Structures Formed by Cryoprotective Agents Used in Freezc-Etching

The freeze etching technique is potentially useful for examining dilute solutions or suspensions of macromolecular materials. Quick freezing of aqueous solutions in Freon or propane at or near liquid nitrogen temperature produces relatively large ice crystals and these crystals may damage the structures to be examined. Cryoprotective agents may reduce damage to the specimem, hut their use often results in the formation of a different set of specimem artifacts.In a study of the structure of polyethylene oxide gels glycerol and sucrose were used as cryoprotective agents. The experiments reported here show some of the structures which can appear when these cryoprotective agents are used.Figure 1 shows a fractured surface of a frozen 25% aqueous solution of sucrose. The branches of dendritic ice crystals surrounded hy ice-sucrose eutectic can be seen. When this fractured surface is etched the ice in the dendrites sublimes giving the type of structure shown in Figure 2. The ice-sucrose eutectic etches much more slowly. It is the smooth continuous structural constituent surrounding the branches of the dendrites.

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Rate of Sublimation of Ice by Radiative Heating in Freeze-Etching

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600002701 ◽

1980 ◽

Vol 38 ◽

pp. 618-619

Author(s):

Yeshayahu Talmon

Keyword(s):

Heat Flux ◽

Freeze Fracture ◽

Constant Heat Flux ◽

Radiative Heating ◽

Constant Heat ◽

Entire Sample ◽

Simplified Method ◽

Freeze Etching ◽

Sublimation Rates ◽

Fractured Surface

To bring out details in the fractured surface of a frozen sample in the freeze fracture/freeze-etch technique,the sample or part of it is warmed to enhance water sublimation.One way to do this is to raise the temperature of the entire sample to about -100°C to -90°C. In this case sublimation rates can be calculated by using plots such as Fig.1 (Talmon and Thomas),or by simplified formulae such as that given by Menold and Liittge. To achieve higher rates of sublimation without heating the entire sample a radiative heater can be used (Echlin et al.). In the present paper a simplified method for the calculation of the rates of sublimation under a constant heat flux F [W/m2] at the surface of the sample from a heater placed directly above the sample is described.

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Molecular Dynamics Study of Aqueous Solution of Polyethylene Oxide: Critical Test of Force Field Models

Soft Materials ◽

10.1080/1539445x.2012.669221 ◽

2013 ◽

Vol 11 (4) ◽

pp. 371-383 ◽

Cited By ~ 11

Author(s):

Yong-Lei Wang ◽

Rochelle S. Lawrence ◽

Zhong-Yuan Lu ◽

Aatto Laaksonen

Keyword(s):

Molecular Dynamics ◽

Aqueous Solution ◽

Force Field ◽

Polyethylene Oxide ◽

Critical Test

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Demicellization of Polyethylene Oxide in Water Solution under Static Magnetic Field Exposure Studied by FTIR Spectroscopy

Advances in Physical Chemistry ◽

10.1155/2013/485865 ◽

2013 ◽

Vol 2013 ◽

pp. 1-8 ◽

Cited By ~ 17

Author(s):

Emanuele Calabrò ◽

Salvatore Magazù

Keyword(s):

Magnetic Field ◽

Aqueous Solution ◽

Ftir Spectroscopy ◽

Static Magnetic Field ◽

Polyethylene Oxide ◽

Water Solution ◽

Infrared Region ◽

Bending Vibrations ◽

Field Exposure ◽

Methylene Groups

FTIR spectroscopy was used to investigate the alterations of the vibration bands in the mid-infrared region of Polyethylene oxide in aqueous solution at 25 mg/mL concentration under exposure up to 4 h to a static magnetic field at 200 mT. FTIR spectroscopic analysis of PEO solution in the range 3500–1000 cm−1 evidenced the stretching vibrations of ether band, C–H symmetric-antisymmetric and bending vibrations of methylene groups, and the C–O–C stretching band. A significant decrease in intensity of symmetric and asymmetric stretching CH2 vibration bands occurred after 2 h and 4 h of exposure, followed by a significant decrease in intensity of scissoring bending in plane CH2 vibration around 1465 cm−1. Finally, the C–O–C stretching band around 1080 cm−1 increased in intensity after 4 h of exposure. This result can be attributed to the increase of formation of the intermolecular hydrogen bonding that occurred in PEO aqueous solution after SMF exposure, due to the reorientation of PEO chain after exposure to SMF. In this scenario, the observed decrease in intensity of CH2 vibration bands can be understood as well considering that the reorientation of PEO chain under the applied SMF induces PEO demicellization.

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Recent progress in the freeze-etching technique

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1971.0042 ◽

1971 ◽

Vol 261 (837) ◽

pp. 121-131 ◽

Cited By ~ 159

Keyword(s):

High Vacuum ◽

Molecular Size ◽

Etching Technique ◽

Structural Distortions ◽

Shadow Casting ◽

Structural Details ◽

Freeze Etching ◽

The One ◽

Insight Into ◽

Made In

The freeze-etching technique must be improved if structures at the molecular size level are to be seen. The limitations of the technique are discussed here together with the progress made in alleviating them. The vitrification of living specimens is limited by the fact that very high freezing rates are needed. The critical freezing rate can be lowered on the one hand by the introduction of antifreeze agents, on the other hand by the application of high hydrostatic pressure. The fracture process may cause structural distortions in the fracture face of the frozen specimen. The ‘double-replica’ method allows one to evaluate such artefacts and provides an insight into the way that membranes split. During etching there exists the danger of contaminating the fracture faces with condensable gases. Because of specimen temperatures below —110 °C, special care has to be taken in eliminating water vapour from the high vacuum. An improvement in coating freeze-etched specimens has resulted from the application of electron guns for evaporation of the highest melting-point metals. If heat transfer from gun to specimen is reduced to a minimum, Pt, Ir, Ta, W and C can be used for shadow casting. Best results are obtained with Pt-C and Ta-W . With the help of decoration effects Pt-C shadow castings give the most information about the fine structural details of the specimen.

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Fine Structure of Swarmers of Cladophora and Chaetomorpha

Journal of Cell Science ◽

10.1242/jcs.9.3.581 ◽

1971 ◽

Vol 9 (3) ◽

pp. 581-601

Author(s):

D. G. ROBINSON ◽

R. D. PRESTON

Keyword(s):

Cell Wall ◽

Fine Structure ◽

Spatial Arrangement ◽

Cell Wall Synthesis ◽

Fibrous Layer ◽

Etching Technique ◽

Freeze Etching

Naked swarmers of both Cladophora rupestris and Chaetomorpha melagonium have been examined by the freeze-etching technique. The swarmers of Cladophora, collected just after settling, reveal several layers of granules external to the plasmalemma and internal to the so-called ‘fibrous-layer’. Chaetomorpha swarmers collected just before settling show extrusion of vesicles through the plasmalemma. The structures associated with the membranes are discussed in relation to known features of these swarmers already observed by sectioning. The role of granules in the synthesis of cell wall microfibrils is strengthened though the spatial arrangement of the granules seen in this investigation does not completely fulfil the ‘ordered granule’ hypothesis. Description of, and comments on, features related to cell wall synthesis, particularly the Golgi and vacuolar systems, are given.

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