Fig. 4: Linear absorption of different resting states of BR and counterion models. | Nature Communications

Fig. 4: Linear absorption of different resting states of BR and counterion models.

From: Retinal photoisomerization versus counterion protonation in light and dark-adapted bacteriorhodopsin and its primary photoproduct

Fig. 4

A The retinal chromophore bound to LYS216 via a positively charged PSB is surrounded by an extended H-bonding network involving another positive sidechain, ARG82, three water molecules, i.e. w401, w402 and w406, and two protonable aspartates, ASP85 and ASP212. B Experimental absorption spectra of the three different resting states (solid curves) are compared with QM/MM theoretical predictions of electronic (S0→S1) transitions energies (at CASPT2//CASSCF/MM level), using the standard complex counterion model with two deprotonated aspartates (dashed sticks) or one protonated ASP sidechain (solid sticks), labeled as “(H)”. The “+” and “−” signs refer to the positive and negative charges associated with the different residues, respectively. Source data are provided as a Source Data file.

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