Spontaneously formed unilamellar vesicles with path-dependent size distribution

We observe the spontaneous formation of path-dependent monodisperse and polydisperse phospholipid unilamellar vesicles (ULV) from two different equilibrium morphologies specifically, disklike micelles and extended lamellae, respectively. On heating beyond a temperature Tc, low temperature disklike micelles, or so-called bicelles, transform into lamellae. Dilution of the lamellar phase, at a fixed temperature, results in a complete unbinding transition and the formation of polydisperse ULV, demonstrating the instability of the lamellar phase. On the other hand, heating of a dilute bicellar phase above Tc results in monodisperse ULV, which on cooling revert back to bicelles for lipid concentrations phi > or = 0.5 wt % and transform into oblate ellipsoids for phi = 0.1 wt %, a morphology not previously seen in "bicellar" lipid mixtures. Monodisperse ULV reform on heating of the oblate ellipsoids.     

Amperometric biosensor based on reductive H2O2 detection using pentacyanoferrate-bound polymer for creatinine determination

Pentacyanoferrate-bound poly(1-vinylimidazole) (PVI[Fe(CN)₅]) was selected as a mediator for amperometric creatinine determination based on the reductive H₂O₂ detection. Creatinine amidohydrolase (CNH), creatine amidohydrolase (CRH), sarcosine oxidase (SOD), peroxidase (POD), and PVI[Fe(CN)₅] were crosslinked with poly(ethylene glycol) diglycidyl ether (PEGDGE) on a glassy carbon (GC) electrode for a creatinine biosensor fabrication. Reduction current was monitored at −0.1 V in the presence of creatinine and O₂. It is revealed that PVI[Fe(CN)₅] is suitable as a mediator for a bioelectrocatalytic reaction of POD, since PVI[Fe(CN)₅] neither reacts with reactants nor works as an electron acceptor of SOD. The amounts of PVI[Fe(CN)₅], PEGDGE, and enzymes were optimized toward creatinine detection. Nafion as a protecting film successfully prevented the enzyme layer from interferences. The detection limit and linear range in creatinine determination were 12 μM and 12–500 μM (R² = 0.993), respectively, and the sensitivity was 11 mA cm⁻² M⁻¹, which is applicable for urine creatinine tests. The results of the creatinine determination for four urine samples measured with this proposed method were compared with Jaffe method, and a good correlation was obtained between the results.     

Influence of cholesterol on the bilayer properties of monounsaturated phosphatidylcholine unilamellar vesicles

The influence of cholesterol on the structure of unilamellar-vesicle (ULV) phospholipid bilayers is studied using small-angle neutron scattering. ULVs made up of short-, mid- and long-chain monounsaturated phospholipids (diCn :1PC, n = 14 , 18, 22, respectively) are examined over a range (0-45mol %) of cholesterol concentrations. Cholesterol's effect on bilayer structure is characterized through changes to the lipid's transmembrane thickness, lateral area and headgroup hydration. For all three lipids, analysis of the experimental data shows that the addition of cholesterol results in a monotonic increase of these parameters. In the case of the short- and mid-chain lipids, this is an expected result, however, such a finding was unexpected for the long-chain lipid. This implies that cholesterol has a pronounced effect on the lipid's hydrocarbon chain organization.     

Concentration-independent spontaneously forming biomimetric vesicles

In this Letter we present small-angle neutron scattering data from a biomimetic system composed of the phospholipids dimyristoyl and dihexanoyl phosphorylcholine (DMPC and DHPC, respectively). Doping DMPC-DHPC multilamellar vesicles with either the negatively charged lipid dimyristoyl phosphorylglycerol (DMPG, net charge -1) or the divalent cation, calcium (Ca2+), leads to the spontaneous formation of energetically stabilized monodisperse unilamellar vesicles whose radii are concentration independent and in contrast with previous experimental observations.     

