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. IntroductionIn this chapter, we deal with applications of spin labeling to molecular dynamics in polymer science. The radical species in these studies are stable so-called spin labels and spin probes. The success of these studies has made the ESR method increasingly popular for polymer investigations. We can characterize the molecular motion and the structure of the polymer chain in a wide temperature range including that above the melting temperature. The ESR method is effective for the characterization of the heterogeneity in mobility and structure of polymer materials as mentioned in Chapter 7. The heterogeneity is one of the most important features in polymer materials including biopolymers and related to the broad distribution of relaxation time of physical properties such as stress and dielectric relaxations, creep etc. Selective spin labeling is very effective for the detection of the molecular motion in the various sites and regions of the polymer systems. We can for example selectively observe the molecular motion of the particular sites in a chain and particular chains in the copolymer and blend systems.In this chapter we present typical applications of the spin labeling method to polymer physics and biopolymer systems.