The organization of biomolecules and bioassemblies is highly governed by the nature and extent of their interactions with water. These interactions are of high intricacy and a broad range of methods based on various principles have been introduced to characterize them. As these methods view the hydration phenomena differently (e.g., in terms of time and length scales), a detailed insight in each particular technique is to promote the overall understanding of the stunning "hydration world." In this prospective mini-review we therefore critically examine time-dependent fluorescence shift (TDFS)-an experimental method with a high potential for studying the hydration in the biological systems. We demonstrate that TDFS is very useful especially for phospholipid bilayers for mapping the interfacial region formed by the hydrated lipid headgroups. TDFS, when properly applied, reports on the degree of hydration and mobility of the hydrated phospholipid segments in the close vicinity of the fluorophore embedded in the bilayer. Here, the interpretation of the recorded TDFS parameters are thoroughly discussed, also in the context of the findings obtained by other experimental techniques addressing the hydration phenomena (e.g., molecular dynamics simulations, NMR spectroscopy, scattering techniques, etc.). The differences in the interpretations of TDFS outputs between phospholipid biomembranes and proteins are also addressed. Additionally, prerequisites for the successful TDFS application are presented (i.e., the proper choice of fluorescence dye for TDFS studies, and TDFS instrumentation). Finally, the effects of ions and oxidized phospholipids on the bilayer organization and headgroup packing viewed from TDFS perspective are presented as application examples.

• Keywords
• biomembranes, calcium, cholesterol, hydration, lipid headgroups, membrane dynamics, oxidized phosholipids, time-dependent fluorescence shift,
• Publication type
• Journal Article MeSH
• Review MeSH

Understanding interactions of calcium with lipid membranes at the molecular level is of great importance in light of their involvement in calcium signaling, association of proteins with cellular membranes, and membrane fusion. We quantify these interactions in detail by employing a combination of spectroscopic methods with atomistic molecular dynamics simulations. Namely, time-resolved fluorescent spectroscopy of lipid vesicles and vibrational sum frequency spectroscopy of lipid monolayers are used to characterize local binding sites of calcium in zwitterionic and anionic model lipid assemblies, while dynamic light scattering and zeta potential measurements are employed for macroscopic characterization of lipid vesicles in calcium-containing environments. To gain additional atomic-level information, the experiments are complemented by molecular simulations that utilize an accurate force field for calcium ions with scaled charges effectively accounting for electronic polarization effects. We demonstrate that lipid membranes have substantial calcium-binding capacity, with several types of binding sites present. Significantly, the binding mode depends on calcium concentration with important implications for calcium buffering, synaptic plasticity, and protein-membrane association.

• MeSH
• Cell Membrane metabolism   MeSH
• Phospholipids chemistry   metabolism   MeSH
• Lipid Bilayers chemistry   metabolism   MeSH
• Liposomes chemistry   metabolism   MeSH
• Models, Molecular MeSH
• Molecular Dynamics Simulation MeSH
• Calcium metabolism   MeSH
• Calcium Signaling MeSH
• Binding Sites MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Names of Substances
• Phospholipids MeSH
• Lipid Bilayers MeSH
• Liposomes MeSH
• Calcium MeSH

The need for detailed biophysical description of cationic lipid membranes, which are commonly used as gene transfection vectors, led us to study the properties of mixed cationic/zwitterionic lipid bilayers. Fluorescence solvent relaxation measurements of 6-dodecanoyl-2-dimethylaminonaphthalene (Laurdan) incorporated in a membrane consisting of cationic dimyristoyltrimethylammoniumpropane (DMTAP) and zwitterionic dimyristoylphosphatidylcholine (DMPC) were performed. The obtained results are compared with a recently measured system consisting of dioleoyltrimethylammoniumpropane (DOTAP) and dioleoylphosphatidylcholine (DOPC) (Jurkiewicz et al. Langmuir 22:8741-8749, 2006). The similar nonmonotonic dependence of the relaxation kinetics on cationic lipid content in the membrane was present for both systems. While the slowest solvent relaxation have been observed for 30 mol% of DOTAP in the DOPC bilayer (Jurkiewicz et al. Langmuir 22:8741-8749, 2006), for DMPC/DMTAP system it was found at 45 mol% of DMTAP, which agrees with the literature. Both membranes increased their hydration upon increased cationic lipid content.

• MeSH
• 2-Naphthylamine analogs & derivatives   chemistry   MeSH
• Dimyristoylphosphatidylcholine chemistry   MeSH
• Fluorescence MeSH
• Fluorescent Dyes chemistry   MeSH
• Cations chemistry   MeSH
• Quaternary Ammonium Compounds chemistry   MeSH
• Laurates chemistry   MeSH
• Lipid Bilayers chemistry   MeSH
• Lipids chemistry   MeSH
• Membranes chemistry   MeSH
• Molecular Structure MeSH
• Myristates chemistry   MeSH
• Solvents chemistry   MeSH
• Water chemistry   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• 1,2-dimyristoyl-3-trimethylammonium propane MeSH Browser
• 2-Naphthylamine MeSH
• Dimyristoylphosphatidylcholine MeSH
• Fluorescent Dyes MeSH
• Cations MeSH
• Quaternary Ammonium Compounds MeSH
• Laurates MeSH
• laurdan MeSH Browser
• Lipid Bilayers MeSH
• Lipids MeSH
• Myristates MeSH
• Solvents MeSH
• Water MeSH