UV-Vis Action Spectroscopy Reveals a Conformational Collapse in Hydrogen-Rich Dinucleotide Cation Radicals.

PubMed

Korn, Joseph A; Urban, Jan; Dang, Andy; Nguyen, Huong T H; Tureček, František

2017-09-07

We report the generation of deoxyriboadenosine dinucleotide cation radicals by gas-phase electron transfer to dinucleotide dications and their noncovalent complexes with crown ether ligands. Stable dinucleotide cation radicals of a novel hydrogen-rich type were generated and characterized by tandem mass spectrometry and UV-vis photodissociation (UVPD) action spectroscopy. Electron structure theory analysis indicated that upon electron attachment the dinucleotide dications underwent a conformational collapse followed by intramolecular proton migrations between the nucleobases to give species whose calculated UV-vis absorption spectra matched the UVPD action spectra. Hydrogen-rich cation radicals generated from chimeric riboadenosine 5'-diesters gave UVPD action spectra that pointed to novel zwitterionic structures consisting of aromatic π-electron anion radicals intercalated between stacked positively charged adenine rings. Analogies with DNA ionization are discussed.

DFT and ENDOR Study of Bixin Radical Cations and Neutral Radicals on Silica-Alumina.

PubMed

Tay-Agbozo, Sefadzi S; Krzyaniak, Matthew D; Bowman, Michael K; Street, Shane; Kispert, Lowell D

2015-06-18

Bixin, a carotenoid found in annatto (Bixa orellana), is unique among natural carotenoids by being water-soluble. We stabilized free radicals from bixin on the surface of silica-alumina (Si-Al) and characterized them by pulsed electron-nuclear double resonance (ENDOR). DFT calculations of unpaired electron spin distribution for various bixin radicals predict the EPR hyperfine couplings. Least-square fitting of experimental ENDOR spectra by spectra calculated from DFT hyperfine couplings characterized the radicals trapped on Si-Al. DFT predicts that the trans bixin radical cation is more stable than the cis bixin radical cation by 1.26 kcal/mol. This small energy difference is consistent with the 26% trans and 23% cis radical cations in the ENDOR spectrum. The remainder of the ENDOR spectrum is due to several neutral radicals formed by loss of a H(+) ion from the 9, 9', 13, or 13' methyl group, a common occurrence in all water-insoluble carotenoids previously studied. Although carboxyl groups of bixin strongly affect its solubility relative to other natural carotenoids, they do not alter properties of its free radicals based on DFT calculations and EPR measurements which remain similar to typical water-insoluble carotenoids.

Strategies for generating peptide radical cations via ion/ion reactions.

PubMed

Gilbert, Joshua D; Fisher, Christine M; Bu, Jiexun; Prentice, Boone M; Redwine, James G; McLuckey, Scott A

2015-02-01

Several approaches for the generation of peptide radical cations using ion/ion reactions coupled with either collision induced dissociation (CID) or ultraviolet photo dissociation (UVPD) are described here. Ion/ion reactions are used to generate electrostatic or covalent complexes comprised of a peptide and a radical reagent. The radical site of the reagent can be generated multiple ways. Reagents containing a carbon-iodine (C-I) bond are subjected to UVPD with 266-nm photons, which selectively cleaves the C-I bond homolytically. Alternatively, reagents containing azo functionalities are collisionally activated to yield radical sites on either side of the azo group. Both of these methods generate an initial radical site on the reagent, which then abstracts a hydrogen from the peptide while the peptide and reagent are held together by either electrostatic interactions or a covalent linkage. These methods are demonstrated via ion/ion reactions between the model peptide RARARAA (doubly protonated) and various distonic anionic radical reagents. The radical site abstracts a hydrogen atom from the peptide, while the charge site abstracts a proton. The net result is the conversion of a doubly protonated peptide to a peptide radical cation. The peptide radical cations have been fragmented via CID and the resulting product ion mass spectra are compared to the control CID spectrum of the singly protonated, even-electron species. This work is then extended to bradykinin, a more broadly studied peptide, for comparison with other radical peptide generation methods. The work presented here provides novel methods for generating peptide radical cations in the gas phase through ion/ion reaction complexes that do not require modification of the peptide in solution or generation of non-covalent complexes in the electrospray process. Copyright © 2015 John Wiley & Sons, Ltd.

Oxidative cyclization reactions: controlling the course of a radical cation-derived reaction with the use of a second nucleophile.

PubMed

Redden, Alison; Perkins, Robert J; Moeller, Kevin D

2013-12-02

Construction of new ring systems: Oxidative cyclizations (see picture; RVC=reticulated vitreous carbon) have been conducted that use two separate intramolecular nucleophiles to trap an enol ether-derived radical cation intermediate. The reactions provide a means for rapidly trapping the radical cation intermediate in a manner that avoids competitive decomposition reactions. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Carotenoid radical cation formation in LH2 of purple bacteria: a quantum chemical study.

PubMed

Wormit, Michael; Dreuw, Andreas

2006-11-30

In LH2 complexes of Rhodobacter sphaeroides the formation of a carotenoid radical cation has recently been observed upon photoexcitation of the carotenoid S2 state. To shed more light onto the yet unknown molecular mechanism leading to carotenoid radical formation in LH2, the interactions between carotenoid and bacteriochlorophyll in LH2 are investigated by means of quantum chemical calculations for three different carotenoids--neurosporene, spheroidene, and spheroidenone--using time-dependent density functional theory. Crossings of the calculated potential energy curve of the electron transfer state with the bacteriochlorophyll Qx state and the carotenoid S1 and S2 states occur along an intermolecular distance coordinate for neurosporene and spheroidene, but for spheroidenone no crossing of the electron transfer state with the carotenoid S1 state could be found. By comparison with recent experiments where no formation of a spheroidenone radical cation has been observed, a molecular mechanism for carotenoid radical cation formation is proposed in which it is formed via a vibrationally excited carotenoid S1 or S*state. Arguments are given why the formation of the carotenoid radical cation does not proceed via the Qx, S2, or higher excited electron transfer states.

Kinetics and Product Branching Fractions of Reactions between a Cation and a Radical: Ar+ + CH3 and O2+ + CH3 (Postprint)

DTIC Science & Technology

2015-01-13

Gross group using a Chen nozzle coupled to a Fourier transform ion cyclotron reso- nance (FT-ICR) mass spectrometer for reactions of the benzyl radical...reactions: A Fourier transform ion cyclotron resonance study of allyl radical reacting with aromatic radical cations. Int. J. Mass Spectrom. 2009, 287, 8

Detection of transient radical cations in electron transfer-initiated Diels-Alder reactions by electrospray ionization mass spectrometry.

PubMed

Fürmeier, Sven; Metzger, Jürgen O

2004-11-10

The coupling of a simple microreactor to an atmospheric pressure ion source, such as electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI), allows the investigation of reactions in solution by mass spectrometry. The tris(p-bromophenyl)aminium hexachloroantimonate (1(*)(+)SbCl(6)(-))-initiated reactions of phenylvinylsulfide (2) and cyclopentadiene (3) and of trans-anethole (5) and isoprene (6) and the dimerization of 1,3-cyclohexadiene (8) to give the respective Diels-Alder products were studied. These preparatively interesting reactions proceed as radical cation chain reactions via the transient radical cations of the respective dienophiles and of the respective Diels-Alder addition products. These radical cations could be detected directly and characterized unambiguously in the reacting solution by ESI-MS-MS. The identity was confirmed by comparison with MS-MS spectra of the authentic radical cations obtained by APCI-MS and by CID experiments of the corresponding molecular ions generated by EI-MS. In addition, substrates and products could be monitored easily in the reacting solution by APCI-MS.

Pulse radiolysis studies of 3,5-dimethyl pyrazole derivatives of selenoethers.

PubMed

Barik, Atanu; Singh, Beena G; Sharma, Asmita; Jain, Vimal K; Priyadarsini, K Indira

2014-11-06

One electron redox reaction of two asymmetric 3,5-dimethyl pyrazole derivatives of selenoethers attached to ethanoic acid (DPSeEA) and propionic acid (DPSePA) were studied by pulse radiolysis technique using transient absorption detection. The reaction of the hydroxyl ((•)OH) radical with DPSeEA or DPSePA at pH 7 produced transients absorbing at 500 nm and at 300 nm, respectively. The absorbance at 500 nm increased with increasing parent concentration indicating formation of dimer radical cations. From the absorbance changes, the equilibrium constants for the formation of dimer radical cation of DPSeEA and DPSePA were estimated as 2020 and 1608 M(-1), respectively. The rate constants at pH 7 for the reaction of the (•)OH radical with DPSeEA and DPSePA were determined to be 9.6 × 10(9) and 1.4 × 10(10) M(-1) s(-1), respectively. The dimer radical cation of DPSeEA and DPSePA decayed by first order kinetics with a rate constant of 2.8 × 10(4) and 5.5 × 10(3) s(-1), respectively. The yield of radical cations of DPSeEA and DPSePA were estimated from the secondary electron transfer reaction, which corresponds to 38% and 48% of (•)OH radical yield, respectively. Some fraction of monomer radical cation undergoes decarboxylation reaction, and the yield of decarboxylation was 25% and 20% for DPSeEA and DPSePA, respectively. These results have implication in understanding their antioxidant activity. The reaction of trichloromethyl peroxyl radical, glutathione, and ascorbic acid further support their antioxidant behavior.

Additional consumption of one egg per day increases serum lutein plus zeaxanthin concentration and lowers oxidized low-density lipoprotein in moderately hypercholesterolemic males.

PubMed

Kishimoto, Yoshimi; Taguchi, Chie; Saita, Emi; Suzuki-Sugihara, Norie; Nishiyama, Hiroshi; Wang, Wei; Masuda, Yasunobu; Kondo, Kazuo

2017-09-01

The egg is a nutrient-dense food and contains antioxidative carotenoids, lutein and zeaxanthin, but its impact on serum cholesterol levels has been a matter of concern, especially for individuals who have high serum cholesterol levels. We conducted this study to determine whether and how the daily additional consumption of one egg affects serum lipid profiles and parameters of LDL oxidation in moderately hypercholesterolemic males. Nineteen male Japanese adults (total cholesterol [TC]>5.2mmol/L) participated, consuming one soft boiled egg per day for 4weeks in addition to their habitual diet. Despite the significant increase in their intake of dietary cholesterol during the intervention period, the subjects' serum concentrations of TC and low-density lipoprotein cholesterol (LDL-C) did not increase. Their serum malondialdehyde modified low-density lipoprotein (MDA-LDL) concentrations were significantly decreased and their LDL oxidation lag times, reflecting the resistance of free-radical-induced LDL lipid peroxidation (ex vivo), was prolonged after 2 and 4weeks. At weeks 2 and 4, the subjects' serum lutein+zeaxanthin concentrations were significantly higher than their baseline values and showed both an inverse relation with MDA-LDL and a positive relationship with the LDL oxidation lag time. These data showed that in moderately hypercholesterolemic males, the additional consumption of one egg per day for 4weeks did not have adverse effects on serum TC or LDL-C, and it might reduce the susceptibility of LDL to oxidation through an increase in the serum lutein and zeaxanthin concentrations. Copyright © 2017 Elsevier Ltd. All rights reserved.

Nature and kinetic analysis of carbon-carbon bond fragmentation reactions of cation radicals derived from SET-oxidation of lignin model compounds.

PubMed

Cho, Dae Won; Parthasarathi, Ramakrishnan; Pimentel, Adam S; Maestas, Gabriel D; Park, Hea Jung; Yoon, Ung Chan; Dunaway-Mariano, Debra; Gnanakaran, S; Langan, Paul; Mariano, Patrick S

2010-10-01

Features of the oxidative cleavage reactions of diastereomers of dimeric lignin model compounds, which are models of the major types of structural units found in the lignin backbone, were examined. Cation radicals of these substances were generated by using SET-sensitized photochemical and Ce(IV) and lignin peroxidase promoted oxidative processes, and the nature and kinetics of their C-C bond cleavage reactions were determined. The results show that significant differences exist between the rates of cation radical C1-C2 bond cleavage reactions of 1,2-diaryl-(β-1) and 1-aryl-2-aryloxy-(β-O-4) propan-1,3-diol structural units found in lignins. Specifically, under all conditions C1-C2 bond cleavage reactions of cation radicals of the β-1 models take place more rapidly than those of the β-O-4 counterparts. The results of DFT calculations on cation radicals of the model compounds show that the C1-C2 bond dissociation energies of the β-1 lignin model compounds are significantly lower than those of the β-O-4 models, providing clear evidence for the source of the rate differences.

Geometrical isomerization of carotenoids mediated by cation radical/dication formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, G.; Wei, C.C.; Jeevarajan, A.S.

1996-03-28

Electrochemical oxidation of all-trans-canthaxanthin and {beta}-carotene in dichloromethane leads to significant trans-to-cis isomerization, with cis isomers accounting for about 40% of the products formed. The electrochemically generated isomers were separated by reverse-phase high-performance liquid chromatography and identified as 9-cis, 13-cis, 15-cis, and 9,13-di-cis isomers of the carotenoids by {sup 1}H-NMR spectroscopy and optical spectroscopy (Q ratio). The results of simultaneous bulk electrolysis and optical absorption spectroscopy indicate the following isomerization mechanism: the all-trans cation radicals and/or dications formed by electrochemical oxidation of all-trans-carotenoids can easily undergo geometrical isomerization to form cis cation radicals and/or dications. The latter are converted bymore » the comproportionation equilibrium to cation radicals which are then transformed to neutral cis-carotenoids by exchanging one electron with neutral carotenoids. AM1 molecular orbital calculations, which show that the energy barriers of configurational transformation from trans to cis are much lower in the cation radical and dication species than in the neutral molecule, strongly support the first step of this mechanism. 36 refs., 5 figs., 2 tabs.« less

One-electron oxidation reactions of purine and pyrimidine bases in cellular DNA

PubMed Central

Cadet, Jean; Wagner, J. Richard; Shafirovich, Vladimir; Geacintov, Nicholas E.

2014-01-01

Purpose The aim of this survey is to critically review the available information on one-electron oxidation reactions of nucleobases in cellular DNA with emphasis on damage induced through the transient generation of purine and pyrimidine radical cations. Since the indirect effect of ionizing radiation mediated by hydroxyl radical is predominant in cells, efforts have been made to selectively ionize bases using suitable one-electron oxidants that consist among others of high intensity UVC laser pulses. Thus, the main oxidation product in cellular DNA was found to be 8-oxo-7,8-dihydroguanine as a result of direct bi-photonic ionization of guanine bases and indirect formation of guanine radical cations through hole transfer reactions from other base radical cations. The formation of 8-oxo-7,8-dihydroguanine and other purine and pyrimidine degradation products was rationalized in terms of the initial generation of related radical cations followed by either hydration or deprotonation reactions in agreement with mechanistic pathways inferred from detailed mechanistic studies. The guanine radical cation has been shown to be implicated in three other nucleophilic additions that give rise to DNA-protein and DNA-DNA cross-links in model systems. Evidence was recently provided for the occurrence of these three reactions in cellular DNA. Conclusion There is growing evidence that one-electron oxidation reactions of nucleobases whose mechanisms have been characterized in model studies involving aqueous solutions take place in a similar way in cells. It may also be pointed out that the above cross-linked lesions are only produced from the guanine radical cation and may be considered as diagnostic products of the direct effect of ionizing radiation. PMID:24369822

One-electron oxidation reactions of purine and pyrimidine bases in cellular DNA.

PubMed

Cadet, Jean; Wagner, J Richard; Shafirovich, Vladimir; Geacintov, Nicholas E

2014-06-01

The aim of this survey is to critically review the available information on one-electron oxidation reactions of nucleobases in cellular DNA with emphasis on damage induced through the transient generation of purine and pyrimidine radical cations. Since the indirect effect of ionizing radiation mediated by hydroxyl radical is predominant in cells, efforts have been made to selectively ionize bases using suitable one-electron oxidants that consist among others of high intensity UVC laser pulses. Thus, the main oxidation product in cellular DNA was found to be 8-oxo-7,8-dihydroguanine as a result of direct bi-photonic ionization of guanine bases and indirect formation of guanine radical cations through hole transfer reactions from other base radical cations. The formation of 8-oxo-7,8-dihydroguanine and other purine and pyrimidine degradation products was rationalized in terms of the initial generation of related radical cations followed by either hydration or deprotonation reactions in agreement with mechanistic pathways inferred from detailed mechanistic studies. The guanine radical cation has been shown to be implicated in three other nucleophilic additions that give rise to DNA-protein and DNA-DNA cross-links in model systems. Evidence was recently provided for the occurrence of these three reactions in cellular DNA. There is growing evidence that one-electron oxidation reactions of nucleobases whose mechanisms have been characterized in model studies involving aqueous solutions take place in a similar way in cells. It may also be pointed out that the above cross-linked lesions are only produced from the guanine radical cation and may be considered as diagnostic products of the direct effect of ionizing radiation.

Kinetic determinations of accurate relative oxidation potentials of amines with reactive radical cations.

PubMed

Gould, Ian R; Wosinska, Zofia M; Farid, Samir

2006-01-01

Accurate oxidation potentials for organic compounds are critical for the evaluation of thermodynamic and kinetic properties of their radical cations. Except when using a specialized apparatus, electrochemical oxidation of molecules with reactive radical cations is usually an irreversible process, providing peak potentials, E(p), rather than thermodynamically meaningful oxidation potentials, E(ox). In a previous study on amines with radical cations that underwent rapid decarboxylation, we estimated E(ox) by correcting the E(p) from cyclic voltammetry with rate constants for decarboxylation obtained using laser flash photolysis. Here we use redox equilibration experiments to determine accurate relative oxidation potentials for the same amines. We also describe an extension of these experiments to show how relative oxidation potentials can be obtained in the absence of equilibrium, from a complete kinetic analysis of the reversible redox kinetics. The results provide support for the previous cyclic voltammetry/laser flash photolysis method for determining oxidation potentials.

Pentachlorophenol radical cations generated on Fe(III)-montmorillonite initiate octachlorodibenzo-p-dioxin formation in clays: DFT and FTIR studies

PubMed Central

Gu, Cheng; Liu, Cun; Johnston, Cliff T.; Teppen, Brian J.; Li, Hui; Boyd, Stephen A.

2011-01-01

Octachlorodibenzodioxin (OCDD) forms spontaneously from pentachlorophenol (PCP) on the surfaces of Fe(III)-saturated smectite clay (1). Here, we used in situ FTIR methods and quantum mechanical calculations to determine the mechanism by which this reaction is initiated. As the clay was dehydrated, vibrational spectra showed new peaks that grew and then reversibly disappeared as the clay rehydrated. First principle DFT calculations of hydrated Fe-PCP clusters reproduced these transient FTIR peaks when inner-sphere complexation and concomitant electron transfer produced Fe(II) and PCP radical cations. Thus, our experimental (FTIR) and theoretical (quantum mechanical) results mutually support the hypothesis that OCDD formation on Fe-smectite surfaces is initiated by the reversible formation of metastable PCP radical cations via single electron transfer from PCP to Fe(III). The negatively charged clay surface apparently selects for this reaction mechanism by stabilizing PCP radical cations. PMID:21254769

Gamma and Ion-Beam Irradiation of DNA: Free Radical Mechanisms, Electron Effects, and Radiation Chemical Track Structure

PubMed Central

Sevilla, Michael D.; Becker, David; Kumar, Anil; Adhikary, Amitava

2016-01-01

The focus of our laboratory’s investigation is to study the direct-type DNA damage mechanisms resulting from γ-ray and ion-beam radiation-induced free radical processes in DNA which lead to molecular damage important to cellular survival. This work compares the results of low LET (γ−) and high LET (ion-beam) radiation to develop a chemical track structure model for ion-beam radiation damage to DNA. Recent studies on protonation states of cytosine cation radicals in the N1-substituted cytosine derivatives in their ground state and 5-methylcytosine cation radicals in ground as well as in excited state are described. Our results exhibit a radical signature of excitations in 5-methylcytosine cation radical. Moreover, our recent theoretical studies elucidate the role of electron-induced reactions (low energy electrons (LEE), presolvated electrons (epre−), and aqueous (or, solvated) electrons (eaq−)). Finally DFT calculations of the ionization potentials of various sugar radicals show the relative reactivity of these species. PMID:27695205

Gamma and ion-beam irradiation of DNA: Free radical mechanisms, electron effects, and radiation chemical track structure

NASA Astrophysics Data System (ADS)

Sevilla, Michael D.; Becker, David; Kumar, Anil; Adhikary, Amitava

2016-11-01

The focus of our laboratory's investigation is to study the direct-type DNA damage mechanisms resulting from γ-ray and ion-beam radiation-induced free radical processes in DNA which lead to molecular damage important to cellular survival. This work compares the results of low LET (γ-) and high LET (ion-beam) radiation to develop a chemical track structure model for ion-beam radiation damage to DNA. Recent studies on protonation states of cytosine cation radicals in the N1-substituted cytosine derivatives in their ground state and 5-methylcytosine cation radicals in ground as well as in excited state are described. Our results exhibit a radical signature of excitations in 5-methylcytosine cation radical. Moreover, our recent theoretical studies elucidate the role of electron-induced reactions (low energy electrons (LEE), presolvated electrons (epre-), and aqueous (or, solvated) electrons (eaq-)). Finally DFT calculations of the ionization potentials of various sugar radicals show the relative reactivity of these species.

The structure and photochemical transformation of cyclopropylacetylene radical cation as revealed by matrix EPR and quantum chemical study

NASA Astrophysics Data System (ADS)

Shiryaeva, Ekaterina S.; Tyurin, Daniil A.; Feldman, Vladimir I.

2012-05-01

The primary radical cation of cyclopropylacetylene was first characterized by EPR spectroscopy in low-temperature freon matrices. The assignment was confirmed by specific deuteration and quantum-chemical calculations at PBE0 and CCSD(T) levels. Photolysis with visible light led to irreversible transformation of the initial species to a ring-open structure. Detailed computational analysis of energy and magnetic resonance parameters of possible reaction products justified formation of pent-3-en-1-yne radical cation (presumably, a (Z)-isomer). This conclusion was also supported by the effect of specific deuteration.

Intramolecular Electron Transfer in Bis(tetraalkyl Hydrazine) and Bis(hydrazyl) Radical Cations.

NASA Astrophysics Data System (ADS)

Chang, Hao

A series of multicyclic bis(hydrazine) and bis(diazenium) compounds connected by relatively rigid hydrocarbon frameworks were prepared for the study of intramolecular electron transfer. The thermodynamics of electron removal of these compounds was investigated by cyclic voltammetry. The difference between the first and second oxidation potentials for the 4 sigma-bonded species was found to be larger for the bis(hydrazyl) radical systems than for the bis(hydrazines) by ca. 0.2 V (4.6 kcal/mol). This indicates a greater degree of interaction between the two nitrogen moieties for the hydrazyl systems, which is consistent with a greater degree of electronic coupling (H _{rm AB}) in these systems. The ESR spectra of the 4 sigma -bonded bis(hydrazine) radical cations indicate localized radical cations, which corresponds to slow intramolecular electron transfer on the ESR timescale. Conversely, the ESR spectra of the corresponding bis(hydrazyl) radical cation systems show nitrogen hyperfine splittings of a(4N) of ca. 4.5 G. This indicates that intramolecular electron transfer between the two nitrogen moieties is fast on the ESR timescale; the rate of exchange, k_ {rm ex} was estimated to be well above 1.9 times 10^8 s^{-1}. The contrast in exchange rates is consistent with the large geometry change upon oxidation which is characteristic of hydrazines. The hydrazyls undergo a smaller geometry change upon oxidation, and thus are expected to exhibit smaller inner-sphere reorganization energies. The optical spectra of these radical species was investigated in hopes of observing absorption bands corresponding to intramolecular electron transfer, as predicted by Hush theory. A broad absorption band was observed in the near IR region for the saturated bis(hydrazyl) radical cation system at 1060 nm (9420 cm^{-1} ) in acetonitrile at room temperature, and was accompanied by a narrower band at 1430 nm (6993 cm^ {-1}). The width of this band was estimated to be 545 nm (6496 cm^{-1}). A much higher energy band was observed in the UV/Vis region, at 520 nm (19,230 cm^{-1}) in acetonitrile for the corresponding bis(hydrazine) radical cation. The width of this band was estimated to be 240 nm (7211 cm^{-1}). The difference in the energies of these absorbance bands, E _{rm op}, reflects the different inner-sphere reorganization energies of the hydrazyl and hydrazine systems. Using Hush analysis, the electron coupling, H_{rm AB} , was calculated to be ca. 3.5 kcal/mol for the bis(hydrazyl) radical cation systems; a smaller value of H_{rm AB} of 1 kcal/mol was obtained for the bis(hydrazine) radical cations. This difference in electronic coupling is consistent with the faster rate of electron transfer, as well as the smaller inner-sphere reorganization energy in the bis(hydrazyl) systems.

17.9.3 Radical cations of diazo compounds

NASA Astrophysics Data System (ADS)

Davies, A. G.

This document is part of Subvolume E2 `Phosphorus-Centered Radicals, Radicals Centered on Other Heteroatoms, Organic Radical Ions' of Volume 26 `Magnetic Properties of Free Radicals' of Landolt-Börnstein Group II `Molecules and Radicals'.

A Theoretical Investigation of the Infrared Spectroscopic Properties of Closed-Shell Polycyclic Aromatic Hydrocarbon Cations

NASA Technical Reports Server (NTRS)

Hudgins, Douglas M.; Bauschlicher, Charles W., Jr.; Allamandola, Louis J.; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

Density functional theory has been employed to calculate the harmonic frequencies and intensities of a range of PAH cations which explore both size and electronic structure effects on the infrared spectroscopic of these species. The sample extends the size range of PAH species considered to more than 50 carbon atoms and includes several representatives from each of two heretofore unexplored categories of PAH cations: (1) fully benzenoid PAH cations whose carbon skeleton is composed of an odd number of carbon atoms and (2) protonated PAH cations. Unlike the radical electronic structures of the PAH cations that have been the subject of previous theoretical and experimental work, the species in these two classes have a closed-shell electronic configuration. The calculated spectra of circumcoronene, C54H18, in both neutral and (radical) cationic form are also reported and compared to those of the other species. Closed-shell species are inherently less reactive than radical (or open-shell) cations and are known to play a role in combustion chemistry. Since interstellar PAHs are typically exposed to abundant atomic hydrogen and are thought to originate under pseudo-combustion conditions in carbon-rich circumstellar shells, such species may represent an important component of the interstellar PAH population. Furthermore, species larger than 50 carbon atoms are more representative of the size of the typical interstellar PAH. Overall, as has been the case for previous studies of PAH radical cations, the general pattern of band positions and intensities are consistent with that of the interstellar infrared emission spectrum. In addition, the spectra of closed-shell and open-shell cations are found to converge with increasing molecular size and are found to be relatively similar for species containing about 50 carbon atoms.

What Hinders Electron Transfer Dissociation (ETD) of DNA Cations?

NASA Astrophysics Data System (ADS)

Hari, Yvonne; Leumann, Christian J.; Schürch, Stefan

2017-12-01

Radical activation methods, such as electron transfer dissociation (ETD), produce structural information complementary to collision-induced dissociation. Herein, electron transfer dissociation of 3-fold protonated DNA hexamers was studied to gain insight into the fragmentation mechanism. The fragmentation patterns of a large set of DNA hexamers confirm cytosine as the primary target of electron transfer. The reported data reveal backbone cleavage by internal electron transfer from the nucleobase to the phosphate linker leading either to a•/ w or d/ z• ion pairs. This reaction pathway contrasts with previous findings on the dissociation processes after electron capture by DNA cations, suggesting multiple, parallel dissociation channels. However, all these channels merely result in partial fragmentation of the precursor ion because the charge-reduced DNA radical cations are quite stable. Two hypotheses are put forward to explain the low dissociation yield of DNA radical cations: it is either attributed to non-covalent interactions between complementary fragments or to the stabilization of the unpaired electron in stacked nucleobases. MS3 experiments suggest that the charge-reduced species is the intact oligonucleotide. Moreover, introducing abasic sites significantly increases the dissociation yield of DNA cations. Consequently, the stabilization of the unpaired electron by π-π-stacking provides an appropriate rationale for the high intensity of DNA radical cations after electron transfer. [Figure not available: see fulltext.

The Chemistry of Separations Ligand Degradation by Organic Radical Cations

DOE PAGES

Mezyk, Stephen P.; Horne, Gregory P.; Mincher, Bruce J.; ...

2016-12-01

Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexants and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normalmore » alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R •+), carbon-centered radicals (R •), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R •+ as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with various ligands. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved.« less

The Chemistry of Separations Ligand Degradation by Organic Radical Cations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mezyk, Stephen P.; Horne, Gregory P.; Mincher, Bruce J.

Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexants and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normalmore » alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R •+), carbon-centered radicals (R •), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R •+ as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with various ligands. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved.« less

Dissociation dynamics of 3- and 4-nitrotoluene radical cations: Coherently driven C-NO2 bond homolysis

NASA Astrophysics Data System (ADS)

Ampadu Boateng, Derrick; Gutsev, Gennady L.; Jena, Puru; Tibbetts, Katharine Moore

2018-04-01

Monosubstituted nitrotoluenes serve as important model compounds for nitroaromatic energetic molecules such as trinitrotoluene. This work investigates the ultrafast nuclear dynamics of 3- and 4-nitrotoluene radical cations using femtosecond pump-probe measurements and the results of density functional theory calculations. Strong-field adiabatic ionization of 3- and 4-nitrotoluene using 1500 nm, 18 fs pulses produces radical cations in the ground electronic state with distinct coherent vibrational excitations. In both nitrotoluene isomers, a one-photon excitation with the probe pulse results in NO2 loss to form C7H7+, which exhibits out-of-phase oscillations in yield with the parent molecular ion. The oscillations in 4-nitrotoluene with a period of 470 fs are attributed to the torsional motion of the NO2 group based on theoretical results showing that the dominant relaxation pathway in 4-nitrotoluene radical cations involves the rotation of the NO2 group away from the planar geometry. The distinctly faster oscillation period of 216 fs in 3-nitrotoluene is attributed to an in-plane bending motion of the NO2 and CH3 moieties based on analysis of the normal modes. These results demonstrate that coherent nuclear motions determine the probability of C-NO2 homolysis in the nitrotoluene radical cations upon optical excitation within several hundred femtoseconds of the initial ionization event.

Characterization of a distonic isomer C6H5C+(OH)OCH2 of methyl benzoate radical cation by associative ion-molecule reactions

NASA Astrophysics Data System (ADS)

Dechamps, Noémie; Flammang, Robert; Gerbaux, Pascal; Nam, Pham-Cam; Nguyen, Minh Tho

2006-03-01

The C6H5C+(OH)OCH2 radical cation, formally a distonic isomer of ionized methyl benzoate, has been prepared by dissociative ionization of neopentyl benzoate, as earlier suggested by Audier et al. [H.E. Audier, A. Milliet, G. Sozzi, S. Hammerum, Org. Mass. Spectrom. 25 (1990) 44]. Its distonic character has now been firmly established by its high reactivity towards neutral methyl isocyanide (ionized methylene transfer) producing N-methyl ketenimine ions. Other mass spectrometric experiments and ab initio quantum chemical calculations also concur with each other pointing toward the existence of a stable distonic radical cation.

Watson-Crick Base Pair Radical Cation as a Model for Oxidative Damage in DNA.

PubMed

Feketeová, Linda; Chan, Bun; Khairallah, George N; Steinmetz, Vincent; Maitre, Philippe; Radom, Leo; O'Hair, Richard A J

2017-07-06

The deleterious cellular effects of ionizing radiation are well-known, but the mechanisms causing DNA damage are poorly understood. The accepted molecular events involve initial oxidation and deprotonation at guanine sites, triggering hydrogen atom abstraction reactions from the sugar moieties, causing DNA strand breaks. Probing the chemistry of the initially formed radical cation has been challenging. Here, we generate, spectroscopically characterize, and examine the reactivity of the Watson-Crick nucleobase pair radical cation in the gas phase. We observe rich chemistry, including proton transfer between the bases and propagation of the radical site in deoxyguanosine from the base to the sugar, thus rupturing the sugar. This first example of a gas-phase model system providing molecular-level details on the chemistry of an ionized DNA base pair paves the way toward a more complete understanding of molecular processes induced by radiation. It also highlights the role of radical propagation in chemistry, biology, and nanotechnology.

The lightest organic radical cation for charge storage in redox flow batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Jinhua; Pan, Baofei; Duan, Wentao

2016-08-25

Electrochemically reversible fluids of high energy density are promising materials for capturing the electrical energy generated from intermittent sources like solar and wind. To meet this technological challenge there is a need to understand the fundamental limits and interplay of electrochemical potential, stability and solubility in “lean” derivatives of redox-active molecules. Here we describe the process of molecular pruning, illustrated for 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene, a molecule known to produce a persistently stable, high-potential radical cation. By systematically shedding molecular fragments considered important for radical cation steric stabilization, we discovered a minimalistic structure that retains long-term stability in its oxidized form. Interestingly, wemore » find the tert-butyl groups are unnecessary; high stability of the radical cation and high solubility are both realized in derivatives having appropriately positioned arene methyl groups. These stability trends are rationalized by mechanistic considerations of the postulated decomposition pathways. We suggest that the molecular pruning approach will uncover lean redox active derivatives for electrochemical energy storage leading to materials with long-term stability and high intrinsic capacity.« less

Surface hopping investigation of the relaxation dynamics in radical cations

DOE PAGES

Assmann, Mariana; Weinacht, Thomas; Matsika, Spiridoula

2016-01-19

Ionization processes can lead to the formation of radical cations with population in several ionic states. In this study, we examine the dynamics of three radical cations starting from an excited ionic state using trajectory surface hopping dynamics in combination with multiconfigurational electronic structure methods. The efficiency of relaxation to the ground state is examined in an effort to understand better whether fragmentation of cations is likely to occur directly on excited states or after relaxation to the ground state. The results on cyclohexadiene, hexatriene, and uracil indicate that relaxation to the ground ionic state is very fast in thesemore » systems, while fragmentation before relaxation is rare. Ultrafast relaxation is facilitated by the close proximity of electronic states and the presence of two- and three-state conical intersections. Furthermore, examining the properties of the systems in the Franck-Condon region can give some insight into the subsequent dynamics.« less

EPR Spectroscopy of Radical Ions of a 2,3-Diamino-1,4-naphthoquinone Derivative.

PubMed

Tarábek, Ján; Wen, Jin; Dron, Paul I; Pospíšil, Lubomír; Michl, Josef

2018-05-18

We report the electron paramagnetic resonance spectra of the radical cation and radical anion of 1,2,2,3-tetramethyl-2,3-dihydro-1 H-naphtho[2,3- d]imidazole-4,9-dione (1) and its doubly 13 C labeled analogue 2, of interest for singlet fission. The hyperfine coupling constants are in excellent agreement with density functional theory calculations and establish the structures beyond doubt. Unlike the radical cation 1 •+ , the radical anion 1 •- and its parent 1 have pyramidalized nitrogen atoms and inequivalent methyl groups 15 and 16, in agreement with the calculations. The distinction is particularly clear with the labeled analogue 2 •- .

Absorption and electroabsorption spectra of carotenoid cation radical and dication

NASA Astrophysics Data System (ADS)

Krawczyk, Stanisław

1998-05-01

Radical cations and dications of two carotenoids astaxanthin and canthaxanthin were prepared by oxidation with FeCl 3 in fluorinated alcohols at room temperature. Absorption and electroabsorption (Stark effect) spectra were recorded for astaxanthin cations in mixed frozen matrices at temperatures about 160 K. The D 0→D 2 transition in cation radical is at 835 nm. The electroabsorption spectrum for the D 0→D 2 transition exhibits a negative change of molecular polarizability, Δ α=-1.2·10 -38 C·m 2/V (-105 A 3), which seems to originate from the change in bond order alternation in the ground state rather than from the electric field-induced interaction of D 1 and D 2 excited states. Absorption spectrum of astaxanthin dication is located at 715-717 nm, between those of D 0→D 2 in cation radical and S 0→S 2 in neutral carotenoid. Its shape reflects a short vibronic progression and strong inhomogeneous broadening. The polarizability change on electronic excitation, Δ α=2.89·10 -38 C·m 2/V (260 A 3), is five times smaller than in neutral astaxanthin. This value reflects the larger energetic distance from the lowest excited state to the higher excited states than in the neutral molecule.

Experimental and theoretical study of 2,6-difluorophenylnitrene, its radical cation, and their rearrangement products in argon matrices.

PubMed

Carra, Claudio; Nussbaum, Rafael; Bally, Thomas

2006-06-12

2,6-Difluorophenylnitrene was reinvestigated both experimentally, in Ar matrices at 10 K, and computationally, by DFT and CASSCF/CASPT2 calculations. Almost-pure samples of both neutral rearrangement products (the bicyclic azirine and the cyclic ketenimine) of a phenylnitrene were prepared and characterized for the first time. These samples were then subjected to X-irradiation in the presence of CH2Cl2 as an electron scavenger, which led to ionization of the neutral intermediates. Thereby, it was shown that only the phenylnitrene and the cyclic ketenimine yield stable radical cations, whereas the bicyclic azirine decays to both of these compounds on ionization. The cyclic ketenimine yields a novel aromatic azatropylium-type radical cation. The electronic structure of the title compound is discussed in detail, and its relation to those of the iso-pi-electronic benzyl radical and phenylcarbene is traced.

Pyridine radical cation and its fluorine substituted derivatives

USGS Publications Warehouse

Bondybey, V.E.; English, J.H.; Shiley, R.H.

1982-01-01

The spectra and relaxation of the pyridine cation and of several of its fluorinated derivatives are studied in low temperature Ne matrices. The ions are generated by direct photoionization of the parent compounds. Of the compounds studied, laser induced → and → fluorescence is observed only for the 2, 6‐difluoropyridine cation. The analysis of the spectrum indicates that the ion is planar both in the and states. The large variety in the spectroscopic and relaxation behavior of fluoropyridine radical cations is explained in terms of their electronic structure and of the differential shifts of the individual electronic states caused by the fluorine substitution.

Synthesis of the iron phthalocyaninate radical cation μ-nitrido dimer and its interaction with hydrogen peroxide

NASA Astrophysics Data System (ADS)

Grishina, E. S.; Makarova, A. S.; Kudrik, E. V.; Makarov, S. V.; Koifman, O. I.

2016-03-01

The iron phthalocyaninate μ-nitrido dimer radical cation, as well as the μ-nitrido dimer complexes of iron phthalocyaninate, was found to have high catalytic activity in the oxidation of organic compounds. It was concluded that this compound is of interest as a model of active intermediates—catalase and oxidase enzymes.

The role of organic solvent radical cations in separations ligand degradation

DOE PAGES

Mezyk, Stephen P.; Mincher, Bruce J.; Dhiman, Surajdevprakash B.; ...

2015-11-04

The dodecane radical cation reaction rate constant with CMPO was measured using ps electron pulse radiolysis/absorption spectroscopy as k = (1.30 ± 0.11) x 1010 M -1 s -1 in dodecane/0.10 M CH 2Cl 2 solution. No reactivity increase occurred when these solutions were pre-contacted with nitric acid, similar to the behavior observed for TODGA. To corroborate these kinetic data with steady-state radiolysis measurements, where acid pre contacted CMPO showed significantly less degradation, it is proposed that the dodecane radical cation always reacts directly with TODGA, but for CMPO the charge-transfer occurs with the CMPO•HNO 3 complex formed in themore » acid contacted solvent.« less

Effect of group electronegativity on electron transfer in bis(hydrazine) radical cations.

PubMed

Qin, Haimei; Zhong, Xinxin; Si, Yubing; Zhang, Weiwei; Zhao, Yi

2011-04-14

The radical cation of 4,10-ditert-butyl-5,9-diisopropyl-4,5,9,10-tetraazatetracyclo[6.2.2.2]-tetradecane (sBI4T(+)), as well as its substituted bis(hydrazine) radical cations, is chosen for the investigation of the electronegativity dependence of its intramolecular electron transfer. To do so, two parameters, reorganization energy and electronic coupling, are calculated with several ab initio approaches. It is found that the electronic couplings decrease with the increase of the group electronegativity while the reorganization energies do not show an explicit dependency. Furthermore, Marcus formula is employed to reveal those effect on the electron transfer rates. The predicted rates of electron transfer generally decrease with increasing group electronegativity, although not monotonically.

Analysis of LhcSR3, a Protein Essential for Feedback De-Excitation in the Green Alga Chlamydomonas reinhardtii

PubMed Central

Bonente, Giulia; Ballottari, Matteo; Truong, Thuy B.; Morosinotto, Tomas; Ahn, Tae K.; Fleming, Graham R.; Niyogi, Krishna K.; Bassi, Roberto

2011-01-01

In photosynthetic organisms, feedback dissipation of excess absorbed light energy balances harvesting of light with metabolic energy consumption. This mechanism prevents photodamage caused by reactive oxygen species produced by the reaction of chlorophyll (Chl) triplet states with O2. Plants have been found to perform the heat dissipation in specific proteins, binding Chls and carotenoids (Cars), that belong to the Lhc family, while triggering of the process is performed by the PsbS subunit, needed for lumenal pH detection. PsbS is not found in algae, suggesting important differences in energy-dependent quenching (qE) machinery. Consistent with this suggestion, a different Lhc-like gene product, called LhcSR3 (formerly known as LI818) has been found to be essential for qE in Chlamydomonas reinhardtii. In this work, we report the production of two recombinant LhcSR isoforms from C. reinhardtii and their biochemical and spectroscopic characterization. We found the following: (i) LhcSR isoforms are Chl a/b– and xanthophyll-binding proteins, contrary to higher plant PsbS; (ii) the LhcSR3 isoform, accumulating in high light, is a strong quencher of Chl excited states, exhibiting a very fast fluorescence decay, with lifetimes below 100 ps, capable of dissipating excitation energy from neighbor antenna proteins; (iii) the LhcSR3 isoform is highly active in the transient formation of Car radical cation, a species proposed to act as a quencher in the heat dissipation process. Remarkably, the radical cation signal is detected at wavelengths corresponding to the Car lutein, rather than to zeaxanthin, implying that the latter, predominant in plants, is not essential; (iv) LhcSR3 is responsive to low pH, the trigger of non-photochemical quenching, since it binds the non-photochemical quenching inhibitor dicyclohexylcarbodiimide, and increases its energy dissipation properties upon acidification. This is the first report of an isolated Lhc protein constitutively active in energy dissipation in its purified form, opening the way to detailed molecular analysis. Owing to its protonatable residues and constitutive excitation energy dissipation, this protein appears to merge both pH-sensing and energy-quenching functions, accomplished respectively by PsbS and monomeric Lhcb proteins in plants. PMID:21267060

Radiolysis of lignin: Prospective mechanism of high-temperature decomposition

NASA Astrophysics Data System (ADS)

Ponomarev, A. V.

2017-12-01

The range of the radiation-thermal processes resulting in conversion of lignin into monomeric phenols is considered. Statistically the most probable places of macromolecule ionization are aromatic units. Release of phenolic products from a lignin macromolecule is the multistage process beginning via fragmentation of primary cation-radicals. Reactions of electrons and small radicals with macromolecules, also as degradation of cation-radicals, result in formation of phenoxyl radicals. Macroradicals possess lower heat stability in comparison with macromolecules. Thermal decomposition of macroradicals leads to release of monohydric and dihydric phenols. The probability of benzenediols formation increases in the presence of alkanes. As noted, partial transformation of lignin into charcoal is inevitable.

Theoretical studies of alkyl radicals in the NaY and HY zeolites.

PubMed

Ghandi, Khashayar; Zahariev, Federico E; Wang, Yan Alexander

2005-08-18

Interplay of quantum mechanical calculations and experimental data on hyperfine coupling constants of ethyl radical in zeolites at several temperatures was engaged to study the geometries and binding energies and to predict the temperature dependence of hyperfine splitting of a series of alkyl radicals in zeolites for the first time. The main focus is on the hyperfine interaction of alkyl radicals in the NaY and HY zeolites. The hyperfine splitting for neutral free radicals and free radical cations is predicted for different zeolite environments. This information can be used to establish the nature of the muoniated alkyl radicals in the NaY and HY zeolites via muSR experiments. The muon hyperfine coupling constants of the ethane radical cation in these zeolites are very large with relatively little dependence on temperature. It was found that the intramolecular dynamics of alkyl free radicals are only weakly affected by their strong binding to zeolites. In contrast, the substrate binding has a significant effect on their intermolecular dynamics.

Characterization of the transient species generated by the photoionization of Berberine: A laser flash photolysis study

NASA Astrophysics Data System (ADS)

Cheng, Ling-Li; Wang, Mei; Zhu, Hui; Li, Kun; Zhu, Rong-Rong; Sun, Xiao-Yu; Yao, Si-De; Wu, Qing-Sheng; Wang, Shi-Long

2009-09-01

Using 266 nm laser flash photolysis it has been demonstrated that Berberine (BBR) in aqueous solution is ionized via a mono-photonic process giving a hydrated electron, anion radical that formed by hydrated electron react with steady state of BBR, and neutral radical that formed from rapid deprotonation of the radical cation of BBR. The quantum yield of photoionization is determined to be 0.03 at room temperature with KI solution used as a reference. Furthermore utilizing pH changing method and the SO 4rad - radical oxidation method, the assignment of radical cation of BBR was further confirmed, the p Ka value of it was calculated, and the related set up rate constant was also determined.

Combining UV photodissociation action spectroscopy with electron transfer dissociation for structure analysis of gas-phase peptide cation-radicals.

PubMed

Shaffer, Christopher J; Pepin, Robert; Tureček, František

2015-12-01

We report the first example of using ultraviolet (UV) photodissociation action spectroscopy for the investigation of gas-phase peptide cation-radicals produced by electron transfer dissociation. z-Type fragment ions (●) Gly-Gly-Lys(+), coordinated to 18-crown-6-ether (CE), are generated, selected by mass and photodissociated in the 200-400 nm region. The UVPD action spectra indicate the presence of valence-bond isomers differing in the position of the Cα radical defect, (α-Gly)-Gly-Lys(+) (CE), Gly-(α-Gly)-Lys(+) (CE) and Gly-Gly-(α-Lys(+))(CE). The isomers are readily distinguishable by UV absorption spectra obtained by time-dependent density functional theory (TD-DFT) calculations. In contrast, conformational isomers of these radical types are calculated to have similar UV spectra. UV photodissociation action spectroscopy represents a new tool for the investigation of transient intermediates of ion-electron reactions. Specifically, z-type cation radicals are shown to undergo spontaneous hydrogen atom migrations upon electron transfer dissociation. Copyright © 2015 John Wiley & Sons, Ltd.

Communication: Ion mobility of the radical cation dimers: (Naphthalene)2+• and naphthalene+•-benzene: Evidence for stacked sandwich and T-shape structures

NASA Astrophysics Data System (ADS)

Platt, Sean P.; Attah, Isaac K.; Aziz, Saadullah; El-Shall, M. Samy

2015-05-01

Dimer radical cations of aromatic and polycyclic aromatic molecules are good model systems for a fundamental understanding of photoconductivity and ferromagnetism in organic materials which depend on the degree of charge delocalization. The structures of the dimer radical cations are difficult to determine theoretically since the potential energy surface is often very flat with multiple shallow minima representing two major classes of isomers adopting the stacked parallel or the T-shape structure. We present experimental results, based on mass-selected ion mobility measurements, on the gas phase structures of the naphthalene+ṡ ṡ naphthalene homodimer and the naphthalene+ṡ ṡ benzene heterodimer radical cations at different temperatures. Ion mobility studies reveal a persistence of the stacked parallel structure of the naphthalene+ṡ ṡ naphthalene homodimer in the temperature range 230-300 K. On the other hand, the results reveal that the naphthalene+ṡ ṡ benzene heterodimer is able to exhibit both the stacked parallel and T-shape structural isomers depending on the experimental conditions. Exploitation of the unique structural motifs among charged homo- and heteroaromatic-aromatic interactions may lead to new opportunities for molecular design and recognition involving charged aromatic systems.

The formation of DNA sugar radicals from photoexcitation of guanine cation radicals.

PubMed

Shukla, Lata I; Pazdro, Robert; Huang, James; DeVreugd, Christopher; Becker, David; Sevilla, Michael D

2004-05-01

In this investigation of radical formation and reaction in gamma- irradiated DNA and model compounds, we report the conversion of the guanine cation radical (one-electron oxidized guanine, G(.+)) to the C1' sugar radical and another sugar radical at the C3' or C4' position (designated C3'(.)/C4'(.)) by visible and UV photolysis. Electron spin resonance (ESR) spectroscopic investigations were performed on salmon testes DNA as well as 5'-dGMP, 3'-dGMP, 2'-deoxyguanosine and other nucleosides/nucleotides as model systems. DNA samples (25- 150 mg/ml D(2)O) were prepared with Tl(3+) or Fe(CN)(3-)(6) as electron scavengers. Upon gamma irradiation of such samples at 77 K, the electron-gain path in the DNA is strongly suppressed and predominantly G(.+) is found; after UV or visible photolysis, the fraction of the C1' sugar radical increases with a concomitant reduction in the fraction of G(.+). In model systems, 3'- dGMP(+.) and 5'-dGMP(+.) were produced by attack of Cl(.-)(2) on the parent nucleotide in 7 M LiCl glass. Subsequent visible photolysis of the 3'-dGMP(+.) (77 K) results predominantly in formation of C1'(.) whereas photolysis of 5'-dGMP(+.) results predominantly in formation of C3'(.)/C4'(.). We propose that sugar radical formation is a result of delocalization of the hole in the electronically excited base cation radical into the sugar ring, followed by deprotonation at specific sites on the sugar.

Sugar Radical Formation by a Proton Coupled Hole Transfer in 2′-Deoxyguanosine Radical Cation (2′-dG•+): A Theoretical Treatment

PubMed Central

Kumar, Anil; Sevilla, Michael D.

2009-01-01

Previous experimental and theoretical work has established that electronic excitation of a guanine cation radical in nucleosides or in DNA itself leads to sugar radical formation by deprotonation from the dexoxyribose sugar. In this work we investigate a ground electronic state pathway for such sugar radical formation in a hydrated one electron oxidized 2′-deoxyguanosine (dG•+ + 7H2O), using density functional theory (DFT) with the B3LYP functional and the 6-31G* basis set. We follow the stretching of the C5′-H bond in dG•+ to gain an understanding of the energy requirements to transfer the hole from the base to sugar ring and then to deprotonate to proton acceptor sites in solution and on the guanine ring. The geometries of reactant (dG•+ + 7H2O), transition state (TS) for deprotonation of C5′ site and product (dG(•C5′, N7-H+) + 7 H2O) were fully optimized. The zero point energy (ZPE) corrected activation energy (TS) for the proton transfer (PT) from C5′ is calculated to be 9.0 kcal/mol and is achieved by stretching the C5′-H bond by 0.13 Å from its equilibrium bond distance (1.099 Å). Remarkably, this small bond stretch is sufficient to transfer the “hole” (positive charge and spin) from guanine to the C5′ site on the deoxyribose group. Beyond the TS, the proton (H+) spontaneously adds to water to form a hydronium ion (H3O+) as an intermediate. The proton subsequently transfers to the N7 site of the guanine (product). The 9 kcal/mol barrier suggests slow thermal conversion of the cation radical to the sugar radical but also suggests that localized vibrational excitations would be sufficient to induce rapid sugar radical formation in DNA base cation radicals. PMID:19754084

A Cell-Targeted Non-Cytotoxic Fluorescent Nanogel Thermometer Created with an Imidazolium-Containing Cationic Radical Initiator.

PubMed

Uchiyama, Seiichi; Tsuji, Toshikazu; Kawamoto, Kyoko; Okano, Kentaro; Fukatsu, Eiko; Noro, Takahiro; Ikado, Kumiko; Yamada, Sayuri; Shibata, Yuka; Hayashi, Teruyuki; Inada, Noriko; Kato, Masaru; Koizumi, Hideki; Tokuyama, Hidetoshi

2018-05-04

A cationic fluorescent nanogel thermometer based on thermo-responsive N-isopropylacrylamide and environment-sensitive benzothiadiazole was developed with a new azo compound bearing imidazolium rings as the first cationic radical initiator. This cationic fluorescent nanogel thermometer showed an excellent ability to enter live mammalian cells in a short incubation period (10 min), a high sensitivity to temperature variations in live cells (temperature resolution of 0.02-0.84 °C in the range 20-40 °C), and remarkable non-cytotoxicity, which permitted ordinary cell proliferation and even differentiation of primary cultured cells. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chain Reaction Polymerization.

ERIC Educational Resources Information Center

McGrath, James E.

1981-01-01

The salient features and importance of chain-reaction polymerization are discussed, including such topics as the thermodynamics of polymerization, free-radical polymerization kinetics, radical polymerization processes, copolymers, and free-radical chain, anionic, cationic, coordination, and ring-opening polymerizations. (JN)

Isomerization and fragmentation reactions of gaseous phenylarsane radical cations and phenylarsanyl cations. A study by tandem mass spectrometry and theoretical calculations.

PubMed

Letzel, Matthias; Kirchhoff, Dirk; Grützmacher, Hans-Friedrich; Stein, Daniel; Grützmacher, Hansjörg

2006-04-28

The unimolecular reactions of radical cations and cations derived from phenylarsane, C6H5AsH2 (1) and dideutero phenylarsane, C6H5AsD2 (1-d2), were investigated by methods of tandem mass spectrometry and theoretical calculations. The mass spectrometric experiments reveal that the molecular ion of phenylarsane, 1*+, exhibits different reactivity at low and high internal excess energy. Only at low internal energy the observed fragmentations are as expected, that is the molecular ion 1*+ decomposes almost exclusively by loss of an H atom. The deuterated derivative 1-d2 with an AsD2 group eliminates selectively a D atom under these conditions. The resulting phenylarsenium ion [C6H5AsH]+, 2+, decomposes rather easily by loss of the As atom to give the benzene radical cation [C6H6]*+ and is therefore of low abundance in the 70 eV EI mass spectrum. At high internal excess energy, the ion 1*+ decomposes very differently either by elimination of an H2 molecule, or by release of the As atom, or by loss of an AsH fragment. Final products of these reactions are either the benzoarsenium ion 4*+, or the benzonium ion [C6H7]+, or the benzene radical cation, [C6H6]*+. As key-steps, these fragmentations contain reductive eliminations from the central As atom under H-H or C-H bond formation. Labeling experiments show that H/D exchange reactions precede these fragmentations and, specifically, that complete positional exchange of the H atoms in 1*+ occurs. Computations at the UMP2/6-311+G(d)//UHF/6-311+G(d) level agree best with the experimental results and suggest: (i) 1*+ rearranges (activation enthalpy of 93 kJ mol(-1)) to a distinctly more stable (DeltaH(r)(298) = -64 kJ mol(-1)) isomer 1 sigma*+ with a structure best represented as a distonic radical cation sigma complex between AsH and benzene. (ii) The six H atoms of the benzene moiety of 1 sigma*+ become equivalent by a fast ring walk of the AsH group. (iii) A reversible isomerization 1+<==>1 sigma*+ scrambles eventually all H atoms over all positions in 1*+. The distonic radical cation 1*+ is predisposed for the elimination of an As atom or an AsH fragment. The calculations are in accordance with the experimentally preferred reactions when the As atom and the AsH fragment are generated in the quartet and triplet state, respectively. Alternatively, 1*(+) undergoes a reductive elimination of H2 from the AsH2 group via a remarkably stable complex of the phenylarsandiyl radical cation, [C6H5As]*+ and an H2 molecule.

Light-induced Conversion of Trp to Gly and Gly Hydroperoxide in IgG1

PubMed Central

Haywood, Jessica; Mozziconacci, Olivier; Allegre, Kevin M.; Kerwin, Bruce A.; Schöneich, Christian

2013-01-01

The exposure of IgG1 in aqueous solution to light with λ = 254 nm or λ > 295 nm yields products consistent with Trp radical cation formation followed by αC-βC cleavage of the Trp side chain. The resulting glycyl radicals are either reduced to Gly, or add oxygen prior to reduction to Gly hydroperoxide. Photoirradiation at λ = 254 nm targets Trp at positions 191 (light chain), 309 and 377 (heavy chain) while photoirradiation at λ > 295 nm targets Trp at position 309 (heavy chain). Mechanistically, the formation of Trp radical cations likely proceeds via photo-induced electron- or hydrogen-transfer to disulfide bonds, yielding thiyl radicals and thiols, where thiols may serve as reductants for the intermediary glycyl or glycylperoxyl radicals. PMID:23363477

Quantification of zeaxanthin stereoisomers and lutein in trout flesh using chiral high-performance liquid chromatography-diode array detection.

PubMed

Prado-Cabrero, Alfonso; Beatty, Stephen; Stack, Jim; Howard, Alan; Nolan, John M

2016-07-01

In our previous work we identified the presence of meso -zeaxanthin [(3R,3'S)-zeaxanthin] in trout flesh and skin (Nolan et al., 2014), but were not able to quantify this carotenoid with the method used at that time. In the present study, we developed a protocol that allows for the quantification of lutein and the three stereoisomers of zeaxanthin [(3R,3'R)-zeaxanthin, meso -zeaxanthin and (3S,3'S)-zeaxanthin] in fish flesh. We tested this protocol in two species of farmed trout ( Oncorhynchus mykiss and Salmo Trutta ), and we detected and quantified these carotenoids. The concentrations of each carotenoid detected (ranging from 1.18 ± 0.68 ng g -1 flesh for meso -zeaxanthin to 38.72 ± 15.87 ng g -1 flesh for lutein) were highly comparable for the two fish species tested. In conclusion, we report, for the first time, the concentrations of zeaxanthin stereoisomers (including meso -zeaxanthin) and lutein in trout flesh. This work adds further to the knowledge on the presence of these carotenoids in the human food chain.

Spectroscopic characterization of the iron-oxo intermediate in cytochrome P450.

PubMed

Jung, Christiane; Schünemann, Volker; Lendzian, Friedhelm; Trautwein, Alfred X; Contzen, Jörg; Galander, Marcus; Böttger, Lars H; Richter, Matthias; Barra, Anne-Laure

2005-10-01

From analogy to chloroperoxidase from Caldariomyces fumago, it is believed that the electronic structure of the intermediate iron-oxo species in the catalytic cycle of cytochrome P450 corresponds to an iron(IV) porphyrin-pi-cation radical (compound I). However, our recent studies on P450cam revealed that after 8 ms a tyrosine radical and iron(IV) were formed in the reaction of ferric P450 with external oxidants in the shunt pathway. The present study on the heme domain of P450BM3 (P450BMP) shows a similar result. In addition to a tyrosine radical, a contribution from a tryptophan radical was found in the electron paramagnetic resonance (EPR) spectra of P450BMP. Here we present comparative multi-frequency EPR (9.6, 94 and 285 GHz) and Mössbauer spectroscopic studies on freeze-quenched intermediates produced using peroxy acetic acid as oxidant for both P450 cytochromes. After 8 ms in both systems, amino acid radicals occurred instead of the proposed iron(IV) porphyrin-pi-cation radical, which may be transiently formed on a much faster time scale. These findings are discussed with respect to other heme thiolate proteins. Our studies demonstrate that intramolecular electron transfer from aromatic amino acids is a common feature in these enzymes. The electron transfer quenches the presumably transiently formed porphyrin-pi-cation radical, which makes it extremely difficult to trap compound I.

Molecular Level Understanding of the Factors Affecting the Stability of Dimethoxy Benzene Catholyte Candidates from First-Principles Investigations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Assary, Rajeev S.; Zhang, Lu; Huang, Jinhua

First-principles simulations are performed to gain molecular level insights into the factors affecting the stability of seven 1,4-dimethoxybenzene (DMB) derivatives. These molecules are potential catholyte candidates for nonaqueous redox flow battery systems. Computations are performed to predict oxidation potentials in various dielectric mediums, intrinsic-reorganization energies, and structural changes of these representative catholyte molecules during the redox process. In order to understand the stability of the DMB-based radical cations, the thermodynamic feasibility of the following reactions is computed using density functional theory: (a) deprotonation, (b) dimerization, (c) hydrolysis, and (d) demethylation. The computations indicate that radical cations of the 2,3-dimethyl andmore » 2,5-dimethyl derivatives are the most stable among the DMB derivatives considered in this study. In the presence of solvents with high-proton solvating ability (water, DMSO, acetonitrile), degradation of cation radical occurring via deprotonation is the most likely mechanism. In the presence of solvents such as propylene carbonate (PC), demethylation was found to be the most likely reaction that causes degradation of radical cations. From the computed enthalpy of activation (Delta H-double dagger) for a demethylation reaction in PC, the 2,5-dimethyl DMB cation radical would exhibit better kinetic stability in comparison to the other candidates. Finally, this investigation suggests that computational studies of structural properties such as redox potentials, reorganization energies, and the computed reaction energetics (deprotonation and demethylation) of charged species can be used to predict the relative stability of a large set of molecules required for the discovery of novel redox active materials for flow battery applications« less

Molecular Level Understanding of the Factors Affecting the Stability of Dimethoxy Benzene Catholyte Candidates from First-Principles Investigations

DOE PAGES

Assary, Rajeev S.; Zhang, Lu; Huang, Jinhua; ...

2016-06-14

First-principles simulations are performed to gain molecular level insights into the factors affecting the stability of seven 1,4-dimethoxybenzene (DMB) derivatives. These molecules are potential catholyte candidates for nonaqueous redox flow battery systems. Computations are performed to predict oxidation potentials in various dielectric mediums, intrinsic-reorganization energies, and structural changes of these representative catholyte molecules during the redox process. In order to understand the stability of the DMB-based radical cations, the thermodynamic feasibility of the following reactions is computed using density functional theory: (a) deprotonation, (b) dimerization, (c) hydrolysis, and (d) demethylation. The computations indicate that radical cations of the 2,3-dimethyl andmore » 2,5-dimethyl derivatives are the most stable among the DMB derivatives considered in this study. In the presence of solvents with high-proton solvating ability (water, DMSO, acetonitrile), degradation of cation radical occurring via deprotonation is the most likely mechanism. In the presence of solvents such as propylene carbonate (PC), demethylation was found to be the most likely reaction that causes degradation of radical cations. From the computed enthalpy of activation (Delta H-double dagger) for a demethylation reaction in PC, the 2,5-dimethyl DMB cation radical would exhibit better kinetic stability in comparison to the other candidates. Finally, this investigation suggests that computational studies of structural properties such as redox potentials, reorganization energies, and the computed reaction energetics (deprotonation and demethylation) of charged species can be used to predict the relative stability of a large set of molecules required for the discovery of novel redox active materials for flow battery applications« less

The lyocell process: Cellulose solutions in N-Methylmorpholine-N-oxide (NMMO) - degradation processes and stabilizers

Treesearch

Thomas Rosenau; Thomas Elder; Antje Potthast; Sixta Herbert; Paul Kosma

2003-01-01

Homolytic (radical) reactions in the system cellulose / N-methylmorpholine-N-oxide (NMMO, 1) involve a primary, nitrogen-centered cation radical (2), and two secondary, carbon-centered radical species (3, 4). Radical formation &om NMMO is strongly promoted by transition metal ions.

Chronoamperometric study of the films formed by 4,4'-bipyridyl cation radical salts on mercury in the presence of iodide ions: consecutive two-dimensional phase transitions.

PubMed

Gómez, L; Ruiz, J J; Camacho, L; Rodríguez-Amaro, R

2005-01-04

This paper reports a new mathematical model for consecutive two-dimensional phase transitions that accounts for the chronoamperometric behavior observed in the formation of electrochemical phases by 4,4'-bipyridyl cation radical (BpyH(2)(*)(+)) on mercury in aqueous iodide solutions. Also, a new interpretation for the induction time is proposed.

Monovalent Cation Activation of the Radical SAM Enzyme Pyruvate Formate-Lyase Activating Enzyme.

PubMed

Shisler, Krista A; Hutcheson, Rachel U; Horitani, Masaki; Duschene, Kaitlin S; Crain, Adam V; Byer, Amanda S; Shepard, Eric M; Rasmussen, Ashley; Yang, Jian; Broderick, William E; Vey, Jessica L; Drennan, Catherine L; Hoffman, Brian M; Broderick, Joan B

2017-08-30

Pyruvate formate-lyase activating enzyme (PFL-AE) is a radical S-adenosyl-l-methionine (SAM) enzyme that installs a catalytically essential glycyl radical on pyruvate formate-lyase. We show that PFL-AE binds a catalytically essential monovalent cation at its active site, yet another parallel with B 12 enzymes, and we characterize this cation site by a combination of structural, biochemical, and spectroscopic approaches. Refinement of the PFL-AE crystal structure reveals Na + as the most likely ion present in the solved structures, and pulsed electron nuclear double resonance (ENDOR) demonstrates that the same cation site is occupied by 23 Na in the solution state of the as-isolated enzyme. A SAM carboxylate-oxygen is an M + ligand, and EPR and circular dichroism spectroscopies reveal that both the site occupancy and the identity of the cation perturb the electronic properties of the SAM-chelated iron-sulfur cluster. ENDOR studies of the PFL-AE/[ 13 C-methyl]-SAM complex show that the target sulfonium positioning varies with the cation, while the observation of an isotropic hyperfine coupling to the cation by ENDOR measurements establishes its intimate, SAM-mediated interaction with the cluster. This monovalent cation site controls enzyme activity: (i) PFL-AE in the absence of any simple monovalent cations has little-no activity; and (ii) among monocations, going down Group 1 of the periodic table from Li + to Cs + , PFL-AE activity sharply maximizes at K + , with NH 4 + closely matching the efficacy of K + . PFL-AE is thus a type I M + -activated enzyme whose M + controls reactivity by interactions with the cosubstrate, SAM, which is bound to the catalytic iron-sulfur cluster.

Formation of tryptophan radicals in irradiated aqueous solutions of hexachloroplatinate(IV): a flash photolysis study.

PubMed

Zang, L; Rodgers, M A

1999-10-01

The oxidation of tryptophan photosensitized by PtCl6(2-) has been investigated in aqueous solutions at different pH using nanosecond laser flash photolysis. Cationic and neutral radicals of tryptophan were detected at pH 2.8 and 8.5, respectively. The generation of the radical was attributed to oxidation by Cl2- that was formed from the homolytic bond cleavage in the excited state of PtCl6(2-). The bimolecular rate constant derived from the kinetics analysis, 2.8 +/- 0.2 x 10(9) M-1 s-1, is in good agreement with the value obtained in earlier pulse radiolysis studies. Both the cationic and neutral radicals decayed by second-order kinetics, consistent with the dimerization process.

Anodic Cyclization Reactions and the Mechanistic Strategies That Enable Optimization.

PubMed

Feng, Ruozhu; Smith, Jake A; Moeller, Kevin D

2017-09-19

Oxidation reactions are powerful tools for synthesis because they allow us to reverse the polarity of electron-rich functional groups, generate highly reactive intermediates, and increase the functionality of molecules. For this reason, oxidation reactions have been and continue to be the subject of intense study. Central to these efforts is the development of mechanism-based strategies that allow us to think about the reactive intermediates that are frequently central to the success of the reactions and the mechanistic pathways that those intermediates trigger. For example, consider oxidative cyclization reactions that are triggered by the removal of an electron from an electron-rich olefin and lead to cyclic products that are functionalized for further elaboration. For these reactions to be successful, the radical cation intermediate must first be generated using conditions that limit its polymerization and then channeled down a productive desired pathway. Following the cyclization, a second oxidation step is necessary for product formation, after which the resulting cation must be quenched in a controlled fashion to avoid undesired elimination reactions. Problems can arise at any one or all of these steps, a fact that frequently complicates reaction optimization and can discourage the development of new transformations. Fortunately, anodic electrochemistry offers an outstanding opportunity to systematically probe the mechanism of oxidative cyclization reactions. The use of electrochemical methods allows for the generation of radical cations under neutral conditions in an environment that helps prevent polymerization of the intermediate. Once the intermediates have been generated, a series of "telltale indicators" can be used to diagnose which step in an oxidative cyclization is problematic for less successful transformation. A set of potential solutions to address each type of problem encountered has been developed. For example, problems with the initial cyclization reaction leading to either polymerization of the radical cation, elimination of a proton from or solvent trapping of that intermediate, or solvent trapping of the radical cation can be identified in the proton NMR spectrum of the crude reaction material. Such an NMR spectrum shows retention of the trapping group. The problems can be addressed by tuning the radical cation, altering the trapping group, or channeling the reactive intermediate down a radical pathway. Specific examples each are shown in this Account. Problems with the second oxidation step can be identified by poor current efficiency or general decomposition in spite of cyclic voltammetry evidence for a rapid cyclization. Solutions involve improving the oxidation conditions for the radical after cyclization by either the addition of a properly placed electron-donating group in the substrate or an increase in the concentration of electrolyte in the reaction (a change that stabilizes the cation generated from the second oxidation step). Problems with the final cation typically lead to overoxidation. Solutions to this problem require an approach that either slows down elimination side reactions or changes the reaction conditions so that the cation can be quickly trapped in an irreversible fashion. Again, this Account highlights these strategies along with the specific experimental protocols utilized.

Theoretical study on the electronic, structural, properties and reactivity of a series of mono-, di-, tri- and tetrachlorothiophenes as well as corresponding radical cation forms as monomers for conducting polymers.

PubMed

Shirani Il Beigi, Hossein; Jameh-Bozorghi, Saeed

2011-03-14

In this paper, electrical and structural properties of mono-, di-, tri- and tetrachlorothiophenes and their radical cations have been studied using the density functional theory and B3LYP method with 6-311++G** basis set. The effects of the number and position of the substituent of chlorine atoms on the properties of the thiophene ring for all chlorothiophenes and their radical cations have been studied. Vibrational frequencies, nuclear chemical shielding constants, spin-density distribution, size and direction of dipole moment vector, ionization potential, electric polarizabilities and NICS values of these compounds have been calculated as well. The analysis of these data showed that double bonds in 3-chlorothiophene are more delocalized and it is the best possible candidate monomer among all chlorothiophenes for the synthesis of corresponding conducting polymers with modified characteristics.

Notable effects of metal salts on UV-vis absorption spectra of α-, β-, γ-, and δ-tocopheroxyl radicals in acetonitrile solution. The complex formation between tocopheroxyls and metal cations.

PubMed

Mukai, Kazuo; Kohno, Yutaro; Ouchi, Aya; Nagaoka, Shin-ichi

2012-08-02

The measurements of the UV-vis absorption spectra of α-, β-, γ-, and δ-tocopheroxyl (α-, β-, γ-, and δ-Toc(•)) radicals were performed by reacting aroxyl (ArO(•)) radical with α-, β-, γ-, and δ-tocopherol (α-, β-, γ-, and δ-TocH), respectively, in acetonitrile solution including three kinds of alkali and alkaline earth metal salts (LiClO(4), NaClO(4), and Mg(ClO(4))(2)) (MX or MX(2)), using stopped-flow spectrophotometry. The maximum wavelengths (λ(max)) of the absorption spectra of the α-, β-, γ-, and δ-Toc(•) located at 425-428 nm without metal salts increased with increasing concentrations of metal salts (0-0.500 M) in acetonitrile and approached some constant values, suggesting (Toc(•)···M(+) (or M(2+))) complex formations. Similarly, the values of the apparent molar extinction coefficient (ε(max)) increased drastically with increasing concentrations of metal salts in acetonitrile and approached some constant values. The result suggests that the formations of Toc(•) dimers were suppressed by the metal ion complex formations of Toc(•) radicals. The stability constants (K) were determined for Li(+), Na(+), and Mg(2+) complexes of α-, β-, γ-, and δ-Toc(•). The K values increased in the order of NaClO(4) < LiClO(4) < Mg(ClO(4))(2), being independent of the kinds of Toc(•) radicals. Furthermore, the K values increased in the order of δ- < γ- < β- < α-Toc(•) radicals for each metal salt. The alkali and alkaline earth metal salts having a smaller ionic radius of the cation and a larger charge of the cation gave a larger shift of the λ(max) value, a larger ε(max) value, and a larger K value. The result of the DFT molecular orbital calculations indicated that the α-, β-, γ-, and δ-Toc(•) radicals were stabilized by the (1:1) complex formation with metal cations (Li(+), Na(+), and Mg(2+)). Stabilization energy (E(S)) due to the complex formation increased in the order of Na(+) < Li(+) < Mg(2+) complexes, being independent of the kinds of Toc(•) radicals. The calculated result also indicated that the metal cations coordinate to the O atom at the sixth position of α-, β-, γ-, and δ-Toc(•) radicals.

Catalytic mechanism of cationic red GTL at wide pH using the Mo-Zn-Al-O nanocatalyst under room conditions.

PubMed

Xu, Yin; Li, Xiaoyi; Sun, Dezhi

2014-09-01

Catalytic mechanism of cationic red GTL at wide pH using the Mo-Zn-Al-O nanocatalyst under room conditions was investigated. The experimental results indicate that initial pH significantly affected the removal of cationic red GTL, the removal of COD, the pH value and residual oxygen in the reaction. In the range of pH value from 4 to 10, decolorization of cationic red GTL was almost above 90%. COD removal efficiency was enhanced with the decrease of pH in CWAO process and 79% of the COD was removed at pH 4.0, whereas only 57% COD removal was observed at pH 10.0. The terminal pH was in the range of 5.0-6.0 and the highest terminal concentrations of aqueous oxygen with 5.5 mg/L were observed at pH = 4.0. The radical inhibition experiments also carried out and the generation of *OH and 1O2 in catalytic wet air oxidation process were detected. It was found that the degradation of cationic red GTL occurs mainly via oxidation by 1O2 radical generated by Mo-Zn-Al-O nanocatalyst under acid conditions and *OH radical under alkaline conditions.

Peroxyl radical reactions with carotenoids in microemulsions: Influence of microemulsion composition and the nature of peroxyl radical precursor.

PubMed

El-Agamey, Ali; McGarvey, David J

2016-01-01

The reactions of acetylperoxyl radicals with different carotenoids (7,7'-dihydro-β-carotene and ζ-carotene) in SDS and CTAC microemulsions of different compositions were investigated using laser flash photolysis (LFP) coupled with kinetic absorption spectroscopy. The primary objective of this study was to explore the influence of microemulsion composition and the type of surfactant used on the yields and kinetics of various transients formed from the reaction of acetylperoxyl radicals with carotenoids. Also, the influence of the site (hydrocarbon phases or aqueous phase) of generation of the peroxyl radical precursor was examined by using 4-acetyl-4-phenylpiperidine hydrochloride (APPHCl) and 1,1-diphenylacetone (11DPA) as water-soluble and lipid-soluble peroxyl radical precursors, respectively. LFP of peroxyl radical precursors with 7,7'-dihydro-β-carotene (77DH) in different microemulsions gives rise to the formation of three distinct transients namely addition radical (λmax=460 nm), near infrared transient1 (NIR, λmax=700 nm) and 7,7'-dihydro-β-carotene radical cation (77DH(•+), λmax=770 nm). In addition, for ζ-carotene (ZETA) two transients (near infrared transient1 (NIR1, λmax=660 nm) and ζ-carotene radical cation (ZETA(•+), λmax=730-740 nm)) are generated following LFP of peroxyl radical precursors in the presence of ζ-carotene (ZETA) in different microemulsions. The results show that the composition of the microemulsion strongly influences the observed yield and kinetics of the transients formed from the reactions of peroxyl radicals (acetylperoxyl radicals) with carotenoids (77DH and ZETA). Also, the type of surfactant used in the microemulsions influences the yield of the transients formed. The dependence of the transient yields and kinetics on microemulsion composition (or the type of surfactant used in the microemulsion) can be attributed to the change of the polarity of the microenvironment of the carotenoid. Furthermore, the nature of the peroxyl radical precursor used (water-soluble or lipid-soluble peroxyl radical precursors) has little influence on the yields and kinetics of the transients formed from the reaction of peroxyl radicals with carotenoids. In the context of the interest in carotenoids as radical scavenging antioxidants, the fates of the addition radicals (formed from the reaction of carotenoid with peroxyl radicals) and carotenoid radical cations are discussed. Copyright © 2015 Elsevier Inc. All rights reserved.

Photodissociation of anisole and absolute photoionization cross-section of the phenoxy radical.

PubMed

Xu, Hong; Pratt, S T

2013-11-21

We have studied the photodissociation dynamics of anisole (C6H5OCH3) at 193 nm and determined the absolute photoionization cross-section of the phenoxy radical at 118.2 nm (10.486 eV) relative to the known cross-section of the methyl radical. Even at this energy, there is extensive fragmentation of the phenoxy radical upon photoionization, which is attributed to ionizing transitions that populate low-lying excited electronic states of the cation. For phenoxy radicals with less than ∼1 eV of internal energy, we find a cross-section for the production of the phenoxy cation of 14.8 ± 3.8 Mb. For radicals with higher internal energy, dissociative ionization is the dominant process, and for internal energies of ∼2.7-3.7 eV, we find a total cross-section (photoionization plus dissociative ionization) of 22.3 ± 4.1 Mb. The results are discussed relative to the recently reported photoionization cross-section of phenol.

Spirulina is an effective dietary source of zeaxanthin to humans

USDA-ARS?s Scientific Manuscript database

Zeaxanthin is a predominant xanthophyll in human eyes and may reduce the risk of cataracts and age-related macular degeneration. Spirulina is an algal food that contains a high concentration of zeaxanthin. In order to determine zeaxanthin bioavailability of spirulina for dietary supplementation in h...

Development of a Dunaliella tertiolecta Strain with Increased Zeaxanthin Content Using Random Mutagenesis

PubMed Central

Kim, Minjae; Ahn, Junhak; Jeon, Hancheol; Jin, EonSeon

2017-01-01

Zeaxanthin is a xanthophyll pigment that is regarded as one of the best carotenoids for the prevention and treatment of degenerative diseases. In the worldwide natural products market, consumers prefer pigments that have been produced from biological sources. In this study, a Dunaliella tertiolecta strain that has 10–15% higher cellular zeaxanthin content than the parent strain (zea1), was obtained by random mutagenesis using ethyl methanesulfonate (EMS) as a mutagen. This mutant, mp3, was grown under various salinities and light intensities to optimize culture conditions for zeaxanthin production. The highest cellular zeaxanthin content was observed at 1.5 M NaCl and 65–85 μmol photons·m−2·s−1, and the highest daily zeaxanthin productivity was observed at 0.6 M NaCl and 140–160 μmol photons·m−2·s−1. The maximal yield of zeaxanthin from mp3 in fed-batch culture was 8 mg·L−1, which was obtained at 0.6 M NaCl and 140–160 μmol photons·m−2·s−1. These results suggest that random mutagenesis with EMS is useful for generating D. tertiolecta strains with increased zeaxanthin content, and also suggest optimal culture conditions for the enhancement of biomass and zeaxanthin production by the zeaxanthin accumulating mutant strains. PMID:28635662

Development of a Dunaliella tertiolecta Strain with Increased Zeaxanthin Content Using Random Mutagenesis.

PubMed

Kim, Minjae; Ahn, Junhak; Jeon, Hancheol; Jin, EonSeon

2017-06-21

Zeaxanthin is a xanthophyll pigment that is regarded as one of the best carotenoids for the prevention and treatment of degenerative diseases. In the worldwide natural products market, consumers prefer pigments that have been produced from biological sources. In this study, a Dunaliella tertiolecta strain that has 10-15% higher cellular zeaxanthin content than the parent strain ( zea1 ), was obtained by random mutagenesis using ethyl methanesulfonate (EMS) as a mutagen. This mutant, mp3 , was grown under various salinities and light intensities to optimize culture conditions for zeaxanthin production. The highest cellular zeaxanthin content was observed at 1.5 M NaCl and 65-85 μmol photons·m -2 ·s -1 , and the highest daily zeaxanthin productivity was observed at 0.6 M NaCl and 140-160 μmol photons·m -2 ·s -1 . The maximal yield of zeaxanthin from mp3 in fed-batch culture was 8 mg·L -1 , which was obtained at 0.6 M NaCl and 140-160 μmol photons·m -2 ·s -1 . These results suggest that random mutagenesis with EMS is useful for generating D. tertiolecta strains with increased zeaxanthin content, and also suggest optimal culture conditions for the enhancement of biomass and zeaxanthin production by the zeaxanthin accumulating mutant strains.

Cooking processes increase bioactive compounds in organic and conventional green beans.

PubMed

Lima, Giuseppina Pace Pereira; Costa, Sergio Marques; Monaco, Kamila de Almeida; Uliana, Maira Rodrigues; Fernandez, Roberto Morato; Correa, Camila Renata; Vianello, Fabio; Cisneros-Zevallos, Luis; Minatel, Igor Otavio

2017-12-01

The influence of cooking methods on chlorophyl, carotenoids, polyamines, polyphenols contents and antioxidant capacity were analyzed in organic and conventional green beans. The initial raw material had a higher content of chlorophyl and total phenolics in conventional green beans, whereas organic cultive favored flavonoid content and antioxidant capacity. Polyamines and carotenoids were similar for the two crop systems. After the cooking process, carotenoids (β-carotene, lutein and zeaxanthin) increased. Microwave heating favored the enhancement of some polar compounds, whereas pressure cooking favored carotenoids. When we used the estimation of the radical scavenging activity by electron spin resonance (ESR) spectroscopy, a reduction of the DPPH radical signal in the presence of green bean extracts was observed, regardless of the mode of cultivation. The highest reduction of the ESR signal ocurred for microwave cooking in organic and conventional green beans, indicating a higher availability of antioxidants with this type of heat treatment.

Cation Radical Accelerated Nucleophilic Aromatic Substitution via Organic Photoredox Catalysis.

PubMed

Tay, Nicholas E S; Nicewicz, David A

2017-11-15

Nucleophilic aromatic substitution (S N Ar) is a direct method for arene functionalization; however, it can be hampered by low reactivity of arene substrates and their availability. Herein we describe a cation radical-accelerated nucleophilic aromatic substitution using methoxy- and benzyloxy-groups as nucleofuges. In particular, lignin-derived aromatics containing guaiacol and veratrole motifs were competent substrates for functionalization. We also demonstrate an example of site-selective substitutive oxygenation with trifluoroethanol to afford the desired trifluoromethylaryl ether.

