TY - JOUR
T1 - Orientation of non-spherical protonated water clusters revealed by infrared absorption dichroism
AU - Daldrop, Jan O.
AU - Saita, Mattia
AU - Heyden, Matthias
AU - Lorenz-Fonfria, Victor A.
AU - Heberle, Joachim
AU - Netz, Roland R.
N1 - Funding Information:
We gratefully acknowledge financial support from the DFG (Grant No. SFB 1078, projects B3 and C1). M.H. is grateful for support from the Cluster of Excellence RESOLV (EXC 1069) funded by the DFG. V.A.L.-F. thanks MINECO for the financial support (Grant No. BFU2016-768050-P and Fellowship No. RYC-2013-13114).
Publisher Copyright:
© 2018 The Author(s).
PY - 2018/12/1
Y1 - 2018/12/1
N2 - Infrared continuum bands that extend over a broad frequency range are a key spectral signature of protonated water clusters. They are observed for many membrane proteins that contain internal water molecules, but their microscopic mechanism has remained unclear. Here we compute infrared spectra for protonated and unprotonated water chains, discs, and droplets from ab initio molecular dynamics simulations. The continuum bands of the protonated clusters exhibit significant anisotropy for chains and discs, with increased absorption along the direction of maximal cluster extension. We show that the continuum band arises from the nuclei motion near the excess charge, with a long-ranged amplification due to the electronic polarizability. Our experimental, polarization-resolved light-dark difference spectrum of the light-driven proton pump bacteriorhodopsin exhibits a pronounced dichroic continuum band. Our results suggest that the protonated water cluster responsible for the continuum band of bacteriorhodopsin is oriented perpendicularly to the membrane normal.
AB - Infrared continuum bands that extend over a broad frequency range are a key spectral signature of protonated water clusters. They are observed for many membrane proteins that contain internal water molecules, but their microscopic mechanism has remained unclear. Here we compute infrared spectra for protonated and unprotonated water chains, discs, and droplets from ab initio molecular dynamics simulations. The continuum bands of the protonated clusters exhibit significant anisotropy for chains and discs, with increased absorption along the direction of maximal cluster extension. We show that the continuum band arises from the nuclei motion near the excess charge, with a long-ranged amplification due to the electronic polarizability. Our experimental, polarization-resolved light-dark difference spectrum of the light-driven proton pump bacteriorhodopsin exhibits a pronounced dichroic continuum band. Our results suggest that the protonated water cluster responsible for the continuum band of bacteriorhodopsin is oriented perpendicularly to the membrane normal.
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U2 - 10.1038/s41467-017-02669-9
DO - 10.1038/s41467-017-02669-9
M3 - Article
C2 - 29358659
AN - SCOPUS:85041014940
SN - 2041-1723
VL - 9
JO - Nature communications
JF - Nature communications
IS - 1
M1 - 311
ER -