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Title: Organocatalytic Stereoselective Ring-Opening Polymerization of Lactide with Dimeric Phosphazene Bases

Abstract

Highly isotactic polylactide with a high melting temperature was synthesized from rac-lactide through an organocatalytic route using dimeric phosphazene base 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2 5,4 5-catenadi(phosphazene) (P2-t-Bu) catalyst at low temperature. Microstructural analysis of the prepared polymer using homodecoupled 1H NMR spectroscopy revealed the formation of a stereoblock architecture containing long isotactic sequence of R- and S- blocks in the main chain. A proposed mechanism involving chain-end control and stereoerror explains the stereoselective polymerization.

Authors:
 [1];  [1];  [2];  [1];  [1];  [1]
  1. Almaden Research Center
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Center for Nanophase Materials Sciences
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
940792
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society; Journal Volume: 129; Journal Issue: 42
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CATALYSTS; POLYMERIZATION; LACTATES; ORGANIC PHOSPHORUS COMPOUNDS; ORGANIC POLYMERS; STEREOCHEMISTRY; MOLECULAR STRUCTURE

Citation Formats

Zhang, Lei, Nederberg, Fredrik, Messman, Jamie M, Pratt, Russel C, Hedrick, James, and Wade, Charles G. Organocatalytic Stereoselective Ring-Opening Polymerization of Lactide with Dimeric Phosphazene Bases. United States: N. p., 2007. Web. doi:10.1021/ja074131c.
Zhang, Lei, Nederberg, Fredrik, Messman, Jamie M, Pratt, Russel C, Hedrick, James, & Wade, Charles G. Organocatalytic Stereoselective Ring-Opening Polymerization of Lactide with Dimeric Phosphazene Bases. United States. doi:10.1021/ja074131c.
Zhang, Lei, Nederberg, Fredrik, Messman, Jamie M, Pratt, Russel C, Hedrick, James, and Wade, Charles G. Mon . "Organocatalytic Stereoselective Ring-Opening Polymerization of Lactide with Dimeric Phosphazene Bases". United States. doi:10.1021/ja074131c.
@article{osti_940792,
title = {Organocatalytic Stereoselective Ring-Opening Polymerization of Lactide with Dimeric Phosphazene Bases},
author = {Zhang, Lei and Nederberg, Fredrik and Messman, Jamie M and Pratt, Russel C and Hedrick, James and Wade, Charles G},
abstractNote = {Highly isotactic polylactide with a high melting temperature was synthesized from rac-lactide through an organocatalytic route using dimeric phosphazene base 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2 5,4 5-catenadi(phosphazene) (P2-t-Bu) catalyst at low temperature. Microstructural analysis of the prepared polymer using homodecoupled 1H NMR spectroscopy revealed the formation of a stereoblock architecture containing long isotactic sequence of R- and S- blocks in the main chain. A proposed mechanism involving chain-end control and stereoerror explains the stereoselective polymerization.},
doi = {10.1021/ja074131c},
journal = {Journal of the American Chemical Society},
number = 42,
volume = 129,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
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  • DNA sliding clamps form an oligomeric ring encircling DNA and serve as a moving platform for DNA-processing proteins. The opening and closing of a sliding-clamp ring is essential to load the clamp onto DNA in order to perform its functions. The molecular details of how clamp rings open and enclose DNA are still not clear. Three PCNA homologues have been found in Sulfolobus solfataricus which form a heterotrimer. Taking advantage of their hetero-oligomeric nature, the structures of the PCNAs in monomeric PCNA3, dimeric PCNA1-PCNA2 and trimeric PCNA1-PCNA2-PCNA3 forms were determined at resolutions of 2.6-1.9 Angstroms . The distinct oligomeric structuresmore » represent different stages in ring formation, which were verified in solution by ultracentrifugation analysis. The heterodimer opens in a V-shape of 130, while the heterotrimers form a ring with a 120 rotation between monomers. The association of a rigid PCNA3 monomer with an opened PCNA1-PCNA2 heterodimer closes the ring and introduces a spring tension in the PCNA1-PCNA2 interface, thus bending the nine-stranded intermolecular [beta]-sheet to fit the 120 rotation. The release of the spring tension as PCNA3 dissociates from the ring may facilitate ring opening. The structural features in different assemblies present a molecular model for clamp ring assembly and opening.« less