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Sample records for acid radical cation

  1. Spectroscopic detection, reactivity, and acid-base behavior of ring-dimethoxylated phenylethanoic acid radical cations and radical zwitterions in aqueous solution.

    PubMed

    Bietti, Massimo; Capone, Alberto

    2004-01-23

    A product and time-resolved kinetic study of the one-electron oxidation of ring-dimethoxylated phenylethanoic acids has been carried out at different pH values. Oxidation leads to the formation of aromatic radical cations or radical zwitterions depending on pH, and pK(a) values for the corresponding acid-base equilibria have been measured. The radical cations undergo decarboxylation with first-order rate constants (k(dec)) ranging from <10(2) to 5.6 x 10(4) s(-1) depending on radical cation stability. A significant increase in k(dec) (between 10 and 40 times) is observed on going from the radical cations to the corresponding radical zwitterions. The results are discussed in terms of the ease of intramolecular side chain to ring electron transfer required for decarboxylation, in both the radical cations and radical zwitterions.

  2. Cationic and radical intermediates in the acid photorelease from aryl sulfonates and phosphates.

    PubMed

    Terpolilli, Marco; Merli, Daniele; Protti, Stefano; Dichiarante, Valentina; Fagnoni, Maurizio; Albini, Angelo

    2011-01-01

    The irradiation of a series of phenyl sulfonates and phosphates leads to the quantitative release of acidity with a reasonable quantum yield (≈0.2). Products characterization, ion chromatography analysis and potentiometric titration are consistent with the intervening of two different paths in this reaction, viz. cationic with phosphates and (mainly) radical with sulfonates.

  3. 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

    2017-02-01

    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.

  4. Reactivity and acid-base behavior of ring-methoxylated arylalkanoic acid radical cations and radical zwitterions in aqueous solution. Influence of structural effects and pH on the benzylic C-H deprotonation pathway.

    PubMed

    Bietti, Massimo; Capone, Alberto

    2006-07-07

    A product and time-resolved kinetic study of the one-electron oxidation of ring-methoxylated phenylpropanoic and phenylbutanoic acids (Ar(CH2)nCO2H, n = 2, 3) has been carried out at different pH values. Oxidation leads to the formation of aromatic radical cations (Ar.+(CH2)nCO2H) or radical zwitterions (Ar.+(CH2)nCO2-) depending on pH, and pKa values for the corresponding acid-base equilibria have been measured. In the radical cation, the acidity of the carboxylic proton decreases by increasing the number of methoxy ring substituents and by increasing the distance between the carboxylic group and the aromatic ring. At pH 1.7 or 6.7, the radical cations or radical zwitterions undergo benzylic C-H deprotonation as the exclusive side-chain fragmentation pathway, as clearly shown by product analysis results. At pH 1.7, the first-order deprotonation rate constants measured for the ring-methoxylated arylalkanoic acid radical cations are similar to those measured previously in acidic aqueous solution for the alpha-C-H deprotonation of structurally related ring-methoxylated alkylaromatic radical cations. In basic solution, the second-order rate constants for reaction of the radical zwitterions with (-)OH (k-OH)) have been obtained. These values are similar to those obtained previously for the (-)OH-induced alpha-C-H deprotonation of structurally related ring-methoxylated alkylaromatic radical cations, indicating that under these conditions the radical zwitterions undergo benzylic C-H deprotonation. Very interestingly, with 3,4-dimethoxyphenylethanoic acid radical zwitterion, that was previously observed to undergo exclusive decarboxylation up to pH 10, competition between decarboxylation and benzylic C-H deprotonation is observed above pH 11.

  5. Electron transfer from aromatic amino acids to guanine and adenine radical cations in pi stacked and T-shaped complexes.

    PubMed

    Butchosa, Cristina; Simon, Sílvia; Voityuk, Alexander A

    2010-04-21

    Similar redox properties of the natural nucleobases and aromatic amino acids make it possible for electron transfer (ET) to occur between these sites in protein-nucleic acid complexes. Using DFT calculations, we estimate the ET rate from aromatic amino acid X (X = Phe, His, Tyr and Trp) to radical cations of guanine (G) and adenine (A) in dimers G-X and A-X with different arrangement of the subunits. We show that irrespective of the mutual orientation of the aromatic rings, the electronic interaction in the systems is strong enough to ensure effective ET from X to G(+) or A(+). Surprisingly, relatively high ET rates are found in T-shaped dimers. This suggests that pi stacking of nucleobases and aromatic amino acids is not required for feasible ET. In most complexes [G-X](+) and [A-X](+), we find the excess charge to be confined to a single site, either the nucleobase or amino acid X. Then, conformational changes may initiate migration of the radical cation state from the nucleobase to X and back. The ET process from Trp and Tyr to G(+) is found to be faster than deprotonation of G(+). Because the last reaction may lead to the formation of highly mutagenic species, the efficient repair of G(+) may play an important role in the protection of genomic DNA from oxidative damage.

  6. Enhancement of a Lewis acid-base interaction via solvation: ammonia molecules and the benzene radical cation.

    PubMed

    Chiang, Chi-Tung; Freindorf, Marek; Furlani, Thomas; DeLeon, Robert L; Richard, John P; Garvey, James F

    2007-07-12

    The interaction between ammonia and the benzene radical cation has been investigated by gas-phase studies of mass selected ion clusters {C(6)H(6)-(NH(3))(n=0-8)}(+) via tandem quadrupole mass spectrometry and through calculations. Experiments show a special stability for the cluster ion that contains four ammonias: {C(6)H(6)(NH(3))(4)}(+). Calculations provide evidence that the first ammonia forms a weak dative bond to the cyclohexadienyl radical cation, {C(6)H(6)-NH(3)}(+), where there is a transfer of electrons from ammonia to benzene. Additional solvating ammonia molecules form stabilizing hydrogen bonds to the ring-bound ammonia {C(6)H(6)-NH(3)}(+).(NH(3))(n), which cause cooperative changes in the structure of the cluster complex. Free ammonia is a weak hydrogen bond donor, but electron transfer from NH(3) to the benzene ring that strengthens the dative bond will increase the hydrogen acidity and the strength of the cluster hydrogen bonds to the added ammonia. A progressive "tightening" of this dative bond is observed upon addition of the first, second, and third ammonia to give a cluster stabilized by three N-(+)H x N hydrogen bonds. This shows that the energetic cost of tightening the dative bond is recovered with dividends in the formation of stable cluster hydrogen bonds.

  7. Halogenated silanes, radicals, and cations

    NASA Astrophysics Data System (ADS)

    Wang, Liming; He, Yi-Liang

    2008-09-01

    Quantum chemistry study has been carried out on the structure and energetics of halogenated silanes, radicals, and cations (SiHxXy0,+1, X = F, Cl, Br; x + y = 1-4). The geometries are optimized at B3LYP/6-31+G(2df,p) level. The adiabatic ionization energiess (IEas), relative energetics of cations, proton affinities (PAs) of silanes, and the enthalpies of formation are predicted using G3(CC) model chemistry. Non-classical ion complex structures are found for hydrogenated cations and transition states connecting classical and non-classical structures are also located. The most stable cations for silylene and silyl radicals have their classical divalent and trivalent structures, and those for silanes have non-classical structures except for SiH3Br+ and SiH2Br2+. The non-classical structures for halosilane cations imply difficulty in experimentally measurement of the adiabatic ionization energies using photoionization or photoelectron studies. For SiH3X, SiH2X2, and SiHX3, the G3(CC) adiabatic IEas to classical ionic structures closest to their neutrals agree better with the photoelectron spectroscopic measurements. The transition states between classical and non-classical structures also hamper the photoionization determination of the appearance energies for silylene cations from silanes. The G3(CC) results for SiHx0,+1 agree excellently with the photoionization mass spectrometric study, and the results for fluorinated and chlorinated species also agree with the previous theoretical predictions at correlation levels from BAC-MP4 to CCSD(T)/CBS. The predicted enthalpy differences between SiH2Cl+, SiHCl2+, and SiCl3+ are also in accordance with previous kinetics study. The G3(CC) results show large discrepancies to the collision-induced charge transfer and/or dissociation reactions involving SiFx+ and SiClx+ ions, for which the G3(CC) enthalpies of formation are also significantly differed from the previous theoretical predictions, especially on SiFx+ (x = 2-4). The G3

  8. Picosecond pulse radiolysis of highly concentrated sulfuric acid solutions: evidence for the oxidation reactivity of radical cation H2O(•+).

    PubMed

    Ma, Jun; Schmidhammer, Uli; Mostafavi, Mehran

    2014-06-12

    Aqueous solution of sulfuric acid is used as a suitable system to investigate the reactivity of the short-lived radical cation H2O(•+) which is generated by radiation in water. Ten aqueous solutions containing sulfuric acid with concentration from 1 to 18 mol L(-1) are studied by picosecond pulse radiolysis. The absorbance of the secondary radical SO4(•-) (or HSO4(•)) formed within the 10 ps electron pulse is measured by a pulse-probe method in the visible range. The analysis of the kinetics show that the radicals of sulfuric acid are formed within the picosecond electron pulse via two parallel mechanisms: direct electron detachment by the electron pulse and oxidation by the radical cation of water H2O(•+). In highly concentrated solution when SO4(2-) is in contact with H2O(•+), the electron transfer becomes competitive against proton transfer with another water molecule. Therefore, H2O(•+) may act as an extremely strong oxidant. The maximum radiolytic yield of scavenged H2O(•+) is estimated to be 5.3 ± 0.1 × 10(-7) mol J(-1).

  9. Radical cation cyclization of 1,5-hexadiene to cyclohexene via the cyclohexane-2,5-diyl radical cation intermediate

    SciTech Connect

    Guo, Q.X.; Qin, X.Z.; Wang, J.T.; Williams, F.

    1988-03-16

    The classical example of a neutral carbon-centered radical cyclization reaction is the regioselective 1,5-ring closure (exocyclization) of the 5-hexenyl radical to the cyclopentylcarbinyl radical. Here the authors report the title reaction, a comparable addition process whereby an ..cap alpha.., omega-diene radical cation reacts by endocyclization and hydrogen shift(s) to produce a cycloolefin radical cation.

  10. Electronic spectrum of 9-methylanthracenium radical cation

    NASA Astrophysics Data System (ADS)

    O'Connor, Gerard D.; Sanelli, Julian A.; Dryza, Vik; Bieske, Evan J.; Schmidt, Timothy W.

    2016-04-01

    The predissociation spectrum of the cold, argon-tagged, 9-methylanthracenium radical cation is reported from 8000 cm-1 to 44 500 cm-1. The reported spectrum contains bands corresponding to at least eight electronic transitions ranging from the near infrared to the ultraviolet. These electronic transitions are assigned through comparison with ab initio energies and intensities. The infrared D1←D0 transitions exhibit significant vibronic activity, which is assigned through comparison with TD-B3LYP excited state frequencies and intensities, as well as modelled vibronic interactions. Dissociation of 9-methylanthracenium is also observed at high visible-photon energies, resulting in the loss of either CH2 or CH3. The relevance of these spectra, and the spectra of other polycyclic aromatic hydrocarbon radical cations, to the largely unassigned diffuse interstellar bands, is discussed.

  11. Cascade Dissociations of Peptide Cation-Radicals. Part 1. Scope and Effects of Amino Acid Residues in Penta-, Nona- and Decapeptides

    PubMed Central

    Chung, Thomas W.; Hui, Renjie; Ledvina, Aaron; Coon, Joshua J.

    2013-01-01

    Amino acid residue-specific backbone and side-chain dissociations of peptide z ions in MS3 spectra were elucidated for over 40 pentapeptides with arginine C-terminated sequences of the AAXAR and AAHXR type, nonapeptides of the AAHAAXYAR and AAHAXAYAR type, and AAHAAXYAAR decapeptides. Peptide zn ions containing amino acid residues with readily transferrable benzylic or tertiary β-hydrogen atoms (Phe, Tyr, His, Trp, Val) underwent facile backbone cleavages to form dominant zn-2 or zn-3 ions. These backbone cleavages are thought to be triggered by a side-chain β-hydrogen atom transfer to the z ion Cα radical site followed by homolytic dissociation of the adjacent Cα—CO bond, forming zn-2 + HNCO cation-radicals that spontaneously dissociate by loss of HNCO. Amino acid residues that do not have readily transferrable β-hydrogen atoms (Gly, Ala) do not undergo the zn → zn-2 dissociations. The backbone cleavages compete with side-chain dissociations in z ions containing Asp and Asn residues. Side-chain dissociations are thought to be triggered by α-hydrogen atom transfers that activate the Cβ—Cγ or Cβ—heteroatom bonds for dissociations that dominate the MS3 spectra of z ions from peptides containing Leu, Cys, Lys, Met, Ser, Arg, Glu and Gln residues. The Lys, Arg, Gln, and Glu residues also participate in γ-hydrogen atom transfers that trigger other side-chain dissociations. PMID:22669761

  12. Oxygen acidity of ring methoxylated 1,1-diarylalkanol radical cations bearing alpha-cyclopropyl groups. The competition between O-neophyl shift and C-cyclopropyl beta-scission in the intermediate 1,1-diarylalkoxyl radicals.

    PubMed

    Bietti, Massimo; Fiorentini, Simone; Pato, Iria Pèrez; Salamone, Michela

    2006-04-14

    A product and time-resolved kinetic study on the reactivity of the radical cations generated from cyclopropyl(4-methoxyphenyl)phenylmethanol (1) and cyclopropyl[bis(4-methoxyphenyl)]methanol (2) has been carried out in aqueous solution. In acidic solution, 1*+ and 2*+ display very low reactivities toward fragmentation, consistent with the presence of groups at Calpha (aryl and cyclopropyl) that after Calpha-Cbeta bond cleavage would produce relatively unstable carbon-centered radicals. In basic solution, 1*+ and 2*+ display oxygen acidity, undergoing -OH-induced deprotonation from the alpha-OH group, leading to the corresponding 1,1-diarylalkoxyl radicals 1r* and 2r*, respectively, as directly observed by time-resolved spectroscopy. The product distributions observed in the reactions of 1*+ and 2*+ under these conditions (cyclopropyl phenyl ketone, cyclopropyl(4-methoxyphenyl) ketone, and 4-methoxybenzophenone from 1*+; cyclopropyl(4-methoxyphenyl) ketone and 4,4'-dimethoxybenzophenone from 2*+) have been rationalized in terms of a water-induced competition between O-neophyl shift and C-cyclopropyl beta-scission in the intermediate 1,1-diarylalkoxyl radicals 1r* and 2r*.

  13. Fragmentation Pathways in the Uracil Radical Cation

    SciTech Connect

    Zhou, Congyi; Matsika, Spiridoula; Kotur, Marija; Weinacht, Thomas C.

    2012-08-24

    We investigate pathways for fragmentation in the uracil radical cation using ab initio electronic structure calculations. We focus on the main fragments produced in pump–probe dissociative ionization experiments. These are fragments with mass to charge ratios (m/z) of 69, 28, 41, and 42. Barriers to dissociation along the ground ionic surface are reported, which provide an estimate of the energetic requirements for the production of the main fragments. Finally, direct and sequential fragmentation mechanisms have been analyzed, and it is concluded that sequential fragmentation after production of fragment with m/z 69 is the dominant mechanism for the production of the smaller fragments.

  14. Cascade dissociations of peptide cation-radicals. Part 1. Scope and effects of amino acid residues in penta-, nona-, and decapeptides.

    PubMed

    Chung, Thomas W; Hui, Renjie; Ledvina, Aaron; Coon, Joshua J; Tureček, Frantisek

    2012-08-01

    Amino acid residue-specific backbone and side-chain dissociations of peptide z ions in MS(3) spectra were elucidated for over 40 pentapeptides with arginine C-terminated sequences of the AAXAR and AAHXR type, nonapeptides of the AAHAAXX"AR and AAHAXAX"AR type, and AAHAAXX"AAR decapeptides. Peptide z(n) ions containing amino acid residues with readily transferrable benzylic or tertiary β-hydrogen atoms (Phe, Tyr, His, Trp, Val) underwent facile backbone cleavages to form dominant z(n-2) or z(n-3) ions. These backbone cleavages are thought to be triggered by a side-chain β-hydrogen atom transfer to the z ion C(α) radical site followed by homolytic dissociation of the adjacent C(α)-CO bond, forming x(n-2) cation-radicals that spontaneously dissociate by loss of HNCO. Amino acid residues that do not have readily transferrable β-hydrogen atoms (Gly, Ala) do not undergo the z(n) → z(n-2) dissociations. The backbone cleavages compete with side-chain dissociations in z ions containing Asp and Asn residues. Side-chain dissociations are thought to be triggered by α-hydrogen atom transfers that activate the C(β)-C(γ) or C(β)-heteroatom bonds for dissociations that dominate the MS(3) spectra of z ions from peptides containing Leu, Cys, Lys, Met, Ser, Arg, Glu, and Gln residues. The Lys, Arg, Gln, and Glu residues also participate in γ-hydrogen atom transfers that trigger other side-chain dissociations.

  15. The pi-Cation Radical of Chlorophyll a.

    PubMed

    Borg, D C; Fajer, J; Felton, R H; Dolphin, D

    1970-10-01

    Chlorophyll a undergoes reversible one-electron oxidation in dichloromethane and butyronitrile. Removal of the electron by controlled potential electrolysis or by stoichiometric charge transfer to a known cation radical yields a radical (epr line width = 9 gauss, g = 2.0025 +/- 0.0001) whose optical spectrum is bleached relative to that of chlorophyll. Upon electrophoresis this bleached species behaves as a cation. By comparison with the known properties of pi-cation radicals of porphyrins and chlorins, the chlorophyll radical is also identified as a pi-cation. Further correlation of optical and epr properties with published studies on photosynthesis leads to the conclusion that oxidized P700, the first photochemical product of photosystem I in green plants, contains a pi-cation radical of the chlorin component of chlorophyll a. This radical is the likely source of the rapidly-decaying, narrow epr signal of photosynthesis.

  16. 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.

  17. Strong Inhibition of O-Atom Transfer Reactivity for Mn(IV)(O)(π-Radical-Cation)(Lewis Acid) versus Mn(V)(O) Porphyrinoid Complexes.

    PubMed

    Zaragoza, Jan Paulo T; Baglia, Regina A; Siegler, Maxime A; Goldberg, David P

    2015-05-27

    The oxygen atom transfer (OAT) reactivity of two valence tautomers of a Mn(V)(O) porphyrinoid complex was compared. The OAT kinetics of Mn(V)(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato(3-)) reacting with a series of triarylphosphine (PAr3) substrates were monitored by stopped-flow UV-vis spectroscopy, and revealed second-order rate constants ranging from 16(1) to 1.43(6) × 10(4) M(-1) s(-1). Characterization of the OAT transition state analogues Mn(III)(OPPh3)(TBP8Cz) and Mn(III)(OP(o-tolyl)3)(TBP8Cz) was carried out by single-crystal X-ray diffraction (XRD). A valence tautomer of the closed-shell Mn(V)(O)(TBP8Cz) can be stabilized by the addition of Lewis and Brønsted acids, resulting in the open-shell Mn(IV)(O)(TBP8Cz(•+)):LA (LA = Zn(II), B(C6F5)3, H(+)) complexes. These Mn(IV)(O)(π-radical-cation) derivatives exhibit dramatically inhibited rates of OAT with the PAr3 substrates (k = 8.5(2) × 10(-3) - 8.7 M(-1) s(-1)), contrasting the previously observed rate increase of H-atom transfer (HAT) for Mn(IV)(O)(TBP8Cz(•+)):LA with phenols. A Hammett analysis showed that the OAT reactivity for Mn(IV)(O)(TBP8Cz(•+)):LA is influenced by the Lewis acid strength. Spectral redox titration of Mn(IV)(O)(TBP8Cz(•+)):Zn(II) gives Ered = 0.69 V vs SCE, which is nearly +700 mV above its valence tautomer Mn(V)(O)(TBP8Cz) (Ered = -0.05 V). These data suggest that the two-electron electrophilicity of the Mn(O) valence tautomers dominate OAT reactivity and do not follow the trend in one-electron redox potentials, which appear to dominate HAT reactivity. This study provides new fundamental insights regarding the relative OAT and HAT reactivity of valence tautomers such as M(V)(O)(porph) versus M(IV)(O)(porph(•+)) (M = Mn or Fe) found in heme enzymes.

  18. Chemistry of ascorbic acid radicals

    SciTech Connect

    Bielski, B.H.J.

    1982-01-01

    The chemistry of ascorbic acid free radicals is reviewed. Particular emphasis is placed on identification and characterization of ascorbate radicals by spectrophotometric and electron paramagnetic resonance techniques, the kinetics of formation and disappearance of ascorbate free radicals in enzymatic and nonenzymatic reactions, the effect of pH upon the spectral and kinetic properties of ascorbate anion radical, and chemical reactivity of ascorbate free radicals.

  19. Reactions and structural investigation of chlorpromazine radical cation

    NASA Astrophysics Data System (ADS)

    Joshi, Ravi; Ghanty, Tapan K.; Mukherjee, T.

    2008-10-01

    Experimental and theoretical studies have been carried out to understand pro-oxidant behaviour of chlorpromazine radical cation (CPZ rad + ). Pulse radiolysis studies have shown that CPZ rad + oxidizes physiological antioxidants (uric acid and bilirubin), and biomolecules like, tyrosine and proteins (bovine serum albumin and casein), thereby acting as a pro-oxidant. Ab-initio quantum chemical calculations suggest structural and electronic changes on oxidation of CPZ. The calculations with Hartree-Fock and density functional methods show that ring nitrogen atom is the site of electron removal from CPZ and sulfur atom is the site of maximum spin in CPZ rad + . The calculations also suggest that oxidation of CPZ leads to increase in planarity of the tricyclic ring as well as tilting of alkyl side chain towards chlorine containing ring. The structural changes on oxidation of CPZ and spin delocalization in CPZ rad + fairly explain the pro-oxidant activity of CPZ.

  20. Comparing the gas-phase fragmentation reactions of protonated and radical cations of the tripeptides GXR

    NASA Astrophysics Data System (ADS)

    Wee, Sheena; O'Hair, Richard A. J.; McFadyen, W. David

    2004-05-01

    Electrospray ionization (ESI) mass spectrometry of methanolic solutions of mixtures of the copper salt (2,2':6',2''-terpyridine)copper(II) nitrate monohydrate ([Cu(II)(tpy)(NO3)2].H2O) and a tripeptide GXR (where X = 1 of the 20 naturally occurring amino acids) yielded [Cu(II)(tpy)(GXR)][radical sign]2+ ions, which were then subjected to collision induced dissociation (CID). In all but one case (GRR), these [Cu(II)(tpy)(GXR)][radical sign]2+ ions fragment to form odd electron GXR[radical sign]+ radical cations with sufficient abundance to examine their gas-phase fragmentation reactions. The GXR[radical sign]+ radical cations undergo a diverse range of fragmentation reactions which depend on the nature of the side chain of X. Many of these reactions can be rationalized as arising from the intermediacy of isomeric distonic ions in which the charge (i.e. proton) is sequestered by the highly basic arginine side chain and the radical site is located at various positions on the tripeptide including the peptide back bone and side chains. The radical sites in these distonic ions often direct the fragmentation reactions via the expulsion of small radicals (to yield even electron ions) or small neutrals (to form radical cations). Both classes of reaction can yield useful structural information, allowing for example, distinction between leucine and isoleucine residues. The gas-phase fragmentation reactions of the GXR[radical sign]+ radical cations are also compared to their even electron [GXR+H]+ and [GXR+2H]2+ counterparts. The [GXR+H]+ ions give fewer sequence ions and more small molecule losses while the [GXR+2H]2+ ions yield more sequence information, consistent with the [`]mobile proton model' described in previous studies. In general, all three classes of ions give complementary structural information, but the GXR[radical sign]+ radical cations exhibit a more diverse loss of small species (radicals and neutrals). Finally, links between these gas-phase results and key

  1. 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.

  2. Surface hopping investigation of the relaxation dynamics in radical cations

    NASA Astrophysics Data System (ADS)

    Assmann, Mariana; Weinacht, Thomas; Matsika, Spiridoula

    2016-01-01

    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 these 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. Examining the properties of the systems in the Franck-Condon region can give some insight into the subsequent dynamics.

  3. Carotenoid cation radicals: electrochemical, optical, and EPR study

    SciTech Connect

    Grant, J.L.; Kramer, V.J.; Ding, R.; Kispert, L.D.

    1988-03-30

    The general aim of this investigation is to determine whether carotenoid cation radicals can be produced, and stabilized, electrochemically. Hence, the authors have undertaken a detailed study of the electrooxidation of various carotenoids (..beta..-carotene (I), ..beta..-apo-8'-carotenal (II), and canthaxanthin (III) using the techniques of cyclic voltammetry, controlled-potential electrolysis (cpe) in conjunction with optical spectroscopy, and EPR spectroscopy coupled with in situ electrolysis. They report the successful generation of carotenoid cation radicals via electrochemical oxidation and, furthermore, the stabilization of these radicals for several minutes in CH/sub 2/Cl/sub 2/ and C/sub 2/H/sub 4/Cl/sub 2/ solvents.

  4. Formation and Dissociation of Phosphorylated Peptide Radical Cations

    NASA Astrophysics Data System (ADS)

    Kong, Ricky P. W.; Quan, Quan; Hao, Qiang; Lai, Cheuk-Kuen; Siu, Chi-Kit; Chu, Ivan K.

    2012-12-01

    In this study, we generated phosphoserine- and phosphothreonine-containing peptide radical cations through low-energy collision-induced dissociation (CID) of the ternary metal-ligand phosphorylated peptide complexes [CuII(terpy) p M]·2+ and [CoIII(salen) p M]·+ [ p M: phosphorylated angiotensin III derivative; terpy: 2,2':6',2''-terpyridine; salen: N, N '-ethylenebis(salicylideneiminato)]. Subsequent CID of the phosphorylated peptide radical cations ( p M·+) revealed fascinating gas-phase radical chemistry, yielding (1) charge-directed b- and y-type product ions, (2) radical-driven product ions through cleavages of peptide backbones and side chains, and (3) different degrees of formation of [M - H3PO4]·+ species through phosphate ester bond cleavage. The CID spectra of the p M·+ species and their non-phosphorylated analogues featured fragment ions of similar sequence, suggesting that the phosphoryl group did not play a significant role in the fragmentation of the peptide backbone or side chain. The extent of neutral H3PO4 loss was influenced by the peptide sequence and the initial sites of the charge and radical. A preliminary density functional theory study, at the B3LYP 6-311++G(d,p) level of theory, of the neutral loss of H3PO4 from a prototypical model— N-acetylphosphorylserine methylamide—revealed several factors governing the elimination of neutral phosphoryl groups through charge- and radical-induced mechanisms.

  5. 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.

  6. Oxoferryl porphyrin cation radicals in model systems: Evidence for variable metal-radical spin coupling

    NASA Astrophysics Data System (ADS)

    Bill, E.; Bominaar, E. L.; Ding, X.-Q.; Trautwein, A. X.; Winkler, H.; Mandon, D.; Weiss, R.; Gold, A.; Jayaraj, K.; Toney, G. E.

    1990-07-01

    Magnetic properties of frozen solutions of highly oxidized iron porphyrin complexes were investigated by EPR and Mössbauer spectroscopy. The Mössbauer spectra, recorded at low temperatures in various magnetic fields, were analyzed on the basis of spin Hamiltonian simulations. Spin coupling between ferryl iron (FeIV) and porphyrin cation radical was taken into account explicitly. Hyperfine and spin-coupling parameters are given for several complexes, together with zero-field parameters. One of the complexes exhibits weak spin coupling, it is the first model system exhibiting properties comparable to those of the oxoferryl cation radical enzyme Horse Radish Peroxidase I.

  7. Tuning aryl, hydrazine radical cation electronic interactions using substituent effects.

    PubMed

    Valverde-Aguilar, Guadalupe; Wang, Xianghuai; Plummer, Edward; Lockard, Jenny V; Zink, Jeffrey I; Luo, Yun; Weaver, Michael N; Nelsen, Stephen F

    2008-08-14

    Absorption spectra for 2,3-diaryl-2,3-diazabicyclo[2.2.2]octane radical cations (2(X)(*+)) and for their monoaryl analogues 2-tert-butyl-3-aryl-2,3-diazabicyclo[2.2.2]octane radical cations (1(X)(*+)) having para chloro, bromo, iodo, cyano, phenyl, and nitro substituents are reported and compared with those for the previously reported 1- and 2(H)(*+) and 1- and 2(OMe)(*+). The calculated geometries and optical absorption spectra for 2(Cl)(*+) demonstrate that p-C6H4Cl lies between p-C6H4OMe and C6H5 in its ability to stabilize the lowest energy optical transition of the radical cation, which involves electron donation from the aryl groups toward the pi*(NN)(+)-centered singly occupied molecular orbital of 2(X)(*+). Resonance Raman spectral determination of the reorganization energy for their lowest energy transitions (lambda(v)(sym)) increase in the same order, having values of 1420, 5300, and 6000 cm(-1) for X = H, Cl, and OMe, respectively. A neighboring orbital analysis using Koopmans-based calculations of relative orbital energies indicates that the diabatic aryl pi-centered molecular orbital that interacts with the dinitrogen pi system lies closest in energy to the bonding pi(NN)-centered orbital and has an electronic coupling with it of about 9200 +/- 600 cm(-1), which does not vary regularly with electron donating power of the X substituent.

  8. Nature of the lowest excited states of neutral polyenyl radicals and polyene radical cations

    NASA Astrophysics Data System (ADS)

    Starcke, Jan Hendrik; Wormit, Michael; Dreuw, Andreas

    2009-10-01

    Due to the close relation of the polyenyl radicals C2n+1H2n+3• and polyene radical cations C2nH2n+2•+ to the neutral linear polyenes, one may suspect their excited states to possess substantial double excitation character, similar to the famous S1 state of neutral polyenes and thus to be equally problematic for simple excited state theories. Using the recently developed unrestricted algebraic-diagrammatic construction scheme of second order perturbation theory and the equation-of-motion coupled-cluster method, the vertical excitation energies, their corresponding oscillator strengths, and the nature of the wave functions of the lowest excited electronic states of the radicals are calculated and analyzed in detail. For the polyenyl radicals two one-photon allowed states are found as D1 and D4 states, with two symmetry-forbidden D2 and D3 states in between, while in the polyene radical cations D1 and D2 are allowed and D3 is forbidden. The order of the states is conserved with increasing chain length. It is found that all low-lying excited states exhibit a significant but similar amount of doubly excited configuration in their wave functions of 15%-20%. Using extrapolation, predictions for the excitation energies of the five lowest excited states of the polyene radical cations are made for longer chain lengths.

  9. 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 CH2Cl2 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•HNO3 complex formed in the acid contacted solvent.

  10. The role of organic solvent radical cations in separations ligand degradation

    SciTech Connect

    Mezyk, Stephen P.; Mincher, Bruce J.; Dhiman, Surajdevprakash B.; Layne, Bobby; Wishart, James F.

    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 CH2Cl2 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•HNO3 complex formed in the acid contacted solvent.

  11. Kinetics for Tautomerizations and Dissociations of Triglycine Radical Cations

    SciTech Connect

    Siu, Chi-Kit; Zhao, Junfang; Laskin, Julia; Chu, Ivan K.; Hopkinson, Alan C.; Siu , K W Michael

    2009-06-01

    Fragmentations of tautomers of the α-centered radical triglycine radical cation, [GGG*]+, [GG*G]+, and [G*GG]+, are charge-driven, giving b-type ions; these are processes that are facilitated by a mobile proton, as in the fragmentation of protonated triglycine (Rodriquez, C.F. et al. J. Am. Chem. Soc. 2001, 123, 3006 - 3012). By contrast, radical centers are less mobile. Two mechanisms have been examined theoretically utilizing density functional theory and Rice-Ramsperger-Kassel-Marcus modeling: (1) a direct hydrogen-atom migration between two α-carbons, and (2) a two-step proton migration involving a canonical [GGG]*+ as an intermediate. Predictions employing the latter mechanism are in good agreement with results of recent CID experiments (Chu, I.K. et al. J. Am. Chem. Soc. 2008, 130, 7862 - 7872).

  12. Acid-base equilibria involved in secondary reactions following the 4-carboxybenzophenone sensitized photooxidation of methionylglycine in aqueous solution. Spectral and time resolution of the decaying (S...N){sup +} radical cation

    SciTech Connect

    Hug, G.L.; Marciniak, B. |; Bobrowski, K. ||

    1996-09-05

    A radical cation with an intramolecular sulfur-nitrogen bond was formed in the photoinitiated transfer of an electron from the sulfur atom of the dipeptide Met-Gly to 4-carboxybenzophenone in its triplet state. The sulfur-nitrogen coupling involved two-center, three-electron bonds. The kinetics of the reactions of these radical cations, which were initiated by a laser flash, were followed over time. The principal method of implementing the spectral resolutions was accomplished through a multiple linear regression technique. This spectral analysis was repeated for numerous time windows during the lifetime of the transients` decays. The resulting concentrations of the transients were consistent with an independent factor analysis. It was found that the decay of the radical cations was multiexponential and that the decay varied with pH. A simplified reaction scheme was proposed whereby the absorbing radical cations can alternatively decay by an irreversible channel or react reversibly with OH{sup -}. Rate constants for the three elementary reactions of this scheme were determined from an analysis of the decay of the concentration of the radical cations. In addition, the equilibrium constant for the reversible reaction was determined by two separate procedures. 35 refs., 7 figs., 2 tabs.

  13. Mechanistic aspects of hydration of guanine radical cations in DNA.

    PubMed

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

    2014-04-23

    The mechanistic aspects of hydration of guanine radical cations, G(•+) in double- and single-stranded oligonucleotides were investigated by direct time-resolved spectroscopic monitoring methods. The G(•+) radical one-electron oxidation products were generated by SO4(•-) radical anions derived from the photolysis of S2O8(2-) anions by 308 nm laser pulses. In neutral aqueous solutions (pH 7.0), after the complete decay of SO4(•-) radicals (∼5 μs after the actinic laser flash) the transient absorbance of neutral guanine radicals, G(-H)(•) with maximum at 312 nm, is dominant. The kinetics of decay of G(-H)(•) radicals depend strongly on the DNA secondary structure. In double-stranded DNA, the G(-H)(•) decay is biphasic with one component decaying with a lifetime of ∼2.2 ms and the other with a lifetime of ∼0.18 s. By contrast, in single-stranded DNA the G(-H)(•) radicals decay monophasically with a ∼ 0.28 s lifetime. The ms decay component in double-stranded DNA is correlated with the enhancement of 8-oxo-7,8-dihydroguanine (8-oxoG) yields which are ∼7 greater than in single-stranded DNA. In double-stranded DNA, it is proposed that the G(-H)(•) radicals retain radical cation character by sharing the N1-proton with the N3-site of C in the [G(•+):C] base pair. This [G(-H)(•):H(+)C ⇆ G(•+):C] equilibrium allows for the hydration of G(•+) followed by formation of 8-oxoG. By contrast, in single-stranded DNA, deprotonation of G(•+) and the irreversible escape of the proton into the aqueous phase competes more effectively with the hydration mechanism, thus diminishing the yield of 8-oxoG, as observed experimentally.

  14. 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

  15. Efficient scavenging of β-carotene radical cations by antiinflammatory salicylates.

    PubMed

    Cheng, Hong; Liang, Ran; Han, Rui-Min; Zhang, Jian-Ping; Skibsted, Leif H

    2014-02-01

    The radical cation generated during photobleaching of β-carotene is scavenged efficiently by the anion of methyl salicylate from wintergreen oil in a second-order reaction approaching the diffusion limit with k2 = 3.2 × 10(9) L mol(-1) s(-1) in 9 : 1 v/v chloroform-methanol at 23 °C, less efficiently by the anion of salicylic acid with 2.2 × 10(8) L mol(-1) s(-1), but still of possible importance for light-exposed tissue. Surprisingly, acetylsalicylate, the aspirin anion, reacts with an intermediate rate in a reaction assigned to the anion of the mixed acetic-salicylic acid anhydride formed through base induced rearrangements. The relative scavenging rate of the β-carotene radical cation by the three salicylates is supported by DFT-calculations.

  16. Spectral properties and reactivity of diarylmethanol radical cations in aqueous solution. Evidence for intramolecular charge resonance.

    PubMed

    Bietti, Massimo; Lanzalunga, Osvaldo

    2002-04-19

    Spectral properties and reactivities of ring-methoxylated diarylmethane and diarylmethanol radical cations, generated in aqueous solution by pulse and gamma-radiolysis and by the one-electron chemical oxidant potassium 12-tungstocobalt(III)ate, have been studied. The radical cations display three bands in the UV, visible, and vis-NIR regions of the spectrum. The vis-NIR band is assigned to an intramolecular charge resonance interaction (CR) between the neutral donor and charged acceptor rings, as indicated by the observation that the relative intensity of the vis-NIR band compared to that of the UV and visible bands does not increase with increasing substrate concentration and that the position and intensity of this band is influenced by the ring-substitution pattern. In acidic solution (pH = 4), monomethoxylated diarylmethanol radical cations 1a.(+ -)1e.(+) decay by C(alpha)-H deprotonation [k = (1.7-1.9) x 10(4)s(-1)] through the intermediacy of a ketyl radical, which is further oxidized in the reaction medium to give the corresponding benzophenones, as evidenced by both time-resolved spectroscopic and product studies. With the dimethoxylated radical cation 2.(+), C(alpha)-H deprotonation is instead significantly slower (k = 6.7 x 10(2)s(-1)). In basic solution, 1a.(+)-1e.(+) undergo (-)OH-induced deprotonation from the alpha-OH group with k(OH.)approximately equal to 1.4 x 10(10)M(-1)s(-1), leading to a ketyl radical anion, which is oxidized in the reaction medium to the corresponding benzophenone.

  17. Electronic spectra of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation and radical

    SciTech Connect

    Peter R. Craig; Miller, John R.; Havlas, Zdenek; Trujillo, Marianela; Rempala, Pawel; Kirby, James P.; Noll, Bruce C.; Michl, Josef

    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 BF4 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 neutral 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

  18. Theoretical studies on the dimerization of substituted paraphenylenediamine radical cations

    NASA Astrophysics Data System (ADS)

    Punyain, Kraiwan; Kelterer, Anne-Marie; Grampp, Günter

    2011-12-01

    Organic radical cations form dicationic dimers in solution, observed experimentally as diamagnetic species in temperature-dependent EPR and low temperature UV/Vis spectroscopy. Dimerization of paraphenylenediamine, N,N-dimethyl-paraphenylenediamine and 2,3,5,6-tetramethyl-paraphenylenediamine radical cation in ethanol/diethylether mixture was investigated theoretically according to geometry, energetics and UV/Vis spectroscopy. Density Functional Theory including dispersion correction describes stable dimers after geometry optimization with conductor-like screening model of solvation and inclusion of the counter-ion. Energy corrections were done on double-hybrid Density Functional Theory with perturbative second-order correlation (B2PLYP-D) including basis set superposition error (BSSE), and multireference Møller-Plesset second-order perturbation theory method (MRMP2) based on complete active space method (CASSCF(2,2)) single point calculation, respectively. All three dication π-dimers exhibit long multicenter π-bonds around 2.9 ± 0.1 Å with strongly interacting orbitals. Substitution with methyl groups does not influence the dimerization process substantially. Dispersion interaction and electrostatic attraction from counter-ion play an important role to stabilize the dication dimers in solution. Dispersion-corrected double hybrid functional B2PLYP-D and CASSCF(2,2) can describe the interaction energetics properly. Vertical excitations were computed with Tamm-Dancoff approximation for time-dependent Density Functional Theory (TDA-DFT) at the B3LYP level with the cc-pVTZ basis set including ethanol solvent molecules explicitly. A strong interaction of the counter-ion and the solvent ethanol with the monomeric species is observed, whereas in the dimers the strong interaction of both radical cation species is the dominating factor for the additional peak in UV/Vis spectra.

  19. In vitro antioxidant and radical-scavenging capacities of Citrullus colocynthes (L) and Artemisia absinthium extracts using promethazine hydrochloride radical cation and contemporary assays.

    PubMed

    Asghar, M Nadeem; Khan, I Ullah; Bano, N

    2011-10-01

    A new, quick and economical decolorization assay based upon the generation of a radical cation made from promethazine hydrochloride (PMZH) is described for screening of antioxidant activity of plants/herbal extracts. PMZH radical cations, produced through a reaction between PMZH and potassium persulfate (K(2)S(2)O(8)) in phosphoric acid medium, have maximum absorption at 515 nm in their first-order derivative spectrum. Theconcentrations of chromagen and K(2)S(2)O(8) were optimized (final concentration of PMZH and K₂S₂O₈ were 0.166 mM and 0.11 mM, respectively) for better stability and sensitivity of the radical cation produced. Agood linear correlation was found between the percentage inhibition and the increasing amounts of standard antioxidants, with correlation coefficients ranging from 0.989 to 0.999. The newly developed assay was employed to evaluate the antioxidant capacity of Citrullus colocynthes L. and Artemisia absinthium extracts. The proposed assay involved a more stable radical cation and required only 1 h for preparation of a working solution in comparison to the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation decolorizaion assay, which was reported to be less sensitive at low pH and almost 12-16 h were required for preparation of a working ABTS solution. Other assays employed to evaluate the antioxidant potential andradical-scavenging capacities of the extracts were the ferric-reducing antioxidant power, 2,2'-diphenyl-1-picrylhydrazyl radical scavenging, total phenolic contents assay, total flavonoid contents and metal-chelating activity assays, and the lipid peroxidation value in linoleic acid emulsion systems. The results indicate that boththe plants have potent free radical-scavenging activity and the ability to prevent lipid peroxidation and radical chain reactions.

  20. Structure and Reactivity of the N-Acetyl-Cysteine Radical Cation and Anion: Does Radical Migration Occur?

    NASA Astrophysics Data System (ADS)

    Osburn, Sandra; Berden, Giel; Oomens, Jos; O'Hair, Richard A. J.; Ryzhov, Victor

    2011-10-01

    The structure and reactivity of the N-acetyl-cysteine radical cation and anion were studied using ion-molecule reactions, infrared multi-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. The radical cation was generated by first nitrosylating the thiol of N-acetyl-cysteine followed by the homolytic cleavage of the S-NO bond in the gas phase. IRMPD spectroscopy coupled with DFT calculations revealed that for the radical cation the radical migrates from its initial position on the sulfur atom to the α-carbon position, which is 2.5 kJ mol-1 lower in energy. The radical migration was confirmed by time-resolved ion-molecule reactions. These results are in contrast with our previous study on cysteine methyl ester radical cation (Osburn et al., Chem. Eur. J. 2011, 17, 873-879) and the study by Sinha et al. for cysteine radical cation ( Phys. Chem. Chem. Phys. 2010, 12, 9794-9800) where the radical was found to stay on the sulfur atom as formed. A similar approach allowed us to form a hydrogen-deficient radical anion of N-acetyl-cysteine, (M - 2H) •- . IRMPD studies and ion-molecule reactions performed on the radical anion showed that the radical remains on the sulfur, which is the initial and more stable (by 63.6 kJ mol-1) position, and does not rearrange.

  1. Magnetic Resonance Studies of Proton Loss from Carotenoid Radical Cations

    SciTech Connect

    Kispert, Lowell D; Focsan, A Ligia; Konovalova, Tatyana A; Lawrence, Jesse; Bowman, Michael K; Dixon, David A; Molnar, Peter; Deli, Jozsef

    2007-06-11

    Carotenoids, intrinsic components of reaction centers and pigment-protein complexes in photosynthetic membranes, play a photoprotective role and serve as a secondary electron donor. Before optimum use of carotenoids can be made in artificial photosynthetic systems, their robust nature in living materials requires extensive characterization of their electron transfer, radical trapping ability, stability, structure in and on various hosts, and photochemical behavior. Pulsed ENDOR and 2D-HYSCORE studies combined with DFT calculations reveal that photo-oxidation of natural zeaxanthin (I) and violaxanthin (II) on silica-alumina produces not only the carotenoid radical cations (Car•+) but also neutral radicals (#Car•) by proton loss from the methyl groups at positions 5 or 5', and possibly 9 or 9' and 13 or 13'. Notably, the proton loss favored in I at the 5 position by DFT calculations, is unfavorable in II due to the epoxide at the 5, 6 position. DFT calculations predict the isotropic methyl proton couplings of 8-10 MHz for Car•+ which agree with the ENDOR for carotenoid α-conjugated radical cations. Large α-proton hyperfine coupling constants (>10 MHz) determined from HYSCORE are assigned from the DFT calculations to neutral carotenoid radicals. Proton loss upon photolysis was also examined as a function of carotenoid polarity [Lycopene (III) versus 8'-apo-β-caroten-8'-al (IV)]; hydrogen bonding [Lutein (V) versus III]; host [silica-alumina versus MCM-41 molecular sieve]; and substituted metal in MCM-41. Loss of H+ from the 5(5'), 9(9') or 13(13') methyl positions has importance in photoprotection. Photoprotection involves nonphotochemical quenching (NPQ) in which 1Ch1* decays via energy transfer to the carotenoid which returns to the ground state by thermal dissipation; or via electron transfer to form a charge transfer state (I •+…Chl•-), lower in energy than 1Chl*. Formation of I •+ results in bond lengthening, a mechanism for nonradiative energy

  2. A Photo Touch on Amines: New Synthetic Adventures of Nitrogen Radical Cations

    PubMed Central

    Maity, Soumitira; Zheng, Nan

    2013-01-01

    Amines have been used as sacrificial electron donors to reduce photoexcited Ru(II) or Ir(III) complexes, during which they are oxidized to nitrogen radical cations. Recently, the synthetic potential of these nitrogen radical cations have caught synthetic organic chemists’ attention. They have been exploited in various transformations yielding a number of elegant methods for amine synthesis. This article highlights recent developments on nitrogen radical cation chemistry under visible-light photocatalysis. PMID:23419975

  3. 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 neutral 19-electron radical,more » 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

  4. Are the Radical Centers in Peptide Radical Cations Mobile? The Generation, Tautomerism, and Dissociation of Isomeric α-Carbon-Centered Triglycine Radical Cations in the Gas Phase

    SciTech Connect

    Chu, Ivan K.; Zhao, Junfang; Xu, Minjie; Siu, Shiu On; Hopkinson, Alan C.; Siu , K W Michael

    2008-05-31

    The mobility of the radical center in three isomeric triglycine radical cationss[G•GG]+, [GG•G]+, and [GGG•]+shas been investigated theoretically via density functional theory (DFT) and experimentally via tandem mass spectrometry. These radical cations were generated by collision-induced dissociations (CIDs) of Cu(II)-containing ternary complexes that contain the tripeptides YGG, GYG, and GGY, respectively (G and Y are the glycine and tyrosine residues, respectively). Dissociative electron transfer within the complexes led to observation of [Y•GG]+, [GY•G]+, and [GGY•]+; CID resulted in cleavage of the tyrosine side chain as p-quinomethide, yielding [G•GG]+, [GG•G]+, and [GGG•]+, respectively. Interconversions between these isomeric triglycine radical cations have relatively high barriers (g44.7 kcal/mol), in support of the thesis that isomerically pure [G•GG]+, [GG•G]+, and [GGG•]+ can be experimentally produced. This is to be contrasted with barriers < 17 kcal/mol that were encountered in the tautomerism of protonated triglycine [Rodriquez C. F. et al. J. Am. Chem. Soc. 2001, 123, 3006-3012]. The CID spectra of [G•GG]+, [GG•G]+, and [GGG•]+ were substantially different, providing experimental proof that initially these ions have distinct structures. DFT calculations showed that direct dissociations are competitive with interconversions followed by dissociation.

  5. Application of the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation assay to a flow injection system for the evaluation of antioxidant activity of some pure compounds and beverages.

    PubMed

    Pellegrini, Nicoletta; Del Rio, Daniele; Colombi, Barbara; Bianchi, Marta; Brighenti, Furio

    2003-01-01

    The 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS(*)(+)) assay was adapted to a flow injection (FI) system to obtain a sensitive and rapid technique for the monitoring of antioxidant activity of pure compounds and complex matrixes, such as beverages and food extracts. The FI system includes a HPLC pump that flows the mobile phase (a solution of ABTS(*)(+) in ethanol) through a 20 microL loop injector, a single bead string reactor filled with acid-washed silanized beads, a delay coil and a photodiode array UV-visible detector. The technique was very sensitive, with limits of detection and of quantification of 4.14 and 9.29 micromol of Trolox/L, respectively, and demonstrated high repeatability and reproducibility. The proposed technique was then applied to the evaluation of the antioxidant activity of some pure compounds, demonstrating good agreement with published data obtained by the original spectrophotometric ABTS(*)(+) assay. Finally, the total antioxidant activity of 10 beverages was determined by both the proposed and the original method. The values ranged from 0.09 mmol L(-)(1) for cola to 49.24 mmol L(-)(1) for espresso coffee and did not result significantly different from those obtained by the original spectrophotometric ABTS(*)(+) assay (Student's paired t-test: t = 1.4074, p = 0.1929). In conclusion, the proposed FI technique seems suitable for the direct, rapid and reliable monitoring of total antioxidant activity of pure compounds and beverages and, due to the ability to operate in continuous, it allows the analysis of about 30 samples h(-)(1) making the assay particularly suitable for large screening of total antioxidant activity in food samples.

  6. Direct observation of hexamethylbenzenium radical cations generated during zeolite methanol-to-olefin catalysis: an ESR study.

    PubMed

    Kim, Sun Jung; Jang, Hoi-Gu; Lee, Jun Kyu; Min, Hyung-Ki; Hong, Suk Bong; Seo, Gon

    2011-09-07

    The generation of hexamethylbenzenium radical cations as the key reaction intermediate in chabazite-type molecular sieve acids (i.e., H-SAPO-34 and H-SSZ-13) during the methanol-to-olefin process has been directly evidenced by ESR spectroscopy.

  7. The chemistry of amine radical cations produced by visible light photoredox catalysis

    PubMed Central

    Hu, Jie; Wang, Jiang; Nguyen, Theresa H

    2013-01-01

    Summary Amine radical cations are highly useful reactive intermediates in amine synthesis. They have displayed several modes of reactivity leading to some highly sought-after synthetic intermediates including iminium ions, α-amino radicals, and distonic ions. One appealing method to access amine radical cations is through one-electron oxidation of the corresponding amines under visible light photoredox conditions. This approach and subsequent chemistries are emerging as a powerful tool in amine synthesis. This article reviews synthetic applications of amine radical cations produced by visible light photocatalysis. PMID:24204409

  8. Halogenated benzene radical cations and ground state degeneracy splitting by asymmetric substitution

    USGS Publications Warehouse

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

    1981-01-01

    The absorption and laser induced fluorescence of several halogenated benzene radical cations were studied in solid Ne matrices. The spectra of 1,2,4-trifluorobenzene, l,3-dichloro-5-fluorobenzene, and l-chloro-3,5- difluorobenzene radical cations are observed and analyzed. Studies of fluorescence polarization and a photoselection technique were used to examine the splitting of the degeneracy of the benzene cation ground state by asymmetric subsitution. ?? 1981 American Institute of Physics.

  9. Influence of "remote" intramolecular hydrogen bonds on the stabilities of phenoxyl radicals and benzyl cations.

    PubMed

    Foti, Mario C; Amorati, Riccardo; Pedulli, Gian Franco; Daquino, Carmelo; Pratt, Derek A; Ingold, K U

    2010-07-02

    Remote intramolecular hydrogen bonds (HBs) in phenols and benzylammonium cations influence the dissociation enthalpies of their O-H and C-N bonds, respectively. The direction of these intramolecular HBs, para --> meta or meta --> para, determines the sign of the variation with respect to molecules lacking remote intramolecular HBs. For example, the O-H bond dissociation enthalpy of 3-methoxy-4-hydroxyphenol, 4, is about 2.5 kcal/mol lower than that of its isomer 3-hydroxy-4-methoxyphenol, 5, although group additivity rules would predict nearly identical values. In the case of 3-methoxy-4-hydroxybenzylammonium and 3-hydroxy-4-methoxybenzylammonium ions, the CBS-QB3 level calculated C-N eterolytic dissociation enthalpy is about 3.7 kcal/mol lower in the former ion. These effects are caused by the strong electron-withdrawing character of the -O(*) and -CH(2)(+) groups in the phenoxyl radical and benzyl cation, respectively, which modulates the strength of the HB. An O-H group in the para position of ArO(*) or ArCH(2)(+) becomes more acidic than in the parent molecules and hence forms stronger HBs with hydrogen bond acceptors (HBAs) in the meta position. Conversely, HBAs, such as OCH(3), in the para position become weaker HBAs in phenoxyl radicals and benzyl cations than in the parent molecules. These product thermochemistries are reflected in the transition states for, and hence in the kinetics of, hydrogen atom abstraction from phenols by free radicals (dpph(*) and ROO(*)). For example, the 298 K rate constant for the 4 + dpph(*) reaction is 22 times greater than that for the 5 + dpph(*) reaction. Fragmentation of ring-substituted benzylammonium ions, generated by ESI-MS, to form the benzyl cations reflects similar remote intramolecular HB effects.

  10. Radiation-induced polymerisation of 2,3-dihydrofuran: free-radical or cationic mechanism?

    NASA Astrophysics Data System (ADS)

    Janovský, Igor; Naumov, Sergej; Knolle, Wolfgang; Mehnert, Reiner

    2005-02-01

    Concentrated (10 mol%) solutions of 2,3-dihydrofuran in CFCl 2CF 2Cl matrix were irradiated at 77 K and several intermediates (dimer radical cation, dihydrofuryl radical, and polymer radicals) were observed by low-temperature EPR spectroscopy. The irradiated solutions yielded after melting a polymeric product, which was characterised by IR spectroscopy and gel permeation chromatography. The polydisperse polymer is assumed to be formed mainly by a cationic process initiated by a dimer carbocation. The free-radical mechanism via the dihydrofuryl radical leads to low molecular weight oligomers only. Quantum chemical calculations support the interpretation of the experimental results.

  11. The Prowess of Photogenerated Amine Radical Cations in Cascade Reactions: From Carbocycles to Heterocycles.

    PubMed

    Morris, Scott A; Wang, Jiang; Zheng, Nan

    2016-09-20

    Cascade reactions represent a class of ideal organic reactions because they empower efficiency, elegance, and novelty. However, development of cascade reactions remains a daunting task for synthetic chemists. Radicals are known to be well suited for cascade reactions. Compared with widely used carbon-based radicals, nitrogen-based radicals, such as neutral aminyl radicals and protonated aminyl radicals (amine radical cations), are underutilized, although they are behind some notable synthetic methods such as the Hofmann-Löffler-Freytag reaction. The constraint on their usage is generally attributed to the limited number of available stable precursors. Since amine radical cations offer increased reactivity and selectivity in chemical transformations compared with neutral aminyl radicals, their generation is of utmost importance. Recently, a surge of reports has been revealed using visible light photoredox catalysis. It has been demonstrated that amines can act as an electron donor in a reductive quenching cycle while the amine itself is oxidized to the amine radical cation. Although a number of methods exist to generate amine radical cations, the photochemical formation of these species offers many practical advantages. In this Account, we discuss our journey to the development of annulation reactions with various π-bonds and electrophilic addition reactions to alkenes using photogenerated amine radical cations. Various carbocycles and heterocycles are produced by these reactions. In our annulation work, we first show that single electron photooxidation of cyclopropylanilines to the amine radical cations triggers ring opening of the strained carbocycle, producing distonic radical cations. These odd-electron species are shown to react with alkenes and alkynes to yield the corresponding cyclopentanes and cyclopentenes in an overall redox neutral process. Further development of this annulation reaction allows us to achieve the [4 + 2] annulation of cyclobutylanilines

  12. UVA-visible photo-excitation of guanine radical cations produces sugar radicals in DNA and model structures

    PubMed Central

    Adhikary, Amitava; Malkhasian, Aramice Y. S.; Collins, Sean; Koppen, Jessica; Becker, David; Sevilla, Michael D.

    2005-01-01

    This work presents evidence that photo-excitation of guanine radical cations results in high yields of deoxyribose sugar radicals in DNA, guanine deoxyribonucleosides and deoxyribonucleotides. In dsDNA at low temperatures, formation of C1′• is observed from photo-excitation of G•+ in the 310–480 nm range with no C1′• formation observed ≥520 nm. Illumination of guanine radical cations in 2′dG, 3′-dGMP and 5′-dGMP in aqueous LiCl glasses at 143 K is found to result in remarkably high yields (∼85–95%) of sugar radicals, namely C1′•, C3′• and C5′•. The amount of each of the sugar radicals formed varies dramatically with compound structure and temperature of illumination. Radical assignments were confirmed using selective deuteration at C5′ or C3′ in 2′-dG and at C8 in all the guanine nucleosides/tides. Studies of the effect of temperature, pH, and wavelength of excitation provide important information about the mechanism of formation of these sugar radicals. Time-dependent density functional theory calculations verify that specific excited states in G•+ show considerable hole delocalization into the sugar structure, in accord with our proposed mechanism of action, namely deprotonation from the sugar moiety of the excited molecular radical cation. PMID:16204456

  13. Fragmentation of alpha-Radical Cations of Arginine-Containing Peptides

    SciTech Connect

    Laskin, Julia; Yang, Zhibo; Ng, Dominic C.; Chu, Ivan K.

    2010-04-01

    Fragmentation pathways of peptide radical cations, M+, with well-defined initial location of the radical site were explored using collision-induced dissociation (CID) experiments. Peptide radical cations were produced by gas-phase fragmentation of CoIII(salen)-peptide complexes [salen = N,N´-ethylenebis (salicylideneaminato)]. Subsequent hydrogen abstraction from the -carbon of the side chain followed by Ca-C bond cleavage results in the loss of a neutral side chain and formation of an a-radical cation with the radical site localized on the a-carbon of the backbone. Similar CID spectra dominated by radical-driven dissociation products were obtained for a number of a-radicals when the basic arginine side chain was present in the sequence. In contrast, proton-driven fragmentation dominates CID spectra of a-radicals produced via the loss of the arginine side chain. Our results suggest that in most cases radical migration precedes fragmentation of large peptide radical cations.

  14. Stabilization and isomerization of radical cations generated by fast electron irradiation of unsaturated organic molecules in a solid argon matrix

    NASA Astrophysics Data System (ADS)

    Feldman, V. I.; Sukhov, F. F.; Orlov, A. Yu.; Tyulpina, I. V.; Ivanchenko, V. K.

    2006-01-01

    Matrix isolation EPR spectroscopy was used to study the fate of "hot" unsaturated radical cations produced by fast electron irradiation in solid argon. It was found that the radical cations of cis-2-butene, trans-2-butene and ethyl vinyl ether resulting from highly exothermic hole transfer (excess energy>6 eV) underwent effective relaxation in an argon matrix. 1-Butene radical cation exhibits isomerization to cis-2-butene radical cation. The role of molecular structure of organic radical cations in excess energy relaxation is discussed.

  15. One-electron oxidation of 2-(4-methoxyphenyl)-2-methylpropanoic and 1-(4-methoxyphenyl)cyclopropanecarboxylic acids in aqueous solution. the involvement of radical cations and the influence of structural effects and pH on the side-chain fragmentation reactivity.

    PubMed

    Bietti, Massimo; Capone, Alberto

    2008-01-18

    A product and time-resolved kinetic study on the one-electron oxidation of 2-(4-methoxyphenyl)-2-methylpropanoic acid (2), 1-(4-methoxyphenyl)cyclopropanecarboxylic acid (3), and of the corresponding methyl esters (substrates 4 and 5, respectively) has been carried out in aqueous solution. With 2, no direct evidence for the formation of an intermediate radical cation 2*+ but only of the decarboxylated 4-methoxycumyl radical has been obtained, indicating either that 2*+ is not formed or that its decarboxylation is too fast to allow detection under the experimental conditions employed (k > 1 x 10(7) s(-1)). With 3, oxidation leads to the formation of the corresponding radical cation 3*+ or radical zwitterion -3*+ depending on pH. At pH 1.0 and 6.7, 3*+ and -3*+ have been observed to undergo decarboxylation as the exclusive side-chain fragmentation pathway with rate constants k = 4.6 x 10(3) and 2.3 x 10(4) s(-1), respectively. With methyl esters 4 and 5, direct evidence for the formation of the corresponding radical cations 4*+ and 5*+ has been obtained. Both radical cations have been observed to display a very low reactivity and an upper limit for their decay rate constants has been determined as k < 10(3) s(-1). Comparison between the one-electron oxidation reactions of 2 and 3 shows that the replacement of the C(CH3)2 moiety with a cyclopropyl group determines a decrease in decarboxylation rate constant of more than 3 orders of magnitude. This large difference in reactivity has been qualitatively explained in terms of three main contributions: substrate oxidation potential, stability of the carbon-centered radical formed after decarboxylation, and stereoelectronic effects. In basic solution, -3*+ and 5*+ have been observed to react with -OH in a process that is assigned to the -OH-induced ring-opening of the cyclopropane ring, and the corresponding second-order rate constants (k-OH) have been obtained. With -3*+, competition between decarboxylation and -OH

  16. UV/Vis Action Spectroscopy and Structures of Tyrosine Peptide Cation Radicals in the Gas Phase.

    PubMed

    Viglino, Emilie; Shaffer, Christopher J; Tureček, František

    2016-06-20

    We report the first application of UV/Vis photodissociation action spectroscopy for the structure elucidation of tyrosine peptide cation radicals produced by oxidative intramolecular electron transfer in gas-phase metal complexes. Oxidation of Tyr-Ala-Ala-Ala-Arg (YAAAR) produces Tyr-O radicals by combined electron and proton transfer involving the phenol and carboxyl groups. Oxidation of Ala-Ala-Ala-Tyr-Arg (AAAYR) produces a mixture of cation radicals involving electron abstraction from the Tyr phenol ring and N-terminal amino group in combination with hydrogen-atom transfer from the Cα positions of the peptide backbone.

  17. Radical cations of sulfides and disulfides: An ESR study

    SciTech Connect

    Bonazzola, L.; Michaut, J.P.; Roncin, J.

    1985-09-15

    Exposure of dilute solutions of dimethylsulfide, methanethiol, tetrahydrothiophene, terbutyl and diterbutyl-sulfides, dimethyl-disulfide, and diterbutyldisulfide, in freon at 77 K to /sup 60/Co ..gamma.. rays gave the corresponding cations. From the reported ESR spectra, g tensors were obtained. It was found that both sulfide and disulfide cations exhibit the same g tensor: (g/sub max/ = 2.034 +- 0.002, g/sub int/ = 2.017 +- 0.001, g/sub min/ = 2.001 +- 0.005). From this result it has been shown that the disulfide cation is planar. This finding was supported by fully optimized geometry ab initio calculations.

  18. Characterization of the hyperline of D1/D0 conical intersections between the maleic acid and fumaric acid anion radicals

    NASA Astrophysics Data System (ADS)

    Takahashi, Ohgi; Sumita, Masato

    2004-10-01

    The cation and anion radicals of symmetrical 1,2-disubstituted ethylenes are expected to have a symmetry-allowed conical intersection (CI) between the ground doublet state (D0) and the lowest excited doublet state (D1) near a 90°-twisted geometry. By the complete active space self-consistent field method, we characterized the hyperline formed by D1/D0 CIs between the anion radicals of maleic acid (cis) and fumaric acid (trans). An implication of the results for the known one-way cis→trans photoisomerization of the maleic acid anion radical and other related ion radicals is presented.

  19. Alkaline earth cation extraction from acid solution

    DOEpatents

    Dietz, Mark; Horwitz, E. Philip

    2003-01-01

    An extractant medium for extracting alkaline earth cations from an aqueous acidic sample solution is described as are a method and apparatus for using the same. The separation medium is free of diluent, free-flowing and particulate, and comprises a Crown ether that is a 4,4'(5')[C.sub.4 -C.sub.8 -alkylcyclohexano]18-Crown-6 dispersed on an inert substrate material.

  20. Fourier transform infrared spectrum of the radical cation of beta-carotene photoinduced in photosystem II.

    PubMed

    Noguchi, T; Mitsuka, T; Inoue, Y

    1994-12-19

    A Fourier-transform infrared (FTIR) spectrum of the radical cation of beta-carotene photoinduced in photosystem II (PSII) membranes was obtained at 80K under oxidizing conditions, by utilizing the light-induced FTIR difference technique. Formation of the beta-carotene cation was monitored with the electronic absorption band at 993 nm. An FTIR spectrum of a chemically-generated beta-carotene cation in chloroform was also measured and compared with the spectrum of PSII. Since the FTIR bands of carotenoid cation have characteristic features with strong intensities, they can be useful markers in studying the reaction of carotenoid in PSII.

  1. EPR and DFT Study of the Polycyclic Aromatic Radical Cations from Friedel-Crafts Alkylation Reactions

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Wu, An-an; Gao, Li-guo; Wang, Han-qing

    2009-02-01

    Electron paramagnetic resonance and electron-nuclear double resonance methods were used to study the polycyclic aromatic radical cations produced in a Friedel-Crafts alkylating system, with m-xylene, or p-xylene and alkyl chloride. The results indicate that the observed electron paramagnetic resonance spectra are due to polycyclic aromatic radicals formed from the parent hydrocarbons. It is suggested that benzyl halides produced in the Friedel-Crafts alkylation reactions undergo Scholl self-condensation to give polycyclic aromatic hydrocarbons, which are converted into corresponding polycyclic aromatic radical cations in the presence of AlCl3. The identification of observed two radicals 2,6-dimethylanthracene and 1,4,5,8-tetramethylanthracene were supported by density functional theory calculations using the B3LYP/6-31G(d,p)//B3LYP/6-31G(d) approach. The theoretical coupling constants support the experimental assignment of the observed radicals.

  2. Theoretical study of second-order hyperpolarizability for nitrogen radical cation

    NASA Astrophysics Data System (ADS)

    Tarazkar, Maryam; Romanov, Dmitri A.; Levis, Robert J.

    2015-05-01

    We report calculations of the static and dynamic hyperpolarizabilities of the nitrogen radical cation in doublet state. The electronic contributions were computed analytically using density functional theory and multi-configurational self-consistent field method with extended basis sets for non-resonant excitation. The open-shell electronic system of nitrogen radical cation provides negative second-order optical nonlinearity, suggesting that the hyperpolarizability coefficient, {{γ }(2)}, in the non-resonant regime is mainly composed of combinations of virtual one-photon transitions rather than two-photon transitions. The second-order optical properties of nitrogen radical cation have been calculated as a function of bond length starting with the neutral molecular geometry (S0 minimum) and stretching the N-N triple bond, reaching the ionic D0 relaxed geometry all the way toward dissociation limit, to investigate the effect of internuclear bond distance on second-order hyperpolarizability.

  3. [Spectral-kinetic characteristics of the cation-radical of pheophytin a].

    PubMed

    Evstigneev, V B

    1977-01-01

    The photochemical generation of pheophytin a cation-radical in acidulated ethanol and aceto nitril has been studied by the method of flash-photolysis. The bands with maxima at 450, 580 and 800 nm correspond to pheophytin a cation-radical in the differential absorption spectra. The efficient rate constants of pheophytin a triplet state desactivation in ethanol, acetonitril, aceton have the following values: 1.5.10(4), 9.10(3), 8.7.10(3) sec(-1) correspondingly. The rate constant of electron transfer from pheophytin a to p-benzoqui-none in ethanol solutions is 7.8.10(9) l/m.sec. The recombination constants of pheophytin a cation-radical with Q-in acetonitril, and with quinone neutral (QH) in acidulated ethanol have the following values: 5.10(9) and 2.10(9) l/m.sec correspondingly.

  4. Fingerprinting DNA oxidation processes: IR characterization of the 5-methyl-2'-deoxycytidine radical cation.

    PubMed

    Bucher, Dominik B; Pilles, Bert M; Pfaffeneder, Toni; Carell, Thomas; Zinth, Wolfgang

    2014-02-24

    Methylated cytidine plays an important role as an epigenetic signal in gene regulation. Its oxidation products are assumed to be involved in active demethylation processes but also in damaging DNA. Here, we report the photochemical production of the 5-methyl-2'-deoxycytidine radical cation via a two-photon ionization process. The radical cation is detected by time-resolved IR spectroscopy and identified by band assignment using density functional theory calculations. Two final oxidation products are characterized with liquid chromatography coupled to mass spectrometry.

  5. Isomerization of 4-vinylcyclohexene radical cation. A tandem mass spectrometry study

    SciTech Connect

    Vollmer, D.; Rempel, D.L.; Gross, M. L. ); Williams, F. )

    1995-02-08

    Investigation by matrix-isolation ESR has shown that 4-vinylcyclohexene, 1, surprisingly undergoes isomerization to the bicyclo[3.2.1]oct-2-ene ion, 3. Here we demonstrate the occurrence of this isomerization in the gas phase by use of tandem (MS/MS) sector and Fourier transform (FT) mass spectrometries. The radical cations of 4-vinylcyclohexene (IE = 8.93 eV) or bicyclo[3.2.1]oct-2-ene (approximately 14 kcal/mol more stable than that of 4-vinylcyclohexene) were formed, in separate trials, in a chemical ionization (CI) source by electron ionization (EI). The radical cations were then studied by obtaining their collisionally activated decomposition (CAD) spectra. The CAD spectra are similar, indicating that the isomerization has occurred. Both the sector and the FT mass spectrometer results reflect those obtained in the matrix-isolation ESR investigation. That is isomerizes to 3 at high internal energy, but is stable at low internal energy. Two mechanisms explain this rearrangement. The second mechanism is questionable because the most stable olefin radical cation formed from 5 is that of bicyclo[2.2.2]-2-octene, which gives different ESR and CAD spectra than those of 1 or 3. The CAD spectrum of bicyclo[2.2.2]-2-octene radical cation indicates that the retro-Diels-Alder loss of ethylene is more facile than that from 1 or 3. 18 refs., 3 figs.

  6. Geometrical isomerization of carotenoids mediated by cation radical/dication formation

    SciTech Connect

    Gao, G.; Wei, C.C.; Jeevarajan, A.S.; Kispert, L.D.

    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 by 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.

  7. Spectroscopy and decay dynamics of several methyl-and fluorine-substituted benzene radical cations

    USGS Publications Warehouse

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

    1981-01-01

    Spectra of several fluorobenzene cation radicals containing 1-3 methyl substituents were observed in solid Ne matrix and analyzed. Comparisons between these compounds and other fluorobenzenes studied previously as well as comparisons between the B?? state lifetimes in the gas phase and in the matrix are used to gain a deeper insight into the B?? state decay dynamics. ?? 1981 American Chemical Society.

  8. A combined EPR and DFT study of the overcrowded aromatic radical cations from Friedel-Crafts alkylation reactions

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Tang, Fu Ming; Wu, Yi Fang

    2011-09-01

    Electron paramagnetic resonance and electron-nuclear double resonance methods were used to study the polycyclic aromatic radical cations produced in a Friedel-Crafts alkylating system, and the following radical cations were indentified: 3,6,11,14-tetramethyl dibenzo (a, c) triphylene and 2,6-dimethyl-9,10-di(p-methylbenzyl) anthracene radical cations. The results indicate that the observed electron paramagnetic resonance spectra are due to overcrowded polycyclic aromatic radical cations formed from the parent hydrocarbons. It is suggested that benzyl halides produced in the Friedel-Crafts alkylation reactions undergo Scholl condensation to give polycyclic aromatic hydrocarbons, which are converted into corresponding polycyclic aromatic radical cations in the presence of AlCl 3. We carried out the theoretical calculation of the isotropic 1H hyperfine coupling constants for studied both PAHs radical cations. The results indicate that the IEFPCM-DFT calculation at B3LYP level with 6-31++G(d,p), EPRII and EPRIII basis sets could well support the experimental hfcc assignment of the observed radicals. Optimized geometry indicates that the aromatic rings in both PAHs radical cations twisted significantly out of co-planarity.

  9. Multi-mode vibronic interactions in the five lowest electronic states of the fluorobenzene radical cation

    NASA Astrophysics Data System (ADS)

    Bâldea, Ioan; Franz, Jan; Szalay, Péter G.; Köppel, Horst

    2006-10-01

    The multi-mode vibronic interactions between the five lowest electronic states of the fluorobenzene radical cation are investigated theoretically, based on ab initio electronic structure data, and employing the linear vibronic coupling model. Low-energy conical intersections, and strong vibronic couplings are found to prevail within the set of X˜-A˜ and B˜-C˜-D˜ cationic states, while the interactions between these two sets of states are found to be rather weak (owing to high-energy conical intersections). The overall intensity distribution of the experimental photoelectron spectrum, as well as the line positions observed in the MATI spectrum, are well reproduced. The vibronic interactions in the X˜-A˜ states are found to be a replica of the multi-mode dynamical Jahn-Teller effect in the parent system, the XE ground state of the benzene radical cation. Ultrafast internal conversion processes within the electronic manifolds in question demonstrate the strength of the nonadiabatic coupling effects and complement the analogous findings for the electronic spectra. The implications for the fluorescence dynamics of the fluorobenzene radical cation are discussed.

  10. Comparison of the Reactivity of the Three Distonic Isomers of the Pyridine Radical Cation Toward Tetrahydrofuran in Solution and in the Gas Phase

    PubMed Central

    Widjaja, Fanny; Jin, Zhicheng; Nash, John J.; Kenttämaa, Hilkka I.

    2013-01-01

    The reactivity of the three distonic isomers of the pyridine radical cation toward tetrahydrofuran is compared in solution and in the gas phase. In solution, the distonic ions were generated by UV photolysis at 300 nm from iodo-precursors in acidic 50:50 tetrahydrofuran/water solutions. In the gas phase, the ions were generated by collisionally activated dissociation (CAD) of protonated iodo-precursors in an FT-ICR mass spectrometer, as described in the literature. The same major reaction, hydrogen atom abstraction, was observed in solution and in the gas phase. Attempts to cleave the iodine atom from the 2-iodopyridinium cation in the gas phase and in solution yielded the 2-pyridyl cation in addition to the desired 2-dehydropyridinium cation. In the gas phase, this ion was ejected prior to the examination of the desired ion’s chemical properties. This was not possible in solution. This study suggests that solvation effects are not significant for radical reactions of charged radicals. On the other hand, the even-electron ion studied, the 2-pyridyl cation, shows substantial solvation effects. For example, in solution, the 2-pyridyl cation forms a stable adduct with tetrahydrofuran, whereas in the gas phase, only addition/elimination reactions were observed. PMID:23345033

  11. (Iso)pagodane radical cations in liquid hydrocarbons: `Time-resolved fluorescence-detected magnetic resonance` study of valence isomeric radical cations

    SciTech Connect

    Trifunac, A.D.; Werst, D.W.; Herges, R.; Neumann, H.; Prinzbach, H.; Etzkorn, M.

    1996-10-02

    The `tight` (T), cyclobutanoid, and the `extended` (E), {pi}-complex-like, four-centred-three-electron radical cations (4c/3e) derived from (iso)pagodanes and from the valence isomeric (iso)dienes can be viewed as well-separated stationary points on the reaction coordinate for the ethylene/ethylene radical cation [2+1]cycloaddition. So far, experimentally verified examples (ESR, CV, PE) are the extended [1.1.1.1](2{sup .+}) and iso-[2.2.1.1](4{sup .+})ions, persistent in fluid solution at room temperature, and the tight iso-[1.1.1.1]{sup .+} and [2.2.1.1]{sup .+} ions, observable only in Freon matrix (CFCl{sub 3}, {gamma}-rays, 77K). According to calculations, these are the thermodynamically more stable ones of the respective pairs of valence isomers. In this communication the direct observation of tight 1{sup .+} and the activation barrier for its isomerization into extended 2{sup .+} are reported. 16 refs., 3 figs., 1 tab.

  12. Fast regeneration of carotenoids from radical cations by isoflavonoid dianions: importance of the carotenoid keto group for electron transfer.

