Pretransition

Fig. 12. The relationship between the mean oceanic residence time, T, yr, and the seawater—cmstal rock partition ratio,, of the elements adapted from Ref. 29. , Pretransition metals I, transition metals , B-metals , nonmetals. Open symbols indicate T-values estimated from sedimentation rates. The sohd line indicates the linear regression fit, and the dashed curves show the Working-Hotelling confidence band at the 0.1% significance level. The horizontal broken line indicates the time required for one stirring revolution of the ocean, T. ...

L. Sallen, P. Sotta, P. Oswald. Pretransitional effects near the hexagonal-micellar phase transition of the CnEOA/HoO lyotropic mixture. J Phys Chem 707 4875-4881, 1997. 

With certain lipid bilayers, a change of physical state referred to as a pretransition occurs 5° to 15°C below the phase transition itself. These pretransitions involve a tilting of the hydrocarbon chains. 

V.G. Pushin and V.V. Kondrat ev, Pretransition phenomena and martensitic transformations, Phys. Met. 

D. Schryvers and L.E. Tanner, Electron microscopy of stress-induced martensite and pretransition... 

We did not extensively discuss the consequences of lateral interactions of surface species adsorbed in adsorption overlayers. They lead to changes in the effective activation energies mainly because of consequences to the interaction energies in coadsorbed pretransition states. At lower temperatures, it can also lead to surface overlayer pattern formation due to phase separation. Such effects cannot be captured by mean-field statistical methods such as the microkinetics approaches but require treatment by dynamic Monte Carlo techniques as discussed in [25]. 

Fig. 14. Factor analysis loadings (first and second spectral components) for thermal unfolding of RNase A as monitored with amide F FTIR and far-UV ECD. In each case a pretransition is evident in the curves before the main transition at 55°C. This full band shape analysis can sense smaller variations and can be partitioned to give added insight. Since the main ECD change could be shown to be loss of intensity, the major structural change was unfolding of a helix. The frequency dispersion of the FTIR change showed that some /3-sheet loss accompanied this pretransitional helix unfolding, but that most sheet loss was in the main transition.

Marsh, D. (1991). Analysis of the chainlength dependence of lipid phase transition temperatures main and pretransitions of phosphatidylcholines main and non-lamellar transitions of phosphatidylethanolamines, Biochem. Biophys. Acta-Biomembranes, 1062, 1-6. 

The signal contained an initial decay in the form of a spike. We may consider three possibilities as originally cansing the photocurrent decay in the pretransit region. 

In addition to the above effects, the intermolecular interaction may affect polymer dynamics through the thermodynamic force. This force makes chains align parallel with each other, and retards the chain rotational diffusion. This slowing down in the isotropic solution is referred to as the pretransition effect. The thermodynamic force also governs the unique rheological behavior of liquid-crystalline solutions as will be explained in Sect. 9. For rodlike polymer solutions, Doi [100] treated the thermodynamic force effects by adding a self-consistent mean field or a molecular field Vscf (a) to the external field potential h in Eq. (40b). Using the second virial approximation (cf. Sect. 2), he formulated Vscf(a), as follows [4] ... 

We may also predict pretransitional enhancement of the height fluctuation. By assuming that ( ) has the profile of the Rayleigh wave, we may calculate the excess free energy in terms of the height deviation h, Eq. (7.3), in the form,... 

Between the pretransition temperature and Tm solid and liquid regions may coexist within a bilayer.101 The term lateral phase separation has been applied to this phenomenon.105 106 Since changes in the equilibrium between solid and liquid can be induced readily, e.g., by changes in the ionic environment surrounding the bilayer, lateral phase separation may be of significance in such phenomena as nerve conduction.107... 

EPR spectrum of tetramethylpiperidine-l-oxyl dissolved in an aqueous dispersion of phospholipids. (Top) above the main bilayer transition temperature Tt (center) between Tt and pretransition temperature (bottom) below pretransition temperature. From Shimshick and McConnell/... 

Much of the interpretation of the observed changes in EPR spectra of spin labels is empirical. For example, the spectra in the accompanying figure can be interpreted to indicate that the spin label dissolves in the lipid to a greater extent at higher temperatures. The ratio/(defined in the figure) is an empirical quantity whose change can be monitored as a function of temperature. Plots of/vs T have been used to identify transition and pretransition temperatures in bilayers.1... 

The coordination chemistry of sea water represents a new and useful approach to understanding the chemical properties of sea water. The coordination chemistry of sea water differs from contemporary coordination chemistry in the following respects most complexes involve pretransition metals, most complexes are labile, the ligands are simpler (water, hydroxide, chloride, carbonate, sulfate), and time and space are important parameters. Principles of coordination chemistry are applied to contemporary research in marine science in four areas analysis of constituents of natural waters, the nature of metallic species in the oceans, the Red Tide problem, and carbonate geochemistry. 

Different Metals. Typically the coordination chemistry of the laboratory deals with the transition metals, usually of the d type, and the coordination chemistry of the metals of Groups I and II is commonly neglected. In contrast, the coordination chemistry of the ocean would, at first, seem to be the exclusive province of the pretransition metals this is seen clearly by looking at an average composition of an ocean (Table I) (36). 

Price, F. P. and Wendorff, J. H. Transitions in mesophase forming systems. I. Transformation kinetics and pretransition effects in cholesteryl myristate. J. Phys. Chem. 75, 2839 (1971)... 

Cevc, G. (1991). Polymorphism of the bilayer membranes in the ordered phase and the molecular origin of the lipid pretransition and rippled lamellaBiochimica et Biophysica Acta, 1062, 59-69. 

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