| Today,the primary disease that endangers the life of people in the world is cardiac disease. One of the main reasons that cause cardiovascular diseases is atheroscleorsis (AS). Many researches show that elevated levels and oxidation of low-density lipoprotein (LDL) are associated with an increased incidence of AS. On the other hand,high-density lipoprotein (HDL) can retard the progression of AS. Therefore,many researchers have studied the techniques that can control the levels of LDL in the blood without a significant loss of HDL. Recently,LDL apheresis has been applied in clinic and achieves a satisactory effect. In this dissertation,the tripeptide,serine-aspartic-glutamic acid (SDE),which existes in the COOH-terminal end of the seven repeats in the ligand binding domain of the LDL receptor and plays an important role in identifying LDL,was synthetized and immobilized onto the polyacrylamide (PAAm) beads as a bionic adsorbent for selective removal of LDL from plasma. And the adsorbability of this novel adsorbent for LDL was determined.In order to prepare the solid supports in accordance with with the request of adsorbent for LDL,PAAm beads were synthesized by inverse suspension polymerization. The composition of the polymerization system is shown as follows:the concentration of monomer and dispersant are 12% and 0.65% respectively,the volume ratio of oil / water isl:3,the mole ratio of AAM and MBA is 18:1. The spherical PAAm beads with average size diameter 111.8um and average porediameter 119.8nm were obtained and can be used as LDL adsorbent's matrices. Compared with the import product,the PAAm beads synthesized by our lab are costeffective.By using the liquid phase synthesis techniques,the protection of amino acids and the intensive purification of peptide were performed. The protected amino acids were Z-Ser (BzL),Boc-Asp (OBzL) and Glu (OBzL)2. The quality of the synthesized tripeptide :Ser-Asp-Glu (SDE) by thin layer chromatography,amino acid analysis and liquid chromatography-mass spectrometry is pure.The PAAm beads with different length arms were obtained by coupling the various length linear spacer,such as ethylene diamine,glutaraldehyde,1,6-diaminohexane and amino caproic acid to PAAm beads. And then the SDE ligands were immobilized on the spacer arms-containing PAAm beads by glutaraldehyde or EDC to prepare the bionic adsorbents. The factors that can influence the immobilized ligand density were also studied. The optimum conditions of coupling SDE ligands through its -NH to PAAm beads by glutaraldehyde are:the initial concentration of 5mg/ml (8g wet PAAm beads) of SDE gives more efficient results than the higher ones;the concentration of glutaraldehyde which activated PAAm beads is 5%;pH of activation is 7.0;the coupling reaction time is at least 4 hours. The optimum conditions of coupling SDE ligands through its -COOH to PAAm beads by EDC are:pH of coupling is 4.6-4.8;the concentration of EDC in reaction system must be higher than the concentration of SDE ligands;the time of coupling reaction is at least 12 hours.The adsorbability of adsorbents was studied in vitro. Experimental results indicated that the adsorbents could selectively adsorb LDL and the adsorbent's efficacy was much improved in the presence of Ca2+. A mechanism that interprets this phenomenon was proposed as follows:the adsorbents can interact with phospholipid of LDL through calcium ion cross-linking of the phospholipid phosphate groups of LDL and the carboxyl groups of SDE ligands. On the other hand,the electrostatic interaction between the positive charge of the phospholipid choline nitrogen of LDL and the negative charge of carboxyl groups of SDE ligands isenhanced by the calcium cross-linking of the phosphate groups of neighboring phospholipids in LDL. So,the probability of adsorption of LDL to adsorbents increases in the presence of Ca2+. In addition,an octahedral coordination geometry that is beneficial to the adsorption for LDL may be formed around a calcium ion between neighboring SDE ligands immobi...
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