    PubMed

    Han, Rui-Min; Chen, Chang-Hui; Tian, Yu-Xi; Zhang, Jian-Ping; Skibsted, Leif H

    2010-01-14

    Electron transfer to radical cations of beta-carotene, zeaxanthin, canthaxanthin, and astaxanthin from each of the three acid/base forms of the diphenolic isoflavonoid daidzein and its C-glycoside puerarin, as studied by laser flash photolysis in homogeneous methanol/chloroform (1/9) solution, was found to depend on carotenoid structures and more significantly on the deprotonation degree of the isoflavonoids. None of the carotenoid radical cations reacted with the neutral forms of the isoflavonoids while the monoanionic and dianionic forms of the isoflavonoids regenerated the oxidized carotenoid. Electron transfer to the beta-carotene radical cation from the puerarin dianion followed second order kinetics with the rate constant at 25 degrees C k(2) = 5.5 x 10(9) M(-1) s(-1), zeaxanthin 8.5 x 10(9) M(-1) s(-1), canthaxanthin 6.5 x 10(10) M(-1) s(-1), and astaxanthin 11.1 x 10(10) M(-1) s(-1) approaching the diffusion limit and establishing a linear free energy relationship between rate constants and driving force. Comparable results found for the daidzein dianion indicate that the steric hindrance from the glucoside is not important suggesting the more reducing but less acidic 4'-OH/4'-O(-) as electron donors. On the basis of the rate constants obtained from kinetic analyses, the keto group of carotenoids is concluded to facilitate electron transfer. The driving force was estimated from oxidation potentials, as determined by cyclic-voltametry for puerarin and daidzein in aqueous solutions at varying pH conditions, which led to the standard reduction potentials E degrees = 1.13 and 1.10 V versus NHE corresponding to the uncharged puerarin and daidzein. For pH > pK(a2), the apparent potentials of both puerarin and daidzein became constants and were E degrees = 0.69 and 0.65 V, respectively. Electron transfer from isoflavonoids to the carotenoid radical cation, as formed during oxidative stress, is faster for astaxanthin than for the other carotenoids, which may relate

  13. Compounds I of catalase and horse radish peroxidase: pi-cation radicals.

    PubMed

    Dolphin, D; Forman, A; Borg, D C; Fajer, J; Felton, R H

    1971-03-01

    Two-electron oxidation of cobaltous octaethylporphyrin [Co(II)(Et)(8)P] yields a stable pi-cation radical [Co(III)(Et)(8)P](2+.), the optical spectrum of which exhibits spectral changes dependent upon the nature of the counterion. Comparison of these spectra with those of Compounds I of horseradish peroxidase and catalase leads us to propose that these Compounds I contain a pi-cation radical of the heme prosthetic group. This proposal explains the oxidation level, optical spectra, and stability of the primary compounds without recourse to properties such as stoichiometric mixtures of special porphyrins, stable Fe(V) porphyrins, or unique conformers of heme porphyrins. Explanations are advanced to account for the missing electron spin resonance signal of Compound I of horseradish peroxidase.

  14. 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

  15. The radical cation of syn-tricyclooctadiene and its rearrangement products

    PubMed

    Bally; Bernhard; Matzinger; Roulin; Sastry; Truttmann; Zhu; Marcinek; Adamus; Kaminski; Gebicki; Williams; Chen; Fulscher

    2000-03-03

    The syn dimer of cyclobutadiene (tricyclo[4.2.0.0(2.5)]octa-3,7-diene, TOD) is subjected to ionization under different conditions and the resulting species are probed by optical and ESR spectroscopy. By means of quantum chemical modelling of the potential energy surfaces and the optical spectra, it is possible to assign the different products that arise spontaneously after ionization or after subsequent warming or illumination of the samples. Based on these findings, we propose a mechanistic scheme which involves a partitioning of the incipient radical cation of TOD between two electronic states. These two states engage in (near) activation-less decay to the more stable valence isomers, cyclooctatetraene (COT*+) and a bis-cyclobutenylium radical cation BCB*+. The latter product undergoes further rearrangement, first to tetracyclo[4.2.0.0(2,4).0(3,5]oct-7-ene (TCO*+) and eventually to bicyclo[4.2.0]octa-2,4,7-triene (BOT*+) which can also be generated photochemically from BCB*+ or TCO*+. The surprising departure of syn-TOD*+ from the least-motion reaction path leading to BOT*+ can be traced to strong vibronic interactions (second-order Jahn-Teller effects) which prevail in both possible ground states of syn-TOD*+. Such effects seem to be more important in determining the intramolecular reactivity of radical cations than orbital or state symmetry rules.

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

    SciTech Connect

    Huang, Jinhua; Pan, Baofei; Duan, Wentao; Wei, Xiaoliang; Assary, Rajeev S.; Su, Liang; Brushett, Fikile; Cheng, Lei; Liao, Chen; Ferrandon, Magali S.; Wang, Wei; Zhang, Zhengcheng; Burrell, Anthony K.; Curtiss, Larry A.; Shkrob, Ilya A.; Moore, Jeffrey S.; Zhang, Lu

    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, we 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.

  17. Carotenoid radical cations as a probe for the molecular mechanism of nonphotochemical quenching in oxygenic photosynthesis.

    PubMed

    Amarie, Sergiu; Standfuss, Jörg; Barros, Tiago; Kühlbrandt, Werner; Dreuw, Andreas; Wachtveitl, Josef

    2007-04-05

    Nonphotochemical quenching (NPQ) is a fundamental mechanism in photosynthesis which protects plants against excess excitation energy and is of crucial importance for their survival and fitness. Recently, carotenoid radical cation (Car*+) formation has been discovered to be a key step for the feedback deexcitation quenching mechanism (qE), a component of NPQ, of which the molecular mechanism and location is still unknown. We have generated and characterized carotenoid radical cations by means of resonant two color, two photon ionization (R2C2PI) spectroscopy. The Car*+ bands have maxima located at 830 nm (violaxanthin), 880 nm (lutein), 900 nm (zeaxanthin), and 920 nm (beta-carotene). The positions of these maxima depend strongly on solution conditions, the number of conjugated C=C bonds, and molecular structure. Furthermore, R2C2PI measurements on the light-harvesting complex of photosystem II (LHC II) samples with or without zeaxanthin (Zea) reveal the violaxanthin (Vio) radical cation (Vio*+) band at 909 nm and the Zea*+ band at 983 nm. The replacement of Vio by Zea in the light-harvesting complex II (LHC II) has no influence on the Chl excitation lifetime, and by exciting the Chls lowest excited state, no additional rise and decay corresponding to the Car*+ signal observed previously during qE was detected in the spectral range investigated (800-1050 nm). On the basis of our findings, the mechanism of qE involving the simple replacement of Vio with Zea in LHC II needs to be reconsidered.

  18. Formation, isomerization, and dissociation of alpha-carbon-centered and pi-centered glycylglycyltryptophan radical cations

    SciTech Connect

    Ng, Dominic C.; Song, Tao; Siu, Shiu On; Siu, Chi-Kit; Laskin, Julia; Chu, Ivan K.

    2010-02-11

    Gas phase fragmentations of two isomeric radical cationic tripeptides of glycylglycyltryptophan-G•GW+ and [GGW]•+—with well-defined initial radical sites at the α-carbon atom and the 3-methylindole ring, respectively, have been studied using collision-induced dissociation (CID), density functional theory (DFT), and Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Substantially different low-energy CID spectra were obtained for these two isomeric GGW structures, suggesting that they did not interconvert on the time scale of these experiments. DFT and RRKM calculations were used to investigate the influence of the kinetics, stabilities, and locations of the radicals on the competition between the isomerization and dissociation channels. The calculated isomerization barrier between the GGW radical cations (>35.4 kcal/mol) was slightly higher than the barrier for competitive dissociation of these species (<30.5 kcal/mol); the corresponding microcanonical rate constants for isomerization obtained from RRKM calculations were all considerably lower than the dissociation rates at all internal energies. Thus, interconversion between the GGW isomers examined in this study cannot compete with their fragmentations.

  19. The radical cation of naphthalene: First correct analysis of its ESR spectrum

    NASA Astrophysics Data System (ADS)

    Gerson, Fabian; Qin, Xue-Zhi

    1988-12-01

    The radical cations of naphthalene ( 1) and its 1,4-dideutero derivative ( 1- d2), generated from the corresponding neutral compounds by γ-rays in a CFCl 3 matrix at 77 K, have been studied by ESR and ENDOR spectroscopy. At 140 K, the hyperfineanisotropy tensors of the protons in 1+• appear to be quasi-axial, presumably as a consequence of the fast rotation about the twofold symmetry axis perpendicular to the molecular plane. The isotropic coupling constants are -0.74±0.01 and -0.187 ± 0.014 mT for the two sets of four equivalent protons in the 1,4,5,8- and 2,3,6,7-positions, respectively. The relative increase in the coupling constant of the 1,4,5,8-protons on going from the radical anion 1-• (-0.495 mT) to the radical cation 1+• (-0.74 mT) is similar to that found for the 1,4-protons in the corresponding radical ions ( 2-• and 2+•) of s-trans-buta-1,3-diene ( 2).

  20. Solvent effects on the resonance Raman spectra of bacteriochlorophyll a cation radical

    NASA Astrophysics Data System (ADS)

    Misono, Yasuhito; Nishizawa, Ei-ichi; Limantara, Leenawaty; Koyama, Yasushi; Itoh, Koichi

    1995-04-01

    Resonance Raman (RR) spectra were measured for the cation radical of bacteriochlorophyll a in acetone, methanol, dichloromethane and mixed solvents of acetone and methanol. The ring-breathing (C a-C m stretching) frequency of the radical (abbreviated as vr+) was observed at 1601 cm -1 in acetone (forming a penta-coordinated monomer), at 1587 cm -1 in a methanol (forming a hexa-coordinated monomer) and at 1600 cm -1 in dichloromethane (forming a penta-coordinated aggregate). The RR spectrum of the radical in dichloromethane is almost identical to the transient RR spectrum ascribed to 'the aggregated T 1 species of Bchl a' formed in the particular solvent by Nishizawa, Limantara, Nanjou, Nagae, Kakuno and Koyama, indicating that their interpretation needs to be revised.

  1. Mechanistic and comparative studies of melatonin and classic antioxidants in terms of their interactions with the ABTS cation radical.

    PubMed

    Tan, Dun-xian; Hardeland, Rüdiger; Manchester, Lucien C; Poeggeler, Burkhard; Lopez-Burillo, Silvia; Mayo, Juan C; Sainz, Rosa M; Reiter, Russel J

    2003-05-01

    Melatonin and classic antioxidants possess the capacity to scavenge ABTSb+ with IC50s of 4, 11, 15.5, 15.5, 17 and 21 microm for melatonin, glutathione, vitamin C, trolox, NADH and NADPH, respectively. In terms of scavenging ABTSb+, melatonin exhibits a different profile than that of the classic antioxidants. Classic antioxidants scavenge one or less ABTSb+, while each melatonin molecule can scavenge more than one ABTSb+, probably with a maximum of four. Classic antioxidants do not synergize when combined in terms of scavenging ABTSb+. However, a synergistic action is observed when melatonin is combined with any of the classic antioxidants. Cyclic voltammetry indicates that melatonin donates an electron at the potential of 715 mV. The scavenging mechanism of melatonin on ABTSb+ may involve multiple-electron donations via intermediates through a stepwise process. Intermediates including the melatoninyl cation radical, the melatoninyl neutral radical and cyclic 3-hydroxymelatonin (cyclic 3-OHM) and N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) seem to participate in these reactions. More interestingly, the pH of the solution dramatically modifies the ABTSb+ scavenging capacity of melatonin while pH changes have no measurable influence on the scavenging activity of classic antioxidants. An acidic pH markedly reduces the ABTSb+ scavenging capacity of melatonin while an increased pH promotes the interaction of melatonin and ABTSb+. The major melatonin metabolites that develop when melatonin interacts with ABTSb+ are cyclic 3-OHM and AFMK. Cyclic 3-OHM is the intermediate between melatonin and AFMK, and cyclic 3-OHM also has the ability to scavenge ABTSb+. Melatonin and the metabolites which are generated via the interaction of melatonin with ABTSb+, i.e. the melatoninyl cation radical, melatoninyl neutral radical and cyclic 3-OHM, all scavenge ABTSb+. This unique cascade action of melatonin, in terms of scavenging, increases its efficiency to neutralized ABTSb+; this

  2. High-field EPR study of carotenoid and chlorophyll cation radicals in photosystem II.

    SciTech Connect

    Lakshmi, K. V.; Reifler, M. J.; Brudvig, G. W.; Poluektov, O. G.; Wagner, A. M.; Thurnuaer, M. C.; Chemistry; Yale Univ.

    2000-11-16

    In photosystem II (PS II), chlorophyll, {beta}-carotene, and cytochrome b{sub 559} are alternate electron donors that may be involved in a photoprotection mechanism. The present study describes the use of high-field EPR spectroscopy to characterize the low-temperature photooxidation of Chl{sub z} and Car cofactors in PS II. The EPR signals of the individual species, previously not resolved at X-band frequency (9 GHz), are resolved at higher D-band frequency (130 GHz) in deuterated Synechococcus lividus PS II. Deuteration of PS II results in significant narrowing of the EPR lines, yielding well-resolved EPR spectra of the Car{sup +} and Chl{sub z}{sup +} radicals at 130 GHz. The g tensors of the individual species were determined by EPR spectral simulations. The g tensor determined for the Car{sup +} radical (g{sub xx} = 2.00335, g{sub yy} = 2.00251, g{sub zz} = 2.00227) is similar to that previously observed for a canthaxanthin cation radical but with a slightly rhombic tensor. The Chl{sub z}{sup +} g tensor (g{sub xx} = 2.00312, g{sub yy} = 2.00263, g{sub zz} = 2.00202) is similar to that of a chlorophyll a cation radical. This study shows that both the carotenoid and chlorophyll radicals are generated in PS II by illumination at temperatures from 6 to 190 K and that there is no interconversion of Car{sup +} and Chl{sub z}{sup +} radicals upon dark annealing at temperatures up to 160 K. This study also establishes the feasibility of using deuteration and high-field EPR to resolve previously unresolvable cofactor signals in PS II.

  3. Quantum chemical insights in energy dissipation and carotenoid radical cation formation in light harvesting complexes.

    PubMed

    Wormit, Michael; Dreuw, Andreas

    2007-06-21

    Light harvesting complexes (LHCs) have been identified in all photosynthetic organisms. To understand their function in light harvesting and energy dissipation, detailed knowledge about possible excitation energy transfer (EET) and electron transfer (ET) processes in these pigment proteins is of prime importance. This again requires the study of electronically excited states of the involved pigment molecules, in LHCs of chlorophylls and carotenoids. This paper represents a critical review of recent quantum chemical calculations on EET and ET processes between pigment pairs relevant for the major LHCs of green plants (LHC-II) and of purple bacteria (LH2). The theoretical methodology for a meaningful investigation of such processes is described in detail, and benefits and limitations of standard methods are discussed. The current status of excited state calculations on chlorophylls and carotenoids is outlined. It is focused on the possibility of EET and ET in the context of chlorophyll fluorescence quenching in LHC-II and carotenoid radical cation formation in LH2. In the context of non-photochemical quenching of green plants, it is shown that replacement of the carotenoid violaxanthin by zeaxanthin in its binding pocket of LHC-II can not result in efficient quenching. In LH2, our computational results give strong evidence that the S(1) states of the carotenoids are involved in carotenoid cation formation. By comparison of theoretical findings with recent experimental data, a general mechanism for carotenoid radical cation formation is suggested.

  4. Electrochemical and electron paramagnetic resonance studies of a carotenoid cation radicals and dications: Effect of deuteration

    SciTech Connect

    Khaled, M.; Hadjipetrou, A.; Kispert, L. )

    1990-06-14

    The oxidation process involving the transfer of two electrons for {beta}-carotene is confirmed by bulk electrolysis in a CH{sub 2}Cl{sub 2} solvent and the observation of {Delta}E = 42 mV from cyclic voltammetric measurements. A similar process is also found to occur for {beta}-apo-8{prime}-carotenal and canthaxanthin. An additional cathodic peak between 0.2 0.5 relative to SCE is shown to be dependent on the initial formation of dications followed by the loss of H{sup +} as evidenced by a large isotope effect and most likely due to the reduction of a carotenoid cation. EPR evidence exists for the formation of radical cations by the reaction of diffusing carotenoid dictations with neutral carotenoids. The rate of formation is consistent with the differences in the diffusion coefficients of the carotenoids deduced by chronocoulometric measurements, being fastest for canthaxanthin.

  5. External electric field promotes proton transfer in the radical cation of adenine-thymine

    NASA Astrophysics Data System (ADS)

    Zhang, Guiqing; Xie, Shijie

    2016-07-01

    According to pKa measurements, it has been predicted that proton transfer would not occur in the radical cation of adenine-thymine (A:T). However, recent theoretical calculations indicate that proton transfer takes place in the base pair in water below the room temperature. We have performed simulations of proton transfer in the cation of B-DNA stack composed of 10 A:T base pairs in water from 20 K to 300 K. Proton transfer occurs below the room temperature, meanwhile it could also be observed at the room temperature under the external electric field. Another case that interests us is that proton transfer bounces back after ˜300 fs from the appearance of proton transfer at low temperatures.

  6. Application of living free radical polymerization for nucleic acid delivery.

    PubMed

    Chu, David S H; Schellinger, Joan G; Shi, Julie; Convertine, Anthony J; Stayton, Patrick S; Pun, Suzie H

    2012-07-17

    Therapeutic gene delivery can alter protein function either through the replacement of nonfunctional genes to restore cellular health or through RNA interference (RNAi) to mask mutated and harmful genes. Researchers have investigated a range of nucleic acid-based therapeutics as potential treatments for hereditary, acquired, and infectious diseases. Candidate drugs include plasmids that induce gene expression and small, interfering RNAs (siRNAs) that silence target genes. Because of their self-assembly with nucleic acids into virus-sized nanoparticles and high transfection efficiency in vitro, cationic polymers have been extensively studied for nucleic acid delivery applications, but toxicity and particle stability have limited the clinical applications of these systems. The advent of living free radical polymerization has improved the quality, control, and reproducibility of these synthesized materials. This process yields well-defined, narrowly disperse materials with designed architectures and molecular weights. As a result, researchers can study the effects of polymer architecture and molecular weight on transfection efficiency and cytotoxicity, which will improve the design of next-generation vectors. In this Account, we review findings from structure-function studies that have elucidated key design motifs necessary for the development of effective nucleic acid vectors. Researchers have used robust methods such as atom transfer radical polymerization (ATRP), reverse addition-fragmentation chain transfer polymerization (RAFT), and ring-opening metastasis polymerization (ROMP) to engineer materials that enhance extracellular stability and cellular specificity and decrease toxicity. In addition, we discuss polymers that are biodegradable, form supramolecular structures, target specific cells, or facilitate endosomal release. Finally, we describe promising materials with a range of in vivo applications from pulmonary gene delivery to DNA vaccines.

  7. The radical cation of anti-tricyclooctadiene and its rearrangement products

    PubMed

    Bally; Bernhard; Matzinger; Truttmann; Zhu; Roulin; Marcinek; Gebicki; Williams; Chen; Roth; Herbertz

    2000-03-03

    The anti dimer of cyclobutadiene (anti-tricyclo[4.2.0.0(2.5)]octa-3,7-diene, TOD) is subjected to ionization by gamma-irradiation in Freon matrices, pulse radiolysis in hydrocarbon matrices, and photoinduced electron transfer in solution. The resulting species are probed by optical and ESR spectroscopy (solid phase) as well as by CIDNP spectroscopy (solution). Thereby it is found that ionization of anti-TOD invariably leads to spontaneous decay to two products, that is bicyclo[4.2.0]octa-2,4,7-triene (BOT) and 1,4-dihydropentalene (1,4-DHP), whose relative yield strongly depends on the conditions of the experiment. Exploration of the C8H8*+ potential energy surface by the B3LYP/6-31G* density functional method leads to a mechanistic hypothesis for the observed rearrangements which involves a bifurcation between a pathway leading to the simple valence isomer, BOT*+, and another one leading to an unprecedented other valence isomer, the anti form of the bicyclo[3.3.0]octa-2,6-diene-4,8-diyl radical cation (anti-BOD*+). The latter product undergoes a very facile H-shift to yield the radical cation of 1,3a-dihydropentalene (1,3a-DHP*+) which ultimately rearrranges by a further H-shift to the observed product, 1,4-DHP*+.

  8. Multistate vibronic interactions in difluorobenzene radical cations. II. Quantum dynamical simulations.

    PubMed

    Faraji, Shirin; Meyer, H-D; Köppel, Horst

    2008-08-21

    The multistate vibronic dynamics in the X-D electronic states of all three difluorobenzene radical cations are investigated theoretically by an ab initio quantum dynamical approach. The vibronic coupling scheme and the ab initio values of the system parameters are adopted from Paper I [S. Faraji and H. Koppel, J. Chem. Phys. 129, 074310 (2008)]. Extensive calculations by wave-packet propagation have been performed with the aid of the multiconfiguration time-dependent Hartree method. Five coupled electronic potential energy surfaces and 10 (11 in the case of the orthoisomer) vibrational degrees of freedom have been included in these calculations. The nonadiabatic interactions lead to the restructuring of the photoelectron spectral envelopes. Ultrafast internal conversion processes within the electronic manifolds in question demonstrate the strength of the nonadiabatic coupling effects and complement the analogous findings for the electronic spectra. The internal conversion dynamics is characterized by a stepwise transfer of the electronic population to the lowest electronic state on a time scale of femtoseconds to picoseconds. A difference between the three isomers is found to be related to the weaker interaction between the sets of X-A and B-C-D states (with high-energy conical intersections) in the meta isomer, as compared to the other isomers. The implications of these findings for the qualitative understanding of the fluorescence dynamics of fluorinated benzene radical cations are discussed.

  9. Zeaxanthin Radical Cation Formation in Minor Light-Harvesting Complexes of Higher Plant Antenna

    SciTech Connect

    Avenson, Thomas H.; Ahn, Tae Kyu; Zigmantas, Donatas; Niyogi, Krishna K.; Li, Zhirong; Ballottari, Matteo; Bassi, Roberto; Fleming, Graham R.

    2008-01-31

    Previous work on intact thylakoid membranes showed that transient formation of a zeaxanthin radical cation was correlated with regulation of photosynthetic light-harvesting via energy-dependent quenching. A molecular mechanism for such quenching was proposed to involve charge transfer within a chlorophyll-zeaxanthin heterodimer. Using near infrared (880-1100 nm) transient absorption spectroscopy, we demonstrate that carotenoid (mainly zeaxanthin) radical cation generation occurs solely in isolated minor light-harvesting complexes that bind zeaxanthin, consistent with the engagement of charge transfer quenching therein. We estimated that less than 0.5percent of the isolated minor complexes undergo charge transfer quenching in vitro, whereas the fraction of minor complexes estimated to be engaged in charge transfer quenching in isolated thylakoids was more than 80 times higher. We conclude that minor complexes which bind zeaxanthin are sites of charge transfer quenching in vivo and that they can assume Non-quenching and Quenching conformations, the equilibrium LHC(N)<--> LHC(Q) of which is modulated by the transthylakoid pH gradient, the PsbS protein, and protein-protein interactions.

  10. Controlling the dissociation dynamics of acetophenone radical cation through excitation of ground and excited state wavepackets

    NASA Astrophysics Data System (ADS)

    Moore Tibbetts, Katharine; Tarazkar, Maryam; Bohinski, Timothy; Romanov, Dmitri A.; Matsika, Spiridoula; Levis, Robert J.

    2015-08-01

    Time-resolved measurements of the acetophenone radical cation prepared via adiabatic ionization with strong field 1270 nm excitation reveal coupled wavepacket dynamics that depend on the intensity of the 790 nm probe pulse. At probe intensities below 7× {10}11 W cm-2, out of phase oscillations between the parent molecular ion and the benzoyl fragment ion are shown to arise from a one-photon excitation from the ground D0 ionic surface to the D1 and/or D2 excited surfaces by the probe pulse. At higher probe intensities, a second set of wavepacket dynamics are observed that couple the benzoyl ion to the phenyl, butadienyl, and acylium fragment ions. Equation of motion coupled cluster calculations of the ten lowest lying ionic surfaces and the dipole couplings between the ground ionic surface D0 and the nine excited states enable elucidation of the dissociation pathways and deduction of potential dissociation mechanisms. The results can lead to improved control schemes for selective dissociation of the acetophenone radical cation.

  11. Infrared Spectroscopic Investigation on CH Bond Acidity in Cationic Alkanes

    NASA Astrophysics Data System (ADS)

    Matsuda, Yoshiyuki; Xie, Min; Fujii, Asuka

    2016-06-01

    We have demonstrated large enhancements of CH bond acidities in alcohol, ether, and amine cations through infrared predissociation spectroscopy based on the vacuum ultraviolet photoionization detection. In this study, we investigate for the cationic alkanes (pentane, hexane, and heptane) with different alkyl chain lengths. The σ electrons are ejected in the ionization of alkanes, while nonbonding electrons are ejected in ionization of alcohols, ethers, and amines. Nevertheless, the acidity enhancements of CH in these cationic alkanes have also been demonstrated by infrared spectroscopy. The correlations of their CH bond acidities with the alkyl chain lengths as well as the mechanisms of their acidity enhancements will be discussed by comparison of infrared spectra and theoretical calculations.

  12. The Effect of the Secondary Structure on Dissociation of Peptide Radical Cations: Fragmentation of Angiotensin III and Its Analogues

    SciTech Connect

    Yang, Zhibo; Lam, Corey; Chu, Ivan K.; Laskin, Julia

    2008-09-28

    Fragmentation of protonated RVYIHPF and RVYIHPF-OMe and the corresponding radical cations was studied using time- and collision energy-resolved surface-induced dissociation (SID) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially equipped to perform SID experiments. Peptide radical cations were produced by gas-phase fragmentation of CoIII(salen)-peptide complexes. Both the energetics and mechanisms of dissociation of even-electron and odd-electron angiotensin III ions are quite different. Protonated molecules are much more stable towards fragmentation than the corresponding radical cations. RRKM modeling of the experimental data suggests that this stability is largely attributed to differences in threshold energies for dissociation while activation entropies are very similar. Detailed analysis of the experimental data obtained for radical cations demonstrated the presence of two distinct structures separated by a high free-energy barrier. The two families of structures were ascribed to the canonical and zwitterionic forms of the radical cations produced in our experiments.

  13. Facile Smiles-type rearrangement in radical cations of N-acyl arylsulfonamides and analogs

    PubMed Central

    Irikura, Karl K.; Todua, Nino G.

    2016-01-01

    RATIONALE N-Alkylation of sulfonylbenzamides was reported recently to cause a dramatic and surprising change in electron ionization mass spectrometry (EIMS), leading to a closed-shell base peak. Only an incomplete, speculative mechanism was available at that time. The fragmentation mechanism is determined in the present work and set in the context of related compounds. METHODS Candidate reaction mechanisms were evaluated theoretically using modest density-functional calculations. The fragmentation mechanism with the lowest barriers was identified and one of its implications tested successfully by experimental 18O-isotopic substitution. RESULTS The amide oxygen atom attacks the arylsulfonyl group at the ipso position (Smiles-type rearrangement), displacing a molecule of SO2. The resulting carboximidate radical cation has a weak C–O bond that breaks easily. The incipient aryloxyl radical abstracts a proton from the amide nitrogen to form the dominant product ion, but if the molecule is N-alkylated this cannot occur. Instead, the neutral aryloxyl radical is lost and a closed-shell, N-alkyl nitrilium ion is the major product. CONCLUSIONS The Smiles-type ion fragmentation mechanism is facile for the title compounds, despite the necessity for carbonyl oxygen to serve as a nucleophile. This rearrangement probably occurs in many of the mass spectra reported for structurally similar compounds, in which the nucleophile may be a thione, arylthio, imine, methylene, or methine moiety. PMID:24573815

  14. Pathways for the reaction of the butadiene radical cation, [C{sub 4}H{sub 6}]{sup {sm{underscore}bullet}+}, with ethylene

    SciTech Connect

    Hofmann, M.; Schaefer, H.F. III

    1999-11-04

    The Diels-Alder (DA) reaction, a [4+2] cycloaddition used to build six membered rings, is one of the most valuable cycloadditions in organic chemistry. In cases where the ene does not add to the diene (even with the help of Lewis acids which may reduce the electron density of one reactant by complexation) one electron oxidation (by an oxidizing agent or by photoinduced electron transfer (PET)) may accelerate the reaction. Reaction pathways for the addition of ethylene, 1, to butadiene radical cation, 2, involving H-shifts have been investigated at the coupled cluster UCCSD(T)/DZP//UMP2(fc)/DZP + ZPE level of theory. Activation energies are relatively low for [1,2]- (10.0 kcal mol{sup {minus}1}, TS-4/20) and [1,5]-hydrogen shifts (7.7 kcal mol{sup {minus}1}, TS-4/26) but are relatively high for [1,4]-(33.8 kcal mol{sup {minus}1}, TS-4/14) and [1,3]-H shifts (e.g., 42.2 kcal mol{sup {minus}1}, TS-12/13; 57.2 kcal mol{sup {minus}1}, TS-16/21). Several rearrangement reactions have been found to occur below the energy limit of separated 1 + 2. The cyclopentenyl cation, [C{sub 5}{sub 7}]{sup +}, 18, experimentally observed as reaction product of the butadiene radical cation, 2, and ethylene, 1, in the gas phase may origin from various reaction pathways. The following reaction sequence has been identified as the lowest in energy path from 1 + 2 to 18 with all relative energies ({Delta}E{degree}) of transition structures below that of 1 + 2: (a) ethylene adds to the butadiene radical cation to form an open-chain distonic intermediate, that undergoes a [1,5]-H shift to the 1,4-hexadiene radical cation; (b) intramolecular [2+1] cycloaddition to methyl-cyclopenta-1,3-diyl intermediates, which can interconvert through a bicyclo[2.1.0]pentane radical cation; (c) [1,2]-H shift to the 3-methyl cyclopentene radical cation; (d) methyl radical loss to give cyclopenten-3-yl cation. Along this reaction pathway, {Delta}H{sup 298} is below that of 1 + 2; max. ({Delta}G{sup 298} by

  15. 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.

  16. Synthesis, Physical Properties and Reactivity of Stable Antiaromatic 1,4-DIHYDROPYRAZINES and Their Associated Radical Cations

    NASA Astrophysics Data System (ADS)

    Brook, David James Rawsthorne

    Self condensation of 3-(chloromethyl)-5,6-dihydro -5,5-dimethyl oxazin-2-one and 3-(chloromethyl)-5,6-dihydro -1,5, 5-trimethylpyrazin-2-one gave the 1,4-dihydropyrazines, 4a,8a-diaza-2,6-dioxa-3,4,7,8-tetrahydro- 4,4,8,8 -tetramethylanthracene-1,5,-dione (DDTTA), and 2,4,4,6,8,8-hexamethyl-2,4a,6,8a-tetraaza - 3,4,7,8-tetrahydroanthracene-1,5-dione (HTTA), respectively. Extension of this reaction to other systems resulted in failure. Thionation of DDTTA with phosphorus pentasulphide in pyridine gave mono and dithiono ester derivatives. The dihydropyrazine rings of these systems were planar and showed long wavelength pi-pi^* electronic absorption resulting in the compounds being coloured. The long wavelength band showed significant solvatochromism. NMR measurements indicated that the rings are also paratropic. DDTTA, HTTA and the thiones all showed reversible one electron oxidation to the radical cation which was characterised by electron spin resonance spectroscopy. HTTA and DDTTA also showed reversible oxidation of the radical cation to the dication. Hydrogenation of DDTTA resulted in a tetrahydropyrazine derivative, 4a,8a-diaza-2,6-dioxa -3,4,7,8,9,9a-hexahydro- 4,4,8,8-tetramethylanthracene -1,5-dione (4.5), which underwent atmospheric oxidation back to DDTTA and the alcohol 4a,8a-diaza-2,6-dioxa-3,4,7,8,9,9a -hexahydro-9a-hydroxy- 4,4,8,8-tetramethylanthracene -1,5-dione (4.6). The HTTA analogue 2,4,4,6,8,8-hexamethyl -3,4,7,8,9,9a-hexahydro- 2,4a,6,8a-tetraazaanthracene -1,5-dione (4.9) is stable under the same conditions. The difference in behaviour was explained as a result of the captodative effect. DDTTA was found to undergo rapid (2 + 2) cycloaddition to the dienophile, 4-phenyl-1,2,4-triazoline -3,5-dione (PTAD). Reaction of DDTTA with ^ {3}O_{2} was found to be solvent dependent. In acetic acid the dioxetane 4a,8a-diaza-2,6-dioxa-9,9a-epidioxy-3,4,7,8,9,9a -hexahydro- 4,4,8,8-tetramethylanthracene -1,5-dione was observed; whereas, in acetonitrile

  17. Dynamics of radical cations of poly(4-hydroxystyrene) in the presence and absence of triphenylsulfonium triflate as determined by pulse radiolysis of its highly concentrated solution

    NASA Astrophysics Data System (ADS)

    Okamoto, Kazumasa; Ishida, Takuya; Yamamoto, Hiroki; Kozawa, Takahiro; Fujiyoshi, Ryoko; Umegaki, Kikuo

    2016-07-01

    Pulse radiolysis of highly concentrated poly(4-hydroxystyrene) (PHS) solutions in cyclohexanone and p-dioxane was performed both with and without an onium-type photoacid generator (PAG). With increasing PHS concentration, the rate constant of deprotonation of PHS radical cations was found to decrease. In the presence of PAG, the yield of the multimer radical cation of PHS was shown to decrease. We found that pairing between the anions produced by the attachment of dissociative electrons of PAGs and the monomer PHS radical cations restrict local molecular motions, leading to the formation of the multimer PHS radical cations.

  18. Single-Crystal X-ray Structures of conductive π-Stacking Dimers of Tetrakis(alkylthio)benzene Radical Cations

    PubMed Central

    Chen, Xiaoyu; Gao, Feng; Yang, Wuqin

    2016-01-01

    Salts containing radical cations of 1,2,4,5-tetrakis(isopropylthio)benzene (TPB) and 1,2,4,5-tetrakis(ethylthio) benzene (TEB) have been successfully synthesized with . These newly synthesized salts have been characterized by UV-Vis absorption, EPR spectroscopy, conductivity measurement, single crystal X-ray diffraction analysis as well as DFT calculation. This study raises the first crystal structure of conductive π-stacking radical cation with single phenyl ring and reveals their conductivity has relationship with the stack structure which affected by the substituent. PMID:27403720

  19. Carotenoid cation radicals produced by the interaction of carotenoids with iodine

    SciTech Connect

    Ding, R.; Grant, J.L.; Metzger, R.M.; Kispert, L.D.

    1988-08-11

    Electron paramagnetic resonance (EPR) and optical absorption spectra of 1,2-dichloroethane and dichloromethane solutions of ..beta..-carotene (C/sub 40/H/sub 56/) and iodine have been studied. EPR studies showed that ..beta..-carotene cation radicals are formed. These radicals form complexes at 77 K, in highly concentrated (0.1 M) iodine solutions, with higher order polyiodide anions, I/sub 5//sup -/, I/sub 7//sup -/, I/sub 9//sup -/ (as evidenced by g value shifts and line-width increases), while at room temperature and in dilute (10/sup -4/-10/sup -5/ M) solutions of iodine only I/sub 3//sup -/ counterions are involved. In dilute solutions (total molar concentratino = 2 x 10/sup -4/ M), a Job plot showed the stoichiometry to be 2:3, indicating the reaction 2C/sub 40/H/sub 56/ + 31/sub 2/ /r equilibrium/ 2C/sub 40/H/sub 56//sup .+/ + 2I/sub 3//sup -/. The radical fraction (EPR) is /approximately/ 2% at 77 K and 0.4% at 300 K (for a 2 mM ..beta..-carotene/0.1 M I/sub 2/ solution); it increases at lower ..beta..-carotene concentrations. Dimers and trimers of ..beta..-carotene cation radicals are formed in dilute solution (I/sub 2/ < 10/sup -4/ M) if (I/sub 2/)/(..beta..-carotene) < 1, and an intense absorption band occurs at lambda/sub max/ /approximately/ 1030 nm. Canthaxanthin and ..beta..-apo-8'-carotenal with I/sub 2/ produce new absorption bands with lambda/sub max/ < 1000 nm; the g values are independent of iodine concentration, suggesting a poorer ability to form complexes with the polyiodide anions. All three carotenoids react with other electron acceptors (7,7,8,8-tetracyanoquinodimethane (TCNQ), tetrachloro-1,4-benzoquinone (chloranil), and Br/sub 2/) according to the electron affinity of the acceptor used.

  20. Density Functional Theory and Mass Spectrometry of Phthalate Fragmentations Mechanisms: Modeling Hyperconjugated Carbocation and Radical Cation Complexes with Neutral Molecules

    NASA Astrophysics Data System (ADS)

    Jeilani, Yassin A.; Cardelino, Beatriz H.; Ibeanusi, Victor M.

    2011-11-01

    This is the first ab initio study of the energetics of the fragmentation mechanisms of phthalate, by mass spectrometry, leading to protonated phthalic anhydride ( m/z 149). Phthalates fragment by two major pathways; namely, the McLafferty + 1 rearrangement and the loss of alkoxy. Both pathways involve a carbonyl oxygen attack to the ortho-carbonyl carbon leading to structures with tetrahedral carbon intermediates that eventually give m/z 149. These pathways were studied by collision induced dissociation (CID) using triple quadrupole mass spectrometry. The proposed McLafferty + 1 pathway proceeds through a distonic M•+, leading to the loss of an allylic-stabilized alkene radical. The McLafferty rearrangement step proceeds through a six-membered ring transition state with a small activation energy ranging 0.4-6.2 kcal/mol; the transfer of a second H from the distonic ion of the rearrangement step proceeds through a radical cation molecule complex. Based on quantum chemical modeling of the cation molecule complexes, two kinds of cation molecule complexes were identified as radical cation molecule complex and hyperconjugated cation molecule complex. This distinction is based on the cation and simplifies future modeling of similar complexes. Optimization of important fragments in these pathways showed cyclized and hydrogen-bonded structures to be favored. An exception was the optimized structure of the protonated phthalic anhydride ( m/z 149) that showed a structure with an open anhydride ring.

  1. Pathways of arachidonic acid peroxyl radical reactions and product formation with guanine radicals.

    PubMed

    Crean, Conor; Geacintov, Nicholas E; Shafirovich, Vladimir

    2008-02-01

    Peroxyl radicals were derived from the one-electron oxidation of polyunsaturated fatty acids by sulfate radicals that were generated by the photodissociation of peroxodisulfate anions in air-equilibrated aqueous solutions. Reactions of these peroxyl and neutral guanine radicals, also generated by oxidation with sulfate radicals, were investigated by laser kinetic spectroscopy, and the guanine oxidation products were identified by HPLC and mass spectrometry methods. Sulfate radicals rapidly oxidize arachidonic (ArAc), linoleic (LnAc), and palmitoleic (PmAc) acids with similar rate constants, (2-4) x 10 (9) M (-1) s (-1). The C-centered radicals derived from the oxidation of ArAc and LnAc include nonconjugated Rn(.) ( approximately 80%) and conjugated bis-allylic Rba(.) ( approximately 20%) radicals. The latter were detectable in the absence of oxygen by their prominent, narrow absorption band at 280 nm. The Rn(.) radicals of ArAc (containing three bis-allylic sites) transform to the Rba(.) radicals via an intramolecular H-atom abstraction [rate constant (7.5 +/- 0.7) x 10 (4) s (-1)]. In contrast, the Rn(.) radicals of LnAc that contain only one bis-allylic site do not transform intramolecularly to the Rba(.) radicals. In the case of PmAc, which contains only one double bond, the Rba(.) radicals are not observed. The Rn(.) radicals of PmAc rapidly combine with oxygen with a rate constant of (3.8 +/- 0.4) x 10(9) M(-1) s(-1). The Rba(.) radicals of ArAc are less reactive and react with oxygen with a rate constant of (2.2 +/- 0.2) x 10 (8) M (-1) s (-1). The ArAc peroxyl radicals formed spontaneously eliminate superoxide radical anions [rate constant = (3.4 +/- 0.3) x 10 (4) M (-1) s (-1)]. The stable oxidative lesions derived from the 2',3',5'-tri- O-acetylguanosine or 2',3',5'-tri- O-acetyl-8-oxo-7,8-dihydroguanosine radicals and their subsequent reactions with ArAc peroxyl radicals were also investigated. The major products found were the 2,5-diamino-4 H

  2. Multistate vibronic interactions in difluorobenzene radical cations. I. Electronic structure calculations.

    PubMed

    Faraji, Shirin; Köppel, Horst

    2008-08-21

    The multimode multistate vibronic interactions between the five lowest electronic states of all three isomers of the difluorobenzene radical cation are investigated theoretically, based on ab initio electronic structure data, and employing a well-established vibronic coupling model. The approach rests on the linear vibronic coupling scheme, augmented by quadratic coupling terms for the totally symmetric modes. The underlying ionization potentials and coupling constants are obtained from ab initio coupled-cluster calculations. Low-energy conical intersections and strong vibronic couplings are found to prevail within the sets of X-A and B-C-D cationic states, while the interactions between these two sets of states are found to be weaker and depend on the isomer. The inclusion of the aforementioned quadratic couplings is found to be essential to correctly reproduce the lowest-energy conical intersections between the two different sets of electronic states. Differences between the three isomers regarding these quantities are pointed out. The results will be used as basis for multidimensional wave-packet dynamical simulations for these coupled potential energy surfaces to be presented in the following paper (Paper II).

  3. 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.

  4. Photoinduced electron-transfer reactions of 2(3H)-furanones and bis(benzofuranones). Spectral and kinetic behavior of radicals and radical cations

    SciTech Connect

    Davis, H.F.; Lohray, B.B.; Gopidas, K.R.; Kumar, C.V.; Das, P.K.; George, M.V.

    1985-10-04

    The spectral and kinetic behaviors of radical cations produced under efficient electron-transfer quenching of 1,4-dicyanonaphthalene or 9,10-dicyanoanthracene singlet by a number of 2(3H)-furanones and bis(benzo-furanones) have been examined by nanosecond laser flash photolysis (337.1 and 425 nm). The efficiencies of net electron transfer in the course of quenching processes are moderately high (0.2-0.6) in acetonitrile. The radical cations from bis(benzofuranones) several 2(3H)-furanones containing a benzyl group at the 3-position undergo fragmentation to benzofuranoxy and furanoxy radicals (+ benzyl or benzofuranoyl carbocations) with rate constants of 0.3 x 10W s . The long-lived furanoxy radicals, independently generated via hydrogen abstraction by tert-butoxy radicals from 2(5H)-furanones and 3-phenyl-2(3H)-benzofuranone, as well as via direct photolysis of 3-benzoyl-3,5-diphenyl-2(3H)-furanone, are characterized by sharply structured absorption spectra and relatively slow second-order decay kinetics (6-8 x 10Y M s in 1:2 benzene-di-tert butyl peroxide, v/v). 28 references, 7 figures, 3 tables.

  5. Facile C(sp(2))-C(sp(2)) bond cleavage in oxalic acid-derived radicals.

    PubMed

    Molt, Robert W; Lecher, Alison M; Clark, Timothy; Bartlett, Rodney J; Richards, Nigel G J

    2015-03-11

    Oxalate decarboxylase (OxDC) catalyzes the Mn-dependent conversion of the oxalate monoanion into CO2 and formate. Many questions remain about the catalytic mechanism of OxDC although it has been proposed that the reaction proceeds via substrate-based radical intermediates. Using coupled cluster theory combined with implicit solvation models we have examined the effects of radical formation on the structure and reactivity of oxalic acid-derived radicals in aqueous solution. Our results show that the calculated solution-phase free-energy barrier for C-C bond cleavage to form CO2 is decreased from 34.2 kcal/mol for oxalic acid to only 9.3 kcal/mol and a maximum of 3.5 kcal/mol for the cationic and neutral oxalic acid-derived radicals, respectively. These studies also show that the C-C σ bonding orbital of the radical cation contains only a single electron, giving rise to an elongated C-C bond distance of 1.7 Å; a similar lengthening of the C-C bond is not observed for the neutral radical. This study provides new chemical insights into the structure and stability of plausible intermediates in the catalytic mechanism of OxDC, and suggests that removal of an electron to form a radical (with or without the concomitant loss of a proton) may be a general strategy for cleaving the unreactive C-C bonds between adjacent sp(2)-hybridized carbon atoms.

  6. The first BETS radical cation salts with dicyanamide anion: Crystal growth, structure and conductivity study

    SciTech Connect

    Kushch, N.D.; Buravov, L.I.; Chekhlov, A.N.; Spitsina, N.G.; Kushch, P.P.; Yagubskii, E.B.; Herdtweck, E.; Kobayashi, A.

    2011-11-15

    Electrochemical oxidation of bis(ethylenedithio)tetraselenafulvalene (BETS) has been investigated. Simple and complex dicyanamides of transition metals (Mn{sup 2+}, Ni{sup 2+} and Fe{sup 2+}) were used as electrolytes. The correlation between composition of prepared radical cation salts and metal nature in electrolytes was established. Manganese dicyanamides provide the formation of BETS salts with the {l_brace}Mn[N(CN){sub 2}]{sub 3}{r_brace}- and [N(CN){sub 2}]-XH{sub 2}O anions. When Ni- or Fe-containing electrolytes were used only metalless BETS salts, {alpha}''-BETS{sub 2}[N(CN){sub 2}].2H{sub 2}O (I) and {theta}-BETS{sub 2}[N(CN){sub 2}].3.6H{sub 2}O (II), formed. Structures and conducting properties of these salts were analyzed. Both salts exhibit layered structure. Conducting radical cation layers have {alpha}'' (I)- or {theta}-type (II). Anion sheets appear as two-dimensional polymer networks of different types. These networks are formed by [N(CN)]{sub 2}{sup -} anions and water molecules interlinked by hydrogen bonds. Salt I is a semiconductor and II demonstrates resistance drop down to150 K at normal pressure and down to 72 K at {approx}0.4 kbar pressure. - Graphical abstract: We studied electrochemical oxidation of BETS donor in the presence of simple and/or complex dicyanamides of transition metals (Ni, Fe, Mn) as electrolytes. New conducting salts {alpha}''-BETS{sub 2}[N(CN){sub 2}].2H{sub 2}O and {theta}-BETS{sub 2}[N(CN){sub 2}].3.8H{sub 2}O have been synthesized and characterized. Highlights: > We studied electrochemical oxidation of BETS donor. > Dicyanamides of transition metals (Ni, Fe, Mn) were used as electrolytes. > We found a well-reproducible synthesis of magnetic superconductor BETS{sub 2}Mn[N(CN){sub 2}]{sub 3}. > Two new metalless BETS salts form when Ni and Fe electrolytes were used. > Their structure and conductivity were investigated.

  7. Separation of certain carboxylic acids utilizing cation exchange membranes

    DOEpatents

    Chum, H.L.; Sopher, D.W.

    1983-05-09

    A method of substantially separating monofunctional lower carboxylic acids from a liquid mixture containing the acids wherein the pH of the mixture is adjusted to a value in the range of from about 1 to about 5 to form protonated acids. The mixture is heated to an elevated temperature not greater than about 100/sup 0/C and brought in contact with one side of a perfluorinated cation exchange membrane having sulfonate or carboxylate groups or mixtures thereof with the mixture containing the protonated acids. A pressure gradient can be established across the membrane with the mixture being under higher pressure, so that protonated monofunctional lower carboxylic acids pass through the membrane at a substantially faster rate than the remainder of the mixture thereby substantially separating the acids from the mixture.

  8. Separation of certain carboxylic acids utilizing cation exchange membranes

    DOEpatents

    Chum, Helena L.; Sopher, David W.

    1984-01-01

    A method of substantially separating monofunctional lower carboxylic acids from a liquid mixture containing the acids wherein the pH of the mixture is adjusted to a value in the range of from about 1 to about 5 to form protonated acids. The mixture is heated to an elevated temperature not greater than about 100.degree. C. and brought in contact with one side of a perfluorinated cation exchange membrane having sulfonate or carboxylate groups or mixtures thereof with the mixture containing the protonated acids. A pressure gradient can be established across the membrane with the mixture being under higher pressure, so that protonated monofunctional lower carboxylic acids pass through the membrane at a substantially faster rate than the remainder of the mixture thereby substantially separating the acids from the mixture.

  9. Iron corrolates: unambiguous chloroiron(III) (corrolate)(2-.) pi-cation radicals.

    PubMed

    Walker, F Ann; Licoccia, Silvia; Paolesse, Roberto

    2006-04-01

    The structures, electron configurations, magnetic susceptibilities, spectroscopic properties, molecular orbital energies and spin density distributions, redox properties and reactivities of iron corrolates having chloride, phenyl, pyridine, NO and other ligands are reviewed. It is shown that with one very strong donor ligand such as phenyl anion the electron configuration of the metal is d(4)S=1 Fe(IV) coordinated to a (corrolate)(3-) anion, while with one weaker donor ligand such as chloride or other halide, the electron configuration is d(5)S=3/2 Fe(III) coordinated to a (corrolate)(2-.) pi-cation radical, with antiferromagnetic coupling between the metal and corrolate radical electron. Many of these complexes have been studied by electrochemical techniques and have rich redox reactivity, in most cases involving two 1-electron oxidations and two 1-electron reductions, and it is not possible to tell, from the shapes of cyclic voltammetric waves, whether the electron is added or removed from the metal or the macrocycle; often infrared, UV-Vis, or EPR spectroscopy can provide this information. (1)H and (13)C NMR spectroscopic methods are most useful in delineating the spin state and pattern of spin density distribution of the complexes listed above, as would also be expected to be the case for the recently-reported formal Fe(V)O corrolate, if this complex were stable enough for characterization by NMR spectroscopy. Iron, manganese and chromium corrolates can be oxidized by iodosylbenzene and other common oxidants used previously with metalloporphyrinates to effect efficient oxidation of substrates. Whether the "resting state" form of these complexes, most generally in the case of iron [FeCl(Corr)], actually has the electron configuration Fe(IV)(Corr)(3-) or Fe(III)(Corr)(2-.) is not relevant to the high-valent reactivity of the complex.

  10. Assigning structures to gas-phase peptide cations and cation-radicals. An infrared multiphoton dissociation, ion mobility, electron transfer, and computational study of a histidine peptide ion.

    PubMed

    Moss, Christopher L; Chamot-Rooke, Julia; Nicol, Edith; Brown, Jeffery; Campuzano, Iain; Richardson, Keith; Williams, Jonathan P; Bush, Matthew F; Bythell, Benjamin; Paizs, Bela; Turecek, Frantisek

    2012-03-15

    Infrared multiphoton dissociation (IRMPD) spectroscopy, using a free-electron laser, and ion mobility measurements, using both drift-cell and traveling-wave instruments, were used to investigate the structure of gas-phase peptide (AAHAL + 2H)(2+) ions produced by electrospray ionization. The experimental data from the IRMPD spectra and collisional cross section (Ω) measurements were consistent with the respective infrared spectra and Ω calculated for the lowest-energy peptide ion conformer obtained by extensive molecular dynamics searches and combined density functional theory and ab initio geometry optimizations and energy calculations. Traveling-wave ion mobility measurements were employed to obtain the Ω of charge-reduced peptide cation-radicals, (AAHAL + 2H)(+●), and the c(3), c(4), z(3), and z(4) fragments from electron-transfer dissociation (ETD) of (AAHAL + 2H)(2+). The experimental Ω for the ETD charge-reduced and fragment ions were consistent with the values calculated for fully optimized ion structures and indicated that the ions retained specific hydrogen bonding motifs from the precursor ion. In particular, the Ω for the doubly protonated ions and charge-reduced cation-radicals were nearly identical, indicating negligible unfolding and small secondary structure changes upon electron transfer. The experimental Ω for the (AAHAL + 2H)(+●) cation-radicals were compatible with both zwitterionic and histidine radical structures formed by electron attachment to different sites in the precursor ion, but did not allow their distinction. The best agreement with the experimental Ω was found for ion structures fully optimized with M06-2X/6-31+G(d,p) and using both projection approximation and trajectory methods to calculate the theoretical Ω values.

  11. The role of the position of the basic residue in the generation and fragmentation of peptide radical cations

    NASA Astrophysics Data System (ADS)

    Wee, Sheena; O'Hair, Richard A. J.; McFadyen, W. David

    2006-03-01

    Using simple di- and tripeptides GX, GGX, GXG, XG and XGG, the influence of the position of the basic residue, X (X = R, K and H), on the formation of peptide radical cations (M+) from [CuII(tpy)M]2+ complexes (where tpy = 2,2':6',2''-terpyridine) was probed. It was found that M+ is formed with greatest abundance when the basic residue is at the C-terminus. For arginine containing peptides, this may be due to further fragmentation of GRG+, RG+ and RGG+ at the MS2 stage. For lysine and histidine containing peptides, when the basic residue is not located at the C-terminus, competing fragmentation pathways that lead to peptide backbone cleavage are more facile than M+ formation. In order to gain some insights into the binding modes of these peptides to [CuII(tpy)]2+, the formation and fragmentation of copper(II) complexes of tripeptides protected as their carboxy methyl/ethyl esters (M-OR', R' = Me/Et) were also probed. The products of the competing fragmentation pathways of [CuII(tpy)M]2+, as well as the formation and fragmentation of [CuII(tpy)(M-OR')]2+, suggest that the unprotected peptides, M, mainly bind as zwitterions to [CuII(tpy)]2+. The fragmentation reactions of the radical cations (M+) were also studied. Radical driven side chain fragmentation reactions of M+ are dependent on both the position of the residue as well as the identity of other residues present in the peptide radical cations. GR and RG, which undergo rearrangement to form a mixed anhydride in their protonated forms, do not undergo the same rearrangement in their radical cation forms.

  12. Self-assembly of three-dimensional supramolecular polymers through cooperative tetrathiafulvalene radical cation dimerization.

    PubMed

    Tian, Jia; Ding, Yu-Di; Zhou, Tian-You; Zhang, Kang-Da; Zhao, Xin; Wang, Hui; Zhang, Dan-Wei; Liu, Yi; Li, Zhan-Ting

    2014-01-07

    The self-assembly of a new type of three-dimensional (3D) supramolecular polymers from tetrahedral monomers in both organic and aqueous media is described. We have designed and synthesized two tetraphenylmethane derivatives T1 and T2, both of which bear four tetrathiafulvalene (TTF) units. When the TTF units were oxidized to the radical cation TTF(.+) , their pre-organized tetrahedral arrangement remarkably enhanced their intermolecular dimerization, leading to the formation of new 3D spherical supramolecular polymers. The structure of the supramolecular polymers has been inferred on the basis of UV/Vis absorption, electron paramagnetic resonance, cyclic voltammetry, and dynamic light scattering (DLS) analysis, as well as by comparing these properties with those of the self-assembled structures of mono-, di-, and tritopic control compounds. DLS experiments revealed that the spherical supramolecular polymers had hydrodynamic diameters of 68 nm for T1 (75 μM) in acetonitrile and 105 nm for T2 (75 μM) in water/acetonitrile (1:1). The 3D spherical structures of the supramolecular polymers formed in different solvents were also supported by SEM and AFM experiments.

  13. 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

  14. Role of. pi. -cation radicals in the enzymatic cycles of peroxidases, catalases, and nitrite and sulfite reductases

    SciTech Connect

    Hanson, L K; Chang, C K; Davis, M S; Fajer, J

    1980-01-01

    Charge iterative extended Hueckel calculations, and magnetic and optical results on porphyrins, chlorins, and isobacteriochlorins (1) suggest that the catalytic cycles of the enzymes horseradish peroxidase, catalase, Neurospora crassa catalase, and nitrite and sulfite reductases proceed via ..pi..-cation radicals of their prosthetic groups; (2) offer distinguishing features for the optical and magnetic spectra of these radicals, pertinent to their detection as enzymatic intermediates; (3) reconcile the seemingly contradictory optical and NMR data on Compounds I of horseradish peroxidase; and (4) predict that the axial ligation of the heme differs for horseradish peroxidase and catalase.

  15. Synthesis of new lipoic acid conjugates and evaluation of their free radical scavenging and neuroprotective activities.

    PubMed

    Bolognesi, Maria Laura; Bergamini, Christian; Fato, Romana; Oiry, Joël; Vasseur, Jean-Jacques; Smietana, Michael

    2014-06-01

    A series of new lipoic acid derivatives were designed and synthesized as multitarget ligands against Alzheimer's disease. In particular, analogues combining both lipoic acid and cysteine core structures were synthesized. The antioxidant properties of these compounds were evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS(•+) ) radical cation scavenging assays and ferrous ion chelation. The antioxidant potential of the synthesized compounds was also evaluated in a cellular context and compared to α-lipoic acid and its reduced form, dihydrolipoic acid. The antioxidant effects observed for these compounds in vitro confirmed the importance of free thiol functions for effective antioxidant capacities. However, these promising in vitro results were not mirrored by the antioxidant activity in T67 cell line. This suggests that multiple factors are at stake and warrant further investigations.

  16. Unconventional hydrogen bonding to organic ions in the gas phase: stepwise association of hydrogen cyanide with the pyridine and pyrimidine radical cations and protonated pyridine.

    PubMed

    Hamid, Ahmed M; El-Shall, M Samy; Hilal, Rifaat; Elroby, Shaaban; Aziz, Saadullah G

    2014-08-07

    Equilibrium thermochemical measurements using the ion mobility drift cell technique have been utilized to investigate the binding energies and entropy changes for the stepwise association of HCN molecules with the pyridine and pyrimidine radical cations forming the C5H5N(+·)(HCN)n and C4H4N2 (+·)(HCN)n clusters, respectively, with n = 1-4. For comparison, the binding of 1-4 HCN molecules to the protonated pyridine C5H5NH(+)(HCN)n has also been investigated. The binding energies of HCN to the pyridine and pyrimidine radical cations are nearly equal (11.4 and 12.0 kcal/mol, respectively) but weaker than the HCN binding to the protonated pyridine (14.0 kcal/mol). The pyridine and pyrimidine radical cations form unconventional carbon-based ionic hydrogen bonds with HCN (CH(δ+)⋯NCH). Protonated pyridine forms a stronger ionic hydrogen bond with HCN (NH(+)⋯NCH) which can be extended to a linear chain with the clustering of additional HCN molecules (NH(+)⋯NCH··NCH⋯NCH) leading to a rapid decrease in the bond strength as the length of the chain increases. The lowest energy structures of the pyridine and pyrimidine radical cation clusters containing 3-4 HCN molecules show a strong tendency for the internal solvation of the radical cation by the HCN molecules where bifurcated structures involving multiple hydrogen bonding sites with the ring hydrogen atoms are formed. The unconventional H-bonds (CH(δ+)⋯NCH) formed between the pyridine or the pyrimidine radical cations and HCN molecules (11-12 kcal/mol) are stronger than the similar (CH(δ+)⋯NCH) bonds formed between the benzene radical cation and HCN molecules (9 kcal/mol) indicating that the CH(δ+) centers in the pyridine and pyrimidine radical cations have more effective charges than in the benzene radical cation.

  17. Some Rearrangements of Free Alkyl Radicals and Alkyl Cations in Solutions

    NASA Astrophysics Data System (ADS)

    Reutov, Oleg A.

    1984-03-01

    The results of studies of rearrangement reactions by the author and his co-workers during the last 20 years are described. A rearrangement of the n-propyl free radical in solutions as a result of the hydrogen 1,3-shift has been discovered and its characteristic features have been investigated (using carbon-14, deuterium, and tritium). The reaction involving the formation of organomercury compounds from mercury salts of carboxylic acids and peroxides has been studied and a mechanism has been proposed for it. New skeletal rearrangements in the thermal decomposition of cycloalkyl peroxides in benzene and bromoform have been discovered. It has been shown by the method of double 13C NMR that some of the reactions involve the formation of species which manifest properties intermediate between those of free radicals and carbonium ions. The mechanism of the thermolysis of peroxides is considered. The skeletal rearrangements and hydride shifts in the deamination and solvolysis of alicyclic compounds have been studied and a number of rearrangements with 1,2-migration of the halogen and in particular the isomerisation of acyloxybromopropanes in organic solvents, which takes place particularly readily, have been observed. The bibliography includes 103 references.

  18. The standard enthalpies of formation of 1- and 2-Adamantyl cations and radicals. An ab initio study

    NASA Astrophysics Data System (ADS)

    Abboud, J.-L. M.; Castaño, O.; Dávalos, J. Z.; Gomperts, R.

    2001-04-01

    The results of a G2(MP2) computational study involving 1- and 2-Adamantyl cations ( 1+, 2+) as well as 1- and 2-Adamantyl radicals ( 1rad , 2rad ) are presented. They provide purely computational thermodynamic data for the following processes: (i) Ionization of 1rad and 2rad , (ii) Exchange of hydrogen atoms or hydride anions between Adamantyl radicals or cations and alkyl radicals or cations, respectively. These data, once combined with the experimental enthalpies of formation of iso -C3H7 rad ,iso -C3H7 + ,tert -C4H9 rad and tert -C4H9 + , allowed us to screen the available experimental data and to define a self-consistent set of experimentally-based standard enthalpies of formation, Δ fH 0 m, for Adamantyl species, namely: Δ fH 0 m( 1+, g)=162.0±2.0 ; Δ fH 0 m( 2+, g)=171.9±2.0 ; Δ fH 0 m( 1rad , g)=17.9±2.1 , Δ fH 0 m( 2rad , g)=16.6±2.0 kcal mol -1.

  19. Resonance Raman spectra of the anion and cation radicals of bacterial photosynthetic pigments

    SciTech Connect

    Diers, J.R.; Bocian, D.F. )

    1994-12-08

    Resonance Raman (RR) spectra are reported for the radical ions of the bacterial photosynthetic pigments bacteriochlorophyll a (BCh) and its metal-free analog bacteriopheophytin a (BPh). The radical anions, BCh[sup [minus

  20. Spectral and Kinetic Properties of Radical Cations Derived from Oxoisoaporphines: Relevance to Electron-Transfer Processes Involving Phytoalexins.

    PubMed

    De la Fuente, Julio R; Kciuk, Gabriel; Aliaga, Christian; Bobrowski, Krzysztof

    2014-05-16

    The thermally induced intermolecular electron transfer reaction in acetonitrile between the tetracyanoethylene (TCNE), a π-electron acceptor with a large electron affinity, and six oxoisoaporphines (2,3-dihydro-7H-dibenzo[de,h]quinolin-7-one, 5-methoxy-2,3-dihydro-7H-dibenzo[de,h]quinolin-7-one, 1-azabenzo[de]anthracen-7-one, 5-methoxy-1-azabenzo[de]anthracen-7-one, 7H-benzo[e]perimidin-7-one, and 2-methyl-7h-benzo[e]perimidin-7-one) is reported. Spectral and kinetic characteristics are presented for radical cations derived from these six oxoisoaporphines either generated by a thermal reaction or generated radiolytically in argon-saturated 1,2-dichloroethane, oxygen-saturated acetone, and acetonitrile. The radical cations of oxoisoaporphines are insensitive to oxygen and are mostly characterized by absorption maxima of their most intense bands located at λmax = 400-410 nm, except of the radical cations derived from 2,3-dihydrooxoisoaporphines. For the latter compounds, the absorption maxima of the most intense absorption bands are located at λmax = 290-295 nm. Their locations are independent of the presence of functional groups and the solvents used. They are formed in bimolecular processes with pseudo-first-order rate constants ranging from 2.1 × 10(5) to 1.5 × 10(6) s(-1) (in solutions containing 10(-4) M of the substrate), depending on the derivative and the solvent used. They are stable either when formed via the electron-transfer reaction with TCNE or when generated in isolation in pulse radiolysis of Ar-saturated 1,2-dichloroethane. In acetone and acetonitrile they decay predominantly by first-order kinetics with the first-order rate constants ranging from 2.3 × 10(4) to 5.1 × 10(4) s(-1). Formation of dimeric radical cations for all of the oxoisoaporphines studied was observed in acetonitrile solutions, and for azaoxoisoaporphines also in acetone solutions. The experimental spectra show a reasonably good agreement with the ZINDO/S semiempirical

  1. Structural evolution and solvation of the OH radical in ionized water radical cations (H2O)n(+), n = 5-8.

    PubMed

    Lu, En-Ping; Pan, Piin-Ruey; Li, Ying-Cheng; Tsai, Ming-Kang; Kuo, Jer-Lai

    2014-09-21

    Structural evolution of ionized water radical cations (H2O)n(+), n = 5-8, is studied by ab intio methods. A structure searching method based on the previous understanding of the hydrogen bond (H-bond) network in neutral and protonated water clusters is found to be effective, covering a wide range of structural isomers of (H2O)n(+). With these local minima, we can analyze both the size and temperature dependence of the structure of (H2O)n(+) and solvation of the OH radical. Agreement between our calculated IR spectra and experimental data in the free OH stretching region confirms that the OH radical preferred to stay on the terminal site of the H-bond network at n = 5 and n = 6. Furthermore, we found that the OH radical began to form H-bonds with water molecules as a H-bond donor at n = 7 and 8. Vibrational signatures of fully solvated OH were found to be located at 3200-3400 cm(-1) coinciding with the additional peaks found in previous experimental data obtained by Mizuse and Fujii.

  2. Characterization of a solvent-separated ion-radical pair in cationized water networks: infrared photodissociation and Ar-attachment experiments for water cluster radical cations (H2O)n+(n = 3-8).

    PubMed

    Mizuse, Kenta; Fujii, Asuka

    2013-02-07

    We present infrared spectra of nominal water cluster radical cations (H(2)O)(n)(+) (n = 3-8), or to be precise, ion-radical complexes H(+)(H(2)O)(n-1)(OH), with and without an Ar tag. These clusters are closely related to the ionizing radiation-induced processes in water and are a good model to characterize solvation structures of the ion-radical pair. The spectra of Ar-tagged species show narrower bandwidths relative to those of the bare clusters due to the reduced internal energy via an Ar-attachment. The observed spectra are analyzed by comparing with those of the similar system, H(+)(H(2)O)(n), and calculated ones. We find that the observed spectra are attributable to ion-radical-separated motifs in n ≥ 5, as reported in the previous study (Mizuse et al. Chem. Sci.2011, 2, 868-876). Beyond the structural trends found in the previous study, we characterize isomeric structures and determine the number of water molecules between the charged site and the OH radical in each cluster size. In all of the characterized cluster structures (n = 5-8), the most favorable position of OH radical is the next neighbor of the charged site (H(3)O(+) or H(5)O(2)(+)). The positions and cluster structures are governed by the balance among the hydrogen-bonding abilities of the charged site, H(2)O, and OH radical. These findings on the ionized water networks lead to understanding of the detailed processes of ionizing radiation-initiated reactions in liquid water and aqueous solutions.

  3. Fragmentation of peptide radical cations containing a tyrosine or tryptophan residue: structural features that favor formation of [x(n-1) + H]˙⁺ and [z(n-1) + H]˙⁺ ions.

    PubMed

    Mädler, Stefanie; Lau, Justin Kai-Chi; Williams, Declan; Wang, Yating; Saminathan, Irine S; Zhao, Junfang; Siu, K W Michael; Hopkinson, Alan C

    2014-06-12

    Peptide radical cations A(n)Y(•+) (where n = 3, 4, or 5) and A5W(•+) have been generated by collision-induced dissociation (CID) of [Cu(II)(tpy)(peptide)](•2+) complexes. Apart from the charge-driven fragmentation at the N-Cα bond of the hetero residue producing either [c + 2H](+) or [z - H](•+) ions and radical-driven fragmentation at the Cα-C bond to give a(+) ions, unusual product ions [x + H](•+) and [z + H](•+) are abundant in the CID spectra of the peptides with the hetero residue in the second or third position of the chain. The formation of these ions requires that both the charge and radical be located on the peptide backbone. Energy-resolved spectra established that the [z + H](•+) ion can be produced either directly from the peptide radical cation or via the fragment ion [x + H](•+). Additionally, backbone dissociation by loss of the C-terminal amino acid giving [b(n-1) - H](•+) increases in abundance with the length of the peptides. Mechanisms by which peptide radical cations dissociate have been modeled using density functional theory (B3LYP/6-31++G** level) on tetrapeptides AYAG(•+), AAYG(•+), and AWAG(•+).

  4. Chemical kinetic behavior of chlorogenic acid in protecting erythrocyte and DNA against radical-induced oxidation.

    PubMed

    Tang, You-Zhi; Liu, Zai-Qun

    2008-11-26

    As an abundant ingredient in coffee, chlorogenic acid (CGA) is a well-known antioxidant. Although some works have dealt with its radical-scavenging property, the present work investigated the protective effects of CGA on the oxidation of DNA and on the hemolysis of human erythrocytes induced by 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH) by means of chemical kinetics. The inhibition period (t(inh)) derived from the protective effect of CGA on erythrocyte and DNA was proportional to its concentration, t(inh) = (n/R(i))[CGA], where R(i) refers to the radical-initiation rate, and n indicates the number of radical-propagation chains terminated by CGA. It was found that the n of CGA to protect erythrocytes was 0.77, lower than that of vitamin E (2.0), but higher than that of vitamin C (0.19). Furthermore, CGA facilitated a mutual protective effect with VE and VC on AAPH-induced hemolysis by increasing n of VE and VC. CGA was also found to be a membrane-stabilizer to protect erythrocytes against hemin-induced hemolysis. Moreover, the n of CGA was only 0.41 in the process of protecting DNA. This fact revealed that CGA served as an efficient antioxidant to protect erythrocytes more than to protect DNA. Finally, the reaction between CGA and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) radical cation (ABTS(+*)) or 2,2'-diphenyl-1-picrylhydrazyl (DPPH) revealed that CGA was able to trap radicals by reducing radicals more than by donating its hydrogen atoms to radicals.

  5. Quantum Chemical Benchmarking, Validation, and Prediction of Acidity Constants for Substituted Pyridinium Ions and Pyridinyl Radicals.

    PubMed

    Keith, John A; Carter, Emily A

    2012-09-11

    Sensibly modeling (photo)electrocatalytic reactions involving proton and electron transfer with computational quantum chemistry requires accurate descriptions of protonated, deprotonated, and radical species in solution. Procedures to do this are generally nontrivial, especially in cases that involve radical anions that are unstable in the gas phase. Recently, pyridinium and the corresponding reduced neutral radical have been postulated as key catalysts in the reduction of CO2 to methanol. To assess practical methodologies to describe the acid/base chemistry of these species, we employed density functional theory (DFT) in tandem with implicit solvation models to calculate acidity constants for 22 substituted pyridinium cations and their corresponding pyridinyl radicals in water solvent. We first benchmarked our calculations against experimental pyridinium deprotonation energies in both gas and aqueous phases. DFT with hybrid exchange-correlation functionals provide chemical accuracy for gas-phase data and allow absolute prediction of experimental pKas with unsigned errors under 1 pKa unit. The accuracy of this economical pKa calculation approach was further verified by benchmarking against highly accurate (but very expensive) CCSD(T)-F12 calculations. We compare the relative importance and sensitivity of these energies to selection of solvation model, solvation energy definitions, implicit solvation cavity definition, basis sets, electron densities, model geometries, and mixed implicit/explicit models. After determining the most accurate model to reproduce experimentally-known pKas from first principles, we apply the same approach to predict pKas for radical pyridinyl species that have been proposed relevant under electrochemical conditions. This work provides considerable insight into the pitfalls using continuum solvation models, particularly when used for radical species.

  6. The cyclopropene radical cation: Rovibrational level structure at low energies from high-resolution photoelectron spectra

    SciTech Connect

    Vasilatou, K.; Michaud, J. M.; Baykusheva, D.; Grassi, G.; Merkt, F.

    2014-08-14

    The cyclopropene radical cation (c-C{sub 3}H{sub 4}{sup +}) is an important but poorly characterized three-membered-ring hydrocarbon. We report on a measurement of the high-resolution photoelectron and photoionization spectra of cyclopropene and several deuterated isotopomers, from which we have determined the rovibrational energy level structure of the X{sup ~+} {sup 2}B{sub 2} ground electronic state of c-C{sub 3}H{sub 4}{sup +} at low energies for the first time. The synthesis of the partially deuterated isotopomers always resulted in mixtures of several isotopomers, differing in their number of D atoms and in the location of these atoms, so that the photoelectron spectra of deuterated samples are superpositions of the spectra of several isotopomers. The rotationally resolved spectra indicate a C{sub 2v}-symmetric R{sub 0} structure for the ground electronic state of c-C{sub 3}H{sub 4}{sup +}. Two vibrational modes of c-C{sub 3}H{sub 4}{sup +} are found to have vibrational wave numbers below 300 cm{sup −1}, which is surprising for such a small cyclic hydrocarbon. The analysis of the isotopic shifts of the vibrational levels enabled the assignment of the lowest-frequency mode (fundamental wave number of ≈110 cm{sup −1} in c-C{sub 3}H{sub 4}{sup +}) to the CH{sub 2} torsional mode (ν{sub 8}{sup +}, A{sub 2} symmetry) and of the second-lowest-frequency mode (≈210 cm{sup −1} in c-C{sub 3}H{sub 4}{sup +}) to a mode combining a CH out-of-plane with a CH{sub 2} rocking motion (ν{sub 15}{sup +}, B{sub 2} symmetry). The potential energy along the CH{sub 2} torsional coordinate is flat near the equilibrium structure and leads to a pronounced anharmonicity.

  7. Optical spectra of protected diamine 10-bond-bridged intervalence radical cations related to N,N,N'N'-tetraalkylbenzidine.

    PubMed

    Nelsen, Stephen F; Luo, Yun; Weaver, Michael N; Lockard, Jenny V; Zink, Jeffrey I

    2006-05-26

    The optical absorption spectra of the delocalized intervalence radical cations of seven o,o'-linked benzidine derivatives that have the nitrogens protected as 9-(9-aza-bicyclo[3.3.1]nonan-3-one) derivatives are discussed and compared with that of the p-phenylene radical cation. The linking units are CH2, CH2CH2, NMe, S, SO2, and C=O, and we also studied H,H (the unlinked benzidine). The lowest-energy absorption band is assigned as the transition from the antibonding combination of symmetrical N and aromatic orbitals to the antibonding combination of the antisymmetric N and aromatic orbitals using TD-DFT calculations, and a good correlation between the observed transition energies and those calculated using the simple Koopmans theorem-based "neutral in-cation geometry" calculations on the UB3LYP/6-31G* structures is found. The use of the two-state model that equates the electronic interaction through the bridge between the amino groups with half of the lowest transition energy is seriously incorrect for these and other delocalized intervalence compounds. The problem of extracting the electronic interactions that actually are involved from calculated transition energies is discussed.

  8. Generation of hydroxyl radicals from metal-loaded humic acids

    SciTech Connect

    Paciolla, M.D.; Jansen, S.A.; Davies, G.

    1999-06-01

    Humic acids (HAs) are naturally occurring biopolymers that are ubiquitous in the environment. They are most commonly found in the soil, drinking water, and a variety of plants. Pharmacological and therapeutic studies involving humic acids have been reported to some extent. However, when certain transition metals are bound to humic acids, e.g., iron and copper, they can be harmful to biological organisms. For this study, humic acids were extracted from German, Irish, and New Hampshire soils that were selectively chosen because of their reich abundance in humic material. Each sample was treated at room temperature with 0.1 M ferric and cupric solutions for 48 h. The amount of iron and copper adsorbed by humic acid was accurately quantitated using atomic absorption spectroscopy. The authors further demonstrate that these metal-loaded humic acids can produce deleterious oxidizing species such as the hydroxyl radical (HO*) through the metal-driven Fenton reaction. Electron paramagnetic resonance (EPR) employing spin trapping techniques with 5,5-dimethylpyrroline N-oxide (DMPO) is used to confirm the generation of hydroxyl radicals. The DMPO-OH adduct with hyperfine splitting constants A{sub N} = A{sub H} = 14.9 G is observed upon the addition of exogenous hydrogen peroxide. The concentration of hydroxyl radical was determined using 4-hydroxytempo (TEMPO-OH) as a spin standard. The presence of another oxidizing species, Fe{double_bond}O{sup 2+}, is also proposed in the absence of hydrogen peroxide.

  9. The loss of NH2O from the N-hydroxyacetamide radical cation CH3C(O)NHOH+

    NASA Astrophysics Data System (ADS)

    Jobst, Karl J.; Burgers, Peter C.; Ruttink, Paul J. A.; Terlouw, Johan K.

    2006-08-01

    A previous study [Ch. Lifshitz, P.J.A. Ruttink, G. Schaftenaar, J.K. Terlouw, Rapid Commun. Mass Spectrom. 1 (1987) 61] shows that metastable N-hydroxyacetamide ions CH3C(O)NHOH+ (HA-1) do not dissociate into CH3CO+ + NHOH by direct bond cleavage but rather yield CH3CO+ + NH2OE The tandem mass spectrometry based experiments of the present study on the isotopologue CH3C(O)NDOD+ reveal that the majority of the metastable ions lose the NH2O radical as NHDO rather than ND2O. A mechanistic analysis using the CBS-QB3 model chemistry shows that the molecular ions HA-1 rearrange into hydrogen-bridged radical cations [OCC(H2)H...N(H)OH]+ whose acetyl cation component then catalyses the transformation NHOH --> NH2O prior to dissociation. The high barrier for the unassisted 1,2-H shift in the free radical, 43 kcal mol-1, is reduced to a mere 7 kcal mol-1 for the catalysed transformation which can be viewed as a quid-pro-quo reaction involving two proton transfers.

