Metastable structures, revealed

Lipid-water gel phases were previously regarded as metastable structures that are formed before separation of water and lipid crystals when the corresponding lamellar liquid crystal is cooled. New information on gel phases (see below) reveals that they can form thermodynamically stable phases with very special structural properties. This characteristic makes them as interesting as the lamellar liquid crystals from a biological point of view. 

Revealing Important Metastable Stmctnres by GA. Metastable RNA structures are transient conformations and therefore are rather difficult targets for an investigation. Simulations of RNA folding by GA can reveal such structures. For example, GA simulations predicted that the RNA primer for replication of ColEl plasmid is folded through an intermediate metastable structure that has a different activity compared to... 

Stability of W/OAV multiple emulsion containing Span 80 and Tween 80 was evaluated with respect to sodium chloride and sodium salicylate concentrations in the inner water phase (Jiao and Burgess, 2002). In this study we observed that the multiple emulsion droplets deformed and there was coalescence of the inner aqueous droplets as we applied an external force (i.e., a microscopic covershp) to multiple emulsion samples on a microscope slide. Under certain conditions (e.g., lipophihc surfactant concentration and internal phase osmotic pressure) the destabilized multiple emulsions formed unique metastable structures that had a dimpled appearance. The formation of these metastable structures correlated with the real time instability of the W/O/W multiple emulsions investigated. Our study revealed that emulsions with a salt concentrations closer to the optimal value calculated by using (1.7) had maximum stability. 

It has been shown that pyramids and domes can coexist at certain conditions and that pyramids are metastable structures that can directly transform into domes with increasing Ge deposition or postannealing treatment [24], Pyramids and domes usually form at high temperatures, whereas the much smaller hut clusters nucleate at lower temperatures. Figure 12.3 shows aO.8 x 0.8 pm atomic force microscopy (AFM) scan of nominally 5.8 ML Ge QDs grown at 500°C. The image reveals small hut clusters of diameters 20 nm with areal density of 1 x 10 cm . ... 

Acetylene forms spontaneously an ordered (2 X 2) surface structure on the Pt(l 11) surface at 300 K, at low exposure under ultrahigh vacuum conditions. The intensity profiles reveal that this structure is metastable, and upon heating to 350-400 K for one hour, it undergoes a transformation to a stable structure with the same (2 X 2) unit cell. Ethylene adsorbs on the Pt(l 11) surface and at 300 K, it forms an ordered (2 X 2) surface structure that is identical to the stable acetylene structure as shown by the intensity profiles. 

Occasionally, long-range disorder and/or different phases may coexist within a crystalline material. Arrangement of molecules in the different regions will necessarily be different in at least some respects. One of the earliest reports of invocation of this phenomenon involves the photodimerization of anthracene in the crystalline state [219]. In the crystal structure of anthracene, the faces of no molecules are separated by <4 A. Yet upon irradiation, a dimer is readily formed. Thomas, Jones, and co-workers used electron microscopy to reveal the coexistence inside normal anthracene crystals of regions of a metastable phase. In the minor phase (space group PI), the C9- -C9. distance is 4.2 A, whereas in the stable crystal it is 4.5 A. The dimerization is proposed to originate in the minor phase of the crystal. 

While the spectrum shown in Figure 1 may be very useful in many applications, it does not reveal structural information. In many cases, such information may be obtained by studying the metastable decomposition of major ions. The Instrument used in this laboratory may be operated in a manner in which an ion such as the (M-H) ion of the fatty acid is selected, even at high resolution if necessary, by using MS-I and its decompositions in the field free region between MS-I and MS-II followed by scanning the second ESA (MS-II). However, the metastable decompositions of the (M-H) ions of the... 

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