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Abstarct Riboflavin (RF), a water-soluble vitamin B 2 , is an endogenous singlet oxygen photosensitizer in human skin and eye. Time profiles of the near-infrared phosphorescence of singlet oxygen generated by RF have been measured in the absence and presence of l -ascorbic acid (AA, vitamin C), 3- O -ethyl- l -ascorbic acid (3-EtAA) and Trolox (TX, a water-soluble analogue of vitamin E) in phosphate buffer (pH 6.8). These substances suppress the RF-photosensitized singlet oxygen generation. For example, the quantum yield of singlet oxygen generation is decreased to a third by adding 0.4 mmol dm−3 AA or TX (the concentration of dissolved oxygen in air-saturated water is 0.27 mmol dm−3). AA and TX are more efficient suppressors of RF-photosensitized singlet oxygen generation than 3-EtAA. The bimolecular rate constants for quenching of the excited singlet and triplet states of RF by AA, 3-EtAA and TX have been determined through measurements of fluorescence and transient absorption. These measurements suggest that the observed suppression is due to the quenching of the excited singlet and triplet states of RF by AA, 3-EtAA and TX. The bimolecular rate constants for quenching of singlet oxygen by AA, 3-EtAA and TX were determined to be 1.8 × 108, 0.27 × 108, and 4.4 × 108 mol−1 dm3 s−1, respectively. [ABSTRACT FROM AUTHOR]

This study was conducted to evaluate the effect of UVA-activated 1% riboflavin solution on structural integrity; mechanical properties and stability; and collagenase-mediated collagen solubilisation resistance of demineralized root dentin collagen matrix. Root dentin specimens demineralized with 17% EDTA for 7 days were treated with 1% RF for 1 min followed by UVA photo-activation at intensity 7 mW/cm 2 for 1 min. Control specimens were completely devoid of riboflavin and/or UVA treatments. Specimens were challenged with bacterial collagenase type-I solution for different time-periods at 37 °C. Collagen solubilisation resistance was evaluated in terms of hydroxyproline (HYP) liberation. Mechanical characterization of dentin specimens before and after 24 h of exposure to collagenase solution was done in terms of apparent-elastic modulus ( E appr ) and ultimate tensile strength (UTS). Variations in dentin collagen-network structure with exposure time in collagenase were visualized by TEM. Crosslinking dentin with UVA-activated riboflavin significantly decreased HYP release and increased E appr and UTS compared to control specimens with storage time in collagenase. Moreover, crosslinked specimens showed higher structural resistance to collagenase effect reflected from dense, well-formed collagen fibrils-network with characteristic collagen cross-banding. UVA-activated riboflavin treatment increased collagenase-mediated collagen degradation resistance and enhanced mechanical stability against collagenase challenges of root dentin after EDTA demineralization. [ABSTRACT FROM AUTHOR]

Transfusion-associated graft-versus-host disease (TA-GVHD) is a life-threatening complication caused by the input of a number of immunocompetent allogeneic lymphocytes. This study focus on the photochemical effects of riboflavin excited by visible light (RB + L) treatment on human lymphocytes, to study the feasibility of using RB + L treatment to prevent adverse immune reactions caused by transfused lymphocytes. 100 μM riboflavin was added to lymphocyte suspensions. After exposure to 400–580 nm visible light with a total energy of 40 J/mL, cells were cultured and the ability of proliferation and cytokine secretion were assayed upon stimuli. Meanwhile, lymphocytes were also treated by gamma-irradiation as parallel to testify the inactivation effect of RB + L. Results showed that γ-irradiation and RB + L treated cells showed a decline in cell viability. After stimulation of phytohemagglutinin (PHA) or anti-CD3 together with anti-CD28, proliferative ability of RB + L treated cells was strongly inhibited when compared to untreated cells. The inhibitive rates of proliferation in RB + L group were also higher than those of cells treated by γ-irradiation. Results of CFSE assays also illustrated hardly any cell division of RB + L and γ-irradiation treated lymphocytes. Besides low level productions of IL-4 and IL-12, cytokine production of TNF-α, IFN-γ and IL-10 by incubation with PHA or IL-1β, IL-2, IL-6, IL-8, IL-10, TNF-α and IFN-γ stimulated by anti-CD3 plus anti-CD28 were suppressed after treatment of RB + L significantly. It was suggested that RB + L/γ-irradiation treatment induced cell apoptosis. These results indicated that RB + L treatment functionally inactivated lymphocytes by inhibiting cell proliferation and cytokine production. RB + L might be an alternative for TA-GVHD prevention. [ABSTRACT FROM AUTHOR]

Crystal violet (CV) is applied in daily use mainly as a commercial dye and antimicrobial agent. Waste water containing CV may affect aquatic ecosystems. Riboflavin, also known as vitamin B 2 , is non-toxic and an essential vitamin required for the functions of the human body. Riboflavin is photosensitive to UV and visible light in terms of generating reactive oxygen species. This study investigated the potential application of blue light on riboflavin, so as to come up with an effective way of degrading CV during its treatment. Photosensitivity of CV leading to degradation in the presence of riboflavin was investigated by light intensity, exposure time, and irradiation dosage. The degradation of CV during riboflavin photolysis treatment was studied by a UV/vis spectrometry and chromatography. The effects of CV degradation on microbial viability are relevant when considering the influences on the ecosystem. This study proved that riboflavin photochemical treatment with blue light degrades CV dye by ROS formation. The riboflavin photolysis-treated CV solution appeared to be transparent during conformational transformations of the CV that was rearranged by free radical species generated from riboflavin photolysis. After riboflavin photolysis, colony-forming units (CFUs) were determined for each CV solution. CFU preservation was 85.2% for the CV dissolved riboflavin solution treated with blue light irradiation at 2.0 mW/cm 2 for 120 min. Degradation of CV by riboflavin photochemical procedures can greatly reduce antimicrobial ability and serve as an environmental friendly waste water treatment method. Our results presented here concerning riboflavin photolysis in degradation of CV provide a novel technique, and a simple and safe practice for environmental decontamination processes. [ABSTRACT FROM AUTHOR]

