Studies On The Interactions Between Small Molecules And Biomacromolecules

The studies of proteins has been an interesting research field in many research areas, such as biology, clinical medicine, medical chemistry, chemistry and so on. Especially, investigating the binding mechanism of drugs to proteins not only helps us to understand the reactions between small molecules and proteins at the molecular level, but also helps us to understand the pharmacology and toxicology of the drugs and shows a good direction to the drug molecules design and exploitation of the new drugs.In this thesis, the binding of flavonoids (farrerol, quercetin and myricetin) to proteins (human serum albumin, lysozyme and catalase) was investigated at different temperatures and simulative physiological pH 7.40 using spectrophotometric technique such as fluorescence emission, circular dichroism (CD) and UV absorption. The binding parameters obtained from the fluorescence quenching equation shows that the flavonoids binding to proteins is quite strong and the quenching process belongs to a static quenching mechanism. Based on the thermodynamic parameters calculated from the van't Hoff equation, the enthalpy changeΔH~0 and entropy changeΔS~0 for the process of flavonoids binding to proteins were evaluated. According to the enthalpy (ΔH~0) and entropy (ΔS~0) changes, the binding mode can be deduced. The binding distance r between the donor (tryptophan residues of proteins) and acceptor (flavonoids) was derived from the fluorescence resonance energy transfer. The results of synchronous fluorescence spectra and CD indicated a conformational change of proteins with the addition of flavonoids, and the loss ofα-helicity upon interaction. The results obtained from spectrophotometric technique shows that the difference of the structure characteristics of flavonoids has a significant effect on their binding affinity for proteins.The distinctions in the binding modes of flavonoids to proteins originated from their different structures. The stereo-structure formed by ring A, B and C were essential for the binding activity of drugs and the -OH groups were the main active groups in drugs. The most biological effects and the loss activity of drugs had related with their binding to protein.