Dipalmitoylphosphatidylcholine Lipid Bilayer Research Articles

Molecular dynamics insight of interaction between the functionalized-carbon nanotube and cancerous cell membrane in doxorubicin delivery

Background and objective:Doxorubicin (DOX) is a known anticancer drug which is widely used in cancer therapy. Carbon nanotubes (CNTs) are among the most promising platforms for smart drug delivery applications. However, due to the toxicity and their low sulubility their application is limited and their functionalization with wide range of biomolecules are suggested. Therefore, the functionalized carbon nanotubes (f-CNT) with carboxyl (CNT-COO) and folic acid (CNT-COO-FA) were investigated as drug-carrier.Methods: Molecular dynamics (MD) simulation along with the Density Functional Theory (DFT) methods are being used to study the drug loading process on functionalized carbon nanotubes.Results: The results indicate that doxorubicin molecules interact more with CNT-COO-FA than CNT-COO. The embedded dipalmitoylphosphatidylcholine (DPPC) lipid bilayer with a folate receptor was considered a cancerous cell’s representative model. Then the drug release from the f-CNTs near the lipid bilayer was simulated. The results showed that CNT-COO-FA with a pH and ligand-sensitive mechanism strongly interacts with cancerous cells, which led to higher drug release, in agreement with the experimental results. The conformational changes of the lipid bilayer and folate receptor during drug release were evaluated. The analysis showed that drug release from CNT-COO-FA has significantly changed lipid bilayer and receptor conformations. The obtained results were interpreted and justified by considering the molecular mechanisms which control the drug delivery in the studied systems.Conclusions: Based on the obtained results, CNT-COO-FA has a better performance during the drug release compared to CNT-COO in delivering doxorubicin. Both pH and ligand sensitive mechanisms are found to be responsible for higher drug delivery efficiency of CNT-COO-FA. In contrast, CNT-COO can only enhance drug delivery efficiently with a pH-sensitive mechanism.

Elucidating lipid conformations in the ripple phase: Machine learning reveals four lipid populations

A new mixed radial-angular, three-particle correlation function method in combination with unsupervised machine learning was applied to examine the emergence of the ripple phase in dipalmitoylphosphatidylcholine (DPPC) lipid bilayers using data from atomistic molecular dynamics simulations of system sizes ranging from 128 to 4096 lipids. Based on the acyl tail conformations, the analysis revealed the presence of four distinct conformational populations of lipids in the ripple phases of the DPPC lipid bilayers. The expected gel-like (ordered; Lo) and fluid-like (disordered; Ld) lipids are found along with their splayed tail equivalents (Lo,s and Ld,s). These lipids differ, based on their gauche distribution and tail packing. The disordered (Ld) and disordered-splayed (Ld,s) lipids spatially cluster in the ripple in the groove side, that is, in an asymmetric manner across the bilayer leaflets. The ripple phase does not contain large numbers of Ld lipids; instead they only exist on the interface of the groove side of the undulation. The bulk of the groove side is a complex coexistence of Lo,Lo,s, and Ld,s lipids. The convex side of the undulation contains predominantly Lo lipids. Thus, the structure of the ripple phase is neither a simple coexistence of ordered and disordered lipids nor a coexistence of ordered interdigitating gel-like (Lo) and ordered-splayed (Lo,s) lipids, but instead a coexistence of an ordered phase and a complex mixed phase. Principal component analysis further confirmed the existence of the four lipid groups.

Structural dynamics of chlorpromazine (CPZ) drug with dipalmitoylphosphatidylcholine (DPPC) lipid: a potential drug for SARS-CoV-2

