【作者】 彭慧；

【导师】 沈之荃； 凌君；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2012， 博士

【摘要】 聚肽材料具有优异的生物相容性和出色的自组装能力,被广泛地用于生物医学领域的研究,如药物释放、组织工程等,并显示出巨大的应用前景。聚肽在这些领域的应用性能与聚肽分子链结构的精确性密切相关。但是,目前可用于催化单体NCA (amino acid-N-carboxyanhydride)活性／可控开环聚合制备聚肽的催化剂非常少且在各自的应用方面有局限性,需要探索开发其它的催化体系。本文主要研究了一系列稀土金属化合物,包括硼氢化稀土(Ln(BH4)3(THF)3)、三(双三甲基硅基氨基)稀土(Ln(NTMS)3)、异丙氧基稀土(Ln(OiPr)3)和三(2,6-二叔丁基4-甲基苯氧基)稀土(Ln(OAr)3)催化NCA开环聚合的特征及聚合机理,并在此基础上合成了具有不同功能端基结构的遥爪型聚肽。本文首次采用Ln(BH4)3(THF)3催化NCA开环聚合制备聚肽。Ln(BH4)3(THF)3(Ln=Sc、Y、La和Dy)是BLG (L-谷氨酸-γ-苄酯)NCA开环聚合的高效催化剂：以DMF为溶剂,在40℃、[BLG NCA]/[Y(BH4)3]=1160、[BLG NCA]=0.5mol/L的条件下反应24h,可以92%的收率得到M。为8.6×104Da、MWD为1.32的聚肽。所得聚肽的分子量(MW)和分子量分布(MWD)与稀土元素的种类及反应温度有关。聚合反应的动力学研究表明：硼氢化稀土催化BLG NCA开环聚合的动力学曲线呈较好的线性关系,可以通过投料比有效地控制聚合物的分子量。Ln(BH4)3(THF)3还可以有效地催化NCA嵌段共聚合成分子量分布窄(MWD<1.2)的嵌段共聚肽和无规共聚肽,有活性聚合的特征。聚合机理研究表明,在常温下Ln(BH4)3(THF)3可以通过两种方式催化NCA开环聚合。第一种是Ln(BH4)3(THF)3直接亲核进攻NCA的5-CO进行链引发和链增长,最终形成α-羟基-ω-氨基聚肽。第二种是Ln(BH4)3(THF)3夺取NCA单体3-NH上的质子,形成N-稀土金属化的NCA进行链引发,通过一种类似于缩聚的方式进行链增长,最终形成α-羧基-ω-氨基聚肽。通过降低反应温度的方法,可以有效地抑制第二种反应路径,从而得到只含有α-羟基-ω-氨基结构的聚肽。本文首次采用氨基稀土催化剂Ln(NTMS)3催化NCA开环聚合制备聚肽。Ln(NTMS)3(Ln=Sc、Y、La、Dy和Lu)是NCA开环聚合的高效催化剂：以DMF为溶剂,在40℃、[BLG NCA]/[Y((NTMS)3]=1040、[BLG NCA]=0.5mol/L的条件下反应24h,可以96%的收率得到M。为6.5×104Da, MWD为1.24的聚肽。所得聚肽的分子量和分子量分布与稀土元素的种类及反应温度有关。在该催化体系中可以通过投料比有效地控制聚合物的分子量。Ln(NTMS)3还可以有效地催化NCA嵌段共聚合成分子量分布窄(MWD<1.2)嵌段共聚肽和无规共聚肽,有活性聚合的特征。聚合机理研究表明,在引发过程中,Ln(NTMS)3同时夺取NCA的3-NH和4-CH质子,分别生成N-稀土金属化的NCA和C-稀土金属化的NCA,同时生成HDMS(六甲基二硅氮烷)。原位产生的HDMS催化NCA开环聚合最终形成α-酰胺基-ω-氨基聚肽。N-稀土金属化的NCA和C-稀土金属化的NCA分别异构化为更为稳定的异腈酸酯烷基羧酸稀土和烯酮氨基甲酸羧酸稀土化合物。在该体系中,我们首次报道了NCA上4-CH质子夺取的反应,证明了4-CH的酸性。该反应不仅提供了NCA在强碱存在的条件下发生消旋现象的直接证据,而且给出了另一种活化单体C-钇基化的NCA存在的证据,解释了强碱性催化剂可催化N-取代NCA聚合的原因。本文首次采用烷氧基和芳氧基稀土催化剂Ln(OR)3(R=iPr or Ar)催化NCA开环聚合制备聚肽。Ln(OR)3(R=iPr or Ar)是NCA开环聚合的高效催化剂：以DMF为溶剂,在40℃、[BLG NCA]/[Y(OAr)3]=760、[BLG NCA]=0.5mol/L的条件下反应24h,可以94%的收率得到Mn为8.8×104Da, MWD为1.33的聚肽。所得聚肽的分子量和分子量分布与反应温度有关。这两种催化体系可制备高分子量的聚肽,但分子量不能通过投料比控制。动力学研究表明,随着聚合反应时间的增加,产率和粘均分子量(Mv,LS)都急剧增加,但Mv,Ls的增加滞后于产率增加。聚合反应机理研究表明,在引发过程中,Ln(OR)3(R=iPr or Ar)夺取NCA单体上3-NH的质子,形成N-稀土金属化的NCA,该NCA引发其它的单体一种类似于缩聚的方式进行链增长,最终形成α-羧基-ω-氨基聚肽。在该催化体系中,还生成了端基为乙内酰脲和乙内酰脲酸的聚肽两种副产物。以La(OAr)3为催化剂,通过加入5～8mol%的2,2-dimethyl-trimethylene carbonate (DTC)单体与s-caprolactone (ε-CL)单体进行无规共聚合,成功制备了低结晶度的共聚酯PCD。将PCD和PCL均聚物制备成电纺膜和热压膜,并测试了结晶度。结果表明,在热压膜中,PCD的结晶度χc从PCL的45%降低至28%。在电纺膜中,PCD的结晶度χc从PCL的79%降低至40%。本文首次发现猪胰脂肪酶(PP酶)可以有效地催化PCD的降解,不能催化PCL的降解。对于PCD电纺膜,10天之内失重就达到80%；对于PCD热压膜,35天之内失重达到70%。研究结果表明,电纺膜的降解速度大于热压膜的降解速度；对于同一种膜,PCD的降解速度远远大于PCL。并通过实验结果,对上述的降解行为进行了解释。降解机理研究表明,PP酶催化PCD的降解采用的是表面侵蚀方式。以水杨酸为模型药物,对PCL和PCD进行了药物释放行为的研究。结果表明,PCD电纺膜显示了可控的药物释放行为,而PCL电纺膜则出现了药物的暴释现象。这两种体系药物释放行为的差异与聚合物结晶度有关。以La(OAr)3为催化剂,以PEG或MPEG为引发剂,成功地制备了两亲性的共聚酯MPECD和PECD。在相近的MW和EO含量的条件下,MPECD更脆,接触角更小,但两者蓄水能力相近。研究发现,PP酶可以有效地催化PCD、 PCD/PECD和PCD/MPECD电纺膜的降解。对于PCD电纺膜,7天之内失重达到92%；对于PCD/PECD和PCD/MPECD电纺膜,23天之内失重达到60%左右。机理研究表明,PP酶催化这三种膜的降解采用的是表面侵蚀机理。由于在PCD/PECD和PCD/MPECD电纺膜的表面上发生了PEG链段的富集过程,阻碍了PP酶与PCD链段的直接接触,使得PCD/PECD和PCD/MPECD电纺膜的降解速率低于PCD电纺膜。更多还原

