Study On New Methods On Ligand Screening Of Affinity Adsorbents

Affinity adsorbents have been widely used in the separation ofbioactive substance, extraction of natural product, blood purification andwaste water treatment, because of its’ high selectivity and wideapplicability. The ligand of affinity adsorbant is one of the key factorswhich affect the selectivity and efficienty of adsorbants. Hence, thedevelopment of convenient, high efficienty and sensitive ligand screeningmethod becomes the key point of the research of affinity adsorbant.In this dissertation, we firstly raise a visible ligand screening methodwhich based on the special optical property of gold colloids, and theeffectiveness of this method was also be investigated. We designed twoligand screening method: One is modify gold nanoparticles withcandidate ligands, the other is modify gold nanoparticles with adsorbate.The adsorbate or ligand polymer was added into the modified goldcolloids, respectively, the affinity of ligands to adsorbate was adtained by the examination of the degree of the color change of gold colloids.The effectiveness, sensitivity and convenience of the two methodswere investigated. According to the screening method, oligo peptideYpSPTpSPS was selected as adsorbate for the first method. LigandsSH-Dpa-Zn2+、SH-DMA、SH-Guanidine、SH-Pyridine were designedconsidering the structure of the adsorbate, which may have coordinationinteraction, electrostatic interaction or hydrogen bond with the adsorbate.The oligo peptide CGGFGGpSG was selected as adsorbate for the secondmethod. Ligands Dpa-Zn2+、DMAPAA and AAn were designed for theadsorbate, which may have coordination interaction, electrostaticinteraction or hydrophobic interaction with the adsorbate. The affinity ofligands to adsorbate was evaluated through the two screening methods,and the sensitivity of the two methods were also investigated. Meanwhile,adsorbents with the same ligands were synthesized, respectively. Thestatic adsorption experiments were carried out to prove the accuracy of the two ligand screening methods.The results showed that both of the two methods were effective,which could preliminary evaluate the affinity of ligands to the adsorbate.The adsorbent synthesized by the screened ligand, which was supposedto have the strongest affinity to the adsorbate, was proved to have thegreatest adsorption ability to the adsorbate.The convenience of the twomethods was equal. The preparation of gold colloids in the first methodwas complex, and the second method needed the synthesise of polymerswith different ligands. The differences in the two methods were asfollows: The sensitivity of the first method was low. The gold colloidcould only change color under strong interaction between ligand andadsorbate. Moreover, only the adsorbate which have more than onefunctional groups could induce the aggregation of gold colloid, so theapplication of this method was limited. However, in the second method,weak interaction between ligand and adsorbate could induce the color change of gold colloid, the sensiticity of this method was improved.Besides, the aggregation of gold colloid was induced by the interactionbetween the ligands in polymer and the adsorbate on gold particles, sothe number of functional group of adsorbate was not restricted. Thismethod only consume little sample, and the operation of this method wassimple, it is a visible and sensitive ligand screening new method.Because the citric acid group on the gold colloid was negative, itmay affect the electrostatic interactions between ligand and adsorbate.Thus, we intend to use polyethylene glycol (PEG) as the stabilizing agentof gold colloid. The effect of the molecular weight of PEG to the stabilityof gold colloid was investigated. The zeta potential of gold colloidsmodified with PEG of different molecular weight, and the saturated PEGmodification amounts were studied through dynamic light scatteringmethod. On the basis of there experiments, PEG5k was selected as thestabilizer of gold colloid, in order to reduce the effect of negative gold colloid to the electrostatic interactions between ligand and adsorbate.Recently, molecular simulation has been widely used in the designof new medicine and ligand screening because of its improvedcalculation module. Here, we screened high affinity ligand for thechinese herb adsorbent through molecular docking method. We designedmany ligands which may have hydrogen bonding enteractions betweenflavone. The ligand with diethylamine group was screened to have thehighest affinity to the flavone, which was calculated by Autodock. Theadsorbent prepared with this ligand could obtain99.4%flavone fromGinkgo Biloka Extract only through one adsorption-desorption process.Besides, we investigated the interactions between artificial receptorsand oligo peptids through molecular docking method. We studied thebinding energies between receptors and oligo peptids, and investigatedthe effectiveness of Autodock in the preliminary screening of oligopeptide receptor. The binding mode and binding site of receptor with oligo peptides was also studied, offering help to the design of newartificial receptors and the mechanism study of the interactions betweenreceptors and oligo peptides.