Excited State Dynamics of Bilirubin Dimethyl Ester-Copper Ions Complex

YAN Shu-jun; LIU Yang-yi; HE Xiao-xiao; ZHENG Ming; CAO Xiao-dan; XU Jian-hua; CHEN Jin-quan

doi:10.3964/j.issn.1000-0593(2020)06-1674-05

[1] . Coordination of Cu2+ with BRE may cause their energy levels to couple to generate a new non-radiative de-excitation pathway leading to a decrease in fluorescence, but further research is needed on the quenching mechanism of Cu2+ on BRE fluorescence. The de-excitation processes of the excited state molecules generally occur on the ultra-fast time scale, which cannot be observed by the traditional steady-state spectroscopy. The visible and infrared-band femtosecond transient absorption spectroscopy techniques were used to study the excited state spectral properties of BRE-Cu2+ complex in this paper. A new quenching mechanism of Cu2+ on the BRE flurescnece was discovered by the transient absorption spectrain the visible and infrared region. We have proposed and confirmed the Ligand-to-metal charge transfer (LMCT) as a result of the fluorescence quenching. Compared with the spectral properties of BRE, the charge transfer state would provide a non-radiative decay pathway to BRE-Cu2+ complex, reducing the fluorescence quantum yield of BRE to 5% of its original value. Moreover, two lifetimes (11 ps and 186 ps) were obtained by fitting the kinetic curves of the transient absorption spectra of the complex. We assign the 11 ps component to the build-up process of the LMCT state, while the 186 ps is the lifetime of the charge transfer state.

[2] Kaplan M, Bromiker R, Hammerman C. Seminars in Perinatology, 2014, 38(7): 429.

[3] Raimondi F, Borrelli A C, Ferrara T, et al. The Journal of Maternal-Fetal & Neonatal Medicine, 2017, 30(17): 2078.

[4] Mancuso C. Neuropharmacology, 2017, 118: 113.

[5] Ramos P, Santos A, Pinto N R, et al. Biological Trace Element Research, 2014, 161(2): 190.

[6] Hulzebos C V, Dijk P H. Seminars in Perinatology, 2014. 38(7): 412.

[7] Braslavsky S E, Holzwarth A R, Schaffner K. Angewandte Chemie International Edition in English, 1983, 22(9): 656.

[8] Overbeek J T G, Vink C L J, Deenstra H. Recueil des Travaux Chimiques des Pays-Bas, 1955, 74(1): 81.

[9] Berera R, van Grondelle R, Kennis J T. Photosynth Res., 2009, 101(2-3): 105.