Liquid Crystalline Orientational Excitations in Biological Membranes

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The biological membrane is considered as key for the formation and proliferation of life. The material exchange across this membrane is responsible for its equilibrium operation as well as during the action potential's propagation. The understanding of underlying mechanisms of these processes is paramount for our fight against many diseases. In the same time, the orientational order of molecules, composing the biological membrane, has already been compared with liquid crystals (LC). However, there was no further detailed comparison of the mechanisms of various excitation modes, taking place in LCs, with respect to similar processes taking place in the biological tissue, such as the biological membrane. We think that the anisotropic properties of LC materials should have very important analogies in biological membranes. Namely, the critical difference of anisotropic diffusion of ions in "simple" molecular double layer membranes (similar to nematic LCs) compared with the case of molecular "stacking" planes of myelin sheaths (similar to smectic LCs) is a good example of the possible use of our knowledge of the physics of nematic and smectic LCs to better understand the processes taking place in various biological membranes. In addition, we have recently discovered the existence of orientational molecular perturbations with long range propagation distances. This gives us the hope to better understand the role of myelin sheaths, the nodes of Ranvier and the triggering mechanism of ionic channels during the action potential's propagation. Once we understand these mechanisms better, we are planning to use photo activated amphiphilic non-toxic azobenzenes, to control the orientational order in such molecular systems (membranes) and thus the mechanisms of material (ionic, etc.) exchange across them. In fact, we have already started some of these experiments and our very first results, obtained with the Ecoli bacteria, are very encouraging. We have shown that light can be used to control their swimming speed which is a key factor for their virulence. We think that this control is obtained by the destabilization of ionic channel via the photoisomerization of azobenzene molecules. In the proposed research, we shall first use LCs and artificial lipid bilayers for our basic studies. Then, we shall study the charge mobility in these materials in the presence of azobenzene molecules during various excitation regimes allowing the control of the equilibrium between Trans and Cis populations of these molecules. Then we shall work with bacteria with bilayer membranes. Finally, we shall develop optogenetic tools allowing the injection and the selective photo activation of azobenzene molecules in myelin rich regions of the brain, trying to control locally the brain activation level. We hope that these studies will help to develop optoelectronic tools and techniques (processes) for the active control of the biological tissue with numerous medical applications.