DPPC Bilayers Research Articles

Update of the CHARMM all-atom additive force field for lipids: validation on six lipid types.

A significant modification to the additive all-atom CHARMM lipid force field (FF) is developed and applied to phospholipid bilayers with both choline and ethanolamine containing head groups and with both saturated and unsaturated aliphatic chains. Motivated by the current CHARMM lipid FF (C27 and C27r) systematically yielding values of the surface area per lipid that are smaller than experimental estimates and gel-like structures of bilayers well above the gel transition temperature, selected torsional, Lennard-Jones and partial atomic charge parameters were modified by targeting both quantum mechanical (QM) and experimental data. QM calculations ranging from high-level ab initio calculations on small molecules to semiempirical QM studies on a 1,2-dipalmitoyl-sn-phosphatidylcholine (DPPC) bilayer in combination with experimental thermodynamic data were used as target data for parameter optimization. These changes were tested with simulations of pure bilayers at high hydration of the following six lipids: DPPC, 1,2-dimyristoyl-sn-phosphatidylcholine (DMPC), 1,2-dilauroyl-sn-phosphatidylcholine (DLPC), 1-palmitoyl-2-oleoyl-sn-phosphatidylcholine (POPC), 1,2-dioleoyl-sn-phosphatidylcholine (DOPC), and 1-palmitoyl-2-oleoyl-sn-phosphatidylethanolamine (POPE); simulations of a low hydration DOPC bilayer were also performed. Agreement with experimental surface area is on average within 2%, and the density profiles agree well with neutron and X-ray diffraction experiments. NMR deuterium order parameters (S(CD)) are well predicted with the new FF, including proper splitting of the S(CD) for the aliphatic carbon adjacent to the carbonyl for DPPC, POPE, and POPC bilayers. The area compressibility modulus and frequency dependence of (13)C NMR relaxation rates of DPPC and the water distribution of low hydration DOPC bilayers also agree well with experiment. Accordingly, the presented lipid FF, referred to as C36, allows for molecular dynamics simulations to be run in the tensionless ensemble (NPT), and is anticipated to be of utility for simulations of pure lipid systems as well as heterogeneous systems including membrane proteins.

Molecular Dynamics and Partitioning of Di‐tert‐butyl Nitroxide in Stratum Corneum Membranes: Effect of Terpenes

In this work, we have used electron paramagnetic resonance (EPR) spectroscopy of the small spin label di-tert-butyl nitroxide (DTBN), which partitions the aqueous and hydrocarbon phases, to study the interaction of the terpenes alpha-terpineol, 1,8-cineole, L(-)-carvone and (+)-limonene with the uppermost skin layer, the stratum corneum, and the membrane models of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The EPR spectra indicated that the terpenes increase both the partition coefficient and the rotational correlation time of the spin labels in the stratum corneum membranes, whereas similar effects were observed in the DMPC and DPPC bilayers only at temperatures below the liquid-crystalline phase. The EPR parameter associated to probe polarity inside the membranes showed thermotropically induced changes, suggesting relocations of spin probe, which were dependent on the membrane phases. While the DMPC and DPPC bilayers showed abrupt changes in the partitioning and rotational correlation time parameters in the phase transitions, the SC membranes were characterized by slight changes in the total range of measured temperatures, presenting the greatest changes or membranes reorganizations in the temperature range of approximately 50 to approximately 74 degrees C. The results suggest that terpenes act as spacers, weakening the hydrogen-bonded network at the polar interface and thus fluidizing the stratum corneum lipids.

Coarse-grained molecular dynamics study of permeability enhancement in DPPC bilayers by incorporation of lysolipid.

The enhanced permeability of flat lipid bilayer membranes at their gel to liquid-crystalline (LC) phase transition has been explored using coarse-grained molecular dynamics. The phase transition temperature, T(m), is deduced by monitoring the area per lipid, the lipid lateral diffusion constant, and the lipid-lipid radial distribution function. We find that a peak in the permeability coincides with the phase transition from the gel to LC state when lysolipid is present. This peak in permeability correlates with a jump in the area per lipid near the same temperature as well as increased fluctuations in the lipid bilayer free volume. At temperatures above T(m), the permeability is only slightly dependent on the amount of lysolipid present. The increased free volume due to the "missing tail" of the lysolipid is partially compensated for by a decrease in area per lipid as the amount of lysolipid increases. We also found that in the coarse-grained model a small amount (< or = 15 mol %) of lysolipid stabilizes the gel phase and increases the phase transition temperature, while a larger amount of lysolipid (20 mol %) reduces T(m) back to that for pure DPPC, and bilayers consisting of > or = 30 mol % lysolipid did not form a gel phase but still exhibited a peak in permeability near T(m) for pure DPPC.

