Lipid bilayers parameter approach

This result demonstrates that the self-spreading dynamics are controllable by tuning the bilayer-substrate interactions. The above-mentioned electrolyte dependence is an example of this fact. Considering that there are many parameters that alter the bilayer-substrate interaction, a diverse approach can be proposed. For example, Nissen et al. investigated the spreading dynamics on the substrate coated with polymetic materials [48]. They found that insertion of a hydrophilic and inert polymer layer under the self-spreading lipid bilayer strongly attenuated the bilayer-substrate interaction. 

We would like to point out that an order parameter indicates the static property of the lipid bilayer, whereas the rotational motion, the oxygen transport parameter (Section 4.1), and the chain bending (Section 4.4) characterize membrane dynamics (membrane fluidity) that report on rotational diffusion of alkyl chains, translational diffusion of oxygen molecules, and frequency of alkyl chain bending, respectively. The EPR spin-labeling approach also makes it possible to monitor another bulk property of lipid bilayer membranes, namely local membrane hydrophobicity. 

The strong point of molecular dynamic simulations is that, for the particular model, the results are (nearly) exact. In particular, the simulations take all necessary excluded-volume correlations into account. However, still it is not advisable to have blind confidence in the predictions of MD. The simulations typically treat the system classically, many parameters that together define the force field are subject to fine-tuning, and one always should be cautious about the statistical certainty. In passing, we will touch upon some more limitations when we discuss more details of MD simulation of lipid systems. We will not go into all the details here, because the use of MD simulation to study the lipid bilayer has recently been reviewed by other authors already [31,32]. Our idea is to present sufficient information to allow a critical evaluation of the method, and to set the stage for comparison with alternative approaches. 

The link from lipid properties to mechanical properties of the bilayers is now feasible within the SCF approach. The next step is to understand the phase behaviour of the lipid systems. It is likely that large-scale (3D) SCF-type calculations are needed to prove the conjectures in the field that particular values of the Helfrich parameters are needed for processes like vesicle fusion, etc. In this context, it may also be extremely interesting to see what happens with the mechanical parameters when the system is molecularly complex (i.e. when the system contains many different types of molecules). Then there will be some hope that novel and deep insights may be obtained into the very basic questions behind nature s choice for the enormous molecular complexity in membrane systems. 

Information about fluidity and viscosity of bilayers of artificial and natural membranes has been obtained from electron spin resonance studies in which the mobility of the spin-labelled species along the surface plane of the membrane is determined (17). However, the monolayer of either lipid, protein, or lipid-protein systems at the air-water interface, makes an ideal model because several parameters can be measured simultaneously. Surface tension, surface pressure, surface potential, surface viscosity, surface fluorescence and microviscosities, surface radioactivity, and spectroscopy may be determined on the same film. Moreover, the films can be picked up on grids from which they may be observed by electron microscopy, studied further for composition, and analyzed for structure by x-ray diffraction and spectroscopy. This approach can provide a clear understanding of the function and morphology of the lipid and lipid-protein surfaces of experimental membranes. However, the first objective is to obtain molecular correlations of surface tension, pressure, potential, and viscosity. 

In his later work, Kinoshita et al. extended the model by assuming Gaussian distribution of the probe orientations before the excitation with respect to the bilayer [116]. The authors compared the theoretical predictions of the Gaussian model with the original model and concluded that, if only two parameters are used, the details of the microscopic description do not have a decisive impact on the quality of the predicted fits. Lipari et al. [117] generalized the approach proposed by Kinosita by taking into account segmental motion of the lipid molecules and... 

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