Riboflavin

Riboflavin is the vitamin commonly called vitamin B2 and a precursor of the cofactors flavin mononucleotide and flavin adenine dinucleotide. The neutral riboflavin structure has molecular formula ${\mathrm{C}}_{17}{\mathrm{H}}_{20}{\mathrm{N}}_4{\mathrm{O}}_6$ and molar mass approximately $376.369\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$. Its defined chemical structure and its nutritional role describe different aspects of the same substance.^[ref]

Riboflavin kinase transfers a phosphoryl group from ATP to riboflavin, producing flavin mononucleotide and ADP. FAD synthase then uses ATP to convert flavin mononucleotide into flavin adenine dinucleotide, releasing diphosphate. These are distinct chemical transformations; the vitamin is not itself the enzyme performing them.^[ref]

An ideal solution calculation connects chemical identity with molar concentration. Dissolving $0.376369\mathrm{mg}$ of pure neutral riboflavin and making the final volume $10.0\mathrm{mL}$ givesThis is a preparation calculation using the stated molar mass, rather than a measurement of uptake or conversion to either cofactor. A mass concentration and a molar concentration cannot be equated numerically without the molecular identity and units.