Highly efficient synthesis of globular (bola)amphiphilic [5:1]hexakisadducts of C60.

We report on the very facile access of a new family of amphiphilic and bola-amphiphilic fullerene [5:1]hexakisadducts 9a-f and 11a-e. The key point for this successful approach is the use of C(2v)-symmetrical fullerene pentakisadduct precursors 2b-f allowing for the completely regioselective addition of a sixth malonate addend to complete the octahedral [5:1] addition pattern. For the synthesis of the new amphiphiles we first developed a new second-generation dendrimer containing 9 tert-butoxycarbonyl (Boc)-protected amino functions at the periphery and two new malonates containing 6 or 18 Boc-protected amino termini, respectively. The hexakisadducts contain up to 18 positive or negative charges at the dendritic moiety and either no or ten positive or negative charges at the unbranched malonate positions after deprotection with trifluoroacetic acid (TFA). The charge state at the termini is pH-dependent. Complete structural characterization of the new compounds was carried out by ESI mass spectrometry and by UV/Vis, FTIR, (1)H NMR and (13)C NMR spectroscopy. We were also able to obtain the first X-ray crystal structure of pentakisadduct (2a) with a C(2v)-symmetrical addition pattern. The new amphiphilic hexakisadducts show interesting solubility properties in water. Initial investigations on the aggregation properties of the amphiphilic hexakisadduct 12c by using dynamic light scattering (DLS) and conductivity measurements, show aggregates with a radius up to 200 nm and a critical micelle concentration (CMC) of approximately 8 mg L(-1).

Charge transfer in sapphyrin-fullerene hybrids employing dendritic ensembles.

A new approach to creating noncovalent charge transfer ensembles is described. It is based on two components that are linked through anion-receptor interactions. The first component is sapphyrin, a pentapyrrolic expanded porphyrin, which is capable of carboxylate anion recognition and more importantly can act as a photodonor when irradiated in the presence of a suitable electron acceptor. The second component is the electron acceptor and consists of one of two different C(60) fullerene cores functionalized with multiple carboxylate anion groups arranged in a dendritic fashion. Depending on the specific choice of the fullerene carboxylate anion dendrimer employed in ensemble construction, 1:1 or 1:2 complexes are formed when the C(60) cores are titrated with sapphyrin. The resulting noncovalent arrays undergo sapphyrin-to-fullerene electron transfer when irradiated with 387 nm light. This gives rise to charge separated states with lifetimes of ca. 470 and 600 ps in the case of the 1:1 and 1:2 sapphyrin-fullerene ensembles, respectively.

Layer-by-layer deposition of molecular oligoelectrolytes-investigation of assembling and degradation behaviour.

The assembly and degradation behavior of oligoelectrolyte multilayer films (OEMs) self assembled by layer-by-layer deposition of positively and negatively charged oligoelectrolytes 1-6 was investigated. Next to colorless oligoelectrolytes we have employed representatives involving chromophores, in particular porphyrins. This allows for the systematic observation of both assembly and disassembly of the OEMs using optical spectroscopy, where chromophore containing building blocks serve as reporter electrolytes. The OEMs investigated in this study were built in a consistent, monomolecular matter and show linear correlation between the absorption and the number of layers. Using the concept of reporter electrolytes we have introduced for the first time also the use of non-chromophoric oligoelectrolytes, such as the new synthesized cationic system 2 as building blocks for OEMs. Moreover, we have investigated for the first time the degradation behavior of OEMs. We demonstrated that two different mechanisms of degradation proceed at the same time. The direct degradation is accompanied by a second release mechanism.

Chromatographic separation and identification of a water-soluble dendritic methano[60]fullerene octadecaacid.

The chromatographic separation of a highly water-soluble dendritic monoadduct methano[60]fullerene octadecaacid (dendrofullerene) with octadecylsilica bonded phases has been studied. It has been found that the RP-HPLC behavior of this dendrofullerene obeys the general rules of stationary-phase and mobile-phase selection for controlling the separation of usually acidic compounds. An RP-HPLC-ESI-MS analysis confirms the identity of the dendrofullerene and allows characterization of the molecular weights of the main impurities contained in the sample. The described methods can control the synthesis and efficiently purify this fullerene derivative, which has been previously shown to be active against mutant infectious clones of HIV-1, which are resistant to AZT and 3TC, drugs that are widely used in AIDS therapy.

Electrostatic complexation and photoinduced electron transfer between Zn-cytochrome c and [olyanionic fullerene dendrimers.

Two dendritic fullerene (DF) monoadducts, 2 and 3, which can carry up to 9 and 18 negative charges, respectively, were examined with respect to electrostatic complexation with Cytochrome c (Cytc). To facilitate comprehensive photophysical investigations, the zinc analogue of Cytc (ZnCytc) was prepared according to a novel, modified procedure. The association of ZnCytc and DF, and consequential photoinduced electron transfer within ZnCytc-DF from the photoexcited protein to the fullerene, was proven by fluorescence spectroscopy and transient absorption spectroscopy. These findings were also supported by circular dichroism as well as by extensive molecular dynamics (MD) simulations.