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At least 703 records · Page 39Linked to original sources
PubMed2004

DNA topoisomerase II is required for the G0-to-S phase transition in Drosophila Schneider cells, but not in yeast.

We previously reported that DNA topoisomerase II (topo II) is required for the G(0)-to-S phase transition in mammalian cells [Hossain et al. (2002) ICRF-193, a catalytic inhibitor of DNA topoisomerase II, inhibits re-entry into the cell division cycle from quiescent state in mammalian cells. Genes Cells 7, 285-294]. In this study, we examined whether the requirement for topo II is evolutionarily conserved in Drosophila and yeast. ICRF-193, a catalytic inhibitor of topo II, inhibited DNA synthesis in Drosophila Schneider cells released from the G(0) (stationary) phase, whereas the drug did not inhibit DNA synthesis in Schneider cells released from the M phase. Depletion of topo II mRNA by RNA-interference (RNAi) in G(0)-phase Schneider cells resulted in significant inhibition of DNA synthesis after release from G(0)-arrest. In the yeast topo II temperature-sensitive (ts) mutant, the initial cycle of DNA synthesis occurred at a restrictive temperature after release from starvation-induced G(0) phase and doubling of the DNA content in the cells was confirmed by both flow cytometry and fluorescence spectrophotometry. DNA synthesis in yeast cells after release from the G(0) phase was also observed in the presence of ICRF-193. Doubling of the DNA content was observed during spore germination of topo II ts mutant yeast at a restrictive temperature as determined by fluorescence spectrophotometry. These results indicate that topo II is required for the G(0)-to-S phase transition in Drosophila Schneider cells, but not in yeast.

Animals↗
PubMed2005

General rule for displacive phase transitions in perovskite compounds revisited by first principles calculations.

A recent high pressure experiment on LaAlO3 has revealed that the compound is an exception for the "general rule" of displacive phase transition associated with zone-boundary phonons. In the present study, the experimental result is successfully confirmed by first principles calculations. The pressure dependence of phonon frequencies as well as the phase transition pressure is quantitatively well reproduced. We found that the behavior is not peculiar to LaAlO3 but rather ubiquitous. RAlO3 (R = La, Nd, Sm, and Gd) and LaGaO3 can be classified in the same group.

Journal Article↗
PubMed2002

Phase transition analogous to Bose-Einstein condensation in systems of noninteracting surfactant aggregates.

Ideal bosons and a classical system of monomers that aggregate forming noninteracting ring polymers are known to have the same partition function. So, the ring polymers have a phase transition, the analogue of Bose-Einstein condensation of bosons. At this phase transition macroscopic polymers are formed. The link between these systems is made via Feynman's path integrals: these integrals are the same for the trajectories of the bosons in imaginary time and for the configurations of the polymers. We show that a transition of this general form occurs within a whole class of aggregating systems. Examples are the lamellae formation in suspensions of disclike micelles or the emulsification failure observed in water-oil-surfactant emulsions. As with bosons, the transition occurs even when aggregates do not interact. The lambda-transition in 4He is believed to be Bose-Einstein condensation modified by interatomic interactions. We suggest that interaggregate interactions too only modify the transition we have found.

Journal Article↗
PubMed2001

Solvent interconnectedness permits measurement of proximal as well as distant phase transitions in polymer mixtures by fluorescence.

We monitored the fluorescence intensity and anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) incorporated in bovine serum albumin (BSA) and dimyristoylphosphatidylcholine (DMPC) vesicle membranes, which in turn were embedded in optically clear gelatin solutions, as a function of temperature. DPH in BSA gave unanticipated large changes in fluorescence intensity and anisotropy at the instant of gelatin gel melting. Both steady state anisotropy and fluorescence intensity reported the gel-sol transition point in gelatin unambiguously, which was independently confirmed as physical-pour point of the gel. In the case of DMPC vesicles, fluorescence intensity indicated the gelatin transition, while the anisotropy indicated DMPC phase transition. This fluorescence methodology uniquely offered a common probe for two distinct transitions in two distinct domains interconnected by the solvent, water.

Dimyristoylphosphatidylcholine↗
PubMed2006

Interplay between two phase transitions: crystallization and liquid-liquid phase separation in a polyolefin blend.

The interplay between liquid-liquid phase separation (LLPS) and crystallization at several compositions in statistical copolymer blends of poly(ethyleneco-hexene) and poly(ethylene-cobutene) has been examined by optical microscopy (OM), atomic force microscopy (AFM), and differential scanning calorimetry (DSC). The phase contrast optical microscopy shows interconnected bicontinuous structures for deeply quenched LLPS, characteristic of spinodal decomposition. After a second quench to a temperature below the melting point, an overwhelming change in crystallization kinetics has been clearly observed, which is caused by the increase of the nucleation rate assisted by concentration fluctuations due to the spontaneous spinodal LLPS. We propose a new mechanism of "fluctuation assisted nucleation" in the crystallization process for such interactive process in a blend system. The experimental results from OM, AFM, and DSC measurements at various conditions are all consistent with the fluctuation assisted nucleation model.

