Studies On Supramolecular Chemistry Related To Intermolecular G-quadruplexes DNA Based On ESI-HRMS

G-rich DNA sequences were widely found in many important fields of human genes,which could self-assemble into G-quadruplex structure under physiological conditions.G-quadruplex DNA is a kind of special DNA secondary structure and metal ions can stabilize the G-quadruplex structure by embedding its central cavity channel and reducing the electrostatic repulsion between oxygen atoms on the guanine.The G-quadruplex can be divided into intramolecular and intermolecular G-quadruplexes according to the numbers of DNA strands.Because the G-quadruplex is involved in vital activities of the human and related to cell proliferation and cancer closely,especially the formation of telomere G-quadruplex is not extended by telomerase and plays an important role in the protection of telomere and inhibits the proliferation of cancer cells,it has aroused widespread concern and become a hot topic in the research of chemistry and biology.This paper studied a series of questions about the formation of intermolecular G-quadruplexes and their complexes by electrospray ionization mass spectrometry?ESI-HRMS?.Firstly,the interactions between G-rich DNA + NH₄⁺,G-rich DNA + NH₄⁺ +Berberine were studied based on the "soft ionization" of ESI-HRMS.And we further discussed the effects of reaction time,dry gas temperature,voltage of Fragmentor,mobile phase H₂O:CH₃OH ratio,analyte concentration and other factors on the formation and detection of the target intermolecular G-quadruplexes and their complexes and finally we made a simple optimization for the next series of studies.Secondly,based on the optimization,the interactions between different cationic NH₄⁺,K⁺ and two G-rich sequences?named G3G4,G4G4?that can form bimolecular G-quadruplexes,three G-rich sequences?named G41,G42,G43?that can form tetramolecular G-quadruplexes were studied by ESI-HRMS.Then the information of intermolecular G-quadruplexes structures and the numbers of bound metal ions were obtained and the stoichiometric changes related to the intermolecular G-quadruplexes were calculated intuitively.We further discussed that the effects of cationic concentration on the formation of intermolecular G-quadruplexes and calculated the linear equations according to the formula.Finally,we found that there were good linear relationships between the intermolecular G-quadruplexes and the cation concentration in a certain concentration range.Thirdly,we further studied the interactions between the small molecule?Berberine?and different intermolecular G-quadruplexes formed in the presence of NH₄⁺ or K⁺ and discussed the effects of Berberine's concentration on the formation of intermolecular G-quadruplexes complexes.Also,the linear relationships between the intermolecular G-quadruplexes and the ligand?Berberine?concentration were calculated according to the formula,and finally we obtained good experimental results.