Morin is a bioactive plant flavonoid of immense importance as a potentially useful therapeutic drug.The interaction between morin and bovine hemoglobin(BHb) was investigated by UV/Vis absorption spectrum and fluorescence quenching spectroscopic methods.The experimental results showed that the fluorescence quenching of BHb by morin is a result of the formation of morin-BHb complex;static quenching was confirmed to result in the fluorescence quenching.The binding site number n(293 K:1.11;308 K:1.08)

apparent binding constant

K

A

(293 K:4.96 L·mol

-1

;308 K:4.64 L·mol

-1

) and corresponding thermodynamic parameters(Δ

H

Θ

=-3.34 kJ·mol

-1

;Δ

G

Θ

=-26.34 kJ·mol

-1

/-27.51 kJ·mol

-1

;Δ

S

Θ

=78.50 J·mol

-1

·K

-1

) were measured at two temperatures.The process of binding morin molecule on BHb was a spontaneous molecular interaction procedure in which entropy increased and Gibbs free energy decreased.The binding distance

r

(

r

=4.13 nm) and energy-transfer efficiency

E

(

E

=0.10) between morin and BHb were obtained according to fluorescence resonance energy transfer.The hydrophobic and electrostatic interactions play a major role in stabilizing the complex.The interaction of morin with BHb does not obviously affect the conformation of tryptophan and tyrosine micro-region of BHb.Thus

the results provided a quantitative understanding of the binding of morin to BHb

which is important in understanding its effect as therapeutic agent in therapy.