Hybrid and Nonhybrid Lipids Exert Common Effects on Membrane Raft Size and Morphology

Frederick A. Heberle *†, Milka Doktorova ‡#, Shih Lin Goh ‡, Robert F. Standaert †§, John Katsaras†, and Gerald W. Feigenson *‡

†Biology and Soft Matter and §Biosciences Divisions,Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States

‡Department of Molecular Biology and Genetics and#Tri-Institutional Training Program in Computational Biology and Medicine, Cornell University, Ithaca, New York 14853, United States

Departments of Biochemistry and Molecular & Cellular Biology and Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996,United States

 Joint Institute for Neutron Sciences, Oak Ridge, Tennessee 37831, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja407624c

Publication Date (Web): September 16, 2013

Copyright © 2013 American Chemical Society

Nanometer-scale domains in cholesterol-rich model membranes emulate lipid rafts in cell plasma membranes (PMs). The physicochemical mechanisms that maintain a finite, small domain size are, however, not well understood. A special role has been postulated for chain-asymmetric or hybrid lipids having a saturated sn-1 chain and an unsaturated sn-2 chain. Hybrid lipids generate nanodomains in some model membranes and are also abundant in the PM. It was proposed that they align in a preferred orientation at the boundary of ordered and disordered phases, lowering the interfacial energy and thus reducing domain size. We used small-angle neutron scattering and fluorescence techniques to detect nanoscopic and modulated liquid phase domains in a mixture composed entirely of nonhybrid lipids and cholesterol. Our results are indistinguishable from those obtained previously for mixtures containing hybrid lipids, conclusively showing that hybrid lipids are not required for the formation of nanoscopic liquid domains and strongly implying a common mechanism for the overall control of raft size and morphology. We discuss implications of these findings for theoretical descriptions of nanodomains.

Shape Memory and Superelastic Ceramics at Small Scales

Alan Lai1, Zehui Du2, Chee Lip Gan2,3, Christopher A. Schuh1,*

Shape memory materials are a class of smart materials able to convert heat into mechanical strain (or strain into heat) by virtue of a martensitic phase transformation. Some brittle materials such as intermetallics and ceramics exhibit a martensitic transformation but fail by cracking at low strains and after only a few applied strain cycles. Here we show that such failure can be suppressed in normally brittle martensitic ceramics by providing a fine-scale structure with few crystal grains. Such oligocrystalline structures reduce internal mismatch stresses during the martensitic transformation and lead to robust shape memory ceramics that are capable of many superelastic cycles up to large strains; here we describe samples cycled as many as 50 times and samples that can withstand strains over 7%. Shape memory ceramics with these properties represent a new class of actuators or smart materials with a set of properties that include high energy output, high energy damping, and high-temperature usage.

Solid Colloids with Surface-Mobile DNA Linkers

Stef A. J. van der Meulen * and Mirjam E. Leunissen

FOM Institute AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja406226b

Publication Date (Web): September 16, 2013

Copyright © 2013 American Chemical Society

Surface functionalization with bioinspired binding groups is increasingly used to steer nano- and microscale self-assembly processes, with complementary DNA “sticky ends” as one of the most notable examples. The fabrication of well-organized structures is complicated, however, by the sharp association/dissociation transitions and the slow rearrangement kinetics intrinsic to collections of discrete, surface-immobilized binding groups and is aggravated by natural nonuniformities in the surface coating. Here, we demonstrate a novel system of solid microparticles functionalized with specific binding groups—in this case DNA linkers—that are fully mobile along the particle surface. These colloids display qualitatively new behavior and circumvent many of the commonly encountered issues. Importantly, the association/dissociation transition, and thereby the temperature window for equilibrium self-assembly, is much broader. We further find that the linkers are uniformly distributed above the DNA melting temperature, while visibly accumulating at the interparticle contacts below this temperature. The unique combination of binding group mobility with nondeformability, monodispersity, and facile manipulation of solid particles should have a profound impact on DNA-mediated and other bioinspired self-assembly approaches. 

