Deactivation pathways of electronically excited states have been investigated in three protonated aromatic amino acids: tryptophan (Trp), tyrosine (Tyr) and phenylalanine (Phe). The protonated amino acids were generated by electrospray and excited with a 266 nm femtosecond laser, the subsequent decay of the excited states being monitored through fragmentation of the ions induced and/or enhanced by another femtosecond pulse at 800 nm. The excited state of TrpH+ decays in 380 fs and gives rise to two channels: hydrogen atom dissociation or internal conversion (IC). In TyrH, the decay is slowed down to 22.3 ps and the fragmentation efficiency of PheH+ is so low that the decay cannot be measured with the available laser. The variation of the excited state lifetime between TrpH+ and TyrH+ can be ascribed to energy differences between the dissociative pi sigma* state and the initially excited pi pi* state.

Objective-To confirm the apparent effectiveness of botulinum toxin (BTX) in hemiparetic patients with ankle plantar flexor and foot invertor spasticity. Methods-Twenty three hemiparetic patients with spasticity of the ankle plantar flexors and foot invertors were included in a randomised double blind, placebo controlled study with BTX. Patients were examined on days 0, 30, 90, and 120 and received one injection of BTX and one of placebo in a random order at day 0 and day 90. Results-Patients reported a clear subjective improvement in foot spasticity after BTX (P = 0-0014) but not after placebo. Significant changes were noted in Ashworth scale values for ankle extensors (P < 0.0001) and invertors (P = 0.0002), and for active ankle dorsiflexion (P = 0-0001). Gait velocity was slightly but not significantly (P = 0-0731) improved after BTX injections. The severity of spasticity did not modify treatment efficacy, but BTX was less effective in patients with longer duration of spasticity (P = 0-0081). Conclusion-The efficacy of BTX injections in the treatment of spastic foot suggests that BTX may be particularly useful during the first year after a stroke.

No abstract

No abstract

Background and Purpose-The goal of this study was to develop a functional MRI (fMRI) paradigm robust and reproducible enough in healthy subjects to be adapted for a follow-up study aiming at evaluating the anatomical substratum of recovery in poststroke aphasia. Methods-Ten right-handed subjects were studied longitudinally using fMRI (7 of them being scanned twice) and compared with a patient with conduction aphasia during the first year of stroke recovery. Results-Controls exhibited reproducible activation patterns between subjects and between sessions during language tasks.In contrast, the patient exhibited dynamic changes in brain activation pattern, particularly in the phonological task, during the 2 fMRI sessions. At 1 month after stroke, language homotopic right areas were recruited, whereas large perilesional left involvement occurred later (12 months). Conclusions-We first demonstrate intersubject robustness and intrasubject reproducibility of our paradigm in 10 healthy subjects and thus its validity in a patient follow-up study over a stroke recovery time course. Indeed, results suggest a spatiotemporal poststroke brain reorganization involving both hemispheres during the recovery course, with an early implication of a new contralateral functional neural network and a later implication of an ipsilateral one.

The photofragmentation of protonated tryptophan has been investigated in a unique experimental setup, in which ion and neutral issued from the photofragmentation are detected in coincidence, in time and in position. From these data are extracted the kinetic energy, the number of neutral fragments associated with an ion, their masses, and the order of the fragmentation steps. Moreover, the fragmentation time scale ranging from tens of nanoseconds to milliseconds is obtained. From all these data, a comprehensive fragmentation mechanism is proposed.

Protonated tryptophan ions (TrpH þ ) are generated by electrospray ionization and dissociated by irradiation with a UV laser. Different photo-fragments are observed among which a new photo-induced dissociation channel leading to the loss of a hydrogen atom that is not observed in conventional collision-induced dissociation. A tryptophan radical cation (Trp þ ) is produced in this process that subsequently leads to the m/z ¼ 130 fragment through a C a -C b bond cleavage, a typical fragmentation product of the Trp þ radical cation generated either by electron impact or by photo-ionization. These results can be understood considering the excited states of protonated tryptophan: UV excitation of TrpH þ produces a mixed pp*/ps* state, the pp* state being mainly located on the indole chromophore while the ps* is mainly on the protonated terminal amino group. This ps* state is repulsive along the N-H bond coordinate and leads either to hydrogen atom detachment producing a Trp þ radical cation that undergoes further fragmentations or to internal conversion to the ground state of the protonated TrpH þ ion.

Photoexcitation of protonated aromatic amino acids leads to C(alpha)[Single Bond]C(beta) bond breakage among other channels. There are two pathways for the C(alpha)[Single Bond]C(beta) bond breakage, one is a slow process (microseconds) that occurs after hydrogen loss from the electronically excited ion, whereas the other is a fast process (nanoseconds). In this paper, a comparative study of the fragmentation of four molecules shows that the presence of the carboxylic acid group is necessary for this fast fragmentation channel to occur. We suggest a mechanism based on light-induced electron transfer from the aromatic ring to the carboxylic acid, followed by a fast internal proton transfer from the ammonium group to the negatively charged carboxylic acid group. The ion formed is a biradical since the aromatic ring is ionized and the carbon of the COOH group has an unpaired electron. Breakage of the weak C(alpha)[Single Bond]C(beta) bond gives two even-electron fragments and is expected to quickly occur. The present experimental results together with the ab initio calculations support the interpretation previously proposed.