Journal Article↗
PubMed2002

Incorporation of cholesterol in sphingomyelin- phosphatidylcholine vesicles has profound effects on detergent-induced phase transitions.

Vesicle <--> micelle transitions are important phenomena during bile formation and intestinal lipid processing. The hepatocyte canalicular membrane outer leaflet contains appreciable amounts of phosphatidylcholine (PC) and sphingomyelin (SM), and both phospholipids are found in the human diet. Dietary SM enrichment inhibits intestinal cholesterol absorption. We therefore studied detergent-induced vesicle --> micelle transitions in SM-PC vesicles. Phase transitions were evaluated by spectrophotometry and cryotransmission electron microscopy (cryo-TEM) after addition of taurocholate (3-7 mM) to SM-PC vesicles (4 mM phospholipid, SM/PC 40%/60%, without or with 1.6 mM cholesterol). After addition of excess (5-7 mM) taurocholate, SM-PC vesicles were more sensitive to micellization than PC vesicles. As shown by sequential cryo-TEM, addition of equimolar (4 mM) taurocholate to SM-PC vesicles induced formation of open vesicles, then (at the absorbance peak) fusion of bilayer fragments into large open structures (around 200 nm diameter) coexisting with some multilamellar or fused vesicles and thread-like micelles and, finally, transformation into an uniform picture with long thread-like micelles. Incorporation of cholesterol in the SM/PC bilayer changed initial vesicular shape from spherical into ellipsoid and profoundly increased detergent resistance. Disk-like micelles and multilamellar vesicles, and then extremely large vesicular structures, were observed by sequential cryo-TEM under these circumstances, with persistently increased absorbance values by spectrophotometry. These findings may be relevant for bile formation and intestinal lipid processing. Inhibition of intestinal cholesterol absorption by dietary SM enrichment may relate to high resistance against bile salt-induced micellization of intestinal lipids in presence of the sphingolipid.

Bile Acids and Salts↗
PubMed1983

Thermal phase transitions in sheep, rat and rabbit surfactant lipids detected by differential scanning calorimetry.

1. The thermal behaviour of sheep, rat and rabbit pulmonary surfactant lipids was investigated using high sensitivity differential scanning calorimetry (DSC). 2. Phase transitions were evident in the surfactant lipids from all three animals, with the upper limit of the phase transition being 30.1 C in the sheep, 36.8 C in the rat and 36.3 C in the rabbit. 3. The relatively greater fluidity of the sheep surfactant lipids in comparison to those of the rat and rabbit was due primarily to differences in their palmitic acid content.

Animals↗
PubMed2000

Phase transitions in the incoherent lattice fluctuations in YBa2Cu3O(7-delta)

The growing body of experimental evidence for the existence of complex textures of charges and spins in the high-temperature superconductors has drawn attention to the so-called 'stripe-phase' models as a possible basis for the mechanism of superconductivity in these materials. Such observations have until now been restricted to systems where the texture dynamics are slow or suppressed altogether, and do not include the important case of YBa2Cu3O(7-delta). It seems likely that the dynamic behaviour of stripes, which has been suggested to undergo several phase transitions as a function of temperature, should also be reflected in the lattice properties of the host materials, and this forms the motivation for our present experiments. Specifically, we use MeV helium ion channelling, an ultrafast real-space probe of atomic displacements (with sub-picometre resolution), to probe incoherent lattice fluctuations in YBa2Cu3O(7-delta) as a function of temperature and oxygen doping. We detect lattice fluctuations that are larger than the expected thermal vibration component, and which show anomalies characteristic of the phase transitions anticipated for a dynamic stripe phase. Comparison of our lattice results with single-particle-tunnelling and photoemission data highlights the importance of spin-charge separation phenomena in the copper oxide superconductors.

Journal Article↗
PubMed2004

Structural influence of erbium centers on silicon nanocrystal phase transitions.

Two different types of erbium-doped silicon nanocrystals, along with undoped, oxide-capped Si dots, are employed to probe the impact of the impurity center location on phase transition pressure. Using a combination of high pressure optical absorption, micro-Raman, and x-ray diffraction measurements in a diamond anvil cell, it is demonstrated that the magnitude of this phase transition elevation is strongly dictated by the average spatial location of impurity centers introduced into the nanocrystal along with the interfacial quality of the surrounding oxide.

Journal Article↗
PubMed2001

Theory for phase transitions in insulating V2O3.

