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Interaction of H 2 @C 60 and Nitroxide through Conformationally Constrained Peptide Bridges
Author(s) -
Garbuio Luca,
Li Yongjun,
Antonello Sabrina,
Gascón José A.,
Lawler Ronald G.,
Lei Xuegong,
Murata Yasujiro,
Turro Nicholas J.,
Maran Flavio
Publication year - 2013
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.12191
Subject(s) - nitroxide mediated radical polymerization , relaxation (psychology) , chemistry , molecule , peptide , hydrogen molecule , spin (aerodynamics) , spectroscopy , hydrogen , computational chemistry , nuclear magnetic resonance , physics , thermodynamics , polymer , organic chemistry , quantum mechanics , psychology , social psychology , biochemistry , radical polymerization , copolymer
We synthesized two molecular systems, in which an endofullerene C 60 , incarcerating one hydrogen molecule (H 2 @C 60 ) and a nitroxide radical are connected by a folded 3 10 ‐helical peptide. The difference between the two molecules is the direction of the peptide orientation. The nuclear spin relaxation rates and the para → ortho conversion rate of the incarcerated hydrogen molecule were determined by 1 H NMR spectroscopy. The experimental results were analyzed using DFT ‐optimized molecular models. The relaxation rates and the conversion rates of the two peptides fall in the expected distance range. One of the two peptides is particularly rigid and thus ideal to keep the H 2 @C 60 /nitroxide separation, r , as large and controlled as possible, which results in particularly low relaxation and conversion rates. Despite the very similar optimized distance, however, the rates measured with the other peptide are considerably higher and thus are compatible with a shorter effective distance. The results strengthen the outcome of previous investigations that while the para → ortho conversion rates satisfactorily obey the Wigner's theory, the nuclear spin relaxation rates are in excellent agreement with the Solomon–Bloembergen equation predicting a 1/ r 6 dependence.