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The phase transitions of liquid 3He are described by truncations of an exact nonperturbative renormalization group equation. The location of the first-order transition lines and the jump in the order parameter are computed quantitatively. At the triple point we find indications of partially universal behavior. We suggest experiments that could help to determine the effective interactions between fermion pairs.
The phase transition from the low- (beta) to the high-temperature (alpha) form of acetonitrile, CH(3)CN, has been directly observed and studied on a unique single crystal. Both the beta and alpha structures have been determined at temperatures close to the transition temperature (206 K and 201 K), taking advantage of the hysteresis. A single crystal of the beta form was obtained for the first time.
Variable temperature Fourier transform infrared (FTIR) spectroscopy was used to study the transition between the micellar and the coagel phases, and between the cubic and the coagel phases, for the hexadecyltrimethylammonium sulfate (CTAS)/water system. The phase transition takes place at 15°C for the coagel to micelle transition and 17°C for the coagel to cubic phase transition. CTAS in the solid state at two temperatures was also studied by FTIR to provide comparison with the aqueous samples on the molecular motion and packing in these phases. The present FTIR data also suggest the formation of rod-like micelles upon the addition of electrolyte, NaCl, to the CTAS/water system.
We have studied the phase transitions of a phospholipidic single-bilayer supported on a mica substrate by real-time temperature-controlled atomic force microscopy. We show the existence of two phase transitions in this bilayer that we attribute to two gel (L(beta))/fluid (L(alpha)) transitions, corresponding to the independent melting of each leaflet of the bilayer. The ratio of each phase with temperature and the large broadening of the transitions' widths have been interpreted through a basic thermodynamic framework in which the surface tension varies during the transitions. The experimental data can be fit with such a model using known thermodynamic parameters.
The orientational order parameters of monofluoropalmitic acids biosynthetically incorporated into membranes of Acholeplasma laidlawii B in the presence of a large excess of a variety of structurally diverse fatty acids have been determined via 19F nuclear magnetic resonance (19F NMR) spectroscopy. It is demonstrated that these monofluoropalmitic acids are relatively nonperturbing membrane probes based upon physical (differential scanning calorimetry), biochemical (membrane lipid analysis), and biological (growth studies) criteria. 19F NMR is shown to convey the same qualitative and quantitative picture of membrane lipid order provided by 2H-NMR techniques and to be sensitive to the structural characteristics of the membrane fatty acyl chains, as well as to the lipid phase transition. Representatives of each naturally occurring class of fatty acyl chain structures, including straight-chain saturated, methyl-branched, monounsaturated, and alicyclic-ring-substituted fatty acids, were studied and the 19F-NMR order parameters were correlated with the lipid phase transitions (determined calorimetrically). The lipid phase transition was the prime determinant of overall orientational order regardless of fatty acid structure. Effects upon orientational order attributable to specific structural substituents were discernible, but were secondary to the effects of the lipid phase transition. In the gel state, relative overall order was directly proportional to the temperature of the particular lipid phase transition. Not only the overall order, but also the order profile across the membrane was sensitive to the presence of particular structural substituents. In particular, in the gel state specific fatty acyl structures demonstrated a characteristic disordering effect in the membrane order profile. These various observations can be merged to provide a unified picture of the manner in which fatty acyl chain chemistry modulates the physical state of membrane lipids.
Adsorption isotherms for various saturated phosphatidylcholines have been obtained. Lipids above and below their phase transition temperature differ only in the amount of water adsorbed and not in the nature of their adsorption isotherms. Cholesterol has an effect similar to that of increasing unsaturation in the hydrocarbon chains. Decreasing the length of the hydrocarbon chains for lipids below their phase transition temperature has no effect on the isotherms. If the chain length is short enough so that the lipids are above their transition temperature, however, a large increase in water adsorption occurs. All of the phospholipids exhibit a rapid increase of electrical conductivity for a few water molecules adsorbed per lipid molecule. All of the phospholipids show a saturation in conductivity at greater amounts of adsorbed water; the shape of the saturation region depends on whether the lipids are above or below their phase transition temperature. The activation energy for the electrical conductivity process depends on whether the hydrated lipids are in the "liquid-like" of the crystalline state, being lower for phospholipids in the liquid-like state. If the lipids are hydrated above their phase transition temperatures, their activation energies are lower than if they are hydrated below the transition temperature. Cholesterol lowers the activation energy. The phosphatidylcholines can be characterized by different activation energies, depending both upon their physical state and the presence of unsaturation in their hydrocarbon chains.
