G. Albarrán

Universidad Nacional Autónoma de México, Ciudad de México, The Federal District, Mexico

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Publications (37)42.98 Total impact

  • Guadalupe Albarran, Maribel Esparza, Edith Mendoza
    Radiation Physics and Chemistry. 02/2015; 107.
  • Guadalupe Albarran, J. Sergio Munguia
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    ABSTRACT: Studies of the radiolytic oxidation of xylenes in aqueous solutions show that, as in the case of toluene, OH radical predominantly adds to the unsubstituted ring positions of the xylenes. Abstraction of H from the methyl groups and addition at the substituted positions is only of minor importance. The distribution of phenolic products observed in the case of meta-xylene shows that OH radical preferentially adds at the positions ortho and para to the methyl substituents. The yield for addition at the position meta to both methyl substituents is significantly less than for addition at the meta position of toluene. This difference indicates that the methyl substituents in meta-xylene act in together to reduce the negative charge at the 5 position.
    Radiation Physics and Chemistry. 01/2014; 97:90–94.
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    ABSTRACT: Absorption spectrophotometric and mass spectrometric properties of 1,2-benzoquinone, prepared in aqueous solution by the hexachloroiridate(IV) oxidation of catechol and isolated by HPLC, are reported. Its absorption spectrum has a broad moderately intense band in the near UV with an extinction coefficient of 1370 M(-1)cm(-1) at its 389 nm maximum. The oscillator strength of this band contrasts with those of the order-of-magnitude stronger approximately 250 nm bands of most 1,4-benzoquinones. Gaussian analysis of its absorption spectrum indicates that it also has modestly intense higher energy bands in the 250-320 nm region. In atmospheric pressure mass spectrometric studies 1,2-benzoquinone exhibits very strong positive and negative mass 109 signals that result from the addition of protons and hydride ions in APCI and ESI ion sources. It is suggested that the hydride adduct is formed as the result of the highly polar character of ortho-quinone. On energetic collision the hydride adduct loses an H atom to produce the 1,2-benzosemiquinone radical anion. The present studies also show that atmospheric pressure mass spectral patterns observed for catechol are dominated by signals of 1,2-benzoquinone resulting from oxidation of catechol in the ion sources. Computational studies of the electronic structures of 1,2-benzoquinone, its proton and hydride ion adducts, and 1,2-benzosemiquinone radical anion are reported. These computational studies show that the structures of the proton and hydride adducts are similar and indicate that the hydride adduct is the proton adduct of a doubly negatively charged 1,2-benzoquinone. The contrast between the properties of 1,2- and 1,4-benzoquinone provides the basis for considerations on the effects of conjugation in aromatic systems.
    The Journal of Physical Chemistry A 07/2010; 114(28):7470-8. · 2.77 Impact Factor
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    Guadalupe Albarran, Robert H Schuler
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    ABSTRACT: HPLC studies of the oxidation of substituted hydroquinones show that the corresponding quinones can, in most cases, be produced quantitatively by two electron transfer to hexachloroiridate(IV). As a consequence the chromatographic and spectroscopic properties of substituted quinones that are not readily available can be determined without the necessity of preparation of an isolatable sample. Absorption spectra and extinction coefficients of bromoquinone, chloroquinone, hydroxyquinone and carboxyquinone anion at pH 7 are reported as illustrative examples. All have intense absorption bands at approximately 250nm that are characteristic of quinones. Oxidation of carboxyhydroquinone at low pH is, however, anomalous in that a hydroxylated carboxyquinone is produced as the result of four electron transfer to hexachloroiridate.
    Talanta 02/2008; 74(4):844-50. · 3.50 Impact Factor
  • Guadalupe Albarrán, Fernando Ramírez-Cahero, Roustam Aliev
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    ABSTRACT: Aqueous solutions of pyridoxine (1mM) without or with additive of K3[Fe(CN)6] (2.5mM) were gamma-irradiated at different doses and dose rate of 2.16kGy/h in the absence of air, in the presence of air or by their saturation with N2O. The radiolytic products were analyzed with HPLC, mass spectrometry and UV spectroscopy. 2,4,5-Trihydroxymethyl-3-pyridinol, pyridoxal, isopyridoxal and 6-hydroxypyridoxine were formed by radiolysis in the absence of K3[Fe(CN)6], and their concentrations were much higher in samples saturated with N2O. Pyridoxi-3,6-quinone was found by radiolysis under all the above-mentioned conditions but only in the presence of K3[Fe(CN)6]. Besides, the pyridoxal formation increased in the presence of this oxidizing agent. G values of pyridoxal formation and pyridoxine degradation were quantified. Some details of the radiolytic product formation were discussed.
