Study of mutagenic activity of fullerene and some of its derivatives using His+ reversions of Salmonella typhimurium as an example

The influence of three new derivatives of fullerence C60 ([61]dimethoxyphosphoryl[61]carbethoxy-methano[60]fullerene, [61]-(dimethoxyphosphoryl-[61]-carbmethoxy-methanofullerene, and 1-methyl-2-(3,5-di-tertbutyl-4-hydroxy-phenyl)-3,4-fulleropyrrolidine) on the appearance of His+ reversions in the Salmonella typhimurium strain BA13 was studied. It was ascertained that the effect of fullerene derivatives on the occurrence of mutations depends on the type of the molecular group with which fullerene interacts. The biological effect is determined not only by the action of the group associated with fullerene. The dependence between the mutagenic effect and properties of the solvents was detected. Exposure to visible light of the culture treated with fullerene derivatives was found to have an antimutagenic effect in the case of [61]dimethoxyphosphoryl[61]carbethoxy-methanofullerene[60]. For two other derivatives, the differences between experimental and control variants were statistically nonsignificant.     

Computational study of enantioselective interaction between C<Subscript>60</Subscript> fullerene and its derivatives with L-histidine

The mechanism of the enantioselective binding of L-histidine with C₆₀ fullerene and its derivatives, (1,2-methanofullerene C₆₀)-61-carboxylic acid, diethyl (1,2-methanofullerene C₆₀)-61-61-dicarboxylate and tert-butyl (1,2-methanofullerene C₆₀)-61-carboxylate based chiral selectors was studied by quantum chemical calculations. All the molecules were fully optimized at RHF/6-31G* basis set. Relative energies between the different complexes were subsequently estimated with single-point electronic energies computed using Møller-Plesset perturbation theory (MP2). Stability and feasibility of all the generated structures were supported by their respective energy minima and fundamental frequencies. It was observed that interaction of fullerene derivatives with L-histidine is due to the existence of hydrogen bonding forces during the complex formation. The intermolecular forces, flow of atomic charges, binding energy, hardness, dipole moment and localization of electrostatic potential are in agreement with enantioselective interaction of L-histidine with C₆₀ fullerene and its derivatives. It is found that theoretical evaluation to be consistent with the experimental data.     

Electronic Trap States in Methanofullerenes

The trap states in three fullerene derivatives, namely PC₆₁BM ([6,6]‐phenyl C₆₁ butyric acid methyl ester), bisPC₆₁BM (bis[6,6]‐phenyl C₆₁ butyric acid methyl ester) and PC₇₁BM ([6,6]‐phenyl C₇₁ butyric acid methyl ester), are investigated by means of thermally stimulated current measurements (TSC). Thereby, the lower limit of the trap densities for all studied methanofullerenes is on the order of 10²² m^?3, with the highest trap density in bisPC₆₁BM and the lowest in PC₆₁BM. Fractional TSC measurements on PC₆₁BM reveal a broad trap distribution instead of discrete trap levels, with activation energies ranging from 15 meV to 270 meV and the maximum at about 75 meV. The activation energies of the most prominent traps in the other two fullerene derivatives are significantly higher, at 96 meV and 223 meV for PC₇₁BM and 184 meV for bisPC₆₁BM, respectively. The influence of these findings on the performance of organic solar cells is discussed.     

Syntheses of water-soluble [60]fullerene derivatives and their enhancing effect on neurite outgrowth in NGF-treated PC12 cells

Water-soluble [60]fullerene (C₆₀) derivatives were synthesized to examine their bioactivities. PC12 cells were used as a model of nerve cells and the bioactivities of synthesized C₆₀ derivatives together with some reported ones were tested. Among the compounds tested, C₆₀/(γ-CyD)₂, C₆₀-bis(γ-CyD) (5) containing C₆₀-mono(γ-CyD) (5′), and C₆₀/PVP were sufficiently soluble in water and showed an enhancing effect on the neurite outgrowth of NGF-treated PC12 cells.     

Light‐Induced Degradation of Polymer:Fullerene Photovoltaic Devices: An Intrinsic or Material‐Dependent Failure Mechanism?