There is an urgent requirement for drug discovery and more importantly drug repositioning due to infectious new Severe Acute Respiratory Syndrome coronavirus 2. As per the recent report published in the journal L'Encéphale in May 2020, there is a planned ReCoVery Study examining the repurposing the chlorpromazine for the treatment of COVID-19. Here, we apply a combined Raman microspectroscopy and DFT-MD approach to investigate the structural dynamics of the Chlorpromazine (CPZ) drug with dipalmitoylphosphatidylcholine (DPPC) lipid bilayer, identifying the specific position of the drug in the DPPC lipid bilayer. The intensity ratios of the Raman peaks I 2935/I 2880, I 1097/I 1064 and I 1097/I 1129 are representative of the interaction of drugs with lipid alkyl chains and furnish conformation of lipid alkyl chains. Raman imaging microscopy for the study of the distribution of CPZ inside the lipid vesicles is reported. We also investigated the influence of order and disorder ratio in the CPZ on the DPPC liposomes prepared on phase transition temperature. HIGHLIGHTS Drug–membrane interactions using micromolar concentrations of both lipid and drugs. Neuroleptic drug and DPPC vesicles composed of DPPC/drug mixtures reveal qualitative differences between the Raman spectra The temperature-controlled Raman microspectroscopic study has demonstrated that below phase-transition temperature, the fatty acid chains of the phospholipids are stiff and packed in a highly ordered array. DFT and MD simulations to understand molecular interactions, structural dynamics, and Raman spectra. Above phase-transition temperature, the chains are disordered and possess more motional freedom. Communicated by Ramaswamy H. Sarma

Effect of biphosphate salt on dipalmitoylphosphatidylcholine bilayer deformation by Tat polypeptide.

Translocation of positively charged cell penetrating peptides (CPP) through cell membrane is important in drug delivery. Here we report all-atom molecular dynamics simulations to investigate how a biphosphate salt in a solvent affects the interaction of a CPP, HIV-1 Tat peptide with model dipalmitoylphosphatidylcholine (DPPC) lipid bilayer. Tat peptide has a large number of basic arginines and a couple of polar glutamines. We observe that in absence of salt, the basic residues of the polypeptide get localized in the vicinity of the membrane without altering the bilayer properties much; polypeptide induce local thinning of the bilayer membrane at the area of localization. In presence of biphosphate salt, the basic residues, dressed by the biphosphate ions, are repelled by the phosphate head groups of the lipid molecules. However, polar glutamine prefers to stay in the vicinity of the bilayer. This leads to larger local bilayer thickness at the contact point by the polar residue and non-uniform bilayer thickness profile. The thickness deformation of bilayer structure disappears upon mutating the polar residue, suggesting importance of the polar residue in bilayer deformation. Our studies point to control bilayer deformation by appropriate peptide sequence and solvent conditions.

Theoretical insights into the uptake of sulfonamides onto phospholipid bilayers: Mechanisms, interaction and toxicity evaluation

Sulfonamides (SAs) are now recognized as the main emerging environmental pollutants in aquatic environments. Although the bioaccumulation capacities of SAs have been confirmed, the pathway for the penetration of the SAs into lipid bilayer has been not fully understood. In this study, the bioaccumulation mechanism of four typical SAs onto the dipalmitoyl phosphatidylcholine (DPPC) lipid bilayer and their effects on the properties of DPPC bilayer were employed and evaluated respectively by using molecular dynamics simulations. Results show that from the viewpoint of thermodynamics, it is favorable for these SAs partitioning to DPPC bilayer. The accommodation of four SAs onto the lipid membrane needs to undergo several processes, which include the contact stage, transformation stage, and absorption stage. Besides, the sulfamethoxazole (SMX) and sulfamethazine (SMZ) show a strong preference for the DPPC phase rather than the interface region while the sulfadiazine (SDZ) and sulfametoxydiazine (SMD) have similar tendencies in the interface region and DPPC phase. Furthermore, the cytotoxicity of SAs is reflected in their ability to affect the electrostatic potential of the membrane and to reduce the thickness of phospholipid bilayers. This molecular-level study provided an insightful understanding of the toxicity and bioaccumulation of SAs.

Anticorrelated position fluctuation of lipids in forming membrane water pores: molecular dynamics simulations study with dengue virus capsid protein