    Radiation Physics and Chemistry 01/2008; 77(5):605-611. · 1.38 Impact Factor
  • Guadalupe Albarran, Robert H Schuler
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    ABSTRACT: Initial radiation chemical yields of 1.48 (2), 0.24 (2), and 2.01 molecules per 100 eV of absorbed energy are reported for addition of *OH radical to each of the ortho, meta, and para positions of phenol. These yields represent 91% of the yield of 5.96 expected for *OH addition to 5 mM phenol and are in general agreement with other previous measurements. Pulse radiolysis experiments show that phenoxy radical is produced in a yield of approximately 0.42 as a result of addition of *OH at phenol's ipso position. The total of these yields (5.84) accounts for the addition of virtually all of the expected *OH radicals. The relative yields for addition to the ortho, meta, and para positions provide a measure of the charge distribution in phenol that correlates quite well with the unpaired spin distribution in phenoxyl radical. This correlation indicates that the OH substituent similarly affects the charge distribution on the aromatic ring of phenol and the unpaired spin distribution in the phenoxyl radical.
    The Journal of Physical Chemistry A 05/2007; 111(13):2507-10. · 2.77 Impact Factor
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    Guadalupe Albarran, Robert H Schuler
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    ABSTRACT: The concerted effects of hydroxyl and methyl substituents in controlling the site of .OH radical attack on aromatics in aqueous solutions are explored using the cresols as typical examples. The distributions of dihydroxytoluenes produced in the radiolysis of aqueous solutions of the cresols containing ferricyanide as a radical oxidant were examined by capillary electrophoretic and liquid chromatographic methods. Because .OH is a strong electrophile, it adds preferentially at the electron-rich sites of an aromatic ring. As a result, the observed distributions of dihydroxytoluenes reflect the charge distributions in the cresols. It is shown that in the case of m-cresol the hydroxyl substituent has a dominant ortho-para directing effect similar to that observed for phenol. In o- and p-cresol, this effect is modified, indicating that the methyl substituent has a significant effect on the electronic structure of those cresols. Correlation of the charge distribution in the cresols indicated by the observed distribution of dihydroxytoluenes with the unpaired spin distribution in the corresponding methylphenoxyl radicals demonstrates that the electronic structures of o- and p-cresol and their corresponding phenoxyl radicals are similarly affected by hydroxyl and methyl substitution. Addition of .OH at the methyl-substituted positions of o- and p-cresol to produce o- and p-dienone is also reported. The observation of these dienones demonstrates that addition of .OH at the ipso positions of alkylated aromatics can be of considerable importance. Mass spectrometric studies show that these dienones have relatively higher proton affinities than their isomeric analogues.
    The Journal of Physical Chemistry A 11/2005; 109(41):9363-70. · 2.77 Impact Factor
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    ABSTRACT: The detection of fullerenes in carbonaceous chondrites and in the geological strata of the Cretaceous–Tertiary boundary layer, associated with the Yucatan bolide impact, can be considered as an indirect evidence of fullerene formation in circumstellar envelopes of mass-losing carbon-rich stars. The large carbon clusters are very stable compounds with the respect to various physical and chemical factors. Nevertheless only scarce data on their behavior under high-dose γ-irradiation are available. This aspect is of crucial importance for the chemistry of interstellar fullerenes, since the existence of the large spherical carbon clusters must finally depend on competition between the rates of their formation and radiation decomposition. In continuation of our studies of the capability of solid C60 fullerene to withstand prolonged γ-irradiation, in the present work we report on a long duration experiment, lasted for ca. 8 months. We found that the degree of C60 decomposition, both in the presence and absence of liquid water, was less than 15%, demonstrating its extreme stability. A similar fullerene stability can be expected in different space environments, where the large carbon clusters are formed, incorporated into interstellar dust particles and subsequently into comets, and travel through the Universe.