Although degradation mechanisms in organic photovoltaic devices continue to receive increased attention, it is only recently that the initial light‐induced failure, or so‐called burn‐in effect, has been considered. Both prototypical polythiophene:fullerene and polycarbazole:fullerene systems exhibit an exponential performance loss of ≈40% upon 150 h of continuous solar illumination. While the decrease in both the short‐circuit current (J_SC) and open‐circuit voltage (V_OC) is the origin of performance loss in poly(3‐hexylthiophene):[6,6]‐phenyl‐C61‐butyric acid methyl ester (P3HT:PC₆₀BM), in poly(N‐9′‐hepta‐decanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)):[6,6]‐phenyl‐C71‐butyric acid methyl ester (PCDTBT:PC₇₀BM) the decline of the fill factor dominates. By systematic variation of the interface layers, active layer thickness, and acceptor in polythiophene:fullerene cells, the loss in J_SC is ascribed to a degradation in the bulk of the P3HT:PC₆₀BM, while the drop in V_OC is reversible and arises from charge trapping at the contact interfaces. By replacing the C₆₀ fullerene derivative with a C₇₀ derivative, or by modifying the electron transport layer, the J_SC or V_OC, respectively, are stabilized. These insights prove that the burn‐in process stems from multiple concurrent failure mechanisms. Comparing the ageing and recovery processes in P3HT and PCDTBT blends results in the conclusion that their interface failures differ in nature and that burn‐in is a material dependent, rather than an intrinsic, failure mechanism.     

The Effect of PCBM Dimerization on the Performance of Bulk Heterojunction Solar Cells

Increasing the lifetime of polymer based organic solar cells is still a major challenge. Here, the photostability of bulk heterojunction solar cells based on the polymer poly[4,4′‐bis(2‐ethylhexyl)dithieno[3,2‐b:2′,3′‐d]silole)‐2,6‐diyl‐alt‐[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thiazole[5,4‐d]thiazole)‐1,8‐diyl] (PDTSTzTz) and the fullerene [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₀BM) under inert atmosphere is investigated. Correlation of electrical measurements on complete devices and UV‐vis absorption measurements as well as high‐performance liquid chromatography (HPLC) analysis on the active materials reveals that photodimerization of PC₆₀BM is responsible for the observed degradation. Simulation of the electrical device parameters shows that this dimerization results in a significant reduction of the charge carrier mobility. Both the dimerization and the associated device performance loss turn out to be reversible upon annealing. BisPC₆₀BM, the bis‐substituted analog of PC₆₀BM, is shown to be resistant towards light exposure, which in turn enables the manufacture of photostable PDTSTzTz:bisPC₆₀BM solar cells.     

Study of cytotoxicity of fullerene C60 derivatives

We investigated the cytotoxicity of the fullerene C₆₀ derivatives. We showed that complexes of C₆₀ fullerene with polyvinylpyrrolidone (m.w. of polyvinylpyrrolidone 10000 and 25000), C₆₀-NO₂-proline and C₆₀-alanine had no toxic effect on HEp-2 cells. Sodium salt of polycarboxylic derivative of fullerene C₆₀ exerted a pronounced toxic effect on this cell culture.     

Simultaneous Open‐Circuit Voltage Enhancement and Short‐Circuit Current Loss in Polymer: Fullerene Solar Cells Correlated by Reduced Quantum Efficiency for Photoinduced Electron Transfer

The limits of maximizing the open‐circuit voltage V_oc in solar cells based on poly[2,7‐(9,9‐didecylfluorene)‐alt‐5,5‐(4,7‐di‐2‐thienyl‐2,1,3‐benzothiadiazole)] (PF10TBT) as a donor using different fullerene derivatives as acceptor are investigated. Bulk heterojunction solar cells with PF10TBT and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) give a V_oc over 1 V and a power conversion efficiency of 4.2%. Devices in which PF10TBT is blended with fullerene bisadduct derivatives give an even higher V_oc, but also a strong decrease in short circuit current (J_sc). The higher V_oc is attributed to the higher LUMO of the acceptors in comparison to PCBM. By investigating the photophysics of PF10TBT:fullerene blends using near‐IR photo‐ and electroluminescence, time‐resolved photoluminescence, and photoinduced absorption we find that the charge transfer (CT) state is not formed efficiently when using fullerene bisadducts. Hence, engineering acceptor materials with a LUMO level that is as high as possible can increase V_oc, but will only provide a higher power conversion efficiency, when the quantum efficiency for charge transfer is preserved. To quantify this, we determine the CT energy (E_CT) and optical band gap (E_g), defined as the lowest first singlet state energy E_S1 of either the donor or acceptor, for each of the blends and find a clear correlation between the free energy for photoinduced electron transfer and J_sc. We find that E_g ? qV_oc > 0.6 eV is a simple, but general criterion for efficient charge generation in donor‐acceptor blends.     

