Structural Aspects of Fullerene ChemistryA Journey through Fullerene Chirality

Synthesis of fullerotetrahydropyridazines via the copper-catalyzed heteroannulation of [60]fullerene with hydrazides

Fullerotetrahydropyridazines have been efficiently synthesized via the copper-catalyzed reaction of [60]fullerene with hydrazides.

Stereoselective synthesis of N-ethyl-2-arylvinyl-5-methyl fulleropyrrolidines: reaction of [60]fullerene with aromatic aldehydes and triethylamine/diethylamine in the absence or presence of manganese(iii) acetate

Reaction of [60]fullerene with aromatic aldehydes and triethylamine/diethylamine afforded a series of novel fulleropyrrolidines.

An extended cluster expansion for ground states of heterofullerenes

It is challenging to determine the ground states of heterofullerenes due to the numerous isomers. Taking the C_60-nB_n heterofullerenes (1 ≤ n ≤ 4) as an example, our first-principles calculations with the isomer enumeration present the most stable structure of C₅₇B₃, which is energetically favored by 0.73 eV than the reported counterpart. It was difficult to conduct the enumeration for the isomers with n beyond 4 because of the expensive first-principle calculations. Here, we propose a nomenclature to enhance structural recognition and adopt an extended cluster expansion to describe the structural stabilities, in which the energies of the heterofullerenes with various concentrations are predicted by linear combination of the multi-body interactions. Unlike the conventional cluster expansion, the interaction parameters are derived from the enumeration of C_60-nB_n (n = 1~4), where there are only 4 coefficients to be fitted as a function of composition for the consideration of local bonding. The cross-validation scores are 1~2 meV per atom for both C₅₅B₅ and C₅₄B₆, ensuring the ground states obtained from our model are in line with the first-principles results. With the help of the structural recognition, the extended cluster expansion could be further applied to other binary systems as an effective complement to the first-principle calculations.

Metal-Based Diversity for Crystalline Metal-Fullerene Frameworks

Four different three-dimensional metal-fullerene frameworks were synthesized through polymerization of two C₆₀ -derived dodecaacids with varying alkyl spacers in the presence of Ca²⁺ , Cu²⁺ or Cd²⁺ ions. Structural analysis of the frameworks was performed by single-crystal X-ray diffraction and porosity of the materials was investigated by sorption measurements.

Highly efficient synthesis of [60]fullerene oxides by plasma jet

Atmospheric pressure nonequilibrium plasma jet has been applied to the synthesis of [60]fullerene oxides (C₆₀O_n) for the first time. C₆₀O and C₆₀O₂ were produced and isolated in high yields up to 44% and 21%, respectively. The structural assignment of C₆₀O was confirmed by comparison with the reported spectroscopic data. Theoretical calculations of ¹³C NMR chemical shifts for eight isomers of C₆₀O₂ were performed and compared with the experimental data to assign the most possible structure for the obtained C₆₀O₂ dominantly as an e isomer.

Fullerenes in Biology and Medicine

Fullerenes and related carbon based derivatives have shown a growing relevance in biology and medicine, mainly due to the unique electronic and structural properties that make them excellent candidates for multiple functionalization. This review focuses on the most recent developments of fullerene derivatives for different biological applications.

Fused-Pentagon-Configuration-Dependent Electron Transfer of Monotitanium-Encapsulated Fullerenes

We introduce monotitanium-based endohedral metallofullerenes (EMFs) using density functional theory calculations. Isomeric C₆₄ fullerenes are initially employed as hosts, and Ti@C₆₄ species show novel features on the electronic structures. Energetically, the preference of titanium residing on triple-fused-pentagon subunits is proposed in theory. More importantly, different from current knowledge on mono-EMFs, electron transfer between titanium and carbon cages is not unified but is essentially dependent on the pentagon distribution of the binding sites, giving rise to variations of the cationic titanium of Ti@C₆₄. Such selective electron-transfer character is extended to the study of the encapsulation of other neighboring metal atoms (i.e., calcium and scandium). Because of their different capabilities to accept d electrons, fullerene cages with distinct fused-pentagon motifs show selective metal encapsulation characters. In addition, some other fullerenes (C₄₄-C₄₈ and C₈₂) are selected as hosts to study the electron-transfer behavior of titanium in smaller fullerenes and larger systems without pentagon adjacency.