The effect of metal ion complexation on the photolysis of riboflavin (RF) using various metal ions (Ag + , Ni 2 + , Co 2 + , Fe 2 + , Ca 2 + , Cd 2 + , Cu 2 + , Mn 2 + , Pb 2 + , Mg 2 + , Zn 2 + , Fe 3 + ) has been studied. Ultraviolet and visible spectral and fluorimetric evidence has been obtained to confirm the formation of metal-RF complexes. The kinetics of photolysis of RF in metal-RF complexes at pH 7.0 has been evaluated. The apparent first-order rate constant ( k obs ) for the photolysis of RF and the formation of lumichrome (LC) and lumiflavin (LF) (0.001 M phosphate buffer) and LC, LF and cyclodehydroriboflavin (CDRF) (0.2–0.4 M phosphate buffer) have been determined. The values of k obs indicate that the rate of photolysis of RF is promoted by divalent and trivalent metal ions. The second-order rate constants ( k ʹ ) for the interaction of metal ions with RF are in the order: Zn 2 + > Mg 2 + > Pb 2 + > Mn 2 + > Cu 2 + > Cd 2 + > Fe 2 + > Ca 2 + > Fe 3 + > Co 2 + > Ni 2 + > Ag + . In phosphate buffer (0.2–0.4 M), an increase in the metal ion concentration leads to a decrease in the formation of LC compared to that of CDRF by different pathways. The photoproducts of RF have been identified and RF and the photoproducts have simultaneously been assayed by a multicomponent spectrometric method. The mode of photolysis of RF in metal-RF complexes has been discussed. [ABSTRACT FROM AUTHOR]

The photodynamic therapy (PDT) is considered as a noninvasive and photo-controlled treatment for various cancers. However, its potential is not fully developed as current clinically approved photosensitizers (PSs) mainly absorb the light in the UV–visible region (less than 700 nm), where the depth of penetration is inadequate for reaching tumor cells under deeper tissue layers. Furthermore, the lack of specific accumulation capability of the conventional PSs in the tumor cells may cause serious toxicity and low treatment efficiency. To address these problems, riboflavin (Rf) conjugated and amine-functionalized nitrogen-doped graphene quantum dots (am-N-GQD) are herein proposed. Rf functions as both photosensitizer and targeting ligand by indirect excitation through intra-particle fluorescence resonance energy transfer (FRET) via two-photon (TP) excited am-N-GQD, to enhance the treatment depth, and further am-N-GQD-Rf accumulation in cancer cells using Rf transporter family (RFVTs) and Rf carrier proteins (RCPs). The one-photon (OP) and two-photon(TP)-PDT effect and cellular internalization ability of the am-N-GQD-Rf were investigated in vitro in different cancel cell lines. Besides the excellent cellular uptake as well TP-PDT capability, the superior biocompatibility of am-N-GQD-Rf in vitro makes it promising candidate in PDT. • Rf was conjugated to am-N-GQD due to its dual action as PS and targeting ligand. • Superior synergic effect in singlet oxygen generation was observed. • Combination of am-N-GQD-Rf with UV or NIR significantly decreased cell viability. • KB cells with overexpressed RFVTs displayed successful uptake of am-N-GQD-Rf. [ABSTRACT FROM AUTHOR]

The removal or inactivation of circulating tumor cells (CTCs) can prevent distant metastasis by hematogenous route, but there is still a lack of mature and effective technical means. In the previous research, our team has initially established a method of riboflavin photosensitized treatment (RPT) for continuous treatment of peripheral blood in vitro for the inactivation of CTCs. The core of this technology is that it can selectively induce apoptosis of CTCs (HCT116 cells) without damaging immunocyte (mainly Peripheral Blood Mononuclear Cells，PBMCs) under specific parameters. To clarify the specific mechanism, firstly, the enrichment of riboflavin in HCT116 cells and PBMCs was observed under fluorescence microscope. Secondly, the apoptotic signaling pathways in HCT116 cells and PBMCs in response to RPT treatment were analyzed by transcriptomics. Finally, the mitochondrial damage in HCT116 cells and PBMCs before and after RPT treatment was observed under electron microscope. The results showed that under the same treatment conditions, HCT116 cells were significantly enriched in riboflavin compared with PBMCs. Besides, RPT treatment reduced the expression of long non﹣coding RNA (lncRNA) NEAT1, an effector gene of HCT116 cells, which further down-regulated the expression of target gene PAX2 and promoted the expression of Bax, leading to mitochondrial outer membrane permeabilization (MOMP), and consequently increased the release of pro-apoptotic factors such as cytochrome c (Cyt C), high-temperature requirement protein A2(HTRA2), apoptosis-inducing factor (AIF), endonuclease G(ENDOG), finally leading to apoptosis of HCT116 cells. In contrast, lncRNA NEAT1 remained unchanged in PBMCs before and after RPT treatment, and was unable to stimulate the PBMCs apoptotic signaling pathway. The results of the study indicated that under the specific treatment conditions, RPT technology could selectively induce apoptosis of HCT116 cells by activating the mitochondrial apoptosis pathway, which would further provide a theoretical and technical support for the effective inactivation of CTCs by RPT technology, thereby reducing the risk of recurrence of malignant tumors and improving the cure rate of malignant tumors. • RPT selectively induce apoptosis of CTCs without damaging immunocyte under specific parameters • HCT116 tumor cells enrich riboflavin • RPT technology promotes apoptosis of HCT116 cells through mitochondrial apoptosis pathway • LncRNA NEAT1 may be the effector molecule of RPT [ABSTRACT FROM AUTHOR]

