Basic Physicochemical Properties Of Pyridine Surface Active Ionic Liquids And Their Interactions With Small Biomolecules

Compared with traditional cationic surfactants,surface active ionic liquids(SAILs)have great economic benefits and development potential.SAILs can participate in many biological processes and have some unique effects that differ from salts or standard buffers.Pyridine-based surface active ionic liquids with longer alkyl side chains have high biodegradability and antibacterial activity.Surface active ionic liquids(SAILs)with octyl pyridine and dodecyl pyridine as cation and oleic acids with different chain lengths as anion have been synthesized:octylpyridine-hexenoic acid([C8Py][HA]),octylpyridine-nonenoic acid([C8Py][NA]),octylpyridine-undecenoic acid([C8Py][UA]),dodecylpyridine-hexenoic acid([C12Py][HA]),dodecylpyridine-nonenoic acid([C12Py][NA])and dodecylpyridine-undecenoic acid([C12Py][UA]).The basic physicochemical properties of SAILs,such as thermal stability,solubility in different organic solvents,conductivity and volume in water,oil-water partition coefficient and antibacterial activity in vitro were determined.The interaction between SAILs and small biomolecules(amino acid,glycyl dipeptide and glycyl tripeptide)was studied by volume,conductivity and UV spectrum.The research on the physicochemical properties of SAILs and their interaction with small biomolecules will provide effective information for its application in industrial and biotechnology fields.The research contents and main conclusions are as follows:(1)Six pyridine-enic acid surface active ionic liquids were synthesized.The thermal decomposition temperature was above 160℃ measured by synchronous thermal analyzer,indicating good thermal stability of SAILs.(2)The solubility of SAILs in eight organic solvents including methanol,ethanol,n-butanol,n-octanol,acetone,dichloromethane,ethyl acetate and n-heptane was determined.It was found that all six SAILs were soluble in methanol with high polarity,and most of them were insoluble in n-heptane with low polarity.(3)The oil-water partition coefficients of the six SAILs in n-octanol/water and n-octanol/pH(=1.2,6.8 and 7.4)phosphate buffers were determined at 25 and 37℃.It was found that the synthesized SAILs had a high lipophilicity.(4)The bacteriostatic properties of six SAILs on Escherichia coli,Bacillus subtilis,Staphylococcus aureus and Salmonella enteritidis in vitro were tested,and the effect of the structure of SAILs on their antibacterial activity was explored.It was found that the antimicrobial activity of SAILs against four strains was related to the length of the pyridyl cationic alkyl chain.The antibacterial activity increases with the growth of the pyridyl cationic alkyl chain,whereas the effect of the length of the anionic alkyl chain is little.(5)The densities of binary systems of(SAILs+water)and ternary systems of(small biomolecules+SAILs+water)at different temperatures were determined.The standard partial molar volume,standard partial molar transfer volume,hydration number,partial molar expansion coefficient,thermal expansion coefficient and Hepler’s constant of the solute in the solution were calculated.The effects of temperature,hydrophobic side chain length of SAILs and structure of small biomolecules on the solute-solvent interactions in solution were discussed.It was found that the increase in temperature,molar mass,and hydrophobicity leads to an increase in the standard partial molar volume of SAILs in water.In the ternary system,the ionic-hydrophobic and hydrophobic-hydrophobic interactions between small biomolecules and SAILs are stronger than the ion-ion interactions.The SAILs studied in water and small biomolecules in the aqueous solution of SAILs are structure-promoting solutes.(6)The conductivity of SAILs in water and in aqueous solutions of small biomolecules at different temperatures was determined.The critical micelle concentration of SAILs at different temperatures was calculated according to williams method,and a series of thermodynamic parameters and limiting molar conductivities of the micelle transformation process were calculated.It was found that temperature,alkyl chain length of SAILs and small biomolecules,as well as the types of SAILs anions had the influence on the formation of micelles.The presence of small biomolecules in aqueous solution promotes the formation of SAILs micelles.The micellization process of SAILs in water and in aqueous small biomolecules solutions occurs spontaneously.The migration rate of ions were decreased owing to the interaction of small biomolecules with SAILs and the increase in the concentration of small biomolecules.(7)The ultraviolet absorption spectrum of(small biomolecules+SAILs+water)ternary systems was measured.The binding constant between SAILs and small biomolecules was calculated.It was found that the binding constant increases with the increase of the alkyl chain length of the two and the number of glycyl groups of small biomolecules,indicating the enhancing interaction.