Hierarchical Self-Assembly of Water-Soluble Fullerene Derivatives into Supramolecular Hydrogels

Controlling the self-assembly of nanoparticle building blocks into macroscale soft matter structures is an open question and of fundamental importance to fields as diverse as nanomedicine and next-generation energy storage. Within the vast library of nanoparticles, the fullerenes-a family of quasi-spherical carbon allotropes-are not explored beyond the most common, C60. Herein, a facile one-pot method is demonstrated for functionalizing fullerenes of different sizes (C60, C70, C84, and C90-92), yielding derivatives that self-assemble in aqueous solution into supramolecular hydrogels with distinct hierarchical structures. It is shown that the mechanical properties of these resultant structures vary drastically depending on the starting material. This work opens new avenues in the search for control of macroscale soft matter structures through tuning of nanoscale building blocks.

Versatile applications of fullerenol nanoparticles

Nanomaterials have become increasingly important over time as research technology has enabled the progressively precise study of materials at the nanoscale. Developing an understanding of how nanomaterials are produced and tuned allows scientists to utilise their unique properties for a variety of applications, many of which are already incorporated into commercial products. Fullerenol nanoparticles C60(OH)n, 2 ≤ n ≤ 44 are fullerene derivatives and are produced synthetically. They have good biocompatibility, low toxicity and no immunological reactivity. In addition, their nanometre size, large surface area to volume ratio, ability to penetrate cell membranes, adaptable surface that can be easily modified with different functional groups, drug release, high physical stability in biological media, ability to remove free radicals, magnetic and optical properties make them desirable candidates for various applications. This review comprehensively summarises the various applications of fullerenol nanoparticles in different scientific fields such as nanobiomedicine, including antibacterial and antiviral agents, and provides an overview of their use in agriculture and biosensor technology. Recommendations are also made for future research that would further elucidate the mechanisms of fullerenols actions.

Structure and Vibrational Spectroscopy of C82 Fullerenol Valent Isomers: An Experimental and Theoretical Joint Study

Gd@C₈₂O_xH_y endohedral complexes for advanced biomedical applications (computer tomography, cancer treatment, etc.) were synthesized using high-frequency arc plasma discharge through a mixture of graphite and Gd₂O₃ oxide. The Gd@C₈₂ endohedral complex was isolated by high-efficiency liquid chromatography and consequently oxidized with the formation of a family of Gd endohedral fullerenols with gross formula Gd@C₈₂O₈(OH)₂₀. Fourier-transformed infrared (FTIR) spectroscopy was used to study the structure and spectroscopic properties of the complexes in combination with the DFTB3 electronic structure calculations and infrared spectra simulations. It was shown that the main IR spectral features are formed by a fullerenole C₈₂ cage that allows one to consider the force constants at the DFTB3 level of theory without consideration of gadolinium endohedral ions inside the carbon cage. Based on the comparison of experimental FTIR and theoretical DFTB3 IR spectra, it was found that oxidation of the C₈₂ cage causes the formation of Gd@C₈₂O₂₈H₂₀, with a breakdown of the integrity of the parent C₈₂ cage with the formation of pores between neighboring carbonyl and carboxyl groups. The Gd@C₈₂O₆(OOH)₂(OH)₁₈ endohedral complex with epoxy, carbonyl and carboxyl groups was considered the most reliable fullerenole structural model.

Self-Assembly in water of C60 fullerene into isotropic nanoparticles or nanoplatelets mediated by a cationic amphiphilic polymer

HYPOTHESIS

To disperse high concentration of C₆₀ fullerene in water, we propose to use an emulsification-evaporation process in the presence of an amphiphilic polymer whose chemical structure has been chosen for inducing specific interaction with fullerene The viscosity enhancement provided by self-assembly of the amphiphilic polymers in water should result in high stability of the suspensions. The organic solvent has also to been chosen so as to maximize the initial fullerene concentration.

EXPERIMENTS

The concentrations of polymer and fullerene, the solvent type and the volume fraction of the organic phase have been varied. Their influence on the concentration of the fullerene dispersions and on the size and shape of the resulting nanoparticles have been investigated by UV-Visible spectroscopy, light scattering and cryo-transmission electron microscopy experiments.