The dynamical behavior of the s-trioxane radical cation-A low-temperature EPR and theoretical study.

PubMed

Naumov, Sergej S; Knolle, Wolfgang; Naumov, Sergej P; Pöppl, Andreas; Janovský, Igor

2014-10-28

The radical cation of s-trioxane, radiolytically generated in a freon (CF3CCl3) matrix, was studied in the 10-140 K temperature region. Reversible changes of the EPR spectra were observed, arising from both ring puckering and ring inversion through the molecular plane. The ESREXN program based on the Liouville density matrix equation, allowing the treatment of dynamical exchange, has been used to analyze the experimental results. Two limiting conformer structures of the s-trioxane radical cation were taken into account, namely "rigid" half-boat and averaged planar ones, differing strongly in their electron distribution. The spectrum due to the "rigid" half-boat conformer can be observed only at very low (<60 K) temperatures, when the exchange of conformers is very slow. Two transition states for interconversion by puckering and ring-inversion were identified, close in activation energy (2.3 and 3.0 kJ/mol calculated). Since the energy difference is very small, both processes set on at a comparable temperature. In the case of nearly complete equilibration (fast exchange) between six energetically equivalent structures at T > 120 K in CF3CCl3, a septet due to six equivalent protons (hfs splitting constant 5.9 mT) is observed, characteristic of the dynamically averaged planar geometry of the radical cation. DFT quantum chemical calculations and spectral simulation including intramolecular dynamical exchange support the interpretation.

Ambient Stable Radical Cations, Diradicaloid π-Dimeric Dications, Closed-Shell Dications, and Diradical Dications of Methylthio-Capped Rylenes.

PubMed

Qi, Qingbiao; Burrezo, Paula Mayorga; Phan, Hoa; Herng, Tun Seng; Gopalakrishna, Tullimilli Y; Zeng, Wangdong; Ding, Jun; Casado, Juan; Wu, Jishan

2017-06-01

Radical cations and dications of π-conjugated systems play vital roles in organic electronic devices, organic conductors, and conducting polymers. Their structures, charge and spin distribution, and mechanism of charge transport are of great interest. In this article, radical cations and dications of a series of newly synthesized methylthio-capped rylenes were synthesized and isolated. Their ground-state structures, physical properties, and solid-state packing were systematically investigated by various experimental methods, such as X-ray crystallographic analysis, UV/Vis/NIR absorption spectroscopy, (spectro-)electrochemistry, nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, superconducting quantum interference device, and Raman spectroscopy, assisted by DFT calculations. It was found that all the charged species show an exceptional stability under ambient air and light conditions due to the efficient spin and charge delocalization over the whole rylene backbone. The dication of hexarylene turned out to have an unusual open-shell singlet rather than closed-shell ground state, thus it can be described as a diradical dication. Dimerization was observed for the radical cations and even the dications in crystals due to the strong intermolecular antiferromagnetic spin-spin interaction and π-π interaction, which result in unique magnetic properties. Such intermolecular association was also observed in solution. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Combining the Power of Irmpd with Ion-Molecule Reactions: the Structure and Reactivity of Radical Ions of Cysteine and its Derivatives

NASA Astrophysics Data System (ADS)

Lesslie, Michael; Osburn, Sandra; Berden, Giel; Oomens, J.; Ryzhov, Victor

2015-06-01

Most of the work on peptide radical cations has involved protons as the source of charge. Nonetheless, using metal ions as charge sources often offers advantages like stabilization of the structure via multidentate coordination and the elimination of the "mobile proton". Moreover, characterization of metal-bound amino acids is of general interest as the interaction of peptide side chains with metal ions in biological systems is known to occur extensively. In the current study, we generate thiyl radicals of cysteine and homocysteine in the gas phase complexed to alkali metal ions. Subsequently, we utilize infrared multiple-photon dissociation (IRMPD) and ion-molecule reactions (IMR) to characterize the structure and reactivity of these radical ions. Our group has worked extensively with the cysteine-based radical cations and anions, characterizing the gas-phase reactivity and rearrangement of the amino acid and several of its derivatives. In a continuation of this work, we are perusing the effects of metal ions as the charge bearing species on the reactivity of the sulfur radical. Our S-nitroso chemistry can easily be used in conjunction with metal ion coordination to produce initial S-based radicals in peptide radical-metal ion complexes. In all cases we have been able to achieve radical formation with significant yield to study reactivity. Ion-molecule reactions of metallated radicals with allyl iodide, dimethyl disulfide, and allyl bromide have all shown decreasing reactivity going down group 1A. Recently, we determined the experimental IR spectra for the homocysteine radical cation with Li+, Na+, and K+ as the charge bearing species at the FELIX facility. For comparison, the protonated IR spectrum of homocysteine has previously been obtained by our group. A preliminary match of the IR spectra has been confirmed. Finally, calculations are underway to determine the bond distances of all the metal adduct structures.

Macular lutein and zeaxanthin are related to brain lutein and zeaxanthin in primates

USDA-ARS?s Scientific Manuscript database

The xanthophyll pigments lutein and zeaxanthin cross the blood-retina barrier to preferentially accumulate in the macular region of the neural retina. There they form macular pigment, protecting the retina from blue light damage and oxidative stress. Lutein and zeaxanthin also accumulate in brain t...

Role of lutein and zeaxanthin in visual and cognitive function throughout the lifespan

USDA-ARS?s Scientific Manuscript database

The relationship between lutein and zeaxanthin and visual and cognitive health throughout the lifespan is compelling. There is a variety of evidence to support a role for lutein and zeaxanthin in vision. Lutein's role in cognition has only recently been considered. Lutein and its isomer, zeaxanthin,...

Effect of Molecular Interactions on Electron-Transfer and Antioxidant Activity of Bis(alkanol)selenides: A Radiation Chemical Study.

PubMed

Kumar, Pavitra V; Singh, Beena G; Phadnis, Prasad P; Jain, Vimal K; Priyadarsini, K Indira

2016-08-16

Understanding electron-transfer processes is crucial for developing organoselenium compounds as antioxidants and anti-inflammatory agents. To find new redox-active selenium antioxidants, we have investigated one-electron-transfer reactions between hydroxyl ((.) OH) radical and three bis(alkanol)selenides (SeROH) of varying alkyl chain length, using nanosecond pulse radiolysis. (.) OH radical reacts with SeROH to form radical adduct, which is converted primarily into a dimer radical cation (>Se∴Se<)(+) and α-{bis(hydroxyl alkyl)}-selenomethine radical along with a minor quantity of an intramolecularly stabilized radical cation. Some of these radicals have been subsequently converted to their corresponding selenoxide, and formaldehyde. Estimated yield of these products showed alkyl chain length dependency and correlated well with their antioxidant ability. Quantum chemical calculations suggested that compounds that formed more stable (>Se∴Se<)(+) , produced higher selenoxide and lower formaldehyde. Comparing these results with those for sulfur analogues confirmed for the first time the distinctive role of selenium in making such compounds better antioxidants. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

On the time behaviour of the concentration of pyrazinium radical cations in the early stage of the Maillard reaction

NASA Astrophysics Data System (ADS)

Stoesser, Reinhard; Klein, Jeannette; Peschke, Simone; Zehl, Andrea; Cämmerer, Bettina; Kroh, Lothar W.

2007-08-01

During the early stage of the Maillard reaction pyrazinium radical cations were detected by ESR within the reaction system D-glucose/glycine. The spectra were characterized by completely resolved hyperfine structure. The partial pressure of oxygen and the radical concentrations were measured directly in the reaction mixture by ESR using solutions of the spin probe TEMPOL and of DPPH, respectively. There are quantitative and qualitative relations of the actual concentration of the radical ions to the partial pressure of oxygen, the temperature-time regime and the mechanical mixing of the reaction system. These macroscopic parameters significantly affect both the induction period and the velocity of the time-dependent formation of free radicals. From in situ variations of p(O 2) and p(Ar) including the connected mixing effects caused by the passing the gases through the reaction mixture, steric and chemical effects of the stabilization of the radical ions were established. The determination of suitable and relevant conditions for stabilization and subsequent radical reactions contributes to the elucidation of the macroscopically known antioxidant activity of Maillard products.

Infrared spectroscopy of ionized corannulene in the gas phase.

PubMed

Alvaro Galué, Héctor; Rice, Corey A; Steill, Jeffrey D; Oomens, Jos

2011-02-07

The gas-phase infrared spectra of radical cationic and protonated corannulene were recorded by infrared multiple-photon dissociation (IRMPD) spectroscopy using the IR free electron laser for infrared experiments. Electrospray ionization was used to generate protonated corannulene and an IRMPD spectrum was recorded in a Fourier-transform ion cyclotron resonance mass spectrometer monitoring H-loss as a function of IR frequency. The radical cation was produced by 193-nm UV photoionization of the vapor of corannulene in a 3D quadrupole trap and IR irradiation produces H, H(2), and C(2)H(x) losses. Summing the spectral response of the three fragmentation channels yields the IRMPD spectrum of the radical cation. The spectra were analyzed with the aid of quantum-chemical calculations carried out at various levels of theory. The good agreement of theoretical and experimental spectra for protonated corannulene indicates that protonation occurs on one of the peripheral C-atoms, forming an sp(3) hybridized carbon. The spectrum of the radical cation was examined taking into account distortions of the C(5v) geometry induced by the Jahn-Teller effect as a consequence of the degenerate (2)E(1) ground electronic state. As indicated by the calculations, the five equivalent C(s) minima are separated by marginal barriers, giving rise to a dynamically distorted system. Although in general the character of the various computed vibrational bands appears to be in order, only a qualitative match to the experimental spectrum is found. Along with a general redshift of the calculated frequencies, the IR intensities of modes in the 1000-1250 cm(-1) region show the largest discrepancy with the harmonic predictions. In addition to CH "in-plane" bending vibrations, these modes also exhibit substantial deformation of the pentagonal inner ring, which may relate directly to the vibronic interaction in the radical cation.

The effects of moderately high temperature on zeaxanthin accumulation and decay.

PubMed

Zhang, Ru; Kramer, David M; Cruz, Jeffrey A; Struck, Kimberly R; Sharkey, Thomas D

2011-09-01

Moderately high temperature reduces photosynthetic capacities of leaves with large effects on thylakoid reactions of photosynthesis, including xanthophyll conversion in the lipid phase of the thylakoid membrane. In previous studies, we have found that leaf temperature of 40°C increased zeaxanthin accumulation in dark-adapted, intact tobacco leaves following a brief illumination, but did not change the amount of zeaxanthin in light-adatped leaves. To investigate heat effects on zeaxanthin accumulation and decay, zeaxanthin level was monitored optically in dark-adapted, intact tobacco and Arabidopsis thaliana leaves at either 23 or 40°C under 45-min illumination. Heated leaves had more zeaxanthin following 3-min light but had less or comparable amounts of zeaxanthin by the end of 45 min of illumination. Zeaxanthin accumulated faster at light initiation and decayed faster upon darkening in leaves at 40°C than leaves at 23°C, indicating that heat increased the activities of both violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZE). In addition, our optical measurement demonstrated in vivo that weak light enhances zeaxanthin decay relative to darkness in intact leaves of tobacco and Arabidopsis, confirming previous observations in isolated spinach chloroplasts. However, the maximum rate of decay is similar for weak light and darkness, and we used the maximum rate of decay following darkness as a measure of the rate of ZE during steady-state light. A simulation indicated that high temperature should cause a large shift in the pH dependence of the amount of zeaxanthin in leaves because of differential effects on VDE and ZE. This allows for the reduction in ΔpH caused by heat to be offset by increased VDE activity relative to ZE.

Lutein/zeaxanthin for the treatment of age-related cataract: AREDS2 randomized trial report no. 4.

PubMed

Chew, Emily Y; SanGiovanni, John Paul; Ferris, Frederick L; Wong, Wai T; Agron, Elvira; Clemons, Traci E; Sperduto, Robert; Danis, Ronald; Chandra, Suresh R; Blodi, Barbara A; Domalpally, Amitha; Elman, Michael J; Antoszyk, Andrew N; Ruby, Alan J; Orth, David; Bressler, Susan B; Fish, Gary E; Hubbard, George B; Klein, Michael L; Friberg, Thomas R; Rosenfeld, Philip J; Toth, Cynthia A; Bernstein, Paul

2013-07-01

Age-related cataract is a leading cause of visual impairment in the United States. The prevalence of age-related cataract is increasing, with an estimated 30.1 million Americans likely to be affected by 2020. To determine whether daily oral supplementation with lutein/zeaxanthin affects the risk for cataract surgery. The Age-Related Eye Disease Study 2 (AREDS2), a multicenter, double-masked clinical trial, enrolled 4203 participants, aged 50 to 85 years, at risk for progression to advanced age-related macular degeneration. Participants were randomly assigned to daily placebo; lutein/zeaxanthin, 10mg/2mg; omega-3 long-chain polyunsaturated fatty acids, 1 g; or a combination to evaluate the effects on the primary outcome of progression to advanced age-related macular degeneration. Cataract surgery was documented at annual study examination with the presence of pseudophakia or aphakia, or reported during telephone calls at 6-month intervals between study visits. Annual best-corrected visual acuity testing was performed. A secondary outcome of AREDS2 was to evaluate the effects of lutein/zeaxanthin on the subsequent need for cataract surgery. A total of 3159 AREDS2 participants were phakic in at least 1 eye and 1389 of 6027 study eyes underwent cataract surgery during the study, with median follow-up of 4.7 years. The 5-year probability of progression to cataract surgery in the no lutein/zeaxanthin group was 24%. For lutein/zeaxanthin vs no lutein/zeaxanthin, the hazard ratios for progression to cataract surgery was 0.96 (95% CI, 0.84-1.10; P = .54). For participants in the lowest quintile of dietary intake of lutein/zeaxanthin, the hazard ratio comparing lutein/zeaxanthin vs no lutein/zeaxanthin for progression to cataract surgery was 0.68 (95% CI, 0.48-0.96; P = .03). The hazard ratio for 3 or more lines of vision loss was 1.03 (95% CI, 0.93-1.13; P = .61 for lutein/zeaxanthin vs no lutein/zeaxanthin). Daily supplementation with lutein/zeaxanthin had no statistically significant overall effect on rates of cataract surgery or vision loss. clinicaltrials.gov Identifier: NCT00345176.

Zeaxanthin-based dietary supplement and topical serum improve hydration and reduce wrinkle count in female subjects.

PubMed

Schwartz, Steve; Frank, Emily; Gierhart, Dennis; Simpson, Paula; Frumento, Robert

2016-12-01

Dietary modification, through supplementation and elimination diets, has become an area of interest to help slow skin aging, reduce symptom severity or prevent reoccurrence of certain dermatologic conditions [Clinical Dermatology vol. 31 (2013) 677-700]. Free radical components (reactive oxygen species or ROS) or lipid peroxide (LPO) is involved in the pathogenesis and progression of accelerated skin aging when prolonged oxidative stress occurs. The use of antioxidant-related therapies such as nutraceuticals is of particular interest in restoring skin homeostasis. Antioxidant carotenoid zeaxanthin is concentrated in the eye and skin tissue and believed to decrease the formation of ROS associated with UV light exposure. With zeaxanthin, phytoceramides, and botanical extracts an oral and topical test product (with zeaxanthin, algae extracts, peptides, hyaluronate) have been developed to improve the appearance and condition of skin when used as directed. Subjects were divided into three groups: two tests (skin formula 1 - oral product alone (ZO-1), skin formula 2- oral product with topical product (ZO-2 + ZT)), and one placebo control. The study consisted of a washout visit, baseline (randomization), week two (2), week four (4), week six (6), week eight (8), and week twelve (12). Key parameters measured were as follows: fine lines, deep lines, total wrinkles, wrinkle severity, radiance/skin color (L, a*, b*), discolorations, and skin pigment homogeneity. Thirty-one subjects completed the twelve-week study; no adverse events were recorded during the study. Statistically significant improvements from baseline mean hydration score were observed in active groups at weeks 2, 6, and 8. A statistically significant difference was observed between mean differences from baseline scores for total wrinkle count at week 4 for the combination active groups compared to placebo. A statistically significant difference from baseline scores for fine lines count was also observed at the week 4 visit compared to placebo for both active groups. Statistically significant differences from baseline scores for average wrinkles severity were seen for week 12 visit for both active groups compared to placebo. We have shown that the combination of zeaxanthin-based dietary supplement plus a topical formulation produces superior hydration to that of placebo. Additionally, we have shown that the combination of oral and topical combination vs. oral alone has superior abilities to improve parameters associated with facial lines and wrinkles compared to placebo, although the dietary supplement alone proved most effective in reducing wrinkle count and severity. © 2016 Wiley Periodicals, Inc.

2-(1,3-Dithiolan-2-ylidene)-5-(1,3-dithian-2-ylidene)-1,3,4,6- tetrathiapentalene(DHDA-TTP), a hybrid of BDH-TTP and BDA-TTP, and its metallic cation-radical salts.

PubMed

Yamada, Jun-ichi; Watanabe, Maki; Toita, Takashi; Akutsu, Hiroki; Nakatsuji, Shin'ichi; Nishikawa, Hiroyuki; Ikemoto, Isao; Kikuchi, Koichi

2002-05-21

The synthesis and electrochemical properties of the DHDA-TTP donor, a hybrid of 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP) and 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP), has been investigated, and its ability to form metallic cation-radical salts is elucidated.

ION EXCHANGE SUBSTANCES BY SAPONIFICATION OF ALLYL PHOSPHATE POLYMERS

DOEpatents

Kennedy, J.

1959-04-14

An ion exchange resin having a relatively high adsorption capacity tor uranyl ion as compared with many common cations is reported. The resin comprises an alphyl-allyl hydrogen phosphate polymer, the alphyl group being either allyl or a lower alkyl group having up to 5 carbon atoins. The resin is prepared by polymerizing compounds such as alkyl-diallyl phosphate and triallyl phosphate in the presence of a free radical generating substance and then partially hydrolyzing the resulting polymer to cause partial replacement of organic radicals by cations. A preferred free radical gencrating agent is dibenzoyl peroxide. The partial hydrolysis is brought about by refluxing the polymer with concentrated aqueous NaOH for three or four hours.

Spin densities from subsystem density-functional theory: Assessment and application to a photosynthetic reaction center complex model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solovyeva, Alisa; Technical University Braunschweig, Institute for Physical and Theoretical Chemistry, Hans-Sommer-Str. 10, 38106 Braunschweig; Pavanello, Michele

2012-05-21

Subsystem density-functional theory (DFT) is a powerful and efficient alternative to Kohn-Sham DFT for large systems composed of several weakly interacting subunits. Here, we provide a systematic investigation of the spin-density distributions obtained in subsystem DFT calculations for radicals in explicit environments. This includes a small radical in a solvent shell, a {pi}-stacked guanine-thymine radical cation, and a benchmark application to a model for the special pair radical cation, which is a dimer of bacteriochlorophyll pigments, from the photosynthetic reaction center of purple bacteria. We investigate the differences in the spin densities resulting from subsystem DFT and Kohn-Sham DFT calculations.more » In these comparisons, we focus on the problem of overdelocalization of spin densities due to the self-interaction error in DFT. It is demonstrated that subsystem DFT can reduce this problem, while it still allows to describe spin-polarization effects crossing the boundaries of the subsystems. In practical calculations of spin densities for radicals in a given environment, it may thus be a pragmatic alternative to Kohn-Sham DFT calculations. In our calculation on the special pair radical cation, we show that the coordinating histidine residues reduce the spin-density asymmetry between the two halves of this system, while inclusion of a larger binding pocket model increases this asymmetry. The unidirectional energy transfer in photosynthetic reaction centers is related to the asymmetry introduced by the protein environment.« less

Isolation and reversible dimerization of a selenium-selenium three-electron σ-bond.

PubMed

Zhang, Senwang; Wang, Xingyong; Su, Yuanting; Qiu, Yunfan; Zhang, Zaichao; Wang, Xinping

2014-06-11

Three-electron σ-bonding that was proposed by Linus Pauling in 1931 has been recognized as important in intermediates encountered in many areas. A number of three-electron bonding systems have been spectroscopically investigated in the gas phase, solution and solid matrix. However, X-ray diffraction studies have only been possible on simple noble gas dimer Xe∴Xe and cyclic framework-constrained N∴N radical cations. Here, we show that a diselena species modified with a naphthalene scaffold can undergo one-electron oxidation using a large and weakly coordinating anion, to afford a room-temperature-stable radical cation containing a Se∴Se three-electron σ-bond. When a small anion is used, a reversible dimerization with phase and marked colour changes is observed: radical cation in solution (blue) but diamagnetic dimer in the solid state (brown). These findings suggest that more examples of three-electron σ-bonds may be stabilized and isolated by using naphthalene scaffolds together with large and weakly coordinating anions.

Transient phenomena in the pulse radiolysis of retinyl polyenes. 5. Association of radical cations with parent molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bobrowski, K.; Das, P.K.

1986-02-27

At relatively high concentrations (1-10 mM) in O/sub 2/-saturated acetone, pulse radiolysis of all-trans-retinal, -retinoic acid, and -methyl retinoate gives rise to fast transient absorption processes that are best explained in terms of association of radical cations with parent polyenes to form dimers. From the concentration dependence of initial decay/formation kinetics, equilibrium constants (K) for monomer/dimer interconversion are measured to be 220-440 M/sup -1/ (in acetone). On going from acetone to 1,2-dichloroethane, K values for retinal and retinoic acid increase almost by an order of magnitude. For all trans-retinol and retinyl acetate, radical cation dimer formation appears to be negligiblemore » in the concentration range 1-10 mM of the polyene substrates (based on the lack of transient absorption changes seen with retinal and retinoic acid/ester). 24 references, 6 figures, 1 table.« less

Regioselectivity of enzymatic and photochemical single electron transfer promoted carbon-carbon bond fragmentation reactions of tetrameric lignin model compounds.

PubMed

Cho, Dae Won; Latham, John A; Park, Hea Jung; Yoon, Ung Chan; Langan, Paul; Dunaway-Mariano, Debra; Mariano, Patrick S

2011-04-15

New types of tetrameric lignin model compounds, which contain the common β-O-4 and β-1 structural subunits found in natural lignins, have been prepared and carbon-carbon bond fragmentation reactions of their cation radicals, formed by photochemical (9,10-dicyanoanthracene) and enzymatic (lignin peroxidase) SET-promoted methods, have been explored. The results show that cation radical intermediates generated from the tetrameric model compounds undergo highly regioselective C-C bond cleavage in their β-1 subunits. The outcomes of these processes suggest that, independent of positive charge and odd-electron distributions, cation radicals of lignins formed by SET to excited states of sensitizers or heme-iron centers in enzymes degrade selectively through bond cleavage reactions in β-1 vs β-O-4 moieties. In addition, the findings made in the enzymatic studies demonstrate that the sterically large tetrameric lignin model compounds undergo lignin peroxidase-catalyzed cleavage via a mechanism involving preliminary formation of an enzyme-substrate complex.

The Generation of Dehydroalanine Residues in Protonated Polypeptides: Ion/Ion Reactions for Introducing Selective Cleavages

NASA Astrophysics Data System (ADS)

Peng, Zhou; Bu, Jiexun; McLuckey, Scott A.

2017-09-01

We examine a gas-phase approach for converting a subset of amino acid residues in polypeptide cations to dehydroalanine (Dha). Subsequent activation of the modified polypeptide ions gives rise to specific cleavage N-terminal to the Dha residue. This process allows for the incorporation of selective cleavages in the structural characterization of polypeptide ions. An ion/ion reaction within the mass spectrometer between a multiply protonated polypeptide and the sulfate radical anion introduces a radical site into the multiply protonated polypeptide reactant. Subsequent collisional activation of the polypeptide radical cation gives rise to radical side chain loss from one of several particular amino acid side chains (e.g., leucine, asparagine, lysine, glutamine, and glutamic acid) to yield a Dha residue. The Dha residues facilitate preferential backbone cleavages to produce signature c- and z-ions, demonstrated with cations derived from melittin, mechano growth factor (MGF), and ubiquitin. The efficiencies for radical side chain loss and for subsequent generation of specific c- and z-ions have been examined as functions of precursor ion charge state and activation conditions using cations of ubiquitin as a model for a small protein. It is noted that these efficiencies are not strongly dependent on ion trap collisional activation conditions but are sensitive to precursor ion charge state. Moderate to low charge states show the greatest overall yields for the specific Dha cleavages, whereas small molecule losses (e.g., water/ammonia) dominate at the lowest charge states and proton catalyzed amide bond cleavages that give rise to b- and y-ions tend to dominate at high charge states. [Figure not available: see fulltext.

Quenching mechanisms and diffusional pathways in micellar systems unravelled by time-resolved magnetic-field effects.

PubMed

Goez, Martin; Henbest, Kevin B; Windham, Emma G; Maeda, Kiminori; Timmel, Christiane R

2009-06-08

Magnetic-field effects (MFEs) are used to investigate the photoreaction of xanthone (A) and DABCO (D) in anionic (SDS) or cationic (DTAC) micelles at high pH (DABCO = 1,4-diazabicyclo[2.2.2]octane, SDS = sodium dodecyl sulfate, DTAC = dodecyl trimethyl ammonium chloride). From MFE experiments with nanosecond time resolution, the radical anion A(.)(-) can be observed without any interference from the much more strongly absorbing triplet (3)A*, the different quenching processes can be separated and their rates can be measured. Triplet (3)A* is quenched dynamically both by the SDS micelle (k(1) = 5.0x10(5) s(-1)) and by DABCO approaching from the aqueous phase (k(2) = 2.0x10(9) M(-1) s(-1)). Static quenching by solubilised DABCO (association constant with the SDS micelles, 1.5 M(-1)) also participates at high DABCO concentrations, but is chemically nonproductive and does not lead to MFE generation. The MFEs stemming from the radical ion pairs A(.)(-) D(.)(+) are about 40 times larger in the anionic micelles than in the cationic ones despite a higher yield of free radicals in the latter case. This can be rationalised by different diffusional dynamics: Because of the location of their precursors, A(.)(-) and D(.)(+) are formed at opposite sides of the micelle boundary. Subsequently, the negatively charged Stern layer of the SDS micelle traps the radical cation, which then undergoes surface diffusion, so both the recombination probability and the spin mixing are high; in contrast, the positive surface charge of the DTAC micelle forces the radical cation into the bulk of the solution, thus efficiently blocking a recombination.

A substrate radical intermediate in the reaction between ribonucleotide reductase from Escherichia coli and 2'-azido-2'-deoxynucleoside diphosphates.

PubMed

Sjöberg, B M; Gräslund, A; Eckstein, F

1983-07-10

The B2 subunit of ribonucleotide reductase from Escherichia coli contains a tyrosine radical which is essential for enzyme activity. In the reaction between ribonucleotide reductase and the substrate analogue 2'-azido-2'-deoxycytidine 5'-diphosphate a new transient radical is formed. The EPR characteristics of this new radical species are consistent with a localization of the unpaired electron at the sugar moiety of the nucleotide. The radical shows hyperfine couplings to a hydrogen and a nitrogen nucleus, the latter probably being part of the azide substituent. The formation of the nucleotide radical in this suicidal reaction is concomitant with the decay of the tyrosine radical of the B2 subunit. Kinetic data argue for a first (pseudosecond) order decay of the B2 radical via generation of the nucleotide radical followed by a slower first order decay of the nucleotide radical. End products in the reaction are cytosine and radical-free protein B2. In the reaction between bacteriophage T4 ribonucleotide reductase and 2'-azido-2'-deoxycytidine 5'-diphosphate an identical nucleotide radical is formed. The present results are consistent with the hypothesis that the appearance and structure of the transient radical mimic stages in the normal reaction pathway of ribonucleotide reductase, postulated to proceed via 3'-hydrogen abstraction and cation radical formation of the substrate nucleotide (Stubbe, J., and Ackles, D. (1980) J. Biol. Chem. 255, 8027-8030). The nucleotide radical described here might be equivalent to such a cation radical intermediate.

Lutein, zeaxanthin, meso-zeaxanthin content in egg yolk and their absence in fish and seafood

USDA-ARS?s Scientific Manuscript database

Lutein (L) and zeaxanthin (Z) are carotenoids that are selectively taken up into the macula of the eye where they may protect against age-related macular degeneration. Meso-zeaxanthin (MZ) is also found in the macula, but is derived from L. It has been reported that MZ was found in certain fish and ...

Electromers of the benzene dimer radical cation.

PubMed

Błoch-Mechkour, Anna; Bally, Thomas

2015-04-28

The well-studied benzene dimer radical cation, which is prototypical for this class of species, has been reinvestigated computationally. Thereby it turned out that both the σ-hemibonded and the half-shifted sandwich structures of the benzene dimer cation, which had been independently proposed, represent stationary points on the B2PLYP-D potential energy surfaces. However, these structures belong to distinct electronic states, both of which are associated with potential surfaces that are very flat with regard to rotation of the two benzene rings in an opposite sense relative to each other. The surfaces of these two "electromers" of the benzene dimer cation are separated by only 3-4 kcal mol(-1) and do not intersect along the rotation coordinate, which represents a rather unique electronic structure situation. When moving on either of the two surfaces the title complex is an extremely fluxional species, in spite of its being bound by over 20 kcal mol(-1).

Isolation of a series of apocarotenoids from the fruits of the red paprika Capsicum annuum L.

PubMed

Maoka, T; Fujiwara, Y; Hashimoto, K; Akimoto, N

2001-03-01

Eleven apocarotenoids (1-11) including five new compounds, 4, 6, 9, 10 and 11, were isolated from the fruits of the red paprika Capsicum annuum L. The structures of new apocarotenoids were determined to be apo-14'-zeaxanthinal (4), apo-13-zeaxanthinone (6), apo-12'-capsorubinal (9), apo-8'-capsorubinal (10), and 9,9'-diapo-10,9'-retro-carotene-9,9'-dione (11) by spectroscopic analysis. The other six known apocarotenoids were identified to be apo-8'-zeaxanthinal (1), apo-10'-zeaxanthinal (2), apo-12'-zeaxanthinal (3), apo-15-zeaxanthinal (5), apo-11-zeaxanthinal (7), and apo-9-zeaxanthinone (8) which have not been previously found in paprika. These apocarotenoids were assumed to be oxidative cleavage products of C(40) carotenoid such as capsanthin in paprika.

l-Tryptophan Radical Cation Electron Spin Resonance Studies: Connecting Solution-derived Hyperfine Coupling Constants with Protein Spectral Interpretations

PubMed Central

Connor, Henry D.; Sturgeon, Bradley E.; Mottley, Carolyn; Sipe, Herbert J.; Mason, Ronald P.

2009-01-01

Fast-flow electron spin resonance (ESR) spectroscopy has been used to detect a free radical formed from the reaction of l-tryptophan with Ce4+ in an acidic aqueous environment. Computer simulations of the ESR spectra from l-tryptophan and several isotopically modified forms strongly support the conclusion that the l-tryptophan radical cation has been detected by ESR for the first time. The hyperfine coupling constants (HFCs) determined from the well-resolved isotropic ESR spectra support experimental and computational efforts to understand l-tryptophan's role in protein catalysis of oxidation-reduction processes. l-tryptophan HFCs facilitated the simulation of fast-flow ESR spectra of free radicals from two related compounds, tryptamine and 3-methylindole. Analysis of these three compounds' β-methylene hydrogen HFC data along with equivalent l-tyrosine data has led to a new computational method that can distinguish between these two amino acid free radicals in proteins without dependence on isotope labeling, electron nuclear double resonance or high-field ESR. This approach also produces geometric parameters (dihedral angles for the β-methylene hydrogens) which should facilitate protein site assignment of observed l-tryptophan radicals as has been done for l-tyrosine radicals. PMID:18433127

Design and Evaluation of a Boron Dipyrrin Electrophore for Redox Flow Batteries.

PubMed

Heiland, Niklas; Cidarér, Clemens; Rohr, Camilla; Piescheck, Mathias; Ahrens, Johannes; Bröring, Martin; Schröder, Uwe

2017-08-29

A boron dipyrrin (BODIPY) dye was designed as a molecular single-component electrophore for redox flow batteries. All positions of the BODIPY core were assessed on the basis of literature data, in particular cyclic voltammetry and density functional calculations, and a minimum required substitution pattern was designed to provide solubility, aggregation, radical cation and anion stabilities, a large potential window, and synthetic accessibility. In-depth electrochemical and physical studies of this electrophore revealed suitable cathodic behavior and stability of the radical anion but rapid anodic decomposition of the radical cation. The three products that formed under the conditions of controlled oxidative electrolysis were isolated, and their structures were determined by spectroscopy and comparison with a synthetic model compound. From these structures, a benzylic radical reactivity, initiated by one-electron oxidation, was concluded to play the major role in this unexpected decomposition. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Radical Cation Salt-initiated Aerobic C-H Phosphorylation of N-Benzylanilines: Synthesis of a-Aminophosphonates.

PubMed

Jia, Xiao Dong; Liu, Xiaofei; Yuan, Yu; Li, Pengfei; Hou, Wentao; He, Kaixuan

2018-06-03

A radical cation salt-initiated phosphorylation of N-benzylanilines was realized through the aerobic oxidation of sp3 C-H bond, providing a series of α-aminophosphonates in high yields. The investigation of the reaction scope revealed that this mild catalyst system is superior in good functional group tolerance and high reaction efficiency. The mechanistic study implied that the cleavage of the sp3 C-H bond was involved in the rate-determining step. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Vibronic spectra of the p-benzoquinone radical anion and cation: a matrix isolation and computational study.

PubMed

Piech, Krzysztof; Bally, Thomas; Ichino, Takatoshi; Stanton, John

2014-02-07

The electronic and vibrational absorption spectra of the radical anion and cation of p-benzoquinone (PBQ) in an Ar matrix between 500 and 40,000 cm(-1) are presented and discussed in detail. Of particular interest is the radical cation, which shows very unusual spectroscopic features that can be understood in terms of vibronic coupling between the ground and a very low-lying excited state. The infrared spectrum of PBQ˙(+) exhibits a very conspicuous and complicated pattern of features above 1900 cm(-1) that is due to this electronic transition, and offers an unusually vivid demonstration of the effects of vibronic coupling in what would usually be a relatively simple region of the electromagnetic spectrum associated only with vibrational transitions. As expected, the intensities of most of the IR transitions leading to levels that couple the ground to the very low-lying first excited state of PBQ˙(+) increase by large factors upon ionization, due to "intensity borrowing" from the D0 → D1 electronic transition. A notable exception is the antisymmetric C=O stretching vibration, which contributes significantly to the vibronic coupling, but has nevertheless quite small intensity in the cation spectrum. This surprising feature is rationalized on the basis of a simple perturbation analysis.

Enhanced Photoreduction of Nitro-aromatic Compounds by Hydrated Electrons Derived from Indole on Natural Montmorillonite.

PubMed

Tian, Haoting; Guo, Yong; Pan, Bo; Gu, Cheng; Li, Hui; Boyd, Stephen A

2015-07-07

A new photoreduction pathway for nitro-aromatic compounds (NACs) and the underlying degradation mechanism are described. 1,3-Dinitrobenzene was reduced to 3-nitroaniline by the widely distributed aromatic molecule indole; the reaction is facilitated by montmorillonite clay mineral under both simulated and natural sunlight irradiation. The novel chemical reaction is strongly affected by the type of exchangeable cation present on montmorillonite. The photoreduction reaction is initiated by the adsorption of 1,3-dinitrobenzene and indole in clay interlayers. Under light irradiation, the excited indole molecule generates a hydrated electron and the indole radical cation. The structural negative charge of montmorillonite plausibly stabilizes the radical cation hence preventing charge recombination. This promotes the release of reactive hydrated electrons for further reductive reactions. Similar results were observed for the photoreduction of nitrobenzene. In situ irradiation time-resolved electron paramagnetic resonance and Fourier transform infrared spectroscopies provided direct evidence for the generation of hydrated electrons and the indole radical cations, which supported the proposed degradation mechanism. In the photoreduction process, the role of clay mineral is to both enhance the generation of hydrated electrons and to provide a constrained reaction environment in the galley regions, which increases the probability of contact between NACs and hydrated electrons.

AFRRI Reports October - December 1990

DTIC Science & Technology

1991-01-01

in the reaction between cytosine radicals and adria- mycin, it is possible that the yield of-DMPO--O,- and of its decomposition product, DMPO-OH, are...mixture due to the decomposition Time (min) of DMPO-O- by 0,7 ’. Fig. 2. Adriamycin radical yield as a function of time. y.lrradiated The electron...radical by decomposition of superoxide spin trapped toionization of thyminc. The thymnine cation and union radicals. adducts, Ato. Pharmn. 21: 262-265

[The assessment and characteristic of dietary supplements with lutein and zeaxanthin on the Polish pharmaceutical market].

PubMed

Hamułka, Jadwiga; Nogal, Dorota

2008-01-01

Lutein and zeaxanthin, two xanthophylls supposed to delay formation eye's disease (AMD, cataract), and found in numerous new dietary supplements appearing on market also in Poland. In the observed period on polish pharmaceutical market was evaluated presence about 50 supplements with lutein and 12 contained zeaxanthin as well. The lutein concentration ranges from 0.25 to 20.0 mg/serving size and zeaxanthin from 0.02 to 0.50 mg. Most of them were multicomponent (multi-vitamin products) in form of capsules or tabs for adults, advised for the eyes' protections or supply of nutritional components with various contents of lutein and zeaxanthin and various costs of daily treatment.

Spontaneous Isomerization of Peptide Cation Radicals Following Electron Transfer Dissociation Revealed by UV-Vis Photodissociation Action Spectroscopy.

PubMed

Imaoka, Naruaki; Houferak, Camille; Murphy, Megan P; Nguyen, Huong T H; Dang, Andy; Tureček, František

2018-01-16

Peptide cation radicals of the z-type were produced by electron transfer dissociation (ETD) of peptide dications and studied by UV-Vis photodissociation (UVPD) action spectroscopy. Cation radicals containing the Asp (D), Asn (N), Glu (E), and Gln (Q) residues were found to spontaneously isomerize by hydrogen atom migrations upon ETD. Canonical N-terminal [z 4 + H] +● fragment ion-radicals of the R-C ● H-CONH- type, initially formed by N-C α bond cleavage, were found to be minor components of the stable ion fraction. Vibronically broadened UV-Vis absorption spectra were calculated by time-dependent density functional theory for several [ ● DAAR + H] + isomers and used to assign structures to the action spectra. The potential energy surface of [ ● DAAR + H] + isomers was mapped by ab initio and density functional theory calculations that revealed multiple isomerization pathways by hydrogen atom migrations. The transition-state energies for the isomerizations were found to be lower than the dissociation thresholds, accounting for the isomerization in non-dissociating ions. The facile isomerization in [ ● XAAR + H] + ions (X = D, N, E, and Q) was attributed to low-energy intermediates having the radical defect in the side chain that can promote hydrogen migration along backbone C α positions. A similar side-chain mediated mechanism is suggested for the facile intermolecular hydrogen migration between the c- and [z + H] ● -ETD fragments containing Asp, Asn, Glu, and Gln residues. Graphical Abstract ᅟ.

Spontaneous Isomerization of Peptide Cation Radicals Following Electron Transfer Dissociation Revealed by UV-Vis Photodissociation Action Spectroscopy

NASA Astrophysics Data System (ADS)

Imaoka, Naruaki; Houferak, Camille; Murphy, Megan P.; Nguyen, Huong T. H.; Dang, Andy; Tureček, František

2018-01-01

Peptide cation radicals of the z-type were produced by electron transfer dissociation (ETD) of peptide dications and studied by UV-Vis photodissociation (UVPD) action spectroscopy. Cation radicals containing the Asp (D), Asn (N), Glu (E), and Gln (Q) residues were found to spontaneously isomerize by hydrogen atom migrations upon ETD. Canonical N-terminal [z4 + H]+● fragment ion-radicals of the R-C●H-CONH- type, initially formed by N-Cα bond cleavage, were found to be minor components of the stable ion fraction. Vibronically broadened UV-Vis absorption spectra were calculated by time-dependent density functional theory for several [●DAAR + H]+ isomers and used to assign structures to the action spectra. The potential energy surface of [●DAAR + H]+ isomers was mapped by ab initio and density functional theory calculations that revealed multiple isomerization pathways by hydrogen atom migrations. The transition-state energies for the isomerizations were found to be lower than the dissociation thresholds, accounting for the isomerization in non-dissociating ions. The facile isomerization in [●XAAR + H]+ ions (X = D, N, E, and Q) was attributed to low-energy intermediates having the radical defect in the side chain that can promote hydrogen migration along backbone Cα positions. A similar side-chain mediated mechanism is suggested for the facile intermolecular hydrogen migration between the c- and [z + H]●-ETD fragments containing Asp, Asn, Glu, and Gln residues. [Figure not available: see fulltext.

Excited state dynamics of the astaxanthin radical cation

NASA Astrophysics Data System (ADS)

Amarie, Sergiu; Förster, Ute; Gildenhoff, Nina; Dreuw, Andreas; Wachtveitl, Josef

2010-07-01

Femtosecond transient absorption spectroscopy in the visible and NIR and ultrafast fluorescence spectroscopy were used to examine the excited state dynamics of astaxanthin and its radical cation. For neutral astaxanthin, two kinetic components corresponding to time constants of 130 fs (decay of the S 2 excited state) and 5.2 ps (nonradiative decay of the S 1 excited state) were sufficient to describe the data. The dynamics of the radical cation proved to be more complex. The main absorption band was shifted to 880 nm (D 0 → D 3 transition), showing a weak additional band at 1320 nm (D 0 → D 1 transition). We found, that D 3 decays to the lower-lying D 2 within 100 fs, followed by a decay to D 1 with a time constant of 0.9 ps. The D 1 state itself exhibited a dual behavior, the majority of the population is transferred to the ground state in 4.9 ps, while a small population decays on a longer timescale of 40 ps. Both transitions from D 1 were found to be fluorescent.

Recent Developments of Versatile Photoinitiating Systems for Cationic Ring Opening Polymerization Operating at Any Wavelengths and under Low Light Intensity Sources.

PubMed

Lalevée, Jacques; Mokbel, Haifaa; Fouassier, Jean-Pierre

2015-04-20

Photoinitiators (PI) or photoinitiating systems (PIS) usable in light induced cationic polymerization (CP) and free radical promoted cationic polymerization (FRPCP) reactions (more specifically for cationic ring opening polymerization (ROP)) together with the involved mechanisms are briefly reviewed. The recent developments of novel two- and three-component PISs for CP and FRPCP upon exposure to low intensity blue to red lights is emphasized in details. Examples of such reactions under various experimental conditions are provided.

Zeaxanthin Binds to Light-Harvesting Complex Stress-Related Protein to Enhance Nonphotochemical Quenching in Physcomitrella patens[W

PubMed Central

Pinnola, Alberta; Dall’Osto, Luca; Gerotto, Caterina; Morosinotto, Tomas; Bassi, Roberto; Alboresi, Alessandro

2013-01-01

Nonphotochemical quenching (NPQ) dissipates excess energy to protect the photosynthetic apparatus from excess light. The moss Physcomitrella patens exhibits strong NPQ by both algal-type light-harvesting complex stress-related (LHCSR)–dependent and plant-type S subunit of Photosystem II (PSBS)-dependent mechanisms. In this work, we studied the dependence of NPQ reactions on zeaxanthin, which is synthesized under light stress by violaxanthin deepoxidase (VDE) from preexisting violaxanthin. We produced vde knockout (KO) plants and showed they underwent a dramatic reduction in thermal dissipation ability and enhanced photoinhibition in excess light conditions. Multiple mutants (vde lhcsr KO and vde psbs KO) showed that zeaxanthin had a major influence on LHCSR-dependent NPQ, in contrast with previous reports in Chlamydomonas reinhardtii. The PSBS-dependent component of quenching was less dependent on zeaxanthin, despite the near-complete violaxanthin to zeaxanthin exchange in LHC proteins. Consistent with this, we provide biochemical evidence that native LHCSR protein binds zeaxanthin upon excess light stress. These findings suggest that zeaxanthin played an important role in the adaptation of modern plants to the enhanced levels of oxygen and excess light intensity of land environments. PMID:24014548

Zeaxanthin binds to light-harvesting complex stress-related protein to enhance nonphotochemical quenching in Physcomitrella patens.

PubMed

Pinnola, Alberta; Dall'Osto, Luca; Gerotto, Caterina; Morosinotto, Tomas; Bassi, Roberto; Alboresi, Alessandro

2013-09-01

Nonphotochemical quenching (NPQ) dissipates excess energy to protect the photosynthetic apparatus from excess light. The moss Physcomitrella patens exhibits strong NPQ by both algal-type light-harvesting complex stress-related (LHCSR)-dependent and plant-type S subunit of Photosystem II (PSBS)-dependent mechanisms. In this work, we studied the dependence of NPQ reactions on zeaxanthin, which is synthesized under light stress by violaxanthin deepoxidase (VDE) from preexisting violaxanthin. We produced vde knockout (KO) plants and showed they underwent a dramatic reduction in thermal dissipation ability and enhanced photoinhibition in excess light conditions. Multiple mutants (vde lhcsr KO and vde psbs KO) showed that zeaxanthin had a major influence on LHCSR-dependent NPQ, in contrast with previous reports in Chlamydomonas reinhardtii. The PSBS-dependent component of quenching was less dependent on zeaxanthin, despite the near-complete violaxanthin to zeaxanthin exchange in LHC proteins. Consistent with this, we provide biochemical evidence that native LHCSR protein binds zeaxanthin upon excess light stress. These findings suggest that zeaxanthin played an important role in the adaptation of modern plants to the enhanced levels of oxygen and excess light intensity of land environments.

Fasting plasma zeaxanthin response to Fructus barbarum L. (wolfberry; Kei Tze) in a food-based human supplementation trial.

PubMed

Cheng, Chung Yuen; Chung, Wai Yuen; Szeto, Yim Tong; Benzie, Iris F F

2005-01-01

Age-related macular degeneration (AMD) is a common disorder that causes irreversible loss of central vision. Increased intake of foods containing zeaxanthin may be effective in preventing AMD because the macula accumulates zeaxanthin and lutein, oxygenated carotenoids with antioxidant and blue light-absorbing properties. Lycium barbarum L. is a small red berry known as Fructus lycii and wolfberry in the West, and Kei Tze and Gou Qi Zi in Asia. Wolfberry is rich in zeaxanthin dipalmitate, and is valued in Chinese culture for being good for vision. The aim of this study, which was a single-blinded, placebo-controlled, human intervention trial of parallel design, was to provide data on how fasting plasma zeaxanthin concentration changes as a result of dietary supplementation with whole wolfberries. Fasting blood was collected from healthy, consenting subjects; fourteen subjects took 15 g/d wolfberry (estimated to contain almost 3 mg zeaxanthin) for 28 d. Repeat fasting blood was collected on day 29. Age- and sex-matched controls (n 13) took no wolfberry. Responses in the two groups were compared using the Mann-Whitney test. After supplementation, plasma zeaxanthin increased 2.5-fold: mean values on day 1 and 29 were 0.038 (sem 0.003) and 0.096 (sem 0.009) micromol/l (P<0.01), respectively, for the supplementation group; and 0.038 (sem 0.003) and 0.043 (sem 0.003) micromol/l (P>0.05), respectively, for the control group. This human supplementation trial shows that zeaxanthin in whole wolfberries is bioavailable and that intake of a modest daily amount markedly increases fasting plasma zeaxanthin levels. These new data will support further study of dietary strategies to maintain macular pigment density.

Effect of aggregation form on bioavailability of zeaxanthin in humans: a randomised cross-over study.

PubMed

Hempel, Judith; Fischer, Anja; Fischer, Monique; Högel, Josef; Bosy-Westphal, Anja; Carle, Reinhold; Schweiggert, Ralf M

2017-11-01

Carotenoid bioavailability from plant and animal food is highly variable depending on numerous factors such as the physical deposition form of carotenoids. As the carotenoid zeaxanthin is believed to play an important role in eye and brain health, we sought to compare the human bioavailability of an H-aggregated with that of a J-aggregated deposition form of zeaxanthin encapsulated into identical formulation matrices. A randomised two-way cross-over study with sixteen participants was designed to compare the post-prandial bioavailability of an H-aggregated zeaxanthin and a J-aggregated zeaxanthin dipalmitate formulation, both delivering 10 mg of free zeaxanthin. Carotenoid levels in TAG-rich lipoprotein fractions were analysed over 9·5 h after test meal consumption. Bioavailability from the J-aggregated formulation (AUC=55·9 nmol h/l) was 23 % higher than from the H-aggregated one (AUC=45·5 nmol h/l), although being only marginally significant (P=0·064). Furthermore, the same formulations were subjected to an internationally recognised in vitro digestion protocol to reveal potential strengths and weaknesses of simulated digestions. In agreement with our human study, liberation of zeaxanthin from the J-aggregated formulation into the simulated duodenal fluids was superior to that from the H-aggregated form. However, micellization rate (bioaccessibility) of the J-aggregated zeaxanthin dipalmitate was lower than that of the H-aggregated zeaxanthin, being contradictory to our in vivo results. An insufficient ester cleavage during simulated digestion was suggested to be the root cause for these observations. In brief, combining our in vitro and in vivo observations, the effect of the different aggregation forms on human bioavailability was lower than expected.

Multi-State Vibronic Interactions in Fluorinated Benzene Radical Cations.

NASA Astrophysics Data System (ADS)

Faraji, S.; Köppel, H.

2009-06-01

Conical intersections of potential energy surfaces have emerged as paradigms for signalling strong nonadiabatic coupling effects. An important class of systems where some of these effects have been analyzed in the literature, are the benzene and benzenoid cations, where the electronic structure, spectroscopy, and dynamics have received great attention in the literature. In the present work a brief overview is given over our theoretical treatments of multi-mode and multi-state vibronic interactions in the benzene radical cation and some of its fluorinated derivatives. The fluorobenzene derivatives are of systematic interest for at least two different reasons. (1) The reduction of symmetry by incomplete fluorination leads to a disappearance of the Jahn-Teller effect present in the parent cation. (2) A specific, more chemical effect of fluorination consists in the energetic increase of the lowest σ-type electronic states of the radical cations. The multi-mode multi-state vibronic interactions between the five lowest electronic states of the fluorobenzene radical cations are investigated theoretically, based on ab initio electronic structure data, and employing the well-established linear vibronic coupling model, augmented by quadratic coupling terms for the totally symmetric vibrational modes. Low-energy conical intersections, and strong vibronic couplings are found to prevail within the set of tilde{X}-tilde{A} and tilde{B}-tilde{C}-tilde{D} cationic states, while the interactions between these two sets of states are found to be weaker and depend on the particular isomer. This is attributed to the different location of the minima of the various conical intersections occurring in these systems. Wave-packet dynamical simulations for these coupled potential energy surfaces, utilizing the powerful multi-configuration time-dependent Hartree method are performed. Ultrafast internal conversion processes and the analysis of the MATI and photo-electron spectra shed new light on the spectroscopy and fluorescence dynamics of these species. W. Domcke, D. R. Yarkony, and H. Köppel, Advanced Series in Physical Chemistry, World Scientific, Singapore (2004). M. H. Beck and A. Jäckle and G. A. Worth and H. -D. Meyer, Phys. Rep. 324, 1 (2000). S. Faraji, H. Köppel, (Part I) ; S. Faraji, H. Köppel, H.-D. Meyer, (Part II) J. Chem. Phys. 129, 074310 (2008).

Simple replacement of violaxanthin by zeaxanthin in LHC-II does not cause chlorophyll fluorescence quenching.

PubMed

Dreuw, Andreas; Wormit, Michael

2008-03-01

Recently, a mechanism for the energy-dependent component (qE) of non-photochemical quenching (NPQ), the fundamental photo-protection mechanism in green plants, has been suggested. Replacement of violaxanthin by zeaxanthin in the binding pocket of the major light harvesting complex LHC-II may be sufficient to invoke efficient chlorophyll fluorescence quenching. Our quantum chemical calculations, however, show that the excited state energies of violaxanthin and zeaxanthin are practically identical when their geometry is constrained to the naturally observed structure of violaxanthin in LHC-II. Therefore, since violaxanthin does not quench LHC-II, zeaxanthin should not either. This theoretical finding is nicely in agreement with experimental results obtained by femtosecond spectroscopy on LHC-II complexes containing violaxanthin or zeaxanthin.

A Mechanistic Study of the Influence of Proton Transfer Processes on the Behavior of Thiol/Disulfide Redox Couples

DTIC Science & Technology

1998-06-29

acidic than its cation radical, McMT4*. Bordwell et al.20 have discussed the relative acidities of thiols (pKnA)and their cation radicals (PKHA+-), and...15) Bordwell , F. G. Ace. Chem. Res. 1988, 21, 456. 16) Parker, V. D.; Tilset, M. J. Am. Chem. Soc. 1988,110, 1649. 17) Bordwell , F. G.; Bausch, M. J...J. Am. Chem. Soc. 1986,108, 2473. 18) Bordwell , F. G.; Cheng, J.-P. J. Am. Chem. Soc. 1989,111, 1792. 19) Parker, V. D.; Handoo, K. L.; Roness, F

Highly planar diarylamine-fused porphyrins and their remarkably stable radical cations† †Electronic supplementary information (ESI) available. CCDC 1469154–1469160. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc02721k Click here for additional data file. Click here for additional data file.

PubMed Central

Fukui, Norihito; Cha, Wonhee; Shimizu, Daiki; Oh, Juwon

2017-01-01

Oxidative fusion reactions of meso-phenoxazino Ni(ii) porphyrin were found to be temperature dependent, giving rise to either a doubly phenylene-fused product at room temperature or a singly phenoxazine-fused product at 70 °C. The latter was further oxidized to a doubly phenoxazine-fused Ni(ii) porphyrin, which was subsequently converted to the corresponding free base porphyrin and Zn(ii) porphyrin. Compared to previously reported diphenylamine-fused porphyrins that displayed a molecular twist, doubly phenoxazine-fused porphyrins exhibited distinctly different properties owing to their highly planar structures, such as larger fluorescence quantum yields, formation of an offset face-to-face dimer both in solution and the solid state, and the generation of a mixed-valence π-radical cation dimer upon electrochemical oxidation. One-electron oxidation of the phenoxazine-fused Ni(ii) porphyrin with Magic Blue gave the corresponding radical cation, which was certainly stable and could be isolated by separation over a silica gel column but slowly chlorinated at the reactive β-positions in the solid state. This finding led to us to examine β,β′-dichlorinated phenoxazine-fused and diphenylamine-fused Ni(ii) porphyrins, which, upon treatment with Magic Blue, provided remarkably stable radical cations to an unprecedented level. It is actually possible to purify these radical cations by silica gel chromatography, and they can be stored for over 6 months without any sign of deterioration. Moreover, they exhibited no degradation even after the CH2Cl2 solution was washed with water. However, subtle structural differences (planar versus partly twisted) led to different crystal packing structures and solid-state magnetic properties. PMID:28451165

A Visible Light Initiating System for Free Radical Promoted Cationic Polymerization

DTIC Science & Technology

1994-02-02

identify the end groups in the polymer of cyclohexene oxide. N,N-Dimethylnaphthyl amine (DNA), a compound with high fluorescence quantum yield, was used...candidates to be polymerized via a cationic mechanism include cyclic ethers, cyclic formals and acetals, vinyl ethers, and epoxy compounds . Of these...reported sensitizer, bears two dimethylamino groups, is direct evidence that an aromatic amine can be present in a cationically photopolymerizable system

A comparative assessment of antioxidant properties, total phenolic content of einkorn, wheat, barley and their malts.

PubMed

Fogarasi, Attila-Levente; Kun, Szilárd; Tankó, Gabriella; Stefanovits-Bányai, Eva; Hegyesné-Vecseri, Beáta

2015-01-15

Two einkorn wheat, one barley, three optional winter cultivation wheat and five winter cultivation wheat samples harvested in Hungary in 2011, and their malts were evaluated for their DPPH radical and ABTS radical cation scavenging activity, ferric reduction capacity (FRAP) and total phenolic content (TPC). All einkorn and barley samples exhibited significant antioxidant activities determined by DPPH and ABTS radical scavenging activities. The einkorn samples show higher polyphenol content than the other wheat samples. In all cases the barley sample had the highest antioxidant potential and polyphenol content. The einkorn malts had high DPPH and ABTS radical cation scavenging activities, but the phenolic content was lower against wheat samples. There was significant difference between the antioxidant potential of optional and winter cultivation wheat samples except on ABTS scavenging activities. Einkorn wheat is potentially a new raw material to produce organic beer that might have beneficial effects with its increased antioxidant potential. Copyright © 2014 Elsevier Ltd. All rights reserved.

A possible role for lutein and zeaxanthin in cognitive function in the elderly

USDA-ARS?s Scientific Manuscript database

Epidemiological studies suggest that dietary lutein and zeaxanthin may be of benefit in maintaining cognitive health. Among the carotenoids, lutein and zeaxanthin, are the only two that cross the blood-retina barrier to form macular pigment (MP) in the eye. They also preferentially accumulate in hum...

Induced High-Yield Production of Zeaxanthin, Lutein, and β-Carotene by a Mutant of Chlorella zofingiensis.

PubMed

Huang, Weiping; Lin, Yan; He, Mingxia; Gong, Yuhao; Huang, Junchao

2018-01-31

Natural resources of zeaxanthin are extremely limited. A Chlorella zofingiensis mutant (CZ-bkt1), which could accumulate high amounts of zeaxanthin, was generated and characterized. CZ-bkt1 was achieved by treating the algal cells with a chemical mutagen followed by a color-based colony-screening approach. CZ-bkt1 was found to consist of a dysfunctional carotenoid ketolase, leading to the accumulation of zeaxanthin rather than to its downstream ketocarotenoid astaxanthin. Light irradiation, glucose, NaCl, and nitrogen deficiency all induced CZ-bkt1 to accumulate zeaxanthin. CZ-bkt1 accumulated zeaxanthin up to 7.00 ± 0.82 mg/g when induced by high-light irradiation and nitrogen deficiency and up to 36.79 ± 2.23 mg/L by additional feeding with glucose. Furthermore, in addition to zeaxanthin, CZ-bkt1 also accumulated high amounts of β-carotene (7.18 ± 0.72 mg/g or 34.64 ± 1.39 mg/L) and lutein (13.81 ± 1.23 mg/g or 33.97 ± 2.61 mg/L). CZ-bkt1 is the sole species up to date with the ability to accumulate high amounts of the three carotenoids that are essential for human health.

Synthesis and redox properties of crowded triarylphosphines possessing ferrocenyl groups.

PubMed

Sutoh, Katsuhide; Sasaki, Shigeru; Yoshifuji, Masaaki

2006-02-06

Crowded triarylphosphines possessing ferrocenyl groups [(4-ferrocenyl-2,6-diisopropylphenyl)(n)(2,4,6-triisopropylphenyl)(3-n)P (5a, n = 1; 5b, n = 2; 5c, n = 3)] were synthesized by the reaction of the corresponding arylcopper(I) reagents with the diarylchlorophosphines. Structures of the triarylphosphines were studied by 1H, 13C, and 31P NMR spectroscopies, and the characteristic patterns of the proton signals of the 2,6-isopropyl groups and upfielded 31P chemical shifts suggest structural similarities of the triarylphosphine moiety to the previously reported tris(2,4,6-triisopropylphenyl)phosphine (2). X-ray crystallography of 5c also revealed that the structure around the phosphorus is similar to that of 1, where the average bond angle and length around the phosphorus atom are 110.8 degrees and 1.854 A, respectively. According to the electrochemical measurements, phosphines 5a, 5b, and 5c are reversibly oxidized in two, three, and four steps, respectively, which suggests significant electronic interaction among the triarylphosphine and the ferrocene redox centers as well as weak interaction among the ferrocene redox centers. The EPR spectra obtained at cryogenic temperature after oxidation of phosphines 5a, 5b, and 5c are superpositions of those for the cation radicals of the crowded triarylphosphine and ferricinium. The solution spectra obtained at 293 K, which consist of two lines typical of the cation radical of the crowded triarylphosphines, become weaker as the number of the ferrocenyl groups increases and the cation radical of 5c does not show EPR signals. These findings suggest not only instability of the tetra(cation radical) of 5c but also the course of oxidation where the ferrocenyl groups in the periphery of the molecules are oxidized at first.

Transient alkylaminium radicals in n-hexane. Condensed-phase ion-molecule reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Werst, D.W.; Trifunac, A.D.

Time-resolved fluorescence detected magnetic resonance (FDMR) is used to observe alkylaminium radicals formed in n-hexane solutions by electron pulse radiolysis. The ease of observation of aminium radical FDMR signals increases with increasing alkyl substitution of the amine solutes. The results are discussed in terms of the ion-molecule reactions, such as proton transfer, which compete with the electron-transfer processes, i.e, the electron transfer from solute molecules to n-hexane radical cations and geminate recombination.

Gas-Phase Oxidation via Ion/Ion Reactions: Pathways and Applications

NASA Astrophysics Data System (ADS)

Pilo, Alice L.; Zhao, Feifei; McLuckey, Scott A.

2017-06-01

Here, we provide an overview of pathways available upon the gas-phase oxidation of peptides and DNA via ion/ion reactions and explore potential applications of these chemistries. The oxidation of thioethers (i.e., methionine residues and S-alkyl cysteine residues), disulfide bonds, S-nitrosylated cysteine residues, and DNA to the [M+H+O]+ derivative via ion/ion reactions with periodate and peroxymono-sulfate anions is demonstrated. The oxidation of neutral basic sites to various oxidized structures, including the [M+H+O]+, [M-H]+, and [M-H-NH3]+ species, via ion/ion reactions is illustrated and the oxidation characteristics of two different oxidizing reagents, periodate and persulfate anions, are compared. Lastly, the highly efficient generation of molecular radical cations via ion/ion reactions with sulfate radical anion is summarized. Activation of the newly generated molecular radical peptide cations results in losses of various neutral side chains, several of which generate dehydroalanine residues that can be used to localize the amino acid from which the dehydroalanine was generated. The chemistries presented herein result in a diverse range of structures that can be used for a variety of applications, including the identification and localization of S-alkyl cysteine residues, the oxidative cleavage of disulfide bonds, and the generation of molecular radical cations from even-electron doubly protonated peptides. [Figure not available: see fulltext.

Photosynthesis, chlorophyll fluorescence, light-harvesting system and photoinhibition resistance of a zeaxanthin-accumulating mutant of Arabidopsis thaliana.

PubMed

Tardy, F; Havaux, M

1996-06-01

The abscisic-acid-deficient aba-1 mutant of Arabidopsis thaliana is unable to epoxidize zeaxanthin. As a consequence, it contains large amounts of this carotenoid and lacks epoxy-xanthophylls. HPLC analysis of pigment contents in leaves, isolated thylakoids and preparations of the major light-harvesting complex of photosystem II (PSII) (LHC-II) indicated that zeaxanthin replaced neoxanthin, violaxanthin and antheraxanthin in the light-harvesting system of PSII in aba-1. Non-denaturing electrophoretic fractionation of solubilized thylakoids showed that the xanthophyll imbalance in aba-1 was associated with a pronounced decrease in trimeric LHC-II in favour of monomeric complexes, with a substantial increase in free pigments (mainly zeaxanthin and chlorophyll b), suggesting a decreased stability of LHC-II. The reduced thermostability of PSII in aba-1 was also deduced from in vivo chlorophyll fluorescence measurements. Wild-type and aba-1 leaves could not be distinguished on the basis of their photosynthetic performance: no significant difference was observed between the two types of leaves for light-limited and light-saturated photosynthetic oxygen evolution, PSII photochemistry and PSII to PSI electron flow. When dark-adapted leaves (grown in white light of 80 mumol m-2s-1) were suddenly exposed to red light of 150 mumol m-2s-1, there was a strong nonphotochemical quenching of chlorophyll fluorescence, the amplitude of which was virtually identical (at steady state) in aba-1 and wild-type leaves, despite the fact that the xanthophyll cycle pigment pool was completely in the form of zeaxanthin in aba-1 and almost exclusively in the form of violaxanthin in the wild type. A high concentration of zeaxanthin in aba-1 thylakoids did not, in itself, provide any particular protection against the photoinhibition of PSII. Taken together, the presented results indicate the following: (1) zeaxanthin can replace epoxy-xanthophylls in LHC-II without significantly affecting the photochemical efficiency of PSII; (2) zeaxanthin does not play any specific role in direct (thermal) energy dissipation in PSII; (3) the photoprotective action of the xanthophyll cycle (rapid photoconversion of violaxanthin to zeaxanthin) is not based on the mere substitution of violaxanthin by zeaxanthin in the chlorophyll antennae.

Aromatic hydroxylation by cytochrome P450: model calculations of mechanism and substituent effects.

PubMed

Bathelt, Christine M; Ridder, Lars; Mulholland, Adrian J; Harvey, Jeremy N

2003-12-10

The mechanism and selectivity of aromatic hydroxylation by cytochrome P450 enzymes is explored using new B3LYP density functional theory computations. The calculations, using a realistic porphyrin model system, show that rate-determining addition of compound I to an aromatic carbon atom proceeds via a transition state with partial radical and cationic character. Reactivity is shown to depend strongly on ring substituents, with both electron-withdrawing and -donating groups strongly decreasing the addition barrier in the para position, and it is shown that the calculated barrier heights can be reproduced by a new dual-parameter equation based on radical and cationic Hammett sigma parameters.

In situ AFM investigation of electrochemically induced surface-initiated atom-transfer radical polymerization.

PubMed

Li, Bin; Yu, Bo; Zhou, Feng

2013-02-12

Electrochemically induced surface-initiated atom-transfer radical polymerization is traced by in situ AFM technology for the first time, which allows visualization of the polymer growth process. It affords a fundamental insight into the surface morphology and growth mechanism simultaneously. Using this technique, the polymerization kinetics of two model monomers were studied, namely the anionic 3-sulfopropyl methacrylate potassium salt (SPMA) and the cationic 2-(metharyloyloxy)ethyltrimethylammonium chloride (METAC). The growth of METAC is significantly improved by screening the ammonium cations by the addition of ionic liquid electrolyte in aqueous solution. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fastest Formation Routes of Nanocarbons in Solution Plasma Processes.

PubMed

Morishita, Tetsunori; Ueno, Tomonaga; Panomsuwan, Gasidit; Hieda, Junko; Yoshida, Akihito; Bratescu, Maria Antoaneta; Saito, Nagahiro

2016-11-14

Although solution-plasma processing enables room-temperature synthesis of nanocarbons, the underlying mechanisms are not well understood. We investigated the routes of solution-plasma-induced nanocarbon formation from hexane, hexadecane, cyclohexane, and benzene. The synthesis rate from benzene was the highest. However, the nanocarbons from linear molecules were more crystalline than those from ring molecules. Linear molecules decomposed into shorter olefins, whereas ring molecules were reconstructed in the plasma. In the saturated ring molecules, C-H dissociation proceeded, followed by conversion into unsaturated ring molecules. However, unsaturated ring molecules were directly polymerized through cation radicals, such as benzene radical cation, and were converted into two- and three-ring molecules at the plasma-solution interface. The nanocarbons from linear molecules were synthesized in plasma from small molecules such as C 2 under heat; the obtained products were the same as those obtained via pyrolysis synthesis. Conversely, the nanocarbons obtained from ring molecules were directly synthesized through an intermediate, such as benzene radical cation, at the interface between plasma and solution, resulting in the same products as those obtained via polymerization. These two different reaction fields provide a reasonable explanation for the fastest synthesis rate observed in the case of benzene.

Fastest Formation Routes of Nanocarbons in Solution Plasma Processes

PubMed Central

Morishita, Tetsunori; Ueno, Tomonaga; Panomsuwan, Gasidit; Hieda, Junko; Yoshida, Akihito; Bratescu, Maria Antoaneta; Saito, Nagahiro

2016-01-01

Although solution-plasma processing enables room-temperature synthesis of nanocarbons, the underlying mechanisms are not well understood. We investigated the routes of solution-plasma-induced nanocarbon formation from hexane, hexadecane, cyclohexane, and benzene. The synthesis rate from benzene was the highest. However, the nanocarbons from linear molecules were more crystalline than those from ring molecules. Linear molecules decomposed into shorter olefins, whereas ring molecules were reconstructed in the plasma. In the saturated ring molecules, C–H dissociation proceeded, followed by conversion into unsaturated ring molecules. However, unsaturated ring molecules were directly polymerized through cation radicals, such as benzene radical cation, and were converted into two- and three-ring molecules at the plasma–solution interface. The nanocarbons from linear molecules were synthesized in plasma from small molecules such as C2 under heat; the obtained products were the same as those obtained via pyrolysis synthesis. Conversely, the nanocarbons obtained from ring molecules were directly synthesized through an intermediate, such as benzene radical cation, at the interface between plasma and solution, resulting in the same products as those obtained via polymerization. These two different reaction fields provide a reasonable explanation for the fastest synthesis rate observed in the case of benzene. PMID:27841288

Electronic spectra of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation and radical

DOE PAGES

Peter R. Craig; Miller, John R.; Havlas, Zdenek; ...

2016-05-02

In this study, properties of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation 1 and its tetra-o-fluoro derivative 1a have been measured and calculated. The B3LYP/TZP optimized geometry of the free cation 1 agrees with a single-crystal X-ray diffraction structure except that in the crystal one of the phenyl substituents is strongly twisted to permit a close-packing interaction of two of its hydrogens with a nearby BF – 4 anion. The low-energy parts of the solution electronic absorption and magnetic circular dichroism (MCD) spectra of 1 and 1a have been interpreted by comparison with TD-DFT (B3LYP/TZP) results. Reduction or pulse radiolysis lead to a neutralmore » 19-electron radical, whose visible absorption and MCD spectra have been recorded and interpreted as well. The reduction is facilitated by ~0.1 V upon going from 1 to 1a« less

Bridge-mediated hopping or superexchange electron-transfer processes in bis(triarylamine) systems

NASA Astrophysics Data System (ADS)

Lambert, Christoph; Nöll, Gilbert; Schelter, Jürgen

2002-09-01

Hopping and superexchange are generally considered to be alternative electron-transfer mechanisms in molecular systems. In this work we used mixed-valence radical cations as model systems for the investigation of electron-transfer pathways. We show that substituents attached to a conjugated bridge connecting two triarylamine redox centres have a marked influence on the near-infrared absorption spectra of the corresponding cations. Spectral analysis, followed by evaluation of the electron-transfer parameters using the Generalized Mulliken-Hush theory and simulation of the potential energy surfaces, indicate that hopping and superexchange are not alternatives, but are both present in the radical cation with a dimethoxybenzene bridge. We found that the type of electron-transfer mechanism depends on the bridge-reorganization energy as well as on the bridge-state energy. Because superexchange and hopping follow different distance laws, our findings have implications for the design of new molecular and polymeric electron-transfer materials.

Stable Organic Radicals as Hole Injection Dopants for Efficient Optoelectronics.

PubMed

Bin, Zhengyang; Guo, Haoqing; Liu, Ziyang; Li, Feng; Duan, Lian

2018-02-07

Precursors of reactive organic radicals have been widely used as n-dopants in electron-transporting materials to improve electron conductivity and enhance electron injection. However, the utilization of organic radicals in hole counterparts has been ignored. In this work, stable organic radicals have been proved for the first time to be efficient dopants to enhance hole injection. From the absorbance spectra and the ultraviolet photoelectron spectra, we could observe an efficient electron transfer between the organic radical, (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl (TTM-1Cz), and the widely used hole injection material, 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN). When the unpaired electron of TTM-1Cz is transferred to HAT-CN, it would be oxidized to a TTM-1Cz cation with a newly formed lowest unoccupied molecular orbital which is quite close to the highest occupied molecular orbital (HOMO) of the hole-transporting material (HTM). In this way, the TTM-1Cz cation would promote the electron extraction from the HOMO of the HTM and improve hole injection. Using TTM-1Cz-doped HAT-CN as the hole injection layer, efficient organic light-emitting diodes with extremely low voltages can be attained.

Closed-Shell Polycyclic Aromatic Hydrocarbon Cations: A New Category of Interstellar Polycyclic Aromatic Hydrocarbons

NASA Technical Reports Server (NTRS)

Hudgins, Douglas M.; Bauschlicher, Charles W., Jr.; Allamandola, Louis J.; DeVincenzi, Donald (Technical Monitor)

2001-01-01

Density functional theory has been employed to calculate the harmonic frequencies and intensities of a range of polycyclic aromatic hydrocarbon (PAH) cations that explore both size and electronic structure effects of the infrared spectroscopic properties of these species. The sample extends the size range of PAH species considered to more than 50 carbon atoms and includes several representatives from each of two heretofore unexplored categories of PAH cations: (1) fully benzenoid PAH cations whose carbon skeleton is composed of an odd number of carbon atoms (C(sub odd) PAHs); and (2) protonated PAH cations (HPAH+). Unlike the radical electronic structures of the PAH cations that have been the subject of previous theoretical and experimental work, the species in these two classes have a closed-shell electronic configuration. The calculated spectra of circumcoronene, C54H18 in both neutral and (radical) cationic form are also reported and compared with those of the other species. Overall, the C(sub odd) PAHs spectra are dominated by strong CC stretching modes near 1600 cm(exp -1) and display spectra that are remarkably insensitive to molecular size. The HPAH+ species evince a more complex spectrum consistent with the added contributions of aliphatic modes and their generally lower symmetry. Finally, for both classes of closed-shell cations, the intensity of the aromatic CH stretching modes is found to increase with molecular size far out of proportion with the number of CH groups, approaching a value more typical of neutral PAHs for the largest species studied.

Lutein and zeaxanthin supplementation reduces photo-oxidative damage and modulates the expression of inflammation related genes in retinal pigment epithelial cells

USDA-ARS?s Scientific Manuscript database

Oxidative damage and inflammation are related to the pathogenesis of age-related macular degeneration (AMD). Epidemiologic studies suggest that insufficient dietary lutein and zeaxanthin intake or lower serum zeaxanthin levels are associated with increased risk for AMD. The objective of this work w...

Pyrimidine Nucleobase Radical Reactivity in DNA and RNA.

PubMed

Greenberg, Marc M

2016-11-01

Nucleobase radicals are major products of the reactions between nucleic acids and hydroxyl radical, which is produced via the indirect effect of ionizing radiation. The nucleobase radicals also result from hydration of cation radicals that are produced via the direct effect of ionizing radiation. The role that nucleobase radicals play in strand scission has been investigated indirectly using ionizing radiation to generate them. More recently, the reactivity of nucleobase radicals resulting from formal hydrogen atom or hydroxyl radical addition to pyrimidines has been studied by independently generating the reactive intermediates via UV-photolysis of synthetic precursors. This approach has provided control over where the reactive intermediates are produced within biopolymers and facilitated studying their reactivity. The contributions to our understanding of pyrimidine nucleobase radical reactivity by this approach are summarized.

Pyrimidine nucleobase radical reactivity in DNA and RNA

NASA Astrophysics Data System (ADS)

Greenberg, Marc M.

2016-11-01

Nucleobase radicals are major products of the reactions between nucleic acids and hydroxyl radical, which is produced via the indirect effect of ionizing radiation. The nucleobase radicals also result from hydration of cation radicals that are produced via the direct effect of ionizing radiation. The role that nucleobase radicals play in strand scission has been investigated indirectly using ionizing radiation to generate them. More recently, the reactivity of nucleobase radicals resulting from formal hydrogen atom or hydroxyl radical addition to pyrimidines has been studied by independently generating the reactive intermediates via UV-photolysis of synthetic precursors. This approach has provided control over where the reactive intermediates are produced within biopolymers and facilitated studying their reactivity. The contributions to our understanding of pyrimidine nucleobase radical reactivity by this approach are summarized.

Visible-Light Initiated Free-Radical/Cationic Ring-Opening Hybrid Photopolymerization of Methacrylate/Epoxy: Polymerization Kinetics, Crosslinking Structure, and Dynamic Mechanical Properties.

PubMed

Ge, Xueping; Ye, Qiang; Song, Linyong; Misra, Anil; Spencer, Paulette

2015-04-01

The effects of polymerization kinetics and chemical miscibility on the crosslinking structure and mechanical properties of polymers cured by visible-light initiated free-radical/cationic ring-opening hybrid photopolymerization are determined. A three-component initiator system is used and the monomer system contains methacrylates and epoxides. The photopolymerization kinetics is monitored in situ by Fourier transform infrared-attenuated total reflectance. The crosslinking structure is studied by modulated differential scanning calorimetry and dynamic mechanical analysis. X-ray microcomputed tomography is used to evaluate microphase separation. The mechanical properties of polymers formed by hybrid formed by free-radical polymerization. These investigations mark the first time that the benefits of the chain transfer reaction between epoxy and hydroxyl groups of methacrylate, on the crosslinking network and microphase separation during hybrid visible-light initiated photopolymerization, have been determined.

Double C-H activation of ethane by metal-free SO2*+ radical cations.

PubMed

de Petris, Giulia; Cartoni, Antonella; Troiani, Anna; Barone, Vincenzo; Cimino, Paola; Angelini, Giancarlo; Ursini, Ornella

2010-06-01

The room-temperature C-H activation of ethane by metal-free SO(2)(*+) radical cations has been investigated under different pressure regimes by mass spectrometric techniques. The major reaction channel is the conversion of ethane to ethylene accompanied by the formation of H(2)SO(2)(*+), the radical cation of sulfoxylic acid. The mechanism of the double C-H activation, in the absence of the single activation product HSO(2)(+), is elucidated by kinetic studies and quantum chemical calculations. Under near single-collision conditions the reaction occurs with rate constant k=1.0 x 10(-9) (+/-30%) cm(3) s(-1) molecule(-1), efficiency=90%, kinetic isotope effect k(H)/k(D)=1.1, and partial H/D scrambling. The theoretical analysis shows that the interaction of SO(2)(*+) with ethane through an oxygen atom directly leads to the C-H activation intermediate. The interaction through sulfur leads to an encounter complex that rapidly converts to the same intermediate. The double C-H activation occurs by a reaction path that lies below the reactants and involves intermediates separated by very low energy barriers, which include a complex of the ethyl cation suitable to undergo H/D scrambling. Key issues in the observed reactivity are electron-transfer processes, in which a crucial role is played by geometrical constraints. The work shows how mechanistic details disclosed by the reactions of metal-free electrophiles may contribute to the current understanding of the C-H activation of ethane.

Electronic Effects on Room-Temperature, Gas-Phase C-H Bond Activations by Cluster Oxides and Metal Carbides: The Methane Challenge.

PubMed

Schwarz, Helmut; Shaik, Sason; Li, Jilai

2017-12-06

This Perspective discusses a story of one molecule (methane), a few metal-oxide cationic clusters (MOCCs), dopants, metal-carbide cations, oriented-electric fields (OEFs), and a dizzying mechanistic landscape of methane activation! One mechanism is hydrogen atom transfer (HAT), which occurs whenever the MOCC possesses a localized oxyl radical (M-O • ). Whenever the radical is delocalized, e.g., in [MgO] n •+ the HAT barrier increases due to the penalty of radical localization. Adding a dopant (Ga 2 O 3 ) to [MgO] 2 •+ localizes the radical and HAT transpires. Whenever the radical is located on the metal centers as in [Al 2 O 2 ] •+ the mechanism crosses over to proton-coupled electron transfer (PCET), wherein the positive Al center acts as a Lewis acid that coordinates the methane molecule, while one of the bridging oxygen atoms abstracts a proton, and the negatively charged CH 3 moiety relocates to the metal fragment. We provide a diagnostic plot of barriers vs reactants' distortion energies, which allows the chemist to distinguish HAT from PCET. Thus, doping of [MgO] 2 •+ by Al 2 O 3 enables HAT and PCET to compete. Similarly, [ZnO] •+ activates methane by PCET generating many products. Adding a CH 3 CN ligand to form [(CH 3 CN)ZnO] •+ leads to a single HAT product. The CH 3 CN dipole acts as an OEF that switches off PCET. [MC] + cations (M = Au, Cu) act by different mechanisms, dictated by the M + -C bond covalence. For example, Cu + , which bonds the carbon atom mostly electrostatically, performs coupling of C to methane to yield ethylene, in a single almost barrier-free step, with an unprecedented atomic choreography catalyzed by the OEF of Cu + .

Transients and cooperative action of β-carotene, vitamin E and C in biological systems in vitro under irradiation

NASA Astrophysics Data System (ADS)

Getoff, Nikola; Platzer, Isabel; Winkelbauer, Cornelia

1999-08-01

Using N •3 species as specific electron acceptor a defined ascorbate radical: AH •↔A •-+H + (λ max=360 nm, ɛ=3400 dm 3 mol -1 cm -1) is observed. The attack of DMSO •+ on vit.E results in a vit.E • radical ( k=1×10 9 dm 3 mol -1 s -1; λ max=425 nm, ɛ=2400 dm 3 mol -1 cm -1; 2 k=4.7×10 8 dm 3 mol -1 s -1). Vit.E-acetate leads to the formation of a radical cation (vit.E-ac •+). β-carotene reacts also with DMSO •+ forming a radical cation, β-car •+ ( k=1.75×10 8 dm 3 mol -1 s -1; λ max=942 nm, ɛ=14 600 dm 3 mol -1 cm -1), which probably leads to the formation of a dimer radical cation, (β-car) •+2 ( k=2.5×10 7 dm 3 mol -1 s -1). Using E.coli bacteria (AB1157) as a model system in vitro it was found that all three vitamins are rather efficient radiation protecting agents. They can also increase the activity of cytostatica, e.g., mitomycin C (MMC), by electron transfer process. The mixture of vit.E-ac and β-car acts contradictory, but adding vit.C to it a strong cooperative enhancement of the MMC activity is observed once again. A relationship between the pulse radiolysis and the radiation biological data is found and discussed. A possible explanation of the previously reported trials concerning the role of vit.E and β-car on the increased occurence of lung and other types of cancer in smokers and drinkers is presented.

