Studies On The Properties Of Quaternary Phosphonium Salts With One Long Alkyl Chain And Their Toxicity To Microbes

Phosphonium salts are easier to be synthesized, and of better thermal and chemical stability, broader and lower mesophase temperature range than corresponding ammonium salts. However, the structure-property relationships of phosphonium salts with one long alkyl chain have not been systematically studied yet, which severely restrict their functional designs and applications as ionic liquids or ionic liquid crystals. In this thesis,30 phosphonium salts with one long alkyl chain were prepared through the nucleophilic additions or anion exchange reactions. Their thermal stabilities, phase transitions and textures, phase transition temperatures and thermodynamic parameters, layer spacing and molecular packing structures were analyzed by thermogravimetric analyzer (TGA), polarized optical microscope (POM), differential scanning calorimetry (DSC) and X-ray diffractometry (XRD), respectively. Their phase properties were contrasted by the structural changes of the length of one long alkyl chain, three equivalent short chains or anions. Results indicate that these phosphonium salts are of excellent thermal stability, and the type of anions leads to more effects on the thermal stability than the length of long alkyl chain. The melting point of these compounds increases with the extension of long alkyl chain, but firstly decreases and then increases with the increasing size of the anion. Although some of phosphonium salts investigated here showed several phase transitions as detected by DSC, the liquid crystal phase didn’t appear when observed by POM. XRD data revealed that phosphonium salts with one long alkyl chain were packed tightly as a lamella structure.Although known as "green solvent", ionic liquid itself is not green actually. Their biological toxicity needs to be studied sufficiently. In this paper, staphylococcus aureus, bacillus subtilis, pseudomonas aeruginosa, escherichia coli and yeast were selected to explore the antibacterial ability of three kinds of quaternary phosphonium salts. The relationships between the molecular structures of phosphonium salts and their microbial toxicity were studied by the analyzation of the inhibition rings and minimum inhibitory concentrations. Gram-negative bacteria showed the best toleration within these investigated quaternary phosphonium salts. Their antibacterial activity firstly improves and then weakens with the extension of long alkyl chain. Generally, the toxicity of quaternary phosphonium salts is largest when the alkyl chain length is 13 or 14. In addition, phosphonium salt with a smaller cationic structure is of much stronger toxicity.