Relaxation of macromolecules

Vugmeyster L, Raleigh DP, Palmer AGr, Vugmeister BE (2003) Beyond the decoupling approximation in the model free approach for the interpretation of NMR relaxation of macromolecules in solution. J Am Chem Soc 125 8400-8404... 

A similar relaxation of orientation for PP-based CPNCs with PP-MA was reported by Lele et al. [2002], The authors presheared the system and then followed the disorientation with XRD. Again, the relaxation time was faster than expected from the theory of Brownian motion. Ren et al. [2000, 2003] studied polystyrene (PS) and poly(isobutylene-co-p-methyl styrene)-based CPNCs. The interlayer spacing in the system was dooi = 2.1 to 2.5 nm thus, it was intercalated only. The authors assumed that the disorientation observed was not governed by Brownian motion but by the stress relaxation of macromolecules. 

Many models for the motional mode of the internuclear vector (C-H vector) to describe the magnetic relaxation of macromolecules have been proposed. Examples are the ellipsoidal or spherical rotational models where an ellipsoidal or spherical molecule undergoes independent diffusional rotations around the long and short axes and the C-H vectors are embedded in the ellipsoidal or spherical molecule.Here consider one model including three independent motions as a pertinent model for long-chain molecules (referred to as the 3t model). In this model, schematically depicted in Fig. 6, the... 

Lipari G and Szabo A 1982 Model-free approach to the interpretation of nuclear magnetic resonance relaxation in macromolecules 1. Theory and range of validity J. Am. Chem. Soc. 104 4546-59... 

Another way to describe deviations from the simple BPP spectral density is the so-called model-free approach of Lipari and Szabo [10]. This takes account of the reduction of the spectral density usually observed in NMR relaxation experiments. Although the model-free approach was first applied mainly to the interpretation of relaxation data of macromolecules, it is now also used for fast internal dynamics of small and middle-sized molecules. For very fast internal motions the spectral density is given by ... 

On the basis of the above data it has been hypothesized that the conductivity of PFCM is due not to the contact between the filler particles but the current passes across the thin (less than 1 -2 microns) polymer interlayers. The conductivity arises when a spontaneous pressure exceeding the threshold value develops in the material. The overstresses apparently arise as a result of PP crystallization in the very narrow gaps between the filler particles [312], Since crystallization must strongly affect the macromolecular conformation whereas the narrowness of the gap and fixed position of molecules on the filler prevent it, the heat released in the process of crystallization must, in part, be spent to overcome this hindrance, whereby a local high pressure may arise in the gap. This effect is possible only where there are gaps of the size comparable with that of macromolecules. The small gap thickness will also hamper pressure relaxation, since the rate of flow from such a narrow clearance should be negligibly small. 

Some information concerning the intramolecular relaxation of the hyperbranched polymers can be obtained from an analysis of the viscoelastic characteristics within the range between the segmental and the terminal relaxation times. In contrast to the behavior of melts with linear chains, in the case of hyperbranched polymers, the range between the distinguished local and terminal relaxations can be characterized by the values of G and G" changing nearly in parallel and by the viscosity variation having a frequency with a considerably different exponent 0. This can be considered as an indication of the extremely broad spectrum of internal relaxations in these macromolecules. To illustrate this effect, the frequency dependences of the complex viscosities for both linear... 

Chain and ring macromolecules are topologically distinct. Thus it is not surprising that many differences in their microscopic properties are observed [127], Besides many other experimental techniques, which were applied to specify these differences, NSE was used to compare the center of mass diffusion and the internal relaxation of linear and cyclic PDMS systems in dilute solutions under good solvent conditions [120,128,129]. An important parameter for these investigations was the molecular mass, which was varied between 800 and 15400 g/mol and which was almost identical for the corresponding linear (L) and ring (R) systems. 

Lipari G. and Szabo A. (1980) Effect of Vibrational Motion on Fluorescence Depolarization and Nuclear Magnetic Resonance Relaxation in Macromolecules and Membranes, Biophys. J. 30, 489—506. Steiner R. F. (1991) Fluorescence Anisotropy Theory and Applications, in Lakowicz J. R. (Ed.), Topics in Fluorescence Spectroscopy, Vol. 2, Principles, Plenum Press, New York, pp. 127-176. 

Lipari G. and Szabo A. (1980) Effect of Vibrational Motion on Fluorescence Depolarization and Nuclear Magnetic Resonance Relaxation in Macromolecules and Membranes, Biophys. J. 30, 489-506. 

The outer angle brackets < > in F t) and C (t) imply an average over the different rods to which the fluorophore is bound. It has been assumed that the motions in the different factors in Eq. (4.24) are statistically independent. Equation (4.24) is expected to be rather generally valid for deformable macromolecules with mean local cylindrical symmetry. Relaxation of the FPA by rotation of the rods around their symmetry axes is contained in C (r). Likewise, relaxation of the FPA by rotation, or end-over-end tumbling, of the rods about their transverse axes is contained in F (t). Motion of the transition dipole with respect to the frame of the rod in which it is attached is contained in / ( ) Further progress requires the evaluation, or estimation, of / (/), F (t), and C (t) for particular models. 

Pokrovskii, V. N. The Mesoscopic Theory of the Slow Relaxation of Linear Macromolecules. Vol. 154, pp. 143-219. 

Meltzer AD, Tirrell DA, Jones AA, Inglefield PT, Hedstrand DM, Tomalia DA. Chain dynamics in poly(amidoamine) dendrimers a study of carbon-13 NMR relaxation parameters. Macromolecules 1992 25 4541-4548. 

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