Improvement in physicochemical parameters of DPPC liposomes and increase in skin permeation of aciclovir and minoxidil by the addition of cationic polymers

1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes were prepared by high-pressure homogeniser and coated with two cationic polymers, chitosan (CS) and for the first time Eudragit EPO (EU), respectively. Compared to the control liposomes, the polymeric liposomes showed greater physicochemical stability in terms of mean particle size and zeta potential at room temperature. In the present study, aciclovir and minoxidil have been used as hydrophilic and hydrophobic candidates. In the presence of the drugs, the polymeric liposomes still showed constant particle size and zeta potential. Influences of polymers and model drugs on thermotropic phase transition of DPPC liposomes were studied by micro-differential scanning calorimetry (microDSC). The influences on configuration of DPPC liposomes were investigated by Fourier transform infrared spectroscopy (FTIR). According to DSC results, cationic polymers had a stabilising effect, whereas aciclovir and minoxidil changed the physical properties of the DPPC bilayers by influencing the main phase transition temperature and erasing the pre-transition. The investigation of C O stretching bands of DPPC at 1736 cm −1 in FTIR spectra showed that aciclovir has strong hydrogen bonding with C O groups of DPPC, whereas carbonyl groups were free in minoxidil presence. Moreover, the coating of liposomes with CS or EU led to higher skin diffusion for both drugs. This could be explained as an effect of positively charged liposomes to interact stronger with skin negatively charged surface and their possible interactions with structures below the stratum corneum.

Interaction between Poly(acrylic acid) and Phospholipid Vesicles: Effect of pH, Concentration, and Molecular Weight

Interactions between phospholipid vesicles and poly(acrylic acid) (PAA) are of fundamental importance for pH-sensitive delivery systems in pharmaceutical applications. In this study, we investigated the behavior of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at varied concentrations of PAA with low and high molecular weights. Differential scanning calorimetry and fluorescence microscopy experiments suggested that hydrogen bonding between the carboxyl group of PAA and the phosphodiester group of the lipid is the main driving force for association under acidic conditions. Complexation between DPPC and PAA depends on the PAA molecular weight and concentration. At high enough concentrations of the large molecular weight PAA, the polymer can completely disrupt the bilayers of DPPC. For the small molecular weight PAA, in contrast, the complexation leads to vesicle aggregation without destroying the bilayers. The difference in complex structure was detected by SEM and a UV-visible spectrophotometer. At alkaline pH, complexation did not occur because of strong dissociation of PAA.

Membrane Diffusion of Tethered DPPC and Tethered PIP3-Bound Protein Systems

We have used molecular dynamics simulations to investigate the diffusion of tethered proteins in lipid bilayers. Coarse-grained (CG) models of DPPC dimers were simulated in a DPPC bilayer with the MARTINI model, and single-lipid diffusion constants compared to those obtained for dimers at various tether lengths. The ratio of diffusion constants matches well with both experimental results and theoretical predictions of a simple bead model. CG models of pleckstrin homology domain (PH) bound to a lipid with a PIP3 (phosphatidylinositol (3,4,5)-trisphosphate) head group were then constructed and compared for the monomer, tethered dimer, and tethered trimer cases.