The traffic of molecules into or out of cells is regulated by many membrane-associated mechanisms. Membrane pores are considered as one of the major passage mechanisms, although molecular-level understanding of pore formation is still vague. The opening of a membrane pore depends on many factors, including the influence of some proteins. The ability of the cell-penetrating peptides and supercharged proteins to form membrane pores has been reported. We studied pore formation through dipalmitoylphosphatidylcholine (DPPC) lipid bilayers by supercharged dengue virus capsid (C) protein. Atomistic molecular dynamics simulations confirmed the formation of membrane pores by a combined effect of the C protein and the membrane electric field. Analyses of simulated trajectories showed highly correlated vertical position fluctuations between the Cα atom of the membrane-anchored arginine residues and the phosphorus atoms of the surrounding DPPC lipids. Certain regions of the bilayer were negatively correlated while the others were positively correlated with respect to the fluctuations of the Cα atom of the anchored arginine residues. When positively correlated lipids in one leaflet vertically aligned with the negatively correlated lipids in the other leaflet, a local anticorrelated region was generated by weakening the bilayer. The membrane pore was always formed close to this anticorrelated region. Once formed, the C protein followed the hydrated pathway provided by the water-filled pores to cross the membrane. Communicated by Ramaswamy H. Sarma

Impact of the Rat R5G, Y10F, and H13R Mutations on Tetrameric Aβ42 β-Barrel in a Lipid Bilayer Membrane Model

Three amino acid substitutions distinguish rat and human Aβ42 peptides and contribute to the difference in toxicity properties. Indeed, aged rodents rarely develop the characteristic lesions of Alzheimer's disease in contrast to humans. Both peptides form, however, amyloid fibrils in buffer solution, but their affinities to the membrane vary. In particular, there is experimental evidence that the rat Aβ42 peptide does not induce Ca2+ fluxes in cells. We recently designed a tetrameric β-barrel structure and showed that this model is severely destabilized for Aβ40 human compared to its Aβ42 human counterpart, explaining the absence of ionic currents of Aβ40 in planar lipid bilayers. In this study, we asked whether our model is destabilized for the rat Aβ42 peptide by using extensive replica exchange molecular dynamics simulation in a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer membrane. Our results show that the much lower propensity of aged rodents to develop Alzheimer's disease symptoms might be correlated to its tetrameric β-barrel stability in the cell membrane.

Glycyrrhizin-induced changes in phospholipid dynamics studied by 1H NMR and MD simulation

Phospholipid bilayer constitutes the basis of the cell membrane. Any changes in its structure and dynamics could significantly affect the properties and functions of the cell membrane and associated proteins. It could, in its turn, affect the mechanism and strength of drug-membrane interaction. Phase transitions in lipid bilayer play an important role in cell life and in transmembrane transport of ions and drug molecules. In the present study we have tried to clarify the mechanism of glycyrrhizin bioactivity by the study of its influence on the lipid dynamics and phase transition of the lipid bilayer. For this purpose, a combination of nuclear magnetic resonance (NMR) and molecular dynamic (MD) simulations was used. Glycyrrhizin is the saponin extracted from licorice root. It displays a wide spectrum of biological activity and is frequently used in traditional medicine since ancient times. Now glycyrrhizin attracts additional attention as a novel multifunctional drug delivery system. We have established that glycyrrhizin interaction with dipalmitoylphosphatidylcholine lipid bilayers leads to changes in lipid mobility and phase transition temperature. NMR and MD results demonstrated that a glycyrrhizin molecule is able to integrate into a lipid bilayer and form stable aggregates inside. We hypothesize that surface curvatures caused by local changes in the lipid composition and the presence of phase boundaries might affect the permeability of the cell membrane.

Effect of C60 nanoparticles on elasticity of small unilamellar vesicles composed of DPPC bilayers**Project supported by the National Natural Science Foundation of China (Grant No. 61475196).

The interaction between C60 nanoparticles and biomembranes has been of great interest in researches over the past decades due to their novel applications as well as potential cytotoxicity. In this work, we study the deformation of the small unilamellar vesicles composed of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers infiltrated with C60 nanoparticles of different molecular concentrations through coarse-grained molecular dynamics simulations. By employing the Helfrich spontaneous curvature model, the bending modulus and the spontaneous curvature of the vesicles with C60 nanoparticles of different concentrations are obtained according to the simulation data. The results show that the bending modulus and the spontaneous curvature of pure DPPC vesicle membranes are approximately 1.6 × 10−19 J and 1.4 nm−1, respectively. Both of them increase linearly approximately as the C60 concentration increases from 0 to 16.3%. The density profiles of vesicles, the order of lipid packing and the diffusion characteristics of DPPC and C60 are also investigated.

