Photodegradation of Riboflavin under Alkaline Conditions: What Can Gas-Phase Photolysis Tell Us about What Happens in Solution?

Abstract

The application of electrospray ionisation mass spectrometry (ESI-MS) as a direct method for detecting reactive intermediates is a technique of developing importance in the routine monitoring of solution-phase reaction pathways. Here, we utilise a novel on-line photolysis ESI-MS approach to detect the photoproducts of riboflavin in aqueous solution under mildly alkaline conditions. Riboflavin is a constituent of many food products, so its breakdown processes are of wide interest. Our on-line photolysis setup allows for solution-phase photolysis to occur within a syringe using UVA LEDs, immediately prior to being introduced into the mass spectrometer via ESI. Gas-phase photofragmentation studies via laser-interfaced mass spectrometry of deprotonated riboflavin, [RF − H]−, the dominant solution-phase species under the conditions of our study, are presented alongside the solution-phase photolysis. The results obtained illustrate the extent to which gas-phase photolysis methods can inform our understanding of the corresponding solution-phase photochemistry. We determine that the solution-phase photofragmentation observed for [RF − H]− closely mirrors the gas-phase photochemistry, with the dominant m/z 241 condensed-phase photoproduct also being observed in gas-phase photodissociation. Further gas-phase photoproducts are observed at m/z 255, 212, and 145. The value of exploring both the gas- and solution-phase photochemistry to characterise photochemical reactions is discussed.

Probing the electronic relaxation pathways and photostability of the synthetic nucleobase Z via laser interfaced mass spectrometry

“…We have not seen such a gradually increasing ion production as a function of excitation energy previously. 10,31,46,47…”

“…We have not seen such a gradually increasing ion production as a function of excitation energy previously. 10,31,46,47 For all of the protomers studied there is a node in the electron density between the C3-O9 atoms, weakening this bond even in the ground electronic state. The steady increase in production of this m/z 139 photofragment with increasing photon energy, Fig.…”

“…However, recent results from our group on biological molecules ( e.g. riboflavin), 10 as well as sunscreen molecules, 11 have shown that such gas-phase measurements can be directly linked to solution-phase photostability. In the current work, we use these gas-phase laser photodissociation techniques to probe the intrinsic photostability of a synthetic nucleobase as an isolated molecule for the first time.…”

A DFT study on the degradation mechanism of vitamin B2

“…While FMF is the intermediate in the photo-degradation, it can also lead to LF and LC in the dark (non-photochemical) basic aqueous solution ( Song et al, 1965 , Ahmad et al, 1980 ). The kinetics of both photolysis of RF ( Woodcock et al, 1982 , Allen and Parks, 1979 : Ahmad et al, 2019 , Gul et al, 2014 , Ahmad et al, 2004 , Ahmad et al, 2010 , Ahmad et al, 2013 , Ahmad et al, 2008 ) and basic hydrolysis of FMF ( Song et al, 1965 , Ahmad et al, 1980 ) have been studied extensively including gas-phase photofragmentation studies of deprotonated riboflavin, [RF − H] − , using laser-interfaced mass spectrometry ( Wong, et al, 2021 ). O—H bond dissociation energies of the phenolic compounds (rutin and catechin) and T 1 state H-atom affinity of RF were evaluated to examine the role of polyphenolic antioxidants against the photo-oxidative damage induced by RF ( Ji and Shen, 2008 ).…”

Photochemical Degradation of the UV Filter Octyl Methoxy Cinnamate Probed via Laser Interfaced Mass Spectrometry

“…the utility of LIMS photodissociation measurements as a straightforward route for identifying photoproducts. [32] Supplementary Materials: The following supporting information can be downloaded at: www.mdpi.com/xxx/s1, Section S1: S1: Raw ion intensity mass spectra of the thermal fragments of [OMC+H] + , Section S2: Photofragment production intensity of the minor photofragments produced by [OMC+H] + obtained via laser-interfaced mass spectrometry.…”