Rotational correlation time temperature dependence

The modification of electrodes with PVC membranes has found applicability in ion selective electrode work [99] (so-called "coated wire electrode ). The molecular motion of species within such electrodes has been investigated by Compton and Waller [100]. Using a range of derivatives of the nitroxide spin probe TEMPO, they were able to show how the rotational correlational time was dependent upon the molecular volume of the probe and, by use of variable-temperature apparatus, how this varied with temperature. The effect of various plasticizers upon the molecular motion within the PVC membrane was investigated, rotational correlational times being dependent upon the nature of the plasticizer and the loading level. The effect of loading level upon the correlation time was shown to correlate with data obtained by Compton Maxwell [101] for the response times of K+ ion selective electrodes based upon PVC modified electrodes. 

For the analysis of the correlation time temperature dependence, the equation (Equation 6.16) was used in the region of fast rotation of ARs. In the region of slow rotations, values were estimated using the S parameter [10] ... 

Reticulum ATPase [105,106], Owing to the long-lived nature of the triplet state, Eosin derivatives are suitable to study protein dynamics in the microsecond-millisecond range. Rotational correlation times are obtained by monitoring the time-dependent anisotropy of the probe s phosphorescence [107-112] and/or the recovery of the ground state absorption [113— 118] or fluorescence [119-122], The decay of the anisotropy allows determination of the mobility of the protein chain that cover the binding site and the rotational diffusion of the protein, the latter being a function of the size and shape of the protein, the viscosity of the medium, and the temperature. 

When the viscosity of the solution increases by using ethyleneglycol or glycerol water mixtures as solvent, the rotational correlation time increases. This determines (1) higher relaxivity values at low frequencies (2) a shift toward lower frequencies of the a>s dispersion (3) the appearance of a second dispersion (ascribed to the a>i dispersion) at high fields. Temperature dependence studies show that the observed rates are not controlled by exchange, but arise from variation of the rotational correlation time. 

Here the parameters ge, /rB, coz, /, Mh and rr were the g-factor of the free electron, the Bohr magneton, the microwave frequency of measurement, the nuclear spin quantum number, its projection, and the molecular rotational correlation time in solution. The anisotropic parameters, A g, A a and eQVj 1(21 — 1) were estimated from line width coefficients, K, K2 and K4, respectively. Thus the analysis of the temperature dependences of coefficients K, K2 and K4 gave the anisotropic parameters, A g, A a and eQV/1(21 — 1) for all molecules. On the other hand,... 

If the motion of an acrylic polymer radical about the Cp bond is hindered, changing the temperature should lead to changes in the TREPR spectrum. This is indeed observed for all acrylic polymers we have examined to date. Simulation of the complete temperature dependence of TREPR spectra of acrylic polymer main-chain radicals should allow information regarding the conformational motion of the polymer in solution to be extracted, such as rotational correlation times, spin-lattice relaxation times (Ti), and activation energies for conformational transitions. 

Table 2. Pressure dependence of the rotational correlation time t2 ( for pure D2O at different temperatures...

ESR spectra of NO2 adsorbed on X- and Y-type zeolites were observed in the temperature range 77-346 K. Based upon spectral simulation using a Brownian diffusion model, motional dynamics of NO2 adsorbed on zeolite surface were analyzed quantitatively. In the case of X-type zeolite, it was found that the ESR spectra below 100 K is near the rigid limit. Above 230 K, the average rotational correlation time decreased from 1.7 x 10 (230 K) to 7.5 x lO sec (325 K) with increasing temperature and its degree of anisotropy was very close to one (N = 1.25). On the other hand, the temperature-dependent ESR spectra of NO2 adsorbed on Y-type zeolite were observed to be somewhat different from that for X-type zeolite. 

The present study has provided a critical test of the importance of cross relaxation involving both water and protein protons in hydrated protein systems. In addition it has successfully demonstrated that the temperature dependence of both the water and protein relaxation is dominated by motions in the water phase and not by motions in the solid phase such as methyl group rotations. While a detailed analysis has not yet been attempted, it appears that a picture of water in the interfacial regions around a protein that is consistent with the NMR relaxation data is one characterized by fast if slightly anisotropic motion. Structural models for water-protein interactions must be consistent with this very fluid character of water in this interfacial region-, however, it is also important to recognize that the time scale appropriate to the present experiments is still long when compared to the rotational correlation times or diffusion times usually associated with water in the pure liquid state. 

We measured the temperature dependence of the absorption decay and obtained at temperatures above 30° C always a factor of 4 for the ratio between the two rotational correlation times (see equation 1, data not shown). This factor strongly suggests that at temperatures >30° Q where the liposome membrane is in the liquid cristalline state, the rotational difiusion of CF CF labelled in subunit m in fact may be regarded as restricted and uniaxial rotation about the bilayer membrane nomim according to the model of Saffinan and Delbriick (9V The rotational correlation time observed for uniaxial rotation of subimit in labelled CRCFj in the membrane was =200 20 ns at 30° C. This rotational relaxation time ror uniaxial anisotropic rotation of the labelled protein can be related to the size of the rotating unit (1,6,9) =(k.T)/(4.S. h-nO... 

Marinovic et al. have examined the effect of temperature on the ESR signals of TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidin-l-yl)oxyl) spin probe embedded NR. The temperature dependence of ESR spectra is due to change in rotational motion of the nitroxide radicals, characterized by the rotational correlation time (tr). " The representative ESR spectra of spin probed NR measured over a wide range of temperature are given in Figure 25.4(a). The separation of the outer maxima (2A f) is maximum for the spectrum of immobilized spin probe molecules at —120 °C and is slightly decreased with the increase in temperature. The shape of the spectral lines are separated when temperature approaches the glass transition temperature (Tg) (—20 °C) and above it, referred as Ts mT (the temperature at which the separation between the lAzz attains 5 mT). 

The first liquid I choose to discuss is water. Hartwig et al. reported H Ti and T2 data at very low fields. The data reproduced and complemented the earlier work by finding evidence of slow exchange processes on the time scale of milliseconds. Qvist et alP reported high-precision measurements of and H spin-lattice relaxation in (emulsified) H2O and D2O, respectively, over 60 °C temperature range down to - 37 °C. The temperature dependence of the experimental rotational correlation time, tr, was described by a singular power law. With the aid of MD simulations, the authors provided a detailed analysis of the rotational dynamics of water... 

In a study already mentioned in section 3.2, Umecky and co-workers presented measurements of Al (7= 5/2) and relaxation in tris(acetyl-acetonato)aluminium(III) and its analogue with the methyls replaced by CF3 groups, dissolved in supercritical carbon dioxide. The Al Ti-values were obtained over a range of temperatures and pressures and the dependences of the rotational correlation time on viscosity and density was investigated. 

The temperature dependence of the Cl line width was checked for a fraction with molecular weight 49,000. The line width became smaller at higher temperatures and was linear in n/T, where n is the solvent viscosity. Fourfold dilution of a 1 M NaCl solution containing the mercurated copolymer caused no changes in the Cl line width. These two experiments were taken to indicate that fast exchange conditions are valid and that the relaxation of the chloride bound in the mercury label is determined by a rotational correlation time, Xg,... 

In polymeric materials the rigid limit can be obtained at ambient temperatures if the polymer is below the glass-transition temperature, Tg otherwise the sample must be cooled. For rotational correlation times between the two limits, the line shape depends strongly on Xq. For imrestricted, isotropic tumbling, rotational correlation times can be determined from the extreme separation 2Azz (Fig. 2c). On the basis of the relative anisotropy defined in equation 6,... 

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