Impact of A2T and D23N Mutations on Tetrameric Aβ42 Barrel within a Dipalmitoylphosphatidylcholine Lipid Bilayer Membrane by Replica Exchange Molecular Dynamics

In Alzheimer's disease (AD), many experimental and computational studies support the amyloid pore hypothesis of the Aβ42 peptide. We recently designed a β-barrel tetramer in a membrane-mimicking environment consistent with some low-resolution experimental data. In this earlier study, by using extensive replica exchange molecular dynamics simulations, we found that the wild-type (WT) Aβ42 peptides have a high propensity to form β-barrels, while the WT Aβ40 peptides do not. In this work, we have investigated the effect of mutations D23N and A2T on the Aβ42 barrel tetramer by using the same enhanced conformational sampling technique. It is known that the D23N mutation leads to early onset AD, while the A2T mutation protects from AD. This computational study in a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer membrane shows that the WT sequence and its A2T variant have similar β-barrel populations and the three-dimensional model is slightly destabilized for D23N compared to its WT sequence. These extensive modeling calculations indicate that the lower and higher induced toxicity of these two mutations in AD cannot be correlated to their β-barrel tetramer stabilities in a DPPC lipid bilayer membrane.

Investigation of benzodiazepines (BZDs) in a DPPC lipid bilayer: Insights from molecular dynamics simulation and DFT calculations

Toxicity is an essential parameter for drug development process and drug design. In this context, the effects of concentration of two Benzodiazepine drugs (diazepam, clonazepam) on fully hydrated dipalmitoylphosphatidylcholine (DPPC) has been studied at 323 K using molecular dynamics simulations. Various properties of bilayer such as membrane area per lipid, mass density distributions, order parameters, radial distribution functions, lateral diffusion, and electrostatic potential have been examined at three different concentrations of each drug. The location of drugs in the membrane are estimated by free energy profiles and to evaluate the results at a more detailed theoretical level, density functional theory (DFT) calculations have been carried out. It was revealed that penetration into the bilayer for diazepam is more favorable than clonazepam. On the other hand, within the fatty acid tail area both drugs are located in the middle of membrane at ∼0.75–1.5 nm from center of bilayer.

Dynamics of heroin molecule inside the lipid membrane: a molecular dynamics study.

Heroin, or diamorphine (C21H23NO5), is an opium product used for various pharmaceutical and euphoric purposes. In this work, the molecular dynamics simulation study of the heroin inside the two lipid bilayers, dipalmitoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) are presented. The whole study was conducted at three different temperatures. The location of the heroin drug, the nature of the diffusion, rotational correlation function and structural variation inside both lipid bilayers is studied. Moreover, the free energy of the solvation of the drug inside both lipid bilayers is calculated. It is found that during the whole molecular dynamics study, the drug locates at the center of both lipid membranes. The effect of the temperature is not seen at the drug location. The nature of the diffusion of the heroin drug is anomalous. The radius of gyration is calculated to study the structural variations of the heroin molecule inside both lipid bilayers. It is found that the heroin molecule does not change its structure at three temperatures. From the rotational correlation function, it is seen that the drug is more hindered for rotation inside the DPPC lipid bilayer as compared to the DMPC lipid bilayer. It is applicable for all three temperatures. The rotational correlation time of the drug is decreased while the temperature of the system is increased. In the case of DMPC, there is an abrupt change in rotational correlation time while the phase is changed.

Interactions of neutral gold nanoparticles with DPPC and POPC lipid bilayers: simulation and experiment.

Molecular dynamics simulations of neutral gold nanoparticles (AuNPs) interacting with dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes were studied using a model system. Spontaneous membrane insertion of AuNPs did not occur on the time scale of atomistic simulations. To overcome the limitations of time scale, we used a harmonic restraining potential to force the AuNPs into the membranes. Free energy calculations indicate that a NP has to cross a free energy barrier of about 134 kJ mol−1 prior to forming a stable contact with the membrane. This energy barrier between lipids and NPs comes from the repulsion between headgroups of lipids and AuNPs. The experimental investigations indicate that, contrary to hydrophobic AuNPs, neutral AuNPs cannot form ion channels across lipid membranes. The adsorption of NPs induces the formation of a highly ordered region in phospholipid bilayers. Our simulation results propose that the cell penetration of small uncoated AuNPs does not involve energy-independent membrane translocation but rather involves the energy-dependent formation of nanoscale membrane holes or energy-dependent endocytosis.