Peroxidase-type reactions suggest a heterolytic/nucleophilic O–O joining mechanism in the heme-dependent chlorite dismutase†

PubMed Central

Mayfield, Jeffrey A.; Blanc, Béatrice; Rodgers, Kenton R.; Lukat-Rodgers, Gudrun S.; DuBois, Jennifer L.

2015-01-01

Heme-containing chlorite dismutases (Clds) catalyze a highly unusual O–O bond forming reaction. The O–O cleaving reactions of hydrogen peroxide and peracetic acid (PAA) with the Cld from Dechloromonas aromatica (DaCld) were studied to better understand the Cl–O cleavage of the natural substrate and subsequent O–O bond formation. While reactions with H2O2 resulted in slow destruction of the heme, at acidic pH, heterolytic cleavage of the O–O bond of PAA cleanly yielded the ferryl porphyrin cation radical (Compound I). At alkaline pH, the reaction proceeds more rapidly and the first observed intermediate is a ferryl heme. Freezequench EPR confirmed that the latter has an uncoupled protein-based radical, indicating that Compound I is the first intermediate formed at all pH values and that radical migration is faster at alkaline pH. These results suggest by analogy that two-electron Cl–O bond cleavage to yield a ferryl-porphyrin cation radical is the most likely initial step in O–O bond formation from chlorite. PMID:24001266

Near-UV Photodissociation of Tryptic Peptide Cation Radicals. Scope and Effects of Amino Acid Residues and Radical Sites

NASA Astrophysics Data System (ADS)

Nguyen, Huong T. H.; Tureček, František

2017-07-01

Peptide cation-radical fragment ions of the z-type, [●AXAR+], [●AXAK+], and [●XAR+], where X = A, C, D, E, F, G, H, K, L, M, N, P, Y, and W, were generated by electron transfer dissociation of peptide dications and investigated by MS3-near-ultraviolet photodissociation (UVPD) at 355 nm. Laser-pulse dependence measurements indicated that the ion populations were homogeneous for most X residues except phenylalanine. UVPD resulted in dissociations of backbone CO-NH bonds that were accompanied by hydrogen atom transfer, producing fragment ions of the [yn]+ type. Compared with collision-induced dissociation, UVPD yielded less side-chain dissociations even for residues that are sensitive to radical-induced side-chain bond cleavages. The backbone dissociations are triggered by transitions to second ( B) excited electronic states in the peptide ion R-CH●-CONH- chromophores that are resonant with the 355-nm photon energy. Electron promotion increases the polarity of the B excited states, R-CH+-C●(O-)NH-, and steers the reaction to proceed by transfer of protons from proximate acidic Cα and amide nitrogen positions.

Synchrotron-based valence shell photoionization of CH radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gans, B., E-mail: berenger.gans@u-psud.fr, E-mail: christian.alcaraz@u-psud.fr; Falvo, C.; Holzmeier, F.

2016-05-28

We report the first experimental observations of X{sup +} {sup 1}Σ{sup +}←X {sup 2}Π and a{sup +} {sup 3}Π←X {sup 2}Π single-photon ionization transitions of the CH radical performed on the DESIRS beamline at the SOLEIL synchrotron facility. The radical was produced by successive hydrogen-atom abstractions on methane by fluorine atoms in a continuous microwave discharge flow tube. Mass-selected ion yields and photoelectron spectra were recorded as a function of photon energy using a double imaging photoelectron/photoion coincidence spectrometer. The ion yield appears to be strongly affected by vibrational and electronic autoionizations, which allow the observation of high Rydberg statesmore » of the neutral species. The photoelectron spectra enable the first direct determinations of the adiabatic ionization potential and the energy of the first triplet state of the cation with respect to its singlet ground state. This work also brings valuable information on the complex electronic structure of the CH radical and its cation and adds new observations to complement our understanding of Rydberg states and autoionization processes.« less

Local description of a polyenic radical cation

NASA Astrophysics Data System (ADS)

Karafiloglou, P.; Kapsomenos, G.

1995-06-01

The various local electronic events occurring in a radical cation of a linear polyene with even number of centers are investigated by means of the calculation of the expectation values of second quantized density operators, in the framework of the general poly-electron population analysis. Two series of calculations in two limit geometries (a strong alternant and a polaron-like one) are performed by using as analysers both natural AOs in ab initio correlated wave functions, as well as the model orthogonal AOs in PPP + full CI ones. The probabilities of finding simultaneously the positive charge (+) and the radical center (·) follows, in accord with basic chemical intuition, an oscillating (even-odd) law, even at distant AO positions. The probability of having a transmission of the (+) charge through the π-bonds (when the (·) is located in one extremity of the polyene) is greater than this of the transmission of the (·). Comparing the radical cation with the parent polyene, it is shown that oxidation creates an important trend of single-double bond inversion even in strongly alternant geometry; this effect is more pronounced in bonds of the middle. The examination of various CDW structures shows that some of them can have small or negligible contributions; this counterintuitive and cooperative effect is rationalized by means of Moffitt's theorem. All the above effects are not the consequence of the polaron-like geometry, but are controlled from the topology of n-centers linearly disposed and involving ( n-1) electrons.

Lutein and zeaxanthin: Role as macular pigment and factors that control bioavailability from egg yolks and nanoemulsions

NASA Astrophysics Data System (ADS)

Vishwanathan, Rohini

Lutein and zeaxanthin, two oxygenated carotenoids, exclusively accumulate in the macula, protecting the underlying photoreceptors and retinal pigment epithelial cells from damaging blue radiation of sunlight. As macular pigment, lutein and zeaxanthin are also potent antioxidants protecting the vulnerable regions of retina from free radical injury. Oxidative stress and cumulative light damage play an important role in pathogenesis of age-related macular degeneration (AMD), the leading cause of vision loss in the elderly population. Antioxidant and lutein supplementation has been shown to decrease the risk and prevent the progression of AMD. The egg yolk is a highly bioavailable source of lutein and zeaxanthin and thus a possible contender for AMD prevention and treatment. Consumption of 2 egg yolks/d for 5 weeks was shown herein to significantly increase serum lutein and zeaxanthin concentration and clinically improve macular pigment concentrations at 0.5° retinal eccentricity in an older adult population taking cholesterol-lowering statins. Four egg yolks/d not only raised serum lutein and zeaxanthin significantly but also macular pigment densities at 0.25°, 0.5° and 1° retinal eccentricity. A positive outcome of the 2 egg yolk consumption was the significant increase in serum HDL-C with a tendency of serum LDL-C to decrease, although not significantly. Four egg yolks/d seemed to cross the threshold for dietary cholesterol tolerance as serum LDL-C tended to increase, although not significantly, despite the significant increase in serum HDL-C. There is a strong possibility that greater build up of lutein and zeaxanthin in the macula may have been observed with 2 egg yolks/d if the intervention period was longer than 5 weeks. Addition of up to 2 eggs a day to the diet is suggested to benefit an older adult population, especially those who are already taking cholesterol-lowering statins by (a) building their macular pigment and possibly protect against AMD and (b) raising serum HDL-C without an adverse affect on serum LDL-C and TC:HDL-C ratio. Increased cholesterol, lutein and zeaxanthin intake from the 2 and 4 egg yolk interventions did not decrease the absorption of other carotenoids, such as alpha-cryptoxanthin, beta-cryptoxanthin, lycopene, alpha-carotene and beta-carotene, tocopherols and retinol from the diet. An unexpected increase was observed in serum alpha-cryptoxanthin and gamma-tocopherol concentrations during the 4 egg yolk phase, these carotenoids are normally present in low concentrations in serum. Lipoprotein distribution of carotenoids and tocopherols was also not affected by the increased egg consumption. In the pursuit of designing a highly bioavailable matrix for lutein/zeaxanthin, similar to the egg yolk micellar matrix, nanoemulsion formulations of lutein were developed using the MicrofluidizerRTM Processor technology. Lutein nanoemulsions are O/W emulsions of lutein which have particle sizes in the nanometer range (≤ 200 nm). Lutein consumed orally as a nanoemulsion was shown to have significantly greater bioavailability than lutein supplement-pills in pilot-scale clinical studies described here. However, lutein nanoemulsions did not raise plasma lutein concentrations to the same extent as egg yolks in a study performed on BALB/c mice. Formation of mixed micelles in the intestinal lumen during digestion and uptake of these micelles by enterocytes are crucial steps that dictate bioavailability i.e. the proportion of ingested lutein/carotenoid that enters the blood circulation and accumulates in the peripheral tissues such as the macula. In-vitro stomach and intestinal digestion experiments showed lutein nanoemulsions have significantly greater micellarization efficiency compared to egg yolks. Nanoemulsions with a phospholipid (PL) emulsifier containing 80% phosphatidyl choline (PC) or Polysorbate 80 as the emulsifier had better ability to form micelles during the intestinal digestion phase compared to a PL emulsifier with only 45% PC content. The micellar matrix coupled with nanometer sized particles thus favored micelle formation even in the absence of additional fat. Despite the greater micellar efficiency with the nanoemulsions, significantly greater lutein uptake by Caco-2 cells was observed from egg yolk micelles compared to nanoemulsion micelles. These findings suggest that even though micellarization efficiency was higher with the nanoemulsions, the fat content of the micelles may play a role in cellular uptake of lutein. The lutein nanoemulsion delivery system could be improved by increasing the triglyceride content and modifying the phospholipid emulsifier (may be using emulsifiers with higher lysoPC content), in such a way so as to increase cellular uptake of lutein without increasing the particle size. Thus, nanometer particle size alone does not necessarily imply greater bioavailability in the case of lutein. The matrix of delivery of lutein is suggested to be of equal importance. With improved bioavailability nanoemulsions of lutein and zeaxanthin added to a beverage would be easier for an older adult population to consume as opposed to large supplement-pills. Nanometer particle size in combination with an ideal matrix may also avoid the need to consume pharmacological doses of these carotenoids to achieve significant health benefits.

Surface functionalized SiO2 nanoparticles with cationic polymers via the combination of mussel inspired chemistry and surface initiated atom transfer radical polymerization: Characterization and enhanced removal of organic dye.

PubMed

Huang, Qiang; Liu, Meiying; Mao, Liucheng; Xu, Dazhuang; Zeng, Guangjian; Huang, Hongye; Jiang, Ruming; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

2017-08-01

Monodispersed SiO 2 particles functionalized with cationic polymers poly-((3-acrylamidopropyl)trimethylammonium chloride) (PAPTCl) were prepared using mussel inspired surface modification strategy and surface initiated atom transfer radical polymerization (SI-ATRP). Fourier transform infrared spectroscopy, transmission electron microscope, thermogravimetric analysis, X-ray photoelectron spectroscopy, and zeta potential were employed to characterize these SiO 2 samples. The adsorption performance of the functionalized SiO 2 (donated as SiO 2 -PDA-PAPTCl) towards anionic organic dye Congo red (CR) was investigated to evaluate their potential environmental applications. We demonstrated that the surface of SiO 2 particles can be successfully functionalized with cationic PAPTCl. The adsorption capability of as-prepared SiO 2 was found to increases from 28.70 and 106.65mg/g after surface grafted with cationic polymers. The significant enhancement in the adsorption capability of SiO 2 -PDA-PAPTCl is mainly attributed to the introduction of cationic polymers. More importantly, this strategy is expected to be promising for fabrication of many other functional polymer nanocomposites for environmental applications due to the universality of mussel inspired chemistry and well designability and good monomer adaptability of SI-ATRP. Copyright © 2017 Elsevier Inc. All rights reserved.

Radiofrequency attenuator and method

DOEpatents

Warner, Benjamin P [Los Alamos, NM; McCleskey, T Mark [Los Alamos, NM; Burrell, Anthony K [Los Alamos, NM; Agrawal, Anoop [Tucson, AZ; Hall, Simon B [Palmerston North, NZ

2009-01-20

Radiofrequency attenuator and method. The attenuator includes a pair of transparent windows. A chamber between the windows is filled with molten salt. Preferred molten salts include quarternary ammonium cations and fluorine-containing anions such as tetrafluoroborate (BF.sub.4.sup.-), hexafluorophosphate (PF.sub.6.sup.-), hexafluoroarsenate (AsF.sub.6.sup.-), trifluoromethylsulfonate (CF.sub.3SO.sub.3.sup.-), bis(trifluoromethylsulfonyl)imide ((CF.sub.3SO.sub.2).sub.2N.sup.-), bis(perfluoroethylsulfonyl)imide ((CF.sub.3CF.sub.2SO.sub.2).sub.2N.sup.-) and tris(trifluoromethylsulfonyl)methide ((CF.sub.3SO.sub.2).sub.3C.sup.-). Radicals or radical cations may be added to or electrochemically generated in the molten salt to enhance the RF attenuation.

Radiofrequency attenuator and method

DOEpatents

Warner, Benjamin P [Los Alamos, NM; McCleskey, T Mark [Los Alamos, NM; Burrell, Anthony K [Los Alamos, NM; Agrawal, Anoop [Tucson, AZ; Hall, Simon B [Palmerston North, NZ

2009-11-10

Radiofrequency attenuator and method. The attenuator includes a pair of transparent windows. A chamber between the windows is filled with molten salt. Preferred molten salts include quarternary ammonium cations and fluorine-containing anions such as tetrafluoroborate (BF.sub.4.sup.-), hexafluorophosphate (PF.sub.6.sup.-), hexafluoroarsenate (AsF.sub.6.sup.-), trifluoromethylsulfonate (CF.sub.3SO.sub.3.sup.-), bis(trifluoromethylsulfonyl)imide ((CF.sub.3SO.sub.2).sub.2N.sup.-), bis(perfluoroethylsulfonyl)imide ((CF.sub.3CF.sub.2SO.sub.2).sub.2N.sup.-) and tris(trifluoromethylsulfonyl)methide ((CF.sub.3SO.sub.2).sub.3 C.sup.-). Radicals or radical cations may be added to or electrochemically generated in the molten salt to enhance the RF attenuation.

The tetrahydrobiopterin radical with high- and low-spin heme in neuronal nitric oxide synthase -- a new indicator of the extent of NOS coupling

PubMed Central

Krzyaniak, Matthew D.; Cruce, Alex A.; Vennam, Preethi; Lockart, Molly; Berka, Vladimir; Tsai, Ah-Lim; Bowman, Michael K.

2016-01-01

Reaction intermediates trapped during the single-turnover reaction of the neuronal ferrous nitric oxide synthase oxygenase domain (Fe(II)nNOSOX) show four EPR spectra of free radicals. Fully-coupled nNOSOX with cofactor (tetrahydrobiopterin, BH4) and substrate (l-arginine) forms the typical BH4 cation radical with an EPR spectrum ~4.0 mT wide and hyperfine tensors similar to reports for a biopterin cation radical in inducible NOSOX (iNOSOX). With excess thiol, nNOSox lacking BH4 and l-arg is known to produce superoxide. In contrast, we find that nNOSOX with BH4 but no l-arg forms two radicals with rather different, fast (~ 250 µs at 5 K) and slower (~ 500 µs at 20 K), electron spin relaxation rates and a combined ~7.0 mT wide EPR spectrum. Rapid freeze-quench CW- and pulsed-EPR measurements are used to identify these radicals and their origin. These two species are the same radical with identical nuclear hyperfine couplings, but with spin-spin couplings to high-spin (4.0 mT component) or low-spin (7.0 mT component) Fe(III) heme. Uncoupled reactions of nNOS leave the enzyme in states that can be chemically reduced to sustain unregulated production of NO and reactive oxygen species in ischemia-reperfusion injury. The broad EPR signal is a convenient indicator of uncoupled nNOS reactions producing low-spin Fe(III) heme. PMID:27989753

Polar-Nonpolar Radical Copolymerization under Li+ Catalysis

DTIC Science & Technology

2008-09-21

bonds or aromatic rings. Thus, we propose that a transfer of a methyl radical from CB11Me12C to IB triggers a radical polymerization chain that yields ...b-PIB and the resulting CB11Me11 byproduct concurrently triggers a cationic polymerization chain that yields l-PIB terminated with a carborate anion...tetrahydrofuran and passed through a column of alumina about five times to remove the bulk of the catalyst. A Soxhlet apparatus was used to recover

Formation and Stabilization of Environmentally Persistent Free Radicals Induced by the Interaction of Anthracene with Fe(III)-Modified Clays.

PubMed

Jia, Hanzhong; Nulaji, Gulimire; Gao, Hongwei; Wang, Fu; Zhu, Yunqing; Wang, Chuanyi

2016-06-21

Environmentally persistent free radicals (EPFRs) are occasionally detected in Superfund sites but the formation of EPFRs induced by polycyclic aromatic hydrocarbons (PAHs) is not well understood. In the present work, the formation of EPFRs on anthracene-contaminated clay minerals was quantitatively monitored via electron paramagnetic resonance (EPR) spectroscopy, and surface/interface-related environmental influential factors were systematically explored. The obtained results suggest that EPFRs are more readily formed on anthracene-contaminated Fe(III)-montmorillonite than in other tested systems. Depending on the reaction condition, more than one type of organic radicals including anthracene-based radical cations with g-factors of 2.0028-2.0030 and oxygenic carbon-centered radicals featured by g-factors of 2.0032-2.0038 were identified. The formed EPFRs are stabilized by their interaction with interlayer surfaces, and such surface-bound EPFRs exhibit slow decay with 1/e-lifetime of 38.46 days. Transformation pathway and possible mechanism are proposed on the basis of experimental results and quantum mechanical simulations. Overall, the formation of EPFRs involves single-electron-transfer from anthracene to Fe(III) initially, followed by H2O addition on formed aromatic radical cation. Because of their potential exposure in soil and atmosphere, such clay surface-associated EPFRs might induce more serious toxicity than PAHs and exerts significant impacts on human health.

Exploring Closed-Shell Cationic Phenalenyl: From Catalysis to Spin Electronics.

PubMed

Mukherjee, Arup; Sau, Samaresh Chandra; Mandal, Swadhin K

2017-07-18

The odd alternant hydrocarbon phenalenyl (PLY) can exist in three different forms, a closed-shell cation, an open-shell radical, and a closed-shell anion, using its nonbonding molecular orbital (NBMO). The chemistry of PLY-based molecules began more than five decades ago, and so far, the progress has mainly involved the open-shell neutral radical state. Over the last two decades, we have witnessed the evolution of a range of PLY-based radicals generating an array of multifunctional materials. However, it has been admitted that the practical applications of PLY radicals are greatly challenged by the low stability of the open-shell (radical) state. Recently, we took a different route to establish the utility of these PLY molecules using the closed-shell cationic state. In such a design, the closed-shell unit of PLY can readily accept free electrons, stabilizing in its NBMO upon generation of the open-shell state of the molecule. Thus, one can synthetically avoid the unstable open-shell state but still take advantage of this state by in situ generating the radical through external electron transfer or spin injection into the empty NBMO. It is worth noting that such approaches using closed-shell phenalenyl have been missing in the literature. This Account focuses on our recent developments using the closed-shell cationic state of the PLY molecule and its application in broad multidisciplinary areas spanning from catalysis to spin electronics. We describe how this concept has been utilized to develop a variety of homogeneous catalysts. For example, this concept was used in designing an iron(III) PLY-based electrocatalyst for a single-compartment H 2 O 2 fuel cell, which delivered the best electrocatalytic activity among previously reported iron complexes, organometallic catalysts for various homogeneous organic transformations (hydroamination and polymerization), an organic Lewis acid catalyst for the ring opening of epoxides, and transition-metal-free C-H functionalization catalysts. Moreover, this concept of using the empty NBMO present in the closed-shell cationic state of the PLY moiety to capture electron(s) was further extended to an entirely different area of spin electronics to design a PLY-based spin-memory device, which worked by a spin-filtration mechanism using an organozinc compound based on a PLY backbone deposited over a ferromagnetic substrate. In this Account, we summarize our recent efforts to understand how this unexplored closed-shell state of the phenalenyl molecule, which has been known for over five decades, can be utilized in devising an array of materials that not only are important from an organometallic chemistry or organic chemistry point of view but also provide new understanding for device physics.

What Is the Structure of the Naphthalene-Benzene Heterodimer Radical Cation? Binding Energy, Charge Delocalization, and Unexpected Charge-Transfer Interaction in Stacked Dimer and Trimer Radical Cations.

PubMed

Attah, Isaac K; Platt, Sean P; Meot-Ner Mautner, Michael; El-Shall, M Samy; Peverati, Roberto; Head-Gordon, Martin

2015-04-02

The binding energy of the naphthalene(+•)(benzene) heterodimer cation has been determined to be 7.9 ± 1 kcal/mol for C10H8(+•)(C6H6) and 8.1 ± 1 kcal/mol for C10H8(+•)(C6D6) by equilibrium thermochemical measurements using the mass-selected drift cell technique. A second benzene molecule binds to the C10H8(+•)(C6D6) dimer with essentially the same energy (8.4 ± 1 kcal/mol), suggesting that the two benzene molecules are stacked on opposite sides of the naphthalene cation in the (C6D6)C10H8(+•)(C6D6) heterotrimer. The lowest-energy isomers of the C10H8(+•)(C6D6) and (C6D6)C10H8(+•)(C6D6) dimer and trimer calculated using the M11/cc-pVTZ method have parallel stacked structures with enthalpies of binding (-ΔH°) of 8.4 and 9.0 kcal/mol, respectively, in excellent agreement with the experimental values. The stacked face-to-face class of isomers is calculated to have substantial charge-transfer stabilization of about 45% of the total interaction energy despite the large difference between the ionization energies of benzene and naphthalene. Similarly, significant delocalization of the positive charge is found among all three fragments of the (C6D6)C10H8(+•)(C6D6) heterotrimer, thus leaving only 46% of the total charge on the central naphthalene moiety. This unexpectedly high charge-transfer component results in activating two benzene molecules in the naphthalene(+•)(benzene)2 heterotrimer cation to associate with a third benzene molecule at 219 K to form a benzene trimer cation and a neutral naphthalene molecule. The global minimum of the C10H8(+•)(C6H6)2 heterotrimer is found to be the one where the naphthalene cation is sandwiched between two benzene molecules. It is remarkable, and rather unusual, that the binding energy of the second benzene molecule is essentially the same as that of the first. This is attributed to the enhanced charge-transfer interaction in the stacked trimer radical cation.

Preparation of highly pure zeaxanthin particles from sea water-cultivated microalgae using supercritical anti-solvent recrystallization.

PubMed

Chen, Chao-Rui; Hong, Siang-En; Wang, Yuan-Chuen; Hsu, Shih-Lan; Hsiang, Daina; Chang, Chieh-Ming J

2012-01-01

Xanthophylls, including zeaxanthin, are considered dietary supplements with a potentially positive impact on age-related macular degeneration. Using pilot-scale column fractionation coupled with supercritical anti-solvent (SAS) recrystallization, highly pure zeaxanthin particulates were prepared from ultrasonic extracts of the microalgae, Nannochloropsis oculata, grown in sea water. Column partition chromatography increased the concentration of zeaxanthin from 36.2 mg/g of the ultrasonic extracts to 425.6 mg/g of the collected column fractions. A response surface methodology was systematically designed for the SAS process by changing feed concentration, CO(2) flow rate and anti-solvent pressure. Zeaxanthin-rich particles with a purity of 84.2% and a recovery of 85.3% were produced using supercritical anti-solvent recrystallization from the column eluate at a feed concentration of 1.5 mg/mL, CO(2) flow rate of 48.6 g/min and pressure of 135 bar. Copyright © 2011 Elsevier Ltd. All rights reserved.

IN VITRO MEASUREMENT OF TOTAL ANTIOXIDANT CAPACITY OF CRATAEGUS MACRACANTHA LODD LEAVES.

PubMed

Miftode, Alina Monica; Stefanache, Alina; Spac, A F; Miftode, R F; Miron, Anca; Dorneanu, V

2016-01-01

Crataegus macracantha Lodd, family Rosaceae, is a very rare species in Europe, and unlike Crataegus monogyna is less investigated for pharmacologic activity. To analyze the ability of the lyophilisate of extract obtained from leaves of Crataegus macracantha Lodd (single plant at the Iaşi Botanical Garden) to capture free radicals in vitro. The lyophilisate obtained in Department of Pharmacognosy, Faculty of Pharmacy, "Grigore T. Popa" University of Medicine and Pharmacy Iaşi. The decreased absorbance of chromophore chlorpromazine radical cation in the presence of the lyophilized solutions was studied spectrophotometrically. The indicator radical cation, obtained by oxidation of chlorpromazine by potassium persulfate, has the maximum absorbance at 525 nm. Ascorbic acid was used as a standard antioxidant. The absorbance of radical solution was determined after the addition of a certain amount of lyophilisate at different time intervals. The antioxidant activity was calculated using the calibration curve obtained by plotting the variation in radical solution absorbance depending on ascorbic acid concentration. For each ascorbic acid concentration the area under the curve was calculated from plotting the percentage inhibition of the absorbance at two pre-established time intervals. The results confirm the antioxidant activity of the leaves of Crataegus Macracantha Lodd and by optimizing the proposed analytical methods the antiradical activity can be quickly evaluated with minimal reagent consumption.

Formation and Stabilization of Combustion-Generated, Environmentally Persistent Radicals on Ni(II)O Supported on a Silica Surface

PubMed Central

Vejerano, Eric; Lomnicki, Slawomir M.; Dellinger, Barry

2013-01-01

Previous studies have indicated Environmentally Persistent Free Radicals (EPFRs) are formed when hydroxyl- and chlorine-substituted aromatics chemisorbed on Cu(II)O and Fe(III)2O3 surfaces and were stabilized through their interactions with the surface metal cation. The current study reports our laboratory investigation on the formation and stabilization of EPFRs on an Ni(II)O surface. The EPFRs were produced by the chemisorption of adsorbates on the supported metal oxide surface and transfer of an electron from the adsorbate to the metal center, resulting in reduction of the metal cation. Depending on the temperature and the nature of the adsorbate, more than one type of organic radical was formed. A phenoxyl-type radical, with g-value between 2.0029 and 2.0044, and a semiquinone-type radical, with g-value from 2.0050 to as high as 2.0081, were observed. The half-lives on Ni(II)O were long and ranged from 1.5 to 5.2 days, which were similar to what were observed on Fe(III)2O3,. The yields of the EPFRs formed on Ni(II)O was ~ 8x higher than on Cu(II)O and ~50x higher than on Fe(III)2O3. PMID:22831558

Lutein, Zeaxanthin, and meso-Zeaxanthin: The Basic and Clinical Science Underlying Carotenoid-based Nutritional Interventions against Ocular Disease

PubMed Central

Bernstein, Paul S.; Li, Binxing; Vachali, Preejith P.; Gorusupudi, Aruna; Shyam, Rajalekshmy; Henriksen, Bradley S.; Nolan, John M.

2015-01-01

The human macula uniquely concentrates three carotenoids: lutein, zeaxanthin, and meso-zeaxanthin. Lutein and zeaxanthin must be obtained from dietary sources such as green leafy vegetables and orange and yellow fruits and vegetables, while meso-zeaxanthin is rarely found in diet and is believed to be formed at the macula by metabolic transformations of ingested carotenoids. Epidemiological studies and large-scale clinical trials such as AREDS2 have brought attention to the potential ocular health and functional benefits of these three xanthophyll carotenoids consumed through the diet or supplements, but the basic science and clinical research underlying recommendations for nutritional interventions against age-related macular degeneration and other eye diseases are underappreciated by clinicians and vision researchers alike. In this review article, we first examine the chemistry, biophysics, and physiology of these yellow pigments that are specifically concentrated in the macula lutea through the means of high-affinity binding proteins and specialized transport and metabolic proteins where they play important roles as short-wavelength (blue) light-absorbers and localized, efficient antioxidants in a region at high risk for light-induced oxidative stress. Next, we turn to clinical evidence supporting functional benefits of these carotenoids in normal eyes and for their potential protective actions against ocular disease from infancy to old age. PMID:26541886

Zeaxanthin improved diabetes-induced anxiety and depression through inhibiting inflammation in hippocampus.

PubMed

Zhou, Xiaoyan; Gan, Tian; Fang, Gaoxia; Wang, Shangshang; Mao, Yizhen; Ying, Changjiang

2018-06-01

It is generally accepted that inflammation plays a key role in anxiety and depression induced by diabetes. However, the underlying mechanism and effective treatment method of these diabetes-associated behavior disorders remain to be determined. In the present study, we attempted to illuminate the implication of zeaxanthin in anxiety, depression and neuroinflammation caused by hyperglycemia, and further elaborate the relevant mechanism under these neuropsychiatric disorders. In the current work, diabetic rats were induced by high glucose and fat diet followed by a single intraperitoneal injection of streptozocin, and zeaxanthin was orally administration every day (From 6th to 19th week). Diabetes-associated anxiety and depression were assessed using open field test (OFT) and Forced swimming test (FST) respectively. Moreover, the levels of interleukin-6 (IL-6), interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in hippocampus were tested using ELISA and WB. Data showed that long-term zeaxanthin treatment improve diabetic symptoms and alleviate anxiety and depression in diabetic rats. Furthermore, excessive production of IL-6, IL-1β and TNF-α could be reduced with zeaxanthin treatment. In conclusion, we suggested that zeaxanthin can ameliorate diabetes-associated anxiety and depression, inhibit inflammation in diabetic rats. Our results could provide a potential therapeutic approach for the treatment of abnormal behavior induced by hyperglycemia.

Increased nutritional quality of plants for long-duration spaceflight missions through choice of plant variety and manipulation of growth conditions

NASA Astrophysics Data System (ADS)

Cohu, Christopher M.; Lombardi, Elizabeth; Adams, William W.; Demmig-Adams, Barbara

2014-02-01

Low levels of radiation during spaceflight increase the incidence of eye damage and consumption of certain carotenoids (especially zeaxanthin), via a whole-food-based diet (rather than from supplements), is recommended to protect human vision against radiation damage. Availability of fresh leafy produce has, furthermore, been identified as desirable for morale during long spaceflight missions. We report that only trace amounts of zeaxanthin are retained post-harvest in leaves grown under conditions conducive to rapid plant growth. We show that growth of plants under cool temperatures and very high light can trigger a greater retention of zeaxanthin, while, however, simultaneously retarding plant growth. We here introduce a novel growth condition—low growth light supplemented with several short daily light pulses of higher intensity—that also triggers zeaxanthin retention, but without causing any growth retardation. Moreover, two plant varieties with different hardiness exhibited a different propensity for zeaxanthin retention. These findings demonstrate that growth light environment and plant variety can be exploited to simultaneously optimize nutritional quality (with respect to zeaxanthin and two other carotenoids important for human vision, lutein and β-carotene) as well as biomass production of leafy greens suitable as bioregenerative systems for long-duration manned spaceflight missions.

Understanding titanium-catalysed radical-radical reactions: a DFT study unravels the complex kinetics of ketone-nitrile couplings.

PubMed

Streuff, Jan; Himmel, Daniel; Younas, Sara L

2018-04-03

The computational investigation of a titanium-catalysed reductive radical-radical coupling is reported. The results match the conclusions from an earlier experimental study and enable a further interpretation of the previously observed complex reaction kinetics. Furthermore, the interplay between neutral and cationic reaction pathways in titanium(iii)-catalysed reactions is investigated for the first time. The results show that hydrochloride additives and reaction byproducts play an important role in the respective equilibria. A full reaction profile is assembled and the computed activation barrier is found to be in reasonable agreement with the experiment. The conclusions are of fundamental importance to the field of low-valent titanium catalysis and the understanding of related catalytic radical-radical coupling reactions.

Raman and IR studies and DFT calculations of the vibrational spectra of 2,4-Dithiouracil and its cation and anion

NASA Astrophysics Data System (ADS)

Singh, R.; Yadav, R. A.

2014-09-01

Raman and FTIR spectra of solid 2,4-Dithiouracil (DTU) at room temperature have been recorded. DFT calculations were carried out to compute the optimized molecular geometries, GAPT charges and fundamental vibrational frequencies along with their corresponding IR intensities, Raman activities and depolarization ratios of the Raman bands for the neutral DTU molecule and its cation (DTU+) and anion (DTU-) using the Gaussian-03 software. Addition of one electron leads to increase in the atomic charges on the sites N1 and N3 and decrease in the atomic charges on the sites S8 and S10. Due to ionization of DTU molecule, the charge at the site C6 decreases in the cationic and anionic radicals of DTU as compared to its neutral species. As a result of anionic radicalization, the C5sbnd C6 bond length increases and loses its double bond character while the C4sbnd C5 bond length decreases. In the case of the DTU+ ion the IR and Raman band corresponding to the out-of-phase coupled Nsbnd H stretching mode is strongest amongst the three species. The anionic DTU radical is found to be the most stable. The two NH out-of-plane bending modes are found to originate due to out-of-phase and in-phase coupling of the two NH bonds in the anion and cation contrary to the case of the neutral DTU molecule in which the out-of-plane bending motions of the two NH bonds are not coupled.

Raman and IR studies and DFT calculations of the vibrational spectra of 2,4-Dithiouracil and its cation and anion.

PubMed

Singh, R; Yadav, R A

2014-09-15

Raman and FTIR spectra of solid 2,4-Dithiouracil (DTU) at room temperature have been recorded. DFT calculations were carried out to compute the optimized molecular geometries, GAPT charges and fundamental vibrational frequencies along with their corresponding IR intensities, Raman activities and depolarization ratios of the Raman bands for the neutral DTU molecule and its cation (DTU+) and anion (DTU-) using the Gaussian-03 software. Addition of one electron leads to increase in the atomic charges on the sites N1 and N3 and decrease in the atomic charges on the sites S8 and S10. Due to ionization of DTU molecule, the charge at the site C6 decreases in the cationic and anionic radicals of DTU as compared to its neutral species. As a result of anionic radicalization, the C5C6 bond length increases and loses its double bond character while the C4C5 bond length decreases. In the case of the DTU+ ion the IR and Raman band corresponding to the out-of-phase coupled NH stretching mode is strongest amongst the three species. The anionic DTU radical is found to be the most stable. The two NH out-of-plane bending modes are found to originate due to out-of-phase and in-phase coupling of the two NH bonds in the anion and cation contrary to the case of the neutral DTU molecule in which the out-of-plane bending motions of the two NH bonds are not coupled. Copyright © 2014 Elsevier B.V. All rights reserved.

New donor-acceptor conjugates based on a trifluorenylporphyrin linked to a redox-switchable ruthenium unit.

PubMed

Merhi, Areej; Zhang, Xu; Yao, Dandan; Drouet, Samuel; Mongin, Olivier; Paul, Frédéric; Williams, J A Gareth; Fox, Mark A; Paul-Roth, Christine O

2015-05-28

Reactions of the 16-electron ruthenium complex [Ru(dppe)2Cl][PF6] with metal-free and zinc ethynylphenyltrifluorenylporphyrins and respectively, gave the new dyads and with ethynylruthenium group as a potential electron donor and the porphyrin as a potential electron acceptor. The redox properties of the porphyrins were investigated by cyclic voltammetry and UV spectroelectrochemistry (SEC), which reveal that the monocation and monoanion of metal-free porphyrin are stable under these conditions whereas the formation of the corresponding radical cation or anion of the zinc porphyrin was accompanied by partial decomplexation of the zinc ion. Oxidations of the dyads and gave stable radical cations as probed using IR, NIR and UV SEC methods. These cations show similar NIR and IR bands to those reported for the known 17-electron [Ru(dppe)2(C[triple bond, length as m-dash]CPh)Cl](+) radical cation. Remarkably, the dyad has four stable redox states +2/+1/0/-1 where the second oxidation and first reduction processes take place at the porphyrin unit. Simulated absorption spectra on at optimised geometries obtained by TD-DFT computations with the CAM-B3LYP functional are shown to be in very good agreement with the observed UV absorption spectra of . The spectra of and their oxidised and reduced species were interpreted with the aid of the TD-DFT data. Fluorescence measurements reveal that the dyads and are only weakly emitting compared to and , indicative of quenching of the porphyrinic singlet excited state by the ruthenium centre.

Transition-Metal Hydride Radical Cations.

PubMed

Hu, Yue; Shaw, Anthony P; Estes, Deven P; Norton, Jack R

2016-08-10

Transition-metal hydride radical cations (TMHRCs) are involved in a variety of chemical and biochemical reactions, making a more thorough understanding of their properties essential for explaining observed reactivity and for the eventual development of new applications. Generally, these species may be treated as the ones formed by one-electron oxidation of diamagnetic analogues that are neutral or cationic. Despite the importance of TMHRCs, the generally sensitive nature of these complexes has hindered their development. However, over the last four decades, many more TMHRCs have been synthesized, characterized, isolated, or hypothesized as reaction intermediates. This comprehensive review focuses on experimental studies of TMHRCs reported through the year 2014, with an emphasis on isolated and observed species. The methods used for the generation or synthesis of TMHRCs are surveyed, followed by a discussion about the stability of these complexes. The fundamental properties of TMHRCs, especially those pertaining to the M-H bond, are described, followed by a detailed treatment of decomposition pathways. Finally, reactions involving TMHRCs as intermediates are described.

UV absorption spectrum of allene radical cations in solid argon

NASA Astrophysics Data System (ADS)

Chin, Chih-Hao; Lin, Meng-Yeh; Huang, Tzu-Ping; Wu, Yu-Jong

2018-05-01

Electron bombardment during deposition of an Ar matrix containing a small proportion of allene generated allene cations. Further irradiation of the matrix sample at 385 nm destroyed the allene cations and formed propyne cations in solid Ar. Both cations were identified according to previously reported IR absorption bands. Using a similar technique, we recorded the ultraviolet absorption spectrum of allene cations in solid Ar. The vibrationally resolved progression recorded in the range of 266-237 nm with intervals of about 800 cm-1 was assigned to the A2E ← X2E transition of allene cations, and the broad continuum absorption recorded in the region of 229-214 nm was assigned to their B2A1 ← X2E transition. These assignments were made based on the observed photolytic behavior of the progressions and the vertical excitation energies and oscillator strengths calculated using time-dependent density functional theory.

Quantum chemical investigation on photodegradation mechanisms of sulfamethoxypyridazine with dissolved inorganic matter and hydroxyl radical.

PubMed

Shah, Shaheen; Hao, Ce

2017-07-01

Sulfamethoxypyridazine (SMP) is one of the commonly used sulfonamide antibiotics (SAs). SAs are mainly studied to undergo triplet-sensitized photodegradation in water under natural sunlight with other coexisting aquatic environmental organic pollutants. In this work, SMP was selected as a representative of SAs. We studied the mechanisms of triplet-sensitized photodegradation of SMP and the influence of selected dissolved inorganic matter, i.e., anions (Br - , Cl - , and NO 3 - ) and cations ions (Ca 2+ , Mg 2+ , and Zn 2+ ) on SMP photodegradation mechanism by quantum chemical methods. In addition, the degradation mechanisms of SMP by hydroxyl radical (OH) were also investigated. The creation of SO 2 extrusion product was accessed with two different energy pathways (pathway-1 and pathway-2) by following two steps (step-I and step-II) in the triplet-sensitized photodegradation of SMP. Due to low activation energy, the pathway-1 was considered as the main pathway to obtain SO 2 extrusion product. Step-II of pathway-1 was measured to be the rate-limiting step (RLS) of SMP photodegradation mechanism and the effect of the selected anions and cations was estimated for this step. All selected anions and cations promoted photodegradation of SMP by dropping the activation energy of pathway-1. The estimated low activation energies of different degradation pathways of SMP with OH radical indicate that OH radical is a very powerful oxidizing agent for SMP degradation via attack through benzene derivative and pyridazine derivative ring. Copyright © 2016. Published by Elsevier B.V.

Efficient radical cation stabilization of PANI-ZnO and PANI-ZnO-GO composites and its optical activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mathavan, T., E-mail: tjmathavan@gmail.com; Divya, A.; Benial, A. Milton Franklin

2016-05-23

Polyaniline (PANI) and its composites PANI-ZnO (Zinc oxide) and PANI-ZnO-GO (Graphene oxide) were successfully constructed. These materials were characterized by electron spin resonance (ESR) technique and ultraviolet visible spectrometry. The parameters such as line width, g-factor and spin concentration were deduced from ESR spectra, from the results the radical cation stabilization of PANI, PANI-ZnO and PANI-ZnO-GO composites were compared by the polaron and bipolaron formation. The absorption features obtained in the UV absorption spectra reveal the band gap of these modified PANI composites and also predicted the information of increasing and decreasing features of signal intensity and spin concentration.

Efficient radical cation stabilization of PANI-ZnO and PANI-ZnO-GO composites and its optical activity

NASA Astrophysics Data System (ADS)

Mathavan, T.; Divya, A.; Archana, J.; Ramasubbu, A.; Benial, A. Milton Franklin; Jothirajan, M. A.

2016-05-01

Polyaniline (PANI) and its composites PANI-ZnO (Zinc oxide) and PANI-ZnO-GO (Graphene oxide) were successfully constructed. These materials were characterized by electron spin resonance (ESR) technique and ultraviolet visible spectrometry. The parameters such as line width, g-factor and spin concentration were deduced from ESR spectra, from the results the radical cation stabilization of PANI, PANI-ZnO and PANI-ZnO-GO composites were compared by the polaron and bipolaron formation. The absorption features obtained in the UV absorption spectra reveal the band gap of these modified PANI composites and also predicted the information of increasing and decreasing features of signal intensity and spin concentration.

Bis(aminoaryl) Carbon-Bridged Oligo(phenylenevinylene)s Expand the Limits of Electronic Couplings.

PubMed

Burrezo, Paula Mayorga; Lin, Nai-Ti; Nakabayashi, Koji; Ohkoshi, Shin-Ichi; Calzado, Eva M; Boj, Pedro G; Díaz García, María A; Franco, Carlos; Rovira, Concepciò; Veciana, Jaume; Moos, Michael; Lambert, Christoph; López Navarrete, Juan T; Tsuji, Hayato; Nakamura, Eiichi; Casado, Juan

2017-03-06

Carbon-bridged bis(aminoaryl) oligo(para-phenylenevinylene)s have been prepared and their optical, electrochemical, and structural properties analyzed. Their radical cations are class III and class II mixed-valence systems, depending on the molecular size, and they show electronic couplings which are among the largest for the self-exchange reaction of purely organic molecules. In their dication states, the antiferromagnetic coupling is progressively tuned with size from quinoidal closed-shell to open-shell biradicals. The data prove that the electronic coupling in the radical cations and the singlet-triplet gap in the dications show similar small attenuation factors, thus allowing charge/spin transfer over rather large distances. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Naphthalene-1,2,3-dithiazolyl and its selenium-containing variants.

PubMed

Oakley, Richard T; Reed, Robert W; Robertson, Craig M; Richardson, John F

2005-03-21

Synthetic routes to salts of the 3H-naphtho[1,2-d][1,2,3]dithiazolylium cation and its three selenium-containing variants (SSeN, SeSN, and SeSeN) are described. The most efficient and general method involves the intermediacy of bis-acetylated aminothiolates and aminoselenolates. These reagents react smoothly with sulfur and selenium halides to afford the desired ring closure products. Electrochemical reduction of the four cations indicates that corresponding radicals (SSN, SSeN, SeSN, and SeSeN) are stable in solution. The EPR spectra of all four have been recorded, and experimental spin distributions have been cross-matched with those obtained from DFT calculations. The selenium-containing radicals are thermally unstable at or slightly above room temperature, but the all-sulfur species has been isolated and characterized crystallographically. In the solid state, the radicals are associated into cofacial dimers which are closely linked to other dimers by intermolecular S---S, S---N, and C-H---aromatic ring interactions.

Does Metal Ion Complexation Make Radical Clocks Run Fast? An Experimental Perspective.

PubMed

Abdel Latif, Marwa K; Spencer, Jared N; Paradzinsky, Mark; Tanko, James M

2017-12-28

The rate constant for the β-scission of the cumyloxyl radical (k β ) was measured in the presence of various added electrolytes in acetonitrile and DMSO solvent. The results show that in CH 3 CN, k β increases in the presence of added electrolyte, roughly paralleling the size of the cation: Li + > Mg 2+ ≈ Na + > n Bu 4 N + > no added electrolyte. As suggested by Bietti et al. earlier, this effect is attributable to stabilizing ion-dipole interactions in the transition state of the developing carbonyl group, a conclusion further amplified by MO calculations (gas phase) reported herein. Compared to the gas phase predictions, however, this effect is seriously attenuated in solution because complexation of the cation to the electrophilic alkoxyl radical (relative to the solvent, CH 3 CN) is very weak. Because the interaction of Li + and Na + is much stronger with DMSO than with CH 3 CN, addition of these ions has no effect on the rate of β-scission.

XMCD for monitoring exchange interactions. The role of the Gd 4f and 5d orbitals in metal-nitronyl nitroxide magnetic chains.

PubMed

Champion, Guillaume; Lalioti, Nikolia; Tangoulis, Vassilis; Arrio, Marie-Anne; Sainctavit, Philippe; Villain, Françoise; Caneschi, Andrea; Gatteschi, Dante; Giorgetti, Christine; Baudelet, François; Verdaguer, Michel; Cartier dit Moulin, Christophe

2003-07-09

We report here the X-ray magnetic circular dichroism (XMCD) study at the Gd M(4,5)- and L(2,3)-edges of two linear magnetic chains involving Gd(III) cations bridged by nitronyl nitroxide radicals. This spectroscopy directly probes the magnetic moments of the 4f and 5d orbitals of the gadolinium ions. We compare macroscopic magnetic measurements and local XMCD signals. The M(4,5)-edges results are in agreement with the J values extracted from the fits of the SQUID magnetic measurements. The L(2,3)-edges signals show that the electronic density in the Gd 5d orbitals depends on the neighbors of the gadolinium cations. Nevertheless, the 5d orbitals do not seem to play any role in the superexchange pathway between radicals through the metal ion proposed to explain the particular magnetic exchange interactions between the radicals in these chains.

A Distonic Radical-Ion for Detection of Traces of Adventitious Molecular Oxygen (O2) in Collision Gases Used in Tandem Mass Spectrometers

NASA Astrophysics Data System (ADS)

Jariwala, Freneil B.; Hibbs, John A.; Weisbecker, Carl S.; Ressler, John; Khade, Rahul L.; Zhang, Yong; Attygalle, Athula B.

2014-09-01

We describe a diagnostic ion that enables rapid semiquantitative evaluation of the degree of oxygen contamination in the collision gases used in tandem mass spectrometers. Upon collision-induced dissociation (CID), the m/z 359 positive ion generated from the analgesic etoricoxib undergoes a facile loss of a methyl sulfone radical [•SO2(CH3); 79-Da] to produce a distonic radical cation of m/z 280. The product-ion spectrum of this m/z 280 ion, recorded under low-energy activation on tandem-in-space QqQ or QqTof mass spectrometers using nitrogen from a generator as the collision gas, or tandem-in-time ion-trap (LCQ, LTQ) mass spectrometers using purified helium as the buffer gas, showed two unexpected peaks at m/z 312 and 295. This enigmatic m/z 312 ion, which bears a mass-to-charge ratio higher than that of the precursor ion, represented an addition of molecular oxygen (O2) to the precursor ion. The exceptional affinity of the m/z 280 radical cation towards oxygen was deployed to develop a method to determine the oxygen content in collision gases.

Differential accumulation and pigmenting ability of dietary carotenoids in colorful finches.

PubMed

McGraw, Kevin J; Hill, Geoffrey E; Navara, Kristen J; Parker, Robert S

2004-01-01

Many animals develop bright red, orange, or yellow carotenoid pigmentation that they use to attract mates. Colorful carotenoid pigments are acquired from the diet and are either directly incorporated as integumentary colorants or metabolized into other forms before deposition. Because animals often obtain several different carotenoids from plant and animal food sources, it is possible that these pigments are accumulated at different levels in the body and may play unique roles in shaping the ultimate color expression of individuals. We studied patterns of carotenoid accumulation and integumentary pigmentation in two colorful finch species--the American goldfinch (Carduelis tristis) and the zebra finch (Taeniopygia guttata). Both species acquire two main hydroxycarotenoids, lutein and zeaxanthin, from their seed diet but transform these into a series of metabolites that are used as colorful pigments in the plumage (goldfinches only) and beak (both species). We conducted a series of carotenoid-supplementation experiments to investigate the relative extent to which lutein and zeaxanthin are accumulated in blood and increase carotenoid coloration in feathers and bare parts. First, we supplemented the diets of both species with either lutein or zeaxanthin and measured plasma pigment status, feather carotenoid concentration (goldfinches only), and integumentary color. Zeaxanthin-supplemented males grew more colorful feathers and beaks than lutein-supplemented males, and in goldfinches incorporated a different ratio of carotenoids in feathers (favoring the accumulation of canary xanthophyll B). We also fed goldfinches different concentrations of a standard lutein-zeaxanthin mix and found that at physiologically normal and high concentrations, birds circulated proportionally more zeaxanthin over lutein than occurred in the diet. Collectively, these results demonstrate that zeaxanthin is preferentially accumulated in the body and serves as a more potent substrate for pigmentation than lutein in these finches.

Zeaxanthin Protects Plant Photosynthesis by Modulating Chlorophyll Triplet Yield in Specific Light-harvesting Antenna Subunits*

PubMed Central

Dall'Osto, Luca; Holt, Nancy E.; Kaligotla, Shanti; Fuciman, Marcel; Cazzaniga, Stefano; Carbonera, Donatella; Frank, Harry A.; Alric, Jean; Bassi, Roberto

2012-01-01

Plants are particularly prone to photo-oxidative damage caused by excess light. Photoprotection is essential for photosynthesis to proceed in oxygenic environments either by scavenging harmful reactive intermediates or preventing their accumulation to avoid photoinhibition. Carotenoids play a key role in protecting photosynthesis from the toxic effect of over-excitation; under excess light conditions, plants accumulate a specific carotenoid, zeaxanthin, that was shown to increase photoprotection. In this work we genetically dissected different components of zeaxanthin-dependent photoprotection. By using time-resolved differential spectroscopy in vivo, we identified a zeaxanthin-dependent optical signal characterized by a red shift in the carotenoid peak of the triplet-minus-singlet spectrum of leaves and pigment-binding proteins. By fractionating thylakoids into their component pigment binding complexes, the signal was found to originate from the monomeric Lhcb4–6 antenna components of Photosystem II and the Lhca1–4 subunits of Photosystem I. By analyzing mutants based on their sensitivity to excess light, the red-shifted triplet-minus-singlet signal was tightly correlated with photoprotection in the chloroplasts, suggesting the signal implies an increased efficiency of zeaxanthin in controlling chlorophyll triplet formation. Fluorescence-detected magnetic resonance analysis showed a decrease in the amplitude of signals assigned to chlorophyll triplets belonging to the monomeric antenna complexes of Photosystem II upon zeaxanthin binding; however, the amplitude of carotenoid triplet signal does not increase correspondingly. Results show that the high light-induced binding of zeaxanthin to specific proteins plays a major role in enhancing photoprotection by modulating the yield of potentially dangerous chlorophyll-excited states in vivo and preventing the production of singlet oxygen. PMID:23066020

Lutein, zeaxanthin, and meso-zeaxanthin: The basic and clinical science underlying carotenoid-based nutritional interventions against ocular disease.

PubMed

Bernstein, Paul S; Li, Binxing; Vachali, Preejith P; Gorusupudi, Aruna; Shyam, Rajalekshmy; Henriksen, Bradley S; Nolan, John M

2016-01-01

The human macula uniquely concentrates three carotenoids: lutein, zeaxanthin, and meso-zeaxanthin. Lutein and zeaxanthin must be obtained from dietary sources such as green leafy vegetables and orange and yellow fruits and vegetables, while meso-zeaxanthin is rarely found in diet and is believed to be formed at the macula by metabolic transformations of ingested carotenoids. Epidemiological studies and large-scale clinical trials such as AREDS2 have brought attention to the potential ocular health and functional benefits of these three xanthophyll carotenoids consumed through the diet or supplements, but the basic science and clinical research underlying recommendations for nutritional interventions against age-related macular degeneration and other eye diseases are underappreciated by clinicians and vision researchers alike. In this review article, we first examine the chemistry, biochemistry, biophysics, and physiology of these yellow pigments that are specifically concentrated in the macula lutea through the means of high-affinity binding proteins and specialized transport and metabolic proteins where they play important roles as short-wavelength (blue) light-absorbers and localized, efficient antioxidants in a region at high risk for light-induced oxidative stress. Next, we turn to clinical evidence supporting functional benefits of these carotenoids in normal eyes and for their potential protective actions against ocular disease from infancy to old age. Copyright © 2015 Elsevier Ltd. All rights reserved.

Concentration-Dependence of Vitamin C in Combinations with Vitamin E and Zeaxanthin on Light-Induced Toxicity to Retinal Pigment Epithelial Cells†

PubMed Central

Różanowska, Małgorzata; Bakker, Linda; Boulton, Michael E.; Różanowski, Bartosz

2012-01-01

The purpose of this study was to determine the effects of increasing concentration of ascorbate alone and in combinations with α-tocopherol and zeaxanthin on phototoxicity to the retinal pigment epithelium. ARPE-19 cells were exposed to rose bengal and visible light in the presence and absence of antioxidants. Toxicity was quantified by an assay of cell reductive activity. 20 min exposure to visible light and photosensitizer decreased cell viability to ~42%. Lipophilic antioxidants increased viabilities to ~70%, ~61% and ~75% for α-tocopherol, zeaxanthin and their combination, respectively. Cell viabilities were ~70%, 56% and 5% after exposures in the presence of 0.35, 0.7 and 1.4 mM ascorbate, respectively. 45 min exposure increased cell death to ~74% and to >95% in the absence and presence of ascorbate, respectively. In the presence of ascorbate, zeaxanthin did not significantly affect phototoxicity. α-Tocopherol and its combination with zeaxanthin enhanced protective effects of ascorbate but did not prevent from ascorbate-mediated deleterious effects. In conclusion, there is a narrow range of concentrations and exposure times where ascorbate exerts photoprotective effects, exceeding which leads to ascorbate-mediated increase in photocytotoxicity. Vitamin E and its combination with zeaxanthin can enhance protective effects of ascorbate but do not ameliorate its deleterious effects. PMID:22924673

Dietary lutein/zeaxanthin partially reduces photoaging and photocarcinogenesis in chronically UVB-irradiated Skh-1 hairless mice.

PubMed

Astner, S; Wu, A; Chen, J; Philips, N; Rius-Diaz, F; Parrado, C; Mihm, M C; Goukassian, D A; Pathak, M A; González, S

2007-01-01

Lutein and zeaxanthin are xanthophyll carotenoids with potent antioxidant properties protecting the skin from acute photodamage. This study extended the investigation to chronic photodamage and photocarcinogenesis. Mice received either a lutein/zeaxanthin-supplemented diet or a standard nonsupplemented diet. Dorsal skin of female Skh-1 hairless mice was exposed to UVB radiation with a cumulative dose of 16,000 mJ/cm(2) for photoaging and 30,200 mJ/cm(2) for photocarcinogenesis. Clinical evaluations were performed weekly, and the animals were sacrificed 24 h after the last UVB exposure. For photoaging experiments, skin fold thickness, suprapapillary plate thickness, mast cell counts and dermal desmosine content were evaluated. For photocarcinogenesis, samples of tumors larger than 2 mm were analyzed for histological characterization, hyperproliferation index, tumor multiplicity, total tumor volume and tumor-free survival time. Results of the photoaging experiment revealed that skin fold thickness and number of infiltrating mast cells following UVB irradiation were significantly less in lutein/zeaxanthin-treated mice when compared to irradiated animals fed the standard diet. The results of the photocarcinogenesis experiment were increased tumor-free survival time, reduced tumor multiplicity and total tumor volume in lutein/zeaxanthin-treated mice in comparison with control irradiated animals fed the standard diet. These data demonstrate that dietary lutein/zeaxanthin supplementation protects the skin against UVB-induced photoaging and photocarcinogenesis. (c) 2007 S. Karger AG, Basel.

VUV Photoionisation of hydrocarbon radicals

NASA Astrophysics Data System (ADS)

Alcaraz, C.; Noller, Bastian; Hemberger, Patrick; Fischer, Ingo; Gans, Bérenger; Boyé-Peronne, Séverine; Douin, Stéphane; Gauyacq, Dolorès; Soldi-Lose, Héloïse; Garcia, Gustavo

2008-09-01

Hydrocarbon radicals CxHy are constituents of various planetary atmospheres, in particular Titan, as a result of the methane photochemistry induced by the solar radiation. They contribute to the neutral chemistry, but are also important for the ionosphere through their photoionisation leading to their cations CxHy +. These cations are also produced by ion-molecule reactions starting from the reaction of the primary ions CH4 + and CH3 + which are created in the non-dissociative and dissociative photoionisation of CH4. This work aims at caracterizing the VUV photoionisation of small hydrocarbon radicals as a function of photon energy. The objective is to provide laboratory data for modelers on the spectroscopy, the thermochemistry, and the reactivity of the radicals and their cations. The hydrocarbon radicals are much less caracterized than stable molecules since they have to be produced in situ in the laboratory experiment. We have adapted at Orsay [1-3] a pyrolysis source (Figure 1) well suited to produce cold beams of hydrocarbon radicals to our experimental setups. Available now at Orsay, we have two new sources of VUV radiation, complementary in terms of tunability and resolution, that can be used for these studies. The first one is the DESIRS beamline [4] at the new french synchrotron, SOLEIL. The second one is the VUV laser developped at the Centre Laser de l'Université Paris-Sud (CLUPS) [5]. At SOLEIL, a photoelectron-photoion coincidence spectrometer is used to monitor the photoionisation on a large photon energy range. At the CLUPS, a pulsedfield ionisation (PFI-ZEKE) spectrometer allows studies at higher resolution on selected photon energies. The first results obtained with these new setups will be presented. References [1] Fischer, I., Schussler, T., Deyerl, H.J., Elhanine, M. & Alcaraz, C., Photoionization and dissociative photoionization of the allyl radical, C3H5. Int. J. Mass Spectrom., 261 (2-3), 227-233 (2007) [2] Schüßler, T., Roth, W., Gerber, T., Alcaraz, C. & Fischer, I., The vacuum ultraviolet photochemistry of radicals: C3H3 and C2H5. Phys. Chem. Chem. Phys., 7 (5), 819-825 (2005) [3] Schüßler, T., Deyerl, H. J., Dummler, S., Fischer, I., Alcaraz, C. & Elhanine, M., The vacuum ultraviolet photochemistry of the allyl radical investigated using synchrotron radiation J. Chem. Phys., 118 (20), 9077-80 (2003) [4] DESIRS, http://www.synchrotronsoleil. fr/portal/page/portal/Recherche/LignesLumiere/ DESIRS [5] CLUPS, http://www.clups.u-psud.fr/

Molecular Dynamics Simulation Study of Solvent and State of Charge Effects on Solid-Phase Structure and Counterion Binding in a Nitroxide Radical Containing Polymer Energy Storage Material

DOE PAGES

Kemper, Travis W.; Gennett, Thomas; Larsen, Ross E.

2016-10-19

Here we performed molecular dynamics simulations to understand the effects of solvent swelling and state of charge (SOC) on the redox active, organic radical cathode material poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA). We show that the polar solvent acetonitrile primarily solvates the nitroxide radical without disrupting the packing of the (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) pendant groups of PTMA. We also simulated bulk PTMA in different SOC, 25%, 50%, 75%, and 100%, by converting the appropriate number of TEMPO groups to the cation charge state and adding BF 4 - counterions to the simulation. At each SOC the packing of PTMA, the solvent, and the counterionsmore » were examined. The binding of the anion to the nitroxide cation site was examined using the potential of mean force and found to be on the order of tens of meV, with a binding energy that decreased with increasing SOC. Additionally, we found that the cation state is stabilized by the presence of a nearby anion by more than 1 eV, and the implications of this stabilization on charge transport are discussed. Finally, we describe the implications of our results for how the SOC of an organic electrode affects electron and anion charge transport during the charging and discharging processes.« less

Transformation of [M + 2H](2+) Peptide Cations to [M - H](+), [M + H + O](+), and M(+•) Cations via Ion/Ion Reactions: Reagent Anions Derived from Persulfate.

PubMed

Pilo, Alice L; Bu, Jiexun; McLuckey, Scott A

2015-07-01

The gas-phase oxidation of doubly protonated peptides is demonstrated here using ion/ion reactions with a suite of reagents derived from persulfate. Intact persulfate anion (HS2O8(-)), peroxymonosulfate anion (HSO5(-)), and sulfate radical anion (SO4(-•)) are all either observed directly upon negative nanoelectrospray ionization (nESI) or easily obtained via beam-type collisional activation of persulfate into the mass spectrometer. Ion/ion reactions between each of these reagents and doubly protonated peptides result in the formation of a long-lived complex. Collisional activation of the complex containing a peroxymonosulfate anion results in oxygen transfer from the reagent to the peptide to generate the [M + H + O](+) species. Activation of the complex containing intact persulfate anion either results in oxygen transfer to generate the [M + H + O](+) species or abstraction of two hydrogen atoms and a proton to generate the [M - H](+) species. Activation of the complex containing sulfate radical anion results in abstraction of one hydrogen atom and a proton to form the peptide radical cation, [M](+•). This suite of reagents allows for the facile transformation of the multiply protonated peptides obtained via nESI into a variety of oxidized species capable of providing complementary information about the sequence and structure of the peptide.

Two Photon Absorption in a Novel Nano-optical Material Based on the Nonconjugated Conductive Polymer, Poly(beta-pinene)

NASA Astrophysics Data System (ADS)

Titus, Jitto; Thakur, Mrinal

2006-03-01

As recently reported, the electrical conductivity of the nonconjugated polymer, poly(beta-pinene) increases by more than ten orders of magnitude upon doping with iodine [1]. The FTIR, optical absorption and EPR measurements have shown that radical cations are formed upon doping and charge-transfer involving the isolated double-bond in poly(beta-pinene). In this report, exceptionally large two-photon absorption in iodine-doped poly(beta-pinene) will be discussed. The linear absorption spectrum of medium-doped poly(beta-pinene) have peaks at about 4 eV and 3.1 eV. The first peak is due to the radical cation and the second due to the charge-transfer between the double bond and the dopant. The two-photon absorption of the medium-doped polymer has been measured at 730-860 nm using open-aperture z-scan with 150 femtosecond pulses from a Ti:Sapphire laser. A two-photon peak at about 1.5 eV with a magnitude of more than 1 cm/MW has been observed. The large magnitude of the two-photon absorption coefficient which is proportional to the imaginary part of the third order susceptibility has been attributed to the special structure of the radical cation and the confinement within a sub-nanometer dimension. [1] Vippa, Rajagopalan and Thakur, J. Poly. Sci. Part B: Poly. Phys., 43, 3695 (2005).

Cofactors involved in light-driven charge separation in photosystem I identified by subpicosecond infrared spectroscopy.

PubMed

Di Donato, Mariangela; Stahl, Andreas D; van Stokkum, Ivo H M; van Grondelle, Rienk; Groot, Marie-Louise

2011-02-01

Photosystem I is one of the key players in the conversion of solar energy into chemical energy. While the chlorophyll dimer P(700) has long been identified as the primary electron donor, the components involved in the primary charge separation process in PSI remain undetermined. Here, we have studied the charge separation dynamics in Photosystem I trimers from Synechococcus elongatus by femtosecond vis-pump/mid-infrared-probe spectroscopy upon excitation at 700, 710, and 715 nm. Because of the high specificity of the infrared region for the redox state and small differences in the molecular structure of pigments, we were able to clearly identify specific marker bands indicating chlorophyll (Chl) oxidation. Magnitudes of chlorophyll cation signals are observed to increase faster than the time resolution of the experiment (~0.2 ps) upon both excitation conditions: 700 nm and selective red excitation. Two models, involving either ultrafast charge separation or charge transfer character of the red pigments in PSI, are discussed to explain this observation. A further increase in the magnitudes of cation signals on a subpicosecond time scale (0.8-1 ps) indicates the formation of the primary radical pair. Evolution in the cation region with time constants of 7 and 40 ps reveals the formation of the secondary radical pair, involving a secondary electron donor. Modeling of the data allows us to extract the spectra of the two radical pairs, which have IR signatures consistent with A+A₀- and P₇₀₀+A₁-. We conclude that the cofactor chlorophyll A acts as the primary donor in PSI. The existence of an equilibrium between the two radical pairs we interpret as concerted hole/electron transfer between the pairs of electron donors and acceptors, until after 40 ps, relaxation leads to a full population of the P₇₀₀+A₁. radical pair.

The long-sought seventeen-electron radical [(C6Me6)Cr(CO)3](+): isolation, crystal structure and substitution reaction.

PubMed

Wang, Wenqing; Wang, Xingyong; Zhang, Zaichao; Yuan, Ningning; Wang, Xinping

2015-05-18

A highly air-sensitive seventeen-electron half-sandwich radical, [(C6Me6)Cr(CO)3](+), which has been long sought over 40 years, was isolated and structurally characterized. EPR spectroscopy and theoretical calculations indicate that the spin density mainly resides on the chromium atom. The radical can undergo a substitution reaction with PPh3 to form a more stable cation, [(C6Me6)Cr(CO)2(PPh3)](+). This work provides a direct observation of the radical process for CO-substitution reactions found in (arene)M(CO)3 (M = Cr, Mo, or W) systems, and suggests that other stable radicals of the type [(arene)M(CO)3](+) are accessible.

Excited states and electrochromism of radical cation of the carotenoid astaxanthin

NASA Astrophysics Data System (ADS)

Krawczyk, Stanisław

1998-09-01

Radical cations of the carotenoid astaxanthin were generated by chemical oxidation with Fe(Cl) 3, and their absorption and electroabsorption (Stark) spectra at temperatures about 150 K were recorded in the spectral range from 5900 to 26000 cm -1 (380 to 1700 nm), covering two absorptive electronic transitions from D 0 (ground) to D 1 and D 2 excited states. The changes in static polarizability are negative and equal -40±10 A 3 for D 0→D 1 and -105±15 A 3 for D 0→D 2, pointing that dominant contribution to polarizabilities results from the coupling of D 1 and D 2 with the ground state. An approximate localization of the next excited state with ground-state parity is estimated based on arguments from perturbation theory.

Effects of mayonnaise on postprandial serum lutein/zeaxanthin and beta-carotene concentrations in humans.

PubMed

Takeda, Sayaka; Masuda, Yasunobu; Usuda, Mika; Marushima, Ranko; Ueji, Toshiyuki; Hasegawa, Mineo; Maruyama, Chizuko

2009-12-01

To clarify the effects of different physical forms of oil on postprandial serum lutein/zeaxanthin and beta-carotene concentrations, we performed a vegetable meal loading test. Eighteen healthy subjects participated in the test, which consisted of broccoli as a control (CON) meal, broccoli with oil (OIL), and broccoli with mayonnaise (MS), consumed in random order. After collection of fasting blood samples, subjects consumed one of the three test meals. Fasting and postprandial changes in serum carotenoids were assessed 2, 4, and 6 h after ingestion of each test meal. Serum lutein/zeaxanthin and beta-carotene concentrations were measured. Although no significant change was noted after the CON meal, the serum lutein/zeaxanthin concentration was higher at 4 h after consumption of the OIL meal, and at 2, 4 and 6 h after consumption of the MS meal, as compared with the fasting state. Serum beta-carotene concentrations did not change after ingestion of either the CON or the OIL meal but were elevated 2, 4, and 6 h after MS ingestion as compared with the fasting state. The incremental areas under the curves (IAUCs) of serum lutein/zeaxanthin and beta-carotene concentrations were higher after the MS meal than after the CON meal. IAUCs after the OIL meal exhibited no statistically significant differences from the CON and MS meals. We suggest that mayonnaise contributes to increase serum lutein/zeaxanthin and beta-carotene concentrations when consumed with vegetables rich in these carotenoids.

Reaction of Photochemically Generated Organic Cations with Colloidal Clays.

DTIC Science & Technology

1983-05-01

University of Notre Dame. IS. KEY WORDS (Continue on reverse aide if neceary end identify by block number) Chemistry of colloidal montmorillonite Absorption...Centlws m ftves n N mee.iy mi Identify by block number) Qi Organic radical cations will dimerize when adsorbed to the surface D of montmorillonite in...1 The Nature and Chemistry of Micelles .... 2 The Nature and Chemistry of Clay Minerals 5 Montmorillonite Catalyzed Color

Antioxidant Effects of Herbal Tea Leaves from Yacon (Smallanthus sonchifolius) on Multiple Free Radical and Reducing Power Assays, Especially on Different Superoxide Anion Radical Generation Systems.

PubMed

Sugahara, Shintaro; Ueda, Yuto; Fukuhara, Kumiko; Kamamuta, Yuki; Matsuda, Yasushi; Murata, Tatsuro; Kuroda, Yasuhiro; Kabata, Kiyotaka; Ono, Masateru; Igoshi, Keiji; Yasuda, Shin

2015-11-01

Yacon (Smallanthus sonchifolius), a native Andean plant, has been cultivated as a crop and locally used as a traditional folk medicine for the people suffering from diabetes and digestive/renal disorders. However, the medicinal properties of this plant and its processed foods have not been completely established. This study investigates the potent antioxidative effects of herbal tea leaves from yacon in different free radical models and a ferric reducing model. A hot-water extract exhibited the highest yield of total polyphenol and scavenging effect on 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical among four extracts prepared with hot water, methanol, ethanol, and ethylacetate. In addition, a higher reducing power of the hot-water extract was similarly demonstrated among these extracts. Varying concentrations of the hot-water extract resulted in different scavenging activities in four synthetic free radical models: DPPH radical (EC50 28.1 μg/mL), 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) cation radical (EC50 23.7 μg/mL), galvinoxyl radical (EC50 3.06 μg/mL), and chlorpromazine cation radical (EC50 475 μg/mL). The yacon tea-leaf extract further demonstrated superoxide anion (O2(-)) radical scavenging effects in the phenazine methosulfate-NADH-nitroblue tetrazolium (EC50 64.5 μg/mL) and xanthine oxidase assay systems (EC50 20.7 μg/mL). Subsequently, incubating human neutrophilic cells in the presence of the tea-leaf extract could suppress the cellular O2(-) radical generation (IC50 65.7 μg/mL) in a phorbol 12-myristate 13-acetate-activated cell model. These results support yacon tea leaves may be a good source of natural antioxidants for preventing O2(-) radical-mediated disorders. Yacon has been considered to be a potent alternative food source for patients who require a dietary cure in regional area, while the leaf part has been provided and consumed as an herbal tea in local markets. We demonstrated here potent antioxidative effects of the tea leaves from yacon in different free radical assays, reducing power assay, and cellular superoxide anion radical generation assay. Results support yacon tea leaves may be a good source of natural antioxidants for preventing O2(-) radical-mediated disorders. © 2015 Institute of Food Technologists®

Formation and stability of gas-phase o-benzoquinone from oxidation of ortho-hydroxyphenyl: A combined neutral and distonic radical study

DOE PAGES

Prendergast, Matthew B.; Kirk, Benjamin B.; Savee, John D.; ...

2015-10-19

Gas-phase product detection studies of o-hydroxyphenyl radical and O 2 are reported at 373, 500, and 600 K, at 4 Torr (533.3 Pa), using VUV time-resolved synchrotron photoionisation mass spectrometry. The dominant products are assigned as o-benzoquinone (C 6H 4O 2, m/z 108) and cyclopentadienone (C 5H 4O, m/z 80). It is concluded that cyclopentadienone forms as a secondary product from prompt decomposition of o-benzoquinone (and dissociative ionization of o-benzoquinone may contribute to the m/z 80 signal at photon energies ≳9.8 eV). Ion-trap reactions of the distonic o-hydroxyphenyl analogue, the 5-ammonium-2-hydroxyphenyl radical cation, with O 2 are also reported andmore » concur with the assignment of o-benzoquinone as the dominant product. In addition, the ion-trap study also provides support for a mechanism where cyclopentadienone is produced by decarbonylation of o-benzoquinone. Kinetic studies compare oxidation of the ammonium-tagged o-hydroxyphenyl and o-methylphenyl radical cations along with trimethylammonium-tagged analogues. Reaction efficiencies are found to be ca. 5% for both charge-tagged o-hydroxyphenyl and o-methylphenyl radicals irrespective of the charged substituent. G3X-K quantum chemical calculations are deployed to rationalise experimental results for o-hydroxyphenyl + O 2 and its charge-tagged counterpart. The prevailing reaction mechanism, after O 2 addition, involves a facile 1,5-H shift in the peroxyl radical and subsequent elimination of OH to yield o-benzoquinone that is reminiscent of the Waddington mechanism for β-hydroxyperoxyl radicals. These results suggest o-hydroxyphenyl + O 2 and decarbonylation of o-benzoquinone serve as plausible OH and CO sources in combustion.« less

The Reactions of Polycyclic Aromatic Hydrocarbons with OH

NASA Technical Reports Server (NTRS)

Ricca, Alessandra; Bauschlicher, Charles W., Jr.; Arnold, James O. (Technical Monitor)

2000-01-01

The OH radical adds to naphthalene and naphthalene cation without a barrier. For the neutrals, the most favorable path for this intermediate is the loss of the OH, and the next most favorable option is the loss of an H atom to form the alcohol. For the cation, the most favorable path appears to be a hydrogen migration followed by the loss of a hydrogen to form the alcohol. The OH at carbon atom 1 is energetically most favorable for both the initial complex and final product. This is true for both the neutrals and cations.

Xanthophylls

USDA-ARS?s Scientific Manuscript database

Xanthophylls are dietary carotenoids found throughout the body and include lutein, zeaxanthin, ß-cryptoxanthin, astaxanthin, and canthaxanthin. Lutein and zeaxanthin selectively accumulate in the macula of the eye and in the brain. Major dietary sources of xanthophylls include green leafy vegetables...

Polymerization as a Model Chain Reaction

ERIC Educational Resources Information Center

Morton, Maurice

1973-01-01

Describes the features of the free radical, anionic, and cationic mechanisms of chain addition polymerization. Indicates that the nature of chain reactions can be best taught through the study of macromolecules. (CC)

Dynamics of intramolecular electron transfer reaction of FAD studied by magnetic field effects on transient absorption spectra.

PubMed

Murakami, Masaaki; Maeda, Kiminori; Arai, Tatsuo

2005-07-07

The kinetics of intermediates generated from intramolecular electron-transfer reaction by photo irradiation of the flavin adenine dinucleotide (FAD) molecule was studied by a magnetic field effect (MFE) on transient absorption (TA) spectra. Existence time of MFE and MFE action spectra have a strong dependence on the pH of solutions. The MFE action spectra have indicated the existence of interconversion between the radical pair and the cation form of the triplet excited state of flavin part. All rate constants of the triplet and the radical pair were determined by analysis of the MFE action spectra and decay kinetics of TA. The obtained values for the interconversion indicate that the formation of cation radical promotes the back electron-transfer reaction to the triplet excited state. Further, rate constants of spin relaxation and recombination have been studied by the time profiles of MFE at various pH. The drastic change of those two factors has been obtained and can be explained by SOC (spin-orbit coupling) induced back electron-transfer promoted by the formation of a stacking conformation at pH > 2.5.

Can membrane-bound carotenoid pigment zeaxanthin carry out a transmembrane proton transfer?

PubMed

Kupisz, Kamila; Sujak, Agnieszka; Patyra, Magdalena; Trebacz, Kazimierz; Gruszecki, Wiesław I

2008-10-01

Polar carotenoid pigment zeaxanthin (beta,beta-carotene-3,3'-diol) incorporated into planar lipid membranes formed with diphytanoyl phosphatidylcholine increases the specific electric resistance of the membrane from ca. 4 to 13 x 10(7) Omega cm2 (at 5 mol% zeaxanthin with respect to lipid). Such an observation is consistent with the well known effect of polar carotenoids in decreasing fluidity and structural stabilization of lipid bilayers. Zeaxanthin incorporated into the lipid membrane at 1 mol% has very small effect on the overall membrane resistance but facilitates equilibration of the transmembrane proton gradient, as demonstrated with the application of the H+-sensitive antimony electrodes. Relatively low changes in the electrical potential suggest that the equilibration process may be associated with a symport/antiport activity or with a transmembrane transfer of the molecules of acid. UV-Vis linear dichroism analysis of multibilayer formed with the same lipid-carotenoid system shows that the transition dipole moment of the pigment molecules forms a mean angle of 21 degrees with respect to the axis normal to the plane of the membrane. This means that zeaxanthin spans the membrane and tends to have its two hydroxyl groups anchored in the opposite polar zones of the membrane. Detailed FTIR analysis of beta-carotene and zeaxanthin indicates that the polyene chain of carotenoids is able to form weak hydrogen bonds with water molecules. Possible molecular mechanisms responsible for proton transport by polyenes are discussed, including direct involvement of the polyene chain in proton transfer and indirect effect of the pigment on physical properties of the membrane.

Photodissociation of pyrene cations: structure and energetics from C16H10(+) to C14(+) and almost everything in between.

PubMed

West, Brandi; Useli-Bacchitta, Francesca; Sabbah, Hassan; Blanchet, Valérie; Bodi, Andras; Mayer, Paul M; Joblin, Christine

2014-09-11

The unimolecular dissociation of the pyrene radical cation, C16H10(+•), has been explored using a combination of computational techniques and experimental approaches, such as multiple photon absorption in the cold ion trap Piège à Ions pour la Recherche et l'Etude de Nouvelles Espèces Astrochimiques (PIRENEA) and imaging photoelectron photoion coincidence spectrometry (iPEPICO). In total, 22 reactions, involving the fragmentation cascade (H, C2H2, and C4H2 loss) from the pyrene radical cation down to the C14(+•) fragment ion, have been studied using PIRENEA. Branching ratios have been measured for reactions from C16H10(+•), C16H8(+•), and C16H5(+). Density functional theory calculations of the fragmentation pathways observed experimentally and postulated theoretically lead to 17 unique structures. One important prediction is the opening of the pyrene ring system starting from the C16H4(+•) radical. In the iPEPICO experiments, only two reactions could be studied, namely, R1 C16H10(+•) → C16H9(+) + H (m/z = 201) and R2 C16H9(+) → C16H8(+•) + H (m/z = 200). The activation energies for these reactions were determined to be 5.4 ± 1.2 and 3.3 ± 1.1 eV, respectively.

Microstructural study of a nitroxide-mediated poly(ethylene oxide)/polystyrene block copolymer (PEO-b-PS) by electrospray tandem mass spectrometry.

PubMed

Girod, Marion; Phan, Trang N T; Charles, Laurence

2008-08-01

Electrospray ionization tandem mass spectrometry has been used to characterize the microstructure of a nitroxide-mediated poly(ethylene oxide)/polystyrene block copolymer, called SG1-capped PEO-b-PS. The main dissociation route of co-oligomers adducted with lithium or silver cation was observed to proceed via the homolytic cleavage of a C-ON bond, aimed at undergoing reversible homolysis during nitroxide mediated polymerization. This cleavage results in the elimination of the terminal SG1 end-group as a radical, inducing a complete depolymerization process of the PS block from the so-formed radical cation. These successive eliminations of styrene molecules allowed a straightforward determination of the PS block size. An alternative fragmentation pathway of the radical cation was shown to provide structural information on the junction group between the two blocks. Proposed dissociation mechanisms were supported by accurate mass measurements. Structural information on the SG1 end-group could be reached from weak abundance fragment ions detected in the low m/z range of the MS/MS spectrum. Amongst fragments typically expected from PS dissociation, only beta ions were produced. Moreover, specific dissociation of the PEO block was not observed to occur in MS/MS, suggesting that these rearrangement reactions do not compete effectively with dissociations of the odd-electron fragment ions. Information about the PEO block length and the initiated end-group were obtained in MS(3) experiments.

Infrared spectroscopy and theory of the formaldehyde cation and its hydroxymethylene isomer

NASA Astrophysics Data System (ADS)

Mauney, D. T.; Mosley, J. D.; Madison, L. R.; McCoy, A. B.; Duncan, M. A.

2016-11-01

Pulsed discharges in supersonic expansions containing the vapor of different precursors (formaldehyde, methanol) produce the m/z = 30 cations with formula [H2,C,O]+. The corresponding [H2,C,O]+ Ar complexes are produced under similar conditions with argon added to the expansion gas. These ions are mass selected in a time-of-flight spectrometer and studied with infrared laser photodissociation spectroscopy. Spectra in the 2300-3000 cm-1 region produce very different vibrational patterns for the ions made from different precursors. Computational studies with harmonic methods and various forms of anharmonic theory allow detailed assignment of these spectra to two isomeric species. Discharges containing formaldehyde produce primarily the corresponding formaldehyde radical cation, CH2O+, whereas those with methanol produce exclusively the cis- and trans-hydroxymethylene cations, HCOH+. The implications for the interstellar chemistry of these cations are discussed.

