Biomedical subjects

Dirk M Guldi

Publications and source records attributed to Dirk M Guldi.

99 records · Page 6Linked to original sources

PubMed2002

Supramolecular self-assembled fullerene nanostructures.

Four ionic fullerene derivatives, which are relatively soluble in polar solvents, are shown to organize into morphologically different nanoscale structures. Spheres, nanorods, and nanotubules form in water depending on the side chain appendage of the fullerene spheroid. Images at different nanoscale structures were obtained via transmission electron microscopy. Also, computer simulations were used for investigating the relative spatial arrangements. The efficient method to fabricate almost perfect and uniformly shaped nanotubular crystals, which order spontaneously by self-assembly, opens the way to the possibility of exploiting the fullerene properties at the nanometer scale.

Carbon↗

PubMed2002

A helical peptide receptor for [60]fullerene.

Two terminally blocked nonapeptides, each made up of six Aib residues, a Gly spacer and two L-Tyr residues in positions 2 and 8 (these are substituted in the side chain with either ferrocenoyl or methyl moieties), have been synthesized by solution methods and fully characterized. FT-IR absorption and two-dimensional NMR analyses indicate that a 3(10)-helical conformation is adopted by these rigid peptides in structure-supporting solvents. An X-ray diffraction investigation shows that the bis-L-Tyr(Me) nonapeptide in the crystal state is folded in a regular right-handed 3(10)-helical structure. As five amino acid units separate the two substituted L-Tyr residues in the peptide sequence, the two side chain moieties will-in solution-face each other after two complete turns of the ternary helix. By carrying out a detailed photophysical analysis, we have demonstrated that the electron-rich, hydrophobic and wide cavity generated by the nonapeptide template with two ferrocenoyloxybenzyl walls is able to host [60]fullerene. Further evidence for this superstructure has been provided in the gas phase by a mass spectrometric investigation.

Amino Acid Sequence↗

PubMed2002

Molecular engineering of C60-based conjugated oligomer ensembles: modulating the competition between photoinduced energy and electron transfer processes.

A series of novel and soluble C60-(pi-conjugated oligomer) dyads were synthesized, starting from suitably functionalized oligomer precursors (i.e., dihexyloxynaphthalene, dihexyloxynaphthalene-thiophene, and dihexyloxybenzene-thiophene). A systematic change in the nature of the oligomeric component allowed (i) tailoring the light absorption of the chromophore by shifting the ground-state absorption from the ultraviolet to the visible region and (ii) varying the oxidation potential of the donor. The resulting electro- and photoactive dyads were examined by electrochemical and photophysical means. In general, both singlet-singlet energy transfer and intramolecular electron transfer were found to take place and, most importantly, to compete with each other in the overall deactivation of the photoexcited oligomer. The selection of polar solvents in combination with the dihexyloxybenzene-thiophene donor shifted the reactivity from an all energy (1a; dihexyloxynaphthalene) to an all electron-transfer scenario (1d, dihexyloxybenzene-thiophene). Encouraged by the favorable electron-transfer properties of dyad 1d, we prepared photodiodes by embedding 1d between asymmetric metal contacts, which showed external monochromatic efficiencies (IPCE) close to 10% at the maximum absorption of the molecule.

Journal Article↗

PubMed2002

Evidence of pronounced electronic coupling in a directly bonded fullerene--ferrocene dyad.

A new donor-acceptor dyad (7) involving a ferrocene moiety as donor and an azafullerene as acceptor has been synthesized by treating bisazafullerenyl (1) with ferrocenium hexafluorophosphate. This compound represents the first example of a fullerene-based dyad where two electroactive groups are connected by only a single sigma-bond. The cyclic voltammetry of 7, in comparison to the corresponding reference systems, clearly reveals strong electronic coupling between the ferrocene and the azafullerene moiety in the ground state. For example, the Fc-based, reversible, one electron oxidation wave is significantly positively shifted by 183 mV with respect to that of the parent ferrocene. This indicates the existence of intramolecular charge transfer (ICT) from the donating Fc to the accepting azafullerenyl group. Photophysical studies on 7 were carried out by means of emission and transient absorption spectroscopy. An instantaneous deactivation of the fullerene singlet excited-state results in the formation of the charge-separated (C59N.-)-(Fc.+) radical pair. From the charge-transfer dynamics with a lower limit of > or = 5 x 10(10) s-1, we infer strong electronic coupling (V) between the azafullerene and the ferrocene moiety of the order of 60 cm-1 in benzonitrile.

