ja7b11712_si_001.pdf (619.3 kB)
Conformational Change-Induced Fluorescence of Bovine Serum Albumin–Gold Complexes
journal contribution
posted on 2018-01-23, 00:00 authored by Jacob
M. Dixon, Shunji EgusaWe
report new findings on the red fluorescent (λem =
640 nm) bovine serum albumin (BSA)–gold (Au) compound initially
described by Xie et al. (J. Am. Chem. Soc. 2009, 131, 888–889) as Au25 nanoclusters. The BSA–Au compounds were further reducible
to yield nanoparticles, suggesting that these compounds were BSA–cationic
Au complexes. We examined the correlations between BSA conformations
(pH-induced as well as denatured) and the resulting fluorescence of
BSA–Au complexes, to understand the possible cationic Au binding
sites. The red fluorescence of the BSA–Au complex was associated
with a particular isoform of BSA, the aged form (pH > 10) of the
five
pH-dependent BSA conformations, while the other conformations, expanded
(pH < 2.7), fast (2.7 < pH < 4.3), normal (4.3 < pH <
8), and basic (8 < pH < 10) did not result in red fluorescence.
There could be internal energy transfer mechanisms to produce red
fluorescence, deduced from excitation–emission map measurements.
The ensemble minimum number of Au(III) per BSA to yield red fluorescence
was <7. We illustrate the presence of multiple specific Au binding
sites in BSA, and present an interpretation of the fluorescence of
the BSA–Au complex, alternative to a single-site nucleation
of a neutral Au25 nanocluster.