Solvatochromic Modeling of Laurdan for Multiple Polarity Analysis of Dihydrosphingomyelin Bilayer

A Quantitative Approach to Characterize the Surface Modification on Nanoparticles Based on Localized Dielectric Environments

Nanoparticles (NPs) are utilized for the functionalization of composite materials and nanofluids. Although oxide NPs (e.g., silica (SiO2)) exhibit less dispersibility in organic solvents or polymers due to their hydrophilic surface, the surface modification using silane coupling agents can improve their dispersibility in media with low dielectric constants. Herein, SiO2 NPs were functionalized using octyltriethoxysilane (OTES, C8) and dodecyltriethoxysilane (DTES, C12), wherein the degrees of surface modification of SiO2@C8 and SiO2@C12 were quantitatively evaluated based on the ratio of modifier to surface silanol group (θ) and the volume fraction of organic modifier to total particle volume (ϕR). The variations of surface properties were revealed by analyzing the Hansen solubility parameters (HSP). Particularly, the surface modification using OTES or DTES significantly affected the polarity (δP) of NPs. The local dielectric environments of surface-modified SiO2 NPs were characterized using a solvatochromic dye, Laurdan. By analyzing the peak position of the steady-state emission spectrum of Laurdan in a NP suspension, the apparent dielectric environments surrounding NPs (εapp) were obtained. A good correlation between ϕR and εapp was observed, indicating that ϕR is a reliable quantity for understanding the properties of surface-modified NPs. Furthermore, the generalized polarization (GP) of NPs was investigated. The surface-modified SiO2 NPs with higher ϕR (≥0.15) exhibited GP > 0, suggesting that the modifiers are well-organized on the surface of NPs. The localized dielectric environment surrounding NPs could be predicted by analyzing the volume fraction of nonpolar moieties derived from modifiers. Alternatively, εapp and GP can be utilized for understanding the properties of inorganic-organic hybrid NPs.

Fluorescent Probes and Quenchers in Studies of Protein Folding and Protein-Lipid Interactions

Fluorescence spectroscopy provides numerous methodological tools for structural and functional studies of biological macromolecules and their complexes. All fluorescence-based approaches require either existence of an intrinsic probe or an introduction of an extrinsic one. Moreover, studies of complex systems often require an additional introduction of a specific quencher molecule acting in combination with a fluorophore to provide structural or thermodynamic information. Here, we review the fundamentals and summarize the latest progress in applications of different classes of fluorescent probes and their specific quenchers, aimed at studies of protein folding and protein-membrane interactions. Specifically, we discuss various environment-sensitive dyes, FRET probes, probes for short-distance measurements, and several probe-quencher pairs for studies of membrane penetration of proteins and peptides. The goals of this review are: (a) to familiarize the readership with the general concept that complex biological systems often require both a probe and a quencher to decipher mechanistic details of functioning and (b) to provide example of the immediate applications of the described methods.

Multiplicity of solvent environments in lipid bilayer revealed by DAS deconvolution of twin probes: Comparative method of Laurdan and Prodan

Laurdan and Prodan were designed for the evaluation of the surrounding hydration state. When inserted into lipid bilayer systems, both probes are located at different positions and their fluorescence properties are drastically varied, depending on their surrounding environment. In this study, a novel method using the above fluorescence probes was proposed on the basis of fluorescence lifetime (τ) and emission peak (λ), called as τ vs. λ plot, determined by global analysis of their multiple fluorescence decays and deconvolution of these decay-associated spectra. According to the evaluation of τ vs. λ plot, the existence of multiple fluorescence components in the membrane was revealed. In addition, their fluorescence distribution properties, described on τ vs. λ plot, of each probe tended to correspond to the phase state and vertical direction of the lipid membrane. To assess the contribution of environmental effect to each distribution, we defined the region in the τ vs. λ plot, which was modeled from a series of solvent mixtures (hexane, acetone, ethanol and water) to emulate the complex environment in the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayer system. The distributions of fluorescence components of Laurdan and Prodan in lipid membranes were classified into each solvent species, and Prodan partition into bulk water was distinguished. The sensitivity of Prodan to the phase pretransition of the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayer system was also observed in increasing the temperature. Noticeably, most of the fluorescence components was assigned to the solvent model, except for a single component that has longer lifetime and shorter emission wavelength. This component was dominant in solid-ordered phase; hence, it is assumed to be a specific component in lipid membranes that cannot be represented by solvents. Although these are still qualitative analytical methods, the unique approach proposed in this study provides novel insights into the multi-focal property of the membrane.

