Head-to-tail interactions in tyrosine/benzophenone dyads in the ground and the excited state: NMR and laser flash photolysis studies.
The formation of head-to-tail contacts in de novo synthesized benzophenone/tyrosine dyads, bp logical sum Tyr, was probed in the ground and excited triplet state by NMR techniques and laser flash photolysis, respectively. The high affinity of triplet-excited ketones towards phenols was used to trace the geometric demands for high reactivity in the excited state. A retardation effect on the rates with increasing hydrogen-bond-acceptor ability of the solvent is correlated with ground-state masking of the phenol. In a given solvent the efficiencies of the intramolecular hydrogen-atom-transfer reaction depend strongly on the properties of the linker: rate constants for the intramolecular quenching of the triplet state cover the range of 10(5) to 10(8) s(-1). The observed order of reactivity correlates to a) the probability of close contacts (from molecular-dynamics simulations) and b) the extent of the electronic overlap between the pi systems of the donor and acceptor moieties (from NMR). A broad survey of the NMR spectra in nine different solvents showed that head-to-tail interactions between the aromatic moieties of the bp logical sum Tyr dyads already exist in the ground state. Favourable aromatic-aromatic interactions in the ground state appear to correspond to high excited-state reactivity.
Hörner
Gerald
G
Faculty of Chemistry, Adam Mickiewicz University Poznan, Grunwaldzka 6, Poznan, Poland. hoerner@amu.edu.pl
Hug
Gordon L
GL
Pogocki
Dariusz
D
Filipiak
Piotr
P
Bauer
Walter
W
Grohmann
Andreas
A
Lämmermann
Anica
A
Pedzinski
Tomasz
T
Marciniak
Bronislaw
B
D001577:Benzophenones / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D007834:Lasers; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010782:Photolysis; D012997:Solvents / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry
D001577:Benzophenones; D012997:Solvents; D014443:Tyrosine; C047723:benzophenone; D006859:Hydrogen