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Biological membranes form the structural boundaries and compartments of cells, owing to their robustness and impermeability facilitated by phospholipid bilayers. The strength of biological membranes is intricately linked to the behavior of membrane pores, whose formation and expansion can lead to membrane rupture. However, processes essential for drug delivery, gene editing via genetic material transfer, and antimicrobial peptide action necessitate controlled membrane disruption for efficient cellular entry. Likewise, fundamental phenomena such as exocytosis, including neurotransmitter release between neurons and hormone secretion for physiological responses, rely on membrane breach to release cargo beyond cell confines. Exocytosis involves the fusion of cargo-contained vesicle membranes with the cell's plasma membrane, resulting in the release of cargo into the extracellular milieu. Post-release, these fused vesicles may either integrate with the plasma membrane, remain stationary, enlarge, or depart the release site through fusion pore closure, which, in turn, can modulate exocytosis rate through site availability. However, the precise mechanism of membrane rupture remains elusive. Similarly, the pathway of membrane fusion facilitated by SNARE proteins, pivotal in cellular fusion machinery, remains a subject of debate. Additionally, the mechanisms governing exocytosis remain incompletely understood. To address these inquiries, we employ ultra-coarse-grained molecular dynamics simulations which can explore these phenomena in physiological timescale. These simulations explore membrane rupture mechanisms via pore formation and expansion under varying membrane tension. Furthermore, the research addresses how SNARE proteins drive membrane fusion. In addition, we also rigorously analyze confocal microscopy data from Ling-Gang Wu's research group and develop a quantitative model to elucidate exocytosis rate regulation. Furthermore, the research verifies the robustness of a mathematical model outlining Ca2+-mediated membrane fusion and establishes that hemifusion diaphragms (HDs), where only the outer leaflets of membranes fuse, act as hubs in the Ca2+-mediated fusion network. This finding casts new light on the role of membranes in SNARE-mediated fusion. In the extra study, we analyzed fission yeast contractile ring behavior based on z-stack confocal microscopy data from Mohan Balasubramanian's research group, offering insights into the mechanism behind a critical step in cytokinesis. Chapter one examines membrane pore energetics and bilayer rupture times through highly coarse-grained simulations operating at submillisecond time scales. No metastable states are detected during pore formation. At lower tensions, small hydrophobic pores mature into large hydrophilic pores that ultimately rupture from reversible hydrophilic pores, aligning with classical tension-dependent rupture times. At higher tensions, membranes rupture directly from small hydrophobic pores, with rupture times exhibiting exponential tension dependence. Upon reaching a minimum hydrophobic pore size, a critical tension threshold prompts immediate rupture. This analysis corroborates established experimental findings but reveals that the high-tension exponential regime is not related to long-lived pre-pore defects but rather to the instability of hydrophilic pores beyond a critical tension, leading to significant changes in pore dynamics and rupture kinetics. Chapter two describes utilizing ultra-coarse-grained simulations to dissect the core requirements of membrane fusion and unravel the intricacies of SNARE-mediated fusion. Remarkably, simulations conducted on a millisecond timescale expose the inefficiency of fusion through simple body forces pushing vesicles together. Successful inter-vesicle fusion hinges on the rod-like structure of fusogens, ensuring their sufficient length for effective fusion and subsequent clearance from the fusion site via entropic forces. Simulations featuring rod-shaped fusogens and SNARE proteins demonstrate the fusion of 50-nanometer vesicles in submilliseconds, propelled by entropic forces that direct a predictable fusion pathway. The entropic force hypothesis of SNARE-mediated membrane fusion garners strong support from these findings, emphasizing the necessity of the rod-like configuration of the SNARE complexes for entropic force generation and fusion. Chapter three focuses on the spatiotemporal dynamics of dense-core vesicle exocytosis events in chromaffin cells, deducing a novel mechanism for exocytosis regulation based on the availability of release sites. Repeated fusion supports membrane reservoir comprising incompletely merged or closed vesicles, occupying release sites and dampening exocytosis frequency. Mathematical modeling suggests reservoir formation relies on locally reduced membrane tension, eliminating the driving force for vesicle merging. Endocytosis facilitates the clearance of unmerged vesicles from the reservoir, ultimately restoring release site availability for subsequent exocytosis events. Chapter four introduces a mathematical model pinpointing the hemifusion diaphragm (HD) as the decision nexus dictating the outcomes of pathways and the fate of final products during multivalent cation-mediated membrane interactions. Transient formation of a high-tension hemifusion interface between membrane-enclosed compartments underscores the model's prediction of fusion, dead-end hemifusion, or vesicle lysis. This comprehensive framework offers predictive insights into interactions mediated by cationic fusogens within membrane-enclosed compartments. Chapter five offers a unique exploration of writhing contractile rings in fission yeast cell ghosts, resulting from controlled digestion of the cell wall and subsequent membrane permeabilization. This innovative approach unveils the intricate dynamics of contractile rings under exceptional circumstances. Writhing of rings is attributed to the detachment of sections from the weakened membrane, followed by their coiling due to apparent twisting torques at anchoring points. Iterative rotations give rise to multiple coils within the rings.

