Viscoelastic Properties Of Cationic Surfactant Gel System And Its Effect On The Activity Of α-Chymotrypsin

Gemini surfactants with short chain spacer groups can form wormlike micelles.Under the suitable micelle length and arrangement conditions,the gel morphology can be obtained.This has potential application in life science,drug delivery and material science.In this thesis,two kinds of small molecular gel systems at acidic and neutral pH were prepared by 14-2-14 cationic gemini surfactants with two methylene spacer groups,respectively.The concentration and temperature of gel formation and the viscoelastic properties of gel were studied.According to the obvious shear thinning behavior of the prepared gel,α-chymotrypsin was encapsulated in the surfactant gel.Then the activity of encapsulated enzyme and the viscoelastic properties of the gel in the presence of enzyme were characterized.Enzyme is an indispensable substance for organisms to maintain their lives,and it is of great application value to stabilize and improve enzyme activity in the field of biology and medicine.This work is the basic research on the application of small molecular gel with bioactivity.The main research contents are as follows:1.Preparation and properties of surfactant acidic gelThe aggregation morphology of quaternary ammonium cationic gemini surfactants doesn’t change in the solvent with different pH value and is useful for preparing the gel of acidic system.Thus,it can be used in some extreme acidic environments in organisms.In order to enhance the stability and biocompatibility of the gel,uridine-5 monophosphate（UMP）was used as acid additive.The hydrogel was prepared by mixing cationic gemini surfactants 14-2-14 and UMP at a molar ratio of 1:1.The gel exhibits three phase regions corresponding to ambient temperature,a white metastable gel below T_m-gel-gel=27°C,a viscous sol above T_gel-sol,and a stable state gel between T_m-gel-gel and T_gel-sol.The temperature T_m-gel-gel,enthalpy change?H_m-gel-gel for the phase transition from the white metastable gel to the steady-state gel and the starting temperature T_gel-sol for the transition from the steady-state gel to the sol were studied by Differential Scanning Calorimeter（DSC）.The results showed that both T_m-gel-gel and T_gel-sol increase with the increase of system concentration.The results of rheological measurement show that the 14-2-14/UMP gel system has typical wormlike micellar characteristics,and the structure of the system increases with the increase of the concentration of 14-2-14/UMP.The results of scanning electron microscope（SEM）showed that the surface of the gel system had honeycomb-like structure,which indicated the existence of three-dimensional network structure.2.Study on the interaction between 14-2-14/UMP gel system andα-chymotrypsin（α-CT）The thermal denaturation ofα-CT in pure water and in dilute 14-2-14/UMP solution was studied by DSC.The experimental results show that the addition of 14-2-14/UMP reduces the denaturation temperature T_m and enthalpy change?H of the enzyme,which indicates that the stability of the enzyme conformation is affected by the additive of 14-2-14/UMP.Its 2^nd and/or 3^rd structures are unfolded esasily.For the 14-2-14/UMP gel syetem,the results of rheological experiments show that the system still presents characteristic wormlike micelle behavior,but it seems that the micelle length becomes shorter and the entanglement density decreases.The zero shear viscosity of the system decreases asα-CT concentration increases.The effect of 14-2-14/UMP gel system onα-CT activity was studied by UV-vis spectroscopy.The enzyme was encapsulated in the gel by the sol-gel method,two-phase gelation method and gel-gel method,respectively.The results showed that the gel had a good protective effect on enzyme activity in acidic environment.3.Study on the interaction between 14-2-14 andα-chymotrypsin in PBSBuffered 14-2-14 gel at neutral pH was used to encapsulateα-CT.The experimental results show that the 14-2-14/PBS gel can load a highα-CT capacity and retain its activity.The residual activity is limitted by the stability of the gel structure.The more stable the gel is at the culture temperature,the higher the loading effect is.The higher the concentration of 14-2-14 is,the larger the residual activity ofα-CT is.The rheological measurement shows the viscoelastic properties of wormlike micelle for 14-2-14/PBS gel.It can be supposed on the experimental results that the entanglement density of micelle in the system increases gradually with the increase of 14-2-14 concentration.Asα-CT concentration increases,theη₀ of the gel decreases,the Newton platform extends to larger shear rate and the phase transition temperature T_gel-solel-sol decreases gradually.It could be considered that the length and entanglement mode of micelle are changed owing to the weak interaction between enzyme and surfactants micellet.