Time Dependent Density Functional Theory Calculations of Large Compact PAH Cations: Implications for the Diffuse Interstellar Bands

NASA Technical Reports Server (NTRS)

Weisman, Jennifer L.; Lee, Timothy J.; Salama, Farid; Gordon-Head, Martin; Kwak, Dochan (Technical Monitor)

2002-01-01

We investigate the electronic absorption spectra of several maximally pericondensed polycyclic aromatic hydrocarbon radical cations with time dependent density functional theory calculations. We find interesting trends in the vertical excitation energies and oscillator strengths for this series containing pyrene through circumcoronene, the largest species containing more than 50 carbon atoms. We discuss the implications of these new results for the size and structure distribution of the diffuse interstellar band carriers.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandit, Shubhrangshu; Preston, Thomas J.; Orr-Ewing, Andrew J., E-mail: a.orr-ewing@bristol.ac.uk

Photodissociation of gaseous bromocyclopropane via its A-band continuum has been studied at excitation wavelengths ranging from 230 nm to 267 nm. Velocity-map images of ground-state bromine atoms (Br), spin-orbit excited bromine atoms (Br{sup ∗}), and C{sub 3}H{sub 5} hydrocarbon radicals reveal the kinetic energies of these various photofragments. Both Br and Br{sup ∗} atoms are predominantly generated via repulsive excited electronic states in a prompt photodissociation process in which the hydrocarbon co-fragment is a cyclopropyl radical. However, the images obtained at the mass of the hydrocarbon radical fragment identify a channel with total kinetic energy greater than that deduced frommore » the Br and Br{sup ∗} images, and with a kinetic energy distribution that exceeds the energetic limit for Br + cyclopropyl radical products. The velocity-map images of these C{sub 3}H{sub 5} fragments have lower angular anisotropies than measured for Br and Br{sup ∗}, indicating molecular restructuring during dissociation. The high kinetic energy C{sub 3}H{sub 5} signals are assigned to allyl radicals generated by a minor photochemical pathway which involves concerted C–Br bond dissociation and cyclopropyl ring-opening following single ultraviolet (UV)-photon absorption. Slow photofragments also contribute to the velocity map images obtained at the C{sub 3}H{sub 5} radical mass, but the corresponding slow Br atoms are not observed. These features in the images are attributed to C{sub 3}H{sub 5}{sup +} from the photodissociation of the C{sub 3}H{sub 5}Br{sup +} molecular cation following two-photon ionization of the parent compound. This assignment is confirmed by 118-nm vacuum ultraviolet ionization studies that prepare the molecular cation in its ground electronic state prior to UV photodissociation.« less

Evidence for concerted ring opening and C-Br bond breaking in UV-excited bromocyclopropane.

PubMed

Pandit, Shubhrangshu; Preston, Thomas J; King, Simon J; Vallance, Claire; Orr-Ewing, Andrew J

2016-06-28

Photodissociation of gaseous bromocyclopropane via its A-band continuum has been studied at excitation wavelengths ranging from 230 nm to 267 nm. Velocity-map images of ground-state bromine atoms (Br), spin-orbit excited bromine atoms (Br(∗)), and C3H5 hydrocarbon radicals reveal the kinetic energies of these various photofragments. Both Br and Br(∗) atoms are predominantly generated via repulsive excited electronic states in a prompt photodissociation process in which the hydrocarbon co-fragment is a cyclopropyl radical. However, the images obtained at the mass of the hydrocarbon radical fragment identify a channel with total kinetic energy greater than that deduced from the Br and Br(∗) images, and with a kinetic energy distribution that exceeds the energetic limit for Br + cyclopropyl radical products. The velocity-map images of these C3H5 fragments have lower angular anisotropies than measured for Br and Br(∗), indicating molecular restructuring during dissociation. The high kinetic energy C3H5 signals are assigned to allyl radicals generated by a minor photochemical pathway which involves concerted C-Br bond dissociation and cyclopropyl ring-opening following single ultraviolet (UV)-photon absorption. Slow photofragments also contribute to the velocity map images obtained at the C3H5 radical mass, but the corresponding slow Br atoms are not observed. These features in the images are attributed to C3H5 (+) from the photodissociation of the C3H5Br(+) molecular cation following two-photon ionization of the parent compound. This assignment is confirmed by 118-nm vacuum ultraviolet ionization studies that prepare the molecular cation in its ground electronic state prior to UV photodissociation.

Ca2+ and Mg2+-enhanced reduction of arsenazo III to its anion free radical metabolite and generation of superoxide anion by an outer mitochondrial membrane azoreductase.

PubMed

Moreno, S N; Mason, R P; Docampo, R

1984-12-10

At the concentrations usually employed as a Ca2+ indicator, arsenazo III underwent a one-electron reduction by rat liver mitochondria to produce an azo anion radical as demonstrated by electron-spin resonance spectroscopy. Either NADH or NADPH could serve as a source of reducing equivalents for the production of this free radical by intact rat liver mitochondria. Under aerobic conditions, addition of arsenazo III to rat liver mitochondria produced an increase in electron flow from NAD(P)H to molecular oxygen, generating superoxide anion. NAD(P)H generated from endogenous mitochondrial NAD(P)+ by intramitochondrial reactions could not be used for the NAD(P)H azoreductase reaction unless the mitochondria were solubilized by detergent or anaerobiosis. In addition, NAD(P)H azoreductase activity was higher in the crude outer mitochondrial membrane fraction than in mitoplasts and intact mitochondria. The steady-state concentration of the azo anion radical and the arsenazo III-stimulated cyanide-insensitive oxygen consumption were enhanced by calcium and magnesium, suggesting that, in addition to an enhanced azo anion radical-stabilization by complexation with the metal ions, enhanced reduction of arsenazo III also occurred. Accordingly, addition of cations to crude outer mitochondrial membrane preparations increased arsenazo III-stimulated cyanide-insensitive O2 consumption, H2O2 formation, and NAD(P)H oxidation. Antipyrylazo III was much less effective than arsenazo III in increasing superoxide anion formation by rat liver mitochondria and gave a much weaker electron spin resonance spectrum of an azo anion radical. These results provide direct evidence of an azoreductase activity associated with the outer mitochondrial membrane and of a stimulation of arsenazo III reduction by cations.

Associations between age-related nuclear cataract and lutein and zeaxanthin in the diet and serum in the Carotenoids in the Age-Related Eye Disease Study, an Ancillary Study of the Women's Health Initiative.

PubMed

Moeller, Suzen M; Voland, Rick; Tinker, Lesley; Blodi, Barbara A; Klein, Michael L; Gehrs, Karen M; Johnson, Elizabeth J; Snodderly, D Max; Wallace, Robert B; Chappell, Richard J; Parekh, Niyati; Ritenbaugh, Cheryl; Mares, Julie A

2008-03-01

To evaluate associations between nuclear cataract (determined from slitlamp photographs between May 2001 and January 2004) and lutein and zeaxanthin in the diet and serum in patients between 1994 and 1998 and macula between 2001 and 2004. A total of 1802 women aged 50 to 79 years in Iowa, Wisconsin, and Oregon with intakes of lutein and zeaxanthin above the 78th (high) and below the 28th (low) percentiles in the Women's Health Initiative Observational Study (1994-1998) were recruited 4 to 7 years later (2001-2004) into the Carotenoids in Age-Related Eye Disease Study. Women in the group with high dietary levels of lutein and zeaxanthin had a 23% lower prevalence of nuclear cataract (age-adjusted odds ratio, 0.77; 95% confidence interval, 0.62-0.96) compared with those with low levels. Multivariable adjustment slightly attenuated the association (odds ratio, 0.81; 95% confidence interval, 0.65-1.01). Women in the highest quintile category of diet or serum levels of lutein and zeaxanthin as compared with those in the lowest quintile category were 32% less likely to have nuclear cataract (multivariable-adjusted odds ratio, 0.68; 95% confidence interval, 0.48-0.97; P for trend = .04; and multivariable-adjusted odds ratio, 0.68; 95% confidence interval, 0.47-0.98; P for trend = .01, respectively). Cross-sectional associations with macular pigment density were inverse but not statistically significant. Diets rich in lutein and zeaxanthin are moderately associated with decreased prevalence of nuclear cataract in older women. However, other protective aspects of such diets may in part explain these relationships.

Enhanced photoprotection by protein-bound vs free xanthophyll pools: a comparative analysis of chlorophyll b and xanthophyll biosynthesis mutants.

PubMed

Dall'Osto, Luca; Cazzaniga, Stefano; Havaux, Michel; Bassi, Roberto

2010-05-01

When light absorbed by plants exceeds the capacity of photosynthesis, the xanthophyll violaxanthin is reversibly de-epoxidized to zeaxanthin in the so-called xanthophyll cycle. Zeaxanthin plays a key role in the protection of photosynthetic organisms against excess light, by promoting rapidly reversible (qE) and long-term (qI) quenching of excited chlorophylls, and preventing lipid oxidation. The photoprotective role of zeaxanthin, either free or bound to light-harvesting complexes (Lhcs), has been investigated by using mutants lacking Chl b (ch1) and/or specific xanthophyll species (npq, lut2). The ch1 mutation causes (1) the absence of Lhcb proteins; (2) strong reduction of the feedback de-excitation (qE); and (3) accumulation of xanthophylls as free pigments into thylakoids. Ch1 mutants showed extreme sensitivity to photo-oxidative stress in high light, due to higher singlet oxygen (¹O₂) release. The double mutant ch1npq1 was more sensitive to photo-oxidation than ch1, showing that zeaxanthin does protect lipids even when free in the membrane. Nevertheless, lack of zeaxanthin had a much stronger impact on the level of lipid peroxidation in Lhcs-containing plants (WT vs npq1) with respect to Lhc-less plants (ch1 vs ch1npq1), implying that its protective effect is enhanced by interaction with antenna proteins. It is proposed that the antioxidant capacity of zeaxanthin is empowered in the presence of PSII-LHCs-Zea complexes, while its effect on enhancement of qE only provides a minor contribution. Comparison of the sensitivity of WT vs npq1 plants to exogenous ¹O₂ suggests that besides the scavenging of ¹O₂, at least one additional mechanism is involved in chloroplast photoprotection.

Studying mechanism of radical reactions: From radiation to nitroxides as research tools

NASA Astrophysics Data System (ADS)

Maimon, Eric; Samuni, Uri; Goldstein, Sara

2018-02-01

Radicals are part of the chemistry of life, and ionizing radiation chemistry serves as an indispensable research tool for elucidation of the mechanism(s) underlying their reactions. The ever-increasing understanding of their involvement in diverse physiological and pathological processes has expanded the search for compounds that can diminish radical-induced damage. This review surveys the areas of research focusing on radical reactions and particularly with stable cyclic nitroxide radicals, which demonstrate unique antioxidative activities. Unlike common antioxidants that are progressively depleted under oxidative stress and yield secondary radicals, nitroxides are efficient radical scavengers yielding in most cases their respective oxoammonium cations, which are readily reduced back in the tissue to the nitroxide thus continuously being recycled. Nitroxides, which not only protect enzymes, cells, and laboratory animals from diverse kinds of biological injury, but also modify the catalytic activity of heme enzymes, could be utilized in chemical and biological systems serving as a research tool for elucidating mechanisms underlying complex chemical and biochemical processes.

Investigation of the antioxidant and radical scavenging activities of some phenolic Schiff bases with different free radicals.

PubMed

Marković, Zoran; Đorović, Jelena; Petrović, Zorica D; Petrović, Vladimir P; Simijonović, Dušica

2015-11-01

The antioxidant properties of some phenolic Schiff bases in the presence of different reactive particles such as (•)OH, (•)OOH, (CH2=CH-O-O(•)), and (-•)O2 were investigated. The thermodynamic values, ΔH BDE, ΔH IP, and ΔH PA, were used for this purpose. Three possible mechanisms for transfer of hydrogen atom, concerted proton-electron transfer (CPET), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) were considered. These mechanisms were tested in solvents of different polarity. On the basis of the obtained results it was shown that SET-PT antioxidant mechanism can be the dominant mechanism when Schiff bases react with radical cation, while SPLET and CPET are competitive mechanisms for radical scavenging of hydroxy radical in all solvents under investigation. Examined Schiff bases react with the peroxy radicals via SPLET mechanism in polar and nonpolar solvents. The superoxide radical anion reacts with these Schiff bases very slowly.

Bioaccessibility and digestive stability of carotenoids in cooked eggs studied using a dynamic in vitro gastrointestinal model.

PubMed

Nimalaratne, Chamila; Savard, Patricia; Gauthier, Sylvie F; Schieber, Andreas; Wu, Jianping

2015-03-25

Among dietary carotenoids, lutein and zeaxanthin are known to protect against age-related macular degeneration, a leading cause of irreversible vision loss in the elderly. Egg yolk is rich in lutein and zeaxanthin, however, the effect of cooking and gastrointestinal digestion on yolk carotenoids is poorly understood. An in vitro dynamic gastrointestinal model (TIM-1) was used to investigate the digestive stability and bioaccessibility of carotenoids from boiled, fried, and scrambled eggs. Bioaccessibility but not digestive stability was significantly affected by the method of cooking. The main egg carotenoids, all-E-lutein and all-E-zeaxanthin, were stable during the digestion with average recoveries of 90 and 88%, respectively. No trans-cis isomerization of carotenoids was observed during digestion. Both all-E-lutein and all-E-zeaxanthin from scrambled eggs showed significantly lower bioaccessibility compared to boiled eggs. The results indicate that the bioaccessibility of egg carotenoids can be affected by different food preparation methods.

Pulse Radiolysis and Computational Studies on a Pyrrolidinium Dicyanamide Ionic Liquid: Detection of the Dimer Radical Anion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, Laboni; Kumar, Rahul; Maity, Dilip K.

A pulse radiolysis study on pyrrolidinium cation based ionic liquids is presented here in this paper. Time-resolved absorption spectra for 1-methyl-1-propylpyrrolidinium dicyanamide (DCA) at 500 ns after the electron pulse show broad absorption bands at wavelengths below 440 nm and at 640 nm. In pyrrolidinium bis(trifluoromethylsulfonyl)imide (NTf 2) and tris(perfluoroethyl)trifluorophosphate (FAP) ILs, the transient absorption below 440 nm is much weaker. The absorption at 500 ns, which increases with wavelength from 500 nm to beyond 800 nm, was assigned to the tail of the solvated electron NIR absorption spectrum, since it disappears in the presence of N 2O. In themore » DCA IL, the presence of a reducing species was confirmed by the formation of pyrene radical anion. The difference in the transient species in the case of the DCA IL compared to other two ILs should be due to the anion, with cations being similar. In pseudohalide ILs such as DCA, radicals are formed by direct hole trapping by the anion (X – + h + → X•), followed by addition to the parent anion. Prediction of the UV/vis absorption spectra of the dimer radical anion by computational calculation supports the experimental results. The oxidizing efficiency of (DCA) 2•– and its reduction potential (E(DCA)2•–/(2DCA–)) have been determined.« less

Pulse Radiolysis and Computational Studies on a Pyrrolidinium Dicyanamide Ionic Liquid: Detection of the Dimer Radical Anion

DOE PAGES

Das, Laboni; Kumar, Rahul; Maity, Dilip K.; ...

2018-03-06

A pulse radiolysis study on pyrrolidinium cation based ionic liquids is presented here in this paper. Time-resolved absorption spectra for 1-methyl-1-propylpyrrolidinium dicyanamide (DCA) at 500 ns after the electron pulse show broad absorption bands at wavelengths below 440 nm and at 640 nm. In pyrrolidinium bis(trifluoromethylsulfonyl)imide (NTf 2) and tris(perfluoroethyl)trifluorophosphate (FAP) ILs, the transient absorption below 440 nm is much weaker. The absorption at 500 ns, which increases with wavelength from 500 nm to beyond 800 nm, was assigned to the tail of the solvated electron NIR absorption spectrum, since it disappears in the presence of N 2O. In themore » DCA IL, the presence of a reducing species was confirmed by the formation of pyrene radical anion. The difference in the transient species in the case of the DCA IL compared to other two ILs should be due to the anion, with cations being similar. In pseudohalide ILs such as DCA, radicals are formed by direct hole trapping by the anion (X – + h + → X•), followed by addition to the parent anion. Prediction of the UV/vis absorption spectra of the dimer radical anion by computational calculation supports the experimental results. The oxidizing efficiency of (DCA) 2•– and its reduction potential (E(DCA)2•–/(2DCA–)) have been determined.« less

Palladium in Non-Aqueous Solvents. Formation, Stability, and Film Forming Properties.

DTIC Science & Technology

1987-07-14

data reported by Furlong7 in which high valent cations induced flocculation faster than monovalent cations. Addition of water to the colloid induced...reactlons Lf acetone with metal atoms. A number of radiolysis studies -f metal o in water -acetone solutions indicate that organ.c rad 2as ic trinsfer...electrons to the particles which act as electron reservoirs anc "an 7enawe as catalysts for water reduction).2’ (CH ) _OH ’,Ag) ZHA 32 If free radicals

Incorporation of carotenoids from paprika oleoresin into human chylomicrons.

PubMed

Pérez-Gálvez, Antonio; Martin, Hans D; Sies, Helmut; Stahl, Wilhelm

2003-06-01

The intake of a carotenoid-rich diet is epidemiologically related to a lower risk for different chronic disorders like cardiovascular disease, some types of cancer or age-related macular degeneration. Red pepper (Capsicum annuum L.) and its dietary products contain a variety of carotenoids, which may contribute to the carotenoid pattern of human blood and tissues. The objective of the present study was to assess the availability of carotenoids from paprika oleoresin, including zeaxanthin, beta-cryptoxanthin, beta-carotene and the paprika-specific oxocarotenoids capsanthin and capsorubin. After overnight fasting, the volunteers (n 9) ingested a single dose of the paprika oleoresin containing 6.4 mg zeaxanthin, 4.2 mg beta-cryptoxanthin, 6.2 mg beta-carotene, 35.0 mg capsanthin and 2.0 mg capsorubin. At different time points the carotenoid pattern in the chylomicron fraction was analysed to evaluate carotenoid absorption. From the major carotenoids present in the paprika oleoresin only zeaxanthin, beta-cryptoxanthin and beta-carotene were detectable in considerable amounts. Although the xanthophylls in paprika oleoresin were mainly present as mono- or di-esters, only free zeaxanthin and beta-cryptoxanthin were found in human samples. The bioavailability of the pepper-specific carotenoids capsanthin and capsorubin from paprika oleoresin is very low. However, oleoresin is a suitable source for the provitamin A carotenoids beta-carotene and beta-cryptoxanthin and the macular pigment zeaxanthin.

Supplementation with macular carotenoids improves visual performance of transgenic mice.

PubMed

Li, Binxing; Rognon, Gregory T; Mattinson, Ty; Vachali, Preejith P; Gorusupudi, Aruna; Chang, Fu-Yen; Ranganathan, Arunkumar; Nelson, Kelly; George, Evan W; Frederick, Jeanne M; Bernstein, Paul S

2018-07-01

Carotenoid supplementation can improve human visual performance, but there is still no validated rodent model to test their effects on visual function in laboratory animals. We recently showed that mice deficient in β-carotene oxygenase 2 (BCO2) and/or β-carotene oxygenase 1 (BCO1) enzymes can accumulate carotenoids in their retinas, allowing us to investigate the effects of carotenoids on the visual performance of mice. Using OptoMotry, a device to measure visual function in rodents, we examined the effect of zeaxanthin, lutein, and β-carotene on visual performance of various BCO knockout mice. We then transgenically expressed the human zeaxanthin-binding protein GSTP1 (hGSTP1) in the rods of bco2 -/- mice to examine if delivering more zeaxanthin to retina will improve their visual function further. The visual performance of bco2 -/- mice fed with zeaxanthin or lutein was significantly improved relative to control mice fed with placebo beadlets. β-Carotene had no significant effect in bco2 -/- mice but modestly improved cone visual function of bco1 -/- mice. Expression of hGSTP1 in the rods of bco2 -/- mice resulted in a 40% increase of retinal zeaxanthin and further improvement of visual performance. This work demonstrates that these "macular pigment mice" may serve as animal models to study carotenoid function in the retina. Copyright © 2018 Elsevier Inc. All rights reserved.

Ionic liquids as an electrolyte for the electro synthesis of organic compounds.

PubMed

Kathiresan, Murugavel; Velayutham, David

2015-12-25

The use of ionic liquids (ILs) as a solvent and an electrolyte for electro organic synthesis has been reviewed. To date several ILs exist, however the ILs based on tetraalkylammonium, pyrrolidinium, piperidinium and imidazolium cations with BF4(-), PF6(-), and TFSI anions have been widely used and explored the most. Electro organic synthesis in ionic liquid media leading to the synthesis of a wide range of organic compounds has been discussed. Anodic oxidation or cathodic reduction will generate radical cation or anion intermediates, respectively. These radicals can undergo self coupling or coupling with other molecules yielding organic compounds of interest. The cation of the IL is known to stabilize the radical anion extensively. This stabilization effect has a specific impact on the electrochemical CO2 reduction and coupling to various organics. The relative stability of the intermediates in IL leads to the formation of specific products in higher yields. Electrochemical reduction of imidazolium or thiazolium based ILs generates N-heterocyclic carbenes that have been shown to catalyze a wide range of base or nucleophile catalyzed organic reactions in IL media, an aspect that falls into the category of organocatalysis. Electrochemical fluorination or selective electrochemical fluorination is another fascinating area that delivers selectively fluorinated organic products in Et3N·nHF or Et4NF·nHF adducts (IL) via anodic oxidation. Oxidative polymerization in ILs has been explored the most; although morphological changes were observed compared to the conventional methods, polymers were obtained in good yields and in some cases ILs were used as dopants to improve the desired properties.

Xanthophyll (lutein, zeaxanthin) content in fruits, vegetables, and corn and egg products

USDA-ARS?s Scientific Manuscript database

Lutein and zeaxanthin are carotenoids that are selectively taken up into the macula of the eye where they are thought to protect against the development of age-related macular degeneration. Current dietary databases make it difficult to ascertain their individual roles in eye health because their co...

Intake of lutein and zeaxanthin differ with age, sex, and ethnicity

USDA-ARS?s Scientific Manuscript database

Lutein and zeaxanthin are carotenoids that are selectively taken up into the macula of the eye where they are thought to protect against age-related macular degeneration (AMD). Current dietary databases make it difficult to ascertain their individual roles in eye health because their concentrations ...

Diazonium cation-exchanged clay: an efficient, unfrequented route for making clay/polymer nanocomposites.

PubMed

Salmi, Zakaria; Benzarti, Karim; Chehimi, Mohamed M

2013-11-05

We describe a simple, off-the-beaten-path strategy for making clay/polymer nanocomposites through tandem diazonium salt interface chemistry and radical photopolymerization. Prior to photopolymerization, sodium montmorillonite (MMT) was ion exchanged with N,N'-dimethylbenzenediazonium cation (DMA) from the tetrafluoroborate salt precursor. DMA acts as a hydrogen donor for benzophenone in solution; this pair of co-initiators permits us to photopolymerize glycidyl methacrylate (GMA) between the lamellae of the diazonium-modified clay, therefore providing intercalated MMT-PGMA nanocomposites with an onset of exfoliation. This work conclusively provides a new approach for bridging reactive and functional polymers to layered nanomaterials via aryl diazonium salts in a simple, fast, efficient cation-exchange approach.

Lignin peroxidase-catalyzed oxidation of nonphenolic trimeric lignin model compounds: fragmentation reactions in the intermediate radical cations.

PubMed

Baciocchi, Enrico; Fabbri, Claudia; Lanzalunga, Osvaldo

2003-11-14

The H(2)O(2)-promoted oxidations of the two nonphenolic beta-O-aryl lignin model trimers 1 and 2, catalyzed by lignin peroxidase (LiP) at pH = 3.5, have been studied. The results have been compared with those obtained in the oxidation of 1 and 2 with the genuine one-electron oxidant potassium 12-tungstocobalt(III)ate. These models present a different substitution pattern of the three aromatic rings, and by one-electron oxidation, they form radical cations with the positive charge, which is localized in the dialkoxylated ring as also evidenced by a pulse radiolysis study. Both the oxidations with the enzymatic and with the chemical systems lead to the formation of products deriving from the cleavage of C-C and C-H bonds in a beta position with respect to the radical cation with the charge residing in the dialkoxylated ring (3,4-dimethoxybenzaldehyde (5) and a trimeric ketone 6 in the oxidation of 1 and a dimeric aldehyde 8 and a trimeric ketone 9 in the oxidation of 2). These products are accompanied by a dimeric aldehyde 7 in the oxidation of 1 and 4-methoxybenzaldehyde (10) in the oxidation of 2. The unexpected formation of these two products has been explained by suggesting that 1.+ and 2.+ can also undergo an intramolecular electron transfer leading to the radical cations 1a.+ and 2a.+ with the charge residing in a monoalkoxylated ring. The fast cleavage of a C-C bond beta to this ring, leading to 7 from 1.+ and to 10 from 2.+, is the driving force of the endoergonic electron transfer. A kinetic steady-state investigation of the LiP-catalyzed oxidation of the trimer 2, the dimeric model 1-(3,4-dimethoxyphenyl)-2-phenoxy-1-ethanol (4), and 3,4-dimethoxybenzyl alcohol (3) has indicated that the turnover number (k(cat)) and the affinity for the enzyme decrease significantly by increasing the size of the model compound. In contrast, the three substrates exhibited a very similar reactivity toward a chemical oxidant [Co(III)W]. This suggests a size-dependent interaction of the enzyme with the substrate which may influence the efficiency of the electron transfer.

Homoleptic 2,2'-bipyridine metalates(-I) of iron and cobalt, one cocrystallized with an anthracene radical anion and the other with neutral anthracene.

PubMed

Brennessel, William W; Ellis, John E

2014-08-01

Homoleptic 2,2'-bipyridine (bipy) metalates of iron and cobalt have been synthesized directly from the corresponding homoleptic anthracene metalates. In the iron structure, bis[([2.2.2]cryptand)potassium(I)] tris(2,2'-bipyridine)ferrate(-I) anthracene(-I), [K(C18H36N2O6)]2[Fe(C10H8N2)3](C14H10), the asymmetric unit contains one potassium complex cation in a general position, the Fe center and one and a half bipy ligands of the ferrate complex on a crystallographic twofold axis that includes the Fe atom, and one half of an anthracene radical anion whose other half is generated by a crystallographic inversion center. The cations and anions are well separated and the geometry about the Fe center is essentially octahedral. In the cobalt structure, ([2.2.2]cryptand)potassium(I) bis(2,2'-bipyridine)cobaltate(-I) anthracene hemisolvate tetrahydrofuran (THF) disolvate, [K(C18H36N2O6)][Co(C10H8N2)2]·0.5C14H10·2C4H8O, the asymmetric unit contains the cation, anion, and both cocrystallized THF solvent molecules in general positions, and one half of a cocrystallized anthracene molecule whose other half is generated by a crystallographic inversion center. The cation and anion are well separated and the ligand planes in the cobaltate anion are periplanar. Each anthracene molecule is midway between and is oriented perpendicular to a pair of symmetry-related bipy ligands such that aromatic donor-acceptor interactions may play a role in the packing arrangement. The lengths of the bonds that connect the bipy rings support the assertion that the ligands are bipy radical anions in the iron structure. However, in the case of cobalt, these lengths are between the known ranges for a bipy radical anion and a bipy dianion, and therefore no conclusion can be made from the crystallography alone. One cocrystallized THF solvent molecule in the cobalt structure was modeled as disordered over three positions with appropriate geometric and thermal restraints, which resulted in a refined component mass ratio of 0.412 (4):0.387 (3):0.201 (3).

Experimental IR and Raman spectra and quantum chemical studies of molecular structures, conformers and vibrational characteristics of L-ascorbic acid and its anion and cation

NASA Astrophysics Data System (ADS)

Yadav, R. A.; Rani, P.; Kumar, M.; Singh, R.; Singh, Priyanka; Singh, N. P.

2011-12-01

IR and spectra of the L-ascorbic acid ( L-AA) also known as vitamin C have been recorded in the region 4000-50 cm -1. In order to make vibrational assignments of the observed IR and Raman bands computations were carried out by employing the RHF and DFT methods to calculate the molecular geometries and harmonic vibrational frequencies along with other related parameters for the neutral L-AA and its singly charged anionic ( L-AA -) and cationic ( L-AA +) species. Significant changes have been found for different characteristics of a number of vibrational modes. The four ν(O-H) modes of the L-AA molecule are found in the order ν(O 9-H 10) > ν(O 19-H 20) > ν(O 7-H 8) > ν(O 14-H 15) which could be due to complexity of hydrogen bonding in the lactone ring and the side chain. The C dbnd O stretching wavenumber ( ν46) decreases by 151 cm -1 in going from the neutral to the anionic species whereas it increases by 151 cm -1 in going from the anionic to the cationic species. The anionic radicals have less kinetic stabilities and high chemical reactivity as compared to the neutral molecule. It is found that the cationic radical of L-AA is kinetically least stable and chemically most reactive as compared to its neutral and anionic species.

Polymerization Initiated at the Sidewalls of Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Tour, James M.; Hudson, Jared L.

2011-01-01

A process has been developed for growing polymer chains via anionic, cationic, or radical polymerization from the side walls of functionalized carbon nanotubes, which will facilitate greater dispersion in polymer matrices, and will greatly enhance reinforcement ability in polymeric material.

Dissociation of protonated N-(3-phenyl-2H-chromen-2-ylidene)-benzenesulfonamide in the gas phase: cyclization via sulfonyl cation transfer.

PubMed

Wang, Shanshan; Dong, Cheng; Yu, Lian; Guo, Cheng; Jiang, Kezhi

2016-01-15

In the tandem mass spectrometry of protonated N-(3-phenyl-2H-chromen-2-ylidene)benzenesulfonamides, the precursor ions have been observed to undergo gas-phase dissociation via two competing channels: (a) the predominant channel involves migration of the sulfonyl cation to the phenyl C atom and the subsequent loss of benzenesulfinic acid along with cyclization reaction, and (b) the minor one involves dissociation of the precursor ion to give an ion/neutral complex of [sulfonyl cation/imine], followed by decomposition to afford sulfonyl cation or the INC-mediated electron transfer to give an imine radical cation. The proposed reaction channels have been supported by theoretical calculations and D-labeling experiments. The gas-phase cyclization reaction originating from the N- to C-sulfonyl cation transfer has been first reported to the best of our knowledge. For the substituted sulfonamides, the presence of electron-donating groups (R(2) -) at the C-ring effectively facilitates the reaction channel of cyclization reaction, whereas that of electron-withdrawing groups inhibits this pathway. Copyright © 2015 John Wiley & Sons, Ltd.

Computational Study of Interstellar Glycine Formation Occurring at Radical Surfaces of Water-ice Dust Particles

NASA Astrophysics Data System (ADS)

Rimola, Albert; Sodupe, Mariona; Ugliengo, Piero

2012-07-01

Glycine is the simplest amino acid, and due to the significant astrobiological implications that suppose its detection, the search for it in the interstellar medium (ISM), meteorites, and comets is intensively investigated. In the present work, quantum mechanical calculations based on density functional theory have been used to model the glycine formation on water-ice clusters present in the ISM. The removal of either one H atom or one electron from the water-ice cluster has been considered to simulate the effect of photolytic radiation and of ionizing particles, respectively, which lead to the formation of OH• radical and H3O+ surface defects. The coupling of incoming CO molecules with the surface OH• radicals on the ice clusters yields the formation of the COOH• radicals via ZPE-corrected energy barriers and reaction energies of about 4-5 kcal mol-1 and -22 kcal mol-1, respectively. The COOH• radicals couple with incoming NH=CH2 molecules (experimentally detected in the ISM) to form the NHCH2COOH• radical glycine through energy barriers of 12 kcal mol-1, exceedingly high at ISM cryogenic temperatures. Nonetheless, when H3O+ is present, one proton may be barrierless transferred to NH=CH2 to give NH2=CH2 +. This latter may react with the COOH• radical to give the NH2CH2COOH+• glycine radical cation which can then be transformed into the NH2CHC(OH)2 +• species (the most stable form of glycine in its radical cation state) or into the NH2CHCOOH• neutral radical glycine. Estimated rate constants of these events suggest that they are kinetically feasible at temperatures of 100-200 K, which indicate that their occurrence may take place in hot molecular cores or in comets exposed to warmer regions of solar systems. Present results provide quantum chemical evidence that defects formed on water ices due to the harsh-physical conditions of the ISM may trigger reactions of cosmochemical interest. The relevance of surface H3O+ ions to facilitate chemical processes by proton transfer (i.e., acting as acidic catalysts) is highlighted, and plausible ways of their formation at the water-ice surface in the ISM are also discussed.

Carotenoid profiling from 27 types of paprika (Capsicum annuum L.) with different colors, shapes, and cultivation methods.

PubMed

Kim, Ji-Sun; An, Chul Geon; Park, Jong-Suk; Lim, Yong Pyo; Kim, Suna

2016-06-15

In this study, we investigated carotenoid profiles and contents from 27 types of paprika with different colors (red, orange, and yellow), shapes (blocky and conical), and cultivation methods (soil and soilless). We simultaneously analyzed 12 kinds of carotenoids using UPLC equipped with an HSS T3 column for 30 min, and we identified six kinds of carotenoids in red paprika and nine types in orange and yellow paprika. Zeaxanthin concentrations in orange paprika were in the range of 85.06±23.37-151.39±5.94 mg/100 g dry weight (dw), which shows that orange paprika is a great source of zeaxanthin. Generally, red paprika is a great source of capsanthin. However, a new cultivar, 'Mini Goggal Red', contained large amounts of zeaxanthin (121.41±30.10 mg/100 g dw) even though its visible color is red. This is very meaningful considering that consumers have a preference for red color and the potent functional value of zeaxanthin. Carotenoid profiles and concentrations in blocky and conical type paprika were not significantly different in red paprika except the 'Mini Goggal Red' cultivar and yellow paprika. Blocky type orange paprika contains plenty of zeaxanthin, unlike conical type orange paprika. Three new cultivars of the conical type were cultivated in both soil culture and soilless culture in the same province, and carotenoid profiles and concentrations were similar, showing that both cultivations methods can be used. Copyright © 2016. Published by Elsevier Ltd.

Plasma carotenoids and tocopherols in relation to prostate-specific antigen (PSA) levels among men with biochemical recurrence of prostate cancer.

PubMed

Antwi, Samuel O; Steck, Susan E; Zhang, Hongmei; Stumm, Lareissa; Zhang, Jiajia; Hurley, Thomas G; Hebert, James R

2015-10-01

Although men presenting with clinically localized prostate cancer (PrCA) often are treated with radical prostatectomy or radiation therapy with curative intent, about 25-40% develop biochemically recurrent PrCA within 5 years of treatment, which has no known cure. Studies suggest that carotenoid and tocopherol intake may be associated with PrCA risk and progression. We examined plasma carotenoid and tocopherol levels in relation to prostate-specific antigen (PSA) levels among men with PSA-defined biochemical recurrence of PrCA. Data analyzed were from a 6-month diet, physical activity and stress-reduction intervention trial conducted in South Carolina among biochemically recurrent PrCA patients (n=39). Plasma carotenoids and tocopherol levels were measured using high-performance liquid chromatography (HPLC). Linear regression was used to estimate least-square means comparing PSA levels of men with high versus low carotenoid/tocopherol levels, adjusting for covariates. After adjusting for baseline PSA level, plasma cis-lutein/zeaxanthin level at 3 months was related inversely to PSA level at 3 months (P=0.0008), while α-tocopherol (P=0.01), β-cryptoxanthin (P=0.01), and all-trans-lycopene (P=0.004) levels at 3 months were related inversely to PSA levels at 6-months. Percent increase in α-tocopherol and trans-β-carotene levels from baseline to month 3 were associated with lower PSA levels at 3 and 6 months. Percent increase in β-cryptoxanthin, cis-lutein/zeaxanthin and all-trans-lycopene were associated with lower PSA levels at 6 months only. Certain plasma carotenoids and tocopherols were related inversely to PSA levels at various timepoints, suggesting that greater intake of foods containing these micronutrients might be beneficial to men with PSA-defined PrCA recurrence. Copyright © 2015. Published by Elsevier Ltd.

Isolation and identification of phenolic antioxidants in black rice bran.

PubMed

Jun, Hyun-Il; Shin, Jae-Wook; Song, Geun-Seoup; Kim, Young-Soo

2015-02-01

Black rice bran contains phenolic compounds of a high antioxidant activity. In this study, the 40% acetone extract of black rice bran was sequentially fractionated to obtain 5 fractions. Out of the 5 fractions, ethyl acetate fraction was subfractionated using the Sephadex LH-20 chromatography. The antioxidant activity of phenolic compounds in the extracts was investigated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical assay, 2,2-azino-bis-(3-ethylenebenzothiozoline-6-sulfonic acid) (ABTS) radical cation assay, reducing power. The subfraction 2 from ethyl acetate fraction had the highest total phenolic contents (TPC) (816.0 μg/mg) and the lowest EC50 values (47.8 μg/mL for DPPH radical assay, 112.8 μg/mL for ABTS radical cation assay, and 49.2 μg/mL for reducing power). These results were 3.1, 1.3, and 2.6 times lower than those of butylated hydroxytoluene (BHT), respectively. At a concentration of 100 μg/mL, the antioxidant activity and TPC of various extracts was closely correlated, with correlation coefficients (R(2) ) higher than 0.86. The major phenolic acid in subfraction 2 was identified as ferulic acid (178.3 μg/mg) by HPLC and LC-ESI/MS/MS analyses. Our finding identified ferulic acid as a major phenolic compound in black rice bran, and supports the potential use of black rice bran as a natural source of antioxidant. © 2015 Institute of Food Technologists®

[Antioxidant activity of cationic whey protein isolate].

PubMed

titova, M E; Komolov, S A; Tikhomirova, N A

2012-01-01

The process of lipid peroxidation (LPO) in biological membranes of cells is carried out by free radical mechanism, a feature of which is the interaction of radicals with other molecules. In this work we investigated the antioxidant activity of cationic whey protein isolate, obtained by the cation-exchange chromatography on KM-cellulose from raw cow's milk, in vitro and in vivo. In biological liquids, which are milk, blood serum, fetal fluids, contains a complex of biologically active substances with a unique multifunctional properties, and which are carrying out a protective, antimicrobial, regenerating, antioxidant, immunomodulatory, regulatory and others functions. Contents of the isolate were determined electrophoretically and by its biological activity. Cationic whey protein isolate included lactoperoxidase, lactoferrin, pancreatic RNase, lysozyme and angeogenin. The given isolate significantly has an antioxidant effect in model experimental systems in vitro and therefore may be considered as a factor that can adjust the intensity of lipid oxidation. In model solutions products of lipid oxidation were obtained by oxidation of phosphatidylcholine by hydrogen peroxide in the presence of a source of iron. The composition of the reaction mixture: 0,4 mM H2O2; 50 mcM of hemin; 2 mg/ml L-alpha-phosphatidylcholine from soybean (Sigma, German). Lipid peroxidation products were formed during the incubation of the reaction mixture for two hours at 37 degrees C. In our studies rats in the adaptation period immediately after isolation from the nest obtained from food given orally native cationic whey protein isolate at the concentration three times higher than in fresh cow's milk. On the manifestation of the antioxidant activity of cationic whey protein isolate in vivo evidence decrease of lipid peroxidation products concentration in the blood of rats from the experimental group receipt whey protein isolate in dos 0,6 mg/g for more than 20% (p<0,05) with oral feeding. Thus, significantly cationic whey protein isolate has an antioxidant effect in model experimental systems, and so can be considered as a factor that can regulate the intensity of lipid oxidation.

Electronic and vibrational spectra of matrix isolated anthracene radical cations - Experimental and theoretical aspects

NASA Technical Reports Server (NTRS)

Szczepanski, Jan; Vala, Martin; Talbi, Dahbia; Parisel, Olivier; Ellinger, Yves

1993-01-01

The IR vibrational and visible/UV electronic absorption spectra of the anthracene cation, An(+), were studied experimentally, in argon matrices at 12 K, as well as theoretically, using ab initio calculations for the vibrational modes and enhanced semiempirical methods with configuration interaction for the electronic spectra. It was found that both approaches predicted well the observed photoelectron spectrum. The theoretical IR intensities showed some remarkable differences between neutral and ionized species (for example, the CH in-plane bending modes and CC in-plane stretching vibrations were predicted to increase by several orders of magnitude upon ionization). Likewise, estimated experimental IR intensities showed a significant increase in the cation band intensities over the neutrals. The implication of these findings for the hypothesis that polycyclic aromatic hydrocarbon cations are responsible for the unidentified IR emission bands from interstellar space is discussed.

A new insight into the oxidative mechanism of caffeine and related methylxanthines in aprotic medium: May caffeine be really considered as an antioxidant?

PubMed

Petrucci, Rita; Zollo, Giuseppe; Curulli, Antonella; Marrosu, Giancarlo

2018-05-12

Antioxidant properties have been recently suggested for caffeine that seems showing protective effects against damages caused by oxidative stress. In particular, a HO scavenging activity has been ascribed to caffeine. Even if the oxidation of caffeine has been widely studied, the antioxidant mechanism is still far to be understood. The electrochemical behavior of caffeine, theobromine and theophylline was studied in aprotic medium by cyclic voltammetry and electrolysis in UV-vis cell; a computational analysis of the molecular structures based on the Density Functional Theory was performed; the reactivity of all substrates towards lead dioxide, superoxide and galvinoxyl radical was followed by UV-vis spectrophotometry. Results supported the mono-electronic oxidation of the C 4 C 5 bond for all substrates at high oxidation potentials, the electron-transfer process leading to a radical cation or a neutral radical according to the starting methylxanthine N 7 -substituted (caffeine and theobromine) or N 7 -unsubstituted (theophylline), respectively. A different following chemical fate might be predicted for the radical cation or the neutral radical. No interaction was evidenced towards the tested reactive oxygen species. No reactivity via H-atom transfer was evidenced for all studied compounds, suggesting that an antiradical activity should be excluded. Some reactivity only with strong oxidants could be predicted via electron-transfer. The acclaimed HO scavenging activity should be interpreted in these terms. The study suggested that CAF might be hardly considered an antioxidant. Beyond the experimental methods used, the discussion of the present results might provide food for thought to the wide audience working on antioxidants. Copyright © 2018. Published by Elsevier B.V.

Experimental and Computational Investigations of the Threshold Photoelectron Spectrum of the HCCN Radical

NASA Astrophysics Data System (ADS)

Gans, B.; Falvo, Cyril; Coudert, L. H.; Garcia, Gustavo A.; Küger, J.; Loison, J.-C.

2017-06-01

The HCCN radical, already detected in the interstellar medium, is also important for nitrile chemistry in Titan's atmosphere. Quite recently the photoionization spectrum of the radical has been recorded using mass selected threshold photoelectron (TPE) spectroscopy and this provided us with the first spectroscopic information about the HCCN} cation. Modeling such a spectrum requires accounting for the non-rigidity of HCCN and for the Renner-Teller effect in HCCN+. In its ^3A'' electronic ground state, HCCN is a non-rigid molecule as the potential for the \\angle{HCC} bending angle is very shallow. Vibronic couplings with the same bending angle leads, in the ^2Π electronic ground state of HCCN+, to a strong Renner-Teller effect giving rise to a bent ^2A' and a quasi-linear ^2A'' state. In this paper the photoionization spectrum of the HCCN radical is simulated. The model developped treats the \\angle{HCC} bending angle as a large amplitude coordinate in both the radical and the cation and accounts for the overall rotation and the Renner-Teller couplings. Gaussian quadrature are used to calculate matrix elements of the three potential energy functions retrieved through ab initio calculations and rovibrational operators going to infinity for the linear configuration are treated rigorously. The HCCN TPE spectrum is computed with the above model calculating all rotational components and choosing the appropriate lineshape. This synthetic spectrum will be shown in the paper and compared with the experimental one.^b Guélin and Cernicharo, A&A 244 (1991) L21 Loison et al., Icarus 247 (2015) 218 Garcia, Krüger, Gans, Falvo, Coudert, and Loison, J. Chem. Phys. (2017) submitted Koput, J. Phys. Chem. A 106 (2002) 6183 Zhao, Zhang, and Sun, J. Phys. Chem. A 112 (2008) 12125

Enhanced photocatalytic activity of TiO2 by surface fluorination in degradation of organic cationic compound.

PubMed

Yang, Shi-ying; Chen, You-yuan; Zheng, Jian-guo; Cui, Ying-jie

2007-01-01

Experiments were carried out to investigate the influence of TiO2 surface fluorination on the photodegradation of a representative organic cationic compound, Methylene Blue (MB). The electropositive MB shows poor adsorption on TiO2 surface; its degradation performs a HO-radical-mediated mechanism. In the F-modified system, the kinetic reaction rate enlarged more than 2.5 fold that was attributed mainly to the accumulating adsorption of MB and the increased photogenerated hole available on the F-modified TiO2 surface.

Glyceryl ether sulfonates for use in oil recovery fluids and processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCoy, D.R.

1984-08-21

Petroleum may be recovered from petroleum containing formations having high salinity by injecting into the formation an aqueous fluid containing an effective amount of a surface active agent characterized by the formula: R/sub 1/(OCH/sub 2/CH(OH)CH/sub 2/) /SUB m/ (R/sub 2/) /SUB n/ OR/sub 3/SO/sub 3/X wherein R/sub 1/ is an alkyl or alkylaryl radical, m is an integer of from 1 to 10, R/sub 2/ is an ethoxy radical and/or 1,2-propoxy radical, n is an integer of from 0 to 10, R/sub 3/ is an ethylene or 1,3-propylene radical, X is a sodium, potassium or ammonium cation; and driving themore » fluid through the formation and thereby displacing and recovering petroleum from the formation.« less

Captopril and 6-mercaptopurine: whose SH possesses higher antioxidant ability?

PubMed

Li, Guo-Xiang; Liu, Zai-Qun

2009-12-01

Antioxidant capacities of captopril (CAP), 6-mercaptopurine (6-MP) and 9-(beta-D-ribofuranosyl)-6-mercaptopurine (6-MPR) were investigated by interacting them with 2,2'-diphenyl-1-picrylhydrazyl (DPPH), galvinoxyl radical, and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cation radical (ABTS(+)(*)), and by protecting DNA and erythrocyte against 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH) induced oxidation. It was found that CAP possessed the highest ability to donate the hydrogen atom in -SH to DPPH and galvinoxyl, while 6-MPR had the strongest ability to reduce ABTS(+)(*). In the process of protecting DNA and erythrocytes against AAPH-induced oxidation, CAP can trap 0.5 and 1.3 radicals, 6-MP can trap 0.6 and 2.2, and 6-MPR can trap 1.0 and 3.0 radicals, respectively. CAP can also protect erythrocytes against hemin-induced hemolysis.

Singlet Oxygen and Free Radical Reactions of Retinoids and Carotenoids—A Review

PubMed Central

Truscott, T. George

2018-01-01

We report on studies of reactions of singlet oxygen with carotenoids and retinoids and a range of free radical studies on carotenoids and retinoids with emphasis on recent work, dietary carotenoids and the role of oxygen in biological processes. Many previous reviews are cited and updated together with new data not previously reviewed. The review does not deal with computational studies but the emphasis is on laboratory-based results. We contrast the ease of study of both singlet oxygen and polyene radical cations compared to neutral radicals. Of particular interest is the switch from anti- to pro-oxidant behavior of a carotenoid with change of oxygen concentration: results for lycopene in a cellular model system show total protection of the human cells studied at zero oxygen concentration, but zero protection at 100% oxygen concentration. PMID:29301252

Comparing Positively and Negatively Charged Distonic Radical Ions in Phenylperoxyl Forming Reactions.

PubMed

Williams, Peggy E; Marshall, David L; Poad, Berwyck L J; Narreddula, Venkateswara R; Kirk, Benjamin B; Trevitt, Adam J; Blanksby, Stephen J

2018-06-04

In the gas phase, arylperoxyl forming reactions play a significant role in low-temperature combustion and atmospheric processing of volatile organic compounds. We have previously demonstrated the application of charge-tagged phenyl radicals to explore the outcomes of these reactions using ion trap mass spectrometry. Here, we present a side-by-side comparison of rates and product distributions from the reaction of positively and negatively charge tagged phenyl radicals with dioxygen. The negatively charged distonic radical ions are found to react with significantly greater efficiency than their positively charged analogues. The product distributions of the anion reactions favor products of phenylperoxyl radical decomposition (e.g., phenoxyl radicals and cyclopentadienone), while the comparable fixed-charge cations yield the stabilized phenylperoxyl radical. Electronic structure calculations rationalize these differences as arising from the influence of the charged moiety on the energetics of rate-determining transition states and reaction intermediates within the phenylperoxyl reaction manifold and predict that this influence could extend to intra-molecular charge-radical separations of up to 14.5 Å. Experimental observations of reactions of the novel 4-(1-carboxylatoadamantyl)phenyl radical anion confirm that the influence of the charge on both rate and product distribution can be modulated by increasing the rigidly imposed separation between charge and radical sites. These findings provide a generalizable framework for predicting the influence of charged groups on polarizable radicals in gas phase distonic radical ions. Graphical Abstract.

Comparing Positively and Negatively Charged Distonic Radical Ions in Phenylperoxyl Forming Reactions

NASA Astrophysics Data System (ADS)

Williams, Peggy E.; Marshall, David L.; Poad, Berwyck L. J.; Narreddula, Venkateswara R.; Kirk, Benjamin B.; Trevitt, Adam J.; Blanksby, Stephen J.

2018-06-01

In the gas phase, arylperoxyl forming reactions play a significant role in low-temperature combustion and atmospheric processing of volatile organic compounds. We have previously demonstrated the application of charge-tagged phenyl radicals to explore the outcomes of these reactions using ion trap mass spectrometry. Here, we present a side-by-side comparison of rates and product distributions from the reaction of positively and negatively charge tagged phenyl radicals with dioxygen. The negatively charged distonic radical ions are found to react with significantly greater efficiency than their positively charged analogues. The product distributions of the anion reactions favor products of phenylperoxyl radical decomposition (e.g., phenoxyl radicals and cyclopentadienone), while the comparable fixed-charge cations yield the stabilized phenylperoxyl radical. Electronic structure calculations rationalize these differences as arising from the influence of the charged moiety on the energetics of rate-determining transition states and reaction intermediates within the phenylperoxyl reaction manifold and predict that this influence could extend to intra-molecular charge-radical separations of up to 14.5 Å. Experimental observations of reactions of the novel 4-(1-carboxylatoadamantyl)phenyl radical anion confirm that the influence of the charge on both rate and product distribution can be modulated by increasing the rigidly imposed separation between charge and radical sites. These findings provide a generalizable framework for predicting the influence of charged groups on polarizable radicals in gas phase distonic radical ions.

Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization.

PubMed

Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

2016-08-01

The efficiencies of charge exchange reaction in dopant-assisted atmospheric pressure chemical ionization (DA-APCI) and dopant-assisted atmospheric pressure photoionization (DA-APPI) mass spectrometry (MS) were compared by flow injection analysis. Fourteen individual compounds and a commercial mixture of 16 polycyclic aromatic hydrocarbons were chosen as model analytes to cover a wide range of polarities, gas-phase ionization energies, and proton affinities. Chlorobenzene was used as the dopant, and methanol/water (80/20) as the solvent. In both techniques, analytes formed the same ions (radical cations, protonated molecules, and/or fragments). However, in DA-APCI, the relative efficiency of charge exchange versus proton transfer was lower than in DA-APPI. This is suggested to be because in DA-APCI both dopant and solvent clusters can be ionized, and the formed reagent ions can react with the analytes via competing charge exchange and proton transfer reactions. In DA-APPI, on the other hand, the main reagents are dopant-derived radical cations, which favor ionization of analytes via charge exchange. The efficiency of charge exchange in both DA-APPI and DA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied (0.05 and 0.1 mL/min). Both DA-APCI and DA-APPI showed the radical cation of chlorobenzene at 0.05-0.1 mL/min flow rate, but at increasing flow rate, the abundance of chlorobenzene M(+.) decreased and reagent ion populations deriving from different gas-phase chemistry were recorded. The formation of these reagent ions explains the decreasing ionization efficiency and the differences in charge exchange between the techniques. Graphical Abstract ᅟ.

Effect of the chelation of metal cation on the antioxidant activity of chondroitin sulfates.

PubMed

Ajisaka, Katsumi; Oyanagi, Yutaka; Miyazaki, Tatsuo; Suzuki, Yasuhiro

2016-06-01

The antioxidant potencies of chondroitin sulfates (CSs) from shark cartilage, salmon cartilage, bovine trachea, and porcine intestinal mucosa were compared by three representative methods for the measurement of the antioxidant activity; DPPH radical scavenging activity, superoxide radical scavenging activity, and hydroxyl radical scavenging activity. CSs from salmon cartilage and bovine trachea showed higher potency in comparison with CSs from shark cartilage and porcine intestinal mucosa. Next, CS from salmon cartilage chelating with Ca(2+), Mg(2+), Mn(2+), or Zn(2+) were prepared, and their antioxidant potencies were compared. CS chelating with Ca(2+) or Mg(2+) ions showed rather decreased DPPH radical scavenging activity in comparison with CS of H(+) form. In contrast, CS chelating with Ca(2+) or Mg(2+) ion showed remarkably enhanced superoxide radical scavenging activity than CS of H(+) or Na(+) form. Moreover, CS chelating with divalent metal ions, Ca(2+), Mg(2+), Mn(2+), or Zn(2+), showed noticeably higher hydroxyl radical scavenging activity than CS of H(+) or Na(+) form. The present results revealed that the scavenging activities of, at least, superoxide radical and hydroxyl radical were enhanced by the chelation with divalent metal ions.

Electrochemistry and electrogenerated chemiluminescence of dithienylbenzothiadiazole derivative. Differential reactivity of donor and acceptor groups and simulations of radical cation-anion and dication-radical anion annihilations.

PubMed

Shen, Mei; Rodríguez-López, Joaquín; Huang, Ju; Liu, Quan; Zhu, Xu-Hui; Bard, Allen J

2010-09-29

We report here the electrochemistry and electrogenerated chemiluminescence (ECL) of a red-emitting dithienylbenzothiadiazole-based molecular fluorophore (4,7-bis(4-(4-sec-butoxyphenyl)-5-(3,5-di(1-naphthyl)phenyl)thiophen-2-yl)-2,1,3-benzothiadiazole, 1b). 1b contains two substituted thiophene groups as strong electron donors at the ends connected directly to a strong electron acceptor, 2,1,3-benzothiadiazole, in the center. Each thiophene moiety is substituted in position 2 by 3,5-di(1-naphthyl)phenyl and in position 3 by 4-sec-butoxyphenyl. Cyclic voltammetry of 1b, with scan rate ranging from 0.05 to 0.75 V/s, shows a single one-electron reduction wave (E°(red) = -1.18 V vs SCE) and two nernstian one-electron oxidation waves (E°(1,ox) = 1.01 V, E°(2,ox) = 1.24 V vs SCE). Reduction of the unsubstituted 2,1,3-benzothiadiazole center shows nernstian behavior with E°(red) = -1.56 V vs SCE. By comparison to a digital simulation, the heterogeneous electron-transfer rate constant for reduction, k(r)° = 1.5 × 10(-3) cm/s, is significantly smaller than those for the oxidations, k(o)° > 0.1 cm/s, possibly indicating that the two substituted end groups have a blocking effect on the reduction of the benzothiadiazole center. The ECL spectrum, produced by electron-transfer annihilation of the reduced and oxidized forms, consists of a single peak with maximum emission at about 635 nm, consistent with the fluorescence of the parent molecule. Relative ECL intensities with respect to 9,10-diphenylanthracene are 330% and 470% for the radical anion-cation and radical anion-dication annihilation, respectively. Radical anion (A(-•))-cation (A(+•)) annihilation produced by potential steps shows symmetric ECL transients during anodic and cathodic pulses, while for anion (A(-•))-dication (A(2+•)) annihilation, transient ECL shows asymmetry in which the anodic pulse is narrower than the cathodic pulse. Digital simulation of the transient ECL experiments showed that the origin of the observed asymmetry is asymmetry in the amount of generated charges rather than instability of the electrogenerated species.

Formation, isomerization, and dissociation of ε- and α-carbon-centered tyrosylglycylglycine radical cations.

PubMed

Lai, Cheuk-Kuen; Mu, Xiaoyan; Hao, Qiang; Hopkinson, Alan C; Chu, Ivan K

2014-11-28

The fragmentation products of the ε-carbon-centered radical cations [Y(ε)˙LG](+) and [Y(ε)˙GL](+), made by 266 nm laser photolysis of protonated 3-iodotyrosine-containing peptides, are substantially different from those of their π-centered isomers [Y(π)˙LG](+) and [Y(π)˙GL](+), made by dissociative electron transfer from ternary metal-ligand-peptide complexes. For leucine-containing peptides the major pathway for the ε-carbon-centered radical cations is loss of the side chain of the leucine residue forming [YG(α)˙G](+) and [YGG(α)˙](+), whereas for the π-radicals it is the side chain of the tyrosine residue that is lost, giving [G(α)˙LG](+) and [G(α)˙GL](+). The fragmentations of the product ions [YG(α)˙G](+) and [YGG(α)˙](+) are compared with those of the isomeric [Y(ε)˙GG](+) and [Y(π)˙GG](+) ions. The collision-induced spectra of ions [Y(ε)˙GG](+) and [YGG(α)˙](+) are identical, showing that interconversion occurs prior to dissociation. For ions [Y(ε)˙GG](+), [Y(π)˙GG](+) and [YG(α)˙G](+) the dissociation products are all distinctly different, indicating that dissociation occurs more readily than isomerization. Density functional theory calculations at B3LYP/6-31++G(d,p) gave the relative enthalpies (in kcal mol(-1) at 0 K) of the five isomers to be [Y(ε)˙GG](+) 0, [Y(π)˙GG](+) -23.7, [YGG(α)˙](+) -28.7, [YG(α)˙G](+) -31.0 and [Y(α)˙GG](+) -38.5. Migration of an α-C-H atom from the terminal glycine residue to the ε-carbon-centered radical in the tyrosine residue, a 1-11 hydrogen atom shift, has a low barrier, 15.5 kcal mol(-1) above [Y(ε)˙GG](+). By comparison, isomerization of [Y(ε)˙GG](+) to [YG(α)˙G](+) by a 1-8 hydrogen atom migration from the α-C-H atom of the central glycine residue has a much higher barrier (50.6 kcal mol(-1)); similarly conversion of [Y(ε)˙GG](+) into [Y(π)˙GG](+) has a higher energy (24.4 kcal mol(-1)).

cis-Stilbene and (1 alpha,2 beta,3 alpha)-(2-ethenyl-3-methoxycyclopropyl)benzene as mechanistic probes in the Mn(III)(salen)-catalyzed epoxidation: influence of the oxygen source and the counterion on the diastereoselectivity of the competitive concerted and radical-type oxygen transfer.

PubMed

Adam, Waldemar; Roschmann, Konrad J; Saha-Möller, Chantu R; Seebach, Dieter

2002-05-08

cis-Stilbene (1) has been epoxidized by a set of diverse oxygen donors [OxD], catalyzed by the Mn(III)(salen)X complexes 3 (X = Cl, PF(6)), to afford a mixture of cis- and trans-epoxides 2. The cis/trans ratios range from 29:71 (extensive isomerization) to 92:8, which depends both on the oxygen source [OxD] and on the counterion X of the catalyst. When (1 alpha,2 beta,3 alpha)-(2-ethenyl-3-methoxycyclopropyl)-benzene (4) is used as substrate, a mechanistic probe which differentiates between radical and cationic intermediates, no cationic ring-opening products are found in this epoxidation reaction; thus, isomerized epoxide product arises from intermediary radicals. The dependence of the diastereoselectivity on the oxygen source is rationalized in terms of a bifurcation step in the catalytic cycle, in which concerted Lewis-acid-activated oxygen transfer competes with stepwise epoxidation by the established Mn(V)(oxo) species. The experimental counterion effect is attributed to the computationally assessed ligand-dependent reaction profiles and stereoselectivities of the singlet, triplet, and quintet spin states available to the manganese species.

Peptide Fragmentation by Corona Discharge Induced Electrochemical Ionization

PubMed Central

Lloyd, John R.; Hess, Sonja

2010-01-01

Fundamental studies have greatly improved our understanding of electrospray, including the underlying electrochemical reactions. Generally regarded as disadvantageous, we have recently shown that corona discharge (CD) can be used as an effective method to create a radical cation species [M]+•, thus optimizing the electrochemical reactions that occur on the surface of the stainless steel (SS) electrospray capillary tip. This technique is known as CD initiated electrochemical ionization (CD-ECI). Here, we report on the fundamental studies using CD-ECI to induce analytically useful in-source fragmentation of a range of molecules that complex transition metals. Compounds that have been selectively fragmented using CD-ECI include enolate forming phenylglycine containing peptides, glycopeptides, nucleosides and phosphopeptides. Collision induced dissociation (CID) or other activation techniques were not necessary for CD-ECI fragmentation. A four step mechanism was proposed: 1. Complexation using either Fe in the SS capillary tip material or Cu(II) as an offline complexation reagent; 2. Electrochemical oxidation of the complexed metal and thus formation of a radical cation (e.g.; Fe - e− → Fe +•); 3. Radical fragmentation of the complexed compound. 4. Electrospray ionization of the fragmented neutrals. Fragmentation patterns resembling b- and y-type ions were observed and allowed the localization of the phosphorylation sites. PMID:20869880

Label-Free Fluorescence Assay of S1 Nuclease and Hydroxyl Radicals Based on Water-Soluble Conjugated Polymers and WS₂ Nanosheets.

PubMed

Li, Junting; Zhao, Qi; Tang, Yanli

2016-06-13

We developed a new method for detecting S1 nuclease and hydroxyl radicals based on the use of water-soluble conjugated poly[9,9-bis(6,6-(N,N,N-trimethylammonium)-fluorene)-2,7-ylenevinylene-co-alt-2,5-dicyano-1,4-phenylene)] (PFVCN) and tungsten disulfide (WS₂) nanosheets. Cationic PFVCN is used as a signal reporter, and single-layer WS₂ is used as a quencher with a negatively charged surface. The ssDNA forms complexes with PFVCN due to much stronger electrostatic interactions between cationic PFVCN and anionic ssDNA, whereas PFVCN emits yellow fluorescence. When ssDNA is hydrolyzed by S1 nuclease or hydroxyl radicals into small fragments, the interactions between the fragmented DNA and PFVCN become weaker, resulting in PFVCN being adsorbed on the surface of WS₂ and the fluorescence being quenched through fluorescence resonance energy transfer. The new method based on PFVCN and WS₂ can sense S1 nuclease with a low detection limit of 5 × 10(-6) U/mL. Additionally, this method is cost-effective by using affordable WS₂ as an energy acceptor without the need for dye-labeled ssDNA. Furthermore, the method provides a new platform for the nuclease assay and reactive oxygen species, and provides promising applications for drug screening.

Artificial photosynthesis using chlorophyll based carotenoid quinone triads: A brief synopsis of research progress as of 31 December 1986

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gust, D.; Moore, T.A.

1986-12-31

The design, synthesis and study of a series of carotenoid-chlorophyll-quinone triad molecules which mimic some of the basic photochemistry and photophysics of natural photosynthesis is sought. The first members of this series have now been prepared, and have been found to mimic photosynthetic charge separation, carotenoid antenna function, and carotenoid photoprotection from singlet oxygen damage. Although the triad molecules mimic the general principle of multistep electron transfer which is found in natural photosynthesis, the details of photosynthetic electron transfer differ in the triads, in that the first electron transfer step involves electron donation from the excited state donor, followed bymore » reduction of the resulting donor radical cation by the carotenoid. In photosynthesis, the electron is moved through several acceptors before the chlorophyll radical cation is reduced. Therefore, our recent work has concentrated on the design and synthesis of new model systems which better mimic certain aspects of natural photosynthesis.« less

Vibrational characterisation of a crystallised oligoaniline: a model compound of polyaniline

NASA Astrophysics Data System (ADS)

Quillard, Sophie; Corraze, Benoı̂t; Boyer, Marie Isabelle; Fayad, Elias; Louarn, Guy; Froyer, Gérard

2001-09-01

We present a detailed study on the vibrational properties of N,N‧-diphenyl-1,4-phenylenediamine in different crystalline forms. A new triclinic form of the molecule has been obtained through appropriate recrystallization procedure. This polymorphism of the crystalline state was associated to different vibrational features. These results are discussed with regards to the possible conformations of the molecule. In order to complete the study, thin solid films of these materials were also elaborated by vacuum sublimation of the molecule, upon selected conditions of rate, deposition and thickness. Spectroscopic measurements of these layers are showed and compared to those obtained on the crystalline solid forms. We performed convenient oxidation processes of this neutral N,N‧-diphenyl-1,4-phenylenediamine (powder and thin solid film) leading to the formation of the correspondent radical cation species. A comparison with radical cation generated in solution by electrochemical oxidative method is done. Vibrational characterisations of this doped oligomer were achieved in each case and finally, the observed differences are discussed in terms of conformation.

Analysis of the pigment stoichiometry of pigment-protein complexes from barley (Hordeum vulgare). The xanthophyll cycle intermediates occur mainly in the light-harvesting complexes of photosystem I and photosystem II.

PubMed Central

Lee, A I; Thornber, J P

1995-01-01

The carotenoid zeaxanthin has been implicated in a nonradiative dissipation of excess excitation energy. To determine its site of action, we have examined the location of zeaxanthin within the thylakoid membrane components. Five pigment-protein complexes were isolated with little loss of pigments: photosystem I (PSI); core complex (CC) I, the core of PSI; CC II, the core of photosystem II (PSII); light-harvesting complex (LHC) IIb, a trimer of the major light-harvesting protein of PSII; and LHC IIa, c, and d, a complex of the monomeric minor light-harvesting proteins of PSII. Zeaxanthin was found predominantly in the LHC complexes. Lesser amounts were present in the CCs possibly because these contained some extraneous LHC polypeptides. The LHC IIb trimer and the monomeric LHC II a, c, and d pigment-proteins from dark-adapted plants each contained, in addition to lutein and neoxanthin, one violaxanthin molecule but little antheraxanthin and no zeaxanthin. Following illumination, each complex had a reduced violaxanthin content, but now more antheraxanthin and zeaxanthin were present. PSI had little or no neoxanthin. The pigment content of LHC I was deduced by subtracting the pigment content of CC I from that of PSI. Our best estimate for the carotenoid content of a LHC IIb trimer from dark-adapted plants is one violaxanthin, two neoxanthins, six luteins, and 0.03 mol of antheraxanthin per mol trimer. The xanthophyll cycle occurs mainly or exclusively within the light-harvesting antennae of both photosystems. PMID:7724673

Interrelationships between maternal carotenoid status and newborn infant macular pigment optical density and carotenoid status.

PubMed

Henriksen, Bradley S; Chan, Gary; Hoffman, Robert O; Sharifzadeh, Mohsen; Ermakov, Igor V; Gellermann, Werner; Bernstein, Paul S

2013-08-15

Deposition of the macular pigment carotenoids lutein and zeaxanthin in the human retina occurs early in life. In this study, we examined the interrelationships of maternal carotenoid status and newborn infant macular pigment levels and systemic carotenoid status. As a secondary measure, we also evaluated the effects of intrauterine growth restriction (IUGR) on carotenoid status in term newborn infants. We measured mother and infant skin carotenoids using resonance Raman spectroscopy (RRS), serum carotenoids by HPLC, and mother breast milk carotenoids by HPLC. We measured infant macular pigment levels using noninvasive blue light reflectometry. We enrolled 30 healthy term infants, their mothers, and 10 IUGR infants and their mothers. A subset of 16 infants was imaged for macular pigment optical density (MPOD). Infant serum zeaxanthin levels correlated with MPOD (r = 0.68, P = 0.007). Mother serum zeaxanthin levels correlated with infant MPOD (r = 0.59, P = 0.032). Infant and mother serum lutein did not correlate with MPOD. Mother-infant correlations were found for total serum carotenoids (r = 0.42, P = 0.020) and skin carotenoids (r = 0.48, P = 0.001). No difference was seen between IUGR infants and controls in total serum or skin carotenoids. Mothers of IUGR infants had lower total serum carotenoids (P = 0.019) and breast milk carotenoids than controls (P = 0.006). Our findings suggest that maternal zeaxanthin status may play a more important role than lutein status in macular pigment deposition in utero. Controlled trials are needed to determine whether maternal zeaxanthin prenatal supplementation can raise infant macular pigment levels and/or improve ocular function.

Antioxidant activity of nine Fabaceae species growing in Serbia and Montenegro.

PubMed

Godevac, Dejan; Zdunić, Gordana; Savikin, Katarina; Vajs, Vlatka; Menković, Nebojsa

2008-04-01

The aim of this study was to investigate antioxidant capacity of nine Fabaceae species collected on the mountains of Serbia and Montenegro. Antioxidant assays with various reaction mechanisms were used, including total phenolic content by Folin-Ciocalteu, DPPH radical scavenging capacity, Trolox equivalent antioxidant capacity (TEAC) values by ABTS radical cation and inhibition of liposome peroxidation. The investigated plants exhibited strong antioxidant capacity in all the tested methods, and among them, Lathyrus binatus, Trifolium pannonicum, and Anthyllis aurea were found to be the most active.

Variation in Carotenoid Content of Kale and Other Vegetables: A Review of Pre- and Post-harvest Effects.

PubMed

Walsh, Rachel P; Bartlett, Hannah; Eperjesi, Frank

2015-11-11

Lutein and zeaxanthin are carotenoids that are selectively taken up into the macula of the eye, where they are thought to protect against the development of age-related macular degeneration. They are obtained from dietary sources, with the highest concentrations found in dark green leafy vegetables, such as kale and spinach. In this Review, compositional variations due to variety/cultivar, stage of maturity, climate or season, farming practice, storage, and processing effects are highlighted. Only data from studies which report on lutein and zeaxanthin content in foods are reported. The main focus is kale; however, other predominantly xanthophyll containing vegetables such as spinach and broccoli are included. A small amount of data about exotic fruits is also referenced for comparison. The qualitative and quantitative composition of carotenoids in fruits and vegetables is known to vary with multiple factors. In kale, lutein and zeaxanthin levels are affected by pre-harvest effects such as maturity, climate, and farming practice. Further research is needed to determine the post-harvest processing and storage effects of lutein and zeaxanthin in kale; this will enable precise suggestions for increasing retinal levels of these nutrients.

Thermal degradation kinetics of all-trans and cis-carotenoids in a light-induced model system.

PubMed

Xiao, Ya-Dong; Huang, Wu-Yang; Li, Da-Jing; Song, Jiang-Feng; Liu, Chun-Quan; Wei, Qiu-Yu; Zhang, Min; Yang, Qiu-Ming

2018-01-15

Thermal degradation kinetics of lutein, zeaxanthin, β-cryptoxanthin, β-carotene was studied at 25, 35, and 45°C in a model system. Qualitative and quantitative analyses of all-trans- and cis-carotenoids were conducted using HPLC-DAD-MS technologies. Kinetic and thermodynamic parameters were calculated by non-linear regression. A total of 29 geometrical isomers and four oxidation products were detected, including all-trans-, keto compounds, mono-cis- and di-cis-isomers. Degradations of all-trans-lutein, zeaxanthin, β-cryptoxanthin, and β-carotene were described by a first-order kinetic model, with the order of rate constants as k β -carotene >k β -cryptoxanthin >k lutein >k zeaxanthin . Activation energies of zeaxanthin, lutein, β-cryptoxanthin, and β-carotene were 65.6, 38.9, 33.9, and 8.6kJ/moL, respectively. cis-carotenoids also followed with the first-order kinetic model, but they did not show a defined sequence of degradation rate constants and activation energies at different temperatures. A possible degradation pathway of four carotenoids was identified to better understand the mechanism of carotenoid degradation. Copyright © 2017 Elsevier Ltd. All rights reserved.

In vitro investigation of the bioaccessibility of carotenoids from raw, frozen and boiled red chili peppers (Capsicum annuum).

PubMed

Pugliese, Alessandro; O'Callaghan, Yvonne; Tundis, Rosa; Galvin, Karen; Menichini, Francesco; O'Brien, Nora; Loizzo, Monica Rosa

2014-01-01

Carotenoid-rich foods are associated with antioxidant activity and the ability to alleviate chronic diseases. The present study investigated the effect of processing on the content and bioaccessibility of carotenoids from 13 cultivars of red chili pepper (Capsicum annuum). Carotenoids in chili peppers were analyzed before an in vitro digestion process. The portion of carotenoid transferred to the micelle fraction (bioaccessibility) was also quantified. β-Carotene, β-cryptoxanthin, capsanthin and antheraxanthin were the most abundant carotenoids. Zeaxanthin, violaxanthin, neoxanthin and lutein were detected at lower concentrations. In general, freezing and boiling reduced carotenoid contents. Capsanthin and zeaxanthin had the highest bioaccessibility at an average value from 36 to 40%, followed by antheraxanthin (26%). Bioaccessibility of β-cryptoxanthin, violaxanthin and β-carotene was lower, averaging 6.1, 4.8 and 4.0%, respectively. Neoxanthin and lutein were not detected in micelles. Freezing increased the bioaccessibility of capsanthin, zeaxanthin, antheraxanthin, β-cryptoxanthin and violaxanthin; β-cryptoxanthin bioaccessibility increased and capsanthin and zeaxanthin bioaccessibility decreased following boiling. Differences in the contents and bioaccessibility of carotenoids in 13 C. annuum cultivars and between the processed methods were herein evidenced.

Repair Activity of trans-Resveratrol toward 2'-Deoxyguanosine Radicals.

PubMed

Cheng, Xing; An, Ping; Li, Shujin; Zhou, Liping

2018-04-26

In the present study, the repair activity of trans-resveratrol toward 2'-deoxyguanosine (dGuo) radicals in polar and nonpolar solvents was studied using density functional theory. The hydrogen transfer/proton coupled electron transfer and single electron transfer (SET) mechanisms between trans-resveratrol and dGuo-radicals were considered. Taking into consideration the molar fraction of neutral trans-resveratrol (ROH) and anionic trans-resveratrol (RO - ), the overall rate constants for repairing dGuo-radicals by trans-resveratrol are 9.94 × 10 8 and 2.01 × 10 9 dm 3 mol -1 s -1 in polar and nonpolar solvents, respectively, and the overall rate constant of repairing cation radical (dGuo •+ ) by trans-resveratrol via an SET mechanism is 7.17 × 10 9 dm 3 mol -1 s -1 . The repair activity of RO - toward dGuo-radicals is better than that of ROH, but the repair activity of ROH toward dGuo •+ is better than that of RO - . Unfortunately, neither ROH nor RO - can repair the 2'-deoxyribose radicals of dGuo. It can therefore be concluded that trans-resveratrol is an effective antioxidant for repairing base radicals of dGuo and dGuo •+ . The study can help us understand the repair activity of trans-resveratrol toward dGuo radicals.

Antioxidant and antigenotoxic activities in Acacia salicina extracts and its protective role against DNA strand scission induced by hydroxyl radical.

PubMed

Chatti, Ines Bouhlel; Boubaker, Jihed; Skandrani, Ines; Bhouri, Wissem; Ghedira, Kamel; Chekir Ghedira, Leila

2011-08-01

The antioxidant potency of Acacia salicina extracts was investigated. Total antioxidant capacity was determined using an ABTS(+) assay. Superoxide radical scavenging was measured using riboflavin-light-nitro blue tetrazolium (NBT) assay. In addition, the content of phenols, total flavonoids and sterols were measured in the tested extracts. The petroleum ether exhibited a potent scavenging activity toward ABTS radical cations. Whereas, chloroform extract showed the highest activity against superoxides radicals and was also able to protect pKS plasmid DNA against hydroxyl radicals induced DNA damages. The antimutagenicity of these extracts was assayed using the Ames assay against Salmonella typhimurium TA98 and S. typhimurium TA 1535 tester strains at different concentrations. These extracts decreased significantly the mutagenecity induced by sodium azide (SA) and 4-nitro-o-phenylenediamine (NOP). The antioxidant and antimutagenecity activities exhibited by A. salicina depended on the chemical composition of the tested extracts. Copyright © 2011 Elsevier Ltd. All rights reserved.

Photochemical and radiation-chemical aspects of matrix acidity effects on some organic systems

NASA Astrophysics Data System (ADS)

Ambroz, H. B.; Przybytniak, G. K.; Wronska, T.; Kemp, T. J.

The role of matrix effects in radiolysis and photolysis is illustrated using two systems: organosulphur compounds and benzenediazonium salts. Their intermediates as detected by low temperature ESR and optical spectroscopy or FAB-MS give evidence that the main reaction pathways depend strongly on these effects. Changes in matrix acidity can control the formation of neutral radical, ion-radical or ionic species which are crucial to the character of the final products of irradiation of organosulphur compounds, which are of great importance in medicine, biology, ecology and industry. Microenvironmental influences determine whether the triplet aryl cation or radical species are detected as the principal or sole intermediates in the decomposition of diazonium salts, a process leading to different stable products with industrial application.

Total antioxidant potential of resinous exudates from Heliotropium species, and a comparison of the ABTS and DPPH methods.

PubMed

Lissi, E A; Modak, B; Torres, R; Escobar, J; Urzua, A

1999-06-01

Total reactive antioxidant potential (TRAP) of resinous exudates from Heliotropium species was evaluated by measuring the bleaching of stable free radicals. The antioxidant capacity of the resinous exudates in Trolox equivalents, evaluated from the bleaching of ABTS derived radical cations, ranged from 2.0 M (H. huascoense) to 5.2 M (H. stenophyllum), indicating a very high concentration of phenolic compounds. Considerably smaller values were obtained by measuring the bleaching of DPPH radicals. The ratio between the values obtained employing ABTS derived radicals and DPPH, ranged from 37 (H. megalanthum) to 4.5 (H. chenopodiaceum variety typica). The magnitude of the difference can be considered as an indication of the relative reactivity of the antioxidants present in the exudates. Similar ratios were observed when stoichiometric coefficients were evaluated for representative purified flavonoids obtained from the resinous exudates.

DNA immobilization and detection on cellulose paper using a surface grown cationic polymer via ATRP.

PubMed

Aied, Ahmed; Zheng, Yu; Pandit, Abhay; Wang, Wenxin

2012-02-01

Cationic polymers with various structures have been widely investigated in the areas of medical diagnostics and molecular biology because of their unique binding properties and capability to interact with biological molecules in complex biological environments. In this work, we report the grafting of a linear cationic polymer from an atom transfer radical polymerization (ATRP) initiator bound to cellulose paper surface. We show successful binding of ATRP initiator onto cellulose paper and grafting of polymer chains from the immobilized initiator with ATRP. The cellulose paper grafted polymer was used in combination with PicoGreen (PG) to demonstrate detection of nucleic acids in the nanogram range in homogeneous solution and in a biological sample (serum). The results showed specific identification of hybridized DNA after addition of PG in both solutions.

Ne matrix spectra of the sym-C6Br3F3+ radical cation

USGS Publications Warehouse

Bondybey, V.E.; Sears, T.J.; Miller, T.A.; Vaughn, C.; English, J.H.; Shiley, R.S.

1981-01-01

The electronic absorption and laser excited, wavelength resolved fluorescence spectra of the title cation have been observed in solid Ne matrix and vibrationally analysed. The vibrational structure of the excited B2A2??? state shows close similarity to the parent compound. The X2E??? ground state structure is strongly perturbed and irregular owing to a large Jahn-Teller distortion. The data are analysed in terms of a recently developed, sophisticated multimode Jahn-Teller theoretical model. We have generated the sym-C6Br3F3+ cations in solid Ne matrix and obtained their wavelength resolved emission and absorption spectra. T ground electronic X2E??? state exhibits an irregular and strongly perturbed vibrational structure, which can be successfully modeled using sophisticated multimode Jahn-Teller theory. ?? 1981.

Molecular hydrogen formation on interstellar PAHs through Eley-Rideal abstraction reactions

NASA Astrophysics Data System (ADS)

Foley, Nolan; Cazaux, S.; Egorov, D.; Boschman, L. M. P. V.; Hoekstra, R.; Schlathölter, T.

2018-06-01

We present experimental data on H2 formation processes on gas-phase polycyclic aromatic hydrocarbon (PAH) cations. This process was studied by exposing coronene radical cations, confined in a radio-frequency ion trap, to gas phase H atoms. Sequential attachment of up to 23 hydrogen atoms has been observed. Exposure to atomic D instead of H allows one to distinguish attachment from competing abstraction reactions, as the latter now leave a unique fingerprint in the measured mass spectra. Modeling of the experimental results using realistic cross sections and barriers for attachment and abstraction yield a 1:2 ratio of abstraction to attachment cross sections. The strong contribution of abstraction indicates that H2 formation on interstellar PAH cations is an order of magnitude more relevant than previously thought.

Theoretical prediction of the ionization energies of the C4H7 radicals: 1-methylallyl, 2-methylallyl, cyclopropylmethyl, and cyclobutyl radicals.

PubMed

Lau, Kai-Chung; Zheng, Wenxu; Wong, Ning-Bew; Li, Wai-Kee

2007-10-21

The ionization energies (IEs) for the 1-methylallyl, 2-methylallyl, cyclopropylmethyl, and cyclobutyl radicals have been calculated by the wave function based ab initio CCSD(T)/CBS approach, which involves the approximation to the complete basis set (CBS) limit at the coupled cluster level with single and double excitations plus quasiperturbative triple excitation [CCSD(T)]. The zero-point vibrational energy correction, the core-valence electronic correction, and the scalar relativistic effect correction are included in these calculations. The present CCSD(T)/CBS results are then compared with the IEs determined in the photoelectron experiment by Schultz et al. [J. Am. Chem. Soc. 106, 7336 (1984)] The predicted IE value (7.881 eV) of 2-methylallyl radical is found to compare very favorably with the experimental value of 7.90+/-0.02 eV. Two ionization transitions for cis-1-methylallyl and trans-1-methylallyl radicals have been considered here. The comparison between the predicted IE values and the previous measurements shows that the photoelectron peak observed by Schultz et al. likely corresponds to the adiabatic ionization transition for the trans-1-methylallyl radical to form trans-1-methylallyl cation. Although a precise IE value for the cyclopropylmethyl radical has not been directly determined, the experimental value deduced indirectly using other known energetic data is found to be in good accord with the present CCSD(T)/CBS prediction. We expect that the Franck-Condon factor for ionization transition of c-C4H7-->bicyclobutonium is much less favorable than that for ionization transition of c-C4H7-->planar-C4H7+, and the observed IE in the previous photoelectron experiment is likely due to the ionization transition for c-C4H7-->planar-C4H7+. Based on our CCSD(T)/CBS prediction, the ionization transition of c-C4H7-->bicyclobutonium with an IE value around 6.92 eV should be taken as the adiabatic ionization transition for the cyclobutyl radical. The present study provides support for the conclusion that the CCSD(T)/CBS approach with high-level energetic corrections can be used to provide reliable IE predictions for C4 hydrocarbon radicals with an uncertainty of +/-22 meV. The CCSD(T)/CBS predictions to the heats of formation for the aforementioned radicals and cations are also presented.

p -Carborane Conjugation in Radical Anions of Cage–Cage and Cage–Phenyl Compounds

DOE PAGES

Cook, Andrew R.; Valášek, Michal; Funston, Alison M.; ...

