What's Cooler Than Being Cool? Ice-Sheet Models Using a Fluidity-Based FOSLS Approach to Nonlinear-Stokes Flow.

This research involves a few First-Order System Least Squares (FOSLS) formulations of a nonlinear-Stokes flow model for ice sheets. In Glen's flow law, a commonly used constitutive equation for ice rheology, the viscosity becomes infinite as the velocity gradients approach zero. This typically occurs near the ice surface or where there is basal sliding. The computational difficulties associated with the infinite viscosity are often overcome by an arbitrary modification of Glen's law that bounds the maximum viscosity. The FOSLS formulations developed in this thesis are designed to overcome this difficulty. The first FOSLS formulation is just the first-order representation of the standard nonlinear, full-Stokes and is known as the viscosity formulation and suffers from the problem above. To overcome the problem of infinite viscosity, two new formulation exploit the fact that the deviatoric stress, the product of viscosity and strain-rate, approaches zero as the viscosity goes to infinity. Using the deviatoric stress as the basis for a first-order system results in the the basic fluidity system. Augmenting the basic fluidity system with a curl-type equation results in the augmented fluidity system, which is more amenable to the iterative solver, Algebraic MultiGrid (AMG). A Nested Iteration (NI) Newton-FOSLS-AMG approach is used to solve the nonlinear-Stokes problems. Several test problems from the ISMIP set of benchmarks is examined to test the effectiveness of the various formulations. These test show that the viscosity based method is more expensive and less accurate. The basic fluidity system shows optimal finite-element convergence. However, there is not yet an efficient iterative solver for this type of system and this is the topic of future research. Alternatively, AMG performs better on the augmented fluidity system when using specific scaling. Unfortunately, this scaling results in reduced finite-element convergence

A full Stokes ice-flow model to assist the interpretation of millennial-scale ice cores at the high-Alpine drilling site Colle Gnifetti, Swiss/Italian Alps

The high-Alpine ice-core drilling site Colle Gnifetti (CG), Monte Rosa, Swiss/Italian Alps, provides climate records over the last millennium and beyond. However, the full exploitation of the oldest part of the existing ice cores requires complementary knowledge of the intricate glacio-meteorological settings, including glacier dynamics. Here, we present new ice-flow modeling studies of CG, focused on characterizing the flow at two neighboring drill sites in the eastern part of the glacier. The3-D full Stokes ice-flow model is thermo-mechanically coupled and includes firn rheology, firn densification and enthalpy transport, and is implemented using the finite element software Elmer/Ice. Measurements of surface velocities, accumulation, borehole inclination, density and englacial temperatures are used to validate the model output. We calculate backward trajectories and map the catchment areas. This constrains, for the first time at this site, the so-called upstream effects for the stable water isotope time series of the two ice cores drilled in 2005 and 2013. The model also provides a 3-D age field of the glacier and independent ice-core chronologies for five ice-core sites. Model results are a valuable addition to the existing glaciological and ice-core datasets. This especially concerns the quantitative estimate of upstream conditions affecting the interpretation of the deep ice-core layers

Direct observation and characterization of DMPC/DHPC aggregates under conditions relevant for biological solution NMR

AbstractWe have used cryo-transmission electron microscopy (cryo-TEM) for inspection of aggregates formed by dimyristoylphosphatidylcholine (DMPC) and dihexanoylphosphatidylcholine (DHPC) in aqueous solution at total phospholipid concentrations cL≤5% and DMPC/DHPC ratios q≤4.0. In combination with ocular inspections, we are able to sketch out this part of phase-diagram at T=14–80 °C. The temperature and the ratio q are the dominating variables for changing sample morphology, while cL to a lesser extent affects the aggregate structure. At q=0.5, small, possibly disc-shaped, aggregates with a diameter of ∼6 nm are formed. At higher q-values, distorted discoidal micelles that tend to short cylindrical micelles are observed. The more well-shaped discs have a diameter of around 20 nm. Upon increasing q or the temperature, long slightly flattened cylindrical micelles that eventually branch are formed. A holey lamellar phase finally appears upon further elevation of q or temperature. The implications for biological NMR work are two. First, discs prepared as membrane mimics are frequently much smaller than predicted by current “ideal bicelle” models. Second, the q≈3 preparations used for aligning water-soluble biomolecules in magnetic fields consist of perforated lamellar sheets. Furthermore, the discovered sequence of morphological transitions may have important implications for the development of bicelle-based membrane protein crystallization methods

