Scheme 2 CS–Michael addition reaction of probe C23 and
SO2 (HSO3-1 in the
solution)
When the probe is combined with HSA, the Michael addition reaction
between the probe and SO2 is rapidly catalyzed by HSA,
and this catalytic effect of HSA greatly improves the detection
sensitivity of SO2. Studies have shown that the amino
group of Lys199 in HSA contributes most of the catalytic
activity.7 The results
of liang et al showed good performance of this probe molecule for the
simultaneous determination of HSA and SO2 molecules in
urine and cells. And this probe was expected to be used in the diagnosis
of liver cancer, drug evaluation, and the study of physiological and
pathological functions of HSA and SO2. In this work, the
structure and fluorescent character of this probe molecule were studied
under density functional theory. The rotation of the unsaturated C-C
bonds in the probe molecule led to several stable structures coexisted.
The transfer between different stable structures provided the
non-radiative energy loss pathway when the probe molecule recovered from
the excited state to the ground state which led to no fluorescence in
this process. The calculated results indicated the red fluorescence
would be generated if the rotation of the unsaturated C-C bonds in the
probe molecule was prohibited such as the probe molecule was stabilized
in the hydrophobic cavity of HSA. The calculation also indicated that
the Michael reaction between the probe molecule and SO2would be another effective way for the stabilization of the probe
molecule and generating blue fluorescence which made this probe molecule
is able of simultaneous determination of HSA and SO2molecules. All the figures were rendered by means of VMD 1.9.3
software8 and the
analyses were finished by using the Multiwfn 3.7
code9.