Molecular dynamics simulations of glyphosate in a DPPC lipid bilayer

Extensive molecular dynamics simulations have been performed to study the effect of glyphosate (in their neutral and charged forms, GLYP and GLYP2−, respectively) on fully hydrated DiPalmitoylPhosphatidylCholine (DPPC) lipid bilayer. First, we calculated the free energy profile (using the Umbrella Sampling technique) for both states of charge of glyphosate. The minimum value for the free energy for GLYP is ∼−60 kJ mol−1 located at z = ±1.7 nm (from the lipid bilayer center), and there is almost no maximum at the center of the lipid bilayer. By contrast, the minimum for GLYP2− is ∼−35 kJ mol−1 located at z = ± 1.4 nm (from the lipid bilayer center), and the maximum reaches ∼35 kJ mol−1 at the center of the lipid bilayer. Then, different lipid bilayer properties were analyzed for different glyphosate:lipid (G:L) ratios. The mean area per lipid was slightly affected, increasing only 5% (in the presence of glyphosate at high concentrations), which is in agreement with the slight decrease in deuterium order parameters. As for the thickness of the bilayer, it is observed that the state of charge produces opposite effects. On one hand, the neutral state produces an increase in the thickness of the lipid bilayer; on the other, the charged form produces a decrease in the thickness, which not depend linearly on the G:L ratios, either. The orientation of the DPPC head groups is practically unaffected throughout the range of the G:L ratios studied. Finally, the mobility of the lipids of the bilayer is strongly affected by the presence of glyphosate, considerably increasing its lateral diffusion coefficient noteworthy (one order of magnitude), with increasing G:L ratio.

Effects of Channel Forming Peptides on Lipid Bilayer Dynamics and Leaflet Coupling

Altering the material properties of lipid bilayers has been shown to affect the biological activity of a number of channel-forming peptides and proteins. A prototypical example is gramicidin, in which the channel formation and lifetime directly depends on the lipid membrane in which it is embedded. However, less is known about how a membrane-spanning channel affects the lipid bilayer properties, particularly the elasticity. Here we use neutron spin echo spectroscopy (NSE) to measure both the collective bending and thickness fluctuation dynamics in dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) bilayers containing gramicidin at low peptide/lipid ratios. At these low concentrations, gramicidin incorporation did not have a measurable effect on the average bilayer structure but significantly impacted the collective membrane dynamics. The bending modulus of DMPC membranes increased with increasing gramicidin concentration, while the trend in DPPC was non-monotonic and first decreased at low gramicidin concentrations before increasing at higher concentrations. In contrast, the thickness fluctuation amplitude increased with increasing gramicidin concentration in both the DMPC and DPPC lipid bilayers. Notably, combining the bending and thickness fluctuation results revealed that the seemingly disparate concentration trends in the DMPC and DPPC lipid bilayers were both consistent with an increase in coupling between the bilayer leaflets with increasing gramicidin concentration. Together these results demonstrate that channel formation can have considerable effects on the surrounding lipid membrane elasticity and highlight the interplay between lipids and peptides in determining the membrane dynamics.

Mechanisms underlying interactions between PAMAM dendron-grafted surfaces with DPPC membranes.

Biofouling is a pervasive problem which demands the creation of smart, antifouling surfaces. Towards this end, we examine the interactions between a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer and a polyamidoamine (PAMAM) dendron-grafted surface. In addition, we investigate the impact of dendron generation on the system behavior. To resolve the multiscale dynamical processes occurring over a large spatial scale, we employ Molecular Dynamics simulations with a coarse-grained implicit solvent force field. Our results demonstrate the transient and equilibrium system dynamics to be determined by the PAMAM dendron generation along with the underlying mechanisms. Higher generation dendrons are observed to favor penetration of the DPPC molecules into the dendron branches, thereby enabling sustained interactions between the membrane and the dendron-grafted surface. Under equilibrium, the membrane adopts a bowl-shaped morphology whose dimensions are determined by the dendron generation and density of interactions. The results from our study can be used to guide the design of novel surfaces with selective antifouling properties which can prevent the adsorption of microorganisms onto lipid membranes.