Lateral diffusion processes in biomimetic polymer membranes

Molecular self-assembly offers an important bottom-up approach to generate new materials with great potential for applications in nano-, life- and medical- sciences and engineering. The interest in “soft” materials suitable for the generation of artificial, biomimetic membranes has increased rapidly over the last years. These membranes combine the advantages of specificity and efficiency found in nature and the robustness and stability of synthetic materials from polymer science. There are currently two approaches to design biomimetic membranes. One uses natural phospholipids, while the other ones uses synthetic lipid mimics as the advanced alternative, which have shown great mechanical and chemical stability compared to their natural counterparts. This is important for technological application where durable devices are required. Biological membrane proteins, which provide selective and very efficient membrane transport, can be inserted into these synthetic block copolymer membranes. This combination of a synthetic membrane with biological membrane proteins is an intriguing phenomenon because the fundamental requirements for successful insertion are still matter of debate. One important issue is that polymeric membranes have thicknesses that exceed the height of the membrane proteins by several factors and the two lengths actually do not match. However, this significant height mismatch can be overcome by choosing a polymer with high flexibility, which has been shown to allow membrane proteins insertion in their active conformation. Flexibility and fluidity are essential membrane properties allowing successful generation of biomimetic membranes. In this thesis, the fluid properties of synthetic membranes composed of synthetic amphiphiles are studied based on a large library of block copolymers. These consist of poly(2-methyloxazoline) (PMOXA) and poly(dimethylsiloxane) (PDMS) and are used as diblock (PMOXA-b-PDMS, AB) and triblock (PMOXA-b-PDMS-b-PMOXA, ABA) copolymers. Variation of the molecular weight induces changes in the membrane thickness and thus the fluidity of the membrane. The diffusion of membrane proteins within synthetic triblock copolymer membranes was investigated. The study revealed that the membrane proteins are mobile even at hydrophobic mismatches of up to 7 nm, which is a factor of seven compared to mismatches existing in biological membranes. The advantage of PDMS-containing block copolymers is their enormous flexibility even at high molecular weights, which provides a similar membrane environment compared to biological phospholipid membranes. This explains and displays the ability of PDMS to compress in contact to membrane proteins. Their diffusion decreases steadily with increasing thickness mismatch. The importance of a very flexible polymer for the generation of biomimetic membranes was elucidated for membrane protein insertion, such as PDMS, which offers high fluidity and high membrane stability within membranes with even large thicknesses. The properties of these synthetic membranes investigated here, i.e. fluidity, lateral diffusion and membrane thickness, are important for the generation of biomimetic membranes for technological applications

