engleski

Accurate Determination of the Orientational Distribution of a Fluorescent Molecule in a Phospholipid Membrane

Orientation of lipophilic dye molecules within a biological membrane can report on the molecular and physico-chemical environment of the membrane. This fact, however, remains underutilized, largely because of our limited quantitative knowledge of molecular orientational distributions and the fact that robust techniques allowing experimental observation of molecular orientations of dyes in biological membranes are only being developed. In order to begin filling this lack of knowledge and to develop appropriate tools, we have investigated the membrane orientational distribution of the 3- hydroxyflavone-based membrane dye F2N12S. Results of our single- and two-photon polarization microscopy observations of linear dichroism of F2N12S-labeled giant unilamellar vesicles are consistent with a Gaussian-like orientational distribution of the transition dipole moment of the dye, with a mean tilt angle of 53.4 ± 0.1 with respect to the bilayer normal and a standard deviation of 14.3 ± 0.5. Independently, by combining quantum chemical calculations and molecular dynamics simulations, we obtained very similar values: a mean tilt angle of 48 ± 4 and standard deviation of 13 ± 2. The good agreement between the experimentally and computationally obtained values gives confidence to the results obtained. It also cross-validates both approaches and opens a door to quantitative investigations of molecular orientations of membrane dyes using polarization microscopy techniques and molecular simulations.

fluorescent probe; phospholipid membrane; two photon electron spectroscopy; molecular dynamics simulations

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