Control of circular-disk stability with membrane stresses

Membrane stresses alter the dynamic behavior and stability of circular-disk elements, such as circular saws and grinding wheels, by shifting the disk's natural frequency spectrum. Such shifts are directly related to variation in the critical rotation speed at which standing-wave-resonance instability occurs. Negative critical-speed variations reduce the disk stability, and positive critical-speed variations increase stability. The present paper theoretically and experimentally investigates the relationship between the state of disk-membrane stress, critical rotation speed, and the frequency spectrum in radially symmetric disk problems. The observed critical-speed variations are theoretically predictable and well understood. The approach of a shifting critical-speed instability can be predicted by monitoring the disk-frequency spectrum.     

Properties of reactively sputtered Mo1−x O x films

Molybdenum oxide (Mo_1–xO_x) films were prepared by reactive rf sputtering of a Mo target in O₂/Ar plasma. The dependence of film properties on various sputtering parameters is investigated. The atomic percentage of oxygen (x) in the Mo_1–xO_x films decreases with sputtering power and increases with the partial pressure of oxygen. Mo_1–xO_x films that exhibit metallic conductivities can be obtained over a wide range of sputtering conditions. The intrinsic film stress of conducting Mo_1–xO_x is compressive. Such M_1–xO_x films were shown by backscattering spectrometry to be excellent diffusion barriers between Al and Si up to 600 °C annealing for 30 min.     

Spontaneously Forming Unilamellar Phospholipid Vesicles

Unilamellar vesicles (ULV) consisting of a single lipid bilayer are of special interest as drug delivery vehicles. Here, we report on a spontaneously forming ULV system composed of the short- and long-chain phospholipids, dihexanoyl (DHPC) and dimyristoyl (DMPC) phosphorylcholine, respectively, doped with the negatively charged lipid, dimyristoyl phosphorylglycerol (DMPG). Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) were employed to systematically investigate the effects of lipid concentration, salinity, and time on vesicle stability. It is found that ULV size is practically constant over a range of lipid concentration and temperature. The spontaneously formed ULV are stable for periods of four months, or greater, without the use of stabilizers.     

Spontaneously forming ellipsoidal phospholipid unilamellar vesicles and their interactions with helical domains of saposin C

We have observed a bimodal distribution of ellipsoidal unilamellar vesicles (ULVs) in a phospholipid mixture composed of dioleoyl phosphatidylserine (DOPS) and dipalmitoyl and dihexanoyl phosphatidylcholine, DPPC and DHPC, respectively. Dynamic light scattering and transmission electron microscopy data indicate a bimodal size distribution of these nanoparticles with hydrodynamic radii of approximately 200 and >500 nm, while small-angle neutron scattering data were fit using a model of coexisting monodisperse morphologies, namely, oblate and triaxial ellipsoidal vesicles. Unlike DOPS ULV formed by sonication, which can fuse days after being formed, these ULVs are stable over a period of 12 months at 4 degrees C. We also report on the structure of these ULVs associated with the two helical peptide domains (H1 and H2) of a glucosylprotein, namely, Saposin C, to gain some insight into protein-membrane interactions.     

Facile self-assembly of porphyrin-embedded polymeric vesicles for theranostic applications

A robust and uniform porphysome, which reveals an efficient photodynamic therapy and contrast-enhanced ultrasonic imaging for theranostic applications, can be fabricated from a 4-armed porphyrin-polylactide conjugate.     

Effect of cations on the structure of bilayers formed by lipopolysaccharides isolated from Pseudomonas aeruginosa PAO1

The asymmetric outer membrane of Gram-negative bacteria contains lipopolysaccharides (LPSs) which contribute significantly to the bacterium's surface properties and play a crucial role in regulating membrane permeability. We report on neutron diffraction studies performed on aligned, self-assembled bilayers of Na-, Ca-, and Mg-salt forms of LPS isolated from Pseudomonas aeruginosa PAO1. From the one-dimensional neutron scattering length density profiles we find that water penetrates Ca2+-LPS bilayers to a lesser extent than either Na+- or Mg2+-LPS bilayers. This differential water penetration could have implications as to how small molecules permeate the outer membrane of Gram-negative bacteria and, possibly, how nonlamellar phases are formed.