Fatty Acid Chemistry at the Oil−Water Interface: Self-Propelled Oil Droplets

Martin M. Hanczyc ,† Taro Toyota ,‡ Takashi Ikegami ,‡ Norman Packard ,† and Tadashi Sugawara *‡
Contribution from ProtoLife Srl, Parco Vega, Via della Liberta 12, Marghera, Venice 30175, Italy, and Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan

Fatty acids have been investigated as boundary structures to construct artificial cells due to their dynamic properties and phase transitions. Here we have explored the possibility that fatty acid systems also demonstrate movement. An oil phase was loaded with a fatty acid anhydride precursor and introduced to an aqueous fatty acid micelle solution. The oil droplets showed autonomous, sustained movement through the aqueous media. Internal convection created a positive feedback loop, and the movement of the oil droplet was sustained as convection drove fresh precursor to the surface to become hydrolyzed. As the system progressed, more surfactant was produced and some of the oil droplets transformed into supramolecular aggregates resembling multilamellar vesicles. The oil droplets also moved directionally within chemical gradients and exhibited a type of chemotaxis.

Self-Propelled Oil Droplets Consuming “Fuel” Surfactant

Taro Toyota †‡, Naoto Maru †, Martin M. Hanczyc §,Takashi Ikegami  and Tadashi Sugawara *†

Department of Basic Science and Department of General Systems Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan, Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage, Chiba 263-8522, Japan, and Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark

A micrometer-sized oil droplet of 4-octylaniline containing 5 mol % of an amphiphilic catalyst exhibited a self-propelled motion, producing tiny oil droplets, in an aqueous dispersion of an amphiphilic precursor of 4-octylaniline. The tiny droplets on the surface of the self-propelled droplet were conveyed to the posterior surface and released to the aqueous solution. Thus the persistent movement becomes possible in this chemical system, because the processing of chemical energy to mechanical movement proceeds by consuming exogenous fuel, not consuming the oil droplet itself. The mechanism of the unidirectional motion is hypothesized in terms of an asymmetric interfacial tension around the surface of the oil droplet.

Programmed Vesicle Fusion Triggers Gene Expression

Filippo Caschera †, Takeshi Sunami ‡, Tomoaki Matsuura ‡§, Hiroaki Suzuki ‡, Martin M. Hanczyc†, and Tetsuya Yomo *‡

Center for Fundamental Living Technology (FLinT), Institute of Physics and Chemistry, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark

Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency, Yamadaoka 1-5, Suita, Osaka 565-0871

Department of Biotechnology, Graduate School of Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka 565-0871, Japan

Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, and Department of Frontier Biosciences, Graduate School of Frontier Biosciences, Osaka University, Yamadaoka 1-5, Suita, Osaka 565-0871, Japan

The membrane properties of phospholipid vesicles can be manipulated to both regulate and initiate encapsulated biochemical reactions and networks. We present evidence for the inhibition and activation of reactions encapsulated in vesicles by the exogenous addition of charged amphiphiles. While the incorporation of cationic amphiphile exerts an inhibitory effect, complementation of additional anionic amphiphiles revitalize the reaction. We demonstrated both the simple hydrolysis reaction of β-glucuronidase and the in vitro gene expression of this enzyme from a DNA template. Furthermore, we show that two vesicle populations decorated separately with positive and negative amphiphiles can fuse selectively to supply feeding components to initiate encapsulated reactions. This mechanism could be one of the rudimentary but effective means to regulate and maintain metabolism in dynamic artificial cell models.

Liposome, self assembly, Oil i water emulsion

Specific and reversible DNA-directed self-assembly of oil-in-water emulsion droplets

Center for Fundamental Living Technology, Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, 5230 Odense M, Denmark;
and b
Artificial Intelligence Laboratory, Department of Informatics, University of Zurich, 8050 Zurich, Switzerland
Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved October 24, 2012 (received for review August 18, 2012)

Higher-order structures that originate from the specific and reversible DNA-directed self-assembly of microscopic building blocks hold great promise for future technologies. Here, we functionalized biotinylated soft colloid oil-in-water emulsion droplets withbiotinylated single-stranded DNA  oligonucleotides using streptavidin as an intermediary linker. We show the components of this
modular linking system to be stable and to induce sequencespecific aggregation of binary mixtures of emulsion droplets. Three length scales were thereby involved: nanoscale DNA base pairing
linking microscopic building blocks resulted in macroscopic aggregates visible to the naked eye. The aggregation process was reversible by changing the temperature and electrolyte concentration and by the addition of competing oligonucleotides. The system was reset and reused by subsequent refunctionalization of the emulsion droplets. DNA-directed self-assembly of oil-in-water
emulsion droplets, therefore, offers a solid basis for programmable and recyclable soft materials that undergo structural rearrangements on demand and that range in application from information technology to medicine.