I. Gomes, N. C. Santos, L. M. A. Oliveira, A. Quintas,P. Eaton, Eulália Pereira,and R. Franco, Probing Surface Properties of Cytochrome c@Au Bionanoconjugates, Journal of Physical Chemistry C, 112(42), 16340–16347 (2008).

Abstract

Bionanoconjugates were created with cytochrome c from horse heart (HCc) or yeast (YCc) and citratestabilized gold nanoparticles (AuNPs). Evidence for the formation of stable HCc-AuNP and YCc-AuNP bionanoconjugates came from a 5 nm red-shift of the surface plasmon resonance band of the AuNPs; increase of the zeta-potential; and direct visualization by Atomic Force Microscopy. Langmuir isotherm fittings of zeta-potential data indicated that higher enthalpy changes are involved in the formation of the HCc-AuNP than in YCc-AuNP. UV-visible and circular dichroism studies of pH-induced aggregation of the bionanoconjugates revealed distinct protonation patterns with an aggregation pH of 8.8 and 6.2, for YCc-AuNP and HCc-AuNP, respectively. No appreciable changes were observed in the secondary structure of HCc in HCc-AuNP. In contrast, YCc in YCc-AuNP presented a decrease in alpha-helix content upon AuNP binding, and an increase in beta sheet content upon pH-induced aggregation. Data discussion is based on the distinct binding modes of both proteins to the AuNPs: via a covalent bond (Cys 102) for YCc; and via electrostatic interaction for HCc.



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