Lineshapes temperature-dependent

Fourier-transform infrared (FT-IR) spectroscopy and small-angle X-ray (SAXS) and neutron (SANS) scattering studies have shown the existence of a further pressure induced gel phase in DPPC bilayers." " Pressure dependent NMR studies yielded complementary information on the pressure-induced gel phases. The gel state of DPPC bilayers shows a variation in lineshapes which depend on the particular pressure and temperature. The types of lineshapes seen in a high pressure investigation of dg2-DPPC by Jonas et al. are... 

If highest resolution is required, then the strategy is to use thermal activation to stir away the conformatonal anisotropy operate as close to the glass transition temperature as possible, up to the point at which Ti lifetime broadening predominates. On the other hand, at lower temperatures the lineshape and its temperature dependence may provide useful information (34). 

Temperature-dependent lineshape changes were observed in an early study of the fluo-renyllithium(TMEDA) complex. A detailed study by lineshape analysis, which was also applied to the TMEDA complex of 2,3-benzofluorenyllithium(TMEDA) (Figure 29f, yielded barriers AG (298) of 44.4 and 41.9 kJmoD for the 180° ring flip in these systems, respectively . A second dynamic process, which was detected via the temperature dependence of, the spin-lattice relaxation time in the rotating frame, is characterized by barriers of 35.1 and 37.6 kJmoD, respectively, and may be ascribed to the ring inversion process. For the fluorenyl complex, a barrier AG (298) of 15.9 kJmoD for the methyl rotation in the TMEDA hgand was determined from temperature-dependent NMR spectra of the deuteriated system. 

The chemical shift lineshape changes observed for the crystalline fraction of melt-recrystallized PTFE from /L14°C to w28°C (Figure 6) are due to reorientation about an axis essentially parallel to Ozz (which is tilted VL2° from the molecular chain axis). The temperature dependence of the line-shape changes can be simulated as an increase in the rate of rotational diffusion about this axis (Figure 6) and this process has an activation energy of 48+11 kcal/mole. In addition, the... 

B-l>. Experimental values for Ac were obtained by least-squares curve fitting of the amorphous lineshapes at temperatures above -40°, to an axially symmetric chemical shift tensor. From these values Sg was calculated with Equation (6), where Ao(T0) was taken as the Ac of the crystalline spectra above room temperature. Figure 12 gives the temperature dependence of the local... 

Fig. 34 Temperature dependence of rJT as determined from the fits of the 13C NMR lineshape in TDAE-C60. The solid line is a guide to the eye...

The temperature dependence of the correlation time for the Jahn-Teller pseudorotation rJT obtained by fitting the 13C NMR lineshapes [ 121 ] is shown in Fig. 34. Although in the present model the unpaired spin density on individual Cg0 ions may be only qualitatively correct, this will only slightly affect the temperature dependence of the rJT. 

Di Pace, A., Cupane, A., Leone, M., and Vitrano, E. and Di Pace A Cupane A Leone M Vitrano E Cordone, L. (1992) Protein dynamics. Vibrational coupling, spectral broadening mechanisms, and anharmonicity effects in carbonmonoxy heme proteins studied by the temperature dependence of the Soret band lineshape Biophys. J. 63, 475-484. 

When the H- H dipole-dipole interaction can be measured for a specific pair of H nuclei, studies of the temperature dependence of both the H NMR line-shape and the H NMR relaxation provide a powerful way of probing the molecular dynamics, even in very low temperature regimes at which the dynamics often exhibit quantum tunnelling behaviour. In such cases, H NMR can be superior to quasielastic neutron scattering experiments in terms of both practicality and resolution. The experimental analysis can be made even more informative by carrying out H NMR measurements on single crystal samples. In principle, studies of both the H NMR lineshape and relaxation properties can be used to derive correlation times (rc) for the motion in practice, however, spin-lattice relaxation time (T measurements are more often used to measure rc as they are sensitive to the effects of motion over considerably wider temperature ranges. 

The 2-site 120° jump motion for the basal molecules switches between these two hydrogen bonding arrangements and clearly requires correlated jumps of the hydroxyl groups of all three basal molecules. On the assumption of Arrhenius behaviour for the temperature dependence of the jump frequencies, the activation energies for the jump motions of the apical and basal deuterons were estimated to be 10 and 21 kj mol-1, respectively. This dynamic model was further supported by analysis of the dependence of the quadrupole echo 2H NMR lineshape on the echo delay and consideration of 2H NMR spin-lattice relaxation time data. 

The temperature dependence of the quadrupole echo 2H NMR lineshape and 2H NMR spin-lattice relaxation time measurements demonstrated that the hydrogen bonding arrangement is dynamic. 

An interesting interpretation of temperature dependent lineshapes based on population changes as a function of temperature has been proposed recently [208]. In particular, variable temperature 15N CP MAS NMR has been employed to investigate proton transfer dynamics and N-H bond lengthening in N-H - -N hydrogen bonds. 

The 15N CP MAS NMR spectra showed temperature-dependent lineshapes which were analysed in terms of near-degenerate triple proton transfer processes, schematically presented above. The equilibrium constants were found... 

The motion actually observed by i.r. absorption is a small part of the whole pattern, since for effective absorption one must match both frequency and wavelength in the electromagnetic and crystal osdllations. Absorption occurs essentially at the frequency of the longest waves present in the crystal These waves are damped by anharmonic interaction with the numerous short-wave modes, except at very low temperatures where interaction with ctystal ddects and surfaces takes over. In spite of the complexity of the process one has to expect a simple lineshape and a fairly simple temperature dependence for a wave propagating in one crystal direction. 

Fig. 19. Temperature dependence of the NMR lineshape for perdeuterated benzene sorbed on NaX (loading 4 C6D6 per supercage) (7).

The results of nuclear magnetic resonance (NMR) measurements on alkali fullerides K cC o reported. The NMR spectra demonstrate that material with 0 < X < 3 is in fact a two-phase system at equilibrium, with x = 0 and x = 3. NMR lineshapes indicate that C o Ions rotate rapidly in the KsC q phase at 300 K, while 50 ions in the insulating KaC o phase are static on the time scale of the lineshape measurement. The temperature dependence of the spin-lattice relaxation rate in the normal state of is found to be characteristic of a metal, indicating the... 

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