FINDINGS

The resulting nanoparticles consist of aggregates of C₆₀ fullerene stabilized by the cationic polymer with morphologies/sizes tunable through fullerene and polymer concentration. At high fullerene concentration, nanoplatelets are obtained that consist in thin 2D nanocrystals. Their suspensions are very stable with time due to the viscosity of the dispersing aqueous medium. The concentration of fullerene nanoparticles dispersed in water is as high as 8 g/L which corresponds to an upper limit that has never been reached so far.

Fullerenes for the treatment of cancer: an emerging tool

Cancer is a most common cause of mortality globally. Available medicines possess severe side effects owing to their non-specific targeting. Hence, there is a need of an alternative in the healthcare system that should have high efficacy with the least side effects, also having the ability to achieve site-specific targeting and be reproducible. This is possible with the help of fullerenes. Fullerenes are having the unique physicochemical and photosensitizer properties. This article discusses the synthesis, functionalization, mechanism, various properties, and applications of C60 fullerenes in the treatment of cancer. The review article also addresses the various factors influencing the activity of fullerenes including the environmental conditions, toxicity profile, and future prospective.

Eco-Friendly and Scalable Synthesis of Fullerenols with High Free Radical Scavenging Ability for Skin Radioprotection

Radiation dermatitis is a common but torturous side effect during radiotherapy, which greatly decreases the life quality of patients and potentially results in detrimental cessation of tumor treatment. Fullerenol, known as "free radical sponge," is a great choice for skin radioprotection because of its broad-spectrum free radical scavenging performance, good chemical stability, and biosafety. In this work, a facile scalable and eco-friendly synthetic method of fullerenols by catalyst assistant mechanical chemistry strategy is provided. As no organic solvent or high concentration of acid and alkali is introduced to this synthetic system, large-scale (>20 g) production of fullerenols with high yield (>95%) is obtained and no complicated purification is required. Then, the skin radioprotective performance of fullerenols is systematically explored for the first time. In vitro results indicate that fullerenols significantly block the reactive oxygen species-induced damage and enhance the viability of irradiated human keratinocyte cells. In vivo experiments suggest that medical sodium hyaluronate hydrogels loaded with fullerenols are suitable for skin administration and powerfully mitigate radiodermatitis via effectively protecting epidermal stem cells. The work not only provides an efficient gram-scale and eco-friendly synthetic method of fullerenols, but also promotes the development of fullerenols as potential skin radioprotectors.

Synthesis, Mass Spectroscopy Detection, and Density Functional Theory Investigations of the Gd Endohedral Complexes of C82 Fullerenols

Gd endohedral complexes of C82 fullerenols were synthesized and mass spectrometry analysis of their composition was carried out. It was established that the synthesis yields a series of fullerenols Gd@C82Ox(OH)y (x = 0, 3; y = 8, 16, 24, 36, 44). The atomic and electronic structure and properties of the synthesized fullerenols were investigated using the density functional theory calculations. It was shown that the presence of endohedral gadolinium increases the reactivity of fullerenols. It is proposed that the high-spin endohedral fullerenols are promising candidates for application in magnetic resonance imaging.

Carbon Nanomaterials: Synthesis, Functionalization and Sensing Applications

Recent advances in nanomaterial design and synthesis has resulted in robust sensing systems that display superior analytical performance. The use of nanomaterials within sensors has accelerated new routes and opportunities for the detection of analytes or target molecules. Among others, carbon-based sensors have reported biocompatibility, better sensitivity, better selectivity and lower limits of detection to reveal a wide range of organic and inorganic molecules. Carbon nanomaterials are among the most extensively studied materials because of their unique properties spanning from the high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency fostering their use in sensing applications. In this paper, a comprehensive review has been made to cover recent developments in the field of carbon-based nanomaterials for sensing applications. The review describes nanomaterials like fullerenes, carbon onions, carbon quantum dots, nanodiamonds, carbon nanotubes, and graphene. Synthesis of these nanostructures has been discussed along with their functionalization methods. The recent application of all these nanomaterials in sensing applications has been highlighted for the principal applicative field and the future prospects and possibilities have been outlined.