SNARE assembly and regulation on membranes

Die Fusion synaptischer Vesikel mit der präsynaptischen Plasmamembran wird durch sogenannte SNARE-Proteine vermittelt. Die vorliegende Arbeit trägt zu einem besseren Verständnis des Verhaltens des vesikelständigen SNARE-Proteins Synaptobrevin, sowohl in seiner nativen Organelle als auch in Liposomen rekonstituiert, bei. Die Reaktivität rekonstituierten Synaptobrevins ist bislang umstritten. So legten kürzlich durchgeführte Studien nahe, dass membranständiges Synaptobrevin nicht effizient in SNARE-Komplexe eingebaut wird (Hu et al., 2002; Kweon et al., 2003b). Deshalb habe ich die Bindungseigenschaften und die SNARE-Komplexbildungsreaktion auf Synaptobrevin exponierenden Membranen untersucht. So wie die lösliche Dömane bindet membranassoziiertes Synaptobrevin den SNAP-25/Syntaxin-Akzeptorkomplex, was zur Bildung eines stabilen, tetrahelikalen SNARE-Bündels führt. Kinetiksimulationen und Anpassung experimenteller Daten trugen dazu bei, den Reaktionsweg der SNARE-Komplexbildung auf Membranen aufzuklären. Die im Rahmen dieser Arbeit durchgeführten Untersuchungen weisen darauf hin, dass es sich um eine robuste Reaktion handelt, die von den meisten endogenen und äußeren Faktoren wie Hirnzytosol, Membranfluidität, Chaotropizität, divalenten Ionen und der Lipidkomposition weitgehend unbeeinflusst bleibt, jedoch durch Anwesenheit schwacher Gegenionen signifikant verstärkt wird. In Einklang mit dieser Beobachtung ist auch die Einbaurate von in Liposomen rekonstituiertem Synaptobrevin in SNARE-Komplexe mit der auf synaptischen Vesikeln vergleichbar. Aufgrund ihrer hohen Reaktivität ist die Regulation von SNARE-Proteinen von hoher Bedeutung. Es ist gezeigt worden, dass Synaptobrevin in Membranen assoziiert an das Vesikelprotein Synaptophysin vorliegt, welches potentiell als SNARE-Regulatorprotein fungiert. Hier konnte ich zeigen, dass die Bindung von Syntaxin/SNAP-25 an Synaptobrevin in der Lage ist, dessen Assoziation an Synaptophysin aufzuheben.Drei monoklonale Antikörper, die sich gegen den ternären SNARE-Komplex nicht jedoch gegen die SNARE-Monomere richten, wurden erfolgreich hergestellt und mithilfe von Immunoblotting, Zellinien und Plasmamembran- Sheets charakterisiert. Ihre Bindungsstellen konnten kartiert werden. Desweiteren waren die Antikörper in der Lage, SNARE-Komplex-dissoziation in einem funktionellen Experiment zu inhibieren und können damit Einblick in die Dissoziationsmaschinerie geben. Auch könnte ihr Einsatz in anderen funktionellen Untersuchungen helfen, noch ausstehende Fragen zu beantworten. Außerdem wurden der Zustand sowie die Dynamik von SNARE-Komplexen in präsynaptischen Nervenendigungen untersucht. Dabei konnte ich zeigen, dass die SNARE-Komplexmengen in ruhenden und stimulierten Synaptosomen vergleichbar sind, was darauf hinweist, dass diese schnell wieder dissoziiert werden, sobald Exozytose stattgefunden hat. Einige SNARE-Komplexe konnten jedoch auf isolierten Organellen mittels Mikroskopie und Immunoblotting detektiert werden. Dieses könnte ein Hinweis darauf sein, dass Komplexdissoziation keine zwingende Vorraussetzung für Endozytose darstellt, wobei nicht ausgeschlossen werden kann, dass es sich bei den detektierten Komplexen um erst in vitro auf isolierten Organellen entstandene Komplexe handelt.The fusion of synaptic vesicles with the pre-synaptic plasma membrane is mediated by SNARE proteins. This work provides key insights into the behaviour of synaptobrevin, the SNARE protein localized to synaptic vesicles, in its native membrane organelle and when it is reconstituted in liposomes. The reactivity of reconstituted synaptobrevin has remained controversial. Recent studies have suggested that synaptobrevin inserted in membranes does not readily engage in SNARE complexes (Hu et al., 2002; Kweon et al., 2003b). I therefore explored the binding characteristics and assembly pathway of the SNAREs on synaptobrevin-bearing membranes. Like its soluble domain, synaptobrevin anchored in membranes binds to the syntaxin/SNAP-25 acceptor complex to form the stable tetra helical coiled coil SNARE bundle. Kinetic simulations and fitting of experimental data helped unravel the SNARE assembly pathway on membranes. Monitoring the effects of endogenous and extraneous factors on SNARE complex assembly suggested that assembly is a robust process, largely unaffected by brain cytosolic factors, membrane fluidity, chaotropicity, divalent ions and lipid composition but is considerably enhanced in the presence of weak counter-ions. In agreement with these observations, SNARE complex assembly rate on liposomes reconstituted with synaptobrevin and on synaptic vesicles was comparable. Being highly reactive molecules, the regulation of SNAREs has considerable importance. Synaptobrevin has been found to be associated in membranes with synaptophysin, an abundant protein localized to the synaptic vesicle and a potential regulator of SNARE complex assembly. I showed here that syntaxin/SNAP-25 binding to synaptobrevin in synaptic vesicles causes its dissociation from synaptophysin.Three monoclonal antibodies recognizing the ternary SNARE complex, but not the monomers, were successfully raised and characterised in immunoblots, cell-lines and plasma-membrane sheets. Their binding sites on the complex were mapped. In a functional assay, the antibodies abolished disassembly of the SNARE complex thus providing insights into the disassembly machinery.The antibodies can be used in other functional assays to answer pertinent questions. The status and dynamics of SNARE complexes was probed in pre-synaptic nerve-terminals. I found that the amount of SNARE complex is comparable in resting and stimulated synaptosomes, suggesting that they rapidly disassemble immediately after exocytosis has occurred. Some amount of complex was, however, found on isolated organelles when monitored by direct imaging or immunoblotting, suggesting that rapid disassembly of the SNARE complex is not a pre-requisite for endocytosis, though it cannot be ruled out that complexes formed on isolated organelles in vitro

