| Serum albumins and DNA are essential substance in the life. They haverespective biological function. Study on the interaction mechanism between smallmolecules and these bio-micromolecules at the molecular level is of current interest inmany research areas such as life science, biology, chemistry, clinical medicine and soon.Much attention has been paid to flavonoids mainly due to some of theirbiological properties, such as antioxidant ability, anti-inflammatory activity,anti-tumor activity, antifungal activity induce, anticancerogenic effects and theirbroad application. Some studies showed, with respect to structural modification offlavonoids, and with substitution at the4′-position or8-position, flavonaids possessgreater antiproliferative activity. In recent years, the effects of biphenyl ornaphthalene at various positions in the A-and B-ring have been accessed.4′-phenyl-3-bromo-8-[N,N-bis(2-hydroxyethyl)aminomethyl]flavone (PBBHAMF) has been designed and synthesized according to related literature. Meanwhile, theinteraction of PBBHAMF with bovine serum albumin (BSA), human serum albumin(HSA) and calf thymus DNA (ct-DNA) has been investigated by using atomic forcemicroscope (AFM), fluorescence spectroscopy, ultraviolet absorption spectroscopy,FT-IR spectroscopy and Circular dichroism spectroscopy. The present work consistsof the following several parts:In the first part, PBBHAMF has been synthesized and the single crystal X-raystructure is given. AFM is carried out and the image of PBBHAMF shows that thenearly spherical shape of particles dispersed on mica surface uniformly. The size ofPBBHAMF is calculated to be1.2nm.In the second part, bovine serum albumin (BSA) and human serum albumin(HSA) have been selected for investigative object. AFM images of BSA/HSA in theabsence and presence of PBBHAMF clearly indicate that all samples show nearlyspherical shape of particles dispersed on mica surface uniformly. The related size iscalculated respectively. Moreover, the binding characteristics and mechanism ofPBBHAMF to BSA/HSA have been investigated using fluorescence spectroscopy andabsorbance spectra, PBBHAMF can quench the endogenous fluorescence of BSA/HSA regularly and the quenching is maily a static quenching process. Thebinding constant Ka, binding sites number n and the average binding distance r areobtained. The thermodynamic parameters are calculated, which demonstrat that theaction force is mainly van der Waals forces and hydrogen bonds. We also focus on theeffect of PBBHAMF on the conformation of BSA/HSA. The spectral changes ofsynchronous fluorescence reveal that the polarities around tyrosine residues aredecreased while the tryptophan residues are placed in a less hydrophobic environment;CD studies indicate the loss of the α-helix structure after the conjugation withPBBHAMF; The second derivative spectra changes prove that the secondary structureof BSA/HSA undergo changes in the bioconjugate system, the fitting curves of thenormalized amide-I peak of BSA/HSA pure and BSA/HSA conjugated studies furthershow a decrease of the α-helix and unordered structures as well as a possible increaseof β-sheet and Turns structures in the BSA secondary structure after the conjugation,while β-sheet or Turns structures have been affected very slightly and some α-helixstructures have been converted into the unordered structures when PBBHAMF isconjugated with HSA.In the third part, the interaction between PBBHAMF and calf thymus DNA havebeen studied. PBBHAMF could quench the fluorescence of the AO-DNA complexwith the use of acridine orange (AO) as a flurescent probe, the quenching mechanismis mainly a static quenching procedure. When bound to DNA, PBBHAMF showshypochromism in absorption spectra, that means intercalation of PBBHAMF intoDNA. Moreover, the increase in relative viscosity and the CD spectral change in274nm also support that the major binding mode is an inserting interaction. The FT-IRspectroscopy demonstrates that there exists electrostatic attraction betweenPBBHAMF and DNA simultaneously. |
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