Laura Tormo

Caging ultrafast proton transfer and twisting motion of 1-hydroxy-2-acetonaphthone

We report on emission studies of 1-hydroxy-2-acetonaphthone (HAN) in solution nanocavities. In neutral water solutions, intramolecular proton transfer in the enol (E*) structure of HAN and a subsequent internal rotation in the formed keto-type tautomer (K*) occur in few tens of ps, to produce a ns-living rotamers (KR*). When caging HAN in cyclodextrins, the dynamics of twisting is greatly affected. Depending on the size of the cage, the isomerization channel leading to KR* can be closed, and emission occurs from K*. In a larger caging cavity, the fast component of the anisotropy decay becomes shorter while the slow one becomes longer.

Ultrafast twisting motions and intramolecular charge-transfer reaction in a cyanine dye trapped in molecular nanocavities

Emission properties of the cyanine dye, 1-(2-naphthyl)-2-ethenyl-(2-benzothiazolium) iodide, in aqueous nanocavities offered by cyclodextrins and in a film of a polymeric matrix were studied by means of steady-state and picosecond time-resolved emission spectroscopy. The results show the occurrence of a fast twisting motion and a subsequent intramolecular charge-transfer reaction. The initial step can be prevented by the size of the nanocavity which governs the spectral position of the fluorescence band and lifetime of the excited encapsulated host.

Dynamical and structural changes of an anesthetic analogue in chemical and biological nanocavities.

We report on photophysical studies of the interaction between an anesthetic analogue, methyl 2-amino-4,5-dimethoxybenzoate (ADMB), with the human serum albumin (HSA) protein and the normal micelle of n-octyl-beta-D-glucopyranoside (OG) in water solutions. We used steady-state and picosecond time-resolved emission spectroscopy to follow the dynamical and structural changes due to their hydrophobicity and confinement on the photophysical behavior of ADMB. The formed 1:1 complex with the protein is robust with an equilibrium constant of 9.6 x 10(4) M(-1) at 293 K. The fluorescence lifetimes of the 1:1 entity become longer (up to approximately 10 ns), and the emission transients show complex behavior due to the heterogeneity of the media. Rotational time (45 ns) from picosecond anisotropy measurements clearly indicates strong confinement in the robust ADMB:HSA complex. For the ADMB:OG one, the anisotropy decays give time constants of 50 and 980 ps, assigned to free and restricted rotors within the micelle, respectively. The process of energy transfer from the excited tryptophan 214 (Trp214) of HSA to the trapped ADMB occurs with an efficiency of 50%, and the calculated distance between both chromophores is 19 A. We believe that these results are important for a better understanding of processes occurring in encapsulated drugs and thus should be relevant to nanopharmacodynamics.

Femtochemistry of Intramolecular Charge and Proton Transfer Reactions in Solution

We report on the first observation of ultrafast intramolecular charge‐ and proton‐transfer reactions in 4′‐dimethylaminoflavonol (DAMF) in solution. Upon femtosecond excitation of a non‐planar structure of DMAF in apolar medium, the intramolecular charge transfer (ICT) does not occur, and a slow (2 ps) proton motion takes place. However, in polar solvents, the ICT is very fast (100–200 fs) and the produced structure is stabilized that proton motion takes place in few or tens of ps.