Spectral Properties and Orientation of Voltage-Sensitive Dyes in Lipid Membranes

Type
Article

Authors
Matson, Maria
Carlsson, Nils
Beke-Somfai, Tamás
Nordén, Bengt

Online Publication Date
2012-07-12

Print Publication Date
2012-07-24

Date
2012-07-12

Abstract
Voltage-sensitive dyes are frequently used for probing variations in the electric potential across cell membranes. The dyes respond by changing their spectral properties: measured as shifts of wavelength of absorption or emission maxima or as changes of absorption or fluorescence intensity. Although such probes have been studied and used for decades, the mechanism behind their voltage sensitivity is still obscure. We ask whether the voltage response is due to electrochromism as a result of direct field interaction on the chromophore or to solvatochromism, which is the focus of this study, as result of changed environment or molecular alignment in the membrane. The spectral properties of three styryl dyes, di-4-ANEPPS, di-8-ANEPPS, and RH421, were investigated in solvents of varying polarity and in model membranes using spectroscopy. Using quantum mechanical calculations, the spectral dependence of monomer and dimer ANEPPS on solvent properties was modeled. Also, the kinetics of binding to lipid membranes and the binding geometry of the probe molecules were found relevant to address. The spectral properties of all three probes were found to be highly sensitive to the local environment, and the probes are oriented nearly parallel with the membrane normal. Slow binding kinetics and scattering in absorption spectra indicate, especially for di-8-ANEPPS, involvement of aggregation. On the basis of the experimental spectra and time-dependent density functional theory calculations, we find that aggregate formation may contribute to the blue-shifts seen for the dyes in decanol and when bound to membrane models. In conclusion, solvatochromic and other intermolecular interactions effects also need to be included when considering electrochromic response voltage-sensitive dyes. © 2012 American Chemical Society.

Citation
Matson M, Carlsson N, Beke-Somfai T, Nordén B (2012) Spectral Properties and Orientation of Voltage-Sensitive Dyes in Lipid Membranes. Langmuir 28: 10808–10817. Available: http://dx.doi.org/10.1021/la301726w.

Acknowledgements
This work was funded by the European Research Council (ERC Senior Advanced Grant to B.N.) and by a grant to B.N. from the King Abdullah University of Science and Technology.

Publisher
American Chemical Society (ACS)

Journal
Langmuir

DOI
10.1021/la301726w

PubMed ID
22738247

Permanent link to this record