Antiamyloid properties of fullerene C<Subscript>60</Subscript> derivatives

A comparative estimation of the ability of complexes of fullerene C₆₀ with polyvinylpyrrolidone and fullerene C₆₀ derivatives (the sodium salt of the polycarboxylic derivative of fullerene C₆₀, sodium fullerenolate), has been carried out. The fullerenes destroyed amyloid fibrils of the Aβ(1–42) peptide of the brain and the muscle X-protein. A study of the effect of fullerenes on muscle actin showed that complexes of fullerene C₆₀ with polyvinylpyrrolidone and sodium fullerenolate did not prevent the filament formation of actin, nor did they destroy its filaments in vitro. Conversely, sodium salt of the polycarboxylic derivative of fullerene C₆₀ destroyed actin filaments and prevented their formation. It was concluded that sodium fullerenolate and complexes of fullerene C₆₀ with polyvinylpyrrolidone are the most effective antiamyloid compounds among the fullerenes examined.     

Molecular Understanding of the Open‐Circuit Voltage of Polymer:Fullerene Solar Cells

The origin of open‐circuit voltage (V_OC) was studied for polymer solar cells based on a blend of poly(3‐hexylthiophene) (P3HT) and seven fullerene derivatives with different LUMO energy levels and side chains. The temperature dependence of J–V characteristics was analyzed by an equivalent circuit model. As a result, V_OC increased with the decrease in the saturation current density J₀ of the device. Furthermore, J₀ was dependent on the activation energy E_A for J₀, which is related to the HOMO–LUMO energy gap between P3HT and fullerene. Interestingly, the pre‐exponential term J₀₀ for J₀ was larger for pristine fullerenes than for substituted fullerene derivatives, suggesting that the electronic coupling between molecules also has substantial impact on V_OC. This is probably because the recombination is non‐diffusion‐lmilited reaction depending on electron transfer at the P3HT/fullerene interface. In summary, the origin of V_OC is ascribed not only to the relative HOMO–LUMO energy gap but also to the electronic couplings between fullerene/fullerene and polymer/fullerene.     

Fullerene Nucleating Agents: A Route Towards Thermally Stable Photovoltaic Blends

The bulk‐heterojunction nanostructure of non‐crystalline polymer:fullerene blends has the tendency to rapidly coarsen when heated above its glass transition temperature, which represents an important degradation mechanism. We demonstrate that fullerene nucleating agents can be used to thermally arrest the nanostructure of photovoltaic blends that comprise a non‐crystalline thiophene‐quinoxaline copolymer and the widely used fullerene derivative [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM). To this end, C₆₀ fullerene is employed to efficiently nucleate PCBM crystallization. Sub‐micrometer‐sized fullerene crystals are formed when as little as 2 wt% C₆₀ with respect to PCBM is added to the blend. These reach an average size of only 200 nanometers upon introduction of more than 8 wt% C₆₀. Solar cells based on C₆₀‐nucleated blends indicate significantly improved thermal stability of the bulk‐heterojunction nanostructure even after annealing at an elevated temperature of 130 °C, which lies above the glass transition temperature of the blend. Moreover, we find that various other compounds, including C₇₀ fullerene, single‐walled carbon nanotubes, and sodium benzoate, as well as a number of commercial nucleating agents—commonly used to clarify isotactic polypropylene—permit to control crystallization of the fullerene phase.     

Sequential Processing for Organic Photovoltaics: Design Rules for Morphology Control by Tailored Semi‐Orthogonal Solvent Blends

Design rules are presented for significantly expanding sequential processing (SqP) into previously inaccessible polymer:fullerene systems by tailoring binary solvent blends for fullerene deposition. Starting with a base solvent that has high fullerene solubility, 2‐chlorophenol (2‐CP), ellipsometry‐based swelling experiments are used to investigate different co‐solvents for the fullerene‐casting solution. By tuning the Flory‐Huggins χ parameter of the 2‐CP/co‐solvent blend, it is possible to optimally swell the polymer of interest for fullerene interdiffusion without dissolution of the polymer underlayer. In this way solar cell power conversion efficiencies are obtained for the PTB7 (poly[(4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)(3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl)]) and PC₆₁BM (phenyl‐C₆₁‐butyric acid methyl ester) materials combination that match those of blend‐cast films. Both semicrystalline (e.g., P3HT (poly(3‐hexylthiophene‐2,5‐diyl)) and entirely amorphous (e.g., PSDTTT (poly[(4,8‐di(2‐butyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)‐alt‐(2,5‐bis(4,4′‐bis(2‐octyl)dithieno[3,2‐b:2′3′‐d]silole‐2,6‐diyl)thiazolo[5,4‐d]thiazole)]) conjugated polymers can be processed into highly efficient photovoltaic devices using the solvent‐blend SqP design rules. Grazing‐incidence wide‐angle x‐ray diffraction experiments confirm that proper choice of the fullerene casting co‐solvent yields well‐ordered interdispersed bulk heterojunction (BHJ) morphologies without the need for subsequent thermal annealing or the use of trace solvent additives (e.g., diiodooctane). The results open SqP to polymer/fullerene systems that are currently incompatible with traditional methods of device fabrication, and make BHJ morphology control a more tractable problem.     