Caffeine metabolites were found to bind riboflavin with dissociation constant in the millimolar region by an exothermic process with positive entropy of reaction, which was found by 1 H NMR and fluorescence spectroscopy to occur predominantly by hydrogen bonding with water being released from riboflavin solvation shell upon caffeine metabolite binding to riboflavin. The caffeine metabolites 1-methyl uric acid and 1,7-dimethyl uric acid were shown by transient absorption laser flash photolysis to be efficient as quenchers of triplet riboflavin with second-order rate constant of 1.4 10 8 L mol − 1 s − 1 and 1.0 10 8 L mol − 1 s − 1 , respectively, in aqueous solution of pH 6.4 at 25 °C and more efficient than the other caffeine metabolite 1,7-dimethyl xanthine with second-order rate constant of 4.2 10 7 L mol − 1 s − 1 . Caffeine was in contrast found to be non-reactive towards triplet riboflavin. Caffeine metabolites rather than caffeine seem accordingly important for the observed protective effect against cutaneous melanoma identified for drinkers of regular but not of decaffeinated coffee. The caffeine metabolites, but not caffeine, were by time resolved single photon counting found to quench singlet excited riboflavin through exothermic formation of ground-state precursor complexes indicating importance of hydrogen bounding through keto-enol tautomer's for protection of oxidizable substrates and sensitive structures against riboflavin photosensitization. [ABSTRACT FROM AUTHOR]

Visible-light irradiation of aqueous-ethanolic solutions of Riboflavin (Rf) in the individual presence of the flavone chrysin (Chr) and its complex with Cu 2 + ([Chr 2 Cu]; 2:1 L:M) generates singlet molecular oxygen O 2 ( 1 Δ g ), that concomitantly interact with both flavone derivatives. Overall ( k t ) and reactive ( k r ) rate constants in the order of 10 7 M − 1 s − 1 were determined for the process. Metal chelation greatly enhances the scavenging ability of [Chr 2 Cu] towards O 2 ( 1 Δ g ) through a mechanism dominated, in > 80%, by the physical component. In this way, practically all O 2 ( 1 Δ g ) is deactivated by the complex without significant loss of the quencher. The isolated flavone quenches O 2 ( 1 Δ g ) in a prevailing reactive fashion. The very low value exhibited by [Chr 2 Cu] for the k r / k t ratio constitutes a positive quality for antioxidative protectors in biological media, where elevated local concentration and high reactivity of significant molecules make them initial targets for O 2 ( 1 Δ g ) aggression. Finally, two interesting properties in the field of free radicals scavenging by [Chr 2 Cu] must be mentioned. In first place metal chelation itself, in the obvious sense of free metal ion withdrawal from the oxidizable medium, prevents the initiation of a free radical-mediated oxidation processes through mechanisms of Fenton or lipid peroxidation. In addition, the incorporation of Cu adds to [Chr 2 Cu] the ability of a free radical scavenger, already described for similar Cu-chelate compounds. This collection of beneficial properties positions the complex as a remarkably promising bioprotector towards ROS-mediated oxidation. A quantification of the efficiency on the initial anti-oxidative effect exerted by Chr and [Chr 2 Cu] towards tryptophan was carried out. The amino acid is an archetypal molecular model, commonly employed to monitor oxidative degradation of proteinaceous media. It was efficiently photoprotected against O 2 ( 1 Δ g )-mediated photooxidation by [Chr 2 Cu]. [ABSTRACT FROM AUTHOR]

A study of the effect of ionic strength on the photodegradation reactions (photoreduction and photoaddition) of riboflavin (RF) in phosphate buffer (pH 7.0) has been carried out using a specific multicomponent spectrometric method. It has been found that the rates of photodegradation reactions of RF are dependent upon the ionic strength of the solutions at different buffer concentrations. The apparent first-order rate constants ( k obs ) for the photodegradation of riboflavin at ionic strengths of 0.1–0.5 (0.5 M phosphate) lie in the range of 7.35–30.32 × 10 − 3 min − 1 . Under these conditions, the rate constants for the formation of the major products, lumichrome (LC) by photoreduction pathway, and cyclodehydroriboflavin (CDRF) by photoaddition pathway, are in the range of 3.80–16.03 and 1.70–6.07 × 10 − 3 min − 1 , respectively. A linear relationship has been observed between log k obs and √ μ/1 + √ μ. A similar plot of log k/k o against √ μ yields a straight line with a value of ~+1 for Z A Z B showing the involvement of a charged species in the rate determining step. NaCl appears to promote the photodegradation reactions of RF probably by an excited state interaction. The implications of ionic strength on RF photodegradation by different pathways and flavin–protein interactions have been discussed. [ABSTRACT FROM AUTHOR]

A study of the formulation of liposomal preparations of riboflavin (RF) with compositional variations in the content of phosphatidylcholine (PC) and their entrapment efficiency (26–42%) have been conducted. Light transmission characteristics of the liposomal preparations have been determined to evaluate their effect on the amount of light passing through the system to initiate a photochemical reaction. Dynamic light scattering (DLS) and atomic force microscopy (AFM) have been used to study the physical characteristics of liposomes. The liposomal preparations of RF have been subjected to photolysis using visible light and the apparent first- order rate constant, k obs , for the degradation of RF have been determined. The values of k obs (1.73–2.29 × 10 − 3 min − 1 ) have been found to decrease linearly with an increase in PC concentration in the range of 12.15 to 14.85 mM. Thus, an increase in PC concentration of liposomes leads to an increase in the stability of RF. RF and its main photoproduct, lumichrome (LC), formed in liposomes have been assayed by a two-component spectrometric method at 356 and 445 nm using an irrelevant absorption correction to compensate for the interference of liposomal components. The fluorescence measurements of RF in liposomes indicate excited singlet state quenching and the formation of a charge-transfer complex between RF and PC. It results in electron transfer from PC to RF to cause photoreduction and stabilization of RF. [ABSTRACT FROM AUTHOR]