Dreidimensionale Strukturbestimmung des Glycin-Betain Transporters BetP mittels Kryo-Elektronen Kristallographie

The soil bacterium Corynebacterium glutamicum has five secondary transporters for compatible solutes allowing it to cope with osmotic stress. The most abundant of them, the transporter BetP, performs a high affinity uptake of glycine-betain when encountering hyperosmotic stress. BetP belongs to the betaine/carnitine/choline/transporter (BCCT) family, and is predicted to have twelve transmembrane helices with both termini facing the cytoplasm. The goal of this thesis is to facilitate understanding of BetP function by determining a three dimensional (3D) model of its structure. Two-dimensional (2D) crystallization of wild-type (WT) BetP has been successfully performed by reconstitution into a mixture of E. coli lipids and bovine cardiolipin, which resulted in vesicular crystals diffracting to 7.5 Å resolution (Ziegler, Morbach et al. 2004). Diffraction patterns of these crystals however showed unfocused spots, generally due to high mosaicity. Better results were obtained by using the constitutively active mutant BetPdeltaC45 in which the first 45 amino acids of the positively charged C-terminus were removed. BetPdeltaC45 crystals obtained under the same conditions for BetP WT were concluded to be pseudo crystals, based on the inconsistence of symmetry. These crystals had BetPdeltaC45 molecules randomly up/downwards inserted into membrane crystals, and cannot be used for structure determination, even though they diffracted up to 7 Å. The problem of pseudo crystal formation could be solved by changing the lipids used for 2D crystallization to a native lipid extract from C. glutamicum cells. This change of lipids improved the crystals to well-ordered packing with exclusive p121_b symmetry. To understand the role of lipids in crystal packing and order, lipids were extracted at different stages during crystallization, and identified by using multiple precursor ion scanning mass spectrometry. The results show that phosphatidyl glycerol (PG) 16:0-18:1 is the most dominant lipid species in C. glutamicum membranes, and that BetP has a preference for the fatty acid moieties 16:0-18:1. Crystallization with synthetic PG 16:0-18:1 proved that an excess of this lipid prevents pseudo crystal formation, but these crystals did not reach the quality as previously achieved by using the C. glutamicum lipids. Apart from the effect of lipids in crystallinity, the concentration and type of salts influenced crystal growth and morphology. High salt conditions (>400 mM LiCl or KCl) yielded tubular crystals, whereas low salt conditions (<300 mM LiCl, NaCl or KCl) led to formation of up to 10 µm large sheet-like crystals. The intermediate concentration gave a mixture of sheet-like and tubular crystals. In terms of resolution, sheets diffracted better than tubes. The sheet-like crystals used for 3D map reconstruction were obtained from a dialysis buffer containing 200 mM NaCl combined with using C. glutamicum lipids. Electron microscopic images were taken from frozen-hydrated crystals using a helium-cooled JEOL 300 SFF microscope or a liquid nitrogen-cooled FEI Tecnai G2 microscope at 300 kV, which allowed optimal data collection and minimized radiation damage to the sample. More than 1000 images of tilt angles up to 50° were taken and evaluated using optical diffraction of a laser beam. The best 200 images were processed with the MRC image processing software package, and 79 images from different tilt angles were merged to the final data set used for calculation of a 3D map at a planar resolution of 8 Å. The structure shows BetPdeltaC45 as a trimer with each monomer consisting of 12 transmembrane alpha-helices. Protein termini and loop regions could not be determined due to the limited resolution of the map. Six of the twelve helices line a central cavity forming a potential substrate-binding chamber. Each monomer shows a central cavity in different sizes and shapes. Thus, the constitutively active BetPdeltaC45 thus forms an unusual asymmetric homotrimer. BetP most likely reflects three different conformational states of secondary transporters: the cytoplasmically open (C), the occluded (O), and the periplasmically open (P) states. The C and O states are similar to BetP WT projection structure, while the P state is discrepant and highly flexible due to the shape and size of the central cavity as well as the lowest intensity of the density. The observation of the P state corresponds well to the constitutively active property of BetPdeltaC45. For the high resolution structure of the C and O states are available, this work presents the first structural information of the P state of a secondary transporter.Thema dieser Arbeit sind die Struktur/Funktionsprinzipien des osmoaktiven Betaintransporters