RESUMO
The synthesis, X-ray crystal and electronic structures of [Fe3(µ3-O)(mpmae)2(OAc)2 Cl3], 1, where mpmae-H = 2-(N-methyl-N-((pyridine-2-yl)methyl)amino)ethanol, are described. This cluster comprises three high-spin ferric ions and exhibits a T-shaped site topology. Variable-frequency electron paramagnetic resonance measurements performed on single crystals of 1 demonstrate a total spin ST = 5/2 ground state, characterized by a small, negative, and nearly axial zero-field splitting tensor D = -0.49 cm-1, E/D ≈ 0.055. Analysis of magnetic susceptibility, magnetization, and magneto-structural correlations further corroborate the presence of a sextet ground-spin state. The observed ground state originates from the strong anti-ferromagnetic interaction of two iron(III) spins, with J = 115(5) cm-1, that, in turn, are only weakly coupled to the spin of the third site, with j = 7(1) cm-1. These exchange interactions lead to a ground state with magnetic properties that are essentially entirely determined by the weakly coupled site. The contributions of the individual spins to the total ground state of the cluster were monitored using variable-field 57Fe Mössbauer spectroscopy. Field-dependent spectra reveal that, while one of the iron sites exhibits a large negative internal field, typical of ferric ions, the other two sites exhibit small, but not null, negative and positive internal fields. A theoretical analysis reveals that these small internal fields originate from the mixing of the lowest ST = 5/2 excited state into the ground state which, in turn, is induced by a minute structural distortion.
RESUMO
PURPOSES: This study tested the hypothesis that our method of knee-joint-tracking training for stroke patients induces significant motor learning effects, and the findings were compared with those of previous studies. METHODS: Six stroke patients and six age-matched healthy controls were recruited. The tracking task involved following computer-generated sine waves of changing frequency (0.2, 0.3, or 0.4 Hz) for each repeating cycle with a plot of the knee-joint angle on a computer monitor as closely as possible. The closed-kinetic chain set involved standing with both hands placed on a support table, with one foot placed on a wooden box and the other foot placed on a digital body-weight scale. The sessions in this study were performed in the following sequence: practice, pretest evaluation, 4 weeks of training, and posttraining evaluation. The tracking performance was evaluated with the accuracy index (AI) score. RESULTS: Tracking training produced a significant improvement not only in the motor-function scores but also in the AI score of the stroke-patient group. The improvement in their AI did not differ significantly from that of the control group. CONCLUSIONS: Our tracking protocol exerted a significant training effect in stroke patients, and the AI improvement was greater than that induced by the most recent protocol. This training will enhance motor skill acquisition and possibly contribute to cortical reorganization.