The profusely employed drugs Piroxicam (Piro), Tenoxicam (Teno) and Meloxicam (Melo) belonging to the non-steroidal antiinflammatory drug (NSAID) family of the Oxicams (Oxis) were studied in the frame of two specific conditions: (a) their ROS scavenging ability, in relation to a possible biological antioxidant action and (b) their photodegradability under environmental conditions, in the context of Oxi-contaminated waters. Singlet molecular oxygen (O 2 ( 1 Δ g )) and superoxide radical anion (O 2 − ) were photogenerated through Riboflavin (Rf, vitamin B2)-photosensitization in aqueous and aqueous-methanolic solutions in the presence of Oxi concentrations in the range 50–500 μM. The visible-light absorber vitamin is currently present in all types of natural waters and constitutes the most frequent endogenous photosensitizer in mammals. Hence, it was employed in order to mimic both natural sceneries of interest. All three Oxis quench O 2 ( 1 Δ g ) with rate constants in the order of 10 8 M − 1 s − 1 showing a significant photodegradation efficiency given by a dominant reactive fashion for deactivation of the oxidative species. Although this is not a desirable property in the context of photoprotection upon prolonged photoirradiation, constitutes in fact a promissory aspect for the degradation NSAIDs, in waste waters. Indirect evidence indicates that Melo is also oxidized through a O 2 − -mediated component. The simultaneous presence of Piro plus tryptophan or tyrosine under Rf-photosensitizing conditions, which has taken the amino acids as photooxidizable model residues in a proteinaceous environment, indicates that the NSAID induces a protection of the biomolecules against photodynamic degradation. [ABSTRACT FROM AUTHOR]

Determination of the superoxide dismutase activity is an important issue in the fields of biochemistry and the medical sciences. In the riboflavin/nitro blue tetrazolium (B 2 /NBT) method, the light sources used for generating superoxide anion radicals from light-excited riboflavin are normally fluorescent lamps. However, the conditions of B 2 /NBT experiments vary. This study investigated the effect of the light source on the light-excitation of riboflavin. The effectiveness of the photolysis was controlled by the wavelength of the light source. The spectra of fluorescent lamps are composed of multiple colour lights, and the emission spectra of fluorescent lamps made by different manufacturers may vary. Blue light was determined to be the most efficient for the photochemical reaction of riboflavin in visible region. The quality of the blue light in fluorescent lamps is critical to the photo-decomposition of riboflavin. A blue light is better than a fluorescent lamp for the photo-decomposition of riboflavin. The performance of the B 2 /NBT method is thereby optimized. [ABSTRACT FROM AUTHOR]

The micronutrients in many cellular processes, riboflavin, flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD) are photo-sensitive to UV and visible light for generating reactive oxygen species (ROS). Produced from phosphorylation of riboflavin, FMN is more water-soluble and rapidly transformed into free riboflavin after ingestion. This study investigated the application of visible blue light with FMN to development of an effective antimicrobial treatment. The photosensitization of bacterial viability with FMN was investigated by light quality, intensity, time, and irradiation dosage. The blue light-induced photochemical reaction with FMN could inactivate Escherichia coli by the generated ROS in damaging nucleic acids, which was validated. This novel photodynamic technique could be a safe practice for photo-induced inactivation of environmental microorganism to achieve hygienic requirements in food processing. [ABSTRACT FROM AUTHOR]

Trace amounts of the widely used β-lactam antibiotics (Atbs) in waste water may cause adverse effects on the ecosystems and contribute to the proliferation of antibiotic-resistant bacteria. On these grounds, kinetic and mechanistic aspects of photosensitized degradation of Ceftriaxone (Cft) and Cefotaxime (Ctx), have been studied in pure water by stationary and time-resolved techniques. Additionally, possible implications of these photoprocesses on the antimicrobial activity of the Atbs have also been investigated. Photoirradiation of aqueous solutions of Cft and Ctx produces the degradation of both Atbs in the presence of Riboflavin (vitamin B2), a well known pigment dissolved in natural aquatic systems. The process occurs through Type I and Type II mechanisms, with effective prevalence of the former. The participation of O 2 − , OH and O 2 ( 1 Δ g ) is supported by experiments of oxygen consumption carried out in the presence of specific scavengers for such reactive oxygen species. Microbiological assays exhibit a parallelism between the rate of Cft and Ctx photodegradation and the loss of their bactericidal capacity on Staphylococcus aureus strains. Results contribute to both understanding kinetic and mechanism aspects of the degradation and predicting on natural decay of Atbs waste water-contaminants. [ABSTRACT FROM AUTHOR]

