Corrins spectra

This procedure illustrates a broadly applicable method which is essentially that of Roth, Dubs, Gotschi, and Eschenmoser,2 for the synthesis of enolizable /1-dicarbonyl compounds. Although there are various methods for the preparation of /3-dicarbonyl systems,3 the scheme of sulfide contraction widens the spectrum of available methods. The procedure can also be utilized in the synthesis of aza and diaza analogs of /3-dicarbonyl systems. Eschenmoser2 has utilized the method to produce vinylogous amides and amidines in connection with the total synthesis of corrins and vitamin B12.4... 

A third factor has been suggested for enhanced resolution of the Co(II) ESR spectrum, because in the enzyme the movement of the acetamide and propionamide side-chains of the corrin ring will be restricted. This restriction would diminish fluctuations in the magnetic environment of the cobalt. 

The application of ESR to the ribonucleotide reductase system indicates that the catalytic intermediate is a Co(I)-species. The appearance of Cob(Il)alamin is probably caused by partial oxidation of the Co(I)-species. In the enzyme bound Co(II)-species the benzimidazole ligand is coordinated, and the corrin ring is bound so tightly that the enzyme produces a unique highly resolved ESR spectrum. 

Use of CD30D or methyl tetrahydrofuran solvents to encourage electron capture, resulted in a complex set of reactions for methyl cobalamine. Initial addition occurred into the w corrin orbital, but on annealing a cobalt centred radical was obtained, the e.s.r. spectrum of which was characteristic of an electron in a d z.y orbital (involving the corrin ring) rather than the expected d2z orbital. However, the final product was the normal Co species formed by loss of methyl. Formally, this requires loss of CH3 , but this step seems highly unlikely. Some form of assisted loss, such as protonation, seems probable. 

Figure9.8 The absorbance of 1.05 x 10 M pinacyanol chloride at 610.0 min pH 9.59 sodium borate buffer (I = 0.1) at 50 °C vs. dodecanoate concentration. The absorption spectrum of pinacyanol chloride in aqueous solution of anionic soaps changes sharply to one characteristic of its solutions in organic solvents within a small range of soap concentration (X ax 610 nm). This effect is attributed to the formation of micelles, in whose hydrocarbon-like layers or cores the dye is solubilized. The concentration of soap at which this spectral change occurs is taken as the cmc. The use of dyes for the determination of cmc values may lead to micelle formation at a concentration below the true cmc. In practice, the method gives only a rough approximation of the cmc. (Adapted, with some modifications, from Corrin et al., 1946.)...

The electronic spectrum of the metal-free corrin resembles that of metal derivatives it seems therefore that the bands are essentially tt-tt transitions modified by the central atom and by the axial ligands.The cob(III)alamins are red, whereas the cob(II)alamins, which are brown, show an additional band at 600 nm. The latter have an EPR spectrum typical of an unpaired electron in the d orbital with some 4s mixing the cob(II)alamin at pH 7 has g = 2.004,... 

Cope rearrangement a [3,3] sigmatropic rearrangement of a 1,5-diene, copolymer a polymer formed from two or more different monomers, corrin ring system a porphyrin ring system without one of the methine bridges. COSY spectrum a 2-D NMR spectrum that shows coupling between sets of protons. 

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