Beatriz M. Illescas

Fullerene sugar balls

Fullerene hexakis-adducts bearing 12 peripheral carbohydrate moieties have been prepared by grafting sugar derivatives onto the fullerene core through the copper mediated Huisgen 1,3-dipolar cycloaddition of azides and alkynes.

Glycofullerenes inhibit viral infection.

Water-soluble glycofullerenes based on a hexakis-adduct of [60]fullerene with an octahedral addition pattern are very attractive compounds providing a spherical presentation of carbohydrates. These tools have been recently described and they have been used to interact with lectins in a multivalent manner. Here, we present the use of these glycofullerenes, including new members with 36 mannoses, as compounds able to inhibit a DC-SIGN-dependent cell infection by pseudotyped viral particles. The results obtained in these experiments demonstrate for the first time that these glycoconjugates are adequate to inhibit efficiently an infection process, and therefore, they can be considered as very promising and interesting tools to interfere in biological events where lectins such as DC-SIGN are involved.

[60]Fullerene as Multivalent Scaffold: Efficient Molecular Recognition of Globular Glycofullerenes by Concanavalin A

Financial support by the MICINN of Spain (CTQ2008-00795/BQU, CTQ2008-01694), the CAM (MADRISOLAR-2 S2009/PPQ-1533), Consolider- Ingenio (CSD2007-00010, Nanociencia Molecular), and the EU (FUNMOL FP7-212942-1) is greatly appreciated. A.M. thanks the MICINN for an FPI Studentship

Cycloadditions to [60]fullerene using microwave irradiation: A convenient and expeditious procedure

Abstract Several Diels-Alder and 1,3-dipolar cycloadditions to C 60 were performed, under microwave irradiation, in a modified domestic microwave oven and a focused microwave reactor. Reactions proceed within minutes to afford the respective cycloadducts in similar or increased yields related to the described methods by conventional heating. This methodology simplifies the procedure and overcomes the drawbacks resulting from the long reaction times required under classical heating conditions.

A New exTTF-Crown Ether Platform To Associate Fullerenes: Cooperative n−π and π−π Effects

A new and readily available exTTF-bis(crown ether), 1, efficiently recognizes C60 as well as C70 by means of cooperative π-π and n-π interactions. The geometrical (concave-convex) and electronic (donor-acceptor) complementarity accounts on one hand for remarkable binding strengths, with association constants reaching 10(7) M(-1) in benzonitrile, and on the other hand for lifetimes of the photogenerated radical ion pair state on the order of 45 ps.

Nanorods versus nanovesicles from amphiphilic dendrofullerenes.

Three new amphiphilic dendrofullerenes endowed with 4, 8, and 16 carboxylic groups have been efficiently prepared by using a click chemistry methodology. These amphiphilic fullerene derivatives aggregate forming micelles, nanorods, or hollow vesicles depending on the concentration and on the solid substrate.

Supramolecular chemistry of π-extended analogues of TTF and carbon nanostructures

The shrewd combination of complementary electroactive molecular fragments through weak, non-covalent forces can be exploited to construct stimuli-responsive assemblies or to achieve self-ordered arrays of electron donor and/or acceptor moieties to be utilized in optoelectronic devices. Among the electron donors, tetrathiafulvalene (TTF) has been particularly fashionable in this field. Comparatively, the supramolecular chemistry of its π-extended analogues was severely underdeveloped. Herein we present a summary of some recent results in the exploration of the non-covalent chemistry of π-extended analogues of tetrathiafulvalene.

A Facile Formation of Electroactive Fullerene Adducts from Sultines via a Diels-Alder Reaction.

