Magnetic properties of tunicate blood cells. II. Ascidia ceratodes.
The magnetic properties of intact blood cells of the tunicate Ascidia ceratodes have been measured up to 50 kOe with a SQUID susceptometer. Analysis of total metal contents by plasma emission spectroscopy and V(IV) content by epr indicates that approximately 5% of the accumulated vanadium is +4 vanadyl ion. Measured values of the magnetic moment Mp at different values of the applied magnetic field H over the temperature range T = 2-100 K depend on the magnitude of the field indicating magnetic anisotropy of the ground state. The slope of the Mp vs. H/T curve at high temperature is significantly higher than expected from electron spin S = 1 per vanadium(III) ion. The model that fits these data best is a dimer with one V(III) S = 1 ion ferromagnetically coupled to a second V(III) S = 1 ion, with spin-coupling constant J = 3.5 cm-1, and 5% of the total vanadium content in the form of a V(IV) S = 1/2 ion. Since vanadium in A. ceratodes is known to reside in at least three different types of blood cell, the excellent fit indicates that the metal is stored predominantly as a dimer regardless of blood cell type. Ferromagnetic coupling implies that the two vanadium ions in the dimer are connected by an unprotonated mu-oxo bridge.
Kustin
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K
Department of Chemistry, Brandeis University, Waltham, Massachusetts 02254-9110, USA.
Robinson
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WE
Frankel
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RB
Spartalian
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D000818:Animals; D001773:Blood Cells / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D008280:Magnetics; D008956:Models, Chemical; D013696:Temperature; D014561:Urochordata / Q000502:physiology*; D014639:Vanadium
D014639:Vanadium