    Advances in Space Research 01/2005; · 1.18 Impact Factor
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    ABSTRACT: It is generally assumed that the large spherical carbon clusters can be generated within circumstellar envelopes of mass-losing carbon-rich stars. The detection of fullerenes in carbonaceous chondrites, in the geological strata of the Cretaceous–Tertiary and the Permian–Triassic boundary layers, associated with bolide impacts, can be considered as an indirect evidence of their formation in circumstellar envelopes. On the other hand, a question arises on the fate of fullerenes in harsh radiation environments: namely, in close proximity to the stars where they have been produced (the gas phase), and in the solid phase after their incorporation into the interstellar grains. The existence of the large spherical carbon clusters must finally depend on competition between the rates of their formation and radiation decomposition. In the present work we estimated the capability of C60 fullerene to withstand prolonged γ-irradiation, under the doses exceeding 6 MGy (1 Gy=1 J kg−1), in the presence and absence of liquid water. The results of high-performance liquid chromatographic and infrared spectroscopic measurements of the irradiated products suggest general pathways of C60 radiolysis in the aqueous phase to be polymerization (most likely cross-linking), breaking the carbon backbone, C–H group formation, and incorporation of oxygen atoms as carbonyl and OH groups. In the absence of water, attachment of other radicals generated in the environment is possible, along with the polymerization. As a whole, crystalline C60 fullerene exhibited an extremely high stability. A similar behavior can be expected in different space environments, where the large carbon clusters are formed, incorporated into interstellar dust particles and subsequently into comets, and travel through the Universe.
    Advances in Space Research 01/2004; · 1.18 Impact Factor
  • Guadalupe Albarran, J. Bentley, Robert. H. Schuler
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    ABSTRACT: The relative rates for addition of ·OH radical to toluene at its ortho, meta, and para sites have been shown to be in the ratios of 0.84:0.41:1. These ratios provide a quantitative basis for considering the effects of alkyl substituents in determining the site of ·OH attack on other aromatics. Because ·OH is a strong electrophile, the relative yields of ·OH adducts provide a measure of the effect of the methyl group on the distribution of negative charge in toluene's aromatic system. Comparison of the partial rate constants observed for reaction at the different sites of toluene, biphenyl, and phenol with theoretical estimates of the distribution of charge in the valence shell indicates that factors other than charge also play some role.
    Journal of Physical Chemistry A - J PHYS CHEM A. 09/2003; 107(39).
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    ABSTRACT: We tried to roughly estimate the capability of C60 to withstand prolonged gamma-irradiation. We exposed C60 to very high irradiation doses exceeding 6 MGy, and analyzed the irradiated samples by high-performance liquid chromatography and infrared spectroscopy.
    03/2003;
  • G. Albarran, R.H. Schuler
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    ABSTRACT: Liquid chromatographic and capillary electrophoretic studies have been used to resolve the products produced in the radiolytic oxidation of salicylic acid in aqueous solution. These studies have shown that, as in the case of phenol, OH radicals preferentially add to the positions ortho and para to the OH substituent. However, in contrast to its reaction with phenol, addition at the ortho position is favored over addition at the para position. Because OH radical is a strong electrophile this difference suggests that the electron population at the ortho position in the salicylate anion is enhanced as a result of the hydrogen bonding in salicylic acid.
    Radiation Physics and Chemistry 01/2003; · 1.38 Impact Factor
  • Robert H. Schuler, Guadalupe Albarran
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    ABSTRACT: The rate constant for reaction of OH radical with toluene in aqueous solutions saturated with N2O or containing 0.1M H2O2 has been determined by pulse radiolysis to be 8.1×109lmol−1s−1. This rate constant is comparable to the value of 7.8×109lmol−1s−1 for reaction with benzene determined under similar conditions. This latter rate constant provides a reference value of 1.3×109lmol−1s−1 with which to compare the partial rate constants for reaction of OH at the various positions of substituted aromatics. Comparison of the kinetic responses in the N2O and H2O2 systems provides a direct measure of the pseudo-first-order rate constant for reaction of O− with water as 7.9×107s−1.
    Radiation Physics and Chemistry 01/2002; 64(3):189-195. · 1.38 Impact Factor
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    ABSTRACT: 4-Hydroxy-4-methyl-2,5-cyclohexadien-1-one has been conclusively identified by its 1H and 13C NMR spectra as a significant initial product in the radiolysis of aqueous solutions of p-cresol. This product is formed as the result of oxidation of the hydroxycyclohexadienyl radicals produced by addition of 12% of the •OH radicals to the aromatic ring at the ipso position adjacent to the methyl group. It has a strong absorption band at 228 nm that is similar to the 246 nm band of p-benzoquinone. Its proton NMR spectrum exhibits strong coupling between two pairs of ring protons. A quartet is observed in the spectrum of the methyl-13C labeled product, confirming that a methyl group is attached to the dienone ring.13C chemical shifts and 13C−H spin−spin splittings of the dienone are reported. Although DFT calculations of the proton NMR parameters are in very good agreement with the experimental values, the calculated chemical shifts of the ring 13C carbons are 4−8 ppm too high, indicating that the DFT calculations do not properly take into account the dienone π system. This conclusion is confirmed by parallel experimental and theoretical studies of 4H-pyran-4-one that provides a model system closely related to the dienone. The observation of 4-hydroxy-4-methyl-2,5-cyclohexadien-1-one as a product in the radiolysis of aqueous solutions is important in demonstrating that addition of •OH radicals to aromatic rings at positions substituted with alkyl groups can be of appreciable importance in the •OH oxidation of aromatic substrates.
