In vivo studies of fullerene-based materials using endohedral metallofullerene radiotracers

Zn(II) released from zinc oxide nano/micro particles suppresses vasculogenesis in human endothelial colony-forming cells

Zinc oxide (ZnO) nanoparticles have been widely used in industry, cosmetics, and biomedicine. Recent studies suggested that these nanoparticles could have a major impact on the cardiovascular system. Endothelial progenitor cells (EPCs) contribute to postnatal endothelial repair and regeneration. The present study dissected the effects of ZnO nanoparticles on vasculogenesis using human endothelial colony forming cells (ECFCs), which participate in post-natal vasculogenesis. Two types of ZnO particles were used (nano and micro), in addition to zinc chloride solutions with zinc ion concentrations equal to those in ZnO nanoparticles. Twenty-four-hour exposure induced cytotoxicity in a dose-dependent manner and increased ECFCs apoptosis in all groups. The exposure also reduced the functional capacity of ECFCs on Matrix gel to form tubules, compared with the control cells. These effects were associated with downregulation of expression of vascular endothelial growth factor receptor, VEGFR2 and CXC chemokine receptor, CXCR4. The results suggest that ZnO nanoparticles suppress vasculogenesis from ECFCs through downregulation of the expression of receptors related to vasculogenesis. These effects are based the concentration of released Zn(II).

Tissue distribution and urinary excretion of intravenously administered chemically functionalized graphene oxide sheets

Providing a pharmacological understanding on how chemically functionalized GO sheets transport in the blood stream and interact with physiological barriers that determine their body excretion and tissue accumulation.

The design of graphene-based materials for biomedical purposes is of great interest. Graphene oxide (GO) sheets represent the most widespread type of graphene materials in biological investigations. In this work, thin GO sheets were synthesized and further chemically functionalized with DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), a stable radiometal chelating agent, by an epoxide opening reaction. We report the tissue distribution of the functionalized GO sheets labeled with radioactive indium (¹¹¹In) after intravenous administration in mice. Whole body single photon emission computed tomography (SPECT/CT) imaging, gamma counting studies, Raman microscopy and histological investigations indicated extensive urinary excretion and predominantly spleen accumulation. Intact GO sheets were detected in the urine of injected mice by Raman spectroscopy, high resolution transmission electron microscopy (HR-TEM) and electron diffraction. These results offer a previously unavailable pharmacological understanding on how chemically functionalized GO sheets transport in the blood stream and interact with physiological barriers that will determine their body excretion and tissue accumulation.

Reactivity of endohedral metallofullerene la2@c80 in nucleophilic and electrophilic attacks: vibronic coupling density approach

The regioselectivities of La2@C80 in thermal nucleophilic and electrophilic attacks were theoretically investigated using vibronic coupling density (VCD) analysis. Nucleophilic and electrophilic cycloadditions to La2@C80 were experimentally reported to yield [6,6] and [6,5] adducts, respectively, as major products. VCD analysis provided a clear explanation for these experimental results. For nucleophilic reactions, it was found that the reactive [6,6] bonds did not have a large lowest unoccupied molecular orbital (LUMO) density and Fukui function but a large potential derivative with respect to a reaction mode. The VCD illustrates the origin of the interaction between the electronic and vibrational states. On the other hand, conventional reactivity indices such as frontier orbital density take only the electronic state into account. The result suggested that the stabilization due to vibronic couplings plays an important role in the regioselectivity of nucleophilic cycloadditions. The VCD with respect to the effective mode could provide a picture of the functional groups, which are the double bonds of ethylene moieties. VCD analysis with respect to hypothetical localized modes enabled the quantitative prediction of regioselectivities.

Radioactive lutetium metallofullerene 177LuxLu(3−x)N@C80–PCBPEG derivative: a potential tumor-targeted theranostic agent

A radioactive metallofullerene ¹⁷⁷Lu_xLu_(3−x)N@C₈₀ was firstly synthesized by means of neutron irradiation on Lu₃N@C₈₀.

