= Kaempferol
\b[Kaempferol] is a <flavonol> with four <hydroxy groups> at positions 3, 5, 7 and $4'$, and neutral <molecular formula> $\mathrm{C_{15}H_{10}O_6}$. ChEBI specifies this substitution pattern and records its structure and <flavonol> classification.<Kaempferol in ChEBI>[CHEBI:28499, definition, formula, structural SMILES and ontology]{ref}
The four <hydroxy groups> do not account for all six oxygen atoms. The recorded structure also contains a ring oxygen and a <carbonyl group>. Counting the groups therefore provides a useful check on the <molecular formula>, while the numbered positions identify connectivity that an elemental formula alone cannot supply.
Using <molar mass> $M\simeq286.24\,\mathrm{g\,mol^{-1}}$, an original $0.100\,\mathrm{mmol}$ amount has mass
$$
m=nM=(0.100\times10^{-3}\,\mathrm{mol})(286.24\,\mathrm{g\,mol^{-1}})
=28.624\,\mathrm{mg}.
$$
That calculation applies to the specified neutral compound. A different derivative, salt, impurity fraction or retained solvent can change the relation between sample mass and kaempferol amount.
A primary experimental discrepancy makes kaempferol particularly useful for understanding <MTT assay> interpretation. In treated breast-cancer-cell cultures, the authors' <crystal violet> cell-number readout decreased while <MTT> <formazan> production increased. They also observed direct reduction in a cell-free system and reduced the interference by washing treated cultures before adding reagent.<Interference of plant extracts, phytoestrogens and antioxidants with the MTT tetrazolium assay by Regina Bruggisser and others>[Abstract, opposing readouts, cell-free reduction and washing experiment]{ref}
An original signal model illustrates the ambiguity. Let the net <MTT> signal be $S=aN+D$, where $N$ is cell number, $a$ the response per cell and $D$ a direct chemical contribution. A control with $aN=1$ and $D=0$ gives $S=1$. A treated sample with cellular contribution $0.6$ and direct contribution $0.8$ gives $S=1.4$ despite the smaller cellular contribution. These chosen numbers illustrate the mechanism; they are not measurements from the paper.
The experimental lesson is to compare an appropriate independent readout and a <tetrazolium cell-free control>. A stronger <formazan optical response> alone does not distinguish more cells, altered per-cell activity and direct reagent reduction.
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