Chain initiation efficiency in cobalt- and nickel-mediated polypeptide synthesis
Chain initiation efficiency in cobalt- and nickel-mediated polypeptide synthesis
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DOI：
10.1021/ja994281q
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发表时间：
2000-06-21
影响因子：
15
通讯作者：
Curtin, SA
中科院分区：
文献类型：
--
作者：
Deming, TJ;Curtin, SA
在某些配体和溶剂的存在下，镍和钴介导的α-氨基酸-N-羧酸酐(NCA)的活性聚合生成的聚合物的相对分子质量比单体与引发剂的初始摩尔比预测的大几倍。这种分子量膨胀可能是由于活性降低的催化中间体的竞争形成，也可能是由于单一催化活性物种的不完全形成。这里提出的证据支持后一种可能性。具体来说，有证据表明，关键的酰胺基金属环活性物种的浓度是通过以下方式原位降低的：(1)将一个NCA单体添加到另一个预引发剂分子中时释放的CO与金属(0)预引发剂络合，(2)由于质子迁移效率低而导致六元氨基烷基金属环中间体的不完全环收缩，以及(3)酰胺基酰胺酸酯活性物种的二聚化得到催化非活性络合物。
In the presence of certain ligands and solvents, nickel- and cobalt-mediated living polymerizations of alpha-amino acid-N-carboxyanhydrides (NCAs) produce polymers with molecular weights several times greater than predicted by initial molar ratios of monomer to initiator. Such molecular weight inflation could result either from competitive formation of catalytic intermediates of reduced activity or from incomplete formation of a single catalytically active species. Evidence is presented here supporting the latter possibility. Specifically, evidence is given that the concentration of the key amido-amidate metallacyclic active species is reduced in situ by (1) complexation of metal(0) preinitiator by CO liberated upon addition of an NCA monomer to another molecule of preinitiator, (2) incomplete ring contraction of a six-membered amido-alkylmetallacyclic intermediate due to inefficient proton migration, and (3) dimerization of the amido-amidate active species to give catalytically inactive complexes.