Benzotriazole UV-stabilizers (BUVSs) are commonly used in industry as solar filters, due to their strong UV light absorption. Because of their extended usage, environmental contamination of waters due to BUVSs constitutes a growing concern. Direct photodegradation of BUVSs is not efficient due to their intrinsic thermal pathways to release the absorbed light. Nevertheless, their abatement in natural environments could be assisted by chromophoric dissolved organic matter. Among the BUVSs, three representative candidates were selected, UV-326, UV-327 and UV-328, to demonstrate the potential of Riboflavin (RF) as a natural visible-light absorbing photocatalyst for the abatement of these recalcitrant pollutants under reductive conditions. The use of visible light and DABCO, as a model sacrificial electron donor, generates the radical anion RFTA.-. This key species reacts with the solar filters, achieving their reductive abatement from the medium. Moreover, the participation of every potential reactive species has been investigated by photophysical techniques, together with determination of the quenching rate constant for every reaction pathway. Consequently, evidence supported the main role of the reductive photodegradation pathway, being RFTA.- the key species in the abatement of BUVSs. [Display omitted] • Tetraacetylated riboflavin (RFTA) acts as a visible light photosensitizer. • Complex systems were evaluated to determine the best photodegradation conditions. • RFTA could be used not only for the oxidation but also for the reduction of BUVSs. • Photoreductive conditions are the most performing ones in the removal of BUVSs. • Photophysical experiments demonstrate the involvement of RFTA.- in the degradation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Maleic Hidrazide (MH) is degraded in the presence of riboflavin and visible light. [•] The photodegradative mechanism of MH is mediated by reactive oxygen species. [•] MH is biodegraded by the bacteria Pseudomonas aeruginosa. [•] The herbicide excerts a bacteriostatic effect on Bacillus subtilis. [ABSTRACT FROM AUTHOR]

Noscapine (NSC) is a benzyl-isoquinoline alkaloid discovered in 1930 as an antitussive agent. Recently, NSC has also been reported to exhibit antitumor activity and, according to computational studies, it is able to attack the protease enzyme of Coronavirus (COVID-19) and thus could be used as antiviral for COVID-19 pandemic. Therefore, an increasing use of this drug could be envisaged in the coming years. NSC is readily metabolized with a half-life of 4.5 h giving rise to cotarnine, hydrocotarnine, and meconine, arising from the oxidative breaking of the C C bond between isoquinoline and phthalide moieties. Because of its potentially increasing use, high concentrations of NSC but also its metabolites will be delivered in the environment and potentially affect natural ecosystems. Thus, the aim of this work is to investigate the degradation of NSC in the presence of naturally occurring photocatalysts. As a matter of fact, the present contribution has demonstrated that NSC can be efficiently degraded in the presence of a derivative of the natural organic dye Riboflavin (RFTA) upon exposure to visible light. Indeed, a detailed study of the mechanism involved in the photodegradation revealed the similarities between the biomimetic and the photocatalyzed processes. In fact, the main photoproducts of NSC were identified as cotarnine and opianic acid based on a careful UPLC-MS2 analysis compared to the independently synthesized standards. The former is coincident with one of the main metabolites obtained in humans, whereas the latter is related to meconine, a second major metabolite of NSC. Photophysical experiments demonstrated that the observed oxidative cleavage is mediated mainly by singlet oxygen in a medium in which the lifetime of 1O 2 is long enough, or by electron transfer to the triplet excited state of RFTA if the photodegradation occurs in aqueous media, where the 1O 2 lifetime is very short. [Display omitted] • Acetylated Riboflavin (RFTA) acts as photocatalytic dye for Noscapine removal. • UFLC-MS2 was used to detect and identify the main oxidation photoproducts. • Photosensitized oxidative cleavage of NSC yields cotarnine and opianic acid. • Kinetic constants between 1RFTA⁎, 3RFTA⁎ and 1O 2 and NSC have been determined. • Oxidation of NSC starts in cotarnine-like moiety according to kinetic results [ABSTRACT FROM AUTHOR]

Abstract: The micronutrients in many cellular processes, riboflavin (vitamin B2), FMN, and FAD are photo-sensitive to UV and visible light to generate reactive oxygen species (ROS). The riboflavin photochemical treatment with UV light has been applied for the inactivation of microorganisms to serve as an effective and safe technology. Ultra-violet or high-intensity radiation is, however, considered as a highly risky practice. This study was working on the application of visible LED lights to riboflavin photochemical reactions to development an effective antimicrobial treatment. The photosensitization of bacterial genome with riboflavin was investigated in vitro and in vivo by light quality and irradiation dosage. The riboflavin photochemical treatment with blue LED light was proved to be able to inactivate E. coli by damaging nucleic acids with ROS generated. Riboflavin is capable of intercalating between the bases of bacterial DNA or RNA and absorbs lights in the visible regions. LED light illumination could be a more accessible and safe practice for riboflavin photochemical treatments to achieve hygienic requirements in vitro. [Copyright &y& Elsevier]

Abstract: Though long-lived transient photoproducts of flavins have received much attention over the last five decades, their spectroscopic characterization remains rudimentary and altogether inconclusive. Lumiflavin and riboflavin have therefore been reexamined, using nanosecond laser photolysis and multichannel detection over a wide spectral range (230–900nm); differential absorption spectra of flavin solutions in aqueous buffer at neutral pH have been recorded; radical cations and semiquinone radicals were generated by quenching the triplets with C (NO2)4 (electron acceptor) and (electron donor), respectively. The problem of estimating the extent of ground state depletion after a single flash has been solved by developing a new strategy that provides reliable lower and upper bounds for the depletion (and for the molar absorption coefficients of the transient species of interest). The spectra of the neutral radicals and triplets of the two flavins are almost identical, but those of the two cations are not. [Copyright &y& Elsevier]

Abstract: Hydrogen sulfide is the third endogenous signaling gasotransmitter, following nitric oxide and carbon monoxide. Recent studies showed that hydrogen sulfide could alleviate many diseases which were related to the oxidative damage of tissues. It reminded us that hydrogen sulfide might serve as an antioxidant to reduce oxidative pressure. This study showed that hydrogen sulfide protected lysozyme from photo-oxidation induced by riboflavin (RF). Laser flash photolysis was used to explore the mechanisms of antioxidant activity of hydrogen sulfide. The scavenging effects of hydrogen sulfide on the triplet state of riboflavin (3RF*) and radicals of tryptophan and tyrosine (TyrO and TrpN ) were attributed to the protection of lysozyme from photo-oxidation. The results suggested that hydrogen sulfide could serve as an antioxidant in alleviation of oxidative pressure. [Copyright &y& Elsevier]

