Journal: The Journal of Physical Chemistry. B

Article Title: The Impact of Carotenoid Energy Levels on the Exciton Dynamics and Singlet–Triplet Annihilation in Isolated Bacterial Light-Harvesting 2 Complexes

doi: 10.1021/acs.jpcb.5c06284

Figure Lengend Snippet: Energy transitions for pigment molecules and the possibility of exciton annihilation. (A) Energy level diagram showing the ground state (S 0 ), the first singlet excited state (S 1 ) and the first triplet excited state (T 1 ) of a pigment. The typical transitions that can occur to and from S 1 are shown. Absorption (Abs); internal conversion (IC); fluorescence (Fluor.); intersystem crossing (ISC); and Förster resonance energy transfer (FRET). Vibrational relaxation is not shown. (B) Schematic showing how exciton–exciton annihilation can occur in a hypothetical network of pigments (here, each circle represents one pigment). Under high-intensity excitation conditions, this could occur within one protein complex. (C) Energy level diagrams showing singlet–singlet annihilation. (D) Energy level diagrams showing singlet–triplet annihilation. Vibrational substates are not shown for simplicity in panels C and D.

Article Snippet: The oxygen content was monitored with a fluorescence oxygen sensor (Neofox FOXY, Ocean Optics).

Techniques: Fluorescence, Förster Resonance Energy Transfer

Journal: The Journal of Physical Chemistry. B

Article Title: The Impact of Carotenoid Energy Levels on the Exciton Dynamics and Singlet–Triplet Annihilation in Isolated Bacterial Light-Harvesting 2 Complexes

doi: 10.1021/acs.jpcb.5c06284

Figure Lengend Snippet: Initial experiments on LH2 complexes containing alternative Cars. (A) Chemical structures of the Car pigments present in LH2 complexes studied in this work. Each LH2 complex predominantly contains only one type of Car. (B) Energy level schematic diagrams of the BChls and relevant Cars in different LH2 complexes. (C) Normalized steady-state absorption spectra of the purified LH2 complexes in detergent micelles at room temperature. (D) The same absorption spectra from (C) but with a magnified x -axis to show the red shift of the B850 band. (E) Steady-state fluorescence spectra of LH2 complexes with excitation at the B800 band (λ exc = 800 nm). (F) Fluorescence decay curves of LH2 complexes by excitation at the B800 band (λ exc = 801 nm) and collecting fluorescence emission at the respective emission maxima (i.e., either 861, 863, or 865 nm). These decay curves were collected with Edinburgh FLS980 instruments using a pulsed laser (EPL-800) to collect the nonquenched fluorescence decay curve, which were later fit to a multiexponential function resulting in the mean lifetime values (τ avg ) reported in the text (IRF: instrument response funcion). All measurements were performed on LH2 in solutions of 0.03% (w/v) LDAO, 20 mM HEPES (pH 7.5), and 150 mM NaCl.

Article Snippet: The oxygen content was monitored with a fluorescence oxygen sensor (Neofox FOXY, Ocean Optics).

Techniques: Purification, Fluorescence

Journal: The Journal of Physical Chemistry. B

Article Title: The Impact of Carotenoid Energy Levels on the Exciton Dynamics and Singlet–Triplet Annihilation in Isolated Bacterial Light-Harvesting 2 Complexes

doi: 10.1021/acs.jpcb.5c06284

Figure Lengend Snippet: Time-resolved fluorescence spectroscopy of LH2 in a detergent at a series of different laser fluence levels. Fluorescence decay curves of (A) LH2 Zeta and (B) LH2 Spir at a low repetition rate of 0.2 MHz with varying laser fluence (1 × 10 13 to 3 × 10 14 hυ/pulse/cm 2 ). Fluorescence decay curves of (D) LH2 Zeta and (E) LH2 Spir at a high repetition rate of 26.6 MHz with varying laser fluence (1 × 10 11 to 3 × 10 14 hυ/pulse/cm 2 ). Scatter plots to compare how the fluorescence lifetime changes with increasing laser fluence for the different LH2 complexes at either (C) low repetition rate (0.2 MHz) or (F) high repetition rate (26.6 MHz). The fluorescence decay curves in panels (A,B,D,E) and from Figure S5 were fitted to appropriate multiexponential decay functions, and the mean fluorescence lifetime was extracted so that the different Car variants could be quantitatively compared, as plotted in panels (C) and (F), where the relative change in lifetime is displayed by comparison to the original lifetime (τ/τ 0 ). All fluorescence decay curves were collected by excitation at the B800 band (λ exc = 801 nm) and measurement of fluorescence emission at the respective emission maxima of the different LH2 complexes (i.e., either 861, 863, or 865 nm). High-quality data could not be acquired at low laser power and 0.2 MHz, preventing measurements below 10 13 hυ/pulse/cm 2 (panel C), but was possible at 26.6 MHz (panel F).

Article Snippet: The oxygen content was monitored with a fluorescence oxygen sensor (Neofox FOXY, Ocean Optics).

Techniques: Fluorescence, Spectroscopy, Comparison

Journal: The Journal of Physical Chemistry. B

Article Title: The Impact of Carotenoid Energy Levels on the Exciton Dynamics and Singlet–Triplet Annihilation in Isolated Bacterial Light-Harvesting 2 Complexes

doi: 10.1021/acs.jpcb.5c06284

Figure Lengend Snippet: Time-resolved fluorescence spectroscopy of LH2 in detergent at a series of different laser repetition rates. Fluorescence decay curves of (A) LH2 Zeta and (B) LH2 Spir at a low laser fluence of 1 × 10 12 hυ/pulse/cm 2 with varying laser repetition rate (1.5 to 26.6 MHz). Fluorescence decay curves of (D) LH2 Zeta and (E) LH2 Spir at a high laser fluence of 3 × 10 14 hυ/pulse/cm 2 with varying laser repetition rate (0.2 to 26.6 MHz). The scatter plots provide a quantitative comparison of how the fluorescence lifetime changes with increasing laser repetition rate for the five different LH2 complexes at either (C) low laser fluence (1 × 10 12 hυ/pulse/cm 2 ) or (F) high laser fluence (3 × 10 14 hυ/pulse/cm 2 ). The fluorescence decay curves shown in panels (A, B, D, E) and from Figure S6 were fitted to appropriate multiexponential decay functions to extract lifetime values for the scatter plots, as described for . Samples were excited at the B800 band (λ exc = 801 nm), and fluorescence emission was collected at the respective emission maxima of different LH2 mutants. High-quality data could not be acquired at low repetition rate and 1 × 10 12 hυ/pulse/cm 2 , preventing measurements below 1.5 MHz (panel C), but was possible at 3 × 10 14 hυ/pulse/cm 2 (panel F).

Article Snippet: The oxygen content was monitored with a fluorescence oxygen sensor (Neofox FOXY, Ocean Optics).

Techniques: Fluorescence, Spectroscopy, Comparison