1P235 1I1325 DPPC脂質二重膜の相についての振る舞いの疎視化模型を用いたREMDによる研究(生体膜・人工膜-構造・物性,口頭発表,第48回日本生物物理学会年会)

1P235 1I1325 DPPC脂質二重膜の相についての振る舞いの疎視化模型を用いたREMDによる研究(生体膜・人工膜-構造・物性,口頭発表,第48回日本生物物理学会年会)

Polysialic acid can mediate membrane interactions by interacting with phospholipids

Polysialic acid (polySia) is expressed on the surface of neural cells, neuroinvasive bacterial cells and several tumor cells. PolySia chains attached to NCAM can influence both trans interactions between membranes of two cells and cis interactions. Here, we report on the involvement of phospholipids in regulation of membrane interactions by polySia. The pH at the surface of liposomes, specific molecular area of phosphatidylcholine molecules, phase transition of DPPC bilayers, cyclic voltammograms of BLMs, and electron micrographs of phosphatidylcholine vesicles were studied after addition of polysialic acid free in solution. The results indicate that polySia chains can associate with phosphatidylcholine bilayers, incorporate into the polar part of a phospholipid monolayer, modulate cis interactions between phosphatidylcholine molecules, and facilitate trans interactions between apposing phospholipid vesicles. These observations imply that polySia attached to NCAM or to lipids can behave similarly.

A molecular dynamics model of rhodamine-labeled phospholipid incorporated into a lipid bilayer

Phospholipids, labeled covalently by a fluorescent dye, are commonly applied in membrane biophysics. In this work, a molecular dynamics model of sulforhodamine attached covalently to a headgroup of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine is developed. It is found that the incorporation of rhodamine-labeled phospholipids into a DPPC bilayer at the low concentration results in small perturbation of the bilayer. In the dye-labeled membrane, the sulforhodamine moiety binds favorably to a polar membrane interface, forming the tilt angle 44° ± 8° to the bilayer normal. The deep location and binding of a bulk sulforhodamine fluorophore lead, therefore, to some ‘softening’ of the membrane structure.

A calorimetric and spectroscopic comparison of the effects of ergosterol and cholesterol on the thermotropic phase behavior and organization of dipalmitoylphosphatidylcholine bilayer membranes

We performed comparative DSC and FTIR spectroscopic measurements of the effects of cholesterol (Chol) and ergosterol (Erg) on the thermotropic phase behavior and organization of DPPC bilayers. Ergosterol is the major sterol in the biological membranes of yeasts, fungi and many protozoa. It differs from Chol in having two additional double bonds, one in the steroid nucleus at C7–8 and another in the alkyl chain at C22–23. Erg also has an additional methyl group in the alkyl chain at C24. Our DSC studies indicate that the incorporation of Erg is more effective than Chol is in reducing the enthalpy of the pretransition. At lower concentrations Erg is also more effective than Chol in reducing the enthalpies of both the sharp and broad components of main phase transition. However, at sterol concentrations from 30 to 50 mol%, Erg is generally less effective at reducing the enthalpy of the broad components and does not completely abolish the cooperative hydrocarbon chain-melting phase transition at 50 mol%, as does Chol. Nevertheless, in this higher ergosterol concentration range, there is no evidence of the formation of ergosterol crystallites. Our FTIR spectroscopic studies demonstrate that Erg incorporation produces a similar ordering of liquid-crystalline DPPC bilayers as does Chol, but an increased degree of hydrogen bonding of the fatty acyl carbonyl groups in the glycerol backbone region of the DPPC bilayer. These and other results indicate that Erg is less miscible in DPPC bilayers at higher concentrations than is Chol. Finally, we provide a tentative molecular explanation for the comparative experimental and computation results obtained for Erg and Chol in phospholipid bilayers, emphasizing the dynamic conformational differences between these two sterols.

Molecular View of Cholesterol Flip-Flop and Chemical Potential in Different Membrane Environments

The relative stability of cholesterol in cellular membranes and the thermodynamics of fluctuations from equilibrium have important consequences for sterol trafficking and lateral domain formation. We used molecular dynamics computer simulations to investigate the partitioning of cholesterol in a systematic set of lipid bilayers. In addition to atomistic simulations, we undertook a large set of coarse grained simulations, which allowed longer time and length scales to be sampled. Our results agree with recent experiments (Steck, T. L.; et al. Biophys. J. 2002, 83, 2118-2125) that the rate of cholesterol flip-flop can be fast on physiological time scales, while extending our understanding of this process to a range of lipids. We predicted that the rate of flip-flop is strongly dependent on the composition of the bilayer. In polyunsaturated bilayers, cholesterol undergoes flip-flop on a submicrosecond time scale, while flip-flop occurs in the second range in saturated bilayers with high cholesterol content. We also calculated the free energy of cholesterol desorption, which can be equated to the excess chemical potential of cholesterol in the bilayer compared to water. The free energy of cholesterol desorption from a DPPC bilayer is 80 kJ/mol, compared to 67 kJ/mol for a DAPC bilayer. In general, cholesterol prefers more ordered and rigid bilayers and has the lowest affinity for bilayers with two polyunsaturated chains. Overall, the simulations provide a detailed molecular level thermodynamic description of cholesterol interactions with lipid bilayers, of fundamental importance to eukaryotic life.

