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spatially move the g-factor principal axis system in a way that corresponds to a torsional axis system in a way that corresponds to a torsional oscillatory process of the type discussed above. For 180' chain axis motion with 0 = 42', g, and g3 are largely interchanged (a complete interchange occurs only at 0 = 45' and a COO bond angle of 90') while g2 is swept from a small angle above the radical plane to the same angle below it. This change in g2 would not be observable in our experimental spectra due to the broad line widths obtained.The spatial change in the orientation of the g-factor principal axis system due to a 180' chain axis rotation a t 0 = 42' is equivalent to that which occurs for a rotation of 90' around the C-O bond; i.e., gl and g3 are largely interchanged and g2 undergoes a small excursion through space. Thus, within the limits of our experimental data, either a 180' chain axis rotation or a rotation around the C-O bond axis of near 90' would explain the observed spectra. In the latter model the peroxyl radical radical would presumably be oriented in the direction of the double-bonded carbons of the linoleic acid chain, in an environment in which there are no sterically hindering hydrogen atoms as there are in triarachidin. The 90' angle "rotation" would then correspond to an oscillatory motion over a low activation barrier provided by the double-bonded structure and, perhaps, by some longer range interactions. Our data cannot at this time distinguish between these two possibilities, viz., actual 180' segmental motion or 90' oscillations around the CO bond.Acknowledgment. We thank the U S . Army Natick Research and Development Center and the Office of Health and Environmental Research of the US. Department of Energy for support of this research.Registry No. Triarachidin, 620-64-4; linoleic acid, 60-33-3.Raman spectra of the carbonyl stretching region of acetic acid-water mixtures have been examined. Factor analysis was applied to digitized Raman spectra of 18 solutions recorded between 1100 and 1900 cm-I, in the concentration range 16.2 (97% (w/v)) to 6.9 M (40% (w/v)). The number of components (NC) contributing to the carbonyl stretching band envelope was found to be 5 (including the bending mode of water). This is consistent with the assumption that monomeric, dimeric, and polymeric species exist at high concentrations and in the pure acid. The spectra recorded at various acid concentrations were resolved with a band-fitting program. The areas of the component bands were normalized with respect to the area of the band assigned to the C-C stretching fundamental at 892 cm-'. From the normalized band areas, the apparent dimerization constant KD for the monomer-cyclic dimer equilibrium was calculated at each concentration. A plot of KD vs. concentration approached 0.06 L mol-' at concentrations below 7 M. IntroductionThe monomer-cyclic dimer equilibrium in the acetic acid-water system has been extensively investigated by various The present study complements the results of the previous workers and ...

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The inorganic coordination chemistry of peroxovanadium compounds relevant to insulin mimesis is reviewed. The structure and kinetic reactivity of solutions of vanadate anion, vanadyl complexes and peroxovanadate complexes are briefly compared. Peroxovanadium compounds contain an oxo group, one or two peroxo ligands (O2(2-)) and an ancillary ligand which is usually bidentate. These compounds approximate a trigonal bipyramidal structure which can be divided conceptually into a polar 'oxo' half and a relatively non-polar organic half. This presents a number of interesting design variations which are discussed with respect to the development of a rudimentary structure-activity correlation of insulin mimetic ability.

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