Experimental General consideration: All reactions were performed under an inert atmosphere of dry N 2 with standard Schlenk techniques unless otherwise noted. All starting materials were purchased from Aldrich Chemical Co. and used without further purification. THF, Et 2 O, and CH 2 Cl 2 were purified using the solvent purification system (Innovation Technologies Co.). Deuterated solvents as chloroform-d 1 (D, 99.8%), methanol-d 4 (D, 99.8%), benzene-d 6 (D, 99.5%) and methylene chloride-d 2 (D, 99.9%) (Cambridge Isotopes) were used as received without further drying. NMR spectra were recorded on a Bruker Avance 400 spectrometer (400.13 MHz for 1 H, 100.62 MHz for 13 C, 376.50 MHz for 19 F), chemical shifts are referenced to the residual solvent peaks and have been reported in parts per million (ppm) relative to TMS (1 H and 13 C) and CFCl 3 (19 F). UV-Vis spectra were recorded on a Varian Cary-3 UV-Visible spectrophotometer. Cyclic voltammetry was performed using a BAS CV-50W analyzer with a scan rate of 500 mV/s to 4 V/s and a typical concentration of 5 mg of the compounds in 3 mL DMF. The electrolytic cell used was a conventional three-compartment cell, in which a Pt working electrode, a Pt auxiliary electrode, and a Ag/AgCl reference electrode were employed. The CV measurements were performed at room temperature using 0.10 M tetrabutylammonium hexafluorophosphate (TBAP) as the supporting electrolyte and DMF as the solvent. The ferrocenium/ferrocene couple was used as the internal standard (E 0 = 0.55 V). Elemental analyses were

In the present study, a series of solid dispersions of the drug nimodipine using polyethylene glycol as carrier were prepared following the hot-melt method. Micro-Raman spectroscopy in conjunction with X-ray powder diffractometry was used for the characterization of the solid structure, including spatial distribution, physical state, and presence of polymorphs, as well as storage stability of nimodipine in its solid formulations. The effect of storage time on drug stability was investigated by examination of the samples 6 months and 18 months after preparation. Confocal microRaman mapping performed on the samples showed that the drug was not uniformly distributed on a microscopic level. The presence of crystals of nimodipine with sizes varying between one and several micrometers was detected, and the crystal size seemed to increase with overall drug content. In samples examined 6 months after preparation it was found that the crystals existed mainly as the racemic compound, whereas after 18 months of storage mainly crystal conglomerates were observed.

The present work examines the behavior of multiwall carbon nanotubes (MWCNT) inside AC electric fields created by three-dimensional electrodes. The response of carbon nanotubes stably suspended in water with the aid of a nonionic surfactant is monitored by combining microscopic observations with on-line measurements of the suspension resistivity. It is found that polarization effects induced by the externally applied AC electric field on MWCNTs can cause their unidirectional orientation and end-to-end contact that result in formations of spatially distributed, long-range, three-dimensional and electrically conducting structures that span the entire gap between the electrodes. The length of the formed structures, which in the present case was approximately 30 times larger than that of an individual carbon nanotube, can be controlled by adjusting the spacing between the electrodes. The influence of main experimental parameters, namely, MWCNT concentration, applied voltage, AC field frequency, and electrode surface topography on the suspension behavior is experimentally examined. Results are demonstrated for applied voltage values, AC field frequencies, and carbon nanotube concentrations in the range 4-40 Vptp, 10 Hz-5 MHz, and 0.001-2.0 wt%, respectively. While higher electric field strengths accelerate the formation of aligned structures, higher frequency values were found to result in suspensions that exhibit smaller electrical resistivity. Carbon nanotube dispersions exposed to an AC electric field exhibit a 100-fold or more decrease in their electrical resistivity, even when carbon nanotube concentrations as low as 0.005 wt% are used.