This work describes the synthesis pathways to the development of optically and thermally responsive nanovalves with fast response times in nanoporous membranes. As an approach, we developed synthesis pathways to couple a thermally responsive polymer with metallic nanoparticles and build a nanocomposite that synergizes the capability of metallic nanoparticles to convert light into heat, and the fast thermal response exhibited by the polymeric material. In addition, we developed a technique to immobilize the synthesized nanocomposite to the surface of nanoporous membranes, which allowed building valves with light and heat triggering responses. This dissertation describes two syntheses pathways developed to produce optically and thermally responsive nanocomposites by coupling metallic nanoparticles, gold and silver, with a thermally responsive polymer, p-N-isopropyl acrylamide (PNIPAM). The coupling is achieved by using PNIPAM as a capping and nucleating agent in the in situ redox reaction of a silver salt with sodium borohydride, and using PNIPAM as a capping and stabilizing agent in the redox reaction of a gold salt with ascorbic acid. The size and shape of the nanoparticles were controlled and the synthesized nanocomposites exhibit “cocoon-like” structures due to the PNIPAM surrounding the metal nanoparticles, giving the capability to aggregate and resolubilize, through many thermal (shown for gold and silver nanocomposites) and optical (shown by exposing to 532 nm wavelength low-power lasers) cycles. The steady state and dynamic heat conduction of the heat generated from the particles was modeled and the results agreed with the observed optical switching at our experimental conditions. Finally, a method to incorporate nanocomposites into nanoporous membranes (NPM) was developed. It involved prior immobilization of PNIPAM through plasma-induced grafting, followed by a reduction in situ of a metallic salt. The composite NPMs showed thermal responses and through simulation of heat conduction within the pores using the model developed in this work we were able to conclude that the synthesized composite membranes will exhibit optical switching when exposed to focused low power lasers. The nanovalves developed in this work have potential applications as optothermally responsive valves for the spatio-temporal delivery of bioactive agents, cell array, and advanced cell culture systems. / text

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Nanoscale visualisation of live cells and cellular components under physiological conditions has long been a goal in microscopy. The objective of this study was to validate the use of Atomic Force Microscopy (AFM) as a new tool in unravelling the mysteries of antimicrobial peptide mechanism of action. Using the simplest AFM imaging technique, we were able to analyse the influence of haemolytic melittin and anti-bacterial magainin 2 on different target membranes at nanometer resolution, without using fixing agents. First, magainin 2 was synthesised and purified by gel permeation chromatography and high performance liquid chromatography (HPLC). The purity of magainin 2 and melittin, isolated from bee venom (Sigma-Aldrich), was verified with electro spray ionisation mass spectrometry (ESI-MS). Second, dose-response experiments were used to determine the optimum peptide/target cell ratio that would allow interaction with the membrane without causing lysis. Third, peptide/target-cell samples were placed on silica plates and visualised using contact mode AFM. Images obtained of the cells before and after peptide treatment, showed distinct changes in cell membrane surface topology. We observed grooves, lesions, membrane collapse and vesiculation depending on the concentration, type of peptide and target-cell used, allowing us to make conclusions regarding the mechanism of action of melittin and magainin 2. In comparison with model membrane studies, our AFM results show that a peptide can function by more than one mechanism of action depending on the structural composition of the membrane, which appears to have specific segregated lateral organisation. Magainin 2 (non-toxic) selectively targets cell membranes using different mechanisms of action. In this way it can lyse bacterial membranes (anti-bacterial agent) using one mechanism, while using another mechanism to interact with mammalian cells at physiological concentrations, without destroying them. In contrast, melittin (toxic) is non-selective, and uses the same mechanism of interaction with bacterial and mammalian cells. In conclusion, we propose a new holistic model for the mechanism of action of antimicrobial peptides. / AFRIKAANSE OPSOMMING: Nanoskaal visualiseering van lewende selle en sellulêre komponente onder fisiologiese toestande is al 'n geruime tyd 'n mikpunt in mikroskopie. Die doel van hierdie studie was om antimikrobiese peptiede se meganisme van werking op teikenselle op nanoskaalvlak met AFM te visualiseer. Sonder om fikseermiddels by te voeg, het