2017-12-14

Optical electron transfer (intervalence) transitions in radical anions of p-carborane oligomers attest to delocalization of electrons between two p-carboranes cages or a p-carborane and a phenyl ring. Oligomers of the 12 vertex p-carborane (C 2B 10H 12) cage, [12], with up to 3 cages were synthesized, as well as p-carboranes with one or two trimethylsilylphenyl groups, [6], attached to the carbon termini. Pulse radiolysis in tetrahydrofuran produced radical anions, determined redox potentials by equilibria and measured their absorption spectra. Density functional theory computations provided critical insight into the optical electron transfer bands and electron delocalization. One case, [6–12–6], showed bothmore » Robin–Day class II and III transitions. The class III transition resulted from a fully delocalized excess electron across both benzene rings and the central p-carborane, with an electronic coupling H ab = 0.46 eV between the cage and either benzene. This unprecedented finding shows that p-carborane bridges are not simply electron withdrawing insulators. In other cases with more than ~1/2 of the excess electron localized on a [12], large cage distortions were triggered, producing a partially open cage with a nido-like structure. This resulted in class II transitions with similar Hab but massive reorganization energies. The computations also predicted delocalization in radical cations, but complexities in cation formation allowed only tentative experimental support of the predictions. Thus, the results with anions provide clear evidence for carborane conjugation that might be exploited in molecular wire materials, which are classically composed of all π-conjugated molecules.« less

Toward Improved Catholyte Materials for Redox Flow Batteries: What Controls Chemical Stability of Persistent Radical Cations?

DOE PAGES

Zhang, Jingjing; Shkrob, Ilya A.; Assary, Rajeev S.; ...

2017-10-06

We report catholyte materials are used to store positive charge in energized fluids circulating through redox flow batteries (RFBs) for electric grid and vehicle applications. Energy-rich radical cations (RCs) are being considered for use as catholyte materials, but to be practically relevant, these RCs (that are typically unstable, reactive species) need to have long lifetimes in liquid electrolytes under the ambient conditions. Only few families of such energetic RCs possess stabilities that are suitable for their use in RFBs; currently, the derivatives of 1,4- dialkoxybenzene look the most promising. In this study, we examine factors that define the chemical andmore » electrochemical stabilities for RCs in this family. To this end, we engineered rigid bis-annulated molecules that by design avoid the two main degradation pathways for such RCs, viz. their deprotonation and radical addition. The decay of the resulting RCs are due to the single remaining reaction: O-dealkylation. We establish the mechanism for this reaction and examine factors controlling its rate. In particular, we demonstrate that this reaction is initiated by the nucleophile attack of the counter anion on the RC partner. The reaction proceeds through the formation of the aroxyl radicals whose secondary reactions yield the corresponding quinones. The O-dealkylation accelerates considerably when the corresponding quinone has poor solubility in the electrolyte, and the rate depends strongly on the solvent polarity. Finally, our mechanistic insights suggest new ways of improving the RC catholytes through molecular engineering and electrolyte optimization.« less

p -Carborane Conjugation in Radical Anions of Cage–Cage and Cage–Phenyl Compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cook, Andrew R.; Valášek, Michal; Funston, Alison M.

Optical electron transfer (intervalence) transitions in radical anions of p-carborane oligomers attest to delocalization of electrons between two p-carboranes cages or a p-carborane and a phenyl ring. Oligomers of the 12 vertex p-carborane (C 2B 10H 12) cage, [12], with up to 3 cages were synthesized, as well as p-carboranes with one or two trimethylsilylphenyl groups, [6], attached to the carbon termini. Pulse radiolysis in tetrahydrofuran produced radical anions, determined redox potentials by equilibria and measured their absorption spectra. Density functional theory computations provided critical insight into the optical electron transfer bands and electron delocalization. One case, [6–12–6], showed bothmore » Robin–Day class II and III transitions. The class III transition resulted from a fully delocalized excess electron across both benzene rings and the central p-carborane, with an electronic coupling H ab = 0.46 eV between the cage and either benzene. This unprecedented finding shows that p-carborane bridges are not simply electron withdrawing insulators. In other cases with more than ~1/2 of the excess electron localized on a [12], large cage distortions were triggered, producing a partially open cage with a nido-like structure. This resulted in class II transitions with similar Hab but massive reorganization energies. The computations also predicted delocalization in radical cations, but complexities in cation formation allowed only tentative experimental support of the predictions. Thus, the results with anions provide clear evidence for carborane conjugation that might be exploited in molecular wire materials, which are classically composed of all π-conjugated molecules.« less

Toward Improved Catholyte Materials for Redox Flow Batteries: What Controls Chemical Stability of Persistent Radical Cations?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jingjing; Shkrob, Ilya A.; Assary, Rajeev S.

We report catholyte materials are used to store positive charge in energized fluids circulating through redox flow batteries (RFBs) for electric grid and vehicle applications. Energy-rich radical cations (RCs) are being considered for use as catholyte materials, but to be practically relevant, these RCs (that are typically unstable, reactive species) need to have long lifetimes in liquid electrolytes under the ambient conditions. Only few families of such energetic RCs possess stabilities that are suitable for their use in RFBs; currently, the derivatives of 1,4- dialkoxybenzene look the most promising. In this study, we examine factors that define the chemical andmore » electrochemical stabilities for RCs in this family. To this end, we engineered rigid bis-annulated molecules that by design avoid the two main degradation pathways for such RCs, viz. their deprotonation and radical addition. The decay of the resulting RCs are due to the single remaining reaction: O-dealkylation. We establish the mechanism for this reaction and examine factors controlling its rate. In particular, we demonstrate that this reaction is initiated by the nucleophile attack of the counter anion on the RC partner. The reaction proceeds through the formation of the aroxyl radicals whose secondary reactions yield the corresponding quinones. The O-dealkylation accelerates considerably when the corresponding quinone has poor solubility in the electrolyte, and the rate depends strongly on the solvent polarity. Finally, our mechanistic insights suggest new ways of improving the RC catholytes through molecular engineering and electrolyte optimization.« less

Applicability of samarium(III) complexes for the role of luminescent molecular sensors for monitoring progress of photopolymerization processes and control of the thickness of polymer coatings

NASA Astrophysics Data System (ADS)

Topa, Monika; Ortyl, Joanna; Chachaj-Brekiesz, Anna; Kamińska-Borek, Iwona; Pilch, Maciej; Popielarz, Roman

2018-06-01

Applicability of 15 trivalent samarium complexes as novel luminescent probes for monitoring progress of photopolymerization processes or thickness of polymer coatings by the Fluorescence Probe Technique (FPT) was studied. Three groups of samarium(III) complexes were evaluated in cationic photopolymerization of triethylene glycol divinyl ether monomer (TEGDVE) and free-radical photopolymerization of trimethylolpropane triacrylate (TMPTA). The complexes were the derivatives of tris(4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate)samarium(III), tris(4,4,4-trifluoro-1-phenyl-1,3-butanedionate)samarium(III) and tris(4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedionate)samarium(III), which were further coordinated with auxiliary ligands, such as 1,10-phenanthroline, triphenylphosphine oxide, tributylphosphine oxide and trioctylphosphine oxide. It has been found that most of the complexes studied are sensitive enough to be used as luminescent probes for monitoring progress of cationic photopolymerization of vinyl ether monomers over entire range of monomer conversions. In the case of free-radical polymerization processes, the samarium(III) complexes are not sensitive enough to changes of microviscosity and/or micropolarity of the medium, so they cannot be used to monitor progress of the polymerization. However, high stability of luminescence intensity of some of these complexes under free-radical polymerization conditions makes them good candidates for application as thickness sensors for polymer coatings prepared by free-radical photopolymerization. A quantitative relationship between a coating thickness and the luminescence intensity of the samarium(III) probes has been derived and verified experimentally within a broad range of the thicknesses.

Electronic absorption spectroscopy of matrix-isolated polycyclic aromatic hydrocarbon cations. I - The naphthalene cation (C10H8/+/)

NASA Technical Reports Server (NTRS)

Salama, F.; Allamandola, L. J.

1991-01-01

The ultraviolet, visible, and near-infrared absorption spectra of naphthalene (C10H8) and its radical ion (C10H8/+/), formed by vacuum ultraviolet irradiation, were measured in argon and neon matrices at 4.2 K. The associated vibronic band systems and their spectroscopic assignments are discussed together with the physical and chemical conditions governing ion production in the solid phase. The absorption coefficients were calculated for the ion and found lower than previous values, presumably due to the low polarizability of the neon matrix.

Interrelationships Between Maternal Carotenoid Status and Newborn Infant Macular Pigment Optical Density and Carotenoid Status

PubMed Central

Henriksen, Bradley S.; Chan, Gary; Hoffman, Robert O.; Sharifzadeh, Mohsen; Ermakov, Igor V.; Gellermann, Werner; Bernstein, Paul S.

2013-01-01

Purpose. Deposition of the macular pigment carotenoids lutein and zeaxanthin in the human retina occurs early in life. In this study, we examined the interrelationships of maternal carotenoid status and newborn infant macular pigment levels and systemic carotenoid status. As a secondary measure, we also evaluated the effects of intrauterine growth restriction (IUGR) on carotenoid status in term newborn infants. Methods. We measured mother and infant skin carotenoids using resonance Raman spectroscopy (RRS), serum carotenoids by HPLC, and mother breast milk carotenoids by HPLC. We measured infant macular pigment levels using noninvasive blue light reflectometry. Results. We enrolled 30 healthy term infants, their mothers, and 10 IUGR infants and their mothers. A subset of 16 infants was imaged for macular pigment optical density (MPOD). Infant serum zeaxanthin levels correlated with MPOD (r = 0.68, P = 0.007). Mother serum zeaxanthin levels correlated with infant MPOD (r = 0.59, P = 0.032). Infant and mother serum lutein did not correlate with MPOD. Mother–infant correlations were found for total serum carotenoids (r = 0.42, P = 0.020) and skin carotenoids (r = 0.48, P = 0.001). No difference was seen between IUGR infants and controls in total serum or skin carotenoids. Mothers of IUGR infants had lower total serum carotenoids (P = 0.019) and breast milk carotenoids than controls (P = 0.006). Conclusions. Our findings suggest that maternal zeaxanthin status may play a more important role than lutein status in macular pigment deposition in utero. Controlled trials are needed to determine whether maternal zeaxanthin prenatal supplementation can raise infant macular pigment levels and/or improve ocular function. PMID:23838770

Effects of season and storage period on accumulation of individual carotenoids in pumpkin flesh (Cucurbita moschata).

PubMed

Jaswir, Irwandi; Shahidan, Norshazila; Othman, Rashidi; Has-Yun Hashim, Yumi Zuhanis; Octavianti, Fitri; bin Salleh, Mohammad Noor

2014-01-01

Carotenoids are antioxidants with pharmaceutical potential. The major carotenoids important to humans are α-carotene, β-carotene, lycopene, lutein, zeaxanthin, and β-cryptoxanthin. Some of the biological functions and actions of these individual carotenoids are quite similar to each other, whereas others are specific. Besides genotype and location, other environmental effects such as temperature, light, mineral uptake, and pH have been found affect carotenoid development in plant tissues and organs. Therefore, this research investigated the effects of the season and storage periods during postharvest handling on the accumulation of carotenoid in pumpkin. This study shows that long-term storage of pumpkins resulted in the accumulation of lutein and β-carotene with a slight decrease in zeaxanthin. The amounts of β-carotene ranged from 174.583±2.105 mg/100g to 692.871±22.019 mg/100g, lutein from 19.841±9.693 mg/100g to 59.481±1.645 mg/100g, and zeaxanthin from not detected to 2.709±0.118 mg/100g. The pumpkins were collected three times in a year; they differed in that zeaxanthin was present only in the first season, while the amounts of β-carotene and lutein were the highest in the second and third seasons, respectively. By identifying the key factors among the postharvest handling conditions that control specific carotenoid accumulations, a greater understanding of how to enhance the nutritional values of pumpkin and other crops will be gained. Postharvest storage conditions can markedly enhance and influence the levels of zeaxanthin, lutein, and β-carotene in pumpkin. This study describes how the magnitudes of these effects depend on the storage period and season.

Antioxidant capacity of flavonoids and a new arylphenol of the resinous exudate from Heliotropium sinuatum.

PubMed

Modak, Brenda; Torres, René; Lissi, Eduardo; delle Monache, Franco

2003-12-01

From the resinous exudate of Heliotropium sinuatum (family Boraginaceae), a new compound: 4-(3',5'-dihydroxynonadecyl)phenol 1, together with eight previously described flavonoids, were isolated and their antioxidant activities were assessed by quenching measurements with ABTS and DPPH cation radicals.

A modified method for studying behavioral paradox of antioxidants and their disproportionate competitive kinetic effect to scavenge the peroxyl radical formation.

PubMed

Masood, Nusrat; Fatima, Kaneez; Luqman, Suaib

2014-01-01

We have described a modified method for evaluating inhibitor of peroxyl radicals, a well-recognized and -documented radical involved in cancer initiation and promotion as well as diseases related to oxidative stress and ageing. We are reporting hydrophilic and lipophilic as well as natural and synthetic forms of antioxidants revealing a diversified behaviour to peroxyl radical in a dose-dependent manner (1 nM-10 μM). A simple kinetic model for the competitive oxidation of an indicator molecule (ABTS) and a various antioxidant by a radical (ROO(•)) is described. The influences of both the concentration of antioxidant and duration of reaction (70 min) on the inhibition of the radical cation absorption are taken into account while determining the activity. The induction time of the reaction was also proposed as a parameter enabling determination of antioxidant content by optimizing and introducing other kinetic parameters in 96-well plate assays. The test evidently improves the original PRTC (peroxyl radical trapping capacity) assay in terms of the amount of chemical used, simultaneous tracking, that is, the generation of the radical taking place continually and the kinetic reduction technique (area under curve, peak value, slope, and Vmax).

Countercurrent flow of supercritical anti-solvent in the production of pure xanthophylls from Nannochloropsis oculata.

PubMed

Cho, Yueh-Cheng; Wang, Yuan-Chuen; Shieh, Chwen-Jen; Lin, Justin Chun-Te; Chang, Chieh-Ming J; Han, Esther

2012-08-10

This study examined pilot scaled elution chromatography coupled with supercritical anti-solvent precipitation (using countercurrent flow) in generating zeaxanthin-rich particulates from a micro-algal species. Ultrasonic agitated acetone extract subjected to column fractionation successfully yielded a fraction containing 349.4 mg/g of zeaxanthin with a recovery of 85%. Subsequently, supercritical anti-solvent (SAS) precipitation of the column fraction at 150 bar and 343 K produced submicron-sized particulates with a concentration of 845.5mg/g of zeaxanthin with a recovery of 90%. Experimental results from a two-factor response surface method SAS precipitation indicated that purity, mean size and morphology of the precipitates were significantly affected by the flow type configuration, feed flow rate and injection time. Copyright © 2012 Elsevier B.V. All rights reserved.

Nucleophilically assisted and cationic ring-opening polymerization of tin-bridged [1]ferrocenophanes.

PubMed

Baumgartner, Thomas; Jäkle, Frieder; Rulkens, Ron; Zech, Gernot; Lough, Alan J; Manners, Ian

2002-08-28

To obtain mechanistic insight, detailed studies of the intriguing "spontaneous" ambient temperature ring-opening polymerization (ROP) of tin-bridged [1]ferrocenophanes Fe(eta-C(5)H(4))(2)SnR(2) 3a (R = t-Bu) and 3b (R = Mes) in solution have been performed. The investigations explored the influence of non-nucleophilic additives such as radicals and radical traps, neutral and anionic nucleophiles, Lewis acids, protic species, and other cationic electrophiles. Significantly, two novel methodologies and mechanisms for the ROP of strained [1]ferrocenophanes are proposed based on this study. First, as the addition of amine nucleophiles such as pyridine was found to strongly accelerate the polymerization rate in solution, a new nucleophilicallyassisted ROP methodology was proposed. This operates at ambient temperature in solution even in the presence of chlorosilanes but, unlike the anionic polymerization of ferrocenophanes, does not involve cyclopentadienyl anions. Second, the addition of small quantities of the electrophilic species H(+) and Bu(3)Sn(+) was found to lead to a cationic ROP process. These studies suggest that the "spontaneous" ROP of tin-bridged [1]ferrocenophanes may be a consequence of the presence of spurious, trace quantities of Lewis basic or acidic impurities. The new ROP mechanisms reported are likely to be of general significance for the ROP of other metallocenophanes (e.g., for thermal ROP in the melt) and for other metallacycles containing group 14 elements.

Expression studies of the zeaxanthin epoxidase gene in nicotiana plumbaginifolia

PubMed

Audran; Borel; Frey; Sotta; Meyer; Simonneau; Marion-Poll

1998-11-01

Abscisic acid (ABA) is a plant hormone involved in the control of a wide range of physiological processes, including adaptation to environmental stress and seed development. In higher plants ABA is a breakdown product of xanthophyll carotenoids (C40) via the C15 intermediate xanthoxin. The ABA2 gene of Nicotiana plumbaginifolia encodes zeaxanthin epoxidase, which catalyzes the conversion of zeaxanthin to violaxanthin. In this study we analyzed steady-state levels of ABA2 mRNA in N. plumbaginifolia. The ABA2 mRNA accumulated in all plant organs, but transcript levels were found to be higher in aerial parts (stems and leaves) than in roots and seeds. In leaves ABA2 mRNA accumulation displayed a day/night cycle; however, the ABA2 protein level remained constant. In roots no diurnal fluctuation in mRNA levels was observed. In seeds the ABA2 mRNA level peaked around the middle of development, when ABA content has been shown to increase in many species. In conditions of drought stress, ABA levels increased in both leaves and roots. A concomitant accumulation of ABA2 mRNA was observed in roots but not in leaves. These results are discussed in relation to the role of zeaxanthin epoxidase both in the xanthophyll cycle and in the synthesis of ABA precursors.

Expression Studies of the Zeaxanthin Epoxidase Gene in Nicotiana plumbaginifolia1

PubMed Central

Audran, Corinne; Borel, Charlotte; Frey, Anne; Sotta, Bruno; Meyer, Christian; Simonneau, Thierry; Marion-Poll, Annie

1998-01-01

Abscisic acid (ABA) is a plant hormone involved in the control of a wide range of physiological processes, including adaptation to environmental stress and seed development. In higher plants ABA is a breakdown product of xanthophyll carotenoids (C40) via the C15 intermediate xanthoxin. The ABA2 gene of Nicotiana plumbaginifolia encodes zeaxanthin epoxidase, which catalyzes the conversion of zeaxanthin to violaxanthin. In this study we analyzed steady-state levels of ABA2 mRNA in N. plumbaginifolia. The ABA2 mRNA accumulated in all plant organs, but transcript levels were found to be higher in aerial parts (stems and leaves) than in roots and seeds. In leaves ABA2 mRNA accumulation displayed a day/night cycle; however, the ABA2 protein level remained constant. In roots no diurnal fluctuation in mRNA levels was observed. In seeds the ABA2 mRNA level peaked around the middle of development, when ABA content has been shown to increase in many species. In conditions of drought stress, ABA levels increased in both leaves and roots. A concomitant accumulation of ABA2 mRNA was observed in roots but not in leaves. These results are discussed in relation to the role of zeaxanthin epoxidase both in the xanthophyll cycle and in the synthesis of ABA precursors. PMID:9808747

Capillary electrochromatography of inorganic cations in open tubular columns with a controllable capacity multilayered stationary phase architecture.

PubMed

Kubán, Pavel; Kubán, Petr; Kubán, Vlastimil; Hauser, Peter C; Bocek, Petr

2008-05-09

In this paper capillary electrochromatography of alkali and alkaline-earth metal cations in open tubular capillary columns is described. Capillary columns are prepared by coating fused silica capillaries of 75 microm I.D. with poly(butadiene-maleic acid) copolymer (PBMA) in multiple layers. Thermally initiated radical polymerization is used to crosslink the stationary phase. Capillary columns with different number of stationary phase layers can be prepared and allow for the adjustment of separation selectivity in the electrochromatographic mode. Fast and sensitive separations of common inorganic cations are achieved in less than 6 min in a 60 cm capillary column with on-column capacitively coupled contactless conductivity detector. Limits of detection (S/N=3) for the determination of alkali and alkaline-earth metal cations range from 0.3 to 2.5 microM and repeatability is better than 0.5, 4.5 and 6.1% for migration times, peak heights and peak areas, respectively.

Oil recovery method utilizing glyceryl ether sulfonates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Naylor, C.G.

1984-03-13

Petroleum may be recovered from petroleum containing formations having high salinity and/or high temperature by injecting into the formation an aqueous fluid containing an effective amount of a surface active agent characterized by the formula: R-O-(A-O)N-(CH2-CH(-CH2-O-CH2-CH2-SO3X)-O)M-H wherein R is an alkyl or alkylaryl radical, AO is an alkylene oxide radical, n is an integer of from 1 to 50, m is an integer from 1 to 10 and X is a sodium, potassium or ammonium cation.

Stabilities of nitrogen containing heterocyclic radicals and geometrical influences on non-radiative processes in organic molecules

NASA Technical Reports Server (NTRS)

Evleth, E. M.

1971-01-01

Theoretical and experimental work on generating radicals by removal of a hydrogen atom from pyrrole, imidazole, indole, and carbazole is reported. Photophysical studies on indolizine and related aza-derivatives show that materials having large S2-S1 energy gaps might exhibit upper state fluorescence. Photodecomposition quantum yields of a series of sterically hindered p-aminobenzene diazonium cations in water were found structurally and wavelength dependent and unquenched in aqueous sodium bromide solutions. Photodecomposition of diazonium materials did not produce a metastable species with a longer lifetime than 1 msec.

Uncovering the Roles of Oxygen in Cr(III) Photoredox Catalysis.

PubMed

Higgins, Robert F; Fatur, Steven M; Shepard, Samuel G; Stevenson, Susan M; Boston, David J; Ferreira, Eric M; Damrauer, Niels H; Rappé, Anthony K; Shores, Matthew P

2016-04-27

A combined experimental and theoretical investigation aims to elucidate the necessary roles of oxygen in photoredox catalysis of radical cation based Diels-Alder cycloadditions mediated by the first-row transition metal complex [Cr(Ph2phen)3](3+), where Ph2phen = bathophenanthroline. We employ a diverse array of techniques, including catalysis screening, electrochemistry, time-resolved spectroscopy, and computational analyses of reaction thermodynamics. Our key finding is that oxygen acts as a renewable energy and electron shuttle following photoexcitation of the Cr(III) catalyst. First, oxygen quenches the excited Cr(3+)* complex; this energy transfer process protects the catalyst from decomposition while preserving a synthetically useful 13 μs excited state and produces singlet oxygen. Second, singlet oxygen returns the reduced catalyst to the Cr(III) ground state, forming superoxide. Third, the superoxide species reduces the Diels-Alder cycloadduct radical cation to the final product and reforms oxygen. We compare the results of these studies with those from cycloadditions mediated by related Ru(II)-containing complexes and find that the distinct reaction pathways are likely part of a unified mechanistic framework where the photophysical and photochemical properties of the catalyst species lead to oxygen-mediated photocatalysis for the Cr-containing complex but radical chain initiation for the Ru congener. These results provide insight into how oxygen can participate as a sustainable reagent in photocatalysis.

Crystal structure of bis­(ethyl­enedi­thio)­tetra­thia­fulvalenium μ2-acetato-bis­[tri­bromido­rhenate(III)] 1,1,2-tri­chloro­ethane hemisolvate

PubMed Central

Golichenko, Alexander A.; Kravchenko, Andrey V.; Omelchenko, Irina V.; Chudak, Denis M.; Starodub, Vladimir A.; Barszcz, Boleslaw; Shtemenko, Alexander V.

2016-01-01

The asymmetric unit of the title salt, (C10H8S8)[Re2Br6(CH3COO)]·0.5C2H3Cl3, contains one bis­(ethyl­enedi­thio)­tetra­thia­fulvalene (ET) radical cation, one μ2-acetato-bis­[tri­bromido­rhenate(III)] anion and a 1,1,2-tri­chloro­ethane mol­ecule with half-occupancy disordered about a twofold rotation axis. The tetra­thia­fulvalene fragment adopts an almost planar configuration typical of the ET radical cation. The C atoms of both ethyl­enedi­thio fragments in the cation are disordered over two orientations with occupancy factors 0.65:0.35 and 0.77:0.23. In the anion, six Br atoms and a μ2-acetate ligand form a strongly distorted cubic O2Br6 coordination polyhedron around the Re2 dinuclear centre. In the crystal, centrosymmetrically related ET cations and Re2O2Br6 anions are linked into dimers by π–π stacking inter­actions [centroid-to-centroid distance = 3.826 (8) Å] and by pairs of additional Re⋯Br contacts [3.131 (3) Å], respectively. The dimers are further packed into a three-dimensional network by non-directional inter­ionic electrostatic forces and by C—H⋯Br and C—H⋯S hydrogen bonds. The disordered 1,1,2-tri­chloro­ethane mol­ecules occupy solvent-accessible channels along the b axis. PMID:27308025

Biocatalytic trifluoromethylation of unprotected phenols

NASA Astrophysics Data System (ADS)

Simon, Robert C.; Busto, Eduardo; Richter, Nina; Resch, Verena; Houk, Kendall N.; Kroutil, Wolfgang

2016-11-01

Organofluorine compounds have become important building blocks for a broad range of advanced materials, polymers, agrochemicals, and increasingly for pharmaceuticals. Despite tremendous progress within the area of fluorination chemistry, methods for the direct introduction of fluoroalkyl-groups into organic molecules without prefunctionalization are still highly desired. Here we present a concept for the introduction of the trifluoromethyl group into unprotected phenols by employing a biocatalyst (laccase), tBuOOH, and either the Langlois' reagent or Baran's zinc sulfinate. The method relies on the recombination of two radical species, namely, the phenol radical cation generated directly by the laccase and the CF3-radical. Various functional groups such as ketone, ester, aldehyde, ether and nitrile are tolerated. This laccase-catalysed trifluoromethylation proceeds under mild conditions and allows accessing trifluoromethyl-substituted phenols that were not available by classical methods.

A Comparison of Eye-Health Nutrients, Lutein (L)/Zeaxanthin (Z) Intakes and L/Z Rich Food Choices between College Students Living in Los Angeles and Taiwan

ERIC Educational Resources Information Center

Wang, Li Hui; Tam, Chick F.; Yang, Hsin Ling; Chen, Yin Chang; Davis, Rebecca; Schwartz, Miriam E.

2008-01-01

Lutein and zeaxanthin (L/Z) were related to macular health. With respect to increasing life expectancy, age-related macular disease (AMD) has become a concern on public health. The objective was to investigate dietary L/Z intake and its related food preference in populations living in different areas. A three-day dietary record and a supplement…

Effect of Dietary Supplementation With Lutein, Zeaxanthin, and ω-3 on Macular Pigment: A Randomized Clinical Trial.

PubMed

Korobelnik, Jean-François; Rougier, Marie-Bénédicte; Delyfer, Marie-Noëlle; Bron, Alain; Merle, Bénédicte M J; Savel, Hélène; Chêne, Geneviève; Delcourt, Cécile; Creuzot-Garcher, Catherine

2017-11-01

Nutritional uptake of lutein, zeaxanthin, and ω-3 polyunsaturated fatty acids may increase macular pigment optical density (MPOD) and thereby protect against the development of age-related macular degeneration (AMD). To estimate the efficiency of dietary supplementation containing lutein, zeaxanthin, ω-3 polyunsaturated fatty acids, and vitamins to increase the density of macular pigment in first-generation offspring of parents with neovascular AMD. This study was a randomized clinical trial (Lutein Influence on Macula of Persons Issued From AMD Parents [LIMPIA]) with a 6-month treatment period, followed by a 6-month follow-up period. Analyses were based on the intent-to-treat principle. The setting was 2 university hospitals in France (at Bordeaux and Dijon) from January 2011 (first participant first visit) to February 2013 (last participant last visit). The analysis was conducted from January to November 2016. Participants were 120 individuals free of any retinal ocular disease. They were first-generation offspring of parents with neovascular AMD. Participants were randomized in a 1:1 ratio to receive either 2 daily dietary supplementation capsules or placebo for 6 months. The primary assessment criterion was the evolution of MPOD after 6 months of supplementation (value of both eligible eyes) measured using the modified MPD-Visucam 200 (Carl Zeiss Meditec) and the modified Heidelberg Retina Angiograph (Heidelberg Engineering) (HRA) at 0.98° eccentricity. The statistical analysis was adjusted for hospital and for risk factors. Overall, 120 participants (60 in each group) were included, and 239 eyes were analyzed (119 in the lutein plus zeaxanthin [L + Z] group and 120 in the placebo group). Their mean (SD) age was 56.7 (6.6) years, and 71.7% (n = 86) were female. A statistically significant increase in plasma lutein and zeaxanthin was shown in the L + Z group after 3 months and 6 months of treatment compared with the placebo group. However, the difference between groups in the evolution of MPOD measured by HRA 0.98° eccentricity between 6 months and baseline was 0.036 (95% CI, -0.037 to 0.110) (P = .33). Among first-generation offspring of parents with neovascular AMD in the LIMPIA trial, MPOD as measured with the modified HRA and the MPD-Visucam was not modified after 6 months of lutein and zeaxanthin dietary supplementation despite plasma levels showing continuous exposure to lutein and zeaxanthin. Further research is necessary to understand the mechanism of absorption and metabolism of these nutrients in the macula, the best way to measure MPOD, and the clinical benefit for the patients. clinicaltrials.gov Identifier: NCT01269697.

Exchangeable cations-mediated photodegradation of polycyclic aromatic hydrocarbons (PAHs) on smectite surface under visible light.

PubMed

Jia, Hanzhong; Li, Li; Chen, Hongxia; Zhao, Yue; Li, Xiyou; Wang, Chuanyi

2015-04-28

Clay minerals saturated with different exchangeable cations are expected to play various roles in photodegradation of polycyclic aromatic hydrocarbons (PAHs) via direct and/or indirect pathways on clay surfaces. In the present study, anthracene and phenanthrene were selected as molecule probes to investigate the roles of exchangeable cations on their photodegradation under visible light irradiation. For five types of cation-modified smectite clays, the photodegradation rate of anthracene and phenanthrene follows the order: Fe(3+)>Al(3+)>Cu(2+)>Ca(2+)>K(+)>Na(+), which is consistent with the binding energy of cation-π interactions between PAHs and exchangeable cations. The result suggests that PAHs photolysis rate depends on cation-π interactions on clay surfaces. Meanwhile, the deposition of anthracene at the Na(+)-smectite and K(+)-smectite surface favors solar light absorption, resulting in enhanced direct photodecomposition of PAHs. On the other hand, smectite clays saturated with Fe(3+), Al(3+), and Cu(2+) are highly photoreactive and can act as potential catalysts giving rise to oxidative radicals such as O2(-) , which initiate the transformation of PAHs. The present work provides valuable insights into understanding the transformation and fate of PAHs in the natural soil environment and sheds light on the development of technologies for contaminated land remediation. Copyright © 2015 Elsevier B.V. All rights reserved.

Photoionization mass spectrometry of ω -phenylalkylamines: Role of radical cation-π interaction

NASA Astrophysics Data System (ADS)

Corinti, Davide; Catone, Daniele; Turchini, Stefano; Rondino, Flaminia; Crestoni, Maria Elisa; Fornarini, Simonetta

2018-04-01

Linear ω-phenylalkylamines of increasing alkyl chain length have been investigated employing synchrotron radiation in the photon energy range from 7 to 15 eV. These molecules have received considerable interest because they bear the skeleton of biologically relevant compounds including neurotransmitters and because of the possible interaction between the amino moiety and the phenyl ring. Recently, the contribution of this interaction has been assayed in both neutral and protonated species, pointing to a role of the polymethylene chain length. In this work, the ionization energy (IE) values of benzylamine (BA), 2-phenylethylamine (2-PEA), 3-phenylpropylamine (3-PPA), and 4-phenylbutylamine (4-PBA) were investigated in order to ascertain the impact of the different alkyl chain lengths and to verify an amino radical cation-π interaction. The IEs obtained experimentally, 8.54, 8.37, 8.29, and 8.31 eV for BA, 2-PEA, 3-PPA and 4-PBA, respectively, show a decreasing trend that is discussed employing calculations at the CBS-QB3 level. Moreover, the appearance energy values for major fragments produced by the photofragmentation process are reported.

Novel polymeric materials from vegetable oils and vinyl monomers: preparation, properties, and applications.

PubMed

Lu, Yongshang; Larock, Richard C

2009-01-01

Veggie-based products: Vegetable-oil-based polymeric materials, prepared by free radical, cationic, and olefin metathesis polymerizations, range from soft rubbers to ductile or rigid plastics, and to high-performance biocomposites and nanocomposites. They display a wide range of thermophysical and mechanical properties and may find promising applications as alternatives to petroleum-based polymers.Vegetable oils are considered to be among the most promising renewable raw materials for polymers, because of their ready availability, inherent biodegradability, and their many versatile applications. Research on and development of vegetable oil based polymeric materials, including thermosetting resins, biocomposites, and nanocomposites, have attracted increasing attention in recent years. This Minireview focuses on the latest developments in the preparation, properties, and applications of vegetable oil based polymeric materials obtained by free radical, cationic, and olefin metathesis polymerizations. The novel vegetable oil based polymeric materials obtained range from soft rubbery materials to ductile or rigid plastics and to high-performance biocomposites and nanocomposites. These vegetable oil based polymeric materials display a wide range of thermophysical and mechanical properties and should find useful applications as alternatives to their petroleum-based counterparts.

Nitration of benzo[a]pyrene adsorbed on coal fly ash particles by nitrogen dioxide: role of thermal activation.

PubMed

Kristovich, Robert L; Dutta, Prabir K

2005-09-15

Nitration of benzo[a]pyrene (BaP) by nitrogen dioxide (NO2) adsorbed on the surface of thermally activated coal fly ash and model aluminosilicate particles led to the formation of nitrobenzo[a]pyrenes as verified by extraction and gas chromatography/mass spectrometry (GC/MS). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was utilized to follow the nitration reaction on the surface of zeolite Y. Nitrobenzo[a]pyrene formation was observed along with the formation of nitrous acid and nitrate species. The formation of the BaP radical cation was also observed on thermally activated aluminosilicate particles by electron spin resonance (ESR) spectroscopy. On the basis of GC/MS, DRIFTS, and ESR spectroscopy results, a mechanism of nitration involving intermediate BaP radical cations generated on thermally activated aluminosilicate particles is proposed. These observations have led to the hypothesis that nitration of adsorbed polyaromatic hydrocarbons on coal fly ash by reaction with nitrogen oxides can occur in the smokestack, but with the aging of the fly ash particles, the extent of the nitration reaction will be diminished.

The use of nanomaterials for mass spectrometry can be uplifting for analyte detection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, J.; Lipson, R. H.

2014-03-31

Surface-Assisted Laser Desorption Ionization (SALDI) involves desorbing and ionizing analyte molecules from a nanoporous substrate by laser irradiation for detection in a mass spectrometer. In this work experiments were designed to better understand the mechanisms governing desorption and ionization for Desorption Ionization On Silicon (DIOS), a variant of SALDI which uses porous silicon (pSi) as a substrate. Experiments are also reported for other nanoporous semiconducting materials (WO{sub 3}, TiO{sub 2}) which exhibit very similar behaviors; specifically, that both protonated analyte ions and analyte radical cations can be generated with relative intensities that depend on the position of the incident lasermore » focus relative to substrate surface. While thermal desorption appears to be important, preliminary evidence suggests that the ionization mechanism leading to protonated analytes involves in part electrons and holes formed when photoexciting the substrate above its electronic band gap, and the presence of defect states within the band gap. Radical cation formation appears to be driven in part by electron transfer due to the large electron affinity of each substrate used in this work.« less

On the formation of the ·CH 2CH 2CH=NH 2+ distonic radical cation upon ionization of cyclopropylamine and allylamine

NASA Astrophysics Data System (ADS)

Nguyen, Minh Tho; Creve, Steven; Ha, Tae-Kyu

1998-08-01

Ab initio molecular orbital and density functional theory calculations have been applied to determine the relative stability of the cyclopropylamine 1 and allylamine (CH 2=CHCH 2NH 2+·2) radical cations and their isomers. It is confirmed that, upon ionization, 1 undergoes barrier-free ring-opening giving the distonic species ·CH 2CH 2CH=NH 2+3. 2 also rearranges by a 1,2-H-shift to the more stable 3 (by 70 kJ/mol) which is, however, less stable than the 1-aminopropene ion (CH 3-CH=CH-NH 2+·4) by 60 kJ/mol. The transition structure TS 2/3 lies 40 kJ/mol higher in energy than TS 3/4. Although QCISD and B3LYP calculations of isotropic hyperfine coupling constants agree reasonably with observed values, supporting the presence of the distonic 3 in ESR matrix experiments, the exclusive observation of 3, but not 4, is intriguing. This emphasizes the role of the matrix in stabilizing 3.

EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

PubMed Central

Bencivenni, Giorgio; Cesari, Riccardo; Nanni, Daniele; El Mkami, Hassane

2010-01-01

Summary The reactions of group 13 metal trichlorides with aromatic azides were examined by CW EPR and pulsed ENDOR spectroscopies. Complex EPR spectra were obtained from reactions of aluminium, gallium and indium trichlorides with phenyl azides containing a variety of substituents. Analysis of the spectra showed that 4-methoxy-, 3-methoxy- and 2-methoxyphenyl azides all gave ‘dimer’ radical cations [ArNHC6H4NH2]+• and trimers [ArNHC6H4NHC6H4NH2]+• followed by polymers. 4-Azidobenzonitrile, with its electron-withdrawing substituent, did not react. In general the aromatic azides appeared to react most rapidly with AlCl3 but this reagent tended to generate much polymer. InCl3 was the least reactive group 13 halide. DFT computations of the radical cations provided corroborating evidence and suggested that the unpaired electrons were accommodated in extensive π-delocalised orbitals. A mechanism to account for the reductive conversion of aromatic azides to the corresponding anilines and thence to the dimers and trimers is proposed. PMID:21049080

Lifetimes and reaction pathways of guanine radical cations and neutral guanine radicals in an oligonucleotide in aqueous solutions.

PubMed

Rokhlenko, Yekaterina; Geacintov, Nicholas E; Shafirovich, Vladimir

2012-03-14

The exposure of guanine in the oligonucleotide 5'-d(TCGCT) to one-electron oxidants leads initially to the formation of the guanine radical cation G(•+), its deptotonation product G(-H)(•), and, ultimately, various two- and four-electron oxidation products via pathways that depend on the oxidants and reaction conditions. We utilized single or successive multiple laser pulses (308 nm, 1 Hz rate) to generate the oxidants CO(3)(•-) and SO(4)(•-) (via the photolysis of S(2)O(8)(2-) in aqueous solutions in the presence and absence of bicarbonate, respectively) at concentrations/pulse that were ∼20-fold lower than the concentration of 5'-d(TCGCT). Time-resolved absorption spectroscopy measurements following single-pulse excitation show that the G(•+) radical (pK(a) = 3.9) can be observed only at low pH and is hydrated within 3 ms at pH 2.5, thus forming the two-electron oxidation product 8-oxo-7,8-dihydroguanosine (8-oxoG). At neutral pH, and single pulse excitation, the principal reactive intermediate is G(-H)(•), which, at best, reacts only slowly with H(2)O and lives for ∼70 ms in the absence of oxidants/other radicals to form base sequence-dependent intrastrand cross-links via the nucleophilic addition of N3-thymidine to C8-guanine (5'-G*CT* and 5'-T*CG*). Alternatively, G(-H)(•) can be oxidized further by reaction with CO(3)(•-), generating the two-electron oxidation products 8-oxoG (C8 addition) and 5-carboxamido-5-formamido-2-iminohydantoin (2Ih, by C5 addition). The four-electron oxidation products, guanidinohydantoin (Gh) and spiroiminodihydantoin (Sp), appear only after a second (or more) laser pulse. The levels of all products, except 8-oxoG, which remains at a low constant value, increase with the number of laser pulses.

Isolation and characterization of charge-tagged phenylperoxyl radicals in the gas phase: direct evidence for products and pathways in low temperature benzene oxidation.

PubMed

Kirk, Benjamin B; Harman, David G; Kenttämaa, Hilkka I; Trevitt, Adam J; Blanksby, Stephen J

2012-12-28

The phenylperoxyl radical has long been accepted as a critical intermediate in the oxidation of benzene and an archetype for arylperoxyl radicals in combustion and atmospheric chemistry. Despite being central to many contemporary mechanisms underpinning these chemistries, reports of the direct detection or isolation of phenylperoxyl radicals are rare and there is little experimental evidence connecting this intermediate with expected product channels. We have prepared and isolated two charge-tagged phenyl radical models in the gas phase [i.e., 4-(N,N,N-trimethylammonium)phenyl radical cation and 4-carboxylatophenyl radical anion] and observed their reactions with dioxygen by ion-trap mass spectrometry. Measured reaction rates show good agreement with prior reports for the neutral system (k(2)[(Me(3)N(+))C(6)H(4)˙ + O(2)] = 2.8 × 10(-11) cm(3) molecule(-1) s(-1), Φ = 4.9%; k(2)[((-)O(2)C)C(6)H(4)˙ + O(2)] = 5.4 × 10(-11) cm(3) molecule(-1) s(-1), Φ = 9.2%) and the resulting mass spectra provide unequivocal evidence for the formation of phenylperoxyl radicals. Collisional activation of isolated phenylperoxyl radicals reveals unimolecular decomposition by three pathways: (i) loss of dioxygen to reform the initial phenyl radical; (ii) loss of atomic oxygen yielding a phenoxyl radical; and (iii) ejection of the formyl radical to give cyclopentadienone. Stable isotope labeling confirms these assignments. Quantum chemical calculations for both charge-tagged and neutral phenylperoxyl radicals confirm that loss of formyl radical is accessible both thermodynamically and entropically and competitive with direct loss of both hydrogen atom and carbon dioxide.

Characterization of the radical-scavenging reaction of 2-O-substituted ascorbic acid derivatives, AA-2G, AA-2P, and AA-2S: a kinetic and stoichiometric study.

PubMed

Takebayashi, Jun; Tai, Akihiro; Gohda, Eiichi; Yamamoto, Itaru

2006-04-01

The aim of this study was to characterize the antioxidant activity of three ascorbic acid (AA) derivatives O-substituted at the C-2 position of AA: ascorbic acid 2-glucoside (AA-2G), ascorbic acid 2-phosphate (AA-2P), and ascorbic acid 2-sulfate (AA-2S). The radical-scavenging activities of these AA derivatives and some common low molecular-weight antioxidants such as uric acid or glutathione against 1,1-diphenyl-picrylhydrazyl (DPPH) radical, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS+), or galvinoxyl radical were kinetically and stoichiometrically evaluated under pH-controlled conditions. Those AA derivatives slowly and continuously reacted with DPPH radical and ABTS+, but not with galvinoxyl radical. They effectively reacted with DPPH radical under acidic conditions and with ABTS+ under neutral conditions. In contrast, AA immediately quenched all species of radicals tested at all pH values investigated. The reactivity of Trolox, a water-soluble vitamin E analogue, was comparable to that of AA in terms of kinetics and stoichiometrics. Uric acid and glutathione exhibited long-lasting radical-scavenging activity against these radicals under certain pH conditions. The radical-scavenging profiles of AA derivatives were closer to those of uric acid and glutathione rather than to that of AA. The number of radicals scavenged by one molecule of AA derivatives, uric acid, or glutathione was equal to or greater than that by AA or Trolox under the appropriate conditions. These data suggest the potential usage of AA derivatives as radical scavengers.

Specific carotenoid pigments in the diet and a bit of oxidative stress in the recipe for producing red carotenoid-based signals

PubMed Central

García-de Blas, Esther; Mateo, Rafael

2016-01-01

Colorful ornaments have been the focus of sexual selection studies since the work of Darwin. Yellow to red coloration is often produced by carotenoid pigments. Different hypotheses have been formulated to explain the evolution of these traits as signals of individual quality. Many of these hypotheses involve the existence of a signal production cost. The carotenoids necessary for signaling can only be obtained from food. In this line, carotenoid-based signals could reveal an individual’s capacity to find sufficient dietary pigments. However, the ingested carotenoids are often yellow and became transformed by the organism to produce pigments of more intense color (red ketocarotenoids). Biotransformation should involve oxidation reactions, although the exact mechanism is poorly known. We tested the hypothesis that carotenoid biotransformation could be costly because a certain level of oxidative stress is required to correctly perform the conversion. The carotenoid-based signals could thus reveal the efficiency of the owner in successfully managing this challenge. In a bird with ketocarotenoid-based ornaments (the red-legged partridge; Alectoris rufa), the availability of different carotenoids in the diet (i.e. astaxanthin, zeaxanthin and lutein) and oxidative stress were manipulated. The carotenoid composition was analyzed and quantified in the ornaments, blood, liver and fat. A number of oxidative stress biomarkers were also measured in the same tissues. First, we found that color and pigment levels in the ornaments depended on food levels of those carotenoids used as substrates in biotransformation. Second, we found that birds exposed to mild levels of a free radical generator (diquat) developed redder bills and deposited higher amounts of ketocarotenoids (astaxanthin) in ornaments. Moreover, the same diquat-exposed birds also showed a weaker resistance to hemolysis when their erythrocytes were exposed to free radicals, with females also enduring higher oxidative damage in plasma lipids. Thus, higher color production would be linked to higher oxidative stress, supporting the biotransformation hypothesis. The recent discovery of an avian oxygenase enzyme involved in converting yellow to red carotenoids may support our results. Nonetheless, the effect could also depend on the abundance of specific substrate carotenoids in the diet. Birds fed with proportionally higher levels of zeaxanthin showed the reddest ornaments with the highest astaxanthin concentrations. Moreover, these birds tended to show the strongest diquat-mediated effect. Therefore, in the evolution of carotenoid-based sexual signals, a biotransformation cost derived from maintaining a well-adjusted redox machinery could coexist with a cost linked to carotenoid acquisition and allocation (i.e. a resource allocation trade-off). PMID:27635308

Formation of singlet oxygen by decomposition of protein hydroperoxide in photosystem II.

PubMed

Pathak, Vinay; Prasad, Ankush; Pospíšil, Pavel

2017-01-01

Singlet oxygen (1O2) is formed by triplet-triplet energy transfer from triplet chlorophyll to O2 via Type II photosensitization reaction in photosystem II (PSII). Formation of triplet chlorophyll is associated with the change in spin state of the excited electron and recombination of triplet radical pair in the PSII antenna complex and reaction center, respectively. Here, we have provided evidence for the formation of 1O2 by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex. Protein hydroperoxide is formed by protein oxidation initiated by highly oxidizing chlorophyll cation radical and hydroxyl radical formed by Type I photosensitization reaction. Under highly oxidizing conditions, protein hydroperoxide is oxidized to protein peroxyl radical which either cyclizes to dioxetane or recombines with another protein peroxyl radical to tetroxide. These highly unstable intermediates decompose to triplet carbonyls which transfer energy to O2 forming 1O2. Data presented in this study show for the first time that 1O2 is formed by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex.

Formation of singlet oxygen by decomposition of protein hydroperoxide in photosystem II

PubMed Central

Pathak, Vinay; Prasad, Ankush

2017-01-01

Singlet oxygen (1O2) is formed by triplet-triplet energy transfer from triplet chlorophyll to O2 via Type II photosensitization reaction in photosystem II (PSII). Formation of triplet chlorophyll is associated with the change in spin state of the excited electron and recombination of triplet radical pair in the PSII antenna complex and reaction center, respectively. Here, we have provided evidence for the formation of 1O2 by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex. Protein hydroperoxide is formed by protein oxidation initiated by highly oxidizing chlorophyll cation radical and hydroxyl radical formed by Type I photosensitization reaction. Under highly oxidizing conditions, protein hydroperoxide is oxidized to protein peroxyl radical which either cyclizes to dioxetane or recombines with another protein peroxyl radical to tetroxide. These highly unstable intermediates decompose to triplet carbonyls which transfer energy to O2 forming 1O2. Data presented in this study show for the first time that 1O2 is formed by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex. PMID:28732060

Vibrational Spectroscopy of Ions and Radicals Present in the Interstellar Medium and in Planetary Atmospheres: A Theoretical Study

NASA Technical Reports Server (NTRS)

Chaban, Galina M.

2004-01-01

Anharmonic vibrational frequencies and intensities are calculated for OH(H2O)n and H(H2O)n radicals (that form on icy particles of the interstellar medium), HCO radical (the main intermediate in the synthesis of organic molecules in space), NH2(-) and C2H(-) anions, H5(+) cation, and other systems relevant to interstellar chemistry. In addition to pure ions and radicals, their complexes with water are studied to assess the effects of water environment on infrared spectra. The calculations are performed using the correlation-corrected vibrational self-consistent field (CC-VSCF) method with ab initio potential surfaces at the MP2 and CCSD(T) levels. Fundamental, overtone, and combination excitations are computed. The results are in good agreement with available experimental data and provide reliable predictions for vibrational excitations not yet measured in laboratory experiments. The data should be useful for interpretation of astronomically observed spectra and identification of ions and radicals present in the interstellar medium and in planetary atmospheres.

Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer

DOE PAGES

Boaz, Nicholas C.; Bell, Seth R.; Groves, John T.

2015-02-04

Ferryl porphyrins, P–Fe IVmore » $=$O, are central reactive intermediates in the catalytic cycles of numerous heme proteins and a variety of model systems. There has been considerable interest in elucidating factors, such as terminal oxo basicity, that may control ferryl reactivity. Here in this study, the sulfonated, water-soluble ferryl porphyrin complexes tetramesitylporphyrin, oxoFe IVTMPS (FeTMPS-II), its 2,6-dichlorophenyl analogue, oxoFe IVTDClPS (FeTDClPS-II), and two other analogues are shown to be protonated under turnover conditions to produce the corresponding bis-aqua-iron(III) porphyrin cation radicals. The results reveal a novel internal electromeric equilibrium, P–Fe IV$=$O $$\\leftrightarrows$$ P +–Fe III(OH 2) 2. Reversible pKa values in the range of 4–6.3 have been measured for this process by pH-jump, UV–vis spectroscopy. Ferryl protonation has important ramifications for C–H bond cleavage reactions mediated by oxoiron(IV) porphyrin cation radicals in protic media. Both solvent O–H and substrate C–H deuterium kinetic isotope effects are observed for these reactions, indicating that hydrocarbon oxidation by these oxoiron(IV) porphyrin cation radicals occurs via a solvent proton-coupled hydrogen atom transfer from the substrate that has not been previously described. The effective FeO–H bond dissociation energies for FeTMPS-II and FeTDClPS-II were estimated from similar kinetic reactivities of the corresponding oxoFe IVTMPS + and oxoFe IVTDClPS + species to be ~92–94 kcal/mol. Similar values were calculated from the two-proton P +–Fe III(OH 2) 2 pK a obs and the porphyrin oxidation potentials, despite a 230 mV range for the iron porphyrins examined. Thus, the iron porphyrin with the lower ring oxidation potential has a compensating higher basicity of the ferryl oxygen. The solvent-derived proton adds significantly to the driving force for C–H bond scission.« less

Equilibrium Acidities and Homolytic Bond Dissociation Enthalpies of the Acidic C-H Bonds in P-(Para-substituted benzyl)triphenylphosphonium Cations and Related Cations.

PubMed

Zhang, Xian-Man; Fry, Albert J.; Bordwell, Frederick G.

1996-06-14

Equilibrium acidities (pK(HA)) of six P-(para-substituted benzyl)triphenylphosphonium (p-GC(6)H(4)CH(2)PPh(3)(+)) cations, P-allyltriphenylphosphonium cation, P-cinnamyltriphenylphosphonium cation, and As-(p-cyanobenzyl)triphenylarsonium cation, together with the oxidation potentials [E(ox)(A(-))] of their conjugate anions (ylides) have been measured in dimethyl sulfoxide (DMSO) solution. The acidifying effects of the alpha-triphenylphosphonium groups on the acidic C-H bonds in toluene and propene were found to be ca 25 pK(HA) units (34 kcal/mol). Introduction of an electron-withdrawing group such as 4-NO(2), 4-CN, or 4-Br into the para position of the benzyl ring in p-GC(6)H(4)CH(2)PPh(3)(+) cations resulted in an additional acidity increase, but introduction of the 4-OEt electron-donating group decreases the acidity. The equilibrium acidities of p-GC(6)H(4)CH(2)PPh(3)(+) cations were nicely linearly correlated with the Hammett sigma(-) constants of the substituents (G) with a slope of 4.78 pK(HA) units (R(2) = 0.992) (Figure 1). Reversible oxidation potentials of the P-(para-substituted benzyl)triphenylphosphonium ylides were obtained by fast scan cyclic voltammetry. The homolytic bond dissociation enthalpies (BDEs) of the acidic C-H bonds in these cations, estimated by combining their equilibrium acidities with the oxidation potentials of their corresponding conjugate anions, showed that the alpha-Ph(3)P(+) groups have negligible stabilizing or destabilizing effects on the adjacent radicals. The equilibrium acidity of As-(p-cyanobenzyl)triphenylarsonium cation is 4 pK(HA) units weaker than that of P-(p-cyanobenzyl)triphenylphosphonium cation, but the BDE of the acidic C-H bond in As-(p-cyanobenzyl)triphenylarsonium cation is ca 2 kcal/mol higher than that in P-(p-cyanobenzyl)triphenylphosphonium cation.

Similarities of Fruit and Vegetable Consumption, Lutein/Zeaxanthin and Lycopene Intakes between Hispanic-American College Students and Their Respective Parents: A Two Generation and Gender Study

ERIC Educational Resources Information Center

Tam, Chick; Janeke, Emilia; Chan, Oi Ling; Xi, Emily; Sarkissian-Pakachet, Ivet; Banchi, Waka

2017-01-01

The purpose of this study was to assess the effects of age and gender on the consumption of fruits and vegetables, lutein/zeaxanthin (lut+zea) and lycopene (lyc) in Hispanic-American college students living in the same household with their respective parents. There were 160 subjects (42 males and 118 females) including 80 young (ages 18-49) and 80…

Zeaxanthin: Review of Toxicological Data and Acceptable Daily Intake

PubMed Central

Edwards, James A.

2016-01-01

Zeaxanthin is a nutritional carotenoid with a considerable amount of safety data based on regulatory studies, which form the basis of its safety evaluation. Subchronic OECD guideline studies with mice and rats receiving beadlet formulations of high purity synthetic zeaxanthin in the diet at dosages up to 1000 mg/kg body weight (bw)/day, and in dogs at over 400 mg/kg bw/day, produced no adverse effects or histopathological changes. In developmental toxicity studies, there was no evidence of fetal toxicity or teratogenicity in rats or rabbits at dosages up to 1000 or 400 mg/kg bw/day, respectively. Formulated zeaxanthin was not mutagenic or clastogenic in a series of in vitro and in vivo tests for genotoxicity. A 52-week chronic oral study in Cynomolgus monkeys at doses of 0.2 and 20 mg/kg bw/day, mainly designed to assess accumulation and effects in primate eyes, showed no adverse effects. In a rat two-generation study, the NOAEL was 150 mg/kg bw/day. In 2012, this dosage was used by EFSA (NDA Panel), in association with a 200-fold safety factor, to propose an Acceptable Daily Intake equivalent to 53 mg/day for a 70 kg adult. The requested use level of 2 mg/day was ratified by the EU Commission. PMID:26885380

The peculiar NPQ regulation in the stramenopile Phaeomonas sp. challenges the xanthophyll cycle dogma.

PubMed

Berne, N; Fabryova, T; Istaz, B; Cardol, P; Bailleul, B

2018-07-01

In changing light conditions, photosynthetic organisms develop different strategies to maintain a fine balance between light harvesting, photochemistry, and photoprotection. One of the most widespread photoprotective mechanisms consists in the dissipation of excess light energy in the form of heat in the photosystem II antenna, which participates to the Non Photochemical Quenching (NPQ) of chlorophyll fluorescence. It is tightly related to the reversible epoxidation of xanthophyll pigments, catalyzed by the two enzymes, the violaxanthin deepoxidase and the zeaxanthin epoxidase. In Phaeomonas sp. (Pinguiophyte, Stramenopiles), we show that the regulation of the heat dissipation process is different from that of the green lineage: the NPQ is strictly proportional to the amount of the xanthophyll pigment zeaxanthin and the xanthophyll cycle enzymes are differently regulated. The violaxanthin deepoxidase is already active in the dark, because of a low luminal pH, and the zeaxanthin epoxidase shows a maximal activity under moderate light conditions, being almost inactive in the dark and under high light. This light-dependency mirrors the one of NPQ: Phaeomonas sp. displays a large NPQ in the dark as well as under high light, which recovers under moderate light. Our results pinpoint zeaxanthin epoxidase activity as the prime regulator of NPQ in Phaeomonas sp. and therefore challenge the deepoxidase-regulated xanthophyll cycle dogma. Copyright © 2018 Elsevier B.V. All rights reserved.

Biocatalytic trifluoromethylation of unprotected phenols

PubMed Central

Simon, Robert C.; Busto, Eduardo; Richter, Nina; Resch, Verena; Houk, Kendall N.; Kroutil, Wolfgang

2016-01-01

Organofluorine compounds have become important building blocks for a broad range of advanced materials, polymers, agrochemicals, and increasingly for pharmaceuticals. Despite tremendous progress within the area of fluorination chemistry, methods for the direct introduction of fluoroalkyl-groups into organic molecules without prefunctionalization are still highly desired. Here we present a concept for the introduction of the trifluoromethyl group into unprotected phenols by employing a biocatalyst (laccase), tBuOOH, and either the Langlois' reagent or Baran's zinc sulfinate. The method relies on the recombination of two radical species, namely, the phenol radical cation generated directly by the laccase and the CF3-radical. Various functional groups such as ketone, ester, aldehyde, ether and nitrile are tolerated. This laccase-catalysed trifluoromethylation proceeds under mild conditions and allows accessing trifluoromethyl-substituted phenols that were not available by classical methods. PMID:27834376

Comparison of macular pigment optical density in patients with dry and wet age-related macular degeneration.

PubMed

Ozyurt, Ayhan; Kocak, Nilufer; Akan, Pınar; Calan, Ozlem Gursoy; Ozturk, Taylan; Kaya, Mahmut; Karahan, Eyup; Kaynak, Suleyman

2017-06-01

The aim of the study was to evaluate the macular pigment optical density (MPOD) levels in patients with wet age-related macular degeneration (AMD), dry AMD, and also in healthy controls. This study was conducted at Department of Ophthalmology, and the study design was a prospective study. Forty-eight patients with wet AMD, 51 patients with dry AMD, and 50 controls were included in the study. All patients were naive to both previous lutein or zeaxanthin administration and any previous intravitreal injections. Fundus reflectance (VISUCAM 500, reflectance of a single 460 nm wavelength) was used to measure the MPOD levels. Three groups were compared regarding age, gender, serum lutein, and zeaxanthin concentrations as well as MPOD levels. Serum lutein and zeaxanthin levels were significantly higher in control group when compared with wet AMD (Group 1) and dry AMD (Group 2) (P = 0.001 and P< 0.001, respectively). Mean MPOD was found to be similar in all of the three study subgroups (P = 0.630). However, maximum MPOD was significantly higher in control group when compared with Group 1 and 2 (P = 0.003). There was no correlation between serum lutein or zeaxanthin concentrations and mean MPOD levels (P = 0.815, r = 0.014 and P = 0.461, r = 0.043, respectively), but there was a weak correlation between serum zeaxanthin concentration and maximum MPOD level (P = 0.042, r = 0.124). Maximum MPOD level was found to be correlated with the level of AMD (Group 1, 2, and 3; r = 0.184, P = 0.041). Maximum MPOD level was found to be lower in patients with AMD when compared with control cases. Mean MPOD and maximum MPOD levels were similar in wet and dry AMD Groups. These results can be applied clinically keeping in mind that MPOD measurements with one wavelength reflectometry may not be completely reliable.

Retinal accumulation of zeaxanthin, lutein, and β-carotene in mice deficient in carotenoid cleavage enzymes.

PubMed

Li, Binxing; Vachali, Preejith P; Shen, Zhengqing; Gorusupudi, Aruna; Nelson, Kelly; Besch, Brian M; Bartschi, Alexis; Longo, Simone; Mattinson, Ty; Shihab, Saeed; Polyakov, Nikolay E; Suntsova, Lyubov P; Dushkin, Alexander V; Bernstein, Paul S

2017-06-01

Carotenoid supplementation can prevent and reduce the risk of age-related macular degeneration (AMD) and other ocular disease, but until now, there has been no validated and well-characterized mouse model which can be employed to investigate the protective mechanism and relevant metabolism of retinal carotenoids. β-Carotene oxygenases 1 and 2 (BCO1 and BCO2) are the only two carotenoid cleavage enzymes found in animals. Mutations of the bco2 gene may cause accumulation of xanthophyll carotenoids in animal tissues, and BCO1 is involved in regulation of the intestinal absorption of carotenoids. To determine whether or not mice deficient in BCO1 and/or BCO2 can serve as a macular pigment mouse model, we investigated the retinal accumulation of carotenoids in these mice when fed with zeaxanthin, lutein, or β-carotene using an optimized carotenoid feeding method. HPLC analysis revealed that all three carotenoids were detected in sera, livers, retinal pigment epithelium (RPE)/choroids, and retinas of all of the mice, except that no carotenoid was detectable in the retinas of wild type (WT) mice. Significantly higher amounts of zeaxanthin and lutein accumulated in the retinas of BCO2 knockout (bco2 -/- ) mice and BCO1/BCO2 double knockout (bco1 -/- /bco2 -/- ) mice relative to BCO1 knockout (bco1 -/- ) mice, while bco1 -/- mice preferred to take up β-carotene. The levels of zeaxanthin and lutein were higher than β-carotene levels in the bco1 -/- /bco2 -/- retina, consistent with preferential uptake of xanthophyll carotenoids by retina. Oxidative metabolites were detected in mice fed with lutein or zeaxanthin but not in mice fed with β-carotene. These results indicate that bco2 -/- and bco1 -/- /bco2 -/- mice could serve as reasonable non-primate models for macular pigment function in the vertebrate eye, while bco1 -/- mice may be more useful for studies related to β-carotene. Copyright © 2017 Elsevier Ltd. All rights reserved.

Direct Observation of Excimer-Mediated Intramolecular Electron Transfer in a Cofacially-Stacked Perylene Bisimide Pair.

PubMed

Sung, Jooyoung; Nowak-Król, Agnieszka; Schlosser, Felix; Fimmel, Benjamin; Kim, Woojae; Kim, Dongho; Würthner, Frank

2016-07-27

We have elucidated excimer-mediated intramolecular electron transfer in cofacially stacked PBIs tethered by two phenylene-butadiynylene loops. The electron transfer between energetically equivalent PBIs is revealed by the simultaneous observation of the PBI radical anion and cation bands in the transient absorption spectra. The fluorescence decay time of the excimer states is in good agreement with the rise time of PBI radical bands in transient absorption spectra suggesting that the electron transfer dynamics proceed via the excimer state. We can conclude that the excimer state effectuates the efficient charge transfer in the cofacially stacked PBI dimer.

Copper-catalyzed aerobic oxidative coupling: From ketone and diamine to pyrazine

PubMed Central

Wu, Kun; Huang, Zhiliang; Qi, Xiaotian; Li, Yingzi; Zhang, Guanghui; Liu, Chao; Yi, Hong; Meng, Lingkui; Bunel, Emilio E.; Miller, Jeffrey T.; Pao, Chih-Wen; Lee, Jyh-Fu; Lan, Yu; Lei, Aiwen

2015-01-01

Copper-catalyzed aerobic oxidative C–H/N–H coupling between simple ketones and diamines was developed toward the synthesis of a variety of pyrazines. Various substituted ketones were compatible for this transformation. Preliminary mechanistic investigations indicated that radical species were involved. X-ray absorption fine structure experiments elucidated that the Cu(II) species 5 coordinated by two N atoms at a distance of 2.04 Å and two O atoms at a shorter distance of 1.98 Å was a reactive one for this aerobic oxidative coupling reaction. Density functional theory calculations suggested that the intramolecular coupling of cationic radicals was favorable in this transformation. PMID:26601302

DNA Binding Hydroxyl Radical Probes.

PubMed

Tang, Vicky J; Konigsfeld, Katie M; Aguilera, Joe A; Milligan, Jamie R

2012-01-01

The hydroxyl radical is the primary mediator of DNA damage by the indirect effect of ionizing radiation. It is a powerful oxidizing agent produced by the radiolysis of water and is responsible for a significant fraction of the DNA damage associated with ionizing radiation. There is therefore an interest in the development of sensitive assays for its detection. The hydroxylation of aromatic groups to produce fluorescent products has been used for this purpose. We have examined four different chromophores which produce fluorescent products when hydroxylated. Of these, the coumarin system suffers from the fewest disadvantages. We have therefore examined its behavior when linked to a cationic peptide ligand designed to bind strongly to DNA.

SAC-CI methodology applied to molecular spectroscopy and photo-biology

NASA Astrophysics Data System (ADS)

Hasegawa, J.; Miyahara, T.; Nakashima, H.; Nakatsuji, H.

2012-06-01

The SAC-CI method was applied to the spectroscopy of radical cations and anions of various organic molecules. It was also applied to photo-biology, in particular, to elucidate the bio-molecular color-tuning mechanism of human visions and to the circular dichroism spectroscopy that is used to understand the helical structures of DNA and RNA.

IDENTIFICATION AND QUANTITATION OF BENZO[A]PYRENE DERIVED DNA ADDUCTS FORMED AT LOW ADDUCTION LEVEL IN MICE LUNG TISSUE

EPA Science Inventory

The two major metabolic pathways of benzo[a]pyrene (BP), as well as other polycyclic aromatic hydrocarbons, that allow for the induction of DNA lesions are monooxygenation that results in diol epoxides (BPDE), and one-electron oxidation that yields a BP radical cation. The DNA ad...

Analytical profiling of selected antioxidants and total antioxidant capacity of goji (Lycium spp.) berries.

PubMed

Protti, Michele; Gualandi, Isacco; Mandrioli, Roberto; Zappoli, Sergio; Tonelli, Domenica; Mercolini, Laura

2017-09-05

Goji berries and derived products represent a relevant source of micronutrients, most of which are natural antioxidants and contribute to the high nutritional quality of these fruits. Three brands of dried goji berries have been analysed by a multidisciplinary approach to get an insight into both their content of selected antioxidants and their antioxidant capacity (AC). The former goal has been achieved by developing a liquid chromatographic method coupled to mass spectrometry and combined to a fast solid phase extraction. Several significant representative antioxidant compounds belonging to the following classes: flavonoids, flavan-3-ols, phenolic acids, amino acids and derivatives, and carotenoids have been taken into account. Quercetin and rutin were found to be the predominant flavonoids, chlorogenic acid was the most abundant phenolic acid and zeaxanthin was the major carotenoid. The AC of the goji berries has been evaluated by four analytical methods in order to estimate the contributions of different reactions involved in radicals scavenging. In particular, AC has been determined using 3 standardised methods (DPPH, ABTS, ORAC) and a recently proposed electrochemical method, which measures the scavenging activity of antioxidants towards OH radicals generated both by hydrogen peroxide photolysis and the Fenton reaction. The results obtained from chemical composition and antioxidant capacity assays confirm the high nutritional and commercial value of goji berries and highlight that the three brands do not exhibit significant differences. Copyright © 2017 Elsevier B.V. All rights reserved.

Syntheses, crystal structures and magnetic properties of complexes based on [Ni(L-L)3]2+ complex cations with dimethylderivatives of 2,2‧-bipyridine and TCNQ

NASA Astrophysics Data System (ADS)

Černák, Juraj; Hegedüs, Michal; Váhovská, Lucia; Kuchár, Juraj; Šoltésová, Daniela; Čižmár, Erik; Feher, Alexander; Falvello, L. R.

2018-03-01

From the aqueous-methanolic systems Ni(NO3)2 - LiTCNQ - 5,5‧-dmbpy and Ni(NO3)2 - LiTCNQ - 4,4‧-dmbpy three novel complexes [Ni(5,5‧-dmbpy)3](TCNQ)2 (1), [Ni(4,4‧-dmbpy)3](TCNQ)2 (2) and [Ni(4,4‧-dmbpy)3]2(TCNQ-TCNQ)(TCNQ)2•0.60H2O (3), were isolated in single crystal form. The new compounds were identified using chemical analyses and IR spectroscopy. Single crystal studies of all samples corroborated their compositions and have shown that their ionic structures contain the complex cations [Ni(5,5‧-dmbpy)]2+ (1) or [Ni(4,4‧-dmbpy)]2+ (2 and 3). The anionic parts of the respective crystal structures 1-3 are formed by TCNQṡ- anion-radicals and in 3 also by a σ-dimerized dianion (TCNQ-TCNQ)2- with a C-C distance of 1.663(5) Å. The supramolecular structures are governed by weak hydrogen bonding interactions. The variable-temperature (2-300 K) magnetic studies of 1 and 3 confirmed the presence of magnetically active Ni(II) atoms with S = 1 and TCNQṡ- anion-radicals with S = 1/2 while the (TCNQ-TCNQ)2- dianion is magnetically silent. The magnetic behavior was described by a complex magnetic model assuming strong antiferromagnetic interactions between some TCNQṡ- anion-radicals.

Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnes, J. C.; Fahrenbach, A. C.; Dyar, S. M.

2012-06-08

The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylene-bridged bipyridinium (P-BIPY2+) unit and a cyclobis (paraquat-p-phenylene) (CBPQT4+) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT4+ ring encircles the DNP unit. Reduction of the CBPQT4+ leads to the CBPQT2(•+) diradical dication while the P-BIPY2+ unit is reduced to its P-BIPY•+ radical cation. A radical-state co-conformation (RSCC) results from movement of the CBPQT2(•+) ring along the dumbbell to surround the P-BIPY•+ unit.more » This shuttling event induces IET to occur between the pyridinium redox centers of the P-BIPY•+ unit, a property which is absent between these redox centers in the free dumbbell and in the 1:1 complex formed between the CBPQT2(•+) ring and the radical cation of methyl-phenylene-viologen (MPV•+). Using electron paramagnetic resonance (EPR) spectroscopy, the process of IET was investigated by monitoring the line broadening at varying temperatures and determining the rate constant (kET = 1.33 × 107 s-1) and activation energy (ΔG‡ = 1.01 kcal mol-1) for electron transfer. These values were compared to the corresponding values predicted, using the optical absorption spectra and Marcus–Hush theory.« less

Redox chemistry of nickel(II) complexes supported by a series of noninnocent β-diketiminate ligands.

PubMed

Takaichi, June; Morimoto, Yuma; Ohkubo, Kei; Shimokawa, Chizu; Hojo, Takayuki; Mori, Seiji; Asahara, Haruyasu; Sugimoto, Hideki; Fujieda, Nobutaka; Nishiwaki, Nagatoshi; Fukuzumi, Shunichi; Itoh, Shinobu

2014-06-16

Nickel complexes of a series of β-diketiminate ligands ((R)L(-), deprotonated form of 2-substituted N-[3-(phenylamino)allylidene]aniline derivatives (R)LH, R = Me, H, Br, CN, and NO2) have been synthesized and structurally characterized. One-electron oxidation of the neutral complexes [Ni(II)((R)L(-))2] by AgSbF6 or [Ru(III)(bpy)3](PF6)3 (bpy = 2,2'-bipyridine) gave the corresponding metastable cationic complexes, which exhibit an EPR spectrum due to a doublet species (S = 1/2) and a characteristic absorption band in near IR region ascribable to a ligand-to-ligand intervalence charge-transfer (LLIVCT) transition. DFT calculations have indicated that the divalent oxidation state of nickel ion (Ni(II)) is retained, whereas one of the β-diketiminate ligands is oxidized to give formally a mixed-valence complex, [Ni(II)((R)L(-))((R)L(•))](+). Thus, the doublet spin state of the oxidized cationic complex can be explained by taking account of the antiferromagnetic interaction between the high-spin nickel(II) ion (S = 1) and the organic radical (S = 1/2) of supporting ligand. A single-crystal structure of one of the cationic complexes (R = H) has been successfully determined to show that both ligands in the cationic complex are structurally equivalent. On the basis of theoretical analysis of the LLIVCT band and DFT calculations as well as the crystal structure, the mixed-valence complexes have been assigned to Robin-Day class III species, where the radical spin is equally delocalized between the two ligands to give the cationic complex, which is best described as [Ni(II)((R)L(0.5•-))2](+). One-electron reduction of the neutral complexes with decamethylcobaltocene gave the anionic complexes when the ligand has the electron-withdrawing substituent (R = CN, NO2, Br). The generated anionic complexes exhibited EPR spectra due to a doublet species (S = 1/2) but showed no LLIVCT band in the near-IR region. Thus, the reduced complexes are best described as the d(9) nickel(I) complexes supported by two anionic β-diketiminate ligands, [Ni(I)((R)L(-))2](-). This conclusion was also supported by DFT calculations. Substituent effects on the electronic structures of the three oxidation states (neutral, cationic, and anionic) of the complexes are systematically evaluated on the basis of DFT calculations.

Flash photolysis and pulse radiolysis studies on collagen Type I in acetic acid solution.

PubMed

Sionkowska, Alina

2006-07-03

An investigation of the photochemical properties of collagen Type I in acetic acid solution was carried out using nanosecond laser irradiation. The transient spectra of collagen solution excited at 266 nm show two bands. One of them with maximum at 295 nm and the second one with maximum at 400 nm. The peak at 400 nm is assigned to tyrosyl radicals. The first peak of the transient absorption spectra at 295 nm is probably due to photoionisation producing collagen radical cation. The transient for collagen solution in acetic acid at 640 nm was not observed. It is evidence that there is no hydrated electron in the irradiated collagen solution. The reactions of hydrated electrons and (*)OH radicals with collagen have been studied by pulse radiolysis. In the absorption spectra of products resulting from the reaction of collagen with e(aq)(-) no characteristic maximum absorption in UV and visible light region has been observed. In the absorption spectra of products resulting from the reaction of the hydroxyl radicals with collagen two bands have been observed. The first one at 320 nm and the second one at 405 nm. Reaction of (*)OH radicals with tyrosine residues in collagen chains gives rise to Tyr phenoxyl radicals (absorption at 400 nm).

Laser-induced oxidation of cholesterol observed during MALDI-TOF mass spectrometry.

PubMed

McAvey, Kevin M; Guan, Bing; Fortier, Chanel A; Tarr, Matthew A; Cole, Richard B

2011-04-01

Conditions for the detection of three odd-electron cholesterol oxidation peaks were determined and these peaks were shown to be artifacts of the matrix-assisted laser desorption time of flight (MALDI-TOF) process. Matrix choice, solvent, laser intensity and cholesterol concentration were systematically varied to characterize the conditions leading to the highest signals of the radical cation peaks, and it was found that initial cholesterol solution concentration and resultant density of solid cholesterol on the MALDI target were important parameters in determining signal intensities. It is proposed that hydroxyl radicals, generated as a result of laser irradiation of the employed 2,5-dihydroxybenzoic acid (DHB) matrix, initiate cholesterol oxidation on the MALDI target. An attempt to induce the odd-electron oxidation peaks by means of adding an oxidizing agent succeeded using an acetonitrile solution of DHB, cholesterol, and cumene hydroperoxide. Moreover, addition of free radical scavengers reduced the abundances of some oxidation products under certain conditions. These results are consistent with the mechanism of oxidation proposed herein involving laser-induced hydroxyl radical production followed by attack on neutral cholesterol. Hydroxyl radical production upon irradiation of dithranol matrix may also be responsible for generation of the same radical peaks observed from cholesterol in dithranol by an analogous mechanism. © American Society for Mass Spectrometry, 2011

CBLB502, an agonist of Toll-like receptor 5, has antioxidant and scavenging free radicals activities in vitro.

PubMed

Li, Weiguang; Ge, Changhui; Yang, Liu; Wang, Ruixue; Lu, Yiming; Gao, Yan; Li, Zhihui; Wu, Yonghong; Zheng, Xiaofei; Wang, Zhaoyan; Zhang, Chenggang

2016-01-01

The bacterial protein flagellin is the known agonist of Toll-like receptor 5 (TLR5). It has been reported that CBLB502, a novel agonist of TLR5 derived from Salmonella flagellin, could reduce radiation toxicity in mouse and primate models, protect mice from dermatitis and oral mucositis caused by radiation, inhibit acute renal ischemic failure, and inhibit the growth of A549 lung cancer cell. The property of CBLB502 is able to bind to TLR5 and activates NF-κB signaling. In this study, we investigated the antioxidant potential and free radicals scavenging properties of CBLB502 in vitro. Interestingly, we found that CBLB502 has a direct and distinct antioxidant capacity and can efficiently scavenge a variety of free radicals, including superoxide anion, hydroxyl radical, and ABTS cation (ABTS(+)). Through wave scanning and kinetic evaluation of scavenging ABTS(+), we found that the ABTS(+) scavenging process of CBLB502 is relatively slow, and the ABTS(+) scavenging activity of CBLB502 has a consistently kinetics characteristics. In conclusion, our results suggested that CBLB502 has antioxidant and scavenging free radicals activities in vitro. It is implied that CBLB502 might partially promote the beneficial protective effect through its scavenging free radicals. Copyright © 2015. Published by Elsevier B.V.

M-type thioredoxins are involved in the xanthophyll cycle and proton motive force to alter NPQ under low-light conditions in Arabidopsis.

PubMed

Da, Qingen; Sun, Ting; Wang, Menglong; Jin, Honglei; Li, Mengshu; Feng, Dongru; Wang, Jinfa; Wang, Hong-Bin; Liu, Bing

2018-02-01

M-type thioredoxins are required to regulate zeaxanthin epoxidase activity and to maintain the steady-state level of the proton motive force, thereby influencing NPQ properties under low-light conditions in Arabidopsis. Non-photochemical quenching (NPQ) helps protect photosynthetic organisms from photooxidative damage via the non-radiative dissipation of energy as heat. Energy-dependent quenching (qE) is a major constituent of NPQ. However, the mechanism underlying the regulation of qE is not well understood. In this study, we demonstrate that the m-type thioredoxins TRX-m1, TRX-m2, and TRX-m4 (TRX-ms) interact with the xanthophyll cycle enzyme zeaxanthin epoxidase (ZE) and are required for maintaining the redox-dependent stabilization of ZE by regulating its intermolecular disulfide bridges. Reduced ZE activity and accumulated zeaxanthin levels were observed under TRX-ms deficiency. Furthermore, concurrent deficiency of TRX-ms resulted in a significant increase in proton motive force (pmf) and acidification of the thylakoid lumen under low irradiance, perhaps due to the significantly reduced ATP synthase activity under TRX-ms deficiency. The increased pmf, combined with acidification of the thylakoid lumen and the accumulation of zeaxanthin, ultimately contribute to the elevated stable qE in VIGS-TRX-m2m4/m1 plants under low-light conditions. Taken together, these results indicate that TRX-ms are involved in regulating NPQ-dependent photoprotection in Arabidopsis.

Engineered maize as a source of astaxanthin: processing and application as fish feed.

PubMed

Breitenbach, Jürgen; Nogueira, Marilise; Farré, Gemma; Zhu, Changfu; Capell, Teresa; Christou, Paul; Fleck, Gunther; Focken, Ulfert; Fraser, Paul D; Sandmann, Gerhard

2016-12-01

Astaxanthin from a transgenic maize line was evaluated as feed supplement source conferring effective pigmentation of rainbow trout flesh. An extraction procedure using ethanol together with the addition of vegetal oil was established. This resulted in an oily astaxanthin preparation which was not sufficiently concentrated for direct application to the feed. Therefore, a concentration process involving multiple phase partitioning steps was implemented to remove 90 % of the oil. The resulting astaxanthin raw material contained non-esterified astaxanthin with 12 % 4-keto zeaxanthin and 2 % zeaxanthin as additional carotenoids. Isomeric analysis confirmed the exclusive presence of the 3S, 3'S astaxanthin enantiomer. The geometrical isomers were 89 % all-E, 8 % 13-Z and 3 % 9-Z. The incorporation of the oily astaxanthin preparation into trout feed was performed to deliver 7 mg/kg astaxanthin in the final feed formulation for the first 3.5 weeks and 72 mg/kg for the final 3.5 weeks of the feeding trial. The resulting pigmentation of the trout fillets was determined by hue values with a colour meter and further confirmed by astaxanthin quantification. Pigmentation properties of the maize-produced natural astaxanthin incorporated to 3.5 µg/g dw in the trout fillet resembles that of chemically synthesized astaxanthin. By comparing the relative carotenoid compositions in feed, flesh and feces, a preferential uptake of zeaxanthin and 4-keto zeaxanthin over astaxanthin was observed.