BetP aus Corynebacterium glutamicum, eines Proteins aus der Familie der Betain/Carnitine/Cholin Transporter (BCCT) welches das kompatible Solut Betain unter Ausnutzung eines Natriumgradienten in die Zelle importiert. Gleichzeitig dient BetP auch als Osmolaritäts- und Temperatursensor der die Menge an importierten Solut ohne Umwege anpassen kann, wenn es z.B. als Folge von Überflutungen oder Dürren zu starken Schwankungen in der Wasseraktivität des bakteriellen Lebensraums kommt. Zum besseren Verständnis von osmoregulatorischen Sekundärtransportern und der BCCT Proteinfamilie wurde die dreidimensionale (3D) Struktur von BetP mittels Elektronenkristallographie bestimmt. Der BetP Wildtyp und eine konstitutiv aktive Mutante mit einem um 45 Aminosäuren gekürzten C-Terminus (BetPdeltaC45) wurden in E. coli überexprimiert und mittels Streptavidin-Affinitätschromatographie aufgereinigt. Die C-terminal gekürzte Mutante wurde gewählt da sie konstitutiv aktiv ist und Betain weitestgehend unabhängig von der Osmolarität der Umgebung über die Membran transportiert, was sie hervorragend geeignet macht den aktiven Zustand von BetP strukturell zu charakterisieren. Sowohl der BetP Wildtyp als auch die BetPdeltaC45 Mutante formten die für die Elektronenkristallographie nötigen zweidimensionalen (2D) Kristalle. Die Entfernung des positiv geladenen C-Terminus in der BetPdeltaC45 Mutante hatte jedoch einen starken Effekt auf die Kristallisierung und führte reproduzierbar zur Bildung von besser geordneten Kristallen mit niedrigerer Mosaizität. Die BetPdeltaC45 Mutante wurde daher für die weitere Optimierung und die 3D Strukturaufklärung verwendet. Neben dem Protein, sind die verwendeten Lipide für die Bildung von geordneten 2D Kristallen von entscheidender Bedeutung. Während der Optimierung wurde BetPdeltaC45 mittels dreier verschiedener Lipidpreparationen kristallisiert. Zum besseren Verständnis des Lipideinflusses auf das Kristallisationsverhalten wurden außerdem Lipidextrakte aus verschiedenen Stadien der Kristallisation hergestellt und die enthaltenen Lipide mittels quantitativer Massenspektrometrie bestimmt. Die Ergebnisse zeigen die Präferenz von BetP für 16:0-18:1 Fettsäurereste und das eine an diesen Resten reiche Lipidmischung die Bildung von Pseudokristallen verhindert. Die besten Kristallisationsergebnisse wurden mit dem nativen C. glutamicum Lipidextrakt erzielt. Die mit dieser Lipidmischung gezüchteten Kristalle formten großflächig kristallin geordnete Platten, die besonders für die Aufnahme von 3D Daten geeignet sind. Wichtiger noch als die Größe war der höhere Ordnungsgrad, welcher die Datenaufnahme bis zu einer Auflösung von 7-8 Å erlaubte und damit die Identifizierung von Transmembranhelices, den grundsätzlichen Strukturbausteinen von Membranproteinen ermöglicht. Zur Bestimmung der 3D Struktur von BetPdeltaC45 wurden elektronenkristallographische Aufnahmen von mehr als 200 Kristallen aufgenommen und die zur Strukturaufklärung nötigen Phasen und Amplituden mittels Bildbearbeitung extrahiert. Die 3D Information wurde aus zwischen 0 und 50 Grad gekippten Aufnahmen der 2D Kristalle gewonnen. Alle Daten wurden unter Einhaltung der p121_b Symmetrie zu einem einheitlichen Datensatz vereinigt, der mit einem mittlerem Phasenresidual von 20.4° eine hohe Qualität aufzeigt. Amplituden und Phasen dieses Datensatzes wurden für die Errechnung einer 3D Dichtekarte verwendet. Die bestimmte Dichte hat eine planare Auflösung von 8 Å und zeigt BetP als Trimer mit 12 länglichen Dichten pro Monomer, welche den 12 mittels Hydrophobizitätsplot vorhergesagten Transmembranhelices zugeordnet wurden. Interessanterweise ist die Anordnung dieser Dichten unterschiedlich für alle drei Monomere, wie eindeutig mittels Analyse einer Kreuzkorrelations-Dichtekarte zwischen den Monomeren und anhand der möglichen Kristallsymmetrien gezeigt werden konnte. Die Unterschiede dieses äußerst ungewöhnlichen asymmetrischen Homotrimers konzentrieren sich um einen von vier Helices umrahmten Hohlraum mit unterschiedlich großen Eintrittsöffnungen für jedes Monomer. Basierend auf der Anordnung des BetP asymmetrischen Homotrimers und bekannten biochemischen Daten wurde ein Modell erstellt in dem sich die Substratbindungstellen in den zentralen Hohlräumen befinden und in dem jedes Monomer des asymmetrischen Homotrimers einen unterschiedlichen Aktivierungszustand einnimmt. Die drei Aktivierungszustände wurden als die cytoplasmatisch offene, die geschlossene und periplastisch offene Konformation von sekundären Transportern interpretiert. Die vorliegende Arbeit liefert die ersten Strukturinformationen für einen Transporter der BCCT Familie und die periplastisch offene Konformation eines Sekundärtransporters und liefert damit wichtige Bausteine für das bessere Verständnis dieser für alle Zellen überlebenswichtigen Klasse von Transportern

