Free Radical Ions Research Articles

Antiparasitic and immunomodulatory potential of oral nanocapsules encapsulated lactoferrin protein against Plasmodium berghei.

To analyze the effect of native buffalo lactoferrin (buLf) protein along with its nanoformulation using alginate-enclosed, chitosan-conjugated, calcium phosphate buffalo Lf nanocapsules (AEC-CCo-CP-buLf NCs) against rodent parasite Plasmodium berghei. BALB/c mice were infected with malaria parasite and efficacy of the proteins (buLf and NCs) was evaluated by measuring parasitemia, initialization, role of miRNA in absorption of NCs, parasite load by histopathology and quantitative determination, cytokine levels, bioavailability and immunohistochemistry to localize Lf protein. NCs significantly reduced the parasite load in mice compared with buLf and untreated group. NCs were found to be modulating the disease profile of mice as shown by immunohistochemistry, free radical ion production and higher survival tendency. Our study confirms that NCs internalized and changed the expression of miRNAs that further enhanced their uptake in various organs leading to inhibitory effect against the parasite as well as maintenance of the Fe metabolism.

Anti-inflammatory effect of certain dimethoxy flavones.

The aim of the present study was to evaluate the anti-inflammatory effect of four dimethoxy flavone derivatives; 7,2'-dimethoxy flavone, 7,3'-dimethoxy flavone, 7,4'-dimethoxy flavone and 7,8,-dimethoxy flavone and to investigate the possible cellular mechanisms involved. The acute anti-inflammatory effect of dimethoxy flavones was investigated by carrageenan induced hind paw oedema in rats. Further, the effect of dimethoxy flavones on certain mediators of pain and inflammation like cyclooxygenases (COX-1 and COX-2), pro-inflammatory cytokines (IL-1β and TNF-α) and free radical scavenging activity (NO and LPO) were investigated by using in vitro tests. The investigated dimethoxy flavones produced a significant, dose and time dependent reduction of carrageenan induced paw oedema in rats with a maximum inhibition of 52.4% observed for 7,4'-dimethoxy flavone. Although, the test compounds inhibited both the isoforms of cyclooxygenase, a higher degree of inhibition on COX-2 was evident. A concentration dependent inhibition of other inflammatory cytokines like tumor necrosis factor-α and interleukin-1β was identified in the present study. 7,4'-dimethoxy flavone was found to be maximally effective in inhibiting nitrite ion free radical generation and 7,8-dimethoxy flavone was more active in inhibiting lipid peroxidation than the other compounds. The results of the present study reveal the anti-inflammatory action of the investigated dimethoxy flavones. Inhibition of cyclooxygenases, cytokines and reactive oxygen species, observed in subsequent experiments may be suggested as possible mechanisms involved in the action of these compounds.

Simple flow injection colorimetric system for determination of paraquat in natural water

A simple and low cost flow injection colorimetric system has been developed for determination of paraquat in natural water. The developed method is based on the reduction of paraquat by using sodium dithionite as a reducing agent in an alkaline medium to produce a blue free radical ion that can be detected by a simple light emitting diode-light dependent resistor (LED-LDR) colorimeter. The standard or sample solution was injected via a set of 3-way solenoid valves into a water carrier stream and flowed to merge with reagent to generate a colored product which is proportional to the concentration of paraquat ion in the solution. Under the optimum condition of the system, i.e., mixing coil length 30cm, flow rate 2.0mLmin−1, sample volume 100μL, concentrations of dithionite 0.1% (w/v) and sodium hydroxide 0.06molL−1, a linear calibration graph in the range of 0.2–10.0mgL−1 with a correlation coefficient of 0.9996, and a limit of detection of 0.15mgL−1 were achieved. Relative standard deviation for 9 replicate injections of 1mgL−1 paraquat is 3.7%. A sample throughput of 40 injectionsh−1 was achieved. The limit of detection can be improved by off-line preconcentration of paraquat employing a column packed with Dowex 50WX8-100 (H) cation exchange resin and eluted with 10% (w/v) ammonium chloride in ammonium buffer solution pH 10. The eluting solution was then injected into the FI system for paraquat determination. The proposed system did not suffer from interferences of some possible ions in natural water and other herbicides. Recoveries obtained by spiking 0.5 and 5.0mgL−1 paraquat standard into water samples were in the range of 104–110% and 101–105%, respectively. The developed system can be conveniently applied for screening of paraquat contaminated in natural water.