Abstract: Riboflavin (RF) is an endogenous cell component and an efficient photosensitizer that can act by both types I and II photochemical mechanisms. Human tumor cells lines cultured in vitro, were used as model to study the effect of a photosensitizer synthesized from riboflavin, the 2′,3′,4′,5′-riboflavin-tetrabutyrate (RTB), to increase the flavin concentration in the human promyelocytic leukemia cell line HL-60 and the human epithelial cervical cancer cell line HeLa. We demonstrate that this compound, alone or with Trp, has a toxic dose-response effect evidenced by abnormal cell morphology and a decrease in the cell proliferation rate. The mechanism of cell death was investigated and the experimental evidence indicates that it proceeds primarily via apoptosis; however, autophagy cannot be discarded. Nuclear fluorescent staining with Hoechst 33258 and transmission electron microscopy of the cells showed condensed chromatin margination at the nuclear periphery and the formation of apoptotic bodies. Furthermore, Caspase-3 activity was demonstrated in both cell lines. In addition, the characteristic apoptotic DNA ladder was observed in HL-60 cells. On the other hand, a high cytoplasmic vacuolization was observed by electron transmission and confocal microscopy. LysoTraker-red localization in the vacuoles was observed by fluorescence microscopy, and a significant decrease in the number of vacuoles and in the cell proliferation rate diminution was observed when irradiation was performed in the presence of the autophagy inhibitor 3-methyladenine. Considering that both cell death mechanisms have a dual role in the killing of tumor cells in vivo, a harmful effect that does not cause inflammation leading to tumor prophylaxis, we conclude that RTB could have potential clinical applications. [Copyright &y& Elsevier]

Abstract: The behavior of melatonin in the riboflavin-sensitized photo-oxidation of lysozyme was monitored. Melatonin was found to prevent aggregation of protein and the decrease of enzyme activity induced by photo-oxidation. Electron spin resonance experiments showed that photo-oxidation of lysozyme in the presence of riboflavin resulted in formation of protein radicals, and melatonin was highly effective in reducing the formation of protein radicals. Direct evidence of melatonin’s ability for quenching the triplet state of riboflavin and singlet oxygen was presented. A mechanism of the protective effect of melatonin on photo-oxidation of protein was proposed and the physiological relevance was discussed. [Copyright &y& Elsevier]

Abstract: The photolysis of riboflavin (RF) in the presence of borate buffer (0.1–0.5M) at pH 8.0–10.5 has been studied using a specific multicomponent spectrophotometric method for the determination of RF and photoproducts, formylmethylflavin (FMF), lumichrome (LC) and lumiflavin (LF). The overall first-order rate constants for the photolysis of RF (1.55–4.36×10−2 min−1) and the rate constants for the formation of FMF (1.16–3.52×10−2 min−1) and LC (0.24–0.84×10−2 min−1) have been determined. The values of all these rate constants decrease with an increase in buffer concentration suggesting the inhibition of photolysis reaction by borate species. The kinetic data support the formation of a RF-borate complex involving the ribityl side chain to cause the inhibition of photolysis. The second-order rate constants for the borate inhibited reaction range from 1.17–3.94×10−2 M−1 min−1. The log k-pH profiles for the reaction at various buffer concentrations indicate a gradual increase in rate, with pH, up to 10 followed by a decrease in rate at pH 10.5 probably due to ionization of RF and quenching of fluorescence by borate species. A graph of second-order rate constants against pH is a sigmoid curve showing that the rate of photolysis increases with an increase in pH. The results suggest the involvement of excited singlet state, in addition to excited triplet state, in the formation of LC. [Copyright &y& Elsevier]

Abstract: The BLUF protein Slr1694 from the cyanobacterium Synechocystis sp. PCC6803 is characterized by absorption and emission spectroscopy. Slr1694 expressed from E. coli which non-covalently binds FAD, FMN, and riboflavin (called Slr1694I), and reconstituted Slr1694 which dominantly contains FAD (called Slr1694II) are investigated. The receptor conformation of Slr1694 (dark adapted form Slr1694r) is transformed to the putative signalling state (light adapted form Slr1694s) with red-shifted absorption and decreased fluorescence efficiency by blue-light excitation. In the dark at 22°C, the signalling state recovers back to the initial receptor state with a time constants of about 14.2s for Slr1694I and 17s for Slr1694II. Quantum yields of signalling state formation of approximately 0.63±0.07 for both Slr1694I and Slr1694II were determined by transient transmission measurements and intensity dependent steady-state transmission measurements. Extended blue-light excitation causes some bound flavin conversion to the hydroquinone form and some photo-degradation, both with low quantum efficiency. The flavin-hydroquinone re-oxidizes slowly back (time constant 5–9min) to the initial flavoquinone form in the dark. A photo-cycle dynamics scheme is presented. [Copyright &y& Elsevier]

Abstract: The BLUF protein BlrB from the non-sulphur anoxyphototrophic purple bacterium Rhodobacter sphaeroides is characterized by absorption and emission spectroscopy. BlrB expressed from E. coli binding FAD, FMN, and riboflavin (called BrlBI) and recombinant BlrB containing only FAD (called BlrBII) are investigated. The dark-adapted proteins exist in two different receptor conformations (receptor states) with different sub-nanosecond fluorescence lifetimes (BLUFr,f and BLUFr,sl). Some of the flavin-cofactor (ca. 8%) is unbound in thermodynamic equilibrium with the bound cofactor. The two receptor conformations are transformed to putative signalling states (BLUFs,f and BLUFs,sl) of decreased fluorescence efficiency and shortened fluorescence lifetime by blue-light excitation. In the dark at room temperature both signalling states recover back to the initial receptor states with a time constant of about 2s. Quantum yields of signalling state formation of about 90% for BlrBII and about 40% for BlrBI were determined by intensity dependent transmission measurements. Extended blue-light excitation causes unbound flavin degradation (formation of lumichrome and lumiflavin-derivatives) and bound cofactor conversion to the semiquinone form. The flavin-semiquinone further reduces and the reduced flavin re-oxidizes back in the dark. A photo-dynamics scheme is presented and relevant quantum efficiencies and time constants are determined. [Copyright &y& Elsevier]

