Interpretation of Phase Boundary Fluctuation Spectra in Biological Membranes with Nanoscale Organization

In this work, we use a computationally less expensive and more automated Support Support Vector Machine algorithm to detect simple and complex interfaces in atomistic and coarse-grained molecular simulation trajectories of phase separating lipid bilayer systems. We find that the power spectral density of the interfacial height fluctuations and in turn line tension of the systems depends on the order parameter used to identify the intrinsic interface. To highlight the effect of length scale used to identify the interface on the fluctuation spectra, we perform a convolution of the boundaries identified at molecular resolution with a 2D Gaussian function of variance equal to the experimental resolution limit. The region of fluctuation spectra that scales according to capillary wave theory formalism relies on the complexity of the interfacial geometry, which may not always be detected at experimental resolutions. We propose that the different q-regimes in the fluctuation spectra can be used to characterize mode dependent interfacial tensions to understand the interfaces beyond the linear line tension calculations.