Effect of Host Cholesterol on the Membrane Dynamics of Outer Membrane Lipids of Mycobacteria

The ability of Mycobacterium tuberculosis to remain dormant after primary infection represents the prime cause of new TB cases throughout the world. Hence, diagnosis and treatment of individuals hosting dormant mycobacterium is one of the crucial strategies to be adopted for the prevention of Tuberculosis. Among many strategies unleashed by the latent bacterium, one of them is scavenging host cholesterol for carbon source. Cholesterol modifies lipid membranes over many scales and here, its effect on mycobacterial membrane biophysics and the subsequent effect on partitioning of antibiotics into cholesterol- enriched mycobacterial membranes was investigated. Our research showed that cholesterol alters the phase state behavior of mycobacterial outer membrane lipids by enhancing the overall membrane order at the headgroup and acyl chain region and is integrated into both ordered and disordered domains/phases, with a preference for the latter. Exogenous cholesterol further alters the drug partitioning behavior of structurally different drugs, pointing to a larger clinical potential of using more hydrophobic medications to target dormant bacteria.

Directly imaging emergence of phase separation in peroxidized lipid membranes

Lipid peroxidation is a process which is key in cell signaling and disease, it is exploited in cancer therapy in the form of photodynamic therapy. The appearance of hydrophilic moieties within the bilayer's hydrocarbon core will dramatically alter the structure and mechanical behavior of membranes. Here, we combine viscosity sensitive fluorophores, advanced microscopy, and X-ray diffraction and molecular simulations to directly and quantitatively measure the bilayer's structural and viscoelastic properties, and correlate these with atomistic molecular modelling. Our results indicate an increase in microviscosity and a decrease in the bending rigidity upon peroxidation of the membranes, contrary to the trend observed with non-oxidized lipids. Fluorescence lifetime imaging microscopy and MD simulations give evidence for the presence of membrane regions of different local order in the oxidized membranes. We hypothesize that oxidation promotes stronger lipid-lipid interactions, which lead to an increase in the lateral heterogeneity within the bilayer and the creation of lipid clusters of higher order.

Revealed Properties of Various Self-Assemblies in Two Catanionic Surfactant Systems in Relation to Their Polarity and Molecular Packing State

A catanionic surfactant system is an aqueous solution or dispersion of cationic and anionic surfactants that spontaneously self-assemble into structures such as micelles, vesicles, and coacervates. Their structural diversity varies depending on the ratios of cationic and anionic surfactants (compositions), the chemical structure of the constituent molecules, etc. Herein, two types of catanionic surfactant systems were systematically characterized: (i) cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), both typical ionic surfactants; and (ii) dodecylmethylimidazolium ammonium bromide ([C₁₂mim]Br) and SDS, where the former is an ionic liquid. By observing the sample appearance, turbidity, and particle size, the phase state of each system was analyzed according to the total concentration of surfactants and the molar ratio of cationic surfactants to the total concentration. Especially, for specific compositions of catanionic surfactant vesicles (cataniosome), the closed structure of the vesicles was confirmed through calcein entrapment and release detected with a fluorescence assay. The polarities of the interface of the prepared self-assemblies were evaluated using a fluorescence probe, Laurdan. The packing state of the molecules in the formed self-assembly structure was estimated using Raman spectroscopy. The results clearly indicate consistent phase-transition behavior for the CTAB-SDS (i) and [C₁₂mim]Br-SDS (ii) systems, depending on the total surfactant concentration and composition, while the membrane properties of the two systems differed. The cataniosome formed in the CTAB-SDS system was in a tightly packed membrane state and more hydrophobic than that formed in the [C₁₂mim]Br-SDS system owing to the difference in the structure of the constituting molecule: [C₁₂mim]Br has a larger head group and shorter acyl chain than CTAB. The self-assembly properties evaluated in this study were compared with those of typical lipid membranes, liposomes (lipid vesicles), to determine a possible application of the catanionic systems with various self-assembly formulations.

