Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session F16: Membranes, Vesicles and Miscelles II |
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Sponsoring Units: GSOFT Chair: Elizabeth Mann, Kent State University Room: 275 |
Tuesday, March 14, 2017 11:15AM - 11:27AM |
F16.00001: A Theoretical Study on the Morphological Phase Diagram of Supported Lipid Bilayers. Xian Kong, Diannan Lu, Zheng Liu, Jianzhong Wu Supported lipid bilayers (SLBs) are widely used in drug delivery, biosensors and biomimetic membranes. The microscopic mechanism of SLB formation and stability is complicated, depending on various factors underlying solvent-mediated lipid-lipid and lipid-substrate interactions. Whereas recent years have witnessed remarkable progress in SLB formation, relatively little is known about how to control SLB stability under diverse solution conditions for broader SLB usage and rational design. In this work, we examine SLB stability using a coarse-grained model in combination with the classical density functional theory (DFT) that accounts for ion-explicit electrostatic interactions, surface hydrophobicity, as well as the molecular characteristics of lipid tails. A morphological phase diagram is constructed for model SBLs in terms of various intrinsic properties of lipid molecules (such as lipid tail length, lipid head size and charge of polar head), substrate conditions (such as surface charge density and hydrophobicity), and solution parameters (such as ion concentration, ion type). The morphological phase diagram provides useful insights on the design and screening of SLB membrane for customized applications. [Preview Abstract] |
Tuesday, March 14, 2017 11:27AM - 11:39AM |
F16.00002: Shear-induced lamellar to vesicle transition in DDAB lipids. Subas Dhakal, Radhakrishna Sureshkumar A detailed knowledge of the response of lipid vesicles and lamellar phases to an externally applied stress is essential to understanding many important cellular processes and cell functions. Using molecular dynamics simulations, we study self-assembly and shear flow dynamics of didodecyldimethylammoniumbromide (DDAB) lipids in water. Simulations show various self-assembled structures such as micelles, vesicles and lamellae depending upon the concentration of DDAB. Shear flow simulations show tumbling dynamics of vesicles and shear-induced structure formation resulting from a lamellar to multi-lamellar vesicle transition above a critical shear rate. The role of vesicle shape and imperfections in the lamellar phase on lamellar to vesicle transition will be discussed. \newline [Preview Abstract] |
Tuesday, March 14, 2017 11:39AM - 11:51AM |
F16.00003: Studying Microgel Volume Phase Transition Kiril Streletzky, Janna Mino, Christian Gunder, Krista Freeman Polysaccharide microgels were synthesized with varying amount of surfactant at LCST and at varying temperatures above it. The amount of crosslinker used was also varied. Formed microgels were characterized by coupled static light scattering and polarized/depolarized dynamic light scattering techniques, spectrophotometry, and wet-cell electronic imaging, yielding microgel size distribution, apparent molecular weight, structure, and water content. Synthesized microgels were reasonably monodisperse below the transition with Rh of 90-600 nm, depending on synthesis conditions. Microgels underwent reversible volume phase transition with volume deswelling ratio of 3 to 30, depending on synthesis conditions. The effects of surfactant and crosslinker concentrations, synthesis temperature, and heating rate on volume phase transition were studied experimentally and analyzed with entropy-based thermodynamic model. [Preview Abstract] |
Tuesday, March 14, 2017 11:51AM - 12:03PM |
F16.00004: Programmed release triggered by osmotic gradients in multicomponent vesicles Ruo-Yu Dong, Hyun-Sook Jang, Steve Granick Polymersomes, a good candidate for encapsulation and delivery of active ingredients, can be constructed with inter-connected multiple compartments. These so-called multisomes on the one hand enable the spatial separation of various incompatible contents or processes, and on the other hand provide an efficient route for inter-compartment communication via the interface semipermeable membrane. Here we show that by establishing osmotic imbalances between different compartments, interesting synergetic morphology changes of the multisomes can be observed. And by further carefully adjusting the osmotic gradients and the arrangement of compartments, we can realize a cascade rupture of these individual units, which may be a new step towards controlled mixing and timed sequences of chemical reactions. [Preview Abstract] |