Dynamically coupling full Stokes and shallow shelf approximation for marine ice sheet flow using Elmer/Ice (v8.3)

Ice flow forced by gravity is governed by the full Stokes (FS) equations, which are computationally expensive to solve due to the nonlinearity introduced by the rheology. Therefore, approximations to the FS equations are commonly used, especially when modeling a marine ice sheet (ice sheet, ice shelf, and/or ice stream) for 103 years or longer. The shallow ice approximation (SIA) and shallow shelf approximation (SSA) are commonly used but are accurate only for certain parts of an ice sheet. Here, we report a novel way of iteratively coupling FS and SSA that has been implemented in Elmer/Ice and applied to conceptual marine ice sheets. The FS–SSA coupling appears to be very accurate; the relative error in velocity compared to FS is below 0.5&thinsp;% for diagnostic runs and below 5&thinsp;% for prognostic runs. Results for grounding line dynamics obtained with the FS–SSA coupling are similar to those obtained from an FS model in an experiment with a periodical temperature forcing over 3000 years that induces grounding line advance and retreat. The rapid convergence of the FS–SSA coupling shows a large potential for reducing computation time, such that modeling a marine ice sheet for thousands of years should become feasible in the near future. Despite inefficient matrix assembly in the current implementation, computation time is reduced by 32&thinsp;%, when the coupling is applied to a 3-D ice shelf.</p

Bicellar systems to modify the phase behaviour of skin stratum corneum lipids

Bicellar systems are a fascinating category of versatile lipid assemblies that comprise bilayered disk-shaped nanoaggregates formed in water by long and short alkyl chain phospholipids. Bicelles bridge the gap between micelles and lipid vesicles by combining the attractive properties of both systems. These structures have recently been proposed in dermatological, cosmetic and pharmaceutical applications. Two new binary bicellar systems composed of cholesterol sulphate (SCHOL) and long-chain phospholipids (dimyristoyl- phosphatidylcholine, DMPC, or dipalmitoyl-phosphatidylcholine, DPPC) are characterised herein by differential scanning calorimetry, fluorescence spectroscopy, X-ray scattering and microscopy. Additionally, a comparative study on skin treated with the new SCHOL systems (DMPC/SCHOL and DPPC/SCHOL) and classic DHPC systems (DMPC/DHPC and DPPC/DHPC) was performed. These studies were conducted to determinate how deeply bicelles penetrate into the skin and the extension of their effect on the phase behaviour of stratum corneum (SC) lipids using attenuated total reflectance-Fourier transform infrared spectroscopy and two-photon excitation fluorescence microscopy. Our results show that SCHOL modified the typical discoidal morphology and the phase behaviour of the systems, inducing coexistence of two phases, liquid-ordered and ripple phases. The effect of the systems on SC lipids depends on their composition and is related to the fluidity of the SC lipid alkyl chains. Thus, systems with DMPC induced more disorder in SC lipids than systems with DPPC, and SCHOL did not modify the lipid arrangement. Perdeuterated systems in the infrared spectroscopy technique supported a different distribution in the tissue for every system. DMPC systems were primarily at the first layers of the SC, whereas DPPC systems were more widely distributed. Systems with SCHOL had enhanced distribution and penetration of bicellar systems throughout the SC. This journal is © 2012 the Owner Societies