Preliminary Study On The Interaction Between Anthocyanins And Proanthocyanidin Polyphenols And DNA Molecules

Plant polyphenols are a class of secondary metabolites that are widely present in plants and have a polyphenolic structure.Plant polyphenols have many biological activities such as anti-oxidation,anti-tumor,prevention of cardiovascular diseases,prevention of diabetes,etc.DNA is the target of many anticancer drugs in scientific research and clinical use.DNA molecular structures have sites that interact with and recognize small molecules,and thus provide a chemical structure basis and information for the development of therapeutic agents for regulating gene expression.The study of interactions between small molecules of DNA and DNA is critical to elucidating the correlation between the molecular structure formed between them and their anticancer activity.In this paper,we selected 5 species plant polyphenols including proanthocyanidins,catechins,epicatechins,Epigallocatechin gallate,cyanidin-3-O-glucoside to study on the interaction between them and DNA.The method and intensity of the interaction between several plant polyphenols and DNA were studied by spectroscopy and atomic force microscopy.The main contents of these investigations were summarized as follows:1.The interaction of cyanidin-3-O-glucoside with DNA molecules was studied.The phenomenon of color reduction and red shift in the results of UV spectroscopy is due to the insertion of aromatic chromophores of cyanidin-3-O-glucoside with base insertion..The results of fluorescence spectroscopy indicate that the interaction between them is static quenching;the stability of cyanidin and DNA forming complex is gradually weakened after the temperature rises.According to the thermodynamic parameters,AH=-9.48×10⁴ J·mol^-1 and ?S=^-181.5 J·mol^-1 are calculated,indicating that the force between them is van der Waals force and hydrogen bonding force.According to the circular dichroism spectrum analysis,when the concentration is increased,the position of the absorption peak is not shifted,and the absorption intensity of the positive absorption peak is decreased,which means that cyanidin-3-O-glucoside interacts with DNA to cause base pair accumulation.The change,the increase in negative band indicates the gradual opening of the double helix structure of ct-DNA,which can be inferred that the helix of ?-DNA is caused by the base insertion of cyanidin-3-O-glucoside with ct-DNA molecule.Sex and base stacking have changed.2.The interaction between catechins,epicatechins and DNA was studied.Characterization of the interaction and intensity between them by UV-Vis spectroscopy,fluorescence spectroscopy,circular dichroism spectroscopy and atomic force microscopy.Fluorescence spectroscopy results showed that catechin and epicatechin quenched the fluorescence of DNA inserted into ethidium bromide?EB?molecules,and the quenching method was static quenching.The thermodynamic parameters of the complex formation of catechin and DNA were ?H=-6.81 ×10⁵ J·mol^-1 and ?S=-2.12× 10³ J·mol^-1.The thermodynamic parameters of epicatechin and DNA interaction are ?H=^-1.96×10⁵ J·mol^-1,AS=-512.9 J·mol^-1.The catechin,epicatechin and DNA binding stability decrease with increasing temperature.AG<0 indicates that the binding process of catechin,epicatechin and DNA is spontaneous.According to the circular dichroism spectroscopy analysis,after the addition of catechin and epicatechin,the double helix of DNA changes with the increase of the concentration of catechin and epicatechin,which indicates that the two are combined.In this study,the interaction of EGCG,a class of ester monomers of catechin,with DNA was also compared.The thermodynamic parameters were calculated such that their interaction ?H=-4.28×10⁵ J·mol^-1,AS=^-1.62×10³ J mol^-1.The reaction is spontaneous.The positive absorption peak at 276 nm of the circular dichroism spectrum decreases with increasing concentration of EGCG,further indicating that EGCG interacts with DNA.According to the comparison of binding constants,the binding constant of EGCG was higher than that of catechin and epicatechin at 25? and 37?,indicating that EGCG has stronger binding ability to DNA.3.The interaction between proanthocyanidins and DNA was studied,and the interaction between the two was observed by the intensity change and red shift of the ultraviolet absorption spectrum.Fluorescence spectroscopy showed that proanthocyanidins can significantly quench the fluorescence intensity of EB-binding DNA.The quenching constant?Ksv?decreases with increasing temperature,and the quenching mode is static quenching.It can be seen from calculation that AH=1.03×10⁵ J·mol^-1,AS=522.9 J·mol^-1,AH and AS are positive numbers,indicating that the proanthocyanidins and DNA are mainly hydrophobic.With the increase of proanthocyanidin concentration,the positive peak of circular dichroism decreased gradually at 276 nm,and the negative peak of 248 nm gradually increased and red shifted,indicating that the addition of proanthocyanidin changed the ?-helix structure of DNA strand.Atomic force microscope results show that the unacting pUC19DNA is an irregular ring,which becomes a small thick coil-like structure after the addition of proanthocyanidins.Atomic force microscopy results of Lambda DNA showed that LambdaDNA is a hexagonal spiral linear structure,which is changed to a thick chain structure with a diameter of 6-7 nm after adding proanthocyanidins.The observation of pUC57DNA showed that its morphology was irregularly ring-shaped.After interaction with proanthocyanidins,the macrocycles were obviously aggregated into small loops with approximate chain structure.The above microscopic results show that proanthocyanidins can cause agglutination of DNA.