  10. Solution-phase mechanistic study and solid-state structure of a tris(bipyridinium radical cation) inclusion complex.

    PubMed

    Fahrenbach, Albert C; Barnes, Jonathan C; Lanfranchi, Don Antoine; Li, Hao; Coskun, Ali; Gassensmith, Jeremiah J; Liu, Zhichang; Benítez, Diego; Trabolsi, Ali; Goddard, William A; Elhabiri, Mourad; Stoddart, J Fraser

    2012-02-15

    The ability of the diradical dicationic cyclobis(paraquat-p-phenylene) (CBPQT(2(•+))) ring to form inclusion complexes with 1,1'-dialkyl-4,4'-bipyridinium radical cationic (BIPY(•+)) guests has been investigated mechanistically and quantitatively. Two BIPY(•+) radical cations, methyl viologen (MV(•+)) and a dibutynyl derivative (V(•+)), were investigated as guests for the CBPQT(2(•+)) ring. Both guests form trisradical complexes, namely, CBPQT(2(•+))⊂MV(•+) and CBPQT(2(•+))⊂V(•+), respectively. The structural details of the CBPQT(2(•+))⊂MV(•+) complex, which were ascertained by single-crystal X-ray crystallography, reveal that MV(•+) is located inside the cavity of the ring in a centrosymmetric fashion: the 1:1 complexes pack in continuous radical cation stacks. A similar solid-state packing was observed in the case of CBPQT(2(•+)) by itself. Quantum mechanical calculations agree well with the superstructure revealed by X-ray crystallography for CBPQT(2(•+))⊂MV(•+) and further suggest an electronic asymmetry in the SOMO caused by radical-pairing interactions. The electronic asymmetry is maintained in solution. The thermodynamic stability of the CBPQT(2(•+))⊂MV(•+) complex was probed by both isothermal titration calorimetry (ITC) and UV/vis spectroscopy, leading to binding constants of (5.0 ± 0.6) × 10(4) M(-1) and (7.9 ± 5.5) × 10(4) M(-1), respectively. The kinetics of association and dissociation were determined by stopped-flow spectroscopy, yielding a k(f) and k(b) of (2.1 ± 0.3) × 10(6) M(-1) s(-1) and 250 ± 50 s(-1), respectively. The electrochemical mechanistic details were studied by variable scan rate cyclic voltammetry (CV), and the experimental data were compared digitally with simulated data, modeled on the proposed mechanism using the thermodynamic and kinetic parameters obtained from ITC, UV/vis, and stopped-flow spectroscopy. In particular, the electrochemical mechanism of association

  11. β-carotene radical cation addition to green tea polyphenols. Mechanism of antioxidant antagonism in peroxidizing liposomes.

    PubMed

    Song, Lin-Lin; Liang, Ran; Li, Dan-Dan; Xing, Ya-Dong; Han, Rui-Min; Zhang, Jian-Ping; Skibsted, Leif H

    2011-12-14

    Green tea polyphenols, (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), and (-)-epigallocatechin gallate (EGCG), all showed antioxidative effect in liposomes for lipid oxidation initiated in the lipid phase (antioxidant efficiency EC > EGCG > ECG > EGC) or in the aqueous phase (EC ≫ EGC > EGCG > ECG) as monitored by the formation of conjugated dienes. For initiation in the lipid phase, β-carotene, itself active as an antioxidant, showed antagonism with the polyphenols (EC > ECG > EGCG > EGC). The Trolox equivalent antioxidant capacity (TEAC EGC > EGCG > ECG > EC) correlates with the lowest phenol O-H bond dissociation enthalpy (BDE) as calculated by density functional theory (DFT). Surface-enhanced Raman spectroscopy (SERS) was used to assess the reducing power of the phenolic hydroxyls in corroboration with DFT calculations. For homogeneous (1:9 v/v methanol/chloroform) solution, the β-carotene radical cation reacted readily with each of the polyphenol monoanions (but not with the neutral polyphenols) with a rate approaching the diffusion limit for EC as studied by laser flash photolysis at 25 °C monitoring the radical cation at 950 nm. The rate constant did not correlate with polyphenol HOMO/LUMO energy gap (DFT calculations), and β-carotene was not regenerated by an electron transfer reaction (monitored at 500 nm). It is suggested that the β-carotene radical cation is rather reacting with the tea polyphenols through addition, as further evidenced by steady-state absorption spectroscopy and liquid chromatography-mass spectroscopy (LC-MS), in effect preventing regeneration of β-carotene as an active lipid phase antioxidant and leading to the observed antagonism.

  12. Determination of peroxy radical-scavenging of lactic acid bacteria.

    PubMed

    Stecchini, M L; Del Torre, M; Munari, M

    2001-02-28

    Responses of lactic acid bacteria (LAB) to peroxy radicals generated via thermal (40 degrees C) decomposition of the diazocompound 2,2,-azo-bis (2-amidinopropane) dihydrochloride (ABAP), were studied. In general, LAB displayed survival curves with shoulders and tails indicative of 'multihit' killing by exposure to peroxy radicals. One strain, Lactococcus lactis subsp. lactis DIP15, producing a slope of 0.0105 in the kinetic analysis when exposed to 4 mM ABAP, exhibited a measurable antioxidant capacity. The other LAB failed to show any significant antioxidant capacity. The antioxidant capacity of strain DIP15 remained constant after cells have been heat-treated, suggesting that compounds bearing free radical scavenging capacity are rather stable.

  13. Heterogeneous Reaction of HO2 Radical with Dicarboxylic Acid Particles

    NASA Astrophysics Data System (ADS)

    Taketani, F.; Kanaya, Y.

    2010-12-01

    HOx(OH+ HO2) radical plays a central role in the tropospheric chemistry. Recently, the heterogeneous loss of HO2 by aerosol particles is a potentially important HOx sink in the troposphere suggested from observation study. However, there have been few studies for loss of HO2 by aerosols. In this study, we measured the HO2 uptake coefficients for four dicarboxylic acids (succinic acid, glutaric acid, adipic acid, and pimelic acid) aerosol particles under ambient conditions (760Torr and 296K) using an aerosol flow tube(AFT) coupled with a chemical conversion /laser-induced fluorescence(CC/LIF) technique. The CC/LIF technique enabled experiments to be performed at almost the same HO2 radical concentration as that in the atmosphere(-10^8 molecules/cm^3). In this system, the effect of the self-reaction of HO2 in the gas phase can be neglected. HO2 radicals were injected into the AFT through a vertically movable Pyrex tube. Injector position dependent profiles of LIF intensity were measured as a function of aerosol concentration at 30% and 70% of relative humilities (RH). Determined HO2 uptake coefficients by succinic acid, glutaric acid, adipic acid, and pimelic acid aerosol particles at 30% RH were 0.05 +/- 0.02, 0.07 +/- 0.03, 0.02 +/- 0.01, and 0.06 +/- 0.03, respectively, while the uptake coefficients by those particles at 70% RH were 0.13 +/- 0.05, 0.13 +/- 0.03, 0.06 +/- 0.01, and 0.11 +/- 0.03, respectively. These results suggest that compositions and relative humidity are significant to the HO2 uptake. We will discuss the potential HO2 loss processes.

  14. Liquid Crystalline Polymers by Cationic Polymerization,

    DTIC Science & Technology

    1986-01-01

    cation mechanism of Scholl reaction the Lewis acid and by the benzylic carbocations . Hydride transfer to benzylic carbenium ions leads to methyl groups...reviewed. Examples from ring-opening, carbocationic , and radical-cation poly- merizations and oligomerizations are discussed. Accesion For DrIC TAB3...Examples from ring- opening, carbocationic , and radical-cation polymeri- zations and oligomerizations are discussed. INTRODUCTION This paper will

  15. Photo-excitation of adenine cation radical [A•+] in the near UV-vis region produces sugar radicals in Adenosine and in its nucleotides

    PubMed Central

    Adhikary, Amitava; Khanduri, Deepti; Kumar, Anil; Sevilla, Michael D.

    2011-01-01

    In this study, we report the formation of ribose sugar radicals in high yields (85 – 100%) via photo-excitation of adenine cation radical (A•+) in Ado and its ribonucleotides. Photo-excitation of A•+ at low temperatures in homogenous aqueous glassy samples of Ado, 2′-AMP, 3′-AMP and 5′-AMP forms sugar radicals predominantly at C5′- and also at C3′-sites. The C5′• and C3′• sugar radicals were identified employing Ado deuterated at specific carbon sites: C1′, C2′, and at C5′. Phosphate substitution is found to deactivate sugar radical formation at the site of substitution. Thus, in 5′-AMP, C3′• is observed to be the main radical formed via photo-excitation at ca. 143 K whereas in 3′-AMP, C5′• is the only species found. These results were supported by results obtained employing 5′-AMP with specific deuteration at C5′-site (i.e., 5′,5′-D,D-5′-AMP). Moreover, contrary to the C5′• observed in 3′-dAMP, we find that C5′• in 3′-AMP shows a clear pH dependent conformational change as evidenced by a large increase in the C4′ β–hyperfine coupling on increasing the pH from 6 to 9. Calculations performed employing DFT (B3LYP/6-31G*) for C5′• in 3′-AMP show that the two conformations of C5′• result from strong hydrogen bond formation between the O5′-H and the 3′-phosphate dianion at higher pHs. Employing time-dependent density functional theory [TD-DFT, B3LYP/6-31G(d)] we show that in the excited state, the hole transfers to the sugar moiety and has significant hole localization at the C5′-site in a number of allowed transitions. This hole localization is proposed to lead to the formation of the neutral C5′-radical (C5′•) via deprotonation. PMID:19367991

  16. Organic conductors and superconductors based on bis(ethylenedithio)tetrathiafulvalene radical cation salts with supramolecular tris(oxalato)metallate anions

    NASA Astrophysics Data System (ADS)

    Prokhorova, T. G.; Yagubskii, E. B.

    2017-02-01

    The results of studies of a family of conductors and superconductors based on bis(ethylenedithio)tetrathiafulvalene radical cation salts with paramagnetic and diamagnetic supramolecular tris(oxalato)metallate anions are collated and analyzed. Methods for the preparation of these salts and various types of packing of conducting layers within the salt structures are considered. The transport properties of crystals of the salts of this family and the effect of guest solvent molecules on these properties are discussed. The contribution of scientists from the Institute of Problems of Chemical Physics, RAS, to the research into organic conductors and superconductors is noted. The bibliography includes 70 references.

  17. Key Role of End-Capping Groups in Optoelectronic Properties of Poly-p-phenylene Cation Radicals

    PubMed Central

    2015-01-01

    Poly-p-phenylenes (PPs) are prototype systems for understanding the charge transport in π-conjugated polymers. In a combined computational and experimental study, we demonstrate that the smooth evolution of redox and optoelectronic properties of PP cation radicals toward the polymeric limit can be significantly altered by electron-donating iso-alkyl and iso-alkoxy end-capping groups. A multiparabolic model (MPM) developed and validated here rationalizes this unexpected effect by interplay of the two modes of hole stabilization: due to the framework of equivalent p-phenylene units and due to the electron-donating end-capping groups. A symmetric, bell-shaped hole in unsubstituted PPs becomes either slightly skewed and shifted toward an end of the molecule in iso-alkyl-capped PPs or highly deformed and concentrated on a terminal unit in PPs with strongly electron-donating iso-alkoxy capping groups. The MPM shows that the observed linear 1/n evolution of the PP cation radical properties toward the polymer limit originates from the hole stabilization due to the growing chain of p-phenylene units, while shifting of the hole toward electron-donating end-capping groups leads to early breakdown of these 1/n dependencies. These insights, along with the readily applicable and flexible multistate parabolic model, can guide studies of complex donor–spacer–acceptor systems and doped molecular wires to aid the design of the next generation materials for long-range charge transport and photovoltaic applications. PMID:25264475

  18. Unconventional hydrogen bonding to organic ions in the gas phase: Stepwise association of hydrogen cyanide with the pyridine and pyrimidine radical cations and protonated pyridine

    SciTech Connect

    Hamid, Ahmed M.; El-Shall, M. Samy; Hilal, Rifaat; Elroby, Shaaban; Aziz, Saadullah G.

    2014-08-07

    Equilibrium thermochemical measurements using the ion mobility drift cell technique have been utilized to investigate the binding energies and entropy changes for the stepwise association of HCN molecules with the pyridine and pyrimidine radical cations forming the C{sub 5}H{sub 5}N{sup +·}(HCN){sub n} and C{sub 4}H{sub 4}N{sub 2}{sup +·}(HCN){sub n} clusters, respectively, with n = 1–4. For comparison, the binding of 1–4 HCN molecules to the protonated pyridine C{sub 5}H{sub 5}NH{sup +}(HCN){sub n} has also been investigated. The binding energies of HCN to the pyridine and pyrimidine radical cations are nearly equal (11.4 and 12.0 kcal/mol, respectively) but weaker than the HCN binding to the protonated pyridine (14.0 kcal/mol). The pyridine and pyrimidine radical cations form unconventional carbon-based ionic hydrogen bonds with HCN (CH{sup δ+}⋯NCH). Protonated pyridine forms a stronger ionic hydrogen bond with HCN (NH{sup +}⋯NCH) which can be extended to a linear chain with the clustering of additional HCN molecules (NH{sup +}⋯NCH··NCH⋯NCH) leading to a rapid decrease in the bond strength as the length of the chain increases. The lowest energy structures of the pyridine and pyrimidine radical cation clusters containing 3-4 HCN molecules show a strong tendency for the internal solvation of the radical cation by the HCN molecules where bifurcated structures involving multiple hydrogen bonding sites with the ring hydrogen atoms are formed. The unconventional H-bonds (CH{sup δ+}⋯NCH) formed between the pyridine or the pyrimidine radical cations and HCN molecules (11–12 kcal/mol) are stronger than the similar (CH{sup δ+}⋯NCH) bonds formed between the benzene radical cation and HCN molecules (9 kcal/mol) indicating that the CH{sup δ+} centers in the pyridine and pyrimidine radical cations have more effective charges than in the benzene radical cation.

  19. Unexpectedly high indoor hydroxyl radical concentrations associated with nitrous acid.

    PubMed

    Gómez Alvarez, Elena; Amedro, Damien; Afif, Charbel; Gligorovski, Sasho; Schoemaecker, Coralie; Schoemacker, Coralie; Fittschen, Christa; Doussin, Jean-Francois; Wortham, Henri

    2013-08-13

    The hydroxyl (OH) radical is the most important oxidant in the atmosphere since it controls its self-oxidizing capacity. The main sources of OH radicals are the photolysis of ozone and the photolysis of nitrous acid (HONO). Due to the attenuation of solar radiation in the indoor environment, the possibility of OH formation through photolytic pathways indoors has been ignored up to now. In the indoor air, the ozonolysis of alkenes has been suggested as an alternative route of OH formation. Models and indirect measurements performed up to now according to this hypothesis suggest concentrations of OH radicals on the order of 10(4)-10(5) molecules per cubic centimeter. Here, we present direct measurements of significant amounts of OH radicals of up to 1.8⋅10(6) molecules per cubic centimeter during an experimental campaign carried out in a school classroom in Marseille. This concentration is on the same order of magnitude of outdoor OH levels in the urban scenario. We also show that photolysis of HONO is an important source of OH radicals indoors under certain conditions (i.e., direct solar irradiation inside the room). Additionally, the OH concentrations were found to follow a linear dependence with the product J(HONO)⋅[HONO]. This was also supported by using a simple quasiphotostationary state model on the OH radical budget. These findings force a change in our understanding of indoor air quality because the reactivity linked to OH would involve formation of secondary species through chemical reactions that are potentially more hazardous than the primary pollutants in the indoor air.

  20. Unexpectedly high indoor hydroxyl radical concentrations associated with nitrous acid

    PubMed Central

    Gómez Alvarez, Elena; Amedro, Damien; Afif, Charbel; Gligorovski, Sasho; Schoemaecker, Coralie; Fittschen, Christa; Doussin, Jean-Francois; Wortham, Henri

    2013-01-01

    The hydroxyl (OH) radical is the most important oxidant in the atmosphere since it controls its self-oxidizing capacity. The main sources of OH radicals are the photolysis of ozone and the photolysis of nitrous acid (HONO). Due to the attenuation of solar radiation in the indoor environment, the possibility of OH formation through photolytic pathways indoors has been ignored up to now. In the indoor air, the ozonolysis of alkenes has been suggested as an alternative route of OH formation. Models and indirect measurements performed up to now according to this hypothesis suggest concentrations of OH radicals on the order of 104–105 molecules per cubic centimeter. Here, we present direct measurements of significant amounts of OH radicals of up to 1.8⋅106 molecules per cubic centimeter during an experimental campaign carried out in a school classroom in Marseille. This concentration is on the same order of magnitude of outdoor OH levels in the urban scenario. We also show that photolysis of HONO is an important source of OH radicals indoors under certain conditions (i.e., direct solar irradiation inside the room). Additionally, the OH concentrations were found to follow a linear dependence with the product J(HONO)⋅[HONO]. This was also supported by using a simple quasiphotostationary state model on the OH radical budget. These findings force a change in our understanding of indoor air quality because the reactivity linked to OH would involve formation of secondary species through chemical reactions that are potentially more hazardous than the primary pollutants in the indoor air. PMID:23898188

  1. Vacancy ion-exclusion chromatography of haloacetic acids on a weakly acidic cation-exchange resin.

    PubMed

    Helaleh, Murad I H; Tanaka, Kazuhiko; Mori, Masanobu; Xu, Qun; Taoda, Hiroshi; Ding, Ming-Yu; Hu, Wenzhi; Hasebe, Kiyoshi; Haddad, Paul R

    2003-05-16

    A new and simple approach is described for the determination of the haloacetic acids (such as mono-, di- and trichloroacetic acids) usually found in drinking water as chlorination by-products after disinfection processes and acetic acid. The new approach, termed vacancy ion-exclusion chromatography, is based on an ion-exclusion mechanism but using the sample solution as the mobile phase, pure water as the injected sample, and a weakly acidic cation-exchange resin column (TSKgel OApak-A) as the stationary phase. The addition of sulfuric acid to the mobile phase results in highly sensitive conductivity detection with sharp and well-shaped peaks, leading to excellent and efficient separations. The elution order was sulfuric acid, dichloroacetic acid, monochloroacetic acid, trichloroacetic acid, and acetic acid. The separation of these acids depends on their pKa values. Acids with lower pKa values were eluted earlier than those with higher pKa, except for trichloroacetic acid due to a hydrophobic-adsorption effect occurring as a side-effect of vacancy ion-exclusion chromatography. The detection limits of these acids in the present study with conductivity detection were 3.4 microM for monochloroacetic acid, 0.86 microM for dichloroacetic acid and 0.15 microM for trichloroacetic acid.

  2. 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.

  3. Activation of Methane by the Pyridine Radical Cation and its Substituted Forms in the Gas Phase

    NASA Astrophysics Data System (ADS)

    Wu, Guohua; Stewart, Hamish; Liu, Zeyu; Wang, Yongcheng; Stace, Anthony J.

    2015-08-01

    We present an experimental study of methane activation by pyridine cation and its substituents in the gas phase. Mass spectrometric experiments in an ion trap demonstrate that pyridine cation and some of its substituent cations are able to react with methane. The deuterated methane experiment has confirmed that the hydrogen atom in the ionic product of reaction does come from methane. The collected information about kinetic isotope effects has been used to distinguish the nature of the bond activation as a hydrogen abstraction. Furthermore, experimental results demonstrated that the substituent groups on the pyridine ring can crucially influence their reactivity in methane bond activation processes. Density functional calculation (DFT) was employed to study the electronic structures of the complex and reaction mechanism of CH4+C5H5N+. The calculations confirmed the hypothesis from the experimental observation, namely, the reaction is rapid with no energy barrier.

  4. Mechanistic examination of Cβ-Cγ bond cleavages of tryptophan residues during dissociations of molecular peptide radical cations.

    PubMed

    Song, Tao; Ma, Ching-Yung; Chu, Ivan K; Siu, Chi-Kit; Laskin, Julia

    2013-02-14

    In this study, we used collision-induced dissociation (CID) to examine the gas-phase fragmentations of [G(n)W](•+) (n = 2-4) and [GXW](•+) (X = C, S, L, F, Y, Q) species. The C(β)-C(γ) bond cleavage of a C-terminal decarboxylated tryptophan residue ([M - CO(2)](•+)) can generate [M - CO(2) - 116](+), [M - CO(2) - 117](•+), and [1H-indole](•+) (m/z 117) species as possible product ions. Competition between the formation of [M - CO(2) - 116](+) and [1H-indole](•+) systems implies the existence of a proton-bound dimer formed between the indole ring and peptide backbone. Formation of such a proton-bound dimer is facile via a protonation of the tryptophan γ-carbon atom as suggested by density functional theory (DFT) calculations. DFT calculations also suggested the initially formed ion 2, the decarboxylated species that is active against C(β)-C(γ) bond cleavage, can efficiently isomerize to form a more stable π-radical isomer (ion 9) as supported by Rice-Ramsperger-Kassel-Marcus (RRKM) modeling. The C(β)-C(γ) bond cleavage of a tryptophan residue also can occur directly from peptide radical cations containing a basic residue. CID of [WG(n)R](•+) (n = 1-3) radical cations consistently resulted in predominant formation of [M - 116](+) product ions. It appears that the basic arginine residue tightly sequesters the proton and allows the charge-remote C(β)-C(γ) bond cleavage to prevail over the charge-directed one. DFT calculations predicted that the barrier for the former is 6.2 kcal mol(-1) lower than that of the latter. Furthermore, the pathway involving a salt-bridge intermediate also was accessible during such a bond cleavage event.

  5. Mechanistic Examination of Cβ–Cγ Bond Cleavages of Tryptophan Residues during Dissociations of Molecular Peptide Radical Cations

    SciTech Connect

    Song, Tao; Ma, Ching-Yung; Chu, Ivan K.; Siu, Chi-Kit; Laskin, Julia

    2013-02-14

    In this study, we used collision-induced dissociation (CID) to examine the gas-phase fragmentations of [GnW]•+ (n = 2-4) and [GXW]•+ (X = C, S, L, F, Y, Q) species. The Cβ–Cγ bond cleavage of a C-terminal decarboxylated tryptophan residue ([M - CO2]•+) can generate [M - CO2 - 116]+, [M - CO2 - 117]•+, and [1H-indole]•+ (m/z 117) species as possible product ions. Competition between the formation of [M - CO2 - 116]+ and [1H-indole]•+ systems implies the existence of a proton-bound dimer formed between the indole ring and peptide backbone. Formation of such a proton-bound dimer is facile via a protonation of the tryptophan γ-carbon atom as suggested by density functional theory (DFT) calculations. DFT calculations also suggested the initially formed ion 2--the decarboxylated species that is active against Cβ–Cγ bond cleavage -can efficiently isomerize to form a more-stable -radical isomer (ion 9) as supported by Rice-Ramsperger-Kassel-Marcus (RRKM) modeling. The Cβ–Cγ bond cleavage of a tryptophan residue also can occur directly from peptide radical cations containing a basic residue. CID of [WGnR]•+ (n = 1-3) radical cations consistently resulted in predominant formation of [M-116]+ product ions. It appears that the basic arginine residue tightly sequesters the proton and allows the charge-remote Cβ–Cγ bond cleavage to prevail over the charge-directed one. DFT calculations predicted the barrier for the former is 6.2 kcal mol -1 lower than that of the latter. Furthermore, the pathway involving a salt-bridge intermediate also was accessible during such a bond cleavage event.

  6. Acid-, base-, and lewis-acid-catalyzed heterolysis of methoxide from an alpha-hydroxy-beta-methoxy radical: models for reactions catalyzed by coenzyme B12-dependent diol dehydratase.

    PubMed

    Xu, Libin; Newcomb, Martin

    2005-11-11

    [Reaction: see text].A model for glycol radicals was employed in laser flash photolysis kinetic studies of catalysis of the fragmentation of a methoxy group adjacent to an alpha-hydroxy radical center. Photolysis of a phenylselenylmethylcyclopropane precursor gave a cyclopropylcarbinyl radical that rapidly ring opened to the target alpha-hydroxy-beta-methoxy radical (3). Heterolysis of the methoxy group in 3 gave an enolyl radical (4a) or an enol ether radical cation (4b), depending upon pH. Radicals 4 contain a 2,2-diphenylcyclopropane reporter group, and they rapidly opened to give UV-observable diphenylalkyl radicals as the final products. No heterolysis was observed for radical 3 under neutral conditions. In basic aqueous acetonitrile solutions, specific base catalysis of the heterolysis was observed; the pK(a) of radical 3 was determined to be 12.5 from kinetic titration plots, and the ketyl radical formed by deprotonation of 3 eliminated methoxide with a rate constant of 5 x 10(7) s(-1). In the presence of carboxylic acids in acetonitrile solutions, radical 3 eliminated methanol in a general acid-catalyzed reaction, and rate constants for protonation of the methoxy group in 3 by several acids were measured. Radical 3 also reacted by fragmentation of methoxide in Lewis-acid-catalyzed heterolysis reactions; ZnBr2, Sc(OTf)3, and BF3 were found to be efficient catalysts. Catalytic rate constants for the heterolysis reactions were in the range of 3 x 10(4) to 2 x 10(6) s(-1). The Lewis-acid-catalyzed heterolysis reactions are fast enough for kinetic competence in coenzyme B12 dependent enzyme-catalyzed reactions of glycols, and Lewis-acid-catalyzed cleavages of beta-ethers in radicals might be applied in synthetic reactions.

  7. Serine effects on collision-induced dissociation and photodissociation of peptide cation radicals of the z(+•) -type.

    PubMed

    Nguyen, Huong T H; Shaffer, Christopher J; Ledvina, Aaron R; Coon, Joshua J; Tureček, František

    2015-02-15

    The serine residue displays specific effects on the dissociations of peptide fragment cation-radicals of the z(+•) type which are produced by electron transfer dissociation. Energy-resolved collision-induced dissociation (ER-CID), time-resolved infrared multiphoton dissociation (TR-IRMPD), and single-photon UV photodissociation at 355 nm revealed several competitive dissociation pathways consisting of loss of OH radical, water, and backbone cleavages occurring at N-terminal and C-terminal positions relative to the serine residue. The activation modes using slow-heating and UV photon absorption resulted in different relative intensities of fragment ions. This indicated that the dissociations proceeded through several channels with different energy-dependent kinetics. The experimental data were interpreted with the help of electron structure calculations that provided fully optimized structures and relative energies for cis and trans amide isomers of the z4(+•) ions as well as isomerization, dissociation, and transition state energies. UV photon absorption by the z4(+•) ions was due to Cα-radical amide groups created by ETD that provided a new chromophore absorbing at 355 nm.

  8. Serine effects on collision-induced dissociation and photodissociation of peptide cation radicals of the z+•-type

    PubMed Central

    Nguyen, Huong T. H.; Shaffer, Christopher J.; Ledvina, Aaron R.; Coon, Joshua J.

    2014-01-01

    The serine residue displays specific effects on the dissociations of peptide fragment cation-radicals of the z+• type which are produced by electron transfer dissociation. Energy-resolved collision-induced dissociation (ER-CID), time-resolved infrared multiphoton dissociation (TR-IRMPD), and single-photon UV photodissociation at 355 nm revealed several competitive dissociation pathways consisting of loss of OH radical, water, and backbone cleavages occurring at N-terminal and C-terminal positions relative to the serine residue. The activation modes using slow-heating and UV photon absorption resulted in different relative intensities of fragment ions. This indicated that the dissociations proceeded through several channels with different energy-dependent kinetics. The experimental data were interpreted with the help of electron structure calculations that provided fully optimized structures and relative energies for cis and trans amide isomers of the z4+• ions as well as isomerization, dissociation, and transition state energies. UV photon absorption by the z4+• ions was due to Cα-radical amide groups created by ETD that provided a new chromophore absorbing at 355 nm. PMID:26005367

  9. Theoretical study of electronically excited radical cations of naphthalene and anthracene as archetypal models for astrophysical observations. Part I. Static aspects.

    PubMed

    Ghanta, S; Reddy, V Sivaranjana; Mahapatra, S

    2011-08-28

    Motivated by the recent discovery of new diffuse interstellar bands and results from laboratory experiments, ab initio quantum chemistry calculations are carried out for the lowest six electronic states of naphthalene and anthracene radical cations. The calculated adiabatic electronic energies are utilized to construct suitable diabatic electronic Hamiltonians in order to perform nuclear dynamics studies in Part II. Complex entanglement of the electronic states is established for both the radical cations and the coupling surfaces among them are also derived in accordance with the symmetry selection rules. Critical examination of the coupling parameters of the Hamiltonian suggests that 29 (out of 48) and 31 (out of 66) vibrational modes are relevant in the nuclear dynamics in the six lowest electronic states of naphthalene and anthracene radical cations, respectively.

  10. 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

  11. ENDOR and ESEEM of the 15N labelled radical cations of chlorophyll a and the primary donor P 700 in photosystem I

    NASA Astrophysics Data System (ADS)

    Käβ, H.; Bittersmann-Weidlich, E.; Andréasson, L.-E.; Bönigk, B.; Lubitz, W.

    1995-05-01

    The hyperfine couplings of the nitrogen nuclei in the radical cations of both 15N-labelled chlorophyll a and the primary donor P 700 in Photosystem I of Synechococcus elongatus and spinach ( Spinacea oleracea) in frozen solutions were investigated by ENDOR and, for confirmation, by two-dimensional ESEEM techniques. In addition, 1H ENDOR experiments were performed on these compounds. The experimental 15N hyperfine couplings of the chlorophyll a radical cation are compared with theoretical ones obtained by RHF-INDO/SP calculations and with the respective hyperfine couplings in the closely related 15N-bacteriochlorophyll a radical cation. Based on the observed 15N and 1H hyperfine couplings two possible models are discussed for P 700+: (a) the special pair model with a strongly asymmetric spin density distribution over the dimer halves; (b) the model of a strongly perturbed chlorophyll a monomer.

  12. Structure of radical cations of saturated heterocyclic compounds with two heteroatoms as studied by electron paramagnetic resonance, electron-nuclear double resonance, and density functional theory calculations.

    PubMed

    Nuzhdin, Kirill B; Nesterov, Sergej V; Tyurin, Daniil A; Feldman, Vladimir I; Wei, Liu; Lund, Anders

    2005-07-21

    The radical cations of piperazine, morpholine, thiomorpholine, and thioxane were investigated by electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy in a solid Freon matrix. Optimized geometry and magnetic parameters of the radical cations were calculated using a density functional theory (DFT)/Perdew-Burke-Ernzerhof (PBE) method. Both experimental and theoretical results suggest that all the studied species adopt chair (or distorted chair) conformations. No evidence for the boat conformers with intramolecular sigma-bonding between heteroatoms were obtained. In the cases of morpholine and thioxane, the oxygen atoms are characterized by relatively small spin populations, whereas a major part of spin density is located at N and S atoms, respectively. The thiomorpholine radical cation exhibits nearly equal spin population of N and S atoms. In most cases (except for thioxane), the calculated magnetic parameters agree with the experimental data reasonably well.

  13. Hydration of the pyrimidine radical cation and stepwise solvation of protonated pyrimidine with water, methanol, and acetonitrile

    NASA Astrophysics Data System (ADS)

    Hamid, Ahmed M.; Sharma, Pramod; Samy El-Shall, M.; Hilal, Rifaat; Elroby, Shaaban; Aziz, Saadullah G.; Alyoubi, Abdulrahman O.

    2013-08-01

    Equilibrium thermochemical measurements using an ion mobility drift cell technique have been utilized to investigate the binding energies and entropy changes associated with the stepwise hydration of the biologically significant ions pyrimidine radical cation and protonated pyrimidine. The binding energy of the hydrated pyrimidine radical cation is weaker than that of the proton-bound dimer pyrimidineH+(H2O) consistent with the formation of a weak carbon-based CHδ+..OH2 hydrogen bond (11.9 kcal/mol) and a stronger NH+..OH2 hydrogen bond (15.6 kcal/mol), respectively. Other proton-bound dimers such as pyrimidineH+(CH3OH) and pyrimidineH+(CH3CN) exhibit higher binding energies (18.2 kcal/mol and 22.8 kcal/mol, respectively) due to the higher proton affinities and dipole moments of acetonitrile and methanol as compared to water. The measured collisional cross sections of the proton-bound dimers provide experimental-based support for the DFT calculated structures at the M06-2x/6-311++G (d,p) level. The calculations show that the hydrated pyrimidine radical cation clusters form internally solvated structures in which the water molecules are bonded to the C4N2H4•+ ion by weak CHδ+..OH2 hydrogen bonds. The hydrated protonated pyrimidine clusters form externally solvated structures where the water molecules are bonded to each other and the ion is external to the water cluster. Dissociative proton transfer reactions C4N2H4•+(H2O)n-1 + H2O → C4N2H3• + (H2O)nH+ and C4N2H5+(H2O)n-1 + H2O → C4N2H4 + (H2O)nH+ are observed for n ≥ 4 where the reactions become thermoneutral or exothermic. The absence of the dissociative proton transfer reaction within the C4N2H5+(CH3CN)n clusters results from the inability of acetonitrile molecules to form extended hydrogen bonding structures such as those formed by water and methanol due to the presence of the methyl groups which block the extension of hydrogen bonding networks.

  14. Hydration of the pyrimidine radical cation and stepwise solvation of protonated pyrimidine with water, methanol, and acetonitrile.

    PubMed

    Hamid, Ahmed M; Sharma, Pramod; El-Shall, M Samy; Hilal, Rifaat; Elroby, Shaaban; Aziz, Saadullah G; Alyoubi, Abdulrahman O

    2013-08-28

    Equilibrium thermochemical measurements using an ion mobility drift cell technique have been utilized to investigate the binding energies and entropy changes associated with the stepwise hydration of the biologically significant ions pyrimidine radical cation and protonated pyrimidine. The binding energy of the hydrated pyrimidine radical cation is weaker than that of the proton-bound dimer pyrimidineH(+)(H2O) consistent with the formation of a weak carbon-based CH(δ+)··OH2 hydrogen bond (11.9 kcal/mol) and a stronger NH(+)··OH2 hydrogen bond (15.6 kcal/mol), respectively. Other proton-bound dimers such as pyrimidineH(+)(CH3OH) and pyrimidineH(+)(CH3CN) exhibit higher binding energies (18.2 kcal/mol and 22.8 kcal/mol, respectively) due to the higher proton affinities and dipole moments of acetonitrile and methanol as compared to water. The measured collisional cross sections of the proton-bound dimers provide experimental-based support for the DFT calculated structures at the M06-2x/6-311++G (d,p) level. The calculations show that the hydrated pyrimidine radical cation clusters form internally solvated structures in which the water molecules are bonded to the C4N2H4(●+) ion by weak CH(δ+)··OH2 hydrogen bonds. The hydrated protonated pyrimidine clusters form externally solvated structures where the water molecules are bonded to each other and the ion is external to the water cluster. Dissociative proton transfer reactions C4N2H4(●+)(H2O)(n-1) + H2O → C4N2H3(●) + (H2O)(n)H(+) and C4N2H5(+)(H2O)(n-1) + H2O → C4N2H4 + (H2O)(n)H(+) are observed for n ≥ 4 where the reactions become thermoneutral or exothermic. The absence of the dissociative proton transfer reaction within the C4N2H5(+)(CH3CN)n clusters results from the inability of acetonitrile molecules to form extended hydrogen bonding structures such as those formed by water and methanol due to the presence of the methyl groups which block the extension of hydrogen bonding networks.

  15. Some polyphenols inhibit the formation of pentyl radical and octanoic acid radical in the reaction mixture of linoleic acid hydroperoxide with ferrous ions.

    PubMed Central

    Iwahashi, H

    2000-01-01

    Effects of some polyphenols and their related compounds (chlorogenic acid, caffeic acid, quinic acid, ferulic acid, gallic acid, D-(+)-catechin, D-(-)-catechin, 4-hydroxy-3-methoxybenzoic acid, salicylic acid, L-dopa, dopamine, L-adrenaline, L-noradrenaline, o-dihydroxybenzene, m-dihydroxybenzene, and p-dihydroxybenzene) on the formation of 13-hydroperoxide octadecadienoic (13-HPODE) acid-derived radicals (pentyl radical and octanoic acid radical) were examined. The ESR spin trapping showed that chlorogenic acid, caffeic acid, gallic acid, D-(+)-catechin, D-(-)-catechin, L-dopa, dopamine, L-adrenaline, L-noradrenaline, and o-dihydroxybenzene inhibited the overall formation of 13-HPODE acid-derived radicals in the reaction mixture of 13-HPODE with ferrous ions. The ESR peak heights of alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN)/13-HPODE-derived radical adducts decreased to 46+/-4% (chlorogenic acid), 54+/-2% (caffeic acid), 49+/-2% (gallic acid), 55+/-1% [D-(+)-catechin], 60+/-3% [D-(-)-catechin], 42+/-1% (L-dopa), 30+/-2% (dopamine), 49+/-2% (L-adrenaline), 24+/-2% (L-noradrenaline), and 54+/-5% (o-dihydroxybenzene) of the control, respectively. The high performance liquid chromatography-electron spin resonance (HPLC-ESR) and high performance liquid chromatography-electron spin resonance-mass spectrometries (HPLC-ESR-MS) showed that caffeic acid inhibited the formation of octanoic acid radical and pentyl radical to 42+/-2% and 52+/-7% of the control, respectively. On the other hand, the polyphenols and their related compounds had few inhibitory effects on the radical formation in the presence of EDTA. Visible absorbance measurement revealed that all the polyphenols exhibiting the inhibitory effect chelate ferrous ions. Above results indicated that the chelation of ferrous ion is essential to the inhibitory effects of the polyphenols. PMID:10677343

  16. 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.

  17. A Visible Light Initiating System for Free Radical Promoted Cationic Polymerization

    DTIC Science & Technology

    1994-02-02

    bis-(4, 4’-dimethylaminoihenyl)methane as the main product and crystal violet, methyl violet, as well as the leuco rorms of these dyes as minor...cation in chain polymerization is reported. The system is based on electron transfer photoreduction of xanthene dye triplets by aromatic amines...Previously, Crivello and Lam 9 had reported attempts to use visible light absorbing dyes to sensitize the decomposition of iodonium salts to initiate

  18. Theoretical study of the electronically excited radical cations of naphthalene and anthracene as archetypal models for astrophysical observations. Part II. Dynamics consequences.

    PubMed

    Ghanta, S; Reddy, V Sivaranjana; Mahapatra, S

    2011-08-28

    Nuclear dynamics is investigated theoretically from first principles by employing the ab initio vibronic models of the prototypical naphthalene and anthracene radical cations developed in Part I. This Part is primarily aimed at corroborating a large amount of available experimental data with a specific final goal to establish an unambiguous link with the current observations in astrophysics and astronomy. The detailed analyses presented here perhaps establish that these two prototypical polycyclic aromatic hydrocarbon radical cations are indeed potential carriers of the observed diffuse interstellar bands.

  19. Evaluation of 2D-ESEEM data of 15N-labeled radical cations of the primary donor P 700 in photosystem I and chlorophyll a

    NASA Astrophysics Data System (ADS)

    Käβ, H.; Lubitz, W.

    1996-03-01

    Hyperfine couplings (hfc's) of the nitrogen nuclei in the 15N-labeled radical cations of chlorophyll a and the primary donor P 700 in photosystem I of spinach were investigated in frozen solution by two-dimensional stimulated echo ESEEM. 15N hfc tensors were evaluated by comparison of the experimental data with simulations of the time domain and frequency domain ESEEM signals. The results are discussed in the framework of a chlorophyll a dimer model for the radical cation of P 700.

  20. Role of configurational gating in intracomplex electron transfer from cytochrome c to the radical cation in cytochrome c peroxidase.

    PubMed

    Mei, H; Wang, K; Peffer, N; Weatherly, G; Cohen, D S; Miller, M; Pielak, G; Durham, B; Millett, F

    1999-05-25

    Electron transfer within complexes of cytochrome c (Cc) and cytochrome c peroxidase (CcP) was studied to determine whether the reactions are gated by fluctuations in configuration. Electron transfer in the physiological complex of yeast Cc (yCc) and CcP was studied using the Ru-39-Cc derivative, in which the H39C/C102T variant of yeast iso-1-cytochrome c is labeled at the single cysteine residue on the back surface with trisbipyridylruthenium(II). Laser excitation of the 1:1 Ru-39-Cc-CcP compound I complex at low ionic strength results in rapid electron transfer from RuII to heme c FeIII, followed by electron transfer from heme c FeII to the Trp-191 indolyl radical cation with a rate constant keta of 2 x 10(6) s-1 at 20 degrees C. keta is not changed by increasing the viscosity up to 40 cP with glycerol and is independent of temperature. These results suggest that this reaction is not gated by fluctuations in the configuration of the complex, but may represent the elementary electron transfer step. The value of keta is consistent with the efficient pathway for electron transfer in the crystalline yCc-CcP complex, which has a distance of 16 A between the edge of heme c and the Trp-191 indole [Pelletier, H., and Kraut, J. (1992) Science 258, 1748-1755]. Electron transfer in the complex of horse Cc (hCc) and CcP was examined using Ru-27-Cc, in which hCc is labeled with trisbipyridylruthenium(II) at Lys-27. Laser excitation of the Ru-27-Cc-CcP complex results in electron transfer from RuII to heme c FeII with a rate constant k1 of 2.3 x 10(7) s-1, followed by oxidation of the Trp-191 indole to a radical cation by RuIII with a rate constant k3 of 7 x 10(6) s-1. The cycle is completed by electron transfer from heme c FeII to the Trp-191 radical cation with a rate constant k4 of 6.1 x 10(4) s-1. The rate constant k4 decreases to 3.4 x 10(3) s-1 as the viscosity is increased to 84 cP, but the rate constants k1 and k3 remain the same. The results are consistent with a

  1. Formaldehyde mediated proton-transport catalysis in the ketene-water radical cation CH2C(O)OH2+

    NASA Astrophysics Data System (ADS)

    Lee, Richard; Ruttink, Paul J. A.; Burgers, Peter C.; Terlouw, Johan K.

    2006-09-01

    Previous studies have shown that the solitary ketene-water ion CH2C(O)OH2+ (1) does not isomerize into CH2C(OH)2+ (2), its more stable hydrogen shift isomer. Tandem mass spectrometry based collision experiments reveal that this isomerization does take place in the CH2O loss from low-energy 1,3-dihydroxyacetone ions (HOCH2)2CO+. A mechanistic analysis using the CBS-QB3 model chemistry shows that such molecular ions rearrange into hydrogen-bridged radical cations [CH2C(O)O(H)-H...OCH2]+ in which the CH2O molecule catalyzes the transformation 1 --> 2 prior to dissociation. The barrier for the unassisted reaction, 29 kcal mol-1, is reduced to a mere 0.6 kcal mol-1 for the catalysed transformation. Formaldehyde is an efficient catalyst because its proton affinity meets the criterion for facile proton-transport catalysis.

  2. Large excited state two photon absorptions in the near infrared region of surprisingly stable radical cations of (ferrocenyl)indenes.

    PubMed

    Orian, Laura; Scuppa, Stefano; Santi, Saverio; Meneghetti, Moreno

    2013-08-21

    Multiphoton absorptions are important non-linear optical processes which allow us to explore excited states with low energy photons giving rise to new possibilities for photoinduced processes. Among these processes, multiphoton absorptions from excited states are particularly interesting because of the large susceptibilities characteristic of excited states. Here we explore the nonlinear transmission measurements recorded with 9 ns laser pulses at 1064 nm of the radical cations of (2-ferrocenyl)indene and of (2-ferrocenyl)-hexamethylindene, two interesting very stable molecules. The non-linear transmission data can be interpreted with a multiphoton sequence of three photon absorptions, the first being a one photon absorption related to the intramolecular charge transfer and the second a two photon absorption from the excited state created with the first process. The two photon absorption cross section is found to be several orders of magnitude larger than those usually found for two photon absorbing systems excited from the ground state.

  3. Ellagic acid inhibits iron-mediated free radical formation.

    PubMed

    Dalvi, Luana T; Moreira, Daniel C; Andrade, Roberto; Ginani, Janini; Alonso, Antonio; Hermes-Lima, Marcelo

    2017-02-15

    Polyphenols are reported to have some health benefits, which are link to their antioxidant properties. In the case of ellagic acid (EA), there is evidence that it has free radical scavenger properties and that it is able to form complexes with metal ions. However, information on a possible link between the formation of iron-EA complexes and their interference in Haber-Weiss/Fenton reactions was not yet determined. Thus, the present study investigated the in vitro antioxidant mechanism of EA in a system containing ascorbate, Fe(III) and different iron ligands (EDTA, citrate and NTA). Iron-mediated oxidative degradation of 2-deoxyribose was poorly inhibited (by 12%) in the presence of EA (50μM) and EDTA. When citrate or NTA - which form weak iron complexes - were used, the 2-deoxyribose protection increased to 89-97% and 45%, respectively. EA also presented equivalent inhibitory effects on iron-mediated oxygen uptake and ascorbyl radical formation. Spectral analyses of iron-EA complexes show that EA removes Fe(III) from EDTA within hours, and from citrate within 1min. This difference in the rate of iron-EA complex formation may explain the antioxidant effects of EA. Furthermore, the EA antioxidant effectiveness was inversely proportional to the Fe(III) concentration, suggesting a competition with EDTA. In conclusion, the results indicate that EA may prevent in vitro free radical formation when it forms a complex with iron ions.

  4. Ellagic acid inhibits iron-mediated free radical formation

    NASA Astrophysics Data System (ADS)

    Dalvi, Luana T.; Moreira, Daniel C.; Andrade, Roberto; Ginani, Janini; Alonso, Antonio; Hermes-Lima, Marcelo

    2017-02-01

    Polyphenols are reported to have some health benefits, which are link to their antioxidant properties. In the case of ellagic acid (EA), there is evidence that it has free radical scavenger properties and that it is able to form complexes with metal ions. However, information on a possible link between the formation of iron-EA complexes and their interference in Haber-Weiss/Fenton reactions was not yet determined. Thus, the present study investigated the in vitro antioxidant mechanism of EA in a system containing ascorbate, Fe(III) and different iron ligands (EDTA, citrate and NTA). Iron-mediated oxidative degradation of 2-deoxyribose was poorly inhibited (by 12%) in the presence of EA (50 μM) and EDTA. When citrate or NTA - which form weak iron complexes - were used, the 2-deoxyribose protection increased to 89-97% and 45%, respectively. EA also presented equivalent inhibitory effects on iron-mediated oxygen uptake and ascorbyl radical formation. Spectral analyses of iron-EA complexes show that EA removes Fe(III) from EDTA within hours, and from citrate within 1 min. This difference in the rate of iron-EA complex formation may explain the antioxidant effects of EA. Furthermore, the EA antioxidant effectiveness was inversely proportional to the Fe(III) concentration, suggesting a competition with EDTA. In conclusion, the results indicate that EA may prevent in vitro free radical formation when it forms a complex with iron ions.

  5. Fluorescence of the perylene radical cation and an inaccessible D0/D1 conical intersection: An MMVB, RASSCF, and TD-DFT computational study

    NASA Astrophysics Data System (ADS)

    Tokmachev, Andrei M.; Boggio-Pasqua, Martial; Mendive-Tapia, David; Bearpark, Michael J.; Robb, Michael A.

    2010-01-01

    The photophysics of the perylene radical cation (Pe•+) was studied using the molecular mechanics-valence bond (MMVB) hybrid force field. Potential energy surfaces of the first three electronic states were investigated. Geometry optimizations of critical points—including conical intersections between the relevant electronic states—were performed using the MMVB analytical energy gradient for cations. No accessible planar conical intersection between the D0 and D1 states of Pe•+ was found; this is consistent with the experimentally observed D1 lifetimes and the observation of D1 emission from this cation in the condensed phase. Benchmark RASSCF and TD-DFT calculations support the reliability of the MMVB results.

  6. Ab Initio Study of Ionized Water Radical Cation (H2O)8(+) in Combination with the Particle Swarm Optimization Method.

    PubMed

    Tang, Mei; Hu, Cui-E; Lv, Zhen-Long; Chen, Xiang-Rong; Cai, Ling-Cang

    2016-12-01

    The structures of cationic water clusters (H2O)8(+) have been globally explored by the particle swarm optimization method in combination with quantum chemical calculations. Geometry optimization and vibrational analysis for the 15 most interesting clusters were computed at the MP2/aug-cc-pVDZ level and infrared spectrum calculation at MPW1K/6-311++G** level. Special attention was paid to the relationships between their configurations and energies. Both MP2 and B3LYP-D3 calculations revealed that the cage-like structure is the most stable, which is different from a five-membered ring lowest energy structure but agrees well with a cage-like structure in the literature. Furthermore, our obtained cage-like structure is more stable by 0.87 and 1.23 kcal/mol than the previously reported structures at MP2 and B3LYP-D3 levels, respectively. Interestingly, on the basis of their relative Gibbs free energies and the temperature dependence of populations, the cage-like structure predominates only at very low temperatures, and the most dominating species transforms into a newfound four-membered ring structure from 100 to 400 K, which can contribute greatly to the experimental infrared spectrum. By topological analysis and reduced density gradient analysis, we also investigated the structural characteristics and bonding strengths of these water cluster radical cations.

  7. Competitive Hydrogen Atom Migrations Accompanying Cascade Dissociations of Peptide Cation-Radicals of the z(+•) Type.

    PubMed

    Ledvina, Aaron R; Coon, Joshua J; Tureček, František

    2015-02-01

    We report a combined experimental and computational study of energy-resolved collision-induced dissociation (ER-CID) and time-resolved infrared multiphoton dissociation (TR-IRMPD) of z4 ions prepared by electron transfer dissociation of peptide (Ala-Ala-Asn-Ala-Arg + 2H)(2+) ions. The z4 cation-radicals, (•)ANAR(+), undergo competitive dissociations by backbone cleavage and loss of a CONH2 radical from the Asn side chain. The backbone cleavage proceeds by radical-assisted dissociation of the Asn Cα-CO bond, forming an x2 ion intermediate which rapidly dissociates by HNCO elimination to yield a stable z2 fragment ion, (•)AR(+). The ER-CID and TR-IRMPD data were consistent with the consecutive nature of the backbone dissociation but showed different branching ratios for the two major fragmentations. The ER-CID data showed branching ratios 0.6-1.0 for the side-chain and backbone cleavages whereas the TR-IRMPD data showed an earlier onset for the latter dissociation. Computational analysis of the potential energy surface with density functional theory and ab initio calculations was carried out to provide structures and energies for the reactant ions as well as several intermediates, products, and transition states. Dissociation pathways for cis and trans amide conformers were distinguished and their energies were evaluated. The threshold dissociation energies for the backbone and side-chain dissociations were similar in accordance with the experimental ER-CID branching ratio. The TR-IRMPD data were interpreted by different absorbances of intermediates produced by hydrogen atom migrations along the dissociation pathways.

  8. Competitive Hydrogen Atom Migrations Accompanying Cascade Dissociations of Peptide Cation-Radicals of the z+• Type

    PubMed Central

    Ledvina, Aaron R.; Coon, Joshua J.

    2014-01-01

    We report a combined experimental and computational study of energy-resolved collision-induced dissociation (ER-CID) and time-resolved infrared multiphoton dissociation (TR-IRMPD) of z4 ions prepared by electron transfer dissociation of peptide (Ala-Ala-Asn-Ala-Arg + 2H)2+ ions. The z4 cation-radicals, •ANAR+, undergo competitive dissociations by backbone cleavage and loss of a CONH2 radical from the Asn side chain. The backbone cleavage proceeds by radical-assisted dissociation of the Asn Cα—CO bond, forming an x2 ion intermediate which rapidly dissociates by HNCO elimination to yield a stable z2 fragment ion, •AR+. The ER-CID and TR-IRMPD data were consistent with the consecutive nature of the backbone dissociation but showed different branching ratios for the two major fragmentations. The ER-CID data showed branching ratios 0.6-1.0 for the side-chain and backbone cleavages whereas the TR-IRMPD data showed an earlier onset for the latter dissociation. Computational analysis of the potential energy surface with density functional theory and ab initio calculations was carried out to provide structures and energies for the reactant ions as well as several intermediates, products, and transition states. Dissociation pathways for cis and trans amide conformers were distinguished and their energies were evaluated. The threshold dissociation energies for the backbone and side-chain dissociations were similar in accordance with the experimental ER-CID branching ratio. The TR-IRMPD data were interpreted by different absorbances of intermediates produced by hydrogen atom migrations along the dissociation pathways. PMID:25844055

  9. Cymantrene radical cation family: spectral and structural characterization of the half-sandwich analogues of ferrocenium ion.

    PubMed

    Laws, Derek R; Chong, Daesung; Nash, Karen; Rheingold, Arnold L; Geiger, William E

    2008-07-30

    The anodic one-electron oxidation of three members of the half-sandwich family of piano-stool compounds MnCp (gamma)(CO) 3, where Cp (gamma) is a generic cyclopentadienyl ligand, has been studied in a CH 2Cl 2/[NBu 4][TFAB] electrolyte (TFAB = [B(C6F5) 4] (-)). The long-sought 17 e (-) radical cation of the parent complex MnCp(CO) 3 (cymantrene, 1, E 1/2 = 0.92 V vs ferrocene) has been shown to be persistent in solutions that use weakly coordinating anions in place of more nucleophilic traditional electrolyte anions. Spectroscopically characterized for the first time, 1 (+) was shown to absorb in the visible (530 nm), near-IR (2066 nm), and IR (2118, 1934 cm (-1)) regions. It was ESR-active at low temperatures (g parallel = 2.213, g perpendicular = 2.079, A parallel (Mn) = 79.2 G, A perpendicular (Mn) = 50 G) and NMR active at room temperature (delta = 22.4 vs TMS). The radical cations of the Cp-functionalized analogues, Mn(eta (5)-C5H 4NH2)(CO) 3, 2, E 1/2 = 0.62 V, and MnCp*(CO) 3 (Cp*= eta (5)-C 5Me 5, 3), E 1/2 = 0.64 V, were generated electrochemically as well by the chemical oxidant [ReCp(CO) 3] (+). The structures of 2 (+) and 3 (+) were determined by X-ray crystallographic studies of their TFAB salts. Compared to the structures of the corresponding neutral compounds, the cations showed elongated Mn-C(O) bonds and shortened C-O bonds, displaying the effect of diminished metal-to-CO backbonding. The bond-length changes in the Mn(CO) 3 moiety were much larger in 3 (+) (avg changes, Mn-C(O) = + 0.142 A, C-O = -0.063 A) than in 2 (+) (avg changes, Mn-C(O) = + 0.006 A, C-O = -0.003 A). Although there were only minor changes in the metal-to-center ring distances upon oxidation of either 2 or 3, there was decidedly less bending of the C(N) atom out of the cyclopentadienyl plane in 2 (+) compared to 2. The optical, vibrational, and magnetic resonance spectra of radicals 2 (+) and 3 (+) were also observed. The spectral data argue for the SOMOs of the 17-electron

  10. Anion size control of the packing in the metallic versus semiconducting chiral radical cation salts (DM-EDT-TTF)2XF6 (X = P, As, Sb).

    PubMed

    Pop, Flavia; Auban-Senzier, Pascale; Canadell, Enric; Avarvari, Narcis

    2016-10-13

    Control of the structural type in metallic enantiopure and racemic radical cation salts is achieved through hydrogen bonding interactions between the chiral donor DM-EDT-TTF and the XF6 anions (X = P, As, Sb), determined by the anion size and the chiral information.

  11. 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.

  12. Theoretical vibrational spectra and thermodynamics of organic semiconductive tetrathiafulvalene and its cation radical.

    PubMed

    Mukherjee, V; Singh, N P

    2014-01-03

    Molecular structure in optimum geometry and vibrational frequencies of pentafulvalene [bicyclopentyliden-2,4,2',4'-tetraene], tetrathiafulvalene [2,2'-bis(1,3-dithiolylidene)] and its cation are calculated. All the calculations are carried out by employing density functional theory incorporated with a suitable basis set. Normal coordinate analysis is also employed to scale the DFT calculated frequencies and to calculate potential energy distributions. The molecular structures and vibrational frequencies are compared for both the pentafulvalene and tetrathiafulvalene molecules. The effect upon geometry and vibrational frequencies of TTF due to charge transfer has also been studied. The vibrational partition function and hence, the thermodynamical properties, such as Helmholtz free energy, entropy, specific heat at constant volume and enthalpy are also calculated and compared for the title molecules. The reason of conductivity of tetrathiafulvalene has been tried to explain on the basis of molecular geometry and normal modes. Study of vibrational partition function exhibits that below 109 K, PFV starts to condense.

  13. Formation of environmentally persistent free radical (EPFR) in iron(III) cation-exchanged smectite clay.

    PubMed

    Nwosu, Ugwumsinachi G; Roy, Amitava; dela Cruz, Albert Leo N; Dellinger, Barry; Cook, Robert

    2016-01-01

    Environmentally persistent free radicals (EPFRs) have been found at a number of Superfund sites, with EPFRs being formed via a proposed redox process at ambient environmental conditions. The possibility of such a redox process taking place at ambient environmental conditions is studied utilizing a surrogate soil system of phenol and iron(III)-exchanged calcium montmorillonite clay, Fe(III)CaM. Sorption of phenol by the Fe(III)CaM is demonstrated by Fourier-transformed infra-red (FT-IR) spectroscopy, as evidenced by the peaks between 1345 cm(-1) and 1595 cm(-1), and at lower frequencies between 694 cm(-1) and 806 cm(-1), as well as X-ray diffraction (XRD) spectroscopy, as shown by an increase in interlayer spacing within Fe(III)CaM. The formation and characterization of the EPFRs is determined by electron paramagnetic resonance (EPR) spectroscopy, showing phenoxyl-type radical with a g-factor of 2.0034 and ΔHP-P of 6.1 G at an average concentration of 7.5 × 10(17) spins per g. EPFRs lifetime data are indicative of oxygen and water molecules being responsible for EPFR decay. The change in the oxidation state of the iron redox center is studied by X-ray absorption near-edge structure (XANES) spectroscopy, showing that 23% of the Fe(III) is reduced to Fe(II). X-ray photoemission spectroscopy (XPS) results confirm the XANES results. These findings, when combined with the EPFR concentration data, demonstrate that the stoichiometry of the EPFR formation under the conditions of this study is 1.5 × 10(-2) spins per Fe(II) atom.

  14. 15N electron nuclear double resonance of the primary donor cation radical P+.865 in reaction centers of Rhodopseudomonas sphaeroides: additional evidence for the dimer model.

    PubMed Central

    Lubitz, W; Isaacson, R A; Abresch, E C; Feher, G

    1984-01-01

    Four 15N hyperfine coupling constants, including signs, have been measured by electron nuclear double resonance (ENDOR) and electron nuclear nuclear triple resonance (TRIPLE) for the bacteriochlorophyll a radical cation, BChla+., in vitro and for the light-induced primary donor radical cation, P+.865, in reaction centers of Rhodopseudomonas sphaeroides R-26. A comparison of the data shows that the hyperfine coupling constants have the same sign in both radicals and are, on the average, smaller by a factor of 2 in P+.865. These results provide additional evidence that P+.865 is a bacteriochlorophyll dimer and are in contradiction with the monomer structure of P+.865 recently proposed by O'Malley and Babcock. The reduction factors of the individual 15N couplings, together with the evidence from proton ENDOR data and molecular orbital calculations, indicate a dimer structure in which only two rings (either I and I or III and III) of the bacteriochlorophyll macrocycles overlap. PMID:6096857

  15. Where Does the Electron Go? Stable and Metastable Peptide Cation Radicals Formed by Electron Transfer

    NASA Astrophysics Data System (ADS)

    Pepin, Robert; Layton, Erik D.; Liu, Yang; Afonso, Carlos; Tureček, František

    2017-01-01

    Electron transfer to doubly and triply charged heptapeptide ions containing polar residues Arg, Lys, and Asp in combination with nonpolar Gly, Ala, and Pro or Leu generates stable and metastable charge-reduced ions, (M + 2H)+●, in addition to standard electron-transfer dissociation (ETD) fragment ions. The metastable (M + 2H)+● ions spontaneously dissociate upon resonant ejection from the linear ion trap, giving irregularly shaped peaks with offset m/ z values. The fractions of stable and metastable (M + 2H)+● ions and their mass shifts depend on the presence of Pro-4 and Leu-4 residues in the peptides, with the Pro-4 sequences giving larger fractions of the stable ions while showing smaller mass shifts for the metastables. Conversion of the Asp and C-terminal carboxyl groups to methyl esters further lowers the charge-reduced ion stability. Collisional activation and photodissociation at 355 nm of mass-selected (M + 2H)+● results in different dissociations that give sequence specific MS3 spectra. With a single exception of charge-reduced (LKGLADR + 2H)+●, the MS3 spectra do not produce ETD sequence fragments of the c and z type. Hence, these (M + 2H)+● ions are covalent radicals, not ion-molecule complexes, undergoing dramatically different dissociations in the ground and excited electronic states. The increased stability of the Pro-4 containing (M + 2H)+● ions is attributed to radicals formed by opening of the Pro ring and undergoing further stabilization by hydrogen atom migrations. UV-VIS photodissociation action spectroscopy and time-dependent density functional theory calculations are used in a case in point study of the stable (LKGPADR + 2H)+● ion produced by ETD. In contrast to singly-reduced peptide ions, doubly reduced (M + 3H)+ ions are stable only when formed from the Pro-4 precursors and show all characteristics of even electron ions regarding no photon absorption at 355 nm or ion-molecule reactions, and exhibiting proton driven

  16. Systematic studies of the mass spectrometric properties of alkaline earth metal cationized amino acids and peptides

    NASA Astrophysics Data System (ADS)

    Küjckelmann, Ulrich; Müller, Dietrich; Weber, Carsten

    1997-07-01

    The results of a systematic study of the gas phase interactions of α-amino acids and peptides (4-15 amino acids) with alkaline earth metals, observed with mass spectrometric techniques, are presented. Furthermore, a model for the cationization with calcium at the C-terminal amino acid arginine in rotaviral polypeptides is presented.

  17. Tree species affect cation exchange capacity (CEC) and cation binding properties of organic matter in acid forest soils.

    PubMed

    Gruba, Piotr; Mulder, Jan

    2015-04-01

    Soil organic matter (SOM) in forest soil is of major importance for cation binding and acid buffering, but its characteristics may differ among soils under different tree species. We investigated acidity, cation exchange properties and Al bonding to SOM in stands of Scots pine, pedunculate oak, Norway spruce, European beech and common hornbeam in southern Poland. The content of total carbon (Ct) was by far the major contributor to total cation exchange capacity (CECt) even in loamy soils and a strong relationship between Ct and CECt was found. The slope of the regression of CECt to Ct increased in the order hornbeam≈oakacid pH range was smallest for hornbeam and oak, and largest for spruce and pine soils. This was supported by the apparent dissociation constant (pKapp) values of SOM, which were largest in soils under oak. The maximum values of Al saturation were similar between the stands. However, maximum Al bonding to SOM occurred at higher pH values in soils under pine and spruce than under oak. Therefore, at any value in the acid pH range, the SOM in pine soil has less Al complexed and more adsorbed H+ than SOM from oak soils. Such differences in Al and H bonding are not only important for pH buffering and metal solubility controls, but also for stabilization of SOM via saturation of functional groups by Al and H.

  18. Pressure-induced spectral changes for the special-pair radical cation of the bacterial photosynthetic reaction center.

    PubMed

    Leiger, Kristjan; Freiberg, Arvi; Dahlbom, Mats G; Hush, Noel S; Reimers, Jeffrey R

    2007-06-07

    The effect of pressure up to 6 kbars on the near to mid infrared absorption spectrum (7500-14,300 cm(-1) or 1333-700 nm) of the oxidized reaction center of Rhodobacter sphaeroides is measured and interpreted using density-functional B3LYP, INDO, and PM5 calculations. Two weak electronic transition origins at approximately 8010 and approximately 10,210 cm(-1) are unambiguously identified. The first transition is assigned to a Qy tripdoublet band that involves, in the localized description of the excitation, a triplet absorption on one of the bacteriochlorophyll molecules (PM) in the reaction center's special pair intensified by the presence of a radical cation on the other (PL). While most chlorophyll transition energies decrease significantly with increasing pressure, the tripdoublet band is found to be almost pressure insensitive. This difference is attributed to the additional increase in the tripdoublet-band energy accompanying compression of the pi-stacked special pair. The second band could either be the anticipated second Qy tripdoublet state, a Qx tripdoublet state, or a state involving excitation from a low-lying doubly occupied orbital to the half-occupied cationic orbital. A variety of absorption bands that are also resolved in the 8300-9600 cm(-1) region are assigned as vibrational structure associated with the first tripdoublet absorption. These sidebands are composites that are shown by the calculations to comprise many unresolved individual modes; while the calculated pressure sensitivity of each individual mode is small, the calculated pressure dependence of the combined sideband structure is qualitatively similar to the observed pressure dependence, preventing the positive identification of possible additional electronic transitions in this spectral region.

  19. 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.

  20. Cationic amino acid transporters play key roles in the survival and transmission of apicomplexan parasites

    PubMed Central

    Rajendran, Esther; Hapuarachchi, Sanduni V.; Miller, Catherine M.; Fairweather, Stephen J.; Cai, Yeping; Smith, Nicholas C.; Cockburn, Ian A.; Bröer, Stefan; Kirk, Kiaran; van Dooren, Giel G.

    2017-01-01

    Apicomplexans are obligate intracellular parasites that scavenge essential nutrients from their hosts via transporter proteins on their plasma membrane. The identities of the transporters that mediate amino acid uptake into apicomplexans are unknown. Here we demonstrate that members of an apicomplexan-specific protein family—the Novel Putative Transporters (NPTs)—play key roles in the uptake of cationic amino acids. We show that an NPT from Toxoplasma gondii (TgNPT1) is a selective arginine transporter that is essential for parasite survival and virulence. We also demonstrate that a homologue of TgNPT1 from the malaria parasite Plasmodium berghei (PbNPT1), shown previously to be essential for the sexual gametocyte stage of the parasite, is a cationic amino acid transporter. This reveals a role for cationic amino acid scavenging in gametocyte biology. Our study demonstrates a critical role for amino acid transporters in the survival, virulence and life cycle progression of these parasites. PMID:28205520

  1. Cationic amino acid transporters play key roles in the survival and transmission of apicomplexan parasites.

    PubMed

    Rajendran, Esther; Hapuarachchi, Sanduni V; Miller, Catherine M; Fairweather, Stephen J; Cai, Yeping; Smith, Nicholas C; Cockburn, Ian A; Bröer, Stefan; Kirk, Kiaran; van Dooren, Giel G

    2017-02-16

    Apicomplexans are obligate intracellular parasites that scavenge essential nutrients from their hosts via transporter proteins on their plasma membrane. The identities of the transporters that mediate amino acid uptake into apicomplexans are unknown. Here we demonstrate that members of an apicomplexan-specific protein family-the Novel Putative Transporters (NPTs)-play key roles in the uptake of cationic amino acids. We show that an NPT from Toxoplasma gondii (TgNPT1) is a selective arginine transporter that is essential for parasite survival and virulence. We also demonstrate that a homologue of TgNPT1 from the malaria parasite Plasmodium berghei (PbNPT1), shown previously to be essential for the sexual gametocyte stage of the parasite, is a cationic amino acid transporter. This reveals a role for cationic amino acid scavenging in gametocyte biology. Our study demonstrates a critical role for amino acid transporters in the survival, virulence and life cycle progression of these parasites.

  2. Radical-derived oxidation products of 5-aminosalicylic acid and N-acetyl-5-aminosalicylic acid.

    PubMed

    Fischer, C; Klotz, U

    1994-11-04

    5-Aminosalicylic acid is an agent effective in the treatment of chronic inflammatory bowel diseases. Its ability to scavenge radicals is considered to be a major factor responsible for its therapeutic efficacy. In this study oxidation products of aminosalicylates with hydroxyl radicals were produced. The compounds that could be discovered by gas chromatographic-mass spectrometric analysis originate from a 1,4-benzoquinone monoimine intermediate which subsequently undergoes multiple reactions such as hydrolysis, reductive 1,4-Michael addition, reoxidation and decarboxylation. Some of these products could represent metabolites formed under in vivo conditions and thus provide a tool for screening biological material from subjects under different clinical conditions.

  3. Theoretical study of reactivity of methane, methyl fluoride, and methyl chloride: Interaction with their radical cations and proton donors

    SciTech Connect

    Hess, B.A. Jr. ); Zahradnik, R. )

    1990-07-18

    This work deals with interactions between CH{sub 4} and CH{sub 4}{sup {sm bullet}+}, CH{sub 3}F and CH{sub 3}F{sup {sm bullet}+}, and CH{sub 3}Cl and CH{sub 3}Cl{sup {sm bullet}+}. The calculated {Delta}H{sub 0} values (MP4/6-31G**//MP2/6-31G**, ZPE included) for processes leading to CH{sub 5}{sup +} and CH{sub 3}{sup {sm bullet}}, and to CFH{sub 4} and CH{sub 2}F{sup {sm bullet}} amount to {minus}1.8 and {minus}21.0 kcal/mol, respectively. The {Delta}H{sub 0} leading to CClH{sub 4}{sup +} and CH{sub 2}Cl{sup {sm bullet}} (MP4/6-31G**//SCF/6-31G**, ZPE included) is {minus}2.3 kcal/mol. The calculated reaction heat for the first interaction is significantly closer to experimental values ({minus}4.16 and {minus}6 kcal/mol, respectively) than their previous theoretical estimates. The structures of the radical cations (CH{sub 4}{sup {sm bullet}+}, CH{sub 3}F{sup {sm bullet}+}) possess features of van der Waals associates.

  4. Accidental degeneracy in the spiropyran radical cation: charge transfer between two orthogonal rings inducing ultra-efficient reactivity.

    PubMed

    Mendive-Tapia, David; Kortekaas, Luuk; Steen, Jorn D; Perrier, Aurélie; Lasorne, Benjamin; Browne, Wesley R; Jacquemin, Denis

    2016-11-16

    Photochromism of the spiropyran radical cation to the corresponding merocyanine form is investigated by a combination of electrochemical oxidation, UV/vis absorption spectroscopy, spectroelectrochemistry and first-principles calculations (TD-DFT, CAS-SCF and CAS-PT2). First, we demonstrate that the ring-opening of mono-spiropyrans occurs upon one-electron oxidation and that it can be driven photochemically as well as thermally, with trapping of the merocyanine by protonation. Second, in order to explain this experimentally observed spectroelectrochemical behaviour we suggest a theoretical mechanism based on the reactivity of the two lowest electronic excited-states, which promotes effective electron transfer from the indoline (nitrogen-ring) to the pyran (oxygen-ring) moieties (and vice versa) through a conical intersection seam of degeneracy. Characterisation of the minimum energy conical intersection on this crossing revealed that it presents a rare diabatic trapping topology. The excited state molecule cannot escape from crossing the intersection seam due to the presence of only one degeneracy-lifting coordinate that efficiently channels into the formation of the merocyanine photoproduct, so giving rise to a "kitchen sink" funnel-like effect. Therefore, assuming rapid relaxation after vertical excitation to a higher electronic state, photoconversion cannot be avoided in the D1 electronic state, which rationalises the remarkably efficient visible light driven excited-state reactivity observed experimentally.

  5. The role of aspartate-235 in the binding of cations to an artificial cavity at the radical site of cytochrome c peroxidase.

    PubMed

    Fitzgerald, M M; Trester, M L; Jensen, G M; McRee, D E; Goodin, D B

    1995-09-01

    The activated state of cytochrome c peroxidase, compound ES, contains a cation radical on the Trp-191 side chain. We recently reported that replacing this tryptophan with glycine creates a buried cavity at the active site that contains ordered solvent and that will specifically bind substituted imidazoles in their protonated cationic forms (Fitzgerald MM, Churchill MJ, McRee DE, Goodin DB, 1994, Biochemistry 33:3807-3818). Proposals that a nearby carboxylate, Asp-235, and competing monovalent cations should modulate the affinity of the W191G cavity for ligand binding are addressed in this study. Competitive binding titrations of the imidazolium ion to W191G as a function of [K+] show that potassium competes weakly with the binding of imidazoles. The dissociation constant observed for potassium binding (18 mM) is more than 3,000-fold higher than that for 1,2-dimethylimidazole (5.5 microM) in the absence of competing cations. Significantly, the W191G-D235N double mutant shows no evidence for binding imidazoles in their cationic or neutral forms, even though the structure of the cavity remains largely unperturbed by replacement of the carboxylate. Refined crystallographic B-values of solvent positions indicate that the weakly bound potassium in W191G is significantly depopulated in the double mutant. These results demonstrate that the buried negative charge of Asp-235 is an essential feature of the cation binding determinant and indicate that this carboxylate plays a critical role in stabilizing the formation of the Trp-191 radical cation.

  6. The role of aspartate-235 in the binding of cations to an artificial cavity at the radical site of cytochrome c peroxidase.

    PubMed Central

    Fitzgerald, M. M.; Trester, M. L.; Jensen, G. M.; McRee, D. E.; Goodin, D. B.

    1995-01-01

    The activated state of cytochrome c peroxidase, compound ES, contains a cation radical on the Trp-191 side chain. We recently reported that replacing this tryptophan with glycine creates a buried cavity at the active site that contains ordered solvent and that will specifically bind substituted imidazoles in their protonated cationic forms (Fitzgerald MM, Churchill MJ, McRee DE, Goodin DB, 1994, Biochemistry 33:3807-3818). Proposals that a nearby carboxylate, Asp-235, and competing monovalent cations should modulate the affinity of the W191G cavity for ligand binding are addressed in this study. Competitive binding titrations of the imidazolium ion to W191G as a function of [K+] show that potassium competes weakly with the binding of imidazoles. The dissociation constant observed for potassium binding (18 mM) is more than 3,000-fold higher than that for 1,2-dimethylimidazole (5.5 microM) in the absence of competing cations. Significantly, the W191G-D235N double mutant shows no evidence for binding imidazoles in their cationic or neutral forms, even though the structure of the cavity remains largely unperturbed by replacement of the carboxylate. Refined crystallographic B-values of solvent positions indicate that the weakly bound potassium in W191G is significantly depopulated in the double mutant. These results demonstrate that the buried negative charge of Asp-235 is an essential feature of the cation binding determinant and indicate that this carboxylate plays a critical role in stabilizing the formation of the Trp-191 radical cation. PMID:8528082

  7. Radical quenching by rosmarinic acid from Lavandula vera MM cell culture.

    PubMed

    Kovacheva, Elena; Georgiev, Milen; Pashova, Svetlana; Angelova, Maria; Ilieva, Mladenka

    2006-01-01

    This study was conducted to evaluate the radical scavenging capacities of extracts and preparations from a Lavandula vera MM plant cell culture with different rosmarinic acid content and to compare them with pure rosmarinic and caffeic acids as well. The methods, which were used are superoxide anion and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt radicals scavenging assays. Results showed that extracts and preparations from Lavandula vera MM possess strong radical scavengers, as the best both radical scavengers appeared to be the fractions with enriched rosmarinic acid content, obtained after ethylacetate fractioning (47.7% inhibition of superoxide radicals and 14.2 microM 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid equivalents, respectively). These data reveal the possibilities for application of these preparations as antioxidants.

  8. A valence bond analysis of electronic degeneracies in Jahn-Teller systems: low-lying states of the cyclopentadienyl radical and cation.

    PubMed

    Zilberg, Shmuel; Haas, Yehuda

    2002-09-11

    The lowest doublet electronic state of the cyclopentadienyl radical (CPDR) and the lowest singlet state of the cyclopentadienyl cation (CPDC) are distorted from the highly symmetric D(5h) structure due to the Jahn-Teller effect. A valence bond analysis based on the phase-change rule of Longuet-Higgins reveals that in both cases the distortion is due to the first-order Jahn-Teller effect. It is shown that, while for the radical an isolated Jahn-Teller degeneracy is expected, in the case of the cation the main Jahn-Teller degeneracy is accompanied by five satellite degeneracies. The method offers a chemically oriented way for identifying the distortive coordinates.

  9. EPR study of radiation-induced radicals in glutaric and amino acid derivatives in solid state

    NASA Astrophysics Data System (ADS)

    Yeşim Dicle, Işık

    2015-05-01

    Gamma radiation-induced radicals of 2-methylglutaric acid (2MG), diethyl amino malonate hydrochloride (DEAMHCl), ethyl malonate monoamide have been investigated at room temperature by the electron paramagnetic resonance technique. The type of radicals formed and their room temperature stability were evaluated. Three different radicals have been detected. The free radicals formed in compounds were attributed to the HOOCCH3ĊCH2CH2 COOH, CH3ĊHCO2CHNH2COCH2CH3 HCl and NH2COCH2COOĊHCH3 radicals, respectively. The results were found to be in good agreement with the existing literature data and theoretical predictions conformation.

  10. A new special pair model comprising meso-di-p-anisylaminoporphyrin: enhancement of visible-light absorptivities and quantification of electronic communication in mixed-valent cation radical.

    PubMed

    Sakamoto, Ryota; Nishikawa, Michihiro; Yamamura, Takeshi; Kume, Shoko; Nishihara, Hiroshi

    2010-03-28

    Slipped cofacial porphyrin dimer 1(2) with di-p-anisylamino groups on the meso-positions shows characteristic photo- and electroproperties making it suitable as a photosynthetic special pair model: more intense and red-shifted absorptivities in the visible region, and electronic communication between the two porphyrins in mixed-valent cation radical 1(2)(+), which is quantified with an IVCT band analysis.

