Isolation and Monitoring of the Endohedral Metallofullerenes Y@C82 and Sc3@C82:On-Line Chromatographic Separation with EPR Detection

The direct coupling of high-performance liquid chromatography (HPLC) with on-line electron paramagnetic resonance (EPR) detection is demonstrated for monitoring separations of endohedral metallofullerenes (M@C2n). The HPLC-EPR approach readily permits detection of the paramagnetic species, such as Y@C82 and Sc3@C82, in the presence of the dominant empty-cage fullerenes (C60, C70) and diamagnetic metallofullerenes (e.g., M2@C2n). The results indicate that on-line EPR provides a noninvasive, selective detector for HPLC metallofullerene separations that is readily adaptable to air-sensitive and/or labile compounds. Specifically, the “EPR-active” metallofullerenes, Y@C82 and Sc3@C82, are selectively monitored on-line for an initial separation of the metallofullerene fraction from the dominant empty-cage fullerenes utilizing a combination of polystyrene columns. This preparative “cleanup” procedure is followed by HPLC-EPR separation and monitoring of Y@C82 and Sc3@C82 species using a selective tripodal π-acidic-phase column (Trident-Tri-DNP) for the final stages of isolation

Ten millennia of hepatitis B virus evolution

Hepatitis B virus (HBV) has been infecting humans for millennia and remains a global health problem, but its past diversity and dispersal routes are largely unknown. We generated HBV genomic data from 137 Eurasians and Native Americans dated between ~10,500 and ~400 years ago. We date the most recent common ancestor of all HBV lineages to between ~20,000 and 12,000 years ago, with the virus present in European and South American hunter-gatherers during the early Holocene. After the European Neolithic transition, Mesolithic HBV strains were replaced by a lineage likely disseminated by early farmers that prevailed throughout western Eurasia for ~4000 years, declining around the end of the 2nd millennium BCE. The only remnant of this prehistoric HBV diversity is the rare genotype G, which appears to have reemerged during the HIV pandemic

Tracing the Geographical Origins of Human Genetic Diversity - A Possible Phylogeographic Scenario

Evidence underlining the Recent Out of Africa theory came from genetic diversity and population bottleneck studies that showed a restricted African origin for modern human dispersal and the non-African populations to be small subsets of the African gene pool; a genetic pattern most accurately explained by a serial founder effect. After the Recent Out of Africa theory was proposed, various researches suggested additional hypotheses on early Homo sapiens genetic and migration history to give more detailed explanations with regard to the origin of the observed diversity among populations from distinct geographical regions. The main aim of this thesis is trying to unify key findings from these studies into one congruent scenario to describe accurately the dynamics in early modern human population phylogeography, from the moment of origin in Africa till the initial settlement throughout the Asian, Oceanian and European continent. Human migration is thought to have originated in Southeast-Africa, the region that contains the highest genetic diversity found today and important ancient population radiations are thought to have occurred in Southwest-Africa. When the founder population left Africa ~85 kiloannum ago (kya), the population thus carried a selected gene pool. Early modern humans may have migrated from Africa to Eurasia along a northern route through the Levant, or along a southern route through the Arabian Peninsula. Since supporting evidence for each route focuses on different time periods, theoretically it is possible that both migrations routes were taken. The Multiple Route hypothesis combines both migration routes to describe human phylogeographic patterns: haplogroup M being the signature of an early southern route migration to Southeast-Asia and N of later northern route migration to West-Eurasia. The hypothesis assumes an African origin for haplogroups (L3)N and M. In contrast, the Single Southern Route hypothesis states that both M and N were carried out in one unique rapid migration event along a southern route to Southeast-Asia. West-Eurasia was colonized by an early offshoot of a South-Indian radiation. This hypothesis assumes an Asian origin for N and M. This thesis finds the Single Southern Route hypothesis the most accurate in describing human phylogeographic patterns. This hypothesis, completed by two additional explanations on human migration (back migration from Asia to Africa and a migration pause in the Levant area) are fundamental to the congruent scenario proposed in the conclusion of this thesis.

Essay : Photolyase & Cryptochrome Diversity during Mammalian Evolution: Starting Points & Hypotheses for Future Research

De begeleider en/of auteur heeft geen toestemming gegeven tot het openbaar maken van de scriptie. The supervisor and/or the author did not authorize public publication of the thesis.

Orientational Dynamics of the Sc3 Trimer in C82: An EPR Study

Electron paramagnetic resonance experiments on endohedral Sc3 in C82 show 22 hyperfine coupling split transitions with unusually large linewidths. Both the nuclear hyperfine coupling and the linewidths are found to be strongly temperature dependent. The data show that the three Sc ions are equivalent, and strongly suggest that they form a trimer which rapidly reorients within the C82 cage. A simple model is proposed which is in good agreement with the data.

Far infrared transmittance of Sc2@C84 and Er2@C82

We have measured the far infrared transmittance of Sc2@C84 and Er2@C82 at 1.5 K between 30 and 200 cm-1. Both materials are observed to have a large primary absorption feature centered at 95 cm-1 with a width of approximately 50 cm-1, as well as a number of secondary absorption features which are different in the two materials. This is the first study of the far infrared properties of metallofullerenes and may help in the determination of the structural and electronic properties of these materials.

Exciton and Hole-Transfer Dynamics in Polymer: Fullerene Blends

Ultrafast hole transfer dynamics from fullerene derivative to polymer in bulk heterojunction blends are studied with visible-pump – IR-probe spectroscopy. The hole transfer process is found to occur in 50/300 fs next to the interface, while a longer 15-ps time is attributed to exciton diffusion towards interface in PC71BM domains. High polaron generation efficiency in P3HT blends indicates excellent intercalation between the polymer and the fullerene even at highest PC71BM concentration thereby yielding a valuable information on the blend morphology

La2@C72: Metal-Mediated Stabilization of a Carbon Cage

In this study, we report production, isolation, and characterization for the relatively small endohedral metallofullerene, La2@C72. As described, La2@C72 is readily isolated from conventional electric-arc-generated carbon/metal soot. This new species was purified by HPLC chromatography and characterized by laser desorption mass spectrometry and UV-vis spectroscopy. The mass spectrum also demonstrates the presence of the monometal species, La@C72, but the absence of empty-cage C72. Since empty-cage C72 has not been successfully isolated to date, the results of the present study are in agreement with the argument for metal-mediated stabilization of the C72 carbon cage by lanthanum ions. The chromatographic retention data suggest that the electronic structure of La2@C72 is consistent with a (La3+)2@C726- species and the prediction of a relatively small dipole moment.

Acceptor Energy Offset Manages Ultrafast Recombination Dynamics in Donor-Acceptor Mixtures

We study charge recombination rates in blends of MEH-PPV and a comprehensive set of low molecular-weight fluorine-based acceptors, using visible-pump – IR-probe photoinduced absorption technique. The positions of acceptor’s HOMO-LUMO levels are engineered by addition of different chemical substituents. The results clearly show the exponential scaling of the charge recombination rate with the acceptor LUMO energy. The minimal donor-acceptor LUMO energy difference required to form a CTC state is estimated as ~0.25 eV