High-resolution J-coupled 13C MAS NMR spectroscopy of lipid membranes

We propose the use of Lee-Goldburg decoupling in high-resolution natural abundance 13C CP-MAS NMR spectroscopy to obtain J-resolved multiplets from membrane lipids, and the use of these in spectral assignment and to investigate changes in molecular and segmental dynamics within chemical shift-resolved lipid groups. Spectroscopic characteristics of hydrated DPPC bilayers are reported, including J1CH-couplings from the liquid crystalline and gel phases. The observed J1thetaCH values are scaled in the Lee-Goldburg experiment by a factor of approximately 3(-1/2) and corrected J1CH values on the order of 150 Hz compare well with indirect measurements. The J-resolved multiplets show J1thetaCH-couplings from the chain region to be approximately 20% lower than couplings determined from the headgroup, with backbone values falling between the two. Sensitivity of Lee-Goldburg decoupling to molecular motions reveals changes in hydrocarbon chain and backbone segmental dynamics across the main phospholipid transition and reduction in headgroup mobility below the pre-transition.

Exploring the Effects of Sterols in Model Lipid Membranes Using Single-Molecule Orientations

Single-molecule orientations of the fluorescent lipid analogue BODIPY-PC doped into lipid monolayers and bilayers of DPPC are used to characterize the structure present in the films as a function of sterol content. Out-of-focus polarized total internal reflection fluorescence microscopy (PTIRF-M) measurements are used to characterize the single-molecule tilt angles with respect to the membrane normal. Tilt angle histograms for Langmuir-Blodgett monolayers of DPPC reveal bimodal distributions at all surface pressures studied. A linear dependence in the dye population oriented normal to the membrane plane with surface pressure is found and used to characterize the equivalent surface pressure of supported bilayers formed through vesicle fusion. These measurements reveal an equivalent surface pressure of approximately 23 mN/m, which is somewhat lower than the currently accepted value of approximately 30-35 mN/m.(1-7) The effect of cholesterol, ergosterol, and lanosterol on membrane structure is also compared between DPPC bilayers and monolayers transferred at approximately 23 mN/m. The addition of cholesterol leads to dramatic changes in the tilt angle histograms while lanosterol has essentially no effect. The addition of ergosterol has a slight influence at higher concentrations. Using the average tilt angle calculated from the single-molecule histograms, the order parameter S is calculated as a function of cholesterol and compared with previous studies.(8-10).

Alternative Mechanisms for the Interaction of the Cell-Penetrating Peptides Penetratin and the TAT Peptide with Lipid Bilayers

Cell-penetrating peptides (CPPs) have recently attracted much interest due to their apparent ability to penetrate cell membranes in an energy-independent manner. Here molecular-dynamics simulation techniques were used to study the interaction of two CPPs: penetratin and the TAT peptide with 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) phospolipid bilayers shed light on alternative mechanisms by which these peptides might cross biological membranes. In contrast to previous simulation studies of charged peptides interacting with lipid bilayers, no spontaneous formation of transmembrane pores was observed. Instead, the simulations suggest that the peptides may enter the cell by micropinocytosis, whereby the peptides induce curvature in the membrane, ultimately leading to the formation of small vesicles within the cell that encapsulate the peptides. Specifically, multiple peptides were observed to induce large deformations in the lipid bilayer that persisted throughout the timescale of the simulations (hundreds of nanoseconds). Pore formation could be induced in simulations in which an external potential was used to pull a single penetratin or TAT peptide into the membrane. With the use of umbrella-sampling techniques, the free energy of inserting a single penetratin peptide into a DPPC bilayer was estimated to be ∼75 kJmol−1, which suggests that the spontaneous penetration of single peptides would require a timescale of at least seconds to minutes. This work also illustrates the extent to which the results of such simulations can depend on the initial conditions, the extent of equilibration, the size of the system, and the conditions under which the simulations are performed. The implications of this with respect to the current systems and to simulations of membrane-peptide interactions in general are discussed.

