Triplet-state spin labels for highly sensitive pulsed dipolar spectroscopy

Site-directed attachment of photoexcitable spin labels for light-induced pulsed dipolar spectroscopy

“…These effects have also been observed in some experimental data. 32,33 Note that experimental LaserIMD traces are typically recorded by moving the Hahn-echo sequence through a fixed laser flash, which results in a mirror inverted trace. As none of the three simulations for the photoexcitable spin labels showed major deviations from those of porphyrin, we concluded that RB, EO and AT12 are suitable labels for LaserIMD measurements.…”

Light‐Induced Pulsed EPR Dipolar Spectroscopy on a Paradigmatic Hemeprotein

“…The first work in this area was conducted on a peptide-based molecular ruler containing a nitroxide probe and porphyrin moiety. [31][32][33] It was found that the relative signal-to-noise of the two techniques depends strongly on the degree of excitation that can be achieved by the pump pulse used in LiDEER, the laser excitation, the relative relaxation times of the two species being investigated and the inter spin distance range that needs to be probed. [29] The dipolar measurements were performed with light-induced DEER (LiDEER), [25,26] a variation of the conventional 4-pulse DEER sequence where a laser pulse is used to generate the triplet state before the application of dichromatic microwave pulses: the detection frequency is resonant with the photo-induced porphyrin triplet and the pump is resonant with the stable nitroxide radical.…”

“…Additionally, for the first time, the LiRIDME sequence, in the five-pulse dead-time free version, is applied to a triplet probe providing evidence that the longitudinal relaxation properties of the triplet state can be favorable for the application of this technique. [31,32] RIDME has previously been shown to be more sensitive than DEER for measuring inter-spin interactions between paramagnetic species with different longitudinal (T 1 ) relaxation times and in the presence of broad EPR spectra. The ReLaserIMD data set is good, characterized by a modulation depth of 18 % and a signal to noise S/N ' 49.…”

Triplet Fullerenes as Prospective Spin Labels for Nanoscale Distance Measurements by Pulsed Dipolar EPR Spectroscopy

“…Recently, triarylmethyl (TAM) radicals have appeared as a new alternative with outstanding spectroscopic properties, which make them applicable for PD EPR distance measurements up to physiological temperatures . Another direction was pioneered by Di Valentin et al., who demonstrated the application of a new kind of spin label for PD EPR, the photoexcited triplet state of porphyrin . A model peptide was labeled with porphyrin and nitroxide, which allowed a high sensitivity PELDOR measurement at 20 K stemming from the hyperpolarization (non‐equilibrium population) of the triplet spin levels of porphyrin.…”