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Journal of Research of the National... 1972The pulse radiolysis of gaseous neopentane has been investigated in the absence and presence of electron scavengers (SF, CDI, CCl). Deuterium labeling experiments show...
The pulse radiolysis of gaseous neopentane has been investigated in the absence and presence of electron scavengers (SF, CDI, CCl). Deuterium labeling experiments show that the stable product molecules can be accounted for by (a) radical combination reactions involving mainly CH and H; (b) hydride ion transfer reactions involving CH , CH , and CH ; (c) neutralization reactions of CH and CH ; and (d) unimolecular dissociation of the parent ion (CH ) and of electronically excited neopentane. Neutralization of the -CH ion, which is the major positive ion in the system occurs as follows: (a) -CH + e → -CH + H and (b) -CH + → 2CH + CH. It is shown that CH produced in hydride ion transfer reaction C H + neo-CH → C H + CH (where C H = CH , CH , and CH ) rearranges to the CHC(CH)CHCH structure prior to neutralization. A detailed accounting of all products produced in the unimolecular and bimolecular reactions led to the conclusion that the ratio of neutral electronically excited molecules to parent ions (N/N) is 0.28.
PubMed: 34565865
DOI: 10.6028/jres.076A.032 -
Journal of the American Chemical Society Sep 2010Manganese superoxide dismutase (MnSOD) from different species differs in its efficiency in removing high concentrations of superoxide (O(2)(-)), due to different levels...
Manganese superoxide dismutase (MnSOD) from different species differs in its efficiency in removing high concentrations of superoxide (O(2)(-)), due to different levels of product inhibition. Human MnSOD exhibits a substantially higher level of product inhibition than the MnSODs from bacteria. In order to investigate the mechanism of product inhibition and whether it is a feature common to eukaryotic MnSODs, we purified MnSOD from Saccharomyces cerevisiae (ScMnSOD). It was a tetramer with 0.6 equiv of Mn per monomer. The catalytic activity of ScMnSOD was investigated by pulse radiolysis and compared with human and two bacterial (Escherichia coli and Deinococcus radiodurans) MnSODs. To our surprise, ScMnSOD most efficiently facilitates removal of high concentrations of O(2)(-) among these MnSODs. The gating value k(2)/k(3) that characterizes the level of product inhibition scales as ScMnSOD > D. radiodurans MnSOD > E. coli MnSOD > human MnSOD. While most MnSODs rest as the oxidized form, ScMnSOD was isolated in the Mn(2+) oxidation state as revealed by its optical and electron paramagnetic resonance spectra. This finding poses the possibility of elucidating the origin of product inhibition by comparing human MnSOD with ScMnSOD.
Topics: Biocatalysis; Deinococcus; Escherichia coli; Humans; Manganese; Oxidation-Reduction; Saccharomyces cerevisiae; Superoxide Dismutase
PubMed: 20726524
DOI: 10.1021/ja104179r -
The Journal of Biological Chemistry Jan 1975The lactate dehydrogenase-catalyzed chain oxidation of NADH (LDH-NADH) by the superoxide radicals, HO2 and O2, has been studied with pulse radiolysis in the pH range...
The lactate dehydrogenase-catalyzed chain oxidation of NADH (LDH-NADH) by the superoxide radicals, HO2 and O2, has been studied with pulse radiolysis in the pH range between 4.5 and 9.0. The rate constants for the oxidation of the LDH-NADH by HO2 and O2 determined at 23 degrees are 1.2 times 10-6 M(-1) s(-1) and 3.6 times 10-4 M(-1) s(-1), respectively. The latter represents an activation of over 1000-fold by the enzyme. A chain reaction mechanism consistent with the results from these kinetic studies has been proposed.
Topics: Animals; Binding Sites; Enzyme Activation; Free Radicals; Hydrogen-Ion Concentration; Kinetics; L-Lactate Dehydrogenase; Mathematics; Myocardium; NAD; Oxidation-Reduction; Oxygen; Protein Binding; Spectrophotometry, Ultraviolet; Swine; Temperature; Time Factors
PubMed: 237890
DOI: No ID Found -
International Journal of Molecular... Sep 2020We report the generation of gold nanoparticles (AuNPs) from the aqueous solution of chloro(2,2',2″-terpyridine)gold(III) ion ([Au(tpy)Cl]) through X-ray radiolysis and...
