Elastometry of Complex Fluid Pendant Capsules

Oil/water interfaces are ubiquitous in nature. Opposing polarities at these interfaces attract surface-active molecules, which can seed complex viscoelastic or even solid interfacial structure. Biorelevant proteins such as hydrophobin, polymers such as PNIPAM, and the asphaltenes in crude oil (CRO) are examples of some systems where such layers can occur. When a pendant drop of CRO is aged in brine, it can form an interfacial elastic membrane of asphaltenes so stiff that it wrinkles and crumples upon retraction. Most of the work studying CRO/brine interfaces focuses on the viscoelastic liquid regime, leaving a wide range of fully solidified, elastic interfaces largely unexplored. In this work, we quantitatively measure elasticity in all phases of drop retraction. In early retraction, the interface shows a fluid viscoelasticity measurable using a Gibbs isotherm or dilatational rheology. Further retraction causes a phase transition to a 2D elastic solid with nonisotropic, nonhomogeneous surface stresses. In this regime, we use new techniques in the elastic membrane theory to fit for the elasticities of these solid capsules. These elastic measurements can help us develop a deeper understanding not only of CRO interfaces but also of the myriad fluid systems with solid interfacial layers.</p

The role of the MEIS homeobox genes in neuroblastoma

We recently found amplification of the TALE homeobox gene MEIS1 in the IMR32 neuroblastoma cell line. We now demonstrate high-level expression of the MEIS1 and MEIS2 genes, as well as efficient expression of most other TALE family member genes in a panel of neuroblastoma cell lines. Stable transfection of MEIS1-expressing cell lines with cDNA encoding a naturally occurring dominant-negative splice variant of MEIS1 (MEIS1E) yielded clones with impaired cell proliferation, gain of differentiated phenotype, and increased contact inhibition and cell death. This indicated a relevance of MEIS expression for neuroblastoma cell growth and proliferation. We therefore determined the gene expression profiles of several MEIS1E transfectants using serial analysis of gene expression (SAGE). A large number of genes showed differential expression as a result of MEIS1E expression. These include genes involved in developmental signalling pathways, chromatin binding, cell cycle control, proliferation, and apoptosis. The results presented provide important clues for the oncogenic function of MEIS1 in neuroblastoma. (C) 2003 Elsevier Science Ireland Ltd. All rights reserve

Membrane Binding of Parkinson's Protein α-Synuclein:Effect of Phosphorylation at Positions 87 and 129 by the S to D Mutation Approach

Human α-synuclein, a protein relevant in the brain with so-far unknown function, plays an important role in Parkinson's disease. The phosphorylation state of αS was related to the disease, prompting interest in this process. The presumed physiological function and the disease action of αS involves membrane interaction. Here, we study the effect of phosphorylation at positions 87 and 129, mimicked by the mutations S87A, S129A (nonphosphorylated) and S87D, S129D (phosphorylated) on membrane binding. Local binding is detected by spin-label continuous-wave electron paramagnetic resonance. For S87A/D, six positions (27, 56, 63, 69, 76, and 90) are probed; and for S129A/D, three (27, 56, and 69). Binding to large unilamellar vesicles of 100 nm diameter of 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine in a 1 : 1 composition is not affected by the phosphorylation state of S129. For phosphorylation at S87, local unbinding of αS from the membrane is observed. We speculate that modulating the local membrane affinity by phosphorylation could tune the way αS interacts with different membranes; for example, tuning its membrane fusion activity

MEIS homeobox genes in neuroblastoma

The common pediatric tumor neuroblastoma originates from primitive neural crest-derived precursor cells of the peripheral nervous system. Neuroblastoma especially affects very young children, and can already be present at birth. Its early onset and cellular origin predict the involvement of developmental control genes in neuroblastoma etiology. These genes are indispensable for the tight regulation of normal embryonic development but as a consequence cause cancer and congenital diseases upon mutation or aberrant expression. To date however, the connotation of these genes in neuroblastoma pathogenesis is scant. This review recapitulates data on the MEIS homeobox control genes in cancer and focuses on neuroblastoma