Charged hybrid block copolymer-lipid-cholesterol vesicles: pH, ionic environment, and composition dependence of phase transitions

The impacts of pH, salt concentration (expressed as Debye length), and composition on the phase behavior of hybrid block copolymer-lipid-cholesterol bilayers incorporating carboxyl-terminated poly(butadiene)-block-poly(ethylene oxide) copolymer (PBdPEO1800^(-)) or/and non-carboxyl-terminated PBdPEO (PBdPEO1800 or/and PBdPEO950), egg sphingomyelin (egg SM), and cholesterol were examined using fluorescence spectroscopy of laurdan. Laurdan emission spectra were decomposed into three lognormal curves as functions of energy. The ratio of the area of the mid-energy peak to the sum of the areas of all three peaks was evaluated as vesicles were cooled, yielding temperature breakpoint values (T_break) expected to be within the range of the phase transition temperature. T_break values displayed dependence on pH, Debye length, and vesicle composition consistent with an electrostatic repulsion contribution to vesicle phase behavior. Increased pH and Debye length, for which a greater dissociated fraction of PBdPEO1800^(-) and a greater energy of electrostatic repulsion would be expected, resulted in T_break values as much as 10 °C less than at low pH or short Debye lengths. Additionally, at Debye lengths comparable to those at physiologically relevant ionic strength, T_break at pH 5.9 was observed to be slightly higher than at pH 7.0 for vesicles containing 50 mol% PBdPEO1800^(-). Electrostatic effects observed for hybrid vesicles incorporating significant amounts of carboxyl-terminated polymer may have the ability to drive phase separation in response to pH drops-such as those observed after endocytosis-in physiologically relevant conditions, suggesting the utility of such materials for drug delivery.

Characterization of phase separation phenomena in hybrid lipid/block copolymer/cholesterol bilayers using laurdan fluorescence with log-normal multipeak analysis

Phase separation phenomena in hybrid lipid/block copolymer/cholesterol bilayers combining polybutadiene-block-polyethylene oxide (PBdPEO), egg sphingomyelin (egg SM), and cholesterol were studied with fluorescence spectroscopy and microscopy for comparison to lipid bilayers composed of palmitoyl oleoyl phosphatidylcholine (POPC), egg SM, and cholesterol. Laurdan emission spectra were decomposed into three lognormal curves. The temperature dependence of the ratios of the areas of the middle and lowest energy peaks revealed temperature break-point (T_break) values that were in better agreement, compared to generalized polarization inflection temperatures, with phase transition temperatures in giant unilamellar vesicles (GUVs). Agreement between GUV and spectroscopy results was further improved for hybrid vesicles by using the ratio of the area of the middle peak to the sum of the areas all three peaks to find the T_break values. For the hybrid vesicles, trends at T_break are hypothesized to be correlated with the mechanisms by which the phase transition takes place, supported by the compositional range as well as the morphologies of domains observed in GUVs. Low miscibility of PBdPEO and egg SM is suggested by the finding of relatively high T_break values at cholesterol contents greater than 30 mol%. Further, GUV phase behavior suggests stronger partitioning of cholesterol into PBdPEO than into POPC, and less miscibility of PBdPEO than POPC with egg SM. These results, summarized using a heat-map, contribute to the limited body of knowledge regarding the effect of cholesterol on hybrid membranes, with potential application toward the development of such materials for drug delivery or membrane protein reconstitution.

Lipid Clustering in Mycobacterial Cell Envelope Layers Governs Spatially Resolved Solvation Dynamics

The mycobacterial cell envelope acts as a multilayered barrier to drugs. However, the role of lipid composition in the properties of different mycobacterial membranes, otherwise dictating their interactions with drugs, is poorly understood. In this study, we found that hydration states, solvation relaxation kinetics, rotational lipid mobility, and lateral lipid diffusion differed between inner and outer mycobacterial membranes. Molecular modeling showed that lipid clustering patterns governed membrane dynamics in the different layers of the cell envelope. By regulating membrane properties, lipid composition and structure modulated water abundance and interactions with lipid head groups. These findings can help deepen our understanding of the physical chemistry underlying membrane structure and function, as well as the interaction of mycobacterial membranes with drugs and host membranes.