Inhalation Exposure to Carbon Nanotubes (CNT) and Carbon Nanofibers (CNF): Methodology and Dosimetry

Carbon nanotubes (CNT) and nanofibers (CNF) are used increasingly in a broad array of commercial products. Given current understandings, the most significant life-cycle exposures to CNT/CNF occur from inhalation when they become airborne at different stages of their life cycle, including workplace, use, and disposal. Increasing awareness of the importance of physicochemical properties as determinants of toxicity of CNT/CNF and existing difficulties in interpreting results of mostly acute rodent inhalation studies to date necessitate a reexamination of standardized inhalation testing guidelines. The current literature on pulmonary exposure to CNT/CNF and associated effects is summarized; recommendations and conclusions are provided that address test guideline modifications for rodent inhalation studies that will improve dosimetric extrapolation modeling for hazard and risk characterization based on the analysis of exposure-dose-response relationships. Several physicochemical parameters for CNT/CNF, including shape, state of agglomeration/aggregation, surface properties, impurities, and density, influence toxicity. This requires an evaluation of the correlation between structure and pulmonary responses. Inhalation, using whole-body exposures of rodents, is recommended for acute to chronic pulmonary exposure studies. Dry powder generator methods for producing CNT/CNF aerosols are preferred, and specific instrumentation to measure mass, particle size and number distribution, and morphology in the exposure chambers are identified. Methods are discussed for establishing experimental exposure concentrations that correlate with realistic human exposures, such that unrealistically high experimental concentrations need to be identified that induce effects under mechanisms that are not relevant for workplace exposures. Recommendations for anchoring data to results seen for positive and negative benchmark materials are included, as well as periods for postexposure observation. A minimum data set of specific bronchoalveolar lavage parameters is recommended. Retained lung burden data need to be gathered such that exposure-dose-response correlations may be analyzed and potency comparisons between materials and mammalian species are obtained considering dose metric parameters for interpretation of results. Finally, a list of research needs is presented to fill data gaps for further improving design, analysis, and interpretation and extrapolation of results of rodent inhalation studies to refine meaningful risk assessments for humans.

The applications of buckminsterfullerene C60 and derivatives in orthopaedic research

Abstract Buckminsterfullerene C60 and derivatives have been extensively explored in biomedical research due to their unique structure and unparalleled physicochemical properties. C60 is characterized as a "free radical sponge" with an anti-oxidant efficacy several hundred-fold higher than conventional anti-oxidants. Also, the C60 core has a strong electron-attracting ability and numerous functional compounds with widely different properties can be added to this fullerene cage. This review focused on the applications of C60 and derivatives in orthopaedic research, such as the treatment of cartilage degeneration, bone destruction, intervertebral disc degeneration (IVDD), vertebral bone marrow disorder, radiculopathy, etc., as well as their toxicity in vitro and in vivo. We suggest that C60 and derivatives, especially the C60 cores coupled with functional groups presenting new biological and pharmacological activities, are advantageous in orthopaedic research and will be promising in clinical performance for musculoskeletal disorders treatment; however, the pharmacokinetics and toxicology of these agents as local/systemic administration need to be carefully determined.

Magnetic resonance nanoparticles for cardiovascular molecular imaging and therapy

Molecular vascular imaging represents a novel tool that promises to change the current medical paradigm of 'see and treat' to a 'detect and prevent' strategy. Nanoparticle agents, such as superparamagnetic nanoparticles and perfluorocarbon nanoparticle emulsions, have been developed for noninvasive imaging, particularly for magnetic resonance imaging. Designed to target specific epitopes in tissues, these agents are beginning to enter clinical trials for cardiovascular applications. The delivery of local therapy with these nanoparticles, using mechanisms such as contact-facilitated drug delivery, is in the advanced stages of preclinical research. Ultimately, combined diagnostic and therapeutic nanoparticle formulations may allow patients to be characterized noninvasively and segmented to receive custom-tailored therapy. This review focuses on recent developments of nanoparticle technologies with an emphasis on cardiovascular applications of magnetic resonance imaging.

Catalytic stereodivergent functionalization of H2@C60

A complete stereocontrol of 1,3-dipolar cycloaddition of N-metalated azomethine ylides onto endohedral fullerene H2@C60 is reported for the first time. The stereodivergent synthesis of either the cis or the trans endohedral cycloadduct is achieved with excellent diastereo- and enantioselectivities.