Antioxidant and Anticancer Activities of Raspberry Extracts

The raspberry (Rubus idaeus) is an economical important berry crop that contains phytochemicals such as polyphenols and flavonoids with potential health benefits. This study addresses the antioxidant and anticancer effects of raspberry and its root extracts. Raspberry and raspberry root were extracted with ethanol, and separated into petroleum ether, chloroform, ethyl acetate, n-butyl alcohol and water fraction. Most extracts showed the powerful activities to scavenge DPPH radical, eliminate hydroxyl free radical ion, and inhibit the growth of human cancer cells, suggesting their promising application on health care.

The Games Radicals Play: Special Issue on Free Radicals and Radical Ions

Chemistry and Physics have aptly been described as “most excellent children of Intellect and Art” [1]. Both these “children” engage with many playthings, and molecules rank as one of their first favorites, especially radicals, which are amongst the most lively and exciting. Checking out radicals dancing to the music of entropy round their potential energy ballrooms is surely both entertaining and enlightening. Radicals’ old favorite convolutions are noteworthy, but the new styles, modes and arrangements appearing on the scene are even more interesting. Some of these are ephemeral and enjoy only a brief appearance, others are retro-types reappearing in new guises, still others are genuinely new and “go viral” in the scientific world. This Special Issue of Molecules contains the observations and reflections of a select group of chemists and physicists fascinated by this spectacle. It contains an eclectic mix reflecting on new modes and advances as well as on permutations and combinations that revive mature themes. [...]

In vitro antioxidant and anti-lipoperoxidative activities of bark extracts of Xylopia aethiopica against ion-mediated toxicity on liver homogenates.

Reactive oxygen species (ROS), products of normal cell metabolism may cause damage to biological macromolecules leading to severe health threats when they are present in high concentrations. Aromatic plants contain phytochemicals rich of antioxidants that prevent oxidant formation or scavenge oxidants produced under oxidative stress conditions. In the present study, we investigated the free radical scavenging effects, the antioxidant and ion toxicity preventive effect of Xylopia aethiopica (X. aethiopica), a plant of the family of Annonaceae used as spice in Cameroon. The scavenging properties of extracts of X. aethiopica were tested on 2, 2-diphenyl-1-picrylhydrazyl (DPPH), nitric oxide (NO), hydroxyl (OH), 2,2'-azinobis(3-ethylbenzthiazoline)-6-sulfonic acid (ABTS) radicals. The total antioxidant capacity was assayed by ferric reducing ability of plasma (FRAP), phosphomolybdenum antioxidant power (PAP), reduction assays. The protective potential was carried on superoxide dismutase (SOD), catalase and peroxidases. The results showed that both the ethanolic (BEE) and the hydroethanolic (BEH) extracts from the barks of X. aethiopica scavenged all the tested radicals. The sample BEH showed the highest total antioxidant capacity both in the FRAP and the PAP. This result was positively correlated to its higher phenolic content (30.74±0.44 CAE/g dried extract). The higher protective capacity of BEH on SOD, catalase and peroxidase activities was comparable to that of the vitamin C used as standard. In conclusion, X. aethiopica has a higher antioxidant and protective potential against ion-mediated oxidative damage and may be considered as a potential drug against metal-mediated toxicity.

