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Biomedical subjects

Angela Bihlmeier

Publications and source records attributed to Angela Bihlmeier.

5 recordsLinked to original sources
PubMed2005

DFT study of fullerene dimers.

Several [2+2] dimerization products of a fullerene Cn (n=50, 52, 54, 56, 58, 60) in its most stable form are presented and discussed. In total, 34 dimers are studied. Only symmetric Cn-Cn dimers (no mixed products) are reported, and only dimers of the fullerenes C50 to C58 with bonds between C atoms in adjacent pentagons are considered. Geometries were optimized within the framework of density functional theory using the Becke-Perdew exchange-correlation functional (BP86) in combination with an empirical dispersive energy correction, which contributes significantly to the binding energy. The results are discussed in the context of the reactivity of adjacent pentagon sites. The lateral interaction between fullerenes is found to be stronger for C50 to C58 than for C60, which is consistent with recent experimental observations. Further, the possibility of polymer formation based on the investigated [2+2] reaction is addressed.

Journal Article↗
PubMed2005

Solid C58 films.

A new solid material has been created in ultra high vacuum by utilizing the aggregation process of C58 molecules deposited onto highly oriented pyrolytic graphite from a mass selected low-energy ion beam comprising C58+. Cluster fluxes of up to 3x10(11) ions s-1 cm-2 with impinging kinetic energies of 6+/-0.5 eV were typically applied. Growth of the solid C58 phase proceeds according to the cluster-aggregation-based Volmer-Weber scenario where initially ramified 2D islands transform into 3D pyramid-like structures at higher coverages. The C58 films created exhibit much higher thermal stability than the C60 solid phase. Sublimation of C58 sets in at a temperature of 700 K. Ultraviolet photoionization spectra (He I, 21.2 eV) yield a molecular ionization potential in the range between 6.6 and 7 eV. Density functional and Hartree-Fock theories suggest that the formation of C58 dimers and higher multimers upon deposition/aggregation gives rise to the high thermal stability and unique electronic properties of this material.

Biomedical Engineering↗
PubMed2004

From weakly coordinating to non-coordinating anions? A simple preparation of the silver salt of the least coordinating anion and its application to determine the ground state structure of the Ag(eta2-P4)2+ cation.

The unexpected but facile preparation of the silver salt of the least coordinating [(RO)3Al-F-Al(OR)3]- anion (R=C(CF3)3) by reaction of Ag[Al(OR)4] with one equivalent of PCl3 is described. The mechanism of the formation of Ag[(RO)3Al-F-Al(OR)3] is explained based on the available experimental data as well as on quantum chemical calculations with the inclusion of entropy and COSMO solvation enthalpies. The crystal structures of (RO)3Al<--OC4H8, Cs+[(RO)2(Me)Al-F-Al(Me)(OR)2]-, Ag(CH2Cl2)3+[(RO)3Al-F-Al(OR)3]- and Ag(eta2-P4)2+[(RO)3Al-F-Al(OR)3]- are described. From the collected data it will be shown that the [(RO)3Al-F-Al(OR)3]- anion is the least coordinating anion currently known. With respect to the fluoride ion affinity of two parent Lewis acids Al(OR)3 of 685 kJ mol(-1), the ligand affinity (441 kJ mol(-1)), the proton and copper decomposition reactions (-983 and -297 kJ mol(-1)) as well as HOMO level and HOMO-LUMO gap and in comparison with [Sb4F21]-, [Sb(OTeF5)6]-, [Al(OR)4]- as well as [B(R(F))4]- (R(F)=CF3 or C6F5) the [(RO)3Al-F-Al(OR)3]- anion is among the best weakly coordinating anions (WCAs) according to each value. In contrast to most of the other cited anions, the [(RO)3Al-F-Al(OR)3] anion is available by a simple preparation in conventional inorganic laboratories. The least coordinating character of this anion was employed to clarify the question of the ground state geometry of the Ag(eta2-P4)2+ cation (D(2h), D(2) or D(2d)?). In agreement with computational data and NMR spectra it could be shown that the rotation along the Ag-(P-P-centroid) vector has no barrier and that the structure adopted in the solid state depends on packing effects which lead to an almost D(2h) symmetric Ag(eta2-P4)2+ cation (0 to 10.6 degrees torsion) for the more symmetrical [Al(OR)4]- anion, but to a D2 symmetric Ag(eta2-P4)2+ cation with a 44 degrees twist angle of the two AgP2 planes for the less symmetrical [(RO)3Al-F-Al(OR)3]- anion. This implies that silver back bonding, suggested by quantum chemical population analyses to be of importance, is only weak.

Journal Article↗
PubMed2004

Ti2: accurate determination of the dissociation energy from matrix resonance Raman spectra and chemical interaction with noble gases.

UV-visible and resonance Raman spectra of Ti(2) isolated in Ar, Kr, and Xe matrices at temperatures of 10 K were measured by using the 514 nm line of an Ar ion laser. The data show that the Ti(2) molecule interacts strongly with Xe, leading to a significant weakening of the Ti[bond]Ti bond strength. The f(Ti[bond]Ti) force constant decreases in the series Ar>Kr>Xe, from 232.8 Nm(-1) in Ar and 225.5 Nm(-1) in Kr to 199.7 Nm(-1) in Xe. Additional experiments in an Ar matrix containing 2 % of Xe indicate the formation of a molecule of the formula Ti(2)Xe. Our spectra for Ti(2) in an Ar matrix give evidence for several previously not observed members of the Stokes progression. The sum of experimental data allows for an improved estimation of the dissociation energy on the basis of a LeRoy-Bernstein-Lam analysis. A dissociation energy of 1.18 eV was derived from this analysis. The UV-visible data give evidence of the vibrational levels of an excited state of Ti(2).

Journal Article↗