  11. Electronic Characterization of Reaction Intermediates: The Fluorenylium, Phenalenylium, and Benz[f]indenylium Cations and Their Radicals.

    PubMed

    Fulara, Jan; Chakraborty, Arghya; Maier, John P

    2016-03-01

    Three vibrationally resolved absorption systems commencing at 538, 518, and 392 nm were detected in a 6 K neon matrix after mass-selected deposition of C13 H9 (+) ions (m/z=165) produced from fluorene in a hot-cathode discharge ion source. The benz[f]indenylium (BfI(+) : 538 nm), fluorenylium (FL9(+) : 518 nm), and phenalenylium (PHL(+) : 392 nm) cations are the absorbing molecules. Two electronic systems corresponding to neutral species are apparent at 490 and 546 nm after irradiation of the matrix with λ<260 nm photons and were assigned to the FL9 and BfI radicals, respectively. The strongest peak at 518 nm is the origin of the 2 (1) B2 ←X̃ (1) A1 absorption of FL9(+) , and the 490 nm band is the 2 (2) A2 ←X̃ (2) B1 origin of FL9. The electronic systems commencing at 538 nm and 546 nm were assigned to the 1 (1) A1 ←X̃ (1) A1 and 1 (2) A2 ←X̃ (2) A2 transitions of BfI(+) and BfI. The 392 nm band is the 1 (1) E'←X̃ (1) A1 ' transition of PHL(+). The electronic spectra of C13 H9 (+) /C13 H9 were assigned on the basis of the vertical excitation energies calculated with SAC-CI and MS-CASPT2 methods.

  12. Does Cation Size Affect Occupancy and Electrostatic Screening of the Nucleic Acid Ion Atmosphere?

    PubMed

    Gebala, Magdalena; Bonilla, Steve; Bisaria, Namita; Herschlag, Daniel

    2016-08-31

    Electrostatics are central to all aspects of nucleic acid behavior, including their folding, condensation, and binding to other molecules, and the energetics of these processes are profoundly influenced by the ion atmosphere that surrounds nucleic acids. Given the highly complex and dynamic nature of the ion atmosphere, understanding its properties and effects will require synergy between computational modeling and experiment. Prior computational models and experiments suggest that cation occupancy in the ion atmosphere depends on the size of the cation. However, the computational models have not been independently tested, and the experimentally observed effects were small. Here, we evaluate a computational model of ion size effects by experimentally testing a blind prediction made from that model, and we present additional experimental results that extend our understanding of the ion atmosphere. Giambasu et al. developed and implemented a three-dimensional reference interaction site (3D-RISM) model for monovalent cations surrounding DNA and RNA helices, and this model predicts that Na(+) would outcompete Cs(+) by 1.8-2.1-fold; i.e., with Cs(+) in 2-fold excess of Na(+) the ion atmosphere would contain an equal number of each cation (Nucleic Acids Res. 2015, 43, 8405). However, our ion counting experiments indicate that there is no significant preference for Na(+) over Cs(+). There is an ∼25% preferential occupancy of Li(+) over larger cations in the ion atmosphere but, counter to general expectations from existing models, no size dependence for the other alkali metal ions. Further, we followed the folding of the P4-P6 RNA and showed that differences in folding with different alkali metal ions observed at high concentration arise from cation-anion interactions and not cation size effects. Overall, our results provide a critical test of a computational prediction, fundamental information about ion atmosphere properties, and parameters that will aid in the

  13. Influence of pH on the decay of β-carotene radical cation in aqueous Triton X-100: A laser flash photolysis study.

    PubMed

    El-Agamey, Ali; El-Hagrasy, Maha A; Suenobu, Tomoyoshi; Fukuzumi, Shunichi

    2015-05-01

    The identification of the spectral information of carotenoid neutral radicals is essential for studying their reactivities towards O2 and thereby evaluating their role in the antioxidant-prooxidant properties of the corresponding carotenoid. Recently, it was reported that β-carotene neutral radical (β-CAR) has an absorption maximum at 750 nm. This contradicts the results of many reports that show carotenoid neutral radicals (CAR) absorb in the same or near to the spectral region as their parent carotenoids. In this manuscript, the influence of pH on the decay of β-carotene radical cation (β-CAR-H(+)), generated in an aqueous solution of 2% Triton X-100 (TX-100), was investigated, employing laser flash photolysis (LFP) coupled with kinetic absorption spectroscopy, to identify the absorption bands of the β-carotene neutral radicals. By increasing the pH value of the solution, the decay of β-CAR-H(+) is enhanced and this enhancement is not associated with the formation of any positive absorption bands over the range 550-900 nm. By comparing these results with the literature, it can be concluded that β-carotene neutral radicals most probably absorb within the same spectral range as that of β-carotene. The reaction pathways of the reaction of β-CAR-H(+) with (-)OH have been discussed.

  14. Organo-Lewis acid as cocatalyst for cationic homogeneous Ziegler-Natta olefin polymerizations

    DOEpatents

    Marks, Tobin J.; Chen, You-Xian

    2001-01-01

    Organo-Lewis acids of the formula BR'R".sub.2 wherein B is boron, R' is fluorinated biphenyl, and R" is a fluorinated phenyl, fluorinated biphenyl, or fluorinated polycyclic fused ring group, and cationic metallocene complexes formed therewith. Such complexes are useful as polymerization catalysts.

  15. A method for the production of weakly acidic cation exchange resins

    NASA Astrophysics Data System (ADS)

    Heller, H.; Werner, F.; Mitschker, A.; Diehl, H. V.; Schaefer, A.

    1991-12-01

    The invention relates to a nonpolluting method for the production of weakly acidic cation exchange resins by saponification of cross-linked acrylonitrile bead polymers, with an alkaline saponification agent at elevated temperature, according to which method the bead polymer and alkaline saponification agent are jointly added only at elevated temperature.

  16. Cation deficiency in the atmosphere as a probable cause of acid rains in North America

    NASA Astrophysics Data System (ADS)

    Varma, G. S.

    In North America, where almost every shower is acidic (pH < 5.65), the proper causes have been studied. It was observed that the main cause behind the acidic rains is the alkali deficient environment which fails to neutralize the acid traces formed in the atmosphere by anthropogenic, biogenic and agricultural activity and not the increase in anions in the atmosphere as was speculated earlier by many workers. The data of 12 BAPMoN stations of America from the period 1974-1980 have revealed that, at most of the stations, the trends of cations are declining and in most cases the concentration of anions have also decreased. Thus the environment in the U.S. is becoming cleaner day by day. The pH values have been correlated with both the 'cations' and 'anions' separately (Fig. 1) for all 12 the BAPMoN stations and strong positive correlations have been observed between pH and cations ( rc) while poor correlations were found for anions ( ra) which reveals that pH of rain is more influenced by cation's activity in the atmosphere which are decreasing rapidly as a result of which the rains in North America are found to be acidic. It is not due to an increase in anions caused by industrialization and automobile emissions.

  17. THE ROLE OF SELECTED CATIONS IN THE FORMATION OF PSEUDOMICELLES IN AQUEOUS HUMIC ACID (R822832)

    EPA Science Inventory

    The fluorescence intensity enhancement of a pyrene probe in aqueous humic acid solutions was assessed in terms of added lanthanide and thorium cations. Among the trivalent ions it was found that size played a role, with the small Lu3+ ion producing the greatest increase in pyrene...

  18. Oxidation of carboxylic acids regenerates hydroxyl radicals in the unpolluted and nighttime troposphere.

    PubMed

    da Silva, Gabriel

    2010-07-01

    The hydroxyl radical (OH) controls the removal of organic compounds from the troposphere. Atmospheric chemistry models significantly under-predict OH levels in unpolluted environments, implying that they are regenerated via some unknown mechanism(s). This work uses computational chemistry to demonstrate that the photochemical oxidation of alkyl carboxylic acids can efficiently regenerate the hydroxyl radical via unimolecular decomposition of alpha-carboxyalkylperoxy radicals. For acetic acid and propanoic acid the proposed mechanism is predicted to dominate in the unpolluted lower troposphere, and it may also operate to some extent in the mid to upper troposphere. Alkyl carboxylic acids are also predicted to act as a new source of nighttime OH throughout the planetary boundary layer, where OH levels are also under-predicted. The thermodynamic requirements for reactions of this class are discussed, and some candidate OH-reforming molecules particularly relevant to aromatic photooxidation are identified. Adopting a broader perspective, the alpha-carboxyalkyl radical precursors that react with O(2) to form the unstable alpha-carboxyalkylperoxy type radicals are also expected to form during combustion, in the interstellar medium, and from the gamma-irradiation of glycine and related amino acids, and the potential importance of this new chemistry in these environments is discussed. Master equation simulations suggest that alpha-carboxyalkyl + O(2) reactions provide a prompt OH source during the autoignition and combustion of biodiesel and other oxygenated biofuels, where carboxylic acids are formed as early stage oxidation products. Ketene combustion is also thought to proceed via these OH-reforming alpha-carboxyalkyl radicals. The in vivo formation of alpha-carboxyalkylperoxy radicals followed by oxidation to the highly reactive OH radical may induce oxidative stress in the human body, in a process initiated by gamma-rays. Finally, the reaction of ketenes with OH to

  19. Characterization of cationic acid phosphatase isozyme from rat liver mitochondria.

    PubMed

    Fujimoto, S; Murakami, K; Hosoda, T; Yamamoto, Y; Watanabe, K; Morinaka, Y; Ohara, A

    1992-05-01

    Acid phosphatase isozyme was highly purified from rat liver mitochondrial fraction. The enzyme showed an isoelectric point value of above 9.5 on isoelectric focusing, and the apparent molecular weight was estimated to be 32000 by Sephadex G-100 gel filtration or 16000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme catalyzed the hydrolysis of adenosine 5'-triphosphate, adenosine 5'-diphosphate, thiamine pyrophosphate, inorganic pyrophosphate, and phosphoprotein such as casein and phosvitin, but not of several phosphomonoesters, except for p-nitrophenyl phosphate and o-phosphotyrosine. The enzyme was not inhibited by L-(+)-tartrate, and was significantly activated by Fe2+ and reducing agents such as ascorbic acid, L-cysteine,and dithiothreitol. The enzyme was found to be distributed in various rat tissues including liver, spleen, kidney, small intestine, lung, stomach, brain and heart, but not in skeletal muscle.

  20. Cationic poly(lactic-co-glycolic acid) iron oxide microspheres for nucleic acid detection

    NASA Astrophysics Data System (ADS)

    Pandey, Chandra Mouli; Sharma, Aditya; Sumana, Gajjala; Tiwari, Ida; Malhotra, Bansi Dhar

    2013-04-01

    Herein, we envisage the possibility of preparing stable cationic poly(lactic-co-glycolic acid) (PLGA) microspheres encapsulating the iron oxide nanoparticles (IONPs; 8-12 nm). The IONPs are incorporated into PLGA in organic phase followed by microsphere formation and chitosan coating in aqueous medium via nano-emulsion technique. The average size of the microspheres, as determined by dynamic light scattering are about 310 nm, while the zeta potential for the composite remains near 35 mV at pH 4.0. These microspheres are electrophoretically deposited onto indium tin oxide (ITO)-coated glass substrate used as cathode and parallel platinum plate as the counter electrode. This platform is utilized to fabricate a DNA biosensor, by immobilizing a probe sequence specific to Escherichia coli. The bioelectrode shows a surface-controlled electrode reaction with the electron transfer coefficient (α) of 0.64 and charge transfer rate constant (ks) of 61.73 s-1. Under the optimal conditions, this biosensor shows a detection limit of 8.7 × 10-14 M and is found to retain about 81% of the initial activity after 9 cycles of use.Herein, we envisage the possibility of preparing stable cationic poly(lactic-co-glycolic acid) (PLGA) microspheres encapsulating the iron oxide nanoparticles (IONPs; 8-12 nm). The IONPs are incorporated into PLGA in organic phase followed by microsphere formation and chitosan coating in aqueous medium via nano-emulsion technique. The average size of the microspheres, as determined by dynamic light scattering are about 310 nm, while the zeta potential for the composite remains near 35 mV at pH 4.0. These microspheres are electrophoretically deposited onto indium tin oxide (ITO)-coated glass substrate used as cathode and parallel platinum plate as the counter electrode. This platform is utilized to fabricate a DNA biosensor, by immobilizing a probe sequence specific to Escherichia coli. The bioelectrode shows a surface-controlled electrode reaction with the

  1. Linoleic acid hydroperoxide reacts with hypochlorous acid, generating peroxyl radical intermediates and singlet molecular oxygen.

    PubMed

    Miyamoto, Sayuri; Martinez, Glaucia R; Rettori, Daniel; Augusto, Ohara; Medeiros, Marisa H G; Di Mascio, Paolo

    2006-01-10

    The reaction of hypochlorous acid (HOCl) with hydrogen peroxide is known to generate stoichiometric amounts of singlet molecular oxygen [O2 (1Deltag)]. This study shows that HOCl can also react with linoleic acid hydroperoxide (LAOOH), generating O2 (1Deltag) with a yield of 13 +/- 2% at physiological pH. Characteristic light emission at 1,270 nm, corresponding to O2 (1Deltag) monomolecular decay, was observed when HOCl was reacted with LAOOH or with liposomes containing phosphatidylcholine hydroperoxides, but not with cumene hydroperoxide or tert-butyl hydroperoxide. The generation of O2 (1Deltag) was confirmed by the acquisition of the spectrum of the light emitted in the near-infrared region showing a band with maximum intensity at 1,270 nm and by the observation of the enhancing effect of deuterium oxide and the quenching effect of sodium azide. Mechanistic studies using 18O-labeled linoleic acid hydroperoxide (LA18O18OH) showed that its reaction with HOCl yields 18O-labeled O2 (1Deltag) [18O2 (1Deltag)], demonstrating that the oxygen atoms in O2 (1Deltag) are derived from the hydroperoxide group. Direct analysis of radical intermediates in the reaction of LAOOH with HOCl by continuous-flow electron paramagnetic resonance spectroscopy showed a doublet signal with a g-value of 2.014 and a hyperfine coupling constant from the alpha-hydrogen of a(H) = 4.3 G, indicating the formation of peroxyl radicals. Taken together, our results clearly demonstrate that HOCl reacts with biologically relevant lipid hydroperoxides, generating O2 (1Deltag). In addition, the detection of 18O2 (1Deltag) and peroxyl radicals strongly supports the involvement of a Russell mechanism in the generation of O2 (1Deltag).

  2. Spectral and Acid-Base Properties of Hydroxyflavones in Micellar Solutions of Cationic Surfactants

    NASA Astrophysics Data System (ADS)

    Lipkovska, N. A.; Barvinchenko, V. N.; Fedyanina, T. V.; Rugal', A. A.

    2014-09-01

    It has been shown that the spectral characteristics (intensity, position of the absorption band) and the acid-base properties in a series of structurally similar hydroxyflavones depend on the concentration of the cationic surfactants miramistin and decamethoxin in aqueous solutions, and the extent of their changes is more pronounced for hydrophobic quercetin than for hydrophilic rutin. For the first time, we have determined the apparent dissociation constants of quercetin and rutin in solutions of these cationic surfactants (pKa1) over a broad concentration range and we have established that they decrease in the series water-decamethoxin-miramistin.

  3. Adsorption Capability of Cationic Dyes (Methylene Blue and Crystal Violet) onto Poly-γ-glutamic Acid.

    PubMed

    Ogata, Fumihiko; Nagai, Noriaki; Kawasaki, Naohito

    2017-01-01

    In this study, the adsorption capability of cationic dyes, which were methylene blue and crystal violet, by poly-γ-glutamic acid (PGA) in a single or binary solution system was investigated. The effect of the molecular weight of PGA, initial dye concentration, solution pH, and temperature on the adsorption of dyes was evaluated. The adsorption mechanism of dyes onto PGA was the interaction between -COOH group on the PGA surface and the polarity groups of dyes. These results indicated that PGA is useful for removal of dyes and cationic organic compounds from a single or binary solution system.

  4. 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.

  5. Acetohydroxamic Acid Complexes with Trivalent f-Block Metal Cations

    SciTech Connect

    Sinkov, Serguei I.; Choppin, Gregory

    2003-11-01

    Acetohydroxamic acid has been studied by optical absorbance spectroscopy as a complex forming reagent for the lighter trivalent lanthanides and actinides (Pu(III) and Am(III)) in aqueous solution at 2.0 M (NaClO4) ionic strength. The highest stoichiometry in all the cases studied has been found to be a 1:4 metal-to-ligand ratio; formation of tetrahydroxamato species requires a high excess of the ligand and alkaline pH, Spectrophotometric monitoring confirmed the presence of Pu(III) by electrochemical reduction of Pu(IV) in the course of the pH titration experiment. The formation constants can be used for optimization of processing flowsheets in the advanced PUREX process.

  6. Effects of structural factors on the pi-dimerization and/or disproportionation of the cation radical of extended TTF containing thiophene-based pi-conjugated spacers.

    PubMed

    Frère, Pierre; Allain, Magali; Elandaloussi, El Hadj; Levillain, Eric; Sauvage, François-Xavier; Riou, Amédée; Roncali, Jean

    2002-02-15

    The electrochemical and chemical oxidation of extended TTF 4 and 5 are analysed by cyclic voltammetry, Visible/NIR and ESR spectroscopies, and the X-ray structures of the new salts 5 x BF(4)(CH(2)Cl(2)) and 4 x ClO(4)(THF)(1/2) are presented. The effects of structural factors on the pi-dimerization or the disproportionation reaction of the cation radical are shown. The oxidation of compound 4 presents the successive formation of stable cation radical and dication species both in dichloromethane (DCM) and in a CH(3)CN/THF mixture. In contrast, for compound 5, the stability of the oxidation states strongly depends on the nature of the solvent. In DCM, the oxidation of 5 proceeds by two close one-electron transfers while in CH(3)CN/THF the dication is directly formed via a two-electron process. The X-ray structures of the two salts reveal the formation of pi-dimers of cation radical. While the dimer (5(2))(2+) is due mainly to pi-pi interactions between the conjugating spacer, the multiplication of the sulfur atoms in compound 4 contributes to stabilize the dimer by the combined effects of S-S and pi-pi interactions. Visible/NIR and ESR experiments confirm the higher tendency of 4(+)(.) to dimerize with the occurrence of dimer and monomer in solution, while for 5(+)(.) only the monomer is detected in DCM. On the other hand, by dissolution of 5 x BF(4)(CH(2)Cl(2)) in CH(3)CN, only the neutral and the dicationic states of compounds 5 are observed owing to the disproportionation reaction.

  7. Ion/molecule reactions of 2-chloro- and 2-bromopropene radical cations with methanol and ethanol--FT-ICR spectrometry and DFT calculations

    NASA Astrophysics Data System (ADS)

    Grützmacher, Hans-Friedrich; Büchner, Michael; Zipse, Hendrik

    2005-02-01

    Continuing the studies of ion/molecule reactions of haloalkene radical cations with nucleophiles, the reactions of the radical cations of 2-chloropropene, 1+, and 2-bromopropene. 2+, with methanol and ethanol, respectively, have been investigated by FT-ICR spectrometry and by computational analysis using DFT calculation (BHLYP/6-311 + G(2d,p)//BHLYP/6-31 + G(d) level). Only slow reactions (reaction efficiency <1%) are observed for 1+/methanol and 2+/methanol. Slow proton transfer is the main process for 1+/methanol besides minor addition of methanol to 1+ followed by loss of HCl or Cl. Addition of methanol accompanied by loss of Br is the exclusive process observed for 2+/methanol. In contrast, both 1+ and 2+ react efficiently with ethanol yielding protonated acetaldehyde as the exclusive (1+) or by far dominant (2+) primary reaction product. The computational analysis of these ion/molecule reactions shows that in the case of 1+/methanol and 2+/methanol all processes are either endothermic or blocked by large activation energies. Nonetheless, addition of methanol to the ionized CC double bond of 1+ or 2+ is exothermic, yielding in each case a pair of isomeric [beta]-distonic methoxonium ions. A new reaction mechanism has been found for the HX (X = Cl, Br) elimination from the less stable isomer of the distonic intermediates. Further, an energetically favorable transition state has been detected for hydrogen atom transfer from the [alpha]-CH2 group of alcohol to the halogenoalkene radical cations. These findings lead to a revised mechanism of the oxidation process and provide a plausible explanation for the excessive H/D exchange between 1+ and CD3OH during their slow reaction.

  8. A search for blues brothers: X-ray crystallographic/spectroscopic characterization of the tetraarylbenzidine cation radical as a product of aging of solid magic blue.

    PubMed

    Talipov, Marat R; Hossain, Mohammad M; Boddeda, Anitha; Thakur, Khushabu; Rathore, Rajendra

    2016-03-14

    Magic blue (MB+˙ SbCl6− salt), i.e. tris-4-bromophenylamminium cation radical, is a routinely employed one-electron oxidant that slowly decomposes in the solid state upon storage to form so called ‘blues brothers’, which often complicate the quantitative analyses of the oxidation processes. Herein, we disclose the identity of the main ‘blues brother’ as the cation radical and dication of tetrakis-(4-bromophenyl)benzidine (TAB) by a combined DFT and experimental approach, including isolation of TAB+˙ SbCl6− and its X-ray crystallography characterization. The formation of TAB in aged magic blue samples occurs by a Scholl-type coupling of a pair of MB followed by a loss of molecular bromine. The recognition of this fact led us to the rational design and synthesis of tris(2-bromo-4-tert-butylphenyl)amine, referred to as ‘blues cousin’ (BC: Eox1 = 0.78 V vs. Fc/Fc+, λmax(BC+˙) = 805 nm, εmax = 9930 cm−1 M−1), whose oxidative dimerization is significantly hampered by positioning the sterically demanding tert-butyl groups at the para-positions of the aryl rings. A ready two-step synthesis of BC from triphenylamine and the high stability of its cation radical (BC+˙) promise that BC will serve as a ready replacement for MB and an oxidant of choice for mechanistic investigations of one-electron transfer processes in organic, inorganic, and organometallic transformations.

  9. Enhanced PCBs sorption on biochars as affected by environmental factors: Humic acid and metal cations.

    PubMed

    Wang, Yu; Wang, Lei; Fang, Guodong; Herath, H M S K; Wang, Yujun; Cang, Long; Xie, Zubin; Zhou, Dongmei

    2013-01-01

    Biochar plays an important role in the behaviors of organic pollutants in the soil environment. The role of humic acid (HA) and metal cations on the adsorption affinity of polychlorinated biphenyls (PCBs) to the biochars in an aqueous medium and an extracted solution from a PCBs-contaminated soil was studied using batch experiments. Biochars were produced with pine needles and wheat straw at 350 °C and 550 °C under anaerobic condition. The results showed that the biochars had high adsorption affinity for PCBs. Pine needle chars adsorbed less nonplanar PCBs than planar ones due to dispersive interactions and separation. Coexistence of HA and metal cations increased PCBs sorption on the biochars accounted for HA adsorption and cation complexation. The results will aid in a better understanding of biochar sorption mechanism of contaminants in the environment.

  10. Ascorbic acid metabolism in protection against free radicals: A radiation model

    SciTech Connect

    Rose, R.C. )

    1990-06-15

    The role of ascorbic acid in scavenging free radicals was evaluated in a model of mammalian colonic epithelium homogenized in physiologic buffer and exposed to ionizing radiation. Ascorbic acid interacts with hydroxyl free radicals, resulting in production of the ascorbate free radical (AFR). Colonic mucosa contains a soluble factor that is heat sensitive, PCA precipitable and is contained within 1,000 MW dialysis tubing; it uses GSH and cysteine to reduce AFR. The factor from rat colon is fractionated between 55 and 70% saturation with solid (NH4)2SO4; a 3-4 fold increase in enzyme activity was achieved. We suggest that the factor is a cytosolic enzyme appropriately referred to as soluble AFR-reductase. This information provides insight into the mechanism by which ascorbic acid protects against damage by hydroxyl free radicals.

  11. A complete map of the ion chemistry of the naphthalene radical cation? DFT and RRKM modeling of a complex potential energy surface

    SciTech Connect

    Solano, Eduardo A.; Mayer, Paul M.

    2015-09-14

    The fragmentation mechanisms of the naphthalene molecular ion to [M–C{sub 4}H{sub 2}]{sup +•}, [M–C{sub 2}H{sub 2}]{sup +•}, [M–H{sub 2}]{sup +•}, and [M–H{sup •}]{sup +} were obtained at the UB3LYP/6-311+G(3df,2p)//UB3LYP/6-31G(d) level of theory and were subsequently used to calculate the microcanonical rate constants, k(E)’s, for all the steps by the Rice-Ramsperger-Kassel-Marcus formalism. The pre-equilibrium and steady state approximations were applied on different regions of the potential energy profiles to obtain the fragmentation k(E)’s and calculate the relative abundances of the ions as a function of energy. These results reproduce acceptably well the imaging photoelectron-photoion coincidence spectra of naphthalene, in the photon-energy range 14.0–18.8 eV that was previously reported by our group. Prior to dissociation, the molecular ion rapidly equilibrates with a set of isomers that includes the Z- and E-phenylvinylacetylene (PVA) radical cations. The naphthalene ion is the predominant isomer below 10 eV internal energy, with the other isomers remaining at steady state concentrations. Later on, new steady-state intermediates are formed, such as the azulene and 1-phenyl-butatriene radical cations. The naphthalene ion does not eject an H atom directly but eliminates an H{sub 2} molecule in a two-step fragmentation. H{sup •} loss occurs instead from the 1-phenyl-butatriene ion. The PVA ions initiate the ejection of diacetylene (C{sub 4}H{sub 2}) to yield the benzene radical cation. Acetylene elimination yields the pentalene cation at low energies (where it can account for 45.9%–100.0% of the rate constant of this channel), in a three-step mechanism starting from the azulene ion. However, above 7.6 eV, the major [M–C{sub 2}H{sub 2}]{sup +•} structure is the phenylacetylene cation.

  12. A complete map of the ion chemistry of the naphthalene radical cation? DFT and RRKM modeling of a complex potential energy surface.

    PubMed

    Solano, Eduardo A; Mayer, Paul M

    2015-09-14

    The fragmentation mechanisms of the naphthalene molecular ion to [M-C4H2](+•), [M-C2H2](+•), [M-H2](+•), and [M-H(•)](+) were obtained at the UB3LYP/6-311+G(3df,2p)//UB3LYP/6-31G(d) level of theory and were subsequently used to calculate the microcanonical rate constants, k(E)'s, for all the steps by the Rice-Ramsperger-Kassel-Marcus formalism. The pre-equilibrium and steady state approximations were applied on different regions of the potential energy profiles to obtain the fragmentation k(E)'s and calculate the relative abundances of the ions as a function of energy. These results reproduce acceptably well the imaging photoelectron-photoion coincidence spectra of naphthalene, in the photon-energy range 14.0-18.8 eV that was previously reported by our group. Prior to dissociation, the molecular ion rapidly equilibrates with a set of isomers that includes the Z- and E-phenylvinylacetylene (PVA) radical cations. The naphthalene ion is the predominant isomer below 10 eV internal energy, with the other isomers remaining at steady state concentrations. Later on, new steady-state intermediates are formed, such as the azulene and 1-phenyl-butatriene radical cations. The naphthalene ion does not eject an H atom directly but eliminates an H2 molecule in a two-step fragmentation. H(•) loss occurs instead from the 1-phenyl-butatriene ion. The PVA ions initiate the ejection of diacetylene (C4H2) to yield the benzene radical cation. Acetylene elimination yields the pentalene cation at low energies (where it can account for 45.9%-100.0% of the rate constant of this channel), in a three-step mechanism starting from the azulene ion. However, above 7.6 eV, the major [M-C2H2](+•) structure is the phenylacetylene cation.

  13. A complete map of the ion chemistry of the naphthalene radical cation? DFT and RRKM modeling of a complex potential energy surface

    NASA Astrophysics Data System (ADS)

    Solano, Eduardo A.; Mayer, Paul M.

    2015-09-01

    The fragmentation mechanisms of the naphthalene molecular ion to [M-C4H2]+•, [M-C2H2]+•, [M-H2]+•, and [M-H•]+ were obtained at the UB3LYP/6-311+G(3df,2p)//UB3LYP/6-31G(d) level of theory and were subsequently used to calculate the microcanonical rate constants, k(E)'s, for all the steps by the Rice-Ramsperger-Kassel-Marcus formalism. The pre-equilibrium and steady state approximations were applied on different regions of the potential energy profiles to obtain the fragmentation k(E)'s and calculate the relative abundances of the ions as a function of energy. These results reproduce acceptably well the imaging photoelectron-photoion coincidence spectra of naphthalene, in the photon-energy range 14.0-18.8 eV that was previously reported by our group. Prior to dissociation, the molecular ion rapidly equilibrates with a set of isomers that includes the Z- and E-phenylvinylacetylene (PVA) radical cations. The naphthalene ion is the predominant isomer below 10 eV internal energy, with the other isomers remaining at steady state concentrations. Later on, new steady-state intermediates are formed, such as the azulene and 1-phenyl-butatriene radical cations. The naphthalene ion does not eject an H atom directly but eliminates an H2 molecule in a two-step fragmentation. H• loss occurs instead from the 1-phenyl-butatriene ion. The PVA ions initiate the ejection of diacetylene (C4H2) to yield the benzene radical cation. Acetylene elimination yields the pentalene cation at low energies (where it can account for 45.9%-100.0% of the rate constant of this channel), in a three-step mechanism starting from the azulene ion. However, above 7.6 eV, the major [M-C2H2]+• structure is the phenylacetylene cation.

  14. Metal cation dependence of interactions with amino acids: bond dissociation energies of Rb(+) and Cs(+) to the acidic amino acids and their amide derivatives.

    PubMed

    Armentrout, P B; Yang, Bo; Rodgers, M T

    2014-04-24

    Metal cation-amino acid interactions are key components controlling the secondary structure and biological function of proteins, enzymes, and macromolecular complexes comprising these species. Determination of pairwise interactions of alkali metal cations with amino acids provides a thermodynamic vocabulary that begins to quantify these fundamental processes. In the present work, we expand a systematic study of such interactions by examining rubidium and cesium cations binding with the acidic amino acids (AA), aspartic acid (Asp) and glutamic acid (Glu), and their amide derivatives, asparagine (Asn) and glutamine (Gln). These eight complexes are formed using electrospray ionization and their bond dissociation energies (BDEs) are determined experimentally using threshold collision-induced dissociation with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy-dependent cross sections include consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. Quantum chemical calculations are conducted at the B3LYP, MP2(full), and M06 levels of theory using def2-TZVPPD basis sets, with results showing reasonable agreement with experiment. At 0 and 298 K, most levels of theory predict that the ground-state conformers for M(+)(Asp) and M(+)(Asn) involve tridentate binding of the metal cation to the backbone carbonyl, amino, and side-chain carbonyl groups, although tridentate binding to the carboxylic acid group and side-chain carbonyl is competitive for M(+)(Asn). For the two longer side-chain amino acids, Glu and Gln, multiple structures are competitive. A comparison of these results to those for the smaller alkali cations, Na(+) and K(+), provides insight into the trends in binding energies associated with the molecular polarizability and dipole moment of the side chain. For all four metal cations, the BDEs are inversely correlated with the size of the metal cation and follow the order Asp < Glu

  15. Contributions of acid deposition and natural processes to cation leaching from forest soils: a review

    SciTech Connect

    Johnson, D.W.; Van Miegroet, H.; Cole, D.W.; Richter, D.D.

    1983-01-01

    Methods of quantifying the roles of atmospheric acid inputs and internal acid generation by carbonic, organic, and nitric acids are illustrated by reviewing data sets from several intensively studied sites in North America. Some of the sites (tropical, Costa Rica (La Selva); temperate deciduous, Tennessee (Walker Branch); and temperate coniferous, Washington (Thompson)) received acid precipitation whereas others (northern, southeast Alaska (Petersburg); and subalpine, Washington Cascades (Findley Lake)) did not. Natural leaching by carbonic acid dominated soil leaching in the tropical and temperate coniferous sites, nitric acid (caused by nitrification) dominated leaching in an N-fixing temperate deciduous site (red alder in Washington), and organic acids dominated surface soil leaching in the subalpine site and contributed to leaching of surface soils in several other sites. Only at the temperate deciduous sites in eastern Tennessee did atmospheric acid input play a major role in soil leaching. In no case, however, are the annual net losses of cations regarded as alarming as compared to soil exchangeable cation capital.

  16. Reactions of 5-methylcytosine cation radicals in DNA and model systems: thermal deprotonation from the 5-methyl group vs. excited state deprotonation from sugar

    PubMed Central

    Adhikary, Amitava; Kumar, Anil; Palmer, Brian J.; Todd, Andrew D.; Heizer, Alicia N.; Sevilla, Michael D.

    2014-01-01

    Purpose To study the formation and subsequent reactions of the 5-methyl-2′-deoxycytidine cation radical (5-Me-2′-dC•+) in nucleosides and DNA-oligomers and compare to one electron oxidized thymidine. Materials and methods Employing electron spin resonance (ESR), cation radical formation and its reactions were investigated in 5-Me-2′-dC, thymidine (Thd) and their derivatives, in fully double stranded (ds) d[GC*GC*GC*GC*]2 and in the 5-Me-C/A mismatched, d[GGAC*AAGC:CCTAATCG], where C* = 5-Me-C. Results We report 5-Me-2′-dC•+ production by one-electron oxidation of 5-Me-2′-dC by Cl2•− via annealing in the dark at 155 K. Progressive annealing of 5-Me-2′-dC•+ at 155 K produces the allylic radical (C-CH2•). However, photoexcitation of 5-Me-2′-dC•+ by 405 nm laser or by photoflood lamp leads to only C3′• formation. Photoexcitation of N3-deprotonated thyminyl radical in Thd and its 5′-nucleotides leads to C3′• formation but not in 3′-TMP which resulted in the allylic radical (U-CH2•) and C5′• production. For excited 5-Me-2′,3′-ddC•+, absence of the 3′-OH group does not prevent C3′• formation. For d[GC*GC*GC*GC*]2 and d[GGAC*AAGC:CCTAATCG], intra-base paired proton transferred form of G cation radical (G(N1-H)•:C(+H+)) is found with no observable 5-Me-2′-dC•+ formation. Photoexcitation of (G(N1-H)•:C(+H+)) in d[GC*GC*GC*GC*]2 produced only C1′• and not the expected photoproducts from 5-Me-2′-dC•+. However, photoexcitation of (G(N1-H)•:C(+H+)) in d[GGAC*AAGC:CCTAATCG] led to C5′• and C1′• formation. Conclusions C-CH2• formation from 5-Me-2′-dC•+ occurs via ground state deprotonation from C5-methyl group on the base. In the excited 5-Me-2′-dC•+ and 5-Me-2′,3′-ddC•+, spin and charge localization at C3′ followed by deprotonation leads to C3′• formation. Thus, deprotonation from C3′ in the excited cation radical is kinetically controlled and sugar C-H bond energies are

  17. Interactive enhancements of ascorbic acid and iron in hydroxyl radical generation in quinone redox cycling.

    PubMed

    Li, Yi; Zhu, Tong; Zhao, Jincai; Xu, Bingye

    2012-09-18

    Quinones are toxicological substances in inhalable particulate matter (PM). The mechanisms by which quinones cause hazardous effects can be complex. Quinones are highly active redox molecules that can go through a redox cycle with their semiquinone radicals, leading to formation of reactive oxygen species. Electron spin resonance spectra have been reported for semiquinone radicals in PM, indicating the importance of ascorbic acid and iron in quinone redox cycling. However, these findings are insufficient for understanding the toxicity associated with quinone exposure. Herein, we investigated the interactions among anthraquinone (AQ), ascorbic acid, and iron in hydroxyl radical (·OH) generation through the AQ redox cycling process in a physiological buffer. We measured ·OH concentration and analyzed the free radical process. Our results showed that AQ, ascorbic acid, and iron have synergistic effects on ·OH generation in quinone redox cycling; i.e., ascorbyl radical oxidized AQ to semiquinone radical and started the redox cycling, iron accelerated this oxidation and enhanced ·OH generation through Fenton reactions, while ascorbic acid and AQ could help iron to release from quartz surface and enhance its bioavailability. Our findings provide direct evidence for the redox cycling hypothesis about airborne particle surface quinone in lung fluid.

  18. 2-Acrylamido-2-methyl-1-propanesulfonic Acid Grafted Poly(vinylidene fluoride-co-hexafluoropropylene)-Based Acid-/Oxidative-Resistant Cation Exchange for Membrane Electrolysis.

    PubMed

    Pandey, Ravi P; Das, Arindam K; Shahi, Vinod K

    2015-12-30

    For developing acid-/oxidative-resistant aliphatic-polymer-based cation-exchange membrane (CEM), macromolecular modification of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) was carried out by controlled chemical grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). To introduce the unsaturation suitable for chemical grafting, dehydrofluorination of commercially available PVDF-co-HFP was achieved under alkaline medium. Sulfonated copolymer (SCP) was prepared by the free radical copolymerization of dehydofluorinated PVDF-co-HFP (DHPVDF-co-HFP) and AMPS in the presence of free radical initiator. Prepared SCP-based CEMs were analyzed for their morphological characteristics, ion-exchange capacity (IEC), water uptake, conductivity, and stabilities (mechanical, chemical, and thermal) in comparison with state-of-art Nafion117 membrane. High bound water content avoids the membrane dehydration, and most optimal (SCP-1.33) membrane exhibited about ∼2.5-fold high bound water content in comparison with that of Nafion117 membrane. Bunsen reaction of iodine-sulfur (I-S) was successfully performed by direct-contact-mode membrane electrolysis in a two-compartment electrolytic cell using different SCP membranes. High current efficiency (83-99%) confirmed absence of any side reaction and 328.05 kJ mol-H2(-1) energy was required for to produce 1 mol of H2 by electrolytic cell with SCP-1.33 membrane. In spite of low conductivity for reported SCP membrane in comparison with that of Nafion117 membrane, SCP-1.33 membrane was assessed as suitable candidate for electrolysis because of its low-cost nature and excellent stabilities in highly acidic environment may be due to partial fluorinated segments in the membrane structure.

  19. Effects of iron and phytic acid on production of extracellular radicals by Enterococcus faecalis.

    PubMed

    Moore, Danny R; Kotake, Yashige; Huycke, Mark M

    2004-12-01

    Enterococcus faecalis is a human intestinal commensal that produces extracellular superoxide, hydrogen peroxide, and hydroxyl radical while colonizing the intestinal tract. To determine whether dietary factors implicated in colorectal cancer affect oxidant production by E. faecalis, radicals were measured in rats colonized with this microorganism while on diets supplemented with iron or phytic acid. Hydroxyl radical activity was measured by assaying for aromatic hydroxylation products of D-phenylalanine using reverse-phase high-performance liquid chromatography and electrochemical detection. In vitro, as expected, iron enhanced, and phytic acid decreased, hydroxyl radical formation by E. faecalis. For rats colonized with E. faecalis given supplemental dietary iron (740 mg elemental iron as ferric phosphate per kg diet) or phytic acid (1.2% w/w), no differences were found in concentrations of urinary ortho- or meta- isomers of D-phenylalanine compared to rats on a basal diet. Aqueous radicals in colonic contents were further assessed ex vivo by electron spin resonance using 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap. Mixtures of thiyl (sulfur-centered) and oxygen-centered radicals were detected across all diets. In vitro, similar spectra were observed when E. faecalis was incubated with hydrogen sulfide, air-oxidized cysteine, or an alkylsulfide, as typical sulfur-containing compounds that might occur in colonic contents. In conclusion, intestinal colonization with E. faecalis in a rat model generates both thiyl and oxygen-centered radicals in colonic contents. Radical formation, however, was not significantly altered by short-term dietary supplementation with iron or phytic acid.

  20. Test for antioxidant ability by scavenging long-lived mutagenic radicals in mammalian cells and by blood test with intentional radicals: an application of gallic acid

    NASA Astrophysics Data System (ADS)

    Kumagai, Jun; Kawaura, Tomoko; Miyazaki, Tetsuo; Prost, Michel; Prost, Emmanuelle; Watanabe, Masami; Quetin-Leclercq, Joëlle

    2003-01-01

    Antioxidant ability of gallic acid (GA) are determined both by electron spin resonance measurement of long-lived radicals produced in γ-ray irradiated Syrian golden hamster embryo cells with GA and by hemolysis measurement with GA when blood cells are submitted to radicals. Scavenging properties of GA are determined by the reaction rate constant with long-lived mutagenic radicals in the cells while the blood test allows to analyze the global effects of this compound: radical scavenger+metal ion chelator+regeneration of intra- and extra-cellular antioxidant.

  1. [Nutrition, acid-base metabolism, cation-anion difference and total base balance in humans].

    PubMed

    Mioni, R; Sala, P; Mioni, G

    2008-01-01

    The relationship between dietary intake and acid-base metabolism has been investigated in the past by means of the inorganic cation-anion difference (C(+)(nm)-A(-)(nm)) method based on dietary ash-acidity titration after the oxidative combustion of food samples. Besides the inorganic components of TA (A(-)(nm)-C(+)(nm)), which are under renal control, there are also metabolizable components (A(-)(nm)-C(+)(nm)) of TA, which are under the control of the intermediate metabolism. The whole body base balance, NBb(W), is obtained only by the application of C(+)(nm)-A(-)(nm) to food, feces and urine, while the metabolizable component (A(-)(nm)-C(+)(nm)) is disregarded. A novel method has been subsequently suggested to calculate the net balance of fixed acid, made up by the difference between the input of net endogenous acid production: NEAP = SO(4)(2-)+A(-)(m)-(C(+)(nm)-A(-)(nm)), and the output of net acid excretion: NAE = TA + NH(4)(+) - HCO(3)(-). This approach has been criticized because 1) it includes metabolizable acids, whose production cannot be measured independently; 2) the specific control of metabolizable acid and base has been incorrectly attributed to the kidney; 3) the inclusion of A-m in the balance input generates an acid overload; 4) the object of measurement in making up a balance has to be the same, a condition not fulfilled as NEAP is different from NAE. Lastly, by rearranging the net balance of the acid equation, the balance of nonmetabolizable acid equation is obtained. Therefore, any discrepancy between these two equations is due to the inaccuracy in the urine measurement of metabolizable cations and/or anions.

  2. Synthesis and Performance Properties of Cationic Fabric Softeners Derived from Free Fatty Acid of Tallow Fat.

    PubMed

    Mondal, Mithun G; Pratap, Amit Prabhakar

    2016-08-01

    Esterquat cationic softener is basically the class of surface active quaternary ammonium compounds. Esterquat compounds were synthesized and their surface behavior, antibacterial activity and Textile softening properties were investigated. Easily found cheap material was used to synthesize cationic fabric softeners. This fabric softener will be a good for commercially and industrially important because their emulsify activity, rewettability dispersing power and softness. Free fatty acids were derived from tallow oil and were treated with triethanolamine and mono-ethanolamine at 140°C. This diester was quaternaries with dimethyl sulphate and benzyl chloride. The synthesized esterquat compounds were characterized by its cationic content, 1H NMR and FT-IR analysis. In addition to the cationic content, surface tension, CMC (critical micelle concentration), rewettability, fabric softening, emulsification and dispersing power were determined as their surface-active properties. The fabric softening activity of esterquat and esteramide prepared from DMS was better softening activity of fabrics compared to untreated cotton and polyester fabrics cloth. The presented result shows that the esterquat made from BCl exhibit the best dispersing power. The esterquat made from DMS both in TEA and MEA shows good rewettability was determined.

  3. Acidic deposition, cation mobilization, and biochemical indicators of stress in healthy red spruce

    USGS Publications Warehouse

    Shortle, W.C.; Smith, K.T.; Minocha, R.; Lawrence, G.B.; David, M.B.

    1997-01-01

    Dendrochemical and biochemical markers link stress in apparently healthy red spruce trees (Picea rubens) to acidic deposition. Acidic deposition to spruce forests of the northeastern USA increased sharply during the 1960s. Previous reports related visible damage of trees at high elevations to root and soil processes. In this report, dendrochemical and foliar biochemical markers indicate perturbations in biological processes in healthy red spruce trees across the northeastern USA. Previous research on the dendrochemistry of red spruce stemwood indicated that under uniform environmental conditions, stemwood concentrations of Ca and Mg decreased with increasing radial distance from the pith. For nine forest locations, frequency analysis shows that 28 and 52% of samples of red spruce stemwood formed in the 1960s are enriched in Ca and Mg, respectively, relative to wood formed prior to and after the 1960s. This enrichment in trees throughout the northeastern USA may be interpretable as a signal of increased availability of essential cations in forest soils. Such a temporary increase in the availability of Ca and Mg could be caused by cation mobilization, a consequence of increased acidic deposition. During cation mobilization, essential Ca and Mg as well as potentially harmful Al become more available for interaction with binding sites in the soil and absorbing roots. As conditions which favor cation mobilization continue, Ca and Mg can be leached or displaced from the soil. A measure of the interaction between Ca and Al is the Al/Ca binding ratio (molar charge ratio of exchangeable Al to exchangeable Ca). As the Al/Ca binding ratio in the root zone increased from 0.3 to 1.9, the foliar concentration of the biochemical stress marker putrescine also increased from 45 to 145 nm g-1. The correlation of the putrescine concentration to the Al/Ca binding ratio (adj. r2 = 0.68, P < 0.027) suggests that foliar stress may be linked to soil chemistry.

  4. Heterogeneous kinetics, products, and mechanisms of ferulic acid particles in the reaction with NO3 radicals

    NASA Astrophysics Data System (ADS)

    Liu, Changgeng; Zhang, Peng; Wen, Xiaoying; Wu, Bin

    2017-03-01

    Methoxyphenols, as an important component of wood burning, are produced by lignin pyrolysis and considered to be the potential tracers for wood smoke emissions. In this work, the heterogeneous reaction between ferulic acid particles and NO3 radicals was investigated. Six products including oxalic acid, 4-vinylguaiacol, vanillin, 5-nitrovanillin, 5-nitroferulic acid, and caffeic acid were confirmed by gas chromatography-mass spectrometry (GC-MS). In addition, the reaction mechanisms were proposed and the main pathways were NO3 electrophilic addition to olefin and the meta-position to the hydroxyl group. The uptake coefficient of NO3 radicals on ferulic acid particles was 0.17 ± 0.02 and the effective rate constant under experimental conditions was (1.71 ± 0.08) × 10-12 cm3 molecule-1 s-1. The results indicate that ferulic acid degradation by NO3 can be an important sink at night.

  5. Kinetics and product branching fractions of reactions between a cation and a radical: Ar(+) + CH3 and O2(+) + CH3.

    PubMed

    Sawyer, Jordan C; Shuman, Nicholas S; Wiens, Justin P; Viggiano, Albert A

    2015-02-12

    A novel technique is described for the measurement of rate constants and product branching fractions of thermal reactions between cation and radical species. The technique is a variant of the variable electron and neutral density attachment mass spectrometry (VENDAMS) method, employing a flowing afterglow-Langmuir probe apparatus. A radical species is produced in situ via dissociative electron attachment to a neutral precursor; this allows for a quantitative derivation of the radical concentration and, as a result, a quantitative determination of rate constants. The technique is applied to the reactions of Ar(+) and O2(+) with CH3 at 300 K. The Ar(+) + CH3 reaction proceeds near the collisional rate constant of 1.1 × 10(-9) cm(3) s(-1) and has three product channels: → CH3(+) + Ar (k = 5 ± 2 × 10(-10) cm(3) s(-1)), → CH2(+) + H + Ar (k = 7 ± 2 × 10(-10) cm(3) s(-1)), → CH(+) + H2 + Ar (k = 5 ± 3 × 10(-11) cm(3) s(-1)). The O2(+) + CH3 reaction is also efficient, with direct charge transfer yielding CH3(+) as the primary product channel. Several results needed to support these measurements are reported, including the kinetics of Ar(+) and O2(+) with CH3I, electron attachment to CH3I, and mutual neutralization of CH3(+) and CH2(+) with I(-).

  6. OH-radical induced degradation of hydroxybenzoic- and hydroxycinnamic acids and formation of aromatic products—A gamma radiolysis study

    NASA Astrophysics Data System (ADS)

    Krimmel, Birgit; Swoboda, Friederike; Solar, Sonja; Reznicek, Gottfried

    2010-12-01

    The OH-radical induced degradation of hydroxybenzoic acids (HBA), hydroxycinnamic acids (HCiA) and methoxylated derivatives, as well as of chlorogenic acid and rosmarinic acid was studied by gamma radiolysis in aerated aqueous solutions. Primary aromatic products resulting from an OH-radical attachment to the ring (hydroxylation), to the position occupied by the methoxyl group (replacement -OCH 3 by -OH) as well as to the propenoic acid side chain of the cinnamic acids (benzaldehyde formations) were analysed by HPLC-UV and LC-ESI-MS. A comparison of the extent of these processes is given for 3,4-dihydroxybenzoic acid, vanillic acid, isovanillic acid, syringic acid, cinnamic acid, 4-hydroxycinnamic acid, caffeic acid, ferulic acid, isoferulic acid, chlorogenic acid, and rosmarinic acid. For all cinnamic acids and derivatives benzaldehydes were significant oxidation products. With the release of caffeic acid from chlorogenic acid the cleavage of a phenolic glycoside could be demonstrated. Reaction mechanisms are discussed.

  7. Tetracycline adsorption on kaolinite: pH, metal cations and humic acid effects.

    PubMed

    Zhao, Yanping; Geng, Jinju; Wang, Xiaorong; Gu, Xueyuan; Gao, Shixiang

    2011-07-01

    Contamination of environmental matrixes by human and animal wastes containing antibiotics is a growing health concern. Because tetracycline is one of the most widely-used antibiotics in the world, it is important to understand the factors that influence its mobility in soils. This study investigated the effects of pH, background electrolyte cations (Li(+), Na(+), K(+), Ca(2+) and Mg(2+)), heavy metal Cu(2+) and humic acid (HA) on tetracycline adsorption onto kaolinite. Results showed that tetracycline was greatly adsorbed by kaolinite over pH 3-6, then decreased with the increase of pH, indicating that tetracycline adsorption mainly through ion exchange of cations species and complexation of zwitterions species. In the presence of five types of cations (Li(+), Na(+), K(+), Ca(2+) and Mg(2+)), tetracycline adsorption decreased in accordance with the increasing of atomic radius and valence of metal cations, which suggested that outer-sphere complexes formed between tetracycline and kaolinite, and the existence of competitor ions lead to the decreasing adsorption. The presence of Cu(2+) greatly enhanced the adsorption probably by acting as a bridge ion between tetracycline species and the edge sites of kaolinite. HA also showed a major effect on the adsorption: at pH < 6, the presence of HA increased the adsorption, while the addition of HA showed little effect on tetracycline adsorption at higher pH. The soil environmental conditions, like pH, metal cations and soil organic matter, strongly influence the adsorption behavior of tetracycline onto kaolinite and need to be considered when assessing the environmental toxicity of tetracycline.

  8. Sorption of REE and TPE from HNO{sub 3} solutions on strong-acid sulfonated cation exchanger KU-2

    SciTech Connect

    Chuveleva, E.A.; Kharitonov, O.V.; Firsova, L.A.

    1995-05-01

    Sorption of rare earths (REE) on the strong-acid sulfonated cation exchanger KU-2 is studied as a function of the solution acidity (0.1-2.0 M HNO{sub 3}) and REE concentration. In concentrated nitrate solutions where M(NO{sub 3}){sub 2}{sup +} and M(NO{sub 3}){sub 2}{sup +} can form and be sorbed by the cation exchanger, the capacity of the exchanger seems to increase by 20%.

  9. [Effects of ascorbic acid on the free radical formations of isoniazid and its metabolites].

    PubMed

    Matsuki, Y; Akazawa, M; Tsuchiya, K; Sakurai, H; Kiwada, H; Goromaru, T

    1991-10-01

    By the use of electron spin resonance (ESR) spectroscopy and of spin-trapping technique, the effects of ascorbic acid on the formation of the free radical intermediates due to isoniazid (INAH) and its metabolites were investigated with a microsomal system. When alpha-(4-pyridyl 1-oxide)-N-tert butylnitrone (4-POBN) was used as a spin trapping agent, the ESR signal due to hydrazine (Hy) was formed to be most intensive among others. Therefore, it was presumed that Hy is a potent intermediate to cause an INAH-induced hepatic injury. In the presence of ascorbic acid (AA), the free radical formation of Hy, INAH and acetyl hydrazine was significantly inhibited, suggesting that AA may affect the INAH-hepatitis. By the addition of inhibitors of cytochrome P-450 like metyrapone and CO, the generation of the radical from Hy decreased, confirming that the radical is formed by the cytochrome P-450 dependent microsome systems. The 4-POBN-trapped radical species generated from Hy was presumed to be the hydrazyl radical by the results of mass spectrometry.

  10. Enhancing Cation Diffusion and Suppressing Anion Diffusion via Lewis-Acidic Polymer Electrolytes.

    PubMed

    Savoie, Brett M; Webb, Michael A; Miller, Thomas F

    2017-02-02

    Solid polymer electrolytes (SPEs) have the potential to increase both the energy density and stability of lithium-based batteries, but low Li(+) conductivity remains a barrier to technological viability. SPEs are designed to maximize Li(+) diffusivity relative to the anion while maintaining sufficient salt solubility. It is thus remarkable that poly(ethylene oxide) (PEO), the most widely used SPE, exhibits Li(+) diffusivity that is an order of magnitude smaller than that of typical counterions at moderate salt concentrations. We show that Lewis-basic polymers like PEO favor slow cation and rapid anion diffusion, while this relationship can be reversed in Lewis-acidic polymers. Using molecular dynamics, polyboranes are identified that achieve up to 10-fold increases in Li(+) diffusivities and significant decreases in anion diffusivities, relative to PEO in the dilute-ion regime. These results illustrate a general principle for increasing Li(+) diffusivity and transference number with chemistries that exhibit weaker cation and stronger anion coordination.

  11. Detection of Anisotropic Hyperfine Components of Chemically Prepared Carotenoid Radical Cations:1D and 2D ESEEM and Pulsed ENDOR Study

    SciTech Connect

    Konovalova, Tatyana A.; Dikanov, Sergei A.; Bowman, Michael K.; Kispert, Lowell D.

    2001-09-06

    Canthaxanthin and 8'-apo-B-caroten-8'-al radical cations chemically prepared on activated silica-alumina and in CH2CI2 solution containing A1C13 were studied by pulsed EPR and ENDOR spectroscopies. Both the 1D three-pulse ESEEM and the 2D HYSCORE spectra of the carotenoid-A1C13 mixtures exhibited the 27 A1 nuclei peak at 3.75 MHz. This indicates electron-transfer interactions between carotenoids and A1III ions resulting in the formation and stabilization of carotenoid radical cations. Davies ENDOR measurements of the canthaxanthin radical cation on silica-alumina determined the hyperfine couplings of B protons belonging to three different methyl groups with ahI=2.6 MHz, aH2=8.6MHz, and ah3 ca. 13 MHz. The principal components of the proton hyperfine tensors were obtained from HYSCORE spectra in A1C13 solutions and on the solid support. Identification of the protons was made on the basis of isotropic hyperfine couplings determined by RHF-INDO/SP molecular orbital calculations. In frozen A1C13 solution, the C(7, 7')Ha and C(14, 14')-Ha a protons were observed for Canthaxanthin and the C(8 or 14')-Ha, C(15')-Ha were observed for 8'-apo-B-caroten-8'-al. On the silica-alumina support, the C(10, 10')-Ha, C(11, 11')-Ha, and C(15,15')-Ha a protons were measured for Canthaxanthin and the C(12)-Ha and C(15')-Ha were measured for 8' apo-B-caroten-8'-al. Some protons with large isotropic couplings (>10 MHz) determined from HYSCORE analysis could be assigned to B protons, but the principal components of their hyperfine tensors are much more anisotropic than those reported previously for B protons. We suggest that cis/trans isomerization of carotenoids on silica-alumina results in stabilization of di-cis isomers with large isotropic couplings for some a protons which are comparable to those of B protons.

  12. Acidic deposition, cation mobilization, and biochemical indicators of stress in healthy red spruce

    SciTech Connect

    Shortle, W.C.; Smith, K.T.; Minocha, R.

    1997-05-01

    Dendrochemical and biochemical markers link stress in apparently healthy red spruce trees (Picea rubens) to acidic deposition. Previous reports related visible damage of trees at high elevations to root and soil processes. In this report, dendrochemical and foliar biochemical markers indicate perturbations in biological processes in healthy red spruce trees across the northeastern USA. Previous research on the dendrochemistry of red spruce stemwood indicated that under uniform environmental conditions, stemwood concentrations of Ca and Mg decreased with increasing radial distance from the pith. For nine forest locations, frequency analysis shows that 28 and 52% of samples of red spruce stemwood formed in the 1960s are enriched in Ca and Mg, respectively, relative to wood formed prior to and after the 1960s. This enrichment in trees throughout the northeastern USA may be interpretable as a signal of increased availability of essential cations in forest soils. Such a temporary increase in the availability of Ca and Mg could be caused by cation mobilization, a consequence of increased acidic deposition. During cation mobilization, essential and Ca and Mg as well as potentially harmful Al become more available for interaction with binding sites in the soil and absorbing roots. As conditions which favor cation mobilization continue, Ca and Mg can be leached or displaced from the soil. A measure of the interaction between Ca and Al is the Al/Ca binding ratio (molar charge ratio of exchangeable Al to exchangeable Ca). As the Al/Ca binding ratio in the root zone increased from 0.3 to 1.9, the foliar concentration of the biochemical stress marker putrescine also increased form 45 to 145 nm g{sup {minus}1}. The correlation of the putrescine concentration to the Al/Ca binding ratio (adj. r{sup 2} = 0.68, P <0.027) suggests that foliar stress may be linked to soil chemistry. 32 refs., 2 figs., 1 tab.

  13. Cationic liposome–nucleic acid complexes for gene delivery and gene silencing

    PubMed Central

    Ewert, Kai K.; Majzoub, Ramsey N.; Leal, Cecília

    2014-01-01

    Cationic liposomes (CLs) are studied worldwide as carriers of DNA and short interfering RNA (siRNA) for gene delivery and gene silencing, and related clinical trials are ongoing. Optimization of transfection efficiency and silencing efficiency by cationic liposome carriers requires a comprehensive understanding of the structures of CL–nucleic acid complexes and the nature of their interactions with cell membranes as well as events leading to release of active nucleic acids within the cytoplasm. Synchrotron x-ray scattering has revealed that CL–nucleic acid complexes spontaneously assemble into distinct liquid crystalline phases including the lamellar, inverse hexagonal, hexagonal, and gyroid cubic phases, and fluorescence microscopy has revealed CL–DNA pathways and interactions with cells. The combining of custom synthesis with characterization techniques and gene expression and silencing assays has begun to unveil structure–function relations in vitro. As a recent example, this review will briefly describe experiments with surface-functionalized PEGylated CL–DNA nanoparticles. The functionalization, which is achieved through custom synthesis, is intended to address and overcome cell targeting and endosomal escape barriers to nucleic acid delivery faced by PEGylated nanoparticles designed for in vivo applications. PMID:25587216

  14. Influence of different free radicals on scavenging potency of gallic acid.

    PubMed

    Đorović, Jelena; Marković, Jasmina M Dimitrić; Stepanić, Višnja; Begović, Nebojša; Amić, Dragan; Marković, Zoran

    2014-07-01

    The M05-2X/6-311++G(d,p) and B3LYP-D2/6-311++G(d,p) models are used to evaluate scavenging potency of gallic acid. The hydrogen atom transfer (HAT), sequential proton loss electron transfer (SPLET), and single electron transfer followed by proton transfer (SET-PT) mechanisms of gallic acid with some radicals ((•)OO(-), (•)OH, and CH3OO(•)) were investigated using the corresponding thermodynamic quantities: bond dissociation enthalpy (BDE), ionization potential (IP), and proton affinity (PA). Namely, the ΔHBDE, ΔHIP, and ΔHPA values of the corresponding reactions in some solvents (water, DMSO, pentylethanoate, and benzene) are investigated using an implicit solvation model (SMD). An approach based on the reactions enthalpies related to the examined mechanisms is applied. This approach shows that a thermodynamically favored mechanism depends on the polarity of reaction media and properties of free radical reactive species. The most acidic 4-OH group of gallic acid is the active site for radical inactivation. The results of this investigation indicate that the SPLET mechanism can be a favored reaction pathway for all three radicals in all solvents, except for (•)OH in the aqueous solution. In water, gallic acid can inactivate (•)OH by the HAT mechanism.

  15. Low molecular weight hyaluronic acid prevents oxygen free radical damage to granulation tissue during wound healing.

    PubMed

    Trabucchi, E; Pallotta, S; Morini, M; Corsi, F; Franceschini, R; Casiraghi, A; Pravettoni, A; Foschi, D; Minghetti, P

    2002-01-01

    Hyaluronic acid protects granulation tissue from oxygen free radical damage and stimulates wound healing, but its molecular weight prevents it from permeating the epidermal barrier A low molecular weight hyaluronic acid preparation is able to permeate the skin, but it is unknown whether or not it retains the scavenging effects of oxygen free radicals in granulation tissue. Our experiments were conducted in rats with excisional or incisional wounds. Wound contraction over 11 days and breaking strength on the fifth day were measured. Oxygen free radical production was induced by intraperitoneal administration of two different xenobiotics: phenazine methosulfate and zymosan. The wounds were treated topically with low molecular weight hyaluronic acid (0.2%) cream or placebo. In the incisional wound group, the effects of superoxide dismutase were also determined. Absolute controls received wounds and placebo but no xenobiotics. Wound healing was significantly slower in the xenobiotic group than in the control groups. These effects were strongly reduced by topical administration of low molecular weight hyaluronic acid (0.2%) cream and in incisional wounds by topically injected superoxide dismutase. Low molecular weight hyaluronic acid is effective as the native compound against oxygen free radicals. Its pharmacological effects through transdermal administration should be tested in appropriate models.

  16. The influence of mono- and divalent cations on the cardiac metabolism of arachidonic acid

    SciTech Connect

    Weis, M.T.; Malik, K.U. )

    1989-06-01

    Our previous study indicated that, in the isolated rabbit heart, perfusion with Ca2+ free Krebs Henseleit buffer (KHB) results in increased conversion of exogenous arachidonic acid to PGE2 and 6-keto-PGF1 alpha, probably as the result of increased availability of substrate to cyclooxygenase. Since perfusion with Ca2+ free buffer is known to cause alterations in the cardiac content of various mono- and divalent cations, the present study was performed to determine: (a) The relationship between the conversion of exogenous arachidonic acid to prostaglandins and cardiac content of Na+, K+, Ca2+ and Mg2+; and (b) Whether enhanced arachidonic acid conversion to prostaglandins during Ca2+ free perfusion is due to reduced incorporation of this fatty acid into tissue lipids. Perfusion of the rabbit heart with Ca2+ free buffer produced a significant reduction in the tissue content of Na+, K+, Ca2+ and Mg2+. However, the production of 6-keto-PGF1 alpha from exogenous arachidonic acid was linearly correlated with tissue Mg2+. These observations, together with our finding that perfusion with Ca2+ free KHB reduced the incorporation of (3H) arachidonic acid into tissue lipids, suggests that Ca2+ free perfusion may, by reducing the activity of arachidonyl CoA synthetase (a Mg2+ dependent enzyme), decrease the acylation of arachidonic acid into lipids, thus increasing the availability of arachidonic acid to cyclooxygenase.

  17. Oxidation of guanine in G, GG, and GGG sequence contexts by aromatic pyrenyl radical cations and carbonate radical anions: relationship between kinetics and distribution of alkali-labile lesions.

    PubMed

    Lee, Young Ae; Durandin, Alexander; Dedon, Peter C; Geacintov, Nicholas E; Shafirovich, Vladimir

    2008-02-14

    Oxidatively generated DNA damage induced by the aromatic radical cation of the pyrene derivative 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene (BPT), and by carbonate radicals anions, was monitored from the initial one-electron transfer, or hole injection step, to the formation of hot alkali-labile chemical end-products monitored by gel electrophoresis. The fractions of BPT molecules bound to double-stranded 20-35-mer oligonucleotides with noncontiguous guanines G and grouped as contiguous GG and GGG sequences were determined by a fluorescence quenching method. Utilizing intense nanosecond 355 nm Nd:YAG laser pulses, the DNA-bound BPT molecules were photoionized to BPT*+ radicals by a consecutive two-photon ionization mechanism. The BPT*+ radicals thus generated within the duplexes selectively oxidize guanine by intraduplex electron-transfer reactions, and the rate constants of these reactions follow the trend 5'-..GGG.. > 5'-..GG.. > 5'-..G... In the case of CO3*- radicals, the oxidation of guanine occurs by intermolecular collision pathways, and the bimolecular rate constants are independent of base sequence context. However, the distributions of the end-products generated by CO3*- radicals, as well as by BPT*+, are base sequence context-dependent and are greater than those in isolated guanines at the 5'-G in 5'-...GG... sequences, and the first two 5'- guanines in the 5'-..GGG sequences. These results help to clarify the conditions that lead to a similar or different base sequence dependence of the initial hole injection step and the final distribution of oxidized, alkali-labile guanine products. In the case of the intermolecular one-electron oxidant CO3*-, the rate constant of hole injection is similar for contiguous and isolated guanines, but the subsequent equilibration of holes by hopping favors trapping and product formation at contiguous guanines, and the sequence dependence of these two phenomena are not correlated. In contrast, in the case of the DNA

  18. Theoretical calculations of Electron Paramagnetic Resonance parameters of liquid phase Orotic acid radical

    NASA Astrophysics Data System (ADS)

    Sarikaya, Ebru Karakaş; Dereli, Ömer

    2017-02-01

    To obtain liquid phase molecular structure, conformational analysis of Orotic acid was performed and six conformers were determined. For these conformations, eight possible radicals were modelled by using Density Functional Theory computations with respect to molecular structure. Electron Paramagnetic Resonance parameters of these model radicals were calculated and then they were compared with the experimental ones. Geometry optimizations of the molecule and modeled radicals were performed using Becke's three-parameter hybrid-exchange functional combined with the Lee-Yang-Parr correlation functional of Density Functional Theory and 6-311++G(d,p) basis sets in p-dioxane solution. Because Orotic acid can be mutagenic in mammalian somatic cells and it is also mutagenic for bacteria and yeast, it has been studied.

  19. A manganese(V)-oxo π-cation radical complex: influence of one-electron oxidation on oxygen-atom transfer.

    PubMed

    Prokop, Katharine A; Neu, Heather M; de Visser, Sam P; Goldberg, David P

    2011-10-12

    One-electron oxidation of Mn(V)-oxo corrolazine 2 affords 2(+), the first example of a Mn(V)(O) π-cation radical porphyrinoid complex, which was characterized by UV-vis, EPR, LDI-MS, and DFT methods. Access to 2 and 2(+) allowed for a direct comparison of their reactivities in oxygen-atom transfer (OAT) reactions. Both complexes are capable of OAT to PPh(3) and RSR substrates, and 2(+) was found to be a more potent oxidant than 2. Analysis of rate constants and activation parameters, together with DFT calculations, points to a concerted OAT mechanism for 2(+) and 2 and indicates that the greater electrophilicity of 2(+) likely plays a dominant role in enhancing its reactivity. These results are relevant to comparisons between Compound I and Compound II in heme enzymes.

  20. Hypomorphic variants of cationic amino acid transporter 3 in males with autism spectrum disorders.

    PubMed

    Nava, Caroline; Rupp, Johanna; Boissel, Jean-Paul; Mignot, Cyril; Rastetter, Agnès; Amiet, Claire; Jacquette, Aurélia; Dupuits, Céline; Bouteiller, Delphine; Keren, Boris; Ruberg, Merle; Faudet, Anne; Doummar, Diane; Philippe, Anne; Périsse, Didier; Laurent, Claudine; Lebrun, Nicolas; Guillemot, Vincent; Chelly, Jamel; Cohen, David; Héron, Delphine; Brice, Alexis; Closs, Ellen I; Depienne, Christel

    2015-12-01

    Cationic amino acid transporters (CATs) mediate the entry of L-type cationic amino acids (arginine, ornithine and lysine) into the cells including neurons. CAT-3, encoded by the SLC7A3 gene on chromosome X, is one of the three CATs present in the human genome, with selective expression in brain. SLC7A3 is highly intolerant to variation in humans, as attested by the low frequency of deleterious variants in available databases, but the impact on variants in this gene in humans remains undefined. In this study, we identified a missense variant in SLC7A3, encoding the CAT-3 cationic amino acid transporter, on chromosome X by exome sequencing in two brothers with autism spectrum disorder (ASD). We then sequenced the SLC7A3 coding sequence in 148 male patients with ASD and identified three additional rare missense variants in unrelated patients. Functional analyses of the mutant transporters showed that two of the four identified variants cause severe or moderate loss of CAT-3 function due to altered protein stability or abnormal trafficking to the plasma membrane. The patient with the most deleterious SLC7A3 variant had high-functioning autism and epilepsy, and also carries a de novo 16p11.2 duplication possibly contributing to his phenotype. This study shows that rare hypomorphic variants of SLC7A3 exist in male individuals and suggest that SLC7A3 variants possibly contribute to the etiology of ASD in male subjects in association with other genetic factors.

  1. Release of free amino acids upon oxidation of peptides and proteins by hydroxyl radicals.

    PubMed

    Liu, Fobang; Lai, Senchao; Tong, Haijie; Lakey, Pascale S J; Shiraiwa, Manabu; Weller, Michael G; Pöschl, Ulrich; Kampf, Christopher J

    2017-03-01

    Hydroxyl radical-induced oxidation of proteins and peptides can lead to the cleavage of the peptide, leading to a release of fragments. Here, we used high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) and pre-column online ortho-phthalaldehyde (OPA) derivatization-based amino acid analysis by HPLC with diode array detection and fluorescence detection to identify and quantify free amino acids released upon oxidation of proteins and peptides by hydroxyl radicals. Bovine serum albumin (BSA), ovalbumin (OVA) as model proteins, and synthetic tripeptides (comprised of varying compositions of the amino acids Gly, Ala, Ser, and Met) were used for reactions with hydroxyl radicals, which were generated by the Fenton reaction of iron ions and hydrogen peroxide. The molar yields of free glycine, aspartic acid, asparagine, and alanine per peptide or protein varied between 4 and 55%. For protein oxidation reactions, the molar yields of Gly (∼32-55% for BSA, ∼10-21% for OVA) were substantially higher than those for the other identified amino acids (∼5-12% for BSA, ∼4-6% for OVA). Upon oxidation of tripeptides with Gly in C-terminal, mid-chain, or N-terminal positions, Gly was preferentially released when it was located at the C-terminal site. Overall, we observe evidence for a site-selective formation of free amino acids in the OH radical-induced oxidation of peptides and proteins, which may be due to a reaction pathway involving nitrogen-centered radicals.

  2. Improved binding of acidic bone matrix proteins to cationized filters during solid phase assays.

    PubMed

    Farach-Carson, M C; Wright, G C; Butler, W T

    1992-01-01

    A number of commercially available matrix filter supports have been designed for the immobilization of proteins following either electrotransfer from sodium dodecyl sulfate (SDS) polyacrylamide gels or direct application during dot blotting assays. These matrices differ with respect to chemical composition, charge, pore size, and degree of hydrophobicity. It follows that the properties of the protein(s) of interest will greatly influence the degree to which they interact with and ultimately bind to various filters. Acidic bone proteins contain diverse post-translational modifications that influence their interactions with solid phase matrices such as those used in immunoblotting (Western or dot blotting) or ion binding (overlay) procedures. This communication describes the results of a study comparing binding of various mixtures of non-collagenous acidic bone matrix phosphoproteins as well as purified osteopontin and osteocalcin to various filters including nitrocellulose and cationized paper or nylon. Based on our findings, we recommend the use of cationized filters for solid phase assays requiring the binding of these acidic macromolecules to background supports.

  3. Biological and surface-active properties of double-chain cationic amino acid-based surfactants.

    PubMed

    Greber, Katarzyna E; Dawgul, Małgorzata; Kamysz, Wojciech; Sawicki, Wiesław; Łukasiak, Jerzy

    2014-08-01

    Cationic amino acid-based surfactants were synthesized via solid phase peptide synthesis and terminal acylation of their α and ε positions with saturated fatty acids. Five new lipopeptides, N-α-acyl-N-ε-acyl lysine analogues, were obtained. Minimum inhibitory concentration and minimum bactericidal (fungicidal) concentration were determined on reference strains of bacteria and fungi to evaluate the antimicrobial activity of the lipopeptides. Toxicity to eukaryotic cells was examined via determination of the haemolytic activities. The surface-active properties of these compounds were evaluated by measuring the surface tension and formation of micelles as a function of concentration in aqueous solution. The cationic surfactants demonstrated diverse antibacterial activities dependent on the length of the fatty acid chain. Gram-negative bacteria and fungi showed a higher resistance than Gram-positive bacterial strains. It was found that the haemolytic activities were also chain length-dependent values. The surface-active properties showed a linear correlation between the alkyl chain length and the critical micelle concentration.

  4. Cationic derivatives of biocompatible hyaluronic acids for delivery of siRNA and antisense oligonucleotides.

    PubMed

    Han, Su-Eun; Kang, Hyungu; Shim, Ga Yong; Kim, Sun Jae; Choi, Han-Gon; Kim, Jiseok; Hahn, Sei Kwang; Oh, Yu-Kyoung

    2009-02-01

    In this study, we tested the use of cationic polymer derivatives of biocompatible hyaluronic acid (HA) as a delivery system of siRNA and antisense oligonucleotides. HA was modified with cationic polymer polyethylenimine (PEI). When compared with PEI alone, cationic PEI derivatives of HA (HA-PEI) provided increased cellular delivery of Small interfering RNA (siRNA) in B16F1, A549, HeLa, and Hep3B tumor cells. Indeed, more than 95% of the cells were positive for siRNA following its delivery with HA-PEI. A survivin-specific siRNA that was delivered using HA-PEI potently reduced the mRNA expression levels of the target gene in all of the cell lines. By contrast, survivin-specific siRNA delivered by PEI alone did not induce a significant reduction in mRNA levels. In green fluorescent protein (GFP)-expressing 293 T cells, a loss of GFP expression was evident in the cells that had been treated with GFP-specific siRNA and HA-PEI complex. The inhibition of target gene expression by antisense oligonucleotide G3139 was also enhanced after delivery with HA-PEI. Moreover, HA-PEI displayed lower cytotoxicity than PEI alone. These results suggest that HA-PEI could be further developed as biocompatible delivery systems of siRNA and antisense oligonucleotides for enhanced cellular uptake and inhibition of target gene expression.

  5. Enantioselective conjugate additions of α-amino radicals via cooperative photoredox and Lewis acid catalysis.

    PubMed

    Ruiz Espelt, Laura; McPherson, Iain S; Wiensch, Eric M; Yoon, Tehshik P

    2015-02-25

    We report the highly enantioselective addition of photogenerated α-amino radicals to Michael acceptors. This method features a dual-catalyst protocol that combines transition metal photoredox catalysis with chiral Lewis acid catalysis. The combination of these two powerful modes of catalysis provides an effective, general strategy to generate and control the reactivity of photogenerated reactive intermediates.

  6. Synthesis of unnatural amino acids from serine derivatives by beta-fragmentation of primary alkoxyl radicals.

    PubMed

    Boto, Alicia; Gallardo, Juan A; Hernández, Dacil; Hernández, Rosendo

    2007-09-14

    The fragmentation of primary alkoxyl radicals has been scarcely used in synthesis since other competing processes (such as oxidation or hydrogen abstraction) usually predominate. However, when serine derivatives were used as substrates, the scission took place in excellent yields. Tandem scission-allylation, -alkylation, or -arylation reactions were subsequently developed. This one-pot methodology was applied to the synthesis of unnatural amino acids, which are useful synthetic blocks or amino acid surrogates in peptidomimetics.

  7. Separation of aliphatic carboxylic acids and benzenecarboxylic acids by ion-exclusion chromatography with various cation-exchange resin columns and sulfuric acid as eluent.

    PubMed

    Ohta, Kazutoku; Ohashi, Masayoshi; Jin, Ji-Ye; Takeuchi, Toyohide; Fujimoto, Chuzo; Choi, Seong-Ho; Ryoo, Jae-Jeong; Lee, Kwang-Pill

    2003-05-16

    The application of various hydrophilic cation-exchange resins for high-performance liquid chromatography (sulfonated silica gel: TSKgel SP-2SW, carboxylated silica gel: TSKgel CM-2SW, sulfonated polymethacrylate resin: TSKgel SP-5PW, carboxylated polymethacrylate resins: TSKgel CM-5PW and TSKgel OA-Pak A) as stationary phases in ion-exclusion chromatography for C1-C7 aliphatic carboxylic acids (formic, acetic, propionic, butyric, isovaleric, valeric, isocaproic, caproic, 2-methylhexanoic and heptanoic acids) and benzenecarboxylic acids (pyromellitic, trimellitic, hemimellitic, o-phthalic, m-phthalic, p-phthalic, benzoic, salicylic acids and phenol) was carried out using diluted sulfuric acid as the eluent. Silica-based cation-exchange resins (TSKgel SP-2SW and TSKgel CM-2SW) were very suitable for the ion-exclusion chromatographic separation of these benzenecarboxylic acids. Excellent simultaneous separation of these benzenecarboxylic acids was achieved on a TSKgel SP-2SW column (150 x 6 mm I.D.) in 17 min using a 2.5 mM sulfuric acid at pH 2.4 as the eluent. Polymethacrylate-based cation-exchange resins (TSKgel SP-5PW, TSKgel CM-5PW and TSKgel OA-Pak A) acted as advanced stationary phases for the ion-exclusion chromatographic separation of these C1-C7 aliphatic carboxylic acids. Excellent simultaneous separation of these C1-C7 acids was achieved on a TSKgel CM-5PW column (150 x 6 mm I.D.) in 32 min using a 0.05 mM sulfuric acid at pH 4.0 as the eluent.