Wetting of Mineral Surfaces by Fatty-Acid-Laden Oil and Brine: Carbonate Effect at Elevated Temperature

Oil recovery yields from sandstone reservoirs strongly depend on the wetting properties of the rock. Carboxylic acids present in crude oil may decrease the water wettability by adsorbing onto the mineral surface via cation interactions. A highly simplified version of this scenario has been mimicked in the lab to study these mechanisms in more detail. In previous studies on oil/brine/mineral systems the formation of fatty acid monolayers on mica was observed, yielding water contact angles in ambient oil of up to 60°. Here we demonstrate that the presence of 2 mM bicarbonate (typical for brines) has a strong influence at temperatures above 40 °C (as in reservoirs), yielding water contact angles in ambient oil up to 160°. Similar behavior was found for a variety of carboxylic acids. On increasing the (even) carbon number of simple fatty acids from 8 to 20, the contact angle becomes larger until it saturates at 16 carbon atoms. Similar hydrophobic layers are formed by pulling a sheet of mica through an oil/water interface at comparable velocities. By studying the nanometer-scale topography and chemistry of these dip-coated samples, we can infer that the adsorbed layer is composed of alternating carboxylic acid bilayers that are held together by a very thin intermediate layer containing calcium and (bi)carbonate ions. Exposure to low-salinity water makes the multilayers disappear and the mineral surface become water-wet again, demonstrating that the presence of these structures can lead to a strong salinity-dependent wettability alteration

Parkinson's Protein α-Synuclein Binds Efficiently and with a Novel Conformation to Two Natural Membrane Mimics

Binding of human α-Synuclein, a protein associated with Parkinson's disease, to natural membranes is thought to be crucial in relation to its pathological and physiological function. Here the binding of αS to small unilamellar vesicles mimicking the inner mitochondrial and the neuronal plasma membrane is studied in situ by continuous wave and pulsed electron paramagnetic resonance. Local binding information of αS spin labeled by MTSL at positions 56 and 69 respectively shows that also helix 2 (residues 50-100) binds firmly to both membranes. By double electron-electron resonance (DEER) on the mutant spin labeled at positions 27 and 56 (αS 27/56) a new conformation on the membrane is found with a distance of 3.6 nm/ 3.7 nm between residues 27 and 56. In view of the low negative charge density of these membranes, the strong interaction is surprising, emphasizing that function and pathology of αS could involve synaptic vesicles and mitochondria

Salinity-dependent contact angle alteration in oil/brine/silicate systems: The effect of temperature

To understand the success of low salinity water flooding in improving oil recovery, it is important to identify the molecular scale mechanisms that control the wettability and thus the adhesion between oil and rock. Previous experiments have attributed the wettability alteration in core flood experiments either to the expansion of the electric double layer or to multicomponent ion exchange reactions or a combination of both. Here, we explore changes of the contact angle of brine droplets on mica in ambient oil (n-decane plus added fatty acid) at variable temperature as a function of the concentration of mono- and divalent cations. For 20 °C and 40 °C, we find that the contact angle decreases by up to 30° with decreasing divalent cation concentration but remains constant upon decreasing the total salinity by removing only monovalent cations, i.e. upon double layer expansion at constant divalent cation concentration. At 60 °C, we find a remarkable increase of the water contact angle of artificial sea water to values of approximately 120°. This value decreases upon dilution to values in the range of 10-40 °C, where the lowest values are again only obtained upon removing the divalent cations. These findings corroborate the conclusion of earlier measurements at room temperature that divalent cations play an essential role in controlling the wettability of carboxylic acid groups to mineral surface, presumably in an ion bridging type mechanism. We also demonstrate that the contact angle reduction occurs very quickly upon flushing a sessile droplet of artificial sea water with divalent cation-free or simply diluted brine, suggesting fast equilibration as required for a successful tertiary water flooding process. Our experiments also demonstrate that, despite the simplicity of the present system, the origins of wettability alteration are rather complex and that synergistic effects can lead to dramatic variations such as the unexpectedly high contact angle at 60 °C

Parameters of distance distributions for αS27/56 bound to SUVs of IMM and NPM and model membranes for comparison.