3-Carboxybenzophenone (3-CB) as an efficient sensitizer in the photooxidation of methionyl-leucine in aqueous solutions: Spectral, kinetic and acid–base properties of 3-CB derived transients

Abstract 3-Carboxybenzophenone (3-CB) was successfully employed in the photooxidation of a selected methionine derivative: methionyl-leucine (Met-Leu). It is also demonstrated that this photosensitizer has an advantage over its isomer, 4-carboxybenzophenone (4-CB), which is a commonly used water-soluble organic photosensitizer. The relative advantage of 3-CB over 4-CB lies in fact that the 3-CB derived transients have less absorption than the corresponding photoinduced transients from 4-CB. In particular ketyl radicals (3-CBH ) and ketyl radical anions (3-CB − ) are substantially less absorbing in the visible and near UV regions (i.e. 370–420 nm) than are the respective transients derived from 4-CB. This feature is very important since it allows a better sampling of the absorption spectra of three-electron-bonded radicals S∴N and S∴O resulting from the sensitized photooxidation of methionine derivatives by triplet 3-CB acting as an electron acceptor. This advantage of 3-CB over 4-CB was demonstrated during spectral resolutions of transient absorption spectra formed during the 3-CB-sensitized photooxidation of Met-Leu. Since the kinetic and spectral characteristics of free radicals and radical ions derived from 3-CB were not determined previously, pulse radiolysis was employed to determine molar absorption coefficients and selected rate constants for the 3-CB radical anion (3-CB − ) and its ketyl radical (3-CBH ). Rate constants were measured for the protonation of 3-CB − by water ( k H 2 O = 5.1 × 10 2 M − 1 s − 1 ) and by H + ( k H + = 6.4 × 10 10 M − 1 s − 1 ). In addition, the acid–base equilibrium constant K a of 3-CBH was characterized by a p K a = 9.5 (±0.1). This K a value is more than one order of magnitude smaller than the literature value of K a for 4-CBH (p K a = 8.2). This observation was interpreted in terms of the difference in electron densities on the carbonyl oxygen atoms in these ketyl radicals, confirmed by DFT (PBE1PBE) calculations and based on a thermodynamic cycle of the protonation process. Using the newly determined p K a value, rate constants for the OH − -assisted deprotonation ( k ( 3 -CBH + HO − ) = 8.9 × 10 8 M − 1 s − 1 ) and the spontaneous dissociation ( k ( 3 -CBH dissociation ) = 20 s − 1 ) of 3-CBH were calculated. Moreover, molar absorption coefficients ( ɛ ) for all of the intermediates derived from 3-CB were measured by pulse radiolysis and laser flash photolysis methods. They were found to be: ɛ 550 (3-CBH ) = 2700 (±200) M −1 cm −1 , ɛ 600 (3-CB − ) = 5200 (±300) M −1 cm −1 , and ɛ 520 ( 3 3-CB*) = 5400 (±300) M −1 cm −1 .

α-Dihydroxychalcone-glycoside (α-DHC) isolated from the heartwood of Pterocarpus marsupium inhibits LPS induced MAPK activation and up regulates HO-1 expression in murine RAW 264.7 macrophage

Three phenolic glycosides isolated from the heartwood of Pterocarpus marsupium showed significant free radical and superoxide ion scavenging activity and antioxidant potential that were comparable to, or several folds higher than those of standard antioxidants, trolox and ascorbic acid. The effective concentrations of these compounds were far below their cytotoxic levels. Compound 3, which was characterized to be α-dihydroxychalcone-glycoside (α-DHC), was the most potent one. Subsequent studies demonstrated that α-DHC effectively reduced nitric oxide and cytokine production by the LPS stimulated RAW 264.7 mouse macrophage cell line. The compound effectively attenuated the expression of inflammation-mediating enzymes COX-2 and iNOS at the mRNA as well as protein levels in a concentration dependent manner. It prevented phosphorylation of all the three MAPKs (JNK, ERK, p38) and eventually blocked the activation of downstream elements contributing to inflammation. Phosphorylation of IκB-α and subsequent translocation of NF-κB into the nucleus were restricted, while the expression of stress responsive gene HO-1 was up-regulated. α-DHC targeted Keap-1 by modifying its cysteine thiols, dissociating it from Nrf-2 and facilitating nuclear entry of the latter; and this in turn induced HO-1 expression. Thus α-DHC exerts its anti-inflammatory activity in a dual manner: by down regulating MAPKs and restricting nuclear stabilization of NF-κB at one end, and by disrupting Nrf-2–Keap-1 complex on the other. In conclusion, the anti-inflammatory potential together with its high therapeutic index envisages α-DHC as a prospective candidate molecule for the development of therapeutic strategy against inflammatory disorders.

