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PubMed1988

In vitro polymorphism and phase transitions of the neurofilamentous network isolated from the giant axon of the squid (Loligo pealei L.).

Using electron microscopy (EM), optical diffraction and image reconstruction techniques, we have demonstrated polymorphism of neurofilamentous network (NFN) in vitro based on phase transitions of the protein assemblies. The specific polymorphic appearances depended upon a number of factors, such as K+, Mg2+, Ca2+ ions, as well as the charge and hydration state of the molecules. Furthermore, modifications initiated by the state of phosphorylation of the sidearm proteins played an important role, especially in determining the sidearm disposition of the NFN. The Ca2+-activated protease removed the sidearms. Other enzymes activated by Ca2+ may initiate new association patterns of the peptide remnants and the intercoiling of two smooth neurofilaments (NFs) into paired helical filament-like (PHF-like) strands. Prolonged storage of the isolated NFs in Rubinson-Baker solution resulted in autocrosslinking and intercoiling of modified NFN components. The in vitro polymorphism and phase transitions of squid NFN induced under controlled conditions have been compared to modifications of cytoskeleton observed by EM in frontal lobe biopsies of Alzheimer patients. We conclude that similar processes, as induced in vitro, do occur in neurons of Alzheimer patients.

Alzheimer Disease↗

PubMed2001

"Devil's staircase"-type phase transition in NaV2O5 under high pressure.

The "devil's staircase"-type phase transition in the quarter-filled spin-ladder compound NaV2O5 has been discovered at low temperature and high pressure by synchrotron radiation x-ray diffraction. A large number of transitions are found to successively take place among higher-order commensurate phases with 2a x 2b x zc type superstructures. The observed temperature and pressure dependence of modulation wave number q(c), defined by 1/z, is well reproduced by the axial next nearest neighbor Ising model. The q(c) is suggested to reflect atomic displacements presumably coupled with charge ordering in this system.

Journal Article↗

PubMed2000

A method to study the phase transition and desorption of self-assembled monolayers on planar gold surfaces.

In-plane resistance of thin gold films (thickness approximately 1,000 A) after the formation of self-assembled monolayers has been measured as a function of temperature. We attribute the observed increase in the slope of the resistance vs temperature plot in the case of octadecanethiol and octanethiol monolayers at characteristic temperatures to phase transitions. The structural transition of 1,4-benzenedimethanethiol is also manifested similarly. Propanethiol does not show any phase transition, as expected. The observed changes in the alkanethiol monolayers are related to the decrease in the lifetime of the parallel vibrational motion of the adsorbate on the gold surface. The increase in slope is followed by a decrease which is attributed to the commencement of desorption of monolayers from the gold surface.

Journal Article↗

PubMed1987

Scanning calorimetry reveals a new phase transition in L-alpha-dipalmitoylphosphatidylcholine.

We report a new phase transition in fully hydrated dispersions of dipalmitoylphosphatidylcholine (DPPC). This new transition, called the sub-subtransition, exhibits a transition enthalpy of 0.25 kcal/mol with a Tm at 6.8 degrees C. Unlike the subtransition, no extended low temperature incubation is required to observe the sub-subtransition. This new sub-subgel (SGII) phase may be a precursor to the subgel (SGI) phase, and this discovery is discussed in relation to the current knowledge regarding the polymorphic gel phases of both ester- and ether-linked lipids with identical acyl chains.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2006

Spontaneous symmetry breaking of population in a nonadiabatically driven atomic trap: an Ising-class phase transition.

We have observed spontaneous symmetry breaking of the population of Brownian particles between two moving potentials in the spatiotemporally symmetric system. Cold atoms preferentially occupy one of the dynamic double-well potentials, produced in the parametrically driven dissipative magneto-optical trap far from equilibrium, above a critical number of atoms. We find that the population asymmetry, which may be interpreted as the biased Brownian motion, can be qualitatively described by the mean-field Ising-class phase transition. This in situ study may be useful for investigation of dynamic phase transition or temporal behavior of critical phenomena.

Journal Article↗

PubMed2001

Metal-insulator and structural phase transition observed by ESR spectroscopy and x-ray diffraction in KC60.

We have performed electron spin resonance (ESR) spectroscopy and x-ray diffraction experiments at low temperature on KC60 single crystals. ESR data reveal the occurrence of a metal-insulator phase transition at about 50 K. In the same temperature range, we observe the stabilization of a superstructure which doubles the volume of the unit cell. We suggest that displacements of the K atoms and a modulation of the C60 charge may be involved in the mechanism of this phase transition. These results shed new light on the subtle interplay of structure, dimensionality, and electronic properties in the AC60 fullerides.

Journal Article↗

PubMed2006

Phase transitions in coupled map lattices and in associated probabilistic cellular automata.