Journal Article↗

PubMed2002

T(h)-symmetrical hexakisadducts of C(60) with a densely packed pi-donor shell can act as energy- or electron-transducing systems.

For the first time several T(h)-symmetrical hexakisadducts of C(60) bearing up to six electro- and photoactive o-phenylene diamine or 9,10-dialkoxyanthracene moieties were synthesized and subjected to photoinduced electron/energy-transfer studies. Both donors form a densely packed pi-donor shell surrounding the fullerene core. In these novel core-shell ensembles (7 and 19), either an efficient energy transfer from the dialkoxyanthracene periphery, or an electron transfer from the o-phenylene diamine periphery transduces the flow of excited-state energy or electrons, respectively, to the fullerene moiety, which resides in the central core. Due to the relatively high reduction potential of the fullerene core, which is anodically shifted by approximately equal to 0.7 V, compared with that of pristine C(60), the outcome of these intramolecular reactions depends mainly on the donor ability of the peripheral system. Interestingly, the charge-separated state in the o-phenylene diamine heptad (7; tau=2380 ns in benzonitrile) is stabilized by a factor of 20 relative to the corresponding o-phenylene diamine dyad (6; tau=120 ns in benzonitrile), an effect that points unequivocally to the optimized storage of charges in this highly functionalized fullerene ensemble.

Journal Article↗

PubMed2002

Energy transfer processes in novel subphthalocyanine-fullerene ensembles.

A series of subphthalocyanine-C(60) dyads in which the two subunits are placed at different distances have been prepared and their electrochemical properties measured. Photophysical measurements reveal energy transfer events following the initial photoexcitation of the subphthalocyanine chromophore.

Journal Article↗

PubMed2002

Organic functionalization of carbon nanotubes.

A very general and versatile method for functionalizing different types of carbon nanotubes is described, using the 1,3-dipolar cycloaddition of azomethine ylides. Approximately one organic group per 100 carbon atoms of the nanotube is introduced, to yield remakably soluble bundles of nanotubes, as seen in transmission electron micrographs. The solubilization of the nanotubes generates a novel, interesting class of materials, which combines the properties of the nanotubes and the organic moiety, thus offering new opportunities for applications in materials science, including the preparation of nanocomposites.

Journal Article↗

PubMed2002

Molecular design of strong single-wall carbon nanotube/polyelectrolyte multilayer composites.

The mechanical failure of hybrid materials made from polymers and single-wall carbon nanotubes (SWNT) is primarily attributed to poor matrix-SWNT connectivity and severe phase segregation. Both problems can be successfully mitigated when the SWNT composite is made following the protocol of layer-by-layer assembly. This deposition technique prevents phase segregation of the polymer/SWNT binary system, and after subsequent crosslinking, the nanometre-scale uniform composite with SWNT loading as high as 50 wt% can be obtained. The free-standing SWNT/polyelectrolyte membranes delaminated from the substrate were found to be exceptionally strong with a tensile strength approaching that of hard ceramics. Because of the lightweight nature of SWNT composites, the prepared free-standing membranes can serve as components for a variety of long-lifetime devices.

Acrylic Resins↗

PubMed2002

Fullerene-porphyrin architectures; photosynthetic antenna and reaction center models.

Fullerenes and porphyrins are molecular architectures ideally suited for devising integrated, multicomponent model systems to transmit and process solar energy. Implementation of C60 as a 3-dimensional electron acceptor holds great expectations on account of their small reorganization energy in electron transfer reactions and has exerted a noteworthy impact on the improvement of light-induced charge-separation. This article describes how the specific compositions of porphyrin chromophores linked to C60--yielding artificial light harvesting antenna and reaction center mimics--have been elegantly utilized to tune the electronic couplings between donor and acceptor sites and the total reorganization energy. Specifically, the effects that these parameters have on the rate, yield and lifetime of the energetic charge-separated states are considered.

Carbon↗