Cobinamides, conformation

A difference in the solid state and solution conformation of 5 -de-oxyadenosylcobinamide (cobinamide coenzyme) has been inferred from the NMR spectrum of cobinamide coenzyme 123) which indicates that the resonance due to the proton at carbon R-l of the ribose is shifted significantly upfield from its expected position. Such an upfield shift would probably have to arise from the ring current of the adenine ring. 

The vitamin B12 and related coenzymes (cobalamins, cobinamides, and corrinoids) have been studied in detail using H and shift and relaxation studies. (595-598) With the aid of lanthanide probes the eonformations of cobalamins in solution are shown to be very similar to those in the crystalline state. The appreciable temperature dependences of the electronic and H NMR spectra are attributed to a conformational change rather than to a 6-eoordinate-5-coordinate equilibrium as previously suggested. (599) The binding of 5 -ATP to the respiratory protein hemoeyanin has been studied by H and NMR. 

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