Study of the Benzocaine Transfer from Aqueous Solution to the Interior of a Biological Membrane

The precise molecular mechanism of general anesthetics remains unknown. It is therefore important to understand where molecules with anesthetic properties localize within biological membranes. We have determined the free energy profile of a benzocaine molecule (BZC) across a biological membrane using molecular dynamics simulation. We use an asymmetric phospholipid bilayer with DPPS in one leaflet of a DPPC bilayer (Lopez Cascales et al. J. Phys. Chem. B 2006, 110, 2358-2363) to model a biological bilayer. From the free energy profile, we predict the zone of actuation of a benzocaine is located in the hydrocarbon region or at the end of the lipid head, depending of the presence of charged lipids (DPPS) in the leaflet. We observe a moderate increase in the disorder of the membrane and in particular an increase in the disorder of DPPS. Static and dynamic physicochemical properties of the benzocaine, such as its dipole orientation, translational diffusion coefficient, and rotational relaxation time were measured.

Computational Studies of Texas Red−1,2-Dihexadecanoyl-sn-glycero-3-phosphoethanolamine—Model Building and Applications

Texas Red-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (TR-DHPE) is a frequently used experimental tool in the study of lipid membranes by fluorescence microscopy techniques. Although it is usually incorporated at low concentration, several experimental studies suggest that fluorescent labels could alter the membrane's behavior. To investigate this possibility, we developed and validated a molecular dynamics model for TR-DHPE. The model was used to simulate TR-DHPE in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers of 127 lipids and 511 lipids. We also simulated a pure 128 DPPC bilayer under the same conditions and found that the results compared well with other simulations and experiments. Texas Red was found to reside in the upper acyl chain region of the bilayer. Coinciding with its position in the bilayer, we found that Texas Red decreased the upper acyl carbon order parameters of neighboring lipids. We analyzed area per lipid at varying distances from the Texas Red and discovered finite size effects in the 1:127 system. In both systems, the Texas Red bound to a DPPC lipid. The model we have developed should also be useful for other biomolecular simulations which try to mimic experimental systems.

Interdigitation and vesicle-to-micelle transformation induced by a local anesthetic tetracaine in phospholipids bilayers

The phase transitions of distearoyl- (DSPC), dipalmitoyl- (DPPC) and dimyristoyl-phosphatidylcholine (DMPC) bilayer membranes were observed by means of differential scanning calorimetry as a function of the concentration of a local anesthetic tetracaine hydrochloride (TC·HCl). The depression of both temperatures of the main- and pre-transition, which is accompanied by a decrease in enthalpy changes for both transitions, was observed initially by the addition of TC·HCl. Bilayer interdigitation, which is accompanied by an increase in enthalpy change for the main transition from the interdigitated gel phase to the liquid crystalline phase, was followed by disappearance of the pretransition. The TC·HCl concentration necessary for the bilayer interdigitation was found to be 10, 21 and 6 mmol kg −1 for DSPC, DPPC and DMPC bilayers, respectively, which was not consistent with the order of acyl-chain length of lipids. Biphasic interactions for the interdigitation, that is, repulsive interaction between polar head groups and van der Waals attractive interaction between hydrophobic chains of lipids, were discussed. On the other hand, vesicle-to-micelle transformation, which is accompanied by a cooperative decrease in enthalpy change for the main transition, was observed at higher concentration of TC·HCl and was confirmed by the vesicle size determined by the dynamic light scattering. The longer the acyl-chain length of lipids, the higher the TC·HCl concentration necessary for the vesicle-to-micelle transformation.

