Solid-State Dynamics in the closo-Carboranes:A (11)B MAS NMR and Molecular Dynamics Study

This work explores the dynamic behaviour of the three closo-carborane isomers (formula C2B10H12) using modern solid-state magic angle spinning (MAS) NMR techniques and relates the experimental measurements to theoretical results obtained using molecular dynamics simulations. At high temperatures and at B0 = 9.4 T, the 11B MAS linewidths are narrow (40-90 Hz) for the three isomers. The rotational correlation times (tauc) calculated by molecular dynamics are on the picosecond timescale, showing a quasi-isotropic rotation at these temperatures, typical for liquid systems. For all three isomers, the values of the 11B spin-lattice relaxation times (T1) show discontinuities as the temperature is decreased, confirming the phase changes reported in the literature. At low temperatures, the 11B MAS spectra of all three isomers exhibit much broader lines. The simulations showed that the molecular reorientation was anisotropic around different symmetry axes for each isomer, and this was supported by the values of the reduced quadrupolar parameter PQeff derived from “dynamic shift” measurements using 11B MQMAS NMR spectroscopy. The behaviour of PQeff as a function of temperature for para-carborane suggests that molecular reorientation is about the C5 symmetry axis of the molecule at low temperatures and this was supported by the molecular dynamics simulations

Influence of Field Current Waveform on Higher Harmonic Content in Cylindrical Synchronous Generator

The paper presents a comparison of the higher harmonics in the induced voltages in the stator windings of cylindrical synchronous generator rated at 8.5 kVA under no-load conditions. The comparison is made for the generator with linear and non-linear magnetic circuit without damping cage using constant and variable field current. The calculations of the electromagnetic parameters are carried out in FEMM program. The simulation results are verified experimentally

METOPROLOL EFFECT ON FATTY ACIDS COMPOSITION OF CELL MEMBRANE PHOSPHOLIPIDS

It is quite well known that β-blockers influence the stability of cell membranes, but the effect of metoprolol on the composition of cell membrane lipids is not established. On the other hand, synchronous culture of Chlorella vulgaris cells, which consists of cells brought to the same developmental stage by cycling lighting, provides a convenient biological model in unidirectional analyses aimed at assessment of effects of xenobiotics on cells. Advantages of the model include short life cycle and possibility to control metabolic processes of the cells across the broad range. We assessed the effect of metoprolol on fatty acids composition of cell membrane phospholipids in consecutive life cycle stages of Chlorella vulgaris. Lipids were extracted using a chlorofonn/methanol method. Phospholipids were precipitated from the chloroform phase with cold acetone and following centrifugation the pellet of phospholipids was hydrolyzed in alkaline solution. Fatty acids were extracted with petroleum ether and then methylated with BF3-methanol. This protocol produced methyl esters of fatty acids which were subjected to GC-MS analysis. Metoprolol had no effect on the number of progeny cells of Chlorella vulgaris throughout their life cycle at the concentration range tested (5x10-5 M, 5x10-6 M, 5x10-7 M). However, we observed stimulation of biological activity of Chlorclla cells as measured by spectrophotomctry at λ=680 nm. Metoprolol, at the highest concentration, increased phospholipids content in mother cells. Simultaneously, relative amount and saturation level of thc fatty acids remained constant