Expanded State Research Articles

Compositional domain immiscibility in whole myelin monolayers at the air–water interface and Langmuir–Blodgett films

Monomolecular layers of whole myelin membrane can be formed at the air–water interface from vesicles or from solvent solution of myelin. The films appear microheterogeneous as seen by epifluorescence and Brewster angle microscopy. The pattern consists mainly of two coexisting liquid phases over the whole compression isotherm. The liquid nature of the phases is apparent from the fluorescent probe behavior, domain mobility, deformability and boundary relaxation due to the line tension of the surface domains. The monolayers were transferred to alkylated glass and fluorescently labeled against myelin components. The immunolabeling of two major proteins of myelin (myelin basic protein, proteolipid-DM20) and of 2′,3′-cyclic nucleotide 3′-phosphodiesterase shows colocalization with probes partitioning preferentially in liquid-expanded lipid domains also containing ganglioside G M1. A different phase showing an enrichment in cholesterol, galactocerebroside and phosphatidylserine markers is also found. The distribution of components is qualitatively independent of the lateral surface pressure and is generally constituted by one phase enriched in charged components in an expanded state coexisting with another phase enriched in non-charged constituents of lower compressibility. The domain immiscibility provides a physical basis for the microheterogeneity found in this membrane model system.

Unmet and undermet need for activities of daily living and instrumental activities of daily living assistance among adults with disabilities: estimates from the 1994 and 1995 disability follow-back surveys.

Accurate assessments of need for disability assistance are essential for effective planning of disability support services, but there is little national data on type and acuity of need. To more fully delineate the type and magnitude of disability assistance needs across the US population, focusing on factors associated with perceived gaps in assistance. Secondary analysis of national household survey. Twenty-five thousand eight hundred five adults identified as disabled in the 1994 and 1995 National Health Interview Surveys. Self-reported assistance deficits with activities of daily living (ADLs) and instrumental activities of daily living (IADLs). An estimated 3.2 million adults with disabilities have at least one assistance deficit, usually involving IADLs like housework. However, approximately 970 thousand adults report one or more assistance deficits with basic ADLs. Compared to adults with met ADL needs, people with ADL assistance deficits are more likely to live alone, to be in poor health, to be a member of a racial or ethnic minority, and to need help with multiple activities. These analyses suggest a relatively high rate of unmet and undermet need for disability assistance in the general population. However, only a small number of these adults report assistance deficits with basic ADLs. This group is a logical target for expanded state or federal personal assistance services programming.

Fluorescence microscopy observation of self-organized microstructure formed by a rare earth compound

The morphologies of monolayers containing Eu(TTA)3Phen (TTA = thenoyltrifluoroacetone, Phen = 1, 10-phenanthroline) were studied at the air/liquid interface on different subphases by fluorescence microscopy (FM). The composite subphase was the basic premise for the stable existence of the rare earth compound at air/liquid interface. The process that rare earth compound phase changes from liquid expanded state to liquid condensed state corresponded to a plateau in the p-A isotherm. In the pure Eu(TTA) 3 Phen monolayer, rod domains of Eu(TTA) 3 Phen formed and packed with no order. In the mixed monolayers with stearic acid (SA), phase transition of SA occurred first and formed domains with an electric gradient field, which induced the rare earth compound to form luminescent ring domains. Influence of intermolecular interaction on the self-organized microstructure was revealed.

Temperature Effect on the Adsorption of Fluorooctanols at the Hexane/Water Interface

The interfacial tensions of the hexane solution of fluorooctanols (1,1,2,2-tetrahydrotridecafluorooctanol, TFC8OH, and 1,1-dihydropentadecafluorooctanol, DFC8OH) against water were measured as a function of temperature and molality under atmospheric pressure. By drawing the interfacial pressure π vs mean area per adsorbed molecule A curves, it was concluded that the adsorbed film of TFC8OH exhibits a first-order phase transition between the gaseous and expanded states and that of DFC8OH shows the two types of phase transitions from the gaseous to the expanded state and from the expanded to the condensed one at the hexane/water interface. The comparison of the π vs A curve between TFC8OH and DFC8OH shows that the intermolecular interaction is enhanced by the substitution of fluorine for hydrogen on the β-carbon of TFC8OH. Furthermore, the difference in the transition pressure between DFC8OH and TFC10OH (1,1,2,2-tetrahydroheptadecafluorodecanol) is explained by the differences in London dispersion force between hydrophobic chains and the dipole moment of their hydroxyl group. The partial molar entropy s̄sH − ssO and energy ūsH − usO changes of adsorption were evaluated and compared to those of TFC10OH. The s̄sH − ssO value is negative and therefore alcohol molecules have smaller entropy at the interface than in the solution, which is attributable to the orientation of the molecules at the interface. The phase transition from the expanded to the condensed state in the adsorbed TFC10OH film causes larger decrease in partial molar entropy than that in the DFC8OH one. This may arise from the larger partial molar entropy of TFC10OH molecules due to the larger entropy of mixing of longer fluorocarbon chain with hexane in the expanded state and the smaller entropy of TFC10OH due to the stronger attractive interaction in the condensed state than that of DFC8OH molecules. The ūsH − usO value is less negative for DFC8OH than for TFC10OH and therefore the energetical stabilization of DFC8OH accompanied by the adsorption from the solution is less than that of TFC10OH. Furthermore, it was concluded that the DFC8OH molecules are stabilized by forming the condensed film at the interface because of the strong molecular interaction between them, and the TFC8OH molecules form mainly tetramers in the hexane solution to lower the energetical state of the system.

