The Reduction of Vitamin B ₁₂

The Catalysis of the Auto-Oxidation of 2-Mercaptoethanol and Other Thiols by Vitamin B12 Derivatives. Polarographic and Other Investigations

“…B12r was absent, although there was a small shoulder at this wavelength. Neither did the spectrum show any resemblance to the reduced cobalamin derivative of Boos, Carr & Conn (1953) which is produced by treating cyanocobalamin with an excess of chromous derivatives and has absorption maxima at 385, 460 and 554 m,. These experiments show that the action of mercaptoethanol on hydroxocobalamin at neutral pH is complex and is not limited to the formation and reoxidation of a reduced derivative such as vitamin B12r. The mechanism of catalysis at neutral pH thus remains obscure.…”

The Formation of Hydridocobalamin and Its Stability in Aqueous Solutions

“…Because of its hydridelike properties, the green product has been called hydridocobalamin by Smith and Mervyn (1963), a name which we shall employ herein. Boos et al (1953) doubtless produced B12r as the brown product of one-equivalent reduction of vitamin B-,2 by chromous ion in EDTA solution. In some experiments, however, these workers must have formed hydridocobalamin since their spectrum of the "reduced vitamin Bn" is closer to that of hydridocobalamin than Bl2r.…”

“…0.1 m EDTA at pH 9.6, the polarographic wave of B12 is replaced by that of Bi2, and the solution acquires the orange-brown color of the latter compound. This reaction, carried out as an amperometric titration, was used by Boos et al (1953) to determine the equivalent weight of vitamin Bn. The addition of a second equivalent of chromous ion to the solution eliminates the Bnr wave, gives rise to an anodic wave with Em = -0.87 v vs. saturated calomel electrode, and changes the color of the solution from orange to green.…”

New pigments derived from vitamin B12 by a strain of Aerobacter aerogenes present in river mud

“…Several reduction products of vitamin B12 involving the central cobalt atom are described in the literature. On catalytic hydrogenation a brownish-coloured reduction product of vitamin B12 (Kaczka, Wolf & Folkers, 1949;Diehl & Murie, 1952;Boos, Carr & Conn, 1953;Beaven & Johnson, 1955) containing bivalent cobalt, as shown by polarographic and titrimetric evidence (Jasalkis & Diehl, 1954), is obtained. This substance is readily reoxidized to hydroxocobalamin by exposure to air.…”

“…This substance is readily reoxidized to hydroxocobalamin by exposure to air. A second, more highly reduced, grey-green substance is also reoxidizable to hydroxocobalamin (Diehl & Murie, 1952;Boos et al 1953;Beaven & Johnson, 1955).…”