Crystallographic Structure Determination of Both [5,6]- and [6,6]-Isomers of Lithium-Ion-Containing Diphenylmethano[60]fullerene

Organic functionalization of lithium-ion-containing [60]fullerene, Li⁺@C₆₀, was performed by using diphenyl(diazo)methane as a stable, readily available diazo compound to obtain lithium-ion-containing [5,6]- and [6,6]-diphenylmethano[60]fullerenes, Li⁺@C₆₁Ph₂. The bis(trifluoromethanesulfonyl)imide (TFSI) salts of [5,6]- and [6,6]-Li⁺@C₆₁Ph₂ were successfully separated by using a cation exchange column with eluent containing LiTFSI. Improved separation protocol and high crystallinity of ionic components in less polar solvents enabled separate crystallization of each isomer. Both [5,6]-open and [6,6]-closed structures of Li⁺@C₆₁Ph₂ were determined by synchrotron radiation X-ray crystallography. Elucidating the [5,6]-open methano[60]fullerene (fulleroid) structure will contribute to materials research on fulleroids.

Synthesis and reactivity of tetraalkoxyl[60]fullerene epoxides, C60(O)(OR)4

Hexachloro[60]fullerene, C60Cl6, was reacted with a mixture of ROH/H2O (R = Me, Et, n-Pr, (CH2)2C≡CH) to form both C60Cl(OH)(OR)4 and C60Cl(OR)5. Only the C60Cl(OH)(OR)4 were isolated with bulky alcohols, ROH (R = (CH2)3C≡CH, (CH2)4C≡CH). Tetrahydro[60]fullerene epoxides, C60(O)(OR)4, were prepared by treating C60Cl(OH)(OR)4 with CuI. The epoxy moiety could be hydrolyzed to the vicinal diol derivatives, C60(OH)2(OR)4, and then oxidized to form dicarbonyl open-cage fullerenes, C60O2(OR)4. CuI was found to convert the terminal alkynyl addends into iodoalkynyl addends on the C60 cage.

Individual (f,t A)- and (f,t C)-Fullerene-Based Nickel(II) Glycinates: Protected Chiral Amino Acids Directly Linked to a Chiral π-Electron System

Stereoselective electrosynthesis of the first individual (^f,t A)- and (^f,t C)-1,4-fullerene derivatives with a non-inherently chiral functionalization pattern is described, as well as the first example of an optically pure protected primary amino acid directly linked to the fullerene through only the chiral α-amino-acid carbon atom. An application of an auxiliary chiral nickel-Schiff base moiety as derivatizing agent allowed separation of (^f,t A)- and (^f,t C)-1,4-fullerene derivatives using an achiral stationary phase, a separation which has never been done before.

Chirality in curved polyaromatic systems

Chiral non-planar polyaromatic systems that display zero, positive or negative Gaussian curvature are analysed and their potential to ‘encode’ chirality of larger sp²-carbon allotropes is evaluated. Shown is a hypothetical peanut-shaped carbon allotrope, where helical chirality results from the interplay of various curvature types.

Manipulation of fullerene superstructures by complexing with polycyclic aromatic compounds

Fullerene superstructures with various nanofeatures were fabricated by the intercalation of polycyclic aromatic compounds (naphthalene, anthracene and pyrene) during the growth of fullerene crystals.

Transition-metal-catalyzed divergent functionalization of [60]fullerene with propargylic esters

Transition-metal-catalyzed divergent reactions between C₆₀ and propargylic esters allow easy access to formal [2 + 2] and [4 + 2] cycloadducts.

Metal-free-mediated synthesis of fulleropyrrolines by the reaction of [60]fullerene with β-substituted ethylamines

Reaction of [60]fullerene with β-substituted ethylamines under air conditions generated a series of scarce fulleropyrrolines with trisubstituted alkene functional groups in moderate yields.

Characterization of New Cationic N,N-Dimethyl[70]fulleropyrrolidinium Iodide Derivatives as Potent HIV-1 Maturation Inhibitors

HIV-1 maturation can be impaired by altering protease (PR) activity, the structure of the Gag-Pol substrate, or the molecular interactions of viral structural proteins. Here we report the synthesis and characterization of new cationic N,N-dimethyl[70]fulleropyrrolidinium iodide derivatives that inhibit more than 99% of HIV-1 infectivity at low micromolar concentrations. Analysis of the HIV-1 life cycle indicated that these compounds inhibit viral maturation by impairing Gag and Gag-Pol processing. Importantly, fullerene derivatives 2a-c did not inhibit in vitro PR activity and strongly interacted with HIV immature capsid protein in pull-down experiments. Furthermore, these compounds potently blocked infectivity of viruses harboring mutant PR that are resistant to multiple PR inhibitors or mutant Gag proteins that confer resistance to the maturation inhibitor Bevirimat. Collectively, our studies indicate fullerene derivatives 2a-c as potent and novel HIV-1 maturation inhibitors.