Ceramide-1-Phosphate, in Contrast to Ceramide, Is Not Segregated into Lateral Lipid Domains in Phosphatidylcholine Bilayers

Sphingolipids are key lipid regulators of cell viability: ceramide is one of the key molecules in inducing programmed cell death (apoptosis), whereas other sphingolipids, such as ceramide 1-phosphate, are mitogenic. The thermotropic and structural behavior of binary systems of N-hexadecanoyl-D-erythro-ceramide (C 16-ceramide) or N-hexadecanoyl-D-erythro-ceramide-1-phosphate (C 16-ceramide-1-phosphate; C 16-C1P) with 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) was studied with DSC and deuterium nuclear magnetic resonance ( 2H-NMR). Partial-phase diagrams (up to a mole fraction of sphingolipids X = 0.40) for both mixtures were constructed based on DSC and 2H-NMR observations. For C 16-ceramide-containing bilayers DSC heating scans showed already at X cer = 0.025 a complex structure of the main-phase transition peak suggestive of lateral-phase separation. The transition width increased significantly upon increasing X cer, and the upper-phase boundary temperature of the mixture shifted to ∼65°C at X cer = 0.40. The temperature range over which 2H-NMR spectra of C 16-ceramide/DPPC- d 62 mixtures displayed coexistence of gel and liquid crystalline domains increased from ∼10° for X cer = 0.1 to ∼21° for X cer = 0.4. For C16-C1P/DPPC mixtures, DSC and 2H-NMR observations indicated that two-phase coexistence was limited to significantly narrower temperature ranges for corresponding C1P concentrations. To complement these findings, C 16-ceramide/1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC) and C16-C1P/POPC mixtures were also studied by 2H-NMR and fluorescence techniques. These observations indicate that DPPC and POPC bilayers are significantly less perturbed by C 16-C1P than by C 16-ceramide and that C 16-C1P is miscible within DPPC bilayers at least up to X C1P = 0.30.

A Calorimetric and Spectroscopic Comparison of the Effects on Ergosterol and Cholesterol on the Thermotropic Phase Behavior and Organization of Dipalmitoylphosphatidylcholine Bilayer Membranes

article i nfo We performed comparative DSC and FTIR spectroscopic measurements of the effects of cholesterol (Chol) and ergosterol (Erg) on the thermotropic phase behavior and organization of DPPC bilayers. Ergosterol is the major sterol in the biological membranes of yeasts, fungi and many protozoa. It differs from Chol in having two additional double bonds, one in the steroid nucleus at C7-8 and another in the alkyl chain at C22-23. Erg also has an additional methyl group in the alkyl chain at C24. Our DSC studies indicate that the incorporation of Erg is more effective than Chol is in reducing the enthalpy of the pretransition. At lower concentrations Erg is also more effective than Chol in reducing the enthalpies of both the sharp and broad components of main phase transition. However, at sterol concentrations from 30 to 50 mol%, Erg is generally less effective at reducing the enthalpy of the broad components and does not completely abolish the cooperative hydrocarbon chain-melting phase transition at 50 mol%, as does Chol. Nevertheless, in this higher ergosterol concentration range, there is no evidence of the formation of ergosterol crystallites. Our FTIR spectroscopic studies demonstrate that Erg incorporation produces a similar ordering of liquid-crystalline DPPC bilayers as does Chol, but an increased degree of hydrogen bonding of the fatty acyl carbonyl groups in the glycerol backbone region of the DPPC bilayer. These and other results indicate that Erg is less miscible in DPPC bilayers at higher concentrations than is Chol. Finally, we provide a tentative molecular explanation for the comparative experimental and computation results obtained for Erg and Chol in phospholipid bilayers, emphasizing the dynamic conformational differences between these two sterols.

Visualizing Lipid/Water and Lipid/Ion Interactions at the Biological Interfaces with Angstrom-Resolution by Frequency Modulation Atomic Force Microscopy

At the interface between biological membranes and their surrounding physiological solution, various interfacial phenomena take place through the interactions between lipid headgroups and water molecules (or ions) and hence have a great impact on the functions and structure of the biological membranes. However, it has been a great challenge to experimentally access such interfacial phenomena with Angstrom resolution.Recently, we have developed an atomic force microscopy (AFM) technique that is capable of visualizing Angstrom-scale structures and phenomena at the solid/liquid interface with piconewton order loading forces. Here we apply this technique to the investigation of the lipid/water and lipid/ion interactions at the biological interfaces.The figure shows an AFM image taken at the interface between the DPPC bilayer on mica and PBS solution. The image shows the molecular-scale corrugations of the lipid headgroups (lower half) and their primary hydration shells (upper half), revealing the existence of a stable hydration layer on the DPPC bilayer with nanometer-scale lateral extent.View Large Image | View Hi-Res Image | Download PowerPoint Slide