The isobutylene-isobutane alkylation process in liquid HF revisited

Details on the mechanism of HF catalyzed isobutylene-isobutane alkylation were investigated. On the basis of available experimental data and high-level quantum chemical calculations, a detailed reaction mechanism is proposed taking into account solvation effects of the medium. On the basis of our computational results, we explain why the density of the liquid media and stirring rates are the most important parameters to achieve maximum yield of alkylate, in agreement with experimental findings. The ab initio Car-Parrinello molecular dynamics calculations show that isobutylene is irreversibly protonated in the liquid HF medium at higher densities, leading to the ion pair formation, which is shown to be a minimum on the potential energy surface after optimization using periodic boundary conditions. The HF medium solvates preferentially the fluoride anion, which is found as solvated [FHF](-) or solvated F(-)center dot(HF)(3). On the other hand, the tert-butyl cation is weakly solvated, where the closest HF molecules appear at a distance of about 2.9 angstrom with the fluorine termination of an HF chain

Effects of a single session of transcranial direct current stimulation on static balance in a patient with hemiparesis: a case study

[Purpose] Cerebrovascular accident (stroke) is characterized by an abrupt onset of focal or global neurological signs and symptoms. Asymmetry of the limbs is common following a stroke due to hemiplegia or hemiparesis. [Subject and Methods] A male patient having suffered an ischemic stroke was initially evaluated using the Timed Up-and-Go Test and the Six-Minute Walk Test. Static balance was evaluated using a force plate (Kistler model 9286BA) for the stabilometry analysis of center of pressure (COP) sway. The data were interpreted using the SWAY software program (BTS Engineering) synchronized with the SMART-D 140(®) system. Anodal transcranial direct current stimulation (tDCS; 2 mA) was applied over the primary motor cortex for 20 minutes during gait training on a treadmill. [Results] Under the condition of eyes open, reductions were found in anteroposterior sway (6.18%), trace length (3.3%) and sway velocity (3.3%) immediately following tDCS. [Conclusion] A single session of anodal tDCS combined with treadmill training had a positive effect on the static balance of a subject with chronic hemiparesis stemming from a stroke