ons die eenvoudigste AFM tegniek gebruik om die effek van hemolitiese melittien en anti-bakteriële magainin 2 op verskillende teikenselle, in nanometer resolusie, waar te neem. Eerstens is Magainin 2 gesintesiseer en gesuiwer met behulp van gelpermeasie chromatografie en hoë doeltreffenheid vloeistof chromatografie (HPLC). Die suiwerheid van magainin 2 en kommersiële bye gif melittien, is bevestig met behulp van elektrosproei-ionisasie massaspektrometrie (ESI-MS). Tweedens, is dosis-respons eksperimente gebruik om die optimale peptied/teikensel verhouding te bepaal voordat membraanliese plaasvind. Derdens, is peptied/teikensel monsters op silika plate gevisualiseer met gebruik van kontak AFM. Die beelde van die selle, voor en na peptied behandeling, het duidelike veranderinge in seltopologie getoon. Ons het groewe, letsels, membraaninstorting en vesikulasie, afhangende van die konsentrasie peptied en teikensel gebruik, waargeneem. Dit het ons toegelaat om tot gevolgtrekkings te kom aangaande die meganisme van werking van melittien en magainin 2. In ooreenstemming met model membraan studies, het ons AFM resultate gewys dat 'n peptied veelvoudige meganismes van werking kan hê, afhangend van die strukturele samestelling van die membraan, wat klaarblyklik laterale segregasie toon. Magainin 2 (nie-giftig) is selektief ten opsigte van teikenselle omdat dit gebruik maak van verskillende meganismes van werking op bakteriële en soogdier selle. In teenstelling is melittien (giftig) nie-selektief, en gebruik dieselfde meganisme van werking op bakteriële en soogdierselle. Ten slotte, stel ons 'n nuwe model vir die meganisme van werking voor.

Two photon microscopy is one of the fastest growing methods of in-vivo imaging of the brain. It has the capability of imaging structures on the scale of 1μm. At this scale the wavelength of the imaging field (usually near infra-red), is comparable to the size of the structures being imaged, which makes the use of ray optics invalid. A better understanding is needed to predict the result of introducing different media into the light path. We use Wolf's integral, which is capable of fulfilling these needs without the shortcomings of ray optics. We predict the effects of aberrating media introduced into the light path like glass cover-slips and then correct the aberration using the same method. We also create a method to predict aberrations when the interfaces of the media in the light-path are not aligned with the propagation direction of the wavefront. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

Biological cells and subcellular organelles are surrounded by membranes to form compartments performing specialized functions. Adsorption or partitioning of biologically active compounds into the membrane is the first step in the process of modification of cell function. This work is concerned with the problem of distribution of charged molecules between water and electrically charged membrane surface and between water and octanol. Part I of this thesis is focused on the electrostatic interactions taking place between charges on the membrane and ions present in the aqueous region of the membrane/water interface. The objective was to explore theoretically the origin of anomalous behavior of Ruthenium Red (RuR), a positively charged hexavalent ion. It was discovered in studies of RuR adsorption to negatively charged membranes that within the framework of the Gouy-Chapman theory of the membrane/water interface, RuR behaves as an ion with effective charge less than its physical charge. Moreover, the effective charge was found to be dependent on the density of electric charge at the membrane surface. Two theoretical models of the interfacial region were examined: the Rod Model and the Maximum Density Model. The Rod Model takes into account steric constraints imposed on RuR at the vicinity of the membrane surface. The Maximum Density Model attempts to account for non-ideal behavior by including repulsive interactions. These theoretical studies illustrate the consequences of finite size and ion-ion interactions of adsorption of large molecular ions to electrically charged membrane surfaces. Part II is an experimental study whose objective was to determine the partition coefficient of the negatively charged 2,3,4,5-tetrachlorophenol (TeCP) between water and octanol. The study was based on spectrophotometric measurements of the equilibrium concentrations of TeCP in water and octanol as a function of pH. The octanol/water partition coefficient for both the non-ionized and ionized species of TeCP were determined. It was found that the partition coefficient of ionized TeCP to lipid membrane is about 400 times greater than that for octanol. This result supports the hypothesis that the octanol/water partition coefficient of ionized chlorophenols cannot be used for predicting their distribution between water and lipid-bilayercontaining elements of the environment.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 128-145).

