Determination of the Nanostructure of Polymer Materials by Electron Paramagnetic Resonance Spectroscopy

Abstract

Electron paramagnetic resonance (EPR) spectroscopy is one the few methods that can characterize structural features in the range between 0.5 and 5 nm in systems that lack long‐range order. Approaches based on EPR spectroscopy provide good structural contrast even in complex materials, as the sites of interest can be selectively labeled or addressed by suitably functionalized spin probes using well established techniques. This article assesses the EPR experiments available for distance measurements on nanoscales in terms of the accessible distance range, precision, and sensitivity. Recommendations are derived for the proper choice of experiment for a given problem. Both simple and sophisticated methods for data analysis are described and their limitations are evaluated. It is discussed which assumptions must be made to extract a pair correlation function from EPR data. Finally, applications to the study of polymer chain conformation and the structure of ionically functionalized diblock copolymers are highlighted.

Spectroscopic and theoretical approaches for studying radical reactions in class I ribonucleotide reductase

“…Pulsed electron-electron double resonance (PELDOR) spectroscopy is a method that monitors weak dipoledipole interactions between the electron spins of radicals that span distances between approximately 15 and 80 Å (Milov et al, 1998;Jeschke, 2002). This method provides a means to measure distances between R1 and R2 in frozen solution and in the presence of the substrate and allosteric effectors, if paramagnetic species can be specifically attached to R1 and R2, respectively.…”

“…This method provides a means to measure distances between R1 and R2 in frozen solution and in the presence of the substrate and allosteric effectors, if paramagnetic species can be specifically attached to R1 and R2, respectively. The advantage over X-ray crystallography is that experiments can be performed under physiologically relevant conditions, with a minimal radical-pair concentration required of approximately 20 mM (Jeschke, 2002). Furthermore, the method gives access not only to distances, but also to the population of the radical pair, allowing the formation and destruction of radicals on a postulated pathway to be followed.…”

Forty Years of the d1/d Parameter

“…Determination of the nanostructure of polymer materials by EPR spectroscopy was considered as one of the few methods that can characterize structural features in the range between 1 and 5 nm in systems that lack long-range order (Jeschke, 2002). Approaches based on various techniques of EPR spectroscopy, such as CW X-band EPR, electron spin echo, ENDOR) provided good structural contrast even in complex materials, because the sites of interest could be selectively labeled or addressed by suitably functionalized spin probes using well established techniques.…”

Intermediate dipolar distances from spin labels

“…Useful information on inter-spin distances, r 12 , can be obtained from standard CW-EPR spectra in the intermediate regime (r 12 % 1:1-2 nm), when the dipolar coupling is less than the width of the powder spectrum of an isolated spin label [1][2][3][4]. This is particularly valuable in the field of site-directed spin labeling where, however, a distribution of distances arises from the flexibility of the spin-label attachment.…”