The photodegradation reactions of riboflavin (RF) in the presence of 0.05–2.00 M phosphate (pH 7.0) have been studied using a specific multicomponent spectrophotometric method. The reactions involve simultaneous photolysis (intramolecular photoreduction) and photoaddition (intramolecular photoaddition) leading to lumichrome (LC) and cyclodehydroriboflavin (CDRF), respectively, as major products. The contribution of each reaction in the overall photodegradation depends upon the phosphate concentration, i.e., higher the phosphate concentration higher the extent of photoaddition. The apparent first-order rate constants for the photodegradation of RF and for the formation of LC and CDRF at 0.25–2.00 M phosphate concentration range from 0.65 to 3.03 × 10-2, and from 0.41 to 0.99 × 10-2 and 0.12 to 1.63 × 10-2 min-1, respectively. The second-order rate constants for the phosphate catalysed photodegradation of RF and for the formation of LC and CDRF are 2.12 × 10-4 and 0.61 × 10-4 and 1.41 × 10-4 M-1 s -1, respectively. Since the formation of CDRF by photoaddition is catalysed by HPO42- ions [Eur. J. Biochem. 57 (1975) 35], it is suggested that H2PO4- ions may be involved in the formation of LC by photolysis. Thus, both H2PO4- and HPO42- ions may catalyse the two major reaction pathways of riboflavin photodegradation, respectively. [Copyright &y& Elsevier]

The effect of the photosensitizer riboflavin (0, 10, 25, 50, 100 μM) and a river humic acid (0, 20, 40, 80 ppm) on the photolysis of 6-aminochrysene (6AC) in 10 mM PBS solution (pH 7.0) was studied. The presence of riboflavin significantly enhanced photolysis rate of 6AC. The photo-transformation half-life of 6AC was 1 or 36 min, respectively, in the presence or absence of riboflavin. The humic acid inhibited the photo-transformation rate of 6AC. The photo-transformation half-lives of 6AC were 37, 56, 92 min at 20, 40, 80 ppm humic acid, respectively. By using LC-MS, the main 6AC photoproduct identified was 5,6-chrysene-quinone along with some minor products. Both 6AC and 5,6-chrysene-quinone exhibited photoinduced cytotoxicity. A photochemical transformation pathway for 6AC was derived. [Copyright &y& Elsevier]

4-Hydroxyquinoline (4-OHQ) and 8-hydroxyquinoline (8-OHQ), two compounds of interest because of their bioactivity and their structural relation with bioactive products, are effectively photooxygenated when irradiated with visible light in the presence of riboflavin (Rf) (vitamin B2) in solution in air-saturated water–methanol (9:1). Rf behaves as a dye-sensitiser, since both quinolines are transparent to visible light. 8-OHQ degrades about five times faster than 4-OHQ. Kinetic data obtained through time-resolved and stationary detection of Rf-electronically excited states indicate that a superoxide radical anion-mediated mechanism exclusively operates for 4-OHQ, whereas singlet molecular oxygen – mainly – plus superoxide radical anion is the species that reacts with 8-OHQ. The sensitiser Rf, which is known to photodegrade under visible-light aerobic irradiation, is regenerated in the presence of any of the quinolines through an electron transfer process that produces superoxide radical anion. The overall picture indicates that both quinolines act as sacrificial scavengers of the photogenerated oxygen species, thus preventing the photodegradation of Rf. [Copyright &y& Elsevier]

There is a current concern, among the scientific community, on the pollutants classified as "persistent organic pollutants (POPs)". Pharmaceuticals and personal care products (PPCPs) belong to this family of contaminants; therefore, it is necessary to find more efficient techniques able to achieve their removal from the environment. This study focuses on two different pharmaceuticals: carbamazepine and atenolol, chosen for their widespread use and their different chemical and medical properties. In this work, an organic dye, acetylated riboflavin, has been used in combination with visible light to achieve the photodegradation of these two POPs in <2 h. Moreover, photophysical experiments demonstrated the involvement of the singlet and triplet excited states of acetylated riboflavin and the generated singlet oxygen in the removal of these drugs. Besides, a detailed UFLC-MS-MS analysis of the photoproducts confirmed the oxidation of the drugs. Finally, a plausible mechanism has been postulated. [Display omitted] • Acetylated Riboflavin (RFTA) works as visible-light photocatalyst for drugs removal. • Carbamazepine (CBZ) and atenolol (ATN) are photodegraded in <2 h. • Kinetic constants between 1RFTA⁎, 3RFTA⁎ and 1O 2 and the drugs have been determined. • UFLC-MS2 was used to detect and identify the oxidation photoproducts. • A plausible mechanism is postulated for CBZ and ATN oxidative photodegradation. [ABSTRACT FROM AUTHOR]

Abstract: The reactions of tryptophan (Trp) and tyrosine (Tyr) with endogenous photosensitizer riboflavin (RF) have gained much interest for their crucial roles in various photobiological processes. In this paper, the quenching mechanisms of triplet state RF by Trp and Tyr have been explored employing density functional theory calculations. It is revealed that the H-atom transfer reaction from Trp and Tyr to triplet state RF is more favorable on thermodynamic grounds compared with direct energy transfer or direct electron transfer pathways. During the photosensitization, RF can photogenerate various reactive oxygen species (ROS) as intermediates, while the present study provides some deeper insights into the photosensitizing behaviors of triplet state RF by reacting directly with Trp and Tyr. [Copyright &y& Elsevier]

