Diphenylhexatriene membrane probes DPH and TMA-DPH: A comparative molecular dynamics simulation study

Abstract

Fluorescence spectroscopy and microscopy have been utilized as tools in membrane biophysics for decades now. Because phospholipids are non-fluorescent, the use of extrinsic membrane probes in this context is commonplace. Among the latter, 1,6-diphenylhexatriene (DPH) and its trimethylammonium derivative (TMA-DPH) have been extensively used. It is widely believed that, owing to its additional charged group, TMA-DPH is anchored at the lipid/water interface and reports on a bilayer region that is distinct from that of the hydrophobic DPH. In this study, we employ atomistic MD simulations to characterize the behavior of DPH and TMA-DPH in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and POPC/cholesterol (4:1) bilayers. We show that although the dynamics of TMA-DPH in these membranes is noticeably more hindered than that of DPH, the location of the average fluorophore of TMA-DPH is only~3-4 Å more shallow than that of DPH. The hindrance observed in the translational and rotational motions of TMA-DPH compared to DPH is mainly not due to significant differences in depth, but to the favorable electrostatic interactions of the former with electronegative lipid atoms instead. By revealing detailed insights on the behavior of these two probes, our results are useful both in the interpretation of past work and in the planning of future experiments using them as membrane reporters.

Preparation of nanoliposomes by microfluidic mixing in herring-bone channel and the role of membrane fluidity in liposomes formation

“…Steady-state anisotropy of the probe in non-organized systems such as in n-heptane reached values 0.001. In organized systems such as liposomes, DPH-TMA is oriented along the hydrocarbon chains 20 in which rotation is reduced and anisotropy is increased. With decreasing fluidity of the bilayer structure, anisotropy values increased from 0.195 (without cholesterol) to 0.265 (50 mol% of cholesterol) ( Fig.…”

“…We tested the effect of lipid membrane fluidity on the final morphology of liposomes expressed as the size distribution, polydispersity, and lamellarity. Based on exact measurements of lipid membrane fluidity (polarization of fluorescence) we predicted the effect of this parameter on the critical size of disc micelle intermediates and therefore their tendency to vesiculate and form liposomes 3,19,20 . Experimental data were compared with theoretical prediction following from the model based on Helfrich bending energy and analyses of the energetics and thermodynamics of vesicle formation 15 .…”

“…Microfluidic mixing as the method using low dispersive energy represents a promising technology to produce complex liposomal preparations 10 and the application of on-chip technology as demonstrated recently 2,11 . Gadolinium complexes are used as MRI contrast agents and liposomes represents a versatile platform for the application of gadolinium in vivo imaging and development of theranostics [18][19][20] . Our manuscript describes the application of microfluidic mixing for the preparation of Ga-liposomal contrast for MRI.…”

Synergy of Phospholipid—Drug Formulations Significantly Deactivates Profibrogenic Human Hepatic Stellate Cells

“…This difference is highlighted by the incubation time of the two probes used. It has been reported that the hydrophobic fluorophore DPH is located in the inner region of the phospholipid bilayer, whereas TMA-DPH is more hindered in translational and rotational motions compared to DPH [59]. Therefore, DPH estimates the motional order of the inner hydrophobic membrane region, while TMA-DPH senses changes in motional order at the interface region.…”

Estudo teórico da interação entre líquido iônico e bicamadas fosfolipídicas

“…Em fase gel, com o maior alinhamento das caudas, o movimento restrito implica menor diferença entre as componentes emitidas (menor anisotropia), crescente de acordo com a fluidez das caudas e maior rotação da sonda. Pela baixa perturbação, a técnica vem sendo utilizada experimentalmente [35] e teoricamente ( [36], [37], [38], [39], [40], [41]).…”