Orientador: Eneida de Paula / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-12T15:46:25Z (GMT). No. of bitstreams: 1 Paula_Eneidade_D.pdf: 7752367 bytes, checksum: 4ac3295742d441a15e315a3d1c9c2c3d (MD5) Previous issue date: 2009 / Resumo: Detergentes constituem uma das ferramentas mais importantes no estudo de membranas biológicas. A eficiência de um detergente em solubilizar biomembranas e suas proteínas depende de suas propriedades físico-químicas e a solubilização parcial pode resultar em membranas resistentes a detergentes (DRMs). A resistência a detergentes dessas frações membranares constituídas principalmente de colesterol, esfingolipídios e proteínas específicas foi analisada nesse trabalho, usando membranas de eritrócitos humanos. Embora não haja evidências experimentais suficientes pra afirmar que DRMs correspondam aos microdomínios naturais existentes em biomembranas, conhecidos como lipid rafts e que também são enriquecidos em colesterol e esfingolipídios, DRMs são bons modelos para o estudo daqueles. A obtenção de DRMs com uso do detergente octaetilenoglicol mono lauril éter (C12E8) a baixa temperatura (4oC) é descrita pela primeira vez. Os detergentes zwiteriônicos ASB-14, ASB-16 e CHAPS também foram testados, mas falharam no isolamento de DRMs com baixa densidade. DRMs obtidas com C12E8 e com Triton X-100 apresentaram um aumento da razão colesterol/proteína de pelo menos três vezes em relação à membrana original. A proteína flotilina-2, considerada um marcador de lipid rafts, foi detectada em DRMs isoladas com Triton X-100 e em DRMs com C12E8 isoladas a partir de células depletadas de colesterol. Proteínas do citoesqueleto também foram encontradas em DRMs, exceto quando as células foram previamente depletadas de colesterol. Resultados de ressonância paramagnética eletrônica com uso de marcadores de spin do tipo doxil-estearato revelaram maior grau de organização das cadeias acila dos lipídios de DRMs em relação à membrana original, independentemente do detergente utilizado. Nossos resultados também mostraram que DRMs de eritrócitos podem ser também obtidos na temperatura fisiológica (37°C) como mesmo conteúdo de colesterol presente em DRMs isoladas a 4°C. A necessidade do uso de carbonato de sódio no protocolo para obtenção de DRMs sugere fortemente a existência de uma associação eletrostática entre DRMs e o citoesqueleto eritrocitário. / Abstract: Detergents constitute an important tool for the study of cell membranes. The solubilization efficiency of a specific detergent depends upon its physicochemical properties so that detergent-resistant membranes (DRMs) can be obtained as a result of the partial solubilization of biological membranes. In this study DRMs which are structures enriched in cholesterol, sphingolipids and specific proteins, were isolated and characterized from human erythrocyte membranes. Although there are no evidences to support that DRMs correspond to the natural existing microdomains of natural membranes, known as lipid rafts which are also cholesterol and sphingolipid-enriched structures, DRMs are good models for the study of rafts. DRMs from erythrocytes obtained with 8 polyoxyethylene lauryl ether (C12E8) at low temperature (4oC) are described here for the first time. The zwitterionic detergents ASB-14, ASB-16 and CHAPS failed to isolate these low buoyant density fractions. Triton X-100 and C12E8 DRMs presented a cholesterol/protein mass ratio 3 times higher than in the whole membrane. Flotillin-2, a marker of lipid rafts, was confined within the DRM fractions obtained with Triton X-100 and it was partially associated with C12E8 DRMs when erythrocyte cells were previously cholesterol-depleted. Association of membrane-skeleton proteins with DRMs was also observed, except when DRMs were prepared from cholesterol-depleted cells. Results of electron paramagnetic resonance through the use of doxyl stearate spin labels revealed that DRMs are highly ordered structures in respect to the original membrane and that their acyl chain packing is not different if prepared with either Triton X-100 or C12E8. We have also found that DRMs from erythrocytes can be isolated at physiological temperature (37°C), presenting the same cholesterol content as in DRMs prepared at 4°C. The fact that we were only able to prepare DRMs when sodium carbonate was used stronglysuggests the existence of an electrostatic association between DRMs and the membrane-skeleton. / Doutorado / Bioquimica / Doutor em Biologia Funcional e Molecular