Dissecting and modeling zeaxanthin- and lutein-dependent nonphotochemical quenching in Arabidopsis thaliana

PubMed Central

Leuenberger, Michelle; Morris, Jonathan M.; Chan, Arnold M.; Leonelli, Lauriebeth

2017-01-01

Photosynthetic organisms use various photoprotective mechanisms to dissipate excess photoexcitation as heat in a process called nonphotochemical quenching (NPQ). Regulation of NPQ allows for a rapid response to changes in light intensity and in vascular plants, is primarily triggered by a pH gradient across the thylakoid membrane (∆pH). The response is mediated by the PsbS protein and various xanthophylls. Time-correlated single-photon counting (TCSPC) measurements were performed on Arabidopsis thaliana to quantify the dependence of the response of NPQ to changes in light intensity on the presence and accumulation of zeaxanthin and lutein. Measurements were performed on WT and mutant plants deficient in one or both of the xanthophylls as well as a transgenic line that accumulates lutein via an engineered lutein epoxide cycle. Changes in the response of NPQ to light acclimation in WT and mutant plants were observed between two successive light acclimation cycles, suggesting that the character of the rapid and reversible response of NPQ in fully dark-acclimated plants is substantially different from in conditions plants are likely to experience caused by changes in light intensity during daylight. Mathematical models of the response of zeaxanthin- and lutein-dependent reversible NPQ were constructed that accurately describe the observed differences between the light acclimation periods. Finally, the WT response of NPQ was reconstructed from isolated components present in mutant plants with a single common scaling factor, which enabled deconvolution of the relative contributions of zeaxanthin- and lutein-dependent NPQ. PMID:28652334

Comparison of the protective effectiveness of NPQ in Arabidopsis plants deficient in PsbS protein and zeaxanthin

PubMed Central

Ware, Maxwell A.; Belgio, Erica; Ruban, Alexander V.

2015-01-01

The efficiency of protective energy dissipation by non-photochemical quenching (NPQ) in photosystem II (PSII) has been recently quantified by a new non-invasive photochemical quenching parameter, qPd. PSII yield (ФPSII) was expressed in terms of NPQ, and the extent of damage to the reaction centres (RCIIs) was calculated via qPd as: ФPSII=qPd×(F v/F m)/{1+[1–(F v/F m)]×NPQ}. Here this approach was used to determine the amount of NPQ required to protect all PSII reaction centres (pNPQ) under a gradually increasing light intensity, in the zeaxanthin-deficient (npq1) Arabidopsis mutant, compared with PsbS protein-deficient (npq4) and wild-type plants. The relationship between maximum pNPQ and tolerated light intensity for all plant genotypes followed similar trends. These results suggest that under a gradually increasing light intensity, where pNPQ is allowed to develop, it is only the amplitude of pNPQ which is the determining factor for protection. However, the use of a sudden constant high light exposure routine revealed that the presence of PsbS, not zeaxanthin, offered better protection for PSII. This was attributed to a slower development of pNPQ in plants lacking PsbS in comparison with plants that lacked zeaxanthin. This research adds further support to the value of pNPQ and qPd as effective parameters for assessing NPQ effectiveness in different types of plants. PMID:25429003

Roles of free radicals in type 1 phototherapeutic agents: aromatic amines, sulfenamides, and sulfenates.

PubMed

Lin, Tien-Sung; Rajagopalan, Raghavan; Shen, Yuefei; Park, Sungho; Poreddy, Amruta R; Asmelash, Bethel; Karwa, Amolkumar S; Taylor, John-Stephen A

2013-07-03

Detailed analyses of the electron spin resonance (ESR) spectra, cell viability, and DNA degradation studies are presented for the photolyzed Type I phototherapeutic agents: aromatic amines, sulfenamides, and sulfenates. The ESR studies provided evidence that copious free radicals can be generated from these N-H, N-S, and S-O containing compounds upon photoirradiation with UV/visible light. The analyses of spectral data allowed us to identify the free radical species. The cell viability studies showed that these agents after exposure to light exert cytotoxicity to kill cancer cells (U937 leukemia cell lines HTC11, KB, and HT29 cell lines) in a dosage- and time-dependent manner. We examined a possible pathway of cell death via DNA degradation by a plasmid cleavage assay for several compounds. The effects of photosensitization with benzophenone in the presence of oxygen were examined. The studies indicate that planar tricyclic amines and sulfenamides tend to form π-electron delocalized aminyl radicals, whereas nonplanar ones tend to yield nitroxide radicals resulting from the recombination of aminyl radicals with oxygen. The ESR studies coupled with the results of cell viability measurements and DNA degradation reveal that planar N-centered radicals can provide higher potency in cell death and allow us to provide some insights on the reaction mechanisms. We also found the formation of azatropylium cations possessing high aromaticity derived from azepines can facilitate secondary electron transfer to form toxic O2(•-) radicals, which can further exert oxidative stress and cause cell death.

Mechanisms for radiation damage in DNA. Progress report, January 1, 1980-December 31, 1980

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sevilla, M D

1980-09-01

In this project several mechanisms are proposed for radiation damage to DNA constituents and DNA, and a series of experiments detailed utilizing electron spin resonance spectrometry to test the proposed mechanisms. Under current investigation are irradiated systems of DNA constituents which may shed light on indirect effects. In addition, studies of radiation effects on lipids have been undertaken which will shed light on the only other proposed site for cell kill, the membrane. Studies completed during the past year are: (1) ..pi.. cations produced in DNA bases by attack of oxidizing radicals; (2) INDO studies of radicals produced in peptidesmore » and carboxylic acid model compounds; (3) electron reactions with carboxylic acids, ketones and aldehydes; and (4) ..gamma..-irradiation of esters and triglycerides. Progress has been made this year in a study of radicals generated in model compounds for the sugar-phosphate backbone.« less

Photo Protection of Haematococcus pluvialis Algae by Astaxanthin: Unique Properties of Astaxanthin Deduced by EPR, Optical and Electrochemical Studies

PubMed Central

Focsan, A. Ligia; Polyakov, Nikolay E.; Kispert, Lowell D.

2017-01-01

The antioxidant astaxanthin is known to accumulate in Haematococcus pluvialis algae under unfavorable environmental conditions for normal cell growth. The accumulated astaxanthin functions as a protective agent against oxidative stress damage, and tolerance to excessive reactive oxygen species (ROS) is greater in astaxanthin-rich cells. The detailed mechanisms of protection have remained elusive, however, our Electron Paramagnetic Resonance (EPR), optical and electrochemical studies on carotenoids suggest that astaxanthin’s efficiency as a protective agent could be related to its ability to form chelate complexes with metals and to be esterified, its inability to aggregate in the ester form, its high oxidation potential and the ability to form proton loss neutral radicals under high illumination in the presence of metal ions. The neutral radical species formed by deprotonation of the radical cations can be very effective quenchers of the excited states of chlorophyll under high irradiation. PMID:29065482

Anodic electrodeposition of NiTSPP from aqueous basic media.

PubMed

Pérez-Morales, Marta; Muñoz, Eulogia; Martín-Romero, María T; Camacho, Luis

2005-06-07

The oxidative electrodeposition of NiTSPP (tetrakis(4-sulfonatophenyl) Ni porphyrin) on ITO electrode from 0.1 M NaOH aqueous solution has been studied, and UV-visible and reflection FTIR spectroscopies have been used to analyze the composition of such film. By use of UV-vis spectroscopy, small absorbance of the film and an almost nulling effect on the Soret band of the porphyrin along the Ni(III)/Ni(II) redox process were observed. The reflection FTIR spectroscopy detected the presence of Ni-OH groups in the reduced film and as well the state of the porphyrin molecules as radical cation. Moreover, the porphyrin has been quantified by means of the area of the vibration bands assigned to the sulfonate groups by using as reference a Langmuir-Blodgett film containing a known surface concentration of NiTSPP. These results lead us propose the formation of a conductor salt by electrocrystallization, with stoichiometries TSPP/Ni(II)(OH)2 and TSPP/Ni(III)OOH, for its reduced and oxidized forms, respectively. In these two forms, the porphyrin rings will be present as radical cation, which may be stabilized through its dimerization or polymerization.

Observation of the Hydrogen Migration in the Cation-Induced Fragmentation of the Pyridine Molecules.

PubMed

Wasowicz, Tomasz J; Pranszke, Bogusław

2016-02-25

The ability to selectively control chemical reactions related to biology, combustion, and catalysis has recently attracted much attention. In particular, the hydrogen atom relocation may be used to manipulate bond-breaking and new bond-forming processes and may hold promise for far-reaching applications. Thus, the hydrogen atom migration preceding fragmentation of the gas-phase pyridine molecules by the H(+), H2(+), He(+), He(2+), and O(+) impact has been studied experimentally in the energy range of 5-2000 eV using collision-induced luminescence spectroscopy. Formation of the excited NH(A(3)Π) radicals was observed among the atomic and diatomic fragments. The structure of the pyridine molecule is lacking of the NH group, therefore observation of its A(3)Π → X(3)Σ(-) emission bands is an evidence of the hydrogen atom relocation prior to the cation-induced fragmentation. The NH(A(3)Π) emission yields indicate that formation of the NH radicals depends on the type of selected projectile and can be controlled by tuning its velocity. The plausible collisional mechanisms as well as fragmentation channels for NH formation in pyridine are discussed.

Two competing ionization processes in electrospray mass spectrometry of indolyl benzo[b]carbazoles: formation of M⁺• versus [M + H]⁺.

PubMed

Zhang, Xiaoping; Jiang, Kezhi; Zou, Jingfeng; Li, Zuguang

2015-02-15

Ionization in electrospray ionization mass spectrometry (ESI-MS) mainly occurs as a result of acid-base reactions or coordination with metal cations. Formation of the radical cation M(+•) in the ESI process has attracted our interest to perform further investigation. A series of indolyl benzo[b]carbazoles were investigated using a quadrupole ion trap mass spectrometer equipped with an ESI source or an atmospheric pressure chemical ionization (APCI) source in the positive-ion mode. Theoretical calculations were performed using the density functional theory (DFT) method at the B3LYP/6-31G(d) level. Both the radical ion M(+•) and the protonated molecule [M + H](+) were obtained by ESI-MS analysis of indolyl benzo[b]carbazoles, while only [M + H](+) was observed in the APCI-MS analysis. The relative intensities of M(+•) and [M + H](+) were significantly affected by several ESI operating parameters and the nature of the substituents. Formation of M(+•) and [M + H](+) was rationalized as two competing ionization processes in the ESI-MS analysis of indolyl benzo[b]carbazoles. Copyright © 2014 John Wiley & Sons, Ltd.

Gold metal liquid-like droplets.

PubMed

Smirnov, Evgeny; Scanlon, Micheál D; Momotenko, Dmitry; Vrubel, Heron; Méndez, Manuel A; Brevet, Pierre-Francois; Girault, Hubert H

2014-09-23

Simple methods to self-assemble coatings and films encompassing nanoparticles are highly desirable in many practical scenarios, yet scarcely any examples of simple, robust approaches to coat macroscopic droplets with continuous, thick (multilayer), reflective and stable liquid nanoparticle films exist. Here, we introduce a facile and rapid one-step route to form films of reflective liquid-like gold that encase macroscopic droplets, and we denote these as gold metal liquid-like droplets (MeLLDs). The present approach takes advantage of the inherent self-assembly of gold nanoparticles at liquid-liquid interfaces and the increase in rates of nanoparticle aggregate trapping at the interface during emulsification. The ease of displacement of the stabilizing citrate ligands by appropriate redox active molecules that act as a lubricating molecular glue is key. Specifically, the heterogeneous interaction of citrate stabilized aqueous gold nanoparticles with the lipophilic electron donor tetrathiafulvalene under emulsified conditions produces gold MeLLDs. This methodology relies exclusively on electrochemical reactions, i.e., the oxidation of tetrathiafulvalene to its radical cation by the gold nanoparticle, and electrostatic interactions between the radical cation and nanoparticles. The gold MeLLDs are reversibly deformable upon compression and decompression and kinetically stable for extended periods of time in excess of a year.

Photochemical Formation and Transformation of Birnessite: Effects of Cations on Micromorphology and Crystal Structure.

PubMed

Zhang, Tengfei; Liu, Lihu; Tan, WenFeng; Suib, Steven L; Qiu, Guohong; Liu, Fan

2018-05-24

As important components with excellent oxidation and adsorption activity in soils and sediments, manganese oxides affect the transportation and fate of nutrients and pollutants in natural environments. In this work, birnessite was formed by photocatalytic oxidation of Mn2+aq in the presence of nitrate under solar irradiation. The effects of concentrations and species of interlayer cations (Na+, Mg2+, and K+) on birnessite crystal structure and micromorphology were investigated. The roles of adsorbed Mn2+ and pH in the transformation of the photosynthetic birnessite were further studied. The results indicated that Mn2+aq was oxidized to birnessite by superoxide radicals (O2•-) generated from the photolysis of NO3- under UV irradiation. The particle size and thickness of birnessite decreased with increasing cation concentration. The birnessite showed a plate-like morphology in the presence of K+, while exhibited a rumpled sheet-like morphology when Na+ or Mg2+ was used. The different micromorphologies of birnessites could be ascribed to the position of cations in the interlayer. The adsorbed Mn2+ and high pH facilitated the reduction of birnessite to low-valence manganese oxides including hausmannite, feitknechtite, and manganite. This study suggests that interlayer cations and Mn2+ play essential roles in the photochemical formation and transformation of birnessite in aqueous environments.

Effects of storage and cooking on the antioxidant capacity of laying hen eggs.

PubMed

Nimalaratne, Chamila; Schieber, Andreas; Wu, Jianping

2016-03-01

The aromatic amino acids and carotenoids are the major contributors to the antioxidant properties of egg yolk. This study aimed to evaluate the effect of simulated retail storage and domestic cooking on the antioxidant activity as well as on the aromatic amino acid and carotenoid contents in ordinary table eggs, omega 3/lutein (n-3/lutein) enriched eggs, and eggs from heritage chicken breeds. The oxygen radical scavenging capacity (ORAC) was the highest in n-3/lutein enriched eggs (161.4μmolTE/gsample), while eggs from heritage white leghorns (HW) showed the lowest levels (127.6μmolTE/gsample). Six weeks of storage at refrigerated temperature did not change the ORAC values, as well as the contents of free amino acid, carotenoid, and malondialdehyde (MDA) in egg yolk. Boiling and frying however, significantly reduced the ORAC value, and the contents of free amino acid, lutein and zeaxanthin, and increased the MDA content in eggs. Our results showed that the antioxidant activity is stable during six weeks of simulated retail storage. Copyright © 2015 Elsevier Ltd. All rights reserved.

Spectroscopic characterization of C7H3(+) and C7H3˙: electronic absorption and fluorescence in 6 K neon matrices.

PubMed

Chakraborty, Arghya; Fulara, Jan; Dietsche, Rainer; Maier, John P

2014-04-21

Mass selective deposition of C7H3(+) (m/z = 87) into solid neon reveals the 1(1)A1←X(1)A1 electronic absorption system of hepta-1,2,3,4,5,6-heptahexaenylium cation B(+) [H2CCCCCCCH](+) with an origin band at 441.3 nm, 1(1)A'←X(1)A' transition of 2,4-pentadiynylium,1-ethynyl cation C(+) [HCCCHCCCCH](+) starting at 414.6 nm and the 1(1)A1←X(1)A1 one of cyclopropenylium,1,3-butadiynyl cation A(+) [HCCCCC<(CH=CH)](+) with an onset at 322.2 nm. Vibrationally resolved fluorescence was observed for isomer B(+) upon laser excitation of the absorption bands in the 1(1)A1←X(1)A1 transition. After neutralization of the cations in the matrix five absorption systems of the C7H3 neutral radicals starting at 530.3, 479.4, 482.3, 325.0 and 302.5 nm were detected. These were identified as the 1(2)A'←X(2)A' and 2(2)A'←X(2)A' electronic transitions of 2-(buta-1,3-diynyl)cycloprop-2yl-1-1ylidene E˙ [HCCCCC<(C=CH2)]˙, 1(2)B1←X(2)B1 of 1,2,3,4,5,6-heptahexaenyl B˙ [H2CCCCCCCH]˙, 3(2)B1←X(2)B1 of 3-buta-1,3-diynyl-cyclopropenyl A˙ [HCCCCC<(CH=CH)]˙ and 2(2)B1←X(2)A2 transition of 1,2-divinylidene-cyclopropanyl radical F˙ [HCC-cyc-(CCHC)-CCH]˙, respectively. The assignment is based on calculated vertical excitation energies using the CASPT2 method. Comparison of the calculated harmonic vibrational frequencies with those inferred from the spectra supports the assignment.

Charge separation in photoredox reactions. Technical progress report, May 1, 1981-May 1, 1984. [N,N,N',N'-tetramethylbenzidine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kevan, L.

1984-05-01

The structural aspects controlling charge separation in molecular photoionization reactions in organized molecular assemblies involving micelles and vesicles are being studied by optical and electron magnetic resonance techniques including the time domain technique of electron spin echo modulation (ESEM). Photoionization of N,N,N',N'-tetramethylbenzidine (TMB) to give the cation radical has been carried out in both liquid and frozen micellar and vesicular solutions. Cation-water interactions have been detected by ESEM analysis and indicate that the cation is localized asymmetrically within these organized molecular assemblies. x-Doxylstearic acid spin probes have been used to determine that the neutral TMB molecule before photoionization is alsomore » localized asymmetrically within such organized molecular assemblies. Electron spin echo detection of laser photogenerated TMB cation in liquid micellar solutions gives a direct measurement of the phase memory magnetic relaxation time which gives additional structural information. The photoionization efficiency has been related to cation-water interactions measured by ESEM. The photoionization efficiency is also dependent on surface charge and is about twofold greater in cationic micelles and vesicles compared to anionic micelles and vesicles. TMB is in a less polar environment in vesicles compared to micelles consistent with ESEM results. The preferential adsorption of metal species at micellar surfaces has been detected by ESEM. Modifications in the micelle surface have been effected by added salts and varying counterions which have been related to cation-water interactions and to the TMB photoionization efficiency. Corresponding changes in the surface and internal micellar structure have been investigated by x-doxylstearic acid spin probes and specifically deuterated surfactants. The decay kinetics of TMB cations in micelles have been interpreted in terms of a time dependent rate constant.« less

Photosensitized degradation of acetaminophen in natural organic matter solutions: The role of triplet states and oxygen.

PubMed

Li, Yanyun; Pan, Yanheng; Lian, Lushi; Yan, Shuwen; Song, Weihua; Yang, Xin

2017-02-01

The photolysis of acetaminophen, a widely used pharmaceutical, in simulated natural organic matter solutions was investigated. The triplet states of natural organic matter ( 3 NOM*) were found to play the dominant role in its photodegradation, while the contributions from hydroxyl radicals and singlet oxygen were negligible. Dissolved oxygen (DO) plays a dual role. From anaerobic to microaerobic (0.5 mg/L DO) conditions, the degradation rate of acetaminophen increased by 4-fold. That suggests the involvement of DO in reactions with the degradation intermediates. With increasing oxygen levels to saturated conditions (26 mg/L DO), the degradation rate became slower, mainly due to DO's quenching effect on 3 NOM*. Superoxide radical (O 2 - ) did not react with acetaminophen directly, but possibly quenched the intermediates to reverse the degradation process. The main photochemical pathways were shown to involve phenoxyl radical and N-radical cations, finally yielding hydroxylated derivatives, dimers and nitrosophenol. A reaction mechanism involving 3 NOM*, oxygen and O 2 - is proposed. Copyright © 2016 Elsevier Ltd. All rights reserved.

Antioxidant and Cytoprotective Activities of Enzymatic Extracts from Rhizoid of Laminaria japonica

PubMed Central

Je, Jae-Young; Park, Soo Yeon; Ahn, Chang-Bum

2017-01-01

Rhizoid of Laminaria japonica was hydrolyzed with proteases and carbohydrases to obtain antioxidant materials. Oxygen radical absorbance capacity (ORAC) of the enzymatic extracts was evaluated and the Protamex extract (PE) exhibited the highest ORAC value. PE also potently scavenged 2,2-diphenyl-1-picrylhydrazyl radical, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic) acid cation radical, and hydrogen peroxide (H2O2) and had good reducing power. PE inhibited hydroxyl radical-induced DNA scission by measuring the conversion of supercoiled pBR322 plasmid DNA to the open circular form. The cytoprotective effect of PE against H2O2-induced hepatic cell damage was also investigated. PE showed a dose-dependent cytoprotective effect in cultured hepatocytes by inhibiting intracellular reactive oxygen species scavenging activity. In addition, PE up-regulated the expression of heme oxygenase-1, which is a cytoprotective enzyme, by activating translocation of nuclear factor-erythroid 2-related factor 2. Taken together, the enzymatic extract of rhizoid of L. japonica, particularly PE, may be useful for antioxidant additives. PMID:29333384

Prediction of Radical Scavenging Activities of Anthocyanins Applying Adaptive Neuro-Fuzzy Inference System (ANFIS) with Quantum Chemical Descriptors

PubMed Central

Jhin, Changho; Hwang, Keum Taek

2014-01-01

Radical scavenging activity of anthocyanins is well known, but only a few studies have been conducted by quantum chemical approach. The adaptive neuro-fuzzy inference system (ANFIS) is an effective technique for solving problems with uncertainty. The purpose of this study was to construct and evaluate quantitative structure-activity relationship (QSAR) models for predicting radical scavenging activities of anthocyanins with good prediction efficiency. ANFIS-applied QSAR models were developed by using quantum chemical descriptors of anthocyanins calculated by semi-empirical PM6 and PM7 methods. Electron affinity (A) and electronegativity (χ) of flavylium cation, and ionization potential (I) of quinoidal base were significantly correlated with radical scavenging activities of anthocyanins. These descriptors were used as independent variables for QSAR models. ANFIS models with two triangular-shaped input fuzzy functions for each independent variable were constructed and optimized by 100 learning epochs. The constructed models using descriptors calculated by both PM6 and PM7 had good prediction efficiency with Q-square of 0.82 and 0.86, respectively. PMID:25153627

Effect of dietary α-tocopherol on the bioavailability of lutein in laying hen.

PubMed

Islam, K M S; Khalil, M; Männer, K; Raila, J; Rawel, H; Zentek, J; Schweigert, F J

2016-10-01

Lutein and its isomer zeaxanthin have gained considerable interest as possible nutritional ingredient in the prevention of age-related macular degeneration (AMD) in humans. Egg yolk is a rich source of these carotenoids. As an oxidative sensitive component, antioxidants such as α-tocopherol (T) might contribute to an improved accumulation in egg yolk. To test this, chickens were fed lutein esters (LE) with and without α-tocopherol as an antioxidant. After depletion on a wheat-soya bean-based lutein-poor diet for 21 days, laying hens (n = 42) were equally divided into three groups and fed the following diets for 21 days: control (basal diet), a LE group (40 mg LE/kg feed) and LE + T group (40 mg LE plus 100 mg T/kg feed). Eggs and blood were collected periodically. Carotenoids and α-tocopherol in yolk and blood plasma were determined by HPLC. Egg yolk was also analysed for total carotenoids using a one-step spectrophotometric method (iCheck((™)) ). Lutein, zeaxanthin, α-tocopherol and total carotenoids in egg yolk were highest after 14 days of feeding and decreased slightly afterwards. At the end of the trial, eggs of LE + T group contained higher amount of lutein (13.72), zeaxanthin (0.65), α-tocopherol (297.40) and total carotenoids (21.6) compared to the LE group (10.96, 0.55, 205.20 and 18.0 mg/kg, respectively, p < 0.05). Blood plasma values of LE + T group contain higher lutein (1.3), zeaxanthin (0.06) and tocopherol (20.1) compared to LE group (1.02, 0.04 and 14.90 mg/l, respectively, p < 0.05). In conclusion, dietary α-tocopherol enhances bioavailability of lutein reflecting higher content in egg yolk and blood plasma. Improved bioavailability might be due to increased absorption of lutein in the presence of tocopherol and/or a greater stability of lutein/zeaxanthin due to the presence of α-tocopherol as an antioxidant. Journal of Animal Physiology and Animal Nutrition © 2016 Blackwell Verlag GmbH.

Lutein is needed for efficient chlorophyll triplet quenching in the major LHCII antenna complex of higher plants and effective photoprotection in vivo under strong light

PubMed Central

Dall'Osto, Luca; Lico, Chiara; Alric, Jean; Giuliano, Giovanni; Havaux, Michel; Bassi, Roberto

2006-01-01

Background Lutein is the most abundant xanthophyll in the photosynthetic apparatus of higher plants. It binds to site L1 of all Lhc proteins, whose occupancy is indispensable for protein folding and quenching chlorophyll triplets. Thus, the lack of a visible phenotype in mutants lacking lutein has been surprising. Results We have re-assessed the lut2.1 phenotypes through biochemical and spectroscopic methods. Lhc proteins from the lut2.1 mutant compensate the lack of lutein by binding violaxanthin in sites L1 and L2. This substitution reduces the capacity for regulatory mechanisms such as NPQ, reduces antenna size, induces the compensatory synthesis of Antheraxanthin + Zeaxanthin, and prevents the trimerization of LHCII complexes. In vitro reconstitution shows that the lack of lutein per se is sufficient to prevent trimerization. lut2.1 showed a reduced capacity for state I – state II transitions, a selective degradation of Lhcb1 and 2, and a higher level of photodamage in high light and/or low temperature, suggesting that violaxanthin cannot fully restore chlorophyll triplet quenching. In vitro photobleaching experiments and time-resolved spectroscopy of carotenoid triplet formation confirmed this hypothesis. The npq1lut2.1 double mutant, lacking both zeaxanthin and lutein, is highly susceptible to light stress. Conclusion Lutein has the specific property of quenching harmful 3Chl* by binding at site L1 of the major LHCII complex and of other Lhc proteins of plants, thus preventing ROS formation. Substitution of lutein by violaxanthin decreases the efficiency of 3Chl* quenching and causes higher ROS yield. The phenotype of lut2.1 mutant in low light is weak only because rescuing mechanisms of photoprotection, namely zeaxanthin synthesis, compensate for the ROS production. We conclude that zeaxanthin is effective in photoprotection of plants lacking lutein due to the multiple effects of zeaxanthin in photoprotection, including ROS scavenging and direct quenching of Chl fluorescence by binding to the L2 allosteric site of Lhc proteins. PMID:17192177

Wheat bran particle size influence on phytochemical extractability and antioxidant properties.

PubMed

Brewer, Lauren Renee; Kubola, Jittawan; Siriamornpun, Sirithon; Herald, Thomas J; Shi, Yong-Cheng

2014-01-01

It is unknown if particle size plays a role in extracting health promoting compounds in wheat bran because the extraction of antioxidant and phenolic compounds with particle size reduction has not been well documented. In this study, unmilled whole bran (coarse treatment) was compared to whole bran milled to medium and fine treatments from the same wheat bran. Antioxidant properties (capacity, ability, power), carotenoids and phenolic compounds (phenolic acids, flavonoids, anthocyanins) were measured and compared. The ability of whole bran fractions of differing particle size distributions to inhibit free radicals was assessed using four in vitro models, namely, diphenylpicrylhydrazyl radical-scavenging activity, ferric reducing/antioxidant power (FRAP) assay, oxygen radical absorbance capacity (ORAC), and total antioxidant capacity. Significant differences in phytochemical concentrations and antioxidant properties were observed between whole bran fractions of reduced particle size distribution for some assays. The coarse treatment exhibited significantly higher antioxidant properties compared to the fine treatment; except for the ORAC value, in which coarse was significantly lower. For soluble and bound extractions, the coarse treatment was comparatively higher in total antioxidant capacity (426.72 mg ascorbic acid eq./g) and FRAP value (53.04 μmol FeSO4/g) than bran milled to the finer treatment (314.55 ascorbic acid eq./g and 40.84 μmol FeSO4/g, respectively). Likewise, the fine treatment was higher in phenolic acid (7.36 mg FAE/g), flavonoid (206.74 μg catechin/g), anthocyanin (63.0 μg/g), and carotenoid contents (beta carotene, 14.25 μg/100 g; zeaxanthin, 35.21 μg/100 g; lutein 174.59 μg/100 g) as compared to the coarse treatment. An increase of surface area to mass increased the ORAC value by over 80%. With reduction in particle size, there was a significant increase in extracted anthocyanins, carotenoids and ORAC value. Particle size does effect the extraction of phytochemicals. Copyright © 2013 Elsevier Ltd. All rights reserved.

Dissecting and modeling zeaxanthin- and lutein-dependent nonphotochemical quenching in Arabidopsis thaliana

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leuenberger, Michelle; Morris, Jonathan M.; Chan, Arnold M.

It is known that photosynthetic organisms use various photoprotective mechanisms to dissipate excess photoexcitation as heat in a process called nonphotochemical quenching (NPQ). Regulation of NPQ allows for a rapid response to changes in light intensity and in vascular plants, is primarily triggered by a pH gradient across the thylakoid membrane (ΔpH). The response is mediated by the PsbS protein and various xanthophylls. Time-correlated single-photon counting (TCSPC) measurements were performed on Arabidopsis thaliana to quantify the dependence of the response of NPQ to changes in light intensity on the presence and accumulation of zeaxanthin and lutein. Measurements were performed onmore » WT and mutant plants deficient in one or both of the xanthophylls as well as a transgenic line that accumulates lutein via an engineered lutein epoxide cycle. Changes in the response of NPQ to light acclimation in WT and mutant plants were observed between two successive light acclimation cycles, suggesting that the character of the rapid and reversible response of NPQ in fully dark-acclimated plants is substantially different from in conditions plants are likely to experience caused by changes in light intensity during daylight. Mathematical models of the response of zeaxanthin- and lutein-dependent reversible NPQ were constructed that accurately describe the observed differences between the light acclimation periods. Finally, the WT response of NPQ was reconstructed from isolated components present in mutant plants with a single common scaling factor, which enabled deconvolution of the relative contributions of zeaxanthin- and lutein-dependent NPQ.« less

Dissecting and modeling zeaxanthin- and lutein-dependent nonphotochemical quenching in Arabidopsis thaliana

DOE PAGES

Leuenberger, Michelle; Morris, Jonathan M.; Chan, Arnold M.; ...

2017-06-26

It is known that photosynthetic organisms use various photoprotective mechanisms to dissipate excess photoexcitation as heat in a process called nonphotochemical quenching (NPQ). Regulation of NPQ allows for a rapid response to changes in light intensity and in vascular plants, is primarily triggered by a pH gradient across the thylakoid membrane (ΔpH). The response is mediated by the PsbS protein and various xanthophylls. Time-correlated single-photon counting (TCSPC) measurements were performed on Arabidopsis thaliana to quantify the dependence of the response of NPQ to changes in light intensity on the presence and accumulation of zeaxanthin and lutein. Measurements were performed onmore » WT and mutant plants deficient in one or both of the xanthophylls as well as a transgenic line that accumulates lutein via an engineered lutein epoxide cycle. Changes in the response of NPQ to light acclimation in WT and mutant plants were observed between two successive light acclimation cycles, suggesting that the character of the rapid and reversible response of NPQ in fully dark-acclimated plants is substantially different from in conditions plants are likely to experience caused by changes in light intensity during daylight. Mathematical models of the response of zeaxanthin- and lutein-dependent reversible NPQ were constructed that accurately describe the observed differences between the light acclimation periods. Finally, the WT response of NPQ was reconstructed from isolated components present in mutant plants with a single common scaling factor, which enabled deconvolution of the relative contributions of zeaxanthin- and lutein-dependent NPQ.« less

Can Xanthophyll-Membrane Interactions Explain Their Selective Presence in the Retina and Brain?

PubMed Central

Widomska, Justyna; Zareba, Mariusz; Subczynski, Witold Karol

2016-01-01

Epidemiological studies demonstrate that a high dietary intake of carotenoids may offer protection against age-related macular degeneration, cancer and cardiovascular and neurodegenerative diseases. Humans cannot synthesize carotenoids and depend on their dietary intake. Major carotenoids that have been found in human plasma can be divided into two groups, carotenes (nonpolar molecules, such as β-carotene, α-carotene or lycopene) and xanthophylls (polar carotenoids that include an oxygen atom in their structure, such as lutein, zeaxanthin and β-cryptoxanthin). Only two dietary carotenoids, namely lutein and zeaxanthin (macular xanthophylls), are selectively accumulated in the human retina. A third carotenoid, meso-zeaxanthin, is formed directly in the human retina from lutein. Additionally, xanthophylls account for about 70% of total carotenoids in all brain regions. Some specific properties of these polar carotenoids must explain why they, among other available carotenoids, were selected during evolution to protect the retina and brain. It is also likely that the selective uptake and deposition of macular xanthophylls in the retina and brain are enhanced by specific xanthophyll-binding proteins. We hypothesize that the high membrane solubility and preferential transmembrane orientation of macular xanthophylls distinguish them from other dietary carotenoids, enhance their chemical and physical stability in retina and brain membranes and maximize their protective action in these organs. Most importantly, xanthophylls are selectively concentrated in the most vulnerable regions of lipid bilayer membranes enriched in polyunsaturated lipids. This localization is ideal if macular xanthophylls are to act as lipid-soluble antioxidants, which is the most accepted mechanism through which lutein and zeaxanthin protect neural tissue against degenerative diseases. PMID:27030822

Analysis of Lutein, Zeaxanthin, and Meso-Zeaxanthin in the Organs of Carotenoid-Supplemented Chickens.

PubMed

Phelan, David; Prado-Cabrero, Alfonso; Nolan, John M

2018-02-03

The macular carotenoids (i.e., lutein (L), zeaxanthin (Z) and meso -zeaxanthin (MZ)) exhibit anti-inflammatory, antioxidant and optical properties that are believed to support human health and function. Studying the accumulation and distribution of these nutrients in tissues and organs, in addition to the eye, is an important step in understanding how these nutrients might support global human function and health (e.g., heart and brain). Chicken is an appropriate animal model with which to study the accumulation of these carotenoids in organs, as the relevant transport molecules and carotenoid binding proteins for L, Z and MZ are present in both humans and chickens. In this experiment, a sample of 3 chickens that were supplemented with L and MZ diacetate (active group) and a sample of 3 chickens that received a standard diet (control group) were analysed. Both groups were analysed for L, Z and MZ concentrations in the brain, eyes, heart, lung, duodenum/pancreas, jejunum/ileum, kidney and breast tissue. L, Z and MZ were identified in all the organs/tissues analysed from the active group. L and Z were identified in all of the organs/tissues analysed from the control group; while, MZ was identified in the eyes of these animals only. The discovery that MZ is accumulated in the tissues and organs of chickens supplemented with this carotenoid is important, given that it is known that a combination of L, Z and MZ exhibits superior antioxidant capacity when compared to any of these carotenoids in isolation.

Comparison of the protective effectiveness of NPQ in Arabidopsis plants deficient in PsbS protein and zeaxanthin.

PubMed

Ware, Maxwell A; Belgio, Erica; Ruban, Alexander V

2015-03-01

The efficiency of protective energy dissipation by non-photochemical quenching (NPQ) in photosystem II (PSII) has been recently quantified by a new non-invasive photochemical quenching parameter, qPd. PSII yield (ФPSII) was expressed in terms of NPQ, and the extent of damage to the reaction centres (RCIIs) was calculated via qPd as: ФPSII=qPd×(F v/F m)/{1+[1-(F v/F m)]×NPQ}. Here this approach was used to determine the amount of NPQ required to protect all PSII reaction centres (pNPQ) under a gradually increasing light intensity, in the zeaxanthin-deficient (npq1) Arabidopsis mutant, compared with PsbS protein-deficient (npq4) and wild-type plants. The relationship between maximum pNPQ and tolerated light intensity for all plant genotypes followed similar trends. These results suggest that under a gradually increasing light intensity, where pNPQ is allowed to develop, it is only the amplitude of pNPQ which is the determining factor for protection. However, the use of a sudden constant high light exposure routine revealed that the presence of PsbS, not zeaxanthin, offered better protection for PSII. This was attributed to a slower development of pNPQ in plants lacking PsbS in comparison with plants that lacked zeaxanthin. This research adds further support to the value of pNPQ and qPd as effective parameters for assessing NPQ effectiveness in different types of plants. © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology.

Computationally Designed Oligomers for High Contrast Black Electrochromic Polymers

DTIC Science & Technology

2017-05-05

SUBJECT TERMS electrochromics, DFf, TDDFT, organic electronics , oligomer, organic polymers 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER... electron -withdrawing behaviors. Another finding was that the same dication was produced regardless of the color or peak morphology of the neutral 5...radical cation states present in the chromophore upon oxidation. The two-ring electron rich dioxythiophene portions of the chromophore (EAc) and/or the

Hemi bonds and noncovalent interactions in the cational systems (XH2P: SHY)+

NASA Astrophysics Data System (ADS)

Li, Xiang; Li, An Yong

2016-08-01

Quantum chemistry ab initio MP2 and CCSD calculations were performed to investigate the P⋯S hemi bonds and noncovalent interactions in the radical cational systems (H3P:SH2)+, (FH2P:SH2)+ and (H3P:SHF)+. The hydride dimer (H3P:SH2)+ has a P⋯S hemi bonding structure and a H-bonding structure, (FH2P:SH2)+ has two hemi bonding structures and a proton-transferred H-bonding structure, (H3P:SHF)+ has two hemi bonding structures and three noncovalent structures. It is remarkable that these hemi bonds also have characters of pnicogen and chalcogen bonds. The binding energy, stability and bonding nature of the hemi bonds were presented.

Study of the effects of hydroxyapatite nanocrystal codoping by pulsed electron paramagnetic resonance methods

NASA Astrophysics Data System (ADS)

Gafurov, M. R.; Biktagirov, T. B.; Mamin, G. V.; Shurtakova, D. V.; Klimashina, E. S.; Putlyaev, V. I.; Orlinskii, S. B.

2016-03-01

The effect of codoping of hydroxyapatite (HAP) nanocrystals with average sizes of 35 ± 15 nm during "wet" synthesis by CO 3 2- carbonate anions and Mn2+ cations on relaxation characteristics (for the times of electron spin-spin relaxation) of the NO 3 2- nitrate radical anion has been studied. By the example of HAP, it has been demonstrated that the electron paramagnetic resonance (EPR) is an efficient method for studying anion-cation (co)doping of nanoscale particles. It has been shown experimentally and by quantummechanical calculations that simultaneous introduction of several ions can be energetically more favorable than their separate inclusion. Possible codoping models have been proposed, and their energy parameters have been calculated.

Direct observation of the oxidation of DNA bases by phosphate radicals formed under radiation: a model of the backbone-to-base hole transfer.

PubMed

Ma, Jun; Marignier, Jean-Louis; Pernot, Pascal; Houée-Levin, Chantal; Kumar, Anil; Sevilla, Michael D; Adhikary, Amitava; Mostafavi, Mehran

2018-05-30

In irradiated DNA, by the base-to-base and backbone-to-base hole transfer processes, the hole (i.e., the unpaired spin) localizes on the most electropositive base, guanine. Phosphate radicals formed via ionization events in the DNA-backbone must play an important role in the backbone-to-base hole transfer process. However, earlier studies on irradiated hydrated DNA, on irradiated DNA-models in frozen aqueous solution and in neat dimethyl phosphate showed the formation of carbon-centered radicals and not phosphate radicals. Therefore, to model the backbone-to-base hole transfer process, we report picosecond pulse radiolysis studies of the reactions between H2PO4˙ with the DNA bases - G, A, T, and C in 6 M H3PO4 at 22 °C. The time-resolved observations show that in 6 M H3PO4, H2PO4˙ causes the one-electron oxidation of adenine, guanine and thymine, by forming the cation radicals via a single electron transfer (SET) process; however, the rate constant of the reaction of H2PO4˙ with cytosine is too low (<107 L mol-1 s-1) to be measured. The rates of these reactions are influenced by the protonation states and the reorganization energies of the base radicals and of the phosphate radical in 6 M H3PO4.

Conformation-Specific Infrared and Ultraviolet Spectroscopy of α-METHYLBENZYL Radical: Probing the State-Dependent Effects of Methyl Rocking against a Radical Site

NASA Astrophysics Data System (ADS)

Kidwell, Nathanael M.; Mehta, Deepali N.; Zwier, Timothy S.; Reilly, Neil J.; Kokkin, Damian L.; McCarthy, Michael C.

2012-06-01

Combustion processes involve a myriad of complex reaction pathways which connect smaller precursors to larger polyaromatic hydrocarbons, many of which are still unknown. In particular, benzyl-type radicals play an important role in combustible fuels due to their intrinsic resonance stabilization and consequent increase in relative concentration. Here, we present a study of the vibronic spectroscopy of α-Methylbenzyl radical (α-MeBz), in which the orientation of the methyl group adjacent to the radical site responds to the electronic interaction extending from the conjugated π-system. Probing the isolated radical, produced in an electrical discharge under jet-cooled conditions, the two-color resonant two-photon ionization, fluorescence excitation, and dispersed fluorescence spectra were obtained in order to determine the ground and excited state barriers to internal rotation and the angular change associated with electronic excitation. Resonant ion-dip infrared spectroscopy (RIDIRS) has also been implemented to elucidate the infrared signatures in the alkyl and aromatic CH stretch regions in order to probe in a complementary way the state-dependent conformational preferences of α-MeBz. We will show that the D0- and D1-RIDIR spectra report sensitively on the strong coupling between the CH stretch vibrations and the C_α-C_β torsional geometry. Furthermore, photoionization efficiency scans were carried out to reveal the adiabatic ionization threshold of α-MeBz and the quantized levels present in the radical cation state.

On the radiation stability of crown ethers in ionic liquids.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shkrob, I.; Marin, T.; Dietz, M.

2011-04-14

Crown ethers (CEs) are macrocyclic ionophores used for the separation of strontium-90 from acidic nuclear waste streams. Room temperature ionic liquids (ILs) are presently being considered as replacements for traditional molecular solvents employed in such separations. It is desirable that the extraction efficacy obtained with such solvents should not deteriorate in the strong radiation fields generated by decaying radionuclides. This deterioration will depend on the extent of radiation damage to both the IL solvent and the CE solute. While radiation damage to ILs has been extensively studied, the issue of the radiation stability of crown ethers, particularly in an ILmore » matrix, has not been adequately addressed. With this in mind, we have employed electron paramagnetic resonance (EPR) spectroscopy to study the formation of CE-related radicals in the radiolysis of selected CEs in ILs incorporating aromatic (imidazolium and pyridinium) cations. The crown ethers have been found to yield primarily hydrogen loss radicals, H atoms, and the formyl radical. In the low-dose regime, the relative yield of these radicals increases linearly with the mole fraction of the solute, suggesting negligible transfer of the excitation energy from the solvent to the solute; that is, the solvent has a 'radioprotective' effect. The damage to the CE in the loading region of practical interest is relatively low. Under such conditions, the main chemical pathway leading to decreased extraction performance is protonation of the macrocycle. At high radiation doses, sufficient to increase the acidity of the IL solvent significantly, such proton complexes compete with the solvent cations as electron traps. In this regime, the CEs will rapidly degrade as the result of H abstraction from the CE ring by the released H atoms. Thus, the radiation dose to which a CE/IL system is exposed must be maintained at a level sufficiently low to avoid this regime.« less

Theoretical study of hyperfine coupling constants and electron spin g factors for X2Σ diatomics from Groups 1 and 2

NASA Astrophysics Data System (ADS)

Bruna, Pablo J.; Grein, Friedrich

The ESR parameters of the cations Be 2 + , Mg 2 + , Ca 2 + , BeMg + , BeCa + , MgCa + and the mixed radicals ZBe, ZMg, ZCa (Z = Li, Na, K), all having a X 2 Σu + (1 σg 2 1 σu )/X 2 Sigma + (1 σ2 2 σ) ground state, have been studied theoretically. The A iso and A dip constants have been calculated with UHF, CISD, MP2, B3LYP, PW91PW91 wavefunctions, and 6-311+G(2df) basis sets. The electron spin g factors (magnetic moment μs) have been evaluated from correlated (MRDCI) wavefunctions, using a Hamiltonian based on Breit-Pauli theory with perturbation expansions up to second order, and 6-311+ G(2d) basis sets. As expected for s-rich radicals, the hyperfine spectra are governed by the A iso terms. Both Δg|| and Δg Υ̂values are negative, but Δg|| lies close to zero. For Δg Υ̂, the coupling with 1 2 Π(u) dominates the sum-over-states expansions. Although the singly occupied MOs (SOMO) are mostly of s character, the | Δg Υ̂| are relatively large, up to 5200 ppm for cationic, and up to 7850 ppm for neutral radicals. These large values are caused by low excitation energies and high magnetic transition moments, the latter due to the fact that the σ*( s - s ) SOMO has the same nodal properties as a p σorbital. Of the radicals considered here, an ESR spectrum is available only for Mg2+. Our theoretical A iso of-287 MHz reproduces well the matrix result (-291 MHz). Calculated values of-10 ppm for Deltag|| and of-1280 ppm for Deltag Υ̂give an average < Δg> =-860 ppm that lies within the experimental range of-600( ±300) ppm in Ne, and of-1300( ±500) ppm in Ar matrices.

Exceptional Morphology-Preserving Evolution of Formamidinium Lead Triiodide Perovskite Thin Films via Organic-Cation Displacement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Yuanyuan; Yang, Mengjin; Pang, Shuping

Here we demonstrate a radically different chemical route for the creation of HC(NH2)2PbI3 (FAPbI3) perovskite thin films. This approach entails a simple exposure of as-synthesized CH3NH3PbI3 (MAPbI3) perovskite thin films to HC(=NH)NH2 (formamidine or FA) gas at 150 degrees C, which leads to rapid displacement of the MA+ cations by FA+ cations in the perovskite structure. The resultant FAPbI3 perovskite thin films preserve the microstructural morphology of the original MAPbI3 thin films exceptionally well. Importantly, the myriad processing innovations that have led to the creation of high-quality MAPbI3 perovskite thin films are directly adaptable to FAPbI3 through this simple, rapidmore » chemical-conversion route. Accordingly, we show that efficiencies of perovskite solar cells fabricated with FAPbI3 thin films created using this route can reach -18%.« less

B-vitamins, carotenoids and α-/γ-tocopherol in raw and roasted nuts.

PubMed

Stuetz, Wolfgang; Schlörmann, Wiebke; Glei, Michael

2017-04-15

The concentrations of B-vitamins, carotenoids and tocopherols in nuts may differ between species and might be influenced by roasting. Thiamine, riboflavin, pyridoxine, lutein, zeaxanthin, β-carotene and α-/γ-tocopherol were determined in different varieties of raw and roasted nuts using HPLC (fluorescence/UV-vis detection). The analysis revealed remarkable concentrations of thiamine and pyridoxine in pistachios (57%, 79% of the recommended daily intake/100g (RDI), respectively) and riboflavin in almonds (119% of the RDI). Pistachios were rich in lutein/zeaxanthin and contained highest β-carotene levels among nuts. Almonds and hazelnuts were abundant in α-tocopherol (>4-fold the RDI for tocopherol equivalents) while pistachios and walnuts were rich in γ-tocopherol. Roasting had a diminishing effect on thiamine, carotenoids and tocopherols especially in almonds and walnuts. Nuts could make a valuable contribution to a healthy diet in regard to B-vitamins, lutein/zeaxanthin and tocopherols. A reduction in micronutrient content by roasting is reliant on the nut variety and specific micronutrient. Copyright © 2016 Elsevier Ltd. All rights reserved.

Scavenging of free-radical metabolites of aniline xenobiotics and drugs by amino acid derivatives: toxicological implications of radical-transfer reactions.

PubMed

Michail, Karim; Baghdasarian, Argishti; Narwaley, Malyaj; Aljuhani, Naif; Siraki, Arno G

2013-12-16

We investigated a novel scavenging mechanism of arylamine free radicals by poly- and monoaminocarboxylates. Free radicals of arylamine xenobiotics and drugs did not react with oxygen in peroxidase-catalyzed reactions; however, they showed marked oxygen uptake in the presence of an aminocarboxylate. These free-radical intermediates were identified using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and electron paramagnetic resonance (EPR) spectrometry. Diethylenetriaminepentaacetic acid (DTPA), a polyaminocarboxylate, caused a concentration-dependent attenuation of N-centered radicals produced by the peroxidative metabolism of arylamines with the subsequent formation of secondary aliphatic carbon-centered radicals stemming from the cosubstrate molecule. Analogously, N,N-dimethylglycine (DMG) and N-methyliminodiacetate (MIDA), but not iminodiacetic acid (IDA), demonstrated a similar scavenging effect of arylamine-derived free radicals in a horseradish peroxidase/H2O2 system. Using human promyelocytic leukemia (HL-60) cell lysate as a model of human neutrophils, DTPA, MIDA, and DMG readily reduced anilinium cation radicals derived from the arylamines and gave rise to the corresponding carbon radicals. The rate of peroxidase-triggered polymerization of aniline was studied as a measure of nitrogen-radical scavenging. Although, IDA had no effect on the rate of aniline polymerization, this was almost nullified in the presence of DTPA and MIDA at half of the molar concentration of the aniline substrate, whereas a 20 molar excess of DMPO caused only a partial inhibition. Furthermore, the yield of formaldehyde, a specific reaction endproduct of the oxidation of aminocarboxylates by aniline free-radical metabolites, was quantitatively determined. Azobenzene, a specific reaction product of peroxidase-catalyzed free-radical dimerization of aniline, was fully abrogated in the presence of DTPA, as confirmed by GC/MS. Under aerobic conditions, a radical-transfer reaction is proposed between aminocarboxylates and arylamine free radicals via the carboxylic group-linked tertiary nitrogen of the deprotonated amino acid derivatives. These findings may have significant implications for the biological fate of arylamine xenobiotic and drug free-radical metabolites.

In vitro and in vivo antioxidant potentials of an ethanolic extract of Ganoderma lucidum in rat mammary carcinogenesis.

PubMed

Deepalakshmi, K; Mirunalini, S; Krishnaveni, M; Arulmozhi, V

2013-11-01

Considering the importance of diet in the prevention of cellular damage caused by reactive oxygen species which has been implicated for several diseases, this present study was undertaken to evaluate the in vitro and in vivo antioxidant potential of the ethanolic extract of the fruiting bodies of Ganoderma lucidum on 7, 12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinogenesis in Sprague Dawley rats. Ganoderma lucidum extract was tested for in vitro antioxidant and radical scavenging assays, such as (ABTS(+)) radical cation decolorization assay, DPPH radical scavenging, hydroxyl radical, and superoxide radical scavenging assays. The in vivo antioxidant potentials were analyzed by SOD, CAT, and GPx in plasma, mammary, and liver tissues. In all the in vitro antioxidant and radical scavenging assays the extract exhibited good scavenging activity. In vivo enzymatic antioxidant levels, such as SOD, CAT, and GPx were decreased in DMBA-induced animals. Moreover, pretreatment with G. lucidum (500 mg · kg(-1) bw) to DMBA-induced animals significantly (P < 0.05) increased the levels of SOD, CAT, and GPx in plasma, mammary, and liver tissues compared to DMBA induced animals. From these findings, it is suggested that G. lucidum extract could be considered as a potential source of natural antioxidants and can be used as an effective chemopreventive agent against mammary cancer. Copyright © 2013 China Pharmaceutical University. Published by Elsevier B.V. All rights reserved.

Probing the Compound I-like reactivity of a bare high-valent oxo iron porphyrin complex: the oxidation of tertiary amines.

PubMed

Chiavarino, Barbara; Cipollini, Romano; Crestoni, Maria Elisa; Fornarini, Simonetta; Lanucara, Francesco; Lapi, Andrea

2008-03-12

The mechanisms of oxidative N-dealkylation of amines by heme enzymes including peroxidases and cytochromes P450 and by functional models for the active Compound I species have long been studied. A debated issue has concerned in particular the character of the primary step initiating the oxidation sequence, either a hydrogen atom transfer (HAT) or an electron transfer (ET) event, facing problems such as the possible contribution of multiple oxidants and complex environmental effects. In the present study, an oxo iron(IV) porphyrin radical cation intermediate 1, [(TPFPP)*+ Fe(IV)=O]+ (TPFPP = meso-tetrakis (pentafluorophenyl)porphinato dianion), functional model of Compound I, has been produced as a bare species. The gas-phase reaction with amines (A) studied by ESI-FT-ICR mass spectrometry has revealed for the first time the elementary steps and the ionic intermediates involved in the oxidative activation. Ionic products are formed involving ET (A*+, the amine radical cation), formal hydride transfer (HT) from the amine ([A(-H)]+, an iminium ion), and oxygen atom transfer (OAT) to the amine (A(O), likely a carbinolamine product), whereas an ionic product involving a net initial HAT event is never observed. The reaction appears to be initiated by an ET event for the majority of the tested amines which included tertiary aliphatic and aromatic amines as well as a cyclic and a secondary amine. For a series of N,N-dimethylanilines the reaction efficiency for the ET activated pathways was found to correlate with the ionization energy of the amine. A stepwise pathway accounts for the C-H bond activation resulting in the formal HT product, namely a primary ET process forming A*+, which is deprotonated at the alpha-C-H bond forming an N-methyl-N-arylaminomethyl radical, A(-H)*, readily oxidized to the iminium ion, [A(-H)]+. The kinetic isotope effect (KIE) for proton transfer (PT) increases as the acidity of the amine radical cation increases and the PT reaction to the base, the ferryl group of (TPFPP)Fe(IV)=O, approaches thermoneutrality. The ET reaction displayed by 1 with gaseous N,N-dimethylaniline finds a counterpart in the ET reactivity of FeO+, reportedly a potent oxidant in the gas phase, and with the barrierless ET process for a model (P)*+ Fe(IV)=O species (where P is the porphine dianion) as found by theoretical calculations. Finally, the remarkable OAT reactivity of 1 with C6F5N(CH3)2 may hint to a mechanism along a route of diverse spin multiplicity.

An exploratory study on the peroxyl-radical-scavenging activity of 2,6-dimethyl-5-hepten-2-ol and its heterocyclic analogues

NASA Astrophysics Data System (ADS)

Stobiecka, Agnieszka; Sikora, Magdalena; Bonikowski, Radosław; Kula, Józef

2016-03-01

The structural properties and radical scavenging activity of 2,6-dimethyl-5-hepten-2-ol (1) and its new heterocyclic analogues, i.e. 2-methyl-4-(5-methylfuran-2-yl)-butan-2-ol (2) and 2-methyl-4-(5-methylthiophen-2-yl)-butan-2-ol (3) and have been studied by using the experimental and theoretical methods for the first time. Activity of title compounds against the peroxyl radical was determined by using standard fluorimetric test, i.e. the Oxygen Radical Absorbance Capacity assay (ORACFL). Furthermore, the electron-donating ability of odorants has been evaluated by using colorimetric ABTS assay. According to the experimental results obtained from the ORACFL test 2,6-dimethyl-5-hepten-2-ol was characterized by the highest activity in comparison with the novel counterparts. Nevertheless, all investigated compounds exhibited pronounced anti-peroxyl radical activity comparable to that exerted by the one of the most prominent antioxidant among the monoterpene alcohols, i.e. by linalool. On the other hand, the title compounds exerted relatively low capacity to quench the radical cation of ABTS. Theoretical calculations based on the Density Functional Theory (DFT) method with the hybrid functional B3LYP were carried out in order to investigate selected structural and electronic properties including the geometrical parameters as well as the energy of frontier molecular orbitals of parent molecules and the resulting radicals. Furthermore, the possible mechanism of peroxyl-radical-scavenging has been determined by using the thermodynamic descriptors such as the bond dissociation enthalpies (BDEs) and ionization potentials (IPs). These theoretical data pointed out the relevance of HAT mechanism in the peroxyl-radical-scavenging exhibited by 2,6-dimethyl-5-hepten-2-ol and its new heterocyclic analogues in polar and non-polar medium.

Antioxidant activity of Caesalpinia digyna root.

PubMed

Srinivasan, R; Chandrasekar, M J N; Nanjan, M J; Suresh, B

2007-09-05

The antioxidant properties of three successive extracts of Caesalpinia digyna Rottler root and the isolated compound, bergenin, were tested using standard in vitro and in vivo models. The amount of the total phenolic compounds present was also determined. The successive methanol extract of Caesalpinia digyna root (CDM) exhibited strong scavenging effect on 2,2-diphenyl-2-picryl hydrazyl (DPPH) free radical, 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulphonic acid) diammonium salt (ABTS) radical cation, hydrogen peroxide, nitric oxide, hydroxyl radical and inhibition of lipid peroxidation. The free radical scavenging effect of CDM was comparable with that of reference antioxidants. The CDM having the highest content of phenolic compounds and strong free radical scavenging effect when administered orally to male albino rats at 100, 200 and 400mg/kg body weight for 7 days, prior to carbontetrachloride (CCl(4)) treatment, caused a significant increase in the levels of catalase (CAT) and superoxide dismutase (SOD) and significant decrease in the levels of lipidperoxidation (LPO) in serum, liver and kidney in a dose dependent manner, when compared to CCl(4) treated control. These results clearly indicate the strong antioxidant property of Caesalpinia digyna root. The study provides a proof for the ethnomedical claims and reported biological activities. The plant has, therefore, very good therapeutic potential.

Selective Gas Capture Ability of Gas-Adsorbent-Incorporated Cellulose Nanofiber Films.

PubMed

Shah, Kinjal J; Imae, Toyoko

2016-05-09

The 2,2,6,6-tetramethylpiperidine-1-oxyl radical-oxidized cellulose nanofibers (TOCNF) were hybridized with cation and anion-exchange organoclays, where poly(amido amine) dendrimers were loaded to enhance the functionality of gas adsorption, since dendrimers have the high adsorbability and the enough selectivity on the gas adsorption. The thin films were prepared from the organoclay-TOCNF hybrids and supplied to the gas adsorption. The adsorption of CO2 and NH3 gases increased with an increasing amount of organoclays in TOCNF films, but the behavior of the increase depended on gases, clays, and dendrimers. The hydrotalcite organoclay-TOCNF films displayed the highest adsorption of both gases, but the desorption of CO2 gas from hydrotalcite organoclay-TOCNF films was drastically high in comparison with the other systems. While the CO2 gas is adsorbed and remained on cationic dendrimer sites in cation-exchange organoclay-TOCNF films, the CO2 gas is adsorbed on cationic clay sites in anion exchange organoclay-TOCNF films, and it is easily desorbed from the films. The NH3 adsorption is inversive to the CO2 adsorption. Then the CO2 molecules adsorbed on the cationic dendrimers and the NH3 molecules adsorbed on the anionic dendrimers are preferably captured in these adsorbents. The present research incorporated dendrimers will be contributing to the development of gas-specialized adsorbents, which are selectively storable only in particular gases.

[Effect of calcium cations on acid-base properties and free radical oxidation of dopamine and pyrocatechol].

PubMed

Lebedev, A V; Ivanova, M V; Timoshin, A A; Ruuge, E K

2008-01-01

Ca2+-induced increase in the rate of pyrocatechol and dopamine oxidation by dioxygen and Ca2+-dependent acid-base properties of the catechols were studied by potentiometric titration, UV/Vis-spectrophotometry, EPR-spectroscopy, and by measurement of oxygen consumption. The effect of Ca2+ on the chain reactions of oxidation can be explained by additional deprotonation (decrease in pKai) of the catechols that accelerates one electron transport to dioxygen and formation of calcium semiquinonate, undergoing further oxidation. The described Ca2+-dependent redox-conversion of ortho-phenols proposes that an additional function of calcium in the cell can be its involvement in free radical oxidoreductive reactions at pH > pKai.

Effects of protonation and metal coordination on intramolecular charge transfer of tetrathiafulvalene compound.

PubMed

Zhu, Qin-Yu; Liu, Yu; Lu, Wen; Zhang, Yong; Bian, Guo-Qing; Niu, Gai-Yan; Dai, Jie

2007-11-26

A protonated bifunctional pyridine-based tetrathiafulvalene (TTF) derivative (DMT-TTF-pyH)NO3 and a copper(II) complex Cu(acac)2(DMT-TTF-py)2 have been obtained and studied. Electronic spectra of the protonated compound show a large ICT (intramolecular charge transfer) band shift (Deltalambda=136 nm) compared with that of the neutral compound. Cyclic voltammetry also shows a large shift of the redox potentials (DeltaE1/2(1)=77 mV). Theoretical calculation suggests that the pyridium substituent is a strong pi-electron acceptor. Crystal structures of the protonated compound and the metal complex have been obtained. The dihedral angle between least-squares planes of the pyridyl group and the dithiole ring might reflect the intensity of the ICT effect between the TTF moiety and the pyridyl group. It is also noteworthy that the TTF moiety could be oxidized to TTF2+ dication by Fe(ClO4)(3).6H2O when forming a metal complex, while the protonated TTF derivative can only be oxidized to the TTF*+ radical cation by Fe(ClO4)(3).6H2O even with an excess amount of the Fe(III) salt, which can be used to control the oxidation process to obtain neutral TTF, TTF*+ radical cation, or TTF2+ dication.

Generation of gas-phase sodiated arenes such as [(Na3(C6H4)+] from benzene dicarboxylate salts.

PubMed

Attygalle, Athula B; Chan, Chang-Ching; Axe, Frank U; Bolgar, Mark

2010-01-01

Upon collision-induced activation, gaseous sodium adducts generated by electrospray ionization of disodium salts of 1,2- 1,3-, and 1,4-benzene dicarboxylic acids (m/z 233) undergo an unprecedented expulsion of CO(2) by a rearrangement process to produce an ion of m/z 189 in which all three sodium atoms are retained. When isolated in a collision cell of a tandem-in-space mass spectrometer, and subjected to collision-induced dissociation (CID), only the m/z 189 ions derived from the meta and para isomers underwent a further CO(2) loss to produce a peak at m/z 145 for a sodiated arene of formula (Na(3)C(6)H(4))(+). This previously unreported m/z 145 ion, which is useful to differentiate meta and para benzene dicarboxylates from their ortho isomer, is in fact the sodium adduct of phenelenedisodium. Moreover, the m/z 189 ion from all three isomers readily expelled a sodium radical to produce a peak at m/z 166 for a radical cation [(*C(6)H(4)CO(2)Na(2))(+)], which then eliminated CO(2) to produce a peak at m/z 122 for the distonic cation (*C(6)H(4)Na(2))(+). Copyright 2009 John Wiley & Sons, Ltd.

TOPICAL REVIEW: Tetrathiapentalene-based organic conductors

NASA Astrophysics Data System (ADS)

Misaki, Yohji

2009-04-01

The synthesis, structure and properties of tetrathiapentalene-based (TTP) organic conductors are reviewed. Among various TTP-type donors, bis-fused tetrathiafulvalene, 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) and its derivatives afford many metallic radical cation salts stable down to low temperatures, regardless of the size and shape of the counter anions. Most BDT-TTP conductors have a β-type donor arrangement with almost uniform stacks. Introduction of appropriate substituents results in molecular packing that differs from the β-type. A vinylogous TTP, 2-(1,3-dithiol-2-ylidene)-5-(2-ethanediylidene-1,3-dithiole)-1,3,4,6-tetrathiapentalene (DTEDT) has yielded an organic superconductor (DTEDT)3Au(CN)2 as well as metallic radical cation salts, regardless of the counter anions. (Thio)pyran analogs of TTP, namely (T)PDT-TTP and its derivatives produce molecular conductors with novel molecular arrangements. A TTP analog with reduced π-electron system 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP) has afforded several organic superconductors. Highly conducting molecular metals with unusual oxidation states (+1, +5/3 and neutral) have been developed on the basis of 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) derivatives and analogous metal derivatives M(dt)2 (M = Ni, Au).

A novel automated direct measurement method for total antioxidant capacity using a new generation, more stable ABTS radical cation.

PubMed

Erel, Ozcan

2004-04-01

To develop a novel colorimetric and automated direct measurement method for total antioxidant capacity (TAC). A new generation, more stable, colored 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid radical cation (ABTS(*+)) was employed. The ABTS(*+) is decolorized by antioxidants according to their concentrations and antioxidant capacities. This change in color is measured as a change in absorbance at 660 nm. This process is applied to an automated analyzer and the assay is calibrated with Trolox. The novel assay is linear up to 6 mmol Trolox equivalent/l, its precision values are lower than 3%, and there is no interference from hemoglobin, bilirubin, EDTA, or citrate. The method developed is significantly correlated with the Randox- total antioxidant status (TAS) assay (r = 0.897, P < 0.0001; n = 91) and with the ferric reducing ability of plasma (FRAP) assay (r = 0.863, P < 0.0001; n = 110). Serum TAC level was lower in patients with major depression (1.69 +/- 0.11 mmol Trolox equivalent/l) than in healthy subjects (1.75 +/- 0.08 mmol Trolox equivalent/l, P = 0.041). This easy, stable, reliable, sensitive, inexpensive, and fully automated method described can be used to measure total antioxidant capacity.

Technical note: Simultaneous carotenoid and vitamin analysis of milk from total mixed ration-fed cows optimized for xanthophyll detection.

PubMed

Stout, M A; Benoist, D M; Drake, M A

2018-06-01

Concentrations of retinol, α-tocopherol, and major carotenoids in dairy products are often determined simultaneously by liquid chromatography. These compounds have different polarity and solubility; thus, extracting them simultaneously can be difficult and inefficient. In milks with low carotenoid concentrations, the xanthophylls lutein and zeaxanthin may not be completely resolved using common extraction techniques. A simplified method was developed to optimize extraction efficiency and the limit of detection and limit of quantification (LoQ) of lutein and zeaxanthin in bovine milk without decreasing sensitivity to other vitamins or carotenoids. The developed method evaluates lutein, zeaxanthin, β-carotene, retinol, and α-tocopherol simultaneously by ultra-high performance liquid chromatography-photodiode array detection. Common saponification temperatures (40-60°C) and concentrations of KOH in water (10-50% KOH wt/vol) were evaluated. Multiple solvents were evaluated for optimal xanthophyll extraction (diethyl ether, dichloromethane, hexane, and tetrahydrofuran) following saponification. The limit of detection and LoQ were defined as 3:1 and 10:1 signal-to-noise ratio, respectively. All experiments were performed in triplicate. The optimal saponification procedure was a concentration of 25% KOH at either 40 or 50°C. Saponified extracts solubilized in solutions containing diethyl ether had greater concentrations of lutein- than hexane- or tetrahydrofuran-based solutions, with peak areas above LoQ values. The solution containing diethyl ether solubilized similar concentrations of retinol, α-tocopherol, and β-carotene when compared with other solutions. The proposed optimized method allows for the simultaneous determination of carotenoids from milk with increased lutein and zeaxanthin sensitivity without sacrificing recovery of retinol, α-tocopherol, and β-carotene. Copyright © 2018 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

The role of the carotenoids, lutein and zeaxanthin, in protecting against age-related macular degeneration: a review based on controversial evidence.

PubMed

Mozaffarieh, Maneli; Sacu, Stefan; Wedrich, Andreas

2003-12-11

A review of the role of the carotenoids, lutein and zeaxanthin, and their function in altering the pathogenesis of age-related macular degeneration (AMD). Medline and Embase search. Recent evidence introduces the possibility that lutein and zeaxanthin, carotenoids found in a variety of fruits and vegetables may protect against the common eye disease of macular degeneration. This potential and the lack to slow the progression of macular degeneration, has fueled high public interest in the health benefits of these carotenoids and prompted their inclusion in various supplements. The body of evidence supporting a role in this disease ranges from basic studies in experimental animals to various other clinical and epidemiological studies. Whilst some epidemiological studies suggest a beneficial role for carotenoids in the prevention of AMD, others are found to be unrelated to it. Results of some clinical studies indicate that the risk for AMD is reduced when levels of the carotenoids are elevated in the serum or diet, but this correlation is not observed in other studies. Published data concerning the toxicity of the carotenoids or the optimum dosage of these supplements is lacking. An intake of dietary supplied nutrients rich in the carotenoids, lutein and zeaxanthin, appears to be beneficial in protecting retinal tissues, but this is not proven. Until scientifically sound knowledge is available we recommend for patients judged to be at risk for AMD to: alter their diet to more dark green leafy vegetables, wear UV protective lenses and a hat when outdoors. Future investigations on the role of nutrition, light exposure, genetics, and combinations of photodynamic therapy with intravitreal steroid (triamcinolone-acetonide) injections hold potential for future treatment possibilities.

Prevention and treatment of age-related macular degeneration: an update for pharmacists.

PubMed

Marshall, Leisa L; Roach, J Michael

2013-11-01

Review the current recommendations for the prevention and treatment of age-related macular degeneration (AMD). Articles indexed in PubMed (National Library of Medicine), the Cochrane Reviews and Trials, Dynamed, and Iowa Drug Information Service (IDIS) in the last 10 years using the key words macular degeneration, agerelated macular degeneration (AMD), AMD and treatment, AMD and prevention. Sixty-nine published papers were reviewed, and criteria supporting the primary objective were used to identify useful resources. The literature included practice guidelines, original research articles, review articles, product prescribing information, and supplement product information for the prevention and treatment of AMD. AMD is a leading cause of visual impairment in older adults. At present there is no cure for advanced AMD, but intravitreal vascular endothelial growth factor inhibitors minimize and even reverse vision loss in patients with AMD of the neovascular type. In the Age-Related Eye Disease Study (AREDS), participants with intermediate AMD who received a supplement combination of vitamins C and E, beta-carotene, and zinc had a greater delay in progression to advanced AMD than those participants who received a portion of these supplements. In the second AREDS, AREDS2, the addition of lutein + zeaxanthin, docosahexaenoic acid (DHA) + eicosapentaenoic acid (EPA), or lutein + zeaxanthin and DHA + EPA to the complete AREDS formulation did not further reduce the risk of progression to advanced AMD. Subgroup analyses indicated that additional research with lutein + zeaxanthin supplementation is warranted as it was beneficial in participants with low dietary intake of lutein + zeaxanthin. A formulation without beta-carotene may be best for most patients, especially smokers or former smokers. Health care professionals will want to consider patient-specific information before recommending ocular health supplements.

Spontaneous grafting of diazonium salts: chemical mechanism on metallic surfaces.

PubMed

Mesnage, Alice; Lefèvre, Xavier; Jégou, Pascale; Deniau, Guy; Palacin, Serge

2012-08-14

The spontaneous reaction of diazonium salts on various substrates has been widely employed since it consists of a simple immersion of the substrate in the diazonium salt solution. As electrochemical processes involving the same diazonium salts, the spontaneous grafting is assumed to give covalently poly(phenylene)-like bonded films. Resistance to solvents and to ultrasonication is commonly accepted as indirect proof of the existence of a covalent bond. However, the most relevant attempts to demonstrate a metal-C interface bond have been obtained by an XPS investigation of spontaneously grafted films on copper. Similarly, our experiments give evidence of such a bond in spontaneously grafted films on nickel substrates in acetonitrile. In the case of gold substrates, the formation of a spontaneous film was unexpected but reported in the literature in parallel to our observations. Even if no interfacial bond was observed, formation of the films was explained by grafting of aryl cations or radicals on the surface arising from dediazoniation, the film growing later by azo coupling, radical addition, or cationic addition on the grafted phenyl layer. Nevertheless, none of these mechanisms fits our experimental results showing the presence of an Au-N bond. In this work, we present a fine spectroscopic analysis of the coatings obtained on gold and nickel substrates that allow us to propose a chemical structure of such films, in particular, their interface with the substrates. After testing the most probable mechanisms, we have concluded in favor of the involvement of two complementary mechanisms which are the direct reaction of diazonium salts with the gold surface that accounts for the observed Au-N interfacial bonds as well as the formation of aryl cations able to graft on the substrate through Au-C linkages.

Estimation of Free Radical Ionization Energies by the Kinetic Method and the Relationship between the Kinetic Method and the Hammett Equation.

PubMed

Chen, G; Wong, P; Cooks, R G

1997-09-01

Substituted 1,2-diphenylethanes undergo competitive dissociations upon electron ionization (EI) to generate substituted benzyl cation and benzyl radical pairs. Application of the kinetic method to the previous reported EI mass spectra of these covalently bound precursor ions (data are taken from McLafferty et al. J. Am. Chem. Soc. 1970, 92, 6867)) is used to estimate the ionization energies of substituted benzyl free radicals. A correlation is observed between the Hammett σ constant of the substituents and the kinetic method parameter, ln(k(x)/k(H)), where k(x) is the rate of fragmentation to give the substituted product ion and k(H) is the rate to give the benzyl ion itself. Systems involving weakly bound cluster ions, including proton-bound dimers of meta- and para-substituted pyridines and meta- and para-substituted anilines, and electron-bound dimers of meta- and para-substituted nitrobenzenes, also show good correlations between the kinetic method parameter and the Hammett σ constant.

Renner-Teller effects in the photoelectron spectra of CNC, CCN, and HCCN.

PubMed

Coudert, Laurent H; Gans, Bérenger; Garcia, Gustavo A; Loison, Jean-Christophe

2018-02-07

The line intensity of photoelectron spectra when either the neutral or cationic species display a Renner-Teller coupling is derived and applied to the modeling of the photoelectron spectra of CNC, CCN, and HCCN. The rovibronic energy levels of these three radicals and of their cations are investigated starting from ab initio results. A model treating simultaneously the bending mode and the overall rotation is developed to deal with the quasilinearity problem in CNC + , CCN + , and HCCN and accounts for the large amplitude nature of their bending mode. This model is extended to treat the Renner-Teller coupling in CNC, CCN, and HCCN + . Based on the derived photoelectron line intensity, the photoelectron spectra of all three molecules are calculated and compared to the experimental ones.

Electronic absorption spectroscopy of matrix-isolated polycyclic aromatic hydrocarbon cations. II. The phenanthrene cation (C14H10+) and its 1-methyl derivative

NASA Technical Reports Server (NTRS)

Salama, F.; Joblin, C.; Allamandola, L. J.

1994-01-01

The ultraviolet, visible, and near infrared absorption spectra of phenanthrene (C14H10), 1-methylphenanthrene [(CH3)C14H9], and their radical ions [C14H10+; (CH3)C14H9+], formed by vacuum-ultraviolet irradiation, were measured in neon matrices at 4.2 K. The associated vibronic band systems and their spectroscopic assignments are discussed. The oscillator strengths were calculated for the phenanthrene ion and found lower than the theoretical predictions. This study presents the first spectroscopic data for phenanthrene and its methyl derivative trapped in a neon matrix where the perturbation of the isolated species by its environment is minimum; a condition crucial to astrophysical applications.

UV + V UV double-resonance studies of autoionizing Rydberg states of the hydroxyl radical

DOE Office of Scientific and Technical Information (OSTI.GOV)

Green, Amy M.; Liu, Fang; Lester, Marsha I., E-mail: milester@sas.upenn.edu

2016-05-14

The hydroxyl radical (OH) is a key oxidant in atmospheric and combustion chemistry. Recently, a sensitive and state-selective ionization method has been developed for detection of the OH radical that utilizes UV excitation on the A{sup 2}Σ{sup +}–X{sup 2}Π transition followed by fixed 118 nm vacuum ultraviolet (VUV) radiation to access autoionizing Rydberg states [J. M. Beames et al., J. Chem. Phys. 134, 241102 (2011)]. The present study uses tunable VUV radiation generated by four-wave mixing to examine the origin of the enhanced ionization efficiency observed for OH radicals prepared in specific A{sup 2}Σ{sup +} intermediate levels. The enhancement ismore » shown to arise from resonant excitation to distinct rotational and fine structure levels of two newly identified {sup 2}Π Rydberg states with an A{sup 3}Π cationic core and a 3d electron followed by ionization. Spectroscopic constants are derived and effects due to uncoupling of the Rydberg electron are revealed for the OH {sup 2}Π Rydberg states. The linewidths indicate a Rydberg state lifetime due to autoionization on the order of a picosecond.« less

Primary photophysical properties of moxifloxacin--a fluoroquinolone antibiotic.

PubMed

Lorenzo, Fernando; Navaratnam, Suppiah; Edge, Ruth; Allen, Norman S

2008-01-01

The photophysical properties of the fluoroquinolone antibiotic moxifloxacin (MOX) were investigated in aqueous media. MOX in water, at pH 7.4, shows two intense absorption bands at 287 and 338 nm (epsilon = 44,000 and 17,000 dm(3) mol(-1) cm(-1), respectively). The absorption and emission properties of MOX are pH-dependent, pK(a) values for the protonation equilibria of both the ground (6.1 and 9.6) and excited singlet states (6.8 and 9.1) of MOX were determined spectroscopically. MOX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Phosphorescence from the excited triplet state in frozen ethanol solution has a quantum yield of 0.046. Laser flash photolysis and pulse radiolysis studies have been carried out to characterize the transient species of MOX in aqueous solution. On laser excitation, MOX undergoes monophotonic photoionization with a quantum yield of 0.14. This leads to the formation of a long-lived cation radical whose absorption is maximum at 470 nm (epsilon(470) = 3400 dm(3) mol(-1) cm(-1)). The photoionization process releases hydrated electron which rapidly reacts (k = 2.8 x 10(10) dm(3) mol(-1) s(-1)) with ground state MOX, yielding a long-lived anion radical with maximum absorption at 390 nm (epsilon(390) = 2400 dm(3) mol(-1) cm(-1)). The cation radical of MOX is able to oxidize protein components tryptophan and tyrosine. The bimolecular rate constants for these reactions are 2.3 x 10(8) dm(3) mol(-1) s(-1) and 1.3 x 10(8) dm(3) mol(-1) s(-1), respectively. Singlet oxygen sensitized by the MOX triplet state was also detected only in oxygen-saturated D(2)O solutions, with a quantum yield of 0.075.

Infrared spectra of the 1-pyridinium (C5H5NH+) cation and pyridinyl (C5H5NH and 4-C5H6N) radicals isolated in solid para-hydrogen.

PubMed

Golec, Barbara; Das, Prasanta; Bahou, Mohammed; Lee, Yuan-Pern

2013-12-19

Protonated pyridine and its neutral counterparts (C5H6N) are important intermediates in organic and biological reactions and in the atmosphere. We have recorded the IR absorption spectra of the 1-pyridinium (C5H5NH(+)) cation, 1-pyridinyl (C5H5NH), and 4-pyridinyl (4-C5H6N) produced on electron bombardment during matrix deposition of a mixture of pyridine (C5H5N) and p-H2 at 3.2 K; all spectra were previously unreported. The IR features of C5H5NH(+) diminished in intensity after the matrix was maintained in darkness for 15 h, whereas those of C5H5NH and 4-C5H6N radicals increased. Irradiation of this matrix with light at 365 nm diminished lines of C5H5NH(+) and C5H5NH but enhanced lines of 4-C5H6N slightly, whereas irradiation at 405 nm diminished lines of 4-C5H6N significantly. Observed wavenumbers and relative intensities of these species agree satisfactorily with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3LYP/6-31++G(d,p) method. Assignments of C5H5NH and 4-C5H6N radicals were further supported by the observation of similar spectra when a Cl2/C5H5N/p-H2 matrix was irradiated first at 365 nm and then with IR light to generate H atoms to induce the H + C5H5N reaction.

Electron-transfer and acid-base properties of a two-electron oxidized form of quaterpyrrole that acts as both an electron donor and an acceptor.

PubMed

Zhang, Min; E, Wenbo; Ohkubo, Kei; Sanchez-Garcia, David; Yoon, Dae-Wi; Sessler, Jonathan L; Fukuzumi, Shunichi; Kadish, Karl M

2008-02-21

Electron-transfer interconversion between the four-electron oxidized form of a quaterpyrrole (abbreviated as P4 for four pyrroles) and the two-electron oxidized form (P4H2) as well as between P4H2 and its fully reduced form (P4H4) bearing analogous substituents in the alpha- and beta-pyrrolic positions was studied by means of cyclic voltammetry and UV-visible spectroelectrochemistry combined with ESR and laser flash photolysis measurements. The two-electron oxidized form, P4H2, acts as both an electron donor and an electron acceptor. The radical cation (P4H2*+) and radical anion (P4H2*-) are both produced by photoinduced electron transfer from dimeric 1-benzyl-1,4-dihydronicotinamide to P4H2, whereas the cation radical form of the compound is also produced by electron-transfer oxidation of P4H2 with [Ru(bpy)3]3+. The ESR spectra of P4H2*+ and P4H2*- were recorded at low temperature and exhibit spin delocalization over all four pyrrole units. Thus, the two-electron oxidized form of the quaterpyrrole (P4H2) displays redox and electronic features analogous to those seen in the case of porphyrins and may be considered as a simple, open-chain model of this well-studied tetrapyrrolic macrocycle. The dynamics of deprotonation from P4H2*+ and disproportionation of P4H2 were examined by laser flash photolysis measurements of photoinduced electron-transfer oxidation and reduction of P4H2, respectively.

Increase in β-ionone, a carotenoid-derived volatile in zeaxanthin-biofortified sweet corn.

PubMed

Gallon, Camilla Z; Fuller, Steven C; Fanning, Kent J; Smyth, Heather E; Pun, Sharon; Martin, Ian F; O'Hare, Timothy J

2013-07-31

Carotenoids are responsible for the yellow color of sweet corn (Zea mays var. saccharata), but are also potentially the source of flavor compounds from the cleavage of carotenoid molecules. The carotenoid-derived volatile, β-ionone, was identified in both standard yellow sweet corn ('Hybrix5') and a zeaxanthin-enhanced experimental variety ('HZ') designed for sufferers of macular degeneration. As β-ionone is highly perceivable at extremely low concentration by humans, it was important to confirm if alterations in carotenoid profile may also affect flavor volatiles. The concentration of β-ionone was most strongly correlated (R(2) > 0.94) with the β-arm carotenoids, β-carotene, β-cryptoxanthin, and zeaxanthin, and to a lesser degree (R(2) = 0.90) with the α-arm carotenoid, zeinoxanthin. No correlation existed with either lutein (R(2) = 0.06) or antheraxanthin (R(2) = 0.10). Delaying harvest of cobs resulted in a significant increase of both carotenoid and β-ionone concentrations, producing a 6-fold increase of β-ionone in 'HZ' and a 2-fold increase in 'Hybrix5', reaching a maximum of 62 μg/kg FW and 24 μg/kg FW, respectively.

Assessment of dietary lutein, zeaxanthin and lycopene intakes and sources in the Spanish survey of dietary intake (2009-2010).

