Ultrafast energy transfer in light-harvesting chlorosomes from the green sulfur bacterium Chlorobium tepidum

Two independent pump-probe techniques were used to study the antenna energy transfer kinetics of intact chlorosomes from the green sulfur bacterium Chlorobium tepidum with femtosecond resolution. The isotropic kinetics revealed by one-color experiments in the BChl c antenna were inhomogeneous with respect to wavelength. Multiexponential analyses of the photobleaching/stimulated emission (PB/SE) decay profiles typically yielded (apart from a approximately 10 fs component that may stem from the initial coherent oscillation) components with lifetimes 1-2 ps and several tens of ps. The largest amplitudes for the latter component occur at 810 nm, the longest wavelength studied. Analyses of most two-color pump-probe profiles with the probe wavelength red-shifted from the pump wavelength yielded no PB/SE rise components. PB/SE components with approximately 1 ps risetime were found in 790 --> 810 and 790 --> 820 nm profiles, in which the probe wavelength is situated well into the BChl a absorption region. A 760 --> 740 nm uphill two-color experiment yielded a PB/SE component with 4-6 ps risetime. Broadband absorption difference spectra of chlorosomes excited at 720 nm (in the blue edge of the 746 nm BChl c Qy band) exhibit approximately 15 nm red-shifting of the PB/SE peak wavelength during the first several hundred fs. Analogous spectra excited at 760 nm (at the red edge) show little dynamic spectral shifting. Our results suggest that inhomogeneous broadening and spectral equilibration play a larger role in the early BChl c antenna kinetics in chlorosomes from C. tepidum than in those from C. aurantiacus, a system studied previously. As in C. aurantiacus, the initial one-color anisotropies r(0) for most BChl c wavelengths are close to 0.4. The corresponding residual anisotropies r(infinity) are typically 0.19-0.25, which is much lower than found in C. aurantiacus (> or = 0.35); the transition moment organization is appreciably less collinear in the BChl c antenna of C. tepidum. However, the final one-color anisotropies at 789 and 801 nm are approximately 0 and 0.09 respectively, and the final anisotropy in time 780 --> 800 nm experiment is approximately -0.1. These facts indicate that the BChI a transition moments themselves exhibit some order, and are directed at an angle > 54.7 degrees on the average from the BChl c moments. The one-color profiles exhibit coherent oscillations at most wavelengths, including 800 nm; Fourier analyses of these oscillations frequently yield components with frequencies 70-80 and 130-140 cm-1.     

Algebraisierung singulärer Hjelmslevgruppen

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The effect of the crystal field strength on the optical spectra of Cr3+ in gallium garnet laser crystals

We have investigated the basic spectroscopic properties of Cr³⁺-doped gallium garnets. Weak crystal fields (Dq/B=2.39–2.55) lead to broad⁴ T ₂⁴ A ₂ fluorescence in the 700–950 nm range depending on the chemical composition of the crystals. At room temperature the⁴ T ₂⁴ A ₂ transition is homogeneously broadened, whereas the 4 K spectra of the² E⁴ A ₂ transition show inequivalent Cr³⁺ sites and inhomogeneous linewidths of 8 cm^–1 in these laser crystals. From 300 to 4 K, the oscillator strength of the⁴ T ₂⁴ A ₂ transition is reduced by a factor of about 0.6 due to the temperature dependent electron phonon coupling. The transition probability of the² E⁴ A ₂ transition correlates with the energetic position of the⁴ T ₂ level, which is admixed into the² E level via spin-orbit coupling. The comparison of the² E⁴ A ₂ phonon sideband structure in garnets of different chemical compositions allows the assignment of some peaks to GaO₄-tetrahedron modes of the garnet structure.     

Transient Repetitive Exposure to Low Level Light Therapy Enhances Collateral Blood Vessel Growth in The Ischemic Hindlimb of The Tight Skin Mouse

The tight skin mouse (Tsk^?/+) is a model of scleroderma characterized by impaired vasoreactivity, increased oxidative stress, attenuated angiogenic response to VEGF and production of the angiogenesis inhibitor angiostatin. Low‐level light therapy (LLLT) stimulates angiogenesis in myocardial infarction and chemotherapy‐induced mucositis. We hypothesize that repetitive LLLT restores vessel growth in the ischemic hindlimb of Tsk^?/+ mice by attenuating angiostatin and enhancing angiomotin effects in vivo. C57Bl/6J and Tsk^?/+ mice underwent ligation of the femoral artery. Relative blood flow to the foot was measured using a laser Doppler imager. Tsk^?/+ mice received LLLT (670 nm, 50 mW cm^?2, 30 J cm^?2) for 10 min per day for 14 days. Vascular density was determined using lycopersicom lectin staining. Immunofluorescent labeling, Western blot analysis and immunoprecipitation were used to determine angiostatin and angiomotin expression. Recovery of blood flow to the ischemic limb was reduced in Tsk^?/+ compared with C57Bl/6 mice 2 weeks after surgery. LLLT treatment of Tsk^?/+ mice restored blood flow to levels observed in C57Bl/6 mice. Vascular density was decreased, angiostatin expression was enhanced and angiomotin depressed in the ischemic hindlimb of Tsk^?/+ mice. LLLT treatment reversed these abnormalities. LLLT stimulates angiogenesis by increasing angiomotin and decreasing angiostatin expression in the ischemic hindlimb of Tsk^?/+ mice.