Interaction of GM 1 glycolipid in phospholipid monolayers with wheat germ agglutinin: effect of phospholipidic environment and subphase

Mixed monolayers of GM 1 glycolipid and stearoyl-oleoyl-phosphatidylcholine (SOPC) or dipalmitoyl-phosphatidycholine (DPPC) phospholipids were studied by surface pressure measurements. The effects induced by GM 1 on the mean molecular areas of mixtures and DPPC phase transition were followed for GM 1 concentrations ranging from 1 to 20 mol.%. Under our experimental conditions, one main parameter influencing the behavior of phospholipid–GM 1 monolayers is the ionic strength of the subphase. Mixed monolayers are in a more expanded state on buffer than on pure water. This could be due to a change of GM 1 orientation at the interface. The interaction of wheat germ agglutinin (WGA), a lectin recognizing specifically GM 1, with these monolayers was quantified in terms of the Gibbs equation. Specific WGA–GM 1 interactions are clearly reduced in the presence of DPPC as compared with SOPC, probably because of the higher packing density of these monolayers. Phospholipid–GM 1 monolayers could also undergo some rearrangements induced by WGA binding.

Characterization of Mixed Monolayers of Phosphatidylcholine and a Dicationic Gemini Surfactant SS-1 with a Langmuir Balance: Effects Of DNA

Monolayers of a cationic gemini surfactant, 2,3-dimethoxy-1,4-bis( N-hexadecyl- N; N-dimethyl-ammonium)butane dibromide (abbreviated as SS-1) and its mixtures with 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC) were studied using a Langmuir balance. More specifically, we measured the force-area ( π- A) curves and determined the elastic area compressibility modulus ( C s −1) as a function of lateral packing pressure and the mole fraction of the cationic lipid ( X SS-1), with and without DNA in the subphase. Both SS-1 and POPC exhibited smooth compression isotherms, indicating their monolayers to be in the liquid expanded state. Even low contents ( X SS-1 < 0.05) of SS-1 in a POPC monolayer condensed the film dramatically, up to 20% at 30 mN/m. This effect is suggested to reflect reorientation of the P −-N + dipole of the POPC headgroup. Accordingly, the magnitude of the condensing effect diminishes with X SS-1 and is not observed for mixed films of dioleoylglycerol and SS-1. Reorientation of the P −-N + dipole is further supported by the pronounced increase in monolayer dipole potential ψ due to SS-1. The presence of DNA in the subphase affected the mixed POPC/SS-1 monolayers differently depending on the constituent lipid stoichiometry as well as on the DNA/SS-1 charge ratio. At a DNA concentration of 0.63 μM (in base pairs) condensation of neat POPC monolayers was evident, and this effect remained up to X SS-1 < 0.5, corresponding to DNA/SS-1 charge ratio of 1.25. An expansion due to DNA, evident as an increase in Δ A/molecule, was observed at X SS-1 > 0.5. At a higher concentration of DNA (1.88 μM base pairs) in the subphase corresponding to DNA/SS-1 charge ratio of 3.75 at X SS-1 = 0.5, condensation was observed at all values of X SS-1.