Effect of gamma radiation and accelerated electron beam on stable paramagnetic centers induction in bone mineral: influence of dose, irradiation temperature and bone defatting

Ionizing radiation has been found to induce stable defects in the crystalline lattice of bone mineral hydroxyapatite, defined as CO(2) (-) radical ions possessing spins. The purpose of our study was to evaluate CO(2) (-) radical ions induced in non-defatted or defatted human compact bone by gamma radiation (G) and accelerated electron beam (EB), applied with two doses at different temperatures. Moreover, the potential effect of free radical ion formation on mechanical parameters of compact bone, tested under compression in the previous studies, was evaluated. Bone rings from femoral shafts of six male donors (age 51 ± 3 years) were collected and assigned to sixteen experimental groups according to different processing methods (non-defatted or defatted), G and EB irradiation dose (25 or 35 kGy), and irradiation temperature [ambient temperature (AT) or dry ice (DI)]. Untreated group served as control. Following grinding under LN2 and lyophilization, CO(2) (-) radical ions in bone powder were measured by electron paramagnetic resonance spectrometry. We have found that irradiation of bone with G and EB induces formation of enormous amounts of CO(2) (-) radical ions, absent from native tissue. Free radical ion formation was dose-dependent when irradiation was performed at AT, and significantly lower in EB as compared to G-irradiated groups. In contrast, no marked effect of dose was observed when deep-frozen (DI) bone samples were irradiated with G or EB, and free radical ion numbers seemed to be slightly higher in EB-irradiated groups. Irradiation at AT induced much higher quantities of CO(2) (-) radical ions then on DI. That effect was more pronounced in G-irradiated bone specimens, probably due to longer exposure time. Similarly, bone defatting protective effect on free radical ion formation was found only in groups irradiated for several hours with gamma radiation at ambient temperature. Ambient irradiation temperature together with exposure time seem to be key parameters promoting CO(2) (-) radical ion formation in bone mineral and may mask the opposite effect of defatting and the possible effect of irradiation type. Significant weak negative correlations between CO(2) (-) radical ion number and some mechanical properties of compact bone rings (Young's modulus and ultimate stress) were found.

Calotropis proceraRoot Extract Has the Capability to Combat Free Radical Mediated Damage

The present study reports the antioxidant and membrane protective activities of Calotropis procera aqueous root extract using several in vitro assays along with the determination of phenolic as well as flavonoid contents. Total phenol and flavonoid contents in extract were 15.67 ± 1.52 mg propyl gallate equivalent/g and 1.62 ± 0.05 mg quercetin equivalent/g, respectively. UV-visual spectroscopic scanning of the extract indicated the presence of glycoside-linked tannins or flavonoids. The extract exhibited appreciable reducing power signifying hydrogen donating potential. DPPH radical scavenging assay revealed substantial free radical scavenging activity (42–90%) in the extracts. Concentration dependent response was observed in the metal ion chelating activity (16–95%). Extracts also provided protection against iron induced lipid peroxidation in rat tissue (liver, brain, and kidney) homogenates. Comparatively better protective efficacy against peroxidative damage was observed in liver (71%) followed by kidney (65%) and brain (60%) tissues. Positive correlation (r 2 = 0.756) was observed between DPPH free radical scavenging activity and reducing power of extract. Similarly strong positive correlation (r 2 ≈ 0.756) was observed between metal ion chelating ability and percentage lipid peroxidation inhibition in different tissues. The study demonstrated considerable protective efficacy in C. procera root aqueous extracts against free radical and metal ion mediated oxidative damage.

Molecular functions of metallothionein and its role in hematological malignancies

Metallothionein (MT) was reported to be a potential negative regulator of apoptosis, and various reports have suggested that it may play roles in carcinogenesis and drug resistance, in at least a portion of cancer cells. The author summarizes the current understanding of the molecular functions of MT for tumor cell growth and drug resistance. These activities are regulated through intracellular metal ion modulation and free radical scavenging. Compared with analyses of solid tumors, few studies have analyzed the roles of MT in hematological malignancies. This review mainly describes the functions of MT in hematopoietic cells. Furthermore, through expression analyses of leukemias and lymphomas, the roles of MT in the biology of these diseases are particularly focused upon.