PubMed

Estévez-Santiago, Rocío; Beltrán-de-Miguel, Beatriz; Olmedilla-Alonso, Begoña

2016-01-01

We assessed the intake and major dietary sources of lutein, zeaxanthin and lycopene (non-provitamin A carotenoids) in Spain using food consumption data from the Spanish National Dietary Intake Survey (2009-2010). Three-day diaries and one 24-h recall were used to collect dietary data and a software application that includes HPLC data was used. Average intake of those carotenoids was 4290.8 μg/d (67.1% total carotenoid intake), mainly from vegetables (3414.0 μg/d), followed by fruits (393.5 μg/d), oils/fats (204.0 μg/d) and eggs/egg products (170.0 μg/d). Main sources of lutein and zeaxanthin were vegetables (62.9% total diet, 1235.2 μg/person/d). Lycopene intake was 3055.6 μg/d (71.2% of non-provitamin A carotenoids), mainly from tomato and by-products (86.3%) and watermelon. Red- and orange-colored fruits and vegetables were the major contributors of non-provitamin carotenoids (3219.0 μg/person/d). Balanced diets should favor fruits and vegetables over other dietary sources (oils, eggs, processed foods) that contain components to be consumed with moderation.

Molecular identification of zeaxanthin epoxidase of Nicotiana plumbaginifolia, a gene involved in abscisic acid biosynthesis and corresponding to the ABA locus of Arabidopsis thaliana.

PubMed Central

Marin, E; Nussaume, L; Quesada, A; Gonneau, M; Sotta, B; Hugueney, P; Frey, A; Marion-Poll, A

1996-01-01

Abscisic acid (ABA) is a plant hormone which plays an important role in seed development and dormancy and in plant response to environmental stresses. An ABA-deficient mutant of Nicotiana plumbaginifolia, aba2, was isolated by transposon tagging using the maize Activator transposon. The aba2 mutant exhibits precocious seed germination and a severe wilty phenotype. The mutant is impaired in the first step of the ABA biosynthesis pathway, the zeaxanthin epoxidation reaction. ABA2 cDNA is able to complement N.plumbaginifolia aba2 and Arabidopsis thaliana aba mutations indicating that these mutants are homologous. ABA2 cDNA encodes a chloroplast-imported protein of 72.5 kDa, sharing similarities with different mono-oxigenases and oxidases of bacterial origin and having an ADP-binding fold and an FAD-binding domain. ABA2 protein, produced in Escherichia coli, exhibits in vitro zeaxanthin epoxidase activity. This is the first report of the isolation of a gene of the ABA biosynthetic pathway. The molecular identification of ABA2 opens the possibility to study the regulation of ABA biosynthesis and its cellular location. Images PMID:8665840

Molecular identification of zeaxanthin epoxidase of Nicotiana plumbaginifolia, a gene involved in abscisic acid biosynthesis and corresponding to the ABA locus of Arabidopsis thaliana.

PubMed

Marin, E; Nussaume, L; Quesada, A; Gonneau, M; Sotta, B; Hugueney, P; Frey, A; Marion-Poll, A

1996-05-15

Abscisic acid (ABA) is a plant hormone which plays an important role in seed development and dormancy and in plant response to environmental stresses. An ABA-deficient mutant of Nicotiana plumbaginifolia, aba2, was isolated by transposon tagging using the maize Activator transposon. The aba2 mutant exhibits precocious seed germination and a severe wilty phenotype. The mutant is impaired in the first step of the ABA biosynthesis pathway, the zeaxanthin epoxidation reaction. ABA2 cDNA is able to complement N.plumbaginifolia aba2 and Arabidopsis thaliana aba mutations indicating that these mutants are homologous. ABA2 cDNA encodes a chloroplast-imported protein of 72.5 kDa, sharing similarities with different mono-oxigenases and oxidases of bacterial origin and having an ADP-binding fold and an FAD-binding domain. ABA2 protein, produced in Escherichia coli, exhibits in vitro zeaxanthin epoxidase activity. This is the first report of the isolation of a gene of the ABA biosynthetic pathway. The molecular identification of ABA2 opens the possibility to study the regulation of ABA biosynthesis and its cellular location.

Antioxidant and radical-scavenging activities of Slovak honeys - An electron paramagnetic resonance study.

PubMed

Zalibera, Michal; Staško, Andrej; Šlebodová, Anna; Jančovičová, Viera; Čermáková, Tatiana; Brezová, Vlasta

2008-09-15

The antioxidant properties of 15 honey samples from different floral sources and various Slovak regions were investigated by means of electron paramagnetic resonance spectroscopy. Cation radical of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) diammonium salt), DPPH (1,1-diphenyl-2-picrylhydrazyl) and hydroxyl radicals generated by the photochemical decomposition of hydrogen peroxide were used as oxidants. The antioxidant activities found with ABTS(+), expressed as trolox equivalent antioxidant capacity (TEAC), ranged from 0.15 to 1.14mmolkg(-1), and those determined with DPPH, from 0.04 to 0.32mmolkg(-1). TEAC values correlated well with results found by elimination of DPPH, and both values revealed a linear relationship with the concentration of phenolics obtained with the Folin-Ciocalteu phenol test (expressed as gallic acid equivalents, GAE). The colour coordinates (CIE L(∗)a(∗)b(∗)), as well as reflectance spectra determined for original honeys using a white background, demonstrated that the colour difference (ΔE(∗)) and coordinate b(∗) interrelate with TEAC values. The radical-scavenging capacities (RSC) of the honey samples determined in the experiments with photochemically decomposed hydrogen peroxide, generating reactive OH radicals in the presence of spin trapping agent, differ from those found with ABTS(+) and DPPH. Here, probably, the reactive OH radicals, having higher redox potential, are scavenged by a variety of compounds not effective with ABTS(+) and DPPH (e.g., saccharides, proteins). Copyright © 2008 Elsevier Ltd. All rights reserved.

Structure of Radicals from X-irradiated Guanine Derivatives: An Experimental and Computational Study of Sodium Guanosine Dihydrate Single Crystals

PubMed Central

Jayatilaka, Nayana; Nelson, William H.

2008-01-01

In sodium guanosine dihydrate single crystals, the guanine moiety is deprotonated at N1 due to growth from high-pH (>12) solutions. EPR and ENDOR study of crystals x-irradiated at 10 K detected evidence for three radical forms. Radical R1,characterized by two proton and two nitrogen hyperfine interactions, was identified as the product of net hydrogenation at N7 of the N1-deprotonated guanine unit. R1 exhibited an unusually distorted structure leading to net positive isotropic components of the hydrogen couplings. Radical R2, characterized by one proton and one nitrogen hyperfine coupling was identified as the primary electron loss product. This product is equivalent to that of deprotonation at N1 by the guanine cation and represents the first ENDOR characterization of that product. Radical R3, characterized by a single hydrogen hyperfine coupling, was identified as the product of net dehydrogenation at C1 of the ribose moiety. The identification of radicals R1-R3 was supported by DFT calculations on several possible structures using the B3LYP/6-311G(2df,p)//6-31G(d,p) approach. Radical R4, detected after warming the crystals to room temperature, was identified as the well-known product of net hydrogenation of C8 of the (N1-deprotonated) guanine component. Radical R1, evidently formed by protonation of the primary electron addition product, was present as roughly 60% of the total radicals detected at 10 K. Radical R2 was present as roughly 27% of the total yield, and the concentration of R3 contributed the remaining 13%. R3 is evidently the product of oneelectron oxidation followed by deprotonation; thus, the balance of oxidation and reduction products is approximately equal within experimental uncertainty. PMID:17249824

Radical Ions of 3-Styryl-quinoxalin-2-one Derivatives Studied by Pulse Radiolysis in Organic Solvents.

PubMed

Skotnicki, Konrad; De la Fuente, Julio R; Cañete, Álvaro; Berrios, Eduardo; Bobrowski, Krzysztof

2018-04-12

The absorption-spectral and kinetic behaviors of radical ions and neutral hydrogenated radicals of seven 3-styryl-quinoxalin-2(1 H)-one (3-SQ) derivatives, one without substituents in the styryl moiety, four others with electron-donating (R = -CH 3 , -OCH 3 , and -N(CH 3 ) 2 ) or electron-withdrawing (R = -OCF 3 ) substituents in the para position in their benzene ring, and remaining two with double methoxy substituents (-OCH 3 ), however, at different positions (meta/para and ortho/meta) have been studied by UV-vis spectrophotometric pulse radiolysis in neat acetonitrile saturated with argon (Ar) and oxygen (O 2 ) and in 2-propanol saturated with Ar, at room temperature. In acetonitrile solutions, the radical anions (4R-SQ •- ) are characterized by two absorption maxima located at λ max = 470-490 nm and λ max = 510-540 nm, with the respective molar absorption coefficients ε 470-490 = 8500-13 100 M -1 cm -1 and ε 510-540 = 6100-10 300 M -1 cm -1 , depending on the substituent (R). All 4R-SQ •- decay in acetonitrile via first-order kinetics, with the rate constants in the range (1.2-1.5) × 10 6 s -1 . In 2-propanol solutions, they decay predominantly through protonation by the solvent, forming neutral hydrogenated radicals (4R-SQH • ), which are characterized by weak absorption bands with λ max = 480-490 nm. Being oxygen-insensitive, the radical cations (4R-SQ •+ ) are characterized by a strong absorption with λ max = 450-630 nm, depending on the substituent (R). They are formed in a charge-transfer reaction between a radical cation derived from acetonitrile (ACN •+ ) and substituted 3-styryl-quinoxalin-2-one derivatives (4R-SQ) with a pseudo-first-order rate constant k = (2.7-4.7) × 10 5 s -1 measured in solutions containing 0.1 mM 4R-3-SQ. The Hammett equation plot gave a very small negative slope (ρ = -0.08), indicating a very weak influence of the substituents in the benzene ring on the rate of charge-transfer reaction. The decay of 4R-SQ •+ in Ar-saturated acetonitrile solutions occurs with a pseudo-first-order rate constant k = (1.6-6.2) × 10 4 s -1 and, in principle, is not affected by the presence of O 2 , suggesting charge-spin delocalization over the whole 3-SQ molecule. Most of the radiolytically generated transient spectra are reasonably well-reproduced by semiempirical PM3-ZINDO/S (for 4R-SQ •- ) and density functional theory quantum mechanics calculations employing M06-2x hybrid functional together with the def2-TZVP basis set (for 4R-SQ •+ ).

Facile doping of anionic narrow-band-gap conjugated polyelectrolytes during dialysis.

PubMed

Mai, Cheng-Kang; Zhou, Huiqiong; Zhang, Yuan; Henson, Zachary B; Nguyen, Thuc-Quyen; Heeger, Alan J; Bazan, Guillermo C

2013-12-02

PCPDTBTSO3 K, an anionic, narrow-band-gap conjugated polyelectrolyte, was found to be doped after dialysis. The proposed doping mechanism involves protonation of the polymer backbone, followed by electron transfer from a neutral chain, to generate radical cations, which are stabilized by the pendant sulfonate anions. Formation of polarons is supported by spectroscopy and electrical-conductivity measurements. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polymeric Ionic Networks with High Charge Density: Solid-like Electrolytes in Lithium Metal Batteries

DOE PAGES

Zhang, Pengfei; Li, Mingtao; Jiang, Xueguang; ...

2015-11-02

Polymerized ionic networks (PINs) with six ion pairs per repeating unit are synthesized by nucleophilic-substitution-mediated polymerization or radical polymerization of monomers bearing six 1-vinylimidazolium cations. PIN-based solid-like electrolytes show good ionic conductivities (up to 5.32 × 10 -3 S cm -1 at 22 °C), wide electrochemical stability windows (up to 5.6 V), and good interfacial compatibility with the electrodes.

A C-di-GMP-proflavine-hemin supramolecular complex has peroxidase activity--implication for a simple colorimetric detection.

PubMed

Nakayama, Shizuka; Roelofs, Kevin; Lee, Vincent T; Sintim, Herman O

2012-03-01

Herein, we demonstrate that the bacterial signaling molecule, c-di-GMP, can enhance the peroxidation of hemin when proflavine is present. The c-di-GMP-proflavine-hemin nucleotidezyme can oxidize the colorless compound 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), ABTS, to the colored radical cation ABTS˙(+) and hence provides simple colorimetric detection of c-di-GMP at low micromolar concentrations.

Inorganic Halogen Oxidizer Research

DTIC Science & Technology

1975-02-26

K. 0. Christe and C. J. Schack, Advances Inorg. Chem. Radiochem. 15. "The NF * Radical Cation. Esr Studies of Radiation Effects in NF„+ Salts...and 25°) in a wide variety of polar and nonpolar solvents, such as aqueous solutions, alcohols, ketones , esters, ethers , and aromatic and halogenated... Studies of Radiation Effects in NF, Salts = 4 S. P. Mishra, M. C R. Symons, K. 0. Christe, R. D. Wilson and R. I. Wagner Received. . . August .9

Vibrational dynamics in dendridic oligoarylamines by Raman spectroscopy and incoherent inelastic neutron scattering.

PubMed

Kulszewicz-Bajer, Irena; Louarn, Guy; Djurado, David; Skorka, Lukasz; Szymanski, Marek; Mevellec, Jean Yves; Rols, Stephane; Pron, Adam

2014-05-15

Vibrational dynamics in triarylamine dendrimers was studied in a complementary way by Raman and infrared (IR) spectroscopies and incoherent inelastic neutron scattering (IINS). Three molecules were investigated, namely, unsubstituted triarylamine dendrimer of the first generation and two dendrimers of the first and second generation, substituted in the crown with butyl groups. To facilitate the assignment of the observed IR and Raman modes as well as the IINS peaks, vibrational models, based on the general valence force field method (GVFF), were calculated for all three compounds studied. A perfect consistency between the calculated and experimental results was found. Moreover, an important complementarity of the vibrational spectroscopies and IINS was established for the investigated dendrimers. The IINS peaks originating mainly from the C-H motions were not restricted by particular selection rules and only dependent on the IINS cross section. To the contrary, Raman and IR bands were imposed by the selection rules and the local geometry of the dendrimers yielding mainly C-C and C-N deformation modes with those of C-H nature of much lower intensity. Raman spectroscopy was also applied to the studies of the oxidation of dendrimers to their cationic forms. A strong Raman resonance effect was observed, since the spectra of the studied compounds, registered at different levels of their oxidation, strongly depended on the position of the excitation line with respect to their electronic spectrum. In particular, the blue (458 nm) excitation line turned out to be insensitive toward the cationic forms yielding very limited spectral information. To the contrary, the use of the red (647 nm) and infrared (1064 nm) excitation lines allowed for an unambiguous monitoring of the spectral changes in dendrimers oxidized to nominally monocationic and tricationic states. The analysis of oxidation-induced spectral changes in the tricationic state indicated that the charge storage configuration predominantly involved one spinless dication of the quinoid bond sequence and one radical cation. However, small numbers of dications were also found in a nominally monocationic state, where only radical cations should have been present. This finding was indicative of some inhomogeneity of the oxidation.

Facile and High-Yielding Synthesis of TAM Biradicals and Monofunctional TAM Radicals.

PubMed

Trukhin, Dmitry V; Rogozhnikova, Olga Yu; Troitskaya, Tatiana I; Vasiliev, Vladimir G; Bowman, Michael K; Tormyshev, Victor M

2016-04-01

Facile and high-yielding procedures for synthesis of monocarboxylic acid derivatives of triarylmethyl radicals (TAMs) were developed. Reaction of methyl thioglycolate with tris(2,3,5,6-tetrathiaaryl)methyl cation smoothly afforded the monosubstituted TAM derivative, which was hydrolyzed to a monocarboxylic acid, with the TAM moiety attached to thioglycolic acid via the sulfur atom. Alternatively, the diamagnetic tricarboxylic acid precursor of Finland trityl was transformed to a trimethyl ester and partially hydrolyzed under controlled conditions. The diester product was isolated and the remaining fractions were converted back to the trimethyl ester for production of more diester. The first representatives of TAM biradicals with different TAM cores and interspin distances were obtained by reaction of these new TAM monocaboxylic acids with N,N'-dimethylethylenediamine.

Acid generation mechanism in anion-bound chemically amplified resists used for extreme ultraviolet lithography

NASA Astrophysics Data System (ADS)

Komuro, Yoshitaka; Yamamoto, Hiroki; Kobayashi, Kazuo; Ohomori, Katsumi; Kozawa, Takahiro

2015-03-01

Extreme ultraviolet (EUV) lithography is the most promising candidate for the high-volume production of semiconductor devices with half-pitches of sub 10nm. An anion-bound polymer(ABP), in which at the anion part of onium salts is polymerized, has attracted much attention from the viewpoint of the control of acid diffusion. In this study, the acid generation mechanism in ABP films was investigated using γ and EUV radiolysis. On the basis of experimental results, the acid generation mechanism in anion-bound chemically amplified resists was proposed. The protons of acids are considered to be mainly generated through the reaction of phenyl radicals with diphenylsulfide radical cations that are produced through the hole transfer to the decomposition products of onium salts.

Acid generation mechanism in anion-bound chemically amplified resists used for extreme ultraviolet lithography

NASA Astrophysics Data System (ADS)

Komuro, Yoshitaka; Yamamoto, Hiroki; Kobayashi, Kazuo; Utsumi, Yoshiyuki; Ohomori, Katsumi; Kozawa, Takahiro

2014-11-01

Extreme ultraviolet (EUV) lithography is the most promising candidate for the high-volume production of semiconductor devices with half-pitches of sub-10 nm. An anion-bound polymer (ABP), in which the anion part of onium salts is polymerized, has attracted much attention from the viewpoint of the control of acid diffusion. In this study, the acid generation mechanism in ABP films was investigated using electron (pulse), γ, and EUV radiolyses. On the basis of experimental results, the acid generation mechanism in anion-bound chemically amplified resists was proposed. The major path for proton generation in the absence of effective proton sources is considered to be the reaction of phenyl radicals with diphenylsulfide radical cations that are produced through hole transfer to the decomposition products of onium salts.

Photo- and radiation chemical induced degradation of lignin model compounds.

PubMed

Lanzalunga; Bietti, M

2000-07-01

The basic mechanistic aspects of the photo- and radiation chemistry of lignin model compounds (LMCs) are discussed with respect to important processes related to lignin degradation. Several reactions occur after direct irradiation, photosensitized or radiation chemically induced oxidation of LMCs. Direct irradiation studies on LMCs have provided supportive evidence for the involvement of hydrogen abstraction reactions from phenols, beta-cleavage of substituted alpha-aryloxyacetophenones and cleavage of ketyl radicals (formed by photoreduction of aromatic ketones or hydrogen abstraction from arylglycerol beta-aryl ethers) in the photoyellowing of lignin rich pulps. Photosensitized and radiation chemically induced generation of reactive oxygen species and their reaction with LMCs are reviewed. The side-chain reactivity of LMC radical cations, generated by radiation chemical means, is also discussed in relation with the enzymatic degradation of lignin.

VUV photoionization and dissociative photoionization of the prebiotic molecule acetyl cyanide: Theory and experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bellili, A.; Hochlaf, M., E-mail: hochlaf@univ-mlv.fr, E-mail: martin.schwell@lisa.u-pec.fr; Schwell, M., E-mail: hochlaf@univ-mlv.fr, E-mail: martin.schwell@lisa.u-pec.fr

2014-10-07

The present combined theoretical and experimental investigation concerns the single photoionization of gas-phase acetyl cyanide and the fragmentation pathways of the resulting cation. Acetyl cyanide (AC) is inspired from both the chemistry of cyanoacetylene and the Strecker reaction which are thought to be at the origin of medium sized prebiotic molecules in the interstellar medium. AC can be formed by reaction from cyanoacetylene and water but also from acetaldehyde and HCN or the corresponding radicals. In view of the interpretation of vacuum ultraviolet (VUV) experimental data obtained using synchrotron radiation, we explored the ground potential energy surface (PES) of acetylmore » cyanide and of its cation using standard and recently implemented explicitly correlated methodologies. Our PES covers the regions of tautomerism (between keto and enol forms) and of the lowest fragmentation channels. This allowed us to deduce accurate thermochemical data for this astrobiologically relevant molecule. Unimolecular decomposition of the AC cation turns out to be very complex. The implications for the evolution of prebiotic molecules under VUV irradiation are discussed.« less

Adenine radicals generated in alternating AT duplexes by direct absorption of low-energy UV radiation.

PubMed

Banyasz, Akos; Ketola, Tiia; Martínez-Fernández, Lara; Improta, Roberto; Markovitsi, Dimitra

2018-04-17

There is increasing evidence that the direct absorption of photons with energies that are lower than the ionization potential of nucleobases may result in oxidative damage to DNA. The present work, which combines nanosecond transient absorption spectroscopy and quantum mechanical calculations, studies this process in alternating adenine-thymine duplexes (AT)n. We show that the one-photon ionization quantum yield of (AT)10 at 266 nm (4.66 eV) is (1.5 ± 0.3) × 10-3. According to our PCM/TD-DFT calculations carried out on model duplexes composed of two base pairs, (AT)1 and (TA)1, simultaneous base pairing and stacking does not induce important changes in the absorption spectra of the adenine radical cation and deprotonated radical. The adenine radicals, thus identified in the time-resolved spectra, disappear with a lifetime of 2.5 ms, giving rise to a reaction product that absorbs at 350 nm. In parallel, the fingerprint of reaction intermediates other than radicals, formed directly from singlet excited states and assigned to AT/TA dimers, is detected at shorter wavelengths. PCM/TD-DFT calculations are carried out to map the pathways leading to such species and to characterize their absorption spectra; we find that, in addition to the path leading to the well-known TA* photoproduct, an AT photo-dimerization path may be operative in duplexes.

Electrochemical models for the radical annihilation reactions in organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Armstrong, Neal R.; Anderson, Jeffrey D.; Lee, Paul A.; McDonald, Erin; Wightman, R. M.; Hall, Hank K.; Hopkins, Tracy; Padias, Anne; Thayumanavan, Sankaran; Barlow, Stephen; Marder, Seth R.

1998-12-01

Bilayer organic light emitting diodes (OLEDs), based upon vacuum deposited molecules, or single layer OLEDs, based upon spin-cast polymeric materials, doped with these same molecules, produce light from emissive states of the lumophores which are created through annihilation reactions of radical species, which can be modeled through solution electrochemistry. Difference seen in solution reduction and oxidation potentials of molecular components of OLEDs are a lower limit estimate to the differences in energy of these same radical species in the condensed phase environmental. The light emitted from an aluminum quinolate (Alq3)/triarylamine (TPD)-based OLED, or an Alq3/PVK single layers OLED, can be reproduce from solution cross reactions of Alq3/TPD+. The efficiency of this process increases as the oxidation potential of the TPD increases, due to added substituents. Radical cations and anions of solubilized version of quinacridone dopants (DIQA) which have been used to enhance efficiencies in these OLEDs, are shown to be electrochemically more stable than Alq3 and Alq3, and DIQA radical annihilation reactions produce the same emissive state as in the quinacridone-doped OLEDs. Electrochemical studies demonstrate the ways in which other dopants might enhance the efficiency and shift the color output of OLEDs, across the entire visible and near-IR spectrum. Chemical degradation pathways of these same molecular components, which they may undergo during OLED operation, are also revealed by these electrochemical studies.

Development of high-productivity, strong cation-exchange adsorbers for protein capture by graft polymerization from membranes with different pore sizes

PubMed Central

Chenette, Heather C.S.; Robinson, Julie R.; Hobley, Eboni; Husson, Scott M.

2012-01-01

This paper describes the surface modification of macroporous membranes using ATRP (atom transfer radical polymerization) to create cation-exchange adsorbers with high protein binding capacity at high product throughput. The work is motivated by the need for a more economical and rapid capture step in downstream processing of protein therapeutics. Membranes with three reported nominal pore sizes (0.2, 0.45, 1.0 μm) were modified with poly(3-sulfopropyl methacrylate, potassium salt) tentacles, to create a high density of protein binding sites. A special formulation was used in which the monomer was protected by a crown ether to enable surface-initiated ATRP of this cationic polyelectrolyte. Success with modification was supported by chemical analysis using Fourier-transform infrared spectroscopy and indirectly by measurement of pure water flux as a function of polymerization time. Uniformity of modification within the membranes was visualized with confocal laser scanning microscopy. Static and dynamic binding capacities were measured using lysozyme protein to allow comparisons with reported performance data for commercial cation-exchange materials. Dynamic binding capacities were measured for flow rates ranging from 13 to 109 column volumes (CV)/min. Results show that this unique ATRP formulation can be used to fabricate cation-exchange membrane adsorbers with dynamic binding capacities as high as 70 mg/mL at a throughput of 100 CV/min and unprecedented productivity of 300 mg/mL/min. PMID:23175597

π to σ Radical Tautomerization in One-Electron Oxidized 1-Methylcytosine and its Analogs

PubMed Central

Adhikary, Amitava; Kumar, Anil; Bishop, Casandra T.; Wiegand, Tyler J.; Hindi, Ragda M.; Adhikary, Ananya; Sevilla, Michael D.

2015-01-01

In this work iminyl σ-radical formation in several one-electron oxidized cytosine analogs including 1-MeC, cidofovir, 2′-deoxycytidine (dCyd), and 2′-deoxycytidine 5′-monophosphate (5′-dCMP) were investigated in homogeneous aqueous (D2O or H2O) glassy solutions at low temperatures employing electron spin resonance (ESR) spectroscopy. Employing density functional theory (DFT) (DFT/B3LYP/6-31G* method), the calculated hyperfine coupling constant (HFCC) values of iminyl σ-radical agree quite well with the experimentally observed ones thus confirming its assignment. ESR and DFT studies show that the cytosine-iminyl σ-radical is a tautomer of the deprotonated cytosine π-cation radical (cytosine π-aminyl radical, C(N4-H)•). Employing 1-MeC samples at various pHs ranging ca. 8 to ca. 11, ESR studies show that the tautomeric equilibrium between C(N4-H)• and the iminyl σ-radical at low temperature is too slow to be established without added base. ESR and DFT studies agree that in the iminyl-σ radical, the unpaired spin is localized to the exocyclic nitrogen (N4) in an in-plane pure p-orbital. This gives rise to an anisotropic nitrogen hyperfine coupling (Azz = 40 G) from N4 and a near isotropic β-nitrogen coupling of 9.7 G from the cytosine ring nitrogen at N3. Iminyl σ-radical should exist in its N3-protonated form as the N3-protonated iminyl σ-radical is stabilized in solution by over 30 kcal/mol (ΔG= −32 kcal/mol) over its conjugate base, the N3-deprotonated form. This is the first observation of an isotropic β-hyperfine ring nitrogen coupling in an N-centered DNA-radical. Our theoretical calculations predict that the cytosine iminyl σ-radical can be formed in dsDNA by a radiation-induced ionization–deprotonation process that is only 10 kcal/mol above the lowest energy path. PMID:26237072

Chemical composition of Lycium europaeum fruit oil obtained by supercritical CO2 extraction and evaluation of its antioxidant activity, cytotoxicity and cell absorption.

PubMed

Rosa, Antonella; Maxia, Andrea; Putzu, Danilo; Atzeri, Angela; Era, Benedetta; Fais, Antonella; Sanna, Cinzia; Piras, Alessandra

2017-09-01

We studied the total phenols and flavonoids, liposoluble antioxidants, fatty acid and triacylglycerol profiles, and oxidative status of oil obtained from Lycium europaeum fruits following supercritical CO 2 extraction (at 30MPa and 40°C). Linoleic (52%), palmitic (18%), oleic (13%), and α-linolenic (6%) were the main oil fatty acids, while trilinolein and palmitodilinolein/oleodilinolein represented the main triacylglycerols. The oil was characterized by high levels of all-trans-zeaxanthin and all-trans-β-carotene (755 and 332μg/g of oil, respectively), α-tocopherol (308μg/g of oil), total phenols (13.6mg gallic acid equivalents/g of oil), and total flavonoids (6.8mg quercetin equivalents/g of oil). The oil showed radical scavenging activities (ABTS and DPPH assays) and inhibited Caco-2 cell growth. Moreover, the incubation of differentiated Caco-2 cells with a non-toxic oil concentration (100μg/mL) induced a significant intracellular accumulation of essential fatty acids. The results qualify L. europaeum oil as a potential source for food/pharmaceutical applications. Copyright © 2017 Elsevier Ltd. All rights reserved.

Generation and reactivity of ketyl radicals with lignin related structures. On the importance of the ketyl pathway in the photoyellowing of lignin containing pulps and papers.

PubMed

Fabbri, Claudia; Bietti, Massimo; Lanzalunga, Osvaldo

2005-04-01

[reaction: see text] Ketyl radicals with lignin related structures have been generated by means of radiation chemical and photochemical techniques. In the former studies ketyl radicals are produced by reaction of alpha-carbonyl-beta-aryl ether lignin models with the solvated electron produced by pulse radiolysis of an aqueous solution at pH 6.0. The UV-vis spectra of ketyl radicals are characterized by three main absorption bands. The shape and position of these bands slightly change when the spectra are recorded in alkaline solution (pH 11.0) being now assigned to the ketyl radical anions and a pKa = 9.5 is determined for the 1-(3,4,5-trimethoxyphenyl)-2-phenoxyethanol-1-yl radical. Decay rates of ketyl radicals are found to be dose dependent and, at low doses, lie in the range (1.7-2.7) x 10(3) s(-1). In the presence of oxygen a fast decay of the ketyl radicals is observed (k2 = 1.8-2.7 x 10(9) M(-1) s(-1)) that is accompanied by the formation of stable products, i.e., the starting ketones. In the photochemical studies ketyl radicals have been produced by charge-transfer (CT) photoactivation of the electron donor-acceptor salts of methyl viologen (MV2+) with alpha-hydroxy-alpha-phenoxymethyl-aryl acetates. This process leads to the instantaneous formation of the reduced acceptor (methyl viologen radical cation, MV+*), as is clearly shown in a laser flash photolysis experiment by the two absorption bands centered at 390 and 605 nm, and an acyloxyl radical [ArC(CO2*))(OH)CH2(OC6H5)], which undergoes a very fast decarboxylation with formation of the ketyl radicals. Steady-state photoirradiation of the CT ion pairs indicates that 1-aryl-2-phenoxyethanones are formed as primary photoproducts by oxidation of ketyl radicals by MV2+ (under argon) or by molecular oxygen. Small amounts of acetophenones are formed by further photolysis of 1-aryl-2-phenoxyethanones and not by beta-fragmentation of the ketyl radicals. The high reactivity of ketyl radicals with oxygen coupled with the low rates of beta-fragmentation of the same species have an important bearing in the context of the photoyellowing of lignin containing pulps and papers.

Consumption of peptide-included and free tryptophan induced by peroxyl radicals: A kinetic study.

PubMed

Fuentes, E; López-Alarcón, C

2014-10-01

It is well-known that tryptophan residues are efficiently oxidized by peroxyl radicals, generating kynurenine, and N-formyl kynurenine as well as hydroperoxide derivatives as products. In the present work we studied the kinetic of such reaction employing free and peptide-included tryptophan. Two azocompounds were used to produce peroxyl radicals: AAPH (2,2'-Azobis(2-methylpropionamidine) dihydrochloride) and ABCVA (4,4'-Azobis(4-cyanovaleric acid)), which generate cationic and anionic peroxyl radicals, respectively. Tryptophan consumption was assessed by fluorescence spectroscopy and the reactions were carried out in phosphate buffer (75mM, pH 7.4) at 45°C. Only a slight effect of the peroxyl radical charge was evidenced on the consumption of free tryptophan and the dipeptide Gly-Trp. Employing AAPH as peroxyl radical source, at low free tryptophan concentrations (1-10µM) near 0.3 mol of tryptophan were consumed per each mol of peroxyl radicals introduced into the system. However, at high free tryptophan concentrations (100µM-1mM) such stoichiometry increased in a tryptophan concentration-way. At 1mM three moles of tryptophan were consumed per mol of AAPH-derived peroxyl radicals, evidencing the presence of chain reactions. A similar behavior was observed when di and tri-peptides (Gly-Trp, Trp-Gly, Gly-Trp-Gly, Trp-Ala, Ala-Trp-Ala) were studied. Nonetheless, at low initial concentration (5µM), the initial consumption rate of tryptophan included in the peptides was two times higher than free tryptophan. In contrast, at high concentration (1mM) free and peptide-included tryptophan showed similar initial consumption rates. These results could be explained considering a disproportionation process of tryptophanyl radicals at low free tryptophan concentrations, a process that would be inhibited when tryptophan is included in peptides. Copyright © 2014. Published by Elsevier Inc.

Electron Transfer Dissociation with Supplemental Activation to Differentiate Aspartic and Isoaspartic Residues in Doubly Charged Peptide Cations

PubMed Central

Chan, Wai Yi Kelly; Chan, T. W. Dominic; O’Connor, Peter B.

2011-01-01

Electron-transfer dissociation (ETD) with supplemental activation of the doubly charged deamidated tryptic digested peptide ions allows differentiation of isoaspartic acid and aspartic acid residues using c + 57 or z• − 57 peaks. The diagnostic peak clearly localizes and characterizes the isoaspartic acid residue. Supplemental activation in ETD of the doubly charged peptide ions involves resonant excitation of the charge reduced precursor radical cations and leads to further dissociation, including extra backbone cleavages and secondary fragmentation. Supplemental activation is essential to obtain a high quality ETD spectrum (especially for doubly charged peptide ions) with sequence information. Unfortunately, the low-resolution of the ion trap mass spectrometer makes detection of the diagnostic peak for the aspartic acid residue difficult due to interference with side-chain loss from arginine and glutamic acid residues. PMID:20304674

Light-switchable polymer from cationic to zwitterionic form: synthesis, characterization, and interactions with DNA and bacterial cells.

PubMed

Sobolčiak, Patrik; Spírek, Mário; Katrlík, Jaroslav; Gemeiner, Peter; Lacík, Igor; Kasák, Peter

2013-04-25

A novel cationic polymer poly(N,N-dimethyl-N-[3-(methacroylamino) propyl]-N-[2-[(2-nitrophenyl)methoxy]-2-oxo-ethyl]ammonium chloride) is synthesized by free-radical polymerization of N-[3-(dimethylamino)propyl] methacrylamide and subsequent quaternization with o-nitrobenzyl 2-chloroacetate. The photolabile o-nitrobenzyl carboxymethyl pendant moiety is transformed to the zwitterionic carboxybetaine form upon the irradiation at 365 nm. This feature is used to condense and, upon the light irradiation, to release double-strand DNA tested by gel electrophoresis and surface plasmon resonance experiments as well as to switch the antibacterial activity to non-toxic character demonstrated for Escherichia coli bacterial cells in solution and at the surface using the self-assembled monolayers. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Shedding Light on the Oxygen Reduction Reaction Mechanism in Ether-Based Electrolyte Solutions: A Study Using Operando UV-Vis Spectroscopy.

PubMed

Hirshberg, Daniel; Sharon, Daniel; Afri, Michal; Lavi, Ronit; Frimer, Aryeh A; Metoki, Noa; Eliaz, Noam; Kwak, Won-Jin; Sun, Yang-Kook; Aurbach, Doron

2018-04-04

Using UV-vis spectroscopy in conjunction with various electrochemical techniques, we have developed a new effective operando methodology for investigating the oxygen reduction reactions (ORRs) and their mechanisms in nonaqueous solutions. We can follow the in situ formation and presence of superoxide moieties during ORR as a function of solvent, cations, anions, and additives in the solution. Thus, using operando UV-vis spectroscopy, we found evidence for the formation of superoxide radical anions during oxygen reduction in LiTFSI/diglyme electrolyte solutions. Nitro blue tetrazolium (NBT) was used to indicate the presence of superoxide moieties based on its unique spectral response. Indeed, the spectral response of NBT containing solutions undergoing ORR could provide a direct indication for the level of association of the Li cations with the electrolyte anions.

Infrared spectroscopy of hydrated polycyclic aromatic hydrocarbon cations: naphthalene+-water.

PubMed

Chatterjee, Kuntal; Dopfer, Otto

2017-12-13

Polycyclic aromatic hydrocarbons (PAHs) are suggested to occur in interstellar media and ice grains. It is important to characterize hydrated PAHs and their cations to explore their stability in interstellar and biological media. Herein, the infrared photodissociation (IRPD) spectrum of the naphthalene + -H 2 O radical cation (Np + -H 2 O) recorded in the O-H and C-H stretch range is analysed by dispersion-corrected density functional theory calculations at the B3LYP-D3/aug-cc-pVTZ level to determine its structure and intermolecular bonding. Monohydration of Np + in its 2 A u ground electronic state leads to the formation of a bifurcated CHO ionic hydrogen bond (H-bond), in which the lone pairs of H 2 O bind to two adjacent CH proton donors of the two aromatic rings. The frequency-dependent branching ratios observed for IRPD of cold Np + -H 2 O-Ar clusters allows the estimation of the dissociation energy of Np + -H 2 O as D 0 ∼ 2800 ± 300 cm -1 . The monohydration motif of Np + differs qualitatively from that of the benzene cation in both structure and binding energy, indicating the strong influence of the multiple aromatic rings on the hydration of PAH + cations. This difference is rationalized by natural bond orbital analysis of the ionic H-bond motif. Comparison with neutral Np-H 2 O reveals the large change in structure and bond strength of the hydrated PAHs upon ionization. While neutral Np-H 2 O is stabilized by weak π H-bonds (OHπ, π-stacking), strong cation-dipole forces favour a planar bifurcated CHO ionic H-bond in Np + -H 2 O.

Probing Intermolecular Electron Delocalization in Dimer Radical Anions by Vibrational Spectroscopy

DOE PAGES

Mani, Tomoyasu; Grills, David C.

2017-07-05

Delocalization of charges is one of the factors controlling charge transport in conjugated molecules. It is considered to play an important role in the performance of a wide range of molecular technologies, including organic solar cells and organic electronics. Dimerization reactions are well-suited as a model to investigate intermolecular spatial delocalization of charges. And while dimerization reactions of radical cations are well investigated, studies on radical anions are still scarce. Upon dimerization of radical anions with neutral counterparts, an electron is considered to delocalize over the two molecules. By using time-resolved infrared (TRIR) detection coupled with pulse radiolysis, we showmore » that radical anions of 4-n-hexyl-4'-cyanobiphenyl (6CB) undergo such dimerization reactions, with an electron equally delocalized over the two molecules. We have recently demonstrated that nitrile ν(C≡N) vibrations respond to the degree of electron localization of nitrile-substituted anions: we can quantify the changes in the electronic charges from the neutral to the anion states in the nitriles by monitoring the ν(C≡N) IR shifts. In the first part of this article, we show that the sensitivity of the ν(C≡N) IR shifts does not depend on solvent polarity. In the second part, we describe how probing the shifts of the nitrile IR vibrational band unambiguously confirms the formation of dimer radical anions, with K dim = 3 × 10 4 M –1. IR findings are corroborated by electronic absorption spectroscopy and electronic structure calculations. We find that the presence of a hexyl chain and the formation of π–π interactions are both crucial for dimerization of radical anions of 6CB with neutral 6CB. Our study provides clear evidence of spatial delocalization of electrons over two molecular fragments.« less

Human 2-Oxoglutarate Dehydrogenase Complex E1 Component Forms a Thiamin-derived Radical by Aerobic Oxidation of the Enamine Intermediate*

PubMed Central

Nemeria, Natalia S.; Ambrus, Attila; Patel, Hetalben; Gerfen, Gary; Adam-Vizi, Vera; Tretter, Laszlo; Zhou, Jieyu; Wang, Junjie; Jordan, Frank

2014-01-01

Herein are reported unique properties of the human 2-oxoglutarate dehydrogenase multienzyme complex (OGDHc), a rate-limiting enzyme in the Krebs (citric acid) cycle. (a) Functionally competent 2-oxoglutarate dehydrogenase (E1o-h) and dihydrolipoyl succinyltransferase components have been expressed according to kinetic and spectroscopic evidence. (b) A stable free radical, consistent with the C2-(C2α-hydroxy)-γ-carboxypropylidene thiamin diphosphate (ThDP) cation radical was detected by electron spin resonance upon reaction of the E1o-h with 2-oxoglutarate (OG) by itself or when assembled from individual components into OGDHc. (c) An unusual stability of the E1o-h-bound C2-(2α-hydroxy)-γ-carboxypropylidene thiamin diphosphate (the “ThDP-enamine”/C2α-carbanion, the first postdecarboxylation intermediate) was observed, probably stabilized by the 5-carboxyl group of OG, not reported before. (d) The reaction of OG with the E1o-h gave rise to superoxide anion and hydrogen peroxide (reactive oxygen species (ROS)). (e) The relatively stable enzyme-bound enamine is the likely substrate for oxidation by O2, leading to the superoxide anion radical (in d) and the radical (in b). (f) The specific activity assessed for ROS formation compared with the NADH (overall complex) activity, as well as the fraction of radical intermediate occupying active centers of E1o-h are consistent with each other and indicate that radical/ROS formation is an “off-pathway” side reaction comprising less than 1% of the “on-pathway” reactivity. However, the nearly ubiquitous presence of OGDHc in human tissues, including the brain, makes these findings of considerable importance in human metabolism and perhaps disease. PMID:25210035

Electrochemistry and Spectroelectrochemistry of Polynuclear Zinc Phthalocyanines: Formation of Mixed Valence Cation Radical Species.

DTIC Science & Technology

1988-02-25

No. No. Copies Cpe Office of Naval Research 2 Dr. David You.)g Attn: Code 1113 Code 334 800 N. Quinc’ Street NORDA Arlington, Virginia 22217-5000 NSTL...Naval Surface Weapons Center Chapel Hill, North Carolina 27514 Silver Spring, Maryland 20910 Or. R. A. Marcus Dr. Michael J. Weaver Department of...Microprocessor model 340 spectrometer. Cyclic and dif, rential pulse voltammetry were performed with a Princeton Applied Research (PARC) model 174A

Chemical manipulation of oxygen vacancy and antibacterial activity in ZnO.

PubMed

V, Lakshmi Prasanna; Vijayaraghavan, Rajagopalan

2017-08-01

Pure and doped ZnO (cation and anion doping) compositions have been designed in order to manipulate oxygen vacancy and antibacterial activity of ZnO. In this connection, we have synthesized and characterized micron sized ZnO, N doped micron sized ZnO, nano ZnO, nano Na and La doped ZnO. The intrinsic vacancies in pure ZnO and the vacancies created by N and Na doping in ZnO have been confirmed by X-ray Photoelectron Spectroscopy(XPS) and Photoluminiscence Spectroscopy(PL). Reactive oxygen species (ROS) such as hydroxyl radicals, superoxide radicals and H 2 O 2 responsible for antibacterial activity have been estimated by PL, UV-Vis spectroscopy and KMnO 4 titrations respectively. It was found that nano Na doped ZnO releases highest amount of ROS followed by nano ZnO, micron N doped ZnO while micron ZnO releases the least amount of ROS. The concentration of vacancies follows the same sequence. This illustrates directly the correlation between ROS and oxygen vacancy in well designed pure and doped ZnO. For the first time, material design in terms of cation doping and anion doping to tune oxygen vacancies has been carried out. Interaction energy (E g ), between the bacteria and nanoparticles has been calculated based on Extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory and is correlated with antibacterial activity. Copyright © 2017 Elsevier B.V. All rights reserved.

Dissociative Ionization and Thermal Decomposition of Cyclopentanone

PubMed Central

Pastoors, Johan I. M.; Bodi, Andras; Hemberger, Patrick

2017-01-01

Abstract Despite the growing use of renewable and sustainable biofuels in transportation, their combustion chemistry is poorly understood, limiting our efforts to reduce harmful emissions. Here we report on the (dissociative) ionization and the thermal decomposition mechanism of cyclopentanone, studied using imaging photoelectron photoion coincidence spectroscopy. The fragmentation of the ions is dominated by loss of CO, C2H4, and C2H5, leading to daughter ions at m/z 56 and 55. Exploring the C5H8O. + potential energy surface reveals hydrogen tunneling to play an important role in low‐energy decarbonylation and probably also in the ethene‐loss processes, yielding 1‐butene and methylketene cations, respectively. At higher energies, pathways without a reverse barrier open up to oxopropenyl and cyclopropanone cations by ethyl‐radical loss and a second ethene‐loss channel, respectively. A statistical Rice–Ramsperger–Kassel–Marcus model is employed to test the viability of this mechanism. The pyrolysis of cyclopentanone is studied at temperatures ranging from about 800 to 1100 K. Closed‐shell pyrolysis products, namely 1,3‐butadiene, ketene, propyne, allene, and ethene, are identified based on their photoion mass‐selected threshold photoelectron spectrum. Furthermore, reactive radical species such as allyl, propargyl, and methyl are found. A reaction mechanism is derived incorporating both stable and reactive species, which were not predicted in prior computational studies. PMID:28692134

Thermal O-H Bond Activation of Water as Mediated by Heteronuclear [Al2Mg2O5]•+: Evidence for Oxygen-Atom Scrambling.

PubMed

Geng, Caiyun; Li, Jilai; Weiske, Thomas; Schwarz, Helmut

2018-06-25

Mechanistic insight into the thermal O-H bond activation of water by the cubane-like, prototypical heteronuclear oxide cluster [Al 2 Mg 2 O 5 ] •+ has been derived from a combined experimental/computational study. Experiments in the highly diluted gas phase using Fourier transform ion-cyclotron resonance mass spectrometry show that hydrogen-atom abstraction from water by the cluster cation [Al 2 Mg 2 O 5 ] •+ occurs at ambient conditions accompanied by the liberation of an OH • radical. Due to a complete randomization of all oxygen atoms prior to fragmentation about 83% of the oxygen atoms of the hydroxyl radical released originate from the oxide cluster itself. The experimental findings are supported by detailed high-level quantum chemical calculations. The theoretical analysis reveals that the transfer of a formal hydrogen atom from water to the metal-oxide cation can proceed mechanistically via proton- or hydrogen-atom transfer exploiting different active sites of the cluster oxide. In addition to the unprecedented oxygen-atom scrambling, one of the more general and quite unexpected findings concerns the role of spin density at the hydrogen-acceptor oxide atom. While this feature is so crucial for [M-O] + /CH 4 couples, it is much less important in the O-H bond activation of water.

Synthesis of well-defined bisbenzoin end-functionalized poly(ε-caprolactone) macrophotoinitiator by combination of ROP and click chemistry and its use in the synthesis of star copolymers by photoinduced free radical promoted cationic polymerization

PubMed Central

Uyar, Zafer; Degirmenci, Mustafa; Genli, Nasrettin; Yilmaz, Ayse

2017-01-01

Abstract A new well-defined bisbenzoin group end-functionalized poly(ε-caprolactone) macrophotoinitiator (PCL-(PI)2) was synthesized by combination of ring opening polymerization (ROP) and click chemistry. The ROP of ε-CL monomer in bulk at 110 °C, by means of a hydroxyl functional initiator namely, 3-cyclohexene-1-methanol in conjunction with stannous-2-ethylhexanoate, (Sn(Oct)2), yielded a well-defined PCL with a cyclohexene end-chain group (PCL-CH). The bromination and subsequent azidation of the cyclohexene end-chain group gave bisazido functionalized poly(ε-caprolactone) (PCL-(N3)2). Separately, an acetylene functionalized benzoin photoinitiator (PI-alkyne) was synthesized by using benzoin and propargyl bromide. Then the click reaction between PCL-(N3)2 and PI-alkyne was performed by Cu(I) catalysis. The spectroscopic studies revealed that poly(ε-caprolactone) with bisbenzoin photoactive functional group at the chain end (PCL-(PI)2) with controlled chain length and low-polydispersity was obtained. This PCL-(PI)2 macrophotoinitiator was used as a precursor in photoinduced free radical promoted cationic polymerization to synthesize an AB2-type miktoarm star copolymer consisting of poly(ε-caprolactone) (PCL, as A block) and poly(cyclohexene oxide) (PCHO, as B block), namely PCL(PCHO)2. PMID:29491778

Radical-cationic gaseous amino acids: a theoretical study.

PubMed

Sutherland, Kailee N; Mineau, Philippe C; Orlova, Galina

2007-08-16

Three major forms of gaseous radical-cationic amino acids (RCAAs), keto (COOH), enolic (C(OH)OH), and zwitterionic (COO(-)), as well as their tautomers, are examined for aliphatic Ala(.+), Pro(.+), and Ser(.+), sulfur-containing Cys(.+), aromatic Trp(.+), Tyr(.+), and Phe(.+), and basic His(.+). The hybrid B3LYP exchange-correlation functional with various basis sets along with the highly correlated CCSD(T) method is used. For all RCAAs considered, the main stabilizing factor is spin delocalization; for His(.+), protonation of the basic side chain is equally important. Minor stabilizing factors are hydrogen bonding and 3e-2c interactions. An efficient spin delocalization along the N-C(alpha)-C(O-)O moiety occurs upon H-transfer from C(alpha) to the carboxylic group to yield the captodative enolic form, which is the lowest-energy isomer for Ala(.+), Pro(.+), Ser(.+), Cys(.+), Tyr(.+), and Phe(.+). This H-transfer occurs in a single step as a 1,3-shift through the sigma-system. For His(.+), the lowest-energy isomer is formed upon H-transfer from C(alpha) to the basic side chain, which results in a keto form, with spin delocalized along the N-C(alpha)-C=O fragment. Trp(.+) is the only RCAA that favors spin delocalization over an aromatic system given the low ionization energy of indole. The lowest-energy isomer of Trp(.+) is a keto form, with no H-transfer.

Prevention of acetic acid-induced colitis by desferrithiocin analogs in a rat model.

PubMed

Bergeron, Raymond J; Wiegand, Jan; Weimar, William R; Nguyen, John Nhut; Sninsky, Charles A

2003-02-01

Iron contributes significantly to the formation of reactive oxygen species via the Fenton reaction. Therefore, we assessed whether a series of desferrithiocin analogs, both carboxylic acids and hydroxamates, could (1) either promote or diminish the iron-mediated oxidation of ascorbate, (2) quench a model radical species, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+), and (3) when applied topically, prevent acetic acid-induced colitis in rats. Surprisingly, most of the desferrithiocin analogs inhibited the Fenton reaction to an approximately equivalent degree; however, substantial differences were observed in the capacity of the analogs to scavenge the model radical cation. Four carboxylic acid desferrithiocin analogs and their respective N-methylhydroxamates were tested along with desferrioxamine and Rowasa, a currently accepted topical therapeutic agent for inflammatory bowel disease (IBD), in a rodent model of acetic acid-induced colitis. The colonic damage was quantitated by two independent measurements. Although neither radical scavenging nor prevention of Fenton chemistry was a definitive predictor of in vivo efficacy, the overall trend is that desferrithiocin analogs substituted with an N-methylhydroxamate in the place of the carboxylic acid are both better free radical scavengers and more active against acetic acid-induced colitis. These results represent an intriguing alternative avenue to the development of improved IBD therapeutic agents.

Fragmentation of neutral amino acids and small peptides by intense, femtosecond laser pulses.

PubMed

Duffy, Martin J; Kelly, Orla; Calvert, Christopher R; King, Raymond B; Belshaw, Louise; Kelly, Thomas J; Costello, John T; Timson, David J; Bryan, William A; Kierspel, Thomas; Turcu, I C Edmond; Cacho, Cephise M; Springate, Emma; Williams, Ian D; Greenwood, Jason B

2013-09-01

High power femtosecond laser pulses have unique properties that could lead to their application as ionization or activation sources in mass spectrometry. By concentrating many photons into pulse lengths approaching the timescales associated with atomic motion, very strong electric field strengths are generated, which can efficiently ionize and fragment molecules without the need for resonant absorption. However, the complex interaction between these pulses and biomolecular species is not well understood. To address this issue, we have studied the interaction of intense, femtosecond pulses with a number of amino acids and small peptides. Unlike previous studies, we have used neutral forms of these molecular targets, which allowed us to investigate dissociation of radical cations without the spectra being complicated by the action of mobile protons. We found fragmentation was dominated by fast, radical-initiated dissociation close to the charge site generated by the initial ionization or from subsequent ultrafast migration of this charge. Fragments with lower yields, which are useful for structural determinations, were also observed and attributed to radical migration caused by hydrogen atom transfer within the molecule.

The Effect of Convolvulus arvensis Dried Extract as a Potential Antioxidant in Food Models

PubMed Central

Mohd Azman, Nurul Aini; Gallego, Maria Gabriela; Juliá, Luis; Fajari, Lluis; Almajano, MaríaPilar

2015-01-01

In this study, the antioxidant activity of the Convolvulus arvensis Linn (CA) ethanol extract has been evaluated by different ways. The antioxidant activity of the extract assessed by 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical cation, the oxygen radical absorbance capacity (ORAC) and the ferric reducing antioxidant power (FRAP) was 1.62 mmol Trolox equivalents (TE)/g DW, 1.71 mmol TE/g DW and 2.11 mmol TE/g DW, respectively. CA ethanol extract exhibited scavenging activity against the methoxy radical initiated by the Fenton reaction and measured by Electron Paramagnetic Resonance (EPR). The antioxidant effects of lyophilised CA measured in beef patties containing 0.1% and 0.3% (w/w) CA stored in modified atmosphere packaging (MAP) (80% O2 and 20% CO2) was determined. A preliminary study of gelatine based film containing CA showed a strong antioxidant effect in preventing the degradation of lipid in muscle food. Thus, the present results indicate that CA extract can be used as a natural food antioxidant. PMID:26785344

Protein hydrolysate from turkey meat and optimization of its antioxidant potential by response surface methodology.

PubMed

Wang, Daoying; Shahidi, Fereidoon

2018-05-01

The objective of this research was to optimize antioxidant potential of hydrolyzed protein using Flavourzyme assisted hydrolysis of turkey meat and compare the antioxidant activity of hydrolysates from turkey meat, chicken, and beef. Response surface methodology (RSM) was used to determine the optimal Flavourzyme hydrolysis conditions for preparation of hydrolysate from turkey meat, which were at a temperature of 50.09°C, pH of 5.42, and processing time of 1.08 hours. For comparison, antioxidant activities of the hydrolysate from turkey meat, chicken, and beef under the optimum conditions were determined using reducing power, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical cation, hydroxyl radical, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities. The antioxidant activity of turkey meat and chicken meat was significantly higher than that of beef (P < 0.05). Therefore Flavourzyme could be regarded as an effective hydrolytic enzyme for preparation of antioxidant hydrolysate from turkey meat, indicating the potential use of it as a functional food ingredient with shelf-life extension purposes.

Implications of Carotenoid Biosynthetic Genes in Apocarotenoid Formation during the Stigma Development of Crocus sativus and Its Closer Relatives1

PubMed Central

Castillo, Raquel; Fernández, José-Antonio; Gómez-Gómez, Lourdes

2005-01-01

Crocus sativus is a triploid sterile plant characterized by its long red stigmas, which produce and store significant quantities of the apocarotenoids crocetin and crocin, formed from the oxidative cleavage of zeaxanthin. Here, we investigate the accumulation and the molecular mechanisms that regulate the synthesis of these apocarotenoids during stigma development in C. sativus. We cloned the cDNAs for phytoene synthase, lycopene-β-cyclase, and β-ring hydroxylase from C. sativus. With the transition of yellow undeveloped to red fully developed stigmas, an accumulation of zeaxanthin was observed, accompanying the expression of CsPSY, phytoene desaturase, and CsLYCb, and the massive accumulation of CsBCH and CsZCD transcripts. We analyzed the expression of these two transcripts in relation to zeaxanthin and apocarotenoid accumulation in other Crocus species. We observed that only the relative levels of zeaxanthin in the stigma of each cultivar were correlated with the level of CsBCH transcripts. By contrast, the expression levels of CsZCD were not mirrored by changes in the apocarotenoid content, suggesting that the reaction catalyzed by the CsBCH enzyme could be the limiting step in the formation of saffron apocarotenoids in the stigma tissue. Phylogenetic analysis of the CsBCH intron sequences allowed us to determine the relationships among 19 Crocus species and to identify the closely related diploids of C. sativus. In addition, we examined the levels of the carotenoid and apocarotenoid biosynthetic genes in the triploid C. sativus and its closer relatives to determine whether the quantities of these specific mRNAs were additive or not in C. sativus. Transcript levels in saffron were clearly higher and nonadditive, suggesting that, in the triploid gene, regulatory interactions that produce novel effects on carotenoid biosynthesis genes are involved. PMID:16183835

Effect of feeding duration of diets containing corn distillers dried grains with solubles on productive performance, egg quality, and lutein and zeaxanthin concentrations of egg yolk in laying hens.

PubMed

Shin, H S; Kim, J W; Kim, J H; Lee, D G; Lee, S; Kil, D Y

2016-10-01

This experiment was conducted to investigate the effect of feeding duration of diets containing corn distillers dried grains with solubles (DDGS) on productive performance, egg quality, and lutein and zeaxanthin concentrations of egg yolk in laying hens. A total of 300 57-week-old Hy-Line Brown laying hens were randomly assigned to one of 5 treatment groups (feeding duration) with 6 replicates consisting of 5 consecutive cages with 2 hens per cage. Diets were formulated to contain either 0% (the control diet) or 20% DDGS. Experimental diets were fed to hens for 12 wk. The feeding duration of diets containing 20% DDGS was 0, 3, 6, 9, or 12 wk before the conclusion of the experiment. Feeding the diet containing 20% DDGS for 3, 6, or 9 wk followed feeding the control diet for 9, 6, or 3 wk, respectively. The data for productive performance were summarized for 12 wk of the feeding trial. Results indicated that increasing feeding duration of diets containing 20% DDGS had no effects on productive performance of laying hens, but increased egg yolk color (linear, P < 0.01), hunter a* value (linear and quadratic, P < 0.01), and b* values (linear, P < 0.05) with a decrease in hunter L* value (linear and quadratic, P < 0.05). Lutein and zeaxanthin concentrations of egg yolks also were increased (linear, P < 0.01) by increasing the feeding duration of diets containing 20% DDGS. In conclusion, feeding diets containing 20% DDGS to laying hens has no adverse effects on productive performance. Increasing the feeding duration of diets containing 20% DDGS improves egg yolk coloration with a concomitant increase in lutein and zeaxanthin concentrations of egg yolks in laying hens. © 2016 Poultry Science Association Inc.

Drug Discovery of Antimicrobial Photosensitizers Using Animal Models

PubMed Central

Sharma, Sulbha K.; Dai, Tianhong; Kharkwal, Gitika B.; Huang, Ying-Ying; Huang, Liyi; Bil De Arce, Vida J.; Tegos, George P.; Hamblin, Michael R.

2012-01-01

Antimicrobial photodynamic therapy (aPDT) is an emerging alternative to antibiotics motivated by growing problems with multi-drug resistant pathogens. aPDT uses non-toxic dyes or photosensitizers (PS) in combination with harmless visible of the correct wavelength to be absorbed by the PS. The excited state PS can form a long-lived triplet state that can interact with molecular oxygen to produce reactive oxygen species such as singlet oxygen and hydroxyl radical that kill the microbial cells. To obtain effective PS for treatment of infections it is necessary to use cationic PS with positive charges that are able to bind to and penetrate different classes of microbial cells. Other drug design criteria require PS with high absorption coefficients in the red/near infra-red regions of the spectrum where light penetration into tissue is maximum, high photostability to minimize photobleaching, and devising compounds that will selectively bind to microbial cells rather than host mammalian cells. Several molecular classes fulfill many of these requirements including phenothiazinium dyes, cationic tetrapyrroles such as porphyrins, phthalocyanines and bacteriochlorins, cationic fullerenes and cationic derivatives of other known PS. Larger structures such as conjugates between PS and cationic polymers, cationic nanoparticles and cationic liposomes that contain PS are also effective. In order to demonstrate in vivo efficacy it is necessary to use animal models of localized infections in which both PS and light can be effectively delivered into the infected area. This review will cover a range of mouse models we have developed using bioluminescent pathogens and a sensitive low light imaging system to non-invasively monitor the progress of the infection in real time. Effective aPDT has been demonstrated in acute lethal infections and chronic biofilm infections; in infections caused by Gram-positive, Gram-negative bacteria and fungi; in infections in wounds, third degree burns, skin abrasions and soft-tissue abscesses. This range of animal models also represents a powerful aid in antimicrobial drug discovery. PMID:21504410

Investigation of geminate recombination of radical ion pairs generated by dissociation of exciplexes in moderately polar solvents using the photoconductivity technique

NASA Astrophysics Data System (ADS)

Lukin, Leonid V.

2009-06-01

A new approach to determination of the recombination rate of radical ion pairs in moderately polar solvents is presented. It is based on an investigation of transient photocurrents caused by dissociation of exciplexes generated in photoinduced electron transfer reactions. It has been shown that the recombination rate of geminate ion pairs can be found from the photocurrent rise time. We have applied such an approach to transient photocurrents observed by Hirata et al. [Y. Hirata, Y. Kanda, N. Mataga, J. Phys. Chem. 87 (1983) 1659] for the pyrene/dicyanobenzene system in solvents of moderate polarity. The increase of the obtained recombination rate of photogenerated ions with increasing polarity of solvent testifies that ions recombine mainly by the backward electron transfer from the dicyanobenzene anions to solvent-separated cations of pyrene.

Morphological control of conductive polymers utilized electrolysis polymerization technique: trial of fabricating biocircuit.

PubMed

Onoda, Mitsuyoshi

2014-10-01

Conductive polymers are a strong contender for making electronic circuits. The growth pattern in conductive polymer synthesis by the electrolysis polymerization method was examined. The growth pattern is deeply related to the coupling reaction of the radical cation and the deprotonation reaction following it and changes suddenly depending on the kind and concentration of the supporting electrolyte and the solvent used. That is, when the electrophilic substitution coupling reaction becomes predominant, the three-dimensional growth form is observed, and when the radical coupling reaction becomes predominant, the two-dimensional growth morphology is observed. In addition, the growth pattern can be comparatively easily controlled by changing the value of the polymerization constant current, and it is considered that the indicator and development for biocircuit research with neuron-type devices made of conjugated polymers was obtained.

Effects of quaternization on the morphological stability and antibacterial activity of electrospun poly(DMAEMA-co-AMA) nanofibers.

PubMed

Xu, Jing-Wei; Wang, Yao; Yang, Yun-Feng; Ye, Xiang-Yu; Yao, Ke; Ji, Jian; Xu, Zhi-Kang

2015-09-01

Electrospun nanofibers with antibacterial activity are greatly promising for medical treatment and water purification. Herein we report antibacterial nanofibers electrospun from a series of poly(dimethylamino ethyl methacrylate-co-alkyl methacrylates) (poly(DMAEMA-co-AMA)) and to distinguish the effects of free and cross-linked cations derived from quanternization on the antibacterial activity. Poly(DMAEMA-co-AMA)s are simply synthesized by free radical polymerization from commercial monomers. DSC analysis indicates that they have Tg lower than room temperature and thus the electrospun nanofibers adhere to each other and evenly tend to form films, instead of keeping cylinderic shape. Benzyl chloride (BC) and p-xylylene dichloride (XDC) can quaternize DMAEMA units and to generate cations on the nanofiber surface. XPS analysis and colorimetric assay determine the quaternization degree and the surface accessible quaternary amines (N(+)), respectively. It is very promising that this quaternization endows the electrospun nanofibers with both stable morphology and antibacterial activity. The BC-quaternized fibers show better antibacterial behavior against Escherichia coli and Staphylococcus aureus than those of the XDC-quaternized/cross-linked ones, because cross-linking suppresses the chain mobility of cations. Our results confirm that antibacterial nanofibers can be facilely prepared and chain mobility of the formed cations is the necessary prerequisite for their antibacterial activity. Copyright © 2015 Elsevier B.V. All rights reserved.

Visible light detoxification by 2,9,16,23-tetracarboxyl phthalocyanine copper modified amorphous titania

NASA Astrophysics Data System (ADS)

Chen, Feng; Deng, Zhigang; Li, Xiaopei; Zhang, Jinlong; Zhao, Jincai

2005-10-01

Visible light detoxification of methyl orange (MO) was achieved with a photo-stable 2,9,16,23-tetracarboxyl phthalocyanine (TcPc)/amorphous TiO 2 hybrid photocatalyst. TcPc/amorphous TiO 2 exhibits an excellent photocatalytic activity under visible irradiation ( λ > 550 nm). Besides the active oxygen species, sensitizer radical cation, TcPc + rad , was also found to react with MO directly and induce the photodegradation of MO significantly for the first time in dye sensitized photocatalytic system.

Colorimetric detection of copper ions in sub-micromolar concentrations using a triarylamine-linked resin bead.

PubMed

Thomas, Tony George; Sreenath, Kesavapillai; Gopidas, Karical R

2012-11-21

The triarylamine derivative ETPA reacts with Cu(2+) to give deeply colored, stable radical cations in acetonitrile solution. ETPA was immobilized on to a tentagel resin bead which was then used for the fabrication of a simple device capable of the colorimetric detection of submicromolar concentrations of Cu(2+) ions in water. The naked eye detection limit reported here for Cu(2+) is one of the lowest ever reported for small molecule sensors.

QTAIM electron density study of natural chalcones

NASA Astrophysics Data System (ADS)

González Moa, María J.; Mandado, Marcos; Cordeiro, M. Natália D. S.; Mosquera, Ricardo A.

2007-09-01

QTAIM atomic and bond properties, ionization potential, and O-H bond dissociation energies calculated at the B3LYP/6-311++G(2d,2p) level indicate the natural chalcones bear a significant radical scavenging activity. However, their ionization potentials indicate they decrease the electron-transfer rate between antioxidant and oxygen that yields the pro-oxidative cations less than other natural antioxidants. Rings A and B display slight and similar positive charges, whereas ring B is involved in exocycle delocalization at a larger extension.

Correlation of Calculated Halonium Ion Structures with Experimental Product Distributions from Terminal Alkenes: The Effect of Electron-Withdrawing Fluorine Substituents on the Structure and Charge Localization of Halonium Ions (PREPRINT)

DTIC Science & Technology

2006-04-03

2) Substituting a vinyl hydrogen with a fluorine presents an interesting situation for electrophilic reactions. The π-bond is less...reactive toward electrophiles due to the electron-withdrawing effect of the vinyl fluorine . Therefore, carbocations or radical cations are destabilized...NUMBER Distributions from Terminal Alkenes: The Effect of Electron-Withdrawing Fluorine Substituents on the Structure and Charge Localization of

Aqueous electrolytes for redox flow battery systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Tianbiao; Li, Bin; Wei, Xiaoliang

An aqueous redox flow battery system includes an aqueous catholyte and an aqueous anolyte. The aqueous catholyte may comprise (i) an optionally substituted thiourea or a nitroxyl radical compound and (ii) a catholyte aqueous supporting solution. The aqueous anolyte may comprise (i) metal cations or a viologen compound and (ii) an anolyte aqueous supporting solution. The catholyte aqueous supporting solution and the anolyte aqueous supporting solution independently may comprise (i) a proton source, (ii) a halide source, or (iii) a proton source and a halide source.

The Electronic Spectra of Phthalocyanine Radical Anions and Cations.

DTIC Science & Technology

1985-03-01

415. (10) McHugh , A.J., Gouterman, M., Weiss, J., Theoret. Chim. Acta, 1972, 24, 346. (11) Henriksson, A. and Sundbom, M., Theoret. Chim. Acta, 1972, 27...oxidisable. The spectra for the nickel (II) Pc species exactly parallel the main group data since no change in oxidation state of the nickel ion is expect- ed18...and no charge transfer is expected in the region under study. 6 In summary, the main group complexes, nickel and cobalt species all have parallel

Synthesis, structures, and properties of crystalline salts with radical anions of metal-containing and metal-free phthalocyanines.

PubMed

Konarev, Dmitri V; Kuzmin, Alexey V; Faraonov, Maxim A; Ishikawa, Manabu; Khasanov, Salavat S; Nakano, Yoshiaki; Otsuka, Akihiro; Yamochi, Hideki; Saito, Gunzi; Lyubovskaya, Rimma N

2015-01-12

Radical anion salts of metal-containing and metal-free phthalocyanines [MPc(3-)](·-), where M = Cu(II), Ni(II), H2, Sn(II), Pb(II), Ti(IV)O, and V(IV)O (1-10) with tetraalkylammonium cations have been obtained as single crystals by phthalocyanine reduction with sodium fluorenone ketyl. Their formation is accompanied by the Pc ligand reduction and affects the molecular structure of metal phthalocyanine radical anions as well as their optical and magnetic properties. Radical anions are characterized by the alternation of short and long C-Nimine bonds in the Pc ligand owing to the disruption of its aromaticity. Salts 1-10 show new bands at 833-1041 nm in the NIR range, whereas the Q- and Soret bands are blue-shifted by 0.13-0.25 eV (38-92 nm) and 0.04-0.07 eV (4-13 nm), respectively. Radical anions with Ni(II), Sn(II), Pb(II), and Ti(IV)O have S = 1/2 spin state, whereas [Cu(II)Pc(3-)](·-) and [V(IV)OPc(3-)](·-) containing paramagnetic Cu(II) and V(IV)O have two S = 1/2 spins per radical anion. Central metal atoms strongly affect EPR spectra of phthalocyanine radical anions. Instead of narrow EPR signals characteristic of metal-free phthalocyanine radical anions [H2Pc(3-)](·-) (linewidth of 0.08-0.24 mT), broad EPR signals are manifested (linewidth of 2-70 mT) with g-factors and linewidths that are strongly temperature-dependent. Salt 11 containing the [Na(I)Pc(2-)](-) anions as well as previously studied [Fe(I)Pc(2-)](-) and [Co(I)Pc(2-)](-) anions that are formed without reduction of the Pc ligand do not show changes in molecular structure or optical and magnetic properties characteristic of [MPc(3-)](·-) in 1-10. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spectral reflectance of carbonate minerals and rocks in the visible and near infrared (0.35 - 2.55 microns) and its applications in carbonate petrology

NASA Technical Reports Server (NTRS)

Gaffey, S. J.

1984-01-01

Reflection spectroscopy in the visible and near infrared (0.35 to 2.55 micron) offers a rapid, inexpensive, nondestructive tool for determining the mineralogy and investigating the minor element chemistry of the hard-to-discriminate carbonate minerals, and can, in one step, provide information previously obtainable only by the combined application of two or more analytical techniques. When light interacts with a mineral certain wavelengths are preferentially absorbed. The number, positions, widths and relative intensities of these absorptions are diagnostic of the mineralogy and chemical composition of the sample. At least seven bands due to vibrations of the carbonate radical occur between 1.60 and 2.55 micron. Positions of these bands vary from one carbonae mineral to another and can be used for mineral identification. Cation mass is the primary factor controlling band position; cation radius plays a secondary role.

Development of UV-curable liquid for in-liquid fluorescence alignment in ultraviolet nanoimprint lithography

NASA Astrophysics Data System (ADS)

Ochiai, Kento; Kikuchi, Eri; Ishito, Yota; Kumagai, Mari; Nakamura, Takahiro; Nakagawa, Masaru

2018-06-01

We studied a fluorescent UV-curable resin suitable for fluorescence alignment in UV nanoimprinting. The addition of a cationic fluorescent dye caused radical photopolymerization of a UV-curable resin by exposure to visible excitation light for fluorescence microscope observation. The microscope observation of a resin film prepared by pressing resin droplets on a silica substrate with a fluorinated silica superstrate revealed that the cationic dye molecules were preferably adsorbed onto the silica surface. It was indicated that the dye molecules concentrated on the silica surface may cause the photocuring. A nonionic fluorescent dye was selected owing to its low polar symmetrical structure and its solubility parameter close to monomers. The fluorescent UV-curable resin with the nonionic dye showed uncured stability to exposure to visible excitation light for 30 min with a light intensity of 8.5 mW cm‑2 detected at 530 nm.

N,N',N"-tris(dihydroxyphosphorylmethyl)-1,4,7-triazacyclononane (Deofix) - a high-affinity, high-specificity chelator for first transition series metal cations with significant deodorant, antimicrobial, and antioxidant activity.

PubMed

Laden, Karl; Zaklad, Haim; Simhon, Elliot D; Klein, Joseph Y; Cyjon, Rosa L; Winchell, Harry S

2003-01-01

Deofix, N,N',N"-tris(dihydroxyphosphorylmethyl)-1,4,7-triazacyclononane, is a high-affinity, high-specificity chelator for first transition series cations such as iron, zinc, manganese, and copper. A 1% solution in 50% ethanol was found to be significantly better at reducing underarm malodor than a solution of 0.3% Triclosan in 50% ethanol. Compared to a 50% alcohol control, Deofix was found to produce a significant reduction in malodor for at least 48 hours. Deofix appears to work by reducing the concentration of first transition series metal ions below the levels needed for microbial cell reproduction and by inhibiting oxidative processes by interfering with catalytic formation of free radicals. Deofix has very low levels of toxicity when measured via a number of screening techniques.

Potentiation of antimicrobial photodynamic inactivation mediated by a cationic fullerene by added iodide: in vitro and in vivo studies

PubMed Central

Zhang, Yunsong; Dai, Tianhong; Wang, Min; Vecchio, Daniela; Chiang, Long Y; Hamblin, Michael R

2016-01-01

Background Antimicrobial photodynamic inactivation with fullerenes bearing cationic charges may overcome resistant microbes. Methods & results We synthesized C60-fullerene (LC16) bearing decaquaternary chain and deca-tertiary-amino groups that facilitates electron-transfer reactions via the photoexcited fullerene. Addition of the harmless salt, potassium iodide (10 mM) potentiated the ultraviolet A (UVA) or white light-mediated killing of Gram-negative bacteria Acinetobacter baumannii, Gram-positive methicillin-resistant Staphylococcus aureus and fungal yeast Candida albicans by 1–2+ logs. Mouse model infected with bioluminescent Acinetobacter baumannii gave increased loss of bioluminescence when iodide (10 mM) was combined with LC16 and UVA/white light. Conclusion The mechanism may involve photoinduced electron reduction of 1(C60>)* or 3(C60>)* by iodide producing I· or I2 followed by subsequent intermolecular electron-transfer events of (C60>)−· to produce reactive radicals. PMID:25723093

Dynamics of an excess hole in the 1-methyl-1-butyl-pyrrolidinium dicyanamide ionic-liquid

NASA Astrophysics Data System (ADS)

Wu, Fei; Xu, Changhui; Margulis, Claudio J.

2018-05-01

In a set of recent publications [C. J. Margulis et al., J. Am. Chem. Soc. 133, 20186 (2011); C. H. Xu et al., J. Am. Chem. Soc. 135, 17528 (2013); C. H. Xu and C. J. Margulis, J. Phys. Chem. B 119, 532 (2015); and K. B. Dhungana et al., J. Phys. Chem. B 121, 8809 (2017)], we explored for selected ionic liquids the early stages of excess charge localization and reactivity relevant both to electrochemical and radiation chemistry processes. In particular, Xu and Margulis [J. Phys. Chem. B 119, 532 (2015)] explored the dynamics of an excess electron in 1-methyl-1-butyl-pyrrolidinium dicyanamide. When electrons are produced from an ionic liquid, the more elusive hole species are also generated. Depending on the nature of cations and anions and the relative alignment of their electronic states in the condensed phase, the very early hole species can nominally be neutral radicals—if the electron is generated from anions—or doubly charged radical cations if their origin is from cations. However, in reality early excess charge localization is more complex and often involves more than one ion. The dynamics and the transient spectroscopy of the hole are the main objects of this study. We find that in the case of 1-methyl-1-butyl-pyrrolidinium dicyanamide, it is the anions that can most easily lose an electron becoming radical species, and that hole localization is mostly on anionic nitrogen. We also find that the driving force for localization of an excess hole appears to be smaller than that for an excess electron in 1-methyl-1-butyl-pyrrolidinium dicyanamide. The early transient hole species can absorb light in the visible, ultraviolet, and near infrared regions, and we are able to identify the type of states being connected by these transitions.

Recyclable catalysts methods of making and using the same

DOEpatents

Dioumaev, Vladimir K.; Bullock, R. Morris

2006-02-28

Organometallic complexes are provided, which include a catalyst containing a transition metal, a ligand and a component having the formula GAr.sup.F. Ar.sup.F is an aromatic ring system selected from phenyl, naphthalenyl, anthracenyl, fluorenyl, or indenyl. The aromatic ring system has at least a substituent selected from fluorine, hydrogen, hydrocarbyl or fluorinated hydrocarbyl, G is substituted or unsubstituted (CH.sub.2).sub.n or (CF.sub.2).sub.n, wherein n is from 1 to 30, wherein further one or more CH.sub.2 or CF.sub.2 groups are optionally replaced by NR, PR, SiR.sub.2, BR, O or S, or R is hydrocarbyl or substituted hydrocarbyl, GAr.sup.F being covalently bonded to either said transition metal or said ligand of said catalyst, thereby rendering said cationic organometallic complex liquid. The catalyst of the organometallic complex can be [CpM(CO).sub.2(NHC)L.sub.k].sup.+A.sup.-, wherein M is an atom of molybdenum or tungsten, Cp is substituted or unsubstituted cyclopentadienyl radical represented by the formula [C.sub.5Q.sup.1Q.sup.2Q.sup.3Q.sup.4Q.sup.5], wherein Q.sup.1 to Q.sup.5 are independently selected from the group consisting of H radical, GAr.sup.F C.sub.1-20 hydrocarbyl radical, substituted hydrocarbyl radical, substituted hydrocarbyl radical substituted by GAr.sup.F, halogen radical, halogen-substituted hydrocarbyl radical, --OR, --C(O)R', --CO.sub.2R', --SiR'.sub.3 and --NR'R'', wherein R' and R'' are independently selected from the group consisting of H radical, C.sub.1-20 hydrocarbyl radical, halogen radical, and halogen-substituted hydrocarbyl radical, wherein said Q.sup.1 to Q.sup.5 radicals are optionally linked to each other to form a stable bridging group, NHC is any N-heterocyclic carbene ligand, L is either any neutral electron donor ligand, wherein k is a number from 0 to 1 or L is an anionic ligand wherein k is 2, and A.sup.- is an anion. Processes using the organometallic complexes as catalysts in catalytic reactions, such as for example, the hydrosilylation of aldehydes, ketones and esters are also provided.

Cationic antimicrobial polymers and their assemblies.

PubMed

Carmona-Ribeiro, Ana Maria; de Melo Carrasco, Letícia Dias

2013-05-10

Cationic compounds are promising candidates for development of antimicrobial agents. Positive charges attached to surfaces, particles, polymers, peptides or bilayers have been used as antimicrobial agents by themselves or in sophisticated formulations. The main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs). The advantage of amphiphilic cationic polymers when compared to small amphiphilic molecules is their enhanced microbicidal activity. Besides, many of these polymeric structures also show low toxicity to human cells; a major requirement for biomedical applications. Determination of the specific elements in polymers, which affect their antimicrobial activity, has been previously difficult due to broad molecular weight distributions and random sequences characteristic of radical polymerization. With the advances in polymerization control, selection of well defined polymers and structures are allowing greater insight into their structure-antimicrobial activity relationship. On the other hand, antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications, such as wound dressing, photodynamic antimicrobial therapy, food packing and preservation and antifouling applications.

Cationic Antimicrobial Polymers and Their Assemblies

PubMed Central

Carmona-Ribeiro, Ana Maria; de Melo Carrasco, Letícia Dias

2013-01-01

Cationic compounds are promising candidates for development of antimicrobial agents. Positive charges attached to surfaces, particles, polymers, peptides or bilayers have been used as antimicrobial agents by themselves or in sophisticated formulations. The main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs). The advantage of amphiphilic cationic polymers when compared to small amphiphilic molecules is their enhanced microbicidal activity. Besides, many of these polymeric structures also show low toxicity to human cells; a major requirement for biomedical applications. Determination of the specific elements in polymers, which affect their antimicrobial activity, has been previously difficult due to broad molecular weight distributions and random sequences characteristic of radical polymerization. With the advances in polymerization control, selection of well defined polymers and structures are allowing greater insight into their structure-antimicrobial activity relationship. On the other hand, antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications, such as wound dressing, photodynamic antimicrobial therapy, food packing and preservation and antifouling applications. PMID:23665898

Cationic polymer brush-modified cellulose nanocrystals for high-affinity virus binding

NASA Astrophysics Data System (ADS)

Rosilo, Henna; McKee, Jason R.; Kontturi, Eero; Koho, Tiia; Hytönen, Vesa P.; Ikkala, Olli; Kostiainen, Mauri A.

2014-09-01

Surfaces capable of high-affinity binding of biomolecules are required in several biotechnological applications, such as purification, transfection, and sensing. Therein, the rod-shaped, colloidal cellulose nanocrystals (CNCs) are appealing due to their large surface area available for functionalization. In order to exploit electrostatic binding, their intrinsically anionic surfaces have to be cationized as biological supramolecules are predominantly anionic. Here we present a facile way to prepare cationic CNCs by surface-initiated atom-transfer radical polymerization of poly(N,N-dimethylaminoethyl methacrylate) and subsequent quaternization of the polymer pendant amino groups. The cationic polymer brush-modified CNCs maintained excellent dispersibility and colloidal stability in water and showed a ζ-potential of +38 mV. Dynamic light scattering and electron microscopy showed that the modified CNCs electrostatically bind cowpea chlorotic mottle virus and norovirus-like particles with high affinity. Addition of only a few weight percent of the modified CNCs in water dispersions sufficed to fully bind the virus capsids to form micrometer-sized assemblies. This enabled the concentration and extraction of the virus particles from solution by low-speed centrifugation. These results show the feasibility of the modified CNCs in virus binding and concentrating, and pave the way for their use as transduction enhancers for viral delivery applications.Surfaces capable of high-affinity binding of biomolecules are required in several biotechnological applications, such as purification, transfection, and sensing. Therein, the rod-shaped, colloidal cellulose nanocrystals (CNCs) are appealing due to their large surface area available for functionalization. In order to exploit electrostatic binding, their intrinsically anionic surfaces have to be cationized as biological supramolecules are predominantly anionic. Here we present a facile way to prepare cationic CNCs by surface-initiated atom-transfer radical polymerization of poly(N,N-dimethylaminoethyl methacrylate) and subsequent quaternization of the polymer pendant amino groups. The cationic polymer brush-modified CNCs maintained excellent dispersibility and colloidal stability in water and showed a ζ-potential of +38 mV. Dynamic light scattering and electron microscopy showed that the modified CNCs electrostatically bind cowpea chlorotic mottle virus and norovirus-like particles with high affinity. Addition of only a few weight percent of the modified CNCs in water dispersions sufficed to fully bind the virus capsids to form micrometer-sized assemblies. This enabled the concentration and extraction of the virus particles from solution by low-speed centrifugation. These results show the feasibility of the modified CNCs in virus binding and concentrating, and pave the way for their use as transduction enhancers for viral delivery applications. Electronic supplementary information (ESI) available: CNC surface chain fraction and degree of substitution after BriBBr modification, NMR spectra of the SI-ATRP reaction mixture at 0 and 120 min, conversion of the DMAEMA monomer during SI-ATRP, DLS size distribution profiles of CNCs and CNC-g-P(QDMAEMA), TEM images of NoV-VLPs and their complexes with CNC-g-P(QDMAEMA) at 0 mM NaCl. See DOI: 10.1039/c4nr03584d

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mani, Tomoyasu; Grills, David C.

