The use of OPH (OPDtox, Reactive Surfaces) to functionalize coatings provides a direct measure of metal-chelation by a protein
in a coating. To assess whether the enzyme
embedded within the film maintained its
chelated metal ligands, the prepared films
were challenged with the organophosphorus
substrate, paraoxon. The OPDtox enhanced
coatings catalytic mechanism demonstrated
bulk volume dependence (Fig. 4), and clearly
demonstrates the ability of metalloenzymes
to chelate the required metal ions.
straints derived from metal accessibility to
the peptides become crucial. One reason
for lower cobalt chloride hexahydrate
binding to the films may be due to the fact
that the cobalt complex is larger than the
other metals that were tested which makes
it harder to interact with the binding site.
Functionalized Coatings with
Metal Chelated Peptide
Nickel, copper and cobalt were selected to
evaluate binding to His6 peptide within the
vinyl latex coating. Copper was chosen due
to the importance of it being used as the
main ingredient of anti-fouling coatings.
The His6 peptide was blended into the
vinyl latex coating and then assessed for impact on the binding properties of the peptide. Binding affinity to the peptide was
performed in a solution assay by suspending free films to a metal solution of 200
mM nickel sulfate, 100 mM copper sulfate
and 42 mM cobalt chloride hexahydrate in
three separate experiments. All of the metal
solutions were adjusted to pH 10 to avoid
hydrogen ions competing for the binding
sites. The exposure time was 24 hours ensure a binding saturation of metals to the
peptides in the coating. The liquid in which
the free films were suspended was then removed and pH 5 water was added to remove the bound metal from the free films.
This elution process occurred for 24 hours
to maximize release of the metal ions back
into solution, due to the competition of the
hydrogen ions with the metals for the binding sites. The wash liquid was then decanted and analyzed for the amount of
metals present using a spectrometer. The
vinyl latex films containing the metal binding peptide His6 bound more nickel, copper and cobalt than in the control films that
did not contain the peptide (Figure 5).
Nickel and copper binding to the films
was stronger when compared to cobalt
binding which occurred at a much lower
concentration. In a polymer system or
coating, the peptide is suspended in the
polymer matrix and diffusional con-
Summary
This study demonstrates that it is possible
to create re-chargeable coatings for metal
ions used as antifouling agents. This plat-
form technology will be used to create anti-
microbial coatings that use metals as a
deterrent for biological growth. Our expe-
rience with other natural peptides that are
not toxic to the environment suggests these
metal-binding peptides can be used as
“drop in” additives for a coating to imbue
it with these functionalities. Peptides can
be chosen to interact with and bind to spe-
cific metals, to change these metals at will,
and to use combinations of metals or pep-
tides with increasingly larger binding coef-
ficients, making the system programmable.
When a specific metal binding peptide is
chosen, an assessment of the polymer sys-
tem can be performed to optimize the per-
formance of the peptide. Since metals are
so abundantly found in seawater, they can
be utilized by marine coatings to prevent bi-
ological growth from occurring without
adding metal ions to the environment (Fig
6). These approaches should reduce the reg-
ulatory concerns of using heavy metals as
antifouling actives.
Methods
Reagents. His6 peptide (21st Century
Biochemicals, Product HIS6-0400) was
Fig 5. His6 peptide was blended into the vinyl latex coating and then assessed for ability to
chelate metals. Although the control films bound free metal in solution, the peptide functionalized coatings chelated significantly more free metal from solution.
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