Journal of the American Chemical Society
Article
functionalized alumina, only the functional groups of the
adsorbed GSSG will determine the ζ potential and IEP, and the
initial particle surface will lose its influence. For native and
ASSOCIATED CONTENT
Supporting Information
■
*
S
Isoelectric point of Al O , Al O −NH , Al O −COOH,
2
3
2
3
2
2
3
−
NH -functionalized alumina, GSSG adsorption shifted the
2
Al O −SO H, and Al O −PO H after a 10 mM KOH
2
3
3
2
3
3
2
particles IEP to more acidic values, which demonstrates the
contribution of free carboxylate groups of GSSG to the
establishment of the new IEP. Those carboxylate groups that
contribute to the particle IEP are unlikely to be involved in
binding between GSSG and the particle surface.
AUTHOR INFORMATION
Author Contributions
These authors contributed equally.
Notes
The authors declare no competing financial interest.
In addition, the ζ potential and IEP of native and -NH2-
functionalized alumina after GSSG adsorption were not
completely governed by negative carboxylate groups which
would have led to a negatively charged and acidic IEP. This
∥
observation suggests a contribution of unbound protonated
+
−
NH3 groups of GSSG to the electrokinetic properties. The
increase of the IEP after DTT treatment confirms the release of
ACKNOWLEDGMENTS
We thank the EuropeanResearch Council for financial support
within the BiocerEng, project no. 205509.
■
GS moieties from native and −NH -functionalized alumina. In
2
contrast, in case of −SO H-functionalized particles, the GSSG
3
adsorption did not alter the IEP and pH-dependent ζ potential
as expected by a substantial influence of the initial particle
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(
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(
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(
CONCLUSIONS
■
(
The surface chemistry of colloidal alumina particles tailored
with −NH , −COOH, −PO H , and −SO H functional groups
2
3
2
3
strongly affects the adsorption and the orientation of GSSG on
the particle surface. Although electrostatic interactions are
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type, concentration, and acidity/basicity of the functional
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charged native alumina in monolayer concentrations via the
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(
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̈
2
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2
3
GSSG adsorbs exclusively onto −SO H modified alumina.
3
(
1
(
Here, GSSG is suggested to bind with both GS moieties via its
two protonated amino groups and only partially covers the
particle surface in a side-on orientation. These results represent
a firm base for further studies on GSSG and peptide adsorption
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under competition with other peptides and proteins. Tailored
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functional groups.
(
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(
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(
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dx.doi.org/10.1021/ja401590c | J. Am. Chem. Soc. 2013, 135, 6307−6316