  8. Elucidating the Higher Stability of Vanadium (V) Cations in Mixed Acid Based Redox Flow Battery Electrolytes

    SciTech Connect

    Vijayakumar, M.; Wang, Wei; Nie, Zimin; Sprenkle, Vincent L.; Hu, Jian Z.

    2013-11-01

    The Vanadium (V) cation structures in mixed acid based electrolyte solution were analysed by density functional theory (DFT) based computational modelling and 51V and 35Cl Nuclear Magnetic Resonance (NMR) spectroscopy. The Vanadium (V) cation exists as di-nuclear [V2O3Cl2.6H2O]2+ compound at higher vanadium concentrations (≥1.75M). In particular, at high temperatures (>295K) this di-nuclear compound undergoes ligand exchange process with nearby solvent chlorine molecule and forms chlorine bonded [V2O3Cl2.6H2O]2+ compound. This chlorine bonded [V2O3Cl2.6H2O]2+ compound might be resistant to the de-protonation reaction which is the initial step in the precipitation reaction in Vanadium based electrolyte solutions. The combined theoretical and experimental approach reveals that formation of chlorine bonded [V2O3Cl2.6H2O]2+ compound might be central to the observed higher thermal stability of mixed acid based Vanadium (V) electrolyte solutions.

  9. Cationic amino acid transporters and beta-defensins in dry eye syndrome.

    PubMed

    Jäger, Kristin; Garreis, Fabian; Dunse, Matthias; Paulsen, Friedrich P

    2010-01-01

    Several diseases concomitant with L-arginine deficiency (diabetes, chronic kidney failure, psoriasis) are significantly associated with dry eye syndrome. One important factor that has so far been neglected is the y(+) transporter. In humans, y(+) accounts for nearly 80% of arginine transport, exclusively carrying the cationic amino acids L-arginine, L-lysine and L-ornithine. y(+) is represented by CAT(cationic amino acid transporter) proteins. L-arginine is a precursor of the moisturizer urea, which has been used in the treatment of dry skin diseases. Although urea has also been shown to be part of the tear film, little attention has been paid to it in this role. Moreover, L-arginine and L-lysine are major components contributing to synthesis of the antimicrobially active beta-defensins induced under dry eye conditions. The first results have demonstrated that transport of L-arginine and L-lysine into epithelial cells is limited by the y(+) transporter at the ocular surface.

  10. Humic acid metal cation interaction studied by spectromicroscopy techniques in combination with quantum chemical calculations.

    PubMed

    Plaschke, M; Rothe, J; Armbruster, M K; Denecke, M A; Naber, A; Geckeis, H

    2010-03-01

    Humic acids (HA) have a high binding capacity towards traces of toxic metal cations, thus affecting their transport in aquatic systems. Eu(III)-HA aggregates are studied by synchrotron-based scanning transmission X-ray microscopy (STXM) at the carbon K-edge and laser scanning luminescence microscopy (LSLM) at the (5)D(0) --> (7)F(1,2) fluorescence emission lines. Both methods provide the necessary spatial resolution in the sub-micrometre range to resolve characteristic aggregate morphologies: optically dense zones embedded in a matrix of less dense material in STXM images correspond to areas with increased Eu(III) luminescence yield in the LSLM micrographs. In the C 1s-NEXAFS of metal-loaded polyacrylic acid (PAA), used as a HA model compound, a distinct complexation effect is identified. This effect is similar to trends observed in the dense fraction of HA/metal cation aggregates. The strongest complexation effect is observed for the Zr(IV)-HA/PAA system. This effect is confirmed by quantum chemical calculations performed at the ab initio level for model complexes with different metal centres and complex geometries. Without the high spatial resolution of STXM and LSLM and without the combination of molecular modelling with experimental results, the different zones indicating a ;pseudo'-phase separation into strong complexing domains and weaker complexing domains of HA would never have been identified. This type of strategy can be used to study metal interaction with other organic material.

  11. A flash-photolysis electron spin resonance study of radicals formed from carboxylic acids; exchange effects in spin-polarized radicals

    NASA Astrophysics Data System (ADS)

    McLauchlan, K. A.; Ritchie, A. J. D.

    The time-integration spectroscopy (TIS) technique has been applied to the study of transient radicals created by flash photolysis of solutions of benzene-1,2,4,5-tetracarboxylic acid (pyromellitic acid), benzene-1,2,-dicarboxylic acid (phthalic acid) and benzene-1,4-dicarboxylic acid (terephthalic acid). In these systems electron transfer, proton transfer and rotational isomerism all affect the spin-polarized spectra observed. The exchange processes are analysed theoretically, in the case of proton exchange for the first time in the polarized situation, and it is shown that the two different exchange processes can be simply differentiated in the time-dependent TIS spectra.

  12. Chemically modified polymeric resins for separation of cations, organic acids, and small polar moleculea by high performance liquid chromatography

    SciTech Connect

    Morris, John B.

    1993-07-01

    This thesis is divided into 4 parts: a review, ion chromatography of metal cations on carboxylic resins, separation of hydrophilic organic acids and small polar compounds on macroporous resin columns, and use of eluent modifiers for liquid chromatographic separation of carboxylic acids using conductivity detection.

  13. Mechanisms leading to oligomers and SOA through aqueous photooxidation: insights from OH radical oxidation of acetic acid and methylglyoxal

    NASA Astrophysics Data System (ADS)

    Tan, Y.; Lim, Y. B.; Altieri, K. E.; Seitzinger, S. P.; Turpin, B. J.

    2012-01-01

    Previous experiments have demonstrated that the aqueous OH radical oxidation of methylglyoxal produces low volatility products including pyruvate, oxalate and oligomers. These products are found predominantly in the particle phase in the atmosphere, suggesting that methylglyoxal is a precursor of secondary organic aerosol (SOA). Acetic acid plays a central role in the aqueous oxidation of methylglyoxal and it is a ubiquitous product of gas phase photochemistry, making it a potential "aqueous" SOA precursor in its own right. However, the fate of acetic acid upon aqueous-phase oxidation is not well understood. In this research, acetic acid (20 μM-10 mM) was oxidized by OH radicals, and pyruvic acid and methylglyoxal experimental samples were analyzed using new analytical methods, in order to better understand the formation of SOA from acetic acid and methylglyoxal. Glyoxylic, glycolic, and oxalic acids formed from acetic acid and OH radicals. In contrast to the aqueous OH radical oxidation of methylglyoxal, the aqueous OH radical oxidation of acetic acid did not produce succinic acid and oligomers. This suggests that the methylgloxal-derived oligomers do not form through the acid catalyzed esterification pathway proposed previously. Using results from these experiments, radical mechanisms responsible for oligomer formation from methylglyoxal oxidation in clouds and wet aerosols are proposed. The importance of acetic acid/acetate as an SOA precursor is also discussed. We hypothesize that this and similar chemistry is central to the daytime formation of oligomers in wet aerosols.

  14. A search for pure compounds suitable for use as matrix in spectroscopic studies of radiation-produced radical cations. III. A selection of compounds based on the thermochemistry of hydrogen and proton transfer reactions between neutral molecules and their cations

    NASA Astrophysics Data System (ADS)

    Van den Bosch, Ann; Ceulemans, Jan

    A systematic investigation is made of the thermochemistry of hydrogen and proton transfer between neutral molecules and their cations covering the entire organic chemistry, with the aim of selecting those compounds that are suitable for use as matrices in spectroscopic studies of radiation-produced radical cations. Compounds that are characterized by positive reaction enthalpies may be considered promising for use as matrices in such studies. Calculations are based on experimentally determined ionization energies and proton affinities and on carbon-hydrogen bond strengths that are arbitrarily taken as 418 kJ.mol -1 (100 kcal.mol -1). Effects of actual deviations from this value are considered. In the aliphatic series of compounds, reaction enthalpies depend strongly on functional groups present. Marked positive reaction enthalpies are obtained for alkenes, alkadienes, thioethers, mercaptans, iodoalkanes and tertiary amines. Non-aromatic cyclic compounds generally behave as their aliphatic counterparts. Thus, positive reaction enthalpies are generally obtained for unsaturated alicyclic hydrocarbons and cyclic thioethers. Positive reaction enthalpies are also obtained for piperidine, quinuclidine, manxine and derivatives. In the homocyclic aromatic series of compounds, reaction enthalpies are generally positive. Thus, positive reaction enthalpies are obtained for aromatic hydrocarbons, fluoro- and chlorobenzenes, aromatic amines (amino group attached directly to the ring) and halo- and methoxyanilines. In the heterocyclic aromatic series of compounds reaction enthalpies are generally negative. This is for instance the case for a large number of pyridine derivatives, di- and triazines and a number of bi- and tricyclic compounds. Positive reaction enthalpies are however obtained for furan and pyrrole.

  15. Sub-millitesla magnetic field effects on the recombination reaction of flavin and ascorbic acid radicals

    NASA Astrophysics Data System (ADS)

    Evans, Emrys W.; Kattnig, Daniel R.; Henbest, Kevin B.; Hore, P. J.; Mackenzie, Stuart R.; Timmel, Christiane R.

    2016-08-01

    Even though the interaction of a <1 mT magnetic field with an electron spin is less than a millionth of the thermal energy at room temperature (kBT), it still can have a profound effect on the quantum yields of radical pair reactions. We present a study of the effects of sub-millitesla magnetic fields on the photoreaction of flavin mononucleotide with ascorbic acid. Direct control of the reaction pathway is achieved by varying the rate of electron transfer from ascorbic acid to the photo-excited flavin. At pH 7.0, we verify the theoretical prediction that, apart from a sign change, the form of the magnetic field effect is independent of the initial spin configuration of the radical pair. The data agree well with model calculations based on a Green's function approach that allows multinuclear spin systems to be treated including the diffusive motion of the radicals, their spin-selective recombination reactions, and the effects of the inter-radical exchange interaction. The protonation states of the radicals are uniquely determined from the form of the magnetic field-dependence. At pH 3.0, the effects of two chemically distinct radical pair complexes combine to produce a pronounced response to ˜500 μT magnetic fields. These findings are relevant to the magnetic responses of cryptochromes (flavin-containing proteins proposed as magnetoreceptors in birds) and may aid the evaluation of effects of weak magnetic fields on other biologically relevant electron transfer processes.

  16. Evaluation of the free-radical-scavenging activity of diclofenac acid on the free-radical-induced haemolysis of human erythrocytes.

    PubMed

    Tang, You-Zhi; Liu, Zai-Qun

    2006-05-01

    Free-radical-induced peroxidation in-vivo is regarded as the aetiology of some diseases and free-radical-scavenging drugs, also called antioxidants (AH), have been widely used to overcome oxidative stress. An in-vitro experimental method, 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH)-induced haemolysis of human erythrocytes can be applied to assess the free-radical-scavenging activity of a drug. The major objectives of this work were focused on three aspects. Firstly, introduction of the chemical kinetic deduction of free-radical-initiating reaction to AAPH-induced haemolysis of human erythrocytes, by which the number of free radicals trapped by an antioxidant, n, can be obtained after finding the quantitative relationship between the inhibition period (t(inh)) and the concentration of the antioxidant, t(inh) = (n/Ri) [AH]. Ri, the free-radical-initiating rate, was initially confirmed by using alpha-tocopherol (VE) whose n was taken as 2. Secondly, the free-radical-scavenging activity of diclofenac acid (DaH) and its sodium salt (DaNaH) was assessed. It has been found that DaH and DaNaH protect human erythrocytes against AAPH-induced haemolysis dose-dependently. In particular, the n values of DaH and DaNaH (4.96 and 3.60) were much higher than some traditional antioxidants, such as 6-hydroxyl-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox, a water-soluble structural analogue of VE, n = 0.30) and L-ascorbic acid (VC, n = 0.25), and L-ascorbyl-6-laurate (VC-12, a lipophilic structural analogue of VC, n = 1.11). Moreover, the free-radical-scavenging activity of lipophilic antioxidants is higher than the corresponding water-soluble species. Thirdly, the free-radical-scavenging activity of mixed antioxidants, VE + DaH, VC-12 + DaH, Trolox + DaNaH and VC + DaNaH, was revealed. The n value of VC, VC-12, VE and Trolox increase in the case of mixed usage with DaH and DaNaH, implying that diclofenac acid can repair the radical of these antioxidants. Thus, a mutual

  17. Formation of stable radicals in catechin/nitrous acid systems: participation of dinitrosocatechin.

    PubMed

    Morina, Filis; Takahama, Umeo; Mojović, Miloš; Popović-Bijelić, Ana; Veljović-Jovanović, Sonja

    2016-03-01

    Catechins are transformed into dinitrosocatechins (diNOcats) and then oxidized to the quinones by salivary nitrite under conditions simulating the stomach. This manuscript deals with formation of stable radicals in the NO group of diNOcat during nitrite-induced oxidation of (+)-catechin and diNOcat at pH 2. We postulated two mechanisms for the stable radical formation; one is nitrous acid-induced oxidation of diNOcat in the A-ring, and the other intermolecular charge transfer from the A-ring of diNOcat and/or diNOcat quinone to the quinone moiety of the B-ring of diNOcat quinone. In addition, an unstable phenoxyl radical, which might be transformed into quinone, was also produced, accompanying the formation of the stable radical on the NO group. Taking the above results into account, we mainly focus on the adverse effects of the radicals and quinone, which may be produced from (+)-catechin in the stomach under the conditions of high salivary nitrite concentrations.

  18. Interaction of cationic peptides with lipoteichoic acid and gram-positive bacteria.

    PubMed

    Scott, M G; Gold, M R; Hancock, R E

    1999-12-01

    Compounds with antiendotoxin properties have been extensively studied for their potential as therapeutic agents for sepsis attributable to gram-negative bacteria. However, with the increasing incidence of gram-positive sepsis, there is interest in identifying compounds with a broad spectrum of action against both gram-positive and gram-negative bacteria. A series of synthetic alpha-helical cationic peptides related to bee melittin and silk moth cecropin have previously been shown to bind lipopolysaccharide (LPS) with high affinity, inhibit LPS-induced tumor necrosis factor alpha (TNF-alpha) production in vitro and in vivo, and kill gram-negative bacteria. In this study, we analyzed whether these peptides were active against gram-positive bacteria; whether they could bind to lipoteichoic acid (LTA), the major proinflammatory structure on gram-positive bacteria; and whether they could block the ability of LTA to promote the release of cytokines by the RAW 264.7 murine macrophage cell line. We found that the cationic peptides demonstrated moderate growth-inhibitory activity toward gram-positive bacteria. In addition, the peptides bound LTA with high affinity. This correlated with the ability of the peptides to block LTA-induced production of TNF and interleukin-6 by RAW 264.7 cells but did not correlate with their ability to kill the bacteria. The peptides also effectively inhibited LTA-induced TNF production in a whole human blood assay. The peptides were also able to partly block the ability of heat-killed Staphylococcus aureus, as well as soluble products of live S. aureus, to stimulate cytokine production by macrophages. Our results indicate that these cationic peptides may be useful to prevent sepsis and inflammation caused by both gram-negative and gram-positive bacteria.

  19. Cation trapping by cellular acidic compartments: Beyond the concept of lysosomotropic drugs

    SciTech Connect

    Marceau, François; Bawolak, Marie-Thérèse; Lodge, Robert; Bouthillier, Johanne; Gagné-Henley, Angélique; Gaudreault, René C.; Morissette, Guillaume

    2012-02-15

    “Lysosomotropic” cationic drugs are known to concentrate in acidic cell compartments due to low retro-diffusion of the protonated molecule (ion trapping); they draw water by an osmotic mechanism, leading to a vacuolar response. Several aspects of this phenomenon were recently reexamined. (1) The proton pump vacuolar (V)-ATPase is the driving force of cationic drug uptake and ensuing vacuolization. In quantitative transport experiments, V-ATPase inhibitors, such as bafilomycin A1, greatly reduced the uptake of cationic drugs and released them in preloaded cells. (2) Pigmented or fluorescent amines are effectively present in a concentrated form in the large vacuoles. (3) Consistent with V-ATPase expression in trans-Golgi, lysosomes and endosomes, a fraction of the vacuoles is consistently labeled with trans-Golgi markers and protein secretion and endocytosis are often inhibited in vacuolar cells. (4) Macroautophagic signaling (accumulation of lipidated and membrane-bound LC3 II) and labeling of the large vacuoles by the autophagy effector LC3 were consistently observed in cells, precisely at incubation periods and amine concentrations that cause vacuolization. Vacuoles also exhibit late endosome/lysosome markers, because they may originate from such organelles or because macroautophagosomes fuse with lysosomes. Autophagosome persistence is likely due to the lack of resolution of autophagy, rather than to nutritional deprivation. (5) Increased lipophilicity decreases the threshold concentration for the vacuolar and autophagic cytopathology, because simple diffusion into cells is limiting. (6) A still unexplained mitotic arrest is consistently observed in cells loaded with amines. An extended recognition of relevant clinical situations is proposed for local or systemic drug administration.

  20. The influence of acid treatments over vermiculite based material as adsorbent for cationic textile dyestuffs.

    PubMed

    Stawiński, Wojciech; Freitas, Olga; Chmielarz, Lucjan; Węgrzyn, Agnieszka; Komędera, Kamila; Błachowski, Artur; Figueiredo, Sónia

    2016-06-01

    The influence of different acid treatments over vermiculite was evaluated. Equilibrium, kinetic and column studies have been conducted. The results showed that vermiculite first treated with nitric acid and then with citric acid has higher adsorption capacity, presenting maximum adsorption capacities in column experiments: for Astrazon Red (AR), 100.8 ± 0.8 mg g(-1) and 54 ± 1 mg g(-1) for modified and raw material, respectively; for Methylene Blue (MB) 150 ± 4 mg g(-1) and 55 ± 2 mg g(-1) for modified and raw material, respectively. Materials characterization by X-ray diffraction, UV-vis-diffuse reflectance spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, X-ray fluorescence, N2 adsorption and CEC determination, has been performed. The results suggest the existence of exchange of interlayer cations, leaching of metals from vermiculite's sheets and formation of an amorphous phase in the material. Adsorption follows pseudo 2(nd) order model kinetics for both dyestuffs and equilibrium occurs accordingly to Langmuir's model for AR and Freundlich's model for MB. In column systems Yan's model is the best fit. The enhanced properties of acid treated vermiculite offer new perspectives for the use of this adsorbent in wastewater treatment.

  1. Acidic pH and divalent cation sensing by PhoQ are dispensable for systemic salmonellae virulence.

    PubMed

    Hicks, Kevin G; Delbecq, Scott P; Sancho-Vaello, Enea; Blanc, Marie-Pierre; Dove, Katja K; Prost, Lynne R; Daley, Margaret E; Zeth, Kornelius; Klevit, Rachel E; Miller, Samuel I

    2015-05-23

    Salmonella PhoQ is a histidine kinase with a periplasmic sensor domain (PD) that promotes virulence by detecting the macrophage phagosome. PhoQ activity is repressed by divalent cations and induced in environments of acidic pH, limited divalent cations, and cationic antimicrobial peptides (CAMP). Previously, it was unclear which signals are sensed by salmonellae to promote PhoQ-mediated virulence. We defined conformational changes produced in the PhoQ PD on exposure to acidic pH that indicate structural flexibility is induced in α-helices 4 and 5, suggesting this region contributes to pH sensing. Therefore, we engineered a disulfide bond between W104C and A128C in the PhoQ PD that restrains conformational flexibility in α-helices 4 and 5. PhoQ(W104C-A128C) is responsive to CAMP, but is inhibited for activation by acidic pH and divalent cation limitation. phoQ(W104C-A128C) Salmonella enterica Typhimurium is virulent in mice, indicating that acidic pH and divalent cation sensing by PhoQ are dispensable for virulence.

  2. Acidic pH and divalent cation sensing by PhoQ are dispensable for systemic salmonellae virulence

    PubMed Central

    Hicks, Kevin G; Delbecq, Scott P; Sancho-Vaello, Enea; Blanc, Marie-Pierre; Dove, Katja K; Prost, Lynne R; Daley, Margaret E; Zeth, Kornelius; Klevit, Rachel E; Miller, Samuel I

    2015-01-01

    Salmonella PhoQ is a histidine kinase with a periplasmic sensor domain (PD) that promotes virulence by detecting the macrophage phagosome. PhoQ activity is repressed by divalent cations and induced in environments of acidic pH, limited divalent cations, and cationic antimicrobial peptides (CAMP). Previously, it was unclear which signals are sensed by salmonellae to promote PhoQ-mediated virulence. We defined conformational changes produced in the PhoQ PD on exposure to acidic pH that indicate structural flexibility is induced in α-helices 4 and 5, suggesting this region contributes to pH sensing. Therefore, we engineered a disulfide bond between W104C and A128C in the PhoQ PD that restrains conformational flexibility in α-helices 4 and 5. PhoQW104C-A128C is responsive to CAMP, but is inhibited for activation by acidic pH and divalent cation limitation. phoQW104C-A128C Salmonella enterica Typhimurium is virulent in mice, indicating that acidic pH and divalent cation sensing by PhoQ are dispensable for virulence. DOI: http://dx.doi.org/10.7554/eLife.06792.001 PMID:26002083

  3. Observation of covalent and electrostatic bonds in nitrogen-containing polycyclic ions formed by gas phase reactions of the benzene radical cation with pyrimidine.

    PubMed

    Attah, Isaac Kwame; Soliman, Abdel-Rahman; Platt, Sean P; Meot-Ner Mautner, Michael; Aziz, Saaudallah G; Samy El-Shall, M

    2017-03-01

    Polycyclic aromatic hydrocarbons (PAHs) and polycyclic aromatic nitrogen heterocyclics (PANHs) are present in ionizing environments, including interstellar clouds and solar nebulae, where their ions can interact with neutral PAH and PANH molecules leading to the formation of a variety of complex organics including large N-containing ions. Herein, we report on the formation of a covalently-bonded (benzene·pyrimidine) radical cation dimer by the gas phase reaction of pyrimidine with the benzene radical cation at room temperature using the mass-selected ion mobility technique. No ligand exchange reactions with benzene and pyrimidine are observed indicating that the binding energy of the (benzene·pyrimidine)˙(+) adduct is significantly higher than both the benzene dimer cation and the proton-bound pyrimidine dimer. The (benzene·pyrimidine)˙(+) adduct shows thermal stability up to 541 K. Thermal dissociation of the (C6D6·C4H4N2)˙(+) adduct at temperatures higher than 500 K produces C4H4N2D(+) (m/z 82) suggesting the transfer of a D atom from the C6D6 moiety to the C4H4N2 moiety before the dissociation of the adduct. Mass-selected ion mobility of the (benzene·pyrimidine)˙(+) dimer reveals the presence of two families of isomers formed by electron impact ionization of the neutral (benzene·pyrimidine) dimer. The slower mobility peak corresponds to a non-covalent family of isomers with larger collision cross sections (76.0 ± 1.8 Å(2)) and the faster peak is consistent with a family of covalent isomers with more compact structures and smaller collision cross sections (67.7 ± 2.2 Å(2)). The mobility measurements at 509 K show only one peak corresponding to the family of stable covalently bonded isomers characterized by smaller collision cross sections (66.9 ± 1.9 Å(2) at 509 K). DFT calculations at the M06-2X/6-311++G** level show that the most stable (benzene·pyrimidine)˙(+) isomer forms a covalent C-N bond with a binding energy of 49.7 kcal mol(-1) and a

  4. Radical scavenging ability of gallic acid toward OH and OOH radicals. Reaction mechanism and rate constants from the density functional theory.

    PubMed

    Marino, Tiziana; Galano, Annia; Russo, Nino

    2014-09-04

    Gallic acid is a ubiquitous compound, widely distributed in the vegetal kingdom and frequently found in the human diet. In the present work, its primary antioxidant activity has been investigated using the density functional theory (DFT), and the quantum mechanics-based test for overall free radical scavenging activity (QM-ORSA) protocol. It was found that gallic acid is a better antioxidant than the reference compound, Trolox, regardless of the polarity of the environment. In addition, gallic acid is predicted to be among the best peroxyl radical scavengers identified so far in nonpolar (lipid) media. This compound is capable of scavenging hydroxyl radicals at diffusion-limited rates, and hydroperoxyl radicals with rate constants in the order of 10(5) M(-1) s(-1). The deprotonation of gallic acid, in aqueous solution, is predicted to increase the protective action of this compound against oxidative stress. Gallic acid was also identified as a versatile scavenger, capable of rapidly deactivating a wide variety of reactive oxygen species (ROS) and reactive nitrogen species (RNS) via electron transfer at physiological pH.

  5. The temperature dependence of the rate constant for the reaction of hydroxyl radicals with nitric acid

    NASA Technical Reports Server (NTRS)

    Kurylo, M. J.; Cornett, K. D.; Murphy, J. L.

    1982-01-01

    The rate constant for the reaction of hydroxyl radicals with nitric acid in the 225-443 K temperature range has been measured by means of the flash photolysis resonance fluorescence technique. Above 300 K, the rate constant levels off in a way that can only be explained by the occurrence of two reaction channels, of which one, operative at low temperatures, proceeds through the formation of an adduct intermediate. The implications of these rate constant values for stratospheric reaction constants is discussed.

  6. Synthesis of 6'-branched locked nucleic acid by a radical TEMPO-scavanged stereoselective mercury cyclization.

    PubMed

    Enderlin, Gerald; Nielsen, Poul

    2008-09-05

    A 6'(R)-hydroxymethyl derivative of the locked nucleic acid (LNA)-thymidine monomer has been synthesized by a stereoselective mercury cyclization and subsequent use of TEMPO as a radical scavenger. This compound was converted to an azide derivative, which in a Huisgen-type [3 + 2] cycloaddition afforded a double-headed nucleoside with a triazole linking an additional thymine to the 6'-position of the LNA-nucleoside monomer.

  7. Free radical mediated formation of 3-monochloropropanediol (3-MCPD) fatty acid diesters.

    PubMed

    Zhang, Xiaowei; Gao, Boyan; Qin, Fang; Shi, Haiming; Jiang, Yuangrong; Xu, Xuebing; Yu, Liangli Lucy

    2013-03-13

    The present study was conducted to test the hypothesis that a free radical was formed and mediated the formation of 3-monochloropropanediol (3-MCPD) fatty acid diesters, a group of food contaminants, from diacylglycerols at high temperature under a low-moisture condition for the first time. The presence of free radicals in a vegetable oil kept at 120 °C for 20 min was demonstrated using an electron spin resonance (ESR) spectroscopy examination with 5,5-dimethylpyrroline-N-oxide (DMPO) as the spin trap agent. ESR investigation also showed an association between thermal treatment degree and the concentration of free radicals. A Fourier transform infrared spectroscopy (FT-IR) analysis of sn-1,2-stearoylglycerol (DSG) at 25 and 120 °C suggested the possible involvement of an ester carbonyl group in forming 3-MCPD diesters. On the basis of these results, a novel free radical mediated chemical mechanism was proposed for 3-MCPD diester formation. Furthermore, a quadrupole-time of flight (Q-TOF) MS/MS investigation was performed and detected the DMPO adducts with the cyclic acyloxonium free radical (CAFR) and its product MS ions, proving the presence of CAFR. Furthermore, the free radical mechanism was validated by the formation of 3-MCPD diesters through reacting DSG with a number of organic and inorganic chlorine sources including chlorine gas at 120 and 240 °C. The findings of this study might lead to the improvement of oil and food processing conditions to reduce the level of 3-MCPD diesters in foods and enhance food safety.

  8. Peroxynitrite-mediated formation of free radicals in human plasma: EPR detection of ascorbyl, albumin-thiyl and uric acid-derived free radicals.

    PubMed Central

    Vásquez-Vivar, J; Santos, A M; Junqueira, V B; Augusto, O

    1996-01-01

    Formation of peroxynitrite by the fast reaction between nitric oxide and superoxide anion may represent a critical control point in cells producing both species, leading to either down-regulation of the physiological effects of superoxide anion and nitric oxide by forming an inert product, nitrate, or to potentiation of their toxic effects by oxidation of nearby molecules by peroxynitrite. (The term peroxynitrite is used to refer to the sum of all possible forms of peroxynitrite anion and peroxynitrous acid unless otherwise specified.) In this report we demonstrate that, in spite of all the antioxidant defences present in human plasma, its interaction with peroxynitrite leads to generation of free radical intermediates such as (i) the ascorbyl radical, detected by direct EPR, (ii) the albumin-thiyl radical, detected by spin-trapping experiments with both N-tert-butyl-alpha-phenylnitrone and 5,5-dimethyl-1-pyrroline N-oxide (DMPO), and (iii) a uric acid-derived free radical, detected as the DMPO radical adduct in plasma whose thiol groups were previously blocked with 5,5-dithiobis-(2-nitrobenzoic acid). The identity of the latter adduct was confirmed by parallel experiments demonstrating that it is not detectable in plasma pretreated with uricase, whereas it is formed in incubations of peroxynitrite with uric acid. Peroxynitrite-mediated oxidations were also followed by oxygen consumption and ascorbate and plasma-thiol depletion. Our results support the view that peroxynitrite-mediated one-electron oxidation of biomolecules may be an important event in its cytotoxic mechanism. In addition, the data have methodological implications by providing support for the use of EPR methodologies for monitoring both free radical reactions and ascorbate concentrations in biological fluids. PMID:8615782

  9. Cationic mononuclear ruthenium carboxylates as catalyst prototypes for self-induced hydrogenation of carboxylic acids.

    PubMed

    Naruto, Masayuki; Saito, Susumu

    2015-08-28

    Carboxylic acids are ubiquitous in bio-renewable and petrochemical sources of carbon. Hydrogenation of carboxylic acids to yield alcohols produces water as the only byproduct, and thus represents a possible next generation, sustainable method for the production of these alternative energy carriers/platform chemicals on a large scale. Reported herein are molecular insights into cationic mononuclear ruthenium carboxylates ([Ru(OCOR)](+)) as prototypical catalysts for the hydrogenation of carboxylic acids. The substrate-derived coordinated carboxylate was found to function initially as a proton acceptor for the heterolytic cleavage of dihydrogen, and subsequently also as an acceptor for the hydride from [Ru-H](+), which was generated in the first step (self-induced catalysis). The hydrogenation proceeded selectively and at high levels of functional group tolerance, a feature that is challenging to achieve with existing heterogeneous/homogeneous catalyst systems. These fundamental insights are expected to significantly benefit the future development of metal carboxylate-catalysed hydrogenation processes of bio-renewable resources.

  10. Cationic mononuclear ruthenium carboxylates as catalyst prototypes for self-induced hydrogenation of carboxylic acids

    PubMed Central

    Naruto, Masayuki; Saito, Susumu

    2015-01-01

    Carboxylic acids are ubiquitous in bio-renewable and petrochemical sources of carbon. Hydrogenation of carboxylic acids to yield alcohols produces water as the only byproduct, and thus represents a possible next generation, sustainable method for the production of these alternative energy carriers/platform chemicals on a large scale. Reported herein are molecular insights into cationic mononuclear ruthenium carboxylates ([Ru(OCOR)]+) as prototypical catalysts for the hydrogenation of carboxylic acids. The substrate-derived coordinated carboxylate was found to function initially as a proton acceptor for the heterolytic cleavage of dihydrogen, and subsequently also as an acceptor for the hydride from [Ru–H]+, which was generated in the first step (self-induced catalysis). The hydrogenation proceeded selectively and at high levels of functional group tolerance, a feature that is challenging to achieve with existing heterogeneous/homogeneous catalyst systems. These fundamental insights are expected to significantly benefit the future development of metal carboxylate-catalysed hydrogenation processes of bio-renewable resources. PMID:26314266

  11. Synthesis, characterization and cation adsorption of p-aminobenzoic acid intercalated on calcium phosphate

    SciTech Connect

    Silva, Camila F.N.; Lazarin, Angélica M.; Sernaglia, Rosana L.; Andreotti, Elza I.S.

    2012-06-15

    Graphical abstract: Scanning electron microscopy photographs of calcium phosphate (a) and intercalated with p-aminobenzoic acid (b). Highlights: ► Calcium phosphate was intercalated with p-aminobenzoic acid. ► Guest molecule contains nitrogen and oxygen atoms from amine and carboxylic groups. ► These basic centers are potentially useful for cation coordination in ethanol solution. ► Crystal morphology of compounds is lamellar, it agrees with expected structural characteristics. -- Abstract: Crystalline lamellar calcium phosphate retained 4-aminobenzoic acid inside its cavity without leaching. The intense infrared bands in the 1033 and 1010 cm{sup −1} interval confirmed the presence of the phosphonate groups attached to the inorganic layer, with sharp and intense peaks in X-ray diffraction patterns, which gave basal distances of 712 and 1578 pm for the original and the intercalated compounds, respectively. Solid-state {sup 31}P nuclear magnetic resonance spectra presented only one peak for the phosphate groups attached to the main inorganic polymeric structure near −2.4 ppm. The adsorption isotherms from ethanol gave the maximum adsorption capacities of 6.44 and 3.34 mmol g{sup −1} for nickel and cobalt, respectively, which stability constant and distribution coefficient followed Co > Ni.

  12. Study of the release of a microencapsulated acid dye in polyamide dyeing using mixed cationic liposomes.

    PubMed

    de Sousa, Isabel S C; Castanheira, Elisabete M S; Rocha Gomes, Jaime I N; Real Oliveira, M Elisabete C D

    2011-06-01

    The main objective of this work was to increase the retarding effect of the acid dye Telon(®) Blue RR (C.I. Acid Blue 62; DyStar, Frankfurt, Germany) release on polyamide fibres dyeing by encapsulation of the dye in liposomes as an alternative to synthetic auxiliaries, in order to reduce effluent pollution. The retarding effect achieved with the use of mixed cationic liposomes of dioctadecyldimethylammonium bromide (DODAB)/soybean lecithin (containing a 10% molar fraction of DODAB) was better in comparison with either pure soybean lecithin liposomes or synthetic auxiliaries. The retarding effect of liposomes on the dye release was analysed through changes in the absorption and fluorescence spectra of the acid dye at different conditions. The effect of temperature (in the range of 25 °C - 70 °C) on the spectroscopic behaviour of the dye in the absence and in presence of polyamide was also studied, in order to simulate the dyeing conditions. Exhaustion curves obtained in dyeing experiments showed that, below 45 °C, the retarding effect of the mixed liposomes (lecithin/DODAB (9:1)) was similar to that of the auxiliaries, but better than the one of pure lecithin liposomes. At higher temperatures (above 45 °C), the system lecithin/DODAB presents a better performance, achieving a higher final exhaustion level when compared with the commercial leveling agent without losing the smoothing effect of lecithin.

  13. The adsorption of cationic dye from aqueous solution onto acid-activated andesite.

    PubMed

    Tsai, Wen-Tien; Hsu, Hsin-Chieh; Su, Ting-Yi; Lin, Keng-Yu; Lin, Chien-Ming; Dai, Tzong-Hung

    2007-08-25

    The adsorption of cationic dye (i.e., methylene blue) onto acid-activated andesite in aqueous solution was studied in a batch system with respect to its kinetics as a function of agitation speed, initial adsorbate concentration, pH, and adsorbent mass. It was found that the resulting acid-activated adsorbent possessed a mesoporous structure with BET surface areas at around 60m(2)/g. The surface characterization of acid-activated andesite was also performed using the zeta-potential measurements, indicating that the charge sign on the surface of the andesite should be negative in a wide pH range (i.e., 3-11). Furthermore, a simplified kinetic model, pseudo-second-order, was tested to investigate the adsorption behaviors of methylene blue onto the clay samples treated under different process conditions. It was found that the adsorption process could be well described with the model. The adsorption capacity parameter of the model obtained in the present work was significantly in line with the process parameters.

  14. Influence of ionization on the conformational preferences of peptide models. Ramachandran surfaces of N-formyl-glycine amide and N-formyl-alanine amide radical cations.

    PubMed

    Gil, Adrià; Sodupe, Mariona; Bertran, Juan

    2009-09-01

    Ramachandran maps of neutral and ionized HCO-Gly-NH2 and HCO-Ala-NH2 peptide models have been built at the B3LYP/6-31++G(d,p) level of calculation. Direct optimizations using B3LYP and the recently developed MPWB1K functional have also been carried out, as well as single-point calculations at the CCSD(T) level of theory with the 6-311++G(2df,2p) basis set. Results indicate that for both peptide models ionization can cause drastic changes in the shape of the PES in such a way that highly disallowed regions in neutral PES become low-energy regions in the radical cation surface. The structures localized in such regions, epsilonL+* and epsilonD+* are highly stabilized due to the formation of 2-centre-3-electron interactions between the two carbonyl oxygens. Inclusion of solvent effects by the conductor-like polarizable continuum model (CPCM) shows that the solute-solvent interaction energy plays an important role in determining the stability order.

  15. The hydrogen-bridged radical cation [NH 2C dbnd O⋯H⋯O dbnd CHCH 3] rad + and its dissociation by proton-transport catalysis

    NASA Astrophysics Data System (ADS)

    Jobst, Karl J.; Terlouw, Johan K.

    2012-01-01

    The title ion (HBRC-1) is an easily accessible hydrogen-bridged radical cation when generated by the decarbonylation of ionized ethyl oxamate, NH2COCOOC2H5. Tandem mass spectrometry experiments and CBS-QB3 model chemistry calculations agree that HBRC-1 dissociates into HC(OH)NH2+ + CH3COrad by proton-transport catalysis. Its CH3CHO component catalyzes the isomerization NH2-C-OHrad + → NH2C(O)Hrad + and the ensuing intermediate [NH2C(O)H⋯OCHCH3]rad + loses CH3COrad by a facile proton transfer. In support of this, lactamide ions ND2C(O)CH(OD)CH3rad + dissociate into DC(OH)ND2+ + CH3COrad via the HBRC-1 isotopologue [ND2CO⋯D⋯OCHCH3]rad +. HBRC-1 also plays a key role in the decarbonylation of its isomer ionized urethan, NH2COOC2H5.

  16. Structural and magnetic effects of meso-substitution in alkyl-substituted metalloporphyrinate pi-cation radicals: characterization of [Fe(TalkylP*)(Cl)]SbCl6 (alkyl = ethyl and n-propyl).

    PubMed

    Li, Ming; Neal, Teresa J; Wyllie, Graeme R A; Schulz, Charles E; Scheidt, W Robert

    2010-09-06

    We report the preparation and characterization of two meso-alkyl substituted porphyrin pi-cation radical derivatives, [Fe(TalkylP(*))(Cl)]SbCl(6) (alkyl = ethyl or propyl). Both complexes have been characterized by UV/vis/near-IR, IR, and Mossbauer spectroscopy, temperature-dependent solid-state magnetic susceptibility measurements, and X-ray structure determinations. All data for both oxidized species are consistent with the formulation of the complexes as ring-oxidized iron(III) porphyrin species. The molecular structures of the two five-coordinate species have the typical square-pyramidal coordination group of high-spin iron(III) derivatives. The crystal structures also reveal that the species form cofacial pi-pi dimers with lateral shifts of 1.44 A and 3.22 A, respectively, for the propyl and ethyl radical derivatives. Both radicals exhibit porphyrin cores with alternating bond distance patterns in the inner 16-membered ring. In addition, [Fe(TEtP(*))(Cl)]SbCl(6) and [Fe(TPrP(*))(Cl)]SbCl(6) have been characterized by temperature-dependent (6-300 K) magnetic susceptibility studies, the best fitting of the temperature-dependent moments reveal strong coupling between iron spins and porphyrin radical, and a smaller magnitude of antiferromagnetic coupling between ring radicals, which are opposite to those found in the five-coordinate iron(III) OEP radicals. The differences in structure and properties of the cation radical meso-alkyl and beta-alkyl derivatives possibly reflect differences in properties of a(1u)- and a(2u)-forming radicals.

  17. TACN-based cationic lipids with amino acid backbone and double tails: materials for non-viral gene delivery.

    PubMed

    Wang, Bing; Yi, Wen-Jing; Zhang, Ji; Zhang, Qin-Fang; Xun, Miao-Miao; Yu, Xiao-Qi

    2014-04-01

    Cationic lipids have become an efficient type of non-viral vectors for gene delivery. In this Letter, four cationic lipids containing 1,4,7-triazacyclononane (TACN) headgroup, glutamic/aspartic acid backbone and dioleyl tails were designed and synthesized. The TACN headgroup gives these lipids excellent pH buffering capacities, which were higher than branched 25 kDa PEI. Cationic liposomes prepared from these lipids and DOPE showed good DNA affinity, and full DNA condensation was found at N/P ratio of 3 via agarose gel electrophoresis. The lipoplexes were characterized by dynamic light scattering (DLS) assay, which gave proper particle sizes and zeta-potentials for transfection. In vitro gene transfection results in two cell lines reveal that TAN (with aspartic acid and amide bond in the structure) shows the best transfection efficiency, which is close to commercially available transfection agent Lipofectamine 2000.

  18. Radical-driven carbonyl-to-acid conversion and acid degradation in tropospheric aqueous systems studied by CAPRAM

    NASA Astrophysics Data System (ADS)

    Tilgner, A.; Herrmann, H.

    2010-12-01

    Model studies on the aqueous phase radical-driven processing of carbonyl compounds and acids in clouds and deliquescent particles were performed. The model exposed that aqueous radical conversions of carbonyl compounds and its oxidation products can contribute potentially to the formation of functionalised organic acids. The main identified C 2-C 4 organic gas phase precursors are ethylene glycol, glycolaldehyde, glyoxal, methylglyoxal and 1,4-butenedial. The aqueous phase is shown to contribute significantly with about 93%/63%, 47%/8%, 31%/4%, 7%/4%, 36%/8% to the multiphase oxidative fate of these compounds under remote/urban conditions. Interestingly, the studies revealed that aqueous chemical processing is not only limited to in-cloud conditions but also proceeds in deliquescent particle phase with significant fluxes. Oxalic acid is shown to be formed preferably in deliquescent particles subsequent to the in-cloud oxidations. Mean aqueous phase oxalate formation fluxes of about 12, 42 and 0.4 ng m -3 h -1 in the remote, urban and maritime scenario, respectively. Additionally, the turnovers of the oxidation of organics such as methylglyoxal by NO 3 radical reactions are identified to be competitive to their OH pendants. At the current state of CAPRAM, mean C 2-C 4 in-cloud oxidation fluxes of about 0.12 and 0.5 μg m -3 h -1 are modelled under the idealised remote and urban cloud conditions. Finally, turnovers from radical oxidations were compared with those of thermal reactions. It is demonstrated that, based on the sparse kinetic data available organic accretion reaction might be of interest in just a few cases for cloud droplets and aqueous particles but generally do not reach the oxidative conversion rates of the main radical oxidants OH and NO 3. Interestingly, oxidation reactions of H 2O 2 are shown to be competitive to the OH radical conversions in cases when H 2O 2 is not readily used up by the S(IV) oxidation.

  19. Oxygen dependency of one-electron reactions generating ascorbate radicals and hydrogen peroxide from ascorbic acid.

    PubMed

    Boatright, William L

    2016-04-01

    The effect of oxygen on the two separate one-electron reactions involved in the oxidation of ascorbic acid was investigated. The rate of ascorbate radical (Asc(-)) formation (and stability) was strongly dependent on the presence of oxygen. A product of ascorbic acid oxidation was measurable levels of hydrogen peroxide, as high as 32.5 μM from 100 μM ascorbic acid. Evidence for a feedback mechanism where hydrogen peroxide generated during the oxidation of ascorbic acid accelerates further oxidation of ascorbic acid is also presented. The second one-electron oxidation reaction of ascorbic acid leading to the disappearance of Asc(-) was also strongly inhibited in samples flushed with argon. In the range of 0.05-1.2 mM ascorbic acid, maximum levels of measurable hydrogen peroxide were achieved with an initial concentration of 0.2 mM ascorbic acid. Hydrogen peroxide generation was greatly diminished at ascorbic acid levels of 0.8 mM or above.

  20. Effect of pH on Fenton process using estimation of hydroxyl radical with salicylic acid as trapping reagent.

    PubMed

    Chang, Chen-Yu; Hsieh, Yung-Hsu; Cheng, Kai-Yuan; Hsieh, Ling-Ling; Cheng, Ta-Chih; Yao, Kuo-Shan

    2008-01-01

    This study estimates the yield of hydroxyl radical using salicylic acid as the trapping reagent and investigates the relationship between hydroxyl radical and pH value. The formation and variation of hydroxyl radical under different pH values were evaluated using reaction products, 2,3-DHBA, 2,5-DHBA, and catechol. The formation rate of hydroxyl radical was dependent on the ratio of ferrous ion to hydrogen peroxide and pH values. The difference between various pH values was explored. The kinetics and mechanisms of hydroxyl radical reactions were established in the Fenton process. Experimental results showed that the best reaction conditions were 8.5 mM H(2)O(2), 1.25 mM Fe(2 + ), Fe(2 + )/H(2)O(2) = 0.147 at pH 3 and the formation rate constant of hydroxyl radical was 1.12 x 10(11) M(-1) s(-1).

  1. Synthesis and properties of a cation exchange resin prepared by the pyrolysis of starch in the presence of phytic acid

    SciTech Connect

    Lehrfeld, J.

    1995-12-01

    A material having cation exchange and adsorption properties was prepared by the controlled pyrolysis of starch in the presence of a commercial phytic acid solution. Resins can be prepared with binding capacities of 0.7-5.7 meq/g. These resins also have the ability to remove atrazine from aqueous solutions.

  2. Cationic liposome-hyaluronic acid hybrid nanoparticles for intranasal vaccination with subunit antigens

    PubMed Central

    Ochyl, Lukasz J.; Akerberg, Jonathan; Moon, James J.

    2015-01-01

    Here we report the development of a new cationic liposome-hyaluronic acid (HA) hybrid nanoparticle (NP) system and present our characterization of these NPs as an intranasal vaccine platform using a model antigen and F1-V, a candidate recombinant antigen for Yersinia pestis, the causative agent of plague. Incubation of cationic liposomes composed of DOTAP and DOPE with anionic HA biopolymer led to efficient ionic complexation and formation of homogenous liposome-polymer hybrid NPs, as evidenced by fluorescence resonance energy transfer, dynamic light scattering, and nanoparticle tracking analyses. Incorporation of cationic liposomes with thiolated HA allowed for facile surface decoration of NPs with thiol-PEG, resulting in the formation of DOTAP/HA core-PEG shell nanostructures. These NPs, termed DOTAP-HA NPs, exhibited improved colloidal stability and prolonged antigen release. In addition, cytotoxicity associated with DOTAP liposomes (LC50 ~0.2 mg/ml) was significantly reduced by at least 20-fold with DOTAP-HA NPs (LC50 > 4 mg/ml), as measured with bone marrow dendritic cells (BMDCs). Furthermore, NPs co-loaded with ovalbumin (OVA) and a molecular adjuvant, monophosphoryl lipid A (MPLA) promoted BMDC maturation and upregulation of co-stimulatory markers, including CD40, CD86, and MHC-II, and C57BL/6 mice vaccinated with NPs via intranasal route generated robust OVA-specific CD8+ T cell and antibody responses. Importantly, intranasal vaccination with NPs co-loaded with F1-V and MPLA induced potent humoral immune responses with 11-, 23-, and 15-fold increases in F1-V-specific total IgG, IgG1, and IgG2c titers in immune sera by day 77, respectively, and induced balanced Th1/Th2 humoral immune responses, compared with the lack of sero-conversion in mice immunized with the equivalent doses of soluble F1-V vaccine. Overall, these results suggest that liposome-polymer hybrid NPs may serve as a promising vaccine delivery platform for intranasal vaccination against Y

  3. Cationic liposome-hyaluronic acid hybrid nanoparticles for intranasal vaccination with subunit antigens.

    PubMed

    Fan, Yuchen; Sahdev, Preety; Ochyl, Lukasz J; J Akerberg, Jonathan; Moon, James J

    2015-06-28

    Here we report the development of a new cationic liposome-hyaluronic acid (HA) hybrid nanoparticle (NP) system and present our characterization of these NPs as an intranasal vaccine platform using a model antigen and F1-V, a candidate recombinant antigen for Yersinia pestis, the causative agent of plague. Incubation of cationic liposomes composed of DOTAP and DOPE with anionic HA biopolymer led to efficient ionic complexation and formation of homogenous liposome-polymer hybrid NPs, as evidenced by fluorescence resonance energy transfer, dynamic light scattering, and nanoparticle tracking analyses. Incorporation of cationic liposomes with thiolated HA allowed for facile surface decoration of NPs with thiol-PEG, resulting in the formation of DOTAP/HA core-PEG shell nanostructures. These NPs, termed DOTAP-HA NPs, exhibited improved colloidal stability and prolonged antigen release. In addition, cytotoxicity associated with DOTAP liposomes (LC50~0.2mg/ml) was significantly reduced by at least 20-fold with DOTAP-HA NPs (LC50>4mg/ml), as measured with bone marrow derived dendritic cells (BMDCs). Furthermore, NPs co-loaded with ovalbumin (OVA) and a molecular adjuvant, monophosphoryl lipid A (MPLA) promoted BMDC maturation and upregulation of co-stimulatory markers, including CD40, CD86, and MHC-II, and C57BL/6 mice vaccinated with NPs via intranasal route generated robust OVA-specific CD8(+) T cell and antibody responses. Importantly, intranasal vaccination with NPs co-loaded with F1-V and MPLA induced potent humoral immune responses with 11-, 23-, and 15-fold increases in F1-V-specific total IgG, IgG1, and IgG2c titers in immune sera by day 77, respectively, and induced balanced Th1/Th2 humoral immune responses, whereas mice immunized with the equivalent doses of soluble F1-V vaccine failed to achieve sero-conversion. Overall, these results suggest that liposome-polymer hybrid NPs may serve as a promising vaccine delivery platform for intranasal vaccination against Y

  4. Vanillic Acid Ameliorates Cationic Bovine Serum Albumin Induced Immune Complex Glomerulonephritis in BALB/c Mice.

    PubMed

    Motiram Kakalij, Rahul; Tejaswini, G; Patil, Madhoosudan A; Dinesh Kumar, B; Diwan, Prakash V

    2016-06-01

    Preclinical Research Vanillic acid (VA) is a dihydroxybenzoic acid derivative widely used as a flavoring agent. It has chemopreventive effects on experimentally-induced carcinogenesis and in ulcerative colitis. The object of the present study was to investigate the effects of VA, alone and in combination with methylprednisolone (MP), on cationic bovine serum albumin (cBSA induced immune-complex glomerulonephritis in female BALB/c mice. Pre-immunization was carried out with cBSA in BALB/c mice and repeated (cBSA, 13 mg/kg, 3 times/week, i.v.) for 6 weeks to induce glomerulonephritis which was confirmed by the presence of severe proteinuria. The effect of VA (50, 100, and 200 mg/kg, p.o.) and its combination with MP (12.5 mg/kg, p.o.) was assessed in the nephrotic disease model. Treatment with VA decreased inflammatory nephrotic injury as evidenced by decreased proteinuria, serum creatinine, blood urea nitrogen, serum IgG1 and TNF-α levels. Co-administration of VA with MP showed an improvement in the immunohistochemistry of glomerular nephrin and podocin. The present results indicate that VA has a nephroprotective effect in the management of autoimmune nephritis. Drug Dev Res 77 : 171-179, 2016.   © 2016 Wiley Periodicals, Inc.

  5. Relative Order of Sulfuric Acid, Bisulfate, Hydronium, and Cations at the Air-Water Interface.

    PubMed

    Hua, Wei; Verreault, Dominique; Allen, Heather C

    2015-11-04

    Sulfuric acid (H2SO4), bisulfate (HSO4(-)), and sulfate (SO4(2-)) are among the most abundant species in tropospheric and stratospheric aerosols due to high levels of atmospheric SO2 emitted from biomass burning and volcanic eruptions. The air/aqueous interfaces of sulfuric acid and bisulfate solutions play key roles in heterogeneous reactions, acid rain, radiative balance, and polar stratospheric cloud nucleation. Molecular-level knowledge about the interfacial distribution of these inorganic species and their perturbation of water organization facilitates a better understanding of the reactivity and growth of atmospheric aerosols and of the aerosol surface charge, thus shedding light on topics of air pollution, climate change, and thundercloud electrification. Here, the air/aqueous interface of NaHSO4, NH4HSO4, and Mg(HSO4)2 salt solutions as well as H2SO4 and HCl acid solutions are investigated by means of vibrational sum frequency generation (VSFG) and heterodyne-detected (HD) VSFG spectroscopy. VSFG spectra of all acid solutions show higher SFG response in the OH-bonded region relative to neat water, with 1.1 M H2SO4 being more enhanced than 1.1 M HCl. In addition, VSFG spectra of bisulfate salt solutions highly resemble that of the dilute H2SO4 solution (0.26 M) at a comparable pH. HD-VSFG (Im χ((2))) spectra of acid and bisulfate salt solutions further reveal that hydrogen-bonded water molecules are oriented preferentially toward the bulk liquid phase. General agreement between Im χ((2)) spectra of 1.1 M H2SO4 and 1.1 M HCl acid solutions indicate that HSO4(-) ions have a similar surface preference as that of chloride (Cl(-)) ions. By comparing the direction and magnitude of the electric fields arising from the interfacial ion distributions and the concentration of each species, the most reasonable relative surface preference that can be deduced from a simplified model follows the order H3O(+) > HSO4(-) > Na(+), NH4(+), Mg(2+) > SO4(2-). Interestingly

  6. 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.

  7. Full dimensional quantum-mechanical simulations for the vibronic dynamics of difluorobenzene radical cation isomers using the multilayer multiconfiguration time-dependent Hartree method

    NASA Astrophysics Data System (ADS)

    Meng, Qingyong; Faraji, Shirin; Vendrell, Oriol; Meyer, Hans-Dieter

    2012-10-01

    Full dimensional multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) calculations of the dynamics of the three difluorobenzene cationic isomers in five lowest-lying doublet electronic states using the ab initio multistate multimode vibronic coupling Hamiltonian (MMVCH) model are carried out using the Heidelberg MCTDH package. The same dynamical problems, but treated with the MCTDH scheme and using a reduced dimensional ab initio MMVCH model, have been previously reported [S. Faraji, H.-D. Meyer, and H. Köppel, "Multistate vibronic interactions in difluorobenzene radical cations. II Quantum dynamical simulations," J. Chem. Phys. 129, 074311 (2008), 10.1063/1.2958918]. For easy comparison with the reduced dimensional results, 11D or 10D ML-MCTDH calculations are also performed. Extensive ML-MCTDH test calculations are performed to find appropriate ML-MCTDH wavefunction structures (ML-trees), and the convergence of the ML-MCTDH calculations are carefully checked to ensure accurate results. Based on the appropriate ML-trees, the photoelectron (PE) spectrum and the mass analyzed threshold ionization (MATI) spectrum are simulated, analyzed, and compared with corresponding experimental spectra. Because of its efficient simulation capability for large systems, ML-MCTDH calculations save a considerable amount of central processing unit (CPU)-time, even when a reduced dimensional MMVCH is used, i.e., the same reduced model as in the corresponding MCTDH calculations. Simulations of the experimental PE spectra by full dimensional ML-MCTDH calculations reproduced main peaks, which originate from different electronic states. The agreement is improved as compared to the reduced dimensionality calculations. Unfortunately, the experimental PE spectra are not very well resolved. Therefore, we compare our calculations additionally with highly resolved MATI spectra, which, however, are only available for the tilde{X} state. Based on a series of ML-MCTDH simulations with

  8. Unexpectedly Enhanced Solubility of Aromatic Amino Acids and Peptides in an Aqueous Solution of Divalent Transition-Metal Cations

    NASA Astrophysics Data System (ADS)

    Shi, Guosheng; Dang, Yaru; Pan, Tingting; Liu, Xing; Liu, Hui; Li, Shaoxian; Zhang, Lijuan; Zhao, Hongwei; Li, Shaoping; Han, Jiaguang; Tai, Renzhong; Zhu, Yiming; Li, Jichen; Ji, Qing; Mole, R. A.; Yu, Dehong; Fang, Haiping

    2016-12-01

    We experimentally observed considerable solubility of tryptophan (Trp) in a CuCl2 aqueous solution, which could reach 2-5 times the solubility of Trp in pure water. Theoretical studies show that the strong cation-π interaction between Cu2 + and the aromatic ring in Trp modifies the electronic distribution of the aromatic ring to enhance significantly the water affinity of Trp. Similar solubility enhancement has also been observed for other divalent transition-metal cations (e.g., Zn2 + and Ni2 + ), another aromatic amino acid (phenylalanine), and three aromatic peptides (Trp-Phe, Phe-Phe, and Trp-Ala-Phe).

  9. Conformational Distortions of π-Cation Radical (β-Oxoporphyrin)copper(II) Derivatives: [Cu(2,7,12-TrioxoOEHP)][SbCl(6)] and [Cu(2,7-DioxoOEiBC)][SbCl(6)].

    PubMed

    Turowska-Tyrk, Ilona; Kang, Seong-Joo; Scheidt, W Robert

    2011-03-01

    The preparation and characterization of two π-cation radical derivatives of copper β-oxo porphyrins is described. [3,3,8,8,13,13,17,18-Octaethyl-(3H,8H,13H)-porphine-2,7,12-trionato (2-)] copper π-cation radical, [Cu(2,7,12-trioxoOEHP(.))](+), and [3,3,8,8,12,13,17,18-octaethyl-(3H,8H)-porphine-2,7-dionato(2-)] copper π-cation radical, [Cu(2,7-dioxoOEiBC(.))](+), have been prepared and characterized by single-crystal X-ray determinations, UV/vis/NIR, and IR spectroscopies. Both molecules have modest distortion from the planarity and show monomeric units in the solid state. [Cu(2,7-dioxoOEiBC(.))](+) shows a concentration dependent near-IR band at 1410 nm. Crystal data for [Cu(2,7,12-trioxoOEHP(.))][SbCl(6)]: tetragonal, space group P4(2)/n, a = 31.085 (14) Å, c = 9.410 (4) Å, V = 9093 Å(3), Z = 8, T = 127 K. Crystal data for [Cu(2,7-dioxoOEiBC(.))][SbCl(6)]: monoclinic, space group P2(1)/n, a = 9.655 (4) Å, b = 20.592 (8) Å, c = 43.347 (17) Åβ = 89.97(1)(°), V = 8618. Å(3), Z = 8, T = 100 K.

  10. Kinetic Reaction Mechanism of Sinapic Acid Scavenging NO2 and OH Radicals: A Theoretical Study

    PubMed Central

    Lu, Yang; Wang, AiHua; Shi, Peng; Zhang, Hui; Li, ZeSheng

    2016-01-01

    The mechanism and kinetics underlying reactions between the naturally-occurring antioxidant sinapic acid (SA) and the very damaging ·NO2 and ·OH were investigated through the density functional theory (DFT). Two most possible reaction mechanisms were studied: hydrogen atom transfer (HAT) and radical adduct formation (RAF). Different reaction channels of neutral and anionic sinapic acid (SA-) scavenging radicals in both atmosphere and water medium were traced independently, and the thermodynamic and kinetic parameters were calculated. We find the most active site of SA/SA- scavenging ·NO2 and ·OH is the –OH group in benzene ring by HAT mechanism, while the RAF mechanism for SA/SA- scavenging ·NO2 seems thermodynamically unfavorable. In water phase, at 298 K, the total rate constants of SA eliminating ·NO2 and ·OH are 1.30×108 and 9.20×109 M-1 S-1 respectively, indicating that sinapic acid is an efficient scavenger for both ·NO2 and ·OH. PMID:27622460

  11. Vitamin C (ascorbic acid) induced hydroxyl radical formation in copper contaminated household drinking water: role of bicarbonate concentration.

    PubMed

    Jansson, Patric J; Asplund, Klara U M; Mäkelä, Johanna C; Lindqvist, Christer; Nordström, Tommy

    2003-08-01

    We have previously shown that Vitamin C (ascorbic acid) can trigger hydroxyl radical formation in copper contaminated household drinking water. We report here that the capacity of ascorbic acid to catalyze hydroxyl radical generation in the drinking water samples is strongly dependent on the bicarbonate concentration (buffer capacity and pH) of the samples. We found that at least 50 mg/l bicarbonate was required in the water samples to maintain the pH over 5.0 after ascorbic acid addition. At this pH, that is higher than the pKa1 4.25 of ascorbic acid, a hydroxyl radical generating redox cycling reaction involving the mono-anion of vitamin C and copper could take place. The ascorbic acid induced hydroxyl radical generating reaction could easily be mimicked in Milli-Q water by supplementing the water with copper and bicarbonate. Our results demonstrate that ascorbic acid can induce a pH dependent hydroxyl radical generating reaction in copper contaminated household tap water that is buffered with bicarbonate. The impact of consuming ascorbic acid together with copper and bicarbonate containing drinking water on human health is discussed.

  12. Breaking the dogma: PCB-derived semiquinone free radicals do not form covalent adducts with DNA, GSH, and amino acids

    PubMed Central

    Wangpradit, Orarat; Rahaman, Asif; Mariappan, S. V. Santhana; Buettner, Garry R.; Robertson, Larry W.; Luthe, Gregor

    2016-01-01

    Covalent bond formations of free radical metabolites with biomolecules like DNA and proteins are thought to constitute a major mechanism of toxicity and carcinogenesis. Glutathione (GSH) is generally accepted as a radical scavenger protecting the cell. In the present study, we investigated a semiquinone radical (SQ•-) metabolite of the semivolatile 4-chlorobiphenyl, using electron paramagnetic resonance spectroscopy, and oxygen consumption. Proton nuclear magnetic resonance (1H NMR) and liquid chromatography–mass spectrometry (LC-MS) were also employed to elucidate the radical interaction with DNA, amino acids, and GSH. We found that DNA and oligonucleotides stabilized SQ•- by electron delocalization in the π-stacking system, resulting in persistent radical intercalated, rather than forming a covalent bond with SQ•-. This finding was strongly supported by the semiempirical calculation of the semioccupied molecular orbital and the linear combination of the atomic orbitals, indicating 9.8 kcal mol−1 energy gain. The insertion of SQ•- into the DNA strand may result in DNA strand breaks and interruption of DNA replication process or even activate radical mediated secondary reactions. The presence of amino acids resulted in a decrease of the electron paramagnetic resonance (EPR) signal of SQ•- and correlated with their isoelectric points. The pH shifts the equilibrium of the dianions of hydroquinone and influenced indirectly the formation of SQ•-. Similar findings were observed with GSH and Cys. GSH and Cys functioned as indirect radical scavengers; their activities depend on their chemical equilibria with the corresponding quinones, and their further reaction via Michael addition. The generally accepted role of GSH as radical scavenger in biological systems should be reconsidered based upon these findings, questioning the generally accepted view of radical interaction of semiquinones with biologically active compounds, like DNA, amino acids, proteins

  13. 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.

  14. A unified description of the electrochemical, charge distribution, and spectroscopic properties of the special-pair radical cation in bacterial photosynthesis.

    PubMed

    Reimers, Jeffrey R; Hush, Noel S

    2004-04-07

    We apply our four-state 70-vibration vibronic-coupling model for the properties of the photosynthetic special-pair radical cation to: (1) interpret the observed correlations between the midpoint potential and the distribution of spin density between the two bacteriochlorophylls for 30 mutants of Rhodobacter sphaeroides, (2) interpret the observed average intervalence hole-transfer absorption energies as a function of spin density for six mutants, and (3) simulate the recently obtained intervalence electroabsorption Stark spectrum of the wild-type reaction center. While three new parameters describing the location of the sites of mutation with respect to the special pair are required to describe the midpoint-potential data, a priori predictions are made for the transition energies and the Stark spectrum. In general, excellent predictions are made of the observed quantities, with deviations being typically of the order of twice the experimental uncertainties. A unified description of many chemical and spectroscopic properties of the bacterial reaction center is thus provided. Central to the analysis is the assumption that the perturbations made to the reaction center, either via mutations of protein residues or by application of an external electric field, act only to independently modify the oxidation potentials of the two halves of the special pair and hence the redox asymmetry E0. While this appears to be a good approximation, clear evidence is presented that effects of mutation can be more extensive than what is allowed for. A thorough set of analytical equations describing the observed properties is obtained using the Born-Oppenheimer adiabatic approximation. These equations are generally appropriate for intervalence charge-transfer problems and include, for the first time, full treatment of both symmetric and antisymmetric vibrational motions. The limits of validity of the adiabatic approach to the full nonadiabatic problem are obtained.

  15. Influence of complexation phenomena with multivalent cations on the analysis of glyphosate and aminomethyl phosphonic acid in water.

    PubMed

    Freuze, Ingrid; Jadas-Hecart, Alain; Royer, Alain; Communal, Pierre-Yves

    2007-12-21

    Experimental and theoretical influence of multivalent cations on the analysis of glyphosate and aminomethyl phosphonic acid (AMPA) was studied in pure water and in one surface water. The procedure chosen, based on derivatization with FMOC-Cl, HPLC separation, and fluorescence detection, appears highly affected at cations concentrations current in natural waters. A detailed speciation study performed with the VMINTEQ software strongly suggests that the complexes formed between analytes and cations do not dissociate during the reaction and do not react with the derivatization agent, so that only the free forms are derivatized. These results point out the necessity of a pre-treatment to prevent these interferences, even in low salinity waters. The different ways conceivable are discussed in terms of kinetic and thermodynamic considerations.

  16. Continuous process of preparation of n-butyl(meth)acrylate by esterification of (meth)acrylic acid by butanol on thermostable sulfo-cation exchanger

    SciTech Connect

    Zheleznaya, L.L.; Karakhanov, R.A.; Lunin, A.F.; Magadov, R.S.; Meshcheryakov, S.V.; Mkrtychan, V.R.; Fomin, V.A.

    1987-11-10

    The authors propose an effective thermostable sulfo-cation exchanger based on polymers with a system of conjugated bonds, sulfopolyphenylene ketone (SPP) differing from the known cation exchangers by the high thermostability (up to 250/sup 0/C), and also having the effect of the stabilization of the double bond in unsaturated monomers. The combination of inhibiting and cation exchange properties makes it also possible to use these sulfo-cation exchangers in the processes of esterification of (meth)acrylic acids by alcohols without addition of special inhibitors. The SPP catalyst was tested in esterification processes of acrylic an methacrylic acid by butanol at a pilot plant.

  17. Kinetics and Thermodynamics of Reserpine Adsorption onto Strong Acidic Cationic Exchange Fiber.

    PubMed

    Guo, Zhanjing; Liu, Xiongmin; Huang, Hongmiao

    2015-01-01

    The kinetics and thermodynamics of the adsorption process of reserpine adsorbed onto the strong acidic cationic exchange fiber (SACEF) were studied by batch adsorption experiments. The adsorption capacity strongly depended on pH values, and the optimum reserpine adsorption onto the SACEF occurred at pH = 5 of reserpine solution. With the increase of temperature and initial concentration, the adsorption capacity increased. The equilibrium was attained within 20 mins. The adsorption process could be better described by the pseudo-second-order model and the Freundlich isotherm model. The calculated activation energy Ea was 4.35 kJ/mol. And the thermodynamic parameters were: 4.97<ΔH<7.44 kJ/mol, -15.29<ΔG<-11.87 kJ/mol and 41.97<ΔS<47.35 J/mol·K. The thermodynamic parameters demonstrated that the adsorption was an endothermic, spontaneous and feasible process of physisorption within the temperature range between 283 K and 323 K and the initial concentration range between 100 mg/L and 300 mg/L. All the results showed that the SACEF had a good adsorption performance for the adsorption of reserpine from alcoholic solution.

  18. Quantitative intracellular localization of cationic lipid-nucleic acid nanoparticles with fluorescence microscopy

    PubMed Central

    Majzoub, Ramsey N.; Ewert, Kai K.; Safinya, Cyrus R.

    2016-01-01

    Summary Current activity in developing synthetic carriers of nucleic acids (NA) and small molecule drugs for therapeutic applications is unprecedented. One promising class of synthetic vectors for the delivery of therapeutic NA is PEGylated cationic lipid (CL)-NA nanoparticles (NPs). Chemically-modified PEG-lipids can be used to surface-functionalize lipid-NA nanoparticles, allowing researchers to design active nanoparticles that can overcome the various intracellular and extracellular barriers to efficient delivery. Optimization of these functionalized vectors requires a comprehensive understanding of their intracellular pathways. In this chapter we present 2 distinct methods for investigating the intracellular activity of PEGylated CL-NA NPs using quantitative analysis of fluorescence microscopy. The first method, spatial localization, will describe how to prepare fluorescently-labeled CL-NA NPs, perform fluorescence microscopy and properly analyze the data to measure the intracellular distribution of nanoparticles and fluorescent signal. We provide software which allows data from multiple cells to be averaged together and yield statistically significant results. The second method, fluorescence colocalization, will describe how to label endocytic organelle via Rab-GFPs and generate micrographs for software-assisted NP-endocytic marker colocalization measurements. These tools will allow researchers to study the endosomal trafficking of CL-NA NPs which can guide their design and improve their efficiency. PMID:27436314

  19. Laccase-mediated transformation of triclosan in aqueous solution with metal cations and humic acid.

    PubMed

    Sun, Kai; Kang, Fuxing; Waigi, Michael Gatheru; Gao, Yanzheng; Huang, Qingguo

    2017-01-01

    Triclosan (TCS) is a broad-spectrum antimicrobial agent that is found extensively in natural aquatic environments. Enzyme-catalyzed oxidative coupling reactions (ECOCRs) can be used to remove TCS in aqueous solution, but there is limited information available to indicate how metal cations (MCs) and natural organic matter (NOM) influence the environmental fate of TCS during laccase-mediated ECOCRs. In this study, we demonstrated that the naturally occurring laccase from Pleurotus ostreatus was effective in removing TCS during ECOCRs, and the oligomerization of TCS was identified as the dominant reaction pathway by high-resolution mass spectrometry (HRMS). The growth inhibition studies of green algae (Chlamydomonas reinhardtii and Scenedesmus obliquus) proved that laccase-mediated ECOCRs could effectively reduce the toxicity of TCS. The presence of dissolved MCs (Mn(2+), Al(3+), Ca(2+), Cu(2+), and Fe(2+) ions) influenced the removal and transformation of TCS via different mechanisms. Additionally, the transformation of TCS in systems with NOM derived from humic acid (HA) was hindered, and the apparent pseudo first-order kinetics rate constants (k) for TCS decreased as the HA concentration increased, which likely corresponded to the combined effect of both noncovalent (sorption) and covalent binding between TCS and humic molecules. Our results provide a novel insight into the fate and transformation of TCS by laccase-mediated ECOCRs in natural aquatic environments in the presence of MCs and NOM.

  20. Insulin receptor aggregation and autophosphorylation in the presence of cationic polyamino acids

    SciTech Connect

    Kohanski, R.A. )

    1989-12-15

    Aggregation and autophosphorylation of the insulin receptor-protein kinase, from cultured 3T3-L1 adipocytes, were studied in the presence of cationic polyamino acids. Poly-L-lysine and poly-L-arginine produced the following effects with the purified receptor: first, the autophosphorylation rate was increased by polycations. Half-maximal stimulation was proportional to polymer length. The rate enhancement was greater at lower ATP concentrations. Second, near-endpoint (equilibrium) autophosphorylation was greater in the presence of the polycations. Polycations inhibited the reverse reaction: ADP + phosphoreceptor yielding ATP + aporeceptor. Third, the (32P)phosphopeptides generated by trypsin digestion of the 32P-beta-subunit, showed that no new autophosphorylation sites resulted from the presence of polycations. Fourth, the polycations, but not insulin, promoted receptor aggregation, and phosphoreceptor aggregated more readily than aporeceptor. Insulin receptor enriched through the wheat germ agglutinin eluate step was compared with purified receptor. Higher concentrations of poly-L-arginine were required to stimulate autophosphorylation and to promote aggregation. Finally, several polycation-dependent substrates present in the wheat germ agglutinin eluate co-aggregated with the insulin receptor. Polycation-stimulated receptor autophosphorylation is linked to a lower KM,app for ATP, but substrate phosphorylation may require the aggregation.

  1. Transport of cationic amino acids by the mouse ecotropic retrovirus receptor.

    PubMed

    Kim, J W; Closs, E I; Albritton, L M; Cunningham, J M

    1991-08-22

    Susceptibility of rodent cells to infection by ecotropic murine leukaemia viruses (MuLV) is determined by binding of the virus envelope to a membrane receptor that has multiple membrane-spanning domains. Cells infected by ecotropic MuLV synthesize envelope protein, gp70, which binds to this receptor, thereby preventing additional infections. The consequences of envelope-MuLV receptor binding for the infected host cell have not been directly determined, partly because the cellular function of the MuLV receptor protein is unknown. Here we report a coincidence in the positions of the first eight putative membrane-spanning domains found in the virus receptor and in two related proteins, the arginine and histidine permeases of Saccharomyces cerevisiae (Fig. 1), but not in any other proteins identified by computer-based sequence comparison of the GenBank data base. Xenopus oocytes injected with receptor-encoding messenger RNA show increased uptake of L-arginine, L-lysine and L-ornithine. The transport properties and the expression pattern of the virus receptor behave in ways previously attributed to y+, the principal transporter of cationic L-amino acids in mammalian cells.

  2. Kinetics and Thermodynamics of Reserpine Adsorption onto Strong Acidic Cationic Exchange Fiber

    PubMed Central

    Guo, Zhanjing; Liu, Xiongmin; Huang, Hongmiao

    2015-01-01

    The kinetics and thermodynamics of the adsorption process of reserpine adsorbed onto the strong acidic cationic exchange fiber (SACEF) were studied by batch adsorption experiments. The adsorption capacity strongly depended on pH values, and the optimum reserpine adsorption onto the SACEF occurred at pH = 5 of reserpine solution. With the increase of temperature and initial concentration, the adsorption capacity increased. The equilibrium was attained within 20 mins. The adsorption process could be better described by the pseudo-second-order model and the Freundlich isotherm model. The calculated activation energy Ea was 4.35 kJ/mol. And the thermodynamic parameters were: 4.97<ΔH<7.44 kJ/mol, -15.29<ΔG<-11.87 kJ/mol and 41.97<ΔS<47.35 J/mol·K. The thermodynamic parameters demonstrated that the adsorption was an endothermic, spontaneous and feasible process of physisorption within the temperature range between 283 K and 323 K and the initial concentration range between 100 mg/L and 300 mg/L. All the results showed that the SACEF had a good adsorption performance for the adsorption of reserpine from alcoholic solution. PMID:26422265

  3. Fractionation of equine antivenom using caprylic acid precipitation in combination with cationic ion-exchange chromatography.

    PubMed

    Raweerith, Rutai; Ratanabanangkoon, Kavi

    2003-11-01

    A combined process of caprylic acid (CA) precipitation and ion-exchange chromatography on SP-Sepharose was studied as a means to fractionate pepsin-digested horse antivenom F(ab')(2) antibody. In the CA precipitation, the optimal concentration for fractionation of F(ab')(2) from pepsin-digested horse plasma was 2%, in which 89.61% of F(ab')(2) antibody activity was recovered in the supernatant with 1.5-fold purification. A significant amount of pepsin was not precipitated and remained active under these conditions. An analytical cation exchanger Protein-Pak SP 8HR HPLC column was tested to establish optimal conditions for the effective separation of IgG, albumin, pepsin and CA from the F(ab')(2) product. From these results, the supernatant from CA precipitation of pepsin-digested plasma was subjected to a SP-Sepharose column chromatography using a linear salt gradient. With stepwise elution, a peak containing F(ab')(2) antibody could be obtained by elution with 0.25 M NaCl. The total recovery of antibody was 65.56% with 2.91-fold purification, which was higher than that achieved by ammonium sulfate precipitation. This process simultaneously and effectively removed residual pepsin, high molecular weight aggregates and CA in the final F(ab')(2) product, and should be suitable for large-scale fractionation of therapeutic equine antivenoms.