Cluster Formation of Polyphilic Molecules Solvated in a DPPC Bilayer.

We analyse the initial stages of cluster formation of polyphilic additive molecules which are solvated in a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer. Our polyphilic molecules comprise an aromatic (trans-bilayer) core domain with (out-of-bilayer) glycerol terminations, complemented with a fluorophilic and an alkyl side chain, both of which are confined within the aliphatic segment of the bilayer. Large-scale molecular dynamics simulations (1 s total duration) of a set of six of such polyphilic additives reveal the initial steps towards supramolecular aggregation induced by the specific philicity properties of the molecules. For our intermediate system size of six polyphiles, the transient but recurrent formation of a trimer is observed on a characteristic timescale of about 100 ns. The alkane/perfluoroalkane side chains show a very distinct conformational distribution inside the bilayer thanks to their different philicity, despite their identical anchoring in the trans-bilayer segment of the polyphile. The diffusive mobility of the polyphilic additives is about the same as that of the surrounding lipids, although it crosses both bilayer leaflets and tends to self-associate.

Stress Propagation through Biological Lipid Bilayers in Silico.

Membrane tension plays various critical roles in the cell. We here asked how fast and how far localized pulses of mechanical stress dynamically propagate through biological lipid bilayers. In both coarse-grained and all-atom molecular dynamics simulations of a dipalmitoylphosphatidylcholine lipid bilayer, we observed nanometer-wide stress pulses, propagating very efficiently longitudinally at a velocity of approximately 1.4 ± 0.5 nm/ps (km/s), in close agreement with the expected speed of sound from experiments. Remarkably, the predicted characteristic attenuation time of the pulses was in the order of tens of picoseconds, implying longitudinal stress propagation over length scales up to several tens of nanometers before damping. Furthermore, the computed dispersion relation leading to such damping was consistent with proposed continuum viscoelastic models of propagation. We suggest this mode of stress propagation as a potential ultrafast mechanism of signaling that may quickly couple mechanosensitive elements in crowded biological membranes.

The Effects of A21G Mutation on Transmembrane Amyloid Beta (11-40) Trimer: An In Silico Study.

Familial Alzheimer's disease (FAD) is passed down in family, which account for 2-3% of about 40 million AD cases worldwide. The Flemish (A21G) mutant of amyloid β (Aβ) exhibits unique properties among all hereditary mutants of FAD, including the lowest aggregation rate. Recent studies showed that Aβ oligomers play a key role in Alzheimer's disease (AD) pathogenesis. They could insert themselves in brain cell membrane, disrupting the membrane integrity and ion homeostasis. However, experimental studies of transmembrane Aβ oligomers have been limited due to their intrinsic heterogeneity. In this work, we extensively studied the A21G mutant of the transmembrane 3Aβ11-40 (A21G 3Aβ11-40) using temperature replica exchange molecular dynamics (REMD) simulations. Results provide detailed information on the conformational distribution and dynamics of transmembrane A21G 3Aβ11-40. Minimal local change from A to G leads to significant conformational changes and wider free energy holes on the free energy surface as well as altered surface charges that lead to weaker affinity to the dipalmitoylphosphatidylcholine (DPPC) lipid bilayers. These results are consistent with experimental data that showed that A21G mutants of Aβ peptides have lower aggregation rates and membrane binding rates.

Membrane phase transition during heating and cooling: molecular insight into reversible melting.

With increasing temperature, lipid bilayers undergo a gel-fluid phase transition, which plays an essential role in many physiological phenomena. In the present work, this first-order phase transition was investigated for variable heating and cooling rates for a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer by means of atomistic molecular dynamics simulations. Alternative methods to track the melting temperature [Formula: see text] are compared. The resulting [Formula: see text] is shown to be independent of the scan rate for small heating rates (0.05-0.3K/ns) implying reversible melting, and increases for larger heating (0.3-4K/ns) or cooling rates (2-0.1K/ns). The reported dependency of the melting temperature on the heating rate is in perfect agreement with a two-state kinetic rate model as suggested previously. Expansion and shrinkage, as well as the dynamics of melting seeds is described. The simulations further exhibit a relative shift between melting seeds in opposing membrane leaflets as predicted from continuum elastic theory.