Understanding the catalytic activity of single‐chain polymeric nanoparticles in water

Abstract

ABSTRACT:The structuring role of benzene-1,3,5-tricarboxamide (BTA) groups for the catalytic activity of single chain polymeric nanoparticles in water was investigated in the transfer hydrogenation of ketones. To this end, a set of segmented, amphiphilic copolymers was prepared, which comprised oligo (ethylene glycol) side chains to impart water solubility, BTA and/or lauryl side chains to induce hydrophobicity and diphenylphosphinostyrene (SDP) units in the middle part as a ligand to bind a ruthenium catalyst. All copolymers were obtained by reversible addition-fragmentation chain transfer (RAFT) polymerization and showed low dispersities (M w /M n 5 1.23-1.38) and controlled molecular weights (M n 5 44-28 kDa). A combination of circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) showed that all copolymers fold into a single chain polymeric nanoparticles (SCPNs) as a result of the helical selfassembly of the pendant BTA units and/or hydrophilic-hydrophobic phase separation. To create catalytic sites, RuCl 2 (PPh 3 ) 3 was incorporated into the copolymers. The Cotton effects of the copolymers before and after Ru(II) loading were identical, indicating that the helical self-assembly of the BTA units and the complexation of SDP ligands and Ru(II) occurs in an orthogonal manner. DLS revealed that after Ru(II) loading, SDP-bearing copolymers retained their single chain character in water, while copolymers lacking SDP units clustered into larger aggregates. The Ru(II) loaded SCPNs were tested in the transfer hydrogenation of cyclohexanone. This study reveals that BTA induced stack formation is not crucial for SCPN formation and catalytic activity; SDP-bearing copolymers folded by Ru(II) complexation and hydrophobic pendants suffice to provide hydrophobic, isolated reaction pockets around Ru(II) complexes. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52,[12][13][14][15][16][17][18][19][20]

What Is Next in Single-Chain Nanoparticles?

“…The Ru(II) loaded SCNP were tested in the transfer hydrogenation of cyclohexanone ( Figure 10). 20 While the folding induced by BTA units was determined to be nonessential to the catalysis, the SCNP-bound catalyst was proven more effective than the free catalyst. In a prior publication from the same researchers, the self-assembled α-helices of a similar system were shown to withstand aqueous catalytic conditions (0.4 M HCOONa and substrate at 40°C), and cyclohexanone was efficiently reduced to cyclohexanol (86% reduced after 18 h).…”

Toward model‐driven engineering of supramolecular copolymers

“…Due to these advances that stem from a thorough understanding of the polymerization mechanisms involved, more and more complex polymeric structures have been synthesized, such as brush polymers, 10,11 dendrimers, [12][13][14] micrometer-sized toroids, 15 and polymers that fold and unfold in a controlled fashion. [16][17][18][19] Concomitant to the development of polymeric structures formed by covalent bonds, supramolecular polymers have been introduced. [20][21][22][23] In these structures, the building blocks of the polymer are connected by noncovalent interactions like hydrophobic interactions, hydrogen-bonding, and metal-ligand bonding.…”

Sequence-Regulated Polymers via Living Radical Polymerization: From Design to Properties and Functions

“…Typically, amphiphilic PEGMA/BTAMA random copolymers carrying hydrophilic poly(ethylene glycol) chains and hydrophobic, chiral benzene-1,3,5-tricarboxamide (BTA) units efficiently self-fold in water via the helical self-assembly of the BTA pendants with hydrogen bond (Figure 7) (50, 52-54). The folding compartments with catalysts were further applicable as enzyme-mimic nanoreactors in water (50,53,54). More importantly, unimer micelles and SCPNs directly reflect the primary structure (molecular weight, composition of monomers and functional groups, end-functional groups etc.)…”

“…The representatives are given: 1) microgel-core star polymers via the intermolecular crosslinking of linear arm polymers (living polymers or macroinitiators) with bifunctional linking agents (divinyl compounds) (Figure 4b) (29)(30)(31)(32); 2) micelles, vesicles, and polymersomes via the intermolecular association of amphiphilic (functional) block copolymers with physical interaction (hydrophobic, hydrogen-bonding, ionic etc.) (43,44); 3) unimer micelles and single-chain polymeric nanoparticles (SCPNs) via the "intramolecular" single-chain folding of amphiphilic (functional) random copolymers with physical interaction or chemical crosslinking (15,(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55).…”

“…Among them, unimer micelles and SCPNs (the third category) uniquely afford single-chain compartments and thereby are often designed as artificial mimics of natural proteins and enzymes (49)(50)(51)(52)(53)(54). Typically, amphiphilic PEGMA/BTAMA random copolymers carrying hydrophilic poly(ethylene glycol) chains and hydrophobic, chiral benzene-1,3,5-tricarboxamide (BTA) units efficiently self-fold in water via the helical self-assembly of the BTA pendants with hydrogen bond (Figure 7) (50, 52-54).…”