【Abstract】 With excellent biocompatible ability and distinguished self-assemble ability, polypeptide has been widely used in biomedical area such as drug release and tissue engineering, and shows great potential in these applications. The performance of polypeptide is closely related to its micro-structure. However, the available catalysts can be used to catalyze living/controlled ring opening polymerization (ROP) of NCA (amino acid-N-carboxyanhydride) to prepare polypeptide are quite rare, and these catalysts still have their limitations in their use. Exploring new catalytic systems is urgently needed. In this paper, we applied four rare earth complexes, i.e., rare earth tris(borohydride)(Ln(BH4)3(THF)3), rare earth tris[bis(trimethylsilyl)amide](Ln(NTMS)3), rare earth isopropoxide (Ln(OiPr)3) and rare earth tris(2,6-di-tert-butyl-4-methylphenolate)(Ln(OAr)3) to catalyze the ROP of NCA. Polymerization features and mechanisms are detailedly studied, and telechelic polypeptides are synthesized.Ln(BH4)3(THF)3has been firstly used to catalyze the ROP of NCA. The results show that Ln(BH4)3(THF)3(Ln=Sc, Y, La and Dy) are efficient catalysts for ROP of BLG (γ-benzyl-L-glutamate) NCA. In40℃,[BLG NCA]/[Y(BH4)3]=1160,[BLG NCA]=0.5mol/L, PBLG (poly(γ-benzyl-L-glutamate)) could be obtained in92%yield with the number average molecular weight (Mn) of8.6×104Da and molecular weight distribution (MWD) of1.32after24h in DMF. Molecular weights (MWs) and MWDs are varied with the rare earth metals and reaction temperature. The kinetic study exhibits a liner relationship indicating a controlled polymerization behavior of this polymerization system. Block and random copolypeptides with narrow MWD (MWD<1.2) can also been synthesized by Ln(BH4)3(THF)3. Polymerization mechanism study shows that Ln(BH4)3(THF)3catalyzes the ROP of NCA through two modes at room temperature. One is nucleophilic attack at the5-CO of NCA by Ln(BH4)3(THF)3to initiate the polymerization, and after propagation and termination, α-hydroxyl-ω-aminotelechelic polypeptide is formed. The other is that Ln(BH4)3(THF)3deprotonates the3-NH group of NCA, leading to a N-rare earthlated NCA which is served as an initiation center and finally affords a α-carboxylic-ω-aminotelechelic polypeptide. By decreasing the reaction temperature, the second reaction mode can be effectively depressed and polypeptide with hydroxyl group can be exclusively synthesized.Ln(NTMS)3has been firstly used to catalyze the ROP of NCA. The results show that Ln(NTMS)3(Ln=Sc, Y, La, Dy and Lu) are efficient catalysts for ROP of BLG NCA. In40℃,[BLG NCA]/[Y((NTMS)3]=1040,[BLG NCA]=0.5mol/L, PBLG with the Mn of6.5×104Da and MWD of1.24could be obtained in96%yield after24h in DMF. MWs and MWDs are varied with the rare earth metals and reaction temperature. The MWs can be efficiently tuned by the feeding ratios. Block and random copolypeptides with narrow MWD (MWD<1.2) can also been synthesized by Ln(NTMS)3. Polymerization mechanism study shows that in the initiation step, Ln(NTMS)3not only deprotonates the3-NH but also deprotonates the4-CH group of NCA, forming N-rare earthlated NCA and C-rare earthlated NCA respectively along with hexamethyldisilazane (HMDS). The in situ HDMS is responsible for further chain growth and finally produces the α-amide-ω-aminotelechelic polypeptide, while N-rare earthlated NCA and C-rare earthlated NCA are isomerized into more stable rare earth α-isocyanato carboxylate and rare earth ketenyl carbamate respectively. In this system, we firstly report deprotonation reaction at4-CH of NCA, proving the acidity of4-CH in NCA. This result not only provides a direct proof for racemization phenomenon of NCA in strong base environment but also sheds light on strong base-catalyzed