The Photochemistry of Riboflavin Tetraacetate and Nucleosides. A Study Using Density Functional Theory, Laser Flash Photolysis, Fluorescence, UV−Vis, and Time Resolved Infrared Spectroscopy

Abstract

The photoreaction between riboflavin tetraacetate and nucleosides was investigated using time-resolved infrared spectroscopy (TRIR), laser flash photolysis with UV−vis detection, fluorescence quenching, absorption spectroscopy, and density functional theory calculations. Riboflavin tetraacetate (RBTA) was studied experimentally with indole and with Sheu and Foote's organic soluble silylated guanosine (G‘). Lumiflavin and (R)-2-amino-(S)-4-hydroxy-(R)-5-(hydroxymethyl)-tetrahydrofuran were used as computational models for RBTA and for the sugar moiety of the nucleoside, respectively, using density functional theory calculations (B3LYP/6-31G* and B3LYP/6-31+G**). Vibrational spectra were also calculated for the transient species. Time-resolved infrared spectroscopic data obtained using RBTA are in excellent agreement with the calculated spectra for the triplet flavin, and in the presence of silylated guanosine, with the formation of the most stable hydroflavin radical, RBTH, by an electron transfer−proton transfer mechanism. Although the gas-phase calculations indicate that abstraction of a hydrogen atom from the sugar is slightly exothermic, this reaction does not proceed at a rate measurable as monitored by TRIR spectroscopy. Singlet RBTA is also quenched by G‘ in methylene chloride. Stern−Volmer analysis of the fluorescence quenching data indicates that this reaction proceeds with a rate constant of 8.7 × 108 M-1 s-1.

Photophysics, Excited‐state Double‐Proton Transfer and Hydrogen‐bonding Properties of 5‐Deazaalloxazines

“…Earlier we have found that for alloxazine derivatives the two observed (usually well‐separated) absorption maxima correspond to two independent π , π * transitions, and each of those π , π * transitions is accompanied by a closely located n , π * transition . In contrast, the lowest energy absorption bands for 5‐DAll and 1,3Me‐5‐DAll correspond to pure π , π * transitions.…”

UV-visible absorption spectrum of FAD and its reduced forms embedded in a cryptochrome protein

“…For this reason, it has been extensively studied in the literature both experimentally 41,44,46,[48][49][50][51][52][53][54][55] and theoretically. 7,11,13,16,[56][57][58][59][60][61][62][63][64] FAD has two main absorption bands, the first band in the blue visible light region and the second band in the UV-A region. In protein, the first is centered around 450 nm with a well-resolved three peak vibrational structure, while the second peak is centred at 368 nm and has two resolved vibrational peaks.…”

Unraveling the flavin-catalyzed photooxidation of benzylic alcohol with transient absorption spectroscopy from sub-pico- to microseconds

“…The corresponding rate of 7.7 Â 10 5 s À1 reflects the diffusional triplet quenching by oxygen in the solution and compares well to similar systems reported in the literature. 24,59,60 Upon addition of MBA, the observed dynamics show significant changes. A model which contains, in addition to the instrument response function, two exponential functions and one constant term was found suitable to fit the data ( Table 2).…”

“…The corresponding rate of 7.7 Â 10 5 s À1 reflects the diffusional triplet quenching by oxygen in the solution and compares well to similar systems reported in the literature. 24,59,60 Upon addition of MBA, the observed dynamics show significant changes.…”