GPC and ESI-MS Analysis of Labeled Poly(1-Hexene): Rapid Determination of Initiated Site Counts during Catalytic Alkene Polymerization Reactions
摘要:
Accurate active-site counts are necessary for the establishment of olefin polymerization kinetics, yet current techniques are often tedious and limited in sensitivity. Herein, we describe the development of a novel method for determining the fraction of initiated catalyst using standard gel-permeation chromatography (GPC). The first insertion of monomer into the chromophore-bearing zirconocene 1 generates a single equivalent of a labeled polymer chain. The polymer-bound label can be quantified as a function of polymer molecular weight using a GPC with a UV detector; simultaneous RI detection allows both the extent of monomer conversion and the molecular-weight distribution to also be established. We estimate that monomer to catalyst ratios of as high as 10 000:1 can be measured using this technique.
Building Functionalized Peptidomimetics: Use of Electroauxiliaries for Introducing N-Acyliminium Ions into Peptides
摘要:
A series of silyl-substituted amino acids have been synthesized, inserted into peptides, and then employed as precursors for oxidatively generating reactive N-acyliminium ions. Both electrochemical and chemical oxidation procedures have been employed. N-Acyliminium ion generation in a solid-phase substrate as well as application to a small library of functionalized dipeptides has been demonstrated. Limitations in terms of how electron-rich the silyl groups can be as well as the compatibility of multiple silyl groups within a longer peptide are defined.
Building Functionalized Peptidomimetics: Use of Electroauxiliaries for Introducing <i>N</i>-Acyliminium Ions into Peptides
作者:Haizhou Sun、Connor Martin、David Kesselring、Rebecca Keller、Kevin D. Moeller
DOI:10.1021/ja064737l
日期:2006.10.1
A series of silyl-substituted amino acids have been synthesized, inserted into peptides, and then employed as precursors for oxidatively generating reactive N-acyliminium ions. Both electrochemical and chemical oxidation procedures have been employed. N-Acyliminium ion generation in a solid-phase substrate as well as application to a small library of functionalized dipeptides has been demonstrated. Limitations in terms of how electron-rich the silyl groups can be as well as the compatibility of multiple silyl groups within a longer peptide are defined.
GPC and ESI-MS Analysis of Labeled Poly(1-Hexene): Rapid Determination of Initiated Site Counts during Catalytic Alkene Polymerization Reactions
作者:Beth M. Moscato、Bolin Zhu、Clark R. Landis
DOI:10.1021/ja105775r
日期:2010.10.20
Accurate active-site counts are necessary for the establishment of olefin polymerization kinetics, yet current techniques are often tedious and limited in sensitivity. Herein, we describe the development of a novel method for determining the fraction of initiated catalyst using standard gel-permeation chromatography (GPC). The first insertion of monomer into the chromophore-bearing zirconocene 1 generates a single equivalent of a labeled polymer chain. The polymer-bound label can be quantified as a function of polymer molecular weight using a GPC with a UV detector; simultaneous RI detection allows both the extent of monomer conversion and the molecular-weight distribution to also be established. We estimate that monomer to catalyst ratios of as high as 10 000:1 can be measured using this technique.