Delocalization of charges is one of the factors controlling charge transport in conjugated molecules. It is considered to play an important role in the performance of a wide range of molecular technologies, including organic solar cells and organic electronics. Dimerization reactions are well-suited as a model to investigate intermolecular spatial delocalization of charges. And while dimerization reactions of radical cations are well investigated, studies on radical anions are still scarce. Upon dimerization of radical anions with neutral counterparts, an electron is considered to delocalize over the two molecules. By using time-resolved infrared (TRIR) detection coupled with pulse radiolysis, we showmore » that radical anions of 4-n-hexyl-4'-cyanobiphenyl (6CB) undergo such dimerization reactions, with an electron equally delocalized over the two molecules. We have recently demonstrated that nitrile ν(C≡N) vibrations respond to the degree of electron localization of nitrile-substituted anions: we can quantify the changes in the electronic charges from the neutral to the anion states in the nitriles by monitoring the ν(C≡N) IR shifts. In the first part of this article, we show that the sensitivity of the ν(C≡N) IR shifts does not depend on solvent polarity. In the second part, we describe how probing the shifts of the nitrile IR vibrational band unambiguously confirms the formation of dimer radical anions, with K dim = 3 × 10 4 M –1. IR findings are corroborated by electronic absorption spectroscopy and electronic structure calculations. We find that the presence of a hexyl chain and the formation of π–π interactions are both crucial for dimerization of radical anions of 6CB with neutral 6CB. Our study provides clear evidence of spatial delocalization of electrons over two molecular fragments.« less

The dependence of α-tocopheroxyl radical reduction by hydroxy-2,3-diarylxanthones on structure and micro-environment.

PubMed

Morlière, Patrice; Patterson, Larry K; Santos, Clementina M M; Silva, Artur M S; Mazière, Jean-Claude; Filipe, Paulo; Gomes, Ana; Fernandes, Eduarda; Garcia, M Beatriz Q; Santus, René

2012-03-14

The flavonoid quercetin is known to reduce the α-tocopheroxyl radical (˙TocO) and reconstitute α-tocopherol (TocOH). Structurally related polyphenolic compounds, hydroxy-2,3-diarylxanthones (XH), exhibit antioxidant activity which exceeds that of quercetin in biological systems. In the present study repair of ˙TocO by a series of these XH has been evaluated using pulse radiolysis. It has been shown that, among the studied XH, only 2,3-bis(3,4-dihydroxyphenyl)-9H-xanthen-9-one (XH9) reduces ˙TocO, though repair depends strongly on the micro-environment. In cationic cetyltrimethylammonium bromide (CTAB) micelles, 30% of ˙TocO radicals are repaired at a rate constant of ~7.4 × 10(6) M(-1) s(-1) by XH9 compared to 1.7 × 10(7) M(-1) s(-1) by ascorbate. Water-soluble Trolox (TrOH) radicals (˙TrO) are restored by XH9 in CTAB (rate constant ~3 × 10(4) M(-1) s(-1)) but not in neutral TX100 micelles where only 15% of ˙TocO are repaired (rate constant ~4.5 × 10(5) M(-1) s(-1)). In basic aqueous solutions ˙TrO is readily reduced by deprotonated XH9 species leading to ionized XH9 radical species (radical pK(a) ~10). An equilibrium is observed (K = 130) yielding an estimate of 130 mV for the reduction potential of the [˙X9,H(+)/XH9] couple at pH 11, lower than the 250 mV for the [˙TrO,H(+)/TrOH] couple. A comparable value (100 mV) has been determined by cyclic voltammetry measurements.

Free radical-scavenging activities of Crataegus monogyna extracts.

PubMed

Bernatoniene, Jurga; Masteikova, Rūta; Majiene, Daiva; Savickas, Arūnas; Kevelaitis, Egidijus; Bernatoniene, Rūta; Dvorácková, Katerina; Civinskiene, Genuvaite; Lekas, Raimundas; Vitkevicius, Konradas; Peciūra, Rimantas

2008-01-01

The aim of this study was to investigate antiradical activity of aqueous and ethanolic hawthorn fruit extracts, their flavonoids, and flavonoid combinations. Total amount of phenolic compounds and the constituents of flavonoids were determined using a high-performance liquid chromatography. The antioxidant activity of Crataegus monogyna extracts and flavonoids (chlorogenic acid, hyperoside, rutin, quercetin, vitexin-2O-rhamnoside, epicatechin, catechin, and procyanidin B(2)) quantitatively was determined using the method of spectrophotometry (diphenyl-1-picrylhydrazyl (DPPH.) radical scavenging assay and 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid)(ABTS.+) radical cation decolorization assay). The level of tyrosine nitration inhibition was determined using a high-performance liquid chromatography. Ethanolic hawthorn fruit extract contained 182+/-4 mg/100 mL phenolic compounds, i.e. threefold more, as compared to aqueous extract. The antioxidant activity according to DPPH. reduction in the ethanolic extracts was higher 2.3 times (P<0.05). The ABTS.+ technique showed that the effect of ethanolic extracts was by 2.5 times stronger than that of aqueous extracts. Tyrosine nitration inhibition test showed that the effect of ethanolic extracts was by 1.4 times stronger than that of aqueous extracts. The investigation of the antiradical activity of the active constituents in aqueous and ethanolic extracts revealed that epicatechin and catechin contribute to radical-scavenging properties more than other components. Procyanidin B(2) only insignificantly influenced the antiradical activity of the extracts. Both aqueous and ethanolic hawthorn extracts had antiradical activity, but ethanolic extract had stronger free radical-scavenging properties, compared to the aqueous extract. The antioxidant activity of the studied preparations was mostly conditioned by epicatechin and catechin. The individual constituents of both extracts had weaker free radical-scavenging properties than the combination of these substances did.

Gas chromatographic-mass spectrometric investigation of n-alkanes and carboxylic acids in bottom sediments of the northern Caspian Sea

NASA Astrophysics Data System (ADS)

Kenzhegaliev, Akimgali; Zhumagaliev, Sagat; Kenzhegalieva, Dina; Orazbayev, Batyr

2018-03-01

Prior to the start of experimental oil production in the Kashagan field (northern part of the Caspian Sea), n-alkanes and carboxylic acids contained in samples obtained from bottom sediments in the area of artificial island "D" were investigated by gas chromatography-mass spectrometry. Concentrations of 10 n-alkanes (composed of C10-C13, C15-C20) and 11 carboxylic acids (composed of C6-C12, C14-C16) were identified and measured. Concentrations of individual alkanes and carboxylic acids in bottom sediments of the various samples varied between 0.001 ÷ 0.88 μg/g and 0.001 ÷ 1.94 μg/g, respectively. Mass spectra, in particular the M+ molecular ion peak and the most intense peaks of fragment ions, are given. The present study illustrates the stability of molecular ions to electronic ionisation and the main fragment ions to the total ion current and shows that the initial fragmentation of alkanes implies radical cleavage of C2H5 rather than CH3. All aliphatic monocarboxylic acids studied were characterised by McLafferty rearrangement leading to the formation of F4 cation-radical with m/z 60 and F3 cation-radical with m/z 88 in the case of ethylhexanoic acid. The formation of oxonium ions presents another important aspect of acid fragmentation. Using mass numbers of oxonium ions and rearrangement ions allows determination of the substitution character in α- and β- C atoms. The essence of our approach is to estimate the infiltration of hydrocarbon fluids from the enclosing formation into sea water, comprising an analysis of derivatives of organic compounds in bottom sediments. Thus, concentrations of derived organic molecules can serve as a basis for estimates of the depth at which hydrocarbon fluids leak, i.e., to serve as an auxiliary technique in the search for hydrocarbon deposits and to repair well leaks.

The thermochemistry of cubane 50 years after its synthesis: a high-level theoretical study of cubane and its derivatives.

PubMed

Agapito, Filipe; Santos, Rui C; Borges dos Santos, Rui M; Martinho Simões, José A

2015-03-26

The gas-phase enthalpy of formation of cubane (603.4 ± 4 kJ mol(-1)) was calculated using an explicitly correlated composite method (W1-F12). The result obtained for cubane, together with the experimental value for the enthalpy of sublimation, 54.8 ± 2.0 kJ mol(-1), led to 548.6 ± 4.5 kJ mol(-1) for the solid-phase enthalpy of formation. This value is only 6.8 kJ mol(-1) higher than the 50-year-old original calorimetric result. The carbon-hydrogen bond dissociation enthalpy (C-H BDE) of cubane (438.4 ± 4 kJ mol(-1)), together with properties relevant for its experimental determination using gas-phase ion thermochemistry, namely the cubane gas-phase acidity (1704.6 ± 4 kJ mol(-1)), cubyl radical electron affinity (45.8 ± 4 kJ mol(-1)), cubane ionization energy (1435.1 ± 4 kJ mol(-1)), cubyl radical cation proton affinity (918.8 ± 4 kJ mol(-1)), cubane cation appearance energy (1099.6 ± 4 kJ mol(-1)), and cubyl ionization energy (661.2 ± 4 kJ mol(-1)), were also determined. These values were compared with those calculated for unstrained hydrocarbons (viz., methane, ethane, and isobutane). The strain energy of cubane (667.2 kJ mol(-1)) and cubyl radical (689.4 kJ mol(-1)) were independently estimated via quasihomodesmotic reactions. These values were related via a simple model to the C-H BDE in cubane. Taking into account the accuracy of the computational method, the comparison with high-precision experimental results, and the data consistency afforded by the relevant thermodynamic cycles, we claim an uncertainty better than ±4 kJ mol(-1) for the new enthalpy of formation values presented.

Catalytic effects of silver plasmonic nanoparticles on the redox reaction leading to ABTS˙+ formation studied using UV-visible and Raman spectroscopy.

PubMed

Garcia-Leis, A; Jancura, D; Antalik, M; Garcia-Ramos, J V; Sanchez-Cortes, S; Jurasekova, Z

2016-09-29

ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) is a compound extensively employed to evaluate the free radical trapping capacity of antioxidant agents and complex mixtures such as biological fluids or foods. This evaluation is usually performed by using a colourimetric experiment, where preformed ABTS radical cation (ABTS˙ + ) molecules are reduced in the presence of an antioxidant causing an intensity decrease of the specific ABTS˙ + UV-visible absorption bands. In this work we report a strong effect of silver plasmonic nanoparticles (Ag NPs) on ABTS leading to the formation of ABTS˙ + . The reaction of ABTS with Ag NPs has been found to be dependent on the interfacial and plasmonic properties of NPs. Specifically, this reaction is pronounced in the presence of spherical nanoparticles prepared by the reduction of silver nitrate with hydroxylamine (AgH) and in the case of star-shaped silver nanoparticles (AgNS). On the other hand, spherical nanoparticles prepared by the reduction of silver nitrate with citrate apparently do not react with ABTS. Additionally, the formation of ABTS˙ + is investigated by surface-enhanced Raman scattering (SERS) and the assignment of the most intense vibrational bands of this compound is performed. The SERS technique enables us to detect this radical cation at very low concentrations of ABTS (∼2 μM). Altogether, these findings allow us to suggest the use of ABTS/Ag NPs-systems as reliable and easy going substrates to test the antioxidant capacity of various compounds, even at concentrations much lower than those usually used in the spectrophotometric assays. Moreover, we have suggested that ABTS could be employed as a suitable agent to investigate the interfacial and plasmonic properties of the metal nanoparticles and, thus, to characterize the nanoparticle metal systems employed for various purposes.

Verification of Meso-Zeaxanthin in Fish

PubMed Central

Nolan, John M; Beatty, Stephen; Meagher, Katie A; Howard, Alan N; Kelly, David; Thurnham, David I

2015-01-01

Background/Objectives The carotenoids lutein (L), zeaxanthin (Z), and meso-zeaxanthin (MZ) accumulate in the central retina (the macula), where they are collectively known as macular pigment (MP). MP has been shown to enhance visual function in both diseased and non-diseased retinae, and therefore an understanding and confirmation of, the origins of these carotenoids is needed. Studies have shown that L and Z are present in many foodstuffs found in a typical Western diet (e.g. spinach, kale, peppers, yellow corn and eggs). It has been shown that MZ is generated from L in the primate retina and earlier reports suggested that MZ was present in some fish species. Recently, however, one research group reported that MZ is not present in fish and suggested that the earlier reports showing MZ in these marine species were a methodological artefact. The current study was designed to investigate the reason for the contradiction, and test for the presence of MZ in fish and some other foods. Methods Raw fruits, vegetables and fish were extracted for carotenoid analysis by high performance liquid chromatography. Results MZ was not detected in any of the fruits or vegetables tested in our study. However, using retention time matching, absorption spectrum comparison, and sample spiking, we verified the presence of MZ in salmon skin, sardine skin, trout skin and trout flesh. Conclusion This study confirmed the presence MZ in nature, and in the human food chain. PMID:25717420

One Target, Two Mechanisms: The Impact of 'Candidatus Liberibacter asiaticus' and Its Vector, Diaphorina citri, on Citrus Leaf Pigments.

PubMed

Killiny, Nabil; Nehela, Yasser

2017-07-01

Huanglongbing (HLB) is currently the largest threat to global citrus production. We examined the effect of HLB pathogen 'Candidatus Liberibacter asiaticus' infection or infestation by its vector, Diaphorina citri, on 'Valencia' sweet orange leaf pigments using high-performance liquid chromatography, followed by gene expression analysis for 46 involved genes in carotenoid and chlorophyll biosynthesis pathways. Both 'Ca. L. asiaticus' and D. citri alter the total citrus leaf pigment balance with a greater impact by 'Ca. L. asiaticus'. Although zeaxanthin was accumulated in 'Ca. L. asiaticus'-infected leaves, chlorophyllide a was increased in D. citri-infested plants. Our findings support the idea that both 'Ca. L. asiaticus' and D. citri affect the citrus pigments and promote symptom development but using two different mechanisms. 'Ca. L. asiaticus' promotes chlorophyll degradation but accelerates the biosynthesis of carotenoid pigments, resulting in accumulation of abscisic acid and its precursor, zeaxanthin. Zeaxanthin also has a photoprotective role. By contrast, D. citri induced the degradation of most carotenoids and accelerated chlorophyll biosynthesis, leading to chlorophyllide a accumulation. Chlorophyllide a might have an antiherbivory role. Accordingly, we suggest that citrus plants try to defend themselves against 'Ca. L. asiaticus' or D. citri using multifaceted defense systems, based on the stressor type. These findings will help in better understanding the tritrophic interactions among plant, pathogen, and vector.

Stability of Commercially Available Macular Carotenoid Supplements in Oil and Powder Formulations

PubMed Central

Phelan, David

2017-01-01

We previously identified that the concentration of zeaxanthin in some commercially available carotenoid supplements did not agree with the product’s label claim. The conclusion of this previous work was that more quality assurance was needed to guarantee concordance between actual and declared concentrations of these nutrients i.e., lutein (L) zeaxanthin (Z) and meso-zeaxanthin (MZ) in commercially available supplements. Since this publication, we performed further analyses using different commercially available macular carotenoid supplements. Three capsules from one batch of eight products were analysed at two different time points. The results have been alarming. All of the powder filled products (n = 3) analysed failed to comply with their label claim (L: 19–74%; Z: 57–73%; MZ: 83–97%); however, the oil filled soft gel products (n = 5) met or were above their label claim (L: 98–122%; Z: 117–162%; MZ: 97–319%). We also identified that the carotenoid content of the oil filled capsules were stable over time (e.g., L average percentage change: −1.7%), but the powder filled supplements degraded over time (e.g., L average percentage change: −17.2%). These data are consistent with our previous work, and emphasize the importance of using carotenoid interventions in oil based formulas rather than powder filled formulas. PMID:29039801

In vitro antioxidant, lipoxygenase and xanthine oxidase inhibitory activities of fractions from Cienfuegosia digitata Cav., Sida alba L. and Sida acuta Burn f. (Malvaceae).

PubMed

Konaté, K; Souza, A; Coulibaly, A Y; Meda, N T R; Kiendrebeogo, M; Lamien-Meda, A; Millogo-Rasolodimby, J; Lamidi, M; Nacoulma, O G

2010-11-15

In this study polyphenol content, antioxidant activity, lipoxygenase (LOX) and Xanthine Oxidase (XO) inhibitory effects of n-hexane, dichloromethane, ethyl acetate and n-butanol fractions of aqueous acetone extracts from S. alba L., S. acuta Burn f and Cienfuegosia digitata Cav. were investigated. The total phenolics, flavonoids, flavonols and total tannins were determined by spectrophotometric methods using Folin-ciocalteu, AlCl3 reagents and tannic acid, respectively. The antioxidant potential was evaluated using three methods: inhibition of free radical 2,2-diphenyl-1-picrylhydramzyl (DPPH), ABTS radical cation decolorization assay and Iron (III) to iron (II) reduction activity (FRAP). For enzymatic activity, lipoxygenase and xanthine oxidase inhibitory activities were used. This study shows a relationship between polyphenol contents, antioxidant and enzymatic activities. Present results showed that ethyl acetate and dichloromethane fractions elicit the highest polyphenol content, antioxidant and enzymatic activities.

Study of the oxidized and non- oxidized bitumen modified with additive «Adgezolin» by using electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Mukhamatdinov, I.; Gafurov, M.; Kemalov, A.; Rodionov, A.; Mamin, G.; Fakhretdinov, P.

2018-05-01

Cationic surfactant (adhesion additive) «Adgezolin» has been developed. It is shown that introduction of «Adgezolin» into the oxidized bitumen increases the relative amount of asphaltenes and monocyclearomatic hydrocarbons. By means of electron paramagnetic resonance (EPR) it is demonstrated that the introduction of additive «Adgezolin» increases the number of paramagnetic «free» carbon radicals (FR) in the oxidized bitumen and decreases that in the unoxidized species. In both types of bitumen shift from the Lorentzian to Gaussian EPR lineshape of FR is obtained that could be connected with as an increase of the samples homogeneity. It is supposed that while in the oxygenated bitumens introduction of additives leads to the disaggregation of asphaltene-resins compounds, in the unoxidized samples the balance is shifted towards formation of di-radicals.

New core-pyrene π structure organophotocatalysts usable as highly efficient photoinitiators

PubMed Central

Telitel, Sofia; Dumur, Frédéric; Faury, Thomas; Graff, Bernadette; Tehfe, Mohamad-Ali; Fouassier, Jean-Pierre

2013-01-01

Summary Eleven di- and trifunctional compounds based on a core-pyrene π structure (Co_Py) were synthesized and investigated for the formation of free radicals. The application of two- and three-component photoinitiating systems (different Co_Pys with the addition of iodonium or sulfonium salts, alkyl halide or amine) was investigated in detail for cationic and radical photopolymerization reactions under near-UV–vis light. The proposed compounds can behave as new photocatalysts. Successful results in terms of rates of polymerization and final conversions were obtained. The strong MO coupling between the six different cores and the pyrene moiety was studied by DFT calculations. The different chemical intermediates are characterized by ESR and laser flash photolysis experiments. The mechanisms involved in the initiation step are discussed, and relationships between the core structure, the Co_Py absorption property, and the polymerization ability are tentatively proposed. PMID:23766803

Electrogenerated chemiluminescence. 59. Rhenium complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richter, M.M.; Debad, J.D.; Bard, A.J.

Re(L)(CO){sub 3}Cl complexes (where L is 1,10-phenanthroline, 2,2`-bipyridine, or a phenanthroline or bipyridine derivative containing methyl groups) are photoluminescent in fluid solution at room temperature. In acetonitrile solutions, these complexes display one chemically reversible one-electron reduction process and one chemically irreversible oxidation process. {lambda}{sub max} for the luminescence is dependent on the nature of L, and a linear relationship between {lambda}{sub max} and the difference in electrode potentials for oxidation and reduction is evident. Electrogenerated chemiluminescence (ECL) was observed in acetonitrile solutions of these complexes (Bu{sub 4}NPF{sub 6} as electrolyte) by stepping the potential of a Pt disk working electrodemore » between potentials sufficient to form the radical anionic and cationic species. The relative amount of light produced during the anodic and cathodic pulses was dependent on the potential limits and pulse duration. ECL was also generated in the presence of coreactants, i.e., with tri-n-propylamine upon stepping the potential sufficiently positive to form the deprotonated tri-n-propylamine radical and the cationic rhenium(II) species Re{sup II}(L)(CO){sub 3}Cl{sup +}. When S{sub 2}O{sub 8}{sup 2-} was present in solution, ECL was also observed for all of the complexes upon stepping to potentials sufficient to form (Re{sup I}(L)(CO){sub 3}Cl){sup -} and the strong oxidant SO{sub 4}{sup .-}. 44 refs., 8 figs.« less

Radical Cations and Acid Protection during Radiolysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mincher, Bruce J.; Zarzana, Christopher A.; Mezyk, Stephen P.

2016-09-09

Ligand molecules for used nuclear fuel separation schemes are exposed to high radiation fields and high concentrations of acid. Thus, an understanding of the complex interactions between extraction ligands, diluent, and acid is critical to understanding the performance of a separation process. The diglycolamides are ligands with important structural similarities to CMPO; however, previous work has shown that their radiolytic degradation has important mechanistic differences from CMPO. The DGAs do not enjoy radioprotection by HNO3 and the kinetics of DGA radiolytic degradation are different. CMPO degrades with pseudo-zero-order kinetics in linear fashion with absorbed dose while the DGAs degrade inmore » pseudo-first-order, exponential fashion. This suggests that the DGAs degrade by simple reaction with some product of direct diluent radiolysis, while CMPO degradation is probably multi-step, with a slow step that is not dependent on the CMPO concentration, and mitigated by HNO 3. It is thus believed that radio-protection and the zero-order radiolytic degradation kinetics are related, and that these phenomena are a function of either the formation of strong acid complexes with CMPO and/or to the presence of the CMPO phenyl ring. Experiments to test both these hypotheses have been designed and partially conducted. This report summarizes findings related to these phenomena for FY16, in satisfaction of milestone M3FT-16IN030104053. It also reports continued kinetic measurements for the reactions of the dodecane radical cation with solvent extraction ligands.« less

Radical Cationic Pathway for the Decay of Ionized Glyme Molecules in Liquid Solution.

PubMed

Taletskiy, Konstantin S; Borovkov, Vsevolod I; Schegoleva, Lyudmila N; Beregovaya, Irina V; Taratayko, Andrey I; Molin, Yuriy N

2015-11-12

Chemical stability of primary radical cations (RCs) generated in irradiated matter determines substantially the radiation resistance of organic materials. Transformations of the RCs of the glyme molecules, R(-O-CH2-CH2-)nO-R (R = CH3, n = 1-4) has been studied on the nanosecond time scale by measuring the magnetic field effects in the recombination fluorescence from irradiated liquid solutions of the glymes. In all cases, the RCs observed were different from that expected for the primary ones and revealed very similar hyperfine couplings independent of the poly(ethylene oxide) chain length and of the substitution of terminal methyl groups by C2H5 or CH2CH2Cl, as has been shown with diglyme as an example. Quantum chemical analysis of possible chemical transformations for the monoglyme RC as a model system allowed us to discover the reaction pathway yielding the methyl vinyl ether RC. The pathway involves intramolecular proton transfer followed by C-O bond cleavage. Only one (-O-CH2-CH2-O-) fragment is involved in this transformation, which is nearly barrierless due to the catalytic effect of adjacent glyme molecules. The rapid formation of the methyl vinyl ether RC in the irradiated monoglyme was confirmed by the numerical simulation of the experimental curves of the time-resolved magnetic field effect. These findings suggest that the R'-O-CH═CH2(•+) formation is a typical decay pathway for the primary RCs in irradiated liquid glymes.

Manganoporphyrin-Polyphenol Multilayer Capsules as Radical and Reactive Oxygen Species (ROS) Scavengers

DOE PAGES

Alford, Aaron; Kozlovskaya, Veronika; Xue, Bing; ...

2017-12-18

Local modulation of oxidative stress is crucial for a variety of biochemical events including cellular differentiation, apoptosis, and defense against pathogens. Currently employed natural and synthetic antioxidants exhibit a lack of biocompatibility, bioavailability, and chemical stability, resulting in limited capability to scavenge reactive oxygen species (ROS). To mediate these drawbacks, we have developed a synergistic manganoporphyrin-polyphenol polymeric nanothin coating and hollow microcapsules with efficient antioxidant activity and controllable ROS modulation. These materials are produced by multilayer assembly of a natural polyphenolic antioxidant, tannic acid (TA), with a synthesized copolymer of polyvinylpyrrolidone containing a manganoporphyrin modality (MnP-PVPON) which mimics the enzymaticmore » antioxidant superoxide dismutase. The redox activity of the copolymer is demonstrated to dramatically increase the antioxidant response of MnP-PVPON/TA capsules versus unmodified PVPON/TA capsules through reduction of a radical cationic dye and to significantly suppress the proliferation of superoxide via cytochrome C competition. Inclusion of MnP-PVPON as an outer layer enhances radical-scavenging activity as compared to localization of the layer in the middle or inner part of the capsule shell. In addition, we demonstrate that TA is crucial for the synergistic radical-scavenging activity of the MnP-PVPON/TA system which exhibits a combined superoxide dismutase-like ability and catalase-like activity in response to the free radical superoxide challenge. The MnP-PVPON/TA capsules exhibit a negligible, 8% loss of shell thickness upon free radical treatment, while PVPON/TA capsules lose 39% of their shell thickness due to the noncatalytic free-radical-scavenging of TA, as demonstrated by small angle neutron scattering (SANS). Finally, we have found the manganoporphyrin-polyphenol capsules to be nontoxic to splenocytes from NOD mice after 48 h incubation. In conclusion, our study illustrates the strong potential of combining catalytic activity of manganoporphyrins with natural polyphenolic antioxidants to design efficient free-radical-scavenging materials that may eventually be used in antioxidant therapies and as free radical dissipating protective carriers of biomolecules for biomedical or industrial applications.« less

Manganoporphyrin-Polyphenol Multilayer Capsules as Radical and Reactive Oxygen Species (ROS) Scavengers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alford, Aaron; Kozlovskaya, Veronika; Xue, Bing

Local modulation of oxidative stress is crucial for a variety of biochemical events including cellular differentiation, apoptosis, and defense against pathogens. Currently employed natural and synthetic antioxidants exhibit a lack of biocompatibility, bioavailability, and chemical stability, resulting in limited capability to scavenge reactive oxygen species (ROS). To mediate these drawbacks, we have developed a synergistic manganoporphyrin-polyphenol polymeric nanothin coating and hollow microcapsules with efficient antioxidant activity and controllable ROS modulation. These materials are produced by multilayer assembly of a natural polyphenolic antioxidant, tannic acid (TA), with a synthesized copolymer of polyvinylpyrrolidone containing a manganoporphyrin modality (MnP-PVPON) which mimics the enzymaticmore » antioxidant superoxide dismutase. The redox activity of the copolymer is demonstrated to dramatically increase the antioxidant response of MnP-PVPON/TA capsules versus unmodified PVPON/TA capsules through reduction of a radical cationic dye and to significantly suppress the proliferation of superoxide via cytochrome C competition. Inclusion of MnP-PVPON as an outer layer enhances radical-scavenging activity as compared to localization of the layer in the middle or inner part of the capsule shell. In addition, we demonstrate that TA is crucial for the synergistic radical-scavenging activity of the MnP-PVPON/TA system which exhibits a combined superoxide dismutase-like ability and catalase-like activity in response to the free radical superoxide challenge. The MnP-PVPON/TA capsules exhibit a negligible, 8% loss of shell thickness upon free radical treatment, while PVPON/TA capsules lose 39% of their shell thickness due to the noncatalytic free-radical-scavenging of TA, as demonstrated by small angle neutron scattering (SANS). Finally, we have found the manganoporphyrin-polyphenol capsules to be nontoxic to splenocytes from NOD mice after 48 h incubation. In conclusion, our study illustrates the strong potential of combining catalytic activity of manganoporphyrins with natural polyphenolic antioxidants to design efficient free-radical-scavenging materials that may eventually be used in antioxidant therapies and as free radical dissipating protective carriers of biomolecules for biomedical or industrial applications.« less

Fluorinated Dodecaphenylporphyrins: Synthetic and Electrochemical Studies Including the First Evidence of Intramolecular Electron Transfer Between an Fe(II) Porphyrin -Anion Radical and an Fe(I) Porphyrin

DOE Office of Scientific and Technical Information (OSTI.GOV)

D'Souza, F.; Forsyth, T.P.; Fukuzumi, S.

1998-10-19

Dodecaphenylporphyrins with varying degrees of fluorination of the peripheral phenyl rings (FXDPPS) were synthesized as model compounds for studying electronic effects in nonplan~ porphyrins, and detailed electrochemical studies of the chloroiron(HI) complexes of these compounds were undertaken. The series of porphyrins, represented as FeDPPCl and as FeFXDPPCl where x = 4, 8 (two isomers), 12, 20,28 or 36, could be reversibly oxidized by two electrons in dichloromethane to give n-cation radicals and n-dications. All of the compounds investigated could also be reduced by three electrons in benzonitrile or pyridine. In benzonitrile, three reversible reductions were observed for the unfluorinated compoundmore » FeDPPC1, whereas the FeFXDPPCl complexes generally exhibited irreversible first and second reductions which were coupled to chemical reactions. The chemical reaction associated with the first reduction involved a loss of the chloride ion after generation of Fe FXDPPC1. The second chemical reaction involved a novel intramolecular electron transfer between the initially generated Fe(H) porphyrin n-anion radical and the final Fe(I) porphyrin reduction product. In pyridine, three reversible one electron reductions were observed with the second reduction affording stable Fe(II) porphyrin o - anion radicals for ail of the complexes investigated.« less

Effects of baking conditions, dough fermentation, and bran particle size on antioxidant properties of whole-wheat pizza crusts.

PubMed

Moore, Jeffrey; Luther, Marla; Cheng, Zhihong; Yu, Liangli Lucy

2009-02-11

This study investigated the effects of processing conditions including bran particle size, dough fermentation time, and baking time and temperature on the extractable antioxidant properties of whole-wheat pizza crust. Experiments were carried out using two different varieties of hard white winter wheat, Trego and Lakin. Antioxidant properties examined included oxygen radical absorbing capacity (ORAC), hydroxyl radical scavenging capacity (HOSC), relative 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity (RDSC), cation 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) radical scavenging capacity, total phenolic contents (TPC), and ferulic acid contents. Results indicated that bran particle size had no effect on the antioxidant properties evaluated. Increasing dough fermentation time from 0 to 48 h had no significant influence on antioxidant properties except HOSC, which increased as much as 28%, possibly as a result of increase in soluble free ferulic acid, which increased as much as 130%. Increasing baking temperature from 204 to 288 degrees C with a 7 min bake time increased all evaluated antioxidant properties by as much as 82%. Increasing baking time from 7 to 14 min with 204 degrees C baking temperature might increase some antioxidant properties as much as 60%. The results from this study suggest that longer dough fermentation times and increased baking time or temperature may be potential approaches to increase the antioxidant availability in whole-wheat pizza crust.

Hydrogen bonded charge transfer molecular salt (4-chloro anilinium-3-nitrophthalate) for photophysical and pharmacological applications

NASA Astrophysics Data System (ADS)

Singaravelan, K.; Chandramohan, A.; Saravanabhavan, M.; Muthu Vijayan Enoch, I. V.; Suganthi, V. S.

2017-09-01

Radical scavenging activity against DPPH radical and binding properties of a hydrogen bonded charge transfer molecular salt 4-chloro anilinium-3-nitrophthalate(CANP) with calf thymus DNA has been studied by electronic absorption and emission spectroscopy. The molecular structure and crystallinity of the CANP salt have been established by carried out powder and single crystal X-ray diffraction analysis which indicated that cation and anion are linked through strong N+sbnd H…O- type of hydrogen bond. FTIR spectroscopic study was carried out to know the various functional groups present in the crystal. 1H and 13C NMR spectra were recorded to further confirm the molecular structure of the salt crystal. The thermal stability of the title salt was established by TG/DTA analyses simultaneously on the powdered sample of the title crystal. Further, the CANP salt was examined against various bacteria and fungi strains which showed a remarkable antimicrobial activity compared to that of the standards Ciproflaxin and Clotrimazole. The results showed that the CANP salt could interact with CT-DNA through intercalation. Antioxidant studies of the substrates alone and synthesized CANP salt showed that the latter has been better radical scavenging activity than that of the former against DPPH radical. The third order nonlinear susceptibility of the CANP salt was established by the Z-scan study.

Raman detection of carotenoid pigments in the human retina

NASA Astrophysics Data System (ADS)

Gellermann, Werner; Ermakov, Igor V.; McClane, Robert W.; Bernstein, Paul S.

2000-04-01

We have used resonance Raman scattering as a novel, non- invasive, in-vivo optical technique to measure the concentration of carotenoid pigment in the human retina. Using argon laser excitation we are able to measure two strong carotenoid resonance Raman signals at 1159 and 1525 wave numbers, respectively. The required laser power levels are within the limits given by safety standards for ocular exposure. Of the approximately ten carotenoid pigment found in normal human serum, the species lutein and zeaxanthin are concentrated in high amounts in the cells of the human macula, which is an approximately 5 mm diameter area of the retina in which the visual acuity is highest. These carotenoids give the macula a characteristic yellow coloration, and it is speculated that these molecules function as filter to attenuate photochemical damage and/or image degradation under bright UV/blue light exposures. In addition, they are thought to act as free-radical scavenging antioxidants. Studies have shown that there may be a link between macular degenerative diseases, the leading cause of blindness in the elderly in the US, and the presence or absence of the carotenoids. We describe an instrument capable of measuring the macular carotenoids in human subjects in a non-invasive, rapid and quantitative way.

Determination of carotenoids and all-trans-retinol in fish eggs by liquid chromatography-electrospray ionization-tandem mass spectrometry.

PubMed

Li, Hongxia; Tyndale, Sélène T; Heath, Daniel D; Letcher, Robert J

2005-02-25

A novel method was developed for the combined determination of carotenoids and retinoids in fish eggs, which incorporates prior analyte isolation using liquid-liquid partitioning to minimize analyte degradation, and fraction analysis using high-performance liquid chromatography-electrospray (positive)-quadrupole mass spectrometry (LC-ESI(+)-MS; SIM or MRM modes). Eggs from Chinook salmon (Oncorhynchus tshawytscha) were used as the model fish egg matrix. The methodology was assessed and validated for beta-carotene, lutein, zeaxanthin, and beta-cryptoxanthin (molecular ion radicals [M](+)), canthaxanthin and astaxanthin ([M+Na](+) adducts) and all-trans-retinol ([(M+H)-H(2)O](+)). Using replicate egg samples (n=5) spiked with beta-cryptoxanthin and beta-carotene before and after extraction, matrix-sourced ESI(+) enhancement was observed as evidenced by comparable %matrix effect and %process efficiency values for beta-cryptoxanthin and beta-carotene of 114-119%. In aquaculture-raised eggs from adult Chinook salmon astaxanthin, all-trans-retinol, lutein and canthaxanthin were identified and determined at concentrations of 4.12, 1.06, 0.12 and 0.45 microg/g (egg wet weight), respectively. To our knowledge, this is the first report on a method for LC-MS determination of carotenoids and retinoids in a fish egg matrix, and the first carotenoid-specific determination in any fish egg sample.

Stability of polyphenols and carotenoids in strawberry and peach yoghurt throughout in vitro gastrointestinal digestion.

PubMed

Oliveira, Ana; Pintado, Manuela

2015-05-01

The aim of this research was to evaluate the influence of in vitro gastrointestinal digestion on the stability and bio-accessibility of phenolic compounds and carotenoids, as well as on the antioxidant activity in strawberry and peach enriched yoghurt. The radical scavenging capacity of strawberry and peach yoghurt was 480 and 550% higher, respectively, at the level of the intestine than in fruit yoghurt not subjected to digestion. In strawberry the amount of bio-accessible anthocyanins increased during gastric digestion and the transition to the intestinal compartment produced a decrease in all the analyzed classes of polyphenols, being more pronounced in pelargonidin-3-glucoside (65%) and pelargonidin-3-rutinoside (58%). In peach the (+)-catechin content strongly decreased (80%), and neochlorogenic, chlorogenic acid, rutin and the carotenoid zeaxanthin decreased at lower levels, between 32-45%, while β-carotene was rather stable under gastric conditions (increased by 12%) during intestinal digestion. Despite the decrease in the concentration of these bioactive compounds after being subjected to in vitro gastrointestinal digestion, results suggest that fruit yoghurt is an important source of bio-accessible polyphenols and carotenoids and that despite some losses induced by digestion conditions, it still releases relevant amounts at the level of the intestine to be absorbed and to promote health benefits.

Effect of added sodium chloride on the molecular environment and photoionization of N,N,N',N'-tetramethylbenzidine in micellar solutions as studied by electron spin echo and electron spin resonance spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maldonado, R.; Kevan, L.; Szajdzinska-Pietek, E.

1984-11-01

The electron spin echo modulation (ESEM) and electron spin resonance (ESR) spectra of the cation radical of N,N,N',N'-tetramethylbenzidine (TMB) in frozen sodium dodecyl sulfate (SDS)= and dodecyltrimethylammonium chloride (DTAC) micelles were studied as a function of sodium chloride concentration. TMB/sup +center-dot/ was produced by photoionization at 350 nm of the parent compound in the micelles at 77 K. From the ESEM analysis it is found that the cation--water interactions increase with salt addition in both anionic and cationic micelles to a maximum near 0.2 M NaCl and then decrease somewhat. The increase is interpreted in terms of an increase inmore » the water density at the micellar surface due to an increased surface concentration of hydrated counterions. The decrease may be due to TMB moving further from the polar micellar surface with added salt. From ESR spectra the photoionization yields of TMB at 77 K were determined. For DTAC micelles the yields are found to decrease with salt addition as expected from electrostatic considerations. For SDS micelles the photoionization yields increase for salt concentrations up to about 0.15 M and decrease for greater salt concentrations up to 0.5 M. The initial increase in cation yield correlates with electrostatic expectations. The decrease may be due to TMB moving further from the polar micellar surface with added salt. The possible effect of differing TMB protonation equilibria between anionic and cationic micelles on the photoionization yields was found to be unimportant by adjusting the bulk solution pH. An important conclusion is that salt addition can be used to optimize charge separation for photoionized solutes in anionic micelles.« less

[Prevention and treatment of age-related macular degeneration by extract of Fructus lycii and its constituents lutein/zeaxanthin: an in vive and in vitro experimental research].

PubMed

Huang, Bing-Lin; Ding, Shu-Hua; Hang, Li; Zheng, Shi-Zhong; Li, Wei; Xu, Xin-rong

2013-04-01

To investigate the in vivo inhibition of extract of Fructus lycii (FL) on the expressions of cathepsin B (Cat B) and cystatin C (Cys C) in high-fat diet and hydroquinone (HQ) induced model mice with age-related macular degeneration (AMD), and to explore the in vitro effects of lutein and zeaxanthin on hydrogen peroxide (H2O2,) induced expressions of matrix metalloproteinase 2 (MMP-2) and tissue inhibitor of metalloproteinase 2 (TIMP-2) on ARPE-19 cells. Fifty female 8-month-old C57BL/6 mice were recruited in this research. Ten mice fed with regular diet was taken as the age control group. The rest 40 mice were fed with high fat diet for 6 months, followed by adding HQ (0. 8%) in the drinking water for 3 consecutive months. Then the modeled mice were randomly divided into the model control group (n =10), the high (at the daily dose of 3.75 g/kg), middle (at the daily dose of 2.50 g/kg), and low dose (at the daily dose of 1.25 g/kg) FL groups, 10 in each group. The extract of FL at each dose was respectively administered to mice by gastrogavage for 3 successive months. By the end of the experiment, the mice were killed and their eyeballs were removed. The protein expressions of Cat B and Cys C were observed by immunohistochemical assay. The mRNA and protein expressions of Cat B and Cys C were detected by real-time PCR and Western blot respectively. The drug concentrations of H2O2, lutein, and zeaxanthin were screened and detected using the activity of cell proliferation. The protein expressions of MMP-2 and TIMP-2 were detected using Western blot. Compared with the age control group, the mRNA and protein expressions of Cat B and Cys C were significantly higher in the in vivo model control group (P <0.05, P <0.01). The mRNA expressions of Cat B and Cys C were weaker in the middle and high dose FL groups than in the model control group (P <0. 05, P <0. 01). In in vitro cells, lutein and zeaxanthin could down-regulate the protein expressions of MMP-2 and TIMP-2 in H202 induced ARPE-19 cells (P <0. 05, P <0. 01). Extract of FL could down-regulate the high protein expressions of Cat B and Cys C in high-fat diet and HQ induced model mice. Lutein and zeaxanthin could down-regulate the protein expressions of MMP-2 and TIMP-2 in H202 induced ARPE-19 cells.

Top-Down Charge Transfer Dissociation (CTD) of Gas-Phase Insulin: Evidence of a One-Step, Two-Electron Oxidation Mechanism

NASA Astrophysics Data System (ADS)

Li, Pengfei; Kreft, Iris; Jackson, Glen P.

2018-02-01

Top-down analyses of protonated insulin cations of charge states of 4+, 5+, or 6+ were performed by exposing the isolated precursor ions to a beam of helium cations with kinetic energy of more than 6 keV, in a technique termed charge transfer dissociation (CTD). The 100 ms charge transfer reaction resulted in approximately 20% conversion efficiency to other intact charge exchange products (CTnoD), and a range of low abundance fragment ions. To increase backbone and sulfide cleavages, and to provide better structural information than straightforward MS2 CTD, the CTnoD oxidized products were isolated and subjected to collisional activation at the MS3 level. The MS3 CTD/CID reaction effectively broke the disulfide linkages, separated the two chains, and yielded more structurally informative fragment ions within the inter-chain cyclic region. CTD also provided doubly oxidized intact product ions at the MS2 level, and resonance ejection of the singly oxidized product ion revealed that the doubly oxidized product originates directly from the isolated precursor ion and not from consecutive CTD reactions of a singly oxidized intermediate. MS4 experiments were employed to help identify potential radical cations and diradical cations, but the results were negative or inconclusive. Nonetheless, the two-electron oxidation process is a demonstration of the very large potential energy (>20 eV) available through CTD, and is a notable capability for a 3D ion trap platform.

Asymmetric photoredox transition-metal catalysis activated by visible light.

PubMed

Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

2014-11-06

Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the 'green' synthesis of non-racemic chiral molecules.

Asymmetric photoredox transition-metal catalysis activated by visible light

NASA Astrophysics Data System (ADS)

Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

2014-11-01

Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the `green' synthesis of non-racemic chiral molecules.

In vitro study on the antioxidant activity of a polyphenol-rich extract from Pinus brutia bark and its fractions.

PubMed

Cretu, Elena; Karonen, Maarit; Salminen, Juha-Pekka; Mircea, Cornelia; Trifan, Adriana; Charalambous, Christiana; Constantinou, Andreas I; Miron, Anca

2013-11-01

A crude hydromethanolic extract from Pinus brutia bark and its fractions (diethyl ether, ethyl acetate, n-butanol, and aqueous fractions) were studied with regard to their phenolic content and antioxidant activities. The total phenolics and proanthocyanidins in each extract were quantified by spectrophotometric methods; the polyphenolic profile was analyzed by RP-HPLC-DAD-ESI-MS. All extracts were tested with regard to their ability to scavenge free radicals (ABTS radical cation, superoxide and hydroxyl radicals), reduce ferric ions, and inhibit 15-lipoxygenase. P. brutia bark extracts had high phenolic contents (303.79±7.34-448.90±1.39 mg/g). Except diethyl ether extract, all other extracts contained proanthocyanidins ranging from 225.79±3.94 to 250.40±1.44 mg/g. Several polyphenols were identified by RP-HPLC-DAD-ESI-MS: taxifolin in diethyl ether extract, a taxifolin-O-hexoside, catechin, procyanidin dimers, and trimers in ethyl acetate extract. Except diethyl ether extract, all other extracts were effective scavengers of superoxide and hydroxyl radicals (EC₅₀=33.5±1.1-54.93±2.85 μg/mL and 0.47±0.06-0.6±0.0 mg/mL, respectively). All extracts had noticeable 15-lipoxygenase inhibitory effects (EC₅₀=22.47±0.75-34.43±2.25 μg/mL). We conclude that P. brutia bark is very promising for the dietary supplements industry due to its high free radical scavenging and 15-lipoxygenase inhibitory effects.

Small Water Cluster Cations

NASA Astrophysics Data System (ADS)

Novakovskaya, Yu. V.; Stepanov, N. F.

Structures of water cluster cations (H_{2}O)^{+}_{n} with n ≤ 5 are optimized at the unrestricted Hartree-Fock level with the 4 - 31 + +G** basis set. Energetic characteristics of the cations are then estimated taking into account the second order perturbation corrections (MP2). After the electron detachment from a neutral cluster, the structure of the latter substantially changes, so that OH and H3O+ fragments can be distinguished in it. In some cations H3O+ is so strongly bonded to water molecules that it is reasonable to speak of the [H2n-1On-1]+ fragments. According to the position of OH, the structures form two groups. In one group, OH acts exclusively as the proton acceptor in H-bonds with water molecules, thus being terminal in the chain-like structures; in the other group it is directly bonded to H3O and, as a proton donor, forms an H-bond with water molecule. Cluster cations do not tend to dissociate into the fragments. However, an external influence of ≤ 0.4 eV is sufficient for the cations of the first group to dissociate into a free OH radical and a protonated cluster H+(H2O)n-1. Extrapolation of the calculated adiabatic ionization potentials of the water clusters to n → ∞ provides a value of 8.6 eV, which can be considered as an estimation of the electron work function of water. This value is close to the experimental photoelectric thresholds of amorphous ice (8.7 ± 0.1 eV) and water (9.39 ± 0.3 eV). Solvation of the electron lowers the value, and an energy of 7 eV can be sufficient for initiating conductivity. This prediction is in accord with the experiment: irradiating ice with ultraviolet light of the photon energy 6.5-6.8 eV initiates photoconductivity, and hydrogen peroxide and H3O+ ions are observed.

Enzyme inhibitory and radical scavenging effects of some antidiabetic plants of Turkey.

PubMed

Orhan, Nilüfer; Hoçbaç, Sanem; Orhan, Didem Deliorman; Asian, Mustafa; Ergun, Fatma

2014-06-01

Ethnopharmacological field surveys demonstrated that many plants, such as Gentiana olivieri, Helichrysum graveolens, Helichrysum plicatum ssp. plicatum, Juniperus oxycedrus ssp. oxycedrus, Juniperus communis var. saxatilis, Viscum album (ssp. album, ssp. austriacum), are used as traditional medicine for diabetes in different regions of Anatolia. The present study was designed to evaluate the in vitro antidiabetic effects of some selected plants, tested in animal models recently. α-glucosidase and α-amylase enzyme inhibitory effects of the plant extracts were investigated and Acarbose was used as a reference drug. Additionally, radical scavenging capacities were determined using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) ABTS radical cation scavenging assay and total phenolic content of the extracts were evaluated using Folin Ciocalteu method. H. graveolens ethanol extract exhibited the highest inhibitory activity (55.7 % ± 2.2) on α-amylase enzyme. Additionally, J. oxycedrus hydro-alcoholic leaf extract had potent α-amylase inhibitory effect, while the hydro-alcoholic extract of J. communis fruit showed the highest α-glucosidase inhibitory activity (IC50: 4.4 μg/ml). Results indicated that, antidiabetic effect of hydro-alcoholic extracts of H. graveolens capitulums, J. communis fruit and J. oxycedrus leaf might arise from inhibition of digestive enzymes.

Interaction mechanism between berberine and the enzyme lysozyme

NASA Astrophysics Data System (ADS)

Cheng, Ling-Li; Wang, Mei; Wu, Ming-Hong; Yao, Si-De; Jiao, Zheng; Wang, Shi-Long

2012-11-01

In the present paper, the interaction between model protein lysozyme (Lys) and antitumorigenic berberine (BBR) was investigated by spectroscopic methods, for finding an efficient and safe photosensitizer with highly active transient products using in photodynamic therapy study. The fluorescence data shows that the binding of BBR could change the environment of the tryptophan (Trp) residues of Lys, and form a new complex. Static quenching is the main fluorescence quenching mechanism between Lys and BBR, and there is one binding site in Lys for BBR and the type of binding force between them was determined to be hydrophobic interaction. Furthermore, the possible interaction mechanism between BBR and Lys under the photoexcitation was studied by laser flash photolysis method, the results demonstrated that BBR neutral radicals (BBR(-H)•) react with Trp (K = 3.4 × 109 M-1 s-1) via electron transfer to give the radical cation (Trp/NH•+) and neutral radical of Trp (TrpN•). Additionally BBR selectively oxidize the Trp residues of Lys was also observed by comparing the transient absorption spectra of their reaction products. Through thermodynamic calculation, the reaction mechanisms between 3BBR∗ and Trp or Lys were determined to be electron transfer process.

Synthesis, characterization, Hirshfeld surface analysis and antioxidant activity of a novel organic-inorganic hybrid material 1-methylpiperazine-1,4-diium bis(nitrate)

NASA Astrophysics Data System (ADS)

Gatfaoui, Sofian; Mezni, Ali; Roisnel, Thierry; Marouani, Houda

2017-07-01

The new inorganic-organic hybrid material 1-methylpiperazine-1,4-diium bis(nitrate) (MPN) have been synthesized and crystallized to the orthorhombic system with space group Pnma and the lattice parameters obtained are a = 10.9385(9) Å, b = 6.5698 Å (4), c = 13.7021(10) Å, V = 984.68(12) Å3 and Z = 4. The trigonal (NO3-) anions are connected to the 1-methylpiperazine-1,4-diium cations via a large number of bifurcated and non-bifurcated Nsbnd H⋯O and Csbnd H⋯O hydrogen bonds. The diprotonated piperazine ring adopts a chair conformation, with the methyl group occupying an equatorial position. Intermolecular interactions in the crystal structure were quantified by Hirshfeld surface analysis. Infrared spectrum confirms the existence of the functional groups in the elaborated material. Optical absorption reveals an important band gap energy indicating stability of the title compound. The DTA/TGA and DSC curves indicate that the crystal is thermally stable up to 180 °C. The antioxidant properties were determined via the DPPH radical scavenging, the ABTS radical scavenging, hydroxyl radical scavenging and ferric reducing power (FRP).

Reaction of 1H-1-oxo-2,4,6,8-tetrakis(tert-butyl)phenoxazine with certain group II-IV metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karsanov, I.V.; Ivakhnenko, E.P.; Khandkarova, V.S.

1987-07-10

It has already been shown that 2-amino-4,6-di(tert-butyl)phenol reacts with 3,5-di(tert-butyl)-o-benzoquinone to form 1H-1-oxo-2,4,6,8-tetrakis(tert-butyl)phenoxazine (I), which is readily reduced by alkali metals to the corresponding semiquinone anion-radical (II), and further to the diamagnetic dianion (IIA). They made use of this ability of (I) to undergo reduction to prepare anion-radical salts with different group II-IV metals in the form of their amalgams. In the EPR spectrum of the anion-radical complex (III) formed in the reduction of (I) by a thallium amalgam, the HFI constants of the unpaired electron with magnetic nuclei of the organic ligand are close to those of the K-saltmore » (II), and a substantial HFI is observed with the /sup 203,205/Tl nuclei. This unequivocally proves that the complex has a semiquinone structure, since an HFI on the /sup 203,205/Tl nuclei of such an order of magnitude is characteristic of o-benzoquinone salts with a thallium cation.« less

Mechanistic insight into the photoredox catalysis of anti-Markovnikov alkene hydrofunctionalization reactions

DOE PAGES

Romero, Nathan A.; Nicewicz, David A.

2014-11-12

Here, we describe our efforts to understand the key mechanistic aspects of the previously reported alkene hydrofunctionalization reactions using 9-mesityl-10-methylacridinium (Mes-Acr +) as a photoredox catalyst. Importantly, we are able to detect alkene cation radical intermediates, and confirm that phenylthiyl radical is capable of oxidizing the persistent acridinyl radical in a fast process that unites the catalytic activity of the photoredox and hydrogen atom transfer (HAT) manifolds. Additionally, we present evidence that diphenyl disulfide ((PhS) 2) operates on a common catalytic cycle with thiophenol (PhSH) by way of photolytic cleaveage of the disulfide bond. Transition structure analysis of the HATmore » step using DFT reveals that the activation barrier for H atom donation from PhSH is significantly lower than 2-phenylmalononitrile (PMN) due to structural reorganization. In the early stages of the reaction, Mes-Acr + is observed to engage in off-cycle adduct formation, presumably as buildup of PhS – becomes significant. The kinetic differences between PhSH and (PhS) 2 as HAT catalysts indicate that the proton transfer step may have significant rate limiting influence.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Seungwoo; Lu, Xiaoyan; Lee, Yong -Min

Here, a mononuclear nonheme iron(V)-imido complex bearing a tetraamido macrocyclic ligand (TAML), [Fe V(NTs)(TAML)] – (1), was oxidized by one-electron oxidants, affording formation of an iron(V)-imido TAML cation radical species, [Fe V(NTs)(TAML +•)] (2); 2 is a diamagnetic (S = 0) complex, resulting from the antiferromagnetic coupling of the low-spin iron(V) ion (S = 1/2) with the one-electron oxidized ligand (TAML +•). 2 is a competent oxidant in C–H bond functionalization and nitrene transfer reaction, showing that the reactivity of 2 is greater than that of 1.

Stabilization of higher-valent states of iron porphyrin by hydroxide and methoxide ligands: electrochemical generation of iron(IV)-oxo porphyrins.

PubMed Central

Lee, W A; Calderwood, T S; Bruice, T C

1985-01-01

An electrochemical study of hydroxide- and methoxide-ligated iron(III) tetraphenylporphyrins possessing ortho-phenyl substituents that block mu-oxo dimer formation has been carried out. Ligation by these strongly basic oxyanions promotes the formation of iron(IV)-oxo porphyrins upon one-electron oxidation. Further one-electron oxidation of the latter provides the iron(IV)-oxo porphyrin pi-cation radical. These results are discussed in terms of chemical model studies and the enzymatic intermediate compounds I and II of the peroxidases. PMID:3859865

Mechanistic Analysis of Oxidative C–H Cleavages Using Inter- and Intramolecular Kinetic Isotope Effects

PubMed Central

Jung, Hyung Hoon; Floreancig, Paul E.

2009-01-01

A series of monodeuterated benzylic and allylic ethers were subjected to oxidative carbon–hydrogen bond cleavage to determine the impact of structural variation on intramolecular kinetic isotope effects in DDQ-mediated cyclization reactions. These values are compared to the corresponding intermolecular kinetic isotope effects that were accessed through subjecting mixtures of non-deuterated and dideuterated substrates to the reaction conditions. The results indicate that carbon–hydrogen bond cleavage is rate determining and that a radical cation is most likely a key intermediate in the reaction mechanism. PMID:20640173

Study of intermediates from transition metal excited-state electron-transfer reactions

NASA Astrophysics Data System (ADS)

Hoffman, M. Z.

1984-03-01

Attention during the past year focused on MV(+)., the reduced methyl viologen radical cation, which is a precursor to the formation of H2 in the photosensitized reduction of water. Through the use of photochemical and radiation chemical techniques, the efficiency of interaction of MV(+). with colloidal Pt, the stability of MV(+). as a function of pH, the quantum yield of formation of MV(+). in the Ru(bpy)3(2+)/MV(2+)/EDTA system, and the formation of photoactive charge-transfer complexes between MV(2+) and sacrificial electron donors were studied.

Identification of StARD3 as a Lutein-binding Protein in the Macula of the Primate Retina†

PubMed Central

Li, Binxing; Vachali, Preejith; Frederick, Jeanne M.; Bernstein, Paul S.

2011-01-01

Lutein, zeaxanthin and their metabolites are the xanthophyll carotenoids that form the macular pigment of the human retina. Epidemiological evidence suggests that high levels of these carotenoids in the diet, serum and macula are associated with decreased risk of age-related macular degeneration (AMD), and the AREDS2 study is prospectively testing this hypothesis. Understanding the biochemical mechanisms underlying the selective uptakes of lutein and zeaxanthin into the human macula may provide important insights into the physiology of the human macula in health and disease. GSTP1 is the macular zeaxanthin-binding protein, but the identity of the human macular lutein-binding protein has remained elusive. Prior identification of the silkworm lutein-binding protein (CBP) as a member of the steroidogenic acute regulatory domain (StARD) protein family, and selective labeling of monkey photoreceptor inner segments by anti-CBP antibody provided an important clue toward identifying the primate retina lutein-binding protein. Homology of CBP to all 15 human StARD proteins was analyzed using database searches, western blotting and immunohistochemistry, and we here provide evidence to identify StARD3 (also known as MLN64) as a human retinal lutein-binding protein. Further, recombinant StARD3 selectively binds lutein with high affinity (KD = 0.45 micromolar) when assessed by surface plasmon resonance (SPR) binding assays. Our results demonstrate previously unrecognized, specific interactions of StARD3 with lutein and provide novel avenues to explore its roles in human macular physiology and disease. PMID:21322544

Lycopene, Lutein and Zeaxanthin May Reduce Faecal Blood, Mucus and Pus but not Abdominal Pain in Individuals with Ulcerative Colitis.

PubMed

Głąbska, Dominika; Guzek, Dominika; Zakrzewska, Paulina; Włodarek, Dariusz; Lech, Gustaw

2016-09-30

The main symptom of ulcerative colitis is diarrhoea, which is often accompanied by painful tenesmus and faecal blood and mucus. It sometimes co-occurs with abdominal pain, fever, feeling of fatigue, loss of appetite and weight loss. Some dietary factors have been indicated as important in the treatment of ulcerative colitis. The aim of the study was to analyse the association between retinoid intake (total vitamin A, retinol, β-carotene, α-carotene, β-cryptoxanthin, lycopene, lutein and zeaxanthin) and ulcerative colitis symptoms (abdominal pain, faecal blood, faecal mucus, faecal pus) in individuals with ulcerative colitis in remission. Assessment of diet was based on self-reported data from each patient's dietary records taken over a period of three typical, random days (2 weekdays and 1 day of the weekend). A total of 56 individuals with ulcerative colitis in remission (19 males and 37 females) were recruited for the study. One in every four individuals with ulcerative colitis in remission was characterised as having inadequate vitamin A intake. Higher lycopene, lutein and zeaxanthin intakes in individuals with ulcerative colitis in remission were associated with lower faecal blood, mucus and pus but not with lower incidence of abdominal pain. Higher carotene intake in individuals with ulcerative colitis in remission may contribute to higher incidence of faecal mucus. Optimising intake of specific retinoids may enhance disease control in individuals with ulcerative colitis. Prospective studies, including patient reported and objective outcomes, are required to confirm this.

Sono- and photoelectrocatalytic processes for the removal of ionic liquids based on the 1-butyl-3-methylimidazolium cation.

PubMed

Mena, Ismael F; Cotillas, Salvador; Díaz, Elena; Sáez, Cristina; Mohedano, Ángel F; Rodrigo, Manuel A

2017-12-06

In this work, sono- and photoelectrolysis of synthetic wastewaters polluted with the ionic liquids 1-Butyl-3-methylimidazolium acetate (BmimAc) and chloride (BmimCl) were investigated with diamond anodes. The results were compared to those attained by enhancing bare electrolysis with irradiation by UV light or with the application of high-frequency ultrasound (US). Despite its complex heterocyclic structure, the Bmim + cation was successfully depleted with the three technologies that were tested and was mainly transformed into four different organic intermediates, an inorganic nitrogen species and carbon dioxide. Regardless of the technology that was evaluated, removal of the heterocyclic ring is much less efficient (and much slower) than oxidation of the counter ion. In turn, the counter ion influences the rate of removal of the ionic liquid cation. Thus, the electrolysis and photoelectrolysis of BmimAc are much less efficient than sonoelectrolysis, but their differences become much less important in the case of BmimCl. In this later case, the most efficient technology is photoelectrolysis. This result is directly related to the generation of free radicals in the solution by irradiation of the electrochemical system with UV light, which contributes significantly to the removal of Bmim + . Copyright © 2017 Elsevier B.V. All rights reserved.

Calculating hyperfine couplings in large ionic crystals containing hundreds of QM atoms: subsystem DFT is the key.

PubMed

Kevorkyants, Ruslan; Wang, Xiqiao; Close, David M; Pavanello, Michele

2013-11-14

We present an application of the linear scaling frozen density embedding (FDE) formulation of subsystem DFT to the calculation of isotropic hyperfine coupling constants (hfcc's) of atoms belonging to a guanine radical cation embedded in a guanine hydrochloride monohydrate crystal. The model systems range from an isolated guanine to a 15,000 atom QM/MM cluster where the QM region is comprised of 36 protonated guanine cations, 36 chlorine anions, and 42 water molecules. Our calculations show that the embedding effects of the surrounding crystal cannot be reproduced by small model systems nor by a pure QM/MM procedure. Instead, a large QM region is needed to fully capture the complicated nature of the embedding effects in this system. The unprecedented system size for a relativistic all-electron isotropic hfcc calculation can be approached in this work because the local nature of the electronic structure of the organic crystals considered is fully captured by the FDE approach.

Ce, Ti modified MCM-48 mesoporous photocatalysts: Effect of the synthesis route on support and metal ion properties

NASA Astrophysics Data System (ADS)

Mureseanu, Mihaela; Filip, Mihaela; Somacescu, Simona; Baran, Adriana; Carja, Gabriela; Parvulescu, Viorica

2018-06-01

New Ti-MCM-48 and CeTi-MCM-48 photocatalysts were obtained by impregnation of the MCM-48 silica support synthesized by a hydrothermal process with aqueous solution of Ti and Ce precursors. The immobilization of metal cations presented a low effect on the porosity, morphology and structure of MCM-48 mesoporous silica support as was evidenced by N2 adsorption-desorption, X-ray diffraction, SEM and TEM electron microscopy. EDAX analysis and X-ray photoelectron microscopy (XPS) indicated that titanium cations were present on the mesoporous silica surface only as Ti4+ species and the effect of ceria on titanium speciation was different, compared to the CeTi-MCM-48 sample, previously obtained by direct synthesis. The photocatalytic properties of mono- and bimetallic catalysts were evaluated in degradation of phenol from water and correlated with the active metallic species concentration, distribution, speciation and their interaction with the support or each other. An advanced oxidation mechanism for phenol degradation by radical species was proposed.

Process for producing high purity isoolefins and dimers thereof by dissociation of ethers

DOEpatents

Smith, L.A. Jr.; Jones, E.M. Jr.; Hearn, D.

1984-05-08

Alkyl tertiary butyl ether or alkyl tertiary amyl ether is dissociated by vapor phase contact with a cation acidic exchange resin at temperatures in the range of 150 to 250 F at LHSV of 0.1 to 20 to produce a stream consisting of unreacted ether, isobutene or isoamylene and an alcohol corresponding to the alkyl radical. After the alcohol is removed, the ether/isoolefin stream may be fractionated to obtain a high purity isoolefin (99+%) or the ether/isoolefin stream can be contacted in liquid phase with a cation acidic exchange resin to selectively dimerize the isoolefin in a highly exothermic reaction, followed by fractionation of the dimerization product to produce high purity diisoolefin (97+%). In the case where the alkyl is C[sub 3] to C[sub 6] and the corresponding alcohol is produced on dissociation of the ether, combined dissociation-distillation may be carried out such that isoolefin is the overhead product and alcohol the bottom. 2 figs.

Process for producing high purity isoolefins and dimers thereof by dissociation of ethers

DOEpatents

Smith, Jr., Lawrence A.; Jones, Jr., Edward M.; Hearn, Dennis

1984-01-01

Alkyl tertiary butyl ether or alkyl tertiary amyl ether is dissociated by vapor phase contact with a cation acidic exchange resin at temperatures in the range of 150.degree. to 250.degree. F. at LHSV of 0.1 to 20 to produce a stream consisting of unreacted ether, isobutene or isoamylene and an alcohol corresponding to the alkyl radical. After the alcohol is removed, the ether/isoolefin stream may be fractionated to obtain a high purity isoolefin (99+%) or the ether/isoolefin stream can be contacted in liquid phase with a cation acidic exchange resin to selectively dimerize the isoolefin in a highly exothermic reaction, followed by fractionation of the dimerization product to produce high purity diisoolefin (97+%). In the case where the alkyl is C.sub.3 to C.sub.6 and the corresponding alcohol is produced on dissociation of the ether, combined dissociation-distillation may be carried out such that isoolefin is the overhead product and alcohol the bottom.

Hydrodynamic interpretation on the rotational diffusion of peroxylamine disulfonate solute dissolved in room temperature ionic liquids as studied by electron paramagnetic resonance spectroscopy.

PubMed

Miyake, Yusuke; Akai, Nobuyuki; Kawai, Akio; Shibuya, Kazuhiko

2011-06-23

Rotational motion of a nitroxide radical, peroxylamine disulfonate (PADS), dissolved in room temperature ionic liquids (RTILs) was studied by analyzing electron paramagnetic resonance spectra of PADS in various RTILs. We determined physical properties of PADS such as the hyperfine coupling constant (A), the temperature dependence of anisotropic rotational correlation times (τ(∥) and τ(⊥)), and rotational anisotropy (N). We observed that the A values remain unchanged for various RTILs, which indicates negligible interaction between the N-O PADS group and the cation of RTIL. Large N values suggest strong interaction of the negative sulfonyl parts of PADS with the cations of RTILs. Most of the τ(∥), τ(⊥), and (τ(∥)τ(⊥))(1/2) values are within the range calculated on the basis of a hydrodynamic theory with stick and slip boundary conditions. It was deduced that this theory could not adequately explain the measured results in some RTILs with smaller BF(4) and PF(6) anions.

[2.2]paracyclophane-bridged mixed-valence compounds: application of a generalized Mulliken-Hush three-level model.

PubMed

Amthor, Stephan; Lambert, Christoph

2006-01-26

A series of [2.2]paracylophane-bridged bis-triarylamine mixed-valence (MV) radical cations were analyzed by a generalized Mulliken-Hush (GMH) three-level model which takes two transitions into account: the intervalence charge transfer (IV-CT) band which is assigned to an optically induced hole transfer (HT) from one triarylamine unit to the second one and a second band associated with a triarylamine radical cation to bridge (in particular, the [2.2]paracyclophane bridge) hole transfer. From the GMH analysis, we conclude that the [2.2]paracyclophane moiety is not the limiting factor which governs the intramolecular charge transfer. AM1-CISD calculations reveal that both through-bond as well as through-space interactions of the [2.2]paracyclophane bridge play an important role for hole transfer processes. These electronic interactions are of course smaller than direct pi-conjugation, but from the order of magnitude of the couplings of the [2.2]paracyclophane MV species, we assume that this bridge is able to mediate significant through-space and through-bond interactions and that the cyclophane bridge acts more like an unsaturated spacer rather than a saturated one. From the exponential dependence of the electronic coupling V between the two triarylamine localized states on the distance r between the two redox centers, we infer that the hole transfer occurs via a superexchange mechanism. Our analysis reveals that even significantly longer pi-conjugated bridges should still mediate significant electronic interactions because the decay constant beta of a series of pi-conjugated MV species is small.

Intramolecular electron-transfer rates in mixed-valence triarylamines: measurement by variable-temperature ESR spectroscopy and comparison with optical data.

PubMed

Lancaster, Kelly; Odom, Susan A; Jones, Simon C; Thayumanavan, S; Marder, Seth R; Brédas, Jean-Luc; Coropceanu, Veaceslav; Barlow, Stephen

2009-02-11

The electron spin resonance spectra of the radical cations of 4,4'-bis[di(4-methoxyphenyl)amino]tolane, E-4,4'-bis[di(4-methoxyphenyl)amino]stilbene, and E,E-1,4-bis{4-[di(4-methoxyphenyl)amino]styryl}benzene in dichloromethane exhibit five lines over a wide temperature range due to equivalent coupling to two 14N nuclei, indicating either delocalization between both nitrogen atoms or rapid intramolecular electron transfer on the electron spin resonance time scale. In contrast, those of the radical cations of 1,4-bis{4-[di(4-methoxyphenyl)amino]phenylethynyl}benzene and E,E-1,4-bis{4-[di(4-n-butoxyphenyl)amino]styryl}-2,5-dicyanobenzene exhibit line shapes that vary strongly with temperature, displaying five lines at room temperature and only three lines at ca. 190 K, indicative of slow electron transfer on the electron spin resonance time scale at low temperatures. The rates of intramolecular electron transfer in the latter compounds were obtained by simulation of the electron spin resonance spectra and display an Arrhenius temperature dependence. The activation barriers obtained from Arrhenius plots are significantly less than anticipated from Hush analyses of the intervalence bands when the diabatic electron-transfer distance, R, is equated to the N[symbol: see text]N distance. Comparison of optical and electron spin resonance data suggests that R is in fact only ca. 40% of the N[symbol: see text]N distance, while the Arrhenius prefactor indicates that the electron transfer falls in the adiabatic regime.

Potential of aryl-urea-benzofuranylthiazoles hybrids as multitasking agents in Alzheimer's disease.

PubMed

Kurt, Belma Zengin; Gazioglu, Isil; Basile, Livia; Sonmez, Fatih; Ginex, Tiziana; Kucukislamoglu, Mustafa; Guccione, Salvatore

2015-09-18

New benzofuranylthiazole derivatives containing the aryl-urea moiety were synthesized and evaluated in vitro as dual acetylcholinesterase (AChE)-butyrylcholinesterase (BuChE) inhibitors. In addition, the cupric reducing antioxidant capacities (CUPRAC) and ABTS cation radical scavenging abilities of the synthesized compounds were assayed. The result showed that all the synthesized compounds exhibited inhibitory activity on both AChE and BuChE with 1-(4-(5-bromobenzofuran-2-yl)thiazol-2-yl)-3-(2-fluorophenyl)urea (e25, IC50 value of 3.85 μM) and 1-(4-iodophenyl)-3-(4-(5-nitrobenzofuran-2-yl)thiazol-2-yl)urea (e38, IC50 value of 2.03 μM) as the strongest inhibitors against AChE and BuChE, respectively. Compound e38 was 8.5-fold more potent than galanthamine. The selectivity index of e25 and e38 was 2.40 and 0.37 against AChE and BuChE, respectively. Compound e2, e4 and e11 (IC50 = 0.2, 0.5 and 1.13 μM, respectively) showed a better ABTS cation radical scavenging ability than the standard quercetin (IC50 = 1.18 μM). Best poses of compounds e38 on BuChE and e25 on AChE indicate that the thiazole ring and the amidic moiety are important sites of interaction with both ChEs. In addition, the benzofuran ring and phenyl ring are anchored to the side chains of both enzymes by π-π(pi-pi) interactions. Copyright © 2015 Elsevier Masson SAS. All rights reserved.

Spectroscopic and Kinetic Characterization of Peroxidase-Like π-Cation Radical Pinch-Porphyrin-Iron(III) Reaction Intermediate Models of Peroxidase Enzymes.

PubMed

Hernández Anzaldo, Samuel; Arroyo Abad, Uriel; León García, Armando; Ramírez Rosales, Daniel; Zamorano Ulloa, Rafael; Reyes Ortega, Yasmi

2016-06-27

The spectroscopic and kinetic characterization of two intermediates from the H₂O₂ oxidation of three dimethyl ester [(proto), (meso), (deuteroporphyrinato) (picdien)]Fe(III) complexes ([FePPPic], [FeMPPic] and [FeDPPic], respectively) pinch-porphyrin peroxidase enzyme models, with s = 5/2 and 3/2 Fe(III) quantum mixed spin (qms) ground states is described herein. The kinetic study by UV/Vis at λmax = 465 nm showed two different types of kinetics during the oxidation process in the guaiacol test for peroxidases (1-3 + guaiacol + H₂O₂ → oxidation guaiacol products). The first intermediate was observed during the first 24 s of the reaction. When the reaction conditions were changed to higher concentration of pinch-porphyrins and hydrogen peroxide only one type of kinetics was observed. Next, the reaction was performed only between pinch-porphyrins-Fe(III) and H₂O₂, resulting in only two types of kinetics that were developed during the first 0-4 s. After this time a self-oxidation process was observed. Our hypotheses state that the formation of the π-cation radicals, reaction intermediates of the pinch-porphyrin-Fe(III) family with the ligand picdien [N,N'-bis-pyridin-2-ylmethyl-propane-1,3-diamine], occurred with unique kinetics that are different from the overall process and was involved in the oxidation pathway. UV-Vis, ¹H-NMR and ESR spectra confirmed the formation of such intermediates. The results in this paper highlight the link between different spectroscopic techniques that positively depict the kinetic traits of artificial compounds with enzyme-like activity.

Ultrafast electron and hole transfer dynamics of a solar cell dye containing hole acceptors on mesoporous TiO2 and Al2O3.

PubMed

Scholz, Mirko; Flender, Oliver; Boschloo, Gerrit; Oum, Kawon; Lenzer, Thomas

2017-03-08

The stability of dye cations against recombination with conduction band electrons in mesoporous TiO 2 electrodes is a key property for improving light harvesting in dye-sensitised solar cells. Using ultrafast transient broadband absorption spectroscopy, we monitor efficient intramolecular hole transfer in the solar cell dye E6 having two peripheral triarylamine acceptors. After photoexcitation, two hole transfer mechanisms are identified: a concerted mechanism for electron injection and hole transfer (2.4 ps) and a sequential mechanism with time constants of 3.9 ps and 30 ps. This way the dye retards unwanted recombination with a TiO 2 conduction band electron by quickly moving the hole further away from the surface. Contact of the E6/TiO 2 surface with the solvent acetonitrile has almost no influence on the electron injection and hole transfer kinetics. Fast hole transfer (2.8 ps) is also observed on a "non-injecting" Al 2 O 3 surface generating a radical cation-radical anion species with a lifetime of 530 ps. The findings confirm the good intramolecular hole transfer properties of this dye on both thin films. In contrast, intramolecular hole transfer does not occur in the mid-polar organic solvent methyl acetate. This is confirmed by TDDFT calculations suggesting a polarity-induced reduction of the driving force for hole transfer. In methyl acetate, only the relaxation of the initially photoexcited core chromophore is observed including solvent relaxation processes of the electronically excited state S 1 /ICT.

Kinetic Study of the Aroxyl-Radical-Scavenging Activity of Five Fatty Acid Esters and Six Carotenoids in Toluene Solution: Structure-Activity Relationship for the Hydrogen Abstraction Reaction.

PubMed

Mukai, Kazuo; Yoshimoto, Maya; Ishikura, Masaharu; Nagaoka, Shin-Ichi

2017-08-17

A kinetic study of the reaction between an aroxyl radical (ArO • ) and fatty acid esters (LHs 1-5, ethyl stearate 1, ethyl oleate 2, ethyl linoleate 3, ethyl linolenate 4, and ethyl arachidonate 5) has been undertaken. The second-order rate constants (k s ) for the reaction of ArO • with LHs 1-5 in toluene at 25.0 °C have been determined spectrophotometrically. The k s values obtained increased in the order of LH 1 < 2 < 3 < 4 < 5, that is, with increasing the number of double bonds included in LHs 1-5. The k s value for LH 5 was 2.93 × 10 -3 M -1 s -1 . From the result, it has been clarified that the reaction of ArO • with LHs 1-5 was explained by an allylic hydrogen abstraction reaction. A similar kinetic study was performed for the reaction of ArO • with six carotenoids (Car-Hs 1-6, astaxanthin 1, β-carotene 2, lycopene 3, capsanthin 4, zeaxanthin 5, and lutein 6). The k s values obtained increased in the order of Car-H 1 < 2 < 3 < 4 < 5 < 6. The k s value for Car-H 6 was 8.4 × 10 -4 M -1 s -1 . The k s values obtained for Car-Hs 1-6 are in the same order as that of the values for LHs 1-5. The results of detailed analyses of the k s values for the above reaction indicated that the reaction was also explained by an allylic hydrogen abstraction reaction. Furthermore, the structure-activity relationship for the reaction was discussed by taking the result of density functional theory calculation reported by Martinez and Barbosa into account.

Chemical composition and inhibitory effects of water extract of Henna leaves on reactive oxygen species, DNA scission and proliferation of cancer cells

PubMed Central

Kumar, Manish; Chandel, Madhu; Kaur, Paramjeet; Pandit, Kritika; Kaur, Varinder; Kaur, Sandeep; Kaur, Satwinderjeet

2016-01-01

From the centuries, Lawsonia inermis L. (Henna) is utilized in traditional health care system as a medicinal and cosmetic agent. The present study was intended to assess antiradical, DNA protective and antiproliferative activity of water extract of Lawsonia inermis L. leaves (W-LI). Antioxidant activity was estimated using various in vitro assays such as DPPH, ABTS, superoxide anion radical scavenging, FRAP, deoxyribose degradation and DNA protection assay. Growth inhibitory effects of W-LI were assessed using MTT assay against different cancer cell lines viz. HeLa, MCF-7, A549, C6 and COLO-205. From the results of antioxidant assays, it was found that W-LI quenched DPPH and ABTS cation radicals with IC50 value of 352.77 µg/ml and 380.87 µg/ml respectively. It demonstrated hydroxyl radical scavenging potential of 59.75 % at highest test dose of 1000 µg/ml in deoxyribose degradation assay. The results of FRAP assay showed that W-LI also possesses significant reducing activity. Extract inhibited hydroxyl radical induced pBR322 plasmid DNA strand scission, thus conferring DNA protection. Growth inhibition of various cancer cell lines was achieved to the varying extent on treatment with W-LI. Further, it was observed that activity was quite promising against colon cancer COLO-205 cells (GI50 121.03 µg/ml). HPLC profiling of W-LI revealed the presence of different polyphenolic compounds such as ellagic acid, catechin, quercetin, kaempferol etc. which might be contributing towards antioxidant and cytotoxic activity. The present study demonstrated that polyphenols rich W-LI extract from leaves of L. inermis possesses ability to inhibit oxidative radicals and cancer cells proliferation. PMID:28337113

Singlet and doublet states UV-vis spectrum and electronic properties of 3-methylchrysene and 4-methylchrysene in glass matrix.

PubMed

Husain, Mudassir M; Tandon, H C; Varadwaj, Pradeep R

2008-03-01

The ultraviolet-visual spectrum of 3-methylchrysene, 4-methylchrysene and their radical cations formed by ultraviolet radiations, were measured in glass matrix at the room temperature. In the measured singlet state spectrum we were able to identify the alpha, p, beta, beta' (Clar's) or (1)L(b), (1)L(a)(1)B(b), (1)B(a) (Platt's notation) bands. The presence of alpha, beta or (1)L(b), (1)B(b) was confirmed by calculating their wavelength ratio lambda(alpha)/lambda(beta). Since matrix induces perturbation in the measured spectrum; it becomes necessary to take into account the perturbation while computing the spectrum. An effort has been made in this work to simulate the electronic spectrum in the same environment as is measured. This study presents the first calculated spectrum of these systems and their cations in glass matrix by semi empirical methods. To observe the magnitude of perturbation and hence to see the spectral shift in glass matrix, the spectrum was calculated in the free state as well. Spectral properties such as frontier orbitals gap, dipole moment, mean polarizabilities and its tensors were also computed both in glass matrix and free state using semiemperical method. The measured bands of 3-methylchrysene cation at wavelength 416.50 and 473.85 nm closely match with the available diffuse intersteallar bands (DIBs) at 417.55 and 472.64 nm, respectively. Also the observed 474.85 nm band of 4-methylchrysene cation matches the DIB at 476.00 nm.

Polyamines control of cation transport across plant membranes: implications for ion homeostasis and abiotic stress signaling.

PubMed

Pottosin, Igor; Shabala, Sergey

2014-01-01

Polyamines are unique polycationic metabolites, controlling a variety of vital functions in plants, including growth and stress responses. Over the last two decades a bulk of data was accumulated providing explicit evidence that polyamines play an essential role in regulating plant membrane transport. The most straightforward example is a blockage of the two major vacuolar cation channels, namely slow (SV) and fast (FV) activating ones, by the micromolar concentrations of polyamines. This effect is direct and fully reversible, with a potency descending in a sequence Spm(4+) > Spd(3+) > Put(2+). On the contrary, effects of polyamines on the plasma membrane (PM) cation and K(+)-selective channels are hardly dependent on polyamine species, display a relatively low affinity, and are likely to be indirect. Polyamines also affect vacuolar and PM H(+) pumps and Ca(2+) pump of the PM. On the other hand, catabolization of polyamines generates H2O2 and other reactive oxygen species (ROS), including hydroxyl radicals. Export of polyamines to the apoplast and their oxidation there by available amine oxidases results in the induction of a novel ion conductance and confers Ca(2+) influx across the PM. This mechanism, initially established for plant responses to pathogen attack (including a hypersensitive response), has been recently shown to mediate plant responses to a variety of abiotic stresses. In this review we summarize the effects of polyamines and their catabolites on cation transport in plants and discuss the implications of these effects for ion homeostasis, signaling, and plant adaptive responses to environment.