Triplet State Of Riboflavin Research Articles

The protective function of hydrogen sulfide for lysozyme against riboflavin-sensitized photo-oxidation

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.

Theoretical analysis of the deactivation reactions of triplet state riboflavin by hydroxycinnamic acid derivatives

A thermodynamic analysis of the deactivation reactions of triplet state riboflavin (RF) by hydroxycinnamic acid derivatives has been performed on the basis of quantum chemical calculations. It was revealed that the H-atom transfer pathway is more thermodynamically feasible in comparison with the direct energy/electron transfer to be involved in the triplet state RF quenching by hydroxycinnamic acid derivatives. The results provide some deeper insights into the protective behaviours of hydroxycinnamic acid derivatives against the RF induced photooxidative damage.

Quenching Reactions of Triplet State Riboflavin by Vitamin C: A Theoretical Investigation

Sir, Vitamin C (ascorbic acid), the water-soluble, smallmolecule antioxidant, is of great biological significance [1, 2]. Previous studies [3, 4] demonstrated that vitamin C can inhibit the photo-oxidative damage caused by riboflavin which can induce Type-I and II photosensitized oxidation mechanisms [5–7]. Considering the fact that many antioxidants can inhibit the riboflavin’s photosensitizing damage through deactivating its triplet state [7–9], it is of significance to investigate the reactions of vitamin C with triplet state riboflavin, which may contribute to the protective effect of vitamin C. In the present study, the quenching mechanisms of triplet state riboflavin by vitamin C were explored by means of density functional theory (DFT) calculations, which have been widely used in investigating both the antioxidant and photosensitization mechanisms of various bioactive compounds [7, 11–14]. The calculation methods are as follows. Firstly, molecular structures of vitamin C (monoanion form in neutral solution) and riboflavin were fully optimized by hybrid functional B3LYP with 6-31G(d,p) Gaussian basis set in vacuo. Then, the lowest triplet excitation energy (ET1) of the two molecules was estimated by time-dependent (TD)DFT with the same basis set in solvent (water). Moreover, as the diffuse functions are essential for treatment of anion and cation radicals, the vertical electron affinities (VEA) and vertical ionization potentials (VIP) of vitamin C and riboflavin were estimated using a combined DFT method labeled as B3LYP/6-31+G(d,p)//B3LYP/6-31G(d,p), which means that B3LYP/6-31+G(d,p) was used to perform a single-point calculation on the basis of B3LYP/631G(d,p)-optimized structures. The O-H bond dissociation enthalpy (BDE) of vitamin C and H-atom affinity (HAA) of riboflavin were calculated by (RO)B3LYP/6311+G(2d,2p)//AM1 method, which takes advantages of accuracy and economy [11]. During the single point calculations, the solvent (water) effect was taken into consideration by employing the self-consistent reaction field (SCRF) method with the polarizable continuum model (PCM) of Tomasi and coworkers [15–17]. All the calculations were accomplished with the Gaussian 03 package of programs [18]. During the photosensitization, riboflavin is initially excited to the singlet state upon irradiation and then may intersystem cross to the relatively long-lived triplet state. Triplet state riboflavin can react with molecular oxygen to photogenerate various reactive oxygen species [5–7] and at the same time, it can be deactivated by vitamin C, theoretically through the following possible pathways. Firstly, triplet state riboflavin (RF) may react with vitamin C (VC) through direct energy transfer (Eq. 1).

Mechanisms of singlet and triplet state riboflavin quenching by 3-hydroxypyridine and 4-hydroxypyridine. A quantum chemical study

In this work, mechanisms of both the singlet and triplet state riboflavin (RF) quenching by 3-hydroxypyridine (3-HP) and 4-hydroxypyridine (4-HP) have been investigated by employing quantum chemical calculations. It was revealed that both the direct electron transfer and H-atom transfer pathways, i.e ., (i) direct electron transfer from zwitterionic forms of 3-HP and 4-HP to excited state RF; (ii) H-atom transfer from enol forms of 3-HP and 4-HP to excited state RF, are thermodynamically favorable to be involved in the excited state RF quenching by 3-HP and 4-HP. The present results provide some deeper insights into the photooxidation of hydroxypyridine-based pesticides in the presence of natural photosensitizers.

A thermodynamic investigation on quenching mechanisms of the singlet and triplet state riboflavin by dopamine

The quenching mechanisms of both the singlet and triplet state riboflavin (RF) by dopamine (DP) were investigated by means of density functional theory calculations in this communication. It was found that both the direct electron transfer and H-atom transfer pathways are thermodynamically feasible for the singlet state RF quenching by DP, while only the H-atom transfer pathway is involved in the triplet state RF quenching by DP.

How α-tocopherol quenches triplet state riboflavin? Insights from theory

In the present study, the quenching mechanisms of triplet state riboflavin (RF) by α-tocopherol (α-T) have been explored employing density functional theory calculations. Three possible pathways, i.e., one-step H-atom transfer, direct electron-transfer and sequential proton-loss electron-transfer are proposed to account for the triplet state RF quenching by α-T in polar protic media.

A theoretical study on the quenching mechanisms of triplet state riboflavin by tryptophan and tyrosine

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.

Theoretical exploration on quenching mechanisms of triplet state riboflavin by xanthone derivatives

Riboflavin (RF), also known as vitamin B 2, is an endogenous photosensitizer and much effort has been devoted to finding chemopreventive agents to alleviate the photosensitizing damage of RF. In this communication, the quenching mechanisms of triplet state RF by xanthone derivatives (XD) were explored by means of theoretical calculations. The results indicate that H-atom transfer-based pathway is more probable than direct energy transfer and direct electron transfer pathways to be involved in the triplet state RF quenching by XD, which may be responsible for the chemopreventive activities of XD on RF induced photosensitizing damage.

Transient species and its properties of melatonin

The photo-physical and photo-chemical properties of melatonin (ML) were studied by 266 nm laser flash photolysis (LFP). ML undergoes photo-ionization to produce radical cation of ML (ML ·+) and hydrated electrons (e - aq ), while excited triplet state 3 ML* is also formed during photolysis. The oxidation via one electron transfer from ML to SO 4 ·- and the triplet state of riboflavin ( 3 RF*) has been also investigated and the rate constants for the process have been determined to be 8.0´10 9 and 1.4´10 9 L×mol -1 ×s -1 respectively. The radical cation of 2,2'-azinobis(3-ethylbenzothiazoline-6- sulfonic acid)(ABTS ·+ ) scavenging capacities of melatonin and other antioxidants are compared in this paper.

Photodegradation of DNA with fluorescent light in the presence of riboflavin, and photoprotection by flavin triplet-state quenchers

Superoxide anion was photogenerated upon illumination of nucleic acids with fluorescent light in a solution containing phosphate buffer, pH 7.8 and riboflavin. DNA was a better reducing substrate for this reaction than was RNA. A similar riboflavin-sensitized photoreaction caused single- and double-strand scissions of supercoiled PM2 DNA as detected by electrophoresis in agarose gels. None of specific scavengers or quenchers for superoxide anion and other active oxygen species prevented the DNA strand breaks. However, among the flavin triplet-state quenchers, potassium iodide, butylated hydroxyanisole, and ferricytochrome c protected the supercoiled DNA from photodegradation; butylated hydroxytoluene, α-tocopherol, tyrosine and hemoglobin did not have any protective effect. These results indicate that triplet-state riboflavin or a derivative formed from it participate directly in the observed riboflavin-sensitized DNA photodegradation and that active oxygen species are not directly involved.