Long-Range Lipid-Water Interaction as Observed by ATR-FTIR Spectroscopy
It is commonly assumed that the structure of water at a lipid-water interface is influenced mostly in the first hydration layer. However, recent results from different experimental methods show that perturbation extends through several hydration layers. Due to its low light penetration depth, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy is specifically suited to study interlamellar water structure in multibilayers. Results obtained by this technique confirm the long-range water structure disturbance. Consequently, in confined membrane environments nearly all water molecules can be perturbed. It is important to note that the behavior of confined water molecules differs significantly in samples prepared in excess water and in partially hydrated samples. We show in what manner the interlamellar water perturbation is influenced by the hydration level and how it is sequentially modified with a step-by-step dehydration of samples either by water evaporation or by osmotic pressure. Our results also indicate that besides different levels of hydration the lipid-water interaction is modulated by different lipid headgroups and different lipid phases as well. Therefore, modification of interlamellar water properties may clarify the role of water-mediated effects in biological processes.
KeywordsATR-FTIR Lipid bilayers Interlamellar water Excess water Long-range water structure effect Water-mediated biological processes
The financial support from the state budget by the Slovenian Research Agency (program No. P1-0060) is acknowledged. The author appreciates collaboration or helpful discussions with Luca Quaroni, Michael Rappolt, Joze Grdadolnik, Primoz Ziherl and Rudolf Podgornik. The author also thanks Iztok Urbancic for carefully reading this manuscript.
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