Transition Curves

Note that the fact that the transition curve ends at pi = 1/2 and p2 = 1 could be predicted from a simple symmetry property (called duality in [kinzel85b]) namely, that any PCA defined by a set of conditional probabilities P(o 01O2O3) is preserved when each of these probabilities undergoes the duality transformation... 

Table 5. Formation of the negatively and positive sequences in water and methanol, indicated by the collagen-like CD spectra and by the shape of the temperature transition curve...

Fig. 23. Temperature transition curve of PTC [(Ala-Hyp-Glyhd, in water/methanol volume ratio 1 1...

All relaxation curves exhibited more than one phase at various degrees of conversion and at different temperatures. This clearly rules out the all-or-none mechanism (AON) although the AON model is able to fit easily to the measured equilibrium transition curve. However, a mechanism has been proposed which allows the existence of side... 

In the case of X = Ala, cooperative equilibrium transition curves have been found starting from n = 8 tripeptide units. The reasons for this extraordinary behavior have been discussed concerning the peptide Col 1-3. CD measurements on peptides having chain lengths of 6 and 7 tripeptide units, seem to point out that these peptides are able to form a small amount of triple helix in water near 0 °C. Thus, the sequence (Ala-Gly-... 

In methanol (100%) starting from a chain length of n = 5 tripeptide units, complete transition curves could be measured (Fig. 30). 

A fit of this relation to the experimentally found equilibrium transition curve, = F(7), yields the parameters AIF and AS°. 

This model does not say anything about the mechanism of triple-helix formation, because even in the case of an AON mechanism, nucleation may take place at many positions of the chains and may lead to products the chains of which are staggered. The AON model is based on the assumption that these products are too instable to exist in measurable concentration. As already mentioned, Weidner and Engel142 succeeded in proving by relaxation measurements of al CB2 that the kinetics of in vitro triple-helix formation is governed by more than one relaxation time. This rules out an AON mechanism, but the fitting to the experimentally found equilibrium transition curves nevertheless showed good accommodation and AH° computed from these curves could be confirmed by calorimetric measurement. 

Figure 34 shows two equilibrium transition curves, one of them being computed with the help of the AON model (I), the other by means of the SZ model (II) for arbitrarily chosen parameters. 

At higher temperatures (T > Tm), model II predicts larger values of 0, because this increases the number of possibilities of forming a helix, in contrast to the AON model (I). On the other hand, at lower temperatures, model I gives more possibilities of the realization of the coiled state and thus the transition curve near = 1 is flat in comparison with the AON case. 

Figure 35 shows how the equilibrium transition curves of [(Ala-Gly-Pro)n]3Lys-Lys shift to higher temperatures with increasing chain length. The continuous curves represent the numerical fit to the experimental transition data. 

The ACp s were calculated by ignoring the smooth-protrusions B BC appearing in the Cp = f(T) curves indicated in Fig. 5, and measuring the distance of the intersection A of the tangents AA of the glassy curve and AB of the transition curve from the horizontal tangent CC of the rubbery part of the curve ACp = f(T). The values of ACp s for the different composites are included, among others, in Table 1. 

Figure 5. Sol-gel transition curve for sample C44 in O.IM NaCl, pH 7, 20°C, with copper ( ) and calcium (O) and phase separation curve with copper ( ) and calcium ( ).

Figure 2 compares the conformational transition curves of wild-type yeast glucan (branch frequency = 0.20) and PGG (branch frequency = 0.50). Wild-type yeast glucan required approximately 0.1M NaOH to disrupt the triple helical conformation, whereas this transition is observed at approximately 0.04 M NaOH with PGG. This trend is consistent with the observation that curdlan, an entirely linear p-D(l-3)-linked glucan, requires approximately 0.25M NaOH to disrupt the ordered conformation (76). Hence, it is concluded that the highly branched PGG molecules only form weak inter-chain associations resulting in the formation of predominantly single-helical zones. 

Fig. 3 Liquid-liquid demixing curves (dashed lines denoted by T ) and liquid-solid transition curves (solid lines denoted by Tm) of polymer solutions with variable energy parameter sets [denoted by T(EV/EC, B/Ec)]. The solution system is made of 32-mers in a 32-sized cubic box. a Theoretical curves b simulation results in the optimized approach [14]...

TES suffer from some limitations such as the small useful temperature range and the non-linearity of the transition curve. The latter drawback is especially evident in roughly patterned TES, as in the case shown in Fig. 15.5 [25], Feedback techniques, similar to those used in electronic amplifiers, minimize these drawback, reducing also the TES time response [26], The superconducting transition temperature (sometimes quite different from those of the bulk metal) of a TES made with one metal layer (single layer) depends on the metal used and on the film thickness. 

Fig. la-d Representation of the principal types of spin transition curves (high spin fraction (7hs) (y axis) vs temperature (T) (x axis) a gradual b abrupt c with hysteresis d two-step e incomplete... 

Despite the relative lack of predictability, the number of systems now known to display a spin transition curve of type (c) is remarkably high, and highest for iron(II) where, significantly, the change in intramolecular dimensions is the greatest for the ions for which SCO is relatively common (Fe(II), Fe(III), Co(II)). 

DSC measurements with a microcalorimeter played a key role in tracing the origin of the step observed in the spin transition curve of [Fe(2-pic)3]-Cl2-EtOH [24]. The mixing entropy derived from the measured heat capacity data showed a significant reduction in the region of the step. This has been... 

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