Antioxidant activity of highly hydroxylated fullerene C60 and its interactions with the analogue of α-tocopherol

Polyhydroxylated fullerenes (fullerenols) are excellent free radical scavengers. Despite the large number of reports on their reactions with reactive oxygen species, there is no report on their ability to trap lipid peroxyl radicals and act as chain-breaking antioxidants. In this work we studied the effect of fullerenol C₆₀(OH)₃₆ on the kinetics of peroxidation of polyunsaturated fatty acid ester (methyl linoleate) dispersed in two model systems that mimic biological systems: Triton X-100 micelles and Large Unilamellar Vesicles, at pH 4, 7 and 10. As a control antioxidant 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC, an analog of α-tocopherol) was used. In micellar systems at pH 4.0, C₆₀(OH)₃₆ reacts with peroxyl radicals with k_inh= (5.8 ± 0.3) × 10³ M^-1s^-1 (for PMHC k_inh = 22 × 10³ M^-1s^-1). Surprisingly, at pH 7 a retardation instead of inhibition was recorded, and at pH 10 no effect on the kinetics of the process was observed. In liposomal systems fullerenol was not active at pH 4.0 but at pH 7.0 k_inh = (8.8 ± 2.6) × 10³ M^-1s^-1 for fullerenol was 30% lower than k_inh for PMHC. Using two fluorescent probes we confirmed that at pH 7.4 fullerenol/fullerenol anions are incorporated into the phospholipid heads of the bilayer. We also studied the cooperation of C₆₀(OH)₃₆ with PMHC: both compounds seem to contribute their peroxyl radical trapping abilities independently at pH 4 whereas at pH 7 and 10 a hyper-synergy was observed. The antioxidant action of C₆₀(OH)₃₆ and its synergy with PMHC was also confirmed for peroxidation of human erythrocytes at pH 7.4. Assuming the simplified structural model of fullerenol limited to 36 hydroxyls as the only functional groups attached to C₆₀ core we found by density-functional theory a low energy structure with OH groups distributed in the form of two polyhydroxyl regions separating two unsubstituted carbon regions with biphenyl-like structure. Our calculations indicate that abstraction of hydrogen atom from fullerenol by peroxyl or tocopheroxyl radical is endoergic. As the electron transfer from fullerenol polyanion to the radicals is also energetically disfavoured, the most probable mechanism of reaction with radicals is subsequent addition of peroxyl/tocopheroxyl radicals to biphenyl moieties surrounded by OH groups.

The Role of Functionalization in the Applications of Carbon Materials: An Overview

The carbon-based materials (CbMs) refer to a class of substances in which the carbon atoms can assume different hybridization states (sp1, sp2, sp3) leading to different allotropic structures -. In these substances, the carbon atoms can form robust covalent bonds with other carbon atoms or with a vast class of metallic and non-metallic elements, giving rise to an enormous number of compounds from small molecules to long chains to solids. This is one of the reasons why the carbon chemistry is at the basis of the organic chemistry and the biochemistry from which life on earth was born. In this context, the surface chemistry assumes a substantial role dictating the physical and chemical properties of the carbon-based materials. Different functionalities are obtained by bonding carbon atoms with heteroatoms (mainly oxygen, nitrogen, sulfur) determining a certain reactivity of the compound which otherwise is rather weak. This holds for classic materials such as the diamond, the graphite, the carbon black and the porous carbon but functionalization is widely applied also to the carbon nanostructures which came at play mainly in the last two decades. As a matter of fact, nowadays, in addition to fabrication of nano and porous structures, the functionalization of CbMs is at the basis of a number of applications as catalysis, energy conversion, sensing, biomedicine, adsorption etc. This work is dedicated to the modification of the surface chemistry reviewing the different approaches also considering the different macro and nano allotropic forms of carbon.

Functionalization of Carbon Nanomaterials for Biomedical Applications

Over the past decade, carbon nanostructures (CNSs) have been widely used in a variety of biomedical applications. Examples are the use of CNSs for drug and protein delivery or in tools to locally dispense nucleic acids to fight tumor affections. CNSs were successfully utilized in diagnostics and in noninvasive and highly sensitive imaging devices thanks to their optical properties in the near infrared region. However, biomedical applications require a complete biocompatibility to avoid adverse reactions of the immune system and CNSs potentials for biodegradability. Water is one of the main constituents of the living matter. Unfortunately, one of the disadvantages of CNSs is their poor solubility. Surface functionalization of CNSs is commonly utilized as an efficient solution to both tune the surface wettability of CNSs and impart biocompatible properties. Grafting functional groups onto the CNSs surface consists in bonding the desired chemical species on the carbon nanoparticles via wet or dry processes leading to the formation of a stable interaction. This latter may be of different nature as the van Der Waals, the electrostatic or the covalent, the π-π interaction, the hydrogen bond etc. depending on the process and on the functional molecule at play. Grafting is utilized for multiple purposes including bonding mimetic agents such as polyethylene glycol, drug/protein adsorption, attaching nanostructures to increase the CNSs opacity to selected wavelengths or provide magnetic properties. This makes the CNSs a very versatile tool for a broad selection of applications as medicinal biochips, new high-performance platforms for magnetic resonance (MR), photothermal therapy, molecular imaging, tissue engineering, and neuroscience. The scope of this work is to highlight up-to-date using of the functionalized carbon materials such as graphene, carbon fibers, carbon nanotubes, fullerene and nanodiamonds in biomedical applications.

