Table 2.

Molar extinction coefficients (ε) of isoflavones as a function of wavelength and solvent

	Solvent	λ (nm)	ε (L/mol/cm)	Reference
Daidzein	96% EtOH	250	20 893	[107]
	100%EtOH	262	24 739	[128]
	n.a.	249	31 563	[129]
	MeOH	248–249	27 100–27 200	a*
	80%MeOH	250	27 542	[130]
Genistein	96% EtOH	263	37 154	[107]
	100%EtOH	262	35 842	[128]
	n.a.	263	35 323	[129]
	EtOH	263	35 000–38 400	a*
	96% EtOH	262.5	37 291	0
	n.a.	261	33 113	[131]
	85% MeOH	261	24 435	[132]
Glycitein	alcohol	256	22 387	[108]
	n.a.	256	25 388	[129]
Daidzin	n.a.	249	26 830	[129]
	n.a.	n.a.	23 749	b*
	MeOH/Water	250	28 561	c
Genistin	MeOH/Water	262.5	39 129	c
	n.a.	262.5	35 323	[133]
	85%aq EtOH	262	39 000–40 000	a*
Glycitin	n.a.	259	26 713	[129]
Acetyldaidzin	n.a.	256	29 007	[129]
Acetylgenistin	n.a.	261	38 946	[129]
Acetylglycitin	n.a.	260	29 595	[129]
Malonyldaidzin	n.a.	258	26 830	[129]
Malonylgenistin	n.a.	260	29 895	[129]
Malonylglycitin	n.a.	260	26 313	[129]
Malonylglycitin	n.a.	260	26 313	[129]
Dihydrodaidzein	n.a.	277	13 600	d*
Dihydrogenistein	n.a.	290	18 300	d*
DMA	n.a.	280	12 023	d*
Equol	n.a.	281	6761	d*
Formononetin	n.a.	256	29 512	[107]
Biochanin-A	n.a.	263	27 542	[107]

λ (nm) = wavelength of absorbance maximum in nanometer; EtOH = ethanol, MeOH = methanol; ε = molar extinction coefficient in L/mol/cm; DMA = O-desmethylangolensin; formononetin = 4′-O-methyl daidzein, Biochanin-A = 4′-O-methyl genistein;

⁰Merck Index 10th edn; n.a. = not available;

^*private communications:

^aSigma-Aldrich;

^bNigel Botting 2004 (University of St Andrews, UK),

^cPurina/Nestle 2006,

^dKristiina Wähälä 1998 (University of Helsinki, Finland).