N-substituted NCA polymerization.Ln(OR)3(R=iPr or Ar) have been firstly used to catalyze the ROP of NCA. The results showed that Ln(OR)3(Ln=Y, La and Dy) were efficient catalysts for ROP of BLG NCA. In40℃,[BLG NCA]/[Y(OAr)3]=760,[BLG NCA]=0.5mol/L, PBLG with the Mn of8.8×104Da and MWD of1.33could be obtained in94%yield after24h. The two systems are especially useful to prepare high MW polypeptides; however, the MWs can not be tuned by the feeding ratios. The kinetic study showed that both yields and MWs were increased dramatically with the reaction time, but the MW’s increasing rate was slower than that of the yield. Polymerization mechanism shows that in the initiation step, Ln(OR)3(R=iPr or Ar) depronates the3-NH of NCA, forming N-rare earthlated NCA. N-rare earthlated NCA serves as the truly initiation center and is responsible for further chain growth and produces α-carboxylic-ω-aminotelechelic polypeptide after termination. In these two systems, polypeptides with the hydantoinic end and hydantoic acid end are also found as by-products.Low crystalline copolyester PCD has been synthesized by random copolymerization of ε-caprolactone (CL) with5～8mol%of2,2-dimethyl-trimethylene carbonate (DTC) in the presence of La(OAr)3as the catalyst. PCD, as well as PCL homopolymer, are fabricated into electrospun mats (EMs) and compression molding films (CMFs) and measured for their crystallinity. The results indicate that in EMs, the crystallinity of PCD has been decreased to40%in comparison with79%for PCL while in CMFs, the corresponding crystallinity is decreased to28%compared to45%for PCL.It is found for the first time that porcine pancreatic lipase (PP lipase) can effectively catalyze the degradation of PCD while it shows no detectable effect on PCL. For PCD EM, the weight loss reached80%within10days while it is70%for PCD CMF within35days. The degradation rates of EMs are faster than CMFs, and PCD’s degradation rate is much faster than PCL. Based on the experimental results, the above degradation behaviors have been explained. Degradation mechanism study shows in PCD degradation catalyzed by PP lipase, surface erosion is the main degradation mode. Salicylic acid is used as a model drug to test the drug release behavior of PCD. It is found PCD EM showed a controlled drug release behavior in comparison with PCL EM which exhibited a burst-release behavior. This difference is closely related with the crystallinity of the two polymer samples.Poly[(ε-caprolactone-r-2,2-dimethyltrimethylene carbonate)-b-PEG-b-(ε-caprolactone-r-2,2-dimethyltrimethylene carbonate)](PECD) and poly[MPEG-b-(ε-caprolactone-r-2,2-dimethyltrimethylene carbonate)](MPECD) have been synthesized by using PEG and MPEG as the initiators and La(OAr)3as the catalysts. With similar MW and EO amount, MPECD is more brittle and has a smaller contact angle. It is found that PP lipase can effectively catalyze the degradations of PCD, PCD/PECD and PCD/MPECD EMs. For PCD EM, the weight loss reaches92%within7days while it is around60%for PCD/PECD or PCD/MPECD EMs within23days. A PEG segment enrichment process on the EM surface is detected, which prevents the contact of PP lipase with PCD segments in the PEG-involved EMs and further decreases the corresponding degradation rates. Surface erosion mechanism is proved in this degradation.更多还原