We show that the recently proposed S = 2 bond model with orbital degrees of freedom for insulating V2O3 not only explains the anomalous magnetic ordering but also other mysteries of the magnetic phase transition. The model contains an additional orbital degree of freedom that exhibits a zero temperature quantum phase transition in the Ising universality class.

Journal Article↗
PubMed2001

Origins of phase transitions in small systems.

The identification and classification of phases in small systems, e.g., nuclei, social and financial networks, clusters, and biological systems, where the traditional definitions of phase transitions are not applicable, is important to obtain a deeper understanding of the phenomena observed in such systems. Within a simple statistical model, we investigate the validity and applicability of different classification schemes for phase transtions in small systems. We show that the whole complex temperature plane contains necessary information in order to give a distinct classification.

Journal Article↗
PubMed2005

Structure and phase transition in self-assembled films of an anti-ferroelectric liquid crystal studied by two-dimensional correlation FTIR spectroscopy.

The FTIR spectra were measured for a self-assembled film of the anti-ferroelectric liquid crystal (AFLC) molecules over a temperature range of 40-150 degrees C. The frequency and intensity variations of the infrared spectra were discussed in terms of changes in molecular orientation, conformation and intra- and/or inter-molecular interaction during phase transitions. The two-dimensional (2d) correlation analysis revealed that two hydrocarbon chains have different orientation behaviors, the shorter hydrocarbon chain is parallel to molecular long axis and the longer one is perpendicular to it. The splitting of the C=O stretching band indicated that the s-cis and the s-trans conformers of the ester group coexist in the self-assembly film. During the phase transitions, in mesogen part the C=O group adjacent to the chiral part is first response with temperature changing, following the C=O group between two phenyl rings, and eventually the phenyl rings; and the respondence with temperature of methyl is slower than that of methylene in alkyl chains.

Phase Transition↗
PubMed2000

Nonequilibrium phase transitions induced by multiplicative noise: effects of self-correlation

A recently introduced lattice model, describing an extended system which exhibits a reentrant (symmetry-breaking, second-order) noise-induced nonequilibrium phase transition, is studied under the assumption that the multiplicative noise leading to the transition is colored. Within an effective Markovian approximation and a mean-field scheme it is found that when the self-correlation time tau of the noise is different from zero, the transition is also reentrant with respect to the spatial coupling D. In other words, at variance with what one expects for equilibrium phase transitions, a large enough value of D favors disorder. Moreover, except for a small region in the parameter subspace determined by the noise intensity sigma and D, an increase in tau usually prevents the formation of an ordered state. These effects are supported by numerical simulations.

Journal Article↗
PubMed1991

Synergistic effects of Ca2+ and wheat germ agglutinin on the lamellar-hexagonal (HII) phase transition of glycophorin-containing egg-phosphatidylethanolamine membranes.

Glycophorin has been reconstituted into egg phosphatidylethanolamine (egg-PtdEtn) membranes. Stable vesicles were obtained at a molar ratio of 8 x 10(-4) of inserted protein/lipid. This macroscopic change from lipid aggregates to lipid vesicles was followed by density gradient centrifugation. Vesicles formed in the presence of protein enclose the dye calcein and are stable with time and temperature. Membrane aggregation does not occur, as was demonstrated by energy-transfer experiments. The phase transition from the fluid lamellar L alpha phase to the inverted hexagonal HII phase observed at 29 degrees C in pure egg-PtdEtn membranes is suppressed and finally disappears in the presence of glycophorin. The transition enthalpy decreases linearly from delta H = 4 kJ/mol in pure lipids to zero at a protein/lipid molar ratio of 1:1000. Ca2+ ions and wheat germ lectin act synergistically on the phase behavior of vesicles containing glycophorin and phosphatidylethanolamine. Differential scanning calorimetry scans show that the lamellar-to-hexagonal phase transition is reinduced. The membranes aggregate and exchange lipid as could be demonstrated by energy transfer experiments. The dye calcein is released but only if the temperature exceeds the lamellar-to-hexagonal phase transition temperature of the pure egg-PtdEtn.

Calcium↗
PubMed2002

Peptide differential display: a novel approach for phase transition in locusts.

Today, the question of the physiological cause of phase transition, the transition from the solitary to the gregarious phase, in locusts remains unanswered. We hereby present a novel approach by which we have attempted to determine whether different phases express or release different peptides in similar physiological conditions. For this purpose, a peptidomic analysis of the corpora cardiaca and hemolymph of crowded and isolated locusts of Schistocerca gregaria was performed using high performance liquid chromatography and matrix-assisted laser desorption ionisation time of flight mass spectrometry. A comparison between the two conditions reveals differences in the number and amount of peptides present in the corpora cardiaca and the hemolymph. Further research will have to identify these phase specific differences and their role in locust phase polymorphism.

Animals↗