397 research outputs found
Excitated state properties of 20-chloro-chlorophyll a
The excited-state and lasing properties of 20-chloro-chlorophyll a in ether solution were compared to those of chlorophyll a. Desactivation parameters and cross-sections were obtained from non-linear absorption spectroscopy in combination with a physico-mathematical methods package. The Cl substituent at C-20 (1) increases both intersystem crossing and internal conversion, (2) produces a blue-shift of the S1 absorption spectrum, and (3) leads to pronounced photochemistry
From chlorophyll a towards bacteriochlorophyll a: Excited-state processes of modified pigments
By means of fluorescence spectroscopy and nonlinear absorption experiments, excited-state processes of the modified pigments [3-acetyl]-chlorophyll a, [31-OH]-bacteriochlorophyll a and [3-vinyl]-bacteriochlorophyll a were investigated and compared with those of chlorophyll a and bacteriochlorophyll a
Ultrafast process in bacterial antennas studied by nonlinear polarization spectroscopy (frequence domain)
Chiral QCD sum rules for open charm mesons
QCD sum rules for chiral partners in the open-charm meson sector are
presented at nonzero baryon net density or temperature. We focus on the
differences between pseudo-scalar and scalar as well as vector and axial-vector
D mesons and derive the corresponding Weinberg type sum rules. This allows for
the identification of such QCD condensates which drive the non-degeneracy of
chiral partners in lowest order of the strong coupling alpha_s and which
therefore may serve as "order parameters" for chiral restoration (or elements
thereof).Comment: 24 pages, 4 figure
Substructure analysis of the bacterial antenna LH II by nonlinear polarization spectroscopy in the frequency domain
Pigment–protein architecture in the light-harvesting antenna complexes of purple bacteria: does the crystal structure reflect the native pigment–protein arrangement?
AbstractStructural analysis of crystallized peripheral (LH2) and core antenna complexes (LH1) of purple bacteria has revealed circular aggregates of high rotational symmetry (C8, C9 and C16, respectively). Quantum-chemical calculations indicate that in particular the waterwheel-like arrangements of pigments should show characteristic structure-sensitive spectroscopic behavior in the near infrared absorption region. Laser-spectroscopic data obtained with non-crystallized, isolated LH2 of Rhodospirillum molischianum are in line with a highly symmetric (C8) circular aggregate, but deviations have been found for LH2 of Rhodobacter sphaeroides and Rhodopseudomonas acidophila. For both the latter, C-shaped incomplete circular aggregates (as seen only recently in electron micrographs of crystallized LH1–reaction center complexes) may be a suitable preliminary model
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