Temperature transitions Thermal

Figure 6. Thermal transition temperatures (T = melting, = isotropization) versus n, the number of methylene units in the polymers containing 4,4 -dihydroxybiphenyl for 1) polyethers ( ) esters (A) T, (A) T. (data from reference 25).

DSC studies have shown that modification alters thermal transition temperatures and the overall enthalpy (AHgei) associated with gelatinization (Tables 10.13 and 10.14). Upon hydroxypropylation, the reactive groups introduced into the starch chains are capable of disrupting the inter-and intra-molecular hydrogen bonds, leading to an increase in accessibility by water that lowers... 

Reports on the action of reduced glutathione give results quite different from the above. The bulky mercaptan does not reduce RNase at all at room temperature. As the thermal transition temperature is approached the reduction appears to be all or none with no evidence of partially reduced intermediates 186). In a study of the recovery of activity after denaturation in 8 M urea, Kim and Paik 187) reported... 

Most studies have concentrated on those conditions where reversible transitions can be demonstrated. However, at neutral pH the thermal transition temperature is high enough to introduce difficulties. Ribo-nuclease kept at 95° at pH 7 for 20 min is irreversibly denatured both in its spectral properties and enzymic activity (337). Tramer and Shugar showed that RNase inactivated at pH 7.8 by heating for 30 min has normalized all of its tyrosine residues as far as alkaline spectrophoto-metric titration is concerned. However, the magnitude of the acid difference spectrum is unaffected although the midpoint has shifted from pH 2 to 3. 

Estimates of Thermal Transition Temperatures in Various Solvents... 

Further information on the binding of tilorone with DNA was derived by studying the thermal melting of the complex27,28. In order to characterize the stability of DNA secondary structure in the presence of tilorone, temperature profiles were run at tilorone/DNA-P molar ratio of 1 5. Tilorone hydrochloride shows a large increase in the thermal transition temperature (rm) of native DNA the Tm of calf thymus DNA was raised from 71.6 to 85.2 °C under these conditions. 

The interaction of tilorone hydrochloride with native DNA stabilizes the double helical structure of the macromolecule towards thermal denaturation. The effect of tilorone hydrochloride on the thermal denaturation of DNA s from various sources having different base composition has been studied28. At a drug to DNA-P molar ratio of 0.21, the Arm increased with increasing AT content of the DNA. This observation indicates that tilorone hydrochloride perferentially binds to the dAT portions of the DNA molecule. This is confirmed by the strong effect of tilorone hydrochloride on the thermal transition temperature of poly d (A-T), ATm = 29 °C. 

Fig.8. Effect of tilorone and congeners on the thermal transition temperature (Tm) of calf thymus DNA. Solvent is 0.01 M Tris-HCl pH 7.0 and the concentrations of DNA-P and congeners are 5 x 10-6M, respectively. Curve 1 = DNA 2 = DNA + MEAA-fluorene 3 = DNA + DEAA-fluorene 4 = DNA + DMAA-dibenzothiophene 5 = DNA + DMAA-dibenzofuran and 6 = DNA + DEAE-fluorenone...

Pfeil (1981) concluded that a-lactalbumin is less stable than lysozyme, with a lower thermal transition temperature, lower denaturational enthalpy, lower heat capacity change, and lower Gibbs free-energy change. 

Figure 2.33 Variation of thermal transition temperatures of poly(vinyl chloride) with plasticizer content.

Ultrasonic nebulizers are less suitable than jet nebulizers for delivery of proteins to the airways because of their thermal sensitivity. In a comparison of eight air-jet and two ultrasonic nebulizers, all air-jet nebulizers maintained the enzymatic activity of rhDNase in both the collected aerosol and the residual volume.With the ultrasonic nebulizers, some thermal denaturation of the enzyme was evident toward the end of the nebulization period when the liquid volume was minimal and its temperature highest. The maximum temperature of the rhDNase solution was 58°C, which was near the thermal transition temperature (approximately 65°C) of the enzymes.f ... 

Table 14. Effect of daunomycin and its derivatives on the thermal transition temperature (Tm) and viscosity of DNA...

Fig. 19. Effect of tilorone on the thermal transition temperature (Tm) of calf thyms DNA. Solvent is 0.01 M Tris. HC1 (pH 7.0), and the DNA concentration is 5xlO "sM in all experiments. Curve 1 represents the melting profile of DNA in the absence of tilorone, and curve 2 is the melting profile of DNA in the presence of lxlO sM tilorone hydrochloride...

There are at least four main thermal transition temperatures (Ty) that are characteristic of vicinal water. These are 15°C, 30°C, 45°C, and 60°C. The... 

Microphase separation and domain formation in block copolymers, which are the result of incompatibility of block chains, have been studied extensively (1,2). In addition to being incompatible, block chains in a copolymer generally have different thermal transition temperatures. The surface tensions of molten block chains also differ. When a crystalline block chain is incorporated into a block copolymer, it is expected that crystallization of the crystalline block chain causes considerable change in resultant morphology. Surface properties of a block copolymer and of its blend with a homopolymer should also be modified by the surface tension difference between block chains and the homopolymer. Since these factors determine the morphological features of a block copolymer both in bulk and at surface, a unified study of morphology, crystallization, and surface activity of any block copolymer is important to our understanding of its physical properties. 

Table V. Thermal Transition Temperatures of PTHF and Block Copolymers...

In a continuation of work on membranes, the 1 3C nmr spectra of membranes from Acholeplasma laidlawii grown on 13C-enrichcd palmitic acid were recorded (Metcalfe et al., 1972 1973a Metcalfe, 1972). The enhanced carboxyl resonance was the only peak observed under conditions where no natural abundance 13 C signals were measurable and the temperature exceeded the thermal transition temperature of the lipids in the membranes. The ability to reduce the 13 C nmr spectra of membranes to a few sharp resonances by incorporating 13 C-enriched lipids biosynthetically allows the T, -values to be obtained. 

As in the case of cycloalkanes, the types of motion in the homologous series of phenylenes is strongly size dependent. Figure 5.1 shows the thermal transition temperatures as a function of phenylene groups and in Table 5.1 the transition entropies are listed. The first member of the series shows no thermal transitions below the melting temperature (Sect. 5.1.1). With the second and third, a condis phase becomes obvious (Sect. 5.1.2) and with the fifth, liquid crystalline states exist in addition (Sect. 5.1.3). Poly-p-phenylene (Sect. 5.1.4) is the limiting member of these molecules. 

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