Profiling the molecular mechanism of fullerene cytotoxicity on tumor cells by RNA-seq

The interest on functionalized fullerenes in the field of nanomedicine has seen a significant increase in the past decade. However, the different methods employed to increase C60 solubility profoundly influence the physicochemical properties and the toxicological effects of these compounds, thus complicating the evaluation of their toxicity and potential therapeutic use. Here we report a whole-transcriptome RNA-seq analysis assessing the effect of two fullerenes (1 and 2) on gene expression in the human MCF7 cell line. Although these two compounds had previously been characterized by in vitro studies as having a cytotoxic and null effect respectively, to date the mechanisms at the basis of this different behavior and, more in general, at the basis of the effect of most fullerene derivatives in living cells are still completely unknown. Our data evidence that: (a) fullerene 2 caused a significant, time-dependent alteration of gene expression, whereas 1 only had a negligible effect; (b) the biological processes mostly influenced over the 48h experimental time course were transcription, protein synthesis, cell cycle progression and cell adhesion; (c) the gene expression signature of 2-treated cells was strikingly similar to those induced by selective inhibitors of mTOR signaling, thus suggesting an effect on this pathway for fullerene 2. Our work represents the first approach toward the application of RNA-seq to the study of the molecular mechanisms underlying the interaction of fullerenes with cellular systems and provides an objective view of the feasibility and the safety of these nanomaterials for a medical application.

Cytotoxic Effects of Hydroxylated Fullerenes in Three Types of Liver Cells

Fullerenes C₆₀ have attracted considerable attention in the biomedical field due to their interesting properties. Although there has been a concern that C₆₀ could be metabolized to hydroxylated fullerenes (C₆₀(OH)_x) in vivo, there is little information on the effect of hydroxylated C₆₀ on liver cells. In the present study, we evaluated the cytotoxic effects of fullerene C₆₀ and various hydroxylated C₆₀ derivatives, C₆₀(OH)₂, C₆₀(OH)_6–12, C₆₀(OH)₁₂ and C₆₀(OH)₃₆, with three different types of liver cells, dRLh-84, HepG2 and primary cultured rat hepatocytes. C₆₀, C₆₀(OH)₂ and C₆₀(OH)₃₆ exhibited little or no cytotoxicity in all of the cell types, while C₆₀(OH)_6–12 and C₆₀(OH)₁₂ induced cytotoxic effects in dRLh-84 cells, accompanied by the appearance of numerous vacuoles around the nucleus. Moreover, mitochondrial activity in liver cells was significantly inhibited by C₆₀(OH)_6–12 and C₆₀(OH)₁₂. These results indicate that the number of hydroxyl groups on C₆₀(OH)_x contribute to the difference of their cytotoxic potential and mitochondrial damage in liver cells.

The ex vivo and in vivo biological performances of graphene oxide and the impact of surfactant on graphene oxide's biocompatibility

Graphene oxide (GO) displays promising properties for biomedical applications including drug delivery and cancer therapeutics. However, GO exposure also raises safety concerns such as potential side effects on health. Here, the biological effects of GO suspended in phosphate buffered saline (PBS) with or without 1% nonionic surfactant Tween 80 were investigated. Based on the ex vivo experiments, Tween 80 significantly affected the interaction between GO and peripheral blood from mice. GO suspension in PBS tended to provoke the aggregation of diluted blood cells, which could be prevented by the addition of Tween 80. After intravenous administration, GO suspension with or without 1% Tween 80 was quickly eliminated by the mononuclear phagocyte system. Nevertheless, GO suspension without Tween 80 showed greater accumulation in lungs than that containing 1% Tween 80. In contrast, less GO was found in livers for GO suspension compared to Tween 80 assisted GO suspension. Organs including hearts, livers, lungs, spleens, kidneys, brains, and testes did not reveal histological alterations. The indexes of peripheral blood showed no change upon GO exposure. Our results together demonstrated that Tween 80 could greatly alter GO's biological performance and determine the pattern of its biodistribution in mice.

