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Updated: Jul 17, 2026

Measuring the Densities of Aqueous Glasses at Cryogenic Temperatures
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Published on: June 28, 2017

Do proteins at low temperature behave as glasses? A single-molecule study.

Jürgen Baier1, Martin F Richter, Richard J Cogdell

  • 1Experimental Physics IV and BIMF, University of Bayreuth, 95440 Bayreuth, Germany.

The Journal of Physical Chemistry. B
|February 3, 2007
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Spectral diffusion in Rhodobacter sphaeroides LH2 complexes reveals distinct relaxation behavior. The standard two-level system model fails to explain pigment-protein dynamics, highlighting differences from glassy systems.

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Area of Science:

  • Biophysics
  • Photosynthesis research
  • Protein dynamics

Background:

  • Bacteriochlorophyll a (BChl a) pigments in light-harvesting complexes (LH2) are crucial for photosynthesis.
  • Understanding spectral diffusion dynamics is key to elucidating energy transfer mechanisms.
  • The standard two-level system (TLS) model is widely used to describe spectral diffusion in amorphous solids.

Purpose of the Study:

  • To investigate the spectral diffusion dynamics of individual BChl a pigments within LH2 complexes.
  • To compare the observed relaxation behavior with predictions from the standard TLS model.
  • To determine if protein-embedded pigments exhibit different relaxation dynamics compared to glasses.

Main Methods:

  • Recording long spectral diffusion trajectories from individual LH2 pigment-protein complexes.
  • Utilizing low temperatures (1.4 K) to capture detailed dynamics.
  • Evaluating spectral cumulants of absorption lines for protein-embedded BChl a pigments.

Main Results:

  • Observed spectral diffusion trajectories from individual LH2 complexes.
  • Calculated spectral cumulants for BChl a absorption lines.
  • Found that the first and second cumulants deviate significantly from TLS model predictions.

Conclusions:

  • The relaxation behavior of LH2 pigment-protein complexes differs fundamentally from that of glasses.
  • The standard TLS model is inadequate for describing spectral diffusion in this protein system.
  • This suggests unique relaxation mechanisms are at play within protein-embedded pigments.