| Polyguanidines usually have excellent water solubility and stability,and they can show affinity with biomacromolecules such as nucleic acids,proteins and cell membranes through electrostatic or hydrogen bonding interactions.Therefore,these compounds have found intense applications in biochemical and biomedical research,serving as antibacterial agents,gene transfection agents,drug delivery vehicles and protein delivery vehicles.Based on the unique properties and important roles of polyguanidines,a series of structurally diverse,cationic oligoguanidines were designed and synthesized in this thesis,taking advantage of their cationicity,alternatingly amphiphilic property,as well as their affinity on DNA,so that these oligomers’potential in serving as gene delivery agent and antimicrobial agent can be evaluated.The delivery of nucleic acids through gene transfection processes is an important means of regulating intracellular physiological processes with an exogenous manner.However,most cationic polymer transfection reagents are cytotoxic,and increase in transfection efficiency typically requires increased charge density of the polymer,which further increases cytotoxicity.In this project,the strong binding ability of guanidine groups to DNA was utilized,and guanidine cations were introduced into the polymer without increasing the charge density,so that reduction in cytotoxicity and enhancement in transfection efficiency could be achieved simultaneously.Specifically,we prepared a guanidine-on-backbone-type cationic oligomer,PPODG,by condensation polymerization of isothiourea and diamine monomers.At a low N/P ratio(2.5),PPODG could effectively condensate DNA to form polyplexes which were taken up by cells through energy-dependent endocytosis,and exhibit lower cytotoxicity and higher transfection efficiency than commercial transfection reagent,PEI25k.These results demonstrated the unique advantages of oligoguanidine materials as tools for gene transfection.After realizing the application of oligoguanidine in gene transfection,we continued to use the same cationic oligoguanidine for antibacterial research.Cationic antibacterial polymers can show excellent antibacterial effects against multidrugresistant bacteria by disrupting their cell membranes,but they also cause damage to eukaryotic cell membranes.Therefore,their applications are limited by toxicity.In this project,we show that the naked DNA in the bacterial cytoplasm can be a new antibacterial target.We introduced guanidine moieties into amphiphilic oligomers,and utilized their binding to DNA as the second antibacterial mechanism for our new antibacterial oligomers.Such antibacterial oligoguanidines with dual antibacterial mechanisms that bind cells and bacterial DNA,and showed good antibacterial ability and resistance-resistant nature in both model cells and animals,indicating their excellent potential in relevant applications.Taking the above antibacterial research as the starting point,this project also proposed a alternating amphiphilic(AA)theory,based on the characteristic feature of the alternating arrangement of hydrophilic and hydrophobic parts on the oligoguanidine backbone.According to the theory,oligoguanidines with higher alternating amphiphilic characteristics may have stronger DNA binding ability,higher antibacterial activity and lower hemolytic activity.Combinatorial chemistry was used to construct an oligomer library with 55 oligoguanidines through condensation polymerization,and the antibacterial activity and hemolytic activity of all oligomers were screened.At the same time,molecular dynamics simulation calculations were carried out based on the oligomer library constructed,and the calculation results supported the AA theory.We proposed to use amphipathic index(AAI)to evaluate the degree of being alternating amphipathic for those oligomers,and the structure-activity relationship between oligoguanidine hemolytic activity and AAI of oligoguanidine was obtained.For the hit oligomer OGc3 in the library,we demonstrated that OGc3 had two antibacterial mechanisms,namely bacterial cell membrane disruption and bacterial DNA binding,and used this material to modify the surface of glass and polycaprolactone(PCL)so that antibacterial surface coating could be established.The OGc3 antibacterial coating exhibited efficient antibacterial activity and broad-spectrum effectiveness,and showed high biocompatibility to red blood cells.With these features,this study provides new ideas for the design of cationic antibacterial polymers and the application of antibacterial coatings on material surfaces... |
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