Thermal/thermodynamic probing

The studies discussed above gives an idea of conformational stability of proteins in ILs as inferred from the t measurement and melting temperature determination followed by various spectroscopic methods. However, stability of a protein/enzyme has contributions from both thermodynamic and kinetic parameters [55]. While thermal unfolding studies help to extract important thermodynamic parameters, stability of the proteins could also arise from the kinetic barrier to the conformational changes in the protein scaffold [55]. However, except for monellin [48], the thermodynamic stability in other cases has not been examined. Thus, in context of stability of proteins/enzymes in ILs, it is important and imperative to study and probe thermal unfolding as well as the thermodynamics and kinetics of the conformational change of the proteins in ILs. 

Radiation probes such as neutrons, x-rays and visible light are used to see the structure of physical systems through elastic scattering experiments. Inelastic scattering experiments measure both the structural and dynamical correlations that exist in a physical system. For a system which is in thermodynamic equilibrium, the molecular dynamics create spatio-temporal correlations which are the manifestation of thermal fluctuations around the equilibrium state. For a condensed phase system, dynamical correlations are intimately linked to its structure. For systems in equilibrium, linear response theory is an appropriate framework to use to inquire on the spatio-temporal correlations resulting from thermod5mamic fluctuations. Appropriate response and correlation functions emerge naturally in this framework, and the role of theory is to understand these correlation functions from first principles. This is the subject of section A3.3.2. 

The light-scattering spectrum which is related to 7 (q, /) by Eq. (3.3.3) consequently probes how a density fluctuation <5/ (q) spontaneously arises and decays due to the thermal motion of the molecules. Density disturbances in macroscopic systems can propagate in the form of sound waves. It follows that light scattering in pure fluids and mixtures will eventually require the use of thermodynamic and hydrodynamic models. In this chapter we do not deal with these complicated theories (see Chapters 9-13) but rather with the simplest possible systems that do not require these theories. Examples of such systems are dilute macromolecular solutions, ideal gases, and bacterial dispersions. ... 

For infinite dilution operation the carrier gas flows directly to the column which is inserted into a thermostated oil bath (to get a more precise temperature control than in a conventional GLC oven). The output of the column is measured with a flame ionization detector or alternately with a thermal conductivity detector. Helium is used today as carrier gas (nitrogen in earlier work). From the difference between the retention time of the injected solvent sample and the retention time of a non-interacting gas (marker gas), the thermodynamic equilibrium behavior can be obtained (equations see below). Most experiments were made up to now with packed columns, but capillary columns were used, too. The experimental conditions must be chosen so that real thermodynamic data can be obtained, i.e., equilibrium bulk absorption conditions. Errors caused by unsuitable gas flow rates, unsuitable polymer loading percentages on the solid support material and support surface effects as well as any interactions between the injected sample and the solid support in packed columns, unsuitable sample size of the injected probes, carrier gas effects, and imprecise knowledge of the real amount of polymer in the column, can be sources of problems, whether data are nominally measured under real thermodynamic equilibrium conditions or not, and have to be eliminated. The sizeable pressure drop through the column must be measured and accounted for. 

Thermodynamics for the sequence with the native state shown in Fig. 4 with the contact interaction potentials By taken from Table III of Ref. 54 reveals that it folds cooperatively in an apparent two-state manner. This is also reflected in the thermal distribution of the overlap function values /i(x) at the folding transition temperature 7> (Fig. 4). A nearly bimodal distribution of h(y) with the peaks at X 0.2 (NBA) and x 0-6 (unfolded state) is observed. There is also nonneghgible contribution from the intermediate values of % representing partially folded structures. Experiments that probe in more detail the thermal unfolding of proteins are beginning to reveal the possible importance of these... 

During the last decade there has been a rapid expansion in the scope of experimental studies on clathrate hydrates. In particular, differential scanning calorimetry studies have been used to obtain direct measurements of thermodynamic properties and accurate measurements of composition [14], and Xe NMR has been used as a direct probe of the environment of the guest molecules [15]. Measurements of the thermal conductivity have also attracted considerable interest [16]. Other related experiments include supersonic beam [6] and thin-film IR [17] studies, which have been used to study some of the processes that might contribute to nucleation of clathrate hydrates. These experiments are beginning to provide the sort of data base that is needed for a fundamental understanding of the behaviour of clathrate hydrates. 

Mini-probes (Figure 6) have been developed for the determination of thermodynamic properties of MIEC as a function of composition Zirconia- or thoria-based tubes, a few mm in diameter, have been used. A metal-metal oxide system serves as a reference. Such cells have been used for the measurement of oxygen potential in urania-based solid solutions or for continuous control of oxygen redistribution in UO2+X under a thermal gradient [Ducroux et al, 1980 Une Oguma, 1982]. 

B, 2 (19), 2868-2873 (e) Zheng, L. and Breiman, J.D. (1998) Measurement of intrinsic fluorescence to probe the conformational flexibility and thermodynamic stability of a single tryptophan protein entrapped in a sol-gel derived glass matrix. Analyst, 123 (8), 1735-1744 (f) Zheng, L Flora, K., and Brennan, J.D. (1998) Improving the performance of a sol-gel-entrapped metalbinding protein by maximizing protein thermal stability before entrapment Chem. Mater., 10 (12), 3974-3983 (g)... 

Organocobalt porphyrin complexes have also yielded useful mechanistic information. The reactions of (tetrakis(p-methoxyphenyl)porphyrinato)cobalt(II) ((TAP)Co(II)) with radicals derived from dialkylazo thermal initiators with acrylic monomers provide evidence for the intermediacy of Co(III)-H species in CCTP. Reaction of (TAP)Co (II) with tertiary alkyl radicals, for example, as derived from AIBN in the presence of monomers that form stable Co-alkyl complexes, such as methyl acrylate, results in quantitative formation of Co(III)-alkyl. Whereas with monomers leading to tertiary C-Co bonds, such as MMA, the Co (II) is very much a spectator as normal polymerization ensues. Thermodynamic and activation parameters have been measured for the dissociation of (TAP)Co(III)-C(CH3)2CN to Co(II) and organic radical in solution as a probe into CCTP mechanism by low-spin Co(II). ... 

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