Abstract A new procedure for the functionalization of C 60 by microwave assisted Diels-Alder reaction with “sultines” is described: an accelerating microwave effect is observed; the electrochemical measurements reveal three reduction waves cathodically shifted compared to C 60

Photoinduced electron transfer between C60 and electroactive units

Abstract A summary of our recent works on fulleropyrrolidines and fullerotriazolines covalently attached to the strong electron-donor tetrathiafulvalene (TTF) is presented. Absorption of light in C 60 -based TTF-containing dyads leads to the formation of the fullerene excited singlet state, which undergoes an intramolecular electron transfer to give the charge-separated (CS) state. A further stabilization of the CS state takes place by gaining aromaticity upon oxidation of the donor (TTF) fragment. Back electron transfer proceeds mainly via formation of the fullerene triplet excited state due to the strong second-order vibronic spin–orbit coupling induced by the sulfur nucleus. Two C 60 -acceptor systems have been also studied in the search for a possible electron transfer from the photoexcited fullerene to the covalently linked electron-acceptor. Formation of the fullerene triplet excited state rather than an intramolecular electron-transfer was observed in both cases.

Gating Charge Recombination Rates through Dynamic Bridges in Tetrathiafulvalene–Fullerene Architectures

Conversion of light into chemical energy is a process that nature has optimized over eons in photosynthetic organisms, such as bacteria, plants, and algae. However, the search for non-natural systems that mimic the complex overall process of photosynthesis has remained a challenge. In particular, the key step of the initial light-induced charge separation between electron donors and acceptors is hampered by its inherent microscopic reversibility, that is, competing charge recombination. Well-defined molecular model systems typically comprise a donor (D) and an acceptor (A) covalently linked by a bridge (B). In the resulting D–B–A structures, the role of the bridge is ideally to facilitate the desired initial photoinduced charge separation, yet, to slow down the undesired charge recombination. Among the many combinations of donors and acceptors that have been explored, those consisting of proaromatic tetrathiafulvalene (TTF) and fullerene derivatives, such as C60, have shown outstanding results. The exceptional electron donating and accepting properties originate from the aromatic stabilization of the formed TTF radical cation and from C60 s unique three dimensional delocalized p-electron system, respectively. This last feature leads to low reorganization energies upon the reduction to the C60 radical anion and allows for the uptake of up to six additional electrons. The photophysical properties of various TTF–C60 conjugates featuring different p-conjugated molecular bridges have been investigated and charge-separated states with lifetimes ranging from a few nanoseconds up to hundreds of microseconds have been realized. Of particular interest are conjugates with p-extended TTF derivatives, in which a conjugated p-quinoid anthracene moiety is placed between the TTF s two 1,3-dithiole rings. Nevertheless, the design of such D–B–A architectures features inherent drawbacks. For example, even with optimized donors and acceptors, the bridge needs to play two opposing roles. On the one hand, it should enhance the coupling between D and A to facilitate the initial charge separation. On the other hand, once the charge-separated state has been formed it should prevent charge recombination by decoupling DC and AC . Clearly, conventional, static bridges have to be a compromise of these two demands. However, if D and A are connected by a dynamic bridge, which can be switched between a coupled and a decoupled form, prolonged charge-separated state lifetimes could potentially be attained without compromising the initial charge separation. Such improved molecular design requires a switch entity that adopts two electronically distinct forms and allows for precise timing of the switching, that is, when the bridge is being coupled or decoupled. Dithienylethenes (DTE) are ideal candidates as switchable bridges as they reversibly interconvert between their ring-open (decoupled) and ring-closed (p-conjugated) forms upon irradiation with light of specific wavelengths. Adopting this new strategy, we prepared four novel D–DTE–A structures connecting either TTF or exTTF acting as D and with C60 functioning as A by photochromic dithienylperhydrocyclopentene or perfluorocyclopentene bridges (Scheme 1). Some researchers have used photochromic units as lightresponsive electronic traps that allow or prevent intramolecular electron transfer from D to A depending on the adopted isomeric form. There are also some examples, in which the electron transfer kinetics are clearly altered by the structural modification of the bridging units by chemical inputs (chelation) or, in mechanically interlocked D and A units, by topological changes. However, herein, we show for the first time that in (ex)TTF–DTE–C60 architectures, the lifetime of the charge-separated state can be significantly shortened or prolonged by performing light-induced structural changes in the bridging unit. [*] Dr. S. Castellanos, Dr. J. Moreno, Prof. Dr. S. Hecht Department of Chemistry Humboldt-Universit t zu Berlin Brook-Taylor-Strasse 2, 12489 Berlin (Germany) E-mail: sh@chemie.hu-berlin.de