EPR Probes with Well-Defined, Long Distances between Two or Three Unpaired Electrons

Abstract

The synthesis of rod- and star-shaped compounds carrying two or three spin labels as end groups is described. The unpaired electrons are 2.8-5.1 nm apart from each other. The shape-persistent scaffolds were obtained through Pd-Cu-catalyzed alkynyl-aryl coupling and Pd-Cu-catalyzed alkyne dimerization in the presence of oxygen using p-phenyleneethynylene as the basic shape-persistent building block. The spin label 1-oxyl-2,2,5,5-tetramethylpyrroline-3-carboxylic acid (4) was attached through esterification of the terminal phenolic OH groups of the scaffold.

How Flexible Are Poly(para‐phenyleneethynylene)s?

“…[7] The principal limitation of EPR techniques is their requirement for spin labeling, so that the label-to-labeldistance distribution P(r LL ) rather than P(r EE ) is measured (Scheme 1). The contribution of the labels to P(r LL ) can be eliminated and thus P(r EE ) obtained by synthesizing [11] and measuring a series of compounds with the same labeling pattern and backbone structure but different backbone length.…”

4,4′,4′′-(Methanetriyl)triphenyl tris(2,2,5,5-tetramethyl-1-oxyl-3-pyrroline-3-carboxylate) benzene trisolvate

“…For the preparation of the title compound see: Godt et al (2000). For a related structure, see: Margraf et al (2009).…”

“…The title compound was prepared as a reference compound for pulsed electron-electron double resonance measurements (Godt et al, 2000).…”

“…The title compound was prepared from tris(4-hydroxyphenyl)methane in analogy to the procedure described by Godt et al (2000). Single crystals were obtained by recrystallization of the compound from benzene.…”

Nuclear spin contrast in structural biology

“…The biradical (Figure 12) has been synthesized for the purposes of EPR spectroscopy [39]. The distance between the radicals on the nitroxide groups is 38 Å.…”