The effect of the hydrophobic Ca2+ ionophore, A23187, on the phospholipid dynamics of large unilamellar vesicle (LUVs: 4: 1 (w/w) mixture of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG] membranes, as a function of A23187 content, was investigated using techniques sensitive to the phospholipid phase transition. The ultrasonic absorption per wavelength, alpha lambda, was determined with a double crystal acoustic interferometer, as a function of temperature and frequency for LUVs in the vicinity of their phospholipid phase transition. Differential scanning calorimetry (DSC) and electron spin resonance (ESR) were also employed to probe the thermodynamics and molecular environment of the hydrocarbon side chains. With increasing A23187 content, the phase transition temperature (Tm) of the LUV suspensions remained near 42.0 degrees C, while the amplitude of alpha lambda at the phase transition increased dramatically. At Tm the relaxation frequency, where alpha lambda max occurs, decreased with A23187 content, suggesting that the relaxation rate of the event responsible for the absorption of ultrasound decreased. The ESR studies showed no change in the fluidity of the bilayer with the inclusion of 2 and 5 mol% A23187 in the C-12 region of the bilayer. Therefore, A23187 in LUV membranes slows the structural relaxation of the hydrocarbon side chains of the phospholipid bilayer at the phase transition.
The adsorption behavior and the phase transition of alkanol and fluoroalkanol at the electrified mercury/aqueous solution interface were investigated by the interfacial tension measurements and the thermodynamic analysis. In the alkanol system, it is found that the phase transitions in low interfacial densities occur: the ones from the zero adsorption to the gaseous or the expanded state and the gaseous to the expanded state at the electrified interface depending on the electrostatic nature as well as the concentration in the bulk phase. These phase transitions were verified by the thermodynamic equations derived by the assumption of coexistence of two phases at the electrified interface. Furthermore the distribution of ionic species in the interfacial region is discussed on the basis of dependence of the interfacial charge density of solution phase on an applied potential. Fluoroalkanol, on the other hand, was practically not adsorbed at the electrified interface within this experimental condition. The zero adsorption of fluoroalkanol molecules suggests the driving force of the adsorption may be the interaction hydrophobic group of alcohol molecule and mercury.
We report our investigation of phase transition of AlxGa1-xN thin films on GaN made by employing first-principles calculations. A critical thickness of two AlGaN molecular layers is determined for the wurtzite-to-zinc blende structural transition under compressive strains, which is associated with the second-nearest-neighbor interaction of electron bonds. Higher AlN mole fractions are found to favor the phase transition because of strong push toward covalency of the Al-N bonds under strains. Electronic structure results show that, after the phase transition, the spontaneous and piezoelectric polarizations of the AlGaN films are significantly reduced.
Extremal dynamics represents a path to self-organized criticality in which the order parameter is tuned to a value of zero. The order parameter is associated with a phase transition to an absorbing state. Given a process that exhibits a phase transition to an absorbing state, we define an "extremal absorbing" process, providing the link to the associated extremal (nonabsorbing) process. Stationary properties of the latter correspond to those at the absorbing-state phase transition in the former. Studying the absorbing version of an extremal dynamics model allows to determine certain critical exponents that are not otherwise accessible. In the case of the Bak-Sneppen (BS) model, the absorbing version is closely related to the "f -avalanche" introduced by Paczuski, Maslov, and Bak [Phys. Rev. E 53, 414 (1996)], or, in spreading simulations to the "BS branching process" also studied by these authors. The corresponding nonextremal process belongs to the directed percolation universality class. We revisit the absorbing BS model, obtaining refined estimates for the threshold and critical exponents in one dimension. We also study an extremal version of the usual contact process, using mean-field theory and simulation. The extremal condition slows the spread of activity and modifies the critical behavior radically, defining an "extremal directed percolation" universality class of absorbing-state phase transitions. Asymmetric updating is a relevant perturbation for this class, even though it is irrelevant for the corresponding nonextremal class.
