights the importance of understanding environmental transformations in risk assessment and uncovers an overlooked mechanism through which nC₆₀/derivatives can modulate the electron transfer process at the nano-bio interface via acting as electron shuttles.