Systematic Characterization of Nanostructured Lipid Carriers from Cetyl Palmitate/Caprylic Triglyceride/Tween 80 Mixtures in an Aqueous Environment

Nanostructured lipid carriers (NLCs) are gaining attention as the new generation of lipid vehicles. These carriers consist of saturated lipids with small drops of liquid oil dispersed into the inner lipid matrix and are stabilized by a surfactant. Conventionally, NLC-based drug delivery systems have been widely studied, and many researchers are looking into the composition of NLC properties to improve the performance of NLCs. The membrane fluidity and polarity of self-assembling lipids are also essential properties that must be affected by membrane compositions; however, such fundamental characteristics have not been studied yet. In this study, NLCs were prepared from cetyl palmitate (CP), caprylic triglyceride (CaTG), and Tween 80 (T80). Structural properties, such as particle size and ζ-potential of the CP/CaTG/T80 ternary mixtures, were investigated. Then, the systematic characterization of self-assembly properties using fluorescence-based analysis was applied for the first time to the NLC system. As a final step, the ternary diagram was developed based on the self-assembly properties to summarize the possible structures formed at different compositions. The results showed four states: micelle-like, oil-in-water (O/W) emulsion-like, solid lipid nanoparticle-like, and intermediate (solid-liquid coexistence). For the purpose of making the lipid matrix more liquified, the heterogeneous state and the disordered state of the O/W emulsion-like structure might fulfill the criteria of NLCs. Finally, the ternary diagram provides new information about the assembly state of NLC constituents that could become an important reference for developing high-performance NLCs.

Changes Caused by Liposomes to the Belousov-Zhabotinsky Reaction

The Belousov-Zhabotinsky (BZ) reaction has been applied to give autonomous dynamic behaviors to artificial systems. This reaction is conducted in an aqueous system, but it produces some hydrophobic intermediates, such as bromine. On the basis of previous works about reactions in the lipid bilayer, we investigated how liposome membranes (water-oil interface) affect the BZ reaction. Herein diacylglycerophosphocholine (PC) molecules with a variety of hydrocarbon tails were selected as components of liposomes, and the BZ reaction in the presence of the liposomes was characterized. As a result, membrane fluidity was the main characteristic leading to changes in the reaction behavior. The decrease of the frequency of oscillations was relevant to membrane fluidity, suggesting the interaction of bromine species in the hydrophobic site of the liposomes. In addition, the heterogeneous membrane (s_o+l_d) of DMPC showed a fast decrease in the amplitude of oscillations. Conclusively, characteristics of the hydrophobic environment play a role in the reaction.

Influence of Membrane Phase on the Optical Properties of DPH

The fluorescent molecule diphenylhexatriene (DPH) has been often used in combination with fluorescence anisotropy measurements, yet little is known regarding the non-linear optical properties. In the current work, we focus on them and extend the application to fluorescence, while paying attention to the conformational versatility of DPH when it is embedded in different membrane phases. Extensive hybrid quantum mechanics/molecular mechanics calculations were performed to investigate the influence of the phase- and temperature-dependent lipid environment on the probe. Already, the transition dipole moments and one-photon absorption spectra obtained in the liquid ordered mixture of sphingomyelin (SM)-cholesterol (Chol) (2:1) differ largely from the ones calculated in the liquid disordered DOPC and solid gel DPPC membranes. Throughout the work, the molecular conformation in SM:Chol is found to differ from the other environments. The two-photon absorption spectra and the ones obtained by hyper-Rayleigh scattering depend strongly on the environment. Finally, a stringent comparison of the fluorescence anisotropy decay and the fluorescence lifetime confirm the use of DPH to gain information upon the surrounding lipids and lipid phases. DPH might thus open the possibility to detect and analyze different biological environments based on its absorption and emission properties.