Current status and future developments of endohedral metallofullerenes

Endohedral metallofullerenes (EMFs), a new class of hybrid molecules formed by encapsulation of metallic species inside fullerene cages, exhibit unique properties that differ distinctly from those of empty fullerenes because of the presence of metals and their hybridization effects via electron transfer. This critical review provides a balanced but not an exhaustive summary regarding almost all aspects of EMFs, including the history, the classification, current progress in the synthesis, extraction, isolation, and characterization of EMFs, as well as their physiochemical properties and applications in fields such as electronics, photovoltaics, biomedicine, and materials science. Emphasis is assigned to experimentally obtained results, especially the X-ray crystallographic characterizations of EMFs and their derivatives, rather than theoretical calculations, although the latter has indeed enhanced our knowledge of metal-cage interactions. Finally, perspectives related to future developments and challenges in the research of EMFs are proposed. (381 references).

Metallofullerene nanoparticles promote osteogenic differentiation of bone marrow stromal cells through BMP signaling pathway

Although endohedral metallofullerenol [Gd@C(82)(OH)(22)](n) nanoparticles have anti-tumor efficiency and mostly deposit in the bones of mice, how these nanoparticles act in bone marrow stromal cells (MSCs) remains largely unknown. Herein, we observed that [Gd@C(82)(OH)(22)](n) nanoparticles facilitated the differentiation of MSCs toward osteoblasts, as evidenced by the enhancement of alkaline phosphatase (ALP) activity and mineralized nodule formation upon [Gd@C(82)(OH)(22)](n) nanoparticle treatment. Mechanistically, the effect of [Gd@C(82)(OH)(22)](n) nanoparticles on ALP activity was inhibited by the addition of noggin as an inhibitor of the BMP signaling pathway. Moreover, the in vivo results of the ovariectomized rats further indicated that [Gd@C(82)(OH)(22)](n) nanoparticles effectively improved bone density and prevented osteoporosis.

Molecular mechanism of pancreatic tumor metastasis inhibition by Gd@C82(OH)22 and its implication for de novo design of nanomedicine

Pancreatic adenocarcinoma is the most lethal of the solid tumors and the fourth-leading cause of cancer-related death in North America. Matrix metalloproteinases (MMPs) have long been targeted as a potential anticancer therapy because of their seminal role in angiogenesis and extracellular matrix (ECM) degradation of tumor survival and invasion. However, the inhibition specificity to MMPs and the molecular-level understanding of the inhibition mechanism remain largely unresolved. Here, we found that endohedral metallofullerenol Gd@C(82)(OH)(22) can successfully inhibit the neoplastic activity with experiments at animal, tissue, and cellular levels. Gd@C(82)(OH)(22) effectively blocks tumor growth in human pancreatic cancer xenografts in a nude mouse model. Enzyme activity assays also show Gd@C(82)(OH)(22) not only suppresses the expression of MMPs but also significantly reduces their activities. We then applied large-scale molecular-dynamics simulations to illustrate the molecular mechanism by studying the Gd@C(82)(OH)(22)-MMP-9 interactions in atomic detail. Our data demonstrated that Gd@C(82)(OH)(22) inhibits MMP-9 mainly via an exocite interaction, whereas the well-known zinc catalytic site only plays a minimal role. Steered by nonspecific electrostatic, hydrophobic, and specific hydrogen-bonding interactions, Gd@C(82)(OH)(22) exhibits specific binding modes near the ligand-specificity loop S1', thereby inhibiting MMP-9 activity. Both the suppression of MMP expression and specific binding mode make Gd@C(82)(OH)(22) a potentially more effective nanomedicine for pancreatic cancer than traditional medicines, which usually target the proteolytic sites directly but fail in selective inhibition. Our findings provide insights for de novo design of nanomedicines for fatal diseases such as pancreatic cancer.

Emerging role of radiolabeled nanoparticles as an effective diagnostic technique

Nanomedicine is emerging as a promising approach for diagnostic applications. Nanoparticles are structures in the nanometer size range, which can present different shapes, compositions, charges, surface modifications, in vitro and in vivo stabilities, and in vivo performances. Nanoparticles can be made of materials of diverse chemical nature, the most common being metals, metal oxides, silicates, polymers, carbon, lipids, and biomolecules. Nanoparticles exist in various morphologies, such as spheres, cylinders, platelets, and tubes. Radiolabeled nanoparticles represent a new class of agent with great potential for clinical applications. This is partly due to their long blood circulation time and plasma stability. In addition, because of the high sensitivity of imaging with radiolabeled compounds, their use has promise of achieving accurate and early diagnosis. This review article focuses on the application of radiolabeled nanoparticles in detecting diseases such as cancer and cardiovascular diseases and also presents an overview about the formulation, stability, and biological properties of the nanoparticles used for diagnostic purposes.