<p>Errors in contribution to fraction ±3% (IMM and NPM) and ±2% (POPG SUVs)</p><p>*reanalyzed from ref. (30)</p><p>Parameters of distance distributions for αS27/56 bound to SUVs of IMM and NPM and model membranes for comparison.</p

Formation and stability of heterogeneous organo-ionic surface layers on geological carbonates

Many geological processes from oil recovery to underground CO2storage are affected by natural molecules adsorbed on rock surfaces. Yet, geochemical models tend to overlook their formation and stability, let alone existence. With a suite of analytical techniques, we address this "missing-link" and describe fundamental mechanisms for (i) the deposition of surface-active molecules in complex brines and oils on underground minerals and (ii) the desorption of heterogeneous sorbents and its dependence on aqueous composition. First, we show that organic and inorganic constituents of both formation water and crude oil form an organo-ionic surface layer on calcite. Primary modifiers are revealed as aqueous and nonaqueous polyaromatic molecules with polar and metal-binding functional groups and solubility characteristics of asphaltenes. Formed via π-stacking and ionic and hydrogen bonding interactions, the heterogeneous organo-ionic layer establishes a physical barrier between the mineral and ambient atmosphere/fluid, impacting the dissolution and wettability of rocks. Second, we investigate desorption of the organo-ionic layer in various brines under flow and static conditions. With chromatographic and spectroscopic methods (including Raman and sum-frequency generation), we show that the release of adsorbed material from carbonate surfaces encompasses key coupled reactions: (i) dissolution of "brine-soluble" asphaltenes, leading to relative interfacial enrichment of bulky "brine-insoluble" asphaltenes, (ii) nanoscale orientational changes of surface asphaltene assemblies, carbonate ions, and water molecules at the brine-rock interface, and (iii) dissolution and surface reconstruction of the carbonate mineral. Through these reactions, the "low-salinity effect" is uncovered as a two-stage desorption process: the initial release or selective extraction of "water-soluble" sorbents and subsequent delamination of residual "water-insoluble" asphaltenes from the dissolving mineral surface. Illuminating the surface reactions of geological minerals, we conclude that surface passivation by heterogeneous organo-ionic matter is not only ubiquitous in nature but also a key regulator of the interfacial chemistry, reactivity and wettability of underground rocks

Membrane-Bound Alpha Synuclein Clusters Induce Impaired Lipid Diffusion and Increased Lipid Packing

The aggregation of membrane-bound α-synuclein (αS) into oligomers and/or amyloid fibrils has been suggested to cause membrane damage in in vitro model phospholipid membrane systems and in vivo. In this study, we investigate how αS interactions that precede the formation of well-defined aggregates influence physical membrane properties. Using three truncated variants of αS with different aggregation propensities and comparable phospholipid membrane binding affinities we show, using fluorescence recovery after photobleaching (FRAP) and fluorescence anisotropy measurements, that formation of αS clusters on supported lipid bilayers (SLBs) impairs lateral lipid diffusion and increases lipid packing beneath the αS clusters. Formation of protein clusters starts immediately after monomer addition. The magnitudes of the changes in effective lipid diffusion and lipid order increase with the protein cluster size. Our results show that the combination of inter-αS and αS-membrane interactions can drive the formation of more ordered lipid domains. Considering the functional involvement of membrane micro-domains in biological membranes, αS-induced domain formation may be relevant for alternative disease mechanisms