Improved Characterization of Raft-Mimicking Phase-Separation Phenomena in Lipid Bilayers Using Laurdan Fluorescence with Log-Normal Multipeak Analysis

The study of biomimetic model membrane systems undergoing liquid-ordered (Lo)-liquid-disordered (Ld) phase separation using spectroscopic methods has played an important role in understanding the properties of lipid rafts in plasma membranes. In particular, the membrane-associated fluorescence probe Laurdan has proved to be a very efficient reporter of Lo-Ld phase separation in lipid bilayers using the general polarization (GP) parameter. A limitation of the GP approach is that it monitors only global average packing so that the contribution of each phase remains undetermined. The decomposition of Laurdan emission spectra has been proposed as an additional approach to overcoming this limitation. Here, further developments of this method for the study of Lo-Ld phase separation are described here for Laurdan in sphingomyelin-phosphatidylcholine-cholesterol large unilamellar vesicles. Lipid compositions corresponding to homogeneous Lo or Ld phases as well as undergoing thermally induced Lo-Ld phase separation were investigated. In addition, the occurrence of phase separation was checked by the fluorescence imaging of giant unilamellar vesicles. Decomposition into three log-normal components is used to show that an intermediate energy component is specifically associated with the occurrence of the Lo phase, with a small contribution from this component occurring above the phase-separation temperature being attributable to phase fluctuations. The ratio R_X of the relative area of this intermediate-energy peak to that of the low-energy peak is shown to provide a straightforward index of Lo-Ld phase separation as a function of temperature, which is occasionally more sensitive than GP. It is also shown that R_X can be used in conjunction with GP to gain further insight into Lo-Ld, the phase-separation processes. This latter feature is illustrated by the influence of the alcohol butanol on the Lo-Ld phase separation in sphingomyelin-phosphatidylcholine-cholesterol bilayers by showing that the effect of the alcohol occurs specifically at the onset of the phase separation, indicating a line tension mechanism. It is proposed that the three components of log-normal decomposition approaching Laurdan emission spectra provide a useful improvement for characterizing Lo-Ld phase-separation phenomena.

Evaluation of Molecular Ordering in Bicelle Bilayer Membranes Based on Induced Circular Dichroism Spectra

Bicelles are submicrometer-sized disc-shaped molecular self-assemblies that can be obtained in aqueous solution by dispersing mixtures of certain amphiphiles. Although phospholipid bicelle and phospholipid vesicle assemblies adopt similar lipid bilayer structures, the differences in bilayer characteristics, especially physicochemical properties such as bilayer fluidity, are not clearly understood. Herein, we report the lipid ordering properties of bicelle bilayer membranes based on induced circular dichroism (ICD) and fluorescence polarization analyses using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a probe. Bicelles were prepared by using 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC), while pure DMPC vesicles and pure DHPC micelles were used as references. At temperatures below the phase transition temperature of DMPC, the bicelles showed lower membrane fluidities, whereas DHPC micelles showed higher membrane fluidity, suggesting no significant differences in bilayer fluidity between the bicelle and vesicle assemblies. The ICD signals of DPH were induced only when the membrane was in ordered (solid-ordered or ripple-gel) phases. In the bicelle systems, the ICD of DPH was more significant than that of the DMPC vesicle. The induced chirality of DPH was dependent on the chirality of the bilayer lipid. Compared to that of the DMPC/DHPC bicelle, the ICD of the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/DHPC bicelle was higher, while that of the bovine sphingomyelin/DHPC bicelle was lower. Because the lipids are tightly packed in the ordered phase, the ICD intensity reflects the molecular ordering state of the lipids in the bicelle bilayer.

Conformational Changes as Driving Force for Phase Recognition: The Case of Laurdan

The development of a universal probe to assess the phase of a lipid membrane is one of the most ambitious goals for fluorescence spectroscopy. The ability of a well-known molecule as Laurdan to reach this aim is here exploited as the behavior of the probe is fully characterized in a dipalmitoylphosphatidylcholine (DPPC) solid gel (So) phase by means of molecular dynamics simulations. Laurdan can take two conformations, depending on whether the carbonyl oxygen points toward the β-position of the naphthalene core (Conf-I) or to the α-position (Conf-II). We observe that Conf-I has an elongated form in this environment, whereas Conf-II takes an L-shape. Interestingly, our theoretical calculations show that these two conformations behave in an opposite way from what is reported in the literature for a DPPC membrane in a liquid disordered (Ld) phase, where Conf-I assumes an L-shape and Conf-II is elongated. Moreover, our results show that in DPPC (So) no intermixing between the conformations is present, whereas it has been seen in a fluid environment such as DOPC (Ld). Through a careful analysis of angle distributions and by means of the rotational autocorrelation function, we predict that the two conformers of Laurdan behave differently in different membrane environments.