Immobilization of enzymes (penicillin amidase and alpha-chymotrypsin) in water-soluble nonstoichiometric polyeloctrolyte complexes (PEC) formed by poly(4-vinyl-N-ethylpyridinium bromide) (polycation) and polymethacrylic acid (polyanion) was carried out. Particles of these PEC consist of a nucleus formed by sequences of salt bonds between the units of oppositely charged polyelectrolytes and the hydrophylic shell formed by ionized groups of polyanions which is in excess in PEC. Such a structure of PEC particles results in a cooperative phase transitions of these systems at slight variations of pH and ionic strength. The work demonstrates phase diagrams of PEC solutions. The values of pH and ionic strength at which phase transitions in solutions of different PEC occur were elucidated. The decrease of pH value from 6.1 to 5.7 leads to reversible phase transition followed by a saltatory increase of Km for immobilized penicillin amidase by 5-10 fold depending on substrate used. The phase transition induced by ionic strength increase up to 0,27 M NaCl doesn't change significantly the Km-value of enzymic reaction. The phenomenon observed can be accounted for by the different structure of PEC particles. The catalytic properties of immobilized chymotrypsin were shown to depend on the loci of enzyme attachment. If the enzyme is bound to polyanion, neither conformational changes of the matrix nor phase transition in solution influence its accessibility for the protein inhibitor, but rather change the binding constant. If the enzyme is attached to polycation, i.e. included in the polycomplex nucleus, two fractions of enzymes accessible and inaccessible for protein inhibitor appear.(ABSTRACT TRUNCATED AT 250 WORDS)
The dependence on chainlength, n, of the temperatures at which the various thermotropic phase transitions in phospholipid bilayers take place can be fitted to high accuracy with an expression of the form: Tt = Tt infinity (1-A/(n-d)) where Tt infinity, A and d are the constants to be fitted. This expression works well with literature values for the main and pretransitions of saturated straight-chain phosphatidylcholines, for the main transition of isobranched- and anteisobranched-chain phosphatidylcholines, and for the main and non-lamellar phase transitions of saturated straight-chain phosphatidylethanolamines, and also for diacylglycerol glycolipids. The parameters in the fit can be related thermodynamically to the calorimetric properties of the phase transition. The constants A and d are related to the end effects in the chainlength dependence of the transition enthalpy and transition entropy, respectively, and the transition temperature extrapolated to infinite chainlength, Tt infinity, is determined by the ratio of the incremental transition enthalpy and transition entropy per methylene group. A reasonable correspondence is found between the chainlength dependence of the transition temperature and of the transition enthalpy and transition entropy for saturated straight-chain diacylphosphatidylcholines. It is likely, however, that the expression for the chainlength dependence of the transition temperature may be of more general applicability, because, on the one hand of the greater inherent precision of the transition temperature measurements, and on the other hand because the expression for the transition temperature is of more general validity, provided that the chainlength dependence of the incremental transition enthalpy and entropy are the same.
Elastin-like polypeptides (ELPs) composed of a VPGXG repeat undergo a reversible phase transition in aqueous solution. They are hydrophilic and soluble in aqueous solution below their transition temperature (T(t)), but they become hydrophobic and aggregate when the temperature is raised above their T(t). In this study, we examine the quantitative uptake of a fluorescence-labeled, thermally responsive ELP as a function of ELP concentration between 5 and 15 microM in solution in response to hyperthermia by three cultured cancer cell lines. Flow cytometry of fluorescein-ELP conjugates showed that hyperthermia enhanced the cellular uptake of the thermally responsive ELP in human ovarian carcinoma cells (SKOV-3) and in HeLa cells at a concentration of 10 microM or higher, but not at a concentration of 5 microM, as compared with the uptake of a thermally inactive ELP control. In FaDu cells, hyperthermia stimulated uptake of the thermally responsive ELP at all solution concentrations of ELP between 5 and 15 microM. In particular, a >2-fold greater uptake of thermally responsive ELP compared with the thermally inactive control ELP was observed for FaDu cells at a solution concentration of 15 microM in heated cells. Confocal fluorescence microscopy of tumor cells incubated with a rhodamine conjugate of the thermally responsive ELP showed that the cytoplasm was uniformly stained below the T(t). Above the T(t), fluorescent particles were observed in the cytoplasm, suggesting that these particles are aggregates of the thermally responsive polypeptide resulting from the ELP phase transition. These studies demonstrate that the endocytotic uptake of a thermally responsive ELP is significantly enhanced by the thermally triggered phase transition of the polypeptide.