    The Journal of Physical Chemistry A 01/2002; 106(50):12178-12183. · 2.77 Impact Factor
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    ABSTRACT: Although the presence of fullerenes in the interstellar medium remains the subject for considerable discussion and waits for an explicit experimental confirmation, it is generally assumed that the large spherical carbon clusters can be generated within circumstellar envelopes of mass-losing carbon-rich stars. The detection of fullerenes in carbonaceous chondrites and in the geological strata of the Cretaceous-Tertiary boundary layer, associated with the Yucatan bolide impact, can be considered as an indirect evidence of their formation in circumstellar envelopes. Even if we accept it, another question arises, on the fate of fullerenes in harsh radiation environments, especially in close proximity to the stars where they have been produced. In other words, the existence of the large spherical carbon clusters must finally depend on competition between the rates of their formation and radiation decomposition. In the present work we estimated the capability of C60 fullerene to withstand prolonged - irradiation, under the doses extended to ca. 103 kGy.
    Advances in Space Research 01/2002; 33(1). · 1.18 Impact Factor
  • G. Albarrán, R. H Schuler
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    ABSTRACT: In this paper, we consider the effect of CH3 and OH substitution on a benzene ring in directing the site of OH radical attack in oxidative processes initiated by the gamma radiolysis of aqueous solutions of phenol and toluene. The analytical method used was micellar electrophoretic capillary chromatography. This approach permits the resolution of the radiolytic products resulting from the oxidation of the hydroxycyclohexadienyl radicals initially produced by addition of OH to the aromatic compounds and allows one to obtain a complete mechanistic picture of the radiation chemical processes.
    Radiation Physics and Chemistry 01/2002; 63(3):661-663. · 1.38 Impact Factor
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    ABSTRACT: Research on the radiolysis of vitamins is of considerable interest since these compounds are important nutritional constituents in foods and in dietetic supplements. In spite of these considerations there are few data and very often difficult to compare for the radiolytic behavior of vitamins. In this work we focused our attention on to the study of the radiolysis of cyanocobalamin (vitamin B12) in solid state and in aqueous solutions. The procedure was followed by HPLC and UV-spectroscopy. The results obtained in aqueous solutions showed a dependence of the decomposition as a linear function of the dose. The G of decomposition for a 1×10−5 M solution was 3.3. In the solid state the vitamin was very stable towards the irradiation in the conditions used in this study with a G=2.1×10−3. A study made with Serratia marcescens as a microbiological contaminant showed that at the sterilization dose there is a destruction of the vitamin in aqueous solution. In the solid state the degree of decomposition was 7%.
    Radiation Physics and Chemistry 03/2000; 57:337-339. · 1.38 Impact Factor
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    ABSTRACT: The results of the radiolysis of aqueous solutions of thiamine (vitamin B1) are presented. The yields for decomposition of thiamine and the product of radiolytic products were determined. The G values decrease as the dose increases. Some radiolytic products were identified. Decomposition of thiamine was slightly dependent on the presence of oxygen and on the pH of the solution. At pH 4.4 with a concentration of 2.5 × 10−4 mol L−1 of thiamine in an oxygen free aqueous solution, the G0 value for decomposition is 5.0.
    Radiation Physics and Chemistry 06/1998; 52(1):401-404. · 1.38 Impact Factor
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    ABSTRACT: Organic compounds sorbed in clay minerals are likely to decompose, mainly because the catalytic activity of these minerals. The aim of this work is to get an insight of the decomposition of alpha ketoglutaric acid in the presence of blocking the edges of the montmorillonite. The results obtained with the system clay-alpha ketoglutaric acid are interpreted in terms that the electron acceptors sites (Lewis sites) are responsible for the decarboxylation reaction.
    Nanostructured Materials 01/1997; 9(1):209-212.
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    ABSTRACT: In this work we characterize the clays of a place named “Las Pulgas”, in the Charo Canyon, State of Michoacan, Mexico. It is found that these mineral species are mainly montmorillonite, cristobalite, tridimite and albite, including quartz. Montmorillonite is the most abundant clay in this region, and has a nanometric twinned small particle habit. All this opens a potential technical application for this nanostructure.
    Nanostructured Materials 01/1997; 9(1):335-338.