Tuesday, March 14, 2017 12:03PM - 12:15PM |
F16.00005: Effects of "sponge forming" agents on the sponge to cubic transition Annela Seddon, Christopher Brasnett, Adam Squires, Tomas Plivelic The addition of small molecules to the bicontinuous cubic phase formed by certain lipids can lead to the formation of a disordered bicontinuous phase known as the sponge phase and transitions between the sponge and cubic phase are an excellent route to the formation of highly oriented cubic phases. [1,2] There are a number of small molecules identified which can lead to the formation of a sponge phase; small amphiphiles such as butanediol are partition at the head-tail interface of the lipid, reducing the interface curvature until the sponge phase is formed. Alternatively, chaotropes such as KSCN interact with the headgroup of the lipid preferentially to water, increasing the headgroup area of the lipid and causing a flattening of the membrane. We have studied the sponge to cubic transition under shear for sponges formed from butanediol, and KSCN with the lipid monoolein and find that a far more ordered cubic phase is formed when a chaotrope is used to form the sponge. In addition, we show that depending on dilution of the sponge forming agent, transitions between oriented cubic phases and oriented lamellar phases can be achieved, despite the presence of a disordered intermediate. [1] A.M.Seddon et al, J.Am.Chem.Soc., 2011, 133, 13860 [2] T. Oka, Langmuir, 2015, 31, 3180 [Preview Abstract] |
Tuesday, March 14, 2017 12:15PM - 12:27PM |
F16.00006: Effects of PEGylation on Liposome Degradation by a Model Phospholipase Pin Zhang, Veronica Villanueva, Alexander Donovan, Binhua Lin, Wei Bu, Ying Liu Polyethylene glycol (PEG) has been conjugated to phospholipids to form liposomes with longer blood circulation time, since PEG brushes prevent non-specific protein adsorption and help particles escape phagocytosis. Although PEG provides steric repulsions, it also affects lipid packing and liposome stability. We report here liposomes hydrolysis catalyzed by secreted phospholipase A2 (sPLA2), with an emphasis on revealing the contradictory effects of PEG. The kinetics of liposome hydrolysis were studied by dynamic light scattering. We measured the hydrolysis lag times of liposomes by monitoring the changes in size after mixing with different concentrations of sPLA2. The results followed two exponential functions, defining regimes of degradation kinetics. The effects of PEGylation on the packing of the phospholipid monolayers were studied using X-ray reflectivity and grazing incidence diffraction. The packing of phospholipid monolayers was just slightly disturbed with the inclusion of 5-10\% PEGylation (PEG Mw 2000-5000). However, sPLA2 induced hydrolysis of liposomes with higher degrees of PEGylation appeared to be attenuated. In sum, the effects of PEGylation on the protection of lipid assemblies overcomes their disturbance on the lipid packing in the range of our experiments. [Preview Abstract] |
Tuesday, March 14, 2017 12:27PM - 12:39PM |
F16.00007: The effects of melittin on water diffusion and membrane structure in DMPC bilayers Zachary Buck, James Torres, Mengjun Bai, Helmut Kaiser, Haskell Taub, Eugene Mamontov, Liam Collins, Andrew Miskowiec, Flemming Hansen Transmembrane proteins are known to affect the structure of their host membrane; however, it is not fully understood how these proteins could alter the diffusion of water in their vicinity. To elucidate such behavior, we have performed quasielastic neutron scattering (QENS) and atomic force microscopy (AFM) measurements on supported lipid bilayers of DMPC exposed to various concentrations of the well-studied antimicrobial peptide, melittin. On monitoring the incoherent elastic neutron intensity as a function of temperature from such samples, we observe an abrupt freezing transition of the associated water not seen in the bare membrane case. Moreover, the change in elastic intensity of this freezing step increases in proportion to melittin concentration, suggesting that water could be freezing onto membrane-bound melittin. Analysis of the quasielastic spectra collected on BASIS at Oak Ridge National Lab provides evidence that near this transition there is a water component which diffuses more slowly than bulk water. Furthermore, \textit{in situ} AFM studies reveal the formation of dimple-like features on the surfaces of such membranes, which are tentatively interpreted as aggregates of melittin responsible for the perturbations observed in the hydration water dynamics. [Preview Abstract] |
