Interaction between TOAC free radical and photoexcited triplet chromophores linked to peptide templates

A Combined Spectroscopic and Theoretical Study of a Series of Conformationally Restricted Hexapeptides Carrying a Rigid Binaphthyl–Nitroxide Donor–Acceptor Pair

“…Very recently, [26] the triplet state relaxation of a series of functionalized peptides, carrying several aromatic moieties (binaphthyl, benzophenone, trypthophan) and a nitroxide quencher as donor ± acceptor pairs, were studied by timeresolved EPR experiments. Electron-exchange interactions were reported to be primarily responsible for the triplet state quenching of the aromatic molecules (EISC to the ground state) and for the generation of Toac spin polarization, induced by spin selective mixing of doublet and quartet.…”

Benzophenone Photophore Flexibility and Proximity: Molecular and Crystal‐State Structure of a Bpa‐Containing Trichogin Dodecapeptide Analogue

“…The systems investigated have been 3 10 ‐13, 14 and mixed 3 10 /α‐helix forming peptides having in the amino acid sequence a Bpa residue along with a helicogenic, stable free radical 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐4‐amino‐4‐carboxylic acid (TOAC) residue15 (Scheme ) incorporated at different relative positions. Upon interaction with the excited triplet, the TOAC nitroxide radical spin sublevel populations assume values that differ from the Boltzmann equilibrium values 11, 12. This spin‐polarization effect produces EPR emission lines whose time evolution reflects the triplet quenching rate.…”

“…Beside this intermolecular application of Bpa directed at mapping the interphase and specifically amino acid‐to‐amino acid contact points between ligand and receptor, recently we have studied the intramolecular quenching of the Bpa photoexcited triplet state by a nitroxide free radical linked to peptide templates by time‐resolved EPR with pulsed‐laser excitation 11, 12. The systems investigated have been 3 10 ‐13, 14 and mixed 3 10 /α‐helix forming peptides having in the amino acid sequence a Bpa residue along with a helicogenic, stable free radical 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐4‐amino‐4‐carboxylic acid (TOAC) residue15 (Scheme ) incorporated at different relative positions.…”

Viscosity effects on optically generated electron and nuclear spin hyperpolarization

“…Here we examine how optical generation of hyperpolarization in the electron spin-system can be maximised through changes to the solution environment, achieving an increased optical NMR enhancement and providing insights relevant to direct use of electronic hyperpolarization in EPR spectroscopy. [4][5][6][7][8] Optically generated triplet states often have a large initial electron spin polarization which has been utilized directly in both EPR and NMR studies. 9 In the solid-state application of triplet polarization to enhance sensitivity in EPR distance measurements using pulsed dipolar spectroscopy have recently attracted significant interest, [10][11][12][13] whereas in NMR impressive enhancements have been observed for matrix nuclei but are much reduced upon transfer to a solution-state substrate.…”