N-Unsubstituted fulleropyrrolidine derivatives: reinvestigation, structural reassignment and new insight

The reaction of [60]fullerene with α-amino acids and aldehydes affording N-unsubstituted 2,5-disubstituted fulleropyrrolidines was reinvestigated. The previously reported stereochemistry should be reassigned. A reversible interconversion between the cis and trans stereoisomers of fulleropyrrolidines was observed for the first time.     

Synthesis of water soluble fulleropyrrolidines bearing biologically active arylpiperazines

New water soluble fulleropyrrolidines endowed with biologically active arylpiperazines have been synthesized by 1,3-dipolar cycloaddition of in situ generated azomethyne ylides to C₆₀. The substitution pattern on the pyrrolidine and piperazine rings ensures their solubility in a H₂O/DMSO (9:1) solvents mixture. The mass spectrometry study reveals a different fragmentation pathway for the fulleropyrrolidines depending upon the substituent on the pyrrolidine nitrogen atom, affording in all cases to differently substituted methanofullerenes. Preliminary biological tests reveal a moderate activity in vitro experiments.     

Diastereoselective synthesis of fulleropyrrolidines from suitably functionalized chiral cyclobutanes

The first diastereoselective synthesis of fulleropyrrolidines endowed with diastereomerically pure functionalized cyclobutanes is reported. The new C(60)-based cyclobutane derivatives 7a,b and 9 are suitably functionalized for further incorporation into peptide surrogates.     

Fabrication of Flowerlike Supramolecular Architectures of Fullerene Derivatives Bearing a Small Nitrophenyl Substituent

Flowerlike supramolecular architectures were fabricated from fulleropyrrolidincs bearing a small para-, meta-, or ortho-nitrophenyl group. The self-assembled architectures were characterized by scanning electron micro-scopy（SEM） and X-ray diffraction（XRD）. It was found that these flowerlike architectures were assembled from na- noplatcs that formed from fundamental subunit of interdigitated lamellar bilayer structure.     

Fluorescence Quenching Study of Zinc Bisporphyrins by Fulleropyrrolidines and Their N-Oxides

Novel phenylene-bridged zinc bisporphyrins （1-4）, fulleropyrrolidines （C60-m, C60-h） and their N-oxides （C60-mo, C60-ho） were synthesized. The fluorescence quenching processes of bisporphyrins in toluene solution by fulleropyrrolidines and their N-oxides were investigated by steady-state fluorescence spectra. The fluorescence quenching constants proved that the fluorescence quenching ability was decreased as reduction of the pyrrolidine functional groups of fullerene surface： C60-h〉C60-m〉C60, and the fluorescence quenching ability was increased about 1.3-7.4 times by utilizing fulleropyrrolidine N-oxides （C60-mo, C60-ho） compared to fulleropyrrolidine compounds （C60-m, C60-h）. The results revealed photoinduced electron transfer （PET） efficiency between bispor-phyrin and fullerene derivatives could be tunable by change of functional groups on fullerene surface.     

Incorporation of fullerene derivatives into smectite clays: a new family of organic-inorganic nanocomposites

Three fulleropyrrolidine derivatives, characterized by the presence of positive charges, were introduced in the interlayer space of montmorillonite. The composites were characterized by powder X-ray diffraction and differential thermal and thermogravimetric (DTA-TGA) analysis, in conjunction with FTIR, UV-Vis, Raman, and (57)Fe-M?ssbauer spectroscopies. Organophilic derivatives were intercalated into organically modified clays, while water-soluble fulleropyrrolidines were introduced into the clay galleries through ion exchange. The experiments, complemented by computer simulations, show that not all the clay-clay platelets are intercalated by the fullerene derivatives and that a sizable amount of charge transfer takes place between the host and the guests.     

Photoaddition reactions of azomethine ylides generated from α-aminonitriles to fullerene C60: Formation of fulleropyrrolidines and reaction efficiencies changes depending on reaction conditions

Photoaddition reactions of C₆₀ with both (trimethylsilyl)methyl and either benzyl or phenethyl group containing α-aminonitriles were carried out to explore how product distributions and reaction efficiencies can be influenced by reaction solvent systems. The results show that photoreactions produce both trimethylsilyl- and cyano group containing fulleropyrrolidines as a major (or exclusive) product. Especially, photoreactions performed in either EtOH containing solution or oxygenated environment take place with a much more efficient manner.     

Synthesis and characterization of a ferrocene-linked bis-fullerene[60] dumbbell

A new [60]fullerene dumbbell consisting of two fulleropyrrolidines connected to a central ferrocene unit by amide linkages has been prepared and fully characterized by elemental analysis, (1)H NMR, UV/Vis, fluorescence and mass spectrometry. The electrochemical properties as determined by cyclic voltammetry show ground state electronic communication between the ferrocene and the fullerene units. In addition, the preparaton of a ferrocene building block for an alternative linking approach is presented.     