Tuesday, March 14, 2017 12:39PM - 12:51PM |
F16.00008: Structure Study on Microemulsion System with an Ionic Liquid (IL) by Small-Angle Neutron Scattering Tae Hui Kang, Shuo Qian, Gregory S. Smith, Changwoo Do, William T. Heller The self-assembly of IL with a long alkyl chains provides molecular level control on the structure enabling applications, including, creating microemulsion with dual functions of extractant and surfactant. The IL, C14MIMCl is not soluble in alkane solvents, even with the addition of octanol. However, with a small amount of water, a water-in-oil micromemulsion forms, that obeys the swelling law with water content. The mixed surfactant system, C14MIMCl/octanol, has different chemistry and molecular geometries depending on its composition. Through the use of SANS, it is possible to determine the impact of the surfactant system on the structure of the microemulsion, as well as to learn the composition of various regions in the structure. The microemulsion system was studied by dilution with octane from 10 to 70 wt{\%}. A strong intensity peak was observed near 0.1 {\AA}$^{\mathrm{-1}}$, and the stable phase shows a structural transition at 30 wt{\%} octane. Contrast variation experiments were done with d-octane and h-octane to understand the structure of the microemulsion, as well as the structural transition. Further, systematic concentration studies of surfactant at constant water-to-oil molar ratio and of water at constant 30 wt{\%} surfactant were performed. [Preview Abstract] |
Tuesday, March 14, 2017 12:51PM - 1:03PM |
F16.00009: Membrane viscosity of surfactant and lipid bilayers measured by neutron spin echo Michihiro Nagao, Elizabeth Kelley, Robert Bradbury, Rana Ashkar, Paul Butler Membrane viscosity, $\mu$, is a fundamental property of surfactant and lipid bilayers that determines the rate at which the membrane deforms and particles can diffuse through the membrane. Given its importance, several experimental methods have been suggested to determine $\mu$, such as measuring the diffusion of lipid or tracer molecules in membranes or using a microfluidic technique to determine the two-dimensional velocity field slices. Here we calculate $\mu$ from measurements of the thermal undulation and thickness fluctuations using neutron spin echo (NSE) spectroscopy, as these motions are controlled by elastic and viscous properties of the membranes. Combining the NSE results with small-angle neutron scattering measurements to estimate the bilayer thickness, we determine $\mu$ together with the bending and area compressibility moduli of the membranes. We demonstrate the present method for lipid and oil-swollen surfactant bilayers. These membranes have orders of magnitude different elastic constants, and the values of $\mu$ extracted from the experiments span 0.01 to 50 nPa s m, which agree with some literature values. [Preview Abstract] |
Tuesday, March 14, 2017 1:03PM - 1:15PM |
F16.00010: Analysis of membrane thickness fluctuations as a local mode Robert Bradbury, Michihiro Nagao The mechanical properties of surfactant membranes have been a focus of work to further understand mechanisms of self-assembly. Indeed, the dynamics of the membranes are controlled by these properties. Neutron spin echo spectroscopy (NSE) has been used to probe membrane undulation and thickness fluctuation dynamics since the technique is sensitive to the length and time scale of these membranes. While quantitative treatment of the undulation fluctuations has been well served by application of a model devised by Zilman and Granek, an asymmetric bilayer model proposed by Bingham, Smye and Olmsted, is known to describe membrane thickness fluctuations in solution. This model predicts peristaltic fluctuations to exist as a local mode when the fluctuation wavelengths are relatively short. Here, we use this concept to analyze the NSE data in an oil-swollen surfactant bilayer. The results are compared with a currently used empirical method and a comparison of the calculated parameters displays a strong correlation between the present and the empirical methods for the values of thickness fluctuation relaxation rate and amplitude. [Preview Abstract] |
Tuesday, March 14, 2017 1:15PM - 1:27PM |
