The binding reactions between topotecan hydrochloride(THC) or 10-hydroxycamptothecin(HCPT) and transferrin bovine(Tf) are studied by fluorescence and UV-Vis absorption spectra.The research results indicate that the combination reaction of them is a single static quenching process,camptothecin derivatives strongly bound Tf with the molar ratio of 1∶1,the equilibrium constant(K0) at 25 oC are as follows,K0(THC)=2.38×105L·mol-1,K0(HCPT) =2.43×106 L·mol-1.The shortest binding distance(r)between donor(Tf) and acceptor(camptothecin derivatives) are obtained by Frster’s nonradiative energy transfer mechanism,rTHC =3.77nm,rHCPT =3.92.The enthalpy change(△H) and entropy change(△S) are calculated at 25 oC and 37 oC,the results indicate that hydrophobic interaction and the diple-diple force play a major role in the binding of camptothecin derivatives and Tf.The results of 1H NMR spectrum show that the active groups of HCPT interacting with Tf are 10-OH.
The synchronous fluorescence spectrometry was used for the first time to eliminate the interference between the emission of the small-molecule drugs and the determination of the endogenous fluorescence of the protein.The synchronous fluorescence spectrometry and UV-Vis were applied to study the interaction between Tetramethrin and BSA in physiological buffer(pH 7.4).The results of the experiment proved that the quenching mechanism of fluorescence of BSA by Tetramethrin was a static quenching procedure.The number of binding potential point(n) and the association constant(K0) at 298K were n=1.13 and K0=1.428×105L·mol-1,respectively.The enthalpy change and the entropy change were calculated to be △H=29.69KJ·mol-1,△S=211.65J·K·mol-1,which showed that the binding mode was mainly the reflection of the hydrophobic interaction.On the basis of the Frster’s non-radiative energy transfer mechanism,the binding distance(r) and the rate of energy transfer(E)between donor(BSA) and acceptor(Tetramethrin) were obtained to be r=5.15nm,E=0.117,respectively.