  4. Expression Profile of Cationic Amino Acid Transporters in Rats with Endotoxin-Induced Uveitis

    PubMed Central

    Chang, Shu-Wen; Lee, Yi-An; Kao, Tzu-Yun

    2016-01-01

    Purpose. The transcellular arginine transportation via cationic amino acid transporter (CAT) is the rate-limiting step in nitric oxide (NO) synthesis, which is crucial in intraocular inflammation. In this study, CAT isoforms and inducible nitric oxide synthase (iNOS) expression was investigated in endotoxin-induced uveitis (EIU). Methods. EIU was induced in Lewis rats by lipopolysaccharide (LPS) injection. In the treatment group, the rats were injected intraperitoneally with the proteasome inhibitor bortezomib before EIU induction. After 24 hours, leukocyte quantification, NO measurement of the aqueous humor, and histopathological examination were evaluated. The expression of CAT isoforms and iNOS was determined by reverse transcription-polymerase chain reaction, western blotting, and immunofluorescence staining. Nuclear factor-kappa B (NF-κB) binding activity was evaluated by electrophoretic mobility shift assay. The mouse macrophage cell line RAW 264.7 was used to validate the in vivo findings. Results. LPS significantly stimulated iNOS, CAT-2A, and CAT-2B mRNA and protein expression but did not affect CAT-1 in EIU rats and RAW 264.7 cells. Bortezomib attenuated inflammation and inhibited iNOS, CAT-2A, and CAT-2B expression through NF-κB inhibition. Conclusions. CAT-2 and iNOS, but not CAT-1, are specifically involved in EIU. NF-κB is essential in the induction of CAT-2 and iNOS in EIU. PMID:27413255

  5. Controversial alkoxyl and peroxyl radical scavenging activity of the tryptophan metabolite 3-hydroxy-anthranilic acid.

    PubMed

    Dorta, E; Aspée, A; Pino, E; González, L; Lissi, E; López-Alarcón, C

    2017-04-01

    3-Hydroxy-anthranilic acid (3-OHAA), a tryptophan metabolite produced in the kynurenine pathway, is an efficient antioxidant towards peroxyl radicals (ROO) derived from the AAPH (2,2'-azobis(2-amidinopropane) dihydrochloride) thermolysis. However, self-reactions of ROO can give rise to alkoxyl radicals (RO), which could strongly affect the fate of scavenging reactions. In the present work, we studied the influence of RO in the scavenging activity of 3-OHAA in three different systems: i) Monitoring of the direct reaction between 3-OHAA and AAPH-derived free radicals (kinetic studies); ii) Evaluation of the protective effect of 3-OHAA on the AAPH-induced consumption of fluorescein; and, iii) Inhibition, given by 3-OHAA, of the AAPH-initiated lipid peroxidation of both, rat brain synaptosomes and homogenate preparations (assessed by chemiluminescence). For such purposes, the fraction of free radicals (f) trapped per 3-OHAA molecule was determined in each system. Kinetic results show that the oxidation of 3-OHAA follows a process dominated by ROO with a zero order kinetic limit in 3-OHAA, and a fraction (fri) equal to 0.88. From the induction times, elicited by 3-OHAA in the kinetic profiles of fluorescein consumption, a fraction (fT) of 0.28 was determined. 3-OHAA also generated induction times in the kinetic profiles of light emission during the AAPH-initiated lipid peroxidation of rat brain synaptosomes and homogenates. From such induction times, fractions of 0.61 and 0.63 were determined for rat brain synaptosomes (fsyn) and homogenates (fhom), respectively. These results show that during the incubation of 3-OHAA and AAPH, a low fraction of ROO self-reacts to generate RO. Nevertheless, when 3-OHAA is employed to protect particular targets, such as fluorescein, rat brain synaptosomes and homogenates, reactions of ROO and/or RO should be considered.

  6. Antioxidant Activity of Caffeic Acid against Iron-Induced Free Radical Generation—A Chemical Approach

    PubMed Central

    Genaro-Mattos, Thiago C.; Maurício, Ângelo Q.; Rettori, Daniel; Alonso, Antonio; Hermes-Lima, Marcelo

    2015-01-01

    Caffeic acid (CA) is a phenolic compound widely found in coffee beans with known beneficial effects in vivo. Many studies showed that CA has anti-inflammatory, anti-mutagenic, antibacterial and anti-carcinogenic properties, which could be linked to its antioxidant activity. Taking in consideration the reported in vitro antioxidant mechanism of other polyphenols, our working hypothesis was that the CA antioxidant activity could be related to its metal-chelating property. With that in mind, we sought to investigate the chemical antioxidant mechanism of CA against in vitro iron-induced oxidative damage under different assay conditions. CA was able to prevent hydroxyl radical formation promoted by the classical Fenton reaction, as determined by 2-deoxyribose (2-DR) oxidative degradation and DMPO hydroxylation. In addition to its ability to prevent hydroxyl radical formation, CA had a great inhibition of membrane lipid peroxidation. In the lipid peroxidation assays CA acted as both metal-chelator and as hydrogen donor, preventing the deleterious action promoted by lipid-derived peroxyl and alkoxyl radicals. Our results indicate that the observed antioxidant effects were mostly due to the formation of iron-CA complexes, which are able to prevent 2-DR oxidation and DMPO hydroxylation. Noteworthy, the formation of iron-CA complexes and prevention of oxidative damage was directly related to the pH of the medium, showing better antioxidant activity at higher pH values. Moreover, in the presence of lipid membranes the antioxidant potency of CA was much higher, indicating its enhanced effectiveness in a hydrophobic environment. Overall, our results show that CA acts as an antioxidant through an iron chelating mechanism, preventing the formation of free hydroxyl radicals and, therefore, inhibiting Fenton-induced oxidative damage. The chemical properties of CA described here—in association with its reported signaling effects—could be an explanation to its beneficial effects

  7. Reactivity of chlorine radical with submicron palmitic acid particles: kinetic measurements and product identification

    NASA Astrophysics Data System (ADS)

    Mendez, M.; Ciuraru, R.; Gosselin, S.; Batut, S.; Visez, N.; Petitprez, D.

    2013-12-01

    The heterogeneous reaction of Cl• radicals with submicron palmitic acid (PA) particles was studied in an aerosol flow tube in the presence or in the absence of O2. Fine particles were generated by homogeneous condensation of PA vapours and introduced into the reactor, where chlorine atoms were produced by photolysis of Cl2 using UV lamps surrounding the reactor. The effective reactive uptake coefficient (γ) has been determined from the rate loss of PA measured by gas chromatography-mass spectrometer (GC/MS) analysis of reacted particles as a function of the chlorine exposure. In the absence of O2, γ = 14 ± 5 indicates efficient secondary chemistry involving Cl2. GC/MS analysis has shown the formation of monochlorinated and polychlorinated compounds in the oxidized particles. Although the PA particles are solid, the complete mass can be consumed. In the presence of oxygen, the reaction is still dominated by secondary chemistry but the propagation chain length is smaller than in the absence of O2, which leads to an uptake coefficient γ = 3 ± 1. In the particulate phase, oxocarboxylic acids and dicarboxylic acids were identified by GC/MS. The formation of alcohols and monocarboxylic acids is also suspected. A reaction pathway for the main products and more functionalized species is proposed. All these results show that solid organic particles could be efficiently oxidized by gas-phase radicals not only on their surface but also in bulk by mechanisms which are still unclear. They help to understand the aging of primary tropospheric aerosol containing fatty acids.

  8. Reactivity of chlorine radical with submicron palmitic acid particles: kinetic measurements and products identification

    NASA Astrophysics Data System (ADS)

    Mendez, M.; Ciuraru, R.; Gosselin, S.; Batut, S.; Visez, N.; Petitprez, D.

    2013-06-01

    The heterogeneous reaction of Cl. radicals with sub-micron palmitic acid (PA) particles was studied in an aerosol flow tube in the presence or in the absence of O2. Fine particles were generated by homogeneous condensation of PA vapors and introduced in the reactor where chlorine atoms are produced by photolysis of Cl2 using UV lamps surrounding the reactor. The effective reactive uptake coefficient (γ) has been determined from the rate loss of PA measured by GC/MS analysis of reacted particles as a function of the chlorine exposure. In the absence of O2, γ = 14 ± 5 indicates efficient secondary chemistry involving Cl2. GC/MS analyses have shown the formation of monochlorinated and polychlorinated compounds in the oxidized particles. Although, the PA particles are solid, the complete mass can be consumed. In the presence of oxygen, the reaction is still dominated by secondary chemistry but the propagation chain length is smaller than in the absence of O2 which leads to an uptake coefficient γ = 3 ± 1. In the particulate phase, oxocarboxylic acids and dicarboxylic acids are identified by GC/MS. Formation of alcohols and monocarboxylic acids are also suspected. All these results show that solid organic particles could be efficiently oxidized by gas-phase radicals not only on their surface, but also in bulk by mechanisms which are still unclear. Furthermore the identified reaction products are explained by a chemical mechanism showing the pathway of the formation of more functionalized products. They help to understand the aging of primary tropospheric aerosol containing fatty acids.

  9. Radical production from photosensitization of imidazoles, benzophenone and 4-benzoylbenzoic acid

    NASA Astrophysics Data System (ADS)

    Corral Arroyo, Pablo; González, Laura; Steimer, Sarah; Volkamer, Rainer; George, Christian; Bartels-Rausch, Thorsten; Ammann, Markus

    2016-04-01

    Reactions promoted by light are key in atmospheric chemistry. Some of them occur in the condensed phase of aerosols which may contain light absorbing organic compounds that provoke photochemical reactions such as humic like material (GEORGE 2005). Our aim is to understand the role these reactions play in atmospheric photochemistry. This work explores the radical reactions initiated by UV light in mixtures of citric acid (CA) and imidazole-2-carboxaldehyde (IC), benzophenone and 4-Benzoylbenzoic acid (BBA) using NO as a probe molecule for HO2, by means of coated wall flow tube experiments. The loss of NO was measured by a chemiluminescence detector (CLD), also configured for the distinction of the products (HONO or NO2). The dependence of the NO loss on the initial NO concentration, the photosensitizer concentration in the film, relative humidity, light intensity, oxygen molar fraction were investigated as well as the HONO and NO2 yields. We found a clear correlation between the loss of NO above the film and the molar ratio of photosensitizer/CA, and also between the NO loss and the light intensity. The variation of the observed NO loss with oxygen corroborates a mechanism, in which the triplet excited state of the photosensitizer is reduced likely by the predominant donor in the system, citric acid, to a reduced ketyl radical. This reactive species is transferring an electron to molecular oxygen, which in turn leads to production of HO2 radicals, which are released to the gas phase. Therefore, in absence of gas phase oxidants, the loss of NO in the gas phase could be related to the production of HO2 radicals in the condensed phase. Relative humidity had a strong impact on the HO2 output, which shows a maximum value at intermediate humidity around 30%, likely due to different competing effects of dilution and reactant mobility. The observed NO2/HONO ratio was around 1.4 consistent with the secondary chemistry of HO2 in presence of NO in the gas phase, indicating no

  10. Sorption of chlorophenols on microporous minerals: mechanism and influence of metal cations, solution pH, and humic acid.

    PubMed

    Yang, Hui; Hu, Yuanan; Cheng, Hefa

    2016-10-01

    Sorption of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) on a range of dealuminated zeolites were investigated to understand the mechanism of their sorption on microporous minerals, while the influence of common metal cations, solution pH, and humic acid was also studied. Sorption of chlorophenols was found to increase with the hydrophobicity of the sorbates and that of the microporous minerals, indicating the important role of hydrophobic interactions, while sorption was also stronger in the micropores of narrower sizes because of greater enhancement of the dispersion interactions. The presence of metal cations could enhance chlorophenol sorption due to the additional electrostatic attraction between metal cations exchanged into the mineral micropores and the chlorophenolates, and this effect was apparent on the mineral sorbent with a high density of surface cations (2.62 sites/nm(2)) in its micropores. Under circum-neutral or acidic conditions, neutral chlorophenol molecules adsorbed into the hydrophobic micropores through displacing the "loosely bound" water molecules, while their sorption was negligible under moderately alkaline conditions due to electrostatic repulsion between the negatively charged zeolite framework and anionic chlorophenolates. The influence of humic acid on sorption of chlorophenols on dealuminated Y zeolites suggests that its molecules did not block the micropores but created a secondary sorption sites by forming a "coating layer" on the external surface of the zeolites. These mechanistic insights could help better understand the interactions of ionizable chlorophenols and metal cations in mineral micropores and guide the selection and design of reusable microporous mineral sorbents for sorptive removal of chlorophenols from aqueous stream.

  11. On the reaction of lupulones, hops β-acids, with 1-hydroxyethyl radical.

    PubMed

    de Almeida, Natália E C; do Nascimento, Eduardo S P; Cardoso, Daniel R

    2012-10-24

    Lupulones, hops β-acids, are one of the main constituents of the hops resin and have an important contribution to the overall bacteriostatic activity of hops during beer brewing. The use of lupulones as natural alternatives to antibiotics is increasing in the food industry and also in bioethanol production. However, lupulones are easy oxidizable and have been shown to be very reactive toward 1-hydroxyethyl radical with apparent bimolecular rate constants close to diffusion control k = 2.9 × 10(8) and 2.6 × 10(8) L mol(-1) s(-1) at 25.0 ± 0.2 °C in ethanol-water solution (10% of ethanol (v/v)) as probed by EPR and ESI-IT-MS/MS spin-trapping competitive kinetics, respectively. The free energy change for an electron-transfer mechanism is ΔG° = 106 kJ/mol as calculated from the oxidation peak potential experimentally determined for lupulones (1.1 V vs NHE) by cyclic voltammetry and the reported reduction potential for 1-hydroxyethyl radical. The major reaction products identified by LC-ESI-IT-MS/MS and ultrahigh-resolution accurate mass spectrometry (orbitrap FT-MS) are hydroxylated lupulone derivatives and 1-hydroxyethyl radical adducts. The lack of pH dependence for the reaction rate constant, the calculated free energy change for electron transfer, and the main reaction products strongly suggest the prenyl side chains at the hops β-acids as the reaction centers rather than the β,β'-triketone moiety.

  12. Indirect UV detection-ion-exclusion/cation-exchange chromatography of common inorganic ions with sulfosalicylic acid eluent.

    PubMed

    Kozaki, Daisuke; Mori, Masanobu; Nakatani, Nobutake; Arai, Kaori; Masuno, Tomoe; Koseki, Masakazu; Itabashi, Hideyuki; Tanaka, Kazuhiko

    2013-01-01

    Herein, we describe indirect UV detection-ion-exclusion/cation-exchange chromatography (IEC/CEC) on a weakly acidic cation-exchange resin in the H(+)-form (TSKgel Super IC-A/C) using sulfosalicylic acid as the eluent. The goal of the study was to characterize the peaks detected by UV detector. The peak directions of analyte ions in UV at 315 nm were negative because the molar absorbance coefficients of analyte anions and cations were lower than that of the sulfosalicylic acid eluent. Good chromatographic resolution and high signal-to-noise ratios of analyte ions were obtained for the separations performed using 1.1 mM sulfosalicylic acid and 1.5 mM 18-crown-6 as the eluent. The relative standard deviations (RSDs) of the peak areas ranged from 0.6 to 4.9%. Lower detection limits of the analytes were achieved using indirect UV detection at 315 nm (0.23 - 0.98 μM) than those obtained with conductometric detection (CD) (0.61 - 2.1 μM) under the optimized elution conditions. The calibration curves were linear in the range from 0.01 to 1.0 mM except for Cl(-), which was from 0.02 to 2.0 mM. The present method was successfully applied to determine common inorganic ions in a pond water sample.

  13. Water soluble and heat resistant polymers by free radical polymerization of lactic acid-based monomers

    NASA Astrophysics Data System (ADS)

    Tanaka, Hitoshi; Kibayashi, Tatsuya; Niwa, Miki

    2013-08-01

    Tactic heat resistant polymer was prepared by free radical polymerization of lactic acid-based monomers, i.e. chiral 2-isopropyl-5-methylene-1,3-dioxolan-4-ones (1). The polymerization of 1 proceeded smoothly without ring-opening to give a polymer with high isotacticity (mm) of 29.7~100% and glass transition temperature (Tg) of 172~213°C. 1 also showed high reactivity in the copolymerization with styrene and methyl methacrylate, and the incorporation of 1 unit in the copolymer structure increased Tg of each polymer. In addition, hydrolysis of poly(1) produced a new type of water soluble poly(lactic acid), i.e. poly(α-hydroxy acrylate), and poly(α-hydroxy acrylate-co-divinyl benzene) hydrogel absorbed water as high as 1000 times of the original polymer weight.

  14. Lipoxygenase-mediated pro-radical effect of melatonin via stimulation of arachidonic acid metabolism

    SciTech Connect

    Radogna, F.; Sestili, P.; Martinelli, C.; Paolillo, M.; Paternoster, L.; Albertini, M.C.; Accorsi, A.; Gualandi, G.; Ghibelli, L.

    2009-07-15

    We have shown that melatonin immediately and transiently stimulates intracellular free radical production on a set of leukocytes, possibly as a consequence of calmodulin binding. We show here that melatonin-induced ROS are produced by lipoxygenase (LOX), since they are prevented by a set of LOX inhibitors, and are accompanied by increase of the 5-LOX product 5-HETE. LOX activation is accompanied by strong liberation of AA; inhibition of Ca{sup 2+}-independent, but not Ca{sup 2+}-dependent, phospholipase A2 (PLA2), prevents both melatonin-induced arachidonic acid and ROS production, whereas LOX inhibition only prevents ROS, indicating that PLA2 is upstream with respect to LOX, as occurs in many signaling pathways. Chlorpromazine, an inhibitor of melatonin-calmodulin interaction, inhibits both ROS and arachidonic acid production, thus possibly placing calmodulin at the origin of a melatonin-induced pro-radical pathway. Interestingly, it is known that Ca{sup 2+}-independent PLA2 binds to calmodulin: our results are compatible with PLA2 being liberated by melatonin from a steady-state calmodulin sequestration, thus initiating an arachidonate signal transduction. These results delineate a novel molecular pathway through which melatonin may participate to the inflammatory response.

  15. Hydrogen bonding in the hydroxysulfinyl radical-formic acid-water system: A theoretical study.

    PubMed

    Tušar, Simona; Lesar, Antonija

    2016-06-30

    Quantum chemical methods have been employed to evaluate the possible configurations of the 1:1 and 1:2 HOSO-formic acid complexes and 1:1:1 HOSO-formic acid-water complexes. The first type of complex involves two H bonds, while the other two types comprise three H bonds in a ring. The complexes are relatively stable, with CBS-QB3 computed binding energies of 14.3 kcal mol(-1) , 23.4 kcal mol(-1) , and 21.1 kcal mol(-1) for the lowest-energy structures of the 1:1, 1:2, and 1:1:1 complexes, respectively. Complex formations induce a large spectral red-shift and an enhancement of the IR intensity for the H-bonded OH stretching modes relative to those in the parent monomers. TDDFT calculations of the low-lying electronic excited states demonstrate that the complexes are photochemically quite stable in the troposphere. Small spectral shifts in comparison to the free HOSO radical suggest that the radical and the complexes would not be easily distinguishable using standard UV/vis absorption spectroscopy. © 2016 Wiley Periodicals, Inc.

  16. A high performance liquid chromatography system for quantification of hydroxyl radical formation by determination of dihydroxy benzoic acids.

    PubMed

    Owen, R W; Wimonwatwatee, T; Spiegelhalder, B; Bartsch, H

    1996-08-01

    The hypoxanthine/xanthine oxidase enzyme system is known to produce the superoxide ion and hydrogen peroxide during the hydroxylation of hypoxanthine via xanthine to uric acid. When chelated iron is included in this system, superoxide reduces iron (III) to iron(II) and the iron(II)-chelate further reacts with hydrogen peroxide to form the highly reactive hydroxyl radical. Because of the limitations of colourimetric and spectrophotometric techniques by which, to date, the mechanisms of hydroxyl radical formation in the hypoxanthine/xanthine oxidase system have been monitored, a high performance liquid chromatography method utilizing the ion-pair reagent tetrabutylammonium hydroxide and salicylic acid as an aromatic probe for quantification of hydroxyl radical formation was set up. In the hypoxanthine/xanthine oxidase system the major products of hydroxyl radical attack on salicylic acid were 2,5-dihydroxy benzoic acid and 2,3-dihydroxy benzoic acid in the approximate ratio of 5:1. That the hydroxyl radical is involved in the hydroxylation of salicylic acid in this system was demonstrated by the potency especially of dimethyl sulphoxide, butanol and ethanol as scavengers. Phytic acid, which is considered to be an important protective dietary constituent against colorectal cancer, inhibited hydroxylation of salicylic acid at a concentration one order of magnitude lower than the classical scavengers, but was only effective in the absence of EDTA. The method has been applied to the study of free radical generation in faeces, and preliminary results indicate that the faecal flora are able to produce reactive oxygen species in abundance.

  17. Phytic acid suppresses 1-methyl-4-phenylpyridinium ion-induced hydroxyl radical generation in rat striatum.

    PubMed

    Obata, Toshio

    2003-07-18

    The present study examined the antioxidant effect of phytic acid on iron (II)-enhanced hydroxyl radical (*OH) generation induced by 1-methyl-4-phenylpyridinium ion (MPP(+)) in the extracellular fluid of rat striatum. Rats were anesthetized, and sodium salicylate in Ringer's solution (0.5 nmol/microl/min) was infused through a microdialysis probe to detect the generation of *OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) in the striatum. Phytic acid (100 microM) did not significantly decrease the levels of MPP(+)-induced *OH formation trapped as 2,3-DHBA. To confirm the generation of *OH by the Fenton-type reaction, iron (II) was infused through a microdialysis probe. Introduction of iron (II) (10 microM) enhanced MPP(+) induced *OH generation. However, phytic acid significantly suppressed iron (II)-enhanced *OH formation after MPP(+) treatment (n=6, P<0.05). These results suggest that the antiradical effect of phytic acid occurs by chelating iron required for the MPP(+)-enhanced *OH generation via the Fenton-type reaction.

  18. A perspective on free radical autoxidation: the physical organic chemistry of polyunsaturated fatty acid and sterol peroxidation.

    PubMed

    Porter, Ned A

    2013-04-19

    This Perspective describes advances from the author's laboratory on the free radical reactions of organic compounds with molecular oxygen. Polyunsaturated fatty acids (PUFAs) and sterols are particularly prone to undergo radical chain oxidation, and evidence suggests that this process, known as lipid peroxidation, occurs in vivo under a variety of conditions that are the result of an oxidative stress. Cyclic peroxides, hydroperoxides, and epoxy alcohols are major products formed from peroxidation, and the basic mechanisms of product formation are now reasonably well understood. These mechanisms include reversible addition of oxygen to carbon radicals, rearrangement and cyclization of allyl and pentadienyl peroxyl radicals, and homolytic substitution of carbon radicals on the peroxide bond. A physical organic approach to the problem of free radicals in biology and medicine is highlighted in this Perspective with stereochemical, kinetic, and extrathermodynamic probes applied to the study of mechanism. A radical clock permits the determination of free radical propagation rate constants, and 7-dehydrocholesterol, the immediate biosynthetic precursor of cholesterol, is found by this clock to be one of the most oxidizable lipids known. The consequences of the extreme reactivity of 7-dehydrocholesterol on human health is the focus of a current research theme in the author's laboratory.

  19. Polyampholyte nanoparticles prepared by self-complexation of cationized poly(γ-glutamic acid) for protein carriers.

    PubMed

    Shen, Heyun; Akagi, Takami; Akashi, Mitsuru

    2012-08-01

    A novel amphoteric poly(amino acid) is synthesized by grafting a cationic amino acid (L-Arg) to γ-PGA to prepare charged NPs. γ-PGA-Arg NPs can be prepared by the self-complexation of a single polymer by intra-/inter-molecular electrostatic interactions when the polymer is dispersed in water. The size and surface charge of the NPs can be regulated by the grafting degree of Arg (41, 56, and 83%). The smallest NPs are obtained at 56% grafting degree of the γ-PGA-Arg copolymer. The 56 and 83% grafting degree NPs are stable for at least 1 week. Depending on their surface charge, these NPs can selectively adsorb anionically or cationically charged proteins.

  20. Determination of some aliphatic carboxylic acids in anaerobic digestion process waters by ion-exclusion chromatography with conductimetric detection on a weakly acidic cation-exchange resin column.

    PubMed

    Ito, Kazuaki; Takayama, Yohichi; Ikedo, Mikaru; Mori, Masanobu; Taoda, Hiroshi; Xu, Qun; Hu, Wenzhi; Sunahara, Hiroshi; Hayashi, Tsuneo; Sato, Shinji; Hirokawa, Takeshi; Tanaka, Kazuhiko

    2004-06-11

    The determination of seven aliphatic carboxylic acids, formic, acetic, propionic, isobutyric, n-butyric, isovaleric and n-valeric acids in anaerobic digestion process waters was examined using ion-exclusion chromatography with conductimetric detection. The analysis of these biologically important carboxylic acids is necessary as a measure for evaluating and controlling the process. The ion-exclusion chromatography system employed consisted of polymethacrylate-based weakly acidic cation-exchange resin columns (TSKgel OApak-A or TSKgel Super IC-A/C). weakly acidic eluent (benzoic acid), and conductimetric detection. Particle size and cation-exchange capacity were 5 microm and 0.1 meq./ml for TSKgel OApak-A and 3 microm and 0.2 meq./ml for TSKgel Super IC-A/C, respectively. A dilute eluent (1.0-2.0 mM) of benzoic acid was effective for the high resolution and highly conductimetric detection of the carboxylic acids. The good separation of isobutyric and n-butyric acids was performed using the TSKgel Super IC-A/C column (150 mm x 6.0 mm i.d. x 2). The simple and good chromatograms were obtained by the optimized ion-exclusion chromatography conditions for real samples from mesophilic anaerobic digestors, thus the aliphatic carboxylic acids were successfully determined without any interferences.

  1. Crystalline bipyridinium radical complexes and uses thereof

    DOEpatents

    Fahrenbach, Albert C.; Barnes, Jonathan C.; Li, Hao; Stoddart, J. Fraser; Basuray, Ashish Neil; Sampath, Srinivasan

    2015-09-01

    Described herein are methods of generating 4,4'-bipyridinium radical cations (BIPY.sup..cndot.+), and methods for utilizing the radical-radical interactions between two or more BIPY.sup..cndot.+ radical cations that ensue for the creation of novel materials for applications in nanotechnology. Synthetic methodologies, crystallographic engineering techniques, methods of physical characterization, and end uses are described.

  2. Reactivity of Cations and Zwitterions Formed in Photochemical and Acid-Catalyzed Reactions from m-Hydroxycycloalkyl-Substituted Phenol Derivatives.

    PubMed

    Cindro, Nikola; Antol, Ivana; Mlinarić-Majerski, Kata; Halasz, Ivan; Wan, Peter; Basarić, Nikola

    2015-12-18

    Three m-substituted phenol derivatives, each with a labile benzylic alcohol group and bearing either protoadamantyl 4, homoadamantyl 5, or a cyclohexyl group 6, were synthesized and their thermal acid-catalyzed and photochemical solvolytic reactivity studied, using preparative irradiations, fluorescence measurements, nanosecond laser flash photolysis, and quantum chemical calculations. The choice of m-hydroxy-substitution was driven by the potential for these phenolic systems to generate m-quinone methides on photolysis, which could ultimately drive the excited-state pathway, as opposed to forming simple benzylic carbocations in the corresponding thermal route. Indeed, thermal acid-catalyzed reactions gave the corresponding cations, which undergo rearrangement and elimination from 4, only elimination from 5, and substitution and elimination from 6. On the other hand, upon photoexcitation of 4-6 to S1 in a polar protic solvent, proton dissociation from the phenol, coupled with elimination of the benzylic OH (as hydroxide ion) gave zwitterions (formal m-quinone methides). The zwitterions exhibit reactivity different from the corresponding cations due to a difference in charge distribution, as shown by DFT calculations. Thus, protoadamantyl zwitterion has a less nonclassical character than the corresponding cation, so it does not undergo 1,2-shift of the carbon atom, as observed in the acid-catalyzed reaction.

  3. Phytic acid suppresses ischemia-induced hydroxyl radical generation in rat myocardium.

    PubMed

    Obata, Toshio; Nakashima, Michiko

    2016-03-05

    The present study examined whether ischemia-reperfusion-induced hydroxyl radical (·OH) generation was attenuated by myo-inositol hexaphosphoric acid (phytic acid). A flexibly mounted microdialysis technique was used to detect the generation of ·OH in in vivo rat hearts. To measure the level of ·OH, sodium salicylate in Ringer's solution (0.5mM or 0.5 nmol/μl/min) was infused directly through a microdialysis probe to detect the generation of ·OH as reflected by the nonenzymatic formation of 2,3-dihydroxybenzoic acid (2,3-DHBA). To confirm the generation of ·OH by Fenton-type reaction, iron(II) was infused through a microdialysis probe. A positive linear correlation between iron(II) and the formation of 2,3-DHBA (R(2)=0.983) was observed. However, the level of 2,3-DHBA in norepinephrine (100 μM) plus phytic acid (100 μM) treated group were significantly lower than those observed in norepinephrine-only-treated group (n=6, *p<0.05). To examine the effect of phytic acid on ischemia-reperfusion-induced ·OH generation, the heart was subjected to myocardial ischemia for 15 min by occlusion of the left anterior descending coronary artery (LAD). When the heart was reperfused, the normal elevation of 2,3-DHBA in the heart dialysate was not observed in animals pretreated with phytic acid. These results suggest that phytic acid is associated with antioxidant effect due to the suppression of iron-induced ·OH generation.

  4. Effect of electrolytes and temperature on dications and radical cations of carotenoids: Electrochemical, optical absorption, and high-performance liquid chromatography studies

    SciTech Connect

    He, Z.; Kispert, L.D.

    1999-11-25

    The effect of supporting electrolytes and temperature on the behavior of dications and radical cations of carotenoids is studied. Cyclic voltammograms (CVs) of canthaxanthin (I) at 23 and {minus}25 C show that Car{sup sm{underscore}bullet+} of I has similar stability during the time of the CV scan, when using tetrabutylammonium perchlorate (TBAPC), tetrabutylammonium tetrafluoroborate (TBATFB), or tetrabutylammonium hexafluorophosphate (TBAHFP) as supporting electrolyte. However, the stability of Car{sup 2+} decreases when using TBAPC or TBATFB; {beta}-carotene (II) shows similar behavior. The CV of I at {minus}25 C shows a strong cathodic wave (wave 6) near {minus}0.15 V (vs Ag) with an intensity about half that of the neutral oxidation wave when TBAPC or TBATFB is the supporting electrolyte. When TBAHFP is used, wave 6 (ca. {minus}0.05 V vs Ag) is ca. 8 times weaker than when TBAPC or TBATFB is used. This wave results from the reduction of a species that may be a decay product of Car{sup 2+} of I. Results show that these electrolytes commonly used in electrochemical studies may affect the studied systems to different extents. In simultaneous bulk electrolysis (BE) and optical absorption spectroscopic measurements, the absorption band of Car{sup 2+} of I in the presence of 0.1 M TBAHFP can be observed by lowering the BE temperature to {minus}20 C. In the presence of 0.1 M TBAPC or TBATFB, this band is not observed, even at {minus}50 C. Isomerization of neutral I (as shown by HPLC and its blue absorption band shift) is observed only when the Car{sup 2+} absorption band is absent during BE. This observation, along with an increase of the neutral absorption band after stopping BE, suggests that the equilibrium Car + Car{sup 2+} {r{underscore}equilibrium} 2Car{sup {sm{underscore}bullet}+} is shifted to the left because Car{sup 2+} decays more quickly than Car{sup {sm{underscore}bullet}+} in the presence of electrolyte and this is a major path for formation of cis

  5. Atmospheric deposition and canopy exchange of anions and cations in two plantation forests under acid rain influence

    NASA Astrophysics Data System (ADS)

    Shen, Weijun; Ren, Huili; Darrel Jenerette, G.; Hui, Dafeng; Ren, Hai

    2013-01-01

    Acid deposition as a widely concerned environmental problem in China has been less studied in plantation forests compared to urban and secondary forests, albeit they constitute 1/3 of the total forested areas of the country. We measured the rainwater amount and chemistry outside and beneath the canopies of two widely distributed plantations (Acacia mangium and Dimocarpus longan) in the severe acid rain influenced Pearl River Delta region of southeastern China for two years. Our results showed that the frequency of acid rain was 96% on the basis of pH value <5.6. The volume-weighted mean (vwm) pH was 4.62 and higher in the dry (Oct.-Mar.) than in the wet (Apr.-Sep.) seasons. The major acidic anion was sulfate with vwm concentration of 140 μeq l-1 and annual deposition flux of 110.3 kg ha-1 yr-1. The major neutralizing cations were calcium (94.8 μeq l-1 and 28 kg ha-1 yr-1) and ammonium (41.2 μeq l-1 and 11.7 kg ha-1 yr-1). Over 95% of these major acidic anions and neutralizing cations were derived from anthropogenic and terrestrial sources as a result of industrial, agricultural and forestry activities. Plantation canopy had marked impacts on rainwater chemistry, with the measured anion and cation concentrations being significantly enriched in throughfall (TF) and stemflow (SF) rainwater by 1.4 (for NO) to 20-fold (for K+) compared to those in bulk precipitation (BP). Dry deposition generally contributed about 13-22% of the total deposition while canopy leaching mainly occurred for K+ (>88%) and NH (10-38%). The two tree species showed distinct impacts on rainfall redistribution and rainwater chemistry due to their differences in canopy architecture and leaf/bark texture, suggesting that species-specific effects should not be overlooked while assessing the acid deposition in forested areas.

  6. Effects of dietary cation-anion difference on the acid-base status of dry cows.

    PubMed

    Vagnoni, D B; Oetzel, G R

    1998-06-01

    Responses in dry matter intake (DMI) and acidbase balance to three sources of anionic salts (dietary cation-anion difference = -63 to -40 meq/kg of dry matter), an acidified fermentation by-product, MgSO4.7H2O + NH4Cl, and MgSO4.7H2O + CaCl2.2H2O + CaSO4, were evaluated relative to the responses of cows fed a control diet (dietary cationanion difference = 203 meq/kg of dry matter) that did not contain anionic salts. Diets were fed for 1-wk periods to eight nonlactating Holsteins assigned to two replicated 4 x 4 Latin squares. Daily DMI increased as time of access to the diet increased up to d 5; mean DMI over d 5 to 7 was reduced by dietary anionic salts. Diets containing anionic salts induced a mild metabolic acidosis that was completely compensated by nonrespiratory mechanisms (decreased blood bicarbonate and base excess; pCO2 and pH values were unaffected). Urinary pH values and bicarbonate excretion were reduced, and urinary NH4+ and titratable acidity excretion were increased, for cows fed diets containing anionic salts. Strong ion difference in urine was decreased by dietary anionic salts because of the relatively greater excretions of Cl- and S2- versus Na+ and K+ by cows fed these diets. Dietary anionic salts decreased mean ruminal pH by 0.12 units, possibly because of the reduced strong ion difference of ruminal fluid. Dietary anionic salts increased mean ruminal NH3 concentration by 2.2 mM, probably because of the higher nonprotein N content of these diets. The strong negative relationship (r2 = 0.95) between urinary pH and net acid excretion by cows fed the diets containing anionic salts suggested that urinary pH measurement might be a useful tool to assess the degree of metabolic acidosis that was imposed by dietary anionic salts.

  7. Divalent cations enhance fluoride binding to Streptococcus mutans and Streptococcus sanguinis cells and subsequently inhibit bacterial acid production.

    PubMed

    Domon-Tawaraya, H; Nakajo, K; Washio, J; Ashizawa, T; Ichino, T; Sugawara, H; Fukumoto, S; Takahashi, N

    2013-01-01

    One preventive effect of topical fluoride application is derived from the fact that fluoride can inhibit bacterial acid production. Furthermore, divalent cations such as Ca(2+) and Mg(2+) increase the binding of fluoride to bacterial cells. These findings suggest that exposure of oral bacteria to fluoride in the presence of divalent cations increases fluoride binding to bacterial cells and subsequently enhances fluoride-induced inhibition of bacterial acid production. This study investigated the effects of fluoride exposure (0-20,000 ppm F) in the presence of Ca(2+) or Mg(2+) prior to glucose challenge on pH fall ability by bacterial sugar fermentation, as well as fluoride binding to bacterial cells by exposure to fluoride, and fluoride release from bacterial cells during bacterial sugar fermentation, using caries-related bacteria, Streptococcus mutans and Streptococcus sanguinis. The pH fall by both streptococci was inhibited by exposure to over 250 ppm F in the presence of Ca(2+) (p < 0.01), whereas in the presence of Mg(2+), the pH fall by S. mutans and S. sanguinis was inhibited after exposure to over 250 and 950 ppm F, respectively (p < 0.05). The amounts of fluoride binding to and released from streptococcal cells increased with the concentration of fluoride the cells were exposed to in the presence of Mg(2+), but were high enough even after 250 ppm F exposure in the presence of Ca(2+). The enhanced inhibition of acid production in the presence of divalent cations is probably due to the improved efficiency of fluoride binding to bacterial cells being improved via these divalent cations.

  8. Free radical scavenging, DNA protection, and inhibition of lipid peroxidation mediated by uric acid.

    PubMed

    Stinefelt, Beth; Leonard, Stephen S; Blemings, Kenneth P; Shi, Xianglin; Klandorf, Hillar

    2005-01-01

    Uric acid (UA) has been proposed to be the dominant antioxidant in birds. The objective of this study was to investigate the quenching effect of varying concentrations of UA, including those found in avian plasma, on specific reactive oxygen species (ROS) and to determine the ability of UA to protect DNA and cellular membranes from ROS-mediated damage. Hydroxyl (OH) and superoxide (O2-) radicals were detected by electron spin resonance (ESR) and their presence was reduced following addition of UA (p <0.05) in a concentration-dependent manner. UA inhibited hydroxyl-mediated DNA damage, indicated by the presence of more precise, dense bands of lambda Hind III DNA after agarose gel electrophoresis and ethidium bromide staining (p <0.05). Lipid peroxidation of silica-exposed RAW 264.7 cell membranes was diminished (p <0.02) after addition of UA to the cell incubation mixture. These studies demonstrate that UA scavenges hydroxyl and superoxide radicals and protects against DNA damage and lipid peroxidation. These results indicate specific antioxidant protection that UA may afford birds against ROS-mediated damage.

  9. DDQ-promoted dehydrogenation from natural rigid polycyclic acids or flexible alkyl acids to generate lactones by a radical ion mechanism.

    PubMed

    Ding, Ye; Huang, Zhangjian; Yin, Jian; Lai, Yisheng; Zhang, Shibo; Zhang, Zhiguo; Fang, Lei; Peng, Sixun; Zhang, Yihua

    2011-09-07

    A novel and facile DDQ-mediated dehydrogenation from natural rigid polycyclic acids or flexible alkyl acids to generate lactones is described. The formation of lactones proceeds by a radical ion mechanism, which has been established by DPPH˙-mediated chemical identification, ESR spectroscopy and an enol intermediate trapping.

  10. The Effects of Trivalent Lanthanide Cationization on the Electron Transfer Dissociation of Acidic Fibrinopeptide B and its Analogs.

    PubMed

    Commodore, Juliette J; Cassady, Carolyn J

    2016-09-01

    Electrospray ionization (ESI) on mixtures of acidic fibrinopeptide B and two peptide analogs with trivalent lanthanide salts generates [M + Met + H](4+), [M + Met](3+), and [M + Met -H](2+), where M = peptide and Met = metal (except radioactive promethium). These ions undergo extensive and highly efficient electron transfer dissociation (ETD) to form metallated and non-metallated c- and z-ions. All metal adducted product ions contain at least two acidic sites, which suggest attachment of the lanthanide cation at the side chains of one or more acidic residues. The three peptides undergo similar fragmentation. ETD on [M + Met + H](4+) leads to cleavage at every residue; the presence of both a metal ion and an extra proton is very effective in promoting sequence-informative fragmentation. Backbone dissociation of [M + Met](3+) is also extensive, although cleavage does not always occur between adjacent glutamic acid residues. For [M + Met - H ](2+), a more limited range of product ions form. All lanthanide metal peptide complexes display similar fragmentation except for europium (Eu). ETD on [M + Eu - H](2+) and [M + Eu](3+) yields a limited amount of peptide backbone cleavage; however, [M + Eu + H](4+) dissociates extensively with cleavage at every residue. With the exception of the results for Eu(III), metallated peptide ion formation by ESI, ETD fragmentation efficiencies, and product ion formation are unaffected by the identity of the lanthanide cation. Adduction with trivalent lanthanide metal ions is a promising tool for sequence analysis of acidic peptides by ETD. Graphical Abstract ᅟ.

  11. The Effects of Trivalent Lanthanide Cationization on the Electron Transfer Dissociation of Acidic Fibrinopeptide B and its Analogs

    NASA Astrophysics Data System (ADS)

    Commodore, Juliette J.; Cassady, Carolyn J.

    2016-09-01

    Electrospray ionization (ESI) on mixtures of acidic fibrinopeptide B and two peptide analogs with trivalent lanthanide salts generates [M + Met + H]4+, [M + Met]3+, and [M + Met -H]2+, where M = peptide and Met = metal (except radioactive promethium). These ions undergo extensive and highly efficient electron transfer dissociation (ETD) to form metallated and non-metallated c- and z-ions. All metal adducted product ions contain at least two acidic sites, which suggest attachment of the lanthanide cation at the side chains of one or more acidic residues. The three peptides undergo similar fragmentation. ETD on [M + Met + H]4+ leads to cleavage at every residue; the presence of both a metal ion and an extra proton is very effective in promoting sequence-informative fragmentation. Backbone dissociation of [M + Met]3+ is also extensive, although cleavage does not always occur between adjacent glutamic acid residues. For [M + Met - H ]2+, a more limited range of product ions form. All lanthanide metal peptide complexes display similar fragmentation except for europium (Eu). ETD on [M + Eu - H]2+ and [M + Eu]3+ yields a limited amount of peptide backbone cleavage; however, [M + Eu + H]4+ dissociates extensively with cleavage at every residue. With the exception of the results for Eu(III), metallated peptide ion formation by ESI, ETD fragmentation efficiencies, and product ion formation are unaffected by the identity of the lanthanide cation. Adduction with trivalent lanthanide metal ions is a promising tool for sequence analysis of acidic peptides by ETD.

  12. Pharmacological characterization of mouse GPRC6A, an L-α-amino-acid receptor modulated by divalent cations

    PubMed Central

    Christiansen, B; Hansen, K B; Wellendorph, P; Bräuner-Osborne, H

    2007-01-01

    Background and purpose: GPRC6A is a novel member of family C of G protein-coupled receptors with so far unknown function. We have recently described both human and mouse GPRC6A as receptors for L-α-amino acids. To date, functional characterization of wild-type GPRC6A has been impaired by the lack of activity in quantitative functional assays. The aim of this study was thus to develop such an assay and extend the pharmacological characterization of GPRC6A. Experimental approach: We have engineered a novel cell-based inositol phosphate turnover assay for wild-type mouse GPRC6A based on transient co-expression with the promiscuous GαqG66D protein, known to increase receptor signalling sensitivity. This assay allowed for measurements of L-α-amino acid potencies. Furthermore, in combination with an assay measuring inward currents at Ca2+-activated chloride channels in Xenopus oocytes, the divalent cation-sensing ability of the receptor was examined. Key results: Using our novel assay, we demonstrate that the basic L-α-amino acids ornithine, lysine, and arginine are the most potent agonists at wild-type mouse GPRC6A. Using two different assay systems, we show that divalent cations do not activate the Gq signalling pathway of mouse GPRC6A per se but positively modulate the amino-acid response. Conclusions and Implications: This is the first reported assay for a wild-type GPRC6A successfully applied for quantitative pharmacological characterization of amino acid and divalent cation responses at mouse GPRC6A. The assay enables further search for GPRC6A ligands such as allosteric modulators, which may provide essential information about the physiological function of GPRC6A. PMID:17245368

  13. Spectral and Kinetic Study of 3-Methylquinoxalin-2-ones Photoreduced by Amino Acids: N-Phenylglycine Radical Chain Reactions and N-Acetyltryptophan Decarboxylation.

    PubMed

    De la Fuente, Julio R; Cañete, Álvaro; Carathanassis, Natalia; Bernazar, Luan; Saitz, Claudio; Díaz-Hernández, Dafne

    2016-05-12

    Transient intermediates were identified in the photoreduction of 3-methylquinoxalin-2-one derivatives by N-phenylglycine, NPG, and N-acetyltryptophan, NAT. For both reductants it can be postulated a sequence of reaction comprising first a photoinduced single electron transfer followed by a proton transfer from the radical cation of the electron donor to the radical anion of the 3-methylquinoxalin-2-one giving rise to the reported products. The effect of the concentrations of NPG and the quinoxalin-2-one on the rate of photoconsumption of this last were quantified, and the lifetimes of the possible intermediates estimated. In the photoreduction by NAT, processes leading to the decarboxylation of NAT and radical adduct product compete with the expected SET from the indoyl N to the excited triplet of quinoxalin-2-ones as revealed by the detection of the deprotonated N-acetyltryptophan radical [NAT-H](•). This radical is formed almost instantly after the laser pulse and has a secondary delayed growth via a delayed proton transfer from the indoyl radical cation NAT(•+) to the quinoxalin-2-one radical anions. The decarboxylation of NAT that mimics C-terminus tryptophan in proteins is biologically relevant because might cause damages at cellular and the whole organism level. As far as we know this is the first report of a radical decarboxylation of N-acetyltryptophan leading to photoproducts.

  14. Water-catalyzed gas-phase reaction of formic acid with hydroxyl radical: A computational investigation

    NASA Astrophysics Data System (ADS)

    Luo, Yi; Maeda, Satoshi; Ohno, Koichi

    2009-02-01

    The reaction of formic acid with hydroxyl radical, which is considered to be relevant to atmospheric chemistry, has been extensively studied. A water-catalyzed process of this reaction is computationally studied here for the first time. The scaled hypersphere search method was used for global exploration of pre-reaction complexes. Calculations were performed at high level of theory, such as CCSD(T)/cc-pVTZ//B3LYP/6-311+G(2df, 2p) and CCSD(T)/cc-pVTZ//MP2/aug-cc-pVDZ. It is found that the water-catalyzed process of this reaction is more kinetically favorable than its non-catalytic process. Such catalytic process may also be of interest for atmospheric chemistry, like the non-catalytic one.

  15. Determination of hydroxyl radicals with salicylic acid in aqueous nitrate and nitrite solutions.

    PubMed

    Yang, Xi; Zhan, Man-jun; Kong, Ling-ren; Wang, Lian-sheng

    2004-01-01

    The qualitative and quantitative analyses of reactive oxygen species are essential to determine their steady-state concentration and related reaction mechanisms in environmental aquatic systems. In this study, salicylic acid was employed as an innovative molecular probe of hydroxyl radical(OH) generated in aqueous nitrate and nitrite solutions through photochemical reactions. Kinetic studies showed that the steady-state concentrations of OH in aqueous NO3- (10 mmol/L, pH = 5) and NO2- (10 mmol/L, pH = 5) solutions under ultraviolet irradiation were at a same magnitude, 10(-15) mol/L. Apparent quantum yields of OH at 313 nm were measured as 0.011 and 0.07 for NO3- and NO2- respectively, all comparable to the results of previous studies.

  16. Lewis acid-water/alcohol complexes as hydrogen atom donors in radical reactions.

    PubMed

    Povie, Guillaume; Renaud, Philippe

    2013-01-01

    Water or low molecular weight alcohols are, due to their availability, low price and low toxicity ideal reagents for organic synthesis. Recently, it was reported that, despite the very strong BDE of the O-H bond, they can be used as hydrogen atom donors in place of expensive and/or toxic group 14 metal hydrides when boron and titanium(III) Lewis acids are present. This finding represents a considerable innovation and uncovers a new perspective on the paradigm of hydrogen atom transfers to radicals. We discuss here the influence of complex formation and other association processes on the efficacy of the hydrogen transfer step. A delicate balance between activation by complex formation and deactivation by further hydrogen bonding is operative.

  17. A pulse radiolysis study of the dynamics of ascorbic acid free radicals within a liposomal environment.

    PubMed

    Kobayashi, Kazuo; Seike, Yumiko; Saeki, Akinori; Kozawa, Takahiro; Takeuchi, Fusako; Tsubaki, Motonari

    2014-10-06

    The dynamics of free-radical species in a model cellular system are examined by measuring the formation and decay of ascorbate radicals within a liposome with pulse radiolysis techniques. Upon pulse radiolysis of an N2O-saturated aqueous solution containing ascorbate-loaded liposome vesicles, ascorbate radicals are formed by the reaction of OH(·) radicals with ascorbate in unilamellar vesicles exclusively, irrespective of the presence of vesicle lipids. The radicals are found to decay rapidly compared with the decay kinetics in an aqueous solution. The distinct radical reaction kinetics in the vesicles and in bulk solution are characterized, and the kinetic data are analyzed.

  18. Preparation of poly(glycidylmethacrylate-divinylbenzene) weak acid cation exchange stationary phases with succinic anhydride, phthalic anhydride, and maleic anhydride for ion chromatography.

    PubMed

    Liu, Junwei; Wang, Yong; Wu, Shuchao; Zhang, Peimin; Zhu, Yan

    2016-08-01

    In this work, poly(glycidylmethacrylate-divinylbenzene) microspheres were prepared and applied for the preparation of weak acid cation exchange stationary phases. Succinic anhydride, phthalic anhydride, and maleic anhydride were selected as carboxylation reagents to prepare three weak acid cation exchangers by direct chemical derivatization reaction without solvent or catalyst. The diameters and dispersity of the microspheres were characterized by scanning electron microscopy; the amount of accessible epoxy groups and mechanical stability were also measured. The weak acid cation exchangers were characterized by Fourier transform infrared spectroscopy; the content of carboxyl groups was measured by traditional acid base titration method. The chromatographic properties were characterized and compared by separating alkali, alkaline earth metal ions and ammonium and polar amines. The separation properties enhanced in the order of succinic anhydride, phthalic anhydride, and maleic anhydride modified poly(glycidylmethacrylate-divinylbenzene) cation exchangers.

  19. Simultaneous determination of cation exchange capacity and surface area of acid activated bentonite powders by methylene blue sorption

    NASA Astrophysics Data System (ADS)

    Yener, Nilgün; Biçer, Cengiz; Önal, Müşerref; Sarıkaya, Yüksel

    2012-01-01

    To distinguish the ion exchanged and physically adsorbed methylene blue cations (MB+) on ionic surfaces, acid activated bentonite samples were used as porous adsorbents. A natural calcium bentonite (CaB) sample from Enez/Edirne, Turkey, was acid activated at 90 °C for 16 h with various HCl/CaB ratios. The irreversible exchange and physical adsorption of MB+ cations on the ionic solids have simultaneously occurred. The ion exchanged (mex) and physically adsorbed (mad) MB+ contents were obtained as the values of sorption capacity at c = 0 and the increase to a plateaus of adsorption isotherms, respectively. The mad value was taken to be monolayer adsorption capacity. Cation exchange capacity (CEC) and specific surface area (SMB) for each sample were calculated from the mex and mad values, respectively. Also, the BET specific surface areas (SBET) and pore size distribution were determined from low temperature nitrogen adsorption/desorption data. A linear correlation between the SMB and SBET values was found.

  20. 5-Aminosalicylic acid protection against oxidative damage to synaptosomal membranes by alkoxyl radicals in vitro.

    PubMed

    Kanski, J; Lauderback, C; Butterfield, D A

    2001-01-01

    The antioxidant properties of 5-aminosalicylic acid in vitro were evaluated in a synaptosomal membrane system prepared from gerbil cortical synaptosomes using EPR spin labeling and spectroscopic techniques. MAL-6 (2,2,6,6-tetramethyl-4-maleimidopiperidin-1-oxyl) and 5-NS (5-nitroxide stearate) spin labels were used to assess changes in protein oxidation and membrane lipid fluidity, respectively. Synaptosomal membranes were subjected to oxidative stress by incubation with 1 mM azo-bis(isobutyronitrile) (AIBN) or 1 mM 2,2'-azobis(amidino propane) dihydrochloride (AAPH) at 37 degrees C for 30 minutes. The EPR analyses of the samples showed significant oxidation of synaptosomal proteins and a decrease in membrane fluidity. 5-Aminosalicylic acid also was evaluated by means of FRAP (the ferric reducing ability of plasma) test as a potential antioxidant. 5-Aminosalicylic acid also showed protection against the oxidation in gerbil cortical synaptosomes system caused by AIBN and AAPH. These results are consistent with the notion of antioxidant protection against free radical induced oxidative stress in synaptosomal membrane system by this agent.

  1. 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

    2017-03-28

    Monodispersed SiO2 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 SiO2 samples. The adsorption performance of the functionalized SiO2 (donated as SiO2-PDA-PAPTCl) towards anionic organic dye Congo red (CR) was investigated to evaluate their potential environmental applications. We demonstrated that the surface of SiO2 particles can be successfully functionalized with cationic PAPTCl. The adsorption capability of as-prepared SiO2 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 SiO2-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.

  2. Determination of melamine and cyromazine in milk by high performance liquid chromatography coupled with online solid-phase extraction using a novel cation-exchange restricted access material synthesized by surface initiated atom transfer radical polymerization.

    PubMed

    Zhang, Yingying; Lin, Shen; Jiang, Ping; Zhu, Xudong; Ling, Jing; Zhang, Wen; Dong, Xiangchao

    2014-04-11

    A novel strong-cation-exchange restricted access material has been synthesized by atom transfer radical polymerization (ATRP). In the synthesis, poly(3-sulfopropyl methacrylate-co-ethylene dimethacrylate), [p(SPM/EDMA)] was grafted on the silica by surface-initiated ATRP first. The poly(glycerol mono-methacrylate) [pGMMA] was then immobilized on the external surface, which created a chemical diffusion barrier for protein exclusion. The resulting Sil-g-p(SPM/EDMA)-g-pGMMA has both functions of protein exclusion and cation exchange, exhibiting the property of cation-exchange restricted access material. The application of Sil-g-p(SPM/EDMA)-g-pGMMA has been studied by the determination of melamine and cyromazine in bovine milk using the online solid-phase extraction/HPLC method. In the process, the Sil-g-p(SPM/EDMA)-g-pGMMA was used for the sample pre-treatment and a HILIC column was employed as the analytical column. The method has shown good accuracy, precision and low limits of detections. The result demonstrated that the Sil-g-p(SPM/EDMA)-g-pGMMA can be used for the cation extraction from biological samples by direct HPLC injection.

  3. Poly(lactic acid) nanoparticles loaded with ursolic acid: Characterization and in vitro evaluation of radical scavenging activity and cytotoxicity.

    PubMed

    Antônio, Emilli; Antunes, Osmar Dos Reis; de Araújo, Isis Souza; Khalil, Najeh Maissar; Mainardes, Rubiana Mara

    2017-02-01

    The purpose of this study was to develop poly(lactic acid) (PLA) nanoparticles containing ursolic acid (UA) by an emulsification-solvent evaporation technique and evaluate the radical scavenging activity over hypochlorous acid (HOCl) and cytotoxicity over erythrocytes and tumor cells. Nanoparticles were successfully obtained and presented mean size of 246nm with spherical or slightly oval morphology, negative zeta potential and 96% of UA encapsulation efficiency. Analyses of FTIR, XRD and DSC-DTG suggest interaction/complexation of UA with PLA matrix and drug amorphization promoted by nanoencapsulation process. Stability study showed that room temperature was the best condition for nanoparticles storage. The in vitro release study showed UA was released from the polymeric matrix over two constants (α, β), suggesting a second order kinetics. After 120h of assay, 60% of UA were released by diffusion. In the HOCl scavenging activity, after 72h of assay UA-loaded nanoparticles presented the same efficacy of free drug. In cytotoxicity test over red blood cells, UA-loaded nanoparticles showed less toxicity on cells than free drug. The cytotoxicity assay over melanoma cells line (B16-F10) showed after 72h that nanoparticles were able to reduce the cell viability in 70%. PLA nanoparticles showed be potential carriers for UA maintaining the antioxidant and antitumor activity of the UA and decreasing its cytotoxicity over normal cells.

  4. Analysis of chromite by cation-exchange using ethylenediaminetetra-acetic acid.

    PubMed

    Jawaid, M; Ingman, F

    1975-12-01

    A method for the separation and determination of five major elements in chromite ore (and chrome-bearing refractories), based on complexation of the metals with EDTA is described. After removal of silica, the cations are separated into two groups by passing the solution through a cation-exchange resin (Dowex 50W-X8, in Na-form) in the presence of an excess of the complexing agent. The optimum conditions for the separation are discussed on the basis of exchange constants that were either known or determined. The first group contains Cr and Fe, which emerge in the filtrate at pH between 1.5 and 2.1, whereas A1, Mg and Ca, which are adsorbed on the resin, form another group. Complexometric titrations are used for the subsequent determination of the cations in each group. The method is simpler and more rapid and accurate for routine analysis than the current methods.

  5. Butoxyacetic acid-induced hemolysis of rat red blood cells: effect of external osmolarity and cations.

    PubMed

    Udden, M M; Patton, C S

    2005-03-28

    Hemolysis is the principal toxicity of acute exposure to ethylene glycol monobutyl ether (EGBE) in rats. EGBE itself is not an active hemolytic agent, but its metabolite, butoxyacetic acid (BAA) formed as a result of dehydrogenase activity is a potent hemolysin. Here we address the role of osmolarity and cation composition of the suspending buffers in the mechanism of BAA-induced hemolysis of rat red blood cells in vitro. Rat erythrocytes were protected from BAA-induced cell swelling and hemolysis by the addition of sucrose to the suspending media. Hemolysis and cell swelling were also reduced by replacing external sodium with potassium. When calcium was not present in the suspending medium or when chelated by EGTA, hemolysis was increased after 2 h incubation with 1 mM or 2 mM BAA. Addition of as little as 0.05 mM CaCl(2) reduced hemolysis significantly while the addition of MgCl(2) had no effect. The dose-response relationship between BAA concentration and hemolysis determined in the presence or absence of calcium showed an increased effect of BAA in the absence of calcium. BAA-induced spherocytosis and cell fragmentation were more pronounced in the absence of calcium. The time course of BAA-induced hemolysis in the presence and absence of calcium demonstrated that the effect of calcium is to delay the onset of hemolysis. Increased intracellular calcium as a result of exposure to BAA was verified by atomic absorption spectroscopy. Charybdotoxin, an inhibitor of the calcium activated potassium channel, blocked the protective effect of calcium suggesting that the delay of onset of hemolysis in the presence of calcium is due to potassium loss caused by this channel. We conclude that the mode of action of BAA is to cause a colloid osmotic lysis of the rat red blood cell. Hemolysis requires external sodium and is associated with calcium uptake. Calcium appears to delay the onset of hemolysis. We speculate that: (1) BAA causes sodium and calcium to enter the cell; (2

  6. Enantioseparation of dansyl amino acids by ultra-high pressure liquid chromatography using cationic β-cyclodextrins as chiral additives.

    PubMed

    Xiao, Yin; Tan, Timothy Thatt Yang; Ng, Siu-Choon

    2011-04-07

    This work reports the application of ultra-high pressure liquid chromatography (UHPLC) for reasonably fast enantiorecognition of some dansyl amino acids by employing three cationic β-cyclodextrins (β-CDs) as chiral additives. Good resolutions were obtained on an Agilent C18 column (2.1 mm i.d.; 1.8 μm; 50 mm length) with 1% (v/v) triethylammonium acetate buffered at pH 4.7 and acetonitrile as the mobile phase. Most of the analytes could be baseline resolved within 10 min. Increased cationic CD concentration or acetonitrile proportion in the mobile phase results in a decreased retention factor but accentuated selectivity. Furthermore, molecular mechanics calculation was performed and found to be consistent with the experimental results.

  7. CO capture and conversion to HOCO radical by ionized water clusters.

    PubMed

    Lee, Han Myoung; Youn, Il-Seung; Kim, Kwang S

    2014-09-04

    The CO molecule can interact with the hydroxyl radical ((•)OH) via either a weak noncovalent interaction or strong covalent bonding. Upon the ionization of neutral water clusters, the resulting water cluster cations produce protonated water clusters and hydroxyl radicals. In this regard, we investigate the interactions of a CO molecule with water dimer and trimer cations using density functional theory (DFT), Möller-Plesset second-order perturbation theory (MP2), and coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. It is found that the reaction products of CO by the water dimer and trimer cations form a HOĊO radical solvated by a protonated water monomer and dimer, respectively. These radicals are useful intermediates to make oxalic acids, formic acids, metal ligands, and so on, which is important in green chemistry.

  8. Examination by EPR spectroscopy of free radicals in melanins isolated from A-375 cells exposed on valproic acid and cisplatin.

    PubMed

    Chodurek, Ewa; Zdybel, Magdalena; Pilawa, Barbara; Dzierzewicz, Zofia

    2012-01-01

    Drug binding by melanin biopolymers influence the effectiveness of the chemotherapy, radiotherapy and photodynamic therapy. Free radicals of melanins take part in formation of their complex with drugs. The aim of this work was to determine the effect of the two compounds: valproic acid (VPA) and cisplatin (CPT) on free radicals properties of melanin isolated from A-375 melanoma cells. Free radicals were examined by an X-band (9.3 GHz) electron paramagnetic resonance (EPR) spectroscopy. EPR spectra were measured for the model synthetic eumelanin - DOPA-melanin, the melanin isolated from the control A-375 cells and these cells treated by VPA, CPT and both VPA and CPT. For all the examined samples broad EPR lines (deltaBpp: 0.48-0.68 mT) with g-factors of 2.0045-2.0060 characteristic for o-semiquinone free radicals were observed. Free radicals concentrations (N) in the tested samples, g-factors, amplitudes (A), integral intensities (I) and linewidths (deltaBpp) of the EPR spectra, were analyzed. The EPR lines were homogeneously broadened. Continuous microwave saturation of the EPR spectra indicated that slow spin-lattice relaxation processes existed in all the tested melanin samples. The relatively slowest spin-lattice relaxation processes characterized melanin isolated from A-375 cells treated with both VPA and CPT. The changes of the EPR spectra with increasing microwave power in the range of 2.2-70 mW were evaluated. Free radicals concentrations in the melanin from A-375 cells were higher than in the synthetic DOPA-melanin. The strong increase of free radicals concentration in the melanin from A-375 cells was observed after their treating by VPA. CPT also caused the increase of free radicals concentrations in the examined natural melanin. The free radicals concentration in melanin isolated from A-375 cells treated with both VPA and CPT was slightly higher than those in melanin from the control cells.

  9. Equilibrium adsorption of caffeic, chlorogenic and rosmarinic acids on cationic cross-linked starch with quaternary ammonium groups.

    PubMed

    Simanaviciute, Deimante; Klimaviciute, Rima; Rutkaite, Ramune

    2017-02-01

    In the present study, the equilibrium adsorption of caffeic acid (CA) and its derivatives, namely, chlorogenic (CGA) and rosmarinic (RA) acids on cationic cross-linked starch (CCS) with degree of substitution of quaternary ammonium groups of 0.42 have been investigated in relation to the structure and acidity of phenolic acids. The Langmuir, Freundlich and Dubinin-Radushkevich adsorption models have been used to describe the equilibrium adsorption of CA, CGA and RA from their initial solutions and solutions having the equimolar amount of NaOH at different temperatures. In the case of adsorption from the initial solutions of acids the values of adsorption parameters were closely related to the dissociation constants of investigated acids. According to the increasing effectiveness of adsorption, phenolic acids could be arranged in the following order: CAacids solutions changed their sorption properties which became mostly related to the acids structure.

  10. Cyclic voltammetry, spectroelectrochemical and photochemical studies of 7,7{prime}-diphenyl-7,7{prime}-diapocarotene cation radicals and dications adsorbed on the surface of electrodes

    SciTech Connect

    Gao, G.; Kispert, L.D.

    1996-10-01

    7,7{prime}-diphenyl-7,7{prime}-diapocarotene in dichloromethane can adsorb on glassy carbon, platinum and gold electrode surfaces upon electrochemical oxidation, resulting in an intense cyclic voltammogram(CV) cathodic peak. Spectroelectrochemical studies of the adsorbed material on ITO electrode surfaces showed that cation radicals, dications and possibly dimers were formed. Irradiation of the surface with visible light resulting in changes in the optical absorption bands. Similar adsorption behavior was also observed by using various supporting electrolytes and solvents. However CV and simultaneous bulk electrolysis-optical spectra obtained in anhydrous acetonitrile show no adsorption. A mechanism involving electrode reactions and adsorption equilibria will be presented.

  11. H and D attachment to naphthalene: spectra and thermochemistry of cold gas-phase 1-C10H9 and 1-C10H8D radicals and cations.

    PubMed

    Krechkivska, Olha; Wilcox, Callan M; Chan, Bun; Jacob, Rebecca; Liu, Yu; Nauta, Klaas; Kable, Scott H; Radom, Leo; Schmidt, Timothy W

    2015-04-02

    Excitation spectra of the 1H-naphthalene (1-C10H9) and 1D-naphthalene (1-C10H8D) radicals, and their cations, are obtained by laser spectroscopy and mass spectrometry of a skimmed free-jet expansion following an electrical discharge. The spectra are assigned on the basis of density functional theory calculations. Isotopic shifts in origin transitions, vibrational frequencies and ionization energies were found to be well reproduced by (time-dependent) density functional theory. Absolute bond dissociation energies, ionization energies and proton affinities were calculated using high-level quantum chemical methods.

  12. Oxygen radicals shaping evolution: why fatty acid catabolism leads to peroxisomes while neurons do without it: FADH₂/NADH flux ratios determining mitochondrial radical formation were crucial for the eukaryotic invention of peroxisomes and catabolic tissue differentiation.

    PubMed

    Speijer, Dave

    2011-02-01

    Oxygen radical formation in mitochondria is a highly important, but incompletely understood, attribute of eukaryotic cells. I propose a kinetic model in which the ratio between electrons entering the respiratory chain via FADH₂ or NADH is a major determinant in radical formation. During the breakdown of glucose, this ratio is low; during fatty acid breakdown, this ratio is much higher. The longer the fatty acid, the higher the ratio and the higher the level of radical formation. This means that very long chain fatty acids should be broken down without generation of FADH₂ for mitochondria. This is accomplished in peroxisomes, thus explaining their role and evolution. The model explains many recent observations regarding radical formation by the respiratory chain. It also sheds light on the reasons for the lack of neuronal fatty acid (beta-) oxidation and for beneficial aspects of unsaturated fatty acids. Last but not least, it has very important implications for all models describing eukaryotic origins.

  13. Volatile organic acid adsorption and cation dissociation by porphyritic andesite for enhancing hydrolysis and acidogenesis of solid food wastes.

    PubMed

    Cheng, Fan; Li, Ming; Li, Dawei; Chen, Ling; Jiang, Weizhong; Kitamura, Yutaka; Li, Baoming

    2010-07-01

    Volatile organic acid adsorption, cation dissociation by porphyritic andesite, and their effects on the hydrolysis and acidogenesis of solid food wastes were evaluated through batch experiments. The acetic acid adsorption experiments show that pH was mainly regulated by H(+) adsorption. The mono-layer and multi-layer adsorption were found under the low (8.3-83.2 mmol/L) and high (133.22-532.89 mmol/L) initial acetic acid concentration, respectively. The dissociated cations concentration in acidic solution showed the predominance of Ca(2+). Porphyritic andesite addition elevated the pH levels and accelerated hydrolysis and acidogenesis in the batch fermentation experiment. Leachate of porphyritic andesite addition achieved the highest hydrolysis constant of 22.1 x 10(-3)kgm(-2)d(-1) and VS degradation rates of 3.9 g L(-1)d(-1). The highest activity of microorganisms represented by specific growth rate of ATP, 0.16d(-1), and specific consumption rate of Ca(2+), 0.18d(-1), was obtained by adding leachate of porphyritic andesite.

  14. Fast and Efficient Separation and Determination of UV-absorbing Amino Acids, Nucleobases, and Creatinine Using a Carboxy-functionalized Cation-exchange Column.

    PubMed

    Yokoyama, Yukio; Fujishima, Takeru; Kurota, Kazuki

    2015-01-01

    This paper presents a new HPLC technique for the determination of biogenic cations such as amino acids and nucleobases, using a weak-acid cation-exchange column. Fourteen analytes, five amino acids and seven bases in addition to creatinine and creatine, were separated in 12 min by means of a two-liquid gradient elution with UV detection. The newly released column packed with a carboxy-functionalized polymethacrylate resin could give excellent selectivity to the organic cations of interest, although such a column is in general suitable for the separation of inorganic common cations. The chromatographic intra-day repeatability was very good with RSDs less than 0.4%, and the quantitation precision based on peak area intensities was also good with RSDs less than 5% for all analytes. The linear calibration lines for quantitation ranged between 5 and 500 μM on 20-μL injections with R(2) more than 0.9990. Since the method could provide concentration data of urinary creatinine and some metabolites simultaneously, for example, the urinary phenylalanine/creatinine ratios for phenylketonuria of inborn errors of metabolism were simply determined through one chromatographic run. The ratios for patients were significantly higher than those for controls. We found that the new weak-acid cation-exchange column was suitable for the separation of organic cations as well as inorganic cations.

  15. Formation of [b3 - 1 + cat]+ ions from metal-cationized tetrapeptides containing beta-alanine, gamma-aminobutyric acid or epsilon-aminocaproic acid residues.

    PubMed

    Osburn, Sandra M; Ochola, Sila O; Talaty, Erach R; Van Stipdonk, Michael J

    2008-11-01

    The presence and position of a single beta-alanine (betaA), gamma-aminobutyric acid (gammaABu) or epsilon-aminocaproic acid (Cap) residue has been shown to have a significant influence on the formation of b(n)+ and y(n)+ product ions from a series of model, protonated peptides. In this study, we examined the effect of the same residues on the formation of analogous [b3 - 1 + cat]+ products from metal (Li+, Na+ and Ag+)-cationized peptides. The larger amino acids suppress formation of b3+ from protonated peptides with general sequence AAXG (where X = beta-alanine, gamma-aminobutyric acid or epsilon-aminocaproic acid), presumably because of the prohibitive effect of larger cyclic intermediates in the 'oxazolone' pathway. However, abundant [b3 - 1 + cat]+ products are generated from metal-cationized versions of AAXG. Using a group of deuterium-labeled and exchanged peptides, we found that formation of [b3 - 1 + cat]+ involves transfer of either amide or alpha-carbon position H atoms, and the tendency to transfer the atom from the alpha-carbon position increases with the size of the amino acid in position X. To account for the transfer of the H atom, a mechanism involving formation of a ketene product as [b3 - 1 + cat]+ is proposed.

  16. Uptake of Nitric Acid, Dinitrogen Pentoxide, Ozone and The Nitrate Radical On A Single Liquid Drop

    NASA Astrophysics Data System (ADS)

    Schütze, M.; Herrmann, H.

    A novel technique for the investigation of uptake processes on gas-liquid interfaces will be presented. It allows the generation and analysis of single liquid drops inside a flow tube reactor. The in situ analysis of the drop is performed by broad band UV-VIS absorption spectroscopy. Using this set-up the uptake of nitric acid and dinitrogen pentoxide on pure water was measured by monitoring the occurrence of the nitrate band centered at a wavelength of 300 nm. The uptake of ozone on NaI solutions of various concentrations was followed by the formation of the triiodide ion which is a product of the oxidation of iodide by ozone. Using aqueous solutions of the dye Alizarin Red S, the uptake of the nitrate radical could be quantified. In order to extract information on fundamental parameters, e.g. the mass accommo- dation coefficients (= a) of the species, a computer model is applied. It solves the diffusion equation for the transport of gas phase species to the interface numerically. The result is a separation of the influence of this process on the rate of the overall uptake process. The mass accommodation coefficients a > 0.03, a = 0.011 and a > 0.02 were obtained for nitric acid, dinitrogen pentoxide and ozone, respectively.

  17. Molecular Dynamics Simulations of Arachidonic Acid-Derived Pentadienyl Radical Intermediate Complexes with COX-1 and COX-2

    PubMed Central

    Furse, Kristina E.; Pratt, Derek A.; Schneider, Claus; Brash, Alan R.; Porter, Ned A.; Lybrand, Terry P.

    2008-01-01

    The two cyclooxygenase enzymes, COX-1 and COX-2, are responsible for the committed step in prostaglandin biosynthesis, and are the targets of the non-steroidal anti-inflammatory drugs aspirin, ibuprofen and the COX-2 selective inhibitors, Celebrex™, Vioxx™ and Bextra™. The enzymes are remarkable in that they catalyze two dioxygenations and two cyclizations of the native substrate, arachidonic acid, with near absolute regio- and stereoselectivity. Several theories have been advanced to explain the nature of enzymatic control over this series of reactions, including suggestions of steric shielding and oxygen channeling. As proposed here, selective radical trapping and spin localization in the substrate-derived pentadienyl radical intermediate can also be envisioned. Herein we describe the results of explicit, 10 ns molecular dynamics simulations of both COX-1 and COX-2 with the substrate-derived pentadienyl radical intermediate bound in the active site. The enzymes’ influence on the conformation of the pentadienyl radical was investigated, along with the accessible space above and below the radical plane, and the width of several channels to the active site that could function as access routes for molecular oxygen. Additional simulations demonstrated the extent of molecular oxygen mobility within the active site. The results suggest that spin localization is unlikely to play a role in enzymatic control of this reaction. Instead, a combination of oxygen channeling, steric shielding and selective radical trapping appears to be responsible. This work adds a dynamic perspective to the strong foundation of static structural data available for these enzymes. PMID:16519515

  18. Derivatives of the cationic plant alkaloids berberine and palmatine amplify protonophorous activity of fatty acids in model membranes and mitochondria.

    PubMed

    Pustovidko, Antonina V; Rokitskaya, Tatiana I; Severina, Inna I; Simonyan, Ruben A; Trendeleva, Tatiana A; Lyamzaev, Konstantin G; Antonenko, Yuri N; Rogov, Anton G; Zvyagilskaya, Renata A; Skulachev, Vladimir P; Chernyak, Boris V

    2013-09-01

    Previously it has been shown by our group that berberine and palmatine, penetrating cations of plant origin, when conjugated with plastoquinone (SkQBerb and SkQPalm), can accumulate in isolated mitochondria or in mitochondria of living cells and effectively protect them from oxidative damage. In the present work, we demonstrate that SkQBerb, SkQPalm, and their analogs lacking the plastoquinone moiety (C10Berb and C10Palm) operate as mitochondria-targeted compounds facilitating protonophorous effect of free fatty acids. These compounds induce proton transport mediated by small concentrations of added fatty acids both in planar and liposomal model lipid membranes. In mitochondria, such an effect can be carried out by endogenous fatty acids and the adenine nucleotide translocase.

  19. Acid-promoted chemoselective introduction of amide functionality onto aromatic compounds mediated by an isocyanate cation generated from carbamate.

    PubMed

    Sumita, Akinari; Kurouchi, Hiroaki; Otani, Yuko; Ohwada, Tomohiko

    2014-10-01

    Carbamates have been used as precursors of isocyanates, but heating in the presence of strong acids is required because cleavage of the C-O bond in carbamates is energy-demanding even in acid media. Direct amidation of aromatic compounds by isocyanate cations generated at room temperature from carbamoyl salicylates in trifluoromethanesulfonic acid (TfOH) was examined. Carbamates with ortho-salicylate as an ether group (carbamoyl salicylates) showed dramatically accelerated O-C bond dissociation in TfOH, which resulted in facile generation of the isocyanate cation. These chemoselective intermolecular aromatic amidation reactions proceeded even at room temperature and showed good compatibility with other electrophilic functionalities and high discrimination between N-monosubstituted carbamate and N,N-disubstituted carbamate. The reaction rates of secondary and tertiary amide formation were markedly different, and this difference was utilized to achieve successive (tandem) amidation reactions of molecules with an N-monosubstituted carbamate and an N,N-disubstituted carbamate with two kinds of aromatic compounds.

  20. Organo-Lewis acids as cocatalysts in cationic metallocene polymerization catalysis. Unusual characteristics of sterically encumbered tris(perfluorobiphenyl)borane

    SciTech Connect

    Chen, Y.X.; Stern, C.L.; Yang, S.; Marks, T.J.

    1996-12-11

    Organo-Lewis acids such as methylalumoxane (MAO) and B(C{sub 6}F{sub 5} ){sub 3} (I) play pivotal roles as alkide/hydride abstractors/ cocatalysts in generating highly active, cationic olefin polymerization catalysts (II; L,L` = anionic ancillary ligands; X{sup -} = weakly coordinating anion). We communicate here the unusual cocatalytic characteristics of the new, sterically encumbered fluoroarylborane, tris(2,2`,2``-perfluorobiphenyl)-borane (PBB, III). Characteristics include substantially different abstractive and ion pair structure/reactivity relationships vis-a-vis I. PPB was synthesized as colorless microcrystals in 76% yield from C{sub 6}F{sub 5}Br. Reaction with group 4 and Th methyls proceeds cleanly to yield cationic complexes, which were characterized by standard {sup 1}H/{sup 13}C/{sup 19}F NMR spectroscopic and analytical techniques. The results illustrate the substantial and surprising differences in cationic complex ion pair structure and reactivity that can be brought about by modifications in fluoroarylborane catalyst architecture. 10 refs., 1 fig., 1 tab.

