Change local motion

With the probe position moving toward the center of the aqueous channel, we detected more ultrafast and less slow solvation components. Note the negligible change of the quasi-bound water contributions, which indicates the complete detection of the two layers of quasi-bound water by all four Trp-probes. For TME, the fluorescence emission peak shifts to 338 nm, and its location moves to the lipid interface (Fig. 18). We did observe a smaller fraction of slow solvation dynamics decreasing from 53% in TBE to 43% in TME and an increase of the ultrafast component from 17% to 26%. The corresponding anisotropy dynamics drops from 726 to 440 ps with a less hindered local motion at the lipid interface. 

In the local mechanical fluctuation model, the local motions of the amino acids on the proximal side of the heme are coupled to the heme through the side group of the proximal histidine. The side chain of the proximal histidine is covalently bonded to the Fe. This bond is the only covalent bond of the heme to the rest of the protein. Thus, motions of the a-helix that contains the proximal histidine are directly coupled the Fe. These motions can push and pull the Fe out of the plane of the heme. Since the CO is bound to the Fe, these motions may induce changes in the CO vibrational transition frequency causing pure dephasing. 

The characteristics of the dynamic mechanical spectrum of SMAA show drastic changes compared with those of the aPS homopolymer even at very low molar fractions of the added comonomer. All the changes observed reflect the ionic interactions. The a relaxation temperature increases with increasing methacrylic acid content as a consequence of a stable network of chemical crosslinks due to anhydride bridge formation. The y relaxation could be related to local motion of methacrylic acid due to the breakdown of the weakest hydrogen bonds. The 3 relaxation could be attributed to local motion of the backbone chain induced by the breakdown of stronger hydrogen bonds than those invoked for the y relaxation. 

First, rotatory and translational diffusion of the macromolecule as a whole occurs. Furthermore, a spectrum of intramolecular motions exists they may be divided into relatively large-scale motions accompanied by a change in the size and shape of the whole macromolecule and small-scale local motions localized within the range of one or several units. When the dependence of local relaxation properties of polymer homologs on the molecular mass (which is observed sometimes) is con-... 

Consider the relation between the correlation function and its spectral density. Slower and faster decays of the correlation function (i.e. slower and faster motions) give narrower and wider distributions of the spectral density, respectively. Figure 11 (a) shows some decay curves of the correlation function for motions with different xc values and (b) indicates the distributions of their respective spectral densities that are obtained by Fourier transform of the decay curves. Here A, B, C in (a) are the decay curves with xca> tcb> and A, B, C in (b) are the distribution of their respective spectral densities. As can be seen, the decay becomes slower and the spectral density distribution becomes narrower as the Xc increases. Assume here that xca cb i cc and the amorphous phase involves two independent motions dictated by xca and xcb whereas the crystalline-amorphous interphase involves two motions dictated by xca and Xcc-Here, xca characterizes a local molecular motion with relation to few carbon atoms in the main molecular chain, and xcb>tcc a somewhat long-ranged motion with relation to a conformational change of ca. 10-20 carbon atoms. In other words, it is assumed that somewhat long-ranged motion is different between the two phases but local motion is the same, the former is dictated by xcb or Xcc and the latter by a common relaxation time xca-... 

The transient absorption method utilized in the experiments reported here is the transient holographic grating technique(7,10). In the transient grating experiment, a pair of polarized excitation pulses is used to create the anisotropic distribution of excited state transition dipoles. The motions of the polymer backbone are monitored by a probe pulse which enters the sample at some chosen time interval after the excitation pulses and probes the orientational distribution of the transition dipoles at that time. By changing the time delay between the excitation and probe pulses, the orientation autocorrelation function of a transition dipole rigidly associated with a backbone bond can be determined. In the present context, the major advantage of the transient grating measurement in relation to typical fluorescence measurements is the fast time resolution (- 50 psec in these experiments). In transient absorption techniques the time resolution is limited by laser pulse widths and not by the speed of electronic detectors. Fast time resolution is necessary for the experiments reported here because of the sub-nanosecond time scales for local motions in very flexible polymers such as polyisoprene. 

Photophysical and photochemical processes in polymer solids are extremely important in that they relate directly to the functions of photoresists and other molecular functional devices. These processes are influenced significantly by the molecular structure of the polymer matrix and its motion. As already discussed in Section 2.1.3, the reactivity of functional groups in polymer solids changes markedly at the glass transition temperature (Tg) of the matrix. Their reactivity is also affected by the / transition temperature, Tp, which corresponds to the relaxation of local motion modes of the main chain and by Ty, the temperature corresponding to the onset of side chain rotation. These transition temperatures can be detected also by other experimental techniques, such as dynamic viscoelasticity measurements, dielectric dispersion, and NMR spectroscopy. The values obtained depend on the frequency of the measurement. Since photochemical and photophysical parameters are measures of the motion of a polymer chain, they provide means to estimate experimentally the values of Tp and Tr. In homogeneous solids, reactions are related to the free volume distribution. This important theoretical parameter can be discussed on the basis of photophysical processes. 

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