Transition behavior, calorimetric

Leprince, O. and Walters-Vertucci, C. A calorimetric study of the glass transition behaviors in axes of Phaseolus vulgaris L. seeds with relevance to storage stability. Plant Physiol, 109,1471, 1995. 

Bassi M, TonelU C, Di Meo A. Glass transition behavior of a microphase segregated polyurethane based on PFPE and IPDI. A calorimetric study. Macromolecules 2003 36(21) 8015-23. 

The A//x r of the transition from T to R is a thermodynamically valuable parameter for understanding the behavior of the enzyme. However, this quantity cannot be measured directly because the transition can only be achieved by addition of a smaU-molecule substrate or an analog thereof. One such analog, N-(phosphonacetyl)-L-aspartate (PALA), is very effective in promoting the T R transition. Calorimetric measurements have been reported [8] for the mixed process of binding the PALA and the accompanying T R transition. The observed A/fm values (per mole of enzyme) depend on the number of moles of PALA bound. 

Bheda et al. ( ) showed that cellulose triacetate forms a mesophase in dichloroacetic acid. Navard and Haudin (18) examined the thermal behavior of liquid crystalline solutions of CTA in TFA. Navard et al. (23) studied the isotropic to anisotropic transitions of solutions of cellulose triacetate in TFA using differential scanning calorimetry. Navard and Haudin (S2) studied the mesophases of cellulose and cellulose triacetate calorimetrically. Navard et al. (83) report similar studies. Meeten and Navard (97) showed the twist of the cholesteric helicoidal structure of CTA and secondary cellulose in TFA is left-handed. 

There have been numerous studies employing calorimetric(19), dynamic mechanical, ( ) dielectric, ( ) and morphological(23,24) techniques to elucidate the solid-state behavior of styrene-ethylene oxide block copolymers. These measurements have focused on transition-temperature phenomena, and they have provided reference data on the bulk properties of the copolymers. The evidence accumulated to date indicates that PS and PEO are incompatible in the bulk. While this appears true, in general, one cannot rule out the possibility that PS and PEO have some limited degree of miscibility in the copolymers. It is also unknown, at this time, what influence an interface (e.g., the air-polymer interface) has... 

Figure 5 shows the thermally induced (10-60°C) changes in the CHj stretching frequency of intact human SC plotted as a function of hydration and reheating. Corresponding data for the extracted lipid samples are depicted in Fig. 6. For SC, the frequency increased with temperature and showed a small, but definite, inflection point between 35 and 45°C. Under dry conditions, the midpoint was estimated to be 45°C, decreasing to a constant value of 35°C as the hydration level was increased. This behavior closely mimicked the calorimetric results described, suggesting that the 35°C inflection observed by IR corresponded to the same endothermic process measured by DSC. However, no evidence of a thermal transition at 35°C was observed by IR in the...

Although studies of the thermotropic phase behavior of singlecomponent multilamellar phospholipid vesicles are necessary and valuable, these systems are not realistic models for biological membranes that normally contain at least several different types of phospholipids and a variety of fatty acyl chains. As a first step toward understanding the interactions of both the polar and apolar portions of different lipids in mixtures, DSC studies of various binary and ternary phospholipid systems have been carried out. Phase diagrams can be constructed by specifying the onset and completion temperatures for the phase transition of a series of mixtures and by an inspection of the shapes of the calorimetric traces. A comparison of the observed transition curves with the theoretical curves supports... 

The occurrence of cholesterol and related sterols in the membranes of eukaryotic cells has prompted many investigations of the effect of cholesterol on the thermotropic phase behavior of phospholipids (see References 23-25). Studies using calorimetric and other physical techniques have established that cholesterol can have profound effects on the physical properties of phospholipid bilayers and plays an important role in controlling the fluidity of biological membranes. Cholesterol induces an intermediate state in phospholipid molecules with which it interacts and, thus, increases the fluidity of the hydrocarbon chains below and decreases the fluidity above the gel-to-liquid-crystalline phase transition temperature. The reader should consult some recent reviews for a more detailed treatment of cholesterol incorporation on the structure and organization of lipid bilayers (23-25). 

Polymorphism. The structural stabihty of margarine is influenced by the properties of the crystal lattice and by the actual amount of solid fat present. Many organic compounds or mixtures such as fats can sohdify in more than one crystalline pattern. The primary crystal forms of triglycerides are designated a, p, and p, which correspond to three principal cross-sectional arrangements of the fatty acid chains (71). These may be differentiated by characteristic x-ray diffraction patterns (72) and heats of transition observed in calorimetric studies (73). Phase behavior of... 

Where and LH are the corresponding activation energy and enthalpy of phase transition and the coefficient defines the maximum probability that molecules will cross the interface between the liquid and SCF (vapor) phases. This simple relationship can explain the behavior of the mass transfer coefficient in Figure 15 when it is dominated by the interfacial resistance. Indeed, increases with temperature T according to Eq. (49) also, both parameters E and A// should decrease with increase of pressure, since the structure and composition of the liquid and vapor phases become very similar to each other around the mixture critical point. The decrease of A/f with pressure for the ethanol-C02 system has been confirmed by interferometric studies of jet mixing described in Section 3.2 and also by calorimetric measurements described by Cordray et al. (68). According to Eq. (43) the diffusion mass transfer coefficient may also increase in parallel with ki as a result of more intensive convection within the diffusion boundary layer. 

The thermochemical properties of the rare-earth orthophosphates [plus Sc(P04) and Y(P04)] have recently been investigated in detail by Ushakov et al. (2001). These workers obtained the formation enthalpies of 14 orthophosphates by using calorimetric techniques and found an almost linear dependence between the enthalpies of formation and the rare-earth radius, from La(P04) (-321.4 kJ/mol) to Lu(P04) (-236.9 kJ/mol) xenotime and pretulite were found to be consistent with this behavior as well. The structural transition from the xenotime structure to the monazite structure was not manifested in a significant discontinuity in the relatively linear trend in the enthalpies of formation. The complete results of these detailed thermochemical studies are tabulated in Ushakov et al. (2001). 

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