Synthesis of 61-bis(1-adamantylcarbamoyl)-1,2-methano[60]fullerene and its antagonistic effect on haloperidol-induced catalepsy in mice

The 61-bis(1-adamantylcarbamoyl)-1,2-methano[60]fullerene was synthesized from N,N'-di(1-adamantyl)malondiamide and C(60) in the presence of 1,8-diazabicyclo[5,4,0]-7-undecene. The intraperitoneal administration of this fullerene derivative (10mg/kg) caused an antagonistic effect on haloperidol-induced catalepsy in mice.     

[60]Fullerene displacement from fac-(dihapto-[60]fullerene)(dihapto-1,2-bis-(1,10-phenanthroline) tricarbonyl tungsten(0)

The Lewis bases triphenyl phosphine and tricyclohexyl phosphine (L) displace [60]fullerene (C₆₀) from fac-(η²-C₆₀)(η²-phen)W(CO)₃ (phen=1,10-phenanthroline) to produce fac-(η²-phen)(η¹-L)W(CO)₃. Under flooding conditions, the reactions were first order with respect to fac-(η²-C₆₀)(η²-phen)W(CO)₃. The order with respect to C₆₀ and L depends on the reaction conditions i.e., whether [C₆₀]/[L] ≈ 0 or 0?It [C₆₀]/[L] ≈ 1. Two limiting cases of an interchange displacement of [60]fullerene from fac-(η²-C₆₀)(η²-phen)W(CO)₃, whose relative contributions to the overall mechanism depend on the nature of the solvent, are proposed based on the rate law and on the activation parameters. The mechanism involves an initial [60]fullerene dissociation to produce (i) the electronically unsaturated intermediate (η²-phen)W(CO)₃ for the dissociative displacement and (ii) the solvated intermediate fac-(solvent)(η²-phen)W(CO)₃ for the solvent-assisted [60]fullerene dissociation. The W-C₆₀ bond energy in fac-(η²-C₆₀)(η²-phen)W(CO)₃ was estimated to be in the vicinity of 105 kJ/mol based on the enthalpy of activation of the step where presumably [60]fullerene dissociates from fac-(η²-C₆₀)(η²-phen)W(CO)₃ to produce (η²-phen)W(CO)₃.     

Electron microscopic study of the effect of fullerene on the formation of amyloid fibrils by the Aβ25–35 peptide

The antiamyloidogenic effect of hydrated fullerence C₆₀ HyFn was shown by electron microscopy. It was found that fullerene binds to growing fibrils formed by the [beta]-amyloid peptide Aβ_25–35 and thus prevents their further growth and interferes with the formation of new fibrils. Instead of long broad helically twisted ‘ribbons’ formed by Aβ_25–35 in the absence of fullerene, short narrow protofibrils form in its presence. These results suggest that fullerenes can be useful in treatment for Alzheimer’s disease.     

New Plant Growth Stimulants Based on Water-Soluble Nanoparticles of N-Substituted Monoamino-Acid Derivatives of Fullerene C60 and the Study of their Mechanisms of Action

Growth-stimulating effects of water-soluble nanoparticles of N-substituted monoamino-acid derivatives of fullerene C₆₀ (L- and D-alanine, L- and D-valine, L- and D-aspartic acid, β-alanine, and γ-aminobutyric and ε-aminocaproic acids in potassium salt form) were investigated. It was found that the nanoparticle size and relative antiradical activity of fullerene derivatives were factors that influence such physiological parameters of field peas as seed germination rate, germination energy, and root growth capacity. It was shown that the relative antiradical activity of nanoparticles in the selected group of compounds was determined by the total surface area of the nanoparticles regardless of the structure of the amino-acid substituent. The possibility of using amino-acid derivatives of fullerene as effective growth stimulating substances has been demonstrated. A dose-dependent effect of N-(monohydrofullerenyl)-D-alanine potassium salt in a concentration range of 10^–9–10^–11 M on the seed-germination rate and germination energy of field peas has been demonstrated.

