Burris Cunningham

The magnetic susceptibility of vitamin B12 and B12b.

It has been stated by Rickes, Brink, Konivszy, Wood, and Folkers (1) that vitamin B12 probably is a hexacoordinated cobalt complex, although these authors do not cite the experimental evidence on which this conclusion is based. Magnetic measurements on pure samples of vitamin B12 and related cobalt compounds may be expected to yield unambiguous evidence concerning the nature of the bonding of the cobalt moiety of these substances. We have available an apparatus for measuring the magnetic susceptibilities of very small samples of solid compounds (2). Through the courtesy of various pharmaceutical laboratories, we have been supplied with samples of vitamin B12 and Bl2b in quantities sufficient for magnetic measurements. The susceptibilities were measured by a modification of the Faraday method, using a sensitive quartz fiber torsion balance to measure the magnetic forces and a 5-in. alnico permanent magnet, with pole pieces especially cut to provide a small region of uniform dH/dx. Since neither the field strength nor its rate of change in the experimental region was known accurately, our measurements are comparative and refer in all cases to the behavior of the test samples as compared with that of samples of reagent grade -FeSO4(NH4) 2 S04 *6H20 under the same experimental conditions. In computing our results, we have taken the value of x for our reference standard to be 29.45 x 10-6 egs units. All measurements were made at room temperature and in air. No corrections were made for the influence of the slight susceptibility of the surrounding air, since these corrections were, in general, of a smaller order of magnitude than the experimental error of the measurements themselves. In all cases in which the quantity of sample was sufficient, at least two portions of the same preparation were investigated separately. This served as a test both for magnetic homogeneity of a particular preparation and to reveal any significant contamination with magnetically active material resulting from our own handling of a sample in preparation for a run. The results of our measurements are summarized in Table 1. Of the 6 preparations of vitamin B12 examined by us, 3 (Upjohn samples 223-WGJ-6, 249-WGJ-7, and 247-WGJ-7) were clearly diamagnetic and are unTABLE 1