Cyanocobalamin was photolyzed in aqueous solutions at natural pH complexes were prepared by dissolving them in a small amount of methanol and diluting with a large excess of water.In some experiments the solutions were degassed by several freezethaw cycles on a vacuum line.For quantumyield measurements the complex concentrations were such as to have essentially complete light absorption.The total amount of photolysis was limited to less than to avoid light absorption by the photoproduct.Emis sion spectra were recorded on a modified apparatus described elsewhere. This apparatus was equipped with a cooled R CA CR photomultiplier.The maxima of the <a href="http://www.targetmol.com/compound/Sevelamer-Carbonate">Targetmol's
Sevelamer Carbonate</a> characteristic a, undybands appear at nm. Upon irradiation with light of wavelengths longer than nm cyanocobalamin underwent the well known photoaquation as indicated by the accompanying spectral changes which include clear isosbestic points. Prolonged irradiation led to the spectrum of aquocobalamin which exhibits the maximum of theyband at nm cobalamin was complete the reaction followed a zeroth order kinetics.Since the characteristic absorption maxima were shifted to slightly other wavelengths it is concluded that only at the axial ligand positions a change took place.In analogy to the photochemi corrins it is assumed that a chloride ligand was substituted by water with the formation of corrin.Although a simultaneous substitution of both axial C l ligands can not be excluded, such a reaction is not likely to occur.Degassing of the solution did not affect these measurements.No emission of solid cyanocobalamin was detected at different exciting wavelengths including the a andybands at temperatures down to about K.At this concentration an association of the complex molecules should not be important.The solid material showed this phosphorescence at room temperature too, but the emission was very weak.However, we were not able to detect this phosphorescence in degassed solution at room tem perature.Although the wavelengths and intensities of the abso rptionmax ima depend on the coo rd in ation center and on addit ional ligands to some extent, the pattern of the spectra is not affected by these influences.Hence it is cer ta in ly reasonable to assign these absorptions to intraligand transit ions of the corr in ligand.These characteristic bands appear also in the spectra of cyanocoba lam in, corr in.Since any other bands were not detected they must either occur at higher energies or they arehidden under or obscured by the intense absorptions of thecorr inligand.These other bands be long to CT and LF excited states wh ich invo lve the coo rd ination center.Consequently, CT states are expected and were observed on ly at veryhigh energies.Gene rally these CT bands are quite intense and easily identi fied.B ut in bo th cases it is expected that the lowest CT states lie above the lowest LF states.However, the relativeordering of the lowest excited corr in and LF states is much more difficult to assess since the LF absorptions have not been observed and shou ld be hidden under the intensecorr in bands.Emission spectroscopy prov ides a tool to determine the nature of the lowest excited state.Asimilar rule has been derived from extensive investigations of po rphyrin complexes wh ich are related tocorr in complexes.