Membrane Surface-Enhanced Raman Spectroscopy for Cholesterol-Modified Lipid Systems: Effect of Gold Nanoparticle Size

A gold nanoparticle (AuNP) has a localized surface plasmon resonance peak depending on its size, which is often utilized for surface-enhanced Raman scattering (SERS). To obtain information on the cholesterol (Chol)-incorporated lipid membranes by SERS, AuNPs (5, 100 nm) were first functionalized by 1-octanethiol and then modified by lipids (AuNP@lipid). In membrane surface-enhanced Raman spectroscopy (MSERS), both signals from 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and Chol molecules were enhanced, depending on preparation conditions (size of AuNPs and lipid/AuNP ratio). The enhancement factors (EFs) were calculated to estimate the efficiency of AuNPs on Raman enhancement. The size of AuNP_100nm@lipid was 152.0 ± 12.8 nm, which showed an surface enhancement Raman spectrum with an EF₂₈₅₀ value of 111 ± 9. The size of AuNP_5nm@lipid prepared with a lipid/AuNP ratio of 1.38 × 10⁴ (lipid molecule/particle) was 275.3 ± 20.2 nm, which showed the highest enhancement with an EF₂₈₅₀ value of 131 ± 21. On the basis of fluorescent probe analyses, the membrane fluidity and polarity of AuNP@lipid were almost similar to DOPC/Chol liposome, indicating an intact membrane of DOPC/Chol after modification with AuNPs. Finally, the membrane properties of AuNP@lipid systems were also discussed on the basis of the obtained MSERS signals.

Melting-Temperature-Dependent Interactions of Ergosterol with Unsaturated and Saturated Lipids in Model Membranes

Sterols such as cholesterol (Chol) and ergosterol (Erg) are known to regulate membrane properties in higher eukaryotes and in lower eukaryotes, respectively. To better understand the modulation of membrane properties by Erg, binary lipid membranes composed of Erg and diacylglycerophosphocholine (PC) were studied in Langmuir monolayer and bilayer vesicle systems. From the excess area measured by pressure-area isotherms, attractive interactions between Erg and saturated PC were significant above the melting temperature (T_m) of PC. Conversely, repulsive interactions were observed at temperatures below T_m. From the analyses of membrane fluidity and polarity using fluorescence probes, similar trends were observed for bilayer systems where Erg had an ordering effect on saturated PC vesicles in the fluid state. However, Chol had a stronger ordering effect than Erg. In unsaturated PC systems, Erg did not alter membrane ordering. These findings demonstrate that the interaction of Erg with the fluid-state PC lipids will maintain lower-eukaryote membranes in a more ordered state, similar to the effect of cholesterol in higher eukaryotes.

Lipid-Surrounding Water Molecules Probed by Time-Resolved Emission Spectra of Laurdan

The hydration states of the interfacial region of lipid bilayers were investigated on the basis of the time-resolved emission spectra (TRES) analysis of 6-lauroyl-2-dimethylamino naphthalene (Laurdan), a common fluorescence probe used to analyze membrane hydration. TRES derived from long and short lifetime components were extracted from samples of different lipid species: 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC), 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC), d- erythro- N-palmitoyl-sphingosylphosphorylcholine (PSM), and a DOPC/PSM binary bilayer system. Neither lifetime component (short or long) corresponded with the hydration properties; the short lifetime component of DOPC (1.97 ns) exhibited a peak at 440 nm, and the long lifetime components of DPPC and PSM (7.76 and 7.77 ns, respectively) exhibited peaks at the same wavelength. This similarity arose from the competition between the collisional quenching and the hydration effects of water molecules. Herein, this phenomenon was investigated using a plot of the lifetime τ and the peak position λ (τ vs λ plot), simultaneously visualizing both effects by deconvoluting the TRES. On the basis of collisional quenching theory, the distribution of the water population per lipid (water map) was generated. According to this theory, the τ vs λ plot was applied to the water map and the calculation of the number of water molecules per lipid, which is consistent with previous reports. This approach provides novel insights for the analysis of molecular hydration states using the fluorescence of Laurdan.