Magnesium-free chlorophyll derivatives

In a few eutrophic waters, absorbance due to pigments derived from algae or other microorganisms may become consequential. Chlorophylls and their degradation products are readily detectable because of their characteristic absorbance and fluorescence spectra. For example, chlorins (magnesium-free, tetrapyrrolic derivatives of chlorophyll) were detected in Mackenzie River (Canada) water at concentrations of up to 1(X) ng/L (Peake et al., 1972) and in other, more contaminated waters these classes of compounds may occur at higher levels. 

We first simply note that there are i) a number of free base compounds of known structure " and ii) a number of magnesium derivatives of known structure " that are related to the naturally occuring chlorophyls. 

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