Spectral fluorescence and polarization characteristics of Z,Z-bilirubin IXα

Abstract

We have studied the spectral fluorescence and polarization characteristics of Z,Z-bilirubin IXα, at room temperature in chloroform and in aqueous buffer medium, within an equilibrium complex with human serum albumin (HSA), and also under low temperature conditions (T = -100 o C) in isobutyl alcohol. We have observed a bathochromic shift of the fluorescence spectra, which is most pronounced for the bilirubin-albumin complex. The following are considered as possible reasons for the observed dependence of the position of the fluorescence (fluorescence excitation) spectra on the excitation (detection) wavelength: structural and spectral differences between the chromophores making up the bilirubin molecule; conformational heterogeneity of the pigment in solution; a contribution to the fluorescence from molecules which have not completed the vibrational relaxation process; inhomogeneous orientational broadening of the levels; heterogeneity of the microenvironment of the chromophores in the protein matrix. We show that polarized fluorescence of bilirubin occurs at room temperature, due to the anomalously short fluorescence lifetime τ (picosecond or subpicosecond ranges). Despite such a short τ, the absorption and emission polarization spectra suggest the presence of intramolecular nonradiative singlet-singlet energy transfer when bilirubin is excited to high vibrational sublevels of the S 1 state (degree of polarization p = 0.11-0.12). When fluorescence is excited on the long-wavelength slope of the absorption band, no transfer occurs: the degree of polarization (p = 0.46-0.47) is close to the limiting value (p = 0.50). We discuss the question of the role played by exciton interactions between chromophores in the bilirubin molecule when it is excited.

A microscopic evaluation of collagen–bilirubin interactions: in vitro surface phenomenon

“…Native bilirubin exhibits the complete green fluorescence as shown in Figure 3(A). The spectral fluorescence and polarization characteristics of Z,Zbilirubin IXα is well established (Plavskii et al, 2007). The native collagen exhibited a very weak fluorescence as shown in Figure 3 (B).…”

Bilirubin remodels murine white adipose tissue by reshaping mitochondrial activity and the coregulator profile of peroxisome proliferator–activated receptor α

“…E configuration). This configuration, now photobilirubin/lumirubin, allows for greater mobility of the pyrrole rings and subsequent emission behavior (38)(39)(40). Utilizing the property of bilirubin to fluoresce, aside from when bound to albumin, we found that the purified PPARa-LBD protein interacts with bilirubin and, when excited, has fluorescence (Fig.…”

Light and Autofluorescence, Multitasking Features in Living Organisms

“…Bilirubin, already recalled in the above "Bioluminescence" section as the fluorophore responsible for the yellow bioluminescence of cryptic eels, can be also a fluorescing biomarker in blood and bile [344]. In fact, bilirubin behaves as a bichromophore because of its molecular structure composed by two asymmetrical dipyrroles covalently linked by a methylene group [345]. This feature is responsible for exciton energy transfer events inside the chromophore, in turn affected by the molecule concentration, excitation wavelength and microenvironment, which can remarkably influence bilirubin absorption, fluorescence and quantum yield [346][347][348].…”