Decomposition of PCBs in transformer oil using an electron beam accelerator

Decomposition of PCBs in commercially used transformer oil used for more than 30 years has been carried out at normal temperature and pressure without any additives using an electron beam accelerator. The experiments were carried out in two ways: batch and continuous pilot plant with 1.5MeV of energy, a 50mA current, and 75kW of power in a commercial scale accelerator.The electron beam irradiation seemed to transform large molecular weight compounds into lower ones, but the impact was considered too small on the physical properties of oil. Residual concentrations of PCBs after irradiation depend on the absorption dose of the electron beam energy, but aliphatic chloride compounds were produced at higher doses of irradiation. As the results from FT-NMR, chloride ions decomposed from the PCBs are likely to react with aliphatic hydro carbon compounds rather than existing as free radical ions in the transformer oil. Since this is a dry process, treated oil can be used as cutting oil or machine oil for heavy equipment without any additional treatments.

Activation of aliphatic C–H bonds by tetracyanobenzene photosensitization. A time-resolved and steady-state investigation

The photochemistry of 1,2,4,5-tetracyanobenzene (TCB) in acetonitrile in the presence of representative aliphatic donors (cyclohexane, 1,4-dioxane and triethylamine) has been investigated by femtosecond (fs) and nanoseconds (ns) flash photolysis as well as steady state irradiation in order to define the kinetic frame for the activation of aliphatic C–H bonds. Unlike in the case of aromatics, no ground state complex (except possibly in the case of triethylamine) or exciplex is formed. The lowest excited singlet is quenched and forms the free radical ions. The efficiency of the process, measured by the yield of TCB˙− (0.84 with cyclohexane, 0.15 with 1,4-dioxane, 0.37 with triethylamine) depends on the rate of return electron transfer, low for a high exothermicity. The chemical reaction following the electron transfer step depends on the properties of the radical cation. Thus, with cyclohexane deprotonation is slow and does not occur measurably on a microsecond scale, while on a longer time scale, the formation of alkyl radicals competes with back electron transfer between the free ions. The deprotonation of amine radical cations is faster and the resulting α-aminoalkyl radicals reduce a further molecule of TCB, causing the accumulation of the radical anion which is indefinitely stable in the absence of oxygen.

Studies on Electrochemical Hydrodeiodination Mechanism of 2-Iodobenzoic Acid on Cu Electrode by in-Situ FTIR Spectroscopy

Abstract. Electrochemical hydrodeiodination of 2-iodobenzoic acid in NaOH solution was investigated using cyclic voltammetry. Compared with Ti and Pt electrodes, Cu electrode exhibited good electrocatalyitc activity for the electroreduction of 2-iodobenzoic acid. In situ FTIR results suggested that the mechanism of the reaction was electrochemical hydrodeiodination process. 2-Iodobenzoic acid was electroreduced to its free radical ion after receiving an electron firstly. Then the free radical ion was further deiodinated to produce benzoic acid free radical at more negative potential. After receiving another electron and proton, benzoic acid was obtained.

Studies on Electrochemical Dechlorination Reaction of 2,4-Dichlorobenzoic Acid on Pd/Ti Electrode

Abstract: Pd/Ti electrode was prepared on Ti substrate electrode in hydrochloric acid containing PdCl2 using cyclic voltammetry. The electrocatalytic performance toward electrochemical reduction reactivity of 2,4-dichlorobenzoic acid (2,4-DCBA) on Cu, Ag, Ti and Pd/Ti was investigated. Compared with Cu, Ag and Ti electrodes, Pd/Ti electrode exhibited a high electrochemical activity for the reduction process of 2,4-DCBA in NaOH solution. In situ FTIR was applied to analyze the electrochemical dechlorination mechanism of 2,4-DCBA systematically. The results showed that 2,4-DCBA was electroreduced to its free radical ion after receiving an electron. Then the 2,4-DCBA free radical took off two chloride ions and produced the benzoic acid free radical. After receiving another two electrons and two protons, the final product benzoic acid was obtained.

