Cobalt and iron initiators for the controlled polymerization of α-amino acid-N-carboxyanhydrides
Cobalt and iron initiators for the controlled polymerization of α-amino acid-N-carboxyanhydrides
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DOI：
10.1021/ma9902899
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发表时间：
1999-06-29
期刊：
影响因子：
5.5
通讯作者：
Deming, TJ
中科院分区：
文献类型：
--
作者：
Deming, TJ
多肽是有趣的聚合物，因为它们的结构复杂性赋予这些材料特定的生物功能。尽管制备高分子量多肽的方法已经存在了100多年，但这种化学反应，即R-氨基酸-N-羧基氰基丙烯酸酯（NCA）的聚合反应，一直受到副反应的困扰。链转移和终止反应限制了这种方法制备缺乏天然蛋白质复杂性的多肽。最近，我们发现零价镍络合物bpyNi（COD）引发NCA的聚合并支持聚合，同时大大消除副反应（等式1）。2在确定了这种引发剂的作用机制之后，我们试图开发基于其他过渡金属的引发剂，看看它们是否可以为聚合提供优势。发现NCA与零价金属的反应化学对于金属铁、钴和镍是通用的，它们都形成由单体氧化加成到穿过OC 5酸酐键的金属上产生的产物。由于零价钴的高反应性，发现络合物（PMe 3）4Co比bpyNi（COD）更快地引发NCA聚合，从而允许在嵌段共聚肽中制备定义明确的氨基酸短序列。
Polypeptides are interesting polymers because their structural complexity imparts these materials with specific biological functions. Although methods for preparation of high-molecular-weight polypeptides have existed for over 100 years, this chemistry, the polymerization of R-amino acid-N-carboxyanhydrides (NCAs), has been plagued by side reactions. 1 Chain transfer and termination reactions have limited this methodology to the preparation of polypeptides that lack the complexity of natural proteins. Recently, we discovered that the zerovalent nickel complex, bpyNi (COD), initiates the polymerization of NCAs and supports polymerization while greatly eliminating side reactions (eq 1). 2 After identifying the mechanism by which this initiator operates, we sought to develop initiators based on other transition metals to see if they might provide advantages for polymerization. It was found that the reaction chemistry of NCAs with zerovalent metals is general for the metals iron, cobalt, and nickel, which all form products resulting from oxidative addition of the monomer to the metal across the OC 5 anhydride bond. Due to the high reactivity of zerovalent cobalt, the complex (PMe3) 4Co was found to initiate NCA polymerizations more rapidly than did bpyNi (COD), allowing the preparation of well-defined short sequences of amino acids in block copolypeptides.