Lipossomos de cloreto de dioctadecildimetilamonio (DODAC) com 0,51µ de diâmetro externo médio e transição de fase ocorrendo em uma faixa estreita de temperaturas (0,5-1,0°C) foram obtidos por vaporização de clorofórmio e comparados com vesículas sonicadas de DODAC (cerca de 250 Å de diâmetro externo). Sacarose foi impermeante através de lipossomos grandes de DODAC ou de vesículas sonicadas de DODAC podendo ser utilizada para determinações de volume interno em ambas as preparações. Volume interno aparente para lipossomos grandes de DODAC foi 9,7 ± 1,3 1/mol e para vesículas sonicadas de DODAC, 0,33 ± 0,20 1/mol (adsorção de sacarose à bicamada de, respectivamente, 0,64 ± 0,30 e 0,20 ± 0,08 1/mol). Lipossomos grandes de DODAC comportaram-se como osmômetros em relação à sacarose e ao KCl (0-50mM KCl). Já as vesículas sonicadas de DODAC foram osmoticamente não-responsivas em relação à sacarose, floculando em presença de KCl. Essa não-responsividade osmótica foi interpretada como decorrente da presença única e exclusiva de água de hidrataçao no compartimento aquoso interno das vesículas sonicadas. Outras propriedades de lipossomos grandes de DODAC foram análogas às apresentadas por lipossomos de fosfolípides. Permeabilidades relativas (KCl como referência incorporado ao compartimento aquoso interno) do NaCl, HCl e sacarose foram similares às descritas para lipossomos de fosfatidilcolina; NaCl e sacarose sendo tão impermeantes quanto o KCl e HCl, sendo ligeiramente mais permeante que o KCl. Nas vizinhanças da temperatura de transição de fase, ocorreu um acentuado aumento da velocidade inicial de encolhimento e a extensão total de encolhimento chegou a um mínimo. A comparaçao de algumas propriedades físicas e funcionais de vesículas sonicadas e de lipossomos grandes de DODAC permitiu concluir que lipossomos grandes de DODAC constituem um modelo mais adequado para estudos de transporte. Adicionalmente, o método de vaporização de clorofórmio foi testado para o dihexadecilfosfato de Na+ (DCP) sendo obtidas dispersões homogêneas desse anfifílico capazes de incorporar um volume de 13 ± 4 1/mol e de responderem como osmômetros a gradientes osmóticos de sacarose, um soluto que praticamente nao é adsorvido à bicamada de DCP e que resultou impermeante através da mesma. / Dioctadecyldimethylammonium chloride (DODAC) liposomes with 0.51µ mean external diameter and sharp phase transitions were obtained by chloroform vaporization and compared with (small) sonicated DODAC vesicles. Sucrose was impermeant through large DODAC liposomes and sonicated vesicles and was used for internal volume determinations. The apparent internal volumes for large DODAC liposomes and sonicated DODAC vesicles were, respectively, 9.7 ± 1.3 and 0.33 ± 0.20 1/mol. (External sucrose adsorption were, respectively, 0.64 ± 0.30 and 0.20 ± 0.08 l/mol). Ideal osmometer behaviour towards KCl over the 0-50mM concentrations range and towards sucrose were observed only for large DODAC liposomes. Sonicated DODAC vesicles were osmotically non responsive towards sucrose and floculate with KCl. Other properties of large DODAC liposomes closely resembled those of phospholipid liposomes. At temperatures near the phase transition temperature, a steep increase in the initial shrinkage rate and a minimum for the total extent of shrinkage occured. Relative permeabilities (KCl as reference entrapped inside) to NaCl, HCl and sucrose were similar to those of phosphatidyl choline liposomes. NaCl and sucrose were as impermeant as KCl, and HCl slighthly more permeant than KCl. Large DODAC liposomes are proposed as an adequate synthetic membrane model, in contrast to sonicated DODAC vesicles. In addition, the chlroform vaporization method was tested for sodium dihexadecylphosphate (DCP). Large DCP liposomes were demonstrated to be impermeant towards sucrose entrapping 13 ± 4 l/mol and behaving as an osmometer towards this solute.

