Synthesis, structure and biological activity of nitroxide malonate methanofullerenes

Reactions of Nitroxides, Part 17. Synthesis, Fungistatic and Bacteriostatic Activity of Novel Five- and Six-Membered Nitroxyl Selenoureas and Selenocarbamates

The reactions of 3-isoselenocyanato-2,2,5,5-tetramethylpyrrolidine-1-oxyl, 3-isoselenocyanatomethyl-2,2,5,5-tetramethyl-3-pyrrolidine-1-oxyl, and 4-isoselenocyanato-2,2,6,6-tetramethylpiperidine-1-oxyl with selected amines and alcohols give the corresponding novel nitroxyl selenoureas and selenocarbamates, all bearing a nitroxyl moiety. Synthesized selenoureas and selenocarbamates show significant activity against pathogenic fungi and bacteria. In contrast to piperidine nitroxides, pyrrolidine, five-membered nitroxyl selenoureas and selenocarbamates show excellent antifungal and antibacterial activity against pathogenic fungi and bacteria, respectively.

Nucleophilic cyclopropanation of [60]fullerene by the addition–elimination mechanism

Information on the synthesis of monofunctionalized methanofullerenes C₆₀ obtained by the addition–elimination mechanism is generalized. The main reagents for cyclopropanation, mechanisms and optimal conditions for the processes, and the prospects for practical application of the products are considered.

Generalized material on the synthesis of monosubstituted methanofullerenes C₆₀, obtained by the addition–elimination mechanism.

Fullerene as a doxorubicin nanotransporter for targeted breast cancer therapy: Capillary electrophoresis analysis

The clinical use of doxorubicin (DOX) is limited by dose-related cardiomyopathy, which becomes more prevalent with increasing cumulative doses of the drug. Complexes of fullerene with DOX were designed and studied using biophysical methods. The ability of DOX to release from fullerene at different pHs was analyzed. It has been shown that the size of the fullerene-DOX complexes was ∼280 nm. The zeta potential for fullerene was -30 mV, for DOX -8 mV, and for fullerene-DOX conjugates -24 mV. Drug release was studied by CE with LIF detection. When fullerene-DOX conjugates were separated in a pH 7.5 buffer, 43% of all DOX signals were derived from free DOX, with the signal increasing as pH decreased. At pH 5.25, all DOX had been released and 100% of the signal was derived from free DOX. The release of DOX from complexes with fullerene at lower pH can be used in targeted antineoplastic therapy, resulting in lower toxicity for less acidic non-target tissue.

Surface modification using TEMPO and its derivatives

This article provides an overview of the methods for surface modification based on the use of stable radicals: 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and its derivatives. Two approaches are discussed. The first relies on the immobilization of TEMPO moieties on the surface of various materials including silicon wafers, silica particles, organic polymers as well as diverse nanomaterials. Applications of such materials with spin labeled surface/interface, in (electro)catalysis, synthesis of novel hybrid nanostructures and nanocomposites as well as in designing of organic magnets and novel energy storage devices are also included in the discussion. The second approach utilizes TEMPO and its derivatives for the grafting of polymer chains and polymer brushes formation on flat and nanostructure surfaces via Nitroxide Mediated Radical Polymerization (NMRP). The influence of such polymer modification on surface/interface physicochemical properties is also presented.

TEMPO functionalized C60 fullerene deposited on gold surface for catalytic oxidation of selected alcohols

C₆₀TEMPO₁₀ catalytic system linked to a microspherical gold support through a covalent S-Au bond was developed. The C₆₀TEMPO₁₀@Au composite catalyst had a particle size of 0.5-0.8 μm and was covered with the fullerenes derivative of 2.3 nm diameter bearing ten nitroxyl groups; the organic film showed up to 50 nm thickness. The catalytic composite allowed for the oxidation under mild conditions of various primary and secondary alcohols to the corresponding aldehyde and ketone analogues with efficiencies as high as 79-98%, thus giving values typical for homogeneous catalysis, while retaining at the same time all the advantages of heterogeneous catalysis, e.g., easy separation by filtration from the reaction mixture. The catalytic activity of the resulting system was studied by means of high pressure liquid chromatography. A redox mechanism was proposed for the process. In the catalytic cycle of the oxidation process, the TEMPO moiety was continuously regenerated in situ with an applied primary oxidant, for example, O₂/Fe³⁺ system. The new intermediate composite components and the final catalyst were characterized by various spectroscopic methods and thermogravimetry. Graphical abstractᅟ.

