Showing papers by "Matthias Meyer published in 2005"

Dissipation of electronic excitation energy within a C60 [6:0]-hexaadduct carrying 12 pyropheophorbide a moieties.

Abstract: The synthesis and photophysical studies of a fullerene [6:0]-hexaadduct that carries 12 pyropheophorbide a units are reported. The synthesis started with the malonate 1, which was coupled under template conditions to C(60)() to give the hexaadduct 2. After removal of the protecting group with acid the dodecakis amino-substituted precursor compound 3 was generated. 3 was not isolated but directly reacted with the N-succinimid ester 4 of pyropheophorbide a (5), which delivered the desired fullerene [6:0]-hexaadduct 6 in excellent yield. The photophysical properties of 6 were studied and compared with those of the fullerene [5:1]-hexaadduct 7 with six pyropheophorbide a groups and the bispyropheophorbide a-fullerene [5:1]-hexaadduct 8. The pyropheophorbide a units in 6 undergo after light absorption very efficient energy transfer as well as partly excitonic interaction. The last process results in formation of energy traps, which could be resolved experimentally. Compared to the reference compounds 7 and 8, 6 has a higher probability of trap formation due to a higher local concentration of dye molecules and shorter distances between them. As a consequence, the excitation energy is delivered rapidly (within 23 ps) to the traps, resulting in decreases of the fluorescence, intersystem crossing, and singlet oxygen quantum yields in comparison with the values of the reference compounds.

A Genomic Region Evolving Toward Different GC Contents in Humans and Chimpanzees Indicates a Recent and Regionally Limited Shift in the Mutation Pattern

Abstract: DNA sequences evolving differently in the human and chimpanzee genomes signal recent and regionally limited changes in the process of DNA sequence evolution. Here we present the comparison of 90 kb from the nonrecombining part of the human Y chromosome to the corresponding part of the chimpanzee genome using gorilla as out-group. Our results reveal a significant difference in the region-specific substitution process among the human and chimpanzee lineages. As a consequence, this region experiences a change in its GC content on the human lineage while it resides in compositional equilibrium on the chimpanzee lineage. Based on our analysis, we suggest a recent and species-specific shift in the region's mutation pattern as the cause of its differing evolution in humans and chimpanzees.

Fluorescence anisotropy and transient absorption of halogenated silicon(IV) phthalocyanines with axial poly(ethylene-glycol) substituents

Abstract: Herein we report the utilization of fluorescence anisotropy to give rough hints on the conformation of three halogenated silicon-phthalocyanines with axially substituted polyethyleneglycol chains in solution. To deconvolute decay data sets from the instrumental response function a scanning fit algorithm was used, which facilitates the visualization of fitting accuracy and correlation of parameters of the assumed decay function. Moreover, to extend our investigation of photophysical properties in the nonlinear domain, the transient absorption in the picosecond range was measured and thus excited state absorption spectra are presented.

Bi-Analyte Surface Enhanced Raman Scattering for unambiguous evidence of single molecule detection

Abstract: A method is proposed to pin down an unambiguous proof for single molecule surface enhanced Raman spectroscopy (SERS). The simultaneous use of two analyte molecules enables a clear confirmation of the single (or few) molecule nature of the signals. This method eliminates most of the uncertainties associated with low dye concentrations in previous experiments. It further shows that single-molecule signals are very common in SERS, both in liquids and on dry substrates.