Catalytic
Reactions on the Surface of Ag Nanoparticles: A Photochemical Effect
and/or Molecule Property?
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Abstract
Using time-dependent
surface-enhanced Raman scattering (TDSERS), we demonstrate the surface-catalyzed
oxidation of 3-hydroxy anthranilic acid (HAA) to its azo derivatives.
No external source either in the form of laser excitation or heat
was required for the surface-catalyzed reaction, which clearly established
that thermal energy alone was sufficient. But the possibility of enhanced
reaction rate due to the surface plasmon resonance could not be ignored.
To mimic in vivo conditions that prevail in healthy and unhealthy
cells, SERS measurements were recorded under different environmental
conditions. It is shown that the surface-catalyzed azo formation and
its isomerization were strongly dependent on the external conditions,
namely, temperature, pH, and environment. A plausible mechanism based
on electron transfer to the adsorbed O<sub>2</sub> is proposed for
the <i>trans–cis</i> isomerization. This study can
lead toward a new strategy of surface-catalyzed reactions not only
for the synthesis of azo dyes but also to distinguish between the
normal and abnormal cells