Non-HPLC rapid separation of metallofullerenes and empty cages with TiCl4 Lewis acid

Rapid and efficient separation/purification of pure metallofullerenes M(x)@C(n) (M = metal; x = 1, 2; n > 70) and carbide metallofullerenes of the type M(y)C(2)@C(n-2) (y = 2, 3, 4; n - 2 > 68) has been reported. The present method utilizes rapid and almost perfect preferential formation of TiCl(4) (generally known as a Lewis acid)-metallofullerene complexes, which easily decompose to provide pure metallofullerene powders by a simple water treatment. The present method enables one to separate the metallofullerenes up to >99% purity within 10 min without using any type of high-performance liquid chromatography (HPLC). It is found that the oxidation potentials of the metallofullerenes are crucial factors for efficient purification. The current separation/purification technique may open a brand-new era for inducing further applications and commercialization of endohedral metallofullerenes.

Applications of functionalized fullerenes in tumor theranostics

Functionalized fullerenes with specific physicochemical properties have been developed for cancer diagnosis and therapy. Notably, metallofullerene is a new class of magnetic resonance imaging (MRI) contrast-enhancing agent, and may have promising applications for clinical diagnosis. Polyhydroxylated and carboxyl fullerenes have been applied to photoacoustic imaging. Moreover, in recent years, functionalized fullerenes have shown potential in tumor therapies, such as photodynamic therapy, photothermal treatment, radiotherapy and chemotherapeutics. Their antitumor effects may be associated with the modulation of oxidative stress, anti-angiogenesis, and immunostimulatory activity. While various types of novel nanoparticle agents have been exploited in tumor theranostics, their distribution, metabolism and toxicity in organisms have also been a source of concern among researchers. The present review summarizes the potential of fullerenes as tumor theranostics agents and their possible underlying mechanisms are discussed.

The primacy of physicochemical characterization of nanomaterials for reliable toxicity assessment: a review of the zebrafish nanotoxicology model

Engineered nanomaterials (ENMs) have become increasingly prevalent in the past two decades in academic, medical, commercial, and industrial settings. The unique properties imbued with nanoparticles, as the physiochemical properties change from the bulk material to the surface atoms, present unique and often challenging characteristics that larger macromolecules do not possess. While nanoparticle characteristics are indeed exciting for unique chemistries, surface properties, and diverse applications, reports of toxicity and environmental impacts have tempered this enthusiasm and given cause for an exponential increase for concomitant nanotoxicology assessment. Currently, nanotoxicology is a steadily growing with new literature and studies being published more frequently than ever before; however, the literature reveals clear, inconsistent trends in nanotoxicological assessment. At the heart of this issue are several key problems including the lack of validated testing protocols and models, further compounded by inadequate physicochemical characterization of the nanomaterials in question and the seminal feedback loop of chemistry to biology back to chemistry. Zebrafish (Danio rerio) are emerging as a strong nanotoxicity model of choice for ease of use, optical transparency, cost, and high degree of genomic homology to humans. This review attempts to amass all contemporary nanotoxicology studies done with the zebrafish and present as much relevant information on physicochemical characteristics as possible. While this report is primarily a physicochemical summary of nanotoxicity studies, we wish to strongly emphasize that for the proper evolution of nanotoxicology, there must be a strong marriage between the physical and biological sciences. More often than not, nanotoxicology studies are reported by groups dominated by one discipline or the other. Regardless of the starting point, nanotoxicology must be seen as an iterative process between chemistry and biology. It is our sincere hope that the future will introduce a paradigm shift in the approach to nanotoxicology with multidisciplinary groups for data analysis to produce predictive and correlative models for the end goal of rapid preclinical development of new therapeutics into the clinic or insertion into environmental protection.

