Paper
RSC Advances
Besides being luminescent sensor, the ionic complex of
Qu(CSA)2 also serves as a denaturant effective in uncoiling the
folded chains of BSA. The unfolding process of BSA was there-
fore evaluated by combined results from the emission and the
CD spectra. A three-step process, involving the rearrangement
of the tertiary structure, the formation of molten globule, and
the collapse of secondary structure, was therefore proposed in
this study. Emission responses of the Trp residue and the added
Qu(CSA)2 were correlated with the three-step unfolding process.
Acknowledgements
We appreciate the nancial support from the Ministry of
Science and Technology, Taiwan, under the contract no.
MOST102-2221-E-110-084-MY3 and 104-2221-E-110-050.
Scheme
2 Proposed mechanism for fluorescent probing of the
Qu(CSA)2-induced BSA unfolding process.
References
globule state still offers additional hydrophobic sites for the
quinine base. The intra-domain contacts may become loose due
to the swelling effect, which facilitates approaches of the
intruding quinine bases to nearby range of the Trp residues
inside the domains. In close vicinities, the bulky quinine bases
sterically rigidied the Trp residue and effectively blocked the
non-radiative decay process of the excited Trp unit resulting in
large emission enhancement of the Trp residue (cf. Fig. 7). The
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the emission to longer wavelengths as the Qu(CSA)2 concen-
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¨
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RSC Adv., 2016, 6, 38201–38208 | 38207