Temperature dependent shifts

There are substantial difficulties in the interpretation of temperature-dependent shifts of protein spectra because of the thermal lability of proteins and the possibility of temperature-dependent conformational transitions. Low-temperature studies in aqueous solutions revealed that for many of the proteins investigated the observed shifts of the fluorescence spectra within narrow temperature ranges were probably the result of cooperative conformational transitions, and not of relaxational shifts/100 1 Spectral shifts have also been observed for proteins in glass-forming solvents, 01) but here there arise difficulties associated with the possible effects of viscous solvents on the protein dynamics. 

Table I lists the comparative parameters for the various indochinite spectra. Two methods were used in preparing these samples. The first two samples listed were prepared by grinding the indochinite specimen and binding the powder with water glass. The other samples were sliced with a diamond saw. The two spectral lines are given with their position, width, height, and area. The quadrupole splitting and isomer shift are listed in the columns labeled QS and IS. (The isomer shift is really a combination of isomer shift and temperature-dependent shift, and the values are relative to iron in palladium.) The raw data points were fitted with a two-peak Lorentzian using an IBM 7094 least-squares fit.

The fluorine shifts of a-aldohexopyranosyl fluorides, having an axially oriented fluorine atom, are at higher field than those of the corresponding, equatorially oriented /8 counterparts, which, in turn, were found to display temperature-dependent shifts. ... 

In 1,1,2,2-tetrachlorethane solution, the spectra of thianthrene and trans-thianthrene 5,10-dioxide are temperature independent for the cis-isomer, the lower-field resonance shifts further downfield with increasing temperature while the signals for 2-, 3-, 7-, and 8- protons remain constant over a 200° range. In chloroform, small, apparant temperature-dependent shifts for thianthrene, at all positions, were attributed to temperature-dependent shifts of the reference solvent signal. Using this, it was shown... 

PPG (at higher temperatures) behaves like a typical pseudoplastic non-Newtonian fluid. The activation energy of the viscosity in dependence of shear rate (284-2846 Hz) and Mn was detected using a capillary rheometer in the temperature range of 150-180°C at 3.0-5.5 kJ/mol (28,900 Da) and 12-13 kJ/mol (117,700 Da) [15]. The temperature-dependent viscosity for a PPG of 46 kDa between 70 and 170°G was also determined by DMA (torsion mode). A master curve was constructed using the time-temperature superposition principle [62] at a reference temperature of 150°G (Fig. 5) (Borchardt and Luinstra, unpublished data). A plateau for G was not observed for this molecular weight. The temperature-dependent shift factors ax were used to determine the Arrhenius activation energy of about 25 kJ/mol (Borchardt and Luinstra, unpublished data). 

For linear thermorheologically simple materials a single temperature-dependent shift factor, aT T), can be used to predict the transient thermal response [20]. The mechanical response is history dependent and involves the use of reduced times, ( ) and (t), which can be found from the shift factor as... 

The equilibrium constant for the reaction between methanol on surface sites and internal sites, K, is the most complex in its temperature and acetylation dependence. In some coals temperature dependences shift about from exothermic to endothermic reactions, and no overall pattern for high rank and low rank coals seems to exist. 

One of the few MAS studies of potassium has been on the superoxide KO2 using a 7.5 mm MAS probe spinning at 5 kHz.167 The two polymorphs (cubic and tetragonal) show different temperature-dependent shifts and co-exist over... 

Curves of stress (divided by absolute temperature) versus log time-to-break at various temperatures can be made to coincide by introducing the temperature-dependent shift factor flT. Application of the same shift factor causes the curves of the elongation at the break br versus the logarithm of time-to-break at various temperatures to coincide. A direct consequence is that all tensile strengths (divided by absolute temperature), when plotted against elongation at break, fall on a common failure envelope, independent of the temperature of testing. Fig. 13.84 shows the behaviour of Viton B elastomer. 

Figure 7 Absorption frequency (Q-branch) vs. temperature for the CO asymmetric stretch of W(CO)6 in the gas phase. A representative error bar is shown. Extrapolation to 450 K (internal vibrational temperature following relaxation of the 2000 cm-1 CO stretch) yields a temperature-dependent shift of 1.1 cm" 1 from the peak position at 326 K, the initial sample temperature.

Thermalization by multiple trapping dominates over direct timneling above 50-100 K. The luminescence energy reflects the carrier distribution and so is expected to have a temperature-dependent shift of the peak energy, given from Eq. (8.16) by... 

Conventionally storage modulus versus frequency and temperature results are presented by extrapolated isotherms called master curves. These are plotted by shifting frequency data with a temperature dependent shift factor, a. Most published results for are based on manual graphic methods. Computer work first aimed at systemizing and automating determinations of shift factor was initiated by a desire to efficiently process the hundreds of data points from each FTMA run. 

Golding s theory of temperature-dependent shifts has been extended to take into account the spin-exchange interaction of the copper atoms. The spin-exchange Hamiltonian is of the type —IJSi.Sj. For the terminal protons H( 1) and H(2) in [6 ] the contact shift can be shown to be given by ... 

Unlike the metabolite-binding or T box riboswitches, RNA thermosensors do not bind a ligand and instead exhibit a temperature-dependent shift in structure. The ROSE (repression of heat-shock gene expression) element, responsible for induction of heat-shock gene expression in rhizobia, has been characterized by NMR. This analysis allowed determination of the three-dimensional structure of the RNA in its inhibitory state (at low temperature) as well as analysis of the structural transitions that occur in the RNA as the temperature is increased. 

A hyperfine effect has been described which can generate a temperature-dependent shift of the centroid of the resonance lines only in rare circumstances. This is the pseudoquadrupole hyperfine interaction [64]. 

These equations reduce to the ones derived by van t Hof and Schmidt and also Harris when the scattering amplitudes in the ground and excited states are identical. We further note that in case of negligible exchange (r i2 34 r,2) for both transitions also Lorentzian lineshapes are predicted with widths determined by T,y. The temperature-dependent shift will now be induced by the acoustic phonons of the crystal. 

Figure 2.15 Construction of the time-temperature superposition and derivation of temperature dependent shift factor.

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