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Light‐Induced Porphyrin‐Based Spectroscopic Ruler for Nanometer Distance Measurements
Author(s) -
Di Valentin Marilena,
Albertini Marco,
Dal Farra Maria Giulia,
Zurlo Enrico,
Orian Laura,
Polimeno Antonino,
Gobbo Marina,
Carbonera Donatella
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201603666
Subject(s) - porphyrin , electron paramagnetic resonance , chemistry , excited state , nitroxide mediated radical polymerization , triplet state , resonance (particle physics) , molecular physics , photochemistry , nuclear magnetic resonance , atomic physics , physics , copolymer , radical polymerization , organic chemistry , polymer
We present a novel pulsed electron paramagnetic resonance (EPR) spectroscopic ruler to test the performance of a recently developed spin‐labeling method based on the photoexcited triplet state ( S =1). Four‐pulse electron double resonance (PELDOR) experiments are carried out on a series of helical peptides, labeled at the N‐terminal end with the porphyrin moiety, which can be excited to the triplet state, and with the nitroxide at various sequence positions, spanning distances in the range 1.8–8 nm. The PELDOR traces provide accurate distance measurements for all the ruler series, showing deep envelope modulations at frequencies varying in a progressive way according to the increasing distance between the spin labels. The upper limit is evaluated and found to be around 8 nm. The PELDOR‐derived distances are in excellent agreement with theoretical predictions. We demonstrate that high sensitivity is acquired using the triplet state as a spin label by comparison with Cu(II)–porphyrin analogues. The new labeling approach has a high potential for measuring nanometer distances in more complex biological systems due to the properties of the porphyrin triplet state.