Reexamination of the Rehm–Weller Data Set Reveals Electron Transfer Quenching That Follows a Sandros–Boltzmann Dependence on Free Energy

In a landmark publication over 40 years ago, Rehm and Weller (RW) showed that the electron transfer quenching constants for excited-state molecules in acetonitrile could be correlated with the excited-state energies and the redox potentials of the electron donors and acceptors. The correlation was interpreted in terms of electron transfer between the molecules in the encounter pair (A*/D ⇌ A(•-)/D(•+) for acceptor A and donor D) and expressed by a semiempirical formula relating the quenching constant, k(q), to the free energy of reaction, ΔG. We have reinvestigated the mechanism for many Rehm and Weller reactions in the endergonic or weakly exergonic regions. We find they are not simple electron transfer processes. Rather, they involve exciplexes as the dominant, kinetically and spectroscopically observable intermediate. Thus, the Rehm-Weller formula rests on an incorrect mechanism. We have remeasured k(q) for many of these reactions and also reevaluated the ΔG values using accurately determined redox potentials and revised excitation energies. We found significant discrepancies in both ΔG and k(q), including A*/D pairs at high endergonicity that did not exhibit any quenching. The revised data were found to obey the Sandros-Boltzmann (SB) equation k(q) = k(lim)/[1 + exp[(ΔG + s)/RT]]. This behavior is attributed to rapid interconversion among the encounter pairs and the exciplex (A*/D ⇌ exciplex ⇌ A(•-)/D(•+)). The quantity k(lim) represents approximately the diffusion-limited rate constant, and s the free energy difference between the radical ion encounter pair and the free radical ions (A(•-)/D(•+) vs A(•-) + D(•+)). The shift relative to ΔG for the overall reaction is positive, s = 0.06 eV, rather than the negative value of -0.06 eV assumed by RW. The positive value of s involves the poorer solvation of A(•-)/D(•+) relative to the free A(•-) + D(•+), which opposes the Coulombic stabilization of A(•-)/D(•+). The SB equation does not involve the microscopic rate constants for interconversion among the encounter pairs and the exciplex. Data that fit this equation contain no information about such rate constants except that they are faster than dissociation of the encounter pairs to (re-)form the corresponding free species (A* + D or A(•-) + D(•+)). All of the present conclusions agree with our recent results for quenching of excited cyanoaromatic acceptors by aromatic donors, with the two data sets showing indistinguishable dependencies of k(q) on ΔG.

Bimolecular Electron Transfers That Follow a Sandros−Boltzmann Dependence on Free Energy

Rate constants (k) for exergonic and endergonic electron-transfer reactions of equilibrating radical cations (A(•+) + B ⇌ A + B(•+)) in acetonitrile could be fit well by a simple Sandros-Boltzmann (SB) function of the reaction free energy (ΔG) having a plateau with a limiting rate constant k(lim) in the exergonic region, followed, near the thermoneutral point, by a steep drop in log k vs ΔG with a slope of 1/RT. Similar behavior was observed for another charge shift reaction, the electron-transfer quenching of excited pyrylium cations (P(+)*) by neutral donors (P(+)* + D → P(•) + D(•+)). In this case, SB dependence was observed when the logarithm of the quenching constant (log k(q)) was plotted vs ΔG + s, where the shift term, s, equals +0.08 eV and ΔG is the free energy change for the net reaction (E(redox) - E(excit)). The shift term is attributed to partial desolvation of the radical cation in the product encounter pair (P(•)/D(•+)), which raises its free energy relative to the free species. Remarkably, electron-transfer quenching of neutral reactants (A* + D → A(•-) + D(•+)) using excited cyanoaromatic acceptors and aromatic hydrocarbon donors was also found to follow an SB dependence of log k(q) on ΔG, with a positive s, +0.06 eV. This positive shift contrasts with the long-accepted prediction of a negative value, -0.06 eV, for the free energy of an A(•-)/D(•+) encounter pair relative to the free radical ions. That prediction incorporated only a Coulombic stabilization of the A(•-)/D(•+) encounter pair relative to the free radical ions. In contrast, the results presented here show that the positive value of s indicates a decrease in solvent stabilization of the A(•-)/D(•+) encounter pair, which outweighs Coulombic stabilization in acetonitrile. These quenching reactions are proposed to proceed via rapidly interconverting encounter pairs with an exciplex as intermediate, A*/D ⇌ exciplex ⇌ A(•-)/D(•+). Weak exciplex fluorescence was observed in each case. For several reactions in the endergonic region, rate constants for the reversible formation and decay of the exciplexes were determined using time-correlated single-photon counting. The quenching constants derived from the transient kinetics agreed well with those from the conventional Stern-Volmer plots. For excited-state electron-transfer processes, caution is required in correlating quenching constants vs reaction free energies when ΔG exceeds ∼+0.1 eV. Beyond this point, additional exciplex deactivation pathways-fluorescence, intersystem crossing, and nonradiative decay-are likely to dominate, resulting in a change in mechanism.