Interaction and protection mechanism between Li@C(60) and nucleic acid bases (NABs): performance of PM6-DH2 on noncovalent interaction of NABs-Li@C60

To discuss the protection mechanism of DNA from radiation as well as assess the performance of PM6-DH2 on noncovalent interactions, the interaction of four nucleic acid bases (NABs) such as adenine (A), cytosine (C), guanine (G), and thymine (T), with Li@C(60) was extensively investigated with the-state-of-art theoretical methods describing noncovalent systems, like M06-2x, PBE-D, and PM6-DH2 methods. In the gas phase, the binding strength of NABs to Li@C(60) from M06-2x decreases in the sequence, G>C>A>T. As dispersion was explicitly included, PBE-D relatively enhances the binding of A and T and corrects the sequence to, G>A>C∼T. PM6-DH2 predicted similar binding energies to those from PBE-D within 0.5 kcal/mol and the same binding sequence, suggesting that the PM6-DH2 method is promising for nano-scale systems. In the aqueous solution, binding of NABs-Li@C(60) is considerably decreased, and the M06-2X and PM6-D methods yield a different sequence from the gas phase, G>A>T>C. The encapsulation of Li atom results in a lower IP for Li@C(60) than those of NABs, and the dominant localization of single-occupied molecular orbital on Li@C(60) moiety of the complexes NABs-Li@C(60) further indicates that an electron would be ejected from Li@C(60) upon radiation and Li@C(60) is therefore able to protect DNA bases from radiation. In addition, it was revealed that Li prefers coordination with the hexagonal ring at Li@C(60) , which clarifies the existing controversy in this respect. Finally, Yang's reduced density gradient approach clearly shows that the weak and strong noncovalent interaction regions in the complexes, NABs-Li@C(60) and (NABs-Li@C(60) )(+).

Cell Internalization Studies of Gadofullerene-(ZME-018) Immunoconjugates into A375m Melanoma Cells

Fullerene (C(60))-monoclonal antibody (mAb) immunoconjugates have been determined to internalize into target cells using water-soluble Gd(3+) ion-filled metallofullerenes (Gd@C(60)[OH](x)). Two separate conjugations of Gd@C(60)(OH)(x) with the antibody ZME-018 and a murine antibody mixture (MuIgG) were performed in a 1:5 mAb/Gd@C(60) ratio. Characterization of the immunoconjugates was established using inductively coupled plasma mass spectrometry (ICP-MS) for Gd(3+) and UV-Vis spectrometry (for Gd@C(60) + C(60)). Once conjugated, enzyme-linked immunosorbent assays showed little change in the specific binding of ZME-018. Each immunoconjugate was exposed to two cancer cell lines, A375m (antigen positive), and T24, bladder carcinoma (antigen negative). Internalization levels of the immunoconjugate were determined at various time points during 24 hours by harvesting and digesting the cells with 70% HNO(3) for Gd(3+) ion analysis by ICP-MS. These results are the first to demonstrate the practicality of a targeted cancer therapy based on fullerene immunotherapy.

Fate and toxicity of metallic and metal-containing nanoparticles for biomedical applications

It is important to obtain a better understanding of the uptake, trafficking, pharmacokinetics, clearance, and role of nanomaterials in biological systems, so that their possible undesirable effects can be avoided. A number of metallic or metal-containing nanomaterials, such as gold nanoparticles and nanorods, quantum dots, iron oxides nanoparticles, and endohedral metallofullerenes, have already been or will soon become very promising for biomedical applications. This review presents a summary of currently available data on the fate and toxicity of these metallic or metal-containing nanoparticles based on animal studies. Several issues regarding the nanotoxicity assessment and future directions on the study of the fate of these nanoparticles are also proposed.

Current-driven dynamics in molecular junctions: endohedral fullerenes

We introduce a new paradigm for single molecule devices based on electronic actuation of the internal atom/cluster motion within a fullerene cage. By combining electronic structure calculations with dynamical simulations, we explore current-triggered dynamics in endohedrally doped fullerene molecular junctions. Inelastic electron tunneling through a Li atom localized resonance in the Au-Li@C(60)-Au junction initiates fascinating, strongly coupled 2D dynamics, wherein the Li atom exhibits large amplitude oscillation with respect to the fullerene wall and the fullerene cage bounces between the gold electrodes, slightly perturbed by the embedded atom motion. Implications to the fields of single molecule electronics and nanoelectromechanical systems are discussed.

