1-2-oleoylphosphatidylcholine and azobenzene

The use of hybrid systems for which the change in properties of one component triggers the change in properties of the other is of outmost importance when "on/off" states are needed. For such a reason, azobenzene compounds are one of the most used probes due to their high photoswitching efficiency. In this study, we consider a new derivative of azobenzene interacting with different lipid membrane phases as a versatile fluorescent probe for phase recognition. By means of a multiscale approach, we found that the cis and trans conformers have different positions and orientations in the different lipid membranes (DOPC for the liquid disordered phase and DPPC for the gel phase), and these have a profound effect on the optical properties of the system, for both one and two photon absorption. In fact, we found that the cis state is the "on" state when the probe is inserted into the DOPC membrane, while it is in the "off" state in the DPPC membrane. This behavior enhances the selectivity of this probe for phase recognition, since the different environments will generate different responses on the same conformer of the probe. The same effect is found for the fluorescence anisotropy analysis, for which the trans (cis) isomer in DOPC (DPPC) presents a fast decay time. Due to the "on/off" effect it is possible to screen the different membrane phases via fluorescence decay time analysis, making this new probe versatile for phase detection.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Azo Compounds; Fluorescent Dyes; Lipid Bilayers; Molecular Dynamics Simulation; Molecular Structure; Phosphatidylcholines; Photochemical Processes

A photosensitive amphiphilic molecule can switch the shape of an assembled vesicle as determined by microscopic observation. Photoisomerization induces a change in membrane fluctuation behavior or a morphological transition between ellipsoid and bud shapes, depending on the asymmetrical degree of the initial shape. The mechanism of this reversible photoswitching in the vesicle morphology is interpreted in terms of a change in the effective cross-sectional area of the photosensitive molecule.

Topics: Azo Compounds; Molecular Structure; Phosphatidylcholines; Photochemistry; Stereoisomerism; Ultraviolet Rays

Photochemical switching has been studied of double-tailed phosphate amphiphiles containing azobenzene units in both tails in aqueous vesicular dispersions and in mixed vesicular systems with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). Since the ease of switching depends on the strength of the bilayer packing, particular emphasis has been placed on the occurrence of H-aggregation in the hydrophobic core of the vesicles. UV-vis spectrometry was employed to monitor H-aggregation and showed how this process depends on the ionic strength and on the mode of preparation of the vesicles. Two types of H-aggregates were observed in mixed DOPC vesicles with 5 mol % of azobenzene phosphate: one with lambda(max) at around 300 nm and one with lambda(max) at 305-320 nm. Those with lambda(max) at 300 nm could not be trans-cis photoisomerized, whereas those with lambda(max) at 305-320 nm are more loosely packed and can be photochemically switched. The permeability of the vesicular bilayers, as probed with leakage experiments using calcein as a fluorescent probe, was examined as another measure for the strength of bilayer packing. Leakage occurred only for DOPC vesicles containing more than 20 mol % of azobenzenephosphate, irradiated with UV light to induce trans-cis photoisomerization. We contend that detailed information on bilayer packing will be of crucial importance for fine-tuning the lateral pressure in vesicular membranes with the ultimate aim to steer the opening and closing of mechanosensitive protein channels of large conductance.

Topics: Azo Compounds; Calorimetry, Differential Scanning; Escherichia coli Proteins; Fluoresceins; Hydrogen; Ion Channels; Light; Lipid Bilayers; Lipids; Liposomes; Membrane Fluidity; Membrane Lipids; Membranes, Artificial; Microscopy, Electron, Transmission; Models, Chemical; Phosphates; Phosphatidylcholines; Phospholipids; Photochemistry; Spectrophotometry, Ultraviolet; Temperature; Ultraviolet Rays