Water-Soluble Polymeric Methanofullerene and Fulleropyrrolidine Derivatives

Water-soluble methanofullerene and fulleropyrrolidine derivatives were synthesized by the reactions of methanofullerenes (MFs) and fulleropyrrolidines (FPs) with poly(N-vinylpyrrolidone) (PVP) bearing one terminal amino group. The products contain MF or FP covalently bound to the polymer, corresponding polymeric complexes, and unreacted PVP. Large aggregates of the polymeric MF and FP derivatives are found in aqueous solutions. The electrooptical properties of the products differ considerably from those of the initial polymer. The phosphorus-containing MF and FP derivatives are capable of cleaving the molecule of plasmid DNA.     

Synthesis of Fulleropyrrolidines under Microwave Irradiation

In recent years, considerable efforts have been devoted to the development of systems in which C60 is covalently linked to an electron donor.[1] Studies[2] on intermolecular photoinduced electron transfer between C60 and triphenyl amine show that triphenyl amine is a good donor. It is envisaged that the use of donor segments consisting of either pyrrole/aniline may extend the lifetime of charge-separated state.[3] Since Gedye[4] demonstrated that many organic reactions can be conducted rapidly under microwave irradiation, here we have successfully synthesized five new fulleropyrrolidines containing triphenyl amine or thiophene dyads under microwave irradiation, which are different from traditional heating. The determination of structures of these fulleropyrrolidines is in progress. On the other hand, we have studied the geometry, electronic structures and frontier orbitals of these N-methyl-pyrrolo[3,4]C60 derivatives by using AM1semiempirical quantum calculation method. The results indicate that there exists strong intramolecular electron transfer in them.     

N-未取代和N-芳基取代的富勒烯吡咯啉：富勒烯官能团化的新的合成砌块

C₆₀, 甘氨酸或N-芳基化的甘氨酸以及脂肪醛或酮在回流的甲苯或氯苯中反应, 制备出两个系列的稳定的可溶性的富勒烯四氢吡咯衍生物. 这些新的富勒烯衍生物可以作为有用的前体制备更加官能团化的富勒烯衍生物.     

Highly efficient retro-cycloaddition reaction of isoxazolino[4,5:1,2][60]- and -[70]fullerenes

Isoxazolino[4,5:1,2][60]- and -[70]fullerenes undergo an efficient retro-cycloaddition reaction to pristine fullerene by thermal treatment in the presence of an excess of a dienophile and Cu(II) catalysis, which can be selectively used in the presence of malonate or pyrrolidine cycloadducts. Trapping experiments using N-phenylmaleimide as dipolarophile have shown that the reaction mechanism occurs by thermal removal of the nitrile oxide 1,3-dipole, in a process which is favored by the presence of Cu(II) as the catalyst. The ESI-MS study supports the observed retro-cycloaddition process for both C60 and C70 derivatives. In contrast to previous electrochemical retro-cycloaddition processes observed in fulleropyrrolidines, isoxazolinofullerenes were stable under oxidative conditions.     

Effect of covalent functionalization of C60 fullerene on its encapsulation by water soluble calixarenes

The molecular encapsulation of functionalized fullerenes (substituted fulleropyrrolidines) with water-soluble calixarenes was studied by photoluminescence and quantum-chemical methods. The results show that both the thiacalix[4]arene-tetrasulfonate and calix[6]arene-hexasulfonate are able to overcome the natural water-repulsive character of fullerenes. However, the functionalization of calixarenes and fullerenes induces significant changes in the molecular encapsulation processes, and the obtained thermodynamic behavior of the complex formation highlights the importance of the entropy. Our results can contribute to the development of the synthesis and design of functionalized calixarenes supporting their application in pharmaceutical and food chemistry.     

Easy access to N-alkylation of N-unsubstituted [60]fulleropyrrolidines: reductive amination using sodium triacetoxyborohydride

[60]Fulleropyrrolidines were used as secondary amines to react with aldehydes through reductive aminations to afford N-alkylated derivatives. In spite of the very weak base activity of the nitrogen atom of N-unsubstituted [60]fulleropyrrolidines, this method was found to be efficient at the aid of sodium triacetoxyborohydride. Several N-alkylated derivatives were synthesized and fully characterized.     

Synthesis and study of novel fulleropyrrolidines bearing biologically active 1,4-dihydropyridines

New fulleropyrrolidines endowed with chlorine-containing biological active 1,4-dihydropyridines (1,4-DHPs) have been synthesised from the respective formyl substituted 1,4-DHPs by following Prato's procedure. The presence of the chlorine atom on C2 of the 1,4-DHP ring brings about important spectroscopical and structural differences in compounds 10a-f related to the parent hydrogen-containing 11a. The mass spectroscopy study reveals different fragmentation patterns for fulleropyrrolidines 10a-f and their precursors 1,4-DHPs, as well as with 11a. Semiempirical calculations (AM1 and PM3) predict a most stable stereoisomer in all cases (RS for 10a-f) and the same RR for 11a. The presence of chlorine atom in 10a-f is responsible for the higher calculated conformational energy barriers in comparison with 11a. The geometry of the 1,4-DHP shows that the presence of fullerene unit does not significantly alter the required conformation for biological activity.     