Analytical tools are applied to investigate piecewise linear coupled map lattices in terms of probabilistic cellular automata. The so-called disorder condition of probabilistic cellular automata is closely related with attracting sets in coupled map lattices. The importance of this condition for the suppression of phase transitions is illustrated by spatially one-dimensional systems. Invariant densities and temporal correlations are calculated explicitly. Ising type phase transitions are found for one-dimensional coupled map lattices acting on repelling sets and for a spatially two-dimensional Miller-Huse-like system with stable long time dynamics. Critical exponents are calculated within a finite size scaling approach. The relevance of detailed balance of the resulting probabilistic cellular automaton for the critical behavior is pointed out.

Journal Article↗

PubMed2001

First- and second-order phase transitions in a driven lattice gas with nearest-neighbor exclusion.

A lattice gas with infinite repulsion between particles separated by < or = 1 lattice spacing, and nearest-neighbor hopping dynamics, is subject to a drive favoring movement along one axis of the square lattice. The equilibrium (zero drive) transition to a phase with sublattice ordering, known to be continuous, shifts to lower density, and becomes discontinuous for large bias. In the ordered nonequilibrium steady state, both the particle and order-parameter densities are nonuniform, with a large fraction of the particles occupying a jammed strip oriented along the drive. The drive thus induces separation into high- and low-density regions in a system with purely repulsive interactions. Increasing the drive can provoke a transition to the ordered phase, and thereby, a sharp reduction in current.

Journal Article↗

PubMed1981

Molecular motions and phase transitions. NMR relaxation times studies of several lecithins.

The spin-lattice relaxation time, T1, and the dipolar energy relaxation time, TD, were measured as a function of temperature. The materials studied were samples of anhydrous L-dipalmitoyl lecithin, DL-dipalmitoyl lecithin, L-dimyristoyl lecithin, DL-dimyristoyl lecithin and their monohydrates, and of anhydrous egg yolk lecithin. It is shown that TD is a much more sensitive parameter than T1 for the determination of the Chapman phase transition. Comparison between T1 and TD provides information about new types of slow molecular motions below and above the phase transition temperature. It is suggested that the relaxation mechanisms for T1 and TD in the gel phase are governed by segmental motion in the phospholipid molecule. A new metastable phase was detected in dimyristoyl lecithin monohydrates. This phase could only be detected from the dipolar energy relaxation times.

Magnetic Resonance Spectroscopy↗

PubMed1991

Cholesterol does not remove the gel-liquid crystalline phase transition of phosphatidylcholines containing two polyenoic acyl chains.

Homoacid (single-acid) phosphatidylcholines containing two linoleate (18:2), arachidonate (20:4), or docosahexaenoate (22:6) chains were dispersed in water to form multilamellar vesicles. The influence of cholesterol on the gel to liquid phase transitions was studied by differential scanning calorimetry (DSC). The pure dipolyenoic phosphatidylcholines exhibited very broad endothermic transitions (widths of 28 to 38 C degrees at scanning rates of 5 C degrees/min) in the temperature range of about -80 degrees C to -30 degrees C. The mixing of cholesterol into the phospholipids in proportions up to 50 mol% had little effect on the temperatures, widths or enthalpy changes associated with the phase transitions. The data suggest that cholesterol does not interfere with the packing of these lipids in the gel state, possibly because the packing is already irregular or because the solubility of cholesterol in these lipids is low, or both.

Calorimetry, Differential Scanning↗

PubMed1998

Evidence of soft-mode quantum phase transitions in electron double layers

Inelastic light scattering by low-energy spin-excitations reveals three distinct configurations of spin of electron double layers in gallium arsenide quantum wells at even-integer quantum Hall states. The transformations among these spin states appear as quantum phase transitions driven by the interplay between Coulomb interactions and Zeeman splittings. One of the transformations correlates with the emergence of a spin-flip intersubband excitation at vanishingly low energy and provides direct evidence of a link between quantum phase transitions and soft collective excitations in a two-dimensional electron system.

Journal Article↗

PubMed1989

The effect of n-alcohols on vesicular permeability induced at the lipid phase transition temperature: a 1H-NMR study.

The effect of a series of n-alcohols on the permeability of small, unilamellar dipalmitoyl phosphatidylcholine (DPPC), dimyristoyl phosphatidylcholine (DMPC) and distearoyl phosphatidylcholine (DSPC) vesicles at the gel-to-liquid crystal phase transition temperature was investigated. It was found that the permeability took the form of the transient lysis of a fraction of the population of vesicles. The effect on this lysis of the n-alcohols was seen to be very chain-length dependent, with a minimum at n = 8 (octan-1-ol) for DPPC vesicles. A similar minimum was observed in the presence of 0.1 mM Triton X-100, but the detergent could then interact with certain of the alcohols to produce permanent channels. The results are discussed in terms of the semi-empirical model of Brasseur et al. (1985) Biochim. Biophys. Acta 814, 227-236, for the interaction of the n-alcohols with a DPPC membrane. The effect of various n-alcohols on the outer and inner monolayers of DPPC vesicles was also studied and the results related to their fluidising effect, allowing channels to open at the phase transition temperature.

Alcohols↗

PubMed1999

Phase Transitions in Neutron Stars and Maximum Masses.