     

Enhanced brain penetration of hexamethonium in complexes with derivatives of fullerene C<Subscript>60</Subscript>

The present report describes development of hexamethonium complexes based on fullerene C₆₀. Hexamethonium has a limited penetration into CNS and therefore can antagonize central effects of nicotine only when given at high doses. In the present studies conducted in laboratory rodents, intraperitoneal administration of hexamethonium-fullerene complexes blocked effects of nicotine (convulsions and locomotor stimulation). When compared to equimolar doses of hexamethonium, complexes of hexamethonium with derivatives of fullerene C₆₀ were 40 times more potent indicating an enhanced ability to interact with central nicotine receptors. Thus, fullerene C₆₀ derivatives should be explored further as potential carrier systems for polar drug delivery into CNS.     

The Crucial Influence of Fullerene Phases on Photogeneration in Organic Bulk Heterojunction Solar Cells

The conjugated polymer, poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) (pBTTT‐C₁₆), allows a systematic tuning of the blend morphology by varying the acceptor type and fraction, making it a well‐suited structural model for studying the fundamental processes in organic bulk heterojunction solar cells. To analyze the role of intercalated and pure fullerene domains on charge carrier photogeneration, time delayed collection field (TDCF) measurements and Fourier‐transform photocurrent spectroscopy (FTPS) are performed on pBTTT‐C₁₆:[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) solar cells with various stoichiometries. A weak influence of excess photon energy on photogeneration along with a photogeneration having a weaker field dependence at increasing fullerene loading is found. The findings are assigned to a dissociation via thermalized charge transfer (CT) states supported by an enhanced electron delocalization along spatially extended PC₆₁BM nanophases that form in addition to a bimolecular crystal (BMC) for PC₆₁BM rich blends. The highly efficient transfer of charge carriers from the BMC into the pure domains are studied further by TDCF measurements performed on non‐intercalated pBTTT‐C₁₆:bisPC₆₁BM blends. They reveal a field dependent charge generation similar to the 1:4 PC₆₁BM blend, demonstrating that the presence of pure acceptor phases is the major driving force for an efficient, field independent CT dissociation.     

A Supramolecular “Double‐Cable” Structure with a 12944 Helix in a Columnar Porphyrin‐C60 Dyad and its Application in Polymer Solar Cells

A novel porphyrin‐C₆₀ dyad (PCD1) is designed and synthesized to investigate and manipulate the supramolecular structure where geometrically isotropic [such as [60]fullerene (C₆₀)] and anisotropic [such as porphyrin (Por)] units coexist. It is observed that PCD1 possesses an enantiomeric phase behavior. The melting temperature of the stable PCD1 thermotropic phase is 160 °C with a latent heat (ΔH) of 18.5 kJ mol^?1. The phase formation is majorly driven by the cooperative intermolecular Por–Por and C₆₀–C₆₀ interactions. Structural analysis reveals that this stable phase possesses a supramolecular “double‐cable” structure with one p‐type Por core columnar channel and three helical n‐type C₆₀ peripheral channels. These “double‐cable” columns further pack into a hexagonal lattice with a = b = 4.65 nm, c = 41.3 nm, α = β = 90°, and γ = 120°. The column repeat unit is determined to possess a 129₄₄ helix. With both donor (D; Pro) and acceptor (A; C₆₀) units having their own connecting channels as well as the large D/A interface within the supramolecular “double‐cable” structure, PCD1 has photogenerated carriers with longer lifetimes compared to the conventional electron acceptor [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester. A phase‐separated columnar morphology is observed in a bulk‐heterojunction (BHJ) material made by the physical blend of a low band‐gap conjugated polymer, [poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta [2,1‐b;3,4‐b′]‐dithiophene)‐alt‐4,7‐(2,1,3‐benzothia‐diazole)] (PCPDTBT), and PCD1. With a specific phase structure in the solid state and in the blend, PCD1 is shown to be a promising candidate as a new electron acceptor in high performance BHJ polymer solar cells.     

Interaction between epoxidised estradiol and fullerene (C60): possible anticancer activity

In this article, the antioxidant activity of fullerene is theoretically studied by applying the density functional theory (DFT) method in terms of its protective effects against the derivatives of estrone that constitute species known to exhibit carcinogenic activity. Several reactions involving fullerene C₆₀ in different possible reactive centres of estradiol and epoxidised estradiol were studied. Surprisingly, the ring that supports the epoxide group is able to react with fullerene by means of a 2+2 cycloaddition, forming a very stable compound. This new compound has the potential to avoid known reactions between the epoxidised molecule and DNA fragments causing the mutagenic process of breast cancer. Therefore, fullerene C₆₀ represents the possibility of a new agent for combating this disease.