Flexibility of the triblock copolymers modulating their penetration and expulsion mechanism in Langmuir monolayers of dihexadecyl phosphoric acid

The surface activity of the poly–[ block (ethylene oxide)]–poly [ block (propylene oxide)]–poly [ block (ethylene oxide)] copolymers (EO) x –(PO) y –(EO) x adsorbed together with dihexadecyl phosphoric acid (DHP), a synthetic phospholipid, is analyzed from their surface pressure and surface potential isotherms. The block copolymers of (EO) x –(PO) y –(EO) x with variable molecular weight (1100–14 000) were dissolved in the subphase for DHP monolayers. The concentration of the copolymers within the aqueous subphase were selected to render an initial surface tension of 60 mN/m. The simultaneous adsorption of the copolymer and DHP is attested by the observation of a liquid expanded state at large areas, absent for pure DHP monolayers. Above some critical surface pressure all copolymers cited above are expelled from the interface. The surface potential isotherms, which give information on the component of the molecular dipole moment normal to the plane of the monolayer, are interpreted in terms of changes in the copolymer conformation as well as in terms of the copolymer desorption from the air–liquid interface. For an equal hydrophobic/hydrophilic ratio, the size of the chains or molecular weight is decisive in the mechanism of the copolymer expulsion from the air–liquid interface.

Interferometric investigation of femtosecond laser-heated expanded states

Simultaneous temporally and spatially resolved measurements of the phase change and reflectivity of S- and P-polarized femtosecond laser probes are obtained from hot expanded states produced by femtosecond laser heating of a solid aluminum target. The combined set of data provides an integral test of equation-of-state models in a regime up to 10 Mbar and densities of 0.01–1 times solid. The results suggest that target stoichiometry at the few Å level should be considered in the analysis of phase and reflectivity measurements in such experiments.

The equilibrium penetration of monolayers. Is equilibrium really established?

In studying the penetration of water-soluble surfactants into water-insoluble monolayers the main theoretical problem is to find a relationship that would enable the amount of surfactant that has entered the monolayer to be calculated from a set of equilibrium surface pressure–area isotherms. Despite many attempts, no current theory gives satisfactory results when applied to experimental data (Langmuir 14 (1998) 2148). One possible reason is that equilibrium had not been established when the surface pressure–area curves were measured. The three experiments reported here suggest that equilibrium is extremely difficult to establish in such systems when the area is low or the surface pressure is high. The essence of these experiments is to try to reach the same final condition by two different routes. In the first route, the one nearly always used in equilibrium penetration measurements, the surfactant is injected under the expanded monolayer, which is then slowly compressed in steps, with time allowed at each step for a steady surface pressure to be attained. In the second procedure, the monolayer is first compressed to a high surface pressure and the surfactant then injected. A stepped expansion isotherm may then be observed. Surface pressure–area per monolayer molecule isotherms, reflection spectra, and slow neutron reflectivity data all show the same pattern: if the surfactant was allowed to penetrate while the monolayer was in an expanded state, it was not completely removed when the monolayer was compressed; but if the monolayer was in a highly compressed state when exposed to the surfactant little penetration took place until the film was expanded. There thus appear to be very large energy barriers to the ejection of surfactant from a compressed monolayer and to the penetration of surfactant into a compressed monolayer. Although these experiments have some limitations, it now seems likely that at least some of the penetration data used in evaluating the various thermodynamic treatments of equilibrium penetration were not equilibrium data.

Maintenance of the DNA puff expanded state is independent of active replication and transcription

The maintenance of the expanded state of DNA puffs II/2B and II/9A in polytene chromosomes from stage 14 x 7 Sciara coprophila salivary glands was assayed after inhibition of RNA synthesis, DNA synthesis, or both processes together. Heat shock conditions were established in order to inhibit transcription. Polypeptides of Mr 72,000 and 36,000 were produced in Sciara after heat shock. The gene encoding the Mr 72,000 polypeptide, the homolog of Drosophila hsp70, was cloned. In situ hybridization detected Sciara hsp70 at bands 4A and 17C on chromosome IV. Sciara hsp70 encodes a 2.3 kb heat shock mRNA. DNA puffs (e.g., DNA puffs 2B and 9A on chromosome II) remained fully expanded even after inhibition of transcription by heat shock or actinomycin D, or after inhibition of DNA replication by aphidicolin, or inhibition of both RNA synthesis and DNA synthesis together by actinomycin D plus aphidicolin. Therefore, maintenance of the DNA puff expanded state in Sciara does not require ongoing transcription and/or replication. Mechanisms for initiation and for maintenance of puffs (open chromatin structure) are discussed.

War in the Tribal Zone: Expanding States and Indigenous Warfare

War in the Tribal Zone: Expanding States and Indigenous Warfare

Superimposed HMM transient detection via target tracking ideas

The quickest detection of superimposed hidden Markov model (HMM) transient signals is addressed. It is assumed that a known HMM is always extant but at an unknown time a second known HMM may also be present, and overlapped with the previous. Two approaches are proposed. The first treats the superimposed HMMs as a unit with an expanded state space, thus converting the problem of detecting superimposed HMMs into detection of a change in HMM, this being readily solved using a previously proposed procedure. Such an approach, though excellent in terms of performance, is not suitable for the superposition of multiple HMMs with large state dimensions due to computational complexity. A second detection scheme (based on multiple target tracking ideas) with much lower computational needs but little loss in terms of performance, is therefore developed.

