Preparation Of Molecular Imprinting Polymer On Silica Gel Particles For Alkaloid And Specific Binding Property

Alkaloid is the main active ingredient contained in Chinese herbal medicine and the various alkaloids have different pharmacological activities. But it is very complicated to purify the alkaloid. This paper investigates the synthesis of novel adsorption materials for matrine and cytisine, and researches the adsorption character and mechanism. The experimental results have important reference values for separating alkaloid.Firstly, via the coupling effect of 2, 3-glycidoxypropyltrimethoxysilane (EPPS), the graft polymerization of acrylonitrile on the surface of silica gel particles was performed in an acidic solution polymerization system by using cerium ammonium sulfate as initiator, and grafted microspheres PAN/ SiO₂ were prepared. The transform reaction of nitrile groups of the grafted PAN to carboxylic groups (AA) was conducted with vitriol as reagent in the presence of H2O, resulting in functional composite-type particles PAA/SiO₂, on which poly (acrylic acid) macromolecules were chemically anchored. The experimental results show that in the graft polymerization process, the grafting degree of PAN can get up to 19g/100g by controlling the used amount of initiator and temperature. The conversion ratio of the nitrile groups is affected greatly by the pH value of the medium and temperature. Under the appropriate conditions, the functional particles PAA/SiO₂ with a nitrile group conversion ratio of 50% can be obtained. This means that the content of PAA on the surface of the functional particles PAA/ SiO₂ is lower. Therefore, grafted microspheres PMAA/ SiO₂ were prepared by grafting from on the surface of the silicon. The adsorption capacity of PMAA/SiO₂ for alkaloid in water is largely improved.The adsorption capacity and adsorption mechanism of PMAA/SiO₂ for alkaloid in water is further studied. The experimental results show that the grafted particle PMAA/SiO₂ has strong adsorption ability for alkaloid. The driving force of the adsorption is the synergism of electrostatic and hydrogen bond interaction. The adsorption capacity has a maximum value at pH=9 for matrine and pH=10 for cytisine. The reaction temperature can exert great effect on the adsorption property of PMAA/SiO₂, and the adsorption capacity is decreased with the increase of the temperature.Then, the molecular imprinting towards the grafted PMAA was performed with alkaloid matrine as template molecule and ethylene glycol diglycidyl ether (EGDE) as crosslinking agent, and the matrine molecule-imprinted material MIP-PMAA/SiO₂ was prepared. Both static and dynamic methods were adopted to study the binding properties and molecule recognition character of MIP-PMAA/SiO₂ for matrine. The experiment results show that MIP-PMAA/SiO₂ possess strong recognition capability for matrine. In relation to cytisine, the selectivity coefficient of PMAA/SiO₂ for matrine is 0.95, and that of MIP-PMAA/SiO₂ for matrine is 8.14. Besides, MIP-PMAA/SiO₂ has excellent elution property.Finally, MIP-PMAA/SiO₂ was prepared with cytisine as a template molecule and EGDE as crosslinking agent, and by right of the intermolecular hydrogen bond and electrostatic interactions between the grafted PMAA macromolecules and cytisine molecules. Both static and dynamic methods were adopted to study the binding properties and molecule recognition character of MIP-PMAA/SiO₂ for cytisine. The experiment results show that MIP-PMAA/SiO₂ possess strong recognition capability for cytisine. In relation to matrine, the selectivity coefficient of PMAA/SiO₂ for cytisine is 1.06, and that of MIP-PMAA/SiO₂ for matrine is 12.08, and in relation to oxymatrine, the selectivity coefficient of MIP-PMAA/SiO₂ for cytisine is increased from 1.03 to 15.05. Besides, MIP-PMAA/SiO₂ has excellent elution property.