Picosecond and steady state, variable intensity and variable temperature emission spectroscopy of bacteriorhodopsin

Area of Science:

• Biophysics
• Spectroscopy
• Photochemistry

Background:

• Bacteriorhodopsin is a light-driven proton pump.
• Understanding its excited-state dynamics is crucial for its function.

Purpose of the Study:

• To determine the emission lifetime of bacteriorhodopsin at 77 K.
• To investigate temperature-dependent changes in its emission spectrum and quantum efficiency.

Main Methods:

• Single-pulse excitation spectroscopy.
• Variable temperature emission quantum efficiency measurements.
• Picosecond time-resolved fluorescence spectroscopy.

Main Results:

• A consistent emission lifetime of 60 ± 15 ps was observed at 77 K across different spectral regions.
• Intensity effects on the lifetime were ruled out.
• Variable temperature studies revealed a new emission component at 670 nm below a certain temperature, potentially from the same electronic state responsible for 720 nm emission.
• A correlation was found between a previously reported 1.0-ps absorption formation time and extrapolated times from quantum efficiency and lifetime data.

Conclusions:

• The study provides a precise picosecond emission lifetime for bacteriorhodopsin at low temperatures.
• Evidence suggests a temperature-dependent excited state contributing to the emission spectrum.
• The findings correlate ultrafast absorption dynamics with fluorescence properties.