A collapsed state functions to self-chaperone RNA folding into a native ribonucleoprotein complex.

Most large RNAs achieve their active, native structures only as complexes with one or more cofactor proteins. By varying the Mg(2+) concentration, the catalytic core of the bI5 group I intron RNA can be manipulated into one of three states, expanded, collapsed or native, or into balanced equilibria between these states. Under near-physiological conditions, the bI5 RNA folds rapidly to a collapsed but non-native state. Hydroxyl radical footprinting demonstrates that assembly with the CBP2 protein cofactor chases the RNA from the collapsed state to the native state. In contrast, CBP2 also binds to the RNA in the expanded state to form many non-native interactions. This structural picture is reinforced by functional splicing experiments showing that RNA in an expanded state forms a non-productive, kinetically trapped complex with CBP2. Thus, rapid folding to the collapsed state functions to self-chaperone bI5 RNA folding by preventing premature interaction with its protein cofactor. This productive, self-chaperoning role for RNA collapsed states may be especially important to avert misassembly of large multi-component RNA-protein machines in the cell.

Estimating a Markov Model That Incorporates First Visit Decisions and Varying Repeat Frequency

Recent articles have demonstrated the value of approaching the analysis of repeat travel using Markov models. The tourism literature identifies behavior that can be introduced into Markov models by expanding the state space. The authors have formulated such models. This article addresses the estimation of parameters of a model for first-time and repeat visitors; if the visitors are repeat then being a frequent or less frequent repeater is addressed. Estimation is for 1991 Travel Industries “In-flight Inbound” data for 1991 Japanese pleasure visitors to the US. Because the estimation is not possible using a standard program, a special estimation program was written. The logic and results of the estimation program, including criteria for determining a reasonable fit, are discussed. It is found that parameters of the model can be estimated and that the fit to the data is possibly good enough that residual variance is random. Unfortunately, other models involving different behavior can be expected to fit the data equally well. So, while a practical implication for researchers is that expanded state space models can be estimated, the challenge raised is that research must establish the actual structure of behavior. Only with that structure defined can valid information be produced for managers.

Conformation and Structural Relaxation of Partially Disentangled Poly(vinyl chloride) Prepared by Freeze-Extracting Dilute Solutions

The partially disentangled poly(vinyl chloride) (PVC) samples were prepared by freeze-extracting from dilute PVC/THF solutions. The conformation of these samples was investigated by infrared and Raman spectroscopy. The structural relaxation behaviors were studied by differential scanning calorimeter (DSC). The results showed that the PVC samples prepared from dilute solutions with concentrations lower than 0.25% were in the expanded state with fewer entanglements. The conformation and structural relaxation of PVC depended strongly on the entanglements in polymers, and the structural relaxation rate increased with decreasing chain entanglements, which is in good agreement with the modeling predictions.

Flexible linear polyelectrolytes in multivalent salt solutions: Solubility conditions

Polyelectrolytes such as single and double stranded DNA and many synthetic polymers undergo two structural transitions upon increasing the concentration of multivalent salt or molecules. First, the expanded-stretched chains in low monovalent salt solutions collapse into nearly neutral compact structures when the density of multivalent salt approaches that of the monomers. With further addition of multivalent salt the chains redissolve acquiring expanded-coiled conformations. We study the redissolution transition using a two state model [F. Solis and M. Olvera de la Cruz, {\it J. Chem. Phys.} {\bf 112} (2000) 2030]. The redissolution occurs when there is a high degree of screening of the electrostatic interactions between monomers, thus reducing the energy of the expanded state. The transition is determined by the chemical potential of the multivalent ions in the solution $\mu$ and the inverse screening length $\kappa$. The transition point also depends on the charge distribution along the chain but is almost independent of the molecular weight and degree of flexibility of the polyelectrolytes. We generate a diagram of $\mu$ versus $\kappa^2$ where we find two regions of expanded conformations, one with charged chains and other with overcharged (inverted charge) chains, separated by a collapsed nearly neutral conformation region. The collapse and redissolution transitions occur when the trajectory of the properties of the salt crosses the boundaries between these regions. We find that in most cases the redissolution occurs within the same expanded branch from which the chain precipitates.