  1. One-step Conjugation of Glycyrrhetinic Acid to Cationic Polymers for High-performance Gene Delivery to Cultured Liver Cell

    PubMed Central

    Cong, Yue; Shi, Bingyang; Lu, Yiqing; Wen, Shihui; Chung, Roger; Jin, Dayong

    2016-01-01

    Gene therapies represent a promising therapeutic route for liver cancers, but major challenges remain in the design of safe and efficient gene-targeting delivery systems. For example, cationic polymers show good transfection efficiency as gene carriers, but are hindered by cytotoxicity and non-specific targeting. Here we report a versatile method of one-step conjugation of glycyrrhetinic acid (GA) to reduce cytotoxicity and improve the cultured liver cell -targeting capability of cationic polymers. We have explored a series of cationic polymer derivatives by coupling different ratios of GA to polypropylenimine (PPI) dendrimer. These new gene carriers (GA-PPI dendrimer) were systematically characterized by UV-vis,1H NMR titration, electron microscopy, zeta potential, dynamic light-scattering, gel electrophoresis, confocal microscopy and flow cytometry. We demonstrate that GA-PPI dendrimers can efficiently load and protect pDNA, via formation of nanostructured GA-PPI/pDNA polyplexes. With optimal GA substitution degree (6.31%), GA-PPI dendrimers deliver higher liver cell transfection efficiency (43.5% vs 22.3%) and lower cytotoxicity (94.3% vs 62.5%, cell viability) than the commercial bench-mark DNA carrier bPEI (25kDa) with cultured liver model cells (HepG2). There results suggest that our new GA-PPI dendrimer are a promising candidate gene carrier for targeted liver cancer therapy. PMID:26902258

  2. Oxidation of glyoxylic acid by cerium(IV): Oxygen-induced enhancement of the primary radical concentration

    SciTech Connect

    Neumann, B. ||; Steinbock, O.; Dalal, N.S. |; Mueller, S.C. |||

    1996-07-25

    In order to help understand the role of oxygen in Ce(IV)-induced oxidation of small carbonic acids, we investigated the reaction of glyoxylic acid (HCOCOOH) and Ce(IV) in 1 M sulfuric acid. Spectrophotometric data showed that in excess of glyoxylic acid the consumption of Ce(IV) obeys pseudo-first-order kinetics, with a rate constant of 8.8 L mol{sup -1} s{sup -1} at 25{degree}C and an activation energy of 80 kJ mol{sup -1}. Rapid-flow EPR measurements revealed an approximately 1:2:1 triplet with a g value of 2.0071{+-}0.0005 and a hyperfine splitting of 7.1{+-}0.2 G, assignable to the primary radical formed by abstraction of a hydrogen atom from hydrated glyoxylic acid. The rate constant for the anaerobic self-decay of the radical was measured as approximately 3.7x10{sup 9} L mol{sup -1} s{sup -1}. Surprisingly, oxygen had no effect on the Ce(IV) kinetics, while the radical decay was significantly inhibited under aerobic conditions (ratio of experimental rate constants = 6.3). Amperometric measurements revealed accompanying oxygen consumption. Analyses based on numerical simulations show that the observed oxygen-induced increase in radical concentration cannot be explained in the framework of standard autooxidation mechanisms. An alternative reaction scheme is suggested which reproduces the observed aerobic radical kinetics and which thus could be relevant to similar oxidation reactions. 30 refs., 7 figs., 2 tabs.

  3. Feasibility investigation on deep ocean compact autonomous Raman spectrometer developed for in-situ detection of acid radical ions

    NASA Astrophysics Data System (ADS)

    Du, Zengfeng; Li, Ying; Chen, Jing; Guo, Jinjia; Zheng, Rong'er

    2015-03-01

    A newly developed Deep Ocean Compact Autonomous Raman Spectrometer (DOCARS) system is introduced and used for in-situ detection of acid radical ions in this paper. To evaluate the feasibility and capability of DOCARS for quantitative analysis of the acid radical ions in the deep ocean, extensive investigations have been carried out both in laboratory and sea trials during the development phase. In the laboratory investigations, Raman spectra of the prepared samples (acid radical ions solutions) were obtained, and analyzed using the method of internal standard normalization in data processing. The Raman signal of acid radical ions was normalized by that of water molecules. The calibration curve showed that the normalized Raman signal intensity of SO{4/2-}, NO{3/-}, and HCO{2/-} increases linearly as the concentration rises with correlation coefficient R 2 of 0.99, 0.99, and 0.98 respectively. The linear function obtained from the calibration curve was then used for the analysis of the spectra data acquired in the sea trial under a simulating chemical field in the deep-sea environment. It was found that the detected concentration of NO{3/-} according to the linear function can reflect the concentration changes of NO{3/-} after the sample was released, and the detection accuracy of the DOCARS system for SO{4/2-} is 8%. All the results showed that the DOCARS system has great potential in quantitative detection of acid radical ions under the deep-sea environment, while the sensitivity of the DOCARS system is expected to be improved.

  4. The Association of Fatty Acid Levels and Gleason Grade among Men Undergoing Radical Prostatectomy

    PubMed Central

    Zhao, Zhiguo; Reinstatler, Lael; Klaassen, Zachary; Xu, Yi; Yang, Xiaoyu; Madi, Rabii; Terris, Martha K.; Qian, Steven Y.; Kelavkar, Uddhav; Moses, Kelvin A.

    2016-01-01

    Background Epidemiological data suggest that omega-6 (ω-6) fatty acids (FAs) may be associated with cancer incidence and/or cancer mortality, whereas ω-3 FAs are potentially protective. We examined the association of the ratio of ω-6 to ω-3 FA (ω-6:ω-3) and individual FA components with pathological results among men with prostate cancer (PCa) undergoing radical prostatectomy. Methods Sixty-nine men were included in the study. Components of ω-6 (linoleic acid (LA), arachidonic acid (AA), and dihomo-γ-linolenic acid (DGLA)) and ω-3 (docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA)) were analyzed by liquid chromatography/mass selective detector separation. Logistic regression analysis was performed to determine association of FA with pathological high grade (Gleason ≥4+3) disease. Results The were 35 men with low grade disease (Gleason ≤3+4) and 34 men with high grade disease. Men with low grade disease were significantly younger (58y vs 61y, p = 0.012) and had lower D’Amico clinical classification (p = 0.001) compared to men with high grade disease. There was no significant association of ω-6:ω-3 with high grade disease (OR 0.93, p = 0.78), however overall ω-6, ω-3, and individual components of ω-6 and ω-3 FAs except EPA were significantly associated with high grade disease (ω-6: OR 3.37, 95% CI: 1.27,8.98; LA: OR 3.33, 95% CI:1.24,8.94; AA: OR 2.93, 95% CI:1.24,6.94; DGLA: OR 3.21, 95% CI:1.28,8.04; ω-3: OR 3.47, 95% CI:1.22,9.83; DHA: OR 3.13, 95% CI:1.26,7.74). ω-6 and ω-3 FA components were highly correlated (Spearman ρ = 0.77). Conclusion Higher levels of individual components of ω-6 and ω-3FAs may be associated with higher-grade PCa. Impact Studies into the causative factors/pathways regarding FAs and prostate carcinogenesis may prove a potential association with PCa aggressiveness. PMID:27880795

  5. Diastereo-specific conformational properties of neutral, protonated and radical cation forms of (1R,2S)-cis- and (1R,2R)-trans-amino-indanol by gas phase spectroscopy.

    PubMed

    Bouchet, Aude; Klyne, Johanna; Piani, Giovanni; Dopfer, Otto; Zehnacker, Anne

    2015-10-21

    Chirality effects on the intramolecular interactions strongly depend on the charge and protonation states. Here, the influence of chirality on the structure of the neutral, protonated, and radical cation forms of (1R,2S)-cis- and (1R,2R)-trans-1-amino-2-indanol diastereomers, prototypical molecules with two chiral centers, is investigated in a molecular beam by laser spectroscopy coupled with quantum chemical calculations. The neutral systems are structurally characterised by double resonance IR-UV spectroscopy, while IR-induced dissociation spectroscopy is employed for the charged molecules. The sterical constraints due to the cyclic nature of the molecule emphasise the chirality effects, which manifest themselves by the formation of an intramolecular hydrogen bond in neutral or protonated (1R,2S)-cis-amino-indanol. In contrast, this interaction is not possible in (1R,2R)-trans-amino-indanol. In the protonated species, chirality also influences the spectroscopic probes in the NH/OH stretch range by fine-tuning subtle effects such as the hyperconjugation between the σ(OH) orbital and σ* orbitals localised on the alicyclic ring. The radical cation undergoes opening of the alicyclic ring, which results in an ionisation-induced loss of the chirality effects.

  6. Hydrogen-atom abstraction from a model amino acid: dependence on the attacking radical.

    PubMed

    Amos, Ruth I J; Chan, Bun; Easton, Christopher J; Radom, Leo

    2015-01-22

    We have used computational chemistry to examine the reactivity of a model amino acid toward hydrogen abstraction by HO•, HOO•, and Br•. The trends in the calculated condensed-phase (acetic acid) free energy barriers are in accord with experimental relative reactivities. Our calculations suggest that HO• is likely to be the abstracting species for reactions with hydrogen peroxide. For HO• abstractions, the barriers decrease as the site of reaction becomes more remote from the electron-withdrawing α-substituents, in accord with a diminishing polar deactivating effect. We find that the transition structures for α- and β-abstractions have additional hydrogen-bonding interactions, which lead to lower gas-phase vibrationless electronic barriers at these positions. Such favorable interactions become less important in a polar solvent such as acetic acid, and this leads to larger calculated barriers when the effect of solvation is taken into account. For Br• abstractions, the α-barrier is the smallest while the β-barrier is the largest, with the barrier gradually becoming smaller further along the side chain. We attribute the low barrier for the α-abstraction in this case to the partial reflection of the thermodynamic effect of the captodatively stabilized α-radical product in the more product-like transition structure, while the trend of decreasing barriers in the order β > γ > δ ∼ ε is explained by the diminishing polar deactivating effect. More generally, the favorable influence of thermodynamic effects on the α-abstraction barrier is found to be smaller when the transition structure for hydrogen abstraction is earlier.

  7. Mutual Lewis acid-base interactions of cations and anions in ionic liquids.

    PubMed

    Holzweber, Markus; Lungwitz, Ralf; Doerfler, Denise; Spange, Stefan; Koel, Mihkel; Hutter, Herbert; Linert, Wolfgang

    2013-01-02

    Solute properties are known to be strongly influenced by solvent molecules due to solvation. This is due to mutual interaction as both the properties of the solute and of the solvent strongly depend on each other. The present paper is based on the idea that ionic liquids are cations solvated by anions and anions solvated by cations. To show this (in this system strongly pronounced) interaction the long time established donor-acceptor concept for solvents and ions in solution by Viktor Gutmann is extended to ionic liquids. A number of solvent parameters, such as the Kamlet-Abboud-Taft and the Dimroth-Reichardt E(T) scale for ionic liquids neglect this mutual influence, which, however, seems to be in fact necessary to get a proper description of ionic liquid properties. It is shown how strong such parameters vary when the influence of the counter ion is taken into account. Furthermore, acceptor and donor numbers for ionic liquids are presented.

  8. Caffeoylquinic acid derived free radicals identified during antioxidant reactions of bitter tea (Ilex latifolia and Ilex kudincha).

    PubMed

    Pirker, Katharina Franziska; Goodman, Bernard Albert

    2010-12-01

    In order to provide some insight into the chemical basis for the antioxidant behaviour of bitter tea, the Chinese medicinal beverage derived from leaves of Ilex kudincha or Ilex latifolia, free radicals generated during the oxidation of aqueous extracts of dried leaves have been investigated by electron paramagnetic resonance (EPR) spectroscopy. With both beverages, the major components in the EPR spectra after accelerated autoxidation under alkaline conditions or oxidation with the superoxide anion radical were comparable to those derived from reactions of caffeoylquinic acids. Thus these reaction products have sufficient stability for biological activity, and the present results suggest that such molecules contribute appreciably to the antioxidant chemistry of these beverages.

  9. On the antioxidant properties of kynurenic acid: free radical scavenging activity and inhibition of oxidative stress.

    PubMed

    Lugo-Huitrón, R; Blanco-Ayala, T; Ugalde-Muñiz, P; Carrillo-Mora, P; Pedraza-Chaverrí, J; Silva-Adaya, D; Maldonado, P D; Torres, I; Pinzón, E; Ortiz-Islas, E; López, T; García, E; Pineda, B; Torres-Ramos, M; Santamaría, A; La Cruz, V Pérez-De

    2011-01-01

    Kynurenic acid (KYNA) is an endogenous metabolite of the kynurenine pathway for tryptophan degradation and an antagonist of both N-methyl-D-aspartate (NMDA) and alpha-7 nicotinic acetylcholine (α7nACh) receptors. KYNA has also been shown to scavenge hydroxyl radicals (OH) under controlled conditions of free radical production. In this work we evaluated the ability of KYNA to scavenge superoxide anion (O(2)(-)) and peroxynitrite (ONOO(-)). The scavenging ability of KYNA (expressed as IC(50) values) was as follows: OH=O(2)(-)>ONOO(-). In parallel, the antiperoxidative and scavenging capacities of KYNA (0-150 μM) were tested in cerebellum and forebrain homogenates exposed to 5 μM FeSO(4) and 2.5 mM 3-nitropropionic acid (3-NPA). Both FeSO(4) and 3-NPA increased lipid peroxidation (LP) and ROS formation in a significant manner in these preparations, whereas KYNA significantly reduced these markers. Reactive oxygen species (ROS) formation were determined in the presence of FeSO(4) and/or KYNA (0-100 μM), both at intra and extracellular levels. An increase in ROS formation was induced by FeSO(4) in forebrain and cerebellum in a time-dependent manner, and KYNA reduced this effect in a concentration-dependent manner. To further know whether the effect of KYNA on oxidative stress is independent of NMDA and nicotinic receptors, we also tested KYNA (0-100 μM) in a biological preparation free of these receptors - defolliculated Xenopus laevis oocytes - incubated with FeSO(4) for 1 h. A 3-fold increase in LP and a 2-fold increase in ROS formation were seen after exposure to FeSO(4), whereas KYNA attenuated these effects in a concentration-dependent manner. In addition, the in vivo formation of OH evoked by an acute infusion of FeSO(4) (100 μM) in the rat striatum was estimated by microdialysis and challenged by a topic infusion of KYNA (1 μM). FeSO(4) increased the striatal OH production, while KYNA mitigated this effect. Altogether, these data strongly suggest that KYNA

  10. Use of a polystyrene-divinylbenzene-based weakly acidic cation-exchange resin column and propionic acid as an eluent in ion-exclusion/adsorption chromatography of aliphatic carboxylic acids and ethanol in food samples.

    PubMed

    Mori, Masanobu; Hironaga, Takahiro; Kajiwara, Hiroe; Nakatani, Nobutake; Kozaki, Daisuke; Itabashi, Hideyuki; Tanaka, Kazuhiko

    2011-01-01

    We developed an ion-exclusion/adsorption chromatography (IEAC) method employing a polystyrene-divinylbenzene-based weakly acidic cation-exchange resin (PS-WCX) column with propionic acid as the eluent for the simultaneous determination of multivalent aliphatic carboxylic acids and ethanol in food samples. The PS-WCX column well resolved mono-, di-, and trivalent carboxylic acids in the acidic eluent. Propionic acid as the eluent gave a higher signal-to-noise ratio, and enabled sensitive conductimetric detection of analyte acids. We found the optimal separation condition to be the combination of a PS-WCX column and 20-mM propionic acid. Practical applicability of the developed method was confirmed by using a short precolumn with a strongly acidic cation-exchange resin in the H(+)-form connected before the separation column; this was to remove cations from food samples by converting them to hydrogen ions. Consequently, common carboxylic acids and ethanol in beer, wine, and soy sauce were successfully separated by the developed method.

  11. Modelling the bacterial photosynthetic reaction center. V. Assignment of the electronic transition observed at 2200 cm-1 in the special-pair radical-cation as a second-highest occupied molecular orbital to highest occupied molecular orbital transition

    NASA Astrophysics Data System (ADS)

    Reimers, Jeffrey R.; Shapley, Warwick A.; Hush, Noel S.

    2003-08-01

    Primary charge separation in photoexcited photosynthetic reaction centers produces the radical cation P+ of a bacteriochlorophyll dimer known as the special-pair P. P+ has an intense electronic transition in the vicinity of 1800-5000 cm-1 which is usually assigned to the interchromophore hole-transfer excitation of the dimer radical cation; in principle, this spectrum can give much insight into key steps of the solar-to-electrical energy-conversion process. The extent to which this transition is localized on one-half of the dimer or delocalized over both is of utmost importance; an authoritative deduction of this quantity from purely spectroscopic arguments requires the detailed assignment of the observed high to medium resolution spectra. For reaction centers containing bacteriochlorophylls a or b, a shoulder is observed at 2200 cm-1 on the low-energy side of the main hole-transfer absorption band, a band whose maximum is near 2700 cm-1. Before quantitative analysis of the hole-transfer absorption in these well-studied systems can be attempted, the nature of the processes leading to this shoulder must be determined. We interpret it as arising from an intrachromophore SHOMO to HOMO transition whose intensity arises wholly through vibronic coupling with the hole-transfer band. A range of ab initio and density-functional calculations are performed to estimate the energy of this transition both for monomeric cations and for P+ of Blastochloris viridis, Rhodobacter sphaeroides, Chlorobium limicola, Chlorobium tepidum, Chlamydomonas reinhardtii, Synochocystis S.6803, spinach photosystems I and II, Heliobacillus mobilis, and finally Heliobacterium modesticaldum, with the results found to qualitatively describe the available experimental data. Subsequent papers in this series provide quantitative analyses of the vibronic coupling and complete spectral simulations based on the model developed herein.

  12. Role of ascorbic acid in scavenging free radicals and lead toxicity from biosystems.

    PubMed

    Tariq, Shabbir A

    2007-09-01

    Free radicals are reactive species that are responsible for damaging normal cells and creating diseases in humans. Antioxidants from natural resources or as supplements can scavenge these radicals. A MedLine search indicates that vitamin C is the most investigated antioxidant responsible for the elimination of free radicals. Its chelating property for the removal of neurotoxic lead, which creates oxidative stress in the human biosystem, was investigated and results indicate its great potential as a lead-detoxifying agent.

  13. [Lavoisier and radicals].

    PubMed

    Lafont, Olivier

    2007-01-01

    Lavoisier and his co-workers (Guyton de Morveau, Bertholet, Fourcroy) considered that acids were constituted of oxygen and of something else that they called radicals. These radicals were known in some cases, i.e. nitrogen for nitrous acid, carbon for carbonic acid, phosphorus for phosphoric acid. In the case of sulfur, the sulfuric radical could be associated with different quantities of oxigen leading to sulfuric or sulfurous acids. In other cases radicals remained unknown at the time i.e. muriatic radical for muriatic acid, or benzoyl radical for benzoic acid. It is interesting to notice that Lavoisier evoked the case of compound radicals constituted of different substances such as carbon and hydrogen.

  14. Hydroxyl radical formation upon oxidation of reduced humic acids by oxygen in the dark.

    PubMed

    Page, Sarah E; Sander, Michael; Arnold, William A; McNeill, Kristopher

    2012-02-07

    Humic acids (HAs) accept and donate electrons in many biogeochemical redox reactions at oxic/anoxic interfaces. The products of oxidation of reduced HAs by O(2) are unknown but are expected to yield reactive oxygen species, potentially including hydroxyl radical (·OH). To quantify the formation of ·OH upon oxidation of reduced HAs by O(2), three HAs were reduced electrochemically to well-defined redox states and were subsequently oxidized by O(2) in the presence of the ·OH probe terephthalate. The formation of ·OH upon oxidation increased with increasing extent of HA reduction. The yield of ·OH ranged from 42 to 160 mmol per mole of electrons donated by the reduced HA. The intermediacy of hydrogen peroxide (H(2)O(2)) in the formation of ·OH was supported by enhancement of ·OH formation upon addition of exogenous H(2)O(2) sources and by the suppression of ·OH formation upon addition of catalase as a quencher of endogenous H(2)O(2). The formation of ·OH in the dark during oxidation of reduced HA represents a previously unknown source of ·OH formation at oxic/anoxic interfaces and may affect the biogeochemical and pollutant redox dynamics at these interfaces.

  15. Characterization of a Cross-Linked Protein-Nucleic Acid Substrate Radical in the Reaction Catalyzed by RlmN

    SciTech Connect

    Silakov, Alexey; Grove, Tyler L.; Radle, Matthew I.; Bauerle, Matthew R.; Green, Michael T.; Rosenzweig, Amy C.; Boal, Amie K.; Booker, Squire J.

    2014-08-14

    RlmN and Cfr are methyltransferases/methylsynthases that belong to the radical S-adenosylmethionine superfamily of enzymes. RlmN catalyzes C2 methylation of adenosine 2503 (A2503) of 23S rRNA, while Cfr catalyzes C8 methylation of the exact same nucleotide, and will subsequently catalyze C2 methylation if the site is unmethylated. A key feature of the unusual mechanisms of catalysis proposed for these enzymes is the attack of a methylene radical, derived from a methylcysteine residue, onto the carbon center undergoing methylation to generate a paramagnetic protein–nucleic acid cross-linked species. This species has been thoroughly characterized during Cfr-dependent C8 methylation, but does not accumulate to detectible levels in RlmN-dependent C2 methylation. Herein, we show that inactive C118S/A variants of RlmN accumulate a substrate-derived paramagnetic species. Characterization of this species by electron paramagnetic resonance spectroscopy in concert with strategic isotopic labeling shows that the radical is delocalized throughout the adenine ring of A2503, although predominant spin density is on N1 and N3. Moreover, 13C hyperfine interactions between the radical and the methylene carbon of the formerly [methyl-13C]Cys355 residue show that the radical species exists in a covalent cross-link between the protein and the nucleic acid substrate. X-ray structures of RlmN C118A show that, in the presence of SAM, the substitution does not alter the active site structure compared to that of the wild-type enzyme. Together, these findings have new mechanistic implications for the role(s) of C118 and its counterpart in Cfr (C105) in catalysis, and suggest involvement of the residue in resolution of the cross-linked species via a radical mediated process

  16. Characterization of a Cross-Linked Protein–Nucleic Acid Substrate Radical in the Reaction Catalyzed by RlmN

    PubMed Central

    2015-01-01

    RlmN and Cfr are methyltransferases/methylsynthases that belong to the radical S-adenosylmethionine superfamily of enzymes. RlmN catalyzes C2 methylation of adenosine 2503 (A2503) of 23S rRNA, while Cfr catalyzes C8 methylation of the exact same nucleotide, and will subsequently catalyze C2 methylation if the site is unmethylated. A key feature of the unusual mechanisms of catalysis proposed for these enzymes is the attack of a methylene radical, derived from a methylcysteine residue, onto the carbon center undergoing methylation to generate a paramagnetic protein–nucleic acid cross-linked species. This species has been thoroughly characterized during Cfr-dependent C8 methylation, but does not accumulate to detectible levels in RlmN-dependent C2 methylation. Herein, we show that inactive C118S/A variants of RlmN accumulate a substrate-derived paramagnetic species. Characterization of this species by electron paramagnetic resonance spectroscopy in concert with strategic isotopic labeling shows that the radical is delocalized throughout the adenine ring of A2503, although predominant spin density is on N1 and N3. Moreover, 13C hyperfine interactions between the radical and the methylene carbon of the formerly [methyl-13C]Cys355 residue show that the radical species exists in a covalent cross-link between the protein and the nucleic acid substrate. X-ray structures of RlmN C118A show that, in the presence of SAM, the substitution does not alter the active site structure compared to that of the wild-type enzyme. Together, these findings have new mechanistic implications for the role(s) of C118 and its counterpart in Cfr (C105) in catalysis, and suggest involvement of the residue in resolution of the cross-linked species via a radical mediated process. PMID:24806349

  17. Envelope-binding domain in the cationic amino acid transporter determines the host range of ecotropic murine retroviruses.

    PubMed Central

    Albritton, L M; Kim, J W; Tseng, L; Cunningham, J M

    1993-01-01

    Infection of rodent cells by ecotropic type C retroviruses requires the expression of a cationic amino acid transporter composed of multiple membrane-spanning domains. By exchanging portions of cDNAs encoding the permissive mouse and nonpermissive human transporters and examining their abilities to specify virus infection upon expression in human 293 cells, we have identified the amino acid residues in the extracellular loop connecting the fifth and sixth membrane-spanning segments of the mouse transporter that are required for both envelope gp70 binding and infection. These findings strongly suggest that the role of the mouse transporter in determining infection is to provide an envelope-binding site. This role is analogous to those of host membrane proteins composed of a single membrane-spanning domain that serve as binding proteins or receptors for other enveloped viruses such as human immunodeficiency virus, Epstein-Barr virus, and murine and human coronaviruses. PMID:8445722

  18. Red-Light Initiated Decomposition of α-Hydroxy Methylperoxy Radical in the Presence of Organic and Inorganic Acids: Implications for the HOx Formation in the Lower Stratosphere.

    PubMed

    Kumar, Manoj; Francisco, Joseph S

    2016-05-05

    Theoretical calculations have been carried out to investigate the gas-phase decomposition of α-hydroxy methylperoxy (HOCH2(OO)) radical in the absence and presence of formic acid, acetic acid, nitric acid, and sulfuric acid. The HOCH2(OO) radical decomposition represents a new source of the HOx radical in troposphere. The results suggest that sulfuric acid will be more effective than other acids in catalyzing the peroxy radical decomposition. However, the significant stability of prereaction and postreaction complexes in all the bimolecular reactions implies a new photomechanism for the acid-mediated decomposition of the HOCH2(OO) radical that involves the visible or near IR overtone excitation of the OH stretching modes or electronic excitation of the O-O peroxy moiety in the acid-bound radical. This new overtone or electronic excitation-based photomechanism for the peroxy radical decomposition may provide useful insight into the missing photolytic source of the HOx at high solar zenith angles corresponding to the dawn or dusk photochemistry.

  19. Binding of Polycarboxylic Acids to Cationic Mixed Micelles: Effects of Polymer Counterion Binding and Polyion Charge Distribution.

    PubMed

    Yoshida; Sokhakian; Dubin

    1998-09-15

    Mixed micelles of cetyltrimethylammonium chloride (CTAC) and n-dodecyl hexaoxyethylene glycol monoether (C12E8) bind to polyanions when the mole fraction of the cationic surfactant exceeds a critical value (Yc). Yc corresponds to a critical micelle surface charge density at which polyelectrolyte will bind to this colloidal particle. Turbidimetric titrations were used to determine Yc for such cationic-nonionic micelles in the presence of acrylic acid and acrylamido-2-methylpropane sulfonate homopolymers (PAA and PAMPS, respectively) and their copolymers with acrylamide, as function of pH, ionic strength, and polyelectrolyte counterion. In 0.20 M NaCl, Yc for PAA is found to be remarkably insensitive to pH, i.e., virtually independent of the apparent polymer charge density xiapp. On the other hand, the expected inverse relationship between Yc and xiapp is observed either for PAA when NaCl is replaced by TMACl (tetramethylammonium chloride), or when xiapp is manipulated using acrylic acid/acrylamide copolymers at high pH. The effective charge density of PAA is thus seen to be suppressed by specific sodium ion binding, indicating that the influence of salts on the interaction of polycarboxylic acids with colloidal particles may differ qualitatively from their effect on the analogous behavior of strong polyanions. Comparisons between homo- and copolymers of acrylic acid were carried out also to test the hypothesis that the "mobility" of charges on PAA at moderate pH (degree of ionization less than unity) could make this "annealed" polymer exhibit the behavior of a more highly charged one. The results, while consistent with this expectation, were obscured by the likely effect of copolymer sequence distributions. Copyright 1998 Academic Press.

  20. Theoretical study on the gas phase reaction of sulfuric acid with hydroxyl radical in the presence of water.

    PubMed

    Long, Bo; Zhang, Wei-Jun; Tan, Xing-Feng; Long, Zheng-Wen; Wang, Yi-Bo; Ren, Da-Sen

    2011-03-03

    The reactions of H2SO4 with the OH radical without water and with water are investigated employing the quantum chemical calculations at the B3LYP/6-311+G(2df,2p) and MP2/aug-cc-pv(T+d)z levels of theory, respectively. The calculated results show that the reaction of H2SO4 with OH and H2O is a very complex mechanism because of the formation of the prereactive complex prior to the transition state and product. There are two prereactive complexes with stabilization energies being -20.28 and -20.67 kcal/mol, respectively. In addition, the single water can lower the energy barriers of the hydrogen abstraction and the proton transfer to 7.51 and 6.37 kcal/mol, respectively from 13.79 and 8.82 kcal/mol with respect to the corresponding prereactive complex. The computed rate constants indicate that the water-assisted reaction of sulfuric acid with OH radical is of greater importance than the reaction of the naked sulfuric acid with the OH radical because the rate constant of the water-assisted process is about 10(3) faster than that of the reaction sulfuric acid with OH. Therefore, the conclusion is obtained that the water-assisted process plays an important role in the sink for the gaseous sulfuric acid in the clean area.

  1. Notable effects of the metal salts on the formation and decay reactions of α-tocopheroxyl radical in acetonitrile solution. The complex formation between α-tocopheroxyl and metal cations.

    PubMed

    Kohno, Yutaro; Fujii, Miyabi; Matsuoka, Chihiro; Hashimoto, Haruka; Ouchi, Aya; Nagaoka, Shin-ichi; Mukai, Kazuo

    2011-08-18

    The measurement of the UV-vis absorption spectrum of α-tocopheroxyl (α-Toc(•)) radical was performed by reacting aroxyl (ArO(•)) radical with α-tocopherol (α-TocH) in acetonitrile solution including four kinds of alkali and alkaline earth metal salts (MX or MX(2)) (LiClO(4), LiI, NaClO(4), and Mg(ClO(4))(2)), using stopped-flow spectrophotometry. The maximum wavelength (λ(max)) of the absorption spectrum of the α-Toc(•) at 425.0 nm increased with increasing concentration of metal salts (0-0.500 M) in acetonitrile, and it approached constant values, suggesting an [α-Toc(•)-M(+) (or M(2+))] complex formation. The stability constants (K) were determined to be 9.2, 2.8, and 45 M(-1) for LiClO(4), NaClO(4), and Mg(ClO(4))(2), respectively. By reacting ArO(•) with α-TocH in acetonitrile, the absorption of ArO(•) disappeared rapidly, while that of α-Toc(•) appeared and then decreased gradually as a result of the bimolecular self-reaction of α-Toc(•) after passing through the maximum. The second-order rate constants (k(s)) obtained for the reaction of α-TocH with ArO(•) increased linearly with an increasing concentration of metal salts. The results indicate that the hydrogen transfer reaction of α-TocH proceeds via an electron transfer intermediate from α-TocH to ArO(•) radicals followed by proton transfer. Both the coordination of metal cations to the one-electron reduced anions of ArO(•) (ArO:(-)) and the coordination of counteranions to the one-electron oxidized cations of α-TocH (α-TocH(•)(+)) may stabilize the intermediate, resulting in the acceleration of electron transfer. A remarkable effect of metal salts on the rate of bimolecular self-reaction (2k(d)) of the α-Toc(•) radical was also observed. The rate constant (2k(d)) decreased rapidly with increasing concentrations of the metal salts. The 2k(d) value decreased at the same concentration of the metal salts in the following order: no metal salt > NaClO(4) > LiClO(4) > Mg

  2. Towards fuel cell membranes with improved lifetime: Aquivion® Perfluorosulfonic Acid membranes containing immobilized radical scavengers

    NASA Astrophysics Data System (ADS)

    D'Urso, C.; Oldani, C.; Baglio, V.; Merlo, L.; Aricò, A. S.

    2014-12-01

    A facile synthesis, based on a wet impregnation technique and a thermal treatment, of a novel silica-supported cerium-oxide-based radical scavenger bearing sulfonic acid functionalities is presented. This material is loaded as a filler in ePTFE reinforced membranes (called R79-02S) prepared starting from Aquivion® Perfluoro-Sulfonic Acid (PFSA) dispersions. The aim is to mitigate the peroxy radicals attack to the polymeric membrane under fuel cell operating conditions. These membranes show much longer (7 times more) life-time in Accelerated Stress Tests (AST) and reduced fluoride release (about one half) in Fenton's tests than the radical scavenger-free membrane without any loss in electrochemical performance. Scavenger-free Aquivion® PFSA-based membrane durability is about 200 h in AST whereas the same membrane containing the newly developed radical scavenger exceeds 1400 h. These results confirm the stability of the modified membranes and the excellent activity of the composite scavenger in mitigating the polymer electrolyte degradation.

  3. Detection and characterization of carrier-mediated cationic amino acid transport in lysosomes of normal and cystinotic human fibroblasts. Role in therapeutic cystine removal

    SciTech Connect

    Pisoni, R.L.; Thoene, J.G.; Christensen, H.N.

    1985-04-25

    The discovery of a trans-stimulation property associated with lysine exodus from lysosomes of human fibroblasts has enabled us to characterize a system mediating the transport of cationic amino acids across the lysosomal membrane of human fibroblasts. The cationic amino acids arginine, lysine, ornithine, diaminobutyrate, histidine, 2-aminoethylcysteine, and the mixed disulfide of cysteine and cysteamine all caused trans-stimulation of the exodus of radiolabeled lysine from the lysosomal fraction of human fibroblasts at pH 6.5. In contrast, neutral and acidic amino acids did not affect the rate of lysine exodus. Trans-stimulation of lysine exodus was observed over the pH range from 5.5 to 7.6, was specific for the L-isomer of the cationic amino acid, and was intolerant to methylation of the alpha-amino group of the amino acid. The lysosomotropic amine, chloroquine, greatly retarded lysine exodus, whereas the presence of sodium ion was without effect. The specificity and lack of Na+ dependence of this lysosomal transport system is similar to that of System y+ present on the plasma membrane of human fibroblasts. An important mechanism by which cysteamine treatment of cystinosis allows cystine escape from lysosomes may be the ability of the mixed disulfide of cysteine and cysteamine formed by sulfhydryl-disulfide exchange to migrate by this newly discovered system mediating cationic amino acid transport.

  4. Simultaneous removal of dyes and metal cations using an acid, acid-base and base modified vermiculite as a sustainable and recyclable adsorbent.

    PubMed

    Stawiński, Wojciech; Węgrzyn, Agnieszka; Freitas, Olga; Chmielarz, Lucjan; Mordarski, Grzegorz; Figueiredo, Sónia

    2017-01-15

    The aim of this work was the modification of vermiculite in order to produce a low cost, efficient and sustainable adsorbent for dyes and metals. Three activation methods consisting of acid, base and combined acid/base treatment were applied to improve the of vermiculite's adsorption properties. Adsorbents were tested in single, bi- and tricomponent solutions containing cationic dyes and Cu(2+) cations. The raw material showed low adsorption capacity for dyes and metal. The acid/base treated vermiculite had very good adsorption capacity toward dyes while the maximum adsorption capacity for Cu(2+) did not change comparing to the starting material. The alkaline treated vermiculite was a good adsorbent for metals, while still being able to remove dyes on the level of the not treated material. Moreover, it was shown that the materials may be regenerated and used in several adsorption-desorption cycles. Furthermore, it was possible to separate adsorbed dyes from metals that were desorbed, using as eluents ethanol/NaCl and 0.05M HNO3, respectively. This opens a possibility for sustainable disposal and neutralization of both of the pollutants or for their further applications in other processes.

  5. Studies of radiation-produced radicals and radical ions

    SciTech Connect

    Williams, T.F.

    1991-01-01

    The radiolytic oxidation of anti-5-methylbicyclo(2.1.0)pentane gives the 1-methylcyclopentene radical cation as the sole rearrangement product H migration whereas oxidation of its syn isomer results in the highly selective formation of the 3-methylcyclopentene radical cation by methyl group migration. Since exactly the same stereoselectivity of olefin formation was observed in corresponding PET (photosensitized electron transfer) studies in the liquid phase, it is concluded that the rearrangement in this case also occurs through the intermediacy of radical cations. Clearly, the radical cation rearrangement must occur very rapidly (10{sup {minus}8}--10{sup {minus}9}s) under liquid-phase conditions at room temperature to compete with back electron transfer, and therefore the hydrogen (or methyl) migration is a fast process under these conditions. An intramolecular cycloaddition reaction was demonstrated in the radical cation rearrangement of 4-vinylcyclohexene to bicyclo(3.2.1)oct-2-ene. ESR studies show that the radiolytic oxidation of quadricyclane in Freon matrices under conditions of high substrate dilution leads to the bicyclo(3.2.0)hepta-2,6-diene radical cation as well as the previously reported norbornadiene radical cation, the former species predominating at sufficiently low concentrations.

  6. Carboxyatractylate inhibits the potentiating effect of lipophylic cation TPP+ on uncoupling activity of fatty acid.

    PubMed

    Dedukhova, V I; Mokhova, E N; Starkov, A A; Leikin YuN

    1993-08-01

    The effect of TPP+ on the fatty acid or FCCP-induced uncoupling in rat heart mitochondria was studied. It was found that (a) TPP+ increases the stimulation of oxygen consumption by palmitic acid or FCCP in the presence of oligomycin, (b) TPP+ greatly enhances the palmitic acid or FCCP-induced delta psi decrease. Both effects of TPP+ were strongly suppressed by carboxyatractylate in the case of palmitate but were not in the case of FCCP. The role of ATP/ADP-antiporter in the TPP+ and palmitic acid effects is discussed.

  7. pH-responsive controlled-release fertilizer with water retention via atom transfer radical polymerization of acrylic acid on mussel-inspired initiator.

    PubMed

    Ma, Zhi-yuan; Jia, Xin; Zhang, Guo-xiang; Hu, Jia-mei; Zhang, Xiu-lan; Liu, Zhi-yong; Wang, He-yun; Zhou, Feng

    2013-06-12

    This work reports a polydopamine-graft-poly(acrylic acid) (Pdop-g-PAA)-coated controlled-release multi-element compound fertilizer with water-retention function by a combination of mussel-inspired chemistry and surface-initiated atom transfer radical polymerization (SI-ATRP) techniques for the first time. The morphology and composition of the products were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), gel permeation chromatography (GPC), and inductively coupled plasma (ICP) emission spectrometry. The results revealed that the stimuli-responsive layer formed by a Pdop inner layer and a PAA outer corona exhibit outstanding selective permeability to charged nutrients and the release rate of encapsulated elements can be tailored by the pH values. At low pH, the Pdop-g-PAA layer can reduce nutrient loss, and at high pH, the coating restrains transportation of negative nutrients but favors the release of cations. Moreover, PAA brushes provide good water-retention property. This Pdop-graft-polymer brushes coating will be effective and promising in the research and development of multi-functional controlled-release fertilizer.

  8. A novel cationic triazatetrabenzcorrole: selective detection of mercury(II) by nucleic acid-induced aggregation.

    PubMed

    Zhou, Yangyang; Deng, Minggang; Du, Yuanyuan; Yan, Shengyong; Huang, Rong; Weng, Xiaocheng; Yang, Chuluo; Zhang, Xiaolian; Zhou, Xiang

    2011-03-07

    In the present work, a novel water-soluble cationic triazatetrabenzcorrole compound was synthesised. Its aggregation and fluorescence quenching properties are demonstrated by serval methods, such as UV-vis and fluorescence spectroscopic studies and naked-eye visualization. Unlike the traditional Hg(2+) sensor based on thymine-Hg(2+)-thymine, we use a novel approach, exploiting the high affinity of Hg(2+) for sulfur in phosphorothioate DNA. Based on the S-Hg(2+)-S pairs, we designed the phosphorothioate DNA T4G4-S3 as an Hg(2+) sensor, which can detect Hg(2+) sensitively and selectively in aqueous solution. And this sensing system is fairly fast and convenient.

  9. Potential role of stabilized Criegee radicals in sulfuric acid production in a high biogenic VOC environment.

    PubMed

    Kim, Saewung; Guenther, Alex; Lefer, Barry; Flynn, James; Griffin, Robert; Rutter, Andrew P; Gong, Longwen; Cevik, Basak Karakurt

    2015-03-17

    We present field observations made in June 2011 downwind of Dallas-Fort Worth, TX, and evaluate the role of stabilized Criegee radicals (sCIs) in gaseous sulfuric acid (H2SO4) production. Zero-dimensional model calculations show that sCI from biogenic volatile organic compounds composed the majority of the sCIs. The main uncertainty associated with an evaluation of H2SO4 production from the sCI reaction channel is the lack of experimentally determined reaction rates for sCIs formed from isoprene ozonolysis with SO2 along with systematic discrepancies in experimentally derived reaction rates between other sCIs and SO2 and water vapor. In general, the maximum of H2SO4 production from the sCI channel is found in the late afternoon as ozone increases toward the late afternoon. The sCI channel, however, contributes minor H2SO4 production compared with the conventional OH channel in the mid-day. Finally, the production and the loss rates of H2SO4 are compared. The application of the recommended mass accommodation coefficient causes significant overestimation of H2SO4 loss rates compared with H2SO4 production rates. However, the application of a lower experimental value for the mass accommodation coefficient provides good agreement between the loss and production rates of H2SO4. The results suggest that the recommended coefficient for the H2O surface may not be suitable for this relatively dry environment.

  10. Dietary intake, neutrophil fatty acid profile, serum antioxidant vitamins and oxygen radical absorbance capacity in patients with ulcerative colitis.

    PubMed

    Kawakami, Yuko; Okada, Hiroyuki; Murakami, Yasuko; Kawakami, Takayo; Ueda, Yukiko; Kunii, Daisuke; Sakamoto, Yachiyo; Shiratori, Yasushi; Okita, Misako

    2007-04-01

    Nutrition may play an important role in the pathogenesis and treatment of ulcerative colitis. Several studies suggest an association between dietary factors and the onset of ulcerative colitis; however, only few studies have examined the relationship between dietary intake and relapse of ulcerative colitis. The aim of this study was to assess the dietary intake and antioxidative capacity of ulcerative colitis patients and to elucidate the efficacy of dietary therapy for ulcerative colitis. Dietary intake, fatty acid composition of phospholipids in plasma and neutrophils, serum fat-soluble vitamin levels, and oxygen radical absorbance capacity were analyzed in 29 ulcerative colitis patients (7 males and 22 females), who were treated at the Department of Gastroenterology, Okayama University Hospital. Total fat intake, fat energy ratio and linoleic acid intake were significantly lower, while protein and carbohydrate intakes were significantly higher, in the patients than age- and sex-matched controls. In the neutrophil phospholipids of ulcerative colitis patients, significantly higher levels of linoleic aicd and arachidonic acid and a lower level of eicosapentaenoic acid were observed. The concentrations of serum retinol and beta-carotene but not alpha-tocopherol were significantly lower and serum oxygen radical absorbance capacity was also lower than in the controls. Significant correlations between serum oxygen radical absorbance capacity and retinol (r = 0.567, p = 0.0031), alpha-tocopherol (r = 0.560, p = 0.0036) and beta-carotene (r = 0.440, p = 0.0279) concentrations were observed in the ulcerative colitis patients. A diet restricting the intake of linoleic acid and supplemented with eicosapentaenoic acid and antioxidative vitamins may be recommendable for the nutritional management of ulcerative colitis patients.

  11. Cascade dissociations of peptide cation-radicals. Part 2. Infrared multiphoton dissociation and mechanistic studies of z-ions from pentapeptides.

    PubMed

    Ledvina, Aaron R; Chung, Thomas W; Hui, Renjie; Coon, Joshua J; Tureček, Frantisek

    2012-08-01

    Dissociations of z(4) ions from pentapeptides AAXAR where X=H, Y, F, W, and V produce dominant z(2) ions that account for >50 % of the fragment ion intensity. The dissociation has been studied in detail by experiment and theory and found to involve several isomerization and bond-breaking steps. Isomerizations in z(4) ions proceed by amide trans→cis rotations followed by radical-induced transfer of a β-hydrogen atom from the side chain, forming stable C(β) radical intermediates. These undergo rate-determining cleavage of the C(α)-CO bond at the X residue followed by loss of the neutral AX fragment, forming x(2) intermediates. The latter were detected by energy-resolved resonant excitation collision-induced dissociation (CID) and infrared multiphoton dissociation (IRMPD) experiments. The x(2) intermediates undergo facile loss of HNCO to form z(2) fragment ions, as also confirmed by energy-resolved CID and IRMPD MS(4) experiments. The loss of HNCO from the x(2) ion from AAHWR is kinetically hampered by the Trp residue that traps the OCNH radical group in a cyclic intermediate.

  12. Cascade Dissociations of Peptide Cation-Radicals. Part2. Infrared Multiphoton Dissociation and Mechanistic Studies of z-Ions from Pentapeptides

    PubMed Central

    Ledvina, Aaron R.; Chung, Thomas W.; Hui, Renjie; Coon, Joshua J.

    2013-01-01

    Dissociations of z4 ions from pentapeptides AAXAR, where X = H, Y, F, W, and V, produce dominant z2 ions that account for >50% of the fragment ion intensity. The dissociation has been studied in detail by experiment and theory and found to involve several isomerization and bond-breaking steps. Isomerizations in z4 ions proceed by amide transcis rotations followed by radical-induced transfer of a β-hydrogen atom from the side chain, forming stable Cβ radical intermediates. These undergo rate-determining cleavage of the Cα—CO bond at the X residue followed by loss of the neutral AX fragment, forming x2 intermediates. The latter were detected by energy-resolved resonant excitation collision-activated dissociation (CAD) and infrared multiphoton dissociation (IRMPD) experiments. The x2 intermediates undergo facile loss of HNCO to form z2 fragment ions, as also confirmed by energy-resolved CAD and IRMPD MS4 experiments. The loss of HNCO from the x2 ion from AAHWR is kinetically hampered by the Trp residue that traps the OCNH radical group in a cyclic intermediate. PMID:22669762

  13. Mechanisms of hydroxyl radical production from abiotic oxidation of pyrite under acidic conditions

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Yuan, Songhu; Liao, Peng

    2016-01-01

    Hydroxyl radicals (radOH) produced from pyrite oxidation by O2 have been recognized, but mechanisms regarding the production under anoxic and oxic conditions are not well understood. In this study, the mechanisms of radOH production from pyrite oxidation under anoxic and oxic conditions were explored using benzoic acid (BA) as an radOH probe. Batch experiments were conducted at pH 2.6 to explore radOH production under anoxic and oxic conditions. The cumulative radOH concentrations produced under anoxic and oxic conditions increased linearly to 7.5 and 52.2 μM, respectively within 10 h at 10 g/L pyrite. Under anoxic conditions, radOH was produced from the oxidation of H2O on the sulfur-deficient sites on pyrite surface, showing an increased production with the increase of pyrite surface exposure due to oxidation. Under oxic conditions, the formation of radOH proceeds predominantly via the two-electron reduction of O2 on pyrite surface along with a minor contribution from the oxidation of H2O on surface sulfur-defects and the reactions of Fe2+/sulfur intermediates with O2. For both O2 reduction and H2O oxidation on the surface sulfur-defects, H2O2 was the predominant intermediate, which subsequently transformed to radOH through Fenton mechanism. The radOH produced had a significant impact on the transformation of contaminants in the environment. Anoxic pyrite suspensions oxidized 13.9% As(III) (C0 = 6.67 μM) and 17.6% sulfanilamide (C0 = 2.91 μM) within 10 h at pH 2.6 and 10 g/L pyrite, while oxic pyrite suspensions improved the oxidation percentages to 55.4% for As(III) and 51.9% for sulfanilamide. The ratios of anoxic to oxic oxidation are consistent with the relative contribution of surface sulfur-defects to radOH production. However, Fe2+ produced from pyrite oxidation competed with the contaminants for radOH, which is of particular significance with the increase of time in a static environment. We conclude that radOH can be produced from abiotic oxidation of

  14. Modelling the bacterial photosynthetic reaction center. VI. Use of density-functional theory to determine the nature of the vibronic coupling between the four lowest-energy electronic states of the special-pair radical cation

    NASA Astrophysics Data System (ADS)

    Reimers, Jeffrey R.; Shapley, Warwick A.; Rendell, Alistair P.; Hush, Noel S.

    2003-08-01

    It is now over ten years since the first FTIR spectra were recorded of the radical cation of the special-pair, a dimer of bacteriochlorophyll molecules that forms the primary electron donor responsible for primary charge separation in bacterial photosynthesis. While spectra of this type promise to reveal much concerning the role of the special pair electron donor in photosynthesis, attempts to model and interpret them have been limited by poor knowledge of the vibrationally specific aspects of the electron-phonon coupling and have thus been restricted to crude model calculations only. We develop techniques through which density-functional theory can be employed to evaluate most of the unknown properties. This includes symmetric-mode displacements, antisymmetric-mode vibronic coupling constants, and interstate electronic couplings evaluated for interactions between the four lowest-energy states of the special-pair cation radical: the ground state, the primary hole-transfer state, and states involving these two combined with SHOMO to HOMO transitions. Geometry optimizations are performed for all four states of the dimer while vibrational analyses are obtained for the first two; vibronic coupling constants are extracted from analysis of stolen infrared transition moments using Herzberg-Teller theory. Quantitatively, these results are employed in the subsequent paper in this series to simulate the observed spectra. Qualitatively, these results indicate that: (1) vibronic coupling occurs through a large number of antisymmetric modes of the dimer rather than through a small number of strongly active modes, (2) the role of symmetric vibrational motions of the dimer is only minor, (3) that the active symmetric modes are significant in number and low in frequency, (4) that vibronic coupling between the hole-transfer state and the SHOMO to HOMO state is relatively weak and influences spectra only near resonance, and (5) that the calculated electronic couplings are

  15. Cationic permethylated 6-monoamino-6-monodeoxy-β-cyclodextrin as chiral selector of dansylated amino acids in capillary electrophoresis.

    PubMed

    Németh, Krisztina; Domonkos, Celesztina; Sarnyai, Virág; Szemán, Julianna; Jicsinszky, László; Szente, Lajos; Visy, Júlia

    2014-10-01

    The resolution power of permethylated 6-monoamino-6-monodeoxy-βCD (PMMABCD) - a single isomer, cationic CD derivative - developed previously for chiral analyses in capillary electrophoresis was further studied here. Dansylated amino acids (Dns-AA) were chosen as amphoteric chiral model compounds. Changes in the resolutions of Dns-AAs by varying pH and selector concentrations were investigated and correlated with their structures and chemical properties (isoelectric point and lipophilicity). Maximal resolutions could be achieved at pH 6 or pH 4. The separations improved with increasing concentration of the selector. Baseline or substantially better resolution for 8 pairs of these Dns-AAs could be achieved. Low CD concentration was enough for the separation of the most apolar Dns-AAs. Chiral discrimination ability of PMMABCD was demonstrated by the separation of an artificial mixture of 8 Dns-AA pairs.

  16. Catalysis of the Oligomerization of O-Phospho-Serine, Aspartic Acid, or Glutamic Acid by Cationic Micelles

    NASA Technical Reports Server (NTRS)

    Bohler, Christof; Hill, Aubrey R., Jr.; Orgel, Leslie E.

    1996-01-01

    Treatment of relatively concentrated aqueous solutions of 0-phospho-serine (50 mM), aspartic acid (100 mM) or glutamic acid (100 mM) with carbonyldiimidazole leads to the formation of an activated intermediate that oligomerizes efficiently. When the concentration of amino acid is reduced tenfold, few long oligomers can be detected. Positively-charged cetyltrimethyl ammonium bromide micelles concentrate the negatively-charged activated intermediates of the amino acids at their surfaces and catalyze efficient oligomerization even from dilute solutions.

  17. Catalysis of the Oligomerization of O-Phospho-Serine, Aspartic Acid, or Glutamic Acid by Cationic Micelles

    NASA Technical Reports Server (NTRS)

    Boehler, Christof; Hill, Aubrey R., Jr.; Orgel, Leslie E.

    1996-01-01

    Treatment of relatively concentrated aqueous solutions of O-phospho-serine (50 mM), aspartic acid (100 mM) or glutamic acid (100 mM) with carbonyldiimidazole leads to the formation of an activated intermediate that oligomerizes efficiently. When the concentration of amino acid is reduced tenfold, few long oligomers can be detected. Positively-charged cetyltrimethyl ammonium bromide micelles concentrate the negatively-charged activated intermediates of the amino acids at their surfaces and catalyze efficient oligomerization even from dilute solutions.

  18. Organo-Lewis acid as cocatalyst for cationic homogenous metallocene Ziegler-Natta olefin polymerizations

    DOEpatents

    Marks, Tobin J.; Chen, You-Xian

    2000-01-01

    The synthesis of the organo-Lewis acid perfluorobiphenylborane (PBB) and the activation of metallocenes for the formation of a variety of highly active homogeneous Ziegler-Natta metallocene olefin polymerization, copolymerization and ring-opening polymerization catalysts is described.

  19. Superior SWNT dispersion by amino acid based amphiphiles: designing biocompatible cationic nanohybrids.

    PubMed

    Brahmachari, Sayanti; Das, Dibyendu; Das, Prasanta Kumar

    2010-11-28

    Stable aqueous SWNT dispersion up to 92% was achieved using amino acid based amphiphiles through a structure-property investigation. The nanohybrids showed remarkable serum stability and biocompatibility to mammalian cells.

  20. A novel cationic microbubble coated with stearic acid-modified polyethylenimine to enhance DNA loading and gene delivery by ultrasound.

    PubMed

    Jin, Qiaofeng; Wang, Zhiyong; Yan, Fei; Deng, Zhiting; Ni, Fei; Wu, Junru; Shandas, Robin; Liu, Xin; Zheng, Hairong

    2013-01-01

    A novel cationic microbubble (MB) for improvement of the DNA loading capacity and the ultrasound-mediated gene delivery efficiency has been developed; it has been prepared with commercial lipids and a stearic acid modified polyethylenimine 600 (Stearic-PEI600) polymer synthesized via acylation reaction of branched PEI600 and stearic acid mediated by N, N'-carbonyldiimidazole (CDI). The MBs' concentration, size distribution, stability and zeta potential (ζ-potential) were measured and the DNA loading capacity was examined as a function of the amount of Stearic-PEI600. The gene transfection efficiency and cytotoxicity were also examined using breast cancer MCF-7 cells via the reporter plasmid pCMV-Luc, encoding the firefly luciferase gene. The results showed that the Stearic-PEI600 polymer caused a significant increase in magnitude of ζ-potential of MBs. The addition of DNA into cationic MBs can shift ζ-potentials from positive to negative values. The DNA loading capacity of the MBs grew linearly from (5±0.2) ×10⁻³ pg/µm² to (20±1.8) ×10⁻³ pg/µm² when Stearic-PEI600 was increased from 5 mol% to 30 mol%. Transfection of MCF-7 cells using 5% PEI600 MBs plus ultrasound exposure yielded 5.76±2.58×10³ p/s/cm²/sr average radiance intensity, was 8.97- and 7.53-fold higher than those treated with plain MBs plus ultrasound (6.41±5.82) ×10² p/s/cm²/sr, (P<0.01) and PEI600 MBs without ultrasound (7.65±6.18) ×10² p/s/cm²/sr, (P<0.01), respectively. However, the PEI600 MBs showed slightly higher cytotoxicity than plain MBs. The cells treated with PEI600-MBs and plain MBs plus ultrasound showed 59.5±6.1% and 71.4±7.1% cell viability, respectively. In conclusion, our study demonstrated that the novel cationic MBs were able to increase DNA loading capacity and gene transfection efficiency and could be potentially applied in targeted gene delivery and therapy.

  1. Benzene carboxylic acid derivatized graphene oxide nanosheets on natural zeolites as effective adsorbents for cationic dye removal.

    PubMed

    Yu, Yang; Murthy, Bandaru N; Shapter, Joseph G; Constantopoulos, Kristina T; Voelcker, Nicolas H; Ellis, Amanda V

    2013-09-15

    Graphene oxide (GO) nanosheets were grafted to acid-treated natural clinoptilolite-rich zeolite powders followed by a coupling reaction with a diazonium salt (4-carboxybenzenediazoniumtetrafluoroborate) to the GO surface. Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) revealed successful grafting of GO nanosheets onto the zeolite surface. The application of the adsorbents for the adsorption of rhodamine B from aqueous solutions was then demonstrated. After reaching adsorption equilibrium the maximum adsorption capacities were shown to be 50.25, 55.56 and 67.56 mg g(-1) for pristine natural zeolite, GO grafted zeolite (GO-zeolite) and benzene carboxylic acid derivatized GO-zeolite powders, respectively. The adsorption behavior was fitted to a Langmuir isotherm and shown to follow a pseudo-second-order reaction model. Further, a relationship between surface functional groups, pH and adsorption efficiency was established. Results indicate that benzene carboxylic acid derivatized GO-zeolite powders are environmentally favorable adsorbents for the removal of cationic dyes from aqueous solutions.

  2. Ligand-functionalized degradable polyplexes formed by cationic poly(aspartic acid)-grafted chitosan-cyclodextrin conjugates.

    PubMed

    Song, Hai-Qing; Li, Rui-Quan; Duan, Shun; Yu, Bingran; Zhao, Hong; Chen, Da-Fu; Xu, Fu-Jian

    2015-03-19

    Polypeptide-based degradable polyplexes attracted considerable attention in drug delivery systems. Polysaccharides including cyclodextrin (CD), dextran, and chitosan (CS) were readily grafted with cationic poly(aspartic acid)s (PAsps). To further enhance the transfection performances of PAsp-based polyplexes, herein, different types of ligand (folic acid, FA)-functionalized degradable polyplexes were proposed based on the PAsp-grafted chitosan-cyclodextrin conjugate (CCPE), where multiple β-CDs were tied on a CS chain. The FA-functionalized CCPE (i.e., CCPE-FA) was obtained via a host-guest interaction between the CD units of CCPE and the adamantane (Ad) species of Ad-modified FA (Ad-FA). The resulting CCPE/pDNA, CCPE-FA/pDNA, and ternary CCPE-FA/CCPE/pDNA (prepared by layer-by-layer assembly) polyplexes were investigated in detail using different cell lines. The CCPE-based polyplexes displayed much higher transfection efficiencies than the CS-based polyplexes reported earlier by us. The ternary polyplexes of CCPE-FA/CCPE/pDNA produced excellent gene transfection abilities in the folate receptor (FR)-positive tumor cells. This work would provide a promising means to produce highly efficient polyplexes for future gene therapy applications.

  3. First-principles data set of 45,892 isolated and cation-coordinated conformers of 20 proteinogenic amino acids

    PubMed Central

    Ropo, Matti; Schneider, Markus; Baldauf, Carsten; Blum, Volker

    2016-01-01

    We present a structural data set of the 20 proteinogenic amino acids and their amino-methylated and acetylated (capped) dipeptides. Different protonation states of the backbone (uncharged and zwitterionic) were considered for the amino acids as well as varied side chain protonation states. Furthermore, we studied amino acids and dipeptides in complex with divalent cations (Ca2+, Ba2+, Sr2+, Cd2+, Pb2+, and Hg2+). The database covers the conformational hierarchies of 280 systems in a wide relative energy range of up to 4 eV (390 kJ/mol), summing up to a total of 45,892 stationary points on the respective potential-energy surfaces. All systems were calculated on equal first-principles footing, applying density-functional theory in the generalized gradient approximation corrected for long-range van der Waals interactions. We show good agreement to available experimental data for gas-phase ion affinities. Our curated data can be utilized, for example, for a wide comparison across chemical space of the building blocks of life, for the parametrization of protein force fields, and for the calculation of reference spectra for biophysical applications. PMID:26881946

  4. Determination of surface-accessible acidic hydroxyls and surface area of lignin by cationic dye adsorption.

    PubMed

    Sipponen, Mika Henrikki; Pihlajaniemi, Ville; Littunen, Kuisma; Pastinen, Ossi; Laakso, Simo

    2014-10-01

    A new colorimetric method for determining the surface-accessible acidic lignin hydroxyl groups in lignocellulose solid fractions was developed. The method is based on selective adsorption of Azure B, a basic dye, onto acidic hydroxyl groups of lignin. Selectivity of adsorption of Azure B on lignin was demonstrated using lignin and cellulose materials as adsorbents. Adsorption isotherms of Azure B on wheat straw (WS), sugarcane bagasse (SGB), oat husk, and isolated lignin materials were determined. The maximum adsorption capacities predicted by the Langmuir isotherms were used to calculate the amounts of surface-accessible acidic hydroxyl groups. WS contained 1.7-times more acidic hydroxyls (0.21 mmol/g) and higher surface area of lignin (84 m(2)/g) than SGB or oat husk materials. Equations for determining the amount of surface-accessible acidic hydroxyls in solid fractions of the three plant materials by a single point measurement were developed. A method for high-throughput characterization of lignocellulosic materials is now available.

  5. Disproportionation of a 2,2-diphenyl-1-picrylhydrazyl radical as a model of reactive oxygen species catalysed by Lewis and/or Brønsted acids.

    PubMed

    Nakanishi, Ikuo; Kawashima, Tomonori; Ohkubo, Kei; Waki, Tsukasa; Uto, Yoshihiro; Kamada, Tadashi; Ozawa, Toshihiko; Matsumoto, Ken-Ichiro; Fukuzumi, Shunichi

    2014-01-25

    Electron-transfer disproportionation of a 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙) occurred in the presence of Sc(3+) acting as a strong Lewis acid in deaerated acetonitrile. In contrast, in the case of weaker Lewis acids than Sc(3+), such as Mg(2+) and Li(+), external protons from acetic acid were required for the disproportionation of DPPH˙ to occur.

  6. Free radical scavengers from the medicinal mushroom Inonotus xeranticus and their proposed biogenesis.

    PubMed

    Lee, In-Kyoung; Jung, Jin-Young; Seok, Soon-Ja; Kim, Wan-Gyu; Yun, Bong-Sik

    2006-11-01

    New free radical scavengers, inoscavin D (1) and methylinoscavin D (2), were isolated from the methanolic extract of the fruiting bodies of Inonotus xeranticus (Hymenochaetaceae), along with the known compounds phelligridin D (3), 3,4-dihydroxybenzaldehyde (4), and 3,4-dihydroxybenzoic acid (5). Their structures were established by various spectroscopic analyses. Compounds 1 and 3 were proposed to be biosynthesized from the oxidative coupling of the precursor hispidin with 3,4-dihydroxybenzaldehyde and 3,4-dihydroxybenzoic acid, respectively. These compounds exhibited significant scavenging activity against the ABTS radical cation, and compounds 2 and 4 displayed moderate superoxide radical scavenging activity.

  7. Influence of fatty acid on lipase-catalyzed synthesis of ascorbyl esters and their free radical scavenging capacity.

    PubMed

    Stojanović, Marija; Carević, Milica; Mihailović, Mladen; Veličković, Dušan; Dimitrijević, Aleksandra; Milosavić, Nenad; Bezbradica, Dejan

    2015-01-01

    Fatty acid (FA) ascorbyl esters are recently emerging food, cosmetic, and pharmaceutical additives, which can be prepared in an eco-friendly way by using lipases as catalysts. Because they are amphiphilic molecules, which possess high free radical scavenging capacity, they can be applied as liposoluble antioxidants as well as emulsifiers and biosurfactants. In this study, the influence of a wide range of acyl donors on ester yield in lipase-catalyzed synthesis and ester antioxidant activity was examined. Among saturated acyl donors, higher yields and antioxidant activities of esters were achieved when short-chain FAs were used. Oleic acid gave the highest yield overall and its ester exhibited a high antioxidant activity. Optimization of experimental factors showed that the highest conversion (60.5%) in acetone was achieved with 5 g L(-1) of lipase, 50 mM of vitamin C, 10-fold molar excess of oleic acid, and 0.7 mL L(-1) of initial water. Obtained results showed that even short- and medium-chain ascorbyl esters could be synthesized with high yields and retained (or even exceeded) free radical scavenging capacity of l-ascorbic acid, indicating prospects of broadening their application in emulsions and liposomes.

  8. The effect of positioning cations on acidity and stability of the framework structure of Y zeolite.

    PubMed

    Deng, Changshun; Zhang, Junji; Dong, Lihui; Huang, Meina; Bin Li; Jin, Guangzhou; Gao, Junbin; Zhang, Feiyue; Fan, Minguang; Zhang, Luoming; Gong, Yanjun

    2016-03-18

    The investigation on the modification of NaY zeolite on LaHY and AEHY (AE refers Ca and Sr and the molar ratio of Ca and Sr is 1:1) zeolites was proformed by XRD, N2-physisorption (BET), XRF, XPS, NH3-TPD, Py-IR, hydrothermal stability, and catalytic cracking test. These results indicate that HY zeolite with ultra low content Na can be obtained from NaY zeolite through four exchange four calcination method. The positioning capability of La(3+) in sodalite cage is much better than that of AE(2+) and about 12 La(3+) can be well coordinated in sodalite cages of one unit cell of Y zeolite. Appropriate acid amount and strength favor the formation of propylene and La(3+) is more suitable for the catalytic cracking of cyclohexane than that of AE(2+). Our results not only elaborate the variation of the strong and weak acid sites as well as the Brönsted and Lewis acid sites with the change of exchanged ion content but also explore the influence of hydrothermal aging of LaHY and AEHY zeolites and find the optimum ion exchange content for the most reserved acid sites. At last, the coordination state and stabilization of ion exchanged Y zeolites were discussed in detail.

  9. The effect of positioning cations on acidity and stability of the framework structure of Y zeolite

    PubMed Central

    Deng, Changshun; Zhang, Junji; Dong, Lihui; Huang, Meina; Bin Li; Jin, Guangzhou; Gao, Junbin; Zhang, Feiyue; Fan, Minguang; Zhang, Luoming; Gong, Yanjun

    2016-01-01

    The investigation on the modification of NaY zeolite on LaHY and AEHY (AE refers Ca and Sr and the molar ratio of Ca and Sr is 1:1) zeolites was proformed by XRD, N2-physisorption (BET), XRF, XPS, NH3-TPD, Py-IR, hydrothermal stability, and catalytic cracking test. These results indicate that HY zeolite with ultra low content Na can be obtained from NaY zeolite through four exchange four calcination method. The positioning capability of La3+ in sodalite cage is much better than that of AE2+ and about 12 La3+ can be well coordinated in sodalite cages of one unit cell of Y zeolite. Appropriate acid amount and strength favor the formation of propylene and La3+ is more suitable for the catalytic cracking of cyclohexane than that of AE2+. Our results not only elaborate the variation of the strong and weak acid sites as well as the Brönsted and Lewis acid sites with the change of exchanged ion content but also explore the influence of hydrothermal aging of LaHY and AEHY zeolites and find the optimum ion exchange content for the most reserved acid sites. At last, the coordination state and stabilization of ion exchanged Y zeolites were discussed in detail. PMID:26987306

  10. The effect of positioning cations on acidity and stability of the framework structure of Y zeolite

    NASA Astrophysics Data System (ADS)

    Deng, Changshun; Zhang, Junji; Dong, Lihui; Huang, Meina; Bin Li; Jin, Guangzhou; Gao, Junbin; Zhang, Feiyue; Fan, Minguang; Zhang, Luoming; Gong, Yanjun

    2016-03-01

    The investigation on the modification of NaY zeolite on LaHY and AEHY (AE refers Ca and Sr and the molar ratio of Ca and Sr is 1:1) zeolites was proformed by XRD, N2-physisorption (BET), XRF, XPS, NH3-TPD, Py-IR, hydrothermal stability, and catalytic cracking test. These results indicate that HY zeolite with ultra low content Na can be obtained from NaY zeolite through four exchange four calcination method. The positioning capability of La3+ in sodalite cage is much better than that of AE2+ and about 12 La3+ can be well coordinated in sodalite cages of one unit cell of Y zeolite. Appropriate acid amount and strength favor the formation of propylene and La3+ is more suitable for the catalytic cracking of cyclohexane than that of AE2+. Our results not only elaborate the variation of the strong and weak acid sites as well as the Brönsted and Lewis acid sites with the change of exchanged ion content but also explore the influence of hydrothermal aging of LaHY and AEHY zeolites and find the optimum ion exchange content for the most reserved acid sites. At last, the coordination state and stabilization of ion exchanged Y zeolites were discussed in detail.

  11. Generation of oxoiron (IV) tetramesitylporphyrin pi-cation radical complexes by m-CPBA oxidation of ferric tetramesitylporphyrin derivatives in butyronitrile at - 78 degrees C. Evidence for the formation of six-coordinate oxoiron (IV) tetramesitylporphyrin pi-cation radical complexes FeIV = O(tmp*)X (X = Cl-, Br-), by Mössbauer and X-ray absorption spectroscopy.

    PubMed

    Wolter, T; Meyer-Klaucke, W; Müther, M; Mandon, D; Winkler, H; Trautwein, A X; Weiss, R

    2000-01-30

    The generation of six-coordinate oxoiron (IV) tetramesitylporphyrin pi-caption radical complexes by m-CPBA (meta-chloroperbenzoic acid) oxidation of ferric tetramesitylporphyrin derivatives in butyronitrile at - 78 degrees C was investigated. UV-Vis and EPR spectroscopies indicate that the axial ligand present in the ferric starting derivatives is retained in the high-valent iron complexes. Indirect evidence for the formation of six-coordinate oxoiron (IV) tetramesitylporphyrin complexes FeIV = O(tmp*)X (X=Cl-, Br-) by m-CPBA oxidation of FeX(tmp) (X=Cl-, Br-) in butyronitrile at - 78 degrees C was also obtained by Mössbauer spectroscopy. Direct confirmation of the presence of a halide ion as second axial ligand of iron in these high-valent iron species was obtained by X-ray absorption spectroscopy. The EXAFS spectra of the samples obtained by m-CPBA oxidation of FeX(tmp) (X=Cl-, Br-) were refined using two different coordination models including both four porphyrinato-nitrogens and the axial oxo group. The two models include (model I) or exclude (model II) the axial halogen. The statistical tests indicate the presence of a halide ion as second axial ligand of iron in both derivatives. The refinements led to the following bond distances: FeIV=O(tmp*)Cl(3):Fe-O=1.66(1),Fe-Cl=2.39(2) and Fe-Np=1.99(1) A;FeIV=O(tmp*)Br(4):Fe-O=1.65(1),Fe-Br=2.93(2), Fe-Np=2.02(1) A. The lengthening of the Fe-X(X=Cl-, Br-) distances relative to those occurring in the ferric precursor porphyrins is, most probably, related to the strong trans influence of the oxoiron(IV) fragment present in 3 or 4.

  12. EPR studies of free radicals in A-2058 human melanoma cells treated by valproic acid and 5,7-dimethoxycoumarin.

    PubMed

    Zdybel, Magdalena; Chodurek, Ewa; Pilawa, Barbara

    2014-01-01

    Free radicals in A-2058 human melanoma cells were studied by the use of electron paramagnetic resonance (EPR) spectroscopy. The aim of this work was to determine the changes in relative free radical concentrations in tumor A-2058 cells after treatment by valproic acid (VPA) and 5,7-dimethoxycoumarin (DMC). The influences of VPA and DMC on free radicals in A-2058 cells were compared with those for human melanoma malignum A-375 and G-361 cells, which were tested by us earlier. Human malignant melanoma A-2058 cells were exposed to interactions with VPA, DMC, and both VPA and DMC. The tumor cells A-2058 were purchased from LGC Standards (Lomianki, Poland), and they were grown in the standard conditions: at 37°C and in an atmosphere containing 95% air and 5% CO2, in the Minimum Essential Medium Eagle (MEM, Sigma-Aldrich). The A-2058 cells were incubated with VPA (1 mM) and DMC (10 μM) for 4 days. The first-derivative EPR spectra of the control A-2058 cells, and the cells treated with VPA, DMC, and both VPA and DMC, were measured by the electron paramagnetic resonance spectrometer of Radiopan (Poznań, Poland) with microwaves from an X-band (9.3 GHz). The parameters of the EPR lines: amplitudes (A), integral intensities (I), line widths (ΔBpp), and g-factors, were analyzed. The changes of amplitudes and line widths with microwave power increasing from 2.2 to 70 mW were drawn evaluated, o-Semiquinone free radicals of melanin biopolymer are mainly responsible for the EPR lines of A-2058 melanoma malignum cells. The amounts of free radicals in A-2058 cells treated with VPA, and both VPA and DMC, were lower than in the untreated control cells. Application of the tested substances (VPA, and both VPA and DMC) as the antitumor compounds was discussed. DMC without VPA did not decrease free radicals concentration in A-2058 cells. The studies con-firmed that EPR spectroscopy may be used to examine interactions of free radicals with antitumor compounds.

  13. Radical formation in the FMN-photosensitized reactions of unsaturated fatty acids bearing double bonds at different positions.

    PubMed

    Nishihama, Nao; Iwahashi, Hideo

    2016-08-15

    -carboxybutyl, 7-carboxyheptyl and 9-carboxynonyl radicals formed in the control reaction mixtures of (z)-6-octadecenoic acid, (z)-9-octadecenoic acid {or (z, z)-9,12-octadecadienoic acid} and (z)-11-octadecenoic acid, respectively. The 4-carboxybutyl, 7-carboxyheptyl and 9-carboxynonyl radicals are all generated through β-scission of alkoxy radicals formed on carboxyl ends of the double bonds of the unsaturated fatty acids. Thus, we could reveal reactive sites of unsaturated fatty acids in the photosensitized reaction of flavin mononucleotide with unsaturated fatty acids bearing a double bond at different positions.

  14. Analysis of cationic structure in some room-temperature molten fluorides and dependence of their ionic conductivity and viscosity on hydrofluoric acid concentration.

    PubMed

    Isogai, Tomohiro; Nakai, Takaaki; Inoue, Hidemi; Nakanishi, Kenta; Kohara, Shinji; Saito, Morihiro; Inaba, Minoru; Tasaka, Akimasa

    2011-08-11

    To understand the ionic and nonionic species in (CH(3))(4)NF·mHF, (CH(3))(3)N·mHF, (C(2)H(5))(4)NF·mHF, and (C(2)H(5))(3)N·mHF melts, the structures of these melts were investigated by infrared spectroscopy, NMR, and high-energy X-ray diffraction. Infrared spectra revealed that three kinds of fluorohydrogenate anions, (FH)(n)F(-) (n = 1, 2, and 3), and molecular hydrofluoric acid (HF) are present in every melt. Ionic conductivity and viscosity of these melts were measured and correlated with their cationic structure. The ionic conductivity of the R(4)N(+)-systems was higher than that of corresponding R(3)NH(+)-systems because a strong N-H···F(HF)(n) interaction prevents the motion of R(3)NH(+) cations in the R(3)N·mHF melts. (CH(3))(4)N(+) and (CH(3))(3)NH(+) cations gave higher ionic conductivity than (C(2)H(5))(4)N(+) and (C(2)H(5))(3)NH(+) cations, respectively, because the ionic radii of former cations were smaller than those of latter. It was concluded that these effects on ionic conductivity can be explained by the cationic structure and the concentration of molecular HF in the melts.

  15. Modulation of Human Cardiac TRPM7 Current by Extracellular Acidic pH Depends upon Extracellular Concentrations of Divalent Cations

    PubMed Central

    Mačianskienė, Regina; Almanaitytė, Mantė; Jekabsone, Aistė; Mubagwa, Kanigula

    2017-01-01

    TRPM7 channels participate in a variety of physiological/pathological processes. TRPM7 currents are modulated by protons but opposing effects of external pH (pHo) (potentiation vs inhibition) have been reported. TRPM7 has been less studied in human cardiomyocytes than in heart-derived non-cardiomyocyte cells. We used the whole-cell patch-clamp technique on isolated human atrial cardiomyocytes to investigate the impact of an acidic pHo on the TRPM7 current. With voltage-dependent and other ion channels inhibited, cardiomyocytes were challenged with external acidification in either the presence or the absence of extracellular divalent cations. TRPM7 outward and inward currents were increased by acidic pHo in extracellular medium containing Ca2+ and Mg2+, but suppressed by acidic pHo in the absence of extracellular Ca2+ and Mg2+. The potentiating effect in the presence of extracellular divalents occurred at pHo below 6 and was voltage-dependent. The inhibitory effect in the absence of extracellular divalents was already marked at pHo of 6 and was practically voltage-independent. TRPM7 current density was higher in cardiomyocytes from patients with history of coronary vascular disease and the difference compared to cardiomyocytes from patients without history of myocardial ischemia increased with acidic pHo. We demonstrate that proton-induced modification of TRPM7 currents depends on the presence of extracellular Ca2+ and Mg2+. Variability of the TRPM7 current density in human cardiomyocytes is related to the clinical history, being higher in atrial fibrillation and in ischemic cardiomyopathy. PMID:28129376

  16. Effect of metallic cations on the efficiency of DNA amplification. Implications for nucleic acid replication during early stages of life

    NASA Astrophysics Data System (ADS)

    Arribas, María; de Vicente, Aránzazu; Arias, Armando; Lázaro, Ester

    2005-04-01

    The process of catalysis of biochemical reactions has been essential since the first organic molecules appeared on Earth. As the complexity of the ensemble of primitive biomolecules was very low, primitive catalysts had necessarily to be very simple molecules or ions. The evolution of catalysts had to be in parallel with the evolution of the molecular species reacting. An example of this parallel evolution is nucleic acid polymerization. Synthesis of primitive short oligonucleotides could have been catalysed by metal ions either in solution or on the surface of minerals such as montmorillonite clays. Some oligonucleotides could start to function as templates for the synthesis of complementary copies and there is experimental evidence supporting the role also played by metal ions in this process. In later stages of evolution, a group of enzymatic proteins, nucleic acid polymerases, has been selected to catalyse nucleic acid replication. The presence of Mg2+ in the active centre of these enzymes suggests that evolution has preserved some of the primitive catalysts, including them as cofactors of more complex molecules. However, the reasons why Mg2+ was selected among other ions that possibly were present in primitive environments are unknown. In this paper we try to approach this question by analysing the amplification efficiency of the polymerase chain reaction of a DNA fragment in the presence of different metal ions. In some cases the conditions of the reaction have been displaced from optimum (by the presence of nucleotide imbalances and a suboptimal Mg2+concentration). The results obtained permit one to draw interesting conclusions about how some metallic cations can help replication to proceed in conditions of limited substrate availability, a circumstance that could have been frequent at prebiotic stages, when nucleic acid synthesis was dependent on the physico-chemical conditions of the environment.