Efficient Photochemical Oxidation of Anisole in Protic Solvents: Electron Transfer driven by Specific Solvent–Solute Interactions

The dynamics of the bimolecular quenching of triplet excited benzophenone by anisole was studied by nanosecond flash photolysis. We carried out a detailed study of the solvent dependence of the reaction rates and efficiencies in a number of protic and non-protic solvents. These studies were augmented by theoretical modelling and experimental investigation of solute/solvent interactions in the triplet excited and the ground state, respectively. The triplet quenching that follows Stern-Volmer kinetics in all cases is profoundly dependent on the nature of the solvent, with the highest reactivity being consistently found in protic solvents. The results in non-protic solvents are compatible with unproductive quenching via a charge-transfer state, whereas the generally fast quenching in protic solvents is accompanied by efficient formation of free-radical products. Analysis of the solvent dependence in terms of Marcus theory reveals the impact of specific solvation of benzophenone by protic solvents on the ET driving force and kinetics. Specific solvation is found to support efficient free radical ion formation in media of moderate and low polarity as well.

Investigation of collision‐induced dissociations involving odd‐electron ion formation under positive electrospray ionization conditions using accurate mass

Collision induced dissociation (CID) has been extensively used for structure elucidation. CID in the electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) modes has been found to generate mostly even-electron fragment ions while it has been occasionally reported to form odd-electron free radical ions. However, the structural requirements and the fragmentation mechanisms for free-radical CIDs have not been well characterized in the literature. For this purpose, we studied a series of aromatic and non-aromatic compounds such as sulfonamides, N-aryl amides, tert-butyl-substituted aromatic compounds, aryl alkyl ethers, and O-alkyl aryl oximes using the LTQ and LTQ Orbitrap linear ion trap mass spectrometers. The accurate measurement of the fragment ion masses established the unambiguous assignment of the fragment structures resulting from the test compounds. Our results showed that free radical fragmentation is structure dependent and is to a large extent correlated with the neighboring groups in the structures that stabilize the newly formed free radical ions.

Correlation between antioxidant effect mechanisms and polyphenol content of Rosa canina

Rosa canina L. is a member of Rosaceae family, which is well-known for its high phenolic contents. These compounds are known to possess antioxidant, antimutagenic and anticarcinogenic effects. However, they have yet to pass controlled clinical trials for efficacy, and their potential for prooxidant activity is an understudied field of research. In order to estimate the correlations between phenolic contents and antioxidant/proxidant effect mechanisms, different concentrations of R. canina fruit extracts were examined in this study. R. canina showed antioxidant activities at all concentrations with respect to the reducing power, hydrogen peroxide scavenging activity and superoxide anion radical scavenging (O2ः-) activity assays, whereas a negative correlation was observed with the metal ion chelating activity and free radical scavenging activity [1,1-diphenyl-2-picryl-hydrazil (DPPH) % inhibition] assays at higher concentrations with the phenolic content of R. canina. These results suggest that R. canina may act not only as an antioxidant, but also as a prooxidant with the effects depending on its concentrations.