A Comparative Monolayer Film Behavior Study of Monoglucosyl Diacylglycerols Containing Linear, Methyl Iso-, and ω-Cyclohexyl Fatty Acids

A comparative monomolecular film study of a series of 1,2-di-O-(α-d-glucopyranosyl)-sn-glycerols in which the acyl chains were 16:0, 18:0, 19:iso, and 15:ω-cyclohexyl, was carried out at the air/water interface. Area/temperature isobars were obtained in the 20° through 60 °C range with the lipids going from fully condensed to fully expanded. It was found that the area/molecule shift between the expanded and condensed states decreased in the order 16:0 and 18:0 > 19:iso > 15-ω-cyclohexyl, with the expanded state of the ω-cyclohexyl glycolipid being the most condensed. Reduction of the area/molecule shift arose through an expansion of the condensed state and a condensation of the expanded state. Isotherms of the straight-chain glycolipids showed only a small expansion on changing the pH from 5.6 to 2.0, but the ω-cyclohexyl glycolipid showed no effect. All the glycolipids studied showed thermal stability up to the 60 °C range, in contrast with previously obtained results on similar phosphatidylcholines, whi...

Flexible Linear Polyelectrolytes in Multivalent Salt Solutions: Solubility Conditions

Single and double stranded DNA and many biological and synthetic polyelectrolytes undergo two structural transitions upon increasing the concentration of multivalent salt or molecules. First, the expanded-stretched chains in low monovalent salt solutions collapse into nearly neutral compact structures when the density of multivalent salt approaches that of the monomers. With further addition of multivalent salt the chains redissolve acquiring expanded-coiled conformations. We study the redissolution transition using a two state model [F. J. Solis and M. Olvera de la Cruz, J. Chem. Phys. 112 (2000) 2030]. The redissolution occurs when there is a high degree of screening of the electrostatic interactions between monomers, thus reducing the energy of the expanded state. The transition is determined by the chemical potential of the multivalent ions in the solution μ and the inverse screening length κ. The transition point also depends on the charge distribution along the chain but is nearly independent of the molecular weight and degree of flexibility of the polyelectrolytes. We generate a diagram of μ versus κ2 where we find two regions of expanded conformations, one with charged chains and the other with overcharged (inverted charge) chains, separated by a collapsed nearly neutral conformation region. The collapse and redissolution transitions occur when the trajectory of the properties of the salt crosses the boundaries between these regions. We find that in most cases the redissolution occurs within the same expanded branch from which the chain precipitates.

Pressure Effect on the Adsorption of 1,1,2,2-Tetrahydrotridecafluorooctanol at the Hexane/Water Interface

The interfacial tension of the hexane solution of 1,1,2,2-tetrahydrotridecafluorooctanol CF3(CF2)5(CH2)2OH (FC8OH) against water was measured as a function of pressure at various concentrations m1 and 298.15 K. There are three series of the break points, two of which result from a phase transition in the adsorbed film at the hexane/water interface and the other one results from a solubility limit of FC8OH in hexane. The curve of the interfacial pressure vs area per adsorbed molecule of FC8OH was drawn and compared with those of the 1,1,2,2-tetrahydroheptadecafluorodecanol CF3(CF2)7(CH2)2OH (FC10OH) and 1,1,2,2-tetrahydrohenicosafluorododecanol CF3(CF2)9(CH2)2OH (FC12OH) systems previously reported. It was concluded that the adsorbed film of FC8OH reveals the first-order phase transitions between a gaseous and an expanded state and that between an expanded and a condensed state. The value of the volume change Δv associated with the adsorption in the gaseous and expanded state decreases rapidly with an increase in m1, while that in the condensed state decreases very slowly. It was described from the curves of Δv vs m1 for FC8OH, FC10OH, and FC12OH at 80 MPa that the expanded state region in the interfacial film structure strongly decreases with increasing the chain length and disappears at the FC12OH film and that the Δv value in the condensed state rapidly decreases with an increase in the chain length. We can explain that the pressure dependence of Δv in the condensed state is produced by the pressure dependence of the partial molar volume of FC8OH in the hexane solution. We concluded that the deposition is not a pure liquid but FC8OH-rich phase containing small quantity of hexane.

Implantation-induced structural changes and hydration in silicate glasses

Profilometer step-height measurements, ion-beam analysis, and electron microscopy have been used to characterize the structural changes and hydration of argon, krypton, and xenon implanted fused silica and soda-lime glass. For both glasses, a structural change from a compacted to an expanded state occurs for energy deposition values near 1023 keV/cm3. This change occurs due to the break-down of the three-membered ring structure, formed near 1020 keV/cm3, by continuing implantation damage and bond-breaking by ambient atmospheres.