  17. Ruminal and Abomasal Starch Hydrolysate Infusions Selectively Decrease the Expression of Cationic Amino Acid Transporter mRNA by Small Intestinal Epithelia of Forage-fed Beef Steers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Although cationic amino acids (CAA) are consid-ered essential to maximize optimal growth of cattle, transporters responsible for CAA absorption by bovine small intestinal epithelia have not been described. This study was conducted to test 2 hypotheses: 1) the duo¬denal, jejunal, and ileal epithelia ...

  18. Interaction of the cesium cation with mono-, di-, and tricarboxylic acids in the gas phase. A Cs+ affinity scale for cesium carboxylates ion pairs.

    PubMed

    Mayeux, Charly; Tammiku-Taul, Jaana; Massi, Lionel; Lohu, Ene-Liis; Burk, Peeter; Maria, Pierre-Charles; Gal, Jean-François

    2009-10-01

    Humic substances (HS), including humic and fulvic acids, play a significant role in the fate of metals in soils. The interaction of metal cations with HS occurs predominantly through the ionized (anionic) acidic functions. In the context of the effect of HS on transport of radioactive cesium isotopes in soils, a study of the interaction between the cesium cation and model carboxylic acids was undertaken. Structure and energetics of the adducts formed between Cs+ and cesium carboxylate salts [Cs+RCOO-] were studied by the kinetic method and density functional theory (DFT). Clusters generated by electrospray ionization mass spectrometry from mixtures of a cesium salt (nitrate, iodide, trifluoroacetate) and carboxylic acids were quantitatively studied by CID. By combining the results of the kinetic method and the energetic data from DFT calculations, a scale of cesium cation affinity, CsCA, was built for 33 cesium carboxylates representing the first scale of cation affinity of molecular salts. The structural effects on the CsCA values are discussed.

  19. Effects of copper sources and dietary cation-anion balance on copper availability and acid-base status in dairy calves.

    PubMed

    Xin, Z; Waterman, D F; Hemken, R W; Harmon, R J; Jackson, J A

    1991-09-01

    Twenty-four Holstein and Jersey calves (14 Holstein), 4 to 11 d of age, were assigned randomly to six treatments in a 2 x 3 factorial arrangement to examine the effects of Cu sources and dietary cation-anion balance on Cu availability and acid-base balance. Treatments were cationic basal diet (20 meq of dietary cation-anion balance on a DM basis), cationic basal diet supplemented with CuO, cationic basal diet supplemented with CuSO4, anionic basal diet (-10 meq), anionic basal diet supplemented with CuO, and anionic basal diet supplemented with CuSO4. Copper sources did not show any effect on growth of calves. The cationic diet increased calf growth compared with the anionic diet at wk 12 of the experiment. Blood pH was increased by the cationic diet in comparison with the anionic diet at wk 8 and 12. Blood pH also was increased by CuSO4 compared with CuO treatment in the early period of the treatment. Blood bicarbonate concentration was decreased by CuO and the anionic diet. Interactions between Cu sources and cation-anion balance were found for blood pH and bicarbonate concentration. Liver Cu concentration was increased by CuSO4 but not by CuO supplementation compared with control. Therefore, CuSO4 was found to be highly available, whereas CuO was a very poorly available source of Cu for young calves.

  20. Conformation of the umifenovir cation in the molecular and crystal structures of four carboxylic acid salts

    NASA Astrophysics Data System (ADS)

    Orola, Liana; Sarcevica, Inese; Kons, Artis; Actins, Andris; Veidis, Mikelis V.

    2014-01-01

    The umifenovir salts of maleic, salicylic, glutaric, and gentisic acid as well as the chloroform solvate of the salicylate were prepared. Single crystals of the five compounds were obtained and their molecular and crystal structures determined by X-ray diffraction. In each structure the conformation of phenyl ring with respect to the indole group of the umifenovir moiety is different. The water solubility and melting points of the studied umifenovir salts have been determined.

  1. Acid-Degradable Cationic Dextran Particles for the Delivery of siRNA Therapeutics

    PubMed Central

    Cohen, Jessica L.; Schubert, Stephanie; Wich, Peter R.; Cui, Lina; Cohen, Joel A.; Mynar, Justin L.; Fréchet, Jean M. J.

    2011-01-01

    We report a new acid-sensitive, biocompatible and biodegradable microparticulate delivery system, spermine modified acetalated-dextran (Spermine-Ac-DEX), which can be used to efficiently encapsulate siRNA. These particles demonstrated efficient gene knockdown in HeLa-luc cells with minimal toxicity. This knockdown was comparable to that obtained using Lipofectamine, a commercially available transfection reagent generally limited to in vitro use due to its high toxicity. PMID:21539393

  2. Synthesis and Lewis acid properties of a ferrocene-based planar-chiral borenium cation.

    PubMed

    Chen, Jiawei; Lalancette, Roger A; Jäkle, Frieder

    2013-05-28

    The first planar chiral ferrocenylborenium species (pR)-3(+) is obtained in the enantiopure form by halide abstraction from the corresponding chloroborane adduct (pR)-2 using Krossing's salt. Competition experiments suggest that the Lewis acidity of (pR)-3(+) is higher than that of B(C6F5)3 towards anions and slightly lower towards neutral Lewis bases. The ferrocenylborenium species (pR)-3(+) is examined as a catalyst for the stereoselective hydrosilylation of ketones.

  3. Titration of fatty acids solubilized in cationic and anionic micelles. Calorimetry and thermodynamic modeling.

    PubMed

    Söderman, Olle; Jönsson, Bengt; Olofsson, Gerd

    2006-02-23

    The electrostatic properties of charged surfactant micelles are investigated through titrations of fatty acid probes solubilized in the micelles. The titration process is followed by means of calorimetric measurements and by determining the pH values as a function of added base. This approach yields a complete thermodynamic description of the titration process. In particular, we find that the process is endothermic at 298 K. This is contrary to the titration of carboxylic acids in water, where DeltaH is approximately 0. To identify the main effect underlying the difference in DeltaH between titration in a micelle and water, a thermodynamic model has been developed which focuses on the transfer properties of charged and uncharged species from bulk water to the surface of a micelle and which incorporates a dielectric discontinuity at the micellar surface. The model relies on the use of the Poisson-Boltzmann equation which is solved using a finite element method. Experimental results and the model calculations imply that the dielectric discontinuity at (or near) the micellar surface plays a major role and hence must be included when analyzing the titration behavior of an acid functionality at the surface of a charged micelle.

  4. Amino Acid Changes in Disease-Associated Variants Differ Radically from Variants Observed in the 1000 Genomes Project Dataset

    PubMed Central

    de Beer, Tjaart A. P.; Laskowski, Roman A.; Parks, Sarah L.; Sipos, Botond; Goldman, Nick; Thornton, Janet M.

    2013-01-01

    The 1000 Genomes Project data provides a natural background dataset for amino acid germline mutations in humans. Since the direction of mutation is known, the amino acid exchange matrix generated from the observed nucleotide variants is asymmetric and the mutabilities of the different amino acids are very different. These differences predominantly reflect preferences for nucleotide mutations in the DNA (especially the high mutation rate of the CpG dinucleotide, which makes arginine mutability very much higher than other amino acids) rather than selection imposed by protein structure constraints, although there is evidence for the latter as well. The variants occur predominantly on the surface of proteins (82%), with a slight preference for sites which are more exposed and less well conserved than random. Mutations to functional residues occur about half as often as expected by chance. The disease-associated amino acid variant distributions in OMIM are radically different from those expected on the basis of the 1000 Genomes dataset. The disease-associated variants preferentially occur in more conserved sites, compared to 1000 Genomes mutations. Many of the amino acid exchange profiles appear to exhibit an anti-correlation, with common exchanges in one dataset being rare in the other. Disease-associated variants exhibit more extreme differences in amino acid size and hydrophobicity. More modelling of the mutational processes at the nucleotide level is needed, but these observations should contribute to an improved prediction of the effects of specific variants in humans. PMID:24348229

  5. Comparison of hydroxyl radical formation in aqueous solutions at different ultrasound frequencies and powers using the salicylic acid dosimeter.

    PubMed

    Milne, Louise; Stewart, Isobel; Bremner, David H

    2013-05-01

    Ultrasonic frequencies of 20kHz, 382kHz, 584kHz, 862kHz (and 998kHz) have been compared with regard to energy output and hydroxyl radical formation utilising the salicylic acid dosimeter. The 862kHz frequency inputs 6 times the number of Watts into water, as measured by calorimetry, with the other frequencies having roughly the same value under very similar conditions. A plausible explanation involving acoustic fountain formation is proposed although enhanced coupling between this frequency and water cannot be discounted. Using the salicylic acid dosimeter and inputting virtually the same Wattages it is established that 862kHz is around 10% more efficient at generating hydroxyl radicals than the 382kHz but both of these are far more effective than the other frequencies. Also, it is found that as temperature increases to 42°C then the total dihydroxybenzoic acid (Total DHBA) produced is virtually identical for 382kHz and 862kHz, though 582kHz is substantially lower, when the power levels are set at approximately 9W for all systems. An equivalent power level of 9W could not be obtained for the 998kHz transducer so a direct comparison could not be made in this instance. These results have implications for the optimum frequencies chosen for both Advanced Oxidation Processes (AOPs) and organic synthesis augmented by ultrasound.

  6. Fourier transform infrared study of the cation radical of P680 in the photosystem II reaction center: evidence for charge delocalization on the chlorophyll dimer.

    PubMed

    Noguchi, T; Tomo, T; Inoue, Y

    1998-09-29

    A Fourier transform infrared (FTIR) difference spectrum of the primary electron donor (P680) of photosystem II upon its photooxidation (P680+/P680) was obtained in the frequency region of 1000-3000 cm-1. The reaction center (RC) complex (D1-D2-Cytb559) was used for the measurements in the presence of ferricyanide as an exogenous electron acceptor. Control measurements of electronic absorption (300-1200 nm) showed that illumination of the RC complex at 150 K induced major oxidation of P680 concomitant with oxidation of a carotenoid and an accessory chlorophyll (Chl). Illumination at 250 K also specifically bleached one of the two beta-carotene molecules bound to the RC complex, and the sample thus treated exhibited little formation of a carotenoid cation on subsequent illumination at 150 K. The P680+/P680 FTIR difference spectrum (with minor contamination of Chl+/Chl) was measured at 150 K using this partially carotenoid-deficient RC complex. The spectrum showed a broad positive band centered at approximately 1940 cm-1, which could be ascribed to an infrared electronic transition of P680+ analogous to that previously observed in various bacterial P+. This finding indicates that a positive charge is delocalized over (or hopping between) the two Chl molecules in P680+. The low intensity of this electronic band compared with that of the bacterial band could have three possible explanations: weak resonance interaction between the constituent Chl molecules, an asymmetric structure of P680+, and the difference in Chl species. Bands in the C=O stretching region (1600-1750 cm-1) were interpreted in comparison with resonance Raman spectra of the RC complex. The negative peaks at 1704 and 1679 cm-1 were proposed as candidates for the keto C9=O bands of P680. The observation that neither of these bands agreed with the main keto C9=O band at 1669 cm-1 in the previous 3P680/P680 FTIR spectrum [Noguchi et al. (1993) Biochemistry 32, 7186-7195] led to the idea that the triplet

  7. Ligand-functionalized degradable polyplexes formed by cationic poly(aspartic acid)-grafted chitosan-cyclodextrin conjugates

    NASA Astrophysics Data System (ADS)

    Song, Hai-Qing; Li, Rui-Quan; Duan, Shun; Yu, Bingran; Zhao, Hong; Chen, Da-Fu; Xu, Fu-Jian

    2015-03-01

    Polypeptide-based degradable polyplexes attracted considerable attention in drug delivery systems. Polysaccharides including cyclodextrin (CD), dextran, and chitosan (CS) were readily grafted with cationic poly(aspartic acid)s (PAsps). To further enhance the transfection performances of PAsp-based polyplexes, herein, different types of ligand (folic acid, FA)-functionalized degradable polyplexes were proposed based on the PAsp-grafted chitosan-cyclodextrin conjugate (CCPE), where multiple β-CDs were tied on a CS chain. The FA-functionalized CCPE (i.e., CCPE-FA) was obtained via a host-guest interaction between the CD units of CCPE and the adamantane (Ad) species of Ad-modified FA (Ad-FA). The resulting CCPE/pDNA, CCPE-FA/pDNA, and ternary CCPE-FA/CCPE/pDNA (prepared by layer-by-layer assembly) polyplexes were investigated in detail using different cell lines. The CCPE-based polyplexes displayed much higher transfection efficiencies than the CS-based polyplexes reported earlier by us. The ternary polyplexes of CCPE-FA/CCPE/pDNA produced excellent gene transfection abilities in the folate receptor (FR)-positive tumor cells. This work would provide a promising means to produce highly efficient polyplexes for future gene therapy applications.Polypeptide-based degradable polyplexes attracted considerable attention in drug delivery systems. Polysaccharides including cyclodextrin (CD), dextran, and chitosan (CS) were readily grafted with cationic poly(aspartic acid)s (PAsps). To further enhance the transfection performances of PAsp-based polyplexes, herein, different types of ligand (folic acid, FA)-functionalized degradable polyplexes were proposed based on the PAsp-grafted chitosan-cyclodextrin conjugate (CCPE), where multiple β-CDs were tied on a CS chain. The FA-functionalized CCPE (i.e., CCPE-FA) was obtained via a host-guest interaction between the CD units of CCPE and the adamantane (Ad) species of Ad-modified FA (Ad-FA). The resulting CCPE/pDNA, CCPE

  8. Interaction of gold nanoparticles with free radicals and their role in enhancing the scavenging activity of ascorbic acid.

    PubMed

    Razzaq, Humaira; Saira, Farhat; Yaqub, Azra; Qureshi, Rumana; Mumtaz, Misbah; Saleemi, Samia

    2016-08-01

    The present study investigates the interaction of citrate stabilized gold nanoparticles (12±1.5nm) (GNPs) with free radicals; 1,1-diphenyl-2-picrylhydrazyl (DPPH) stable and electrochemically generated superoxide, O2(-). Different experiments were designed to understand the interaction between GNPs and DPPH by employing cyclic voltammetry, UV-vis spectroscopy and computational chemistry using 6-311G basis set. The increase in heterogeneous rate constant, ksh, of DPPH upon addition of GNPs pointed towards possible complex formation, DPPH-GNPs which were further explained by a model assuming surface adsorption of DPPH on GNPs. Further, the model was validated by studying interaction of GNPs with a biologically important free radical, O2(-). Exciting result in terms of disappearance of anodic peak after GNPs addition confirmed that gold nanoparticles interacted with stable as well as unstable free radicals. Also, the stoichiometry of the most stable complex GNP-DPPH was determined from UV-vis spectroscopy by applying Job's method. The GNP-DPPH complex was found to be active with 46.0% reduction of the IC50 value of standard antioxidant, ascorbic acid (AA), indicating its role in enhancing antioxidant activity. Hence, this study presents a simple and potential approach to enhance the efficiency of natural antioxidants without modifying their structure, or involving the complex functionalization of GNPs with antioxidants.

  9. Sulfate radical-induced degradation of Acid Orange 7 by a new magnetic composite catalyzed peroxymonosulfate oxidation process.

    PubMed

    Chen, Dan; Ma, Xiaolong; Zhou, Jizhi; Chen, Xi; Qian, Guangren

    2014-08-30

    We synthesized a novel magnetic composite, Fe3O4/Cu(Ni)Cr-LDH, as a heterogeneous catalyst for the degradation of organic dyes in the solution using sulfate radical-based advanced oxidation processes. The physicochemical properties of the composite synthesized via two-step microwave hydrothermal method were characterized by several techniques, such as X-ray diffraction (XRD), inductively coupled plasma (ICP), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The degradation tests were performed at 25°C with Acid Orange 7 (AO7) initial concentration of 25mg/L and AO7/peroxymonosulfate (PMS) molar ratio of 1:10, which showed that the complete degradation by Fe3O4/Cu1.5Ni0.5Cr-LDH could be achieved and the mineralization rate could reach 46%. PMS was activated by Cu (II) and Fe (II/III) of Fe3O4/Cu(Ni)Cr-LDH to generate sulfate radicals (SO4(-)). Subsequently, the organic functional groups of AO7 molecules were destroyed by sulfate radicals (SO4(-)), inducing the degradation of AO7. Moreover, the catalytic behavior of the catalysts could be reused five times. Therefore, our work suggested that the Fe3O4/Cu(Ni)Cr-LDH composite could be applied widely for the treatment of organic dyes in wastewater.

  10. ω-Alkynyl lipid surrogates for polyunsaturated fatty acids: free radical and enzymatic oxidations.

    PubMed

    Beavers, William N; Serwa, Remigiusz; Shimozu, Yuki; Tallman, Keri A; Vaught, Melissa; Dalvie, Esha D; Marnett, Lawrence J; Porter, Ned A

    2014-08-13

    Lipid and lipid metabolite profiling are important parameters in understanding the pathogenesis of many diseases. Alkynylated polyunsaturated fatty acids are potentially useful probes for tracking the fate of fatty acid metabolites. The nonenzymatic and enzymatic oxidations of ω-alkynyl linoleic acid and ω-alkynyl arachidonic acid were compared to that of linoleic and arachidonic acid. There was no detectable difference in the primary products of nonenzymatic oxidation, which comprised cis,trans-hydroxy fatty acids. Similar hydroxy fatty acid products were formed when ω-alkynyl linoleic acid and ω-alkynyl arachidonic acid were reacted with lipoxygenase enzymes that introduce oxygen at different positions in the carbon chains. The rates of oxidation of ω-alkynylated fatty acids were reduced compared to those of the natural fatty acids. Cyclooxygenase-1 and -2 did not oxidize alkynyl linoleic but efficiently oxidized alkynyl arachidonic acid. The products were identified as alkynyl 11-hydroxy-eicosatetraenoic acid, alkynyl 11-hydroxy-8,9-epoxy-eicosatrienoic acid, and alkynyl prostaglandins. This deviation from the metabolic profile of arachidonic acid may limit the utility of alkynyl arachidonic acid in the tracking of cyclooxygenase-based lipid oxidation. The formation of alkynyl 11-hydroxy-8,9-epoxy-eicosatrienoic acid compared to alkynyl prostaglandins suggests that the ω-alkyne group causes a conformational change in the fatty acid bound to the enzyme, which reduces the efficiency of cyclization of dioxalanyl intermediates to endoperoxide intermediates. Overall, ω-alkynyl linoleic acid and ω-alkynyl arachidonic acid appear to be metabolically competent surrogates for tracking the fate of polyunsaturated fatty acids when looking at models involving autoxidation and oxidation by lipoxygenases.

  11. Communication: Oscillating charge migration between lone pairs persists without significant interaction with nuclear motion in the glycine and Gly-Gly-NH-CH{sub 3} radical cations

    SciTech Connect

    Vacher, Morgane; Bearpark, Michael J.; Robb, Michael A.

    2014-05-28

    Coupled electron-nuclear dynamics has been studied, using the Ehrenfest method, for four conformations of the glycine molecule and a single conformation of Gly-Gly-NH-CH{sub 3}. The initial electronic wavepacket was a superposition of eigenstates corresponding to ionization from the σ lone pairs associated with the carbonyl oxygens and the amine nitrogen. For glycine, oscillating charge migration (when the nuclei were frozen) was observed for the 4 conformers studied with periods ranging from 2 to 5 fs, depending on the energy gap between the lone pair cationic states. When coupled nuclear motion was allowed (which was mainly NH{sub 2} partial inversion), the oscillations hardly changed. For Gly-Gly-NH-CH{sub 3}, charge migration between the carbonyl oxygens and the NH{sub 2} lone pair can be observed with a period similar to glycine itself, also without interaction with nuclear motion. These simulations suggest that charge migration between lone pairs can occur independently of the nuclear motion.

  12. Neutral, cationic, and anionic low-spin iron(III) complexes stabilized by amidophenolate and iminobenzosemiquinonate radical in N,N,O ligands.

    PubMed

    Rajput, Amit; Sharma, Anuj K; Barman, Suman K; Koley, Debasis; Steinert, Markus; Mukherjee, Rabindranath

    2014-01-06

    A brownish-black complex [Fe(III)(L)2] (1) (S = 0), supported by two tridentate redox-active azo-appended o-amidophenolates [H2L = 2-(2-phenylazo)-anilino-4,6-di-tert-butylphenol], has been synthesized and structurally characterized. In CH2Cl2 1 displays two oxidative and two reductive 1e(-) redox processes at E1/2 values of 0.48 and 1.06 V and -0.42 and -1.48 V vs SCE, respectively. The one-electron oxidized form [1](+) isolated as a green solid [Fe(III)(L)2][BF4] (2) (S = 1/2) has been structurally characterized. Isolation of a dark ink-blue one-electron reduced form [1](-) has also been achieved [Co(III)(η(5)-C10H15)2][Fe(III)(L)2] (3) (S = 1/2). Mössbauer spectral parameters unequivocally establish that 1 is a low-spin (LS) Fe(III) complex. Careful analysis of Mössbauer spectral data of 2 and 3 at 200 and 80 K reveal that each complex has a major LS Fe(III) and a minor LS Fe(II) component (redox isomers): [Fe(III){(L(ISQ))(-•)}2](+) and [Fe(II){(L(IBQ))(0)}{(L(ISQ))(-•)}](+) (2) and [Fe(III){(L(AP))(2-)}2](-) and [Fe(II){(L(ISQ))(-•)}{(L(AP))(2-)}](-) (3). Notably, for both at 8 K mainly the major component exists. Broken-Symmetry (BS) Density Functional Theory (DFT) calculations at the B3LYP level reveals that in 1 the unpaired electron of LS Fe(III) is strongly antiferromagnetically coupled with a π-radical of o-iminobenzosemiquinonate(1-) (L(ISQ))(-•) form of the ligand, delocalized over two ligands providing 3- charge (X-ray structure). DFT calculations reveal that the unpaired electron in 2 is due to (L(ISQ))(-•) [LS Fe(III) (SFe = 1/2) is strongly antiferromagnetically coupled to one of the (L(ISQ))(-•) radicals (Srad = 1/2)] and 3 is primarily a LS Fe(III) complex, supported by two o-amidophenolate(2-) ligands. Time-Dependent-DFT calculations shed light on the origin of UV-vis-NIR spectral absorptions for 1-3. The collective consideration of Mössbauer, variable-temperature (77-298 K) electron paramagnetic resonance (EPR), and absorption

  13. Modulation of linoleic acid-binding properties of human serum albumin by divalent metal cations.

    PubMed

    Nemashkalova, Ekaterina L; Permyakov, Eugene A; Permyakov, Sergei E; Litus, Ekaterina A

    2017-03-16

    Human serum albumin (HSA) is an abundant multiligand carrier protein, linked to progression of Alzheimer's disease (AD). Blood HSA serves as a depot of amyloid β (Aβ) peptide. Aβ peptide-buffering properties of HSA depend on interaction with its ligands. Some of the ligands, namely, linoleic acid (LA), zinc and copper ions are involved into AD progression. To clarify the interplay between LA and metal ion binding to HSA, the dependence of LA binding to HSA on Zn(2+), Cu(2+), Mg(2+) and Ca(2+) levels and structural consequences of these interactions have been explored. Seven LA molecules are bound per HSA molecule in the absence of the metal ions. Zn(2+) binding to HSA causes a loss of one bound LA molecule, while the other metals studied exert an opposite effect (1-2 extra LA molecules are bound). In most cases, the observed effects are not related to the metal-induced changes in HSA quaternary structure. However, the Zn(2+)-induced decline in LA capacity of HSA could be due to accumulation of multimeric HSA forms. Opposite to Ca(2+)/Mg(2+)-binding, Zn(2+) or Cu(2+) association with HSA induces marked changes in its hydrophobic surface. Overall, the divalent metal ions modulate LA capacity and affinity of HSA to a different extent. LA- and Ca(2+)-binding to HSA synergistically support each other. Zn(2+) and Cu(2+) induce more pronounced changes in hydrophobic surface and quaternary structure of HSA and its LA capacity. A misbalanced metabolism of these ions in AD could modify interactions of HSA with LA, other fatty acids and hydrophobic substances, associated with AD.

  14. ESR study of photoinduced free radicals by visible light in hair and the effects of ascorbic acid (vitamin C).

    PubMed

    Chikvaidze, E; Khachatryan, I

    2011-08-01

    The ESR spectra of melanin's free radicals in natural black and red hair have been investigated. It is shown that the ESR spectrum of black hair is slightly asymmetric singlet with g=2.0037 and ΔH=0.5 mTl. The ESR spectrum of red hair with g=2.0053 differs from the spectrum of black hair. Using the method of saturation was shown that ESR spectrum of red hair represents a superposition of two signals: a singlet, relating to the black hair, and a triplet from red hair's pheomelanin. Under the influence of visible light (blue with λ(max) =450 nm, green with λ(max) =510 nm and red with λ(max) =650 nm) in both types of hair (black and red), the photoinduced free radicals appear, which indicates an increase in the intensity of already existing ESR spectrum of hair. It should be noted that the ESR spectra of red hair from various donors are different. The antioxidant ascorbic acid (vitamin C) has the different effect on the photoinduced free radicals. In particular, in the case of black hair, the concentration of photoinduced free radicals is slightly reduced, whereas in red hair, the disappearance of the triplet in the spectrum is observed, and at the same time, the spectrum becomes a singlet, the intensity of which increases sharply. It is assumed that the antioxidants, effective for black hair, may be ineffective for red hair and vice versa. Therefore, in each, specific case is necessary to investigate the effectiveness of an antioxidant separately.

  15. Mercaptobenzoic acid-palladium(0) complexes as active catalysts for S-benzylation with benzylic alcohols via (η(3)-benzyl)palladium(II) cations in water.

    PubMed

    Hikawa, Hidemasa; Azumaya, Isao

    2014-08-21

    Mercaptobenzoic acid-palladium(0) complexes show high catalytic activity for S-benzylation with benzylic alcohols via the (η(3)-benzyl)palladium(II) cation in water. Notably, these palladium(0) complexes could play an important role in formation of active (η(3)-benzyl)palladium(II) cation complexes followed by S-benzylation. Hammett studies on the rate constants of S-benzylation by various substituted alcohols show good correlation between log(kX/kH) and the σ(+) value of the respective substituents. From the slope, negative ρ values are obtained, suggesting that there is a build-up of positive charge in the transition state. Water plays an important role in the catalytic system for sp(3) C-O bond activation and stabilization of the activated Pd(II) cation species. The catalytic system can be performed using only 2.5 mol% Pd2(dba)3 without the phosphine ligand or other additives.

  16. Facile preparation of a cationic poly(amino acid) vesicle for potential drug and gene co-delivery

    NASA Astrophysics Data System (ADS)

    Ding, Jianxun; Xiao, Chunsheng; He, Chaoliang; Li, Mingqiang; Li, Di; Zhuang, Xiuli; Chen, Xuesi

    2011-12-01

    A novel pH-responsive poly(amino acid) grafted with oligocation was prepared through the combination of ring-opening polymerization (ROP) and subsequent atom transfer radical polymerization (ATRP). Firstly, poly(γ-2-chloroethyl-L-glutamate) (PCELG) with a pendent 2-chloroethyl group was synthesized through ROP of γ-2-chloroethyl-L-glutamate N-carboxyanhydride (CELG NCA) using n-hexylamine as the initiator. Then, PCELG was used to initiate the ARTP of 2-aminoethyl methacrylate hydrochloride (AMA), yielding poly(L-glutamate)-graft-oligo(2-aminoethyl methacrylate hydrochloride) (PLG-g-OAMA). The pKa of PLG-g-OAMA was 7.3 established by the acid-base titration method. The amphiphilic poly(amino acid) could directly self-assemble into a vesicle in PBS. The vesicle was characterized by TEM and DLS. Hydrophilic DOX·HCl was loaded into the hollow core of the vesicle. The in vitro release behavior of DOX·HCl from the vesicle in PBS could be adjusted by the solution pH. In vitro cell experiments revealed that the vesicle could reduce the toxicity of the DOX·HCl. In addition, the preliminary gel retardation assay displayed that PLG-g-OAMA could efficiently bind DNA at a PLG-g-OAMA/DNA weight ratio of 0.3 or above, indicating its potential use as a gene carrier. More in-depth studies of the PLG-g-OAMA vesicle for drug and gene co-delivery in vitro and in vivo are in progress.

  17. Antioxidant effects of resveratrol and its analogues against the free-radical-induced peroxidation of linoleic acid in micelles.

    PubMed

    Fang, Jian-Guo; Lu, Man; Chen, Zhi-Hua; Zhu, Hui-He; Li, Yan; Yang, Li; Wu, Long-Min; Liu, Zhong-Li

    2002-09-16

    The antioxidant effect of resveratrol (3,4',5-trihydroxy-trans-stilbene) and its analogues, that is, 4-hydroxy-trans-stilbene (4-HS), 3,5-dihydroxy-trans-stilbene (3,5-DHS), 4,4'-dihydroxy-trans-stilbene (4,4'-DHS), 3,4-dihydroxy-trans-stilbene (3,4-DHS), 3,4,5-trihydroxy-trans-stilbene (3,4,5-THS) and 3,4,4'-trihydroxy-trans-stilbene (3,4,4'-THS), against the peroxidation of linoleic acid has been studied in sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) micelles. The peroxidation was initiated thermally by a water-soluble azo initiator 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH), and the reaction kinetics were studied by monitoring the formation of linoleic acid hydroperoxides. The synergistic antioxidant effect of these compounds with alpha-tocopherol (vitamin E) was also studied by following the decay kinetics of alpha-tocopherol and the reaction intermediate, the alpha-tocopheroxyl radical. Kinetic analysis of the antioxidant process demonstrates that these compounds are effective antioxidants in micelles used either alone or in combination with alpha-tocopherol. The antioxidative action involves trapping the propagating lipid peroxyl radical and reducing the alpha-tocopheroxyl radical to regenerate alpha-tocopherol. It was found that the antioxidant activity of resveratrol analogues depends significantly on the position of the hydroxyl groups, the oxidation potential of the molecule and the reaction medium. Molecules with ortho-dihydroxyl and/or para-hydroxyl functionalities possess high activity.

  18. Calcium phenylphosphonate as a host for 4-aminobenzoic acid-Synthesis, characterization, and cation adsorption from ethanol solution

    SciTech Connect

    Lazarin, Angelica M.; Ganzerli, Thiago A.; Sernaglia, Rosana L.; Andreotti, Elza I.S.; Airoldi, Claudio

    2009-11-15

    Crystalline lamellar calcium phenylphosphonate retained 4-aminobenzoic acid inside its cavity without leaching. The intense infrared bands in the 1160-695 cm{sup -1} interval confirmed the presence of the phosphonate groups attached to the inorganic layer, with sharp and intense peaks in X-ray diffraction patterns, which gave basal distances of 1532 and 1751 pm for the original and the intercalated compounds, respectively. The thermogravimetric curves of both layered compounds showed the release of water molecules and the organic moiety in distinct stages, to yield a final Ca(PO{sub 3}){sub 2} residue. Solid-state {sup 31}P nuclear magnetic resonance spectra presented only one peak for the phenylphosphonate groups attached to the main inorganic polymeric structure near 12.4 ppm. The adsorption isotherms from ethanol gave the maximum adsorption capacities of 1.68 and 0.50 mmol g{sup -1} for copper and cobalt, respectively, whose average stability constants followed Co > Cu; the number of ligands was determined as four for both cations.

  19. Cationic Lipid-Nucleic Acid Complexes for Gene Delivery And Silencing: Pathways And Mechanisms for Plasmid Dna And Sirna

    SciTech Connect

    Ewert, K.K.; Zidovska, A.; Ahmad, A.; Bouxsein, N.F.; Evans, H.M.; McAllister, C.S.; Samuel, C.E.; Safinya, C.R.; /SLAC

    2012-07-17

    Motivated by the promises of gene therapy, there is great interest in developing non-viral lipid-based vectors for therapeutic applications due to their low immunogenicity, low toxicity, ease of production, and the potential of transferring large pieces of DNA into cells. In fact, cationic liposome (CL) based vectors are among the prevalent synthetic carriers of nucleic acids (NAs) currently used in gene therapy clinical trials worldwide. These vectors are studied both for gene delivery with CL-DNA complexes and gene silencing with CL-siRNA (short interfering RNA) complexes. However, their transfection efficiencies and silencing efficiencies remain low compared to those of engineered viral vectors. This reflects the currently poor understanding of transfection-related mechanisms at the molecular and self-assembled levels, including a lack of knowledge about interactions between membranes and double stranded NAs and between CL-NA complexes and cellular components. In this review we describe our recent efforts to improve the mechanistic understanding of transfection by CL-NA complexes, which will help to design optimal lipid-based carriers of DNA and siRNA for therapeutic gene delivery and gene silencing.

  20. Role of cationic amino acids in the Na+/dicarboxylate co-transporter NaDC-1.

    PubMed Central

    Pajor, A M; Kahn, E S; Gangula, R

    2000-01-01

    The role of cationic amino acids in the Na(+)/dicarboxylate co-transporter NaDC-1 was investigated by site-directed mutagenesis and subsequent expression of mutant transporters in Xenopus oocytes. Of the ten residues chosen for mutagenesis, eight (Lys-34, Lys-107, Arg-108, Lys-333, Lys-390, Arg-368, Lys-414 and Arg-541) were found to be non-essential for function or targeting. Only two conserved residues, Lys-84 (at the cytoplasmic end of helix 3) and Arg-349 (at the extracellular end of helix 7), were found to be important for transport. Both mutant transporters were expressed at the plasma membrane. The mutation of Lys-84 to Ala resulted in an increased K(m) for succinate of 1.8 mM, compared with 0.3 mM in the wild-type NaDC-1. The R349A mutant had Na(+) and citrate kinetics that were similar to those of the wild type. However, succinate handling in the R349A mutant was altered, with evidence of inhibition at high succinate concentrations. In conclusion, charge neutralization of Lys-84 and Arg-349 in NaDC-1 affects succinate handling, suggesting that these residues might have roles in substrate binding. PMID:10970779

  1. Development of helix-stabilized cell-penetrating peptides containing cationic α,α-disubstituted amino acids as helical promoters.

    PubMed

    Yamashita, Hiroko; Misawa, Takashi; Oba, Makoto; Tanaka, Masakazu; Naito, Mikihiko; Kurihara, Masaaki; Demizu, Yosuke

    2017-03-15

    Cell-penetrating peptides (CPP) have attracted many scientists' attention as intracellular delivery tools due to their high cargo molecule transportation efficiency and low cytotoxicity. Therefore, in many research fields CPP, such as HIV-Tat and oligoarginine (Rn), are used to deliver hydrophilic drugs and biomolecules, including proteins, DNA, and RNA. We designed four types of CPP that contained cationic α,α-disubstituted amino acids (Api(C2Gu) and Api(C4Gu)) as helical promoters; i.e., 1-4 [FAM-β-Ala-(l-Arg-l-Arg-Xaa)3-(Gly)3-NH2 (1: Xaa=Api(C2Gu), 2: Xaa=Api(C4Gu)), 3: FAM-β-Ala-(l-Arg)8-Api(C2Gu)-(Gly)3-NH2, and 4: FAM-β-Ala-(l-Arg)5-Api(C2Gu)-(l-Arg)2-Api(C2Gu)-(Gly)3-NH2], and investigated their preferred secondary structures and cell membrane-penetrating ability. As a result, we found that the permeation efficiency of the CPP was affected by the number of helical promoters in their sequences. Specially, peptide 1, which contained three Api(C2Gu) residues, formed a stable helical structure and passed through the cell membrane more efficiently than the other peptides. Moreover, it was demonstrated that the spatial arrangement of the peptides' side chains also influenced their permeability and the helical stabilization of their main chains.

  2. Estradiol augments while progesterone inhibits arginine transport in human endothelial cells through modulation of cationic amino acid transporter-1.

    PubMed

    Bentur, Ohad S; Schwartz, Doron; Chernichovski, Tamara; Ingbir, Merav; Weinstein, Talia; Chernin, Gil; Schwartz, Idit F

    2015-08-15

    Decreased generation of nitric oxide (NO) by endothelial NO synthase (eNOS) characterizes endothelial dysfunction (ECD). Delivery of arginine to eNOS by cationic amino acid transporter-1 (CAT-1) was shown to modulate eNOS activity. We found in female rats, but not in males, that CAT-1 activity is preserved with age and in chronic renal failure, two experimental models of ECD. In contrast, during pregnancy CAT-1 is inhibited. We hypothesize that female sex hormones regulate arginine transport. Arginine uptake in human umbilical vein endothelial cells (HUVEC) was determined following incubation with either 17β-estradiol (E2) or progesterone. Exposure to E2 (50 and 100 nM) for 30 min resulted in a significant increase in arginine transport and reduction in phosphorylated CAT-1 (the inactive form) protein content. This was coupled with a decrease in phosphorylated MAPK/extracellular signal-regulated kinase (ERK) 1/2. Progesterone (1 and 100 pM for 30 min) attenuated arginine uptake and increased phosphorylated CAT-1, phosphorylated protein kinase Cα (PKCα), and phosphorylated ERK1/2 protein content. GO-6976 (PKCα inhibitor) prevented the progesterone-induced decrease in arginine transport. Coincubation with both progesterone and estrogen for 30 min resulted in attenuated arginine transport. While estradiol increases arginine transport and CAT-1 activity through modulation of constitutive signaling transduction pathways involving ERK, progesterone inhibits arginine transport and CAT-1 via both PKCα and ERK1/2 phosphorylation, an effect that predominates over estradiol.

  3. Brevibacillin, a cationic lipopeptide that binds to lipoteichoic acid and subsequently disrupts cytoplasmic membrane of Staphylococcus aureus.

    PubMed

    Yang, Xu; Huang, En; Yousef, Ahmed E

    2017-01-01

    Brevibacillin is a newly-discovered antimicrobial lipopeptide produced by Brevibacillus laterosporus OSY-I1. It is active against Gram-positive bacteria, including antibiotic resistant strains. This research was initiated to investigate the mechanism of action of brevibacillin against an indicator strain, Staphylococcus aureus ATCC 6538. Results of the study proved that brevibacillin binds to lipoteichoic acid (LTA) on cell wall before interacting with cell membrane. Additionally, brevibacillin disrupts S. aureus cytoplasmic membrane by increasing its permeability, depolarization and potassium leakage. Therefore, cytoplasmic membrane serves as a major target for brevibacillin. Despite the presence of multiple sites on S. aureus cell envelope, scanning electron microscope observation didn't reveal evidence of cell lysis or any morphological defects in cells treated with brevibacillin. Based on the results of this study, we propose that the electrostatic interaction between the cationic brevibacillin and the anionic LTA helped the accumulation of the antimicrobial agent at cell surface; this was followed by translocation of the lipopeptide to the cytoplasmic membrane and disrupting its vital functions.

  4. Radical S-adenosyl methionine epimerases: regioselective introduction of diverse D-amino acid patterns into peptide natural products.

    PubMed

    Morinaka, Brandon I; Vagstad, Anna L; Helf, Maximilian J; Gugger, Muriel; Kegler, Carsten; Freeman, Michael F; Bode, Helge B; Piel, Jörn

    2014-08-04

    PoyD is a radical S-adenosyl methionine epimerase that introduces multiple D-configured amino acids at alternating positions into the highly complex marine peptides polytheonamide A and B. This novel post-translational modification contributes to the ability of the polytheonamides to form unimolecular minimalistic ion channels and its cytotoxic activity at picomolar levels. Using a genome mining approach we have identified additional PoyD homologues in various bacteria. Three enzymes were expressed in E. coli with their cognate as well as engineered peptide precursors and shown to introduce diverse D-amino acid patterns into all-L peptides. The data reveal a family of architecturally and functionally distinct enzymes that exhibit high regioselectivity, substrate promiscuity, and irreversible action and thus provide attractive opportunities for peptide engineering.

  5. Immobilized transition metal-based radical scavengers and their effect on durability of Aquivion® perfluorosulfonic acid membranes

    NASA Astrophysics Data System (ADS)

    D'Urso, C.; Oldani, C.; Baglio, V.; Merlo, L.; Aricò, A. S.

    2016-01-01

    A simple and broadly applicable preparation procedure to obtain silica-supported transition metal (namely Cr, Co and Mn)-based radical scavengers, containing sulfonic acid functionalities, is reported. These systems are widely characterised in terms of structure, bulk and surface composition and morphology by X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), X-Ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The scavenger material is loaded in ePTFE reinforced membranes prepared from Aquivion® perfluorosulfonic acid (PFSA) dispersions. All these composite membranes show longer lifetime in Accelerated Stress Tests (AST) and reduced fluoride release in Fenton's tests than the scavenger-free membranes without any loss in electrochemical performance. The Cr-scavenger-based polymer electrolyte shows a three-time larger stability than the pristine membrane.

  6. Novel Salted Anionic-Cationic Polymethacrylate Polymer Blends for Sustained Release of Acidic And Basic Drugs.

    PubMed

    Obeidat, Wasfy M; Qasim, Duaa; Nokhodchi, Ali; Al-Jabery, Ahmad; Sallam, Al-Sayed

    2016-05-02

    Since a unique matrix tablet formulation that independently controls the release of various drug types is in a great demand, the objective of this research was to develop a sustained release matrix tablet as a universal dosage form using a binary mixture of the salt forms of Eudragit polymers rather than their interpolyelectrolyte complexes. Tablets were prepared by wet granulation and compressed at different compression forces, depending on drug type. Dissolution tests were conducted using USP XXII rotating paddle apparatus at 50 rpm at 37°C in consecutive pH stages. Tablets containing Ibuprofen (IB) as a model acidic drug and Metronidazole (MD) as a model basic drug showed controlled/sustained release behavior. For IB tablets containing 80% Ibuprofen and 5% (w/w) polymeric combination; the time for 50% of the drug release was about 24 hours compared to 8.5 hours for plain tablets containing 80% IB. In case of MD, the drug release extended to about 7 hours for tablets containing 80% MD and 5% (w/w) polymeric combination, compared to about 1 hour for plain tablets containing 80% MD. In terms of extending the release of medications, the dissolution profiles of the tablets containing polymeric salts forms were found to be statistically superior to tablets prepared by direct compression of the polymers in their powdered base forms, and superior to tablets containing the same polymers granulated using isopropyl alcohol. The findings indicated the significance of combining the polymers in their salt forms in controlling the release of various drug types from matrices.

  7. Influence of a 4-aminomethylbenzoic acid residue on competitive fragmentation pathways during collision-induced dissociation of metal-cationized peptides.

    PubMed

    Osburn, Sandra; Ochola, Sila; Talaty, Erach; Van Stipdonk, Michael

    2007-01-01

    Formation of [bn+17+cat]+ is a prominent collision-induced dissociation (CID) pathway for Li+- and Na+-cationized peptides. Dissociation of protonated and Ag+-cationized peptides instead favors formation of the rival bn+/[bn-1+cat]+ species. In this study the influence of a 4-aminomethylbenzoic acid (4AMBz) residue on the relative intensities of [b(3)-1+cat]+ and [b(3)+17+cat]+ fragment ions was investigated using several model tetrapeptides including those with the general formula A(4AMBz)AX and A(4AMBz)GX (where X=G, A, V). For Li+- and Na+-cationized versions of the peptides there was a significant increase in the intensity of [b(3)-1+cat]+ for the peptides that contain the 4AMBz residue, and in some cases the complete elimination of the [b(3)+17+cat]+ pathway. The influence of the 4AMBz residue may be attributed to the fact that [b(3)-1+cat]+ would be a highly conjugated species containing an aromatic ring substituent. Comparison of CID profiles generated from Na+-cationized AAGV and A(4AMBz)GV suggests an apparent decrease in the critical energy for generation of [b(3)-1+Na]+ relative to that of [b(3)+17+Na]+ when the aromatic amino acid occupies a position such that it leads to the formation of the highly conjugated oxazolinone, thus leading to an increase in formation rate for the former compared to the latter.

  8. Acid-base treated vermiculite as high performance adsorbent: Insights into the mechanism of cationic dyes adsorption, regeneration, recyclability and stability studies.

    PubMed

    Stawiński, Wojciech; Węgrzyn, Agnieszka; Dańko, Tomasz; Freitas, Olga; Figueiredo, Sónia; Chmielarz, Lucjan

    2017-04-01

    Additional treatment with NaOH of acid activated vermiculite results in even higher increase in the adsorption capacity in comparison to samples modified only in acidic solution (first step of activation) with respect to raw material. Optimization of treatment conditions and adsorption capacity for two cationic dyes (methylene blue (MB) and astrazon red (AR)), also as binary mixture, was evaluated. The capacity, based on column studies, increased from 48 ± 2 to 203 ± 4 mg g(-1) in the case of methylene blue and from 51 ± 1 to 127 ± 2 mg g(-1) in the case of astrazon red on starting and acid-base treated material, respectively. It was shown that adsorption mechanism changes for both cationic dyes after NaOH treatment and it results in decrease of adsorption rate. In binary mixtures methylene blue is bound stronger by adsorbent and astrazon red may be removed in initial stage of adsorption. Extensive studies on desorption/regeneration process proved high efficiency in recyclable use of all materials. Although cation exchange capacity decreases due to acid treatment, after base treatment exchange properties are used more efficiently. On the other hand, increased specific surface area has less significant contribution into the adsorption potential of studied materials. Obtained adsorbents worked efficiently in 7 adsorption-regeneration cycles and loss of adsorption capacity was observed only in two first cycles.

  9. Effect of ascorbic acid (vitamin C) on the ESR spectra of the red and black hair: pheomelanin free radicals are not always present in red hair.

    PubMed

    Chikvaidze, Eduard; Topeshashvili, Maia

    2015-12-01

    Increased incidence of melanoma in the population with red hair is conditioned by synthesis of pheomelanin pigments in the skin and their phototoxic properties. The recent research has shown that free radicals of pheomelanin are produced not only by the influence of UV irradiation, but also in UV-independent pathways of oxidative stress. It has been ascertained, that the color of the hair is not always determinant of the amount of pheolemanin radicals in red hair. Therefore, in order to evaluate the risk of melanoma in different individuals, it is necessary to define the amount of free radicals of pheomelanin in red hair using ESR spectroscopy method. Besides, it is very important to find effective antioxidant, capable of neutralizing free radicals of pheomelanin. It was proved that ascorbic acid neutralizes free radicals of pheomelanin very effectively. The main goal of our research was to define the presumably optimal concentration of ascorbic acid as an antioxidant and study the kinetics of the influence of this concentration on red and black hair. It has been found out, that ascorbic acid influences the free radicals of red and black hair, and its appropriate optimal concentration is 10 mM. The obtained results can be considered in dermatology and cosmetology.

  10. [Formation of hydrogen peroxide and hydroxyl radicals in aqueous solutions of L-amino acids by the action of X-rays and heat].

    PubMed

    Shtarkman, I N; Gudkov, S V; Chernikov, A V; Bruskov, V I

    2008-01-01

    The action of 1 mM solutions of L-amino acids in 5 mM phosphate buffer, pH 7.4, on the production of hydrogen peroxide and hydroxyl radicals under the action of X-rays and heating has been studied. Hydrogen peroxide was estimated by the method of enhanced luminescence in a system luminol-paraiodophenol-peroxidase and hydroxyl radicals were determined by using the fluorescence probe coumarin-3-carboxylic acid. It was shown that amino acids can be divided by their influence on H202 formation into three groups: those that reduce the yield of H202, that do not influence it, and that increase it. A similar action of amino acids was observed upon heating, but the composition of the groups was different. All amino acids lowered the formation of hydroxyl radicals under the action of X-rays, and the most effective among them were Cys > His > Phe = Met = Trp > Tyr. Met, His and Phe lowered the amount of hydroxyl radicals by heating, Ser raised it, whereas Tyr and Pro did not change it. Thus, amino acids differently influence the formation of reactive oxygen species by the action of X-rays and heat, and some of amino acids reveal themselves as effective natural antioxidants.

  11. Molecular physiology of the insect K-activated amino acid transporter 1 (KAAT1) and cation-anion activated amino acid transporter/channel 1 (CAATCH1) in the light of the structure of the homologous protein LeuT.

    PubMed

    Castagna, M; Bossi, E; Sacchi, V F

    2009-06-01

    K-activated amino acid transporter 1 (KAAT1) and cation-anion-activated amino acid transporter/channel 1 (CAATCH1) are amino acid cotransporters, belonging to the Na/Cl-dependent neurotransmitter transporter family (also called SLC6/NSS), that have been cloned from Manduca sexta midgut. They have been thoroughly studied by expression in Xenopus laevis oocytes, and structure/function analyses have made it possible to identify the structural determinants of their cation and amino acid selectivity. About 40 mutants of these proteins have been studied by measuring amino acid uptake and current/voltage relationships. The results obtained since the cloning of KAAT1 and CAATCH1 are here discussed in the light of the 3D model of the first crystallized member of the family, the leucine transporter LeuT.

  12. Free Radical Reactions in Food.

    ERIC Educational Resources Information Center

    Taub, Irwin A.

    1984-01-01

    Discusses reactions of free radicals that determine the chemistry of many fresh, processed, and stored foods. Focuses on reactions involving ascorbic acid, myoglobin, and palmitate radicals as representative radicals derived from a vitamin, metallo-protein, and saturated lipid. Basic concepts related to free radical structure, formation, and…

  13. Abscisic acid related compounds and lignans in prunes (Prunus domestica L.) and their oxygen radical absorbance capacity (ORAC).

    PubMed

    Kikuzaki, Hiroe; Kayano, Shin-ichi; Fukutsuka, Naoko; Aoki, Asuka; Kasamatsu, Kumi; Yamasaki, Yuka; Mitani, Takahiko; Nakatani, Nobuji

    2004-01-28

    Four new abscisic acid related compounds (1-4), together with (+)-abscisic acid (5), (+)-beta-D-glucopyranosyl abscisate (6), (6S,9R)-roseoside (7), and two lignan glucosides ((+)-pinoresinol mono-beta-D-glucopyranoside (8) and 3-(beta-D-glucopyranosyloxymethyl)-2- (4-hydroxy-3-methoxyphenyl)-5-(3-hydroxypropyl)-7-methoxy-(2R,3S)-dihydrobenzofuran (9)) were isolated from the antioxidative ethanol extract of prunes (Prunus domestica L.). The structures of 1-4 were elucidated on the basis of NMR and MS spectrometric data to be rel-5-(3S,8S-dihydroxy-1R,5S-dimethyl-7-oxa-6-oxobicyclo[3,2,1]oct-8-yl)-3-methyl-2Z,4E-pentadienoic acid (1), rel-5-(3S,8S-dihydroxy-1R,5S-dimethyl-7-oxa-6-oxobicyclo[3,2,1]oct-8-yl)-3-methyl-2Z,4E-pentadienoic acid 3'-O-beta-d-glucopyranoside (2), rel-5-(1R,5S-dimethyl-3R,4R,8S-trihydroxy-7-oxa-6-oxobicyclo[3,2,1]oct-8-yl)-3-methyl-2Z,4E-pentadienoic acid (3), and rel-5-(1R,5S-dimethyl-3R,4R,8S-trihydroxy-7-oxabicyclo[3,2,1]- oct-8-yl)-3-methyl-2Z,4E-pentadienoic acid (4). The antioxidant activities of these isolated compounds were evaluated on the basis of oxygen radical absorbance capacity (ORAC). The ORAC values of abscisic acid related compounds (1-7) were very low. Two lignans (8 and 9) were more effective antioxidants whose ORAC values were 1.09 and 2.33 micromol of Trolox equiv/micromol, respectively.

  14. Dynamics of the separation of amino acid and mineral salt in the stationary dialysis of solutions with an MK-40 profiled sulfo group cation exchange membrane

    NASA Astrophysics Data System (ADS)

    Vasil'eva, V. I.; Vorob'eva, E. A.

    2012-11-01

    The conjugated diffusion transport of amino acid and mineral salt through a profiled sulfo group cation exchange membrane that simulates the extraction of amino acid from wash waters of microbiological production containing mineral components not used in synthesis is studied. The competitive nature of the conjugation of flows resulting in a decrease in the rate of the mass transfer of components and their separation factor is established from a comparative analysis of experimental data on the diffusion transfer of phenylalanine and sodium chloride in the form of hydrogen from individual and mixed solutions through a profiled sulfo group cation exchange membrane. The range of concentrations and the ratio of components in solution corresponding to the effective separation of phenylalanine and sodium chloride are determined.

  15. Free radical grafting of gallic acid (GA) on cellulose nanocrystals (CNCS) and evaluation of antioxidant reinforced gellan gum films

    NASA Astrophysics Data System (ADS)

    Criado, P.; Fraschini, C.; Salmieri, S.; Becher, D.; Safrany, A.; Lacroix, M.

    2016-01-01

    Antiradical properties were introduced on cellulose nanocrystals (CNCs) by redox pair (RP) initiator and γ-radiation treatments. Different procedures were tested on CNC, first a 2 h reaction of hydrogen peroxide (H2O2)/ascorbic acid (AA) was performed on CNC solution. γ-Radiation treatment at 20 kGy dose was then applied and immediately after GA was reacted during 24 h with the pretreated CNCs, giving CNC-H2O2-AA-γ-GA. The formation of new carboxylic acids and carbonyl groups were characterized by FT-IR at 1650 and 1730 cm-1 respectively. Carboxylic acid functionalities were also analyzed by conductometric titration where an increase from 49 to 134 mmol COOH kg-1 was found from native to irradiated CNCs. A similar increase in the carboxylic acid content (132 mmol kg-1) was observed for CNC-H2O2-AA-γ-GA, showing the highest radical scavenging properties (8 mM Trolox eq/mg CNC). Thermogravimetric analysis confirmed the structural changes onto CNC. Film packaging containing 20% of CNC-H2O2-AA-γ-GA was then added to a gellan-based film packaging. A significant improvement (p<0.05) of the tensile strength (TS), the tensile modulus (TM) and the elongation at break (EB) and water vapor permeability reduction was observed when CNC-H2O2-AA-γ-GA was added to the film packaging formulation.

  16. Evaluation of the Antiradical Properties of Phenolic Acids

    PubMed Central

    Koroleva, Olga; Torkova, Anna; Nikolaev, Ilya; Khrameeva, Ekaterina; Fedorova, Tatyana; Tsentalovich, Mikhail; Amarowicz, Ryszard

    2014-01-01

    Antioxidant capacity (AOC) against peroxyl radical and 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) radical cation was measured for a series of p-hydroxybenzoic (HB) and p-hydroxycinnamic (HC) acids at different pH. Quantum-chemical computation was performed using Gaussian 3.0 software package to calculate the geometry and energy parameters of the same compounds. Significant correlations were revealed between AOC and a number of calculated parameters. The most significant AOC descriptors for the studied compounds against peroxyl radical were found to be HOMO energy, rigidity (η) and Mulliken charge on the carbon atom in m-position to the phenolic hydroxyl. The most significant descriptor of the antioxidant properties against the ABTS radical cation at pH 7.40 is electron transfer enthalpy from the phenolate ion. The mechanism of AOC realization has been proposed for HB and HC acids against both radicals. PMID:25229820

  17. Evaluation of the antiradical properties of phenolic acids.

    PubMed

    Koroleva, Olga; Torkova, Anna; Nikolaev, Ilya; Khrameeva, Ekaterina; Fedorova, Tatyana; Tsentalovich, Mikhail; Amarowicz, Ryszard

    2014-09-16

    Antioxidant capacity (AOC) against peroxyl radical and 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) radical cation was measured for a series of p-hydroxybenzoic (HB) and p-hydroxycinnamic (HC) acids at different pH. Quantum-chemical computation was performed using Gaussian 3.0 software package to calculate the geometry and energy parameters of the same compounds. Significant correlations were revealed between AOC and a number of calculated parameters. The most significant AOC descriptors for the studied compounds against peroxyl radical were found to be HOMO energy, rigidity (η) and Mulliken charge on the carbon atom in m-position to the phenolic hydroxyl. The most significant descriptor of the antioxidant properties against the ABTS radical cation at рН 7.40 is electron transfer enthalpy from the phenolate ion. The mechanism of AOC realization has been proposed for HB and HC acids against both radicals.

  18. An anti-oxidant, α-lipoic acid conjugated oleoyl-sn-phosphatidylcholineas a helper lipid in cationic liposomal formulations.

    PubMed

    Dharmalingam, Priya; Marrapu, Balakrishna; Voshavar, Chandrashekhar; Nadella, Rasagna; Rangasami, Vignesh Kumar; Shaji, R V; Abbas, Salar; Prasad, R B N; Kaki, Shiva Shanker; Marepally, Srujan

    2017-04-01

    Development of safe non-viral carrier systems for efficient intra-cellular delivery of drugs and genes hold promise in the area of translational research. Liposome based delivery systems have emerged as one of the attractive strategies for efficient delivery of drugs and nucleic acids. To this end, number of investigations was carried on liposomal formulations using lipids for achieving higher efficiency in transfection with lower cytotoxicities. In our efforts to develop safer and efficient liposomal delivery systems, we synthesized a novel anti-oxidant lipid, α-lipoyl, oleyl-sn-phosphatidylcholine (LOPC) and used as a helper lipid in combination with a cationic amphiphile, Di-Stearyl Dihydroxy Ethyl Ammonium Chloride (DSDEAC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) at varying concentrations of LOPC. DNA binding properties of the liposomal formulations (DS, DS LA1, DS LA2 and DS LA3) revealed that increasing the percentage of single aliphatic chain lipid LOPC, did not affect the DNA binding properties. But, transfection profiles of these liposomal formulations in 3 different cell lines (HeLa, HEK 293 and MCF7) showed difference in their efficacies. Results showed that optimal percentage of LOPC i.e. 25% in DSDEAC and DOPC at 1:1 molar ratio (DS LA1) enhanced transfection as compared to DSDEAC:DOPC alone. The endosomal escape studies with NBD labelled lysotracker and Rhodamine labelled liposomal formulations revealed that DS LA1 and DS LA2 facilitated the release of genetic cargo with a better efficiency than their counter parts. Reactive Oxygen Species (ROS), a key modulator of necroptosis were lowered with the treatment of DS LA1 than other liposomal formulations. Here in, we present a novel liposomal formulation using DSDEAC and DOPC at 1:1 molar ratio doped with 25-50% (mole ratio) LOPC as an efficient delivery system for enhanced transfection with quenching of ROS levels compared to formulations without LOPC.

  19. Precipitation of Metallic Cations by the Acidic Exopolysaccharides from Bradyrhizobium japonicum and Bradyrhizobium (Chamaecytisus) Strain BGA-1

    PubMed Central

    Corzo, J.; León-Barrios, M.; Hernando-Rico, V.; Gutierrez-Navarro, A. M.

    1994-01-01

    The interaction between the acidic exopolysaccharides produced by two Bradyrhizobium strains and several metal cations has been studied. Aqueous solutions in the millimolar range of Fe3+ but not of Fe2+ precipitated the exopolysaccharides from Bradyrhizobium (Chamaecytisus) strain BGA-1 and, to a lesser extent, Bradyrhizobium japonicum USDA 110. The precipitation was pH dependent, with a maximum around pH 3. The precipitate was redissolved by changing the pH and by Fe3+ reduction or chelation. Deacetylation of B. japonicum polysaccharide increased its precipitation by Fe3+. At pH near neutrality, the polysaccharide from Bradyrhizobium (Chamaecytisus) strain BGA-1 stabilized Fe3+ solutions, despite the insolubility of Fe(OH)3. Aluminum precipitated Bradyrhizobium (Chamaecytisus) polysaccharide but not the polysaccharide produced by B. japonicum. The precipitation showed a maximum at about pH 4.8, and the precipitate was redissolved after Al3+ chelation with EDTA. Precipitation was inhibited by increases in the ionic strength over 10 mM. Bradyrhizobium (Chamaecytisus) polysaccharide was also precipitated by Th4+, Sn2+, Mn2+, and Co2+. The presence of Fe3+ increased the exopolysaccharide precipitation by aluminum. No precipitation, gelation, or increase in turbidity of polysaccharide solutions occurred when K+, Na+, Ca2+, Mg2+, Cu2+, Cd2+, Pb2+, Zn2+, Hg2+, or U6+ was added at several pH values. The results suggest that the precipitation is based on the interaction between carboxylate groups from different polysaccharide chains and the partially hydrolyzed aquoions of Fe3+, Al3+, Th4+, and Sn2+. PMID:16349466

  20. Formation of a cobalt(III)-phenoxyl radical complex by acetic acid promoted aerobic oxidation of a Co(II)salen complex.

    PubMed

    Vinck, Evi; Murphy, Damien M; Fallis, Ian A; Strevens, Robert R; Van Doorslaer, Sabine

    2010-03-01

    The activation of N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino Co(II), [Co(II)(1)], by the addition of acetic acid under aerobic conditions has been investigated by a range of spectroscopic techniques including continuous-wave EPR, HYSCORE, pulsed ENDOR, and resonance Raman. These measurements have revealed for the first time the formation of a coordinated cobalt(III)-bound phenoxyl radical labeled [Co(III)(1(*))(OAc)(n)](OAc)(m) (n = m = 1 or n = 2, m = 0). This cobalt(III)-bound phenoxyl radical is characterized by the following spin Hamiltonian parameters: g(x) = 2.0060, g(y) = 2.0031, g(z) = 1.9943, A(x) = 17 MHz, A(y) = 55 MHz, and A(z) = 14 MHz. Although the radical contains coordinated acetate(s), the experiments unambiguously proved that the phenoxyl radical is situated on ligand (1) as opposed to a phenoxyl radical ligated to cobalt in the axial position. Density functional theory computations on different models corroborate the stability of such a phenoxyl radical species and suggest the ligation of one or two acetate molecules to the complex. A mechanism is proposed, which accounts for the formation of this unusual and extremely robust phenoxyl radical, never previously observed for [Co(1)].

  1. Higher reactivity of apolipoprotein B-100 and alpha-tocopherol compared to sialic acid moiety of low-density lipoprotein (LDL) in radical reaction.

    PubMed

    Matsukawa, Nao; Nariyama, Yoko; Hashimoto, Ryoko; Kojo, Shosuke

    2003-09-01

    Radical reaction of low-density lipoprotein (LDL) is a key step in atherogenesis and causes both a decrease in the sialic acid moiety and modification of apolipoprotein B-100 (apoB). Although apoB modification (cross-link and fragmentation) increases in atherosclerosis, the change in apoB-bound sialic acid in atherosclerosis is controversial. To elucidate the physiological implications of desialylation of LDL by radical reaction, the reactivity of sialic acid of LDL was compared with that of apoB, which underwent facile fragmentation in radical reactions. ApoB was determined by immunoblot analysis with anti-apoB antiserum, and the sialic acid moiety was measured by blot analysis with a biotin-bound lectin [biotin-SSA from Japanese elderberry (Sambucus sieboldiana)] specific to sialic acid. When human LDL was oxidized with Cu(2+) at 37 degrees C, apoB and apoB-attached sialic acid decreased simultaneously. Comparison of the staining bands with anti-apoB and with biotin-SSA shows that sialic acid moieties still remain on fragmented apoB proteins, indicating that the decrease in sialic acid is much slower than that of apoB fragmentation. In addition, human plasma was oxidized with 400 microM of Cu(2+) at 37 degrees C. Similar analysis indicates that the decrease in sialic acid attached to apoB also results from the fragmentation of apoB. This study indicates that the fragmentation of apoB proceeds at a much faster rate than the decrease in sialic acid content when a free radical reaction is induced in isolated LDL as well as in plasma LDL exposed to Cu(2+)-induced oxidative stress. On the basis of these results, the modification of apoB is much more sensitive than the decrease in sialic acid as an indicator of oxidative stress.

  2. Electrochemical genosensor based on peptide nucleic acid-mediated PCR and asymmetric PCR techniques: Electrostatic interactions with a metal cation.

    PubMed

    Kerman, Kagan; Vestergaard, Mun'delanji; Nagatani, Naoki; Takamura, Yuzuru; Tamiya, Eiichi

    2006-04-01

    The unique structure of peptide nucleic acids (PNAs), linking the N-(2-aminoethyl)glycine units that create a neutral backbone, and prevent it from acting as a primer for DNA polymerase, has been utilized in an electrochemical biosensor scheme for simple and sensitive detection of hybridization. When the PNA is targeted against a single-nucleotide polymorphism (SNP) or wild-type site on the gene, PNA-mediated polymerase chain reaction (PCR) clamping method effectively blocks the formation of a PCR product. In our report, PNA probe for PCR clamping was targeted against the wild-type site of alcohol dehydrogenase. The electrostatic interactions between the negatively charged DNA and neutral PNA molecules with redox-active metal cation cobalt(III)hexamine ([Co(NH3)6]3+) were monitored using differential pulse voltammetry. The electrostatic binding of [Co(NH3)6]3+ to DNA provided the basis for the discrimination against PNA/PNA, PNA/DNA, and DNA/DNA hybrid molecules. We have optimized the experimental conditions, such as probe concentration, [Co(NH3)6]3+ concentration, accumulation time for [Co(NH3)6]3+, and target concentration. A new pretreatment method has also been employed to allow fast and simple detection of hybridization reaction between the PCR amplicon and the probe on glassy carbon electrode (GCE) surface. This method was based on the application of a high-temperature treatment (95 degrees C, 5 min), followed by a 1-min incubation in the presence of DNA primers. The excess concentration of DNA primers prevented the rehybridization of the denatured strands, while enabling the target gene sequence to bind with the immobilized probe. Additionally, asymmetric PCR was employed to detect the presence of genetically modified organism in standard Roundup Ready soybean samples. The amplicons of asymmetric PCR, which were predominantly single-stranded DNA as a result of unequal primer concentration, hybridized with the DNA probe on the sensor surface efficiently. The

  3. DFT investigation of Ni(II) adsorption onto MA-DTPA/PVDF chelating membrane in the presence of coexistent cations and organic acids.

    PubMed

    Song, Laizhou; Zhao, Xiaodan; Fu, Jie; Wang, Xiuli; Sheng, Yiping; Liu, Xiaowei

    2012-01-15

    Melamine-diethylenetriaminepentaacetic acid/polyvinylidene fluoride (MA-DTPA/PVDF) chelating membrane bearing polyaminecarboxylate groups was used to remove Ni(II) from nickel plating effluents. Adsorption experiments were conducted to study the adsorption of the membrane towards Ni(II) in Ni(II)-Ca(II), Ni(II)-NH(4)(+), Ni(II)-Fe(III) binary systems, and Ni(II)-lactic acid, Ni(II)-succinic acid and Ni(II)-citric acid complex systems. For the ternary nickel plating processes, the effects of 3d transition metals including Fe(II), Co(II), Cu(II) and Zn(II) on Ni(II) adsorption were evaluated. The influences of the aforementioned coexistent cations and organic acids were elucidated by the continuum solvation model (COSMO)-corrected density functional theory (DFT) method. Geometries and complexation energies were analyzed for metal-MA-DTPA and Ni(II)-organic acid complexes. DFT results accord with the experimental data, indicating that DFT is helpful to evaluate the complexation between the membrane and metal cations. The coexistent Ca(II) tends to form more stable complex with MA-DTPA ligand than NH(4)(+) and Fe(III), and can interfere with the formation of Ni(II)-MA-DTPA complex. The complexing sequence of 3d metals with MA-DTPA ligand is Zn(II)acid complexes follow the order of lactic acidacidacid, but cannot be comparable to that of Ni(II)-MA-DTPA complex.

  4. Measurement of hydroxyl radical-generated methane sulfinic acid by high-performance liquid chromatography and electrochemical detection.

    PubMed

    Jahnke, L S

    1999-05-01

    A liquid chromatographic (HPLC) method has been developed for direct quantitative determination of methane sulfinic acid (MSA) produced by hydroxyl radical oxidation of dimethyl sulfoxide. This method measures MSA directly by HPLC separation and electrochemical oxidation following rapid extraction from intact cells. MSA can be measured in tissue extracts at 0.04 nmol (equivalent to 2 microM). Using this technique, MSA production in paraquat-treated bean leaves is demonstrated. When compared with the widely used dye-binding technique, this method simplifies the preparation of the extract by eliminating two steps required in the dye-binding method: removal of interfering lipophilic compounds and the derivitization (color reaction) of the MSA.

  5. Highly selective capture of nucleosides with boronic acid functionalized polymer brushes prepared by atom transfer radical polymerization.

    PubMed

    Cheng, Ting; Zhu, Shuqiang; Zhu, Bin; Liu, Xiaoyan; Zhang, Haixia

    2016-04-01

    The nucleoside or modified nucleoside level in biological fluids reflects the pathological or physiological state of the body. Boronate affinity absorbents are widely used to selectively extract nucleosides from complex samples. In this work, a novel functionalized absorbent was synthesized by attaching 4-mercaptophenylboronic acid to gold nanoparticles on modified attapulgite. The surface of the attapulgite was modified by poly(acryloyloxyethyltrimethyl ammonium chloride) by atom transfer radical polymerization, creating many polymer brushes on the surface. The resultant material exhibited superior binding capacity (30.83 mg/g) for adenosine and was able to capture cis-diol nucleosides from 1000-fold interferences. Finally, to demonstrate its potential for biomolecule extraction, this boronate affinity material was used to preconcentrate nucleosides from human urine and plasma.

  6. Sulphonic acid strong cation-exchange restricted access columns in sample cleanup for profiling of endogenous peptides in multidimensional liquid chromatography. Structure and function of strong cation-exchange restricted access materials.

    PubMed

    Machtejevas, E; Denoyel, R; Meneses, J M; Kudirkaite, V; Grimes, B A; Lubda, D; Unger, K K

    2006-08-04

    In this work, the pore structural parameters and size exclusion properties of LiChrospher strong cation-exchange and reverse phase restricted access materials (RAM) are analysed. The molecular weight size exclusion limit for polystyrenes was found to be about 17.7 kDa, while for standard proteins, the molecular weight size exclusion limit was higher, at approximately 25 kDa. The average pore diameter on a volume basis calculated from the pore network model changes from 8.5 nm (native LiChrospher) to 8.6 nm (diol derivative) to 8.2 nm (sulphonic acid derivative) to 6.9 nm (n-octadecyl derivative). Additional characterisations were performed on restricted access materials with nitrogen sorption at 77 K, water adsorption at 25 degrees C, intrusion-extrusion of water (in order to evaluate the hydrophobic properties of the pores of the hydrophobic RAM), and zeta potential measurements by microelectrophoresis. For peptide analysis out of the biofluids, the strong cation-exchange functionality seems to be particularly suitable mainly because of the high loadability of the strong cation-exchange restricted access material (SCX-RAM) and the fact that one can work under non-denaturing conditions to perform effective chromatographic separations. For bacitracin, the dynamic capacity of the SCX-RAM columns does not reach its maximum value in the analysed range. For lysozyme, the dynamic capacity reaches a value of 0.08 mg/ml of column volume before column is overloaded. Additionally, the proper column operating conditions that lead to the total effective working time of the RAM column to be equal to approximately 500 injections (depending on the type of sample), is comprehensively described. The SCX-RAM column was used in the same system analysing urine samples for the period of 1 month (approximately 150 injections) with run-to-run reproducibility below 5% RSD and below 10% RSD for the relative fractions.

  7. Systemic elevations of free radical oxidation products of arachidonic acid are associated with angiographic evidence of coronary artery disease.

    PubMed

    Shishehbor, Mehdi H; Zhang, Renliang; Medina, Hector; Brennan, Marie-Luise; Brennan, Danielle M; Ellis, Stephen G; Topol, Eric J; Hazen, Stanley L

    2006-12-01

    Oxidant stress is widely believed to participate in cardiovascular disease pathogenesis. However, progress in defining appropriate systemic antioxidant targeted therapies has been hindered by uncertainty in defining clinically relevant systemic oxidant stress measures. In a case control study, 50 subjects with CAD (>50% stenosis in one or more major coronary vessels) and 54 without CAD (<30% stenosis in all major coronary vessels) were tested. Plasma was isolated and stored under conditions designed to prevent artificial lipid peroxidation. Systemic levels of multiple (n=9) specific fatty acid oxidation products including individual hydroxyoctadecadienoic acids (HODEs), hydroxyeicosatetraenoic acids (HETEs), and F(2)-isoprostanes were simultaneously measured by high-performance liquid chromatography (HPLC) with on-line tandem mass spectrometry, along with traditional risk factors and C-reactive protein (CRP) levels. Of the markers monitored, only 9-HETE and F(2)-isoprostanes, both products of free radical-mediated arachidonic acid oxidation, were significantly elevated in patients with angiographically defined CAD (9-HETE, 8.7 +/- 4 vs 6.8 +/- 4 micromol/mol arachidonate, P = 0.011; and F(2)-isoprostanes, 9.4 +/- 5 vs 6.2 +/- 3 micromol/mol arachidonate, P < 0.001). In multivariable analyses with simultaneous adjustment for Framingham risk score and C-reactive protein, 9-HETE (4th quartile OR = 4.8, 95% CI=1.3 to 17.1; P = 0.016) and F(2)-isoprostanes (4th quartile OR=9.7, 95% CI=2.56 to 36.9; P < 0.001) remained strong and independent predictors of CAD risk. Systemic levels of 9-HETE and F(2)-isoprostanes are independently associated with angiographic evidence of CAD and appear superior to other specific oxidation products of arachidonic and linoleic acids as predictors of the presence of angiographically evident coronary artery disease.

  8. A global assessment of precipitation chemistry and deposition of sulfur, nitrogen, sea salt, base cations, organic acids, acidity and pH, and phosphorus

    NASA Astrophysics Data System (ADS)

    Vet, Robert; Artz, Richard S.; Carou, Silvina

    2014-08-01

    Investigating and assessing the chemical composition of precipitation and atmospheric deposition is essential to understanding how atmospheric pollutants contribute to contemporary environmental concerns including ecosystem acidification and eutrophication, loss of biodiversity, air pollution and global climate change. Evidence of the link between atmospheric deposition and these environmental issues is well established. The state of scientific understanding of this link is that present levels of atmospheric deposition of sulfur and nitrogen adversely affect terrestrial and aquatic ecosystems, putting forest sustainability and aquatic biodiversity at risk. Nitrogen and phosphorus loadings are linked to impacts on the diversity of terrestrial and aquatic vegetation through biological cycling, and atmospheric deposition plays a major role in the emission-transport-conversion-loss cycle of chemicals in the atmosphere as well as the formation of particulate matter and ozone in the troposphere. Evidence also shows that atmospheric constituents are changing the earth's climate through direct and indirect atmospheric processes. This Special Issue, comprising a single article titled "A global assessment of precipitation chemistry and deposition of sulfur, nitrogen, sea salt, base cations, organic acids, acidity and pH, and phosphorus", presents a recent comprehensive review of precipitation chemistry and atmospheric deposition at global and regional scales. The information in the Special Issue, including all supporting data sets and maps, is anticipated to be of great value not only to the atmospheric deposition community but also to other science communities including those that study ecosystem impacts, human health effects, nutrient processing, climate change, global and hemispheric modeling and biogeochemical cycling. Understanding and quantifying pollutant loss from the atmosphere is, and will remain, an important component of each of these scientific fields as they

  9. Thioglycolic acid grafted onto silica gel and its properties in relation to extracting cations from ethanolic solution determined by calorimetric technique.

    PubMed

    Arakaki, Luiza N H; Espínola, José G P; da Fonseca, Maria G; de Oliveira, Severino F; de Sousa, Antonio N; Arakaki, Tomaz; Airoldi, Claudio

    2004-05-01

    Thioglycolic acid was immobilized onto silica gel surface using 3-aminopropyltrimethoxysilane as precursor silylating agent to yield silica. The amount of thioglycolic acid immobilized was 1.03 mmol per gram of silica. This new surface displayed a chelating moiety containing nitrogen, sulfur, and oxygen basic centers which are potentially capable of extracting cations from ethanolic so