Photoinduced intramolecular hydrogen atom transfer in 2-(2-hydroxyphenyl)benzoxazole and 2-(2-hydroxyphenyl)benzothiazole studied by laser flash photolysis

2002 ◽  
pp. 1296-1301 ◽  
Author(s):  
Masashi Ikegami ◽  
Tatsuo Arai
Keyword(s):  
Hydrogen Atom ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Intramolecular Hydrogen

Intramolecular H-atom transfer reactions in rigid peptides — Correlated solvent and structural effects

2011 ◽  
Vol 89 (3) ◽  
pp. 266-279 ◽  
Author(s):  
Anna Lewandowska ◽  
Gordon L. Hug ◽  
Gerald Hörner ◽  
Dariusz Pogocki ◽  
Franciszek Kazmierczak ◽  
...  
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Population Analysis ◽  
Laser Flash ◽  
Hydrogen Atom Transfer ◽  
Nanosecond Laser ◽  
Atom Transfer ◽  
Structural Effects ◽  
Dynamics Simulations ◽  
Intramolecular Hydrogen

The rates and the mechanism of intramolecular hydrogen-atom transfer across the rigid diketopiperazine spacer in two epimeric benzophenone–tyrosine dyads were studied by nanosecond laser flash photolysis in 12 non-protic and protic solvents. Effects of the stereochemistry on the ground-state structures and conformational equilibria and dynamics have been addressed by means of NMR-based population analysis and long-term molecular-dynamics simulations. The excited triplet state of the benzophenone is found to be quenched intramolecularly by the remote phenol moiety with rates that are highly dependent on the solvent and on the relative benzophenone–phenol orientation. In agreement with previous studies, the kinetic diversity, with rates ranging from <105 s−1 to 2 × 107 s−1, can be attributed to retarding effects of the bulk viscosity and to effects of specific solvation, which can be both rate retarding and rate accelerating. As an extension of the previous knowledge, however, the phenomenology of the kinetic solvent effects, that is, the nature of the predominating solvent parameter and its absolute impact on the reactivity, is found to be highly correlated with structural effects.

Sign in / Sign up

Export Citation Format

Share Document