Gd³⁺ complexes as potential spin labels for high field pulsed EPR distance measurements

Pulse electron-electron double resonance distance measurements between two high spin Gd³⁺ ions in a novel bis-Gd³⁺ complex involving two pyridine-based gadolinium tetracarboxylate systems linked by a rigid aryl-alkyne unit were carried out at Ka- and W-band frequencies. The experimental distance found was 2.02 ± 0.02 nm, and it was further compared with the Gd³⁺-Gd³⁺ distance (2.2126 nm) determined by density functional theory.