Chemistry of endohedral metallofullerenes: the role of metals

Recent breakthroughs achieved in the chemical functionalization of endohedral metallofullerenes (EMFs), especially single crystallographic X-ray characterizations of their derivatives, have presented fundamentally new insights into the structures and properties of these metal-carbon hybrid molecules, and have also brought immense potential applications. In particular, the interplay between the encapsulated metallic species and the fullerene cage has been well investigated. On one hand, the position and motion of the encapsulated metals can be effectively controlled by exohedral modification. On the other hand, the cage structures, the chemical behaviours of cage carbons and thus the chemical reactivity of the whole molecule are also apparently influenced by the electronic configuration and geometrical conformation of the internal metals via strong metal-cage interactions. In this article, we contribute a systematic review of the important chemical transformations of EMFs reported to date, including disilylation, 1,3-dipolar cycloaddition with ylides, cyclopropanation with carbenes and carbanions, cycloaddition with dienes and benzyne, radical reactions, and other miscellaneous reactions, in addition to noncovalent interactions such as supramolecular complexation. The roles that internal metals play in controlling the reactivity of cage carbons are particularly emphasized. Finally, some applicable materials based on EMFs and their derivatives are summarized and practical perspectives are proposed.

Small Molecules in C60 and C70: Which Complexes Could Be Stabilized?

The recent syntheses of complexes involving some small molecules in opened fullerenes and those of hydrogen molecule(s) in C60 and C70 are accompanied in the literature by numerous computations for endohedral fullerene complexes which cope with the problem of the stability of these complexes. In this contribution, stabilization energies of endohedral complexes of C60 and C70 with H2, N2, CO, HCN, H2O, H2S, NH3, CH4, CO2, C2H2, H2CO, and CH3OH guests have been estimated using symmetry-adapted perturbation theory, which, contrary to the standard DFT and some other approaches, correctly describes the dispersion contribution of the host-guest interactions. On the basis of these calculations, the endohedral complexes with all these guests were found stable in the larger fullerene, while the C60 cage was found too small to host the latter four molecules. Except for H2 and H2CO, a stabilization effect for most guests in the C60 cage is about 30 kJ/mol. For H2 and H2O guests, a typical supramolecular effect is observed; namely, the stabilization in the smaller cage is equal to or larger than that in the larger C70 host. Except for the water molecule where the induction interaction plays a non-negligible role, in all complexes the main stabilization effect comes from the dispersion interaction. The information on the stability of hypothetical endohedral fullerene complexes and physical factors contributing to it can be of importance in designing future experiments contributing to their applications.

Review: Do engineered nanoparticles pose a significant threat to the aquatic environment?

Nanotechnology is a rapidly growing industry of global economic importance, exploiting the novel characteristics of materials manufactured at the nanoscale. The properties of engineered nanoparticles (ENPs) that make them useful in a wide range of industrial applications, however, have led to concerns regarding their potential impact on human and environmental health. The aquatic environment is particularly at risk of exposure to ENPs, as it acts as a sink for most environmental contaminants. This paper critically evaluates what is currently known about sources and discharge of ENPs to the aquatic environment and how the physicochemical characteristics of ENPs affect their fate and behaviour and thus availability for uptake into aquatic organisms, and assesses reported toxicological effects. Having reviewed the ecotoxicological information, the conclusion is that whilst there are data indicating some nanoparticles have the potential to induce harm in exposed aquatic organisms, there is insufficient evidence for harm, for known/modelled environmental concentrations for almost all ENPs considered. This conclusion, however, must be balanced by the fact that there are significant gaps in our understanding on the fate and behaviour of ENPs in the aquatic environment. Greater confidence in the assessments on ENP impacts in aquatic systems to enable effective comparisons across studies urgently requires more standardised approaches for ENP hazard identification, and critically, more thorough characterisations on the exposed particles. There is also an urgent need for the advancement of tools and techniques that can accurately quantify and visualise uptake of nanoparticles into biological tissues.

