Spin Labeling and Molecular Dynamics

Abstract Measurements of temperature dependent ESR spectra of spin labels trapped in the polymer matrices is very effective for the evaluation of molecular mobility (molecular motion) of polymer chains. We can characterize the molecular motion of the particular sites in different region by the ESR method. It is possible to detect the mobility of polymer material at the segment or atomic level. ESR studies help to relate the features of the nanometer scale to macroscopic properties of the polymer materials. We present examples of spin labeling studies in the polymer science to help readers new to the field understand how and for what areas the method is effective. In the first part, we give a simple review of the spin labeling method and present applications in the polymer physics related to relaxation phenomena in various systems. In the second part applications to biopolymer system are introduced to help the clarification of various mechanisms of bio-membranes. 

In this chapter we present typical applications of the spin labeling method to polymer physics and biopolymer systems. 

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These fluctuations may be studied by neutron scattering, spin labeling, and x-ray scattering techniques. There is also evidence from molecular dynamics simulations that local fluctuations near inclusions are smaller than those in the unperturbed bilayers [123,124]. 

Ashikawa, I., J.-J. Yin, W. K. Subczynski, T. Kouyama, J. S. Hyde, and A. Kusumi. 1994. Molecular organization and dynamics in bacteriorhodopsin-rich reconstituted membranes Discrimination of lipid environments by the oxygen transport parameter using a pulse ESR spin-labeling technique. Biochemistry 33 4947 1952. 

As an example, we will consider the molecular dynamical behavior of egg white lysozyme. The temperature dependence of mobility of fluorescence, spin and Mossbauer labels attached to lysozyme was found to be similar to other investigated proteins the monotonic increase typical for rigid polymers in dry states and in samples with water content (wt) was less than the critical value (wtcr) and drastically burst when wt > wtcr at T > 200 K took place (Frolov et al., 1978 Likhtenshtein, 1979). At similar conditions, experiments on the temperature dependence of heat capacity indicated only a monotonic steady increase for rigid organic material. Recently, in the fully dried lysozyme crystal, similar monotonic behavior of heat capacity was observed in temperatures between 8 and 30°C. At D20 content more than 24 wt %, a slight deviation from the monotony was observed at temperatures above approximately 185 K, which most probably is due to the eutectic melting of NaCl/2H20 present in the samples to prevent water crystallization (Miyazaki et al., 2000). 

Likhtenshtein G.I. (1979b) Study of protein dynamics by spin-labeling, Mosbauer spectroscopy, and NMR, in Losche, A. (eds.), Special Collogue Amper on Dynamic Processes in Molecular Systems, Leipzig, Karl-Marx University, pp 100-107. 

Likhtenshtein, G. I. (1976a) Spin Labeling Method in Molecular Biology. N. Y., Wiley Interscience. Likhtenshtein G. I. (1976b) Water and protein dynamics, in Alfsen, A. and Bertran, A. J. L eau et les Systemes Biologoque, CNR, Paris, pp. 45-43. 

Lai, C. S., Joseph, J., and Shih, C. C. (1989), Molecular dynamics of antitumor ether-linked phospholipids in model membranes A spin-label study,Biochem. Biophys. Res. Commun., 160,1189-1195. 

Various 2H, 13C and 31P NMR techniques were used to follow the slowing down of molecular dynamics during the glass transition.3 In particular, 2H NMR proved very powerful since solely molecular reorientation is probed and isotopic labeling is easily achieved. Fig. 7 shows the correlation time windows of the major 2H NMR techniques. Two reference frequencies exist The Larmor frequency col determining the sensitivity of the spin-lattice relaxation and the coupling constant 8q fixing the time window of line-shape experiments. 

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