2 + 2] cycloaddition reaction to Sc3N@I(h)-C80. The formation of very stable [5,6]- and [6,6]-adducts

The [2 + 2] cycloaddition reaction of Sc(3)N@I(h)-C(80) with benzyne was successfully conducted for the first time. The reaction affords both the [5,6]- and [6,6]-monoadducts with a four-membered ring attached to the cage surface on 5,6- and 6,6-ring fusions, respectively. The compounds were characterized by MALDI-TOF, NMR, UV-vis-NIR spectroscopy and single-crystal X-ray structure determination. The electrochemical behavior of both monoadducts was investigated. The [5,6]-regioisomer displays reversible cathodic behavior similar to that observed for the fulleropyrrolidines with a 5,6-addition pattern. Surprisingly, the [6,6]-regioisomer also exhibits reversible cathodic behavior. The interconversion reaction of the isomers was also explored, and the results showed that both monoadducts are thermally very stable.     

Theoretical study of the highly diastereoselective 1,3-dipolar cycloaddition of 1,4-dihydropyridine-containing azomethine ylides to [60]fullerene (Prato's reaction)

The 1,3-dipolar cycloaddition of azomethine ylides bearing the biologically active 1,4-dihydropiridine ring to C(60) was investigated by means of quantum mechanical calculations at the semiempirical AM1 and DFT (B3LYP/6-31G) methods. The presence of two chiral centers and one chiral axis in the resulting fulleropyrrolidines leads to four possible [6,6] cycloaddition products. Formation of atropoisomers has also been considered. The transition-state structures were computed for the four different cycloaddition pathways to find out the lowest activation energy stereoisomer. In all cases, a frequency analysis and an IRC calculation were carried out to fully characterize the located transition-state structures. AM1 results and single-point energy calculations at the B3LYP/6-31G//AM1 level for the four transition-state structures yield activation energies values below 5 kcal/mol.     

Regioselective intramolecular Pauson-Khand reactions of C60: an electrochemical study and theoretical underpinning

Suitably functionalized fulleropyrrolidines endowed with one or two propargyl groups at the C-2 position of the pyrrolidine ring (1,6-enynes) react efficiently and regioselectively with [Co2(CO)8] to afford the respective Pauson-Khand products with an unprecedented three (5 a-d, 7, and 24) or five (25) pentagonal rings, respectively, fused onto the fullerene sphere. Fulleropyrrolidines with 1,7-, 1,9-, 1,10-, or 1,11-enyne moieties do not undergo the PK reaction and, instead, the intermediate dicobalt complexes formed with the alkynyl group are isolated in quantitative yields. These differences in reactivity have been studied by DFT calculations with a generalized gradient approximation (GGA) functional and several important energy and structural differences were found for the intermediates formed by the interaction between the coordinatively unsaturated Co atom and the pi system of C60 in 1,6- and 1,7-enynes. The different lengths of the alkyne chains are responsible for the observed reactivities. Cyclic voltammetry reveals that the presence of the cyclopentenone's carbonyl group connected directly to the C60 core results in PK compounds with remarkable electron-accepting ability.     

Polyhedral oligomeric silsesquioxane bound fulleropyrrolidines

The first reported examples of polyhedral oligomeric silsesquioxane (POSS) cages containing a fulleropyrrolidine species are reported herein. Monosubstituted POSS‐dioxalane species were synthesized through the hydrosilylation of a silyl‐dioxalane with mono‐vinyl substituted POSS. Subsequent deprotection yielded the desired aldehyde functionality. An alternative synthetic pathway, involving the nucleophilic substitution of mono‐benzyl chloride POSS with 4‐hydroxybenzaldehyde yielded the desired aldehyde functionality. Each mono‐aldehyde POSS was then reacted with N‐methylglycine and C₆₀ to yield the desired POSS fulleropyrrolidines. The prepared compounds were characterized by multinuclear NMR, electrospray mass spectrometry, elemental analysis, UV–vis, fluorescence and optical power limiting measurements. Copyright © 2008 John Wiley & Sons, Ltd.     

Monomeric fullerenes in lipid membranes: effects of molecular shape and polarity

We report a combined theoretical and experimental study on the single-molecule interaction of fullerenes with phospholipid membranes. We studied pristine C(60) (1) and two N-substituted fulleropyrrolidines (2 and 3), one of which (3) bore a paramagnetic nitroxide group. Theoretical predictions of fullerene distribution and permeability across lipid bilayers were combined with electron paramagnetic resonance (EPR) experiments in aligned DMPC/DHPC bicelles containing the paramagnetic fulleropyrrolidine 3 or either one of the diamagnetic fullerenes together with spin-labeled lipids. We found that, at low concentrations, fullerenes are present in the bilayer as single molecules. Their preferred location in the membrane is only slightly influenced by the derivatization: all derivatives were confined just below the hydrophilic/hydrophobic interface, because of the key role played by dispersion interactions between the highly polarizable fullerene cage and the hydrocarbon chains, which are especially tight within this region. However, the deviation from spherical shape is sufficient to induce a preferential orientation of 2 and 3 in the membrane. We predict that monomeric fullerenes spontaneously penetrate the bilayer, in agreement with the results of molecular dynamics simulations, but we point out the limits of the currently used permeability model when applied to hydrophobic solutes.