Hydrogen-bonding modulation of excited-state properties of flavins in a model of aqueous confined environment

Abstract

The singlet and triplet excited states properties of lumiflavin (LF), riboflavin (RF), flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) in reversed micelles (RM) of sodium docusate (AOT) in n-hexane solutions were evaluated as a function of the water to surfactant molar ratio, w(0) = [H(2)O]/[AOT], by both steady-state and time-resolved absorption and fluorescence spectroscopy. The results indicated that hydrogen-bonding interactions between the isoalloxazine ring of the flavins with the water molecules of the micellar interior play a crucial role on the modulation of the excited state properties of the flavins. Fluorescence dynamic experiments in the RM, allowed the calculation of similar values for both the internal rotational time of the flavins (θ(i)) and the hydrogen-bonding relaxation time (τ(HB)), e.g.≈ 7 and 1.5 ns at w(0) = 1 and 20, respectively. In turn, the triplet state lifetimes of the flavins were also enlarged in RM solutions at low w(0), without modifications of their quantum yields. A hydrogen bonding relaxation model is proposed to explain the singlet excited state properties of the flavins, while the changes of the triplet state decays of the flavins were related with the global composition and strength of the hydrogen bonding network inside of the RM.

Enhancement of Photophysical and Photosensitizing Properties of Flavin Adenine Dinucleotide by Mutagenesis of the C‐Terminal Extension of a Bacterial Flavodoxin Reductase

“…The larger blue‐shift and narrower band of the cofactor fluorescence emission indicates that the isoalloxazine ring of FAD in WT Rc FPR (Figure 4 a) senses a much less polar environment than in the modified proteins and in bulk aqueous buffer 4. 15b Furthermore, both steady‐state and dynamic anisotropy data for WT Rc FPR are single‐fold larger than for the modified enzymes (Table 3), confirming that the isoalloxazine ring of FAD in the WT enzyme is more deeply buried than in the modified enzymes. This local rigidity of the isoalloxazine ring in the WT enzyme seems to be a key factor in maintaining its interaction with the Tyr66 residue, and hence induces an efficient quenching effect of 1 FAD* as discussed before.…”

“…Transient absorption signals of the excited triplet state of FAD ( 3 FAD*) in both air‐ and argon‐saturated buffer solutions were recorded at 710 nm with the m‐LFP 112 laser‐flash photolysis system (Luzchem Research Inc., Ottawa, Canada) using the third harmonic from a Minilite II (Continuum Inc., Santa Clara, CA) Nd‐YAG laser (355 nm, 7 ns full‐width at half‐maximum, FWHM, 5 mJ per pulse) as the excitation source 15b…”

Imaging Adenosine Triphosphate (ATP)

“…For example, autofluorescence of flavins such as flavin adenine dinucleotide (FAD) have been long used to visualize metabolic changes in live samples and continues to be used as a “label-free imaging” option (Quinn et al , 2013; Jahn et al , 2015). This background could convolute fluorescent signals when using sensors at low expression levels, but at moderate sensor expression this is less likely because the lower extinction coefficient (~10,000 M −1 ·cm −1 ) and fluorescence quantum yield (< 0.01 to 0.06) of FAD (Valle et al , 2012). In order to mitigate problems with spectral overlap with FAD autofluorescence and to generate spectral diversity for multi-sensor imaging, Nakano et al .…”

Nanoenvironmental effect in AOT reverse micelles on the triplet excited state properties of flavins and quenching by molecular oxygen

“…Steady‐state and time‐resolved techniques used in this work were fully described in previous reports …”

“…This fact, together with the photobiological relevance of flavin cofactors in blue‐light photoreceptors flavoproteins, invites to explore the nanoenvironmental control of the confined water on the photophysical and photochemical properties of flavins. Recently, we reported that the spectroscopic and singlet excited state properties of lumiflavin (LF), riboflavin (RF), flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD) (Scheme ) in Aerosol‐OT (AOT) RM dispersed in n ‐hexane were dominated by the capability of the water pool molecules to form hydrogen‐bonding interactions with the isoalloxazine ring …”