Biocompatible [60]/[70] Fullerenols: Potent Defense against Oxidative Injury Induced by Reduplicative Chemotherapy

Chemotherapy as a conventional cancer treatment suffers from critical systemic side effects, which is generally considered as the consequence of reactive oxygen species (ROS). Fullerenes have been widely studied for their excellent performance in radicals scavenging. In the present study, we report a solid-liquid reaction to synthesize fullerenols and their application as ROS scavengers in chemotherapy protection. The solid-liquid reaction is carried out without catalyst and suitable for mass production. The novel [60]/[70] fullerenols show a high stability in water, and the [70] fullerenols (C₇₀-OH) exhibit radical scavenging capability superior to that of [60] fullerenols (C₆₀-OH) in chemotherapy protection. The mouse model for single and reduplicative chemotherapy-induced liver injury demonstrates their protective effects in the chemotherapeutic process, which is confirmed by histopathological examinations and hematological index. The increase of the hepatic l-glutathione (GSH) level and downregulated expression of the cytochrome P-450 2E1 (CYP2E1) give the possible mechanism associated with the impact of fullerenols on the metabolism of doxorubicin. The novel fullerenols may be promising protective agents to satisfy the demand for future clinical chemotherapy.

On mechanism of antioxidant effect of fullerenols

Fullerenols are nanosized water-soluble polyhydroxylated derivatives of fullerenes, specific allotropic form of carbon, bioactive compounds and perspective pharmaceutical agents. Antioxidant activity of fullerenols was studied in model solutions of organic and inorganic toxicants of oxidative type - 1,4-benzoquinone and potassium ferricyanide. Two fullerenol preparations were tested: С₆₀О_2-4(ОН)_20-24 and mixture of two types of fullerenols С₆₀О_2-4(ОН)_20-24+С₇₀О_2-4(ОН)_20-24. Bacteria-based and enzyme-based bioluminescent assays were used to evaluate a decrease in cellular and biochemical toxicities, respectively. Additionally, the enzyme-based assay was used for the direct monitoring of efficiency of the oxidative enzymatic processes. The bacteria-based and enzyme-based assays showed similar peculiarities of the detoxification processes: (1) ultralow concentrations of fullerenols were active (ca 10^-17-10^-4 and 10^-17-10^-5 g/L, respectively), (2) no monotonic dependence of detoxification efficiency on fullerenol concentrations was observed, and (3) detoxification of organic oxidizer solutions was more effective than that of the inorganic oxidizer. The antioxidant effect of highly diluted fullerenol solutions on bacterial cells was attributed to hormesis phenomenon; the detoxification was concerned with stimulation of adaptive cellular response under low-dose exposures. Sequence analysis of 16S ribosomal RNA was carried out; it did not reveal mutations in bacterial DNA. The suggestion was made that hydrophobic membrane-dependent processes are involved to the detoxifying mechanism. Catalytic activity of fullerenol (10^-8 g/L) in NADH-dependent enzymatic reactions was demonstrated and supposed to contribute to adaptive bacterial response.