Using the most recent realistic effective interactions for nuclear matter with a smooth extrapolation to high densities including causality, we constrain the equation of state and calculate maximum masses of rotating neutron stars. First- and second-order phase transitions to, e.g., quark matter at high densities are included. If neutron star masses of approximately 2.3 M middle dot in circle from quasi-periodic oscillations in low-mass X-ray binaries are confirmed, a soft equation of state as well as strong phase transitions can be excluded in neutron star cores.

Journal Article↗

PubMed1984

Kinetics of the main phase transition of hydrated lecithin monitored by real-time X-ray diffraction.

A method is described for observing and recording in real-time x-ray diffraction from an unoriented hydrated membrane lipid, dipalmitoylphosphatidylcholine (DPPC), through its thermotropic gel/liquid crystal phase transition. Synchrotron radiation from the Cornell High Energy Synchrotron Source (Ithaca, New York) was used as an x-ray source of extremely high brilliance and the dynamic display of the diffraction image was effected using a three-stage image intensifier tube coupled to an external fluorescent screen. The image on the output phosphor was sufficiently intense to be recorded cinematographically and to be displayed on a television monitor using a vidicon camera at 30 frames X s1. These measurements set an upper limit of 2 s on the DPPC gel----liquid crystal phase transition and indicate that the transition is a two-state process. The real-time method couples the power of x-ray diffraction as a structural probe with the ability to follow kinetics of structural changes. The method does not require an exogenous probe, is relatively nonperturbing, and can be used with membranes in a variety of physical states and with unstable samples. The method has the additional advantage over its static measurement counterpart in that it is more likely to detect transiently stable intermediates if present.

Chemical Phenomena↗

PubMed2003

Phase transition in a swarm algorithm for self-organized construction.

This paper reports on a system where very simple, noncommunicating mobile agents in a cellular (lattice) environment use purely local rules to construct connected structures from initially randomly distributed building blocks. We study the effect of block density on the final structure, demonstrating a percolationlike phase transition: Low block densities lead to the formation of small, disconnected structures but a single connected structure emerges abruptly beyond a critical density. The empirical study of the structure at the transition point shows scaling behavior, providing strong evidence for criticality. We also demonstrate that a simple change of rules can completely change the phase-transition effect. The results have implications for the self-organized construction of complex structures by swarms.

Journal Article↗

PubMed2004

Low concentration of dioleoylphosphatidic acid induces an inverted hexagonal (H II) phase transition in dipalmitoleoylphosphatidylethanolamine membranes.

We have investigated the effects of anionic dioleoylphosphatidic acid (DOPA) on the structure and phase behavior of dipalmitoleoylphosphatidylethanolamine (DPOPE) membranes by small-angle X-ray scattering. The results of X-ray diffraction experiments indicate that an L(alpha) to H(II) phase transition in DPOPE membranes occurred at 2.5 mol% DOPA, and above 4.0 mol% they were completely in the H(II) phase. And in the presence of 0.5 M KCl, the critical concentration of DOPA was decreased to 0.6 mol%. These results show that low concentrations of DOPA stabilize the H(II) phase rather than the L(alpha) phase in DPOPE membranes. The absolute spontaneous curvature of DPOPE membrane was gradually decreased with an increase in DOPA concentrations. On the basis of these results, the H(II) phase stability in DPOPE membranes due to low DOPA concentrations is discussed by the spontaneous curvature of monolayer membrane, the packing energy of alkyl chains of the membrane and lipid packing parameter.

Alkanesulfonic Acids↗

PubMed2000

Conformational transformation coupled with the order-disorder phase transition in 2-methyl-1,3-cyclohexanedione crystals.

The half-chair conformation of the dynamically disordered molecular ring of 2-methyl-1,3-cyclohexanedione, C(7)H(10)O(2), transforms to a sofa below Tc = 244 K, when the crystal undergoes a continuous phase transition induced by the onset of halting large-amplitude vibrations of methylene groups C(4)H(2) and C(5)H(2). The temperature dependence of the crystal structure has been investigated by X-ray diffraction. The Ibam symmetry of the crystal reduces below Tc to space group Pccn. The mechanism of the phase transition and of the conversion of the ring conformation is discussed.

Journal Article↗

PubMedDate not supplied

[Relationship between the depth of acute hypothermia and the composition and phase transitions of mitochondrial lipids of dog and white rat myocardium].

It has been found in the experiments on white rats and dogs that the increase of body temperature by 8--10 degrees in myocardium mitochondria composition of phospholipids is changed, microviscosity of lipids decreases, the phase transition is shifted to the low temperature region. Changes in white rats' mitochondria are expressed to a greater extent. When the body temperature is decreased by 18--20 degrees microviscosity of lipids in dog myocardium mitochondria increases, that of white rats is maintained on the same level. Effect of the composition of membrane lipids on the temerature of phase transitions during hypothermia is discussed, as well as possible dependence of the stability of animals towards low temperatures on the degree of reconstruction of the membrane lipids.

Animals↗