F16.00011: Formation and characterization of artificial lipid bilayers on optical fibers Pauline Toussaint, Laurent Dreesen Transports across cellular membranes are at the basis of a lot of biological processes such as the transmission of information in neurons. Their characterization is therefore of crucial interest. As they are equivalent to biological membranes, artificial lipid bilayers can be created to study membranes and transmembrane proteins properties or transmembrane transports. The aim of this work is to develop a new method for the fabrication of artificial membranes, based on the use of optical fibers as support for the bilayer, and for their characterization by fluorescence measurements. We use microfluidics on fibers to create two phospholipid monolayers that we approach close enough to form a bilayer. The membrane formation is checked using fluorescein or a fluorescent sodium probe, Tetra (tetramethylammonium) salt (sodium green), whose optical signal depends on sodium concentration. [Preview Abstract] |
Tuesday, March 14, 2017 1:27PM - 1:39PM |
F16.00012: Effect of hydrodynamic interactions on quasi two-dimensional reaction rates Naomi Oppenheimer, Howard Stone The Brownian motion of two particles in three dimensions serves as a model for predicting the diffusion-limited reaction rate as first discussed by Smoluchowski (1916). Deutch and Felderhof (J. Chem. Phys., 1973) extended the calculation to account for hydrodynamic interactions between the particles and the target, which results in a reduction of the rate coefficient by about half. Many chemical reactions take place in quasi two-dimensional systems, such as on the membrane or surface of a cell. We perform a Smoluchowski-like calculation in a quasi two-dimensional geometry, i.e. a membrane surrounded by fluid, and account for hydrodynamic interactions between the particles. We show that rate coefficients are reduced relative to the case of no interactions. The reduction is more pronounced than the three-dimensional case due to the long range nature of two-dimensional flows. [Preview Abstract] |
Tuesday, March 14, 2017 1:39PM - 1:51PM |
F16.00013: Spreading of dispersions of lipid nanoparticles on hydrophobic and superhydrophobic surfaces Guruswamy Kumaraswamy, Manoj Kumar, Mayuresh Kulkarni, CG Narendiran, Ashish Orpe, Arun Banpurkar Glycerol monooleate is a hydrophobic lipid that exhibits a rich phase behavior. At high water concentrations, it organizes to form a bicontinuous phase with Pn3m symmetry that is stable with excess water. It is therefore possible to obtain stable aqueous dispersions of polymer stabilized, lipid nanoparticles with internal Pn3m symmetry. Such particles, termed cubosomes, can carry payloads of both hydrophobic as well as hydrophilic molecules and hold promise for delivery of pharmaceuticals, agrochemicals, etc. We describe the behaviour of aqueous drops of cubosome dispersions as they impinge on hydrophobic and superhydrophobic surfaces. On impingement, the spreading of these drop is similar to that of water drops. However, while water drops retract and rebound from the surface, cubosome dispersions do not retract. We demonstrate that this can be attributed to rapid adsorption of cubosomes on the surface and their reorganization to form a thin, approximately 3 nm layer on the substrate. Remarkably, we show that while drops of water roll off inclined superhydrophobic lotus leaf surfaces, drops of cubosome dispersions do not. These results have implications for the delivery of agrochemicals to plant surfaces. [Preview Abstract] |
Tuesday, March 14, 2017 1:51PM - 2:03PM |
F16.00014: Soaking it up: new lipid sponge phases and their applications Christopher Brasnett, Annela Seddon Recent work has demonstrated that cubic lipid systems may be doped with charged lipids, with important consequences for their physical properties. Among others, Tyler et al. have reported some of the largest lipid cubic phases seen to date using this technique\footnote{A. Tyler et al. \textit{Soft Matter}, \textbf{2015}, 11, 3279-3286}. The sponge phase is a disordered bicontinuous phase, formed when the membrane curvature of a cubic phase is reduced through the addition of butane diol\footnote{V. Cherezov et al. \textit{J. Mol. Biol.} \textbf{2006} 357, 1605-1618}. Additionally, it is known that sponge phases may be converted back into highly ordered cubic ones\footnote{A. Seddon et al, \textit{J. Am. Chem. Soc.}, \textbf{2011}, 133, 13860}. Whilst past work has concentrated on sponge phases formed from monoolein, we have investigated the properties and behaviour of a bipartite sponge phase formed of monoolein and DOPG, and their conversion to cubic phases using shear. Furthermore, as both the sponge and cubic phase are of interest with respect to their applications in protein crystallography\footnote{A. W{\"o}hri et al. \textit{Structure} \textbf{2008}, 16, 1003-1009}, we have explored the interaction of the protein light-harvesting complex with the lipid system. [Preview Abstract] |
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