Peculiarities of melting and crystallization of n-decane in a porous glass

Melting and crystallization of n-decane embedded into porous glass with the mean pore size of about 6.4 nm were studied using acoustic and DSC methods. Smearing of the phase transitions, decrease of melting and freezing temperatures, pronounced hysteresis between melting and crystallization were revealed by both methods. In DSC measurements for the pore filling factors 70% and higher double peaks were observed upon cooling while only single peaks were present upon heating. Also a high reduction of the corresponding phase transition heats was revealed. Melting and freezing intervals determined by acoustic and DSC methods strongly differed from each other. A model which qualitatively explains the observed anomalies is proposed. It supposes the formation of liquid layers on the surface of the pores.     

Optical investigation of the vertical diffusion of manganese in planar structures based on CdTe and Cd1 − x Mg x Te with ultrathin MnTe layers

The emission spectra of planar structures based on CdTe and Cd_{1 ? x} Mg _x Te containing periodically built-in MnTe layers with a nominal thickness of one monolayer have been investigated. The luminescence spectra and luminescence excitation spectra of manganese ions and excitons, as well as the dependences of the spectra on the temperature and magnetic field strength, are used to determine the actual distribution of manganese ions. The full width at half-maximum of the profile describing the change in the concentration of manganese in the growth direction of the structures is estimated to be 7–8 monolayers.     

Calorimetric study of the native and postdenatured structures in starches with different degree of hydration

DSC studies of melting process of annealed native structures and postdenatured ones in low-amylose starches with different degrees of hydration were carried out. The starch recrystallization at different thermal treatments of the samples was studied both after the complete and partial destroy of native structures. It has been shown that native structures as well as postdenatured ones possess the ability to perfection, which is most clearly seen at the annealing at temperatures inside their melting ranges. The results obtained demonstrate that at the same duration of annealing the process of crystal perfection for secondary starch structures proceed more intensively compared to the native ones. The presence of the remained native structures in partial melt in contrast to the remained gel ones restricts the ability of the recrystallized structures to perfection.     

Calorimetric Study of the Glass Transition Process in Humid Proteins and DNA

By method of differential scanning calorimetry the absolute values of heat capacity for the systemwater–biopolymer (globular and fibrillar proteins and DNA) were measured in a wide range of temperatures (from -30 up to 130°C) and concentrations of proteins both in native and denatured states. Thermal properties of humid denatured biopolymers demonstrate a characteristic anomaly in the form of the heat capacity jump at temperature depending on the bound water content. It has been shown that in the systems studied a glass transition, where water serves as a native plasticizer, is observed. It has been established that the S-shaped character of all heat capacity curves obtained on dehydration for native and denatured biopolymers is due to the gradual transition to the glassy state of both native and denatured samples. It was found that thermally denatured humid small globular proteins at subsequent dissolving in water at room temperature are able to restore their native structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

DSC Study of the Postdenaturated Structures in Biopolymer–water Systems

The temperature dependences of heat capacity for water–denaturated biopolymer (globular proteins, collagen and DNA) were measured in a wide range of temperatures (0–140°C) and water content of the systems. It has been shown that thermally denaturated globular proteins (lysozyme, myoglobin and catalase) are able to form the thermoreversible heat-set structures under the certain conditions studied. The additional endothermal maximum observed is the calorimetric manifestation of the phase transition related to the melting of these thermotropic non-native structures. The melting gels are completely formed just after denaturation during relatively short time and only their prolonged state at T>T _d leads to their transformation to thermoirreversible non-melting ones. The post denaturated structures from water-denaturated protein (Mb, Lys and RN-ase) systems with a different amount of free water were also studied. The thermoreversible cold-set gels are formed from both water-denaturated DNA and water-denaturated collagen systems. These thermotropic structures are metastable. A spatial gel network of both collagen and DNA is formed from the native-like renaturated structures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dehydrated native biopolymers - a unique representative of glassy systems

DSC study of native and denatured biopolymers with different chemical and steric structure was carried out in a wide range of temperatures and water contents. It was shown that all the native and denatured humid biopolymers studied are glassy systems. The residues of native structures surviving after partial dehydration prevent the glass transition at the glass transition temperatures of the denatured biopolymers. In dehydrated native biopolymers the processes of melting and glass transition take place in the same temperature range that leads to a large change of the heat capacity across denaturation.