Oxidation-induced water-solubilization and chemical functionalization of fullerenes C60, Gd@C60 and Gd@C82: atomistic insights into the formation mechanisms and structures of fullerenols synthesized by different methods

Water-solubilization is the prerequisite to endow the pristinely hydrophobic fullerenes with biocompatibility and biofunctionality, which has been widely applied to derive fullerene-based nanomaterials for biomedical applications. Oxidation reactions using O2 and H2O2 are the most commonly used approaches to this end, through which fullerenols with different structural features can be obtained. Despite the progress in the syntheses and bioapplications of fullerenols, their formation mechanisms and structures at the atomic level, which substantialize their physical properties and biofunctions, have been little understood. Using density functional theory calculations, we comparatively study the mechanisms and product structures for the oxidations of C60, Gd@C60 and Gd@C82 using both O2 and H2O2 as oxidizing agents under both neutral and alkaline aqueous conditions. We predict the formation mechanisms and product structures corresponding to the different synthetic conditions. Briefly, the H2O2 oxidations of C60, Gd@C60 and Gd@C82 under neutral conditions do not occur readily at room temperature because of the high energy barriers, whereas the H2O2 oxidations can readily proceed under alkaline conditions. The oxygen-containing groups of the fullerenols obtained under these conditions include hydroxyl, carbonyl, hemiacetal and deprotonated vic-diol. In contrast, through O2 oxidation under alkaline conditions, the most probable oxygen-containing groups for C60 fullerenols are epoxide and deprotonated vic-diol, and those for Gd@C60 and Gd@C82 fullerenols are hydroxyls and carbonyls. The results explain a wide range of experimental findings reported before. More importantly, they provide atomistic-level insights into the formation mechanisms and structures for various fullerenols, which are of fundamental interest for understanding their biomedical applications in the future.

Thermodynamics of the interaction of sweeteners and lactisole with fullerenols as an artificial sweet taste receptor model

The thermodynamics of the mimetic interaction of lactisole and sweeteners with fullerenols as a synthetic sweet receptor model was elucidated by Isothermal Titration Calorimetry (ITC) technique. The presence of lactisole resulted in great differences in thermodynamics of the sweeteners binding with fullerenols in which lactisole led to much more entropy contribution to the free energy compared with the interaction of sweeteners with fullerenols. Two interaction equilibrium states were found in ITC titration profiles and competitive binding of lactisole and sweeteners with fullerenols was disclosed. Our results indicated that the larger value of the ratio of two equilibrium constant K1/K2, the more effectively lactisole inhibited the sweetness of the sweetener. The combined results of sensory evaluation and ITC thermodynamics revealed that introducing a synthetic receptor model to interact with the sweeteners and inhibitors helps to understand the inhibition mechanism and the thermodynamic basis for the initiation of sweetness inhibition.

Medical Applications of Water-Soluble Polyhydroxylated Fullerene Derivatives

The promising positive results in reducing superoxide free radicals (O2-.), generated by invitro xanthine and xanthine oxidase, have been demonstrated in the evaluation of potential uses of novel water-soluble [60] fullerenols as free radical scavengers. Observation reveals the inherent application of fullerenols in a wide range of medical and clinical areas as preventive alternatives for a long-term medical treatment.

Polyhydroxylated C60 as an Hypercross-Linking Agent

Polyhydroxylated fullerene derivatives (fullerenols) were utilized as an efficient hypercross-linking agent for the synthesis of elastic poly(tetramethylene oxide)-based polyurethane networks with excellent thermal mechanical properties. Polyhydroxylated fullerenes were synthesized from the hydrolysis of polycyclosulfated fullerene derivatives in the presence of water at 85-90 °C or in aqueous NaOH solution at ambient temperature.

Elastomeric Conductive Ipn From Polyaniline And Fullerene-Based Networks

Polyhydroxylated fullerenes were utilized as an efficient hyper cross-linking agent in the synthesis of polyurethane networks. The resultant elastomers exhibited greatly enhanced thermal stability in comparison with those of the corresponding linear polyurethane and analogous elastomers, which were cross-linked by 1,1,1- tris(hydroxymethyl)ethane. A synthetic method leading to the preparation of a thin layer of conductive polyaniline/polyurethane IPN at the near surface of a fullerenol- based elastomeric substrate was demonstrated, using aqueous ammonium persulfate as an oxidizing agent in the presence of HCI. This new material exhibits a conductivity of 2.0 S/cm at ambient temperatures with the retention of most bulk properties of the parent elastomer, such as elongation and tensile strength at break.

