Peptide with a cobalt complex oxidizes polystyrene microparticles
Polystyrene is a widespread plastic that is essentially not
recyclable when mixed with other materials and is not biodegradable. In
the journal Angewandte Chemie, a German research team has
introduced a biohybrid catalyst that oxidizes polystyrene microparticles
to facilitate their subsequent degradation. The catalyst consists of a
specially constructed “anchor peptide” that adheres to polystyrene
surfaces and a cobalt complex that oxidizes polystyrene.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
Polystyrene—alone or in combination with other polymers—has
many applications, from yogurt containers to instrument housings. In its
foam form, mainly known under the trademarked name Styrofoam, it is, for
example, used for insulation and packaging. A big disadvantage of
polystyrene is its poor biodegradability, which leads to environmental
pollution. When clean and not mixed with other materials, polystyrene is
recyclable, but not when it is contaminated, or combined with other
materials. In municipal recycling programs, mixed polystyrene plastic
waste and degradation products, such as polystyrene nano- and
microparticles, are difficult to process. The problem lies in the fact
that polystyrene is water-repellent and nonpolar and thus cannot react
with common polar reactants.
For a simple, economical, and energy efficient process to
break down mixed polystyrene waste, the polystyrene must first be
equipped with polar functional groups. A team led by Ulrich Schwaneberg
and Jun Okuda at the RWTH in Aachen (Germany) has now developed a novel
biohybrid catalyst to carry out this step. The catalyst is based on
compounds known as anchor peptides coupled with a cobalt complex.
Anchor peptides are short peptide chains than can attach to
surfaces. The team developed a special anchor peptide (LCI, Liquid
Chromatography Peak I) that binds to the surface of polystyrene. One
gram of this peptide is enough to coat a surface of up to 654 m2
with a monolayer within minutes by either spraying or dipping.
A catalytically active cobalt complex is attached to the
anchor peptide via a short linking piece. The cobalt atom is
“surrounded” by a macrocyclic ligand, a ring made of eight carbon and
four nitrogen atoms (TACD, 1,4,7,10-tetraazacyclododecane). The catalyst
accelerates oxidation of the C–H bonds in polystyrene to form polar OH
groups (hydroxylation) by reaction with Oxone (potassium
peroxymonosulfate), a common oxidizing agent. The binding of the anchor
peptides is material-specific so in this case they immobilize the
catalytically active cobalt near the polystyrene surface, which
accelerates the reaction. This simple, inexpensive, and energy-efficient
process is scalable through dipping and spray applications and is
suitable for use on an industrial scale.
Through the use of conjugated chemical catalysts, this
hybrid catalyst concept employing material-specific binding by anchor
peptides could allow for the material-specific breakdown of further
hydrophobic polymers such as polypropylene and polyethylene that cannot
be economically broken down by enzymes.
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About the Author
Prof. Ulrich Schwaneberg and Prof. Jun Okuda
at RWTH Aachen University (Germany) have combined their expertise in protein engineering, design
of metallozymes, and polymerization catalysis to jointly develop the
field of biohybrid catalysts. This research has been focused on teaching
enzymes new reactions and thereby developing sustainable processes for
the synthesis and depolymerization of polymers.
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