Handbook of Lipid Bilayers, Second Edition
View Section, Preface. View Section, Table of Contents. View Section, Section 1. Physical Chemistry Fundamentals for Food Packaging. View Section, 1. View Section, 2. View Section, 3. View Section, 4. View Section, 5. Plasticization and Polymer Morphology. View Section, Section 2. Active and Intelligent Packaging. View Section, 6.
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Antioxidative Packaging System. View Section, 7. Antimicrobial Packaging Systems. View Section, 8. Intelligent Packaging for Food Products.
View Section, Section 3. Edible Coating and Films. View Section, 9. Edible Films and Coatings: A Review.
View Section, Edible Coating and Film Materials: Proteins. Edible Coating and Film Materials: Carbohydrates. View Section, Section 4.
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Biopolymer Packaging. Bioplastics for Food Packaging: Chemistry and Physics.
Utilization of Bioplastics for Food Packaging Industry. Thermoplastic Starch. View Section, Section 5. Commercial Food Packaging Innovations. Microwavable Food Packaging. Packaging for Nonthermal Food Processing. Eco-Design for Food Packaging Innovations. View Section, Index.
However, one caveat of fluorescence techniques is the need to use dye-labeled variants of the lipid of interest, thus potentially perturbing the structural and dynamic properties of the native species. Nevertheless, in view of the widespread use of optically modified lipids for studying lipid bilayer dynamics, it is highly desirable to well assess this point. Here, fluorescence correlation spectroscopy FCS and molecular dynamics MD simulations have been combined together to uncover subtle structural and dynamic effects in DOPC planar membranes enriched with a standard Rhodamine-labeled lipid.
Moreover, results highlight the existing interplay between dye concentration, lipid lateral diffusion and membrane permeability, thus suggesting possible implications for future optical microscopy studies of biophysical processes occurring at the membrane level.
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Plasma membrane not only provides the necessary compartmentalization to protect the cell, but is directly involved in a variety of vital cellular processes such as signaling, transport of biomaterial, cell adhesion, etc… 1. To comply with such a variety of roles, the plasma membrane requires a high degree of structural plasticity.
For such reasons, in recent years a great effort has been directed towards the understanding of lipid diffusion and self-organization at a molecular level. Among others, fluorescence-based optical microscopy methods have gradually emerged as versatile, quantitative tools to investigate the complex spatiotemporal organization of lipid membranes in both model bilayers and living cells: both localization-based e. Irrespective of the particular technique chosen, however, a common requisite for optical microscopy measurements is labelling the molecule of interest with a fluorescent tracer, or probe.
In studies on lipids, in particular, optical probes are typically chosen as lipid analogs 7 , such as the dialkylcarbocyanines, or dye-labeled lipids, such as Bodipy, Rhodamine or Atto 8. In the typical configuration of a comparative study, the measured dynamics of the labeled lipid will depend, and provide information, on several crucial aspects, such as the water content 9 , the aqueous phase composition ionic strength and other soluble species, like sugars , the specific lipid composition i.
Moreover, these investigations will also provide information on the lipid phase, including the possible co-existence of liquid-disordered L d , liquid-ordered L o or raft-like domains. Still, in all these optical microscopy studies, the implicit assumption is made of ignoring the perturbing effect of the probe, based on the consideration that any spurious effect, if present, is irrelevant with respect to the physico-chemical properties under study.
While this is perhaps a reasonable assumption to make, especially in comparative studies involving systems of variable chemical compositions, it is worth noting that optical probes have often shown a non-neutral role when tagged to biomolecules, as it was recently reported by some of us in the context of cell-penetrating peptides and their interaction with biomembranes 10 , Along the same line, previous studies in which different optical probes have been tested in the same lipid bilayer systems, have reported either different 12 , 13 or comparable 14 lipid diffusion properties, making the interpretation of the results not always straightforward.
Besides, diffusion measurements based on dye-labeled lipids have been shown to depend on lipid bilayer compositions, but also on the dye concentration Based on these considerations, it appears desirable to better assess the role of a tracer molecule when exploited for studying lipid diffusion in planar membranes. In this context, molecular dynamics MD simulations represent a valuable tool to gather structural and dynamic features of complex biosystems not easily accessible from experiments 16 , 17 , However, care has to be taken in order to fruitfully exploit MD techniques, since previous studies have highlighted unwanted artifacts due to the limited timescale and the typical finite size of the atomistic models.
For example, local lipid diffusion was shown to be affected by the system size in small bilayer models 19 , 20 , 21 and displayed anomalous non-Brownian behavior when evaluated at short timescales i. Thus, here we propose a combination of FCS experiments and extended atomistic MD simulations to shed light on some important features concerning lipid dynamics and lipid structural properties within a simple 1,2-dioleoyl-sn-glycerophosphocholine DOPC bilayer. Through such an integrated approach, our study attempts at better assessing the possible direct and indirect effects of a typical dye-labeled lipid, here Rhodamine B linked to 1,2-dioleoyl-snphosphatidylehanolamine hereafter referred to as RHB, see scheme of the molecule in Fig.
In particular, we evaluated the hydrodynamic effect of the Rhodamine B fluorophore and investigated the effects of RHB concentration on the structural and dynamic properties of the lipid bilayer.
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Moreover, we have characterized the effect of the dye-driven RHB self-aggregation with concentration and the relevant impact that the formed dye-labeled lipid clusters Fig. RHB lipids are shown in yellow, with nitrogen in blue, while DOPC lipids are in gray with corresponding phosphate atoms in red; water is omitted.
In b — e , only RHB lipids in one leaflet are displayed for the sake of clarity. Structural properties of the DOPC membrane upon insertion of a dye-labeled lipid were investigated using atomistic MD simulations. Accordingly, we have observed no contacts occurring during the four replica simulations in the considered time interval see Supplementary Fig. First, we evaluated the membrane thickness and the average area per lipid as compared to the pristine DOPC membrane. Bilayer thickness was defined as the average distance between phosphate headgroups of both leaflets.
Average thickness of the pure DOPC system was found to be Average area per lipid ApL is the most common determining feature in the packing of the lipid bilayer and structure. Results are reported in Fig. RDFs show two main peaks and a less pronounced third peak corresponding to successive lipid shells, where the first shell extends from 6. Positions of the first two RDF peaks, which determine the probability of finding phosphate groups in the neighboring shells, are consistent throughout all lipid membrane simulations, although peak height is somewhat different in the two simulations as a result of local lipid rearrangements upon RHB insertion: in terms of P-P RDF, the lipid bilayer appears less structured around RHB lipids.
In turn, this perturbation may affect the local DOPC structure in the second shell, but this is expected to be an even smaller effect.
Note that the three lines appear as superimposed on one another. In all diagrams, error bars correspond to one standard error. Error bars of pure DOPC system black lines are negligible and then omitted for clarity in all plots. Furthermore, we calculated the deuterium order parameters, S CD , for both hydrocarbon chains i.