Efficient synthesis of fullerenol in anion form for the preparation of electrodeposited films

The first electrochemical characterization of the much-studied "fullerenols" has been carried out. The fullerenol was prepared by the reaction of C(60) in deoxygenated tetrahydrofuran with an aqueous NaOH solution using sodium zincate as an electrophilic reagent. The obtained fullerenol is not simply polyhydroxylated C(60) but is a structurally and electronically complex C(60) anion with a molecular formula of Na(+) (2)[C(60) (OH)(12)(O)(2)](2-). This negatively charged fullerenol is in the form of a spherical cluster of 50 nm in diameter, and it can migrate in the same solution to an anode surface and be oxidized into the less soluble fullerenol C(60)O(OH)(12), when 10 V is applied to the electroplating bath. A uniform film, with a particle of 50-250 nm in diameter and a thickness of a few 10-100s of nanometers, is obtained by drying the fullerenol covered anode. This is the first time that studies of water-soluble fullerenols acting as anions for electrodeposited film preparation have been reported. The deposition mechanism has been further demonstrated by electrochemical measurements and dissolved oxygen concentration testing to be an oxidation process consisting of two anodic oxygen evolution processes.

Aqueous Compatible Fullerene-Doxorubicin Conjugates

Covalent conjugates of fullerene C(60) and the highly effective anticancer drug doxorubicin (DOX) were prepared and studied. The conjugation was through the amide linkage to preserve the intrinsic properties of DOX and fullerene cage. As designed, the conjugates with hydrophilic ethylene glycol spacers exhibited much improved aqueous compatibility, with significant solubility in water-DMSO mixtures. The anti-neoplastic activities of DOX were apparently unaffected in the conjugates according to evaluations in vitro with a human breast cancer cell line.

From the molecular behaviors of fullerene derivatives C50X2 (X = H, F, Cl, Br, OH) to the general parallels among isostructural derivatives of fullerenes and carbon nanotubes

A systematic investigation of all possible isomers of fullerene derivatives C50X2 (X = H, F, Cl, Br, OH) has been performed using the semiempirical AM1 method. The equilibrium geometrical structures, heats of formation, HOMO-LUMO energy gaps, ionization potentials, electronic affinities, strain and aromaticity have been studied. The results indicate that the selection rule for two groups adding to fullerene C50 is independent of the type of functional group. The isomer-78, which corresponds to a 1,4-addition at the six-membered ring located on the equator, is the most stable isomer for C50X2 (X = H, F, Cl, Br, OH). The driving force governing the stabilities of the presently studied C50X2 isomers is the strain inherent in the C50 cage. The contribution of the conjugation effect to the stabilization is not able to compete with that of the strain. The more stable C50X2 isomers have larger ionization potentials and smaller electronic affinities compared with C50, which suggests that it is more difficult to oxidize and reduce C50X2 than to oxidize and reduce C50. Energies as well as HOMO-LUMO gaps of isostructural C50X2 (X = H, F, Cl, Br, OH) isomers are almost parallel, i.e., energy differences between isostructural isomers of any two kinds of C50X2 derivatives are constant. This phenomenon can be called H/F/Cl/Br/OH parallels, which may result from the same degree of perturbation for addition of different functional groups to the structure of the parent carbon cage. H/F parallels are generalized characteristics among not only isostructural isomers of fullerenes but also isostructural isomers of carbon nanotubes. Furthermore, it is predictable that general H/F/Cl/Br/OH... parallels may exist among various derivatives of other fullerenes and carbon nanotubes.

Transformation of aggregated C60 in the aqueous phase by UV irradiation

This study demonstrates that water-stable C60 cluster (nC60) undergoes a photochemical transformation(s) when irradiated with monochromatic UV light at 254 nm. Upon UV exposure, characteristic absorption of nC60 in the visible (ca. 450-550 nm, indicative of a cluster structure) and UV regions (indicative of underivatized molecular C60) gradually disappeared. Concurrently, a new product with absorption centered at 210 nm formed. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses confirmed a complete reduction in aggregation and formation of a soluble product. Negligible loss of total organic carbon (TOC) and drastic retardation in degradation kinetics in the absence of oxygen collectively implied that photochemical transformation was accomplished via oxidative pathway without carbon mineralization. MS (LDI), FTIR, and XPS analyses indicated a 60 carbon cage product, containing various oxygen functional groups such as epoxides and ethers. In addition, this product demonstrated significantly less antibacterial effects on Escherichia coli when compared to the parent nC60. The results of this study suggest that accurate assessment of C60 in environmental life cycles and impact should consider the light-mediated transformation of C60 in the aqueous phase and resulting water-soluble products.

