NAD+ -- nicotinamide adenine dinucleotide

NAD+ -- nicotinamide adenine dinucleotide.

I am confused at the first place why it is called "dinucleotide".

Nucleotide composes of sugar, phosphate, and base.

Base is the molecule which accept proton. So, I search whether nitrogen-containing ring like nicotinamide can be classified as "base". -- > answer is "yes".

Acid-base properties of nitrogen-containing functional groups. (2019, May 21). University of Minnesota Morris. https://chem.libretexts.org/@go/page/151166

Nicotinamide has two functional groups: 1) amide (NC=O), 2) imine (c1ccncc1).

Nicotinamide can be dissolved in water and yields pH around ~9. (source: https://www.chemicalbook.com/ChemicalProductProperty_EN_CB1130111.htm)

Thus, the reason we call dinucleotide because nicotinamide is considered as base.Besides, it is not necessary to confine bases from nucleotides only to ATGCU.