scholarly journals Fission of Lipid-Vesicles by Membrane Phase Transitions in Thermal Convection

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Patrick W. Kudella ◽  
Katharina Preißinger ◽  
Matthias Morasch ◽  
Christina F. Dirscherl ◽  
Dieter Braun ◽  
...  
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Temperature Gradient ◽  
Temperature Drop ◽  
Lipid Vesicles ◽  
Membrane Phase ◽  
Transition Width ◽  
Shear Forces ◽  
Induced Membrane ◽  
Spherical Vesicles

AbstractUnilamellar lipid vesicles can serve as model for protocells. We present a vesicle fission mechanism in a thermal gradient under flow in a convection chamber, where vesicles cycle cold and hot regions periodically. Crucial to obtain fission of the vesicles in this scenario is a temperature-induced membrane phase transition that vesicles experience multiple times. We model the temperature gradient of the chamber with a capillary to study single vesicles on their way through the temperature gradient in an external field of shear forces. Starting in the gel-like phase the spherical vesicles are heated above their main melting temperature resulting in a dumbbell-deformation. Further downstream a temperature drop below the transition temperature induces splitting of the vesicles without further physical or chemical intervention. This mechanism also holds for less cooperative systems, as shown here for a lipid alloy with a broad transition temperature width of 8 K. We find a critical tether length that can be understood from the transition width and the locally applied temperature gradient. This combination of a temperature-induced membrane phase transition and realistic flow scenarios as given e.g. in a white smoker enable a fission mechanism that can contribute to the understanding of more advanced protocell cycles.

The structure of membranes and membrane proteins embedded in amorphous ice

1992 ◽  
Vol 50 (1) ◽  
pp. 432-433
Author(s):  
Uwe Lücken ◽  
Joachim Jäger
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Membrane Proteins ◽  
Phase Transition Temperature ◽  
Lipid Vesicles ◽  
Freezing Stress ◽  
Amorphous Ice ◽  
Different Temperatures ◽  
Band Pass ◽  
Lipid Polymorphism

TEM imaging of frozen-hydrated lipid vesicles has been done by several groups Thermotrophic and lyotrophic polymorphism has been reported. By using image processing, computer simulation and tilt experiments, we tried to learn about the influence of freezing-stress and defocus artifacts on the lipid polymorphism and fine structure of the bilayer profile. We show integrated membrane proteins do modulate the bilayer structure and the morphology of the vesicles.Phase transitions of DMPC vesicles were visualized after freezing under equilibrium conditions at different temperatures in a controlled-environment vitrification system. Below the main phase transition temperature of 24°C (Fig. 1), vesicles show a facetted appearance due to the quasicrystalline areas. A gradual increase in temperature leads to melting processes with different morphology in the bilayer profile. Far above the phase transition temperature the bilayer profile is still present. In the band-pass-filtered images (Fig. 2) no significant change in the width of the bilayer profile is visible.

The Finite Size Effect on The Metal-Insulator Transition of VO2 Films Grown by MOCVD

1991 ◽  
Vol 237 ◽  
Author(s):  
Hyung Kook Kim ◽  
R. P. Chiarello ◽  
Hoydoo You ◽  
M. H. L. Chang ◽  
T. J. Zhang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Particle Size ◽  
Transition Temperature ◽  
Size Effect ◽  
Thermal Hysteresis ◽  
Finite Size ◽  
Finite Size Effect ◽  
Transition Width ◽  
Metal Insulator ◽  
Out Of Plane

ABSTRACTWe studied the finite size effect on the metal-insulator phase transition and the accompanying tetragonal to monoclinic structural phase transition of VO2 films grown by MOCVD. X-ray diffraction measurements and electrical conductivity measurements were done as a function of temperature for VO2 films with out-of plane particle size ranging from 60–310Å. Each VO2 film was grown on a thin TiO2 buffer layer, which in turn was grown by MOCVD on a polished sapphire (1120) substrate. The transition was found to be first order. As the out-of plane particle size becomes larger, the transition temperature shifts and the transition width narrows. For the 60Å film the transition was observed at ∼61°C with a transition width of ∼10°C, while for the 310Å film the transition temperature was ∼59°C and the transition width ∼2°C. We also observed thermal hysteresis for each film, which became smaller with increasing particle size.

scholarly journals Study of the interaction between the antitumour protein α-sarcin and phospholipid vesicles

1989 ◽  
Vol 258 (2) ◽  
pp. 569-575 ◽  
Author(s):  
M Gasset ◽  
A Martinez del Pozo ◽  
M Oñaderra ◽  
J G Gavilanes
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Ionic Strength ◽  
Phase Transition Temperature ◽  
Acyl Chain ◽  
Lipid Vesicles ◽  
Model Systems ◽  
Molar Ratio ◽  
Phospholipid Vesicles ◽  
Acidic Vesicles

alpha-Sarcin is a single polypeptide chain protein which exhibits antitumour activity by degrading the larger ribosomal RNA of tumour cells. We describe the interaction of a alpha-sarcin with lipid model systems. The protein specifically interacts with negatively-charged phospholipid vesicles, resulting in protein-lipid complexes which can be isolated by ultracentrifugation in a sucrose gradient. alpha-Sarcin causes aggregation of such vesicles. The extent of this interaction progressively decreases when the molar ratio of phosphatidylcholine increases in acidic vesicles. The kinetics of the vesicle aggregation induced by the protein have been measured. This process is dependent on the ratio of alpha-sarcin present in the protein-lipid system. A saturation plot is observed from phospholipid vesicles-protein titrations. The saturating protein/lipid molar ratio is 1:50. The effect produced by the antitumour protein on the lipid vesicles is dependent on neither the length nor the degree of unsaturation of the phospholipid acyl chain. However, the aggregation is dependent on temperature, being many times higher above the phase transition temperature of the corresponding phospholipid than below it. The effects of pH and ionic strength have also been considered. An increase in the ionic strength does not abolish the protein-lipid interaction. The effect of pH may be related to conformational changes of the protein. Binding experiments reveal a strong interaction between alpha-sarcin and acidic vesicles, with Kd = 0.06 microM. The peptide bonds of the protein are protected against trypsin hydrolysis upon binding to acidic vesicles. The interaction of the protein with phosphatidylglycerol vesicles does not modify the phase transition temperature of the lipid, although it decreases the amplitude of the change of fluorescence anisotropy associated to the co-operative melting of 1,6-diphenyl-1,3,5-hexatriene (DPH)-labelled vesicles. The results are interpreted in terms of the existence of both electrostatic and hydrophobic components for the interaction between phospholipid vesicles and the antitumour protein.

scholarly journals Study of physical properties of a ferrimagnetic spinel Cu1.5Mn1.5O4: spin dynamics, magnetocaloric effect and critical behavior

RSC Advances ◽  
2021 ◽  
Vol 11 (41) ◽  
pp. 25664-25676
Author(s):  
Abir Hadded ◽  
Jalel Massoudi ◽  
Sirine Gharbi ◽  
Essebti Dhahri ◽  
A. Tozri ◽  
...  
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Physical Properties ◽  
Magnetocaloric Effect ◽  
Phase Transition Temperature ◽  
Magnetic Phase Transition ◽  
Critical Behavior ◽  
Magnetic Phase ◽  
Spin Dynamics ◽  
Critical Behaviour

The present work reports a detailed study of the spin dynamics, magnetocaloric effect and critical behaviour near the magnetic phase transition temperature, of a ferrimagnetic spinel Cu1.5Mn1.5O4.

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