This article presents a brief review of literature on the physical chemistry of lipid phase transitions with emphasis on their kinetic properties. The theoretical foundations of perturbation techniques, and specifically the volume-perturbation technique are discussed in some detail. These are presented as a rationale for, and introduction to, a volume-perturbation kinetic calorimeter that we have constructed for measurement of the kinetics of lipid phase transitions. The instrument has been applied to study the gel-liquid crystalline phase transition in a variety of phospholipid bilayer systems. The design and implementation of the volume-perturbation calorimeter are presented along with a discussion of the techniques of data analysis. Finally, we present typical results obtained with this methodology for a multilamellar vesicle dispersion of dipalmitoylphosphatidylcholine.
Water vapor absorption and desorption at 25 degrees C and phase transition temperatures of phospholipid bilayers were measured as a function of relative humidity (RH) to better understand how the patterns of water vapor absorption and desorption are linked to corresponding phase changes induced by the level of hydration. Comparisons were made of the dipalmitoyl and palmitoyloleyol esters of glycerol derivatized with phosphatidyl-choline, -glycerol, -ethanolamine and with phosphatidic acid. The results suggest that the extent of water vapor absorption and desorption at a given RH reflects the combined effects of water-polar group interaction and access of water to the polar region as controlled by intra- and interbilayer molecular packing and intermolecular attractive and repulsive interactions. The results further suggest that the extent of water vapor absorption and desorption over a range of relative humidities reflects the combined effects of the polar group's ability to interact with water, the access that water has to the polar groups as determined by molecular size and various intermolecular and intrabilayer forces of attraction and repulsion, and interbilayer interactions which influence the degree of order/disorder present in the overall solid-state structure. This behavior is also reflected in the changes observed in the various bilayer phase transition temperatures as a function of RH. Analyses of absorption isotherms suggests that after exceeding a critical RH, water initially interacting with these phospholipids most likely forms either stoichiometric or nonstoichiometric crystal hydrates, as with the disaturated derivatives, or hydrated mesophases, as with the gel states of the monounsaturated derivatives.
Earth's magnetosphere during substorms exhibits a number of characteristic features such as the signatures of low effective dimension, hysteresis, and power-law spectra of fluctuations on different scales. The largest substorm phenomena are in reasonable agreement with low-dimensional magnetospheric models and in particular those of inverse bifurcation. However, deviations from the low-dimensional picture are also quite considerable, making the nonequilibrium phase transition more appropriate as a dynamical analog of the substorm activity. On the other hand, the multiscale magnetospheric dynamics cannot be limited to the features of self-organized criticality (SOC), which is based on a class of mathematical analogs of sandpiles. Like real sandpiles, during substorms the magnetosphere demonstrates features, that are distinct from SOC and are closer to those of conventional phase transitions. While the multiscale substorm activity resembles second-order phase transitions, the largest substorm avalanches are shown to reveal the features of first-order nonequilibrium transitions including hysteresis phenomena and a global structure of the type of a temperature-pressure-density diagram. Moreover, this diagram allows one to find a critical exponent, that reflects the multiscale aspect of the substorm activity, different from the power-law frequency and scale spectra of autonomous systems, although quite consistent with second-order phase transitions. In contrast to SOC exponents, this exponent relates input and output parameters of the magnetosphere. Using an analogy to the dynamical Ising model in the mean-field approximation, we show the connection between the data-derived exponent of nonequilibrium transitions in the magnetosphere and the standard critical exponent beta of equilibrium second-order phase transitions.
The hydrodynamic theory for the smectic-A phase and the isotropic phase is generalized to the macroscopic dynamics in the vicinity of the isotropic-smectic-A phase transition. The macroscopic dynamic equations are presented on the isotropic side as well as on the smectic-A side of the phase transition, incorporating the effect of an external electric field. Specific experiments to test some of the effects contained in the macroscopic dynamic equations are suggested.
Based on the structural data of phases alpha (hexagonal; 756-972 K), beta (monoclinic; 605-751 K), gamma (incommensurate, monoclinic; 295 K) and delta (lock-in, monoclinic; 110 K) of sodium carbonate, Na2CO3, we could draw a parallel between the phase transitions and the evolution of the second coordination sphere of the C atoms. The temperature-dependent structures observed in the beta phase are reproduced in the incommensurate gamma phase as a modulation wave, which relates to the content of the symmetrically equivalent {110} lattice planes in the alpha phase. By decreasing the temperature, the phase transitions are associated with a stepwise increase in the number of Na ions participating in the second coordination sphere of the C atoms. Over the full temperature range, this number increases from 3 to 7. The C-O distances and the mobility of the O atoms depends on the number of Na ions in the vicinity of the C atoms.