[6,6]-Open and [6,6]-closed isomers of C70(CF2): synthesis, electrochemical and quantum chemical investigation

Novel difluoromethylenated [70]fullerene derivatives, C70(CF2 )n (n=1-3), were obtained by the reaction of C70 with sodium difluorochloroacetate. Two major products, isomeric C70(CF2 ) mono-adducts with [6,6]-open and [6,6]-closed configurations, were isolated and their homofullerene and methanofullerene structures were reliably determined by a variety of methods that included X-ray analysis and high-level spectroscopic techniques. The [6,6]-open isomer of C70(CF2 ) constitutes the first homofullerene example of a non-hetero [70]fullerene derivative in which functionalisation involves the most reactive bond in the polar region of the cage. Voltammetric estimation of the electron affinity of the C70(CF2 ) isomers showed that it is substantially higher for the [6,6]-open isomer (the 70-electron π-conjugated system is retained) than the [6,6]-closed form, the latter being similar to the electron affinity of pristine C70. In situ ESR spectroelectrochemical investigation of the C70(CF2 ) radical anions and DFT calculations of the hyperfine coupling constants provide evidence for the first example of an inter-conversion between the [6,6]-closed and [6,6]-open forms of a cage-modified fullerene driven by an electrochemical one-electron transfer. Thus, [6,6]-closed C70(CF2 ) constitutes an interesting example of a redox-switchable fullerene derivative.

MULTIFUNCTIONAL FULLERENE- AND METALLOFULLERENE-BASED NANOBIOMATERIALS

Recent advances in nanotechnology have enabled the synthesis and characterization of nanomaterials suitable for applications in the field of biology and medicine. Due to their unique physico-chemical properties, carbon-based nanomaterials such as fullerenes, metallofullerenes, carbon nanotubes and graphene have been widely investigated as multifunctional materials for applications in tissue engineering, molecular imaging, therapeutics, drug delivery and biosensing. In this review, we focus on the multifunctional capabilities of fullerenes and metallofullerenes for diagnosis and therapy. Specifically, we review recent advances toward the development of fullerene- and metallofullerene-based magnetic resonance imaging (MRI) and X-ray imaging contrast agents, drug and gene delivery vehicles, and photodynamic therapy agents. We also discuss in vitro and in vivo toxicity, and biocompatibility issues associated with the use of fullerenes and metallofullerenes for biomedical applications.

Comparison of Nuclear Spin Relaxation of H2O@C60 and H2@C60 and Their Nitroxide Derivatives

The successful synthesis of H2O@C60 makes possible the study of magnetic interactions of an isolated water molecule in a geometrically well-defined hydrophobic environment. Comparisons are made between the T1 values of H2O@C60 and the previously studied H2@C60 and their nitroxide derivatives. The value of T1 is approximately six times longer for H2O@C60 than for H2@C60 at room temperature, is independent of solvent viscosity or polarity, and increases monotonically with decreasing temperature, implying that T1 is dominated by the spin-rotation interaction. Paramagnetic nitroxides, either attached covalently to the C60 cage or added to the medium, produce strikingly similar T1 enhancements for H2O@C60 and H2@C60 that are consistent with through-space interaction between the internal nuclear spins and the external electron spin. This indicates that it should be possible to apply to the endo-H2O molecule the same methodologies for manipulating the ortho and para spin isomers that have proven successful for H2@C60.