The Driving Force of Photoinduced Charge Separation in Metal-Cluster-Encapsulated Triphenylamine-[80]fullerenes

Understanding photoinduced charge separation in fullerene-based dye-sensitized solar cells is crucial for the development of photovoltaic devices. We investigate here how the driving force of the charge separation process in conjugates of M@C₈₀ (M=Sc₃ N, Sc₃ CH, Sc₃ NC, Sc₄ O₂ , and Sc₄ O₃ ) with triphenylamine (TPA) depends on the nature of the metal cluster. Both singlet and triplet excited-state electron-transfer reactions are considered. These results based on TD-DFT calculations demonstrate that the driving force of charge separation in TPA-M@C₈₀ can be tuned well by varying the structure of the metal cluster encapsulated inside the fullerene cage.

Reductive Hydrogenation of Cs -C70 (CF3 )8 and C1 -C70 (CF3 )10

CF3 -derivatized fullerenes prove once again to be promising scaffolds for regioselective fullerene functionalization: now with the smallest possible addends-hydrogen atoms. Hydrogenation of Cs -C70 (CF3 )8 and C1 -C70 (CF3 )10 by means of reduction with Zn/Cu couple in the presence of water proceeds regioselectively, yielding only one major isomer of C70 (CF3 )8 H2 and only two for C70 (CF3 )10 H2 , whose addition patterns are combined in the only abundant isomer of C70 (CF3 )10 H4 . The observed selectivity is governed by the electronic structure of trifluoromethylated substrates. Interestingly, we discovered that Clar's theory can be utilized to predict the regiochemistry of functionalization, and we look forward to testing it on forthcoming cases of derivatization of pre-functionalized fullerene building blocks.

Theoretical estimation of the rate of photoinduced charge transfer reactions in triphenylamine C60 donor-acceptor conjugate

Fullerene-based molecular heterojunctions such as the [6,6]-pyrrolidine-C60 donor-acceptor conjugate containing triphenylamine (TPA) are potential materials for high-efficient dye-sensitized solar cells. In this work, we estimate the rate constants for the photoinduced charge separation and charge recombination processes in TPA-C60 using the unrestricted and time-dependent DFT methods. Different schemes are applied to evaluate excited state properties and electron transfer parameters (reorganization energies, electronic couplings, and Gibbs energies). The use of open-shell singlet or triplet states, several density functionals, and continuum solvation models is discussed. Strengths and limitations of the computational approaches are highlighted. The present benchmark study provides an overview of the expected performance of DFT-based methodologies in the description of photoinduced charge transfer reactions in fullerene heterojunctions. © 2016 Wiley Periodicals, Inc.

Polarization response of clathrate hydrates capsulated with guest molecules

Clathrate hydrates are characterized by their water cages encapsulating various guest atoms or molecules. The polarization effect of these guest-cage complexes was studied with combined density functional theory and finite-field calculations. An addition rule was noted for these systems whose total polarizability is approximately equal to the polarizability sum of the guest and the cage. However, their distributional polarizability computed with Hirshfeld partitioning scheme indicates that the guest-cage interaction has considerable influence on their polarization response. The polarization of encapsulated guest is reduced while the polarization of water cage is enhanced. The counteraction of these two opposite effects leads to the almost unchanged total polarizability. Further analysis reveals that the reduced polarizability of encapsulated guest results from the shielding effect of water cage against the external field and the enhanced polarizability of water cage from the enhanced bonding of hydrogen bonds among water molecules. Although the charge transfer through the hydrogen bonds is rather small in the water cage, the polarization response of clathrate hydrates is sensitive to the changes of hydrogen bonding strength. The guest encapsulation strengthens the hydrogen bonding network and leads to enhanced polarizability.

Cu-Catalyzed Click Reaction in Carbohydrate Chemistry

Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC), popularly known as the "click reaction", serves as the most potent and highly dependable tool for facile construction of simple to complex architectures at the molecular level. Click-knitted threads of two exclusively different molecular entities have created some really interesting structures for more than 15 years with a broad spectrum of applicability, including in the fascinating fields of synthetic chemistry, medicinal science, biochemistry, pharmacology, material science, and catalysis. The unique properties of the carbohydrate moiety and the advantages of highly chemo- and regioselective click chemistry, such as mild reaction conditions, efficient performance with a wide range of solvents, and compatibility with different functionalities, together produce miraculous neoglycoconjugates and neoglycopolymers with various synthetic, biological, and pharmaceutical applications. In this review we highlight the successful advancement of Cu(I)-catalyzed click chemistry in glycoscience and its applications as well as future scope in different streams of applied sciences.

Silver(i)-mediated three-component annulation reaction of [60]fullerene, sulfonylhydrazones, and nitriles: leading to diverse disubstituted [60]fullerene-fused dihydropyrroles

A novel Ag(i)-mediated three-component annulation reaction of C₆₀, sulfonylhydrazones, and nitriles is developed for the synthesis of diverse disubstituted C₆₀-fused dihydropyrroles.