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1990 (1)
1980 (1)
1Author    MarcoL H Gruwel, RoderickE. WasylishenRequires cookie*
 Title    A Deuterium NMR Study of some Ammonium Tetraphenylborates  
 Abstract    Deuterium nmr has been used to study the rotational dynamics of the ammonium ion in ammo-nium tetraphenylborate and of the cation in a series of methylammonium tetraphenylborates. The results of variable temperature 2 H relaxation measurements (T 1Z and T 1Q) on the parent compound, ND 4 B(C 6 H 5) 4 , lead to a low activation energy for reorientation of the ND 4 ion, 5.0 ± 0.5 kJ mol -1 , indicative of weak cation-anion interactions. Related studies of the tetramethyl-d 12 ammonium salt indicate rapid jumps of the whole cation (T <|10 -5 S) over the complete temperature range investi-gated, 137 to 385 K, with an activation energy of 14.1 + 0.5 kJ mol" 1 . Deuterium nmr lineshape studies of the methylammonium salt indicate rapid reorientation of the CD 3 and ND 3 groups about their C 3 axes; however, the motion of the C-N axis is restricted to large amplitude librations. Similar studies of the dimethylammonium salt indicate methyl group jumps at 245 K; at temperatures above 320 K the cation also undergoes two-site jumps about the C 2 axis. In the case of the trimethylam-monium salt, the nmr lineshapes indicate methyl group jumps superimposed on C 3 rotations of the complete cation about the N-H bond axis over the temperature interval 185-348 K. In all the tetraphenylborate salts studied, the 2 H nmr lineshapes indicate substantial librational motion of the cation at room temperature. 
  Reference    Z. Naturforsch. 45a, 55—66 (1990); received August 31 1989 
  Published    1990 
  Keywords    2 H nmr, rotation, ammonium derivatives, tetraphenylborates 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0055.pdf 
 Identifier    ZNA-1990-45a-0055 
 Volume    45 
2Author    Maja Mischel, Ingolf LamRequires cookie*
 Title    Dielectrophoretic Rotation in Budding Yeast Cells  
 Abstract    Rotation of budding yeast cells in an alternating non-uniform electric field of low frequency was investigated. Rotation frequency was found to be proportional to field strength above a threshold, and varied from cell to cell. The threshold is inversely correlated with the mom ent of inertia of the cells, while the slope of rotation frequency versus field strength increases with the moment. Rotation frequencies varied between 1 and 10 cycles per second. Clear differences between the dielectrophoretic behaviour o f living and heat-inactivated yeast cells were observed. 
  Reference    Z. Naturforsch. 35c, 1111 (1980); received July 21/Septem ber 10 1980 
  Published    1980 
  Keywords    Dielectrophoresis, Rotation, Yeast, N onuniform Electric Fields 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-1111_n.pdf 
 Identifier    ZNC-1980-35c-1111_n 
 Volume    35