Ultrasonic absorption mechanisms in aqueous solutions of bovine hemoglobin.

of an internal rotation; the greater time for the carbon compound indicates some frictional resistance to rotation. Both dimethoxy compounds have similar relaxation times, as also have the tetramethoxy compounds. The greater size and substantially higher dipole moments of the silicon compounds, however, should produce a proportionately greater contribution from the molecular tumbling motion. The relaxation time for end-over-end rotation is approximately proportional to the molar volume and, when several relaxation mechanisms occur, the relative weighting of each depends upon the square of its orientating dipole moment.16 Consequently, these results are only explicable if the internal dielectric relaxation by rotation of the methoxy groups occurs more readily in the silicon compounds. With three methoxy groups the carbon and silicon compounds have similar dipole moments but the four and a half-fold difference between their T valuw again demonstrates the greater freedom of rotation in the silicon compound.