Zero-field splitting of the lowest excited triplet states of C(60) and C(70) and benzene

The electronic structure of the lowest excited triplet states of C(60) and C(70) are characterized by a magnetic interaction between the unpaired electrons for which the zero-field-splitting parameter D is negative for the former and positive for the latter molecule. The sign of D has so far been qualitatively understood, and its magnitude has been found to critically depend on the degree of delocalization of the singly occupied molecular orbitals. In this contribution, the effect of spin polarization to the zero-field-splitting parameters of the fullerenes is evaluated, the inclusion of which results in quantitative agreement between the experimental and calculated D values. The direct spin-spin contribution is found to be dominant for both molecules. For C(60), a significant contribution of 20% of the total zero-field splitting has been found to derive from spin polarization. The physical reason for the sign difference of D for C(60) and C(70) is traced back to the relative phases of the local p(z) orbitals of adjacent carbon atoms near the equatorial plane in both singly occupied molecular orbitals. These relative phases differ for C(60) and C(70), because C(70) has an additional set of ten carbon atoms in its equatorial plane as compared to C(60). Additionally, the triplet wave function of C(70) is found to contain significant multireference character. In order to evaluate the effect of spin polarization in multireference systems, the zero-field-splitting parameters of the lowest triplet state of benzene have been evaluated in an illustrative and insightful calculation as well. Though this prototypical molecule is much smaller than C(60) and C(70), the electronic structure of its lowest excited triplet state is also of multireference character. For benzene, 18% of the total zero-field splitting arises from spin polarization.

Evaluation of extraction methods for quantification of aqueous fullerenes in urine

There is a growing concern about the human and environmental health effects of fullerenes (e.g., C(60)) due to their increasing application in research, medicine, and industry. Toxicological and pharmacokinetic research requires standard methods for extraction and detection of fullerenes from biological matrices such as urine. The present study validates the use of liquid-liquid extraction (LLE) and solid-phase extraction (SPE) methods in conjunction with liquid chromatography-mass spectrometry (LC-MS) for the quantitative determination of C(60) in human and synthetic urine as compared with ultrapure water. Glacial acetic acid, which is necessary to prevent emulsions during LLE, inhibited C(60) detection by LC-MS, but this could be mitigated with evaporation. Aqueous C(60) aggregates (nC(60)) were spiked at 180 μg/L into the components of a synthetic urine recipe to determine their individual impacts on extraction and detection. Urea, creatinine, and a complex protein (i.e., gelatin) were found to impair SPE, leading to a low recovery rate of 43 ± 4% for C(60) spiked into human urine. In contrast, C(60) was consistently recovered from synthetic matrices using LLE, and recovery in human urine was 80 ± 6%. These results suggest that LLE combined with LC-MS is suitable for studying the clearance of fullerenes from the body. LLE is a robust technique that holds promise for extracting C(60) from other complex biological matrices (e.g., blood, sweat, amniotic fluid) in toxicological studies, enabling a better understanding of the behavior of fullerenes in human and animal systems and facilitating a more comprehensive risk evaluation of fullerenes.

Low-toxic and safe nanomaterials by surface-chemical design, carbon nanotubes, fullerenes, metallofullerenes, and graphenes

The toxicity grade for a bulk material can be approximately determined by three factors (chemical composition, dose, and exposure route). However, for a nanomaterial it depends on more than ten factors. Interestingly, some nano-factors (like huge surface adsorbability, small size, etc.) that endow nanomaterials with new biomedical functions are also potential causes leading to toxicity or damage to the living organism. Is it possible to create safe nanomaterials if such a number of complicated factors need to be regulated? We herein try to find answers to this important question. We first discuss chemical processes that are applicable for nanosurface modifications, in order to improve biocompatibility, regulate ADME, and reduce the toxicity of carbon nanomaterials (carbon nanotubes, fullerenes, metallofullerenes, and graphenes). Then the biological/toxicological effects of surface-modified and unmodified carbon nanomaterials are comparatively discussed from two aspects: the lowered toxic responses or the enhanced biomedical functions. We summarize the eight biggest challenges in creating low-toxicity and safer nanomaterials and some significant topics of future research needs: to find out safer nanofactors; to establish controllable surface modifications and simpler chemistries for low-toxic nanomaterials; to explore the nanotoxicity mechanisms; to justify the validity of current toxicological theories in nanotoxicology; to create standardized nanomaterials for toxicity tests; to build theoretical models for cellular and molecular interactions of nanoparticles; and to establish systematical knowledge frameworks for nanotoxicology.