Recent studies focus on usage of blue light of λ = 450 nm in combination with photosensitizers to treat surface skin disorders, including cancers. In search of convenient therapeutic factor we studied riboflavin analogue 3-methyl-tetraacetylriboflavin (3MeTARF) as potential sensitizer. Riboflavin (Rfl) itself, non -toxic in the darkness, upon absorption of UVA and blue light, may act as photosensitizer. However, Rfl efficiency is limited due to its susceptibility to photodecomposition. Riboflavin's acetylated analogue, 3MeTARF, bears substituents in ribose chain, which inhibit intramolecular processes leading to degradation. Upon excitation, this compound, reveals higher photochemical resistance, remaining a good singlet oxygen generator. Thus, being more stable as the sensitizer, might be much more efficient in photodynamic processes. The objective of undertaken study was to elucidate mechanisms of 3MeTARF photoreactivity under the irradiation with blue light in comparison to its mater compound, riboflavin. We approached this goal by using spectroscopic methods, like direct singlet oxygen phosphorescence detection at 1270 nm, EPR spin trapping and oximetry. Additionally, we tested both riboflavin and 3MeTARF phototoxicity against melanoma cells (WM115) and we studied mechanism of photodynamic cell death, as well. Moreover, 3MeTARF induces apoptosis in melanoma cells at ten times lower concentration than riboflavin itself. Our studies confirmed that 3MeTARF remains stable upon blue light activation and is more efficient photosensitizer than Rfl. • 3MeTARF is more photoreactive and phototoxic to melanoma cells than riboflavin itself • singlet oxygen or free radicals, formed during studied flavins irradiation, react with riboflavin but not with 3MeTARF • 3MeTARF is photochemically much more stable than riboflavin [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) fluorescent lamp (FL) was applied in mainstream riboflavin photochemical method (RPM) to inactivate pathogens in blood components. Low UV irradiance emitted by UV-FL resulted in more time to achieve effective inactivation. A novel light emitting diode (LED) UV illumination with adjustable irradiance was developed by us. Two strains of drug-resistant bacteria (DRB), pan-drug resistant Acinetobacter baumannii (PDRAB) and methicillin-resistant Staphylococcus aureus (MRSA) were cultured and used for evaluating the inactivation effectiveness of RPM using UV-LED or UV-FL against DRB in plasma or platelets. Three plasma factors and four platelet parameters were measured after treatments. There was a linear relationship between UV-LED irradiance and electric current, the minimum UV irradiance was 24 mW/cm2, and the maximum was 258 mW/cm2. At the same UV dose of 15 J/cm2, inactivation effectiveness of UV-LED with 258 mW/cm2 against PDRAB in plasma or platelets were comparable to that of UV-FL with 16 mW/cm2, both above 98%. UV-FL treatment required 10–15 min, but UV-LED only required 1–2 min. However, MRSA showed a resistance to UV-LED (inactivation effectiveness was around 40%) compared with UV-FL (inactivation effectiveness was above 98%). The retention of fibrinogen, factor V, factor VII in plasma and platelet counts in platelets with UV-LED treatment were significantly higher than UV-FL at the same UV dose. The treatment of RPM using UV-LED with high UV irradiance was able to dramatically shorten inactivation time against PDRAB in plasma or platelets and improve retention of blood components compared with UV-FL. • The UV-LED illumination was developed to apply in riboflavin photochemical method to inactivate pathogens in blood. • UV-LED and UV-FL were demonstrated to inactivate two strains of drug-resistant bacteria in plasma or platelets. • The advantage of UV-LED compared with UV-FL used in riboflavin photochemical method was clarified. [ABSTRACT FROM AUTHOR]

Surgical resection is one of the most common radical treatments for cancers. However, tumors may be compressed or the local intravascular pressure may be increased during surgical manipulation, causing the shedding and entry of tumor cells into the blood circulation and hence distant recurrence and metastasis of tumors. We have preliminarily established a method of riboflavin photosensitization treatment (RPT) for inactivation of circulating tumor cells. This technology promises to solve the problems of shedding and entry of solid tumor cells into blood circulation before surgical manipulation, and almost unavoidable hematogenous dissemination of tumor cells during surgical resection. In the present study, apoptosis detection and tumorigenicity experiment in immunodeficient mice were conducted to evaluate the effect of RPT for inactivation of circulating tumor cells respectively. Next, functional evaluation was carried out for the immune cells through detecting apoptosis rate and cytokine secretion of lymphocyte. Finally, thromboelastography (TEG) and free hemoglobin were detected to assess peripheral blood coagulation and red blood cell damage. The results showed that RPT (50 μmol/L riboflavin, 10.8 J/cm2 UV) could effectively make tumor cell lose the ability of proliferation in the peripheral blood. In the meantime, the damage caused to peripheral blood coagulation, immune cell function and red blood cells was generally acceptable. The results of the study showed that RPT had huge potential in addressing the problems of shedding and entry of solid tumor cells into blood circulation before surgical manipulation, and almost unavoidable hematogenous dissemination of tumor cells during surgical resection. This therapy is expected to be an auxiliary and supportive method to reduce the risk of hematogenous metastasis and recurrence of cancers, and to increase the surgical success rate of malignant solid tumors. • HCT116 cells are more vulnerable to RPT than lymphocytes. • RPT under certain conditions can inactivate HCT116 cells and maintain the RBC, the function of coagulation and immune. 3. RPT is expected to be used in inactivation of CTCs. [ABSTRACT FROM AUTHOR]