Synthesis And Antibacterial Of Polypyridine Ruthenium(â…¡) Complexes With Three Natural Active Ingredients

Antibiotic resistance has become a major problem in the world’s public health care.Many skin diseases,pneumonia,pericarditis,sepsis and other diseases are caused by Staphylococcus aureus（S.aureus）infection,and sepsis infection has a mortality rate of more than 80%.Metal complexes have always played an important role in the history of human medicine and they have been recognized as an important source of new antibiotics.Polypyridine structure is a typical nitrogen-containing heterocyclic compound,and its advantage lies in the transfer of electrons and energy transfer properties.Traditional Chinese medicine（TCM）has natural antibacterial activity.For example,Coptis chinensis,Scutellaria and Honeysuckle,etc.have been used as antibacterial and anti-inflammation for thousands of years.In this paper,polypyridine was designed and synthesized as an auxiliary ligand,natural active ingredients were introduced,Ru（Ⅱ）complexes were modified gradually,and their activity against S.aureus was researched.The dominating research contents as follows.1.The ligand L¹ modified by Rhein was synthesized,and four complexes[Ru（bpy）₂L¹]（PF₆）₂（1）,[Ru（dmb）₂L¹]（PF₆）₂（2）,[Ru（dtb）₂L¹]（PF₆）₂（3）,[Ru（phen）₂L¹]（PF₆）₂（4）with cis-Ru（bpy）₂Cl₂,cis-Ru（dmb）₂Cl₂,cis-Ru（dtb）₂Cl₂,cis-Ru（phen）₂Cl₂as auxiliary ligands were synthesized,bpy=2,2-bipyridine,dmb=4,4’-dimethyl-2,2’-bipyridine,dtb=4,4’-di-tert-butyl-2,2’-bipyridine,phen=1,10-phenanthroline.The structure of complexes 1-4 was characterized.The antibacterial activity of the four complexes against S.aureus was investigated.The results showed that only complex 3 had a significant antibacterial effect with a minimum inhibitory concentration（MIC）of 3.9μg/m L and a minimum bactericidal concentration（MBC）of 384μg/m L.Meanwhile,complex 3 was found that could fleetly kill bacteria in the study of bactericidal kinetics.In addition,complex 3 was found that could significantly inhibit the formation of biofilms.In the hemolysis assay,complex 3showed little cytotoxicity to mammalian erythrocytes.the synergism between complex 3 and common antibiotics,such as amikacin,tobramycin against S.aureus was also detected using the checkerboard method.Most importantly,complex 3 is resistant to S.aureus.Finally,the crack of bacterial cell membrane was found by microscope observation.2.The ligand L² modified by bile acid was synthesized,and four complexes[Ru（bpy）₂L²]（PF₆）₂（5）,[Ru（dmb）₂L²]（PF₆）₂（6）,[Ru（dtb）₂L²]（PF₆）₂（7）,[Ru（phen）₂L²]（PF₆）₂（8）with cis-Ru（bpy）₂Cl₂,cis-Ru（dmb）₂Cl₂,cis-Ru（dtb）₂Cl₂,cis-Ru（phen）₂Cl₂as auxiliary ligands were synthesized.The structure of complexes5-8 was characterized.Antimicrobial activities of four complexes against S.aureus were research.Each complex had obvious antibacterial effect on S.aureus,with MIC of 1-125μg/m L and MBC of 3.9-500μg/m L.Complex 7 had the best antibacterial activity（MIC=1μg/m L,MBC=3.9μg/m L）.Meanwhile,complex 7 was found that could fleetly kill bacteria in the study of bactericidal kinetics and could significantly inhibit the formation of biofilms.In hemolysis experiments,complex 7was found that could significantly inhibit the secretion of bacterial toxins with little cytotoxicity to mammalian erythrocytes.Furthermore,the synergism between complex 7 and common antibiotics,such as amikacin,tobramycin,against S.aureus was also detected using the checkerboard method.Finally,a mouse skin infection model was established to evaluate the antibacterial activity of complex 7 in vivo,showing that complex 7 could effectively promote wound healing in mice infecting with S.aureus.Besides,the results of histopathological research were consistent with the results of hemolysis test,that the complex 7 was almost non-toxic.Finally,it is found that its antibacterial mechanism may be broken by microscopy.3.The ligand L³ modified by glycyrrhetinic acid（GA）was synthesized,and fourcomplexes[Ru（bpy）₂L³]（PF₆）₂（9）,[Ru（dmb）₂L³]（PF₆）₂（10）,[Ru（dtb）₂L³]（PF₆）₂（11）,[Ru（phen）₂L³]（PF₆）₂（12）with cis-Ru（bpy）₂Cl₂,cis-Ru（dmb）₂Cl₂,cis-Ru（dtb）₂Cl₂,cis-Ru（phen）₂Cl₂as auxiliary ligands were synthesized.The structure of complexes 9-12 was characterized.Antimicrobial activities of four complexes against S.aureus were research,MIC=3.9-125μg/m L,MBC=7.8-1000μg/m L.The best antibacterial activity is complex 10（MIC=3.9μg/m L,MBC=7.8μg/m L）.Meanwhile,complex 10 was found that could significantly inhibit the formation of biofilms.The membrane-compromising action mode was suggested to be their potential antibactericidal mechanism.In hemolysis experiments,complex 10 hardly showed cytotoxicity to mammalian erythrocytes.Furthermore,the synergism between complex 10 and common antibiotics,such as ampicillin,chloramphenicol,tetracyclines and ofloxacin,against S.aureus was also detected using the checkerboard method.Finally,a mouse skin infection model was established to evaluate the antibacterial activity of complex 10 in vivo,showing that complex 10 could effectively promote wound healing in mice infecting with S.aureus.Besides,the results of histopathological research were consistent with the results of hemolysis test,that the complex 10 was almost non-toxic.Moreover,the antibacterial mechanism was found that could disrupt bacterial cell membranes by fluorescence staining and scanning electron microscopy（SEM）.