Lipossomos de cloreto de dioctadecildimetilamonio (DODAC) com 0,51µ de diâmetro externo médio e transição de fase ocorrendo em uma faixa estreita de temperaturas (0,5-1,0°C) foram obtidos por vaporização de clorofórmio e comparados com vesículas sonicadas de DODAC (cerca de 250 Å de diâmetro externo). Sacarose foi impermeante através de lipossomos grandes de DODAC ou de vesículas sonicadas de DODAC podendo ser utilizada para determinações de volume interno em ambas as preparações. Volume interno aparente para lipossomos grandes de DODAC foi 9,7 ± 1,3 1/mol e para vesículas sonicadas de DODAC, 0,33 ± 0,20 1/mol (adsorção de sacarose à bicamada de, respectivamente, 0,64 ± 0,30 e 0,20 ± 0,08 1/mol). Lipossomos grandes de DODAC comportaram-se como osmômetros em relação à sacarose e ao KCl (0-50mM KCl). Já as vesículas sonicadas de DODAC foram osmoticamente não-responsivas em relação à sacarose, floculando em presença de KCl. Essa não-responsividade osmótica foi interpretada como decorrente da presença única e exclusiva de água de hidrataçao no compartimento aquoso interno das vesículas sonicadas. Outras propriedades de lipossomos grandes de DODAC foram análogas às apresentadas por lipossomos de fosfolípides. Permeabilidades relativas (KCl como referência incorporado ao compartimento aquoso interno) do NaCl, HCl e sacarose foram similares às descritas para lipossomos de fosfatidilcolina; NaCl e sacarose sendo tão impermeantes quanto o KCl e HCl, sendo ligeiramente mais permeante que o KCl. Nas vizinhanças da temperatura de transição de fase, ocorreu um acentuado aumento da velocidade inicial de encolhimento e a extensão total de encolhimento chegou a um mínimo. A comparaçao de algumas propriedades físicas e funcionais de vesículas sonicadas e de lipossomos grandes de DODAC permitiu concluir que lipossomos grandes de DODAC constituem um modelo mais adequado para estudos de transporte. Adicionalmente, o método de vaporização de clorofórmio foi testado para o dihexadecilfosfato de Na+ (DCP) sendo obtidas dispersões homogêneas desse anfifílico capazes de incorporar um volume de 13 ± 4 1/mol e de responderem como osmômetros a gradientes osmóticos de sacarose, um soluto que praticamente nao é adsorvido à bicamada de DCP e que resultou impermeante através da mesma. / Dioctadecyldimethylammonium chloride (DODAC) liposomes with 0.51µ mean external diameter and sharp phase transitions were obtained by chloroform vaporization and compared with (small) sonicated DODAC vesicles. Sucrose was impermeant through large DODAC liposomes and sonicated vesicles and was used for internal volume determinations. The apparent internal volumes for large DODAC liposomes and sonicated DODAC vesicles were, respectively, 9.7 ± 1.3 and 0.33 ± 0.20 1/mol. (External sucrose adsorption were, respectively, 0.64 ± 0.30 and 0.20 ± 0.08 l/mol). Ideal osmometer behaviour towards KCl over the 0-50mM concentrations range and towards sucrose were observed only for large DODAC liposomes. Sonicated DODAC vesicles were osmotically non responsive towards sucrose and floculate with KCl. Other properties of large DODAC liposomes closely resembled those of phospholipid liposomes. At temperatures near the phase transition temperature, a steep increase in the initial shrinkage rate and a minimum for the total extent of shrinkage occured. Relative permeabilities (KCl as reference entrapped inside) to NaCl, HCl and sucrose were similar to those of phosphatidyl choline liposomes. NaCl and sucrose were as impermeant as KCl, and HCl slighthly more permeant than KCl. Large DODAC liposomes are proposed as an adequate synthetic membrane model, in contrast to sonicated DODAC vesicles. In addition, the chlroform vaporization method was tested for sodium dihexadecylphosphate (DCP). Large DCP liposomes were demonstrated to be impermeant towards sucrose entrapping 13 ± 4 l/mol and behaving as an osmometer towards this solute.