# What is the representation for Sulfur in organic matter?

We often represent organic matter with the following equation:

$$(CH_2O)_x(NH_3)_y(H_3PO_4)_z \tag{0}$$

For example, the organic matter with the Redfield ratio has the form of $$(CH_2O)_{106}(NH_3)_{16}(H_3PO_4)_1$$.

But if we want to put inside the element Sulfur ($$S$$), which form below should we use?

$$(CH_2O)_x(NH_3)_y(H_3PO_4)_z(H_2S)_m \tag{1}$$

$$(CH_2O)_x(NH_3)_y(H_3PO_4)_z(S)_m \tag{2}$$

$$(CH_2O)_x(NH_3)_y(H_3PO_4)_z(SO_4)_m \tag{3}$$.

These different forms assume the different covalency of sulphur (-2, 0, or +6). Which form above should we take to describe the composition of organic matter with S?

I guess maybe Eq.(2) $$(CH_2O)_x(NH_3)_y(H_3PO_4)_z(S)_m$$? Because in this way, sulfur has the covalency of zero, which is the same as carbon (0).

I asked this question because I found many papers use the Eq.0 to build the mineralization of organic matter (e.g., O2 oxidation, [R1] in Table 2 here. See Fig.1 below). The amount of O2 depends on the assumption that carbon in OM has the covelency of zero (then, 1 mole of C corresponds to 1 mole of O2).

Since I didn't find a paper that put S into the OM compositon to balance the similar equation like [R1] in Fig.1, I am curious about which covalency value is "more common" for such an equation (because Sulfur's covalency can affect the amount of O2 needed). • Welcome to Biology.SE! Please provide a more focused question. Those chemical formulae are gross simplifications of the species that exist in biological compounds. For example, carbon and nitrogen commonly participate in both single and double bonds with themselves and other elements (also in aromatic contexts), and can also form triple bonds in biological molecules. Similarly sulfur can occur in several oxidation states. This makes your question in its current form impossible to answer in any way that I can see as meaningful and so I'm going to vote to close as "Needs details or clarity". ... Nov 20, 2020 at 22:12
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• @tyersome Thanks for your advice! I have edited my question to make it more clear. Yes for example carbon in the organic matter has several oxidation states, but when modelling it, we often assume its oxidation state is 0. Under this assumption, we can balance the equation. So I'm curious about if there is a common "assumption" for sulfur.
– T X
Nov 21, 2020 at 1:24