Synthesis,Characterization And Biological Toxicity Of Some Piperazinium- And Guanidinium-based Ionic Liquids

In this work, eight piperazinium-and four guanidinium-based ionic liquids (ILs) have been synthesized and characterized by 1H nuclear magnetic resonance (1H NMR) and elemental analysis. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) are used to determine the thermochemical properties. Some fundamental data are provided for the further researches and applications of these ILs.The antimicrobial effects of 12 ILs on E. coli (gram negative bacteria) and S. aureus (gram positive bacteria) are evaluated on the basis of the minimum inhibitory concentration (MIC) measurements with the optical density (OD) method and double dilution method. The membrane damages of bacteria in the presence of ILs are observed by scanning electron microscopy (SEM). Antimicrobial activities of piperazinium- and guanidinium-based ILs are greatly influenced by the structure of different cationic and anionic species. The ILs with the phenyl group on the cation are the species with relatively high antimicrobial activities among the studied ILs. The antibacterial activities for the ILs with the same anion increase with the length increase of the side chain on the cations. The ILs with the [BF4]- anion are the species have relatively high antimicrobial activities, and the antimicrobial activities of the ILs with I- are higher than those with [C2OSO3]-. The SEM images indicate that the damages to bacteria increase with the concentration increase of a given IL, and also with the increase of the antibacterial activity among these ILs. The damages to E. coli are greater than those to S. aureus for the same ILs. The damaged bacteria appear with different degrees of concave and convex on the membranes and with the cytoplasm flow out of cells.The cytotoxicity data of the ILs on human embryonic kidney cells (HEK-293) and rat glioma cells (C6) are obtained by the MTT cell viability assay, and the half inhibitory concentrations (IC50) are obtained by the corresponding survival curves. The cell cycles on HEK-293 and C6 are analyzed by the flow cytometry (FCM). The damages of three cells in the presence of ILs are observed by the cell dyeing experiments on microscope. The damages of ILs to HEK-293 cells are greater than those to C6 cells, which are tumor cells with fast cell proliferation and strong resistance. The ILs containing [BF4]- have relatively high cytotoxicities, and those containing the phenyl group or longer alkyl side chain in the cations are more toxic.For the HEK-293 and C6 cells, the FCM results show that less cell debris are observed, and the cells are well dyed when they are not treated with ILs. The cycles of HEK-293 cells and C6 cells change a lot when treated with ILs. The cell cycles are significantly changed for HEK-293 cells even at the low concentration of 0.1 mg·mL-1, while those are changed for C6 cells only at the concentration higher than 1.0 mg·mL-1. The ILs with [BF4]-anions have more significant effects on HEK-293 cells than those with [Lac]- anion. [Phpi][BF4] has the most significant effects on cell cycles of C6 cells among three ILs with the [BF4]- anions. For most of the cell cycles, the number of cells in Gl phase is decreased, and those in S and G2 phases are increased when compared with the controls. The cell cycles change more significantly with the decrease of the IC50 values of the ILs.From the cell dyeing experiments, the morphologies of three kinds of cells are observed to be damaged to different extents in the presence of the ILs. When the C6 cells are treated with the ILs at the low concentration of 0.5 mg·mL-1, they can maintain the original morphology, and few cytoplasms flow out. When the concentration reaches to that as high as 10 mg·mL-1, the morphology is damaged seriously, and most of the cells only remain the nucleuses. Compared with the C6 cells, the HEK-293 cells are more sensitive to the ILs. The morphology of the HEK-293 cells is difficult to be kept when the cells are treated with the ILs even at the low concentration of 0.5 mg·mL-1. Furthermore, the morphological changes of GSE-1 cells are greatly influenced by different ILs. The IL [(C2)22(C1)2(C1)23gu]I and the ILs with [Lac]- anion are highly destructive to the morphology.