Isothermal titration calorimetry study of the interaction of sweeteners with fullerenols as an artificial sweet taste receptor model

A fullerenol-based synthetic sweetness receptor model, consisting of polyhydroxy groups for potential hydrogen bond donor along with a spherical hydrophobic center, was proposed according to the widely accepted sweetness hypothesis. An isothermal titration calorimetry (ITC) technique was used to study mimetic interaction of this sweet receptor model with a series of sweeteners having increasing sweetness intensity. The results showed that ITC is an effective method to provide thorough and precise characterization of the energies of molecular complex formation. Binding of all of the studied sweeteners with fullerenols was found through two sets of site models. More heat was released from sweeter synthetic compounds binding with fullerenols than from less sweet carbohydrates. The results imply that hydrogen bond formation is necessary for the sweeteners to bind to the fullerenol receptor in the first stage, whereas hydrophobic effect and conformation changes that lead to favorable entropy changes occur in most cases. The preliminary results of this study help to cover the lack of information about the thermodynamic basis of understanding of the initiation of the sweet sensation. It also adds complementary physicochemical measurements available for comparison with the sweetness hypothesis. On the other hand, a correlation between the thermodynamic parameters and sweetness intensity has been made as well, which exhibits potential as a useful tool in sensory analysis.

Effect of encapsulating agents on dispersion status and photochemical reactivity of C60 in the aqueous phase

This study demonstrates that the degree of C60 clustering in the aqueous phase is strongly dependent on the type and concentration of encapsulating agents, such as surfactant, polymer, and natural organic matter that interact with C60. The degree of C60 clustering was quantitatively analyzed using ultraviolet-visible spectral characteristics. The dispersion status played a critical role in determining the photochemical reactivity of C60, in particular, its ability to mediate energy transfer and to produce singlet oxygen in the presence of oxygen. Consistent with findings in the organic phase, C60 in the aqueous phase lost its intrinsic photochemical reactivity when they formed aggregates. Experiments performed using a laser flash photolysis suggested that the loss of reactivity resulted from a drastic decrease in lifetime of a key reaction intermediate, that is, triplet-state C60. This study suggests that the photochemical reactivity of C60 in the aqueous phase, which has been linked to oxidative damage in biological systems in earlier studies, is strongly dependent on the media environment surrounding C60.

In situ synthesis of carbon nanotubes on heated scanning probes using dip pen techniques

Carbon nanotubes (CNT) were synthesized on heated scanning probes and under ambient conditions without requiring Chemical vapor deposition (CVD) apparatus or process gases. In this study, dip pen nanolithography (DPN) techniques were utilized for deposition of catalyst precursors on the scanning probe tips in the form of aqueous solution of metal salts--prior to the synthesis of the CNT. A layer of fullerene (C(60)) of approximately 200 nm thickness was vapor deposited on the scanning probe tip prior to the deposition of the metal catalyst. During the in situ synthesis of the CNT on the scanning probes, the temperature of the heated scanning probes reached 350-400 degrees C. Hence the scanning probes were heated in an inert atmosphere to prevent potential oxidation of the deposited fullerene layer. The synthesized CNTs were subsequently characterized using SEM and Raman spectroscopy. The Raman spectroscopy showed peaks in the Radial breathing mode (RBM), as well as the defect (D) and graphitic (G) bands. The RBM peaks indicate that the single walled carbon nanotube (SWCNT) ranged in diameter from 0.9-1.5 nm. The peaks in the Raman spectra are indicative of SWCNT mixtures (metallic and semconducting) and possibly multiwalled carbon nanotube (MWCNT). Hence this process can be optimized to synthesize SWCNT of a specific chirality (metallic or semiconducting). This study differs from an earlier study reported in the literature involving synthesis of CNT on scanning probes where the process temperatures typically exceeded 700 degrees C, and resulted in synthesis of highly graphitic MWCNT (Sunden, et al., 2006).

Facile synthesis of highly water-soluble fullerenes more than half-covered by hydroxyl groups

Using a novel hydrogen peroxide heating method, we synthesized milky white, water-soluble polyhydroxylated fullerenes (fullerenols) with 36-40 hydroxyl groups (estimated average) along with 8-9 secondary bound water molecules. The fullerenols exhibited high water solubility up to 58.9 mg/mL in a neutral (pH = 7) condition. Dynamic light scattering analysis showed a high dispersion property, to give a narrow particle size distribution within 0.7-2.0 nm.