Phytochrome Models, II. The Fluorescence of Biliverdin Dimethyl Ester¹⁾

Abstract

Biliverdin dimethyl ester (2) in freshly prepared ethanolic solution showed fluorescence maxima at 710 and 770 nm which were shifted to 725 and 806 nm on monoprotonation. % for 2 and 2H' was similar at room temperature (1.1 . and 2.7 .respectively), and it increased at 77 K to 5.0 .for 2 and to 2.6 . lo-' for 2H'. This acid effect was reversed on neutralization. The pK, values of 2 were 4.3 kO.1 at room temperature and ca. 5.3 at 77 K, and those of the fluorescent state were higher by ApK = 1.5 and 4.4, respectively. Certain differences between the absorption and fluorescence excitation spectra reflect either anomalous relaxation properties of excited *2 and *2Hf or non-identity of the emitting species with the predominant ground state absorbers, or both. The changes of QF with temperature and protonation of 2 are interpreted in terms of radiationless deactivation induced by twisting around the methine-ring bonds and by intramolecular proton exchange in 2. These conclusions are supported by fluorescence measurements of the pyrromethenes 4, 5 , and 8, the pyrromethenone 9, and bilirubin dimethyl ester (10). When a degassed neutral ethanolic solution of 2 was left to stand in the dark at room temperature, or when an acidic solution was neutralized, a new fluorescence maximum at 500 nm (excitation spectrum at 77 K: Lax = 470 nm) developed. This emission disappeared again on addition of acid. It is ascribed to 10-ethoxy-or 10-hydroxybilirubin dimethyl ester (12) whose formation by nucleophilic addition of solvent or trace water to 2 is reversed on protonation, affording 2H'.

Time-resolved fluorescence analysis of the recombinant photosystem II antenna complex CP29. Effects of zeaxanthin, pH and phosphorylation

“…Absorption spectra were measured on an Aminco DW 2000 spectrophotometer; steady-state fluorescence emission spectra were measured on a Jasco spectrofluorimeter model FP 777 and/or on a Spex Fluorolog [26]. CD spectra were obtained at 8 8C with a Jasco J-600 spectropolarimeter.…”

Fluorescence of Trans-4-Cyano-4′-dimethylaminostilbene; No Evidence for a TICT State

“…22]. Emission spectra were recorded on a spectrofluorimeter (Spex-Fluorolog) equipped with a photon-counting detection system using a red sensitive photomultiplier (RCA C31034) and a unit which corrects the spectral sensitivity of the photomultiplier and the lamp [23]. <P ( was determined using 9,10-diphenylanthracene in air-saturated ethanol (<Z> f =0.68 and 1.0 at 25 and -196°C, respectively [24]) as fluorescence standard and with the same absorption at /.…”

Morphology of a novel cyanobacterium and characterization of light-harvesting complexes from it: Implications for phycobiliprotein evolution

“…Free bilins or pyrromethenes (the latter are analogues of the two central rings of the bilin chromophore) have a quantum yield offluorescence that is less than 0.001 and may have two paths for radiationless deactivation of a singlet state: intramolecular proton exchange between the pyrrole nitrogens and twisting modes of the methine-ring bonds (33). Bilins bound to protein or pyrromethenes complexed with boron or bromide can have fluorescence quantum yields that are 102 or 103 times higher than the yield of the free chromophores (33). It is possible that highly fluorescent bilin conformers can be selectively stabilized by both covalent and noncovalent protein-chromophore interactions.…”