We report the generation of gold nanoparticles (AuNPs) from the aqueous solution of chloro(2,2',2″-terpyridine)gold(III) ion ([Au(tpy)Cl]) through X-ray radiolysis and optical excitation at a synchrotron. The original purpose of the experiment was to investigate the photoinduced structural changes of [Au(tpy)Cl] upon 400 nm excitation using time-resolved X-ray liquidography (TRXL). Initially, the TRXL data did not show any signal that would suggest structural changes of the solute molecule, but after an induction time, the TRXL data started to show sharp peaks and valleys. In the early phase, AuNPs with two types of morphology, dendrites, and spheres, were formed by the reducing action of hydrated electrons generated by the X-ray radiolysis of water, thereby allowing the detection of TRXL data due to the laser-induced lattice expansion and relaxation of AuNPs. Along with the lattice expansion, the dendritic and spherical AuNPs were transformed into smaller, raspberry-shaped AuNPs of a relatively uniform size via ablation by the optical femtosecond laser pulse used for the TRXL experiment. Density functional theory calculations confirm that the reduction potential of the metal complex relative to the hydration potential of X-ray-generated electrons determines the facile AuNP formation observed for [Au(tpy)Cl].
Topics: Electrons; Gold; Gold Compounds; Laser Therapy; Lasers; Metal Nanoparticles; Particle Size; Pulse Radiolysis; Solutions; Synchrotrons; Water; X-Ray Diffraction; X-Rays
PubMed: 32992497
DOI: 10.3390/ijms21197125 -
Chemical Science Sep 2021Conjugated molecular chains have the potential to act as "molecular wires" that can be employed in a variety of technologies, including catalysis, molecular electronics,...
Conjugated molecular chains have the potential to act as "molecular wires" that can be employed in a variety of technologies, including catalysis, molecular electronics, and quantum information technologies. Their successful application relies on a detailed understanding of the factors governing the electronic energy landscape and the dynamics of electrons in such molecules. We can gain insights into the energetics and dynamics of charges in conjugated molecules using time-resolved infrared (TRIR) detection combined with pulse radiolysis. Nitrile (C[triple bond, length as m-dash]N) bands can act as IR probes for charges, based on IR frequency shifts, because of their exquisite sensitivity to the degree of electron delocalization and induced electric field. Here, we show that the IR intensity and linewidth can also provide unique and complementary information on the nature of charges. Quantifications of IR intensity and linewidth in a series of nitrile-functionalized oligophenylenes reveal that the C[triple bond, length as m-dash]N vibration is coupled to the nuclear and electronic structural changes, which become more prominent when an excess charge is present. We synthesized a new series of ladder-type oligophenylenes that possess planar aromatic structures, as revealed by X-ray crystallography. Using these, we demonstrate that C[triple bond, length as m-dash]N vibrations can report charge fluctuations associated with nuclear movements, namely those driven by motions of flexible dihedral angles. This happens only when a charge has room to fluctuate in space.
PubMed: 34667576
DOI: 10.1039/d1sc03455c -
International Journal of Molecular... Dec 2023In the retina, retinoids involved in vision are under constant threat of oxidation, and their oxidation products exhibit deleterious properties. Using pulse radiolysis,...
In the retina, retinoids involved in vision are under constant threat of oxidation, and their oxidation products exhibit deleterious properties. Using pulse radiolysis, this study determined that the bimolecular rate constants of scavenging cation radicals of retinoids by taurine are smaller than 2 × 10 Ms whereas lutein scavenges cation radicals of all three retinoids with the bimolecular rate constants approach the diffusion-controlled limits, while zeaxanthin is only 1.4-1.6-fold less effective. Despite that lutein exhibits greater scavenging rate constants of retinoid cation radicals than other antioxidants, the greater concentrations of ascorbate in the retina suggest that ascorbate may be the main protectant of all visual cycle retinoids from oxidative degradation, while α-tocopherol may play a substantial role in the protection of retinaldehyde but is relatively inefficient in the protection of retinol or retinyl palmitate. While the protection of retinoids by lutein and zeaxanthin appears inefficient in the retinal periphery, it can be quite substantial in the macula. Although the determined rate constants of scavenging the cation radicals of retinol and retinaldehyde by dopa-melanin are relatively small, the high concentration of melanin in the RPE melanosomes suggests they can be scavenged if they are in proximity to melanin-containing pigment granules.
Topics: Retinoids; Vitamin A; Melanins; Retinaldehyde; Lutein; Zeaxanthins; Taurine; Cations
PubMed: 38203675
DOI: 10.3390/ijms25010506 -
The Journal of Physical Chemistry. B Nov 2008The intramolecular reaction of cysteine thiyl radicals with peptide and protein alphaC-H bonds represents a potential mechanism for irreversible protein oxidation. Here,...
Reversible intramolecular hydrogen transfer between cysteine thiyl radicals and glycine and alanine in model peptides: absolute rate constants derived from pulse radiolysis and laser flash photolysis.
The intramolecular reaction of cysteine thiyl radicals with peptide and protein alphaC-H bonds represents a potential mechanism for irreversible protein oxidation. Here, we have measured absolute rate constants for these reversible hydrogen transfer reactions by means of pulse radiolysis and laser flash photolysis of model peptides. For N-Ac-CysGly6 and N-Ac-CysGly2AspGly3, Cys thiyl radicals abstract hydrogen atoms from Gly with k(f) = (1.0-1.1 x 10(5) s(-1), generating carbon-centered radicals, while the reverse reaction proceeds with k(r) = (8.0-8.9) x 10(5) s(-1). The forward reaction shows a normal kinetic isotope effect of k(H)/k(D) = 6.9, while the reverse reaction shows a significantly higher normal kinetic isotope effect of 17.6, suggesting a contribution of tunneling. For N-Ac-CysAla2AspAla3, cysteine thiyl radicals abstract hydrogen atoms from Ala with k(f) = (0.9-1.0) x 10(4) s(-1), while the reverse reaction proceeds with k(r) = 1.0 x 10(5) s(-1). The order of reactivity, Gly > Ala, is in accord with previous studies on intermolecular reactions of thiyl radicals with these amino acids. The fact that k(f) < k(r) suggests some secondary structure of the model peptides, which prevents the adoption of extended conformations, for which calculations of homolytic bond dissociation energies would have predicted k(f) > k(r). Despite k(f) < k(r), model calculations show that intramolecular hydrogen abstraction by Cys thiyl radicals can lead to significant oxidation of other amino acids in the presence of physiologic oxygen concentrations.
Topics: Alanine; Cysteine; Glycine; Hydrogen; Kinetics; Peptides; Photochemistry
PubMed: 18973367
DOI: 10.1021/jp805133u -
The Journal of Physical Chemistry. B Feb 20235-Azidomethyl-2'-deoxyuridine (5-AmdU, ) has been successfully employed for the metabolic labeling of DNA and fluorescent imaging of live cells. 5-AmdU also demonstrated...
5-Azidomethyl-2'-deoxyuridine (5-AmdU, ) has been successfully employed for the metabolic labeling of DNA and fluorescent imaging of live cells. 5-AmdU also demonstrated significant radiosensitization in breast cancer cells via site-specific nitrogen-centered radical (π-aminyl (U-5-CH-NH), , and σ-iminyl (U-5-CH═N), ) formation. This work shows that these nitrogen-centered radicals are not formed via the reduction of the azido group in 6-azidomethyluridine (6-AmU, ). Radical assignments were performed using electron spin resonance (ESR) in supercooled solutions, pulse radiolysis in aqueous solutions, and theoretical (DFT) calculations. Radiation-produced electron addition to leads to the facile N loss, forming a stable neutral C-centered allylic radical (U-6-CH, ) through dissociative electron attachment (DEA) via the transient negative ion, TNI (U-6-CH-N), in agreement with DFT calculations. In contrast, TNI (U-5-CH-N) of , via facile N loss (DEA) and protonation from the surrounding water, forms radical . Subsequently, undergoes rapid H-atom abstraction from and produces the metastable intermediate α-azidoalkyl radical (U-5-CH-N). U-5-CH-N converts facilely to radical . N loss from U-6-CH-N is thermodynamically controlled, whereas N loss from U-5-CH-N is dictated by protonation from the surrounding waters and resonance conjugation of the azidomethyl side chain at C5 with the pyrimidine ring.
Topics: Nitrogen; Nucleosides; Azides; Electrons; Electron Spin Resonance Spectroscopy; Water; Free Radicals
PubMed: 36780335
DOI: 10.1021/acs.jpcb.2c08257 -
FEBS Letters Jul 2004Peroxiredoxins are an ubiquitous family of peroxidases widely distributed among prokaryotes and eukaryotes. Peroxiredoxin 5, which is the last discovered mammalian...
Peroxiredoxins are an ubiquitous family of peroxidases widely distributed among prokaryotes and eukaryotes. Peroxiredoxin 5, which is the last discovered mammalian member, was previously shown to reduce peroxides with the use of reducing equivalents derived from thioredoxin. We report here that human peroxiredoxin 5 is also a peroxynitrite reductase. Analysis of peroxiredoxin 5 mutants, in which each of the cysteine residues was mutated, suggests that the nucleophilic attack on the O-O bond of peroxynitrite is performed by the N-terminal peroxidatic Cys(47). Moreover, with the use of pulse radiolysis, we show that human peroxiredoxin 5 reduces peroxynitrite with an unequalled high rate constant of (7+/-3)x10(7) M(-1)s(-1).
Topics: Amino Acid Sequence; Animals; Humans; Invertebrates; Kinetics; Mammals; Molecular Sequence Data; Oxidoreductases; Peroxidases; Peroxiredoxins; Sequence Alignment; Sequence Homology, Amino Acid
PubMed: 15280035
DOI: 10.1016/j.febslet.2004.06.080 -
European Journal of Biochemistry Oct 19821. Pulse-radiolysis experiments were performed in the presence of methyl viologen and cytochrome c3. After the pulse, methyl viologen radicals are formed and the...
A pulse-radiolysis study of cytochrome c3. Kinetics of the reduction of cytochrome c3 by methyl viologen radicals and the characterisation of the redox properties of cytochrome c3 from Desulfovibrio vulgaris (Hildenborough).
1. Pulse-radiolysis experiments were performed in the presence of methyl viologen and cytochrome c3. After the pulse, methyl viologen radicals are formed and the kinetics of these radicals with cytochrome c3 are studied, The reaction between cytochrome c3 and methyl viologen radicals (MV+) is diffusion controlled. The ionic strength dependence and the pH-dependence of this reaction were studied. From the ionic strength dependence (at pH 7.8) we found that the net charge of the fully oxidized cytochrome c3 molecule was Z = + 4.7 +/- 0.7. 2. After the pulse an equilibrium is reached for the reaction of MV+ with cytochrome c3. From this equilibrium an apparent midpoint potential can be obtained. The apparent midpoint potential of this multihaem molecule was found to depend on the degree of reduction, alpha. With the help of the Nernst equation an empirical equation is obtained to describe this dependence of the midpoint potential: E0 = - 0.250 - 0.088 alpha (in V). 3. An estimation is made of the energy of interaction between the haems due to electrostatic interactions (delta epsilon less than 32 mV) and due to ionic strength effects (- 12 mV less than delta epsilon less than 26 mV). The results suggest that the redox properties of the individual haems in the cytochrome c3 molecule are dependent on the degree of reduction of the other haems in the molecule. 4. The reaction of cytochrome c3 with MV+ or with ethanol radicals (EtOH) has been compared with the reactions of horse-heart cytochrome c and of metmyoglobin with the same radicals. The reaction of MV+ or EtOH with horse-heart cytochrome c is found to be diffusion controlled; the reactions with metmyoglobin on the other hand are most probably controlled by an activation energy.
Topics: Animals; Bacterial Proteins; Chemical Phenomena; Chemistry; Cytochrome c Group; Desulfovibrio; Free Radicals; Horses; Kinetics